orthodontic brackets

This is a low level pdf intended for free download . picture quality might be poor

ORTHODONTIC BRACKETS SELECTION, PLACEMENT AND DEBONDING

Dr. Haris Khan B.D.S., F.C.P.S,F.F.D RCSI Assistant Professor Orthodontics The University Of Lahore Pakistan

COPYRIGHT All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the publisher, except in the case of brief quotations embodied in critical reviews and certain other noncommercial uses permitted by copyright law. For permission requests, write to the publisher, or contact at [email protected] PUBLICATION DATA ISBN-13: 978-1508936275 ISBN-10: 1508936277 Library of Congress Control Number: 2015905934 CreateSpace Independent Publishing Platform, North Charleston, SC DEDICATION This book is dedicated to my supervisors Dr. M. Waheed ul Hamid and Dr. Irfan ul Haq

ACKNOWLEDGEMENT I highly acknowledge the efforts and inspiration made by Dr. Ateeq ul Reham to write this book. I am thankful to Dr. Fayyaz Ahmad and Dr. Munawer Manzoor for providing me the technical guidance on various aspects of brackets. I am also thankful to Dr. Erum Bashir for doing the proofreading, Dr. lubna batool for provided used brackets from her clinical practice and Mr Jahanzeb for doing the composing of this book.

CONTRIBUTOR, EDITOR AND AUTHOR Dr. Haris Khan B.D.S , F.C.P.S,F.F.D RCSI Assistant Professor Orthodontics UOL, Pakistan

PREFACE In this era of pre-adjusted brackets, the existing literature on orthodontics limits itself to wire bending treatment practices. Since contemporary authors were not trained on the pre-adjusted bracket mechanics, hence they were handicapped to broach on the subject at the relevant point in time. In present day orthodontics, many orthodontists still resort to wire bending methods to close extraction spaces or to correct three dimensional positions of the teeth. Chapters on orthodontic brackets in various books either focus on theoretical perspective or are devoid of essential correlation of brackets,vis-a-vis their intended clinical use. Some authors have depicted fancy graphics to demonstrate clinical use of brackets. To address such obvious lacunae, I started working on orthodontic brackets in the year 2012 by collecting the brackets which were debonded during my clinical practice.This took me through the entire literature on orthodontic brackets as presented in various journals and manufacturer catalogues. This provided me an access to real time pictures of brackets using special micro lenses and portable microscopes. This book was authored to cater for all aspects of orthodontic brackets. The focus being to provide students with real time pictures of different brackets available in the market and to determine their behaviour in oral cavity and their appearance after debonding. The main emphasis being on three vital aspects viz; the selection, placement and debonding,this book has accordingly been designed to comprise these three sections. Real times of new and used brackets have been specifically included to provide the students a realistic insight of brackets.Care has been taken to ensure correlation of clinical situation and various bracket selection criterions. This book has materialized after an enormous effort of two years in data collection and a year further in arranging the data in a convenient book form. I deeply acknowledge the help and encouragement provided my colleagues in consummating this endeavor. I earnestly hope that this effort would go a long way in providing ready help to students. Haris Khan

Table of Contents Historical Perspective of Orthodontic Brackets

1

Material Perspective of Orthodontic Brackets

13

Selection of Bracket Base

41

Selection of Bracket Slot

61

Selection of Auxiliary and Convenience features

77

Selection of Bracket Prescription

83

Placement of Orthodontic Brackets

153

Bonding in Orthodontics

189

Debonding of Orthodontic Brackets

203

Adhesive Remnants Removal

239

Recycling of Orthodontic Brackets

255

CHAPTER

1

Historical Perspective of Orthodontic Brackets In this Chapter

History

Begg Appliance

Pierre Fauchard

Other Appliances

Modifications of bandeau appliance

Modification of Standard Edgewise Appliance

Development of edgewise appliance

Self ligating brackets

E Arch

Light wire Appliances

Pin and Tube Appliance

Lingual brackets

Ribbon Arch Appliance

Customized labial brackets

Edgewise Appliance Orthodontic brackets are important part of fixed appliances which are temporarily attached to the teeth during the course of orthodontic treatment. They are used to deliver forces from the wires or other power modules to the teeth. Before going into the details of orthodontic brackets a historic preview on the evolution of brackets is given. History The origin of orthodontic brackets can well be coined with the origin of orthodontics and the human desire to align crooked teeth. The first written record1 to correct crowded or protruded teeth is found 3000 years ago. Orthodontic appliances to correct maligned teeth have been found in Greek, Etruscan and Egyptian artifacts 2 .These ranges from crude metal wire loupes to metal bands wrapped around individual teeth in ancient Egyptian mummies3. Pliny the Elder

1

(23-79 AD) was the first to mechanically align elongated teeth4. Pierre Fauchard Pierre Fauchard (1678 –1761) a French dentist was the first to make a scientific attempt to align irregular teeth by an appliance named Bandeau (Figure 1.1 & 1.2).This appliance was made of precious metal and it was shaped like a horse shoe to align teeth by arch expansion. Fauchard also used to reposition irregular teeth with his Pelican forceps and then ligate them with neighboring teeth until healing took place. Fauchard published his work in 1728 in his landmark book entitled The Surgeon Dentist: A Treatise on the Teeth.

Historical perspective of Orthodontic Brackets

CHAPTER

1

another French dentist used swelling threads and wooden wedges to separate crowded teeth. Horace H. Hayden (1769-1844) invented bands with soldered knobs to correct tooth rotation.

Figure 1.1

Pierre Fauchard

In 1803, Joseph Fox invented a modified version of bandeau appliance that consisted of silver or gold rim. Silk thread was used as mode of attachment and force transfer between the rim and teeth. These silk threads were adjusted after every three weeks (Figure 1.3a). Blocks of ivory were used to disocclude the occlusion and to prevent interference with tooth movement. J. M. A. Schange (1841) a French dentist wrote the first book exclusively on orthodontics. He modified bandeau appliance and took anchorage by skeletal cribs attached to molars (Figure 1.3 b). He also invented an appliance to move malposed teeth within the arch (Figure 1.3 c).Harris in 1850 attached metal caps to molar and took anchorage from palate in his expansion appliance (Figure 1.3d) Development of edgewise appliance Norman W. Kingsley (1825-1896) and Calvin S. Case (1847-1923) advocated extraction for orthodontic purpose. Though Norman W. Kingsley later abandoned his extraction philosophy. This extraction philosophy later influenced the basic design of orthodontics braces.

Figure 1.2 Bandeau Appliance

Modifications of bandeau appliance Fauchard's bandeau appliance was further refined by another fellow French dentist Etienne Bourdet (1722-1789) who was a dentist to the King of France in his time. Etienne Bourdet was also the pioneer of lingual orthodontics by expanding the arch by metal framework placed on the lingual side. Christophe François Delabarre (1787-1862)

Edward Hartley Angle5 (1855-1930) was the most dominant and influential figure in orthodontics and is regarded as the “Father of Modern Orthodontics.” (Figure 1.4). Because of Edward Angle, orthodontics was recognized as a distant and separate science6 from general dentistry. In his initial days of orthodontic practice Angle advocated extraction in orthodontics .But latter on the basis of Wolff's law that “bone in a healthy person will adapt to applied load” Angle abandoned extraction treatment. Also another reason to abandon extraction treatment was failure to get satisfactory result after extracting 1st maxillary

2

B

C

D


A

Figure 1.3 A. Joseph Fox modified bandeau appliance having ivory blocks to disocclude teeth. B . Schange modified bandeau appliance having skeletal cribs attached to molars. C. Schange appliance to align malposed teeth .D. Harris appliance having metal molar caps and utilizing palatal anchorage for dental expansion.

premolars of his wife, Anna Hopkins. It is reported that Angle even after leaving extraction therapy condoned it privately5 .In July 1911 in a meeting of National Dental Association after a heated debate between orthodontist and on Angle recommendations extraction was omitted from orthodontics. Angle developed four major orthodontic appliance systems which lays the basis of contemporary fixed braces .These appliances were 1. E Arch

3

The first device developed by Angle was E arch in late 1890s but it was introduced in 1900 (Figure 1.5) .This appliance was in fact a mix of

Figure 1.4

Dr. Edward Hartley Angle


CHAPTER ideas from previous expansion appliance. In this appliance a heavy labial arch extends around the arch with the end of the wire threaded and placed in the molar bands .The heavy labial wire was directly ligated to the malposed teeth by a thin metal wire. The E arch was expanded by activating a small nut placed on the threaded portion of the arch wire .This creates space in the arch for the alignment of malposed teeth. As E arch was only cable of tipping movements and so it provided no axial control of tooth position. Angle modified the heavy labial archwire into 4 different designs depending upon the treatment type. These modifications were 1. Basic E arch was used in mandible with Backer's anchorage (Class II elastics).

1

2. Pin and Tube Appliance To have a better control over position of all the teeth and to achieve their bodily movement Angle banded the entire arch in his Pin and tube appliance, which was introduced in 1910(Figure 1.6). In this appliance small pins were soldered on the arch wire and these pins fit in the vertical tubes of the bands. Changes in the angulation of the pins, mesial or distal, labial or lingual resulted in bodily movement of the teeth. As a great degree of precision was needed to insert pins into the tubes and also position of these pins were needed to be changed at each appointment this appliance became impractical with time. It is said that Angle and one of his student ever mastered the appliance.

2. Ribbed E-Arch was used with expansion and by tying brass ligatures around the teeth to the arch. 3. Modified E-Arch was used with high pull headgear and without threaded pins. 4. E-arch with hooks in upper canine region was used with class II elastics.

Figure 1.6

Different parts of pin and tube appliance

3. Ribbon Arch Appliance Figure1.5.

E Arch

In 1916 Angle introduced his Ribbon arch appliance which was a modified version of pin and tube appliance (Figure 1.7). In this appliance the tubes were modified to provide a vertically positioned rectangular slot that was

4

rectangular wire was inserted into the slot and retained in the slot by ligature wires. Edgewise brackets were also associated with some limitations. There was deformation of soft gold slot on insertion of heavy wire. Failure of gold eyelets on the bands and decalcification of enamel under the bands was common. Complex wire bending was required to control tooth position in all three planes (Figure 1.8). This was time consuming process and needed considerable skills from the orthodontist. Even with these limitations the invention of edgewise appliance was a turning point in orthodontic fixed appliance therapy. Most of the contemporary brackets are modification of this edgewise appliance.

Figure 1.7

Different parts of Ribbon arch appliance

4. Edgewise Appliance In ribbon arch appliances the span between the first premolar and molar was too short to place the stiff archwire and its friction sleeve nut into the molar tube and the premolar slot. To overcome these difficulties Angle developed the edgewise appliance between 1923 to 1925 and that was introduced in orthodontics in 1928 (Figure 1.8). These brackets were attached to bands and were made of soft gold .The edgewise brackets (0.022” x 0.028”) had a horizontal slot instead of vertical slot in which the rectangular wire was rotated 90° to its previous orientation in the ribbon arch appliance so the name Edgewise was given which means sideway or towards the edge. A 0.0215” x 0.0275” 7 gold

5

Figure 1.8 A. Edgewise bracket. B. Edgewise bracket with eyelets . To have a better rotational control ligature wire were passed through eyelets and then over the main arch wire. C. Wire ligated with metal ligature in edgewise D. Complex wire bending incorporating 1st, 2nd and 3rd order bends.

Begg Appliance Paul Raymond Begg (1889-1983) was an Australian who studied under Angle from March 1924 to November 1925 on both Ribbon arch and Edgewise Appliance (Figure 1.9). He returned to Australia in 1927 and moved away from Angle's non extraction philosophy. In 1933 he modified Angle's ribbon arch appliance


facing occlusally. A ribbon shaped gold arch wire of 0.010x 0.020 inches was placed in the slot and held in position by brass pins .This appliance though having better spring qualities than its predecessor appliances but it has poor control on root position .

1


CHAPTER

Figure 1.9

Paul Remend Begg

simply by turning the slot of the bracket upside down. Begg appliance had gingival facing slot. Begg also replaced the heavy 0.010 x 0.020 inch rectangular gold wire of ribbon arch with 0.016 inch round stainless steel wire so the appliance is also named as light wire appliance. Begg published8 his appliance and mechanics in 1956 (Figure 1.10).To hold the wire within the slot different types of pins were used(Figure 1.10). Begg light wire appliance used differential anchorage during tooth movement. As tooth movement in Begg philosophy was done on light wire so the appliance had poor control on root position so different auxiliary springs were used with Begg appliance later in the treatment to correct root position.

Figure 1.10 A. Begg appliance in situ. Auxiliary springs for torqueing and correcting root angulation. B. Begg bracket with wire in place.C. Different types of pins used in Begg Appliance.

Other Appliances Joseph E. Johnson (1888-1969) developed his light forces twin-wire appliance in 1929 and published9 it in 1934(Figure 1.11).In this appliance two light wires (0.010 inch) were used simultaneously during treatment. Spencer R. Atkinson (1886-1970) invented the Universal brackets based on use of light forces in 1929 but the appliance was introduced10 in 1937. The appliance was called Universal brackets as it allowed all types of tooth

6

Figure 1.11

Twin wire appliance

movements. The brackets have two slots, a smaller edgewise gingival slot and a larger vertical incisor slot (Figure 1.12). The wires were held in place by lock pins. Charles H. Tweed, Jr (1895-1970) advocated extractions in orthodontics and successfully advocated extraction therapy by demonstrating his cases in AAO meeting in 1940. Modification of Standard Edgewise Appliance Brainerd F. Swain (1911-1999) attached two

Figure 1.12

7

Universal Brackets

A twin bracket with curved base

edgewise brackets separated by a gap to a single base and called it the twin or “Siamese brackets”. These brackets provided excellent rotational control without the use of auxiliary eyelets (Figure 1.13).Initially these brackets were made for incisors and molars but later the base of these twin brackets were carved and adapted for canines and premolars. These brackets were available in 4 different sizes. These were extra wide, standard, intermediate and junior sized. Paul D. Lewis (1896-1992) modified 11 edgewise bracket for better rotational control by soldering curved rotation arms to a single bracket that contacted the inside of the arch wire. Lewis brackets (Figure 1.14) were available with regular and curved bases. Lewis also made brackets with vertical slot. Howard M. Lang12 (1914-94) modified Lewis brackets by using straight arms or wings with holes for ligature tying (Figure 1.15). Glendon Terwilliger13 soldered brackets on bands in such a way that they should express tip and torque position. Holdaway 14 (1952) suggested that lower buccal segment brackets should be angulated over the band by an amount proportional to the severity of the malocclusion.Steiner15 in (1953) introduced 0.018 x0.022 inch bracket slot for better torque control. Steiner also introduced brackets like Lewis bracket which has single slot and rotational arms.


Figure 1.13


CHAPTER

1

closed vertical slot of 0.018” x 0.046” to conventional edgewise brackets to accept doubled 0.018 auxiliary wire(Figure 1.16). The vertical slot is formed when bracket is welded to a band.

Figure 1.16

Figure 1.14 Straight and curved Lewis brackets. The advantage of these brackets is that they provide good rotational control without decreasing inter bracket distance.

Broussard brackets with vertical slot

Inspired from the work of Jaraback and James, and by analyzing study models of non-treated ideal occlusion patients, Lawrence F. Andrew 18 advocated six keys to normal occlusion and based his straight wire appliance (SWA) to achieve these goals (Figure 1.17). Andrew made many modifications19, 20, 21 in his appliance with time. The preadjusted edgewise brackets have tip, torque, in and out bends built within the brackets (Figure1.18). It was believed that these appliances don't required wire bending hence the name Straight wire appliance was given to them.

Figure 1.15 Lang brackets. A Lang bracket unlike lewis bracket don't flatten the curvature of arch wire on canines.

Buonocore 16 in 1955 introduced acid etching which paved the path for attaching brackets directly to the teeth. John J Stifter in 1958 made edgewise brackets consisting of a male and female part. The female part remained attached to the tooth while there were many male parts to choose, to provide tooth guidance in all three planes of space. Ivan F. Lee in 1959 introduced commercially viable anterior brackets with built in torque while Jarabak and James A. Fizzell demonstrated the first brackets with builtin torque and tip in an annual meeting of AAO in 1960. Garford Broussard17 in 1964 added a

Figure 1.17

Lawrence F. Andrew

8

Figure 1.18 Preadjusted edgewise brackets. Andrew introduced these brackets in 1972.

The builtin tip, torque and in and out bends were called prescription of brackets. Andrew developed different brackets for different skeletal patterns and for extraction and nonextraction cases. Andrew believed that his straight wire appliance will attain all the Six Keys to Normal Occlusion. Almost all of the modern orthodontic brackets in preadjusted edgewise system are based on minor modification of Andrew's work. To overcome the difficulty to choose brackets from Andrew's different bracket series, 22 Ronald H. Roth (1933-2005) (Figure 1.19) refined Andrew’s SWA in 1976 by combining extraction and nonextraction series of brackets to make his own prescription called “Roth setup.” 23 After Andrew and Roth work, a plethora of bracket designs and prescription were made in the name of SWA with very little modifications to correct unknown problems or to suit personally advocated mechanics. Many of these appliances don't even fillful the basic requirement of straight wire appliance. It doesn't mean that all these prescriptions are useless. Some modern bracket series have very useful auxiliary and prescription features too but they are not game changer as Angle and Andrew work was. Some famous prescription of present day in addition to Andrew and Roth prescription are Alexander's prescription by R.G. “Wick”

9

Figure 1.19

Ronald H. Roth (1933-2005)

Self ligating brackets The concept of self ligation in orthodontic brackets came from Begg technique of using brass pins to hold the wire within the brackets .The first self ligating bracket was purposed by Stolzenberg24 in 1935. The first commercially produced self ligating bracket was named Edgelok and manufactured by Ormco in 1972. Self ligating brackets are divided into active and passive ligating brackets depending upon the mechanism of closure of ligating clip and holding the wire in slot (Figure 1.20). Self ligating brackets are available in almost all the prescriptions in which conventional brackets are available. Light wire Appliances Light wire appliance makes tooth movement on


Alexander (1978) using 0.018” slot brackets and 0.017x0.025” wire and MBT prescription (1997) by Richard P. McLaughlin, John C. Bennett and Hugo J. Trevisi.


CHAPTER

1

A

Figure 1.20

Active and passive self ligating brackets

light round wires using the concept of differential anchorage, where differential anchorage 25is pitting bodily movement of one group of teeth (stationary anchorage units) against tipping movement of another group of teeth (simple anchorage units). In the light wire appliances retraction of anterior teeth is done by tipping movement .Begg brackets were true differential force light wire appliance. These were the most famous appliance in 1960s but introduction of Andrew prescription and later Roth prescription hasten their decline as Begg brackets had poor three dimensional control over tooth position and complex finishing mechanics. Peter Kesling26 in the late 1988 introduced his Tip Edge brackets(Figure 1.21). These brackets were modification of edgewise brackets which used treatment mechanics of light wire and differential anchorage of Begg system. Root uprightning was done by side winder springs. A modification of Tip Edge bracket was Tip Edge plus27 by Parkhouse in 2007(Figure 1.21b). It uses an auxiliary horizontal slot beneath the main archwire slot. A round 0.14” super elastic NiTi wire is passed in the final stages of treatment instead of using side winders.

B Figure 1.21

A. Tip edge B. Tip edge plus brackets

Lingual Brackets Lingual brackets (figure 1.21) have a long history but they were first reported in 1978 by Kinja Fujita28 in Japan, to avoid injury to lips and cheeks by the brackets for patients who practiced martial arts. Lingual brackets were introduce in United States in1982 by Alexander 29 . Craven Kurz developed his lingual bracket series, the seventh generation of which was reported in 1990s.As lingual surface of tooth has more variations than labial surface so use of lingual bracket customized for individual patients is on the rise (Figure 1.22). Customized labial brackets Customized labial bracket uses CAD/CAM technology similar to customized lingual brackets. Not only brackets, but wires are also customized for each individual patient. As increased cost is involved in these brackets fabrication so these brackets have yet to gain popularity.

10

8. Begg PR. Differential force in orthodontic treatment. Int J Orthod 1956;42:481-489. 9. Johnson JE. Twin wire alignment appliance. Int J Orthod 1934;20:946-963. 10. Atkinson SR. The strategy of orthodontic treatment. J Am Dent Assoc 1937;24:560-574. 11. Lewis PD. Space closure in extraction cases. Am J Orthod 1950;36:172-91. 12. Gottlieb EL, Wildman AJ, Lang HM, Lee IF, Strauch EC Jr. The Edgelok bracket. J Clin Orthod 1972;6:613-23. 13. Dougherty HL Sr. The Curriculum II orthodontic program at the University of California at San Francisco School of Dentistry from 1929 until 1969. Am J Orthod Dentofacial Orthop 1999; 115:595-7.

A

14. Holdaway RA. Bracket angulation as applied to the edgewise appliance. Angle Orthod 1952;22:227-36. 15. Steiner CC. Power storage and delivery in orthodontic appliances. Am J Orthod 1953;39:859-80. 16. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34:849-53. 17. Broussard JG, Broussard CJ,Buck HR. Clinical applications of the Broussard auxiliary edgewise bracket Am J Orthod 1964;50:881-09. 18. Andrews LF. The six keys to normal occlusion. Am J Orthod 1972;62:296-309.

B Figure 1.22 A. Preadjusted lingual bracket B. Customize brackets Incognito by 3M Unitek

19. Andrews LF. The straight-wire appliance, origin, controversy, commentary. Journal of Clinical Orthodontics 1976; 10:99–114. 20. Andrews LF. The straight-wire appliance. Explained and compared. Journal of Clinical Orthodontics 1976; 10:174–195. 21. Andrews LF. The straight-wire appliance. British Journal of Orthodontics1979; 6:124–143. 22. Roth RH. The straight-wire appliance 17 years later. J Clin Orthod. 1987 Sep;21(9):632-42.

References 1. Weinberger BW. Historical résumé of the evolution and growthof orthodontia. J Am Dent Assoc 1934;21:2001-21. 2. Proffit WR, Fields HW, editors. Contemporary orthodontics. 3rd ed. Saint Louis: Mosby; 2000. 3. Wahl N. Orthodontics in 3 millennia. Chapter 1: Antiquity to the mid19th century. Am J Orthod Dentofacial Orthop. 2005 Feb;127(2):2559. 4. Asbell MB. A brief history of orthodontics. Am J Orthod Dentofacial Orthop 1990;98:176-83. 5. Chapman H. Orthodontics: fifty years in retrospect. Am J Orthod 1955;41:421-42. 6. Weinberger BW. Dr Edward Hartley Angle: his influence on orthodontics. Am J Orthod 1950;36:596-607. 7. Cross JJ. The Tweed philosophy: the Tweed years. Semin Orthod.

11

23. Roth RH. Treatment mechanics for the straight wire appliance. In: Graber TM, Swain BF, eds. Orthodontics: Current principles and techniques. St Louis: Mosby; 1985. 24. Stolzenberg J. The Russell attachment and its improved advantages. Int J Orthod Dent Child. 1935;21:837–840. 25. Kesling CK. Differential anchorage and the Edgewise appliance. J Clin Orthod. 1989 Jun;23(6):402-9. 26. Kesling PC. Dynamics of the Tip-Edge bracket. Am J Orthod Dentofacial Orthop 1989; 96: 16–28. 27. Parkhouse R. Tip-Edge Orthodontics and the Plus Bracket. 2nd ed. : Mosby; 2008. 28. Fujita K: Development of lingual bracket technique: esthetic and hygiene approach to orthodontic treatment. J Jpn Res Soc Dent Mater Appliances 46:81-86, 1978. 29. Alexander, C.M, Alexander, R.G, Gorman, J.C et al. Lingual orthodontics: a status report. Part 1. J Clin Orthod. 1982; 16: 255–262.


1996 Dec; 2(4):231-6.


CHAPTER

1

12

CHAPTER

2

Material Perspective of Orthodontic Brackets In this Chapter

Introduction Manufacturing Techniques

Plastic Brackets Plastic Polyoxymethylene brackets

Casting

Polyurethane brackets

Milling

Composite plastic brackets

Sintering Metal injection molding (MIM)

Ceramics Brackets Aluminum oxide or Alumina (Al2O3) brackets

Ceramic injection molding (CIM)

Monocrystalline brackets

Plastic injection molding (PIM)

Polycrystalline brackets

Brazing

Zirconia brackets

Cold working

Calcium phosphate ceramic brackets

Metal Brackets Stainless steel brackets Cobalt chromium brackets Titanium brackets Precious metal brackets

Introduction Contemporary orthodontic brackets are modification of a standard edgewise brackets developed by Edward H Angle. At the time of edgewise brackets invention stainless steel alloy although invented was in the phase of evolution and orthodontic brackets soldered to bands were largely made of 14 karat or 18 karat gold. Rudolf Schwarz 1 was the first to use

13

stainless steel in edgewise appliances. Ernest Sheldon Friel (1888-1970) a pupil of the Angle (Angle School, 1909) used stainless orthodontic bands for the first time in 1935.Apart from stainless steel different other materials have also been introduced with time to meet the orthodontists and patient's need. Modern orthodontic brackets are made up of three different types of materials which are as follow :

Material perspective of Orthodontic Brackets

CHAPTER 1. Metal brackets (Stainless steel, titanium and cobalt chromium) 2. Plastic brackets 3. Ceramic brackets (Monocrystalline and Polycrystalline ) All these types of brackets materials are in use for contemporary orthodontics with all of them having their own benefits and limitations. An ideal bracket in terms of material prospective should have following qualities. 1. Biocompatible in oral environment. 2. Low cost. 3. High modulus of elasticity. 4. High corrosion resistance. 5. No magnetic properties. 6. No friction on bracket wire interaction. 7. Correct strength and hardness. 8. Resist staining and discoloration in oral environment. 9. Resist plaque deposition. 10. Meet patient aesthetic demands. Unfortunately none of the contemporary materials used for bracket manufacturing meet all the above mentioned qualities. Before going into the details of different materials a brief description of various techniques used for brackets manufacturing are given so that the orthodontists have a better understanding of the brackets they select and use. Manufacturing Techniques Most of the orthodontic metal brackets are predominantly manufactured 2 by casting, milling and metal injection molding 3, 4.

2

Casting In casting processes the ingredients of alloy are melted and the liquid material is poured into a mold of the desired shape and allowed to solidify. Casting can be used to produce one piece orthodontic brackets or individual bracket components which are then brazed or welded together. Casting procedure is usually reserved for fabrication of complex parts like mesh and wings of the brackets (Figure 2.1). The slot of the bracket can also be produced by casting procedure but many manufacturers prefer to make slot by milling or machining process. In terms of brackets fabrication casting is the most expensive of all brackets manufacturing techniques as 90% of metal is lost in runners and sprues. In manufacturing orthodontic brackets casting technique is reserved for metal brackets. Casting can also produce single piece brackets but casted brackets are softer5 than milled brackets and usually stronger than metal injection molded brackets made of the same type of steel. Clinical notes Casted bracket parts which are brazed together have potential side effects of releasing cytotoxic agents, being separated from each other on applying orthodontic loading such as torqueing movements. It is a common problem with two unit casted brackets that slot/wings component become detached on applying debonding forces while the base of bracket remains attached to the teeth (Figure 2.2).Removing only the base component from teeth is cumbersome and usually require grinding the base with a diamond bur on a high speed handpiece . The areas of the bracket where two parts are joined together by brazing provide a potential plaque accumulation area. If a cast mesh is welded or brazed to a bracket base the brazing or welding material may cover

14

Casting error in slot manufacturing can change prescription of the brackets (Figure2.3).

Figure 2.3 Casting error in the slot of the bracket. Such errors allow decrease dimension wires inserted within the slot so increases the torque play.

Milling

Figure2.1 A bracket mesh made by casting. This mesh will be joined to the bracket base by welding or brazing.

Milling or machining is a process of giving certain shape by using a cutting instrument which is usually a nonabrasive rotatory cutting instrument. In case of orthodontic brackets a single piece bracket can be produced by milling process but manufacturer usually prefer to produce individual parts by this process (Figure 2.4). Milling or machining is good for economically producing geometrically simple parts such as hooks of brackets and slots. But milling of orthodontic brackets is expensive as compared to the metal injection molding process as 50% to 75% material becomes scrap while giving the final shape. Milling is also prone to human errors (Figure 2.5). Contemporary orthodontic metal brackets are manufactured by the computer numerated

Figure 2.2 Faulty casting procedures can lead to cracks on bracket wings and slots and can lead to wing fracture during clinical use. Such fractures are annoying for the orthodontist as these brackets need to be changed.

15

Figure 2.4 Hook of a bracket produced by milling process.


some of the bracket mesh area and may decrease the bond strength.


CHAPTER

2

debunking or debinding procedure. In this process heat or solvent or combination of both are used to remove up to 90% of the binders which are usually waxes or thermoplastic resins from the green part. At the end of debinding procedure the green part is converted into same size porous structure called brown part. Figure 2.5 Milling errors in slot of the bracket with irregular slot walls. Such manufacturing faults decrease torque expression and increases friction resistance.

controlled (CNC) milling processes in which brackets are made by taking a single piece of metal which is cut and formed by a computerized machine to create the bracket. Sintering Sintering is a process to create various objects from powder, based on the principle of atomic diffusion. In this process the powdered material is contained in a mold and heated to a temperature below its melting point. The atoms in the particles diffuse across the boundaries of the particles thus uniting the various particles and creating one solid single unit. Sintering is used both for metal and ceramic brackets manufacturing.

The brown part then undergo a sintering process in which it is heated in a high temperature furnace up to 1400 C° under controlled or vacuumed environment. Sintering process causes removal of the residual binders from the brown part leading to its shrinkage by 17% to 22 %. As the brown part was oversized, the final product is about the same size as required. In some cases final finishing touches are given by secondary thermal procedure or surface treatment. In case of MIM technique metal powder is stainless steel, titanium or cobalt chromium. A description of MIM procedure is given in figure 2.6.

Metal injection molding (MIM) Metal injection molding (MIM) is a powder metallurgy process developed in early 1980s in USA. The technique makes use of CAD/CAM technology. In this process fine metal powder called metal dust with particle size as small as 15 microns4 is combined with plasticizers, organic binders, lubricants and dispersants to form a homogenous mixture called feedstock. The feedstock is molded by injection molding machine into specific shapes .The new molded product called the green body or green part is fragile and is 17% to 22% larger than the final product3. Green body is processed through a

Figure 2.6 Flow chart of metal injection molding

Advantages of metal injection molding 1. The bracket is made in a single piece with a high degree of precision. 2. In MIM brackets no brazing is involved so there are fewer chances of cytotoxicity.

16

4. MIM brackets are inexpensive as little material is wasted during the fabrication process. 5. MIM brackets have increased corrosion resistance. MIM brackets are free from the corrosion risk associated with the galvanic couple of brazing alloys with stainless steel so MIM brackets are a good choice in nickel allergic patients. 6. MIM brackets that have undergone secondary thermal or surface treatment during manufacturing have smooth surface, offering decreased friction resistance.

Limitations of metal injection molding 1. MIM brackets have surface porosity due to shrinkage during sintering. This results in decrease in mechanical strength and also produces greater friction on sliding mechanics if surface treatment is not done. 2. As wings and base of the brackets are made from the same material and have the same hardness so mechanical debonding of brackets is technically more difficult by a peel off force as compared to conventional brackets (Figure 2.7). 3. Brackets manufactured by MIM have lower Vickers hardness 3 than conventional brackets of same material grade. Comparison of brackets made by different manufacturing techniques is given in figure 2.8. Clinical Notes

Figure 2.7 A MIM bracket that has been debonded by mechanical method using debonding pliers. The bracket is broken in the middle and can't be recycled. In conventional brackets base part are made of soft steel while slot part is made from hardened steel. The soft base is easily peeled off from the tooth on applying debonding force while the harder slot part maintains its shape. The harder slot also helps in greater expression of the built in torque. In contrast a bracket fabricated from MIM has less hardness than conventional brackets thus have less torque expression than conventional brackets. As the base and slot component are made of same grade material mechanical debonding usually results in distortion of the slot and the base of the bracket. This distortion can be avoided by inserting a segment of full dimensions rectangular wire5 within the slot at times of debonding.

17

Stainless steel metal injection molded brackets made of conventional grades in stainless steel were found to have equal hardness3 to that of NiTi wires and less than stainless steel wires. So MIM brackets will distort if too much torque is introduced into the wires or if the orthodontist jump to higher dimensions wires without following the proper sequence of wires during treatment (Figure 2.9). So it is wise to sequentially move from smaller to larger dimensions stainless steel wires. Many orthodontists prefer to use high torque value brackets to compensate the torque loss by slot distortion. Though NiTi wires are poor in torque expression but full dimension NiTi wires can be used with high torqued MIM brackets for effective torque expression.


3. MIM brackets wings don't separate from brackets on clinical loading and debonding.


CHAPTER

A

B

D

2

C

F

E

Figure 2.8 Comparison of brackets made by different manufacturing techniques. A. MIM bracket .The bracket surface is flat and smooth .The bracket stem has a uniform blend with the bracket base. Such brackets offer little retention for plaque accumulation. B. Slot wall of a MIM bracket .The slot surface is smooth but has long horizontal lines. Such horizontal lines can add to friction resistance. C .A bracket fabricated from casting. The bracket has a smooth surface. The topography of the bracket is irregular but not plaque retentive. D. The slot wall surface of casted bracket which is smooth and offer less friction than MIM. E. A bracket fabricated from casting, parts joined by brazing and slot machined by milling. The junction between the stem and base area is irregular and offer plaque retention area. F. The slot of the bracket made by milling processes. The slot wall is irregular and will offer more friction resistance than MIM and casted slots.

A

E

B

F

C

D

G

H

Figure 2.9 Comparison of slot distortion between two different grades of MIM manufactured brackets on introduction of torque in the wire. A. Low grade SS MIM bracket with straight 0.021”x0.025” wires inserted. B. Same bracket with 30° torque introduced in the wire. C & D. Comparison between slots of brackets before wire insertion (0.021”x0.025”) and after torqued wire (0.021”x0.025”) insertion. In bracket D the slot of the brackets has significantly been distorted due to introduction of torque in the wire. In Figure E, F, G, H same setting was used with a higher grade of the SS MIM bracket. In a Figure H expansion of the slot is evident but it is less than what was seen in brackets made of lower grade SS MIM.

Ceramic injection molding (CIM) CIM is used for manufacturing of ceramic brackets and is similar to metal injection molding with the exception that ceramic

powder is used instead of metal powder and sintering temperature is maintained at 2000 C°. In case of ceramic brackets CIM technique is the contemporary preferred method for polycrystalline brackets manufacturing.

18

Plastic brackets are manufactured by plastic injection molding. The manufacturing process is similar to that used for metal or ceramic brackets. Brazing In this process a metal filler alloy is used to join two metals by heating the filler above its melting point. The liquid filler is taken up by the joined metals using capillary action. Brazing is similar to soldering except the former uses a higher temperature to melt the metal filler alloy. In orthodontics, brazing process is used for stainless steel brackets. Many orthodontic companies traditionally produce individual bracket parts (base, wings and mesh) from different grades of stainless steel and then join them together by brazing (Figure 2.10). An ideal brazing alloy for orthodontic purpose should have the following properties: 1. It should have a good compatibility in terms of chemical nature and appearance with stainless steel or any other bracket material used. 2. It should have good mechanical strength to hold the joined parts together under masticatory and orthodontic loading. 3. The brazing cycle temperature should be less than the sensitization temperature of stainless steel. 4. A brazing alloy shouldn't contain or causes the release of cytotoxic elements like Ni, Cd, Cu, and Zn. 5. Brazing alloys should have galvanic compatibility with saliva and with stainless steel alloys. Galvanic corrosion causes 7 progressive dissolution of brazing filler metal thus weakening the joint between two parts of the bracket. This can

19

lead to detachment of the wings or mesh from the bracket base during orthodontic therapy or at the debonding stage. Brazing alloys commonly used in orthodontics are Ag, Ni, Cu, and Au. Unfortunately none of these fulfill the ideal criteria of a brazing alloy and always are associated with some limitations. Silver Ag based brazing alloy contains cadmium8 which is added in this brazing alloy to lower the melting temperature and improve wetting6. Cadmium is shown to be cytotoxic. Silver based brazing can also release cytotoxic9, 10, 11 copper and zinc ions by forming a galvanic couple with stainless steel in water. Chromium carbide precipitation also occurs by Ag based brazing because of a higher sensitizing temperature range. Gold (Au) based brazing also forms a galvanic couple with stainless steel and lead to dissolution of stainless steel because gold is a more noble metal than stainless steel. Dissolution of stainless steel can cause a decrease in its corrosion resistance and release of nickel. Nickel is well known to cause nickel allergy in presensitized nickel allergic patients. Nickel based brazing may release Ni while Cu Clinical Notes Brackets joined by nickel based brazing shouldn't be used in patients with nickel sensitivity. Base method of debonding should be used in mechanical debonding of stainless steel brackets manufactured by the brazing process because using the wing method of debonding may result in detachment of wings or mesh from the base. Removing the base or mesh alone from the tooth is a time consuming process. Flame method of recycling should be avoided in brazed brackets as there are greater chances of corrosion of these brackets with this method.


Plastic injection molding (PIM)


CHAPTER

2

based brazing will release copper. Both have known cytotoxic effects.

A

C

B

E

F

D

Figure. 2.10 A. Bracket in which slot/wing component is joined with the base component using silver brazing. Such brackets are known to release cytotoxic cadmium in the oral cavity .B .Copper brazing used to unite bracket parts. Copper brazing may release Cu which can cause cytotoxic effects. C. Nickel brazing. Such brackets should be avoided in patients with nickel hypersensitivity to avoid nickel allergy. D .A gauze mesh brazed manufactured separately and brazed to bracket base. Sometimes at debonding these brackets meshe become separated from the main bracket body and remain attached to the tooth. Removal of the mesh alone from the tooth is a cumbersome process and usually requires grinding the mesh with high speed handpiece. E. Magnified view of the bracket mesh brazed to bracket base.The mesh is brazed at the corners of the bracket. Such corner areas provide poor retention for bonding adhesives and so decrease the bond strength and providing potential areas for bacterial accumulation. F. A bracket having silver brazing. Picture at time of debonding after two years of clinical use. Degradation of the brazing alloy is evident with fissures, cracks and color change in the brazed area.

Cold working Cold working is a process in which repeated bending of the material is done while the material is cold. This process is used to increase hardness of the material. Cold working is used in manufacturing of metal brackets. But a stainless steel bracket in which cold work has been done has greater chances of carbide precipitation at a lower temperature so coldworked stainless steel brackets with low carbon contents should be used12 to minimize carbide precipitation. Selection of brackets based on manufacturing processes Manufacturers usually don't provide the

details and the type of manufacturing processes until a personal query is raised. With slightly limitations all types of brackets manufactured by different techniques work fine in most of the cases if the correct manufacturing technique and standard have been followed. Some selection criteria's of brackets based on manufacturing technique are given. 1.Casted brackets have well-polished surfaces and are a good choice for sliding mechanics and torque expression. 2.Many manufacturers don't have state of art technology. If a milling process is used in slots or other brackets parts manufacturing,

20

Metal Brackets There are four main types of metal brackets used in modern orthodontics.These are: 1. Stainless steel brackets

3.In case a brazing process is used in bracket manufacturing always try to avoid bracket based on nickel brazing. Avoid brazed bracket recycled with flame or chemical method.

2. Cobalt chromium brackets

4.MIM brackets are usually good for all types of cases. If there are special torque consideration in a case either use the proper sequence of wires or use MIM brackets made of higher grades of SS.

1. Stainless steel brackets

With the availability of on demand quality products from china, many manufacturers and distributers prefer cheap quality products. This is a nightmare for young orthodontists. All new brackets look good in catalogs, all brackets shine in their packing's, but it is after one to two years of clinical use you came to know how they work. Keep in mind all brackets degrade in oral cavity so always seek an advice from seniors about which product line of a specific company degrade less? A comparison between new and used brackets is given in figure 2.11.

3. Titanium brackets 4. Precious metal brackets

In metallurgy, stainless steel, also known as inox steel is a steel alloy with a minimum of 10.5% chromium content by mass. Stainless steel can be classified into different types of crystalline structures and each type of stainless steel has been given a specific SAE (Society of Automotive Engineers) or AISI (American Iron and Steel Institute) number depending upon composition of elements in the alloy. Low numbers have little additional alloy metal and are soft, while higher AISI numbers have greater hardness and increased corrosion resistance. Orthodontic brackets13, 14 should have the correct hardness and strength to withstand and deliver the forces from the wires to the teeth. Most of the orthodontic brackets are made of stainless steel14, 15, 16, 17 because it provides optimum properties required for an orthodontic bracket. Before going into the details of different types of stainless steel used for manufacturing of orthodontic brackets some important aspects related to stainless steel brackets are discussed as they affect the selection of these brackets. Corrosion resistance

Figure 2.11 A comparison of new and used, same company bracket made by MIM SS.Don't select brackets on their new look but how they behave in the oral cavity.

21

Corrosion is the gradual destruction of materials by chemical reaction against their environment. Corrosion of orthodontic brackets will degrade their physical strength, color and increases


always select brackets in which computer numerated controlled (CNC) milling processes is used as this manufacturing technique has less chances of errors in bracket fabrication.


CHAPTER

2

surface roughness by dissolution of the bracket material. This rough surface will act as a site for plaque accumulation and bacterial growth so further corroding and discoloring the brackets. In stainless steel, corrosion resistance18 is provided by self-healing passive surface layer of chromium oxide which prevents surface corrosion by blocking the oxygen diffusion to the steel surface. Breaking of the chromium oxide layer will increase the permeability of stainless steel for liquid and gases. This will start a chain reaction resulting in degradation of stainless steel and the release of its composite elements which in some cases are cytotoxic. The pH of the environment in which orthodontic brackets are used has a significant effect on the integrity of the chromium oxide layer. As most of the brackets have to remain for long term in the oral cavity so there is increase interaction of brackets with oral fluids which lead to greater chances of brackets chromium oxide layer breakup (Figure 2.12). Corrosion of orthodontic brackets can also occur due to Cl-ions in saliva, food, certain mouth washes 19 , acidic drinks, bacteria and their waste products and selective interactions with gases such as oxygen and carbon dioxide.

A

B

C Figure 2.12 A. Labial surface of the tooth at time of debonding. Corrosion products and adhesive remnants of on the enamel surface. These corrosion products cause s release of cytotoxic elements in oral fluids and also causes discoloration and decalcification of enamel .B. Corrosion of brackets after 2.5 years of clinical use. There is a change in color and texture of the bracket. Bracket corrosion affects its appearance and prescription. C. Bracket base of mesh corrosion. Mesh Corrosion of bracket base will cause a decrease in shear bond strength in case of reusing a bracket.

Clinical notes

Nickel Allergy

At the time of bonding of orthodontic brackets all adhesive flash around the brackets should be removed. Any remained flash around the bracket base will act as a site for bacterial accumulation thus leading to increase chances of bracket corrosion. Good oral hygiene measures by the patients and clinicians should be ensured. The patients should be advised to limit his use of acidic and high sugar juices. Even if the same wire is activated, removing and cleaning the wire and slot with air and water spray is a good practice to limit corrosion of the brackets.

One of the most annoying aspects of stainless steel brackets is that they can cause nickel allergy in nickel sensitive patients. Nickel sensitivity is more common in females and more common due to cutaneous exposure than subcutaneous exposure. Corrosion resistance of steel brackets is more important 20 than its nickel contents because if the corrosion resistance is good then ions won't be released from the brackets. Nickle free brackets are brackets with good corrosion resistance should be used. Higher grades SS has low nickel contents and better corrosion resistance. But it is difficult to

22

is due to the reason that considerable strength of the steel is lost during machining or casting of the brackets. Also owing to complex shape of the bracket parts, same degree of cold working cannot be applied to the brackets as it is applied to the wires. The Vickers hardness of a slot /wings of conventional brackets was found to be close to that of NiTi wire which has VHN of 300 to 43023.The Vickers hardness of some MIM brackets3 was between 154 to 287 VHN which is much lower than that of conventional brackets. The effect of decrease Vickers hardness and mismatch of Vickers hardness between slot and wire is explained in figure 2.14 and 2.15.

Figure 2.13 A bar chart on percentage of nickel in different types of stainless steel

Vickers Hardness The Vickers hardness test measures the hardness of a material and was developed by Robert L. Smith and George E. Sandland in 1921.Vickers hardness of orthodontic slots should ideally be equal to orthodontic wires for proper expression of the prescription built into the brackets. The Vickers hardness of the bracket base should ideally be less than that of slots. This arrangement will help in easy debonding of brackets. If the hardness of the base is greater than optimum limits mechanical debonding of brackets will become difficult as peel off force cannot be applied to the brackets. In conventional orthodontic brackets which are made from casting and milling process the slot/wings component is usually made of harder steel which is usually 17-4 PH while the base component is made of softer steel which is usually 316 SS. This arrangement helps in easy debonding of brackets but even with this combination the Vickers hardness of slot /wings component of a conventional bracket which is 400 VHN21 is less than stainless steel wires which have a Vickers hardness of 600 VHN22.This decrease hardness of brackets slot

23

A

B

Figure 2.14 A. Slot wall of a new MIM bracket. B. The slot of wall of a used bracket on which sliding mechanics was done on 0.019x 0.025” SS wire. The slot walls have lost their smoothness with clinical use. The increase roughness has been contributed by ploughing effect of harder SS wire on sliding mechanics and to a minor extent by corrosion of the slot.

A

B Figure 2.15 A. Rough area on front side of bracket base. B. Rough bracket wings. Such areas are usually formed by rough instrumentation during ligature insertion and removal. Such areas are potential plaque retention areas. The bracket should have optimum hardness to avoid the creation of such areas.

Clinical Notes Greater the mismatch of Vickers hardness between the stainless steel wires and


machine higher grade SS into orthodontic brackets. A bar chart of different stainless steel, showing their nickel contents is given in figure 2.13.


CHAPTER brackets greater would be the wear of softer material by ploughing effects and greater friction would be offered on sliding mechanics. Conventional brackets are more effective in sliding mechanics, torque expression than MIM brackets. MIM brackets are peeled off from the tooth on debonding but are usually distorted to the extent that they can't be recycled. NiTi wires though are poor in torque expression, can be used with high torque prescriptions but problem of their increased friction with sliding mechanics remains. Types of stainless steel Almost all manufacturers of orthodontic brackets only tell the type of brackets and don't reveal the exact composition of their brackets. Different types of stainless steel based on their metallurgic structure are used for manufacturing of orthodontic brackets. The data is collected from different articles published in orthodontic journals.

2

comparison with other types of stainless steels. The standard orthodontic twin brackets are usually manufactured from austenitic type 302 , 303SE ,303L ,304 ,304L,316 ,316L and 318 7,24 with 304 L and 316 L mostly used material12,25,26,27 . The L designation refers to lower carbon contents of steel. The lower carbon contents in stainless steel eliminate harmful carbide precipitation thus decreasing the susceptibility to corrosion. But low carbon steel has decreased strength . 316 SS and 316-L SS are used where higher corrosion resistance especially to chloride is required.316 SS is used more commonly for making base components and because of increased corrosion resistance have shown28 to release less nickel. The composition of various austenitic stainless steel brackets is given in table 2.1. A 316 L bracket is shown in figure 2.16.

Austenitic Stainless steel (300 SERIES) This is one of the most popular types of stainless steel alloy24 used in orthodontics as a bracket and wire material due to its good corrosion resistance, excellent formability and low cost in

Figure 2.16 316L SS bracket

Table 2.1. Composition of Austenitic stainless steel brackets AISI

Fe%

C%

Cr%

Ni%

Mn%

Si%

P%

S%

Others %

303

Balance

0.15

17-20

8-10

2.00

1.00

0.20

0.15

0.6 Mo

304

Balance

0.08

18-20

8-10

2.00

1.00

0.05

0.03

304L

Balance

0.03

18-20

8-12

2.00

1.00

0.05

0.03

316

Balance

0.08

16-19

10-13

2.00

1.00

0.05

0.03

2-3 Mo

316L

Balance

0.03

16-19

10-13

2.00

1.00

0.05

0.03

2-3 Mo

317

Balance

0.08

18-20

11-14

2.00

1.00

0.05

0.03

3-4 Mo

Fe=Iron. Iron balance means the rest is iron by % weight which is usually in the range of 69 to 72 %.In this table C=Carbon, Cr= Chromium, Ni=Nickel, Mn=Manganese, Si=Silicon, P=Phosphorus, S=Sulfur and Mo =Molybdenum. These values are for reference as many more elements are added in stainless brackets by the manufacturer to improve their mechanical properties.

24

Super stainless steel is defined as SS with pitting resistance equivalent value of 40. Super stainless steel has higher molybdenum and nitrogen content than conventionally used SS. Super SS12 show good frictional properties, higher resistance to chloride pitting and crevice corrosion. Super SS had only been used in vitro studies12. No information in any company catalogue is present that they manufacture brackets with supper stainless steel. Precipitation-hardening (PH) martensitic stainless steel (17-4 PH or S17400) This form of stainless steel has corrosion resistance equal to austenitic stainless 304 but

has better strength than the latter. 17-4 PH or S17400 precipitation– hardening alloy type has lower nickel contents but have poor localized corrosion resistance12.It has been shown28 that more nickel is released from 17-4 PH than 316 SS as the former have less corrosion resistance than 316 SS. So 17-4 PH is not a good choice for patients with nickel sensitivity. 17-4 PH stainless steel is usually used for manufacturing wing component of brackets or for making mini brackets because of its higher hardness and strength 14. Composition of precipitation-hardening (PH) martensitic stainless steel is given in table 2.2. A bracket made from 17-4 PH stainless steel is shown in figure 2.17.

Table 2.2. Composition of Precipitation-hardening (PH) martensitic stainless steel AISI

Fe%

C%

Cr%

Ni%

630/17-4 Balance 0.07 15.5-17 3-5 PH 631/17-7 Balance 0.09 16-18 6.5-7.5 PH Where Nb is niobium Al=Aluminum , Cu = Copper

Mn%

Si%

P%

S%

Others %

1.00

1.00

0.04

0.03

4Cu, 3Nb

1.00

1.00

0.04

0.04

0.081.5AI

less than austenitic stainless steel but stabilized ferritic stainless steel (AISI 441) has equal corrosion resistance to that of 316 SS. Due to decrease carbon contents , this form of steel has less strength than austenitic stainless steel. Some companies manufacture nickel free brackets from super ferritic stainless steel but their composition is not known (figure 2.18).

Figure 2.17 Brackets made from 17-4 PH SS

Ferritic Stainless steel Ferritic stainless steel has main alloying elements as chromium, titanium, molybdenum, small amount of carbon and no nickel. Generally corrosion resistance of this steel is

25

Figure 2.18 bracket

Super-Ferritic Stainless Steel BIOMIM


Super austenitic stainless steel


CHAPTER 2205 Duplex stainless steel A duplex stainless steel is a combination of austenite and delta ferrite stainless steel. A duplex stainless steel is twice as strong as austenitic stainless steel and also has improved resistance to localized corrosion particularly pitting, crevice corrosion and stress corrosion. It is composed of high chromium contents (1932%), molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. A duplex stainless steel has been proposed25 as an alternative to 316 L stainless steel brackets but no such bracket material is mentioned in the catalogs of orthodontic brackets manufacturers. Martensitic Stainless steel This forms of stainless steel though extremely tough and strong is not used for orthodontic brackets because of poor corrosion resistance. A short description of different elements used in stainless steel alloy is given so the orthodontist must have a basic knowledge why each element is added in the alloy. Carbon Carbon is added to stainless steel to give hardness and strength. Increase carbon contents may give increased hardness but there is also a risk of increase chromium carbide formation due to localized corrosion in the oral fluids. Chromium

2

chances of nickel ion release under the influence of oral fluids. To minimize the risk of hypersensitivity reactions to nickel, the corrosion resistance of stainless steel should be maximized to control the nickel ion release from the alloy. Manganese Manganese, like nickel, is an austenite forming element and has been used as a substitute for nickel. Nitrogen Nitrogen has the effect of increasing the austenitic stability of stainless steel. Like nickel it is also an austenite forming element. Molybdenum Molybdenum is added to improve resistance of SS to pitting corrosion especially by chlorides. Titanium Titanium is added for carbide stabilization and to increase corrosion resistance. Phosphorus Phosphorus aids to increase strength and corrosion resistance. It also lowers the temperature for sintering. Niobium (Columbium) and Tantalum Niobium is added to steel in order to stabilize carbon and to improve corrosion resistance.

Chromium is added to steel to increase its resistance to oxidation. Chromium forms thin passive surface chromium oxide layer which prevents surface corrosion by blocking the oxygen diffusion to the steel surface.

Copper is added to stainless steel to produce precipitation hardening properties.

Nickel

Selenium and Sulfur

Nickel is used to stabilize austenitic phases of stainless steel. So it improves resistance to oxidation and corrosion. Since the nickel atoms are not strongly bonded to form some intermetallic compounds so there are greater

Selenium is added to steel to make it more machinable and workable, but it also decreases hardness and strength.

Copper

Cobalt chromium brackets

26

Stainless steel brackets with good corrosion resistance should be selected. Good corrosion resistance of a bracket is more important than its nickel contents. Ideally SS brackets should not be used for nickel sensitive patients. Conventional SS brackets with softer base component and harder slot/wings component should be preffered.17-4 PH MIM brackets are a good choice for proper torque expression. New bracket should always be the first choice by orthodontists to avoid corrosion.

Cobalt chromium brackets were introduced in mid 1990s as a low nickel alternative to stainless steel. Cobalt chromium brackets are fabricated from casting or metal injection molding. Type and Composition of Cobalt based alloys Cobalt based alloys can be divided into three categories .These are: 1. Cobalt based wear resistant alloys 2. Cobalt based high temperature alloys 3. Cobalt based corrosion resistant alloys In these alloys cobalt based wear resistant alloys are used29 presently for orthodontic brackets manufacturing .In cobalt based wear resistant alloys CoCr brackets are made from ASTM F75 CoCr where ASTM stands for American Society for Testing and Materials. The amount of nickel in this alloy is kept low 29and is up to 0.5 %. Composition of cobalt based wear resistant alloys is given in table 2.3. A cobalt chromium bracket is shown in figure 2.19.

Table 2.3 Cobalt-Base Wear-Resistant Alloys Cr 25-30% Mo 7% max W 2-15% C 0.25-3.3% Fe 3% max Ni 0.5%max Si 2% Mn 1% Co Balanced Where Cr=Chromium, Mo=Molybdenum, W = Tungsten, C =Carbon, Fe = Iron, Ni=Nickel, Si = Silicon

Properties of Cobalt Chromium Brackets Friction Resistance In terms of friction resistance cobalt chromium brackets show comparable30, 31 but slightly less amount of friction than that of stainless steel brackets when used with stainless steel wires. But CoCr brackets offer more friction than titanium brackets30 with both stainless steel and beta titanium wires. Corrosion Resistance Because of increase chromium contents there is less chance of corrosion32 of cobalt chromium brackets.

Figure 2.19 Nu- Edge® Mini Cobalt Chromium Brackets by TP orthodontics with 0.5 % nickel.

27


Selection of Stainless steel brackets


CHAPTER Selection Cobalt chromium alloys have good corrosion resistance and have a highly polished surface. But due to less favorable friction properties with different types of wires, selection of CoCr brackets over titanium and steel brackets is a matter of personal choice than logical basis. Titanium Brackets Titanium metal has excellent biocompatibility and increased corrosion resistance18, 33, 34 so it has wide ranging surgical application from artificial heart valves and hip joints to dental implants. In orthodontics to overcome the release of nickel from stainless steel brackets which may cause nickel allergy in some patients, titanium brackets have been introduced35, 36 as nickel free alternatives to stainless steel in mid 1990s. Types of Titanium From material science perspective titanium has the following three types:

2

4 CP titanium, which offers highest strength and moderate formability. Composition of different grades of CP titanium is given in table 2.5. Contemporary titanium brackets21, 37 are either manufactured from alpha titanium grade 2 and 4 or alpha-beta titanium (Ti-6Al-4V).Grade 2 CP titanium is usually used to make base component of brackets due to its decreased strength while the wing component is made from much harder titanium alloy, the alpha -beta titanium Ti-6Al -4V.Both these components are laser welded to make a single unit of bracket. As explained before for stainless brackets combination of harder slot/wings part and softer base part has clinical importance. The softer base part will allow easy mechanical debonding while harder slot/wings part will allow expression of torque. Due to release of vanadium37from titanium alloy Ti-6Al-4V which may have biological hazardous effects some manufacturer make single unit milled or metal injection molded bracket from grade 4 CP titanium.

Characteristics of Titanium brackets 1. αTitanium Corrosion Resistance 2. β titanium 3. α &β Titanium Alpha titanium is commercially pure (CP) unalloyed titanium while the other two types are titanium alloys.β titanium include Ti-15V-3Cr3Sn-3Al alloy while α-β titanium included Ti6Al-4V alloy. Alloyed titanium has greater strength than unalloyed titanium. Chemical composition of various types of titanium is given in table 2.4. Commercially pure (CP) titanium is further classified into four grades depending upon degree of impurity, primary oxygen within the unalloyed titanium. Grade 1CP titanium has the lowest strength but highest purity, corrosion resistance and formability as compared to grade

Titanium and titanium alloy brackets have greater corrosion resistance than stainless steel brackets. This is due to the presence of thin passive protective layer of titanium dioxide over the titanium. This layer of titanium dioxide is more stable23 than its counterpart layer of chromium oxide on stainless steel. The composition of titanium dioxide layer which is also called rutile is given in table 2.6. Brackets in which two parts are joined together by welding have greater chances of galvanic corrosion than one piece milled or MIM brackets. A titanium bracket is shown in figure 2.20.

28

All titanium alloys show galling and fretting on sliding but due to the presence of passive layer of titanium dioxide, titanium brackets have comparable38-40 or less30 friction resistance than steel brackets when stainless steel arch wires are used both in passive and active configuration. Passive configuration is one in which there is clearance in the slot and no binding from torque or angulation is present whereas active configuration has binding in the slot. Titanium brackets also give least friction30 with beta titanium wires as compared to other metal brackets. The passive layer of titanium dioxide remains stable39 during sliding mechanics. So

Figure 2.20 Equilibrium Ti bracket by Dentaurum

Table 2.4. Chemical composition of various types of titanium Crystal Structure

Ti

Al

V

Mo

Sn

Fe

Cr

Others

Unalloyed titanium (α)

100

-

-

-

-

-

-

-

Ti-6Al-4V(α + β)

90

6

4

-

-

-

-

-

Ti-4.5Al-3V-2Fe-2Mo(α+β)

88.5

4.5

3

2

-

2

-

-

Ti-15V-3Cr-3Sn-3Al(β)

76

3

15

-

3

-

3

-

Ti-20V-4A1-1SN(β)

75

4

20

-

1

-

-

-

Ti-22V-4A1(β)

74

4

22

-

-

-

-

-

Ti-16 V-4 S n -3 Al-3Nb (β)

74

3

16

-

4

-

-

3(Nb)

Table 2.5. Composition of different grades of CP titanium Composition

Grade 1

Grade 2

Grade 3

Grade 4

Nitrogen max.

0.03

0.03

0.05

0.05

Carbon max.

0.08

0.08

0.08

0.08

Hydrogen max.

0.015

0.015

0.015

0.015

Iron max.

0.20

0.30

0.30

0.50

Oxygen max.

0.18

0.25

0.35

0.40

Titanium

Balance

Balance

Balance

Balance

Table 2.6. Composition of titanium dioxide layer

29

Carbon

Fluoride

Hydrogen

Iron

Nitrogen

Oxygen

Titanium

42.0%

2.3%

0%

0%

1.5%

40.1%

14.1%


Friction characteristics


CHAPTER Clinical notes If greater torque is required it is better to use titanium brackets whose slot /wings components are made of titanium alloy than using brackets made from commercially pure titanium. For doing sliding mechanics in nickel sensitive patients30 use titanium brackets with beta titanium wires though loop mechanics are better option than doing sliding mechanics. titanium brackets can effectively be used with stainless steel wires for sliding mechanics just like stainless brackets. Within titanium brackets titanium alloys have less friction26 coefficient than CP titanium. Bond Strength Titanum brackets has greater bond strength than SS brackets (Figure 2.21)

Figure 2.21 Titanium has less contact angles with liquid and adhesives than stainless steel. So theoretically titanium brackets offer greater bond strength than SS brackets.

Limitations of titanium brackets Following limitations can be associated with titanium brackets. 1. Some titanium brackets can release elements like vanadium which may have undesirable biological effects43-45 under certain conditions. 2. The laser welding used for joining different components of titanium brackets may leave gaps between these parts thus decreasing the mechanical strength and these areas act as plaque retentive areas thus increasing chances of crevice corrosion37. There are also greater chances of galvanic corrosion in laser welded brackets.

2

3. Titanium brackets have a rough surface as compared to other metal brackets so there are greater chances46 of plaque Selection Titanium brackets should ideally be selected in patients with nickel allergy. As the surface hardness of titanium is comparable to that of teeth, titanium brackets cause less tooth wear. So these brackets can also be selected for deep bite cases and patients having bruxism to avoid tooth wear. accumulation and discoloration. Titanium brackets may undergo crevices and pitting corrosion47, 48 when used with fluoride containing mouthwashes. Precious metal brackets Precious metal brackets are usually steel brackets plated with precious metals18 like gold, platinum and palladium (Figure 2.22). Of these brackets 16, 18 and 24 karat gold plated brackets are most commonly used especially in lingual orthodontics. Gold is historically used for different dental prosthesis because of its property of non-reactivity. Traditional edgewise brackets were made of gold but due to the higher cost associated with it; gold has universally been replaced by stainless steel brackets and wires. No study was found in literature on torque expression, hardness and friction properties of these brackets. It is

Figure 2.22.

A 22 karat plated gold bracket

30

These brackets can be used in nickel sensitive patients. As these brackets are usually expensive so it is an aesthetic preference by the patient over titanium brackets in nickel sensitive patients. These brackets are still a popular choice for manufacturers in lingual orthodontics because of easy machinability with gold metal. generally assumed that these brackets behave in the same way as steel brackets as the core of these brackets is made of stainless steel. Plastic Brackets The first commercially available plastic brackets were introduced49 in 1963 by Morton Cohen and Elliott Silverman. Plastic brackets are either translucent or transparent to fulfill aesthetic demand during treatment and to make the treatment less visible. Plastic brackets are usually manufactured from plastic injection molding and are good alternative of metal brackets for patients having nickel allergy. Conventional plastic brackets were made of unfilled polycarbonate. These brackets were associated with certain drawbacks. Some of these drawbacks are given below:

31

rectangular wires engaged in plastic brackets is extremely difficult if not impossible because deformation or creep51, 52 of the bracket slot occurs. 3. Wings fracture of plastic brackets is also common because of decreased strength and wear resistance. 4. Plastic brackets offer greater friction to wires on sliding mechanics as compared to stainless steel brackets because of rough surfaces of bracket slot. Also the slot of the bracket is softer than SS wires so there are greater ploughing effects on sliding steel wires. 5. Some conventional unfilled plastic brackets need application of special primer53 for bonding. 6. Plastic brackets have been reported52, 54 to have lower shear bond strength as compared to conventional brackets. 7. Polycarbonate plastic brackets are produced by the reaction of Bisphenol A and phosgene CoCl2. There are biocompatibility issues 55 with polycarbonate brackets due to Bisphenol A release. Advancement in plastic brackets

1. They undergo water absorption in the oral cavity. Water absorption has plasticizing effects on the brackets with resultant decrease in mechanical properties of the brackets. Staining, increase bacterial growth over the brackets and foul odor from the mouth are also reported disadvantages of unfilled polycarbonate plastic brackets.

To overcome the problems of conventional plastic brackets, different materials were used for manufacturing of plastic brackets. These materials include polyoxymethylene, filled polycarbonate, polyurethane brackets and hybrid polymers.

2. The unfilled polycarbonate plastic bracket has a stiffness which is 60 times 50 less than that of stainless steel brackets. This decreased strength problem is further aggravated by plasticizing effect of water absorption. Giving torque to the teeth on

In 1997 plastic polyoxymethylene brackets were introduced 56 (Figure 2.23). The manufacturer claims that these brackets have better color stability, physical properties, low friction resistance and safe debonding

Plastic Polyoxymethylene Brackets


Selection of Precious metal brackets


CHAPTER characteristics. Researchers have voiced concern50 over the use of these brackets for orthodontic purpose as it was shown that these brackets release toxic formaldehyde in the oral cavity on degradation.

Figure 2.23 Polyoxymethylene bracket by Forestadent

Simple or medical grade polyurethane is used to manufacture modern plastic brackets (Figure 2.24). Unfilled polyurethane57 is usually used for bracket manufacturing. These brackets don't need a special primer for bonding and usually has a mechanical retentive base. These brackets don't use plasticizer and have shown to have increased strength, good color stability, less friction resistance. These brackets are either tooth colored or transparent.

2

Composite plastic brackets To overcome the problems of unfilled polycarbonate brackets, fillers were added to polycarbonate brackets so the term composite brackets was originated. Later fiber glass reinforced, ceramic reinforced and hybrid copolymer brackets were included under the name of composite brackets (Figure 2.25). To solve friction and to some extent slot creep problems, the slot of plastic brackets was replaced57 by austenitic stainless steel, niobium, silver and Ag-Cu alloy. It is claimed51 that these composite plastic brackets overcome all the disadvantages related to conventional unfilled polycarbonate brackets, however, controversy exist58 about this claim. Jia and colleagues59 showed that modern plastic brackets perform better with certain bonding cements and have acceptable 57 bond strength. Conventional plastic brackets were superseded by ceramic brackets but advancement in composite brackets and drawbacks of ceramic brackets has given renewed clinician interest in plastic brackets as they are safer for enamel integrity59 both during treatment and at debonding.

Figure 2.25 Composite bracket

Selection of plastic brackets. Figure 2.24 Orthoflex by Ortho Technologies (Medical grade polyurethane)

In plastic brackets ideally composite or polyurethane plastic brackets should be

32

Ceramic Brackets Ceramics are broad class of inorganic materials which are neither metallic nor polymer. Ceramics includes glasses, clays, precious stones and metal oxides. Ceramic is 3rd known hardest material and is harder60 than stainless steel and enamel. Ceramic brackets were introduced in the early 1980s and extensively marketed in the mid1980s to make patients braces less visible. As ceramic brackets are transparent or translucent they mask the appearance of fix orthodontic appliances. Advantages of ceramic brackets Ceramic brackets provide high bond strength, superior aesthetic, high wear resistance and better color stability over the plastic brackets. Because of shortcoming of plastic brackets

33

ceramic brackets have gained increased interest especially in adults. Ceramic brackets are inert and can safely be bonded in patients with nickel and chromium allergy. Disadvantages High bond strength, extra hardness and brittle nature of ceramics are the causes of different disadvantages associated with ceramic brackets. Some of the disadvantages are as follows. 1. Due to increase hardness there is difficulty in debonding, more chances of enamel damage and bracket fracture on debonding and tooth attrition61. Clinical notes Heavy forces can cause fracture of ceramic brackets. Heavy forces are usually applied during accidental impact or during debonding of ceramic brackets. Such scenario can be avoided by practicing recommended debonding techniques and avoiding bonding ceramic brackets in patient involved in sports where chances of accidental impact is greater such as footballers ,boxers etc. Enamel wear or tooth attrition occurs from ceramic brackets in clinical practice especially on upper incisor edges or their lingual aspects in deep bite cases or if lower brackets were bonded too incisal. Attrition of upper canine tips can also occur if upper canines come in contact with the lower canine ceramic bracket during canine retractions in class 2 cases. Proper placement of ceramic brackets is always mandatory as for all other types of brackets. If the patient has some parafunctional habit, ideally ceramic brackets in lower arch shouldn't be placed. Deep bites should be opened up before placing ceramic brackets on lower dentition.


selected. Plastic or composite brackets are good choice for patients with aesthetic concerns requiring minor tooth movement usually in adult patients. A patient having nickel allergy is also a good candidate for plastic brackets but plastic brackets with stainless steel slot should be avoided .In cases requiring sliding mechanics metal lined slots in plastic brackets or a combination of plastic and metal brackets is also used. Canine to canine plastic brackets are given to fulfill patient's aesthetic concern and posterior metal brackets are used for efficient sliding mechanics. This method is effective in cases where no considerable torque on anterior dentition is needed. Owing to decrease wear resistance of plastic brackets and safe debonding characteristics plastic brackets are also used in patients with esthetic concerns and where ceramic brackets are contraindicated. Those cases are deep bite cases, enamel hypoplasia, enamel cracks and root canal treated teeth.


CHAPTER Deep bites can be opened by the intrusion of upper incisors, proclining upper incisors, placing bite blocks or using bite turbos. Placing metal or plastic brackets on lower dentition is also a viable option in deep bite cases. The same is true to avoid canine attrition during canine retractions. 2. Discoloration of ceramic brackets also occurs in cases with longer treatment time and due to stress corrosion 62, 63. Clinical Notes In clinical practice many times the main reason for selecting ceramic brackets are aesthetic concerns of the patients. But unfortunately the aesthetic results of ceramic brackets are not absolute. Some polycrystalline brackets discolor with time if used with some specific diet. It is reported that caffeine containing diet, lipstick and mouth washes discolor64 the polycrystalline ceramic brackets. No mix adhesives have been contraindicated with ceramic brackets by Swartz60 because they discolors with time. So while using polycrystalline brackets no mix adhesives should be avoided and the patient should be advised regarding the potential chances of bracket discoloration from diet or life style factors. 3. Ceramic, being the 3rd hardest material is harder than stainless steel wires. Clinical Notes Ceramic brackets are harder than stainless steel wires so they offer greater friction in closing extraction spaces on sliding mechanics. So loop mechanics are preferred with ceramic brackets on closing spaces. For sliding mechanics ceramic brackets with metal slots should be used or combination of anterior ceramic and posterior metal brackets can also be used.

2

To avoid posterior anchorage loss while retracting anterior dentition on sliding mechanics, anchorage should be reinforced with implants, headgear, and TPA Nance appliance. A safe way for enmass retractions of anterior dentition is to use implant in posterior part of the arch for anchorage reinforcement. Canines can also be retracted ahead of incisors to decrease anchorage demands. Some clinicians use round wires to decrease friction during tooth movement which results in roller coaster effect resulting in increase in overbite and enamel wear of upper incisors by lower ceramic brackets. It is better to use ceramic brackets with metal slots on rectangular wires than retracting teeth on round wires.

4. Due to brittle nature of ceramics there is always danger of ceramic bracket fracture on engaging heavier wire in brackets slots or if there is torsion in the wire. Torque expression characteristics of ceramics are poor. Clinical Notes Using tight steel ligatures increases the surface roughness of bracket wings and so decreases their fracture strength. Always avoid too much tightening of the steel ligatures on ceramic brackets. Extra care should also be exercised while cutting these ligatures as the sharp cutter may leave scratch marks on the bracket surface or may accidentally cut the bracket wings. Giving increase torque on a rectangular wire can also lead to bracket slot fracture. Engaging full dimensions rectangular wires in the slot sometimes also lead to bracket fracture. Progressive torque should always be given in ceramic brackets. Using same dimension NiTi or TMA wires are a better option before moving to steel wires. In cases involving full engagement on steel wires like orthognathic surgeries, or fixed functional appliances ceramic brackets should not be used.

34

6. Ceramic brackets have increased bond strength as compared to other brackets. So these are contraindicated 65 in patients with enamel cracks, restorations or devitalized teeth, hypoplastic teeth and hypocalcified teeth. 7. Ceramic brackets are made bulkier to resist fracture. Bulkier brackets are more conspicuous and may cause soft tissue injury. 8. Ceramic is bonded with directional ionic and covalent bonds66. These brackets cannot be debonded like metal brackets Clinical notes To avoid ceramic brackets fracture semi twin design is used instead of true twin design. Tying elastic ligature in semi twin brackets require a heavier force of insertion and different wrist movement than used in tying a ligature in conventional brackets.

Monocrystalline Brackets Monocrystalline brackets are also called clear sapphire or monocrystalline sapphire brackets (Figure 2.26). Monocrystalline brackets were initially manufactured from naturally occurring sapphire but contemporary monocrystalline brackets are manufactured from synthetic sapphire. Monocrystalline brackets have a clear transparent appearance. Monocrystalline brackets are manufactured by melting pure aluminum oxide particles on temperature above 2100 °C and then allow it to cool slowly thus permitting complete crystallization. This results in a single large crystal rod or bar of aluminum oxide from which brackets are milled by using various cutting tools (ultrasonic cutting techniques, diamond cutting or Nd:YAG lasers). As a result of milling, stresses are introduced into the crystal which is relieved by heat treatment 60, 68.

There are three types of ceramic brackets used for orthodontic purpose which are made of aluminum oxide, Zirconia or calcium phosphate. 1. Aluminum oxide or Alumina (Al2O3) Brackets Alumina is formed when aluminum is added to steel to remove dissolved oxygen from the steel. For orthodontic purpose alumina may be used in two ways60, 67. 1. S i n g l e c r y s t a l m a t e r i a l o r Monocrystalline brackets 2. Multiple crystals or Polycrystalline brackets

35

Figure 2.26 Monocystalline bracket

Polycrystalline Brackets As polycrystalline brackets contain multiple crystals of alumina hence are called polycrystalline (Figure 2.27). These brackets are manufactured by sintering of aluminum oxide. The process involves blending of micron size (average particle size 0.3 μm) aluminum oxide particles using a


5. Ceramic brackets are radiolucent and so can't be detected by x rays if accidentally aspired or swallowed during debonding.


CHAPTER binder and molding the mixture into desired shape. The molded part is then heated at temperature which is in excess of 1800 °C but below the melting point of aluminum oxide, to burn out the binder particles and the molded mixture is fused together. Magnesia69 is used in sintering process of the manufacturing of polycrystalline brackets to facilitate growth of grain boundaries of crystals. Diamond cutting tools are then used to machine the slot of brackets. Heat treatment is also done to reduce stress and imperfections. Heat treatment after machining must be carefully controlled to prevent further grain fusion which could detract the physical properties of the brackets. The particle size of final ceramic bracket is between 20 to 30 μm. Molding of polycrystalline brackets can also be done by ceramic injection molding which does not require the parts to be machined and so eliminate structural imperfection caused by the cutting process. The injection molded brackets have shown to have increased fracture resistance68.

2

Zirconia Brackets Zirconia (ZrO2) is material extracted from the beach sand of Australia .Partially stabilized Zirconia brackets were introduced as an alternative to polycrystalline alumina brackets to have better fracture resistance(Figure 2.28). Polycrystalline Zirconia brackets are manufactured by mixing ultrafine Zirconia powder with 5% by weight yttrium oxide. By the impression molding technique specific bracket shape is given and sintering is done. Hot isostatic pressing is employed to remove residual porosity from brackets. Stabilized polycrystalline Zirconia brackets are cheaper and have greater fracture resistance because of the phase transformation toughness among all ceramic brackets while controversy76, 77 exist whether they have equivalent or better friction properties over other ceramic brackets. As polycrystalline zirconium oxide brackets are opaque and have a yellowish tint as compared to polycrystalline brackets, so these brackets failed to gain much popularity as an aesthetic appliance.

The larger the crystal size of a polycrystalline bracket less would be grain boundaries, clearer would be the bracket, however bracket become weaker when the grain size reaches 30 micron60.

Figure 2.28 Cooperation

Coby Zirconia ceramic brackets by YDM

Calcium phosphate ceramics Figure 2.27

Polycrystalline Bracket

A new type of orthodontic brackets has been introduced by Tomy international Japan which

36

Monocrystalline brackets

Polycrystalline brackets

1. Monocrystalline brackets are transparent as they contain a single crystal of aluminum oxide.

Polycrystalline brackets have decreased optical clarity and are translucent. In polycrystalline brackets as the binder is involved in manufacturing process to fuse multiple particles so there are greater chances of impurities in bracket as compared to monocrystalline brackets. Also multiple crystals in polycrystalline bracket mean increases in the number of grain boundaries and so decreases in optical clarity.

2. Monocrystalline brackets resist staining.

Polycrystalline brackets discolor with time if used with some specific diet.

3. Monocrystalline brackets are expensive70 because shaping single crystal into bracket by cutting tools is a delicate process. 4. Monocrystalline brackets have greater71 tensile strength .The tensile strength of monocrystalline brackets is 1800 MPa. 5. Monocrystalline fracture strength decreases 66 with time. 6. Monocrystalline brackets though having greater tensile strength fracture easily 66, 72 than polycrystalline brackets. Monocrystalline brackets being made from a single crystals fracture at once due to lack of grain boundaries and so are more brittle. 7. Monocrystalline brackets have more smooth surfaces than polycrystalline brackets but have equivalent friction resistance73. 8. Bond strength values of monocrystalline versus polycrystalline brackets are controversial in literature 72, 74.

Polycrystalline brackets are inexpensive because the molding process is simple and large quantities of brackets can be manufactured. The tensile strength of polycrystalline brackets is 380 MPa which is less than monocrystalline brackets. Polycrystalline bracket strength remains unchanged with time. Polycrystalline brackets have multiple grain boundaries which resist crack propogation.

is made of calcium phosphate ceramics .The manufacturer of this bracket claims that these brackets have excellent biocompatibility, low friction properties and hardness equivalent to the enamel surface, which eliminates fears of dental abrasion due to contact with tooth surface even when the patient has deep-bite. No

37

Polycrystalline brackets have a rough surface as compared to monocrystalline brackets.

information is available by the manufacturer about the exact composition and manufacturing technique of this bracket. Calcium phosphate is usually used in dentistry for bone prosthesis. It has been reported78 that calcium phosphate ceramic brackets have lower but clinical acceptable bond strength


Table 7.Comparison between Monocrystalline and Polycrystalline Bracket


CHAPTER than conventional ceramic brackets and these brackets don't cause enamel damage. Selection of ceramic brackets Ceramic brackets are usually selected for patients who have aesthetic concerns. Due to iatrogenic damages associated with ceramic brackets they should only be selected when clinicians have proper knowledge of mechanics and proper instrumentation for debonding is available. Monocrystalline brackets give better aesthetic than polycrystalline brackets but are more expensive and fracture easily and more with time. Zirconia brackets are rarely used in contemporary orthodontics. Calcium phosphate ceramics is manufactured by only one company and not much is known about these brackets so selection of these brackets is a personal preference.

2

Vivo: Aging and Related Phenomena. New York, NY: Quintessence; 2003:141–156. 8. Brockhurst PJ, Pham HL. Orthodontic silver brazing alloys. AustOrthod J. 1989;11:96–99. 9. Mockers O, Deroze D, Camps J. Cytotoxicity of orthodontic bands, brackets and archwires in vitro. Dent Mater. 2002;18:311– 317. 10. Grimsdottir MR, Hensten-Pettersen A. Cytotoxic and antibacterial effects of orthodontic appliances. Scand J Dent Res. 1993;101: 229–231. 11. Grimsdottir MR, Hensten-Pettersen A, Kullmann A. Cytotoxic effect of orthodontic appliances. Eur J Orthod. 1992;14:47–53. 12. Oh KT, Choo SU, Kim KM, Kim KN. A stainless steel bracket for orthodontic application. Eur J Orthod. 2005 Jun;27(3):237-44. 13. Feldner JC, Sarkar NK, Sheridan JJ, Lancaster DM. In vitro torquedeformation characteristics of orthodontic polycarbonate brackets. Am J Orthod Dentofacial Orthop. 1994 Sep;106(3):265-72. 14. Flores DA, Choi LK, Caruso JM, Tomlinson JL, Scott GE, Jeiroudi MT. Deformation of metal brackets: a comparative study. Angle Orthod. 1994;64(4):283-90. 15. Maijer R, Smith DC. Corrosion of orthodontic bracket bases. Am J Orthod. 1982 Jan;81(1):43-8. 16. Creekmore TD, Kunik RL. Straight wire: the next generation. Am J Orthod Dentofacial Orthop. 1993 Jul;104(1):8-20. 17. Arici S, Regan D. Alternatives to ceramic brackets: the tensile bond strengths of two aesthetic brackets compared ex vivo with stainless steel foil-mesh bracket bases. Br J Orthod. 1997 May;24(2):133-7.)

References

18. Eliades T, Athanasiou AE. In vivo aging of orthodontic alloys: implications for corrosion potential, nickel release, and biocompatibility. Angle Orthod. 2002 Jun;72(3):222-37.

1. Hotz RP. The changing pattern of European orthodontics. Br J Orthod 1973; 1:4-8.

19. Schiff N, Dalard F, Lissac M, Morgon L, Grosgogeat B. Corrosion resistance of three orthodontic brackets: a comparative study of three fluoride mouthwashes. Eur J Orthod. 2005 Dec;27(6):541-9.

2. Matasa C. Characterization of used orthodontic brackets. In: Eliades G, Eliades T, Brantley WA, Watts DC, eds. Dental Materials in Vivo: Aging and Related Phenomena. New York, NY: Quintessence; 2003:141–156. 3. Zinelis S, Annousaki O, Makou M, Eliades T. Metallurgical characterization of orthodontic brackets produced by Metal Injection Molding (MIM). Angle Orthod. 2005 Nov;75(6):1024-31. 4. Floria G, Franchi L. Metal injection molding in orthodontics.Virtual J Orthod. 1997:2.1. 5. Coley-Smith A, Rock WP. Distortion of metallic orthodontic brackets after clinical use and debond by two methods. Br J Orthod. 1999 Jun;26(2):135-9. 6. Zinelis S, Annousaki O, Makou M, Eliades T. Elemental composition of brazing alloys in metallic orthodontic brackets.Angle Orthod. 2004;74:394–399. 7. Matassa C. Characterization of used orthodontic brackets. In: Eliades G, Eliades T, Brantley WA, Watts DC, eds. Dental Materials In

20. Oh KT, Choo SU, Kim KM, Kim KN. A stainless steel bracket for orthodontic application. Eur J Orthod. 2005 Jun;27(3):237-44. 21. Eliades T, Zinelis S, Eliades G, Athanasiou T. Characterization of as-received, retrieved and recycled stainless steel brackets. J Orofac Orthop. 2003;64:80–87. 22. Hunt NP, Cunningham SJ, Golden CG, Sherif M. An investigation into the effects of polishing on surface hardness and corrosion of orthodontic archwires. Angle Orthod. 1999;69: 433–440. 23. Brantley WA. Orthodontic wires. In: Brantley W, Eliades T, eds. Orthodontic Materials: Scientific and Clinical Aspects. Stuttgart, Germany: Thieme; 2001:95. 24. Eliades, T., Eliades, G., Brantley, W.A. (2001). Orthodontic brackets, in: Brantley, W. A., Eliades, T. (Eds.), Orthodontic Materials: scientific and clinical aspects Thieme, Stuttgart, 146-147. 25. Platt JA, Guzman A, Zuccari A, Thornburg DW, Rhodes BF, Oshida Y, Moore BK. Corrosion behavior of 2205 duplex stainless steel. Am J Orthod Dentofacial Orthop. 1997 Jul;112(1):69-79.) 26. Eliades T. Orthodontic materials research and applications: part 2.

38

27. Matasa CG. Direct bonding metallic brackets: where are they heading? Am J Orthod Dentofacial Orthop. 1992 Dec;102(6):552-60. 28. Eliades T, Zinelis S, Eliades G, Athanasiou AE. Nickel content of asreceived, retrieved, and recycled stainless steel brackets. Am J Orthod Dentofacial Orthop. 2002 Aug;122(2):217-20.

44. Martyn CN. The epidemiology of Alzheimer's disease in relation to aluminium. Ciba Found Symp 1992;169:69—79. 45. Huang YC, Ghio AJ, Stonehuerner J, McGee J, Carter JD,Grambow SC, Devlin RB. The role of soluble components in ambient fine particlesinduced changes in human lungs and blood. Inhal Toxicol 2003;15:327—42. 46. Harzer W, Schröter A, Gedrange T, Muschter F. Sensitivity of titanium brackets to the corrosive influence of fluoride-containing toothpaste and tea. Angle Orthod. 2001 Aug;71(4):318-23.

29. Haddad AC, Tortamano A, Souza AL, Oliveira PV. An in vitro comparison of nickel and chromium release from brackets. Braz Oral Res. 2009 Oct-Dec;23(4):399-406.

47. Reclaru L, Meyer JM. Effects of fluorides on titanium and other dental alloys in dentistry. Biomaterials. 1998;19:85–92.

30. Nair SV, Padmanabhan R, Janardhanam P. Evaluation of the effect of bracket and archwire composition on frictional forces in the buccal segments.Indian J Dent Res 2012;23:203-208.

48. Toumelin-Chemla F, Rouelle F, Burdairon G. Corrosive properties of fluoride-containing odontologic gels against titanium. J Dent. 1996;24:109–115.

31. Moore MM, Harrington E, Rock WP. Factors affecting friction in the pre-adjusted appliance. Eur J Orthod. 2004 Dec;26(6):579-83.

49. Brandt S. JCO interviews Dr Elliott Silverman, Dr Morton Cohen, and Dr A. J. Gwinnett on bonding. J Clin Orthod 1979 ; 13:236-51.

32. Schiff N, Dalard F, Lissac M, Morgon L, Grosgogeat B. Corrosion resistance of three orthodontic brackets: a comparative study of three fluoride mouthwashes. Eur J Orthod. 2005 Dec;27(6):541-9.

50. Kusy RP, Whitley JQ. Degradation of plastic polyoxymethylene brackets and the subsequent release of toxic formaldehyde. Am J Orthod Dentofacial Orthop. 2005 Apr;127(4):420-7.

33. Eliades T. Passive film growth on titanium alloys: physicochemical and biologic considerations. Int J Oral Maxillofac Implants 1997;12:621—7.

51. Feldner JC, Sarkar NK, Sheridan JJ, Lancaster DM. In vitro torquedeformation characteristics of orthodontic polycarbonate brackets. Am J Orthod Dentofacial Orthop 1994;106:265-72.

34. Park JB, Lakes RS. Biomaterials: an introduction, 2nd ed. New York: Plenum; 1992. p. 92, 107, and 231.

52. Aird JC, Durning P. Fracture of polycarbonate edgewise brackets: a clinical and SEM study. Br J Orthod. 1987;14:191–195.

35. Hamula DW, Hamula W, Sernetz F. Pure titanium orthodontic brackets. J Clin Orthod 1996;30:140-4.

53. Buzzitta VA, Hallgren SE, Powers JM. Bond strength of orthodontic direct-bonding cement-bracket systems as studied in vitro. Am J Orthod. 1982 Feb;81(2):87-92.

36. Michelberger DJ, Eadie RL, Faulkner MG, Glover KE, Prasad NG, Major PW. The friction and wear patterns of orthodontic brackets and archwires in the dry state. Am J Orthod Dentofacial Orthop. 2000 Dec;118(6):662-74.

54. de Pulido LG, Powers JM. Bond strength of orthodontic directbonding cement-plastic bracket systems in vitro. Am J Orthod 1983;83:124-30.

37. Gioka C, Bourauel C, Zinelis S, Eliades T, Silikas N, Eliades G. Titanium orthodontic brackets: structure, composition, hardness and ionic release. Dent Mater. 2004 Sep;20(7):693-700.

55. Suzuki K, Ishikawa K, Sugiyama K, Furuta H, Nishimura F 2000 Content and release of bisphenol A from polycarbonate dental products. Dental Materials 19: 389–395.

38. Kapur R, Sinha PK, Nanda RS. Frictional resistance in orthodontic brackets with repeated use. Am J Orthod Dentofacial Orthop 1999;116:400-4.

56. Foerster R. Plastic orthodontic bracket for retaining wire bridge with projections of second plastic. German Patent DE19618364; 1997. p. 1-8.

39. Kusy RP, O'grady PW. Evaluation of titanium brackets for orthodontic treatment: Part II--The active configuration. Am J Orthod Dentofacial Orthop. 2000 Dec;118(6):675-84.

57. Ali O, Makou M, Papadopoulos T, Eliades G Laboratory evaluation of modern plastic brackets. Eur J Orthod. 2012 Oct;34(5):595-602.

40. Kusy RP, Whitley JQ, Ambrose WW, Newman JG. Evaluation of titanium brackets for orthodontic treatment: part I. The passive configuration. Am J Orthod Dentofacial Orthop. 1998 Nov;114(5):55872. 41. Ou DX, Wang ZM, Guo HM, Li S, Bai YX. Bond strengths of customized titanium brackets manufactured by selective laser melting. Zhonghua Kou Qiang Yi Xue Za Zhi. 2013 Jul;48(7):419-22. 42. Nandini S,Reddy V,Reddy S. Titanium brackets as an innovation to replace stainless steel.J Sci Heath Res .2013 Dec ;2 (3):7-9. 43. Rogers MA, Simon DG. A preliminary study of dietary aluminium intake and risk of Alzheimer's disease. Age Ageing 1999;28:205—9.

58. Liu J K, Chang L T, Chuang S F, Shieh D B 2002 Shear Bond Strengths of Plastic Brackets With a Mechanical Base, Angle orthodontist 72: 142-145. 59. Eliades T, Viazis AD, Lekka M. Failure mode analysis of ceramic brackets bonded to enamel. Am J Orthod Dentofacial Orthop. 1993;104:21–26. 60. Swartz ML. Ceramic brackets. J Clin Orthod. 1988 Feb;22(2):82-8. 61. Douglass JB. Enamel wear caused by ceramic brackets. Am J Orthod Dentofacial Orthop. 1989 Feb;95(2):96-8. 62. Michalske TA, Bunker BC, Freiman SW. Stress corrosion of ionic and mixed ionic/covalent solids. J Am Ceram Soc. 1986;69:721–724. 63. Salem J, Powers L, Allen R, Calomino A. Slow crack growth and

39


Current status and projected future developments in materials and biocompatibility. Am J Orthod Dentofacial Orthop. 2007 Feb;131(2):253-62.


CHAPTER

2

fracture toughness of sapphire for a window application. Proceedings of SPIE: The International Society for Optical Engineering. 2001;4375:41–52. 64. Ghafari J. Problems associated with ceramic brackets suggest limiting use to selected teeth.Angle Orthod. 1992 Summer ;62 (2) :14552. 65. Bishara SE, Trulove TS. Comparisons of different debonding techniques for ceramic brackets: an in vitro study. Part I. Background and methods. Am J Orthod Dentofacial Orthop. 1990 Aug;98(2):14553. 66. Flores DA, Caruso JM, Scott GE, Jeiroudi MT. The fracture strength of ceramic brackets: a comparative study. Angle Orthod. 1990 Winter;60(4):269-76. 67. Birnie, D. Ceramic brackets. Br. J. Orthod., 17:71-5, 1990. 68. Bordeaux JM, Moore RN, Bagby MD. Comparative evaluation of ceramic bracket base designs. Am J Ortho Dentofacial Orthop. 1994. 1 O5:552-560. 69. Soni K, Thompson A, Harmer M, Williams D, Chabala J, Levi-Setti R. Solute segregation to grain bondaries in MgO doped alumina. Appl Phys Lett. 1995;66:2795–2797. 70. Scott GE Jr. Fracture toughness and surface cracks—the key to understanding ceramic brackets. Angle Orthod. 1988; 58:5–8. 71. Johnson G, Walker MP, Kula K. Fracture strength of ceramic bracket tie wings subjected to tension. Angle Orthod. 2005 Jan;75(1):95-100. 72. Viazis AD, Cavanaugh G, Bevis RR. Bond strength of ceramic brackets under shear stress: an in vitro report. Am J Orthod Dentofacial Orthop. 1990 Sep;98(3):214-21. 73. Cacciafesta V, Sfondrini MF, Scribante A, Klersy C, Auricchio F. Evaluation of friction of conventional and metalinsert ceramic brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop. 2003 Oct;124(4):403-9. 74. Klocke A, Korbmacher HM, Huck LG, Ghosh J, Kahl-Nieke B. Plasma arc curing of ceramic brackets: an evaluation of shear bond strength and debonding characteristics. Am J Orthod Dentofacial Orthop. 2003 Sep;124(3):309-15. 75. Monticello J. The comparative shearing strength of five contemporary ceramic brackets, master's thesis,University of Detroit, 1990. 76. Springate SD, Winchester LJ. An evaluation of zirconium oxide brackets: a preliminary laboratory and clinical report. Br J Orthod 1991; 18: 203–9. 77. Keith O, Kusy RP, Whitley JQ. Ziconia brackets: an evaluation of morphology and coefficient of friction. Am J Orthod Dentofac Orthop 1994; 106: 605–14.). 78. Meguro D, Hayakawa T, Kawasaki M, Kasai K. Shear bond strength of calcium phosphate ceramic brackets to human enamel. Angle Orthod. 2006 Mar;76(2):301-5.

40

CHAPTER

3

Selection of Bracket Base In this Chapter

Bracket Base Retention Design Stainless steel Brackets Mechanical Retention Perforated bases Mesh type bases Integral bases Photoetched bases Microetced bases Metal sintered bases Laser structured bases Plasma coated brackets

Chemical Retention Stainless steel brackets and Cross infection

Plastic Brackets Chemical Retention Mechanical Retention Combination of chemical and mechanical retention

Ceramic Brackets Chemical Retention Mechanical Retention Micromechanical retention Ceramic brackets with prestressed base Combination of different retention designs

Bracket base surface area Bracket base shape

Titanium Brackets

Bracket identification marks

Cobalt Chromium Brackets

Torque in the Base

The base component of orthodontic brackets makes possible the attachment of a bracket to the tooth. This attachment must be strong enough to transfer orthodontic forces from the wires to the teeth, withstand masticatory loads and should easily be removed at the end of treatment.

41

Precious metal Brackets

Bracket Base Retention Design Orthodontic brackets are attached to teeth or other supporting structures of porcelain, metal, composite and acrylic through various commercially available adhesives. To increase retention of bracket bases to adhesives various chemical, mechanical or combination of both retention designs have been added to the bracket base. Though the exact manufacturing details


CHAPTER are not provided from the manufacturer some basic informations are available. 1) Stainless steel Brackets Most orthodontic brackets used in contemporary orthodontics are made of stainless steel which mostly uses mechanical retention because stainless steel doesn't form any chemical union with adhesives. Stainless steel bracket base is either integral part of the bracket or is made separately and then joined to the main body of the bracket by brazing or welding (Figure 3.1).Different types of stainless steel bracket bases are given in the following text. 1. Perforated bases Brackets with perforated bases are one of the oldest bracket designs for mechanical retention1 (Figure 3.2). The original metal pad consists of one row of peripheral perforation. The basic idea was to allow greater penetration and free flow of adhesive cement through the bracket base to increase the bond strength. But unfortunately excessive adhesive coming out of the holes of bracket base was potential plaque retention area which get discolored with time so raised esthetic concerns by the patients and don't provide superior retention as compared to other designs2,3,4,5,6. Because of these disadvantages perforated bracket bases went into disuse. 2. Mesh type bases Mesh type bases have replaced perforated bases and are most popular type used in contemporary orthodontics. Following different terms are used for mesh based bases in literature and by manufacturer owing to slight variation in mesh design.

3

a) Foil mesh base b) Gauze or woven mesh base c) Mini mesh base d) Micro mesh base e) Optimesh base f) Ormesh base g) Laminated mesh base h) Single mesh base I) Double mesh base j) Supermesh base Description of some important mesh designs is as follows. a) Foil mesh base In orthodontic literature the term foil mesh base is used interchangeably with gauze or woven mesh base. But there are slight differences in the manufacturing design between foil mesh and woven mesh base (Figure 3.3) .Foil mesh bases are more esthetic and hygienic than perforated bases because of their smooth covered surface 2, 3, 7, 8 . Foil and woven mesh bases provide superior retention than perforated bases and many other bracket base designs used in contemporary orthodontics 4, 7, 9. Foil mesh bases can be simple or microetched, photoetched or plasma coated by the manufacturer. The foil mesh is either brazed or welded on to the bracket base. The spot welding of foil mesh to bracket base results in decreased base surface areas and so bond strength 2, 4, 10 therefore spot welding have been taken over by silver based laser welding 11. Foil mesh bases can be single mesh or double mesh.

42

Selection of Bracket Base Figure 3.1 Bracket bases can either be integral part of the bracket made by casting or MIM procedure or these bases can be made separately and then joined to the main body of bracket by brazing or welding process. A. Bracket base made separately by casting and joined by brazing to base of the main bracket body. This design of base usually adds to the height of the bracket making the brackets more conspicuous. Increase height of the bracket also effects its torque expression. B.A gauze mesh made separately and brazed to the bracket base. Brazing in this part of the bracket decrease the flow of adhesive in the mesh and decreases the bond strength. C. A bracket mesh which is integral part of the bracket made by MIM.

Figure 3.2 A perforated base. Due to discoloration of the bonding adhesive coming out of the perforated bases these brackets raised esthetic concerns by the patients. Brackets with perforated bases have been abandoned from mainstream orthodontics.

43

Figure 3.3 Difference between foil mesh base and woven mesh base. A. Woven or gauze mesh base. In woven mesh or gauze mesh base two separate wires of same diameter are woven over each other B. Foil mesh base. In foil mesh base a single wire is used to make the mesh base.


CHAPTER

3

a) Single mesh base

c) Super mesh

Single mesh base also known as monolayer base has a single layer of mesh attached to the bracket base (Figure 3.4). Single mesh base is the most popular design used in orthodontic brackets.

Super mesh base is a type of double mesh base that consist of superficial or outer mesh of 100 gauge over a deep or inner mesh of 200 gauge.

b) Double mesh base Double mesh is also known as bilayer or dual mesh (Figure 3.5). Superficial layer of double mesh is coarse mesh (80gauge) while deep layer is fine mesh (150 gauge) 12 . In terms of effectiveness Bishara13 found comparable bond strength of single and double mesh brackets.

Clinical Notes Single mesh can be easily recycled and reused. In double mesh recycling by thermal or sandblasting method can leave adhesive in deep layer thus decreasing the bond strength of recycled brackets. Following characteristics of a mesh base should be kept in mind while selecting mesh based bracket bases14. 1. Mesh Number or size or Mesh gauge Defined as number of openings of a mesh per linear inch from center of the wire to center of the wire 3, 13. Mesh size reported in orthodontic literature ranges from 40 to 100 gauge (40, 60, 70, 80,100 gauge). So a 40 gauge mesh has 40 openings per linear inch .More is the gauge number finer would be the mesh. 100 gauge is a fine mesh while 40 gauge is coarse mesh. In literature up to 80 gauges mesh is taken as coarse mesh 1, 12.

Figure 3.4 A single mesh base. Single mesh base is one of the most popular designs in orthodontic brackets.

Literature about selecting proper mesh number is controversial and support increase bond strength for coarse mesh 11,15,16,17 , fine mesh 4,9, 60 gauge 3,18,19, 60 to 70 gauge 16, 100 gauge mesh 20.Cucu21found no clinically significant difference between 80 gauge and 100 gauge mesh. A personal view of this author after going through many manufacturers' websites is that single 80 gauge mesh was most manufactured base design. 2. Wire diameter of the mesh

Figure 3.5 Double mesh base of woven type. The diameter of wire in outer mesh is increased while the inner mesh has decreased mesh diameter.

Though the manufacturer never reveals the exact diameter of the wire used for making

44

3. Aperture diameter or mesh diameter It is the diameter of a single mesh opening. It's usually given in microns or micrometer (µm) .In literature 13, 16 it ranges from 75 to 700 µm. Mesh diameter may be equal to wire diameters of the mesh in case of a fine mesh or greater than its wire diameter in case of coarse mesh. Increasing wire diameter will decrease the aperture diameter (Figure 3.7).

Figure 3.6 A.60 gauge mesh. B. 80 gauge mesh. C. 100 gauge mesh. Greater the number of opening per linear inch greater would be the mesh number.

mesh of bracket bases but studies have shown various diameters. Usually more the mesh number less is the wire diameter. The wire diameter is usually given in inches or micrometer (µm) and ranges in literature from 0.0021 to 0.0080 inch. Wire diameter

45

Figure 3.7 Both brackets have 80 gauge mesh. Bracket A has increase aperture diameter while bracket B has increased wire diameter.


of mesh shouldn't be confused with mesh diameters of brackets. Wire diameter of mesh should be optimum as increased diameter will hinder adhesive flow while the decrease in wire diameter will increase the risk of wire breakage and faulty mesh design.


CHAPTER

3

4. Open area %

Clinical Notes

It's the total amount of open area on a bracket base available for adhesive penetration and depends upon the aperture diameter. Greater the aperture diameter greater is the open area percentage. Sandblasting and microetching also increases the open area percentage. A greater open area % helps better penetration and more room for adhesive thus increases the bond strength of the bracket (Figure 3.8). In literature 13,16 the open area percentage ranges from 21.2 % to 55.5% of the bracket base surface area.

The choice of adhesive is correlated with the choice of the bracket mesh. Greater the mesh number lesser would be the aperture diameter, so a less viscous or less filled adhesive would be required to flow into the opening of the mesh. If the mesh number of the bracket is increased a point will be reached at which the contact angle of adhesive with metal will prevent the flow of adhesive in a single aperture. Decreasing the filler contents of adhesive to increase its viscosity will decrease its strength and also increase correct bracket position difficult because increased flow of adhesive will slide the bracket downward in time interval between bracket placement and adhesive curing. Decreasing the mesh number will many times decrease the wire diameter of the mesh. Such brackets are poor choices for recycling as mesh wire will break during debonding or during recycling especially with sandblasting (Figure 3.9). Also the increased open areas have its limitation. An excessively increased open area will decrease mechanical retention of the adhesive and so the bond strength.

Figure 3.8 Two debonded brackets. Bracket A has more open area %, so the adhesive is still retained in the mesh of the bracket due to better penetration. Bracket B has less penetration of the adhesive due to decreased open area %.

Figure 3.9 60 gauges woven mesh on recycling with 90 micron aluminum oxide. As the diameter of the wire in mesh decreased there are greater chances of wire damage on recycling. A damaged mesh will provide poor mechanical retention to brackets and so decreases their bond strength.

46


e) Sandblasted foil mesh Some clinician use chair side sandblasting units to roughen the mesh and increase its mechanical retention (Figure 3.10). Sandblasting is usually done with 50 µm aluminum oxide particles for 5 seconds maintaining a distance of 10 mm from the handpiece tip to bracket base. The line pressure is maintained at 90 psi 22. Sandblasting the bracket for more than 9 seconds can damage the foil mesh. Most clinician uses sandblasting on deboned brackets to recycle them rather than doing it on new brackets.

Figure 3.10 A foil mesh base sandblasted to increase the bond strength by giving macro and micro retention to the adhesive. Macro retention is provided by openings of bracket mesh and microretention is produced by sandblasting.

3. Integral bases Integral bases are fabricated in one unit with the brackets. They are manufactured by casting (cast integral base), milling (machined integral base) or metal injection molding (MIM) procedure. Integral bases have furrows, pits and undercut channels for retention 23(Figure 3.11). There is conflict in literature 9, 18, 22, 23, 24, 25 regarding bond strength of integral bases. 4. Photoetch bases Photoetching or photochemical etching is a

47

Figure 3.11 A. An integral base with pits in the base. Such smaller pits provide greater open areas in the bracket base but this open area is too large to provide good mechanical retention to the bracket. The bracket base is sandblasted to increase the bond strength by microretention. B. A integral base made by casting of 304 SS. Open area of the bracket is optimum for providing good adhesive flow and mechanical retention.

process that removes metal using a chemical reaction and thus creating small indentation in the bracket base. In this process parts of bracket base that are to be etched are exposed to chemical while the other parts are covered with a photo etching resistant material. The whole process is done using the computer generated templates for etching in a clean controlled environment. The photo etched processes can also be applied to foil mesh bases to increase their mechanical retention (Figure 3.12). Photoetched bases have reported4,7,25 less bond strength than foil mesh bases .


CHAPTER

3

7. Laser structured bases These bracket bases are treated with a laser beam (Nd:YAG) to create retentive holes by burning out the metal (Figure 3.14).The laser structured bases have increased bond strength than mesh type bases 26.

Figure 3.12 strength.

Photoetch foil mesh to increase bond

5. Microetced bases Microetching of brackets is done by the manufacturer by a grit blasting procedure (Figure 3.13). Microetching of brackets in dental office can be done by sandblasting .Microetching does a more uniform etching than the photoetching.

Figure 3.13 A bracket by GAC with microethed bases. These types of brackets only provide microretention for adhesives.

Figure 3.14 The laser structured bases of discovery brackets by Dentaurum. A. A new laser structured base. B. A recycled base after sandblasting. New laser structured base has better bond strength than mesh type bases but laser structured bases recycled by sandblasting or flame method has poor bond strength.

8. Plasma coated brackets 6. Metal sintered bases In this type of bases a porous structure is created on the bracket base by fusion of metal powder or ceramic particles to increase mechanical retention of the base.

In this process finely grounded metallic and non-metallic materials are deposited on a bracket base in a molten or semi molten state thus increasing roughness and surface area of bracket base. Plasma coating can be done on mesh foil bases or on a smooth base. Even a


A

B

C

D

F

E

G

Figure 3.15 A&B .These sticky packings should be avoided. C. Properly packed brackets. D, E, F show insects or their body parts in sticky bracket packings. G. Corrosion product of the bracket bases .As bracket bases continuously remain in touch with liquid solution so their corrosion occur. These pictures are from some well reputed companie's products. The situation is much worse with other companies.

49


CHAPTER smooth plasma coated brackets have shown accepted bond strength 27. Chemical Retention Although stainless steel brackets predominantly use mechanical retention some clinicians have also reported salinated mesh on grooved bases 25 . Commercially available silane coupling agents can also be applied to silanized metal brackets to give chemical retention to the brackets. Silica plus silane coating of stainless steel brackets is usually done with brackets recycled by sandblasting or flame method to increase their bond strength. Stainless steel brackets and Cross infection Usually orthodontists use the bracket in the as received state and don't go for sterilization of the brackets as this may affect bracket properties. It is thought that these brackets have been kept and packed by the manufacturer in an aseptic environment. Unfortunately that's not the case with many of the brackets we get from renowned manufacturers. Packing of the brackets is very important and in some packings it's usually the base part of the bracket which is attached to the packing base, is involved in cross infection (Figure 3.15.)

3

Rest of the base designs should be selected on personal experience. Mechanical retention is best suited with stainless steel brackets. Chemical retention should be avoided both with new and recycled brackets. Packing using sticky substances for attaching the brackets to packing should be avoided. Titanium Brackets Titanium brackets like stainless steel brackets uses mechanical retention in the form of mesh or laser structured bases. The only difference between SS brackets and titanium brackets is the presence of titanium oxide layer in titanium brackets which form a chemical bond with the adhesive. So chemical retention is also provided because of material properties of the brackets. The same selection principles of stainless steel brackets base applies to the titanium brackets. Cobalt Chromium Brackets Cobalt chromium brackets base can provide both mechanical and chemical retention (Figure 3.16). Mechanical retention is provided with mesh base type similar to stainless steel

Selection of Stainless steel bracket bases In stainless steel brackets, foil or woven mesh type bases are universally used. The mesh number of the bracket should be selected in accordance with bonding adhesive the orthodontist uses. As filled adhesive is used mostly in contemporary orthodontics it's my personal experience that 80 gauge mesh is suitable for most of the luting adhesives. Double mesh and super mesh bases are poor in recycling so are laser structured bases. The new laser structured mesh has the highest bond strength but has poor strength after recycling so it is good for single use only.

Figure 3.16 NV ® Hybrid Bracket with poly mesh base from TP orthodontics.

50


brackets. Chemical retention is provided with covering the bracket base with a chemical layer (PrimeKote® polymer by TP orthodontics). The polymer mesh base provides better penetration of curing light so it also increases the bond strength of brackets (Figure 3.16). Selection of CoCr bracket is similar to SS bases. Precious metal brackets Precious metal bases have main body of stainless steel that is coated with precious metals so these brackets use the same form of bracket base design as SS brackets. Mostly precious metal bracket bases uses mesh type retention design (Figure 3.17).

A

B Figure 3.18 A . Single unit plastic brackets with mechanical retention base. B. A two unit plastic bracket with mechanical retention base.Both units are joined together by a strong adhesive .

Types of Plastic brackets base Chemical retention

Figure 3.17 bracket

80 gauge mesh base of 22 karat gold plated

Plastic Brackets Plastic bracket base can either be integral part of the bracket in a single unit bracket made by plastic injection molding or individual parts of the plastic brackets are made by casting of plastic material (Figure 3.18). These individual parts are than joined together by a strong plastic adhesive. For retention of adhesive cements plastic brackets uses either chemical, mechanical retention or combination of both.

51

Chemical retention is added to some plastic brackets by application of special primer 19. However some researchers have disputed that chemical retention is provided with application of this primer. They claimed28 that application of plastic primer which is methyl methacrylate polymer causes swelling of plastic bracket base and so increase the penetration of adhesives in the base of bracket. Clinical Notes Plastic brackets have decreased bond strength than ceramic and metal brackets. As recycled plastic brackets have mostly lower bond strength than new brackets so to increase their bond strength silane coupling agents can be added to the bracket base.


CHAPTER Some experimental studies29 have also used silica coatings and silane coupling agent to plastic brackets to increase their bond strength. Mechanical retention Contemporary plastic or composite brackets usually use mechanical retention for bonding. Mechanical retention is provided in the form of grooves, undercut channels, round-angled square protrusions or mesh (Figure 3.19). Micromechanical retention can also be added by sandblasting the bracket base30.

3

Combination of chemical and mechanical retention Some contemporary plastic brackets use combination of mechanical and chemical retention. Chemical retention is provided with application of plastic bracket primer on bracket bases before bonding and mechanical retention is provided by mean of undercuts channels. Selection of plastic brackets base Plastic brackets with only chemical retention are usually not available in contemporary orthodontics. Mechanical retention base or a combination of mechanical and chemical retention base can be selected as no difference in terms of bond strength have been reported between different bracket base designs .

Ceramic Brackets Ceramic bracket base is usually manufactured in one unit with the main bracket body. In ceramic brackets, bases are available in four different designs to aid retention of adhesive. These are: 1) Chemical retention 2) Mechanical Retention 3) Micromechanical retention 4) Bracket using the combination of above designs 1) Chemical retention

Figure 3.19 brackets.

Different retention base design of plastic

Ceramic is an inorganic inert material so it doesn't form any union with organic adhesives used for bonding of orthodontic brackets. To aid retention of adhesives on ceramics, coupling agents are used. Coupling agents are used to provide a stable bond between two otherwise nonbonding and incompatible surfaces. Orthodontic

52

Silanes are silicone compounds which are bifunctional molecules that contain both organic and inorganic reactives in the same molecule. There are many types of silane coupling agents, but for ceramic brackets trialoxy silanes are used with following formula.

Ceramic brackets using chemical retention by addition of silane coupling agents have a smooth shinny surface and are usually marketed by the manufacturer. Chemical retention by silane coupling agents to ceramic brackets was given in early days to offer strong retention for successful marketing of brackets(Figure 3.21). However it was not without disadvantages. The biggest disadvantage was enamel fracture during accidental impact or debonding .This was due to high bond strength, brittle nature and hardness of ceramic brackets. Clinical Notes

Where R group is a nonhydrolyzable organic radical X is a hydrolyzable group typically alkoxy, halogen,chlorine or amine. The most common alkoxy groups are methoxy, ethoxy or acetoxy, which reacts with water to form silanol (Si-OH) and ultimately form an oxane (Si-0-M) bond between the inorganic substrate. To make things simple this is the R group of one end of the molecule that unites with the luting adhesive and X group at the other end of molecule that unites with silica coated ceramic bracket bases (Figure 3.20).

Figure 3.20

53

Silane coupling agents can also to be applied in dental office by commercially available preactivated silanes. They are available either in one bottle solution in the form of prehydrolyzed silane by 1-5 vol% in a solution to ethanol and water. To increase shelf life of silane coupling agent two bottle solutions is also available. This system consists of unhydrolzed silane with ethanol in one bottle and acid solution (acetic acid or carboxylic acid ) in the other bottle. The two solutions are mixed to allow activation of silanes. Silane coupling agents can also be applied to metal and plastic brackets to increase their bond strength.

Figure 3.21 A ceramic bracket with chemical retention base. Ceramic brackets with chemical retention base alone are no longer manufactured and marketed.


ceramic bracket bases are coated with silane coupling agents to provide chemical retention for the bonding adhesives. Prior to application of silane coupling agents ceramic bracket bases are also silica coated 31.


CHAPTER Modification of Chemical retention base Smooth surfaces of chemical retention base lead to even stress distribution of debonding and thus offer higher bond strength32. To counteract this problem chemical retentive base was made rough by protruding ceramic crystals in polycrystalline brackets. Silane coupling agents are applied to only the protruding surfaces and not on the whole bracket surface area thus decreasing the bond strength and facilitating easy debonding. Another modification to chemical retention base was to add a thin polycarbonate laminate usually an epoxy resin or polymer layer over the chemically treated bracket bases so the union of adhesive is with plastic bases rather than with saline coupling agents (Figure 3.22). It has been reported33 that with this base design bracket is easily debonded in a peel off fashion like metal brackets and so no enamel damage occurs. This type of bracket design34 has lower and clinically acceptable bond strength. Bond failure of these brackets occurs at bracket adhesive interference.

3

retention designs have been introduced into contemporary ceramic brackets. Mechanical retention of ceramic brackets is provided with dovetail grooves, undercut channels, roundangled square protrusions, protruded buttons or laser structured bases (Figure 3.23).

Figure 3.23 Different mechanical retention base design of ceramic brackets.

Mechanical retention using grooves have edge angles at 90o and have crosscuts to prevent sliding of brackets along the undercuts. Because of this assembly35 in mechanical retention by grooves, stress of debonding is concentrated at localized area resulting in bond failure at bracket adhesive interference.

Figure 3.22 InVu® brackets by TP orthodontics with polymer mesh base. These brackets are debonded similar to metal brackets.

Mechanical Retention Chemical retention base of ceramic brackets is associated with increased chances of enamel damage due to increased bond strength. To avoid iatrogenic enamel damage that is related with chemical retention bases, mechanical

As mechanical retention of ceramic brackets provides lower bond strength32 than chemical retention bases so it doesn't cause any iatrogenic effects on enamel during accidental impact or debonding. Bond strength of mechanically retained ceramic brackets depends upon its design and is usually higher36 than metal brackets. Micromechanical retention Micromechanical retention is given in the form

54


of randomly arrange crystals or spherical glass particles emerging out of the bracket base in polycrystalline brackets and in the case of monocrystalline brackets a thin coat of crystals is added to brackets base (Figure 3.24).

Figure 3.25 Ceramic bracket micro mechanical with stress concentrator for easy debonding.

Combination of different retention designs Mechanical retention can be combined with chemical retention to decrease bond strength of ceremic brackets. Mechanical and micromechanical retention can also be combined to give better retention of adhesives on bracket base.

Figure 3.24 A bracket with micromechanical retention .A. Monocrystalline bracket. B Polycrystalline bracket.

Ceramic brackets with prestressed base Some polycrystalline bracket using micromechanical retention has prestressed bracket bases (Figure 3.25).So when debonding force is applied these brackets collapse at these prestressed areas and bond failure occur at bracket adhesive interference or cohesive failure occur within the adhesive thus preventing enamel damage 37. These brackets have shown debonding properties similar to metal brackets 38.

55

Figure 3.26 A Bracket using mechanical retention grooves with silane coating to increase the bond strength.

Clinical Notes Chemical retention of ceramic brackets alone is usually not used in orthodontics. Apart from using various modified bracket base designs with ceramic brackets, orthodontist can decrease the bond strength of these brackets by using low filled adhesives 39, 40. Low filled adhesives have


CHAPTER

3

lower bond strength than high filled adhesives. Another alternative is to use glass ionomer or resin modified glass ionomer41 cements (RMGIC) with ceramic brackets as glass ionomer cements have shown to have decreased 42,43 but clinically acceptable bond strength32, 44, 46 than composite resins . Though bond failure of glass ionomer cement is present at enamel adhesive interference but no enamel damage is reported 44, 45 with this adhesive cement because RMGIC has lower bond strength. Glass ionomer cement also has the added advantage of fluoride release and so it prevents enamel decalcification and formation of white spot lesions during orthodontic treatment. Selection of ceramic bracket base Ceramic bracket base using only chemical retention is neither marketed nowadays nor should be used due to risk associated with enamel damage. All other commercially available ceramic brackets are acceptable for orthodontic purpose as long as suitable or recommended debonded techniques are used. My personal recommendation after going through all the available literature and personal experience is that ceramic brackets with plastic base or prestressed base should be used as it debond safer than other base types. Bracket base surface area An important technical specification that affects the bond strength of orthodontic bracket is its base surface area. Most orthodontists presently use twin brackets. The surface area 26,47 of these brackets range from 12.5mm2 to 28.5 mm2. Greater the retentive bracket base area greater would be the bond strength and vice versa (Figure 3.27). But there is practical limitations

Figure 3.27 Greater the retentive bracket base surface area greater would be the bond strength.If the base surface area is not retentive then no matter how much wider is the bracket the bond strength will remain minimum or bracket will fail to bond. The above brackets have manufacturing faults which have increased the surface area but area is not retentive. So instead of favoring bond strength the area can act as plaque reservoir and may lead to development of white spot lesion under the bracket base.

of increasing or decreasing the bracket base surface area. Proffit 48 purposed that width of the bracket shouldn't be more than half of the width of the tooth while MacColl49 recommended that bracket base surface area should be around 6.82 mm2. Usually the manufacturer of brackets keep a larger base area to give better bond strength and rotational control .

Clinical implication of Bracket base surface area Increase Bracket base surface area Advantages This has the following advantages: 1. Increased bond strength. This is helpful especially in case of plastic brackets which offer less bond strength than other type of brackets. Clinically acceptable bond strength50 is around 5.9 to 7.8 Mpa but bond strength shouldn't exceed 51 than 13.5Mpa to avoid enamel damage.

56

3. Larger bases also give better rotational control and better tip expression. Disadvantages 1. A large bracket base area will result in a bulkier and more conspicuous bracket thus rendering poor aesthetics. 2. Larger bracket base area is especially damaging in ceramic brackets having chemical retention as bond strength is already much higher than recommended. 3. More adhesive needs to be placed on the bracket base so more would be the cost of bonding brackets. 4. A larger bracket base can interfere with occlusion at one end and gingiva at the other end. Decreased Bracket base surface area

areas of wings are difficult to brush. So it has greater chances of plaque accumulation and development of white spot lesion. Both these situations can be managed by optimum bracket placement and adhesive curing by the orthodontist and proper brushing by the patient. Bracket base shape Bracket base shape can be rectangular, round, circular, rhomboid, oval and triangular (Figure 3.28). This difference is usually due to patent issues. But whatever the overall shape of the bracket the base of a bracket should be compound contoured. A compound contoured base mean that the base should have a shape that matches with shape of tooth for which it is made. For example as the labial surface of the incisor is a flat the base of incisor brackets should also be flat and that a canine bracket base should be convex as the of canine labial surface is convex. Another aspect of the bracket base is its landing on the tooth (Figure 3.29). It can be 3 point landings or 4 point landing. I think again this is a patent issue and there is no difference in bracket landing as long as bracket bases are compound contoured.

Decrease bracket base surface area means smaller and more esthetic brackets which have fewer chances to cause soft tissue and occlusal trauma. But these brackets have less bond strength, are difficult to fabricate, need a stronger material for manufacturing and give less coverage under the wings so lead to greater chances of white spot lesion. Note Demineralization or development of white spot lesion and its relation to bracket base surface area is controversial topic. A larger bracket base area means there are greater chances of leakage and more chances of adhesive voids under the bracket so greater chances of development of white spot lesions. In turn smaller brackets don't efficiently cover the wings of brackets. Under

57

Figure 3.28 Different bracket base designs in posterior dentition. Many manufacturer claims self-purposed advantages of these designs but this is basically more related with patent of design than theoretical basis. All designs are good as long as the bracket is compound contoured and seats good on the tooth.


2. Brackets with large bracket base areas can cover the underside of wings so protecting the tooth from plaque which usually accumulates under the wings as this area is most difficult to clean.


CHAPTER

3

Figure 3.29 3 point bracket base landing on the tooth versus 4 point landing. This is a patent issue between companies and don't hold clinical significance as long as base is compound contoured Figure 3.31 Torque in base is built in by adjusting the size of triangle in the base of bracket.

Bracket identification marks Some manufacturers for ease of identification places tooth notation systems on the base of brackets (Figure 3.30).With these types of base designs sandblasting to increase the bond strength on new or recycled brackets should be avoided as it will erase these identification marks.

Andrew proposed that for proper bracket placement the slot point (center of arch wire slot ) of bracket, the base point ( center of bracket base ) of bracket and center of clinical crown (FA point) should be in one line (Fig3.32).

Figure 3.32 In the ideal placed brackets the slot point the base point and FA point should be in one line .This is only possible when the torque is built in the base of the bracket.

Figure 3.30 A lower right canine bracket.

Torque in the Base A true characteristic of straight wire appliance is that it should have torque in the base52-54. Torque in base is built by the manufacturer by adjusting the size of triangle in the base of the bracket (Figure 3.31).

In brackets in which torque is built in face of the bracket the base point and FA point are in one line but slot point don't coincide with them (Figure 3.33). So when heavy wires are placed such arrangements lead to vertical bracket positioning errors though torque expression is normal. These vertical position errors can range 0.7 mm in lower and 0.5 mm in upper arch. It is usually claimed that these vertical positioning errors will lead to different expression of torque due to morphology difference of tooth surface. The clinical significance of torque in the base versus torque in the face is controversial 55.

58

Selection of bases on important variables Ideally a bracket with torque in the base should be selected to avoid vertical position errors. The bracket should have a compound contoured base (contoured both horizontally and vertically). In selecting mini-series of brackets the bracket base surface area shouldn't be less than 6 mm2. In cases of ceramic brackets less bracket base surfaces are beneficial to bond strength, but the potential benefit should not compromise the overall strength of brackets.

1. Sheykholeslam Z, Brandt S. Some factors affecting the bonding of orthodontic attachments to tooth surface. J Clin Orthod. 1977 Nov;11(11):734-43. 2. Reynolds IR, von Fraunhofer JA. Direct bonding of orthodontic attachments to teeth: the relation of adhesive bond strength to gauze mesh size. Br J Orthod. 1976 Apr;3(2):91-5. 3. Thanos CE, Munholland T, Caputo A. Adhesion of mesh-based direct bonding brackets. Am J Orthod. 1979:75:421-430. 4. Lopez JI. Retentive shear strengths of various bonding attachment bases. Am J Orthod. 1980 Jun;77(6):669-78. 5. Faust JB, Grego GN, Fan PL, Powers JM. Penetration coefficient, tensile strength, and bond strength of thirteen direct bonding orthodontic cements. Am J Orthod. 1978 May;73(5):512-25. 6. Zachrisson BJ. A posttreatment evaluation of direct bonding in orthodontics. Am J Orthod. 1977 Feb;71(2):173-89. 7. Maijer R, Smith DC. Variables influencing the bond strength of metal orthodontic bracket bases. Am. J. Orthod .1981; 79: 20-34. 8. Zachrisson BU, Brobakken BO. Clinical comparison of direct versus indirect bonding with different bracket types and adhesives. Am J Orthod 1978;74:62-77. 9. Smith NR, Reynolds IR. A comparison of three bracket bases: an in vitro study. Br J Orthod. 1991 Feb;18(1):29-35. 10. Dickinson PT, Powers JM. Evaluation of fourteen direct-bonding orthodontic bases. Am J Orthod. 1980 Dec;78(6):630-9. 11. Wang WN, Li CH, Chou TH, Wang DD, Lin LH, Lin CT. Bond strength of various bracket base designs. Am J Orthod Dentofacial Orthop. 2004 Jan;125(1):65-70. 12. Knox J, Kralj B, Hubsch P, Middleton J, Jones ML. An evaluation of the quality of orthodontic attachment offered by single- and doublemesh bracket bases using the finite element method of stress analysis. Angle Orthod. 2001 Apr;71(2):149-55. 13. Bishara SE, Soliman MM, Oonsombat C, Laffoon JF, Ajlouni R. The effect of variation in mesh-base design on the shear bond strength of orthodontic brackets. Angle Orthod. 2004 Jun;74(3):400-4. 14. Matasa CG. Do Adhesives and Sealants Really Seal the Brackets' Pad? II. Surface Tension. Orthod Mat Insider. 2003a; 15: 4-8. 15. Reynolds IR, von Fraunhofer JA. Direct bonding in orthodontics: a comparison of attachments. Br J Orthod. 1977 Apr;4(2):65-9. 16. Matasa CG. In Search of a Better Bond: State of the Art. Orthod Mat Insider. 2003b; 15: 1. 17. Low T, von Fraunhofer JA. The direct use of composite materials in adhesive dentistry. Br Dent J. 1976 Oct 5;141(7):207-13.

Figure 3.33 Comparison of torque in the base versus torque in the face. The torque in the face can cause the vertical positioning errors.

18. Sharma-Sayal SK, Rossouw PE, Kulkarni GV, Titley KC. The influence of orthodontic bracket base design on shear bond strength. Am J Orthod Dentofacial Orthop. 2003 Jul;124(1):74-82. 19. Buzzitta VA, Hallgren SE, Powers JM. Bond strength of orthodontic direct-bonding cement-bracket systems as studied in vitro. Am J Orthod. 1982 Feb;81(2):87-92.

59


References


CHAPTER 20. Knox J, Hubsch P, Jones ML, Middleton J. The influence of bracket base design on the strength of the bracket-cement interface. Br J Orthod 2000;27:249-54. 21. Cucu M, Driessen CH, Ferreira PD. The influence of orthodontic bracket base diameter and mesh size on bond strength. SADJ. 2002 Jan;57(1):16-20. 22. MacColl GA, Rossouw PE, Titley KC, Yamin C. The relationship between bond strength and orthodontic bracket base surface area with conventional and microetched foil-mesh bases. Am J Orthod Dentofacial Orthop. 1998 Mar;113(3):276-81. 23. Ferguson JW, Read MJ, Watts DC. Bond strengths of an integral bracket-base combination: an in vitro study. Eur J Orthod. 1984 Nov;6(4):267-76. 24. Regan D, van Noort R. Bond strengths of two integral bracket-base combinations: an in vitro comparison with foil-mesh. Eur J Orthod. 1989 May;11(2):144-53. 25. Siomka LV, Powers JM. In vitro bond strength of treated directbonding metal bases. Am J Orthod. 1985;88:133-6. 26. Sorel O, El Alam R, Chagneau F, Cathelineau G. Comparison of bond strength between simple foil mesh and laser-structured base retention brackets. Am J Orthod Dentofacial Orthop. 2002 Sep;122(3):260-6. 27. Droese V, Diedrich P. The tensile bonding strength of metal plasmacoated bracket bases. Fortschr Kieferorthop. 1992 Jun;53(3):142-52.

3

Dentofacial Orthop. 1997 Nov;112(5):552-9. 38. Liu JK, Chung CH, Chang CY, Shieh DB. Bond strength and debonding characteristics of a new ceramic bracket. Am J Orthod Dentofacial Orthop. 2005 Dec;128(6):761-5; quiz 802. 39. Joseph VP, Rossouw E. The shear pond strengths of stainless steel and ceramic brackets used with chemically and light-activated composit resins. Am J Orthod Dentofacial Orthop 1990;97:121-125. 40. Storm ER. De bonding ceramic brackets. J Clin Orthod 1990;2491-94. 41. Larmour CJ, McCabe JF, Gordon PH. An ex vivo assessment of resin-modified glass ionomer bonding systems in relation to ceramic bracket debond. J Orthod. 2000 Dec;27(4):329-32. 42. Compton AM, Meyers CE Jr, Hondrum SO, Lorton L. Comparison of the shear bond strength of a light-cured glass ionomer and a chemically cured glass ionomer for use as an orthodontic bonding agent. Am J Orthod Dentofacial Orthop. 1992 Feb;101(2):138-44. 43. Bishara SE, VonWald L, Olsen ME, Laffoon JF, Jakobsen JR. Effect of light-cure time on the initial shear bond strength of a glass-ionomer adhesive. Am J Orthod Dentofacial Orthop. 2000 Feb;117(2):164-8. 44. Cacciafesta V, Süssenberger U, Jost-Brinkmann PG, Miethke RR. Shear bond strengths of ceramic brackets bonded with different lightcured glass ionomer cements: an in vitro study. Eur J Orthod. 1998 Apr;20(2):177-87.

28. Eliades T ,Brantley WA. Orthodontic materials. Scientific and Clinical Aspects.New York: Thieme;2001.

45. Larmour CJ, McCabe JF, Gordon PH. An ex vivo assessment of resin-modified glass ionomer bonding systems in relation to ceramic bracket debond. J Orthod. 2000 Dec;27(4):329-32.

29. Faltermeier A, Behr M, Müssig D.Esthetic brackets: the influence of filler level on color stability. Am J Orthod Dentofacial Orthop. 2007 Jul;132(1):5.e13-6.

46. Haydar B, Sarikaya S, Cehreli ZC. Comparison of shear bond strength of three bonding agents with metal and ceramic brackets. Angle Orthod. 1999 Oct;69(5): 457-62.

30. Zhang ZC, Giordano R, Shen G, Chou LL, Qian YF. Shear bond strength of an experimental composite bracket. J Orofac Orthop. 2013 Jul;74(4):319-31.

47. Dickinson PT, Powers JM. Evaluation of fourteen direct-bonding orthodontic bases. Am J Orthod. 1980 Dec;78(6):630-9.

31. Swartz ML. Ceramic brackets. J Clin Orthod. 1988 Feb;22(2):82-8. 32. Viazis AD, Cavanaugh G, Bevis RR. Bond strength of ceramic brackets under shear stress: an in vitro report. Am J Orthod Dentofac Orthop 1990; 98: 214-221. 33. Elekdag-Turk S, Isci D, Ozkalayci N, Turk T. Debonding characteristics of a polymer mesh base ceramic bracket bonded with two different conditioning methods. Eur J Orthod. 2009 Feb;31(1):849. 34. Olsen ME, Bishara SE, Jakobsen JR. Evaluation of the shear bond strength of different ceramic bracket base designs. Angle Orthod. 1997;67(3):179-82. 35. Odegaard J, Segner D. Shear bond strength of metal brackets compared with a new ceramic bracket. Am J Orthod Dentofac Orthop 1988; 94: 201-206. 36. Kukiattrakoon B, Samruajbenjakul B. Shear bond strength of ceramic brackets with various base designs bonded to aluminous and fluorapatite ceramics. Eur J Orthod. 2010 Feb;32(1):87-93. 37. Bishara SE, Olsen ME, Von Wald L. Evaluation of debonding characteristics of a new collapsible ceramic bracket. Am J Orthod

48. Proffi t W R , Fields H W , Ackerman J L 2000 Mechanical principles in orthodontic force control . In: Proffi t W R (ed.). Contemporary orthodontics. Mosby , St Louis , pp. 326 -362. 49. MacColl GA, Rossouw PE, Titley KC, Yamin C. The relationship between bond strength and orthodontic bracket base surface area with conventional and microetched foil-mesh bases. Am J Orthod Dentofacial Orthop. 1998 Mar;113(3):276-81. 50. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-8. 51. Retief DH. Failure at the dental adhesive-etched enamel interface. J Oral Rehabil 1974;1:265-84. 52. Andrews, L.F.The Straight Wire Applianee: Syllabus of philosophy and techniques, 2nd ed., L.F. Andrews Foundation for Orthodontic Education and Research, San Diego, 1975. 53. Andrews, L.F.: Straight Wire: The Concept and Appliance, L.A. Wells Co., San Diego, 1989. 54. Andrews, L.F.: JCO Interviews on the Straight-Wire Appliance, J. Clin. Orthod. 24:493-508, 1990. 55. Ferguson JW. Torque-in-base: another straight-wire myth? Br J Orthod. 1990 Feb;17(1):57-61.

60

CHAPTER

4

Selection of Bracket Slot In this Chapter

Introduction

Bidemensional mechanics

Type of bends for 3 dimensional tooth movements

Morphology of the brackets

Dimensions of Edgewise slot Accessary slots Tip edge brackets

Gingival offset brackets Slot modifications to reduce friction Ligation: The fourth wall of Bracket slot Tie Wings of the brackets

Advantages of 0.018” slot Advantages of 0.022” slot

Introduction Slot is part of the bracket in which the wire is engaged to express the builtin prescription of the bracket. The slot of the bracket has seen much evolution with time. It started from occlusal opening slot in Angle ribbon arch appliance to gingival opening slot in Begg appliance and front opening slot in Angle edgewise system. In contemporary orthodontics edgewise slot is universally accepted .Vertical slots are still used in some bracket series but usually as an accessary slot. When bracket slot was first introduced they were simple openings in which a bended wire incorporating all the necessary tooth movements was inserted. The brackets having such passive slots were called standard brackets. With time 1st, 2nd and 3rd order bends

61

were incorporated in brackets to produce respective tooth movements 1. Before going into the details of slot a brief description of these bends and associated movements are given. Type of bends for 3 dimensional tooth movements First order bends (In or out bends) First order bends are given to accomplish first order tooth movements which are in a labiolingual or buccopalatal direction. 1st order bends can be made in horizontal direction in the wires such as the step bends, or are accommodated in the brackets (Figure 4.1). As different teeth in the arch have different width these bends made in the wire or built into the bracket are used to accommodate different tooth width. Vertical step bends that don't change the


CHAPTER

4

angulation of the teeth are also considered as 1st order bends. First order bends in brackets are incorporated by increasing the prominence of the bracket.

A

B

C Figure 4.1 A. A line showing different prominence of the teeth in natural dentition due to difference in width of the teeth. B. Wire bending done to compensate 1st order tooth movement. This type of wire bending is usually done in conventional edgewise system. C. First order bends built within the bracket. This is evident with different prominence of the brackets in upper arch.

Clinical Notes The clinician should always use same companie's brackets. If a bracket is debonded either the bracket should be recycled and reused or a new bracket of same company should be used. Different companies have different prominence of the brackets(Figure 4.2). So using different companie's brackets will result in first order tooth position problems in a finished case.

Figure 4.2 Maxillary lateral incisor brackets from two different manufacturers having same builtin prescription. The height or prominence of these brackets is different.

Second Order Bends (Tip or Angulation bends) These bends are made in vertical plane in the wire to accommodate tooth angulation and root parallelism. Second order bends can also be incorporated in the brackets by placing the slot at an angle to the base (Figure 4.3).

Clinical Notes Different bracket prescription have different builtin tip. An experienced clinician can use combination of brackets from different prescription provided that they have the same prominence. It is a good practice to use brackets of single manufacturer while altering the prescription.

62

A

B

C A Figure 4.3 A. 2nd order bends are for crown or root movement in mesiodistal direction and can be incooperated in the bracket (B) or can be made in the wire (C).

Third order bends (Torque)

B Third order bends are used to position the roots labial or lingual. Third order bends are placed in the wire by twisting it in a clockwise or counterclockwise direction. In case of brackets 3rd order bends are either placed in base or in slot of the brackets but placing the torque in the base is a preferred method (Figure 4.4). Clinical Notes Bracket prominence of different brackets should be kept in mind when altering bracket prescription for using customized torque values. If a smaller dimension wire is engaged within the bracket there would be play between the wire and the bracket and all torque within the bracket won't be expressed. Torque built into the bracket can

63

C Figure 4.4 A. 3rd order bends are for root movement in labiolingual or buccopalatal direction .It can be achieved by placing a twist in the wire (B) or building torque in the base of the brackets (C ).

Brackets with torque built in the face or slot of the bracket can result in vertical position errors. The brackets having no builtin in/out, tip and torque are called standard edgewise brackets introduced by Angle while brackets having all


fully be expressed on engagement of full dimensional wire within the slot. If clinician are keen on using light wires then torque can be expressed by giving twist in the wires or by using torqueing springs.


CHAPTER these features builtin are called preadjusted brackets introduced by Andrew. A term usually confused by the students is difference between tip and tipping movement. Tip is the angulation of the tooth in the mesiodistal direction while tipping is a type of tooth movement. A tipping tooth movement can result in decrease or increase of tip and torque of a tooth. Dimensions of Edgewise slot The edgewise slot purposed by Angle and carried forward by Andrew in preadjusted brackets have two dimensions 2, vertical and horizontal. In original edgewise slot the vertical height which is height of base of slot or opening of the face is 0.022 inch and horizontal length of walls is 0.028 inch (Figure 4.5).

4

smaller dimension and so more flexible stainless steel wires can fill the slot much more early and easily. But introduction of stainless steel also turned out to be a blessing in disguise for the 0.022 “ slot . As the original edgewise appliance introduced by Angle was meant for only nonextraction cases and so filling the slot was mandatory for expression of torque built within the wires. As modern orthodontist became more liberal and started doing extractions where ever it deemed necessary so the need to close the extraction space arises. One popular way of doing it was sliding the teeth on the wire which was more time efficient than making loops on wires to close extraction spaces. Sliding mechanics plus the introduction of more elastic wires which helps in initial leveling and alignment has again turned the tide in favor of 0.022” slot.

0.028”

0.022”

0.025”

Figure 4.5 Slot dimension of a conventional edgewise bracket. This slot dimension is still the most popular choice in preadjusted edgewise appliance. The 0.022” dimension is called base of the bracket while 0.028” is walls of the bracket.

Modification of slot dimension The original 0.022” slot was modified3 with time into 0.018 x0.025 inch slot (Figure 4.6).The reason behind this modification was that when edgewise appliance was introduced by Angle, gold wires were used with 0.022” slot. With the introduction of stainless steel in orthodontics in 1930s orthodontist were troubled with the use of full dimension stainless steel wires in the slot which were 50 % more stiffer than gold. As gold became very expansive option with time the slot size of the bracket was reduced to 0.018 inch. In this slot

0.018”

Figure 4.6

A bracket with 0.018x 0.025 inch slot.

Variations in 0.022” and 0.018” slot Both 0.022” and 0.018” slots have variation in the horizontal dimension. Theses variations are basically for ease of mechanics. These are: 0.022”x0.030” slot and 0.018”x0.028” slot The horizontal dimension in these variations is increased so that the wire is fully seated in the slot and express all the torque built within the bracket .It is also useful when accessary wire is needed to be passed along with main archwire

64

Accessary slots

brackets and light round super elastic wires in case of tip edge plus brackets are used to move the main archwire from open to closed dimensions.

Accessory slots are available for ease of mechanics in edgewise brackets (Figure 4.7). Vertical slots are mainly available for use with torqueing or tipping springs. Accessary horizontal slot beneath the main slot is integral component of tip edge plus brackets. Some experimental brackets 6 also feature both 0.022” and 0.018” slot in a single bracket but addition of another slot in the bracket make the bracket bulkier.

A

B A Figure 4.8 A tip edge and a tip edge plus bracket.Tip edge plus bracket has a acessory slot in which a 0.014” or 0.016” superelastic NiTi wire is passed in final stages of treatment.

Advantages of 0.018” slot Using 0.018” slot has following advantages:

B Figure 4.7 A. A accessary horizontal slot attached to main horizontal slot. Such slots are used for piggyback mechanics and intrusion arches. B. vertical slot are used with auxiliary springs.

Tip edge bracket A variation of 0.022”x0.028” slot is found in tip edge or tip edge plus brackets (Figure 4.8) . The bracket has open dimensions of 0.028”x0.028” to accommodate tipping of teeth and close dimensions of 0.022”x0.028” to express final torque. Auxiliary springs in case of tip edge

65

1. In 0.018” slot as smaller dimension wires are used which have more flexibility than larger wires used in 0.022” slot so filling the slot is more early and easily achieved. 2. Smaller dimension of the 0.018” slot mean that these brackets can be made smaller than 0.022” slot brackets. Narrower the brackets more would be the inter bracket distance and increased would be the flexibility of the wires used. Increase flexibility of wire is essential in alignment and leveling. With advent of superelastic NiTi wires which apply light continuous


in cases requiring piggy back mechanics and utility arches .


CHAPTER

teeth on wires for space closure. Loop mechanics for space closure can also be done on 0.022” slot but these are more efficiently done on 0.018” slot.

force this advantage of smaller dimension of 0.018 slot has turned clinically insignificant. 3. Due to increased flexibility and gaps between the brackets, wire loops or wire bending can easily be incorporated between the brackets 7. Also due to filling of slots friction increase between the slots and the wires. That's why 0.018” slot are more favored by orthodontists who are good in wire bending and prefer loop mechanics for space closure. This doesn't mean that sliding mechanics cannot be done on 0.018” slot. Sliding mechanics can be done on these brackets too but it is more efficient to do it on 0.022” slot.

4) As larger dimension wires are used that have higher stiffness .These wires keep teeth upright during sliding mechanics. 5) 0.022” slot brackets are usually wider than 0.018” slot though it not always the case as in case of mini brackets. Wide brackets have less contact angle between the wire and the bracket slot. So less friction is offered by the bracket (Figure 4.9). Also due to increased width the moment arm of bracket which is half the width of the bracket is increased so these brackets offer better rotational and root position control. Wide brackets also provide greater bracket base surface area and so increased bond strength.

4. Using maximum engagement wire results in more torque expression by 0.018” slot 8, 9. This greater torque expression is important in anterior dentition where torque loss occur during retraction of these teeth. Detterline 10 reported that 0.018” slot is more time efficient in surgical cases than 0.022” slot because decompensation is easily done by efficient torque expression. 5. It is reported10, 11, 12 that cases treated with 0.018” slot take less time than 0.022” slot but the results are not clinically significant.

4

A

Advantages of 0.022” slot The 0.022” slot has the following advantages. 1) The 0.022”slot due to its wider dimensions offers more options in wire selection. 2) The larger slot allows more easy insertion of wires at the initial visits 13. 3) As undersized wires are used there is more clearance between the slot and the wire .So there is less binding of wire to slot 14. Because of this reason 0.022” slot is preferred by orthodontists who opt sliding of

B Figure 4.9 A. Wider brackets have less contact angle so offer less friction. B. Greater moment arm provided by a wide bracket results in better control of root position during tooth movement.

Bidemensional mechanics Some clinicians 15, 16 favor to use advantages of both 0.018” and 0.022” slots by combining both in a single appliance. Incisor brackets with 0.018” slot and canine and posterior brackets with 0.022” slots are used. With this technique torque control is maintained 2 on incisors during

66

In cases requiring extraction space closure with sliding mechanics on ceramic brackets the buccal segment is bonded with metal brackets and labial segment with ceramic brackets. This combination is also sometimes termed as bidimensional mechanics. In this combination anterior ceramic brackets preserve aesthetic while posterior metal brackets help to reduce friction during sliding mechanics. Also posterior metal brackets help to reduce cost of treatment as ceramic brackets are more expensive than metal brackets.

Selection of slot The selection of slot is more a matter of personal choice. Usually clinician who favor loop mechanics for space closure prefer 0.018” slot while clinician who choose sliding mechanics for space closure favor 0.022” slot. But an experienced clinician with wise choice of wires can do both mechanics on both these slots. As 0.018” slot is more efficient in torque expression, cases requiring greater torque expression are usually treated with 0.0.18” slot brackets. Such case included Class II div 2, surgical cases requiring decompensation and growth modification cases.

Till this consensus is not reached the clinician should select slot according to space closing mechanics they prefer. Brackets with vertical slot are good option for clinicians who prefer to use light wires during treatment and correct tip and torque with auxiliary springs. For selection of tip edge plus brackets the clinician must have good knowledge of mechanics used with that system. Tip Edge plus brackets employ differential tooth movement based on Begg's philosophy which is far different than concept of bodily movement used in preadjusted orthodontics. Bidemsional slot philosophy is usually used in lingual orthodontics. Morphology of the brackets The brackets can be classified according to their morphology into 1. Single slot brackets When edgewise brackets were first made available they had only one slot. So they were called single brackets (Figure 4.10). Due to single slot interbracket distance was increased and these brackets were good for the initial leveling, alignment and closing spaces with loop mechanics. But these brackets have poor rotational and tip control.

According to a survey 1 7 54% of orthodontists prefer 0.022 inch slot size, 40.5% used 0.018 inch slot and 5% used a combination of above slots(bidimensional mechanics) or some other bracket style. To decrease confusion in selection of slot size there are increased efforts by some orthodontists to bring uniformity in slot size and give it a standard measuring unit3,4,5,18.

67

A

B

Figure 4.10 A. Attract bracket by Ormco for pedo patients. B. A single slot bracket in Alexander prescription.


anterior retraction or posterior protraction while sliding mechanics on posterior teeth are easily done. Bidimensional mechanics are more popular in lingual than labial orthodontics.


CHAPTER 2. Twin or Siamese bracket This design of bracket has two slots. Most of the contemporary brackets are available in this design. Twin brackets are further divided into true twin or semi twin brackets. a) True twin brackets

4

In these brackets a connecting arm is present between mesial and distal tie wings (Figure 4.12). Semi twin brackets are usually ceramic or plastic brackets. Some mini-series of metal brackets are also available in semi twin design. The mesial and distal tie wings are joined together to give increased strength to the brackets.

In these brackets there are separate mesial and distal tie wings. Twin brackets are usually available in metal but can be made in plastic or ceramic material (Figure 4.11). b) Semi twin brackets

A

A

B

B C Figure 4.11 True twin Siamese (A) Metal bracket (B) Polycrystalline ceramic bracket

Figure 4.12 Semi twin bracket in (A) Metal (B) Polycrystalline Ceramic and (C) Composite plastic bracket

68

A clinical problem with use of semi twin bracket is placement of ligatures. As most orthodontists use standard twin brackets so they have good reflexes to place the ligature on these brackets. But placing ligature on semi twin bracket need different rotation of the wrist as the saddle area is covered by arms connecting the wings. In true twin brackets the initial direction of ligature placement is vertical usually from gingival to incisal wing but in semi twin brackets because of saddle area obstruction it is horizontal. As the horizontal distance in most standard twin bracket is greater than vertical distance so there is greater stretch of the ligature in semi twin bracket during its placement. This may lead to bracket deboning on ligature tying. This is more common with newly bonded plastic brackets.

between wire and bracket on sliding mechanics. Mini brackets should ideally be selected in only nonextraction cases. True mini twin bracket made of metal is a good choice in 0.018” slot but my personal opinion is that it's not a good choice in 0.022” slot if someone is aiming for sliding mechanics until all the clinical crowns are small . Mini brackets are added advantage in ceramic brackets because decrease surface area mean decrease bond strength but not a good choice in plastic brackets because they have already decreased bond strength. Using semi twin bracket is a good option in ceramic and plastic brackets. Single bracket is really used because of poor angulation and rotational control until it's a part of a specific prescription. Gingival offset brackets

Both true twin and semi twin brackets can be divided into standard size and miniature type. Miniature or mini twin bracket as the name indicates is smaller in size than the standard twin bracket. The miniature size of metal bracket is more common with semi twin brackets .Mini twin brackets though are more aesthetic and less conspicuous but has the disadvantages of narrow brackets explained before. Mini twin brackets are available in both 0.018” and 0.022” slots.

Selection of bracket according to morphology In case of metal brackets true twin brackets are strong enough to withstand orthodontic loading and debonding forces. Mini brackets have poor rotational and axial control due to decreased moment arm and would offer more friction on sliding mechanics due to greater contact angle

69

Usually the slot of the bracket is universally placed on the middle of the bracket base. Many a time especially in young patients, lower premolar clinical crown is short. Placing the standard brackets in such scenario results in interference of the bracket with occlusion and also the base of bracket irritates the gingiva (Figure 4.13). In such circumstances slot of bracket is modified by placing it more gingival on the base so that the gingival tie wings are hardly covered by the base. This modification prevents occlusal interference and gingival irritation, while the bracket maintains it optimum surface area to give good bond strength 19. A randomized control clinical trial 20 concluded that gingival offset mandibular premolar brackets have lower bond failure rate than standard brackets. Many manufacturers make gingival offset brackets for lower premolars but these brackets


Clinical Notes


CHAPTER

4

Clinical Notes Stainless steel slot aesthetic brackets should not be used in nickel allergic patients. Metal slot ceramic brackets shouldn't be recycled with flame method because it will discolor the slot thus jeopardizing the esthetic value of brackets. Limitation of metal slots in aesthetic brackets

A

B

Figure 4.13 Comparison between normal and gingival offset bracket. A . Gingival offset premolar bracket in which the slot is placed more gingival on the base. B. Normal premolar bracket .Slot is placed in the middle of the bracket.

are also a good choice in upper premolars where optimum placement of bracket is hindered by gingiva due to short clinical crown. Slot modifications to reduce friction Friction in orthodontics is especially a problem during tooth movement. Friction is offered from the slot, wires and oral environment. Friction from the slot is especially a problem in case of ceramic and plastic brackets. To reduce friction some manufacturers have replaced the slot with metal usually stainless steel, titanium, gold and niobium (Figure 4.14).

Metal slot used in aesthetic brackets are usually placed after the bracket is manufactured and held within the slot of bracket by unknown material. The hardness of this material is usually not known and can affect the torque expression of brackets. In many ceramic brackets it is noticed that material flow in the slot thus decreasing slot dimension and increasing friction resistance. Usually there are void between the slot and bracket that act as plaque retention area thus obliterating the esthetic advantage of the brackets. The finishing of slot is also poor as compared to much cheaper metal brackets (Figure 4.15). In plastic brackets the metal slot is effective in sliding mechanics but not in torque expression and creep or expansion of the slot occur on giving torque in the wire (Figure 4.16 ). Apart from metal lined slots some ceramic bracket slots are silica lined 21 to give better aesthetics and decrease friction. Some manufacturer make bumps in the floor to decrease friction resistance on sliding mechanics but effectiveness of such slots is just a manufacturer claim and not evidence based 22 (Figure 4.17). Chamfered Slot Walls

A

B

Figure 4.14 A .Plastic bracket with stainless steel metal slot. B. Polycrystalline ceramic bracket with metal lined SS slot.

Slot walls of the bracket are chamfered or rounded for easy insertion of wires, increase inter-bracket distance and decrease friction (Figure 4.18). Rounding of slot walls and floors

70

B

C

Figure 4.15 A. A ceramic bracket with metal attached to the bracket by unknown material. Also base of the bracket is irregular offering greater friction. B. A new ceramic bracket with foreign material on slot base and walls. Also slot design is not elegant as there is some part of ceramic on both mesial and distal sides of the slot base .If this ceramic is at the level of slot it will increase friction resistance and if it slightly below the level it will act as a plaque retention area. C. Gaps between metal slot wall and bracket slot wall. These gaps will act as a potential plaque retention area and will also affect the torque characteristics of the brackets.

A

B Figure 4.16 A. Corrosion in base of the slot in just 4 months of clinical use of a plastic bracket. In metal lined aesthetic brackets both clinician and manufacturer are more focused on the plastic or ceramic part and less on metal part which led to embracement in clinical cases. B. A slot wall distorted by introduction of 15° torque in 0.019”x0.025” wire .Even a metal slot in plastic bracket is usually not enough to withstand extra torque application because thin walls of metal slot are not supported well by plastic behind it.

Selection of modified slots In cases requiring sliding mechanics on aesthetic brackets metal slot is always an advantage. Though aesthetic brackets are

71

Figure 4.17 A bracket with bump or hump in base of bracket. Such design does not decrease friction resistance but make full insertion of the wire in the slot difficult thus effecting the torque characteristics of the brackets.

more expansive than metal brackets but their metal slot has not the level of perfection found in metal brackets. While selecting these brackets a careful physical inspection of brackets slots should be done. Stainless steel slot should be avoided in nickel sensitive patients. Plastic brackets with metal slot are good in sliding mechanics but poor in torque expression. So cases in which extra torque is required such as class II div 2, palatally or buccally displaced teeth and impacted teeth plastic brackets should be avoided even they are with metal slot. Slight chamfering of the slot is advantageous but too much chamfering will increase the dimensions of the slot and so increases the wire play. Rounding of the slot


A


CHAPTER base or humps to decrease friction resistance is not evidence based so selection of these brackets is only a personal choice.

A

B Figure 4.18 A. Chamfered slot walls of a ceramic bracket .B. A composite bracket with rounded slot base. This type of slot base is made so that the wire only touches the walls of the brackets and a minimum base area. Decrease friction offered by these slot bases is not evidence based but these bases are known to increase wire play in the slot.

increases torque play and result in decrease in effective torque expressed from the brackets. Ligation: The fourth wall of Bracket slot Wires once inserted into the slot should remain within the slot till next appointment. As the edgewise bracket slot has three fixed walls, so there is a fair chances that the wire will come out of the slot opening until or unless a mechanism is present that make up the fourth wall of the slot and prevent the wire from coming out. This fourth wall is traditionally been provided by ligatures. Traditional wire ligatures were used to keep the wire within the slot. For many decades thin stainless steel wires were used as ligatures which provide durable, cheap and effective ligation. Though stainless steel ligature are still used but due to increased chair side time which is on the average23 11 minutes to tie these ligature, steel ligatures are taken over by elastic ligatures.

4

Clinical notes Steel ligatures though largely have been taken over by elastic ligatures are still used in cases where there is a need to express more torque i-e lower arch in growth modification cases , impacted canines and cases in which teeth are palatally or buccally displaced. Steel ligature are also a reliable mechanism of ligation in rotated teeth, piggy back mechanics and surgical cases. Steel ligatures are also used on teeth undergoing translation because if wisely ligated they offer less friction as compared to elastic ligatures. Elastic ligatures are mostly used in contemporary orthodontics for ligation of wire within the slot. Elastic ligatures though provide very good ligation at the time of insertion have a rapid force decay rate and almost half of the force is lost in the first 24 hours 24. They also get discolor with time so increases esthetic concern of the patients. To overcome these problems associated with steel and elastic ligatures self-ligating brackets were introduced. Though the history of self-ligating bracket is very old starting back to 1935 but they have only gained much popularity in the last decade 25. Self-ligating brackets are available in all type of materials in which conventional brackets are available. Self-ligating brackets are of two types depending upon the type of ligation they provide. (Figure 4.19) 1. Active self-ligating brackets 2. Passive self-ligating brackets Active self-ligating brackets are one in which ligating clip is occupying some of the slot space. This clip is flexible and caries some energy. While the passive self-ligating clip doesn't cover the slot space and is usually hard. So an active clip will push a rectangular wire into the slot and in some grossly displaced teeth round wire is

72

Torque Expression

A

B Figure 4.19 A . Forestadent active self ligating bracket. B. A passive self-ligating bracket.

also pushed in, while a passive clip will simply prevent the wire whether round or rectangular from coming out of the slot. Too much have been written on self-ligating brackets and its proposed benefits in different orthodontic books. In following text only evidence based findings would be given. Oral hygiene A systematic review by Nascimento 26 found no evidence of self-ligating brackets related to less formation of streptococcus mutans colonies as compared to conventional brackets. So claims by manufacturers that these brackets are more hygienic are not evidence based. Treatment time and initial pain A systematic review by Celar 27 found no evidence that self-ligating brackets are related with less initial pain, less number of visits and less treatment time than conventional brackets. Friction resistance Ehsani 28 in a systematic review concluded that self-ligating brackets show less friction resistance on round wires if used on well aligned arches but there is no evidence of decrease

73

30

Archambault found that active stainless steel self-ligating brackets show less wire play than passive self-ligating brackets. So there would be more torque expression from active selfligating brackets than passive self-ligating brackets. Advantages over conventional brackets Fleming 31 after a systematic review concluded that there is insufficient evidence for use of selfligating fixed orthodontic appliances over conventional appliance systems or vice versa. Chen et al 32 in a systematic review found that current evidence only support that with use of self-ligating bracket there is shortened chair time and slightly less incisor proclination over conventional systems. Tie Wings of the brackets The tie wings of the bracket act as a retention area to hold the ligatures. Ideal tie wings should

Selection of self-ligating brackets Evidence mentioned above make it clear that selection of self-ligating bracket is a matter of personal choice. Self-ligating brackets are expensive than conventional brackets so the Orthodontists must evaluate cost versus benefit before selecting selfligating brackets. From the present evidence self-ligating brackets seem to be a better choice in growth modification cases and nonextraction cases having lower arch crowding or increased lower incisor inclination. Active self-ligating brackets should be preferred over passive selfligating brackets.


friction resistance on rectangular wires. A low 29 level of evidence suggested that there is no clinically significant difference in terms of friction resistance between active and passive self-ligating brackets on SS wires.


CHAPTER have following characteristics. 1) Tie wings should have ample under wings area to hold the ligature .Down draft under tie wings provide more safe and easy ligation (Figure 4.20).

4

2) Tie wings should be rounded or chamfered to avoid soft tissue injury. 3) Tie wings should be strong enough to with stand force of ligation. Clinical Notes Many clinicians make gingival tie wings longer to facilitate easy ligation (Figure 4.22). But using longer tie wings will increase play of the wire. Brackets with longer tie wings should be avoided in cases requiring special torque requirement.

A

B Figure 4.20 A. A metal bracket with down draft tie wing. B. A ceramic bracket with straight tie wing .Such tie wings provides poor retention for ligature.

Figure 4.22

Bracket with longer gingival tie wings

Clinical Notes Placing ligatures is especially a problem in mandibular incisors where the brackets are small to match the smaller teeth (Figure 4.21). The problem is further aggravated when the lower incisor also needed to be lace-backed. So brackets with ample under tie wings area should be selected especially in lower incisors.

References 1. Andrews LF. The six keys to normal occlusion. Am J Orthod 1972; 62:296-309. 2. Proffit WR, Fields HW, Sarver DM. Contemporary Orthodontics. 4th ed. St Louis, Mo: Mosby Elsevier; 2007:376–377. 3. Peck S. Orthodontic slot size: it's time to retool. Angle Orthod. 2001 Oct;71(5): 329-30. 4. Kusy RP, Whitley JQ. Assessment of second-order clearances between orthodontic archwires and bracket slots via the critical contact angle for binding. Angle Orthod 1999;69:71-80. 5. Kusy RP. "Two" much of a good thing? Then let's pick one slot size and make it metric. Am J Orthod Dentofacial Orthop. 2002 Apr;121(4):337-8. 6. Shen G, Chen RJ, Hu Z, Qian YF. The effects of a newly designed twinslot bracket on severely malpositioned teeth--a typodont experimental study. Eur J Orthod. 2008 Aug;30(4):401-6. 7. Swartz ML. Comprehensive fixed appliance therapy. In: McNamara JA, Brudon WL, eds. Orthodontics and Dentofacial Orthopedics. Ann Arbor, Mich: Needham Press; 2001:149–151.

Figure 4.21 A lower incisor bracket with smaller tie wings .Placing ligature on these tie wings is extremely difficult especially when laceback wire is also passed through these brackets to make units of teeth

8. Epstein MB. Benefits and rationale of differential bracket slot sizes: the use of 0.018-inch and 0.022-inch slot sizes within a single bracket system. Angle Orthod. 2002;72:1–2.

74

10. Detterline DA, Isikbay SC, Brizendine EJ, Kula KS. Clinical outcomes of 0.018-inch and 0.022-inch bracket slot using the ABO objective grading system. Angle Orthod. 2010 May;80(3):528-32. 11. Vu C, Roberts WE, Hartsfield JK, Ofner S. Treatment complexity index for assessing the relationship of treatment duration and outcomes in a graduate orthodontics clinic. Am J Orthod Dentofacial Orthop. 2008;133:9.e1–e13. 12. Amditis C, Smith LF. The duration of fixed orthodontictreatment: a comparison of two groups of patients treated using edgewise brackets with 0.0180 and 0.0220 slots. Aust Orthod J. 2000; 16:34–39. 13. Frantz RC. Achieving excellence in orthodontics with a selfligating appliance system. In: Graber TM, Vanarsdall RL, Vig KW, eds. Orthodontics: Current Principles and Techniques. 4th ed. St Louis, Mo: Mosby; 2005:834–836. 14. Mclaughlin RP, Bennett JC, Trevesi HJ, systemized orthodontic treatment mechanics , mosby 2001. 15. Schudy FF, Schudy GF. The bimetric system. Am J Orthod. 1975; 67:57–91. 16. Gianelly AA, Bednar JR, Dietz VS. A dimensional edgewise technique. J Clin Orthod. 1985; 19:418–421. 17. Keim RG, Gottlieb EL, Nelson AH, Vogel DS. 2002 JCO study of orthodontic diagnosis and treatment procedures: part 1: results and trends. J Clin Orthod. 2002; 36:553–568. 18. Rubin RM. A plea for agreement. Angle Orthod 2001; 71. 19. Thind BS, Larmour CJ, Stirrups DR, Lloyd CH.An ex vivo assessment of gingivally offset lower premolar brackets. J Orthod. 2004 Mar;31(1):34-40. 20. Thind BS, Stirrups DR, Hewage S. Bond failure of gingivally offset mandibular premolar brackets: a randomized controlled clinical trial. Am J Orthod Dentofacial Orthop. 2009 Jan;135(1):49-53. 21. Russell JS. Aesthetic orthodontic brackets. J Orthod. 2005 Jun; 32(2):146-63. 22. Thorstenson JA, Kusy RP. Resistance to sliding of orthodontic brackets with bumps in slot floors and walls: effects of second-order angulation. Dent Mater 2004; 20: 881–892. 23. Shivapuja PK, Berger J. A comparative study of conventional ligation and self-ligation bracket systems. Am J Orthod Dentofac Orthop. 1994;106:472–480. 24. Taloumis LJ, et al. Force decay and deformation of orthodontic elastomeric ligatures. Am J Orthod Dentofac Orthop. 1997;111:1–11. 25. Graber LW, Vanarsdall RL & Vig KW Orthodontics: Current Principles and Techniques. 5th ed. E: Elsevier; 2011. 26. do Nascimento LE, de Souza MM, Azevedo AR, Maia LC. Are selfligating brackets related to less formation of Streptococcus mutans colonies? A systematic review. Dental Press J Orthod. 2014 JanFeb;19(1):60-8. 27. Čelar A, Schedlberger M, Dörfler P, Bertl M. Systematic review on selfligating vs. conventional brackets: initial pain, number of visits, treatment

75

time. J Orofac Orthop. 2013 Jan;74(1):40-51. 28. Ehsani S, Mandich MA, El-Bialy TH, Flores-Mir C. Frictional resistance in self-ligating orthodontic brackets and conventionally ligated brackets. A systematic review. Angle Orthod. 2009 May;79(3):592-601. 29. Krishnan M, Kalathil S, Abraham KM. Comparative evaluation of frictional forces in active and passive self-ligating brackets with various archwire alloys. Am J Orthod Dentofacial Orthop. 2009 Nov;136(5):67582. 30. Archambault A et al Torque expression in stainless steel orthodontic brackets. A systematic review. Angle Orthod. 2010 Jan;80(1):201-10. 31. Fleming PS, Johal A. Self-ligating brackets in orthodontics. A systematic review. Angle Orthod. 2010 May;80(3):575-84. 32. Chen SS et al .Systematic review of self-ligating brackets. Am J Orthod Dentofacial Orthop. 2010 Jun;137(6):726.e1-726.e18; discussion 726-7.


9. Sifakakis et al . Torque expression of 0.018 and 0.022 inch conventional brackets. Eur J Orthod. 2013 Oct;35(5):610-4.


CHAPTER

4

76

CHAPTER

5

Selection of Auxiliary and convenience features In this Chapter

Auxiliary features Power arms Accessary slots Convenience features Vertical Mid Scribe line Shape of brackets Bracket identification

Many auxiliary and convenience features are added to the brackets and tubes to make treatment mechanics easier and convenient.

Auxiliary features Power arms Power arms are added to the brackets on its gingival side to control root position during translation of the teeth. The reason for making power arms on gingival side is to bring the force application closer to the center of resistance of the teeth. Andrew1 proposed that for effective control of root position during translation, the mesiodistal length of bracket plus height of power arm should be equal to distance from the slot point to tooth center of resistance (Figure 5.1). As root of canine is longer than other teeth so power arm of canine tooth would also be

77

longer than other teeth. But there are practical limitations in increasing the width of bracket and height of power arm. A wider bracket will decrease interbracket distance so increasing the wire stiffness and thus greater time would be needed in alignment and leveling. Also a wider bracket will be more noticeable, thus increasing aesthetic concerns of the patients. The height of power arm is limited by soft tissue present around the tooth as long power arm will impinge on the gingiva either making ideal bracket placement difficult or leading to gingival hyperplasia due to soft tissue impingement. Advantages of power arm 1. Power arm makes the application of force delivery system such as springs, power chains, and elastics much easier and close to

Selection of Auxiliary and convenience features

CHAPTER

5

the center of resistance of the tooth. 2. Power arm also gives a better retention area for the ligatures and settling elastics during finishing stage of treatment (Figure 5.2). So power arm is helpful even the tooth doesn't need translation. 3. Power arms are also helpful in orthognathic surgery in tying of surgical splints to the main archwire and the brackets.

Figure 5.2 A case with settling elastics .The upper premolar bracket has a kobayashi hook attached to help better retention of settling elastics. On canine bracket elastics can easily be attached as it got an integral bracket hook.

Clinical Notes The direction of translation is the key in selecting power arm. The power arm should always be present in direction of translation. If a tooth needs protraction during treatment as in case of upper 1st premolars extraction with moderate anchorage, the upper second premolar is moved forward so power arm should be present on mesiogingival side of the 2nd premolar bracket. In same extraction case canine needs to be retracted in the extraction space so power arm should be on distogingival aspect of canine bracket (Figure 5.3). In distalization of molars, both canines and premolars are moved backward or retracted, so power arms should be present on distogingival side of the brackets on both premolars and canines. Figure .5.1 Where A = Distance between the middle of bracket or slot point to center of resistance of the tooth B= Mesiodistal length of the bracket C= Height of the power arm An ideal bracket on a tooth needing translation should follow the following rule: A=B+C. This is very important mechanical consideration while selecting brackets. If a wider bracket is selected than B is increased in equation so C should be decreased to accommodate B. If this is not done and contemporary mechanics are followed where some play is present between wires and brackets then extra tip would be expressed by the brackets. Greater the play of the wire in the brackets greater would be the extra tip expressed. The opposite is true in smaller or miniseries brackets where B is small and C needs to be large to accommodate B. If this is not done, there would be loss of tip during tooth translation.

In situation where canines and premolars are moved forward as in case of generalized spacing the canine's bracket should ideally have a hook on it's mesial. Unfortunately most cases in contemporary orthodontics need canine's retraction so manufacturers make canine's brackets with distal power arms and orthodontists have no other choice to use these brackets. In case power arm is not present on the ideal side of the bracket then there are greater chances of tooth rotation while translation.

78

The power arm should be on gingival side of the bracket and in the direction of translation. For teeth with long roots the power arm should also be long though mostly this criterion is not fissible for the orthodontists to fulfill.

B

A

Figure 5.3 A. Right lower 2nd premolar bracket with power arm on mesial side .This bracket is useful in lower 1st premolar extraction with moderate anchorage, where 2nd premolar needs mesialization. B. Left lower 1st premolar with distal power arm. This type of bracket is useful in lower 2nd premolar extraction where power modules can be added from molars to 1st premolars on distal power arm.

The shape of the power arm can be rounded, mushroom shaped or in the form of a hook (Figure 5.4). Hook design power arm allows easy engagement of power modules but takes more time in placement of ligatures and are usually less acceptable by the patients. To address this problem most manufacturers make ball end power arms.

A

B

Miniseries brackets available in the market shouldn't be selected in extraction cases where space after extraction is closed by translation of teeth. Mini brackets having small mesiodistal length should have long power arms, which is usually not the case with commercially available mini brackets. These brackets are more effective for cases requiring minimum or no translation of teeth during treatment. Accessary slots Accessary slots can be horizontal and vertical. Horizontal accessary slot can be used to pass accessary wires and is very important part in tip edge plus brackets but are also present on conventional preadjusted brackets to help intrusion of teeth, extrusion of teeth and piggy back mechanics. Vertical accessary slot can be used to pass torqueing springs, uprighting springs, rotation springs and auxiliary power pins (Figure 5.5). In some cases vertical slot is used for indirect anchorage by engaging a wire from implant to vertical slot of bracket. Vertical slot is added in designs of some ceramic brackets to facilitate easy debonding (Figure 5.5 D).

Convenience features Vertical Mid Scribe line

C

79

Figure 5.4 A left upper canine with (A) rounded (B) mushroom shaped (C) hook shaped power arm.

A mid scribe line help in easy placement of brackets (Figure 5.6). The mid scribe line should follow long axis of the tooth for ideal bracket placement. The vertical mid scribe line also act as an instrument channel during bracket positioning. A continuous vertical scribe line is


Selection of power arm on brackets


CHAPTER

5

preferred. Scribe line is usually not found in ceramic and semi twin metal brackets.

A B

A

B

C Figure 5.6 A. Metal bracket with continuous scribe line. B. Interrupted scribe line. C. A ceramic bracket with no scribe line. Such brackets give poor guidance in axial bracket positioning

Shape of brackets The shape of the bracket can be rhomboidal, rectangular or triangular. These different shapes are more related with patent issues than clinical importance. Whatever the shape of the bracket, an ideal bracket shouldn't interfere with occlusion, soft tissues, provide good rotational control and keep optimum interbracket distance.

C

Bracket identification

D Figure 5.5 A. Accessory horizontal slot in Damon Q bracket Ormco. B. Vertical slot in an American orthodontics brackets. C. Various accessories used with vertical slot brackets. D. A polycrystalline ceramic bracket with vertical slot to aid easy debonding. Auxillary springs can also be used in this vertical slot.

Manufacturers engrave different marks on brackets to make identification of the brackets easy. A dimple or bracket number is usually added on the disto-gingival tie wing of the bracket. Some manufacturers also color code that dimples for easy identification of the bracket while others put bracket number on back of the bracket (Figure 5.7).

80


B

A

C

D

E

F

G

Figure 5.7 A. Plus sign on distogingival tie wing of a gold bracket. B.A plastic dimple on 1st premolar. C. A right lower 1st premolar with number engraved by lasers on distogingival wing. An arrow on the scribe line of the bracket is point in gingival direction to help the clinician recognize the different sides of bracket. D. Different color coding on wings of commercially available brackets. Different manufacturers use different color coding for their bracket series. E&F .In ceramic material the marks are usually made from unknown colors which usually erode in a couple of hour in the oral cavity. In some bracket both gingival wings are color code. This is usually the case where power arm is present on distogingival wing. In case power arm is not present than distogingival tie wing have an extra ring build within the main ring. G.A identification mark on bracket base of a left upper 1st premolar.

Clinical notes Many identification marks used on metal brackets are made of plastic material. The composition of these plastic materials is usually not known. Many of these identification marks are removed from the brackets in the first few hours of bonding

81

and are usually swallowed by the patient. Other that remains on the brackets gets discolored with time and raise aesthetic concerns of the patient. A personal recommendation is to use identification marks that are made of metal or some laser markings.


CHAPTER In some cheap ceramic brackets the marks were made from even women's nail polish! (Figure 5.8).

5

Reference 1. Andrews LF. Straight-Wire-The Concept and Appliance; L. A. WellsCo., San Diego, California. 92107: 1989.

A

B

C

Figure 5.8 A .Ceramic bracket with marking made by ladies nail polish. B. Plastic dimple tear on instrumentation. C. Plastic dimple discolored in clinical used

Many other convenience features are also added to the brackets such as access bevels on the slots for steel ligature cutters, De-ligation saddles for easy removal of elastic ligatures etc. (Figure 5.9). Other convenient features like accessary tube, headgear tubes are also added to brackets especially to molar brackets.

Figure 5.9 saddle

Bracket having acess bevel and deligation

82

CHAPTER

6

Selection of Bracket Prescription In this Chapter

Introduction Andrew Prescription Key I: Interarch Relationship Key II: Crown Angulation or Mesiodistal Crown tip

Different Bracket prescriptions Roth Prescription Limitations of Roth Prescription MBT Prescription Alteration of prescription

Key III: Crown inclination or Torque Key IV: Absence of Rotations Key V: Tight Contact points Key VI: Flat Occlusal plane or Curve of Spee Limitations of Andrew prescription

Introduction Angle introduced edgewise brackets to have a better control on three dimensional positions of the teeth. But the problem in these brackets was that complex wire bending was required to control the tooth position. Andrew 1,2 modified the standard edgewise brackets developed by Angle by introducing tip, torque and in& outs in his preadjusted edgewise brackets .The amount of tip torque and in & outs built within preadjusted brackets were called prescription of the brackets. After Andrew a lot of orthodontists introduced their versions of bracket prescription sometimes based on studies and many times based on clinical experience. Each clinician

83

who advocated a specific prescription also advocated specific mechanics during the course of treatment for expression of the prescription. In medicine to treat a disease properly, the right diagnosis should be made. That helps the physician to advise the right prescription of drug .Same is true in orthodontics. After making a right diagnosis and treatment planning of a malocclusion the right prescription should be used. Using the right prescription, simplify the treatment mechanics which will save considerable chairside time. In most cases there would be minimal or no need of wire bending during the course of orthodontic treatment.


CHAPTER A detailed description on evolution of different types of orthodontic prescriptions is given in this chapter. Main focus is given to the development of Andrew prescription because all other prescriptions are either variations or based on Andrew's data. Andrew Prescription Lawrence F. Andrew1 introduced the first preadjusted brackets where all the bending's needed in archwire in standard edgewise bracket system were built within the brackets. It was proposed that this appliance does not require wire bending during treatment hence the name Straight wire appliance (SWA) was given to it. Andrew after a study on 120 non-orthodontic ideal occlusion dental casts concluded that in order to attain ideal occlusion some characteristics must be present within the occlusion. These characteristics were divided into six keys. Based on these 6 keys Andrew developed his prescription of brackets, so that using this bracket prescription no wire bending would be required during treatment and at the end of treatment, all the six keys to normal occlusion would be attained. Andrew apart from studying these nonorthodontic ideal occlusion dental casts also studied 1150 orthodontic treated cases so that his prescription could also address some of the problems not found in ideal occlusion e.g. Extraction cases where molar relation may deviate from class I relationship. Most of the modern preadjusted brackets are minor modification of Andrew straight wire appliance. To give a better understanding of prescription so that clinician can make an easy selection of brackets a complete description of Andrew six keys to normal occlusion and how prescription components evolve from each key is given. Details on how a prescription in bracket is transferred to a tooth are also given

6

with each key so that the readers can have a clear knowledge of effects and limitations of a prescription. Key I: Interarch Relationship Key I as originally proposed by Andrew 1 was molar relationship. But in 1989 Andrew2 changed the key from molar relationship to interarch relationship. Interarch relationship is broader and more definite description of occlusal relationship than relying on molar relations only. Interarch relationship as key 1 is considered in this text because it will clear the reader's mind about the basis and need of prescription. Key I have seven parts 2 which are given below: Part 1 The mesiobuccal cusp of the maxillary first permanent molar fits in the groove between the mesial and middle buccal cusps of the mandibular first permanent molar. Part 2 The distal marginal ridge of maxillary 1st molar occludes with mesial marginal ridge of the mandibular 2nd molar. Previously1 this relation was. "The distal surface of the distobuccal cusp of maxillary 1st molar made contact and occluded with the mesial surface of the mesiobuccal cusp of the mandibular second molar." The closer these two surfaces of maxillary 1st and mandibular 2nd molar contact and occlude , the better would be the opportunity for normal occlusion. Part 3 The mesiolingual cusp of the maxillary 1st permanent molar occludes in the central fossa of mandibular 1st permanent molar.

84

The buccal cusp of the maxillary premolars have cusp embrasure relationship with mandibular premolars. The maxillary 2nd premolar buccal cusp lies between embrasure of mandibular 1st molar and mandibular 2nd premolar. Buccal cusp of maxillary 1st premolar lies in the embrasure between mandibular 1st and 2nd premolars. Clinical Notes To check if a case has attained Key I, always judge from buccal aspect clinically and both from buccal and lingual aspects on the dental cast. Part 5 The lingual cusp of the maxillary premolars has a cusp fossa relationship with mandibular premolars. Part 6 The maxillary canine tip lies slight mesial to the embrasure between mandibular canine and 1st premolar. Part 7 The maxillary incisors overlap the mandibular incisor with their dental midlines coinciding. A description of key I is given in figure 6.1.

A Figure 6.1

85

Incorporating key I into bracket prescription Key I is interrelated with next 5 keys to normal occlusion. Key I will only be achieved when the rest of the keys have been achieved too. To attain key I, a preadjusted bracket should have built in 1st, 2nd and 3rd order bends and brackets should be optimally placed on the tooth. Only description of 1st order bends and how and why they are included in the prescription would be given here. The rest would be discussed in their respective keys. To incorporate the right amount of 1st order bends with in his prescription Andrew 2 measured the facial prominence of each tooth within the arch of an ideal occlusion case .This was done by measuring the distance from the embrasure line to most prominent facial point of each tooth, where embrasure line is imaginary line at crown mid transverse plane that connects the facial portion of contact areas of a single crown or all the crowns in an arch when the crowns are optimally placed. Figure 6.2 and table 6.1. From the figure 6.2 and table 6.1 it is clear that in maxillary arch lateral incisors have least facial prominence while in mandibular arch both central and lateral incisors have least facial prominence. These values were built within the base or stem of the brackets so that at the end of leveling and alignment all the brackets slots

B An ideal occlusion case meeting all the criteria of key I . A .Buccal aspects . B. Lingual aspects


Part 4


CHAPTER

6

have same level of prominence while all the teeth have the prominence value found in table 6.1. How it works? To build the right amount of prominence within the brackets, Andrew incooperated a simple rule that the distance between most prominent facial point of the crown and the embrasure line is inversely proportional to the distance between slot point and most prominent facial point of crown in mid transverse plane.(Figure 6.3A) . This means that if a tooth has less facial prominence of crown it would have increased bracket prominence (Figure 6.3B&C). The slot point is the mid of the bracket slot in all three planes of space. For the ease of simplicity since we are viewing the tooth from lateral side so base of the slot instead of slot point would be used in this text.

A

B Figure 6.2 Facial prominence of teeth in the arch .The distance between embrasure line and most prominent facial point of each tooth is the prominence of the tooth. A. Average maxillary arch crown prominence. B. Average mandibular arch crown prominence. These prominence values are incorporated into the brackets by varying the distance from base of slot to base of brackets.

So in maxillary arch lateral incisor bracket would be the most prominent bracket in mid transverse plane. When such a bracket is placed on the tooth a palatal force is expressed by the flexible wire on this tooth as compared to neighboring teeth which absorb reactionary labial or buccal force because less prominent brackets are placed on them . So eventually on heavy wires maxillary lateral incisor crowns are found to be less prominent than central incisors and canine crowns while all the brackets slot point or slot bases are at same level of prominence . In Andrew's prescription (table 6.2) of fully programmed standard brackets, maxillary

Table 6.1.Crown prominence in maxillary and mandibular arch Canine

1stpremolar

2ndpremolar

1st Molar

2nd Molar

Maxillary Arch

Central Lateral incisors incisors 2.1mm 1.65mm

2.5mm

2.4mm

2.4mm

2.9mm

2.9mm

Mandibular arch

1.2mm

1.9mm

2.35mm

2.35mm

2.5mm

2.5mm

Teeth

1.2mm

86

leveling. This difference in bracket prominence is same as difference in teeth prominence as measured from embrasure line (2.1mm 1.65mm =0.45 mm). The same rule is true for all other brackets in both maxillary and mandibular arch.

Table 6.2.Bracket prominence in maxillary and mandibular arch in Andrew prescription Canine

1stpremolar

2ndpremolar

1st Molar

2nd Molar

Maxillary Arch

Central Lateral incisors incisors 1.8mm 2.25mm

1.4mm

1.5mm

1.5mm

1mm

1mm

Mandibular arch

2.3mm

1.6mm

1.15mm

1.15mm

1mm

1mm

Teeth

2.3mm

B

C

A

Figure 6.3 A. In this figure A= embrasure line, B= most prominent facial point of crown, C= Slot base. Slot base is taken instead of slot point for ease of simplicity. Distance A to B ∝1 ∕Distance B to C. So if distance between A to B is smaller as in the case of maxillary lateral incisor crown, distance B to C should be larger. B. Upper incisor brackets. In maxillary arch the prominence of lateral incisor is least in the arch so its bracket slot base is highest in prominence. After subsequent leveling of the slot base with other brackets in maxillary arch lateral incisors will move palatally equal to the amount of its bracket prominence as compared to the other brackets. C. Mandibular brackets. Mandibular central and lateral brackets are greater in prominence than other brackets in the arch. This is because these teeth have least prominence in the arch in term of first order position. In the figure some brackets like mandibular canine have different prominence than recommended values .This is because of manufacturer error of placing the right amount of prominence in the brackets

Clinical notes Clinicians usually change brackets for altering bracket prescriptions. But using brackets from different series of brackets may result in first order difference between brackets (Figure 6.4). It is better to select brackets from same manufacturer while altering the prescription.

Figure 6. 4 Lateral incisor brackets from three different manufacturers. First two brackets are in MBT prescription. Bracket C is in Roth prescription.

87


central incisor bracket has prominence of 1.8 mm; maxillary lateral incisor bracket has prominence of 2.25mm). The difference between maxillary central and lateral incisor bracket prominence is 0.45 mm (2.25mm 1.8mm =0.45mm). So lateral incisor bracket slot base would be 0.45 mm more inward after


CHAPTER Molars offsets Maxillary molars Another important consideration is molar offset bends. Part 1 of key I state that mesiobuccal cusp of the maxillary first permanent molar occlude in the groove between the mesial and middle buccal cusps of the mandibular first permanent molar. To achieve this part as a treatment goal one must have clear understanding of tooth morphology. The mesiobuccal groove of the mandibular first molar is more facially prominent than its distobuccal groove relative to the embrasure line. To occlude with mesiobuccal groove of mandibular first molar the mesiobuccal cusp of maxillary 1st molar should have more facial prominence or in orthodontic terms should have an offset or mesial buccal orientation. Andrew measured this maxillary molar offset by measuring the angle between embrasure line and a line connecting the buccal cusps of the molars. The offset was found to be 10° in normal occlusion where molar relation was class I (Figure 6.5). The mandibular 2nd molar also have a prominent buccal groove, though distobuccal groove is not

6

present within 2nd mandibular molar. The maxillary 2nd molar should also have an offset of 10° so that its mesiobuccal cusp should be properly occluded in buccal grove of mandibular 2nd molar. How it works? The rule of thumb used in bracket manufacturing is that plane of bracket or base should always be parallel to the facial plane of crown. Further, tube of the bracket should also be straight when tooth is in its ideal position. In case of maxillary 1st molar in Class I molar relationship the distobuccal half of the tooth is slightly palatal to mesiobuccal half. Placing a tube base with parallel slot having a 0°angle or offset between tube base and slot on the buccal surface of tooth will result in opening of slot more buccal on mesial side and more palatal on distal side. This will cause molar to rotate mesiopalatal and distobuccal on subsequent leveling on orthodontic wires. At the end of leveling when the slot is straight to other neighboring bracket slots the mesiobuccal and distobuccal cusps of the molars have the same level of prominence. To avoid this problem more tube material is added under the slot on its distal half giving the tube distal offset on its base so the that the tube make an angle of 10° with its base. When such a tube is aligned and its opening become straight, the distal half of tube base and so the molar is more inward or palatal as compared to the mesial half (Figure 6.6). The same rule is true for maxillary 2nd molars brackets and tubes. Mandibular molars

Figure 6.5 Molar offset. The angle between the embrasure line and the line connecting the buccal cusps of the teeth is 10° for both the maxillary 1st and 2nd molars.

A zero degree angle was measured in mandibular molars between embrasure line and buccal line joining middle and mesial buccal cusp. So no offset was incorporated in mandibular molar tubes in normal occlusion (Figure 6.7 A&C). In mandibular molars the plane of bracket tube is parallel to bracket base and to the facial plane of crown (Figure 6.7 B).

88


A

B

C

E

D

F

Figure 6.6 A&B Mesial and distal opening of a 0° offset double molar tube .The distance of tubes slots from their base is same on both mesial and distal side C& D Mesial and distal opening of a 10° distal offset single molar tube. The distance of tube slot from its base is less on mesial side as compared to distal side .As the distal side of tube slot is more outward buccaly so these molar tubes are called distal offset tubes. E. A 0° offset tube as base of the molar tube and its slot are parallel to each other. F. A 10° distal offset molar tube as slot of the tube makes an angle of 10° with its base.(continued....)

89


CHAPTER

6

G H

I

J

Figure 6.6 G. A 0° offset molar tube placed on maxillary 1st molar .As the slot of the tube is angular to the facial surficial of the tooth so on subsequent alignment both mesial and distal cusps of the molar would have equal facial prominence resulting in 0° offset molar. H. A 10° distal offset bracket placed on the maxillary 1st molar. A distal offset tube is used to bring mesial offset in the molar. The slot of the tube makes an angle of 10° with the embrasure line and is parallel to the facial surface of the tooth so on subsequent alignment the mesial cusp of the molar would be more facially prominent than the distal cusp. I.A 0° offset tube placed on a well aligned maxillary 1st molar. As the distal surface of the molar is less facially prominent so the slot is more inward distally though there is no offset in the tube. J. A 10° molar offset tube placed on maxillary 1st molar in a well aligned arch .Even there is a distal offset, the slot is straight because decrease prominence of the distal cusp of the molar is compensated by the offset in the tube.

B A Figure 6.7. A. A mandibular 1st molar having 0° offset. B. A 0° offset molar tube place on the molar. As the embrasure line, facial surface of the tooth and slot of the tube make an angle of 0° so the mesial and middle cusp have the same level of prominence after leveling and alignment. C. A 0° offset molar tube placed on a well aligned molar. As mesial and middle cusps have equal level of facial prominence so the tube has a straight opening.

C

90

In an ideal occlusion non orthodontic patients, posterior dentition having Class II or Class III relations and anterior dentition having Class 1 relations is not technically possible as all the teeth are present. But such relations are a frequent finding in orthodontically treated cases in which extraction of premolars have been done. In case of such relations only part 6 &7 of key I is applicable. For better understanding of molar relations a classification of class I, II and III molar is given in figure 6.8.

Andrew from his study of 1150 orthodontic treated cases proposed that a class II molar relation should have following characteristics. Characteristics of Class II molar relationship Part 1 The mesiobuccal cusp of maxillary 1st molar lies in the embrasure between mandibular 1st molar and 2nd premolar. Part 2 The distobuccal cusp of maxillary 1st molar occludes in the mesiobuccal groove of mandibular first molar. Part 3 The mesiolingual cusp of maxillary 1st molar occludes with the mesial marginal ridge of mandibular 1st molar. Part 4 The canine and incisor relation should follow key I part 6&7.

A

Characteristics of class II molars are given in figure 6.9. Characteristics of Class III molar relationship No occlusal relation was proposed for class III molar relationship by Andrew. But from my understanding, a class III molar relation should have following characteristics. Part 1

B Figure 6.8 A. Zones of Class I, II& III molar relationship on the mandibular cast in accordance with ABO standards. The mesiobuccal cusp of the maxillary 1st molar occluding in these zones will decide the molar relations. B. Mesiobuccal cusp of the maxillary 1st molar.

91

The mesiobuccal cusp of maxillary 1st molar should lie in the embrasure between mandibular 1st molar and 2nd molar. Part 2 The distobuccal cusp of maxillary 1st molar should occlude in the buccal groove of


Molar offset in dental class II&III


CHAPTER

A Figure 6.9

B Buccal and lingual view of class II molar relationship

mandibular 2nd molar. Part 3 The mesiolingual cusp of maxillary 1st molar occludes with the marginal ridge of mandibular 2nd molar. Part 4 nd

The buccal cusp of maxillary 2 premolar should occlude with the mesiobuccal groove of the mandibular 1st molar. Part 5 The canine and incisor relation should follow key I part 6&7. Characteristics of class III molars are given in figure 6.10. Both in class II and III molar relationship, the mesiobuccal cusp of 1st molar have relation with

the corresponding embrasure which is less prominent facially than the mesiobuccal groove of the mandibular 1st molar (Figure 6.11). To have a proper relationship of the maxillary 1st molar with corresponding embrasure, there shouldn't be any offset on maxillary 1st or 2nd molar in class II or III molar relationships. Key II: Crown Angulation or Mesiodistal Crown tip Crown angulation as the name indicates, is the angulation of long axis of the clinical crown (LACC) or facial axis of clinical crown (FACC).Crown angulation is measured by the angle formed between LACC or FACC and line perpendicular to the occlusal plane. The long axis of the crown of all the teeth, except molars is judged from the mid developmental ridge, where mid developmental ridge is the most prominent and centermost vertical portion of the labial or buccal surface of the crown (Figure

A Figure 6.10

6

B Buccal and lingual view of class III molar relationship

92

C

Figure 6.11 Molar relations in Class I, II & III. 10° maxillary 1st molar offset is present on all three figures. A. Placing an offset in class I molar relation will result in proper occlusion .B&C. Placing an offset in Class in II or III molar relations will result in increased transverse overjet in mesial half of the molar.

6.12 A&B) .In case of molars the long axis of the clinical crown is judged from dominant vertical groove on buccal surface of the molars (Figure 6.12 C&D). For measuring tip or angulation values, Andrew initially used long axis of clinical crown and later2 advocated facial axis of clinical crown (FACC).Though Andrew believed that there is difference between long axis and facial axis of clinical crown but he used mid developmental ridged or vertical buccal groove in case of molar to define these long axis positions. 1

Andrew recommended that the gingival portion of the long axis of the crown should be distal to the incisor portion. Crown tip is expressed in degrees with positive (+ve) or negative (-ve) sign. Positive sign indicate that gingival portion of the long axis of the crown is more distal to the incisor portion while negative sign indicates the opposite. Crown angulation is best judged from buccal or labial perspective depending upon the type of teeth viewed. Both maxillary and mandibular dentitions have positive crown angulations in ideal occlusion.

Occlusal Plane

Occlusal Plane perpendicular

FACC or LACC

Occlusal Plane

Occlusal Plane perpendicular

Dominent Vertical Groove

Occlusal Plane perpend.

FACC or LACC

A

Occlusal Plane

B

C

D

Figure 6.12 Crown tip or angulation of different teeth. A & B. Upper and lower central incisors. The crown angulation of upper and lower incisors is measured from mid developmental ridge. C & D. Upper and lower 1st molars. Crown tip or angulations of upper and lower molars are measured from dominant vertical buccal groove.

93


B

A


CHAPTER Incorporating key II into Bracket prescription Proper crown angulation is necessary to get a good occlusal and esthetic results. More the angulation of the teeth more the space they will occupy in the arch (Figure 6.13). Over angulating

6

plane over the bracket base so that one side of the slot is vertically high than the other. This will cause a straight wire to rotate the bracket on subsequent leveling of slots. The required angle of rotation of the slot was taken from Andrew's measurements and incorporated in his standard series brackets. Mechanism of tip expression is explained in figure 6.14. Tip compensation in Andrew Translation series brackets

B

A

Figure 6.13 A. Ideal angulation of upper central and lateral incisors. B. increased angulation of upper central and lateral incisor. Because of increased angulation these incisors are occupying more space than ideally angulated incisors.

the teeth will disturb the embrasures /connectors relations and will result in development of black triangles. If the teeth are under angulated, spaces would be present within the arch which would be difficult to close without altering the occlusal relations or giving proper tip/angulation. To incorporate the right amount of tip within his bracket prescription, Andrew measured average angulation of teeth from his study of 120 ideal nonorthodontic treatment casts. The average value of tooth angulation are given in table 6.3.

How it works? In Straight wire appliance tip or angulation is incorporated in the face or slot of the bracket by placing the slot at an angle in the mesiodistal

Tip expression is not a problem when the teeth are not translated. But it is a common finding that when a tooth is translated mesial there is increase in its angulation and when a tooth is moved distal there is decreased in its angulation. This rule is not applicable to incisor teeth because of their position in the arch. Andrew 2 proposed that for effective tip expression, the mesiodistal length of slot should equal to distance from the slot point to the tooth center of resistance (Figure 6.15). Such brackets length is technically not possible. So power arms were added to bracket to cover up rest of the length. The length of power arm plus mesiodistal length of the bracket should be equal to the distance between slot points to the tooth center of resistance. For complete expression of tip the power arm and bracket should be activated collectively during translation and full dimension wires should be used. Since engaging full dimensional wire is technically not possible, especially during sliding mechanics and also there are soft tissue limitation on increasing the length of power arm, some loss of tip during sliding is inevitable. To maintain control over three dimensional

Table 6.3.Tooth angulation in ideal occlusion in non-orthodontic patients Canine

1stpremolar

2ndpremolar

1st Molar

2nd Molar

Maxillary Arch

Central Lateral incisors incisors +5° +9°

+11°

+2°

+2°

+5°

+5°

Mandibular arch

+2°

+5°

+2°

+2°

+2°

+2°

Teeth

+2°

94

Selection of Bracket Prescription Figure 6.14 Maxillary left side brackets .Archwire slot on mesial side of the bracket is downward directed while on the distal side it is upward directed.On engagement of flexible wire after ideal bracket placement the mesial and distal slot of bracket will rotate in the clockwise direction and so will the teeth. Due to clockwise rotation of the teeth in left side of the arch the incisal portion of teeth would be more mesial than the gingival portion. In this way tip is expressed. There is anticlockwise rotation of brackets for expression of tip on right side of the maxillary arch. In maxillary arch for positive tip the mesial part of slot is directed downward as compared to distal part and for negative tip mesial part would be directed upward. In mandibular arch for positive tip expression, the mesial part of the slot should be directed upward/occlusal and vice versa.

positions during tooth translation in extraction or spacing cases, Andrew developed the translation series brackets. These translation series brackets were of three types : 1. Minimum translation series brackets for 0.1 to 2mm translation 2. Medium Translation series brackets for 2.1 to 4mm translation 3. Maximum Translation series brackets for greater than 4mm translation

Figure 6.15 For effective control of root position during translation the mesiodistal length of bracket plus height of power arm should be equal to distance from the slot point to tooth center of resistance.

95

To compensate the change in tooth angulation during mesial or distal translation, Andrew introduced counter mesiodistal tip in his translation series brackets. A 2° tip was added to the slots of standard brackets in case of intended

Table 6.4.Angulation /Tip for Minimum Translation series brackets for 0.1 to 2mm Translation Maxilla Mandible Tooth Distal Translation Mesial Translation Distal Translation Mesial Translation Canine 13° 9° 7° 3° st 1 Premolar 4° 0° 4° 0° 2nd Premolar 4° 0° 4° 0° 1st Molar 7° 3° 4° 0° nd 2 Molar 7° 3° 4° 0°


CHAPTER

6

Table 6.5.Angulation /Tip for Medium Translation series brackets for 2.1 to 4mm Translation Maxilla Mandible Tooth Distal Translation Mesial Translation Distal Translation Mesial Translation Canine 14° 8° 8° 2° st 1 Premolar 5° -1° 5° -1° 2nd Premolar 5° -1° 5° -1° 1st Molar 8° 2° 5° -1° nd 2 Molar 8° 2° 5° -1°

Table 6.6.Angulation/Tip for Maximum Translation series brackets for greater than 4mm Translation Maxilla Mandible Tooth Distal Translation Mesial Translation Distal Translation Mesial Translation Canine 15° 7° 9° 1° 1st Premolar 6° -2° 6° -2° 2nd Premolar 6° -2° 6° -2° st 1 Molar 9° 1° 6° -2° 2nd Molar 9° 1° 6° -2°

distal movement in minimum translation series brackets and in cases of intended mesial movement, 2° was subtracted from the slot. 3° was added or subtracted from standard series brackets for distal or mesial translation in medium translation series brackets. 4° was added or subtracted from standard series brackets for distal or mesial translation in maximum translation series brackets. Tip/angulation values for minimum, medium and maximum translation series brackets are given in table 6.4-6.6. Note: Usually distal translation of the molars and mesial translation of canines is not done in orthodontic practice so there are few cases which benefit from these angulation values. Some of the angulations values are given for clarity of concept as actuals brackets having such tip values are not manufactured. Take the example of a mandibular canine with +5° tip in standard bracket. Suppose it's an extraction case of 1st premolar. If it is planned to retract this canine into the premolar space a translation series bracket would be required. If intended distal movement of the canine is less than 2.1 mm ,a minimum translation series bracket would be used that will have an

effective bracket slot angulation of 7° , 5° of standard tip and 2° of countermesiodistal tip added to the slot . If the intended retraction of mandibular canine is between 2.1 to 4mm a medium translation series bracket is selected which have a 5°+3°=8° tip built within the slot. For maximum translation series, bracket having 9° tip would be used on canine when retraction is greater than 4mm. In cases of spacing in lower arch and mesial movement of mandibular canine is intended following tip/angulation values were introduced in translation series brackets. Minimum translation series bracket of mandibular canine for mesial translation (0.12mm translation) =+3° Medium Translation series brackets of mandibular canine for mesial translation (2.1 4mm translation) =+2° Maximum translation series brackets of mandibular canine for mesial translation (˃4mm translation) =+1° Molar Class II & III Relationship As explained before, in ideal occlusion cases in

96

In a finished case a zero degree angulation of maxillary molars should be present in both class

B

A

D

II & III molar relationship. But what angulation brackets, tubes or bands should be used if molar is translated to that position? To the best of my knowledge Andrew didn't propose molar angulation changes for class II &III relationship for translation series brackets. But my understanding is that the same principles of angulation should be applied considering zero degree as ideal angulation. So if final relation of

E

C

F

Figure 6.16 A. Molar Class I relationship. For molar Class I relation Andrew proposed that FACC of maxillary molar which is dominant vertical buccal groove should be 5° to a line 90° to the occlusal plane. B. In case of class II molar relation keeping 5° positive tip in the molars will result in hanging of distal cusps of maxillary 1st molar and poor interdigitation of its mesiobuccal cusp.C. Giving a 0° to the maxillary 1st molar will result in proper interdigitation. D. Class I molar relationship on the dental cast. E. Class II molar relationship on the dental cast. F . Mandibular 1st molar showing the transition from class I to class II position . In class I position the distobuccal cusp of the maxillary 1st molar was occluding at point A on the mandibular 2nd molar while the mesibuccal cusp was occluding at point B on mandibular 1st molar. In the Class II molar relations, the distobuccal cusp will jump to point B on mandibular 1st molar while the mesiobuccal cusp will occlude at point C on mandibular 2nd premolar . So distobuccal cusp of maxillary 1st molar has jumped from a lower position to a higher position while mesiobuccal cusp of maxillary 1st has fallen from a higher position to a lower position. Keeping the same amount of tip won't allow the maxillary 1st molar to rotate for an ideal occlusion resulting in premature contacts of distobuccal cusp of maxillary 1st molar with buccal groove of manidulbar 1st molar while the mesiobuccal cusp of maxillary 1st molar will remain out of occolusion . To avoid these improper occlusal results in an orthodontic treated case, tip of maxillary molars is decreased from 5° to 0°.

97


which the molar relation is class I the angulation or tip of both 1st and 2nd maxillary molars should be +5°. But keeping a 5° tip in class II or Class III molar relations will result in poor occlusion due to hanging or more downward position of distal surface of the molars (Figure 6.16).


CHAPTER

G

J

H

K

6

I

L

Figure 6.16 G&H.Class I and III molar relationship with 5° tip in maxillary 1st molar . Note the poor occlusal contact of mesiobuccal cusp of the maxillary 1st molar in class III relationship . These relations can be improved by rotating molar couterclockwise so that angulation of molar become 0° with occlusal plane perpendicular. I . A molar with 0° angulation with occlusal plane perpendicular having proper relationship with lower molar.J,K,L show transition of molar relation from class I to III. Since there is similarity in change in relationship to that of class II molars so same rules of teeth angulation will apply here. Giving a 0° tip to maxillary molars will result in proper occlusal relationship.

molar is planned full cusp class II and 1.5mm maxillary molar mesialization is intended, -2° countermesiodistal tip should be present. For 3mm molar mesialization -3° countermesiodistal tip and for 5 mm mesialization -4° countermesiodistal tip should be present. For 2.5mm molar distalization for attaining a class II molar relationship +2° of countermesiodistal tip should be used though it doesn't usually happen that one distalize molar to attain class II molar relations.

molar offset. If a 0° offset is present on molar there would be a mesiobuccal rotation of the molar and it is well know that a rotated teeth occupy more space. So how this extra space is acquired in class II & III molar relationship where a 0° maxillary molar offset is recommended for 1st and 2nd molar? This extra space is provided by placing the maxillary molars in class II& III position at their right angulation which is a 0° instead of 5° of class I molar.

Relation between Tip and molar offset

Some orthodontic literature and manufacturer catalogs claim 10° molar offset as antirotation in molar. This is a misconception as 10° offset in a molar in class I position is its natural position and not rotated position. Instead, 0° offset in a molar in Class II &III relations is a rotated position of molar, intentionally created to give a

An important aspect which must be well understood is relation of molar offset and angulation of molars in class II & III molar relationship. In class I molar relationship maxillary 1st and 2nd molar should have 10°

98


better occlusion. Factors effecting Expression of Tip 1. Play of the wire 2. Manufacturer tolerance of the wire and slot 3. Mesiodistal length of the bracket 4. Height of power arm 5. Force applied during translation 6. Type of bracket ligation 7. Direction of tooth movement 8. Position of neighboring brackets Play of the wire effect torque more than tip. Almost the entire tip is expressed in a 0.018”wire on 0.018”x0.025” slot. Most of the tip in a 0.022” slot is expressed on a 0.020” wire. Manufacturer tolerance of the wire and slot also increases the play of wire leading to loss of tip. Greater the force applied to translate the teeth in extraction cases and weaker the ligation of wire in brackets, greater would be the chances of tip loss. Position of neighboring teeth and their brackets can cause increase or decrease of tip in cases where wire play is present. Rests of the factors have been explained before. Key III: Crown inclination (labiolingual or buccolingual inclination) It is inclination of long axis of clinical crown (LACC). Crown inclination is measured by angle formed by a line tangent to the middle of the labial or buccal long axis or facial axis of the clinical crown (LACC or FACC) and a line that is 90° to the occlusal plane (Figure 6.17). Crown inclination is measured in degrees with positive or negative sign. A positive sign is given when gingival portion of the tangent line or gingival portion of crown is lingual or palatal to the incisor portion. A minus or negative sign is given when gingival portion of the tangent

99

Figure 6.17 Normal inclination of upper incisor crown as measured with reference to occlusal plane perpendicular.

line or gingival portion of crown is buccal or labial to the incisor portion. In maxillary incisors the gingival portion of crown is lingual or palatal to the incisor portion. The incisor portion is more labial for central incisor than lateral incisor. So there is a positive torque in maxillary incisors. In maxillary canines to premolars, cusp or occlusal portion of clinical crown is more palatal than gingival portion of the clinical crown. The same trend is seen in molar teeth but it is more pronounced.So there is negative torque in maxillary posterior segment and canines. In lower teeth a negative crown inclination is found from incisors to second molars. This negative torque increases progressively from incisors to molars. Proper torque is for proper occlusion. An increased positive torque will cause arch expansion and space opening within the arch while increased negative torque will collapse the arch and there would be lack of space within the arch. Increased positive or negative torque can result in root damage and periodontal recession by bringing the roots


CHAPTER close to or out of the cortical bone. Incorporating key II into Bracket prescription Torque is incorporated in straight wire appliance by varying the thickness of base or stem under the slot so that the slot comes at an angle to the base in vertical plane (Figure 6.18). Some manufacturers also introduce torque by

A

6

placing the slot at an angle over the stem but torque in base is favored. In measuring the average inclinations, most of the variations were found in incisors torque. This is because of the fact that apart from skeletal class I ,mild skeletal class II & III pattern can also exhibit class I occlusal relationship. Andrew standard brackets are effective for ANB differential of up to 5°.As the

B

Figure 6.18 A .Bracket with slot placed at an angle over the bracket. Thickness of the base and height of bracket stem is modified to introduce torque within the bracket. B. Bracket with zero degree torque as base of bracket is parallel with base of slot and is at right angle to slot walls.

Table 6.7.Inclination values for Andrews’ Standard bracket prescription (Class I molar and skeletal relationship) Tooth Maxilla Mandible Central incisor +7° -1° Lateral incisor +3° -1° Canine -7° -11° st 1 Premolar -7° -17° 2nd Premolar -7° -22° 1st Molar -9° -30° nd 2 Molar -9° -35°

distance between upper and lower alveolar processes vary with different skeletal relations of the jaws, it is technically not possible to keep the same amount of torque in the incisors for all the three skeletal relations. Doing so will results in bringing root closer or out of the alveolar cortex in case of moderate to severe skeletal discrepancy. To avoid such technical limitations and iatrogenic damages, Andrew proposed different torque values for upper and lower incisors in skeletal class I,II and III relations. For class II skeletal relations (ANB greater than 5°) 2° maxillary central incisor and -2 °

maxillary lateral incisor torque was proposed (Table 6.8). For skeletal class III (ANB less than 0°) 12° maxillary central incisor and 8° maxillary lateral incisor torque was proposed (Table 6.9). The above mentioned values of incisors torque were also confirmed by an unpublished cephalometric study of 100 cases by Andrew. An important finding in that study was that the maxillary lateral incisor torque is always 4° less than maxillary central incisor torque while mandibular central and lateral incisor have same amount of inclination.

100

Tooth Central incisor Lateral incisor

Maxilla 2° -2°

Mandible 4° 4°

Table 6.9.Incisor Torque in Skeletal Class III Tooth Central incisor Lateral incisor

Maxilla 12° 8°

Positive torque is incooperated in the brackets in maxillary arch by directing the slot downward and negative torque is incooperated by directing the slot upward. In mandibular arch the opposite rule hold true and positive torque is introduced within the brackets by directing the slot upward while negative torque

Mandible -6° -6°

is introduced in the bracket by directing the slot downward (Figure 6.19). Another problem is torque loss in maxillary molars during translation in extraction cases .As maxillary molars are three rooted teeth with dominant palatal root. So when a maxillary molar is translated especially mesial, the palatal

A

B Figure 6.19 Builtin torque in upper and lower arch brackets with slots walls at an angle with bracket base. A. Maxillary brackets from incisors to 2nd premolar. The maxillary central and lateral incisor brackets slots are directed downward towards incisor edge so they have builtin positive torque. Central incisor bracket have more positive torque than lateral incisor bracket. Maxillary canine and premolars bracket slots are directed upward so they have builtin negative torque. In the figure maxillary canine bracket have less negative torque than premolars brackets. This is because the brackets don't have builtin Andrew nd prescription and diagram is given for the ease of understanding. B. Mandibular brackets from central incisor to 2 premolar. All the bracket slots have a downward directed opening except canine. So all the brackets have negative torque while canine has zero torque. Again mandibular arch brackets are not in Andrew prescription and are only given for ease of understanding of torque.

root lag behind and causes the tooth to tip buccally. At the end of translation buccal cusps are more gingival and palatal cusps are more occlusal. This clinical problem is resolved by counterbuccolingual tip feature built within the tube or band which adds more negative torque in band or tube .This negative torque is builtin by rotating the base of the tube upward around its vertical axis, so when slot is aligned by rotating in a clockwise direction more negative torque would be expressed (Figure 6.20). More the tooth is translated greater would be the amount of overcorrection needed for maxillary

101

Figure 6.20 A molar with hanging palatal cusps which is usually the result of translation or expansion. To correct this problem more negative torque is added to molar band or tube .In figure the tube with negative torque is attached to the molar. As slot of the tube is clockwise rotated a straight rectangular wire passing through the slot will cause counterclockwise rotation of the molar. To counter palatal cusps hanging during translation counterbuccolingual tip feature is built within the tube slot.


Table 6.8.Incisor Torque in Skeletal Class II


CHAPTER molars. Following counter buccolingual tip values are added on maxillary molars.-4° of torque is added to maxillary molars in standard brackets for minimum translation series brackets.-5° torque is added in medium translation series brackets and -6° torque or counterbuccolingual tip is added in case of maximum translation series brackets. So following torque values are found in maxillary molars in translation series bracket. Minimum Translation series bracket for maxillary 1st and 2nd molars (0.1-2mm translation) =-9°+-4°=-13° Medium Translation series brackets for maxillary 1st and 2nd molars (2.1 -4mm translation) =-9°+-5°=-14° Maximum Translation series brackets for maxillary 1st and 2nd molars (˃4mm translation) =-9°+-6° = -15° How torque is expressed? A common question mostly asked is how torque is expressed from the bracket and how tooth

A

C

6

would have proper inclination at the end of treatment? In case of brackets, torque is expressed by interaction of brackets and the wires. Torque is always expressed when wire engages the slot of the bracket at an angle and wire is passing through multiple teeth. As round wire can't engage the bracket at an angle and will simply rotate within the slot, so torque expression is not possible by round wires. A rectangular or square wire can engage the bracket at an angle if the slot of the bracket is not straight on insertion of these wires. This can occur if there is builtin torque within the wire or bracket. Morphology of the teeth can affect the position of the slot, while builtin torque in the neighboring brackets can effect orientation of the wires. The amount of torque expressed by the brackets wires interaction depends upon amount of force delivered from the wires to the brackets over a period of time, but force levels should be in optimum limits for torque expression. A higher dimension wire will deliver heavier forces on smaller contact angle than small dimension

B

D

E

Figure 6.21 A. Straight rectangular wire. Straight rectangular wires are used in preadjusted edgewise system also called straight wire appliance. Straight wires are used because all the features for control of three dimensional tooth positions are built within the brackets. B. Twisted or torqued rectangular wire. A torqued rectangular wire is usually used in standard edgewise system but can also be used in straight wire appliance if there is need for extra torque application. C. A rectangular wire passing passively through a bracket slot .If the wire don't contact the slot at an angle no torque would be expressed by the bracket no matter how much torque is built within the bracket and how larger is the wires dimensions. Even if torque is introduced in the wire but if it don't contact the slot at an angle no torque would be expressed. D. A rectangular wire twisted in a counterclockwise direction in the bracket. A wire contacting the slot at an angle and twisting in a counterclockwise direction will express positive torque in maxillary arch and negative torque in mandibular arch. E. A wire contacting the slot in a clockwise direction. Such contact will express negative torque in maxillary arch and positive torque in mandibular arch. (continued....)

102

G

Figure 6.21 F.A round wire in a bracket slot. Whatever their dimensions, round wires will never express torque because they will simply rotate within the slot. G. Torqued wire inserted into the bracket contacting the slot at an angle.

A

B

C

D

Figure 6.22 A. An upper central incisor bracket placed at ideal height over the labial surface of the tooth. As the slot opening is directed downward so insertion of a straight rectangular or square wire will rotate the slot and so the tooth in clock wise direction resulting in expression of positive torque. B. Central incisor bracket inverted and placed over the same tooth. Inverting the bracket slot, rotate the slot and make it upward direction. Straightening of the slot on passing straight rectangular wire will result counterclockwise rotation of the slot and tooth and so expression of negative torque. C&D. The opposite rule hold true in mandibular arch. If the slot opening is upward directed in mandibular arch than positive torque would be expressed on straightening of the slot and vice versa.

rectangular or square wires of the same material. A complete description of torque expression is given in figure 6.21. Another aspect of torque expression is how positive or negative torque is expressed from the brackets? In preadjusted brackets the torque is already built within the brackets by angulating the slot over the base or varying the thickness of the base so that the slot opening is upward or downward directed. As explained before for positive torque expression in

103

maxillary arch the slot opening should be angulated downward and for negative torque slot opening should be angulated upward (fig 6.22 A&B). The opposite rule hold true in mandibular arch (6.22 C&D). When a straight rectangular or square wire is passed through the slot it would engage the slot at an angle and will straighten the slot with time. Straightening of an angulated slot will cause rotation of long axis of the teeth and so expression of bracket torque. Description of different types of torque expression is given in figure 6.23.


F


CHAPTER

6

or decrease the torque present within the brackets. A positive torque given in wire will augment positive torque present within brackets and vice versa. An important question asked by young graduates is that how certain amount of torque is expressed by a prescription?

A

B Figure 6.23 A. upward twist is given in the wire for positive torque in maxillary arch and negative torque in mandibular arch. The twist is given by modified torqueing pliers. The outer plier is moved upward as shown by the arrow to torque the wire. B. Outer plier moved downward to give downward twist to wire. This downward twist in wire will result in negative torque to corresponding teeth if the wire is inserted in upper arch and positive torque to corresponding teeth if wire is inserted in lower arch.

Clinical Notes Sometimes clinician wants to add extra torque to the teeth like in case of class II div 2, impacted canines and palatally placed incisors. The extra torque is given by giving twist in rectangular wires. As opposed to brackets, torsion in wires is given in the direction of movement. An upward directed twist is given in the wire for positive torque in maxillary arch and negative torque in mandibular arch (Figure 6.23 A). A downward directed twist is given in wire for negative torque expression in maxillary arch and positive torque in mandibular arch (Figure 6.23 B).Torque given in the wire will increase

The answer to this question is that in standard edgewise appliance amount of torque given by wire bending was more of guesswork. In Andrew prescription torque is built within the brackets. As the brackets have a compound contoured bases so their bases lies parallel to labial surface of teeth on which it is attached. Bracket base can rightly be said as an extended labial portion of the teeth. In brackets as explained before slot is always at an angle to the bracket base if there is builtin torque within the brackets. So when the bracket base is straight the slot is at an angle to the base that is equivalent to the builtin torque. In mathematical sense the opposite is also true that when the slot is straightened the base is at an angle to the slot with the amount of angulation equivalent to the builtin torque. As bracket base is attached to teeth so the surface of the teeth will achieve the same level of angulation as that of bracket base when the slot is straighten by straight rectangular wire. The description is given in figure 6.24. Theoretically a slot can fully be straightened when a full dimension wire is passed through it. That wire in Andrew prescription using 0.022x0.028 inch slot would be 0.021.5x0.028 inch wire. The bracket should always be bonded at a position that was used as a reference for measuring crown torque. Andrew used middle of labial surface of clinical crown in vertical plane for measuring torque. So bracket base should be placed at middle of labial surface of clinical crown if required amount of torque is needed to be introduced within the teeth.

104


A

B

C

Figure 6.24 A.Maxillary central incisor bracket with slot at +7° to the bracket base. The slot of the bracket is facing downward. In a zero torque bracket the slot walls are at right angle to the base and slot base parallel to bracket base. But in this bracket the slot walls make an angle of 97° with the bracket base as bracket has +7° builtin torque. B. Straightening of slot. The straightening of the slot occurs when full dimension rectangular wires are passed through the slot after required alignment and leveling. In a straight slot the walls of the slot are parallel to occlusal plane while the base of the slot is parallel to occlusal plane perpendicular. When the slot becomes straight, the base of bracket becomes angular equal to the amount of builtin torque. C. A maxillary central incisor bracket with +7° builtin torque bonded at middle of labial portion of central incisor. As the slot of the bracket is straight so the base has turned angular equal to the amount of builtin torque. Base of the bracket being attached to labial surface of the crown will also make the crown angular or inclined equal to the amount of builtin bracket torque. Note that when the slot is straight the base of bracket and middle of the LACC or FACC is making an angle of 7° with occlusal plane perpendicular.

Another important aspect about amount of torque expression is pretreatment inclination of the teeth. A simple a rule of thumb should be remembered “When the slots of the brackets are straight no further torque is expressed on insertion of a straight wire”. Now take the example of maxillary central incisor. The middle of labial surface of this incisor should have 7° inclination to occlusal plane perpendicular in ideal occlusion .If a maxillary central incisor bracket with +7° builtin torque is bonded to central incisor which already has an ideal inclination of 7° to occlusal plane perpendicular than no torque would be expressed on passing a full dimensional wire. But if the same incisor has an inclination of -7° to occlusal plane perpendicular as happen in class II div 2; +14° torque would be expressed on engagement of full dimensional wire to make incisor inclination to +7°. In case of class 2 div1 the middle of LACC of central incisor

105

inclination can be at +20° to occlusal plane perpendicular. In this case central incisor bracket having +7° torque will deliver -13° torque to the central incisor on engagement of a full dimension wire so that the inclination of incisor will become +7° to occlusal plane perpendicular (Figure 6.25). From the above discussion it is clear that if the entire torque built within the bracket is expressed on engagement of full dimension wires, the final inclination of incisors would be same no matter from where one started. Andrew advocated using full dimension rectangular wires for final expression of torque. But there are some practical limitations of using full dimension wires in the slot. Engaging a full dimension wire in slot is practically not possible because a full dimensional wire will generate extra friction making sliding mechanics difficult if not impossible. Full dimensional


CHAPTER

B

A

6

C

Figure 6.25. Pretreatment inclination of teeth effect the amount of torque expressed by the brackets. A. A maxillary incisor with ideal inclination. Bonding a bracket to an incisor having the same amount of inclination as bracket builtin torque will not result in expression of any torque i-e the bracket will act as a zero torque bracket. B. A positive +7° bracket placed on a maxillary central incisor having increased inclination .In maxillary incisors the opening of bracket should be downward directed if it has to express positive torque. In case of class II div 1 the inclination of maxillary incisors is already increased. Placing a positive torque bracket of +7° on an incisor already having an inclination of 20° with occlusal plane perpendicular will result in orientation of bracket opening in upward direction .On insertion of full dimensional rectangular wire; this bracket will express negative torque instead of positive torque. In ideal scenario a change of -13° in maxillary incisor inclination on full torque expression would occur so that the final inclination of incisor would be +7°. C .A retroclined maxillary central incisor with -7° inclination with occlusal plane perpendicular. A +7° torque bracket placed on this incisor will make the slot opening downward directed, so positive torque would be expressed on engagement of full dimensional rectangular wire. On expression of entire torque built within the bracket the inclination of tooth will become +7° resulting in an overall change of +14° in incisor inclination.

wire also would be too stiff and so good fitted that it cannot easily be inserted and removed from the brackets by hand and also will generate heavy forces which would be painful for the patient and might debond the bracket on insertion. So in clinical orthodontics smaller dimensional wires are used. On insertion of smaller dimensional wires, expression of torque from a bracket depend upon the following factors:

3) Stiffness of the wires 4) Diminution of force 5) Material of brackets 6) Vertical position of brackets on teeth 7) Inclination of neighboring teeth 8) Direction of tooth movement 9) Prominence of the slot

1) Play of the wire within the slot

1) Play of the wire within the slot

2) Interbracket distance

When a smaller dimension wire is used in a

A

B

C

Figure 6.26 Play of wire in the slot on insertion of smaller dimension wires. A. 0.016x0.022 inch wire. B. 0.019x0.025 inch wire. C. 0.021x0.025 inch wire .The bracket dimension is 0.022x0.028 inch. Smaller the dimension of the wire, greater is the gap between the slot walls and the wire. The play in vertical dimension or width of slot affect torque more than play in prominence or length of the slot.

106

To measure free play of wire in the slot different mathematical formulas and techniques are used. Without going into the details of these, theoretical torque play and effective torque of wires in bracket slot as measured by Sernetz4 is given Table 6.10&6.11. These values were given with assumption that their minimal edge rounding up to 0.03 mm of slot and slot width is 0.46 mm (slot 0.018x0.025 inch) or 0.56 mm (slot 0.022x0.028inch). Take the example of 0.018x0.025 inch wire in a 0.018” and 0.022” slot from the tables 6.10&6.11. There is 1° of free play of this wire in 0.018” slot and 11.4° play in 0.022” slot. Using this wire on a maxillary central incisor having +7° torque bracket will result in expression of +6° torque in 0.018” and 0° in 0.022” slot. In 0.018” slot introducing a 1° torque in the wire by torqueing it will make the inclination of incisor to +7° but in case of 0.022” slot 11.4 ° torque in the wire would be required to express all the bracket torque. An alternative approach is to use customize central incisor bracket having 8° torque in 0.018” slot and 18.4° torque in 0.022” slot to express +7° torque on 0.018x0.025 inch wire. The formula and tables presented by Sernetz

107

are mostly quoted in orthodontic literature but they also have some flaws. They didn't take into consideration of many other factors that also affect torque play like type of ligation, wire tolerance etc. A systematic review by Archambault5 showed that greater torque play than Sernetz calculated values. However, these tables are still valid for rough calculation of torque play and the effective torque expressed by brackets wires interaction. Torque or wire play is affected by following factors. a) Manufacture tolerance of slot and wire b) Edge bevel of slot and wire c) Mechanotherapy d) Type of ligation e) Defects in brackets slot f) Aging of brackets a) Manufacture tolerance of slot and wire Dimensions of bracket slots are usually not as accurate 6 - 1 2 as claimed by the manufacturer. Many manufacturers also intentionally keep slot dimension larger so that the clinician could pass full dimension wire with ease in the bracket slot. Usually the manufacture tolerance13 in 0.018” slot ranges from 0.0182” to 0.0192” while in a 0.022” slot it ranges from 0.023” to 0.030”. Larger the bracket slot than prescribed value greater would be the play of the wire within the slot and greater would be the torque loss. Like dimensions of the bracket slot, dimensions of the wire are also not accurate 6, 7, 12, 14 as claimed by the manufacturers and there is more variation in dimensions of the wire than dimensions of the slot. In archwires the dimensions are kept smaller


slot there would be a gap between the slot walls and the wire. This gap will cause certain rotation or free play of the wire in the slot (Figure 6.26). Because of this play or free space, not all the torque built within the bracket is expressed on passing the wire .To express the required amount of torque either we have to introduce torque or torsion in the wire by pliers or have to use a bracket with extra torque built within to accommodate the amount of play of the wire. The amount of torsion in the wire or extra torque built within the bracket should be equal to the amount of play of the wire with in the slot.


CHAPTER by manufacturer to aid easy insertion of wire within slot but this arrangement results in torque loss. The manufacturer tolerance in archwires ranges from 0.0178” for 0.018” wire and 0.0215” for 0.022” wire. The physical properties like stiffness of the wires and bracket vary between manufacturer products as properties of the material is affected by the manufacturing process and additional elements added to enhance the material properties. This can also result in change in torque expression. Because of difference 6 in different measurement units there is difference in slot and wire size of European and American wires and brackets. The 0.022-inch slots in European made brackets are oversized by 4.22% even if no other manufacturing variability is present. Also European wires are oversized than American wires. Using

6

European made brackets with American made wires can result in increased torque play. a) Edge bevel of slot and wire Edge bevel of slot and wire or edge rounding is done by the manufacturer so that the wires are easily inserted into the slot (Figure 6.27). Edge bevel in the slot can be present as rounding of slot floor or walls edges. Both slot15 and wire bevel6, 16, 17 results in decreased wire dimension and so increase in play of the wire in the slot resulting in increase in torque loss. Different manufacturers keep different edge bevel of wires and slots. So torque play varies between manufacturers even in same continent. Edge bevel of the wires effect torque play more than edge bevel of slots.

Table 6.10

Table 6.11

108

Tighter the ligation better would be the wire seated within the bracket slot and more would be the torque expressed. Elastic ligature has a rapid force decay rate so they are less effective in torque expression as compared to steel ligatures. Clinician usually prefers to use soft elastic ligature by stretching the ligature with the help of dental probe at initial leveling and alignment and use tight elastic ligature at heavy wires for expression of torque. Active self-ligating bracket5, 22 shows less play and so more torque expression than passive selfligating brackets. The design of bracket also affects ligation of wire and its play in the slot (Figure 6.30).

A

B

A

C

B

Figure 6.27 A .Beveling of slot walls. B. A wire with beveled edges, so decreasing the dimension of the wire. C. A beveled wire inserted into a bracket. There is increase wire play because of beveling of the wire.

c) Mechanotherapy Wires used in sliding mechanics shouldn't be used for torque application as there is considerable loss of surface layer6, 18 . Torqueing pliers may deform the archwire 19 giving less torque values so it is better to add some extra torque while using torqueing pliers (Fig 6.28). If greater torque is required it's better to use a high torque prescription brackets because high torque prescription brackets express more torque than low torque prescription brackets 21. Giving repeated torque on the wires will cause plastic deformation 20 of the bracket (Fig 6.29) and will diminish torque expression from brackets.

109

Figure 6.28 A. The edges of the wires are roughened and rounded by torqueing pliers. Loss of edges of a rectangular wire will lead to increase wire play in the slot. B. A wire used for 7 months in sliding mechanics. Due to friction between wire and brackets the surface layer of the wire is lost decreasing the dimension of the wire. It's a common clinical practice to use the same wire for torque expression after sliding mechanics. But it is better to use a new wire for torque application after sliding mechanics.

Figure 6.29. Comparison between new bracket and bracket after torque application by torsion in wire. If greater torque is required it is better to use a high torque brackets than using low torque brackets and introducing torque in the wire. Insertion of heavy pretorqued wire will always causes some plastic deformation of brackets as Vickers hardness of SS wires is usually greater than SS brackets. Many a time the clinician doesn't have choice to change the bracket


d) Type of ligation


CHAPTER prescription and torque in wire is needed. But if first torque introduction in wire don't provide the required inclination change then it is better to use a new bracket with added torque on the wire. On heavy wires the new bracket can be placed passively on wire guidance. A clinical tip is that while placing bracket on wire guidance using a straight wire to place the bracket instead of existing torqued wire. Doing this will also help to produce torque on insertion of previously used torqued wire.

6

A

B

Figure 6.30 A maxillary premolar bracket with negative builtin torque as opening of slot is facing upward. Slot dimensions in this bracket are 0.022x0.030 inch. The height of the underarm of gingival tie wing is greater than occlusal tie wing so ligature will exert lighter force on gingival edge of the wire than occlusal .This is usually a problem on lighter rectangular wires such as 0.016x0.016 inch or 0.016x0.022 inch. Unfortunately these are the wires which are usually used for torque application by twisting the wire as heavier torqued wires are too stiff to be inserted in the slot. Another aspect of this type of bracket design is that the gingival edge of the wire is facing upward if negative torque is given in wire and it is the part of the wire where ligature will affect less force. So effective torque is decreased .Such a bracket design cannot be avoided as we all engage ligature from gingival side to prevent soft tissue injury on instrument slip. So some torque loss on these brackets on smaller dimension wires is inevitable.

C Figure 6.31 Defects in bracket slot. A. Crack in the middle of bracket slot base due to manufacturing defect. With this defect the slot would be expanded on insertion of heavy wires. B. A manufacturing innovation for easy debonding of ceramic brackets. Such design prevents insertion of heavy wire in the slot so increasing the wire play. C. Bracket material extending from the slot wall thus preventing insertion of heavy wire in the slot.

e) Defects in brackets slots Defects in brackets slot can cause increase torque play. These defects are due to poor manufacturing or ill design of slot (Figure 6.31). More defects in brackets slots are found when using recycled brackets than new brackets (Figure 6.32). Recycled brackets should be avoided in teeth requiring extra torque. f) Aging of brackets Bracket left in the oral cavity undergo aging in the form of corrosion and plaque accumulation (Figure 6.33). Corrosion will

A

B Figure 6.32 Bracket debonded by technique not favorable for reusing brackets. Recycling and reusing such brackets will result in increased torque play due to decrease dimension of the wire that can be inserted within the slot.

110

Stiffer the wire more the torque would be expressed by bracket wire interaction. A stainless steel wire will express more torque 24, 25, 26 than a same dimension TMA or NiTi wire. But the problem with stiffer wires is that they are difficult to insert and generate heavy forces. It's a good practice to use flexible wires initially and later use same dimension stiffer wires when torqueing movement is required at larger dimension wires. This sequence also prevents bracket fracture in case of ceramic brackets.

A

B

3) Diminution of force

C Figure 6.33 Aging changes in brackets. With time corrosion resistance of bracket decreases resulting in increase in bracket roughness. This increase roughness offers more plaque retention and calculus formation. Calculus in bracket slot initially prevents the insertion of heavier wires but latter under the load of torqueing forces the calculus breaks thus increasing the wire play.

increase the dimension of the slot while calculus accumulation will prevent insertion of heavier wire. Unfortunately these aging changes are found more at the time of treatment when torque application is required. 1) Interbracket distance As the interbracket distance increases, stiffness of wire decreases. So less torque 23 would be expressed on increasing the interbracket distance. In lingual brackets as there is decreased interbracket distance greater torque is expressed as compared to labial brackets using same dimensional wires.

111

A minimum threshold of force is always required to cause tooth movement. When torsion is given in the wire within its elastic limit or the wire is twisted within the bracket slot due to builtin torque, the wires tend to returns to its original shape with time. As the wire returns to its shape there is gradual reduction of force so that a point comes when the forces transmitted from the wire to brackets are beyond the level of torqueing movement of teeth. Force loss in archwire was found in following sequence27 SS >NiTi>TMA. 4) Material of brackets Plastic and ceramic brackets are less effective in torque expression than stainless steel brackets. Titanium brackets are more effective28 in torque expression than stainless steel brackets. 5) Vertical position of brackets on teeth Andrew used the center of long axis of clinical crown to measure torque values of individual teeth. These torque values were then incooperated in his bracket prescription. As teeth don't have uniform morphology throughout their clinical crown length29 so location of brackets will affect


2) Stiffness of wires


CHAPTER their torque expression13, 30-32. In fact bracket will only express it's builtin torque and incline the surface of the tooth where it is bonded to an inclination equivalent to the amount of builtin torque (Figure 6.34). Due to uneven morphology of crown if the bracket is not placed at the middle of clinical crown, the middle of clinical crown won't have an inclination found in an ideal occlusion, leading to poor occlusal results.

Zone 1 Increase Positive torque zone

Zone 2 Ideal Positive torque zone

Zone 3 Negative torque zone

Figure 6.34 The morphology of the labial surface of the tooth can be divided into three zones. Zone 2 is the middle of the clinical crown. This is the zone where inclination of the tooth was measured by Andrew and the amount of inclination measured was incooperated into the bracket. Andrew advocated placing the bracket in this middle zone. Zone 1 is gingival to the middle zone. This zone has increased positive torque than zone 2. If bracket is needed to be placed in this zone it must have increased torque. Suppose this zone have +12° torque when the middle zone have +7° torque. Placing the +7° torque bracket in this gingival zone and expressing all the torque of the bracket will result in orientation of zone 1 +7° to occlusal plane perpendicular. This 5° decrease in inclination of zone 1 will automatically decreases the inclination of zone 2 and make it 2° to occlusal plane perpendicular. So the overall picture we get is that placing the bracket gingival to require position will result in expression of more negative torque because we are taking middle of clinical crown as reference to measure inclination. Zone 3 is incisal to the middle of clinical crown and has negative torque. If someone wishes to place bracket in this zone the bracket must have negative torque to keep other parts of the labial surface of crown at their optimum inclination. Placing a bracket meant for middle of the clinical crown which have positive torque in zone 3 will result in positive inclination of this part of the tooth thus increasing positive inclination of other parts of the crown too. Suppose +7° torque bracket is placed in zone 3 having a negative inclination of -5° to occlusal plane perpendicular .On expression of full torque, zone 3 inclination will become +7° while zone 2 inclination will become +19°.

6

The morphology of teeth apart from mandibular incisors 33 is such that when the bracket is placed gingival to middle of clinical crown negative inclination of the middle of clinical crown is increased 32. The opposite is also true that when bracket is placed incisor to the middle of clinical crown positive inclination of middle of clinical crown increases. A description of brackets placed at different clinical heights is given in figure 6.35. Mestriner 33 in a study on mandibular dentition found that 1mm of height change of the brackets from occlusal to cervical will effect torque expression of approximately 2° in central and lateral incisors, 3° in canines and 8° in premolars and molars. While other studies reports 34-36 that a height change of 1 to 3 mm can affect torque up to 10° to 15°. The difference in torque variation between these different studies is related to the type of tooth measured. Incisors have less sharp changes in surface topography than canine and premolars. Middle zone of the incisor is larger while that of canine and premolars is smaller (Figure 6.36). 7) Inclination of neighboring teeth Torque in a bracket is expressed when wire is passed through multiple brackets bonded to teeth. If full dimension wires are used then the entire builtin bracket torque would be expressed. But as we don't use full dimension wires for ease of mechanics so inclination of neighboring teeth and bracket torque of neighboring teeth effect torque expression of brackets. For example an increased negative torque on canine will increase positive torque on lateral incisor due to reactionary forces, if there is wire play present during torque application. 8) Direction of tooth movement

112

A

B

A

C

D

B

Figure 6.36 A. An upper central incisor labial surface. B. Upper canine labial surface. The surface of the incisor is less convex than canine so bracket position variation on canine has more sharp effect on change in inclination as compared to incisors. The variation is greater if the bracket is placed gingival as there is sharp steep in inclination in the gingival area.

Direction of tooth movement also effect torque expression if there is play in the wire. Mesial movement and intrusion of incisor produce lingual root torque while distal movement and extrusion produces labial root torque 13. 9) Prominence of slot

E Figure 6.35 The same zone of torque exists in mandibular arch. Zone 2 the middle zone have negative inclination which should usually be found in ideal occlusion cases. Zone 1, the gingival zone has less negative inclination than zone 2 while zone 3 the incisal zone has more negative inclination than zone 2.Placing a bracket which is meant for middle zone on zone 1 will increase negative inclination of zone1thus also increasing the negative inclination of zone 2 & 3.Placing the same bracket on zone 3 will decrease its negative inclination thus decreasing the negative inclination of whole crown or it will increase the positive inclination of the crown.

113

Prominence of bracket slot effects its torque expression. As the bracket prominence increase the transverse distance between slot and center of resistance increase so decreasing the torque expression of the bracket. Clinical Notes While selecting brackets prominence of brackets should be kept in mind. Brackets with less prominence which are strong enough to withstand orthodontic loading should be selected (Figure 6.37).


Bracket placed at different heights of canine crown is shown. Straightening the bracket slot and superimposition of different bracket heights is done. Gingival the bracket is placed more would be the negative inclination of the tooth and more the bracket is placed incisal more would be its positive inclination. A variation in morphology is usually found in mandibular incisors because they have flat labial surface of crowns. So incisal zone of mandibular incisors, many a time have same inclination as middle zone.


CHAPTER

6

A

B

C Figure 6.37 Maxillary arch bracket sets from three different manufacturers. Set A has the least prominence so it would be most effective in torque expression.

Interaction between tip and torque the wagon wheel effects Andrew pointed out the interaction between angulation and inclination of the teeth in anterior part of the maxilla. On increasing the maxillary incisors inclination or torque, the roots of incisor come close to each other. As maxillary incisors have a positive tooth angulation or mesial crown tip so increase in torque will result in decrease in tip or angulation of tooth. It was found1 that increase in torque of 4° will decrease tooth angulation by 1° in maxillary incisors. The interaction between tip and torque was verified on a rectangular wire containing vertical wire spurs. On giving palatal root torque to these vertical wire spurs which were supposed to behave like maxillary incisors, the spurs ends come closer to each other and the whole assembly of rectangular wire and vertical spurs look like a wagon wheel so the phenomenon is called wagon wheel effects (Figure 6.38).

Clinical implication of wagon wheel effects The lost tip or angulation due to increase in torque must be accommodated in the brackets prescription. If maxillary central incisor torque is increased from 7° to12° as in the case of class III incisor relationship than 1.25 ° of maxillary central incisor tip should also be increased. Proper occlusal and esthetic results cannot be obtained if tip is missing in the maxillary incisors. Clinical notes Clinician often encounter with problem of root approximation in incisor area at the final stages of treatment. Many a time it is because of poor axial placement of brackets but sometimes the axial position of brackets both clinically and on x ray seems fine. To correct the problem of root approximation either give proper torque or if ideal torque

114


A

B

C Figure 6.38. To see wagon wheel effect Andrew attached four vertical spurs on a rectangular wire. The vertical wires represent four maxillary incisors. When the positive torque or palatal root torque is given on this wire distal to laterals at both ends, the ends of the vertical spurs will move towards each other thus decreasing their mesiodistal inclination. It was found that a positive torque of 4° will decrease the angulation or tip by 1°. A. Vertical spurs attached to a 0.021x0.025 inch wire considering it a wire for upper arch. B. Positive torque given to same wire, which results in decrease in angulation of vertical spurs. C. Negative torque given in same wire which results in increase in inclination of spurs. The same ratio of 4:1 was applicable to increase in tip .Though wagon wheel effects were proposed for maxillary incisors but my personal understanding is that it is also true for mandibular incisors because mandibular incisors like maxillary incisors are also present on a semicircular area though smaller in size .

cannot be given as in camouflage cases, brackets should be debonded and rebonded in overcorrect position .

Key IV: Absence of Rotations The fourth key to normal occlusion is that no teeth should be rotated within the arch. If teeth are rotated with in the arch, space management would be difficult and proper occlusion won't be established. Incisors teeth both maxillary and mandibular have very small labiolingual width as compared to mesiodistal width so derotation of incisors will need space within the arch .In contrast canines and molars teeth will give space on correction of rotation . Only a complete 90° rotation of canines and molars will need space for correction of rotation. In premolars most of the time

115

correction of rotation will give space within the arch .Only ovoid shaped premolars will need space for correction of rotation. Incorporating key IV into prescription There are three types of tooth rotation that are encountered in orthodontic cases: 1. Natural rotation present before start of treatment. 2. Tooth rotation because of faulty bracket placement. 3. Tooth rotation because of mechanics and treatment plan.

orthodontic

Natural rotation and faulty brackets placement can be corrected by placing brackets with compound contoured base at mesiodistal center of the tooth at optimal height (Figure 6.39).


CHAPTER Rotation should be corrected early in the treatment at round wires and correction maintained throughout the treatment.

A

6

poor. The teeth are usually rotated in the direction of rotation. For effective rotation control Andrew proposed that the mesiodistal bracket length should be equal to distance from the slot point to the tooth vertical axis (Figure 6.40). As this distance is usually greater than bracket length, Andrew added counter rotation in slot component of brackets. This was done by rotating the slot so that the slot base is closer to the bracket base on the side which need to be buccaly or labial out and slot base is away from the bracket base which needed to moved palatal

A B Figure 6.39 A. Bracket placed at mesiodistal center of maxillary central incisors. To avoid rotation of tooth the brackets should be placed at mesiodistal center of the tooth. B. A bracket bonded on a rotated premolar at mesiodistal center.

B

Meisal

Distal

Figure 6.41. A. Bracket with equal prominence of mesial and distal tie wings and so the slot. A mandibular left canine bracket with mesial wing slightly more prominent and so is its slot than distal wing. As builtin counter rotation in the bracket is only 2° so it is barely noticeable.

Figure 6.40 For rotation control during tooth translation the mesiodistal length of bracket (A) should be equal to the distance from the slot point to the tooth vertical axis (B). This is not technically possible in posterior dentition so counter rotation is added to the brackets.

Rotation control is very easy in nonextraction case where bracket is placed at ideal location. In extraction cases rotational control of the teeth is

or lingual (Figure 6.41) . The greater the distance the tooth is translated greater would be the counter rotation. For translation series brackets Andrew recommended 2° slot rotation for minimum series brackets, 4° slot rotation for medium series brackets and 6° slot rotation for maximum series brackets. This antirotation feature would be present in all

116

How it works? For counter rotation the slot is rotated at an angle over the base of bracket. Suppose a maxillary canine has to be translated distally in a premolar extraction space. So when distal translation of canine or any other teeth is done the direction of translation will cause the canine to rotate mesial out. To counter this problem,

rotation of canine occur,so at end of translation tooth would have zero rotation. A description of above example is given in figure 6.42. Factors effecting rotation of a tooth during translation are 1. Play of wire within the slot 2. Using small mesiodistal length of bracket 3. Poor ligation or low quality ligatures 4. Heavy forces during translation 5. Distorted slots 6. Low stiffness of the wire Key V: Tight Contact points The 5th key state that contacts point should be tight and there should be no spaces between the teeth.

A Meisal

Distal

B Figure 6.42 A canine bracket with builtin counter rotation for distal movement. On initial alignment because of design of bracket slot the tooth would be rotated mesiopalatal. This is to counter the distopalatal rotation of canine that occur during retraction of canine in extraction or distalization cases. Greater the amount of translation the greater would be the builtin counter rotation.

depth of the distal slot base in a twin canine bracket would be closer to its bracket base than the mesial slot base. On leveling the distal portion of tooth will move out or buccally and mesial portion of tooth will move palatally. So at the end of leveling the canine would be rotated mesial in on translation,distal out

117

Tight contact point can be achieved by attaining rest of the keys of normal occlusion and careful treatment planning (Figure 6.43). Nothing special is built within straight wire appliance (SWA) to give tight contact points. This key should be achieved for proper space management, good gingival health, aesthetic and good final occlusal outcome. In a finished case if the contact points are not tight and there is no genuine tooth size discrepancy it is usually because less than required tip or torque is given to the teeth. But genuine tooth size discrepancies pose special problems. In those cases if size of the teeth is small a composite build up or prosthetic crowns should be given and if size of the teeth is large tooth size reduction or extraction should be done. Case example of importance of tight contact points and their relation with Andrew's other keys is given in figure 6.43. Key VI: Flat Occlusal plane or Curve of Spee Curve of spee should be flat or slightly


teeth undergoing translation excluding incisors.


CHAPTER

6

A

B Figure 6.43. A. Improper tip of central incisors and lack of torque in lateral incisors. To compensate it canine was moved forward leaving poor contact point between canine and premolar. B. A case with good occlusal results and proper contact points due to proper tip, torque, prominence and lack of rotation characteristics.

A

B

Figure 6.44 A. increased curve of spee. If curve of spee is increased or deep, there would be less space for upper incisor. Occlusion would be disturbed both anteriorly and posteriorly. B. Reverse curve of spee. If the curve of spee is decreased or reversed in lower arch than there would be excessive space in the upper arch.

increased at the end of treatment. Clinical implication of Key VI Nothing is built within bracket prescription to accommodate key VI because it is more related with position of the brackets on the teeth. Accomplishing this key is very important for a good occlusal outcome. Andrew found that nonorthodontic dentition has flat to slight curve of spee and preposition of flat curve of spee was given to accommodate natural tendency of curve of spee to increase with age due to growth of lower jaw and its growth rotation. Banding or

bonding the second molars also help in leveling of curve of spee .Usually leveling 1mm of curve of spee 37 require less than 1mm of space. A description of curve of spee is given in the figure 6.44. Limitations of Andrew prescription Large inventory In Andrew system to deal with different types of arch discrepancies there are 12 maxillary and 11 mandibular sets, which are combination of five different types of brackets .These are

118

T1 – Minimum Translation Brackets T2 – Medium Translation Brackets T3 – Maximum Translation Brackets T4 – Maxillary Molar tubes or bands for Class II&III Andrew gave such a big inventory to make the treatment more individualized. But unfortunately this became one of the biggest limitations of his prescription. Making so many different types of brackets means that there is need for more machinery, more space, more work force and so more finances needed for the manufacturer. Also when there are so many different types of brackets, more time and education is needed for the orthodontist to get a better understanding for making the right choice in each case. So when there is no Magic formula available, orthodontics will remain only for professional orthodontists. This means loss of valuable clientage for the manufacturers. Unfortunately the problem in orthodontics is that if the orthodontist is customizing treatment

by bracket prescription or by wire bending he is wasting his time but if the manufacturer is customizing brackets it's an innovation and you have to pay for that innovation. For the orthodontist keeping a large inventory at orthodontic office means there is need for more financial resources and more office space. This is obviously against the core rules of good office financial management. So unfortunately the very benefit of Andrew prescription to provide individualized treatment to some extent became the most limiting factor of its wide acceptance. Tip and Torque Both tip and torque values placed in Andrew prescription are slight different from Andrew original findings of normal occlusion 2. Tip in Andrew Straight wire appliance and actual tip from his study are given in table 6.12. There is overall increased in tip in SWA as compared to Andrew original findings. For change in tip values it is generally presumed that Andrew made the changes to accommodate wagon wheel effects. There are some questions in this regard that for the time being have no

Table 6.12

answers. Do we need to accommodate wagon wheel effect in class I incisor torque as it is natural position of the incisors within the arch? If wagon wheel effects occur due to anatomy of area and our treatment mechanics, why not the tip is decreased in the prescription in case of class II incisor torque and increased in case of class III incisor torque?

119

Torque values were also changed by Andrew to some extent than original norms (table 6.13).Overall there is decrease in torque values in SWA as compared to original findings. After going through Andrew work my understanding is that Andrew changed the upper incisor torque values to incorporate finding of his unpublished 100 cases cephalometric study. For example in


S – Standard Brackets


CHAPTER

6

Table 6.13

original Andrew's norms the maxillary central incisor class I torque was 6.11° while the lateral incisor torque was 4.42°.In cephalometric study Andrew found that there is always 4° difference between maxillary central and lateral incisor torque. So I presume that he changed the torque of central to 7° and lateral to 3° to make that study count. Other values were changed either to incorporate clinical experience or to round off values for ease of standardization.

Apart from this, Andrew also didn't take in consideration various factors that affect the expression of tip and torque especially the play of the wire. This is because Andrew advocated full dimension wires at the end of treatment for expression of entire builtin tip and torque. Because of their increased stiffness use of full dimension wires have been abandoned and so the problem started with expression of the prescription. Counter-rotation Andrew incorporation of counter rotation into the slot was also not appreciated by many. Though effective during space closure but if the orthodontist remain on a heavier wire for long time using effective ligation of wire to consolidate tooth position or torque correction after space closure the teeth having counter rotation brackets will become rotated due to expression of prescription . So Andrew prescription presents a dilemma for clinician in extraction cases. Moving to heavier

wire for better tip and torque expression as Andrew didn't accommodated wire play in his prescription but such wire will cause counter rotation expression. Many clinicians who favors counter rotation in brackets for extraction cases and also have included counter rotation in their own prescription advocate that as relapse is inevitable so the rotation is part of over correction and it will eventually be relapsed during the settling phase. But the practical problem a young orthodontist face today is that he has to display his finished case in exam and complete the settling phase with elastics or wire bending than going on natural settling with retainers. It is difficult to settle teeth into occlusion when they are rotated. Correction of rotation will leave space in the arch and there are many different retainers of modern day such as fix retainers and vacuum formed retainers that don't allow settling to the extent as Hawley retainers do. So orthodontists are left with two choices when using counter rotation brackets at the end of treatment. Replace bracket with standard brackets or resort to wire bending. Limitations in Mechanics As expression of bracket prescription depend upon what mechanics one uses, many clinicians who later made their own prescription pointed out some mechanics flaws present in Andrew philosophy for case treatment. These were 1) Anchorage loss

120

2) Leveling Curve of Spee Many clinicians also didn't agree with Andrew philosophy of leveling curve of spee with compensatory curves in wires in maxillary arch and reverse curves in wire in mandibular arch. 3) Roller coaster effects In early years of SWA class II elastics were used for sliding mechanics. In order to overcome friction heavy forces were used. Increased anterior tip, vertical component of elastics and heavy forces resulted in deepening of anterior bite and opening of lateral bite. This effect was called Roller Coaster Effect (Figure 6.45).

of variation32 between long axis of clinical crown and long axis of the tooth. Placing the bracket just by keeping in mind the long axis of clinical crown will result in poor root parallelism in many cases. Also due to increase tip built into Andrew prescription there are chance of root approximation of teeth especially between maxillary canines and premolars. 5) Bracket Height Andrew advocated bracket placement at mid of long axis or facial axis of clinical crown also called LA point(long axis point) or FA point(facial axis point). Judging the FA point or LA point on a tooth was a matter of clinical experience. Some clinicians3, 38 didn't agree with validity of placing bracket at the FA point to get an ideal occlusion while others39, 40 advocated that there are greater chances of error in placing bracket on FA point and gave fixed distance from incisor edge and suggested using special gauges for bracket placement. Effects of change in height on bracket prescription have been discussed before. Because of these limitations different types of bracket prescription were put forward with time. Whether these new bracket prescriptions solved any practical limitation of Andrew prescription is still debatable but there is a general consensus that they solved the problem of manufacturers and general dentists in the form of “A Single Fairytale Bracket Set for All Types of Malocclusion”. Different Bracket prescriptions

Figure 6.45 Roller coaster effects and anterior deep bite and lateral open bite.

4) Root parallelism Andrew measured tip values by using long axis or facial axis of clinical crown and not the whole tooth. There is always some degree

121

With time so many clinicians put forward their own prescriptions of brackets .For effective use of these prescriptions many of them also advocated their own treatment mechanics and bracket position on teeth. Even some clinician went to the extent to recommend certain commercial brands of wires for effective


As tip built into Andrew appliance was more than what Andrew found in his original research so this increased tip put strain on posterior anchorage and also cause anterior anchorage loss at the initial stages of treatment. Anchorage control was also difficult in extraction case.


CHAPTER expression of their prescription. Some of these prescriptions were also even disowned after copyright of the patent was expired. Other prescriptions were changed with time after hit and trials reveals the flaws within them. In many cases same prescription vary between different bracket manufacturers. It is because, to avoid copyright and patent violation many manufacturers produce the same prescription with minor changes in tip and torque values. Even different values in 0.018” and 0.022” slots of same prescription are sold by the manufacturers. This is due to more clearance between wire and slot in 0.022” slot so 0.022” slots are sometimes made in higher torque values41 than 0.018 “ slot. Many text books of orthodontics show charts containing only tip and torque and no importance is given to counter rotation and mesial offset. Some bracket sold in the markets has prescriptions which are never endorsed by any clinician, meaning manufacturers also make their own prescriptions! Table 6.14 Maxillary Arch

So it's not possible to give details of each prescription and each variation. Some prescriptions are given in tables 6.14&15. Though every effort is made to give the original prescription as purposed by the inventor but readers may find some values of tip or torque different from what they use to know for the reasons explained before. Roth Prescription Ronald H. Roth (1933-2005) put forward his modified version of Andrew prescription in 1976 which he called3 Roth Prescription of the Andrew Appliance. Roth based his prescription on following principles: I. Small inventory .A single bracket set for all types of malocclusion. II. Overcorrection, especially in torque of brackets to accommodate relapse and

Maxillary arch values of different prescriptions Canine

1 st Premolar

2 nd Premolar

Tip°

Torque° Tip°

Torque°

Tip°

Torque°

Tip°

Torque° Tip°

Offset° Torque° Tip ° offset

+9

+9

–3

+10

–6

0

–8

4

–10

0

13

– 10

0

10

Central incisor

Lateral incisor

Torque° Tip°

Torque°

+5

Alexander +15

6

1 st Molar

2 nd M olar

Begg

0

0

0

0

0

0

0

0

0

0

0

0

6

0

0

6

Burstone

+7

+5

+3

+8

–7

+10

–7

0

–7

0

–10

–5

10

–10

0

6

Damon (standard torque)

+15

+5

+6

+9

+7

+5

-11

+2

-11

+2

-18

0

12

-27

0

6

Hasund

+20

+3

+14

+9

–2

+6

–10

+2

– 10

+2

– 20

+3

10

– 25

+5

6

Hilgers

+22

+5

+14

+8

+7

+10

–7

0

–7

0

–10

0

14

–10

0

10

Ricketts®– IV. Dimension

+22

0

+14

+8

+7

+5

0

0

0

0

0

0

15

–10

0

12

Ricketts® Standard

+22

0

+14

+8

+7

+5

0

0

0

0

0

0

0

0

0

0

Standard Edgewise

0

0

0

0

0°

0

0

0

0

0

0

0

0

0

0

0

Tweed

0

0

0

0

0

0

0

0

0

0

0

0

0/6

0

0

0/6

122

Mandibular Arch

Mandibular arch values of different prescriptions

Central incisor

Lateral incisor

Canine

1 st Premolar

Torque° Tip°

Torque° Tip°

Torque° Tip°

Torque°

2 nd Premolar Tip°

Torque°

1 st Molar

Tip°

2 nd M olar

Torque° Tip°

Offset°

Torque° Tip ° offset

-5

+2

+5

+6

–7

+6

–7

0

–9

0

–10

0

0

0

0

5

Begg

0

0

0

0

0

0

0

0

0

0

0

0

6

0

0

6

Burstone

–1

0

–1

0

– 11

+6

–17

0

–22

0

– 27

0

5

–27

+2

6

Damon (standard torque)

-3

2

-3

+4

+7

+5

-12

+4

+4

-28

+2

2

-10

0

5

Hasund

0

0

0

+5

0

+5

–10

+2

–15

+2

-22

+4

0

– 25

+2

6

Hilgers

–1

0

–1

0

+7

+6

–11

0

–17

0

–25

0

7

–25

0

6

Ricketts®– IV. Dimension Ricketts®

0

0

0

0

+7

+5

0°

-7 ex -14 nex

0

–22°

–5

12

–27

0

16

0

0

0

0

+7

+5

0

0

0

0

0

0

0

0

0

0

Standard Edgewise

0

0

0

0

0°

0

0

0

0

0

0

0

0

0

0

0

Tweed

0

0

0

0

0

0

0

0

0

0

0

0

0/6

0

0/6

Alexander

-7ex 0 nex

-17

Standard

diminution of force. III. Leveling of curve of spee to some extent by placing anterior brackets more incisal. IV. More torque in anterior brackets to accommodate torque loss by wire play. V. Super torque brackets for rapid correction of torque in class II div2 cases. VI. Roth proposed a new archform called TruArch to be used with his prescription. Roth advocated selection of archwire is important as it effects the rotational position of teeth. Wider the archform more positive torque would be expressed and vice versa. Roth archform was most prominent and wide at mesiobuccal cusp of the first molars. VII. Different translation philosophy. According to Roth tipping of the teeth to some extent is accepted on round wires.

123

VIII. Many auxiliary features were added to

0

brackets such as double and triple tubes, addition of hooks for ease of mechanics. How Roth Made this Prescription? Dr. Andrew in one of his articles42 commented on origin of Roth prescription. According to Andrew, Dr. Roth found that a high percentage of his cases can be treated by using Andrews' class III incisor torque brackets for maxillary arch and class I incisor torque brackets for mandibular arch. For buccal segment Roth used Series 1-C and Series II-Classic. Where series 1-C was given in all 1st premolar extraction cases where both maxillary and mandibular canines are given maximum translation series brackets and both arches 2nd premolars are given minimum translation series brackets while molars are given standard SWA. Series IIClassic brackets were used in case of extraction of maxillary 1st and mandibular 2nd premolars because of class II molar relationship. In this series maxillary canines and lower posterior


Table 6.15


CHAPTER Table 6.16. Teeth

Roth Prescription

Central incisors

Lateral incisors

1st & 2nd Premolar

Canine

Torque Tip Torque Tip Torque Tip° ° ° ° ° °

Maxillary Arch

+12

Mandibul ar arch

-1

6

+5

+8

+9

-2

+13

1st &2nd Molar

Rotatio Torque Tip Rotation Tip Torq Rotation° n° ° ° ° ° ue°

2MR

-7

0

2 MR

0

-14 14DR/0° Class II

+2

-1

+2

-11

+7

2 DR

-17 P1&

-1

4DR

-1

-30

4DR

-22 P2

Where MR=Mesial Rotation to counter distal translation. DR= Distal rotation to counter mesial translation. P1 = 1st Premolar P2 =2nd Premolar , Class II= Molar Class II in cases where only upper 1st or 2nd premolars are extracted .Reference for above Table 3, 40. are given maximum translation series brackets and lower canine and upper posterior are given minimum translation series brackets.

Roth prescription is given in table 6.16. These comments by Andrew about Roth prescription were made in 1976 and in the same year Roth43 wrote an article about his 5 year practice changing experience with Andrew prescription. Unfortunately he didn't reveal anything about his specific selection of brackets from Andrew's work. It was in 1987, that Roth3 published his prescription and given justification for it. That prescription is far different from Andrew's comments. The only comment true is about maxillary and mandibular incisor tip and torque. A personal review of literature by this author couldn't find a prescription by name of Roth that matches Andrew's comments. The first published Roth prescription is given in table 6.16.

An evaluation of origin of this prescription is given. Maxillary Arch.

Canines The maxillary canine tip is taken from minimum translation series brackets made for distal translation. Canine torque was Roth personal calculation of torque to accommodate wire play. Canine counter rotation feature was also taken from Andrew distal translation group in minimum translation series brackets. Premolars Both 1st and 2nd premolar tip was taken from minimum translation series brackets requiring mesial translation. Premolar torque was taken from Andrew standard SWA. Counter rotation feature was taken from minimum translation series brackets for distal translation. Molars Both 1st and 2nd maxillary tip was selected from Andrew Class II molar tip. Torque of molars was selected from Andrew medium translation series brackets. Counter rotation values for molars were taken from medium translation series for mesial translation.

124

mesial translation.

In maxillary arch both canine and premolars brackets have minimum translation features builtin. If one tooth need to be minimally translated in extraction space in most of the cases than the other tooth need to be maximally translated to close the extraction space. Premolars have counter rotation feature for distal translation. It's a common finding that in most of our cases premolars needed to be translated mesially than distally. Also premolar counter rotation feature don't correlate well with molar except in 2nd premolar extraction cases where molar need mesial translation and 1st premolar need distal traction.

Controversy

The molar tip is meant for class II relationship while offset is meant for class I molar relationship. Mandibular Arch Canines Canine tip is taken from minimum translation series brackets for mesial translation while torque is taken from Andrew standard SWA. Counter rotation feature for canine is taken from minimum translation series for mesial translation. Premolars Premolars tip correlate with Andrew medium translation series brackets. Torque values remain similar to standard SWA while counter rotation feature values are from medium translation series for mesial translation. Molars Molars have tip of medium translation series for mesial translation. 1st mandibular molar torque remain same as that of standard SWA while 2nd molar torque was made equal to 1st molar. Counter rotation feature were also taken from medium translation series brackets for

125

In mandibular arch canine is given minimum translation series counter rotation feature and tip values while molars and premolars have medium translation series values. Second molar torque was made equal to 1st molar. Giving less torque on second molar increase their chances of coming in cross bite as it's a common finding that 2nd molars are usually present slightly buccally as compared to 1st molar in finished cases using Roth prescription. Roth Justification for his prescription Roth3 while giving his prescription gave some justification for the specific selection. Maxillary Arch Roth3 justified his prescription by explaining that 5° extra torque was added to maxillary incisors keeping is line with his treatment philosophy of overcorrection and accommodating torque loss by wire play. So without moving to full dimension wires the clinician can attain natural inclination of incisors. For canines, Roth used -2° torque which was 5° less than Andrew prescription. This was done to avoid reactionary effect of building more positive torque into the incisors brackets. This is explained in the figure 6.46. The final torque of canine would be -7° due to reactionary forces from the wire and because of wire play. If no wire play is present the final torque of the canine would be -2°. Also canine tip was increased by +2° to accommodate tip loss in extraction cases as distal translation of canine take place and it is also helpful to get better canine guidance. Canines was also given 2° rotation to mesial so that when it is translated distal, mesial builtin rotation compensate the effect of distal


Controversy


CHAPTER

6

A

B

C

Figure 6.46 A .A rectangular wire passed through maxillary incisors and canine brackets. The slots opening of the maxillary incisors is facing downward causing the wire to rotate clockwise on exiting the lateral incisor bracket. This clockwise rotated wire when passes through canine bracket whose slot opening is facing upward will cause the canine bracket to rotate clockwise while canine bracket slot will cause the wire and so the incisor brackets to rotate counterclockwise. So positive torque would be expressed on incisors and negative torque would be expressed on canine. If the incisors have more positive torque, than reactionary forces of wire leaving from incisors will cause more negative torque on canine. This only happen when wire play is present. If no wire play is present all the torque built within the bracket would be expressed. B. Wire exiting lateral incisor in a clockwise fashion. C. Wire engaging canine bracket clockwise at an angle thus negative torque expression in canine.

rotation that occur during distal translation of canine. Premolar torque was kept the same while the tip was decreased. Though there was no justification given for using minimum translation angulation in both premolars nor does there is any logical basis of decreasing tip after giving 2° mesial offset for counter rotation. This decreased tip can accommodate increased tip on canine but the roots of these teeth come close to each other at end of treatment. Also 2° mesial rotation was added to premolar brackets. The justification was that this was done to counter the of effect distal traction of these teeth. As Roth favored headgears in his mechanotherapy this addition seems logical. On 1st and 2nd molars buccal root torque was increased from -9° to -14°.The increased torque

A

B Figure 6.47 According to Roth -14° torque should be given to maxillary molar to counter the effect of palatal cusp hanging during translation. A. Palatal cusp hanging in maxillary molar after translation. B. No cusp hanging.

126

Roth gave no rational explanation for increasing molar offset or distal rotation from 10° of Andrew's value to 14°. This can be due to get an ideal molar relationship after the mandibular molar offset was also increased by 4°, otherwise Roth Class II elastics or headgear mechanics don't favor increased maxillary molar offset. The angulation of molar was decreased to 0° from Andrew's value of 5°.As Roth places bands at different angulation than Andrew's bands. So 0°tip was in fact 5° tip of Class I

A

B

C Figure 6.48 A. The mesiobuccal cusp of the molar is more vertically prominent than distobuccal cusp and the dominant buccal groove is slightly aiming backward at an angle of 5° to occlusal plane perpendicular. B. Tube with builtin 5° tip in Andrew prescription are placed more gingival on mesial. This make the vertical axis of the tube parallel to dominant buccal groove but base of the tube is not parallel to the buccal cusps. The tube will express 5° tip. C. If tube with 5° is placed parallel to buccal cusps as recommended in Roth and MBT system, the mesial slot of the

127

tube would be facing downward. So a 5° tube will act as a 10° tube. But if the tube with 0° tip is placed parallel to buccal cusps than the final outcome would be 5° of molar angulation.

molar (Figure 6.48). Otherwise actually giving a 0° tip to molars in class I position will result in poor angulation of molars. For Class II div 2 Roth proposed super torque for maxillary anterior brackets. Prescription values of super torque brackets are found in many manufacturers catalogs. The values given in table 6.17 are taken from a manufacturer catalog ( DENTSPLY GAC ). This super torque prescription will correct decrease inclination of incisors in class II div 2 more efficiently. Use of different canine tip depends upon clinical scenario (Figure 6.49). In super torque prescription positive torque is present on both upper and lower canines. This is because both upper and lower canines usually have increased negative inclination in class II div 2. Another reason for choosing positive torque on canines is to counteract the reactionary effect of increasing positive torque on incisors for reasons explained before. Roth also proposed 0° offset for molars in cases where final relation is full cusp class II molars. Such are the case where only upper premolars are extracted. In such cases Roth also recommended that his super torque incisor prescription should be used. It was reasoned that as half the molar width is smaller than the mesiodistal width of bicuspid so that extra space would be utilized by the anterior torque. Super torque Prescription The super torque prescription of Roth was indeed genius innovation and it will help to correct upper incisor inclination in less time but full torque expression built within the brackets should be avoided.


can counter the effect of hanging of mesiolingual cusp on translation (Figure 6.47).


CHAPTER

6

Table 6.17.Roth prescription (Super or Extra torque) Teeth

Central incisor

Lateral incisor

Canine

1st and 2nd Premolar

Torque °

Tip °

Torque °

Tip °

Torque °

Tip °

Rotation °

Torque °

Tip °

Rotation °

Maxillary arch

+17

+5

+10

+9

+3

+9

+4MR

//

//

//

Mandibula r Arch

//

0

//

//

//

and +13 //

//

//

+3

+5

Note.

Mandibular dentition

Super torque values were taken from a catalog and may or may not be endorsed by Roth .Some of the justifications in favor of Roth work was also this author logical reasoning.

Roth justification

A

B Figure 6.49 A. If tip of the canine is decreased at start of treatment then standard tip of 13° should be used. B. If tip of canine is increased at the start of treatment which is usually the case in some types of class II div 2 cases where canine is overlapping the incisors; decrease tip of 9° should be used.

Not much was changed from Andrew's in Roth prescription in lower dentition. Canine angulation was increased 2° in an effort to give canine guidance and give better canine class I relationship. Distal tip and distal rotation was introduced in lower prescription because Roth believe that lower teeth settle more mesial than upper and also rotate while settling so using modifications will counter the relapse factor. Both the lower molars have same torque. Decreasing the tip in lower arch would also decrease the anchorage demands. Roth proposed that as his appliance rest on mesiobuccal cusp rather than buccal groove so same torque on molars is justified. In super torque prescription only the lower canine's brackets are present. Tip was maintained at norms while positive root torque was added to canine. This prescription values is only suited when the upper laterals and canines have pushed the lower canine inward. In that case usually the lower canine root is more labial and crown is lingual. Conclusion of above discussion Roth work was not an innovation rather it was a

128

Difference from Andrew Prescription The question which is usually asked is which prescription is better, Andrew prescription or Roth prescription? The simple answer is that both works if you follow the treatment philosophy of what their inventor said. There is a saying about contemporary prescriptions. “They don't have a brain you have to use your own.” When using Andrew prescription you have to use your brain to choose the best brackets that suits your case. Many times the selection is composed of brackets from all 5 types of Andrew series. In Andrew prescription you need to express all the tip and torque present within the bracket by simply going to heavy wires. The main disadvantage of Andrew prescription is that one needs wire bending to level curve of spee and the finishing wires are usually curved wires. While in Roth prescription you simply get the bracket set but after bonding brackets to teeth till end of treatment some variation in bracket position and wire bending is necessary. In Roth philosophy instead of resorting to wire bending as Andrew did, curve of spee is leveled by virtue of bracket positioning. In Roth prescription you don't need to go to full dimension wires. When Andrew place 7° torque in his maxillary central incisor brackets he means that your incisor should be at 7° inclination with occlusal plane perpendicular at the end of treatment. But when Roth place 12° or 17°torque in his upper incisors brackets he doesn't aim to attain all the torque built within

129

the bracket. Doing so will bring the roots out of lingual cortex. So one needs to be extra vigilant while using Roth prescription. In Roth treatment mechanics tipping of teeth is allowed so is using smaller dimension wires for closing spaces. Tipping plus smaller dimension wires means that not all the torque would be expressed from the brackets. So in Roth terms while using a 12° or 17° brackets one need to express only 8 to 10 ° torque. The 1° to 3° extra torque from norms attained during treatment would eventually be lost in relapse during the settling. So a finish case has a 7° incisor torque. But it's always difficult to tell that the teeth have attained the required torque and the assessment is more of a guesswork based on final occlusion. So both Andrew and Roth aim at similar final occlusal results, but the pathway is different. One cannot use Andrew treatment philosophy with Roth prescription to get the required results and vice versa. Limitations of Roth Prescription Inventory Roth prescription like Andrew has a multiple inventory. Roth prescription started as a single bracket set but with time having hit and trials multiple options were available. The present day Roth prescription are available as Roth standard prescription available in option of upper premolar in mesial rotation or distal rotation, Roth super or extra torque for class II div 2 and Roth surgical for surgical cases. So person of Roth statue also reached the conclusion that it's not possible to treat all types of malocclusion with a single bracket set. Lack of variability Cotemporary Roth prescription contain multiple bracket sets. But the level variability found in Andrew prescription is missing in Roth. In Roth prescription standard brackets are


wise selection of brackets from Andrews' work that favors mechanics used by Roth on most of the patients he treated at his office. Roth humbly named his prescription as Roth prescription of Andrew appliance.


CHAPTER meant to treat most types of malocclusion. So we have one single bracket set for extraction and nonextraction cases. We are bound to use brackets with increased tip and counter rotation in nonextraction case where teeth are not supposed to translate. In translation or extraction case we use same brackets for every type of extraction and so translation of teeth. It is well understood that, greater the amount of translation needed greater tip, torque and counter rotation would be required. Using standard Roth series brackets in cases requiring greater translation of teeth would be lead to less over corrections present at the end of treatment. So by using Roth prescription and reaching the same dimensions of archwire we do most overcorrection of teeth position in cases where we required least i-e the nonextraction case and we do least over correction in case where we required most i-e extraction cases requiring more than 4.1 mm of translation. Mechanotherapy Today's orthodontists want their cases to be well settled down when they deboned it. But Roth prescription is based on the assumption of overcorrection to accommodate relapse. By using Roth brackets we presume that same amount of relapse will occur in all type of cases. Present day evidence 44-47 on relapse doesn't support this assumption. As relapse is unpredictable, so if Roth philosophy of overcorrection in finished cases is followed then some cases may relapse more than is required to achieve ideal results while in other cases there may be no relapse at all and orthodontists are left with no other option but to cause a force relapse to correct over correction. Unlike Andrew prescription where full dimensional archwires are used in both extraction and nonextraction cases in Roth prescription, arch wire selection need to vary between extraction and nonextraction cases to get the desired results.

6

Root Parallelism Like Andrew prescription Roth prescription also has problem with root parallelism especially in maxillary canines. The canine root comes very close to the premolar root after expression of tip. Though it is claimed that not all the tip would be expressed because of wire play, yet wire play is less a problem with tip than torque. So if someone wants to attain +7° center incisor torque in Roth standard prescription having +12° build in torque, the minimum wire he would need is 0.021”x0.025” on 0.022”x0.028” slot. Such wire will theoretically express +7.9° of torque on incisor but more than 12° of tip on canine as the play of the wire is 0.001” in vertical dimension. Contemporary Roth prescription Roth prescription available commercially today is different from what originated in 1970s and justified and advertised in 1980s.The difference is more evident in counter rotation. I have no idea whether the present day Roth prescription found in different catalogs and books is also endorsed by its founder. Different Roth Prescription values are given in table 6.18&6.19. Roth Surgical Prescription All the values are same of standard series prescription except upper canine. The upper canine has -2° torque, 9° tip and 4° mesial rotation. This prescription values seem to be effective for class III surgical cases but not for class II. Standard Roth prescription Standard Roth prescription taken from two different sources is given. Table 6.18 values are from a reputed manufacturer 48 catalog while table 6.19 values are from a widely recognized under and postgraduate text book 49.

130

In table 6.18 there are some much required modifications. Mesial rotation of maxillary canine is increased to accommodate greater translation of this tooth in extraction cases. Also counter rotation in mandibular canine is reversed from distal rotation to mesial rotation. This surely will help translation of canine in premolar extraction cases. In both first and second maxillary premolars counter rotation is reversed to distal rotation. Distal rotation will favor planned anchorage loss as we required in

many of the 1st premolar extraction cases. In the table 6.19, canine angulation is taken from Roth extra torque prescription. No counter rotation value is given for canines and premolars. So it is generally presumed by students that no counter rotation exists in both maxillary and mandibular canines and premolars. Zero tip and torque is present in mandibular incisor which don't have any precedent in Roth work. 9° tip is used for

Table 6.19 1stPremola r

2ndPremola r

1st Molar

Torq ue°

Tip°

Tor que °

Ti p°

Torq ue°

Ti p°

Torq ue°

Rotati on°

Ti p°

Torq ue°

Rotati on°

9

-2

0

-7

0

-7

0

-14

14

0

-14

14

7

-11

0

17

-1

-22

1

-30

4

0

-30

4

Central incisors

Lateral incisors

Canine

Tip °

Tor que °

Tip

Torq ue°

Tip°

Maxillar y Arch

5

12

9

8

Mandib ular arch

0

0

0

0

Teeth

maxillary canine which is usually a part of super torque series and not a part of standard Roth prescription. MBT Prescription MBT is an abbreviation for Richard McLaughlin, John Bennett and Hugo Trevisi. These three orthodontists from three different parts of the world worked together to introduce their own prescription of brackets called MBT prescription in 199750. The bracket prescription was made to accommodate specific mechanics

131

Roth Prescription 2nd Molar

advocated by these orthodontists. The prescription was based on following principles: 1. Light continuous force. 2. Lacebacks, bendbacks and elastic module assisted retractions. 3. Sliding mechanics on a 0.019”x0.025” SS wire in 0.022”x0.028” slot bracket. 4. Use of specific arch form close to patient natural arch form. Three different arch forms were advocated. These were tapered, ovoid


Table 6.18


CHAPTER

6

Table 6.20 MBT Prescription Central incisors

Lateral incisors

Canine

1stPremol ar

2ndPremola r

1st Molar

Tip °

Tor que °

Tip

Torq ue°

Tip °

Torque °

Tip °

Tor que °

Ti p°

Torq ue°

Ti p°

Torq ue°

Rotati on°

Ti p°

Torq ue°

Rotati on°

Maxillar y Arch

4

17, 22

8

10

8

+7,0, -7

0

-7

0

-7

0

-14

10

0

-14

10

Mandib ular arch

0

-6

0

-6

3

-6,0 ,+6

2

12

2

-17

0

-20

0

0

-10

0

Teeth

and square archform. 5. Selection of brackets in specific malocclusions and alteration of prescription in some specific clinical problems. 6. Bracket positioning at specific height on the teeth taking guidance from bracket positioning charts and using specific bracket positioning gauges. 7. Using curves in the wire to level curve of spee. MBT prescription is given below in table 6.20. Origin of MBT Prescription The inventors of this prescription claimed that after working for 15 years they put forward their treatment mechanics 52-53 and then introduced this prescription in 1997 to facilitate those treatment mechanics. Andrew original findings and two Japanese studies 54, 55 were also taken into consideration apart from their own clinical understanding in the making of this prescription. Justification of MBT prescription The inventors of MBT prescription gave the following justification for making of their prescription. Incisors

2nd Molar

Incisors angulation or tip in both maxillary and mandibular arches were decreased because there was no need to compensate wagon wheel effects if clinician use lacebacks during alignment and leveling and elastic modules combined with lacebacks for space closure. To counter torque loss during space closure and overjet reduction, positive torque in maxillary incisors is increased from Andrews' values. Two torque options are provided for central incisors. Cases like class II div 2 can benefit from higher torque value of 22°. Negative lower incisor torque was increased to counter increased incisor proclination that occur during leveling curve of spee. Canines Canine tip was decreased and it was taken from Andrew original research finding 39.Both maxillary and mandibular canine torque is available in 3 different options. In maxillary arch -7° is taken from Andrew original research findings while 0° and +7° torque taken to accommodate different malocclusion.+7° torque is good for cases with buccally placed canines. 0° and +7° torque brackets are also good for cases with narrow maxilla. In mandibular arch negative torque is decreased in canines to decrease incidence of gingival recession. When there is increased negative torque the canine crown moves away from the

132

Premolars 0° tip was given in upper premolars to allow these teeth to angulate more towards class I position. Another reason to decrease tip values is that there are less chances of anchorage loss in MBT system because of light continuous force treatment mechanics. In lower premolars the Andrew prescription value of tip was retained as these values are close to Andrew's original findings and also these help to better orient lower premolars toward class I position. Torque values in maxillary premolars were retained from Andrew's prescription as they were found satisfactory in most cases. In mandibular premolars torque values were decreased to avoid gingival recession which is usually present in this area and to avoid mandibular arch narrowing which will in turn cause maxillary arch narrowing. Decrease negative torque on premolars will also help to decrease torque on molars. Molars Tip in the maxillary molars is decreased to 0°. But positioning bands or tubes parallel to buccal cusps or occlusal plane rather than buccal groove was advocated. Because of different placement position a 0° tip will make molar angulation 5° for reason explained in Roth prescription. The lower molars are given a 0° tip instead of 2° and it is advocated that lower molar tubes or bands should be placed parallel to occlusal plane rather than taking buccal groove as a reference. Placing the molar tubes with 0° tip parallel to occlusal plane will make the final orientation of buccal groove 2° to

133

occlusal plane perpendicular. So in terms of orientation of maxillary and mandibular molar there is no difference in final orientation of molars in case treated in accordance with Andrew prescription and MBT prescription. Maxillary molar torque was increased from Andrew standard prescription to -14° to avoid palatal cusp hanging. In mandibular molars torque was significantly decreased especially the lower 2nd molar torque to support expanded maxilla, to accommodate decreased negative torque anterior in the arch and to prevent lingual rolling of the lower molars which occur due to use of class II elastic. Proposed advantages of MBT prescription Following advantages for MBT prescription have been purposed by its inventors Incisors Brackets The increased torque on maxillary incisors will rapidly correct incisor torque in class II div 2 cases. Increased positive torque on upper incisors and negative torque on lower incisors is helpful in class III camouflage cases and cases treated with class II elastics. Decreased tip will decrease demand on anchorage in initial leveling and alignment. Because of 0° tip in lower incisors the lower incisor brackets are interchangeable. Canine Brackets Positive and zero torque brackets are helpful in maxillary expansion and buccaly placed canine's cases. Zero torque brackets are especially helpful in gingival recession cases and extraction cases to keep roots of teeth in middle of alveolar process while translation into extraction space. Zero or positive torque lower canine's brackets are also helpful in class II div2 cases where the canine root is placed too labial. Maxillary negative torque brackets are helpful in palatally impacted canines for proper root placement while the positive torque


labial soft tissue and its roots move closer to labial cortex thus increasing incidence of gingival recession. Also maxillary expansion will favor from decreased negative torque in lower canines as the lower canines crowns will move out to support the expanded maxillary canines.


CHAPTER brackets are helpful in cases where canine is substituting the lateral incisor. Premolars Brackets 0° tip in upper premolars brackets mean left side brackets can be used on right side and vice versa. 0.5mm increased prominence of brackets is made for small maxillary 2nd premolars if required. No tip in upper and positive tip in lower premolars will help to achieve class I dental relations. Premolar tubes have been made for lower 2nd premolars to prevent occlusal interference in some cases. Molar Tubes and bands In cases where final molars relations are class II; placing 10° distal offset tube will yield poor occlusal results. Placing lower 2nd molar tube which has torque very close to upper 1st molar and 0° tip and offset will yield required results. It is better to place opposite side of lower tube to have proper orientation of the hook. Many companies make straight hooks in lower molar bands so placing same side lower 2nd molar band on upper 1st molar will also yield the required results. Class II elastics will cause less lingual rolling of lower molars as they have decreased negative torque. This negative torque in lower molars is also advantageous in maxillary expansion cases while upright lower teeth will support the expanded upper arch. Critical evaluation of origin of MBT prescription Critical evaluation is given here to open reader's mind of different aspects and limitations of the prescription and is no way meant to downplay the inventors work. Before going in evaluation of the prescription itself, a brief insight is given about the mechanics on which the prescription is based.

6

Canine Tie Backs Canine tie backs and lacebacks are important part of MBT treatment philosophy. According to MBT inventors this component of treatment mechanics helps to control tip and prevent anchorage loss in initial stages of treatment. This also helps to avoid wagon wheel effects compensation in their bracket prescription. But different clinician can tie canine lacebacks with different force 56 and different force level can be applied by same clinician at different appointments. A randomized clinical trial 57 has shown that maxillary canine lacebacks don't cause mesial molar movement and can prevent incisor proclination up to 1mm.But in mandibular arch58 canine lacebacks don't cause any change in incisor position but can cause significant posterior anchorage loss up to 0.8mm so canine tip backs shouldn't be used in mandibular arch. So decreasing tip in maxillary arch can be justified to some extent but not in mandibular arch. Elastic module tiebacks or Active ligature Elastic module tie backs or active ligatures have been recommended for space closure in MBT system. The inventor proposed that using these elastic modules activated by laceback wire apply light continuous force for space closure. Also use of these modules doesn't cause loss of tip in incisors and there is no need to go for wagon wheel effect compensation. Effective torque control on incisor is also proposed benefit of these modules. A randomized clinical trial by Dixon60 comparing three methods of space closure showed that elastic module tiebacks are least effective in space closure as compared to NiTi coil springs and power chains. NiTi springs have more than double the rate of space closure per month as compared to active ligatures. A systematic review61 also concluded that NiTi coil springs closes space at a faster rate and

134

Wagon wheel effects The inventors of MBT prescription claims that, their mechanics apply light continuous forces so there is no need to go for wagon wheel effects compensation. But this claim has a technical shortcoming. Wagon wheel effects are due to shape effect of a semicircle. As premaxillary and anterior mandible alveolar area is shaped like a semicircle so wagon wheel effects are inevitable. Increasing positive torque on the teeth, whether they are incisors or canines in this semicircle area will bring their roots closer to each other. It won't be affected whether forces given are light or heavy for this torqueing movement. Space requirement It has been explained before that increase in tip will take space and decrease in tip will give space. Torque whether positive or negative will need space, until the arch is expanded. Decreasing or increasing tip to give better occlusion will change space requirements in the arch. In MBT system tip is decreased and torque is increased. But the interesting space management issue is that by following MBT mechanics you will express the entire tip built within the bracket but not all the torque. For example, a central incisor bracket of maxillary incisor has 4° tip and 17° torque. By following MBT mechanics we will theoretically express up to 3.9° of tip but only 7° torque. So decrease tip in MBT system will leave spaces in the arch. After treating more than 150 extraction cases with MBT system, I personally feel that decreasing tip in maxillary arch has created problem in closing spaces especially in anterior teeth. In many cases I resorted to build up of maxillary incisors even there was no Bolton deficiency or tip and torque problems.

135

Sliding mechanics and torque expression MBT system as claimed by its inventors works best on 0.022” slot and sliding mechanics should be used on 0.019”x0.025” wire. A 0.019”x0.025” wire has 9.5° to 10° play on 0.022” slot. When full dimension wires are used final torque expressed is exactly what is built into the brackets. As explained before in Andrew key 3 that when wire play is present many factors start affecting the torque expression. So when wire play is present and full arch is bonded, measuring effective torque on each tooth is like measuring forces in an indiscriminate force system. For example if all other factors are constant and brackets are placed at the same height with all the teeth having 0° inclination to occlusal plane perpendicular, then a 0.019”x0.025” wire passing through an upper central incisors having 17° torque and lateral incisors having a 10° torque will not express any torque as the wire play would be less than 10°. But if the same wire is extended posteriorly and it passes through the canine which has -7° torque then wire engages slot of canine at an angle of 7°. Becasuse canine lateral incisor torque difference is 17° and there is 10° play so torque expressed would be 7°. As a result of it positive torque would be expressed on lateral incisor bracket and negative torque would be expressed on canine bracket. Most of this torque would be expressed on lateral incisor as it got smaller roots and relatively thin bone around it. As the inclination of both these teeth changes so the orientation of their slots to neighboring slots. In lateral incisor as slot opening rotate in a counterclockwise direction due to expression of the torque the difference in its slot orientation from that of central incisor slot increase. If out of 7° torque more than 3° is expressed on lateral incisor then wire exiting lateral incisor bracket will engage central incisor bracket at an angle and also will result in expression of positive torque on that teeth.


produces a more consistent force as compared to using active ligatures in sliding mechanics. From this evidence it is clear that elastic module lack evidence for their use in space closure.


CHAPTER Another factor that comes into play when wire is extended posteriorly from incisors to canine is orientation of the wire. Because of positive torque in incisor bracket their slot opening would be directed downward so a rectangular archwire exiting the slot would be upward directed. Engaging this wire in canine will cause intrusion of canine, negative torque and slight counterclockwise rotation of canine crown as force is buccal to center of resistance of canine. The counterclockwise rotation of crown will decrease some negative torque of canine. The incisor will get extrusive and positive torque effects. On the canine side if wire is extended posteriorly into 1st premolar bracket that has -7° torque than no torque would be expressed on 1st premolar as the difference between bracket torque on canine and premolar would be less than 10°.No torque would be expressed on 2nd premolar having -7° torque and 1st molar having -14° torque. But the situation is much more different in clinical cases where different brackets are positioned at different heights, different teeth have different inclination with reference to occlusal plane perpendicular, different bone density around different roots having different root length, different interbracket distance between teeth and different teeth have different crown morphology. Apart from crown morphology all these factors are irrelevant in torque expression and the entire builtin bracket torque is expressed when a full dimension wire engages the slot. Critical analysis of origin of prescription is given. Maxillary Arch Incisors 1. Central incisor The maxillary central incisor bracket is

6

available in two torque options +17° and +22°.The +17° torque option is not new in orthodontics. It was already used before MBT prescription as part of Roth super torque prescription for class II div 2. The +22° torque is something new but an important part of MBT system as present in Roth was that you don't have to express all the builtin torque of prescription. Whether the builtin torque is +17° or +22° you have to express only 7° in case of class I or +12° in case of class III camouflage. As the MBT system advocate 0.019”x0.025” wire for sliding mechanics, so the effective torque expressed theoretically taking 10° wire play would be +7° in +17° torque bracket and +12° in +22° torque bracket . +7° torque for upper incisor was present in class I skeletal pattern in Andrew findings and +12° torque was recommended for Class III camouflage. The inventors of MBT prescription claimed that they have taken in consideration of Andrews' original findings, standard SWA appliance prescription and two Japanese studies while making of this prescription. If these values were taken into consideration the mean torque of these four studies for central incisor would have been +9°. Central incisor tip is kept at 4°. This is close to mean tip of different studies which is 3.98° and Andrew original norms of 3.59°.The wagon wheel effects were not compensated in central incisor tip. 2. Lateral incisors Lateral incisor torque is kept at 10°.If Andrew cephalometric study have been followed the lateral incisor torque should have been 13°. The wire play of a 0.019”x0.25” wire will theoretically result in expression of no or 0° torque on maxillary lateral incisor in 0.022” slot. If straight archwire is passed the lateral incisor would always be 7° less than central incisor.

136

Tip value is also decreased from Andrew original norms and is taken from inventors own clinical experience. The mean value of tip from different studies is 3° for 1st premolar and 4° for 2nd premolar. Decreasing the tip to facilitate class I relations will severely jeopardies the space requirement in the arch and contacts point wouldn't be tight without resorting to composite build ups.

Tip or angulation value of lateral incisor is taken from Andrew original norms. An input from different studies should have resulted in mean lateral incisor of 7° and not 8°.

Molars

Canines Canine torque is available in three different options -7°, 0° and +7°. -7° is the prescribed torque and other 2 options are to deal a certain group of clinical cases. -7° torque is clearly taken from Andrew standard SWA or original norms as input taken from all studies have resulted in a -3° mean torque on canine. In clinical setting reactionary torque of incisors should also be added in this negative torque of canine if wire play is present during expression of torque. Tip value in canine is also taken from original Andrew's original norms but mean tip value of 8.7° from different studies is also close to MBT prescription. Premolars 1st and 2nd premolar torque is taken from standard SWA prescription values. Input from different studies would also make this torque value as -7°.Unfortunately changing the mechanics will change the torque values. Using 0.019”x0.025” wire instead of full dimension wires on standard SWA prescription values will result in expression of decreased torque on premolars as canine anteriorly and molar posteriorly has also negative torque so torque on premolars would be lost in wire play.

137

Torque values for 1st and 2nd molar are same as that found in Andrew medium translation series molar brackets and that of Roth prescription. The mean input of different studies is -7° for 1st and 2nd molars so torque values of MBT prescription for 1st and 2nd molar are more negative than Andrew original norms and combined input of different studies. Tip of both molars is kept at 0° but different positioning of molar brackets is advocated that technically make 0° tip into 5° which is same as that found in standard SWA for class I molars. The mean tip of different studies is 5 ° for 1st molar but 2.3° for 2nd molar. 10° distal offset is also present in maxillary 1st and 2nd molar tube. This is ideal for class I molars. In case of class II molar relationship it is advocated to band lower 2nd molar of opposite side on 1st molar. But lower 2nd molar has 4° less torque than upper 1st molar and molar band position also need to be altered to get only 0° tip. Ideally upper 2nd molars should also be banded with lower 2nd molars of opposite side. Mandibular Arch Incisors Lower incisors have class III incisors torque values of Andrew SWA. The mean input of different studies is 0.4° torque for lower central incisor and -0.5° for lateral incisor. Tip in lower incisors is also decreased and is


Input from 3 studies and Andrew SWA should have resulted in lateral incisor torque of 6°. So such input was never taken. In reality lateral incisor torque is virtually decreased if someone is following MBT mechanics with MBT prescription. If one is aiming to attain ideal central incisor torque of 7° on a straight wire he will get 0° torque on lateral incisor following the same mechanics.


CHAPTER close to Andrew original norms. The mean tip of different studies would be 1° for central and 0.8° for lateral incisors. As the lower incisors are also present on a semicircle shaped area the wagon wheel effect needed to be compensated by decreasing the tip on increasing negative torque. Canines Lower canine tip is available in three options 6°, 0° and +6°. The -6° is the standard prescription while the other two are recommended for some specific type of malocclusion. There is far less negative torque in MBT prescription than Andrew original finding and Andrew prescription. The mean torque of different studies input and original SWA is -10°. So torque on canine is taken from inventor own clinical experience. Tip on lower canines in MBT system is close to Andrew original norms and mean tip of different studies. Premolars Negative torque on lower premolars is decreased and is far less than Andrew original norms and mean value of different studies. Negative torque was decreased to match with decrease in negative torque in molar area, to support expanded maxilla and to prevent gingival recession in susceptible cases. But it's not necessary that maxilla would be constricted or need expansion in all the cases or gingival recession would be present in all the cases. Bicuspid tip is same as that of Andrew standard SWA. Taking mean value of different studies and standard SWA would result in 1st premolar tip of 2.4° and 2nd premolar tip of 3.5°. Molars Negative torque on lower molars is decreased and is far less than Andrew original norms and mean of different studies. This decreased

6

negative torque helps to prevent lingual rolling of the lower molars in case someone uses class II elastics or fixed functional appliances. But majority of the cases in orthodontic practice don't use these mechanics and using such torque value increase the incidence of crossbite. 0° tip in lower 1st and 2nd molar is technically 2° tip because of difference in band placement position in Andrew and MBT prescription. So tip values for molars are same as Andrew standard SWA. These tip values are less than mean of different studies and Andrew's original findings. From the above review it is clear that MBT system has also its shortcomings. Selection of Prescription All the prescriptions work fine if one follows the inventor's advocated mechanics. All the prescriptions have their own limitations that needed to be compensated by wire bending or elastics to some extent. We still don't have a prescription where a straight wire is used throughout the treatment and no wire bending is required. Also lack of consensus on ideal position of the bracket on the tooth limits the adaptation of a single prescription 62 universally. Jain et al found that there is no clinical significance in final outcome between MBT and Roth prescription and quality of treatment depend upon clinician experience and judgment. Moesi 63 in a study on Roth versus MBT prescription found that it is difficult to judge on a finished case that which prescription was used during treatment. Unfortunately it's a reality that in ideally finished cases where a prescription can best be judged are only done in teaching hospitals and most of the clinician doesn't aim for the required level of perfection in their clinical practice so tip and torque of the bracket are not appreciated to the extent it deserves.

138

Alteration of prescription Alteration of the prescription is done by experienced clinician to deal certain types of malocclusion. Alteration can be done by adding different prescription together or alternating different tooth brackets in same prescription. A few examples of alteration of different prescriptions are given. Class II div 1growth modification In growth modification with fixed functional appliances in class II cases, MBT and Roth prescription can be combined. Roth prescription has decreased incisor torque on maxillary incisors as compared to MBT prescription while MBT prescription has increased negative torque on lower incisors to keep the lower incisors roots upright. Clinician either uses Roth prescription on maxillary incisors only and all other teeth are bonded with MBT prescription or MBT prescription is used on mandibular incisors only and Roth prescription is bonded on all other teeth. This approach of bracket position will keep lower incisors roots upright during their mesialization while upper incisor inclination is decreased thus decreasing the severity of class II and adding a camouflage to it (Case example 1). Class II camouflage Class II camouflage requires decrease of upper incisor torque and increase of lower incisor

139

torque. In extraction cases this can be done either by modifying the mechanics or using low prescription positive torque on upper incisors and increased negative torque brackets on lower incisors. In modified mechanics using a light rectangular wire for retraction of upper incisors will result in loss of incisor inclination while using heavier wire for mesializing of lower incisors having negative torque brackets will keep their roots upright and prevent excessive inclination change of these incisors. Using Roth maxillary incisor brackets on upper incisors and MBT mandibular incisor brackets on lower incisors is a viable option to decrease the positive incisor torque. The MBT brackets on lower incisor will maintain their inclination while mesializing lower incisor either by class II elastics or any other mechanics. In case lower incisors are retroclined which is mostly not the case in majority of class II cases as dental compensations are present for skeletal pattern, MBT brackets can be inverted to introduce positive torque and increase inclination of lower incisors. If at the end of the final stages of overjet correction maxillary incisor inclination is still increased upper incisor brackets can be inverted to decrease their inclination. Placing the brackets upside down will reverse its torque and make maxillary incisors torque negative while tip will remain the same (Figure 6.50). When the clinician feel that required torque has been expressed and inclination of incisors is ideal the clinician should either move back to lighter wires or debond the case after necessary settling. (Case example 2) Class II Surgical cases In class II surgical cases increased positive torque is used on maxillary incisor and increased negative torque is used on mandibular incisors to make decompensating easier. MBT prescription is well suited for this task.


Clinician should choose a prescription in which they find ease with mechanics advocated for that prescription. Due to various limitation of all prescription some degree of wire bending and bracket position alteration is always required and clinician should remain mentally prepared for that. All the cases must be finished in light of Andrews' six keys or any other parameters set by local examination bodies or ethical councils.


CHAPTER

A

6

B

Figure 6.50 A. A left maxillary central incisor bracket. B. Same bracket inverted upside down. Inverting the bracket will reverse the torque but the tip will remain the same. Both brackets have positive tip as mesial slot of the bracket is facing downward.

Case example 1. A young patient having skeletal class II with increased overjet was treated with jasper jumper appliance. The mandibular incisors were bonded with MBT prescription while all other teeth were bonded with Roth prescription. The increased negative torque in MBT prescription will keep the lower incisors upright during fixed functional phase. A class II fixed functional appliance cause lower incisor proclination.

140

Selection of Bracket Prescription Case example 2. An adult patient was presented with class II skeletal base and class II sub division right molar relations, having increased overjet and increase curve of spee in lower arch at the start of treatment. The case was treated with orthodontic comouflage. MBT brackets were bonded on lower incisors to maintain their inclination with use of class II elastics . All other teeth were bonded with Roth prescription.At the end of treatment as upper incisor inclination was increased and there was some overjet remaining the upper incisor brackets were inverted to close the overjet and correct incisor inclination. Unfortunately more than required negative torque was expressed on upper incisors.

Class II div 2 In class II div 2 usually both upper and lower incisors are retroclined. Roth advocated extra

141

or super torque prescription for this malocclusion. Usually super torque prescription is not available worldwide due to its low demand so clinician uses MBT


CHAPTER prescription. MBT prescription has increased upper incisors torque. Usually 22° torque option is selected for upper central incisors depending upon degree of retroclination of upper incisors. For lower incisors if they are retroclined MBT lower incisor brackets are

6

bonded inverted thus making their torque positive. But in case of normal or increased inclination of lower incisors MBT brackets are placed in their normal upright position. (Case example 3)

Case example 3. A moderate class II div II in an adult patient in which upper incisors were retroclined and lower incisors were having normal inclination. Case was treated with MBT prescription and 0.021” x 0.025” wire was used as final working wire to express greater amount of positive torque on upper incisors. As the lower incisors have normal inclination, lower incisor brackets were placed in normal upright position.

142

In class III camouflage lower incisors brackets need increased negative torque while upper incisors brackets need increased positive torque. So MBT prescription is well suited for class III camouflage cases. Even 22° torque option of maxillary central incisors can be used. An important modification that is done in class III camouflage is reversing the tip of lower canine brackets to improve class I canine relationship. This is done by alternating lower contralateral canine's brackets. Using right side bracket on left side will reverse the tip but keep the torque unchanged. As MBT prescription has decreased tip on lower canines as compared to Roth prescription so many clinician alternate Roth prescription brackets on lower canines. Class III surgical cases In Class III surgical cases for effective decompensation upper incisors needed to be retroclined while lower incisors needed to be proclined. If it is an extraction case the upper incisors can easily be retroclined and their inclination can be decreased by using smaller dimension rectangular wires like 0.016x0.022 inch SS for retraction during sliding mechanics. The lower incisor inclination can be increased by placing inverted MBT brackets on lower incisors so that their torque will become positive.

143

If the case is nonextraction both upper and lower incisor need decompensation then MBT brackets are inverted on both upper and lower incisors. Inverting the brackets on both upper and lower incisors will reverse their torque. Placing +6° torque bracket is not a problem on lower incisors but placing a -17° central and 10° lateral maxillary incisors bracket is an issue. So when required torque is attained on upper incisors the brackets are debonded and placed in their normal upright position. If these inverted brackets are kept throughout the treatment then chances of incisors root damage

increase as orthodontists need to keep heavy wires in the brackets during surgery and these wires will express majority of the bracket torque. Rebonded brackets will only change the torque introduced in the incisors when more than required negative torque was previously introduced. There is no need to rebond lower incisors brackets as there is small torque differential between upright and inverted brackets. Rest of the teeth can be bonded with MBT or Roth prescription. As large torque differential is present in upper incisors on inverting MBT prescription, regular visit of the patient is necessary once the patient is on heavy wires. Some clinicians instead of inverting MBT upper incisors bracket uses inverted Roth incisors brackets as they have smaller torque differential on inverting the brackets. Palatally placed upper lateral incisors A common malocclusion that is usually encountered is palatally displaced maxillary lateral incisors. After bringing the tooth in the arch and doing necessary leveling and alignment the crown of the tooth become aligned but the root remain more palatally placed than required. This clinical situation can easily be handled by placing inverted lateral incisor bracket in MBT or Roth prescription. Usually this torque problem is encountered near the end of treatment so when the required torque is expressed, the case is shifted to lighter wires, necessary settling is done and the brackets are debonded. But if there is ample time remaining to do any other mechanics then brackets on lateral incisors are debonded and rebonded in their upright position using wire guidance. Keeping heavy rectangular stainless steel wires even after the required torque has been expressed will result in expression of extra torque that will increase chances of lateral incisor root resorption from labial cortical plate (Case example 4).


Class III camouflage

6


CHAPTER

Case example 4. An adult patient with severe crowding in upper and lower arch. Both maxillary lateral incisors were palatally displaced due to crowding. The case was treated with extraction of maxillary and mandibular 1st premolars. MBT prescription was used and maxillary lateral incisor brackets were placed inverted to express negative torque on lateral incisor. Near end of treatment stage shown. On right maxillary lateral incisor optimum torque is expressed while left lateral incisor root is still palatally displaced. Right maxillary lateral incisors bracket was placed upright after optimum torque was expressed while left lateral incisors bracket is still placed inverted.

144

For cases in which lower incisors are lingually displaced MBT brackets are well suited but if someone is using Roth prescription which has decreased negative torque on lower incisors, MBT prescription bracket can be substituted for Roth brackets on lower incisors. Maxillary lateral incisor Substitution Cases requiring extraction of maxillary lateral incisors or missing lateral incisors needs canines to substitute lateral incisors. In such cases lateral incisors brackets are placed on canine after flattening the labial surface of canine. The canine brackets are placed on 1st premolars. (Case example 5) Palatally impacted Maxillary canines Palatally impacted maxillary canines when exposed and brought in the arch will have their roots lagging back in the palate. Increased negative torque is required on these brackets. MBT brackets with -7° torque are well suited for these situations. In case only MBT +7° torque bracket are available for maxillary canines then inverting the brackets will make them -7° torque brackets while tip will remain the same. If someone is using Roth prescription, MBT prescription brackets with negative torque replace Roth brackets only on canines. (Case report 6 & 7) Buccally displaced maxillary canines Buccally displaced maxillary canines have a prominent canine buldge. Positive torque brackets should be used on the maxillary canines to place their root in middle of alveolar process or slightly more palatal. Positive torque option on canine is available in MBT prescription but not in Roth. In buccally displaced maxillary canines either canine bracket of Roth prescription should be inverted or MBT positive torque canine brackets should be combined with Roth prescription (Case

145

example 8 & 9).


Lingually placed lower incisor

6


CHAPTER

Case example 5. A Case with a peg right maxillary lateral and missing left maxillary lateral. Deciduous canine was present on left side of the maxillary arch. Mandibular arch has severe crowding. The case was planned with extraction of lower 1st premolars and upper peg lateral on right and deciduous canine on left. In maxillary arch labial surface, tip and proximal surface of the canines were reshaped to match the appearance of lateral incisors. The lateral incisors brackets were bonded on canines in mesiodistal middle of the tooth. Canine brackets were bonded to maxillary 1st premolars slightly distal to mesiodistal middle of teeth. Group function instead of canine guided occlusion was aimed in this case.

146

Case example 7. A palatally impacted canine case also treated with MBT prescription but unfortunately with 0° bracket as negative torque bracket was not available. Note no buccal canine bulge is present and the canine also has improper position of the gingival zenith.

147


Case example 6 .A palatally impacted canine. MBT negative torque bracket of -7° bracket was used on impacted canine after its eruption .At the end of treatment canine has optimum buccal bulge and soft tissue margins.

6


CHAPTER

Case example 8. A young patient presented with moderate crowding in upper and mild crowding in lower arch. Molar relation was class II end-on bilaterally. Maxillary left canine was buccally placed. Space was created in maxillary arch by distalization of molars with cervical pull headgear and in mandibular arch space was created with proclination of incisors. After space creation in upper arch positive torque on maxillary canine was given by choosing a +7° bracket from MBT prescription.

148

Selection of Bracket Prescription Case example 9. A young patient was presented with severe crowding in upper arch with bilateral buccally placed canines. Space in maxillary arch was created by distalization of molars with distal jet. MBT prescription was chosen with +7° torque of canine bracket. As right canine was more buccally placed at start of treatment it need extra torque by wire bending than using a 0.019”x0.025” wire with +7° torque canine brackets. Unfortunately that was not given and right side canine is not having optimum inclination at the end of treatment.

1. Andrews LF. The six keys to normal occlusion. Am J Orthod 1972; 62:296-309.

4. Sernetz F. Qualität und Normung orthodontischer Produkte aus der Sicht des Herstellers. Kieferorthopädische Mitteilungen 1993; 7: 13-26.

2. Andrews LF. Straight-Wire-The Concept and Appliance; L. A. WellsCo., San Diego, California. 92107: 1989.

5. Archambault et al, Torque expression in stainless steel orthodontic brackets. A systematic review. Angle Orthod. 2010 Jan;80(1):201-10.

3. Roth RH. The straight-wire appliance 17 years later. J Clin Orthod. 1987 Sep; 21(9):632-42.

6.

References

149

Siatkowski R. Loss of anterior torque


CHAPTER control due to variations in bracket slot and archwire dimensions. J Clin Orthod. 1999;33: 508–510. 7. Dolci GS, Spohr AM, Zimmer ER, Marchioro EM. Assessment of the dimensions and surface characteristics of orthodontic wires and bracket slots. Dental Press J Orthod. 2013 MarApr;18(2):69-75. 8. Major TW, Carey JP, Nobes DS, Major PW. Orthodontic Bracket Manufacturing Tolerances and Dimensional Differences between Select SelfLigating Brackets. J Dent Biomech. 2010 Jun 27;2010:781321. 9. Kusy R, Whitley J. Assessment of secondorder clearances between orthodontic archwires and bracket slots via the critical contact angle for binding. Angle Orthod. 1999;69:71–80. 10. Cash AC, Good SA, Curtis RV, McDonald F. An evaluation of slot size in orthodontic brackets-are standards as expected? Angle Orthod. 2004 Aug;74(4):450-3. 11. Bhalla NB, Good SA, McDonald F, Sherriff M, Cash AC. Assessment of slot sizes in self-ligating brackets using electron microscopy. Aust Orthod J. 2010 May;26(1):38-41. 12. Joch A, Pichelmayer M, Weiland F. Bracket slot and archwire dimensions: manufacturing precision and third order clearance. J Orthod. 2010 Dec;37(4):241-9. 13. Creekmore TD, Kunik RLStraight wire: the next generation. Am J Orthod Dentofacial Orthop. 1993 Jul;104(1):8-20. 14. Fischer-Brandies H, Orthuber W, Es-Souni M, Meyer S. Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters. J Orofac Orthop. 2000;61(4):258-65. 15. Thorstenson JA, Kusy RP. Resistance to sliding of orthodontic brackets with bumps in slot floors and walls: effects of second-order

6

angulation. Dent Mater 2004; 20: 881–892. 16. Sebanc J, Brantley WA, Pincsak JJ, Conover JP. Variability of effective root torque as a function of edge bevel on orthodontic arch wires. Am J Orthod. 1984 Jul;86(1):43-51. 17. Meling TR, Odegaard J. The effect of crosssectional dimensional variations of square and rectangular chrome-cobalt archwires on torsion. Angle Orthod. 1998 Jun;68(3):239-48. 18. Siatkowski, R.E.: Wear and tear from sliding mechanics, J. Clin.Orthod. 31:812-813, 1997. 19. Gmyrek H, Bourauel C, Richter G, Harzer W. Torque capacity of metal and plastic brackets with reference to materials, application, technology and biomechanics. J Orofac Orthop. 2002 Mar;63(2):113-28. 20. Major TW, Carey JP, Nobes DS, Heo G, Major PW. Deformation and warping of the bracket slot in select self-ligating orthodontic brackets due to an applied third order torque. J Orthod. 2012 Mar;39(1):25-33. 21. Sifakakis et al . Torque expression of 0.018 and 0.022 inch conventional brackets. Eur J Orthod. 2013 Oct;35(5):610-4. 22. Badawi HM, Toogood RW, Carey JP, Heo G, Major PW. Torque expression of self-ligating brackets. Am J Orthod Dentofacial Orthop. 2008 May;133(5):721-8. 23. Kapur-Wadhwa R. Physical and mechanical properties affecting torque control. J Clin Orthod. 2004 Jun;38(6):335-40 24. Archambault A, Major TW, Carey JP, Heo G, Badawi H, Major PW. A comparison of torque expression between stainless steel, titanium molybdenum alloy, and copper nickel titanium wires in metallic self-ligating brackets. Angle Orthod. 2010 Sep;80(5):884-9. 25.

Morina E, Eliades T, Pandis N, Jäger A,

150

26. Kusy R P 1983 On the use of nomograms to determine the elastic property ratios of orthodontic arch wires. American Journal of Orthodontics 83: 374–381. 27. Montasser MA et al. Force loss in archwireguided tooth movement of conventional and selfligating brackets. Eur J Orthod. 2014 Feb;36(1):31-8. 28. Kapur, R.; Sinha, P.K.; and Nanda, R.S.: Comparison of load transmission and bracket deformation between titanium and stainless steel brackets, Am. J. Orthod. 116:275-278, 1999. 29. Smith RN, Karmo M, Russell J, Brook AH. The variability of the curvature of the labial surface of the upper anterior teeth along the facial axis of the clinical crown. Arch Oral Biol. 2007 Nov;52(11):1037-42. 30. Vigorito JW, Moresca R, Dominguez GC, Tortamano A. Influence of the convexity of the upper central incisor on the torque expression of preadjusted brackets. J Clin Orthod. 2006 Jan;40(1):42-6. 31. Germane N, Bentley B, Isaacson RJ, Revere JH Jr. The morphology of canines in relation to preadjusted appliances. Angle Orthod. 1990 Spring;60(1):49-54. 32. Van Loenen M, Degrieck J, De Pauw G, Dermaut L. Anterior tooth morphology and its effect on torque. Eur J Orthod. 2005 Jun;27(3):25862. 33. Mestriner MA, Enoki C, Mucha JN. Normal torque of the buccal surface of mandibular teeth and its relationship with bracket positioning: a study in normal occlusion. Braz Dent J. 2006; 17(2): 155 60.

151

34.

Germane N, Bentley BE Jr, Isaacson RJ.

Three biologic variables modifying faciolingual tooth angulation by straight-wire appliances. Am J Orthod Dentofacial Orthop. 1989 Oct;96(4):312-9. 35. Miethke R R. Third order tooth movements with straight wire appliances. Influence of vestibular tooth crown morphology in the vertical plane . Journal of Orofacial Orthopedics.1997;58:186-197. 36. Meyer M, Nelson G. Preadjusted edgewise appliances: theory and practice . Am J Orthod.1987; 73:485-498. 37. Afzal A1, Ahmed I. Leveling curve of Spee and its effect on mandibular arch length. J Coll Physicians Surg Pak. 2006 Nov;16(11):709-11. 38. Roth RH. Functional occlusion for the Orthodontist. Part III. J Clin Orthod. 1981 Mar;15(3):174-9, 182-98. 39. Mclaughlin RP, Bennett JC, Trevisi H.Systemized Orthodontic Treatment Mechanics. New York:Mosby,2005. 40. S a m i r E . B i s h a r a . Te x t b o o k o f Orthodontics.New York: Saunders,2001. 41. P ro f f i t W R , F i e l d s H W 2 0 0 0 Contemporary orthodontics, 3rd edn. Mosby, St Louis, p. 344. 42. Andrews LF. The straight-wire appliance: extraction brackets and classification of treatment. J Clin Orthod.1976d; 10: 360-379. 43. Roth RH. Five year clinical evaluation of the Andrews straight-wire appliance. J Clin Orthod. 1976 Nov;10(11):836-50. 44. Little RM. Stability and relapse of mandibular anterior alignment: University of Washington studies. Semin Orthod. 1999 Sep;5(3):191-204. 45. Freitas KM et al. Postretention relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction. Am J


Bourauel C. Torque expression of self-ligating brackets compared with conventional metallic, ceramic, and plastic brackets. Eur J Orthod. 2008 Jun;30(3):233-8.


CHAPTER Orthod Dentofacial Orthop. 2004 Apr;125(4):4807. 46. Little RM. Stability and relapse of dental arch alignment. Br J Orthod. 1990 Aug;17(3):23541. 47. Erdinc AE, Nanda RS, Işiksal E. Relapse of anterior crowding in patients treated with extraction and nonextraction of premolars. Am J Orthod Dentofacial Orthop. 2006 Jun;129(6):77584. 48. DENTSPLY. . http://www.dentsply.com/enus/orthodontics/brackets/metal-twin brackets (accessed 15 Sept 2014). 49. Proffit WR, Fields HW & Sarver DM Contemporary Orthodontics. 5th ed. New York: Mosby; 2012. 50. McLaughlin RP, Bennett JC, Trevisi H.The MBT™ Versatile+Appliance System, series, 19982007 3M. 51. Mclaughlin RP, Bennett JC. The transit ion from standard edgewise to preadjusted appliance systems. J Clin Orthod. 1989 Mar;23(3):142-53. 52. Bennett JC, Mclaughlin RP. Controlled space closure with a preadjusted appliance system. J Clin Orthod. 1990 Apr;24(4):251-60. 53. Mclaughlin RP, Bennett JC .Finishing and detailing with a preadjusted appliance system. J Clin Orthod. 1991 Apr;25(4):251-64. 54. Sebata E. An orthodontic study of teeth and dental arch form on the Japanese normal occlusions. Shikwa Gakuho. 1980 Jul;80(7):94569.

6

2006 Dec;33(4):270-5. 57. Usmani T, O'Brien KD, Worthington HV,et al. A randomized clinical trial to compare the effectiveness of canine lacebacks with reference to canine tip. J Orthod. 2002 Dec;29(4):281-6. 58. Irvine R, Power S, McDonald F. The effectiveness of laceback ligatures: a randomized controlled clinical trial. J Orthod. 2004 Dec;31(4):303-11. 59. Samuels RH, Rudge SJ, Mair LH. A clinical study of space closure with nickel-titanium closed coil springs and an elastic module. Am J Orthod Dentofacial Orthop. 1998 Jul;114(1):73-9. 60. Dixon V, Read MJ, O'Brien KD, Worthington HV, Mandall NA. A randomized clinical trial to compare three methods of orthodontic space closure. J Orthod. 2002 Mar;29(1):31-6. 61. Barlow M, Kula K. Factors influencing efficiency of sliding mechanics to close extraction space: a systematic review. Orthod Craniofac Res. 2008 May;11(2):65-73. 62. Jain M, Varghese J, Mascarenhas R, Mogra S et al. Assessment of clinical outcomes of Roth and MBT bracket prescription using the American Board of Orthodontics Objective Grading System. Contemp Clin Dent. 2013 Jul;4(3):307-12. 63. Moesi B , Dyer F, Benson PE. Roth versus MBT: does bracket prescription have an effect on the subjective outcome of pre-adjusted edgewise treatment? Eur J Orthod. 2013 Apr;35(2):236-43.

55. Watanabe K, Koga M. A morphometric study with setup models for bracket design. Angle Orthod. 2001 Dec;71(6):499-511. 56. Khambay BS, McHugh S, Millett DT. Magnitude and reproducibility of forces generated by clinicians during laceback placement. J Orthod.

152

CHAPTER

7

Placement of orthodontic brackets In this Chapter

Mesiodistal position of brackets Checking mesiodistal position of the brackets Modifications in mesiodistal position of the bracket Axial or long axis position of the brackets

Importance of vertical position of brackets Bracket positioning gauges Parts of gauges Position of the gauge during bracket placement

Importance of axial position of brackets

Bracket placement by wire guidance

Checking axial position of brackets

Position of clinician during brackets placement

Modifications in axial position of brackets Vertical position of brackets Modifications in Vertical position of the brackets

Prescriptions in preadjusted edgewise brackets are built after taking prescription values from a certain point or area on labial surface of the tooth. The prescription built into the bracket will work best if the brackets are placed at that specific area. Mostly that specific area where the brackets needed to be placed is also pinpointed by the inventor of the prescription. During orthodontic bonding of preadjusted brackets the orthodontist must place brackets accurately in vertical, mesiodistal and axial planes as advocated for that prescription or based on his clinical experience. These

153

accurately placed brackets will give better control on three dimension position of the teeth during treatment. An accurately placed bracket will also result in better expression of its builtin prescription and orthodontist will need less wire bending and complex mechanics during the course of treatment. Mesiodistal position of brackets It is a general saying in orthodontics that brackets should be placed at mesiodistal center of the teeth. This statement is partially correct as this rule can't be applied to all the teeth. A more

Placement of orthodontic brackets

CHAPTER

7

clear description for right mesiodistal position of brackets was given by Andrew1 that brackets should ideally be placed at the mid developmental ridge of the teeth. The correct mesiodistal position of brackets on different teeth is given as under. Maxillary and mandibular incisors Bracket should ideally be placed at mesiodistal center of maxillary and mandibular incisors. The mid developmental ridge of these teeth is also present at their mesiodistal center of the labial surface (Figure 7.1).

Figure 7.2 The vertical lines on maxillary and mandibular canines indicate the mid developmental ridge of the canines and ideally the middle of the brackets should coincide with this line.

Mandibular Premolars

Figure 7.1 Vertical lines showing mesiodistal center of the upper and lower incisors. Brackets should be placed at the recommended height on this line.

Maxillary and mandibular Canines Placing brackets at the mesiodistal center of the canines will result in contact point error and slight rotation of the teeth as the mid developmental ridge of upper and lower canines lies slightly mesial to the mesiodistal center of the teeth and is more mesial in case of lower canines. So bracket is placed slightly off center and toward mesial, in case of canines (Figure 7.2).

Roth 2 purposed that premolars brackets should be placed at area of maximum convexity which is usually the mesiodistal center of the teeth and mid developmental ridge also lies in this area. Sometimes the area of maximum convexity lies slightly mesial to the mesiodistal center but degree of mesial deviation is less than that of canines. The difference between bracket placement on premolars and anterior teeth is presence of a lingual cusp on premolars which must be taken into consideration while placing the brackets. In mandibular premolars the buccal and lingual cusps lies at the same level in the mesiodistal perspective. So when placing lower premolars brackets the scribe line of the bracket should coincide with line connecting the buccal and lingual cusps (Figure 7.3).

154

Maxillary Premolars Bracket placement on maxillary premolars is

A

C

B

D

Figure.7.4 A. Keeping the buccal and lingual cusps of maxillary premolars in the same mesiodistal perspective will cause poor occlusal results. B&C. When the buccal cusps tip of the maxillary premolars are in line with lower embrasures their lingual cusps lies slightly mesial to embrasures and rest at their corresponding teeth fossas. D. A bracket bonded slightly mesial to line connecting the buccal and lingual cusp of maxillary 2nd premolar. Bonding the bracket in this position will rotate the buccal cusps distally and lingual cusp slightly mesial to get ideal relationship in a class I molar relationship.

155


Figure 7.3 A left lower 2nd premolar bracket bonded so that the line connecting the buccal and lingual cusps passes through the scribe line of the bracket. This is because buccal and lingual cusp of the lower premolars should be present at the same level in mesiodistal perspective.

different from mandibular premolars as maxillary premolars should have slightly rotated position at the end the treatment. According to Andrew six keys of normal occlusion the buccal cusps of upper premolars should have a cusp embrasure relationship with lower premolars while the lingual cusps have cusp fossa relationship with lower premolars in class I & II molar occlusion. So if the buccal and lingual cusp are in one line in the mesiodistal perspective than both buccal and lingual cusps will have a cusp embrasure relationship with lower dentition. Such a relation is not acceptable (Figure 7.4A). According to Andrew1 the buccal cusps of upper premolars should be slightly more distal than the lingual cusps in the mesiodistal perspective (Figure 7.4A&C). So in maxillary premolars, brackets should be placed so that the scribe line of the bracket is slightly mesial of up to 0.5 mm to the line connecting the buccal and lingual cusps (Figure 7.4D ).


CHAPTER

E

7

F

Figure.7.4 E &F Like class I in class II molar finished cases maxillary premolar buccal cusp is slightly distal to lingual cusp in mesiodistal perspective to give ideal occlusal relationships.

According to McNamara3 such a position will also help to improve class I & II dental relationships (Figure 7.4 E&F). For class III molar finished cases though there are no guidelines available in the literature but my personal experience is that upper premolars should be bonded like class I cases in surgical and orthopedic treatment. But if the orthodontist is aiming class III camouflage than upper premolars bracket should be bonded slightly distal to mid developmental ridge so that the buccal and lingual cusp have same prominence in mesiodistal perspective. Such arrangement always help to improve the dental relationship in class III camouflage with final molar relationship in class III and canine relationship in class I. Maxillary and mandibular molars Conventionally bands are placed on the molars. The most suitable band is one that snugly fit the tooth. Whether molar bands or tubes are used, the optimum mesiodistal position is decided by taking the mesiobuccal cusp as reference. The mesial opening of the tube should lie below the mesiobuccal cusp at the correct vertical height (Figure7.5).

Figure 7.5 Bands placed on upper and lower molars. The mesial opening of the tube lies below the mesiobuccal cusp of the molars. The rule hold true for both 1st and 2nd molars in both arches.

checked under both direct and indirect vision .For indirect vision diagnostic mirror is used (Figure 7.6). Generally mesiodistal position of upper incisors, premolars and molars brackets is checked under indirect vision.

Checking mesiodistal position of the brackets

A

The mesiodistal position of the bracket can be

Figure 7.6 Mouth mirror used to check mesiodistal position of brackets in indirect vision. A. Upper incisors

156

Figure 7.7 A rotated maxillary 2nd premolar. As the tooth is distopalatally rotated so the bracket is placed slightly more distal than its required position.

C Figure 7.6 B. Lower incisors. C. Upper premolar and molar.

Modifications in mesiodistal position of the bracket Alteration in mesiodistal position of the bracket will alter the prescription of the bracket in terms of counter rotation. Some situations where mesiodistal position of the bracket is altered are given. Rotated teeth In case of rotated teeth the bracket should always be placed more on side of rotation in the mesiodistal plane (Figure 7.7). This overcorrected position of the bracket will result in early correction of the rotation and will also accommodate the relapse factor after debonding.

Clinical Notes Sometimes due to severe rotation or crowding the position of the tooth is such that it's not possible to place bracket at the right mesiodistal center of the tooth (Figure 7.8). In such situations the bracket should be placed as far as possible toward the mesiodistal center of the tooth or toward the rotation. A flexible wire is passed and only the brackets wings toward the rotation are ligated. At subsequent visit the tooth is usually derotated enough to place bracket at the right mesiodistal position. So the bracket is debonded and either a recycled or new bracket is rebonded at the correct mesiodistal position.

Figure 7.8 Rotated right upper central incisor. Correct mesiodistal position of the bracket is not possible on the first bonding visit due to rotation. The bracket should be placed as far mesial as possible. The mesial side of the bracket should not come in contact with left side incisor because it will hinder the full insertion of the wire and also make ligature placement extremely difficult if not impossible.

157


B


CHAPTER Clinical Notes Sometimes the tooth is rotated 180° so that the lingual side is on the labial side. Many times this form of rotation is accepted. In such situation the bracket is bonded on the side of the tooth which is facing labial or buccal (Figure 7.9).

7

improves the occlusal relation with the mandibular canine. The palatal cusp needs to be grounded to avoid premature contact with opposing dentition. Axial or long axis position of the brackets Axial or long axis position of the bracket is related to the angulation or tip of the teeth. In conventional edgewise system where there was no builtin tip, the brackets were placed angulated on the tooth. The amount of bracket angulation on the tooth was equal to the amount of tip required (Figure 7.10).

Figure 7.9 Right lower lateral is rotated 180°.The rotation was accepted and bracket placed on lingual side of the tooth which was facing labially.

Clinical Notes Another situation is maxillary lateral incisor substitution by canine. In this situation the slightly convex labial surface of canine is made flat to give it shape of lateral incisor and bracket is bonded at mesiodistal center of reshaped canine instead of slightly mesial. Placing the bracket at the mid developmental ridge area will cause poor contact point with the central incisor as canine is also reshaped mesiodistally. On premolar tooth which will become future canine the canine bracket is placed distal to the mesiodistal center of the tooth. Placing the bracket distally will rotate the tooth mesiopalatally which increases the mesiodistal width of future canine tooth, bringing the convex part of the tooth mesial so that it look similar to the mid developmental ridge of canine. This position of bracket also helps to hide the palatal cusp of premolar and

Figure 7.10 Standard edgewise brackets has no builtin tip. Bracket position didn't follow long axis of the crown or root and were placed angular on the tooth equal to the amount of tip required.

In preadjusted edgewise system as the tip is already built within the brackets so placing the bracket similar to standard edgewise will result in increase or decrease of builtin tip. In preadjusted edgewise system brackets are positioned on the tooth so that their wings and scribe line are parallel to long axis of clinical crowns or long axis of the tooth (Figure 7.11). But there is always some difference between the angulation of long axis of the crown and long axis of the tooth in the mesiodistal plane (Figure 7.12). Also placing bracket according to long axis of tooth may result in wrong mesiodistal

158

Figure 7.12 There is always some difference between long axis of clinical crown and long axis of the tooth.

B

C Figure 7.11 A&B. A preadjusted bracket of maxillary left lateral incisor .Placing the bracket parallel to long axis of clinical crown will cause tooth to rotate in a clockwise direction and express the builtin tip. C. Bracket placed so that long axis of the tooth is parallel to long axis of bracket wings and scribe line.

position of bracket on the crown. Andrew purposed1, 4 that as the clinical crown is only visible in the mouth so the angulation of the tooth should be taken by taking the angulation of long axis of clinical crown (LACC) and not the long axis of the entire tooth. But taking only the long axis of clinical crown may result in poor root parallelism and in some cases root resorption due to roots approximation of adjacent tooth (Figure 7.13).

159

Figure 7.13 A lateral incisor bracket placed with reference to long axis of clinical crown. X ray showing that long axis of bracket not coinciding with long axis of the root and because of this root of the lateral incisor is in close contact with central incisor root increasing chances of root resorption in this area.

So brackets should ideally be placed by taking the clinical crown as reference but root position should also be kept in mind. If there are chances of adjacent root resorption by taking clinical crown as reference then bracket position should be modified and long axis of the tooth should be


A


CHAPTER taken as reference. Taking the long axis of tooth can many a time results in poor proportions of connectors and embrasures (Figure 7.14). These proportions can be corrected at end of treatment either by composite build up or interproximal reduction.

7

Clinical notes Some clinicians also take incisor edge as guideline for long axis positioning of brackets. But incisor edge is mostly uneven due to trauma, attrition and mamelons. So incisor edge shouldn't be taken as a reference point for long axis position of the bracket. Also gingival zenith shouldn't be taken as a reference for long axis position of the bracket as it can be effected by uneven pattern of gingival recession (Figure 7.15). Importance of axial position of brackets

A

B

Correct axial position of the bracket is very important for proper occlusal and esthetic relationship. As preadjusted brackets have built in tip, a poor axial position of the bracket will result in expression of increase or decrease positive or negative tip. Increase in tip may increase space requirement in the arch and also increase risk of adjacent root approximation (Figure 7.16). Change in tooth angulation will also affect the golden proportions of connectors and embrasures and so the smile esthetics of the teeth. Checking axial position of brackets The axial position of the brackets is checked under both direct and indirect vision. Usually maxillary anterior brackets and mandibular brackets are checked under direct vision from labial side of the tooth while maxillary posterior brackets are checked under indirect vision using diagnostic mouth mirrors.

C Figure 7.14 A. Golden proportion of connectors that ideally should be present in finished cases. B .A case with dilacerated central incisor root. If there is root dilacerations, placing bracket by following the clinical crown will result in ideal connector areas but greater chances of root approximation and so root resorption. C. Bracket placed by following the long axis of the roots. The golden proportion of connectors is distorted. They can be resorted by composite built up or interproximal stripping at the end of treatment.

If there is doubt in position of maxillary anterior brackets especially lateral incisor brackets some clinicians favor to use indirect vision by diagnostic mirror and use guidance from lingual side of tooth. Modifications in axial position of brackets Modifications are made in axial position in the

160

B

C

Figure 7.15 A. Mamelons on central incisors. These mamelons will give a different long axis position of the tooth if taken as reference for bracket positioning. B. Attrition of the incisor edge will also effect long axis position of the teeth. C. Gingival zenith shifted mesial from their ideal position due to gingival recession. Taking gingival zenith as reference for axial position of the bracket in these cases will result in wrong placement of the brackets.

A

B

C

Figure 7.16 A&B. Preadjusted brackets not placed in accordance with long axis of the tooth will result in increase or decrease expression of tip than the built in tip. C.A x ray showing that both decreased and increased tip of incisors due to angular bracket placement. This increases chances of root approximation and root resorption. D&E. Over angulated brackets placed on central incisors can result poor proportion of connectors and embrasures leading to development of black triangles.

E following circumstances. 1. To avoid chances of root resorption due to adjacent root approximation.

achieving golden proportions of connectors and embrasures.

2. To avoid root resorption from dental or orthodontic implants (Figure 7.17).

5. In some surgical cases bracket position is modified to move roots away from surgical site (Wassmound procedure in maxilla, Subapical osteotomy).

3. To avoid root resorption from teeth impacted in the bones. i-e impacted canines or mesiodens (Figure 7.18, Case example 7.1).

6. If teeth have slightly smaller size such as peg laterals than it is better to increase the angulation of the teeth rather then to go for composite build ups.

4. To accommodate crown morphology for

161

D

Vertical position of brackets


A


CHAPTER

7

From the time of bracket evolution till date, orthodontists have much debated the vertical position of the bracket but have failed to reach a consensus to lay down a uniform protocol.

Figure 7.17 Orthodontic implants inserted for intrusion of maxillary incisor. Note the position of lateral incisors at both ends. The gingival wings of the brackets are facing distal so they will rotate both lateral incisor roots toward mesial. Initially such bracket placement will create space for implant insertion and during intrusion it will ensure that roots of lateral remain away from implants. Once the intrusion is completed and the implants are removed, bracket position is corrected so that lateral incisor have optimum angulation.

Angle5 proposed that bands should be placed on the tooth where they best fit mechanically and bracket soldered to bands should be present on center of the labial surface of the tooth. For anterior teeth6 bands should be present at the junction of the middle and the incisal thirds of the crown. When bonding was made available, edgewise and Begg brackets were placed on tooth with help of gauges 7 , 8 using one standard measurement for all the patients. The vertical positioning errors were corrected by wire bending which was integral part of the treatment. With the advent of straight wire appliance 9 vertical position of the bracket gained more importance. As morphology of tooth is not uniform throughout its length changing the vertical position of the bracket will result in different expression of its builtin prescription. Almost every orthodontist who devised a bracket prescription also has advocated a certain vertical position for those brackets so that the builtin prescription should be fully expressed. Different guidelines for vertical position of the brackets are given. Some commonly used systems are explained in detail so that the readers should have clear knowledge of positioning bracket at the right vertical height. Andrew Guidelines for bracket placement. Andrew1 proposed that an ideal bracket siting site should have the following properties.

Figure 7.18 A mesiodens present between roots of the upper central incisors. Brackets are placed so that wings of the brackets are facing mesial on gingival side. This will rotate both the central incisors roots away from mesiodens and will give good access to surgeons for removing it without causing any damage to central incisor roots. The bracket position needs to be corrected after mesiodens removal otherwise black triangle will result in central incisors.

1) It should be free of occlusal and gingival interference. 2) The brackets siting site on a tooth should have consistent angular relationship with its occlusal plane and to the occlusal plane of

162


A

B

Case Example 7.1 .A 16 year old patient was presented with bilateral palatally impacted canines with class II subdivision left molar relationship on a moderate class II skeletal base. Right upper 1 st premolar and left upper 2nd premolar were having mesial directed dilacerated roots. Extraction of both 1st premolars in maxillary arch and only right 1st premolar in mandibular arch was planned. Initial records are given here. A. At first bonding visit bands were placed first and all maxillary arch brackets were bonded according to wire guidance of 0.019”x0.025” wire. First order bends were given for better placement of brackets. Placing brackets on wire guidance will avoid long phase of leveling and alignment before canine exposure and also root of the teeth will remain at their place. Upper 1st premolars were not bonded as they will need extraction while maxillary laterals were not bonded because their roots are close to impacted canines. B. Once the canines were exposed and erupted both lateral incisors and canines were bonded too. Bracket position of all upper teeth was corrected .Segmental technique used in lower arch to relive lower incisor crowding and help midline correction. Continued

163


CHAPTER

7

C

D

E

F

H

G

I Case Example 1 continued C&D. Rectangular wire in place .Central incisors have poor proportion of connectors even their roots have ideal angulation and brackets are place according to long axis of the clinical crown.E.Central incisor brackets were repositioned so that gingival part of the bracket is more mesial than incisor part.This will move the connectors down and will decrease the incisal embrassure.Mild stripping of mesial side of central incisors was also done to avoid black triangles. F,G,H&I. Post treatment records are given. Maxillary incisor dentition have ideal proportions of connectors. In OPG there is good root parallelism. The root of maxillary left 2nd premolar is close to canine because of dilaceration.

164

3) When the teeth are ideally positioned, the middle of each bracket site must be at the Andrew plane, where Andrew plane is a surface plane on which mid transverse plane of every crown in an arch will fall when the teeth are optimally positioned. The FA point was found to contain all these three characteristics. Where FA point (facial axis point) is center of facial axis of clinical crown (FACC) and it virtually divides the clinical crown into occlusal half and gingival half. The FACC on each tooth correspond to mid-developmental ridge and in case of molar it is dominant vertical buccal groove. A description of FACC, FA point and Andrew plane is given in figure 7.19.

Figure 7.19

In some of his old writings Andrew 9 also proposed using LA point (long axis point) for bracket positioning, where LA point is the mid of long axis of clinical crown (LACC).Though Andrew1 later disown LACC and LA point but amazingly description of LACC or FACC remain the same in Andrew writings that was mid developmental ridge and dominant vertical buccal groove in case of molars. Andrew from one of his study concluded that clinician can easily visualize the center of clinical crown and only need eye gauging for accurate vertical and mesiodistal bracket placement. In Andrew recommended technique FA point is valid for healthy teeth. In case of

165

gingival recession Andrew1 quoted Gargiulo study10 that 1.8 mm should be subtracted from anatomical crown to find the correct value of clinical crown. This measurement must be adjusted while placing bracket at FA point in cases with gingival recession. Andrew 1 proposed that bracket must be accurately placed within 2° of FACC and base point or middle of the bracket should be within 0.5 mm of FA point. Limitations of Andrew's Recommendations Placing brackets with only guessing the correct position will result in vertical positioning errors. Not every orthodontist will place the bracket at the same height. Even the same orthodontist, after accidental debonding of bracket will rebond the bracket at a slightly different height. There would always be a controversy between two orthodontists on the right vertical height. Placing bracket is also troublesome in gingival recession and gingival enlargement as vertical adjustment in bracket height in millimeters is again a matter of guesswork. Also no consideration was given for incisal and occlusal edges which are functional and esthetic units of teeth. Even an error of 0.5 mm in anterior teeth is noticed by esthetic conscious patients. Eliades11 found out that positioning bracket at FA point results in marginal ridge discrepancy and poor occlusal contacts. Roth Guidelines Roth12 like Andrew also proposed center of clinical crown for ideal bracket placement to be used with his prescription. However Roth 13 advocated that for his prescription anterior brackets should be placed slightly more incisor than Andrew proposed center of clinical crown or FA point to level the curve of spee. According to Roth the upper central and lateral


arch when all the teeth are ideally placed.


CHAPTER incisor should either be at the same level or lateral incisor should be 0.5 mm less prominent than central incisor. The central incisors will elongate 0.5 mm to 1mm more than the lateral incisors after settling. Maxillary canine should be 1 to 1.5 mm below the occlusal plane while mandibular canine should be 0.5 to 1 mm above the occlusal plane. The upper and lower canines also should be 1mm more prominent than lateral incisors and bicuspid. Most variation in bracket position are found in bicuspids. In bicuspids the bracket should be placed at area of maximum convexity which in most cases is center of clinical crown. In case of increase curve of spee the lower canine brackets should be placed more occlusal than the premolar brackets to avoid future wire bending to level the curve of spee.

7

Table 7.1. Speed Bracket position guide for Roth prescription Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar

Maxilla 4 mm 4 mm 4.5 mm 4.5 mm 4.5 mm 4 mm 3.5 mm

Mandible 4 mm 4 mm 4.5 mm 4.5 mm 4.5 mm 4 mm 4 mm

the most variable in the arch so premolar bracket height (X) should be taken as reference .All the other brackets are placed with reference to premolar bracket height (X). To find premolar bracket height, premolar clinical crown height is taken and is divided into half. The premolar normal bracket height (X) is usually 4.5 mm. The chart for bracket height measurement is given (Table 7.2).

Limitations Roth recommendations are good to attain a functional occlusion but merely guessing the right height while placing brackets with such accuracy in millimeters is usually not possible. Roth recommendation has same limitations in vertical accuracy of brackets as of Andrew's recommendations. To overcome vertical positioning errors many clinicians uses gauge to place bracket using Roth guidelines. According to Roth canine or premolar teeth should be taken as reference while placing brackets. A bracket positioning chart (table 7.1) advocated for speed brackets having Roth prescription is given. No reference is found in literature whether this chart is supported by Roth or it's just manufacturer recommendation. Alexander Guidelines

Table 7.2. Alexander Bracket placement chart with Premolars (X) taken as Reference Teeth Central incisor Lateral incisor Canine Premolars 1st Molars 2nd Molars

Maxilla =X X-0.5mm X+0.5mm X X-0.5mm X-1mm

Mandible X-0.5mm X-0.5mm X+0.5mm X X-0.5mm Not given

Limitation of above chart Premolars in upper and lower arch were bonded at same height. As 1st premolars cusps are longer than 2nd premolars especially in lower arch so bonding all the premolar at the same height will result in marginal ridges discrepancy and premature occlusal contacts. Also no value was given for lower 2nd molars. To correct these discrepancies Alexander15 modified his bracket positioning chart (Table 7.3).

Alexander 14 advocated individualizing bracket positioning for each patient to effectively use his bracket prescription. According to Alexander as premolar clinical crown height is

166

Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molars 2nd Molars

Maxilla =X X-0.25mm X+0.5mm X X-0.5mm X-0.5mm X-1.5mm

Mandible X-0.5mm X-0.5mm X+0.5mm X X-0.5mm X-0.5mm X-0.5mm

X=4mm for small crown and 4.5 mm for average crown and 5 mm for large size crown. In case of 1st premolar extraction 2nd premolar is taken as reference. Alexander advocated specific positioning gauges for bracket placement. For ideal smile arc relationship Alexander proposed that maxillary lateral incisors brackets should be placed 0.25 mm more incisal from central incisor. Limitations Alexander bracket positioning chart though help to level incisor edges and give good anterior aesthetics but taking premolar clinical crown height as a reference mean the clinician is denying all the variations in other teeth clinical crown heights and morphology. Taking half the height of clinical crowns in premolars may result in marginal ridges discrepancy and occlusal interferences. Wire bending is usually needed to accommodate height differential and settle down the occlusion. In modified chart the lateral incisor bracket position was 0.25 mm more incisal than central incisor. In my personal opinion it is extremely difficult to place bracket with 0.25 mm accuracy even with the help of gauge because of the play between slot supporting part of the gauge and slot of the bracket. Interestingly the Wick stick gauge developed by Alexander as far as I know is not calibrated in 0.25 mm difference between its parts. In modified Alexander bracket positioning chart upper 2nd molar height is 1 mm greater than 1st molar. This

167

Table 7.4. Bishara bracket placement chart Teeth Maxilla Mandible Central incisor 4mm 3.5mm Lateral incisor 3.5 mm 3.5mm Canine 4.5 4.5mm Premolars and 4 4.0mm Molars

can create marginal ridge discrepancy between the maxillary molars in many cases. Bishara vertical bracket positioning chart Bishara16 recommended a vertical bracket positioning chart (Table 7.4) for ideal bracket positioning. The charts consist of standard measurement which would be used for all types of cases. Bracket positioning gauges are used to place the brackets. Placing brackets from fixed distance from incisors and occlusal edges will give good anterior aesthetics. Limitations As the method contains a standard chart for all types of cases so it fails to address individual variations. Also it's a matter of common clinical experience that molars cusps are smaller than premolars. Placing brackets at the same height will result poor marginal ridge relations and opposing occlusal interferences. Gu ZX17 found that to level marginal ridges 2nd premolar bracket height should be 0.5 mm greater than 1st molar and 1st premolar bracket height should be at least 0.5 mm greater than 2nd premolar so using Bishara chart will leave marginal ridge discrepancy. McLaughlin or MBT vertical bracket positioning chart McLaughlin 18 after conducting four different studies on crown height proposed his own method of bracket positioning. The method consist of measuring crown heights, matching obtained values with McLaughlin proposed charts formulated from his study and placing brackets by special gauges.


Table 7.3.Alexander Bracket placement chart with 1st Premolars (X) taken as Reference


CHAPTER The method is given as follow: 1) Measure the clinical crown height of fully erupted teeth on the upper and lower study cast by dividers and millimeter rulers. 2) To obtain middle of clinical crown divide the measured height of each crown into half and round the obtained value to the nearest 0.5mm.For example if crown height is 10.75mm.Half the crown height would be 5.4 mm. Make this measurement to 5.5 mm. 3) Create separate rows of measurements for maxillary and mandibular teeth. Now compare your values of maxillary and mandibular teeth with that of proposed charts. If your chart measurement don't exactly tally with that of proposed MBT charts then find a row on the chart which matches most of your recorded measurements. 4) After a specific row is selected, each for maxillary and mandibular teeth, position the bracket following the standard bonding procedure. 5) Place the bracket on tooth in the mesiodistal and vertical middle of clinical crown by visualizing it. After placing the bracket on the tooth use the bracket positioning gauge (advocated special gauges made by 3M Unitek) to adjust the height of the bracket. By firmly positioning the bracket, cement flash will be squeezed from underneath the bracket. Remove the flash and cure the brackets. 6) Light cure cements are preferred for brackets bonding because they give longer working time. Charts for vertical bracket positioning are given (Table 7.5-7.8).In charts average values for children and adults are also given. In children the average values are 0.5 mm less on all teeth than corresponding values for adult teeth.

7

Table 7.5.Recommended bracket positioning chart for maxillary arch(mm) Cent ral

Late ral

Cani ne

6 5.5 5 4.5 4

5.5 5 4.5 4 3.5

6 5.5 5 4.5 4.0

1st Prem olar 5.5 5 4.5 4 3.5

2nd Prem olar 5 4.5 4 3.5 3

1st Mo lar 4 3.5 3 2.5 2

2nd Mo lar 2 2 2 2 2

Table 7.6.Recommended bracket positioning chart for mandibular arch (mm) Cent ral

Late ral

Cani ne

5 4.5 4 3.5 3

5 4.5 4 3.5 3

5.5 5 4.5 4 3.5

1st Prem olar 5 4.5 4 3.5 3

2nd Prem olar 4.5 4 3.5 3 2.5

1st Mo lar 3.5 3 2.5 2 2

2nd Mo lar 3.5 3 2.5 2 2

Table 7.7.Average values for bracket positioning In Adults Central

Lateral

Canine

1st Premolar

2nd Premolar

1st Molar

2nd Molar

5 4

4.5 4

5 4.5

4.5 4

4 3.5

3 2.5

2 2.5

Table 7.8.Average values for Bracket positioning in children Central

Lateral

Canine

1st Premolar

2nd Premolar

1st Molar

2nd Molar

4.5 3.5

4 3.5

4.5 4

4 3.5

3.5 3

2.5 2

2 2

Limitations Due to individual variation of cusps height in premolar region marginal ridges height difference is seen in finished cases as posterior bracketing is not optimum17 to level marginal ridges. Kalange method Ricketts19 advocated the leveling of marginal ridges in finished cases in posterior dentition. Kalange20 devised a practical method to level the marginal ridges by bracket placement.

168

Kalange method of ideal bracket placement has the following steps. 1) Select a snugly fit 1st molar band in both arches. Measure the distance from occlusal edge of molar band to its slot. In case tubes are placed on the molars instead of bands then draw a line on the buccal side of molars connecting its mesial and distal marginal ridges. The slot of the tube lies 2 to 2.5 mm below molar marginal ridge line. The lines are drawn on dental cast in case of indirect bonding or on the natural teeth in case of direct bonding with a thin pencil.(Figure 7.20)

Figure 7.20 Horizontal lines drawn on the molars. Lower line is the marginal ridge line while the upper line is slot line for molar tube.

2) Join the mesial and distal marginal ridge of premolars on the buccal side in upper and lower cast. Draw another line gingival to this marginal ridge line. The distance between these two lines should be equal to the distance measured from the molar band edge to its slot or in case of tube it should be 2 to 2.5 mm (Figure 7.21). This second gingival line is called the slot line. The bracket slot of premolar brackets should be coinciding with this slot line. Mark a line in the mesiodistal center of the tooth following long axis of clinical crown. The wings and

169

Figure 7.21 Marginal ridge line, slot line and long axis line on the 1st and 2nd premolars.

scribe line of the brackets should be parallel to this line for axial correction of bracket. 3) Measure the distance from cusp tip of premolars, ideally from 1st premolars in both arches and transfer it to respective arch central incisors taking the incisor edge as reference point (Figure 7.22). So the slot line of premolars and central incisor are at same distance from cusp tips or incisor edges. This distance should ideally be 4 mm for mandibular incisors and 4.5 mm for maxillary incisors. For open bite cases this distance should be increased from the incisor edge for incisor bracket placement and for deep bite cases this distance should


Kalange though favors indirect bonding but his technique of bracket positioning can be used in direct bonding too.


CHAPTER

7

center incisors. 4) The maxillary lateral incisors slot line should be decreased by 0.5 mm from the incisor edge while for mandibular lateral incisor slot line distance should be same as

Figure 7.22 Bracket height of central incisor taken from 1st premolar slot line.

be decreased from the incisor edge. Vertical line showing the long axis of clinical crown is also drawn in mesiodistal center of the

Figure 7.24 on the tooth.

Canine bracket slot line measured and drawn

central incisors (Figure 7.23). 5) The maxillary and mandibular canines slot line distance should be 1 mm more from their respective central incisor slot lines. In case of canines the canine tip should be taken as reference (Figure 7.24). 6) Vertical lines are also drawn on all the teeth to mark the mesiodistal middle of the crown. Limitations of Kalange method Figure 7.23 In maxillary arch distance from the central incisor edge to slot line is measured and is decreased 0.5 mm. This distance is then transferred to the maxillary lateral incisor. In mandibular arch central and lateral incisor are bonded at same level.

Kalange method is good to level marginal ridges and give good anterior aesthetic by placing anterior tooth edges at optimum level.

170

In using Kalange method of bracket positioning for direct bonding lines are drawn by pencil on the teeth. Some clinicians point out that these Figure 7.26 The proximal edges of the band which correspond to the molar marginal ridge are usually at different height than their buccal counterparts.

accommodated in final calculation or it is a better option to draw marginal ridge line and slot line on molars too even a band is to be placed on molars. Modified Kalange Method

Figure 7.25 Lines drawn on the labial surface of the teeth can give good indication of bracket orientation without passing through the bracket sitting area.

pencil lines on the teeth will interfere with bond strength. To contour this problem slot line and vertical line should not cross the final bracket sitting area (Figure 7.25).Even if these lines don't cross the bracket sitting area they give a realistic guidance for correct orientation of brackets. Selecting the height from molar band edge to slot can also result in vertical positioning errors. Most of the companies make molar bands with occlusal proximal edges which lie next to marginal ridges more gingival than buccal and lingual edges (Figure 7.26). This variation is more pronounced in upper arch. As these are proximal edges of the band that must be in level with the marginal ridges so distance from buccal edge will result in faulty bracket positioning. Either height difference between buccal and proximal edges should be

171

I use a personally devised modified method in which molar and premolar brackets are bonded with respect to marginal ridges and instead of transferring 1st premolar height to central it transferred to lateral incisor in maxillary arch. A MBT advocated gauge is used to transfer closet height from 1st premolar to lateral incisor. Central incisor and canines are bonded at same height. In lower arch 1st premolar height is transferred to both central and lateral incisors and canine tip are kept 0.5 mm more prominent. Viazis guidelines Central incisors brackets are taken as reference. Both maxillary central incisor bracket (X) and mandibular central incisor bracket (Y) are placed at FA point which is center of clinical crown. The distance from the incisor edge to FA Table 7.9.Viazis (Bio efficient brackets ) Vertical position guide 20 Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar

Maxilla X mm X-0.5mm X+1mm =X mm =X mm X-0.5 mm X-1 mm

Mandible Y mm =Y mm Y+1 mm =Y mm =Y mm Y-0.5 mm Y-1 mm


But this method ignores individual variation in crown height of anterior teeth. Placing anterior brackets too incisal or gingival will result in different torque expression than builtin bracket torque due to morphological variations of the teeth.

7


CHAPTER Table 7.10.Gianelly Vertical Bracket position guide Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar

Maxilla 4.5mm 4mm 4.5mm 4mm 4mm 3.5mm 3mm or 3.5 mm

Mandible 3.5mm 3.5mm 4mm 4mm 4mm 3.5mm 3mm or 3.5 mm

Table 7.11 Terrell L Root(Level Anchorage system ) Bracket position guide 21 Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar

Maxilla 4.5mm 4mm 5mm 4mm 4mm 3.5mm

2nd Molar

3mm

Mandible 4mm 4mm 4.5mm 4.5mm 5mm 4mm to center 3mm to mesial

Table 7.12.John T Lindquist(Lewis Brackets) position guide 21 Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar

Maxilla 4.5mm 4mm 5mm 4.5mm 4.5mm 3.5mm 3.5mm

Mandible 4mm 4mm 4.5mm 5mm 5mm 4mm 4mm

Table 7.13.By William Thompson21 Modern Begg four stages light wire appliance Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar


Mandible 3.5mm 3.5mm 4mm 3.5mm 3.5mm 3.5mm 3.5mm

Table 7.14.System used with Begg Appliance 22 Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar

Maxilla and Mandible 3.5 mm 3.5mm 4mm 4mm 4mm 5

Table 7.15.Bracket position used for tweed philosophy 17 Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar


Mandible 4mm 4mm 5mm 4.5mm 4.5mm 4.5mm 4.5mm

Table 7.16.Swain Bracket position guide 23 Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar 1st Molar 2nd Molar

Maxilla 3.5 mm 3.5 mm 4.5 mm 3.5 mm 3.5 mm 3.5 mm 3 mm

Mandible 3.5 mm 3.5 mm 4 mm 3.5 mm 3.5 mm 3.5 mm 3.5 mm

Table 7.17.Ormco bracket (Bios Brackets) position guide Teeth Central incisor Lateral incisor Canine 1st Premolars 2nd Premolar

Maxilla 4.4 mm 3.8mm 4.4mm 4.1mm 3.6mm

Mandible 3.9 mm 3.9mm 4.6mm 3.9mm 3.9mm

Table 7.18.Mcnamara Recommendations McNamara 3 proposed that bracket should be placed on maxillary incisors at 3.5 to 4mm from incisor edge. Maxillary central incisors and canines should be at one level while the lateral incisors should be placed 0.5mm more incisal. In lower arch brackets are placed slightly incisal than middle of the tooth.

172

point is measured. Rest of the brackets are placed with reference to these brackets at proposed distance (Table 7.9) with the help of bracket positioning gauges. Some other bracket positioning charts recommended with time are given. Modifications in Vertical position of the brackets The vertical position of the bracket is altered under some circumstances to give proper occlusion and aesthetic at the end of treatment. Some clinical scenarios where alteration in vertical position of the bracket is recommended are given below. 1. Openbite

173

In openbite cases if the plan is to nonsurgically treat the case, then it is advised by many clinicians that bracket position should be modified to close the bite. This is done by placing the brackets more gingival on the tooth which are in openbite. In most case of openbite, only maxillary anterior teeth are contributing to openbite and so bracket position alteration

should be done in maxillary arch only. But if mandibular arch has a reverse curve of spee then bracket position alteration should also be done in mandibular arch too. Different rules for bracket placement in openbite case have been advocated by different clinicians. Only MBT and Alexander guidelines would be given here. Alexander 14 proposed that for anterior open bite cases teeth which are in open bite should be bonded 0.5mm more gingival while teeth which are in occlusion should be bonded 0.5mm more occlusal. While in MBT system it has been proposed that teeth which are in open bite should be bonded 0.5 mm more gingival than their prescribed position. Rests of the brackets are bonded at their normal height. Case examples for anterior openbite are given in case examples 7.2-7.4. 2. Deep bite In deep bite cases brackets are bonded following opposite rules of openbite cases. In MBT system teeth which are in deep bite are bonded 0.5mm more incisal while in Alexander discipline teeth which are in deep bite are bonded 0.5 mm more incisal while other teeth are bonded 0.5 mm more gingival (case example 7.5). 3. Irregular incisor edges If there are irregular incisor edges or long cusp tips the clinician has 3 options to manage the situation. 1. Recontouring of the incisor edges or cusp tips before bracket placement. 2. Recontouring of the incisor edges or cusp tips at end of treatment. 3. Composite filling of the incisor edges and cusp tips. Ideally teeth should be recontoured previous


Table 7.19.Burstone method Burstone 24 proposed that maxillary posterior attachments should be placed as far gingival as possible without the bracket impinging the gingiva. This is usually 3.4 to 4mm. The final position of upper canine tip should be 0.5 to 1mm more occlusal to bicuspids while the maxillary central incisor are at the same level of bicuspids. The maxillary lateral incisor edge is 0.5 mm gingival to central incisor. The first molar bracket is attached so that its marginal ridge is leveled with bicuspids while second molar bracket is attached so that its marginal ridge is level with 1st molars. In mandibular dentition the incisor and bicuspid are at the same level while canine tip is 0.5 to 1mm occlusal .Molar attachment are done similarly like maxillary arch with leveling the marginal ridges.

7


CHAPTER

Case Example 7.2 Anterior openbite in an adult patient. The openbite has both dental and skeletal component. Dentally the openbite is contributed by upper and lower anterior teeth. The case was planned by upper 1st and lower 2nd premolar extractions. In upper arch as only the anterior teeth are contributing to openbite so brackets are positioned 0.5mm more gingival from canine to canine in maxillary arch in MBT system. In lower arch only the incisors are contributing to openbite so incisor brackets are bonded 0.5 mm more gingival than its calculated values on MBT charts. If Alexander charts are used to bond the same case the same rule will follow on upper canine to canine and lower incisors. But bracket position is also altered in posterior dentition. In both maxillary and mandibular posterior teeth which are in occlusion, brackets are bonded 0.5mm more occlusal.

Case Example 7.3 A n adult patient with skeletal openbite. The case was to be treated nonextraction and surgically by differential maxillary impaction and mandibular setback. No alteration in bracket position was done but mechanics were changed. In lower arch continuous archwire was used while in maxillary arch wire bending was used to divide upper arch into 3 segments. Canine to canine and premolars to 2nd molars on both sides. In surgical cases no dental camouflage of openbite is done by varying the bracket position.

174

Placement of orthodontic brackets Case Example 7.4 An openbite case treated with upper 1st and lower 2nd premolar extraction. In this case the upper incisor were composite build up and all the brackets from 2nd premolar in upper and 1st premolar lower arch were bonded 0.5mm more gingival while the 1st and 2nd molar tube were bonded 0.5 mm more occlusal in accordance with Alexander guidelines. If one follow McLaughlin guidelines molars would be bonded according to chart values while all other teeth would be bonded 0.5 mm more gingival.

Case Example 7.5 Deepbite A patient with class II div 2 having deepbite. The case was planned with extraction of upper 1st premolars. At initial bonding only upper arch was bonded. In deepbite cases it is usually not possible to bond lower arch at the start of treatment without raising the bite. In this case instead of raising the bite maxillary incisors were initially proclined to attain their normal inclination. Brackets were bonded using MBT system. Brackets on maxillary six anterior teeth were bonded 0.5mm more incisal than their advocated position on the chart. Once the maxillary incisors were proclined and bite was sufficiently open to place lower brackets lower anterior six brackets were also bonded 0.5 mm more incisal from there recommended position on the chart. All posterior brackets in both maxillary and mandibular arches were bonded at their recommended height.

175

7


CHAPTER

Case Example 7.6 Irregular incisor edges An adult patient with missing right lower 1st molar with class II molar relation bilaterally. The case was planned with extraction of upper 1st molars. As the right upper central incisor edge is rounded it was made flat at start of the treatment and all the brackets were bonded according to my personal modified method combining Kalange and McLaughlin method.

Case Example 7.7 Irregular incisor edges A young patient with severe skeletal class II. The patient was given a hybrid twin block. The left maxillary central incisor in this case was broken because of trauma. Instead of reshaping the incisor it was rebuild with composite filling .Reshaping the incisor would lead to exposure of the pulp in this case. After functional phase the brackets were bonded normal using a modified method.

176

start of treatment. Usually composite filling is reserved for cases with openbite or large broken area of incisors. See case example 7.8. 4.Long canine tip In cases where canine tip is long it's better

Case example 7.8 Irregular incisor edges A young patient presented with class II div 1 was treated with twin block and fixed braces. Incisor edges were irregular at the start of treatment. Brackets were bonded according to MBT charts but upper incisors were bonded 0.5mm more gingival. In cases where you are doubtful about final overbite it's better to leave incisor edges as such. As the overbite was ideal at the end of treatment so incisor edges were reshaped. If this case have openbite at end or minimum overbite then I would have gone for composite build up to increase the overbite.

177


to bracket placement. If teeth are recontoured previous to orthodontic treatment there is no need to alter the bracket height. But if it is planned to recontour at the end of orthodontic treatment or composite filling is needed at the end of treatment then height modification of bracket is done at the


CHAPTER

7

Case example 7.9 A case with buccally placed canine having long tip due to lack of function and attrition. Brackets were placed 1 mm more gingival and when the canine came in final occlusion the tip was rounded 0.5 mm. The extra 0.5 mm prominence of canine was kept to accommodate vertical relapse as the canine was high in the arch. Leaving the canine tip as such and going for ideal bracket placement will leave small open bite areas mesial and distal to the canine.

to place brackets 0.5mm more gingival than standard values and reshape canine tips at the end of treatment. Another option is to reshape canine tip at the start of the treatment and place bracket at its ideal position. Long Clinical Notes Placing bracket more gingival on canine will bring it down. As the canine move down the thick cingulum part of the canine come in contact with lower dentition and prevent further downward movement of the canine. It is a good clinical practice to also reshape the lingual portion of canine when extruding it otherwise poor occlusion and premature contacts will result. Case example 7.10

Case example 7.10 A case with bilateral attrition of maxillary canine. Canine brackets were bonded 0.5mm more gingival but no reduction in thickness of lingual side was done. In final occlusion lingual side of canine came in premature occlusion before the canine can settle down. Even settling elastic couldn't bring the canine down .Openbite in canine area were present due to a small mistake in an otherwise well finished cases.

In case of attrition of the canine the brackets are placed 0.5-1 mm more gingival, depending upon the severity of attrition. The canine tip is reshaped at the end of treatment.

canine tips are usually found in impacted canines or canine placed out of occlusion. Lack of attrition will leave the tip longer than usual (case example 7.9). 5. Attrition of the canine

Figure 7.27 Left maxillary lateral incisor placed high in the arch. As the lateral incisor is placed extremely high so bracket is placed 1mm more higher than recommended values of charts to accommodate the relapse factor. All other brackets are placed at their recommended heights.

178

High buccally placed teeth should be bonded 0.5 to 1mm high than their recommended position to accommodate the relapse factor. The higher the tooth is present in the arch greater the relapse factor should be added (Figure 7.27). 7. Gingival recession Individual teeth with up to 1.5mm gingival recession can be bonded more gingival so that at end of treatment their gingival margins should be at the ideal height. But incisor or occlusal edge needed to be reshaped by equal amount. In teeth with more than 1.5 mm of gingival recession an expert opinion from periodontist should be taken and many a time gingival grafting is a viable option than bracket position alteration. 8. Premolar extraction cases In MBT system for 1st premolars extraction cases to avoid vertical step at extraction site vertical height of bracket should be increased by 0.5mm on upper and lower 2nd premolars and 1st molars. In lower arch vertical height of 2nd molar should also be increased by 0.5mm. In case of 2nd premolars extraction upper and lower molars vertical height should be increased by 0.5mm.The same rule of change in vertical height in posterior dentition after premolar extraction can also be applied to other systems of bracket positioning. 9. Molar interference If there is interference in molar region McLaughlin 18 recommended that either place the bracket or tube more gingival where interference is present and give a step bend in the wire or bite blocks should be placed at the start of treatment or all lower arch brackets should be placed more

179

gingival by equal proportions. Importance of vertical position of brackets The vertical position of bracket is related to the torque of the brackets. As inclination of the teeth is measured at certain height on the labial surface of tooth and this value was built within bracket prescription so alternating the vertical position of the bracket will affect the torque of Selection of Optimum Vertical Height As so many guidelines are present for vertical height the clinicians are often confused which height should be chosen? Only Andrew advocated a vertical height where he actually developed his prescription. Unfortunately it has its own limitations. Rests of them are only clinical experiences or they are not devised by inventor of any prescription. Till the orthodontists don't agree on a single reliable and reproducible method of vertical bracket positioning the best solution is use a vertical height that is advocated by the inventor of the prescription. Experience and knowledge with time will lead many clinicians to use a modified vertical position of their own which work with certain prescription on a certain population group. the brackets. Change in vertical position will have small effects of torque on teeth which has nearly flat labial surface such as incisors while teeth with convex labial surface such as canines and premolars has profound effect on change in vertical position of the brackets. A detail description of importance of vertical position is given in chapter 6. A diagrammatic description of change in vertical height and its effects on root position is given in figure 7.28. Bracket positioning gauges Bracket positioning gauges are used to ensure vertical accuracy of brackets on the teeth. Many


6. High buccally placed teeth

7


CHAPTER

Figure 7.28 In upper row brackets are placed at different heights on maxillary central incisors. The slots of the brackets are then straightened imagining that full torque is expressed and the brackets are superimposed. Superimposition of the brackets show that brackets placed incisal will express more positive torque while brackets placed gingival will express more negative torque. In lower row a bracket was placed on a maxillary central incisor having ideal inclination of +7° with occlusal plane perpendicular and alveolar bone boundaries were stimulated. Superimposing this tooth bracket with brackets placed at different heights is shown. It is clear from the figure that small variation in bracket positioning are acceptable but large variations will cause the roots of incisor to come in contact with alveolar cortex so increasing chances of root resorption. If the root cross the alveolar cortex severe mobility of the tooth will result and extraction become necessary.

180

All bracket positioning gauges have a holding

Figure 7.29

A Boone gauge

Figure 7.32

Figure 7.30 Straight rod shaped gauges similar to Alexander Wick stick for 0.22” and 0.018” slot.

Figure 7.31 Gauges recommended in MBT system

different instruments have been recommended to check for vertical accuracy of seated brackets ranging from periodontal probes to rulers but in contemporary orthodontics two types of gauges or their variations are usually used. These are: 1. Star shaped gauges or Boone bracket gauges (Figure 7.29). 2. Straight rod shaped gauges or Dougherty gauges (Figure7.30&7.31). Most variations are found in Dougherty gauges and these are also the author favorite for bracket placement.

181

Parts of the gauges.

arm for holding the gauge with fingers during bracket positioning, a tooth supporting arm which rest on the incisor or occlusal surface of the tooth and a slot supporting arm which is seated in slot of the bracket. The holding arm is the longest part of gauges while the slot supporting arm is the shortest part of the gauges. Different slot supporting arms are available for 0.018” and 0.022” slots. Different parts of the bracket gauges are given in figure 7.32. Position of the gauge during bracket placement Positioning the gauge for checking the vertical height is very important. In an unpublished study i found out that a faulty positioning of gauge can change bracket height up to 2mm (Figure 7.33). For correct positioning the gauge should be held in hand at right angle so that the orthodontist vision should also be at right angel to the gauge. As explained before variation in position of the bracket will result in change in torque expression. Also variation of 2mm in brackets height in anterior dentition has serious implication in terms of anterior aesthetic and


Parts of gauges

7


CHAPTER

Figure 7.33 Varying the angle the gauge over tooth can change the height of the bracket which is usually in the range of 2mm. As the angle between the gauge and tooth decrease height of the bracket on the tooth increases.

Figure 7.34 A Gauge placed perpendicular to the buccal surface of the molar.

Figure 7.35 Gauge placed perpendicular to buccal surface of canine.

smile arc.

(Figure 7.34).

The gauge should always be placed perpendicular to the labial or buccal surface of the teeth. This makes the gauges parallel to the occlusal surface in all the teeth except incisors

In lower arch if the incisors are upright the gauge should be placed parallel to the occlusal plane(Figure 7.36A). But if the lower incisors

182


A

B

C Figure 7.36 A. If mandibular incisors have normal inclination the gauge is placed straight and perpendicular to the labial surface. B. If the inclinational is increased the gauge is placed below the occlusal plane. C. If the inclination is decreased the gauge is placed above the level of occlusal plane so that it remains perpendicular to orientation of labial surface of teeth.

are proclined the gauge is placed below the occlusal plane and if the lower incisors are retroclined the gauge is directed from above the occlusal plane (Figure 7.36B&C).

183

In case of upper incisors the gauge is placed slightly upward angulated usually 15° to 20° to the occlusal plane to make it perpendicular to the labial surface of the tooth as the upper incisor are slightly inclined forward over basal bone(Figure 7.37). In case class II div 1 incisor relationship where the upper incisors are proclined the gauge is angulated more upward as compared to normal incisor inclination (Figure 7.37). In case of class II div 2 the gauge lies below the occlusal plane angulated at an

Figure 7.37 Different angulation of gauge in class I, class II div 1 and 2.

angle depending upon the severity of malocclusion (Figure 7.37). Bracket placement by wire guidance In this technique all the steps of conventional bonding are done in usual way but before curing the bracket a heavy wire is passed through the bracket slot and its bonded neighboring brackets and bands. The mesiodistal position of the bracket is corrected manually while axial and vertical positions are guided by the heavy wire. If clinician want to place brackets from start of


CHAPTER treatment on wire guidance then wire guidance is usually taken by passing the wire through bands and then placing brackets on wire guidance. If no band is placed then first bracket is placed in usual way and all other brackets are placed on its wire guidance. Orthodontic brackets can be placed by wire guidance if brackets are debonded when 0.016x0.022 inch or heavier wire is in place. If brackets are placed in usual way then due to small human errors, mostly it is not possible to place the existing working wire after bracket rebonding and clinician need to move back on lighter wires. If position of bracket was correct before being debonded then same recycled or new bracket can be bonded using existing wire guidance. Brackets can also be placed on wire guidance from the start of treatment if clinician does not want to change the angulation of teeth and want to do some specific mechanics without any time delay. Such scenario is usually found in cases of impacted teeth where neighboring teeth roots are close to impacted teeth and any delay may result in increased risk of root resorption from impacted teeth. Placing brackets on wire guidance is also helpful in adjunctive orthodontics when only one tooth need uprighting to create space for future prosthesis. In such cases a heavy wire is selected and all the brackets are placed on its guidance while the tooth needing uprighting is bonded in normal way without wire guidance. Position of clinician during brackets placement In orthodontics literature very little interest has been given to position of the orthodontist for bracket placement. It is generally said that while placing brackets orthodontist should maintain a single position at which he can see the teeth at right angle. Also the head of the patient should not be moved again and again as

7

this is not comfortable for the patient. I do agree that changing chair position by the orthodontist or changing the position of the patients head is not comfortable for both the patient and the orthodontist but for good bracket positioning this need to be done. As the patient hasn't visited the orthodontist to have rest on his dental chair and also the orthodontist should set aside his comfort for his work as he is paid for it. Some positions used during bracket placement are given to clarify the readers mind (Figure 7.38). Before placing the brackets the position of the dental unit should be properly adjusted. Usually a dental unit is adjusted between 140° to 150. At this position the clinician can easily see the brackets at right angle. This setting also helps to see axial position of some brackets from 12 o' clock position. The clinician position for bracket placement given here are for right handed orthodontist. For left handed orthodontist similar positions would be used from the left side. Upper and lower incisor bracket positioning For upper central and lateral incisors, the bracket should be placed with the bracket holder on the mesiodistal and vertical center of the tooth with the clinician sitting at 8 0' clock position and the patient head tilted on his right side toward the clinician. After the bracket is placed, the height of the bracket is checked with bracket positioner. The patient head is made straight and orthodontist check it from 9 o'clock positions with the gauge at right angle to his vision. To check the mesiodistal and axial position of the bracket the orthodontist moves to 12 o' clock position and place a diagnostic mouth mirror at the incisor edge to indirectly check the mesiodistal position of the bracket. This indirect vision also help to correct the axial or long axis position of the bracket to some extent but direct vision will give an excellent picture whether the wings of the bracket and the

184


Figure 7.38 Different positions of the clinician during bracket placement. 12, 9 and 3 o'clock positions are shown.

185

bracket scribe line is parallel to long axis of clinical crown. While checking axial inclination of maxillary lateral incisors brackets it is a good practice to tilt the head of the patient to opposite side. For right maxillary lateral the patient head should be tilted toward left side and versa.

brackets. Diagnostic mouth mirror can be placed gingival to the bracket to check mesiodistal position of the bracket. Some clinician prefer to check mesiodistal and axial position of lower incisor bracket from 8 o' clock position under direct vision with patients head tilted towards the orthodontist.

The lower incisors brackets are placed in a similar fashion as upper incisors brackets. Vertical height is checked from 9 o' clock position while 12 o'clock position is used to check to mesiodistal and axial position of

Upper and lower canines Positioning of right upper and lower canines brackets is done at 9 o' clock position with the mesiodistal and axial placement checked from the same position while the vertical height of


CHAPTER the bracket is checked with gauge from 11 o' clock position. For left side upper and lower canines the brackets are placed from 9 o' clock position with the patient head tilted toward right. The mesiodistal and axial positions of brackets are checked under direct vision from the same 9 o'clock position. Upper and lower bicuspids Upper right bicuspids brackets are placed at 9 o' clock positions and its vertical height is checked with gauge from 11 o' clock position with patients head slightly tilted toward left. Many a time the cheek retractor hinders the correct positioning of the bracket positioning gauge. In such circumstances it's better to grip the retractor with left hand and slightly retract it while position the gauge so that it is at right angle to tooth long axis and to the clinician vision. Check the mesiodistal position of the bracket from 11 or 12 o' clock position with diagnostic mirror using indirect vision. This vision also gives some hint about axial position of the bracket but the correct axial position is checked from 9 o' clock position under direct vision with patient head tilted toward left. Right lower bicuspids brackets are placed on the tooth at 9 o'clock position. The vertical height is checked and adjusted from 11o'clock position. The clinician check axial and mesiodistal position of the bracket at 10 o'clock position under direct vision. Some clinician can recheck the mesiodistal position of the bracket under indirect vision by placing diagnostic mirror on occlusal surface of bracket. Upper left bicuspids are placed at 9 o' clock position with the patient head tilted toward right. The mesiodistal position is checked under indirect vision with diagnostic mirror from 12 o' clock with the patient head tilted toward right. The 12 o'clock position also give a good view for axial position of bracket under indirect vision but it's better to see axial position of bracket from 8 o'clock position under direct

7

vision with the patients head tilted toward right. Lower left bicuspid brackets are placed from 9 o'clock positions with the patient head tilted toward right. The mesiodistal and axial position of the brackets are confirmed at 8 o'clock position under direct vision. Some clinician prefer to place left side cuspids and bicuspids brackets from the left side using equivalent positions that were used on right side. Reference 1. Andrews LF. Straight-Wire-The Concept and Appliance; L. A. WellsCo., San Diego, California. 92107: 1989. 2. Graber TM Orthodontics: Current Principles & Techniques. : Mosby; 1984. 3. McNamara JA, Brudon W & Brudon L. Orthodontic and Orthopedic Treatment in the Mixed Dentition. : Needham Pr; 1993. 4. Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972 Sep; 62(3):296-309. 5. Angle HE. The latest and best in orthodontic mechanism. Dental Cosmos 1928; 70:11-43. 6. Taylor RMS. Variations in morphology of teeth. New York: Charles C. Thomas, 1978. 7. McLaughlin RP, Bennett JC, Trevisi H .Systemized Orthodontic Treatment Mechanics. 2nd ed.: Mosby; 2001. 8. Parkhouse R. Tip-Edge Orthodontics and the Plus Bracket. 2nd ed.: Mosby; 2008. 9. Andrews LF. The six keys to normal occlusion. Am J Orthod 1972; 62:296-309. 10. Gargiulo AW, Wentz FM, Orban B: Dimension and relations of the dentogngival junction in humans, J Periodontal 32:262,1961. 11. Eliades T, Gioka C, Papaconstantinou S, Bradley TG. Premolar bracket position revised: proximal and occlusal contacts assessment. World J Orthod. 2005 Summer;6(2):149-

186

12. Roth RH. Functional occlusion for the Orthodontist. Part III. J Clin Orthod. 1981 Mar;15(3):174-9, 182-98. 13. Roth RH.The straight-wire appliance 17 years later. J Clin Orthod. 1987 Sep;21(9):632-42. 14. Alexander RG. The vari-simplex discipline. Part 1. Concept and appliance design. J Clin Orthod. 1983 Jun;17(6):380-92. 15. Alexander RG .The 20 Principles of the Alexander Discipline. Chicago: Quintessence Pub.; 2008. 16. Bishara.SE Textbook of Orthodontics. Saunders; 2001. 17. Gu ZX, Duan YZ, Ding Y, Li BR, Shu L, Chen XP. Study on the height of marginal ridge to cusp in posterior teeth and its effect on brackets placement. Hua Xi Kou Qiang Yi Xue Za Zhi. 2008 Jun;26(3):271-4. 18. McLaughlin RP, Bennett JC. Bracket placement with the preadjusted appliance. J Clin Orthod. 1995 May;29(5):302-11. 19. Ricketts RM. Bioprogressive therapy as an answer to orthodontic needs. Part I. Am J Orthod. 1976 Sep;70(3):24168. 20. Viazis AD Atlas of Orthodontics: A Guide to Clinical Efficiency. : Saunders; 1998. 21. Graber TM Orthodontics: Current Principles & Techniques. : Mosby; 1984. 22. Salzman JA Orthodontics in Daily Practice. : Lippincott Williams and Wilkins ; 1974. 23. Swain BF. Dr. Brainerd F. Swain on current appliance therapy. Interview by Sidney Bradt. J Clin Orthod. 1980 Apr;14(4):250-64. 24. Burstone CJ Modern Edgewise Mechanics and the Segmented Arch Technique. : ORMCO Corporation; 1985.

187


55.


CHAPTER

7

188

CHAPTER

8

Bonding in Orthodontics In this Chapter

Tooth Cleaning Enamel Roughening or acid Etching Sealing the etched enamel surface Bonding Bonding in special circumstances Indirect bonding

Historically orthodontic brackets were soldered to bands and eventually banded to teeth. As bands need space between the contact points at time of their placement and leave spaces between teeth at end of treatment so they were not a preferred method. With the introduction of acid etching by Buonocore 1 in 1955 banding of teeth was eventually abandoned with time and is now only used on molars in cases requiring special mechanics like headgears. Extensive details about bonding are given in almost all the text books of orthodontics so only a brief review on this topic would be given here. Bonding of brackets can be done either directly or indirectly. Steps in direct bonding of bracket are given. 1. Tooth cleaning

189

2. Enamel roughening of labial or lingual surface of tooth by acid etching 3. Sealing of etched surface 4. Bonding 1) Tooth Cleaning This step is only done in patients in whom there is plaque or thick pellicle layer over the enamel surface at the time of bonding. If only pellicle is present then pumicing of teeth alone is sufficient but if plaque or calculus is also present over the enamel surface then scaling is done which is followed by pumicing (Figure 8.1).

8


CHAPTER

Figure 8.1 Pumicing teeth with a polishing paste and pumice powder.

A

Clinical Notes Pumicing before etching is controversial 2-4 if conventional etching is done but clinician should do pumicing if self-etching primer 5-7 is used. 2) Enamel Roughening or acid Etching Enamel roughening or acid etching is done to create retention areas for the adhesive on the enamel surface. Moisture control is important during this step and rest of the steps that follows. Good moisture control is provided by using cheek/lip retractors and high volume section. This arrangement of moisture control is usually sufficient in majority of the cases but in some cases where patients have increased salivary flow, special gadgets are available that combine lip/ cheek retractors, saliva ejectors and tongue guards (Figure 8.2). Cotton rolls are also used to increase moisture control. Some clinician also uses antisialogogue like atropine sulphate to create a dry field for brackets bonding. Antisialogogues can be used on patients having excessive salivary flow but evidence 8 doesn't support their routine use during orthodontic bonding. Before going for enamel conditioning enamel surface should be dried with oil free air. Enamel conditioning is conventionally

B Figure 8.2 A Nola dry field system combining all the necessary gadgets for good moisture control during enamel conditioning. This system is especially helpful in indirect bonding.

done with 35 - 37% phosphoric acid. Enamel roughening by sandblasting has also been proposed but sandblasted enamel yield lower bond strength 9-13than acid etched enamel. Sandblasting first followed by conventional etching have also been proposed but bond strength of brackets with this combination technique is controversial 14, 15 than doing conventional acid etching alone. Lasers have also been advocated for enamel etching 16-19 either alone or in combination 20 with acid etching. But due to high cost of lasers and more safer application of conventional etching the use of laser for enamel roughing is still a novel approach in orthodontics. In enamel etching with 37% phosphoric acid the acid is available in both liquid and gel form. The liquid form of the acid has

190

enamel should be frosty white after drying the etched surface (Figure 8.5). Clinical Notes Decreasing the etching time will decrease the bond strength. Ceramic brackets show decreased bond strength 21,22 when enamel surface was etched for only 20 seconds than 60 seconds etching.

A

Figure 8.4 A warm air tooth dryer by Lancer orthodontics.

B Figure 8.3 A. Acid gel used to etch lower incisors. B. Acid in liquid form. As liquid form of acid has more viscosity so there are greater chances of this acid flowing and touching the gingiva in mandibular teeth etching.

Clinical notes Some clinician prefers to use 10 or 20% polyacrylic acid etching for ceramic brackets to decrease their bond strength.

191

Etching should ideally be done for 25 to 60 seconds. At the end of etching the acid should be washed away from the tooth surface with an abundant water spray. The acid plus water spray should be immediately be sucked from patient mouth with high volume suction. The enamel surface is then dried with oil free air. Some clinicians use special warm air drier to dry the enamel surface (Figure 8.4). The

Figure 8.5 Frosty white enamel surface after drying the etched enamel surface.

Moisture control should be maintained at every cost. Sometimes due to irritation by the washed away acid patient immediately rinse after etching. If this happen or saliva comes in contact with etched surface due to other reasons the tooth surface should be dried and re-etched again for a few seconds. Clinical Notes Some clinicians recommend use of selfetching primer in case of ceramic brackets


decreased viscosity and usually flows after its application and come in contact with gingiva thus causing soft tissue irritation. Also liquid form will etch more than required enamel surface. So a gel form should always be preferred (Figure 8.3). It's always better to etch the enamel surface only on the future bracket siting area. When large area of the enamel is etched then most of the time clinician don't seal the entire area by primer and these rough surface act as future plaque retention areas.


CHAPTER to decrease their bond strength but there is no evidence 23 to support this theory. 3) Sealing the etched enamel surface The dry etched enamel surface is sealed with application of primer or bonding agent (Figure 8.6). The primer is applied to the tooth surface with the help of a primer brush. Only a thin coat of primer is sufficient to seal the enamel surface. Most clinicians then light cure the primer or bonding agent. Different types of curing lights are available in the market but LED lights in wavelength between 420-480nm are usually used (Figure 8.7). Plasma arc curing lights can do curing in least time24 but they are expensive than LED dental curing lights. A systematic review 25 found no difference between different curing lights in term of bracket failure. So any light can be selected depending upon clinician ease of use and cost effectiveness. With LED curing light, primer on enamel surface is cured for 5 seconds. Some clinicians don't cure the primer separately and after placing the bracket with adhesive on the tooth cure both the primer and adhesive together. In self-cure cements the sealant layer is cured by placement of bracket with attached adhesives. Moisture insensitive primer (MIP) and selfetching primer (SEP) are also available. In SEP etching and sealing is done in one phase.

8

A randomized control trial 29 showed that bond strength is not affected by saliva contamination in case of SEP and MIP. There is controversy 30-32on the use of sealants in orthodontic bonding but the proposed advantages are increased bond strength and prevention of microleakage under the brackets.

A

B Figure 8.6 A. A primer bottle with application brush. B. Primer applied to lateral incisor surface.

Clinical Notes Evidence 26, 27 shows that SEP can save time during clinical bonding but evidence related to increased risk of bond failure with SEP is controversial with latest limited evidence 28 showing that there is no difference between SEP and conventional etching in terms of bond failure.

Figure 8.7 A LED B curing light with wavelength between 425-490 nm.

4) Bonding After the application of sealant on the tooth

192

adhesive is applied directly from the tube to the bracket base. A thin layer of adhesive is usually used. The adhesive can be spread over the bracket base with the help of dental probe.

Figure 8.10 Composite flash present around the bracket base. This composite flash is removed with the help of a dental probe. This flash must be removed as it will act as potential plaque retention area and also will lead to gingival irritation and development of white spot lesions.

Clinical Notes Usually application of primer on the tooth surface and adhesive on the bracket base go side by side. The clinician etches the enamel surface and applies primer on it while his assistant apply adhesive over the bracket base at the same time. Adhesive precoated brackets are also available from many manufacturers. The proposed advantages of these brackets are

Figure 8.8

Applying bonding agent on the bracket base.

1.Less chair side time. 2.Better infection control. 3.Consistent adhesive layer thickness on all the brackets.

A

4.Less flash removal on bracket placement. In adhesive precoated brackets each bracket is sealed in a special packing. Due to increase cost associated with these brackets many clinicians don't find them a cost effective choice.

B Figure 8.9

193

An adhesive tube from 3M Unitek. The


surface the bracket is prepared by first wetting the bracket base with primer (Figure 8.8). Usually a thin layer of primer is applied. After the application of primer clinicians light cure the primer and then apply adhesive on the bracket surface. Some clinicians don't apply primer over the bracket base and directly apply adhesive on the base. No evidence is available to support any technique and clinicians are free to use the technique in accordance with their clinical experience. A thin layer of adhesive is usually applied over the bracket base and the brackets are placed over their proposed final position on teeth (Figure 8.9). A heavy force is usually applied from the back of bracket holder to squeeze out all the extra composite from underneath the bracket (Figure 8.10).This extra composite is called flash and it is removed from around the bracket with the help of dental probe.


CHAPTER Choice of adhesive Choosing the right adhesive for bracket bonding is very important. Luting adhesive are recommended over filling adhesive for orthodontic bracket bonding. In composite resins different commercially available adhesives are present in the market. All manufacturers claim that their adhesive provides better bond strength over other companie's products. While choosing a composite resin adhesive the orthodontist must remember that fixed braces are temporarly attached to teeth and bond strength of 5.9 to 7.8 MPa is clinically acceptable. A comparative study by Sharma 33 concluded that commercially available adhesives have higher bond strength than minimum recommended limits. Resin modified Glass ionomer cement (RM-GIC) is usually chosen for cases with amelogenesis and dentinogenesis imperfect as it is generally thought that it provide lower bond strength than composite resin but a systematic review 34 showed that RM-GIC have the same clinical bracket failure rate as composite resin adhesives after 1 year.

After the placement of brackets on the teeth usually the mesiodistal position of the brackets is checked first then the vertical usually with the help of positioning gauge and the last position that is checked and corrected is axial. For axial position checking some guidance is also taken from patient study cast and OPG. Clinical notes The position of the bracket is corrected with dental probe or interdental scaler. A common problem that is encountered while correcting the position is that bracket gets attached with the instrument if the

8

instrument or the bracket has magnetic properties. This problem is common with brackets undergone machining or milling during manufacturing (Figure 8.11). Such brackets will also offer greater friction during sliding mechanics. Brackets and instruments having magnetic properties should be avoided for good bonding. Using adhesive with increase filler contents will also prevent increase bracket movement or it's detachment from tooth during position correction.

Figure 8.11 A bracket having magnetic properties. Such brackets are difficult to bond at right position and also offer greater resistance to sliding.

Once all the positions of a bracket are checked, the bracket is cured at its place. Usually one bracket is cured for 20 seconds with LED B curing light (Figure 8.12).Mostly an orange protective cover is present over the curing light but orthodontists and his assistant should also wear protective goggles during bracket curing procedure (Figure 8.13). The patient should also be given protective goggles or he should be advised to close his eyes during the curing process. Bonding in special circumstances Etching of bleached enamel In some cases bonding of brackets on

194

Figure 8.13 curing.

Protective goggles used during bracket

previously bleached teeth is need. As decreased bond strength 35-37 have been reported with previously bleached enamel so different waiting times for bonding of brackets after bleaching have been recommended. The range of waiting time 38-40 is from 24 hours to 14 days.

Indirect bonding

Bonding on Porcelain or ceramics

In indirect bonding brackets are first individually placed on patient's dental cast and then transferred by special carrier trays into the patient's mouth. The purpose of indirect bonding is to accurately place brackets and save bonding time in clinical practice. In initial days of their introduction, indirect bonding yield lower bond strength than direct bonding but latest laboratory studies 45-47 have shown that brackets bonded by indirect and direct method have equivalent bond strength.

In orthodontic many a time porcelain crowns or veneers are present on teeth before start of

There are various techniques available for indirect bonding. The author follows Sondhi

Bonding brackets to acrylic crowns Composite resins have good adhesion with acrylic crowns. Microretention on the crowns is introduced with fluted carbide burs or roughing the crown surface with the help of a dental probe. After crown roughening most clinicians then bond bracket without the application of primer on the crown surface.

195

Sandblasting with aluminum oxide provide the lowest bond strength 41 on porcelain or ceramic veneers. Conventional etching with phosphoric acid and application of silane coupling agent 42 usually cause less enamel damage. Er: YAG lasers 41, 43 though provide optimum bond strength and minimum porcelain damage still remains a novel approach. 9.6% hydrofluoric acid alone or combination with silane coupling agents is usually used. According to Bishara44 hydrofluoric acid followed by silane coupling is the most reliable technique but this also produces the greatest damage to the porcelain surface.


Figure 8.12 Brackets cured by LED curing light.

treatment and they need to be bonded during the course of orthodontic treatment. To bond brackets, labial surface of prosthesis is needed to be roughened. Various methods used for roughening of porcelain surface are diamond burs, sandblasting with aluminum trioxide, sandblasting with silica and use of silane coupling agents, conventional etching and silane coupling agents, etching with 9.6% hydrofluoric acid, 9.6% hydrofluoric acid and silane coupling agents and use of Er: YAG lasers. No clinical trial is available in the literature on this issue and only laboratory studies are present.


CHAPTER

8

technique with few personal modifications .The technique is given as follow. Technique 1. Take an impression of patient teeth with a dimensional stable impression material and pour it in dental hard stone. 2. Apply a water soluble separating medium over the dental model. I usually prefer a cold mold seal but other water soluble products can also be used (Figure 8.14).

Figure 8.15

Bracket placed and cured over the dental cast.

Figure 8.16 Separating medium applied over the brackets to avoid adhesion of brackets to soft silicon vacuum formed tray.

Figure 8.14 Cold mold seal being applied on the maxillary dental cast with help of brush. The model has palatal coverage which ideally should not be present for good vacuum formation of trays. If present the palatal coverage should be removed on a dental model trimmer.

3. Place brackets over the dental model. There is no need to place primer on the dental stone. Place primer and adhesive on bracket in the same way as done in direct bonding or adhesive precoated brackets can be used. The brackets should be placed at the ideal location on the model and flash around the brackets should be removed. The brackets are then cured by LED curing light as light cure adhesives are used (Figure 8.15).

the brackets a 1 mm thin soft silicone tray is vacuum formed over the brackets.(Figure 8.17)

A

4. Water soluble separating media is then applied on the bonded brackets. A very thin coat of the media is applied. A thick coat will cause poor retention of the brackets in carrier tray (Figure 8.16). 5. After applying the separating medium on

B

196

C Figure 8.17 A. Palatal coverage of model trimmed for easy vacuum formation. B. Model placed in a vacuum former. C. Soft tray trimmed for easy placement of hard tray.

6. Apply a thin coat of water soluble separating media over the vacuum formed soft tray placed on the dental model. This will help in easy separation of carrier soft tray from supporting hard tray. 7. Vacuum form a 1 mm thick hard silicone tray over the soft tray. This outer hard tray will support the inner soft tray and prevent it from distortion during insertion in the mouth (Figure 8.18).

10. Light cure the base of each bracket for atleast 5 seconds so that any uncured adhesive usually left in the middle of the brackets at the initial curing is cured and hardened. 11. Wash the inside surface of the tray with tap water so that any separating medium or any other cast material is removed from the cured adhesive over the bracket base. 12. Sandblast each bracket base for 1 second, keeping 10 mm distance between bracket base and the blaster tip. Line pressure is maintained at 90 psi and 50 µm aluminum oxide sand is used. This step is done to remove any attached dental cast material over the adhesive and also to roughen the adhesive. Some clinicians instead of using sandblasting scratch the adhesive surface with dental probe. 13. Wash the trays again to remove any sand particles or other dust particles.

Figure 8.18 A 1mm thick hard tray vacuum formed over a soft tray. The yellowish tinge in the tray is that of a separating medium applied between the trays.

8. Cut both trays on the dental cast with help of cutting disc. The trays are cut on the lingual side so that it covers half of all the clinical crowns. On labial side the trays cut at level of gingival wings or hooks of the brackets if present.

197

14. Separate the two trays from each other. This can easily be done by engaging the dental probe tip between two trays and lifting the upper hard tray. This step is done to aid final cutting of the two trays and also to remove any adhesion areas between the two trays if present (Figure 8.19). Sometime the outer hard tray is so well adapted over the inner soft tray and brackets that the two trays cannot be separated. Peeling the soft tray forcefully can many times lead to removal


9. The model is then immersed in water for atleast 10 minutes to dissolve the separating media. After 10 minutes the trays along with brackets are removed from model in one piece. Usually a dental probe is used to lift the trays from the model on one side by engaging the probe between the soft tray and the model. If good separating medium was used all the brackets will remain within the carrier tray.


CHAPTER of the brackets from the soft tray. If this is the case it is better to cut the hard tray at the level of gingival wings and sometimes 0.5 mm above it to remove any undercut area. On brackets having hooks the hard tray over it should be cut at the level of mesial or gingival wing and not at the level of hook.

Figure 8.19 Hard tray separated from soft tray for final cutting and removal of any adhesion area between two trays. Trays are only of one segment of the arch.

15. Once the hard tray is removed from the soft tray, both trays are trimmed. The soft tray is trimmed with the help of scissor so that it is extended 0.5-1mm below the bracket gingival wings while the hard tray is cut at the level of gingival wings or some area of gingival wings can be left uncovered from the hard tray. The hard tray is cut with the help of cutting disc. 16. A small middle mark is cut on the hard tray which coincide with corresponding upper or lower dental midline. This midline mark will act as a reference point during trays insertion and help in correct placement of the trays. 17. If any bracket comes out of the soft tray it should be adjusted back into the tray. But if the tray has poor retention for the bracket then the bracket should be taken out and placed by direct bonding after recycling its base by sandblasting.

8

18. After both trays are trimmed to required size, the soft tray is seated within the hard tray. The clinician can practice placing the trays over the models. If such an exercise is made the trays should be washed and dried after that. The trays are now ready for indirect bonding. 19. For indirect bonding I mainly use Sondhi indirect bonding kit by 3M Unitek. This kit consists of two bottles having semi liquid solutions. The liquid is poured in separate small plastic wells provided with the kit. Liquid from bottle A is placed with a primer brush on the etched tooth surface and liquid from bottle B is placed on the bracket base surface covered with adhesive. Separate brushes are used for liquid A and B. Indirect bonding kits containing two bottle solutions are also available from many other manufacturers and clinicians can also use them according to their convenience. 20. The patient teeth are cleaned and etched similar to direct bonding. Good isolation of teeth and high volume suction is necessary as whole arch is etched in a single go. After etching and drying the enamel liquid from bottle A is pasted over all the teeth that needed to be bonded. Liquid B is pasted over the entire brackets base surface. It is better to apply liquid first over the brackets than on enamel to prevent moisture contamination or it can be applied simultaneously by taking help of an extra assistant. 21. After applying liquid over the brackets and enamel surface the trays are placed by taking guidance from mid reference mark. Once the trays are firmly seated, movement of the trays should be avoided. Finger pressure should be maintained over the trays for atleast one and a half minute or depending upon specific product recommendations (Figure 8.20). 22. After 2 minutes of trays insertion, the

198

Figure 8.20

Indirect bonding of upper arch.

Clinical Notes

trays are removed separately. The hard tray is removed first by engaging the dental probe tip between hard and soft tray from the labial side. Rotating the probe handle will lift off the hard tray from the soft tray.

Ideally tubes are bonded to molars in indirect bonding but if bands needed to be cemented than they should be placed after indirect bonding. Separators shouldn't be passed in molars after taking of impression for fabrication of indirect trays. If extraction is required during treatment it should also be done after indirect bonding.

23. The soft tray is then peeled off from the brackets by first lifting it from one end in posterior segment with the help of probe and then griping it with fingers. Some clinician instead of giving a peel off force rotate the tray from labial to lingual starting from one side with the help of dental probe. My personal experience with indirect bonding is that there are less chances of bracket failure if the tray is rotated labial to lingual at each tooth with help of dental probe than to peel it off from the brackets.

If the case has severe malocclusion the indirect trays can be cut into 2 to 3 segments for easy insertion. If clinicians are new in indirect bonding they should initially select case with well aligned arches and divide the tray into three segments, one anterior and two posteriors for easy insertion. Bonding by indirect method should be done within 7 days of taking the impression for bonding.

24. Check position of each tooth clinically. If some bracket is not placed at its ideal location debond it, recycle it and rebond it with direct bonding.

References

Clinical Notes Sondhi indirect bonding kit is chemically cured so it usually give less time for trays insertion. A better option is to use Transbond supreme lv, a light cure version by the same company. In this light cure adhesive there is no need to apply any special primer on the etched enamel surface. Enamel surface is etched and any primer can be applied on it. All the bracket bases in the indirect tray covered with adhesive are coated with a very thin layer of

199

1.

Buonocore MG. A simple method of increasing the

adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955; 34:849-53. 2.

Barry GR. A clinical investigation of the effects of

omission of pumice prophylaxis on band and bond failure. Br J Orthod. 1995 Aug;22(3):245-8. 3.

Ireland AJ, Sherriff M. The effect of pumicing on the in

vivo use of a resin modified glass poly(alkenoate) cement and a conventional no-mix composite for bonding orthodontic brackets. J Orthod. 2002 Sep;29(3):217-20; discussion 196.


Transbond supreme lv. The trays are positioned in the mouth and each bracket is cured for 10seconds with LED curing light. Soft and hard trays are then removed in normal fashion and wires are passed immediately after that.


CHAPTER 4.

Lindauer SJ et al. Effect of pumice prophylaxis on the

14.

8

Suma S, Anita G, Chandra Shekar BR, Kallury A. The

bond strength of orthodontic brackets. Am J Orthod Dentofacial

effect of air abrasion on the retention of metallic brackets

Orthop. 1997 Jun;111(6):599-605.

bonded to fluorosed enamel surface. Indian J Dent Res. 2012 Mar-Apr;23(2):230-5.

5.

Burgess AM, Sherriff M, Ireland AJ. Self-etching

primers: is prophylactic pumicing necessary? A randomized

15.

Miles PG. Does microetching enamel reduce bracket

clinical trial. Angle Orthod. 2006 Jan;76(1):114-8.

failure when indirect bonding mandibular posterior teeth? Aust Orthod J. 2008 May;24(1):1-4.

6.

Lill DJ, Lindauer SJ, Tüfekçi E, Shroff B. Importance

of pumice prophylaxis for bonding with self-etch primer. Am J

16.

Uşümez S, Orhan M, Uşümez A. Laser etching of

Orthod Dentofacial Orthop. 2008 Mar;133(3):423-6; quiz

enamel for direct bonding with an Er,Cr:YSGG hydrokinetic

476.e2.

laser system. Am J Orthod Dentofacial Orthop. 2002 Dec;122(6):649-56.

7.

Pandis N, Eliades T. A comparative in vivo

assessment of the long-term failure rate of 2 self-etching

17.

primers. Am J Orthod Dentofacial Orthop. 2005 Jul;128(1):96-

for orthodontic bonding. Am J Orthod Dentofacial Orthop.

8.

2008 Aug;134(2):193-7.

8.

Ponduri S, Turnbull N, Birnie D, Ireland AJ, Sandy

JR. Does atropine sulphate improve orthodontic bond survival?

18.

Ozer T, Başaran G, Berk N. Laser etching of enamel

Berk N, Başaran G, Ozer T. Comparison of

sandblasting, laser irradiation, and conventional acid etching

A randomized clinical trial. Am J Orthod Dentofacial Orthop.

for orthodontic bonding of molar tubes. Eur J Orthod. 2008

2007 Nov;132(5):663-70.

Apr;30(2):183-9.

9.

Gray GB, Carey GP, Jagger DC. An in vitro

19.

Başaran EG, Ayna E, Başaran G, Beydemir K.

investigation of a comparison of bond strengths of composite to

Influence of different power outputs of erbium,

etched and air-abraded human enamel surfaces. J Prosthodont.

chromium:yttrium-scandium-gallium-garnet laser and acid

2006 Jan-Feb;15(1):2-8.

etching on shear bond strengths of a dual-cure resin cement to enamel. Lasers Med Sci. 2011 Jan;26(1):13-9.

10.

Olsen ME, Bishara SE, Damon P, Jakobsen JR.

Comparison of shear bond strength and surface structure

20.

Dundar B, Guzel KG. An analysis of the shear

between conventional acid etching and air-abrasion of human

strength of the bond between enamel and porcelain laminate

enamel. Am J Orthod Dentofacial Orthop. 1997

veneers with different etching systems: acid and Er,Cr:YSGG

Nov;112(5):502-6.

laser separately and combined. Lasers Med Sci. 2011 Nov;26(6):777-82.

11.

Canay S, Kocadereli I, Ak"ca E. The effect of enamel

air abrasion on the retention of bonded metallic orthodontic

21.

brackets. Am J Orthod Dentofacial Orthop. 2000

SA, Valdrighi HC, Correr-Sobrinho L, Vedovello Filho M. Effect

Jan;117(1):15-9.

Costa AR, Correr AB, Puppin-Rontani RM, Vedovello

of bonding material, etching time and silane on the bond strength of metallic orthodontic brackets to ceramic. Braz Dent

12.

van Waveren Hogervorst WL, Feilzer AJ, Prahl-

J. 2012;23(3):223-7.

Andersen B. The air-abrasion technique versus the conventional acid-etching technique: A quantification of

22.

Gonçalves PR, Moraes RR, Costa AR, Correr AB,

surface enamel loss and a comparison of shear bond strength.

Nouer PR, Sinhoreti MA, Correr-Sobrinho L. Effect of etching

Am J Orthod Dentofacial Orthop. 2000 Jan;117(1):20-6.

time and light source on the bond strength of metallic brackets to ceramic. Braz Dent J. 2011;22(3):245-8.

13.

Abu Alhaija ES, Al-Wahadni AM. Evaluation of shear

bond strength with different enamel pre-treatments. Eur J Orthod. 2004 Apr;26(2):179-84.

23.

Fleming PS. Limited evidence suggests no difference

in orthodontic attachment failure rates with the acid-etch technique and self-etch primers. Evid Based Dent. 2014

200

34.

Mickenautsch S, Yengopal V, Banerjee A. Retention of

orthodontic brackets bonded with resin-modified GIC versus 24.

Sfondrini MF, Cacciafesta V, Scribante A, Klersy C.

Plasma arc versus halogen light curing of orthodontic brackets:

composite resin adhesives--a quantitative systematic review of clinical trials. Clin Oral Investig. 2012 Feb;16(1):1-14.

A 12 month clinical study of bond failures. Am J Orthod Dentofacial Orthop. 2004;125:342–347.

35.

Ozoe R, Endo T, Abe R, Shinkai K, Katoh Y. Initial

shear bond strength of orthodontic brackets bonded to bleached 25.

Fleming PS, Eliades T, Katsaros C, Pandis N. Curing

lights for orthodontic bonding: a systematic review and meta-

teeth with a self-etching adhesive system. Quintessence Int. 2012 May;43(5):e60-6.

analysis. Am J Orthod Dentofacial Orthop. 2013 Apr;143(4 Suppl):S92-103.

36.

Ustdal A, Uysal T, Akdogan G, Kurt G. Effect of 16%

carbamide peroxide bleaching agent on the shear bond strength 26.

Fleming PS, Johal A, Pandis N. Self-etch primers and

conventional acid-etch technique for orthodontic bonding: a

of orthodontic brackets. World J Orthod. 2009 Fall;10(3):2115.

systematic review and meta-analysis. Am J Orthod Dentofacial Orthop. 2012 Jul;142(1):83-94.

37.

Adanir N, Türkkahraman H, Güngör AY. Effects of

fluorosis and bleaching on shear bond strengths of orthodontic 27.

Elkhadem A, Orabi N. Weak evidence suggests higher

brackets. Eur J Dent. 2007 Oct;1(4):230-5.

risk for bracket bonding failure with self-etch primer compared to conventional acid etch over 12 months. Evid Based Dent. 2013;14(2):52-3.

38.

Oztaş E, Bağdelen G, Kiliçoğlu H, Ulukapi H, Aydin I.

The effect of enamel bleaching on the shear bond strengths of metal and ceramic brackets. Eur J Orthod. 2012

28.

Fleming PS. Limited evidence suggests no difference

Apr;34(2):232-7.

in orthodontic attachment failure rates with the acid-etch technique and self-etch primers. Evid Based Dent. 2014

39.

Jun;15(2):48-9.

Laffoon JF. The effect of tooth bleaching on the shear bond

Bishara SE, Oonsombat C, Soliman MM, Ajlouni R,

strength of orthodontic brackets. Am J Orthod Dentofacial 29.

Goswami A, Mitali B, Roy B. Shear bond strength

Orthop. 2005 Dec;128(6):755-60.

comparison of moisture-insensitive primer and self-etching primer. J Orthod Sci. 2014 Jul;3(3):89-93.

40.

Bulut H, Turkun M, Kaya AD. Effect of an

antioxidizing agent on the shear bond strength of brackets 30.

Varlik SK, Ulusoy C. Effect of light-cured filled

sealant on shear bond strength of metal and ceramic brackets

bonded to bleached human enamel. Am J Orthod Dentofacial Orthop. 2006 Feb;129(2):266-72.

bonded with a resin-modified glass ionomer cement. Am J Orthod Dentofacial Orthop. 2009 Feb;135(2):194-8.

41.

Aksakalli S, Ileri Z, Yavuz T, Malkoc MA, Ozturk N.

Porcelain laminate veneer conditioning for orthodontic 31.

Mahajan V. Effect of light-cured filled sealant on the

bonding: SEM-EDX analysis. Lasers Med Sci. 2014 Oct 26.

shear bond strength of metal, ceramic and titanium brackets bonded with resin-modified glass ionomer cement. Indian J

42.

Dent Res. 2013 Nov-Dec;24(6):745-9.

surface alterations and refinishing after use of two orthodontic

Herion DT, Ferracane JL, Covell DA Jr. Porcelain

bonding methods. Angle Orthod. 2010 Jan;80(1):167-74. 32.

Bishara SE, Oonsombat C, Soliman MM, Warren J.

Effects of using a new protective sealant on the bond strength of orthodontic brackets. Angle Orthod. 2005 Mar;75(2):243-6.

43.

Yassaei S, Moradi F, Aghili H, Kamran MH. Shear

bond strength of orthodontic brackets bonded to porcelain following etching with Er:YAG laser versus hydrofluoric acid.

33.

Sharma S et al. A comparison of shear bond strength

Orthodontics (Chic.). 2013;14(1):e82-7.

of orthodontic brackets bonded with four different orthodontic adhesives. J Orthod Sci. 2014 Apr;3(2):29-33.

44.

Bishara SE, Ajlouni R, Oonsombat C, Laffoon J.

Bonding orthodontic brackets to porcelain using different

201


Jun;15(2):48-9.


CHAPTER

8

adhesives/enamel conditioners: a comparative study. World J Orthod. 2005 Spring;6(1):17-24. 45.

Swetha M, Pai VS, Sanjay N, Nandini S. Indirect

versus direct bonding--a shear bond strength comparison: an in vitro study. J Contemp Dent Pract. 2011 Jul 1;12(4):232-8. 46.

Yi GK, Dunn WJ, Taloumis LJ. Shear bond strength

comparison between direct and indirect bonded orthodontic brackets. Am J Orthod Dentofacial Orthop. 2003 Nov;124(5):577-81. 47.

Linn BJ, Berzins DW, Dhuru VB, Bradley TG. A

comparison of bond strength between direct- and indirectbonding methods. Angle Orthod. 2006 Mar;76(2):289-94.

202

CHAPTER

9

Debonding of orthodontic brackets In this Chapter

Mechanical debonding of orthodontic brackets Base Method Wing method Mechanical debonding of metal brackets Debonding plier Ligature cutters Weingart plier

Debonding by solvents Debonding by Notching Ultrasonic debonding Impulse debonding Thermal Debonding Hot instruments Tips Electrothermal debonding Laser debonding

Howe plier Lift-off Debonding Instrument (LODI) Bracket and adhesive removing plier Self ligating brackets debonding Lingual brackets debonding Mechanical debonding of plastic brackets Mechanical debonding of ceramic brackets Fixed orthodontic brackets are temporary appliances which are attached to the teeth for certain period of time depending upon the severity of malocclusion and needed to be removed at the end of treatment. The removal process is either called debonding or debracketing. Debonding of orthodontic brackets is done in clinical practice at two

203

occasions. First scenario is when position of bracket is not considered correct and the second scenario is at the end of orthodontic treatment. The objective1 of debonding is to remove orthodontic brackets and adhesive remnants from the tooth and restore the tooth surface to its pretreatment condition without causing any

Debonding of orthodontic brackets

CHAPTER

9

iatrogenic damage to enamel and tooth supporting structures. So debonding procedure in orthodontics can be divided into two steps2. Step 1: Removal of bracket from the tooth Step 2: Removal of adhesive remnants from enamel In debonding orthodontic brackets from the tooth the site of bond failure is very important. Bond failure is accessed by adhesive remnant index (Table & Figure 9.1).Bond failure can be adhesive and occur between bracket and adhesive or between enamel and adhesive or it can be cohesive occurring between the adhesives cement itself. Though controversial but bond failure at bracket adhesive interference is considered more advantageous as there is little damage to the enamel but more adhesive needed to be removed from the tooth. If bond failure occurs at enamel adhesive interference there are more chances of enamel damage but it also carry the benefit that less adhesive needed to be removed from the tooth. It is important to avoid iatrogenic damages to the tooth during bracket and adhesive remnants removal as improper debonding results in cracks on enamel surface and enamel prisms fracture. Esthetic problems, tooth sensitivity, increasing risk of caries and pulp necrosis may also be seen after improper debonding.

A

B

C

Different methods of deboning orthodontic brackets are as follow. Table 9.1 Modified Adhesive remnant index by Artun3 Score 0 1

Description All adhesive left on the bracket base More than half of the adhesive left on the bracket base 2 Less than half of the adhesive left on the bracket base 3 No adhesive left on the bracket base. The original index was based on enamel surface rather than on bracket base.

D Figure 9.1 A. The entire adhesive remained on the bracket base so ARI score 0. B. More than half of the adhesive remained on the bracket base ARI score 1. The picture contains a plastic bracket. C. Less than half the adhesive left on the bracket base with ARI score 2. D. No adhesive left on the bracket base with ARI score 3.

204

2. Debonding by solvents 3. Debonding by Notching

brackets fail to debond then a simultaneous peel off force is also added. Tensile or pulling and shear or push (upward or downward directed) debonding force is not given to orthodontic brackets in clinical practice.

4. Ultrasonic debonding 5. Impulse debonding 6. Thermal debonding 1. Mechanical debonding of orthodontic brackets The most common mean of debonding orthodontic bracket in clinical practice is by using debonding pliers. To achieve this goal two methods are used based upon at which level the pliers are placed on the bracket during debonding. A) Base Method B) Wing method

A

A. Base Method In this method the beaks of the plier are placed at the level of adhesive layer between the bracket and tooth. Base method of bracket debonding has three variations. i. Horizontal or mesiodistal base method ii. Vertical base method iii. Diagonal method

B In horizontal base method the beak of the pliers are placed mesiodistal at the level of the adhesive while in vertical base method the beaks are placed occlusogingival in a vertical fashion(Figure 9.2).In diagonal base method the beaks of the plier are placed distoincisal to mesiogingival or distogingival to mesioincisal (Figure 9.2 C).

205

c

Clinical Notes

C

Usually a squeezing force is given to pliers in all variations of base method but if the

Figure 9.2 A. Horizontal base method. B. Vertical base method. C. Diagonal base method.


1. Mechanical debonding


CHAPTER In base method of debonding up to 1.5 times more debonding force4 is required as compared to wing method. The mechanical base method of debonding often produce sudden bond failure5 as heavy forces are being applied by the plier so there are chances of injury to the surrounding soft tissue by the plier beaks. In base method of debonding the bond failure usually occur within the adhesive or at the level of enamel adhesive interference. So there are less chances of bracket distortion and many debonded brackets can be recycled after this method.

9

A

Clinical Notes Adhesive layer beneath a properly bonded bracket usually have a thickness below 0.5mm. So pliers used with base method should have very thin sharp blades to engage this layer. A plier with thick blades will cover greater area of the bracket base and so will cause distortion of the bracket (Figure 9.3 &9.4). But no matter how thin the blades of the plier are, some coverage of bracket base is inevitable.

B

C Figure 9.4 Bracket base distortion by thick blades of the plier during different variation of base method. Such brackets are not suitable for recycling. A. Base distortion on horizontal base method. B. Base distortion on vertical base method .C. Base distortion on diagonal base method.

Figure 9.3 Two debonding pliers with different blades width. Ideally for base method a plier with thin sharp blades should be used. Thick blades will cause distortion of the bracket base on debonding.

Clinical Notes In base method of mechanical debonding of brackets there is risk of enamel damage by tip and blades of pliers and due to heavy forces that are generated close to the enamel. Also

heavy force applied during this method may cause discomfort for the patient as the teeth are usually sensitive and show some degree of mobility at end of orthodontic treatment. Patient discomfort can be decreased by placing a gauze pack or cotton roll between the teeth and asking the patient to bite on it (Figure 9.5). In base method of debonding the clinician has poor grip over the bracket so there are greater

206

Horizontal base method should be preferred with brackets having hook as it will limit proper instrument placement in diagonal and vertical base method.

A Figure 9.5 A gauze pack between teeth to avoid discomfort during debonding.

B

Figure 9.6 Fingers placed over the plier in base method of debonding to control the amount of force and preventing bracket dislodging in the oral cavity and soft tissue injury by pliers beaks. Care should be taken that finger should be at sufficient distance from the blades of the pliers otherwise injury to the fingers can occur.

B. Wing Method Wing method of debonding is similar to base method of debonding with the only difference is that the beaks or blades of the pliers are placed at the level of bracket wings rather than at the base level. Wing method of

207

C Figure 9.7 A . Horizontal wing method . B Vertical wing method. C . Diagonal wing method.

Wing method is usually reserved for metal and plastic brackets and is usually not suitable for ceramic brackets as it will cause wing fracture of the ceramic brackets. Two types of forces can be applied to metal


debonding has same horizontal, vertical and diagonal variations like that of base method but horizontal variation is most commonly used (Figure 9.7).

chances of bracket to get dislodged in oral cavity. To avoid such problem it is a good practice to squeeze plier with one hand and keep the thumb and index finger of the other hand over back side of plier head to prevent accidental dislodging of the bracket and avoid soft tissue damage on sudden debonding. (Figure 9.6).


CHAPTER brackets by wing method. 1. Squeezing force 2. Subsequent squeezing and peel off force Squeezing force will peel off the bracket at its both ends depending on which variation of wing method is used. For example a horizontal wing method used with squeezing force will peel off the bracket at both mesial and distal ends. In bracket debonding by subsequent squeezing and peel off force, an initial squeezing force is given to get proper grip of bracket and then a peel off is given by rotation movement of the wrist to lift the bracket at its one end. Less force is required to debond a bracket by squeezing force only. In wing method, the bond failure usually occurs at the level of bracket adhesive interference.

9

If vertical wing method is used with these types of brackets then both type of forces can be used depending upon whether the plier blades are placed above the level of slot base or below it. In canine and posterior brackets horizontal wing method is preferred as hook of the bracket interfere with pliers in diagonal and vertical wing methods.

A

Clinical Notes In wing method of debonding the type of force given is related with type of plier and bracket used (Figure 9.8). Pliers with broad tip are usually reserved for subsequent squeezing and peel off force. As these pliers also cover some part of the stem of the bracket a squeezing force alone usually don't results in debonding of the brackets. Example of these pliers includes Weingart and Howe pliers. A debonding plier with thin blades can be used both with squeezing only or subsequent squeezing and peel off force depending upon at which level the plier is placed. If the plier is placed above the level of slot base then a squeezing force only is sufficient to debond the bracket but if the beaks of the plier is placed below the slot base then a subsequent squeezing and peel off force is necessary. This is true for all variations of wing method with Siamese or twin brackets. But in case of single bracket and semi twin brackets a subsequent squeezing and peel off force is the only option if horizontal or diagonal wing method is used.

B Figure 9.8 A. A debonding plier with thin blades. These pliers though can be placed both above and below the slot base level but placing them above the slot base is preferred method. A squeezing force only is sufficient with these pliers to debond the bracket. B. A Howe plier. As the pliers have broad blades so they cover some part of the bracket stem for proper grip. A subsequent squeezing and peel of force is given with these pliers.

In wing method of debonding, higher the plier is placed over the bracket greater would be the chances of slot distortion. A squeezing force only used with wing method of debonding will result in distortion of the bracket slot in almost all the instance (Figure 9.9). Clinical Notes In wing method if recycling is intended it is a good practice to keep a slot keeper or a full dimension wire in the slot and use vertical

208

A

B

clinician wants to avoid patient discomfort by applying minimum debonding force and when recycling of bracket is not the intention. Base method can be used with all types of brackets but wing method should be avoided with ceramic brackets. Manufacturing process of the brackets also affect their debonding choice especially with wing method. Bracket manufactured by conventional methods having different hardness of slot/wing and base components are easily debonded by wing method if good brazing and welding procedure is used. But in brackets manufactured by MIM process, all parts of the bracket have same hardness so using a wing method with squeezing only force will distort the slot without debonding the bracket in most of the instance. So either subsequent squeezing and peel off force should be used with MIM brackets in wing method or a base method should be preferred. In case of gingival hyperplasia wing method of debonding is usually used. Wing method of debonding is also a preferred choice with brackets bonded on metal or porcelain structures.

C Figure 9.9 Bracket wing distortion by A. Horizontal wing method. B. Vertical wing method. C. Diagonal wing method.

Selection of mechanical debonding method Base method is a preferred method during early and middle stages of treatment when debonded brackets can be recycled and reused on the same patient. Wing method is usually used at end of treatment when

209

In patients with weak enamel structures like cracked teeth, restored teeth, amelogenesis or dentinogenesis imperfecta a wing method should be preferred over the base method as there are more forces applied and more chances of enamel damage in the later method.

Mechanical debonding of metal brackets The most atraumatic method of orthodontic metal bracket removal is to peel them off from the tooth and cause bond failure at the bracket adhesive interference. Many types of pliers are being used in


wing method with subsequent squeezing and peel off force.


CHAPTER contemporary orthodontics to debond metal brackets. Almost all manufacturers make their own pliers and also have advertised some special pliers for debonding brackets. These pliers have their own benefits and limits. It is not possible to explain details of all the pliers but some of the most commonly used methods are discussed below. Bracket removing plier or Debonding plier This is one of the most commonly used pliers to debond orthodontic brackets (Figure 9.10). Both base and wing methods with all their variations can be used with this plier depending on clinician desire of final outcome.

9

debonding plier may leave more adhesive remnants on the enamel but is least harmful for the enamel. Enamel damage was found only 4 % with these pliers6. 2. Debonding plier can be used with both base and wing method of debonding. Disadvantages Debonding pliers cannot be used with wire in place in horizontal wing method. Ligature cutters/Side Cutters Ligature cutters or side cutters are used to debond orthodontic brackets by only base method of debonding (Figure 9.12). All the variation of base methods can be used with ligature cutters. Advantages 1. Ligature cutter is a routine part of the dental office so orthodontists don't have to bear extra cost to buy a new instrument. 2. Debonding occurs in less than a second so Clinical Notes Some clinicians prefer a debonding plier in which beaks of the plier remain 2-3 mm apart on full closure of the plier (Figure 9.11). It is believed that these pliers prevent base distortion on base method and also are less destructive for the enamel. But larger the gap between the beaks of the plier, greater would be their chances of ineffectiveness during wing method.

Figure 9.10 A debonding plier. The plier can be used with both base and wing method.

Advantages 1. Wing method of debonding by using

Figure 9.11 Debonding plier with 2 mm gap between the beaks on full closure.

210


Figure 9.12. Ligature wire cutter used with different methods of bracket removal.

it is a time efficient method. 3. Ligature cutters can debond the bracket even if the wire is within the slot. Disadvantage The main disadvantages of this method are: 1. There are greater chances of soft tissue injury with sharp beaks of ligature cutters. 2. As heavy forces are transmitted at bracket adhesive interference there is greater risk of enamel damage.

A

3. Debonding brackets by ligature cutter is not advocated 6 if other methods of debonding are available. Clinical notes Many clinicians use straight wire cutter with base method of debonding. The blades of straight wire cutter are thicker than ligature cutter so there are greater chances of bracket base distortion (Figure 9.13).

211

B Figure 9.13 A. Ligature cutter used with vertical base method. B. Straight wire cutter used instead of ligature cutter with vertical base method. The blades of the straight wire cutter are thick so using it will result in distortion of the bracket base.


CHAPTER

9

Weingart plier

Howe plier

Weingart plier is used only with the wing method of debonding. Beaks of Weingart plier are wider than debonding plier so when gripping the wings of the bracket some area of bracket stem is also covered by the plier. Greater force is required to debond bracket by Weingart plier as compared to debonding plier (Figure 9.14). Effort should be made holding plier high on the bracket without compromising the grip of the plier.

Howe plier is also used with wing method of mechanical debonding (Figure 9.15). Owing to broader tip of Howe plier debonding forces are evenly distributed throughout the bracket and there are less chances of enamel damage7. But more debonding forces are applied with Howe plier as compared to debonding plier so debonding plier is recommended over Howe plier. Also Howe pliers are not routine instrument used in dental office.

Clinical notes In debonding brackets with Weingart plier subsequent squeezing and peel off force is given. All variations of wing method can be used with Weingart plier but horizontal wing method is most preferred method with this plier. As more force is required to debond brackets with Weingart plier so this plier is second to debonding plier.

Figure 9.15 Howe plier used with wing method of debonding. Horizontal wing method is most compatible with Howe plier.

Lift-off Debonding Instrument (LODI)

Figure 9.14 of debonding.

A Weingart plier used with wing method

Lift off debonding instrument or LODI is a pistol grip debonding instrument in which a wire loop is used to engage the bracket wings (Figure 9.16).To debond a bracket instrument is placed over the bracket and one of the bracket wing is engaged in the wire loop of the plier. Then trigger is lightly squeezed until both the beaks of instrument rest evenly on the tooth surface. After proper seating of plier the trigger is squeezed slightly harder until the bracket is lifted from the tooth surface. By squeezing the trigger of the plier a tension force is delivered to the brackets wing hooked in the wire loop and bracket is debonded (Figure 9.17).

212

Advantages The advantages of LODI are: 1. LODI doesn't cause bracket base distortion8. So it can be used as an alternative for debonding pliers9.

Figure 9.16 A lift off debonding instrument with its wire loop. The wire loop is used to engage the wings of the plier. For debonding miniature and full size brackets separate wire loops are available.

2. Less force is required10 for debonding when tension is applied by LODI as compared to conventional debonding plier. 3. With lift off debonding instrument patient experience less pain11 as compared to debonding with side cutters. 4. Brackets can be recycled6 and reused after debonding if wire is left in place or a slot keeper is used. Disadvantages Some of disadvantages associated with lift off debonding plier are: 1. LODI bracket removal technique is associated with ceramic damage12 while debonding brackets on ceramic veneers. 2. Wing damage of bracket may occur if the wings are brazed to the bracket body. So ideally use metal injection molded brackets to debond with these pliers.

Figure 9.17 Bracket debonding by LODI. The bracket is debonded by a tension force.

Clinical Notes Lift off debonding instrument can be used in two ways either the archwire may be left in situ or the slot keeper which is a 0.018x0.022 inch wire embedded in a plastic handle may be placed in the bracket slot after the working arch wire removal. In either case, the presence of a

213

3. Wire loop may break during debonding so it is needed to be replaced periodically. 4. LODI is not routine part of dental office.

Clinical notes LODI is effective in bracket debonding7 but as tension force is involved there are greater chances of enamel damage6.


wire in the slot would help to maintain the slot dimensions and bracket can be recycled in future if required.


CHAPTER

9

Bracket and adhesive removing plier Bracket and adhesive removing pliers are used like a band removing plier (Figure 9.18). One end of the plier which contains a plastic head (Teflon pad) is placed over the incisal or occlusal part of tooth and the other metal end of the plier grip the bracket from the gingival side close to bracket adhesive interference. Giving squeezing force to the plier delivers a shear force to the bracket. The same plier can be used for adhesive remnants removal on the tooth after debonding.

Figure 9.18 A adhesive removing plier.

Clinical Notes Adhesive removing plier delivers a shear force to the tooth so there are greater chances of enamel damage. Also more force is needed to debond a bracket so this technique is more painful for the patient.

Figure 9.19 A debonding plier specially made for selfligating brackets.

on all brackets for easy ligation. These hooks interfere with both vertical wing and base method and make diagonal base and wing method almost impossible to execute. Another difference between labial and lingual brackets is larger bracket base area and smaller slot area of lingual brackets thus providing a smaller lever arm to peel off bracket by wing method of debonding (Figure 9.20). Also lingual brackets have single slot or these are in semi twin design. So squeezing the brackets by horizontal wing method don't work.

Self ligating brackets debonding Self-ligating brackets can also be debonded by conventional method. Ideally the self ligating clip of the bracket should be open while debonding the bracket. Usually base method is preferred if self-ligating brackets needed to be recycled. Some manufacturers recommend special pliers for debonding their self ligating brackets (Figure 9.19). Lingual brackets debonding Lingual brackets have different shape from labial brackets so the same general principle of debonding cannot be applied to these brackets. In lingual brackets gingival hooks are present

Figure 9.20 A lingual bracket on which vertical wing debonding method with squeezing force was used .As slot of bracket is much smaller than base so a smaller lever arm was provided by the slot resulting in distortion of the slot without debonding of the bracket.

214

debond anterior lingual brackets modified pliers are available in the market (Figure 9.23).

Figure 9.21 Horizontal wing method. Subsequent squeezing and peel off force is used.

Horizontal base method works fine on lingual brackets on buccal segment teeth. But the most preferred method with lingual brackets in both anterior and posterior segment in upper and lower arch is using a combination of vertical base and wing method (Figure 9.22). On the incisal side the plier engages the bracket base and on the gingival side the plier engages the bracket hook. The bracket is peeled off from the gingival side by rotation movement of the wrist.

Figure 9.23 Various pliers used for debonding lingual brackets. As it's difficult to grip anterior lingual brackets with conventional labial debonding pliers so special lingual debonding pliers are available commercially.

Clinical notes If recycling of lingual brackets is intended then horizontal wing method should be used with subsequent squeezing and peel off force.

Selection of mechanical debonding method for metal brackets.

Figure 9.22 Combination of wing and base method for debonding lingual brackets .The bracket is peeled from the gingival side.

Usually a debonding plier is used for lingual brackets with both base and wing method. To

215

Bracket removing plier is usually a preferred instrument for debonding conventional and self-ligating bracket as it can be used with both base and wing method. For lingual brackets in lower arch conventional debonding plier can be used but for maxillary anterior lingual brackets special debonding pliers usually made by manufacturer of brackets are recommended.


To debond lingual brackets horizontal wing method with subsequent squeezing and peel off force is used (Figure 9.21). On molar teeth only a horizontal wing method with squeezing force alone will debond the brackets as lingual molar brackets are similar to labial brackets.


CHAPTER

9

Mechanical debonding of plastic brackets Plastic brackets can be debonded with both base and wing method but base method is preferred (Figure 9.24 & 9.25). As plastic brackets exhibit bending distortion on debonding they can easily be peeled off from the tooth with bond failure occurring at bracket adhesive interference. There is little danger of enamel damage on debonding the brackets as plastic brackets are associated with less bond strength than metal and ceramic brackets. But care should be taken not to damage enamel in base method by beaks of the pliers.

Fig 9.25 Plastic bracket deboned with wing method. Wing method is a less preferred method with plastic brackets

Clinical Notes In wing method of debonding plastic brackets horizontal wing method is preferred. Vertical or diagonal wing method usually results in distortion of the bracket slot without debonding the bracket with both squeezing and peel off of force (Figure 9.26). In horizontal wing method a subsequent squeezing and peel off force is given. A squeezing force alone usually results in distortion of the slot in horizontal wing method. Using horizontal wing method with squeezing force only on plastic brackets with metal slot usually results in detachment of slot from main bracket body (Figure 9.27).

Figure 9.24 Base method of debonding. Base method is most preferred method in plastic brackets.

On debonding composite plastic brackets special care should be taken as some of them show odd behavior on debonding especially ceramic reinforced plastic brackets (Figure 9.28). Ceramic reinforced plastic brackets should be debonded by base method of debonding.

216


A

B Figure 9.26 Bracket distortion with A. Vertical wing method. B. Diagonal wing method.

Figure 9.28 Ceramic reinforced plastic brackets. Using wing method will cause bracket fracture similar to ceramic brackets. A base method should be used with theses brackets.

Selection of mechanical debonding technique for plastic brackets For plastic brackets ideally base method of debonding should be used. Both debonding plier and ligature wire cutter can be used to debond the bracket by base method.

Mechanical debonding of ceramic brackets Mechanical debonding techniques have also been used with ceramic brackets. As most fixed appliance cases in orthodontic practice are done with metal brackets so orthodontist use their instinct mechanical debonding techniques of metal brackets to ceramic brackets which result in either bracket fracture or enamel damage. The reason behind this is that orthodontist failed to appreciate two main differences between ceramics and metal brackets. These are: 1) Bond strength Figure 9.27 Using horizontal wing method on plastic brackets with metal slots usually results in detachment of metal slot from the main bracket body.

217

2) Physical properties


CHAPTER The tensile strength of enamel is 14.5 MPa 13 and it has been reported that enamel fracture can occur at bracket bond strength of 13.5 MPa 14 . To save enamel fracture during debonding clinical acceptable bond strength shouldn't exceed 13.5 MPa. The minimum bond strength to withstand orthodontic and masticatory forces is recommended between 6 to 8 MPa 15 for all types of brackets. The bond strength of ceramic brackets whether it is in chemical or mechanical retention base is almost always greater than metal brackets and is usually greater than 13.5 MPa. Theoretically any bracket that has bond strength greater than 13.5 MPa should always fracture the enamel. But it is not true for metal brackets which if even have bond strength greater than 13.5 MPa don't fracture the enamel. The difference comes in physical properties of the brackets and the type of force we give during debonding. In terms of physical properties, ceramics are third hardest material known to humans in which strong ionic and covalent bonds are present to hold the atoms 16, 17. These bonds are directional and don't allow slip planes. In contrast stainless steel is softer than ceramic and has metallic bonds which allow slip planes. To avoid enamel damage peel off forces are given to orthodontic brackets instead of tensile forces. These peel off forces when given to stainless steel brackets result in distortion or elongation of the metal due to presence of slip planes and stresses are redistributed and relieved. Distortion of stainless steel brackets also causes cohesive failure within the adhesive or adhesive failure at the bracket adhesive interference. But unfortunately these peels off forces cannot be given to ceramic brackets as the elongation of ceramic brackets before failure is only 1% as compared to stainless steel brackets which elongate 20 % before failure 17. So when same peel off debonding forces are applied to ceramic brackets, redistribution and

9

relieve of stress doesn't occur due to lack of slip planes and strong interatomic bonding. If these forces are applied at thin sections of ceramic brackets like bracket wings or if bracket has some inner fault lines due impurities or preexisting cracks, fracture of bracket will occur. But if these deboning forces are applied at thick section of brackets like bracket base, stresses are transferred to adhesive cement. In case of ceramic brackets especially with chemical retention base, bond between adhesive and bracket is strong and lack of bracket distortion don't cause bond failure at bracket adhesive interference. So debonding forces are eventually transferred to enamel and causes its fracture. Debonding methods Before debonding any ceramic bracket by mechanical means always remove flash around the bracket base with a carbide bur on slow or high speed handpiece using a water coolant. This will allow easy grip of the plier in base method of debonding and also help decrease bond strength of the bracket. Ceramic brackets being brittle can easily fracture and can dislodge in oral cavity of patient or fragments of bracket can fly and may enter the eyes. A gauze pack or cotton roll is also placed in the patient mouth during mechanical debonding of the bracket to prevent dislodgment of the bracket in the oral cavity and decreased the pain on sensitive teeth. Protective dental glasses should be used by the dentist and his assistant (Figure 9.29). Protective glasses can also be given to the patient or at least he is requested to close his eyes during debonding procedure.

Figure 9.29 Protective Dental glasses

218

A

manufacturers recommend their special pliers (Figure 9.30) or a specific debonding technique for their manufactured brackets. Some ceramic brackets have collapsible base and debonded with wing method (Figure 9.31).

C

B

Figure 9.30 Various debonding pliers used with only a specific type of ceramic brackets. A. Transcend series 6000 debonding plier by 3 M Unitek. B. Orthoclassic debonding plier to debond their version of ceramic brackets. C. Forestadent debonding plier. Omrco nexsus system also uses this plier. As the plier fully enclosed the bracket thus decreasing the likelihood of flying debris on bracket fracture.

A

D

B

C

E

Figure 9.31 A &B. Clarity advance ceramic brackets with a collapsible base. The manufacturer recommends debonding this bracket with horizontal wing method using Howe or Weingart plier. Bond failure occurs similar to metal brackets 18 C&D. Clarity brackets with metal lined slot. Vertical slot and a collapsible base are added to bracket to aid easy debonding of brackets on horizontal wing method with Howe or Weingart pliers. E. Special pliers are also available from manufacturer to debond Clarity metal lined brackets. continued...

219


For mechanical debonding of ceramic brackets the best available option to debond the bracket is follow manufacturer recommendations. This saves the clinician from any legal issue in case some iatrogenic damage occurs. Many


CHAPTER

F Figure 9.31 F. Bracket with chemical retention and collapsible base. Vertical wing method is recommended to debond this bracket. Collapsible base brackets though cannot be recycled and reused but are safest in terms of debonding characteristics.

When manufacturer recommendations are not present then usually a base method of debonding should be applied (Figure 9.32). All variations of base method can be employed with ceramic brackets. Swartz 17 recommended that for debonding chemical retention ceramic brackets, base method of debonding with squeeze only force can be used so that bond failure occur within the adhesive and for debonding mechanical ceramic bases slow peeling force should be applied at bracket base. Ceramic brackets with plastic bases can be debonded with base method with subsequent squeezing and peel off force. These brackets will debond similar to metal bracket without causing enamel damage. Wing method should be avoided with ceramic brackets as it will cause bracket fracture (Figure 9.33). If proper debonding technique is not followed there are greater risks of enamel damage (Figure 9.34).

9

B Figure 9.32 Ceramic bracket debonded with A. Vertical base method. B. Horizontal base method.

Figure 9.33 A polycrystalline bracket fragments. Bracket was fractured after debonding with horizontal wing method with a debonding plier

Figure 9.34 Enamel damage caused by debonding the bracket with a peel off force using a Weingart plier with horizontal wing method.

Clinical Notes If proper debonding techniques fails or risk of enamel damage is great due to nonvital teeth, enamel cracks, enamel hypoplasia or if the patient teeth are sensitive, grinding of ceramic brackets is the only option.

A

220

Grinding of ceramic brackets is usually done with high speed diamond burs or low speed green stones with water coolant. This process is time consuming. To save time wings of the brackets can be cut with ligature cutter and then main body of ceramic bracket is grinded (Figure 9.35).

Figure 9.36

A debonding plier with replaceable tips.

Advantages The advantages of mechanical debonding of ceramic brackets are: 1. Time efficient 2. Most debonding pliers are normal armamentarium of orthodontic office. Disadvantages The disadvantages associated with mechanical debonding of ceramic brackets are:

Figure 9.35 Grinding of ceramic bracket done as bracket wings fractured during debonding. Its best to break the remaining bracket wings by ligature cutters and grind the remaining bracket base.

Clinical notes For debonding ceramic brackets with conventional pliers it is recommended 19 that sharp edge plier with narrow blades are preferred over wide dull blades. Narrow blades have less contact area and generate less force. For debonding brackets all that is needed is to cause fracture in the brittle adhesive. As ceramic brackets are harder than stainless steel so debonding of the brackets cause wear of the instrument. Debonding pliers with replaceable tips are usually used (Figure 9.36).

221

1. Brittleness may cause problems such as breakage of bracket during mechanical debonding. 2. Aspiration of fragments if bracket is fractured or failed. As ceramic brackets are radiolucent it is almost impossible to locate them if aspirated. 3. Injury by the flying debris to patient oral mucosa or clinician eyes on bracket fracture. 4. Portion of broken bracket need to be grounded with high speed handpiece thus increasing the debonding time. 5. The probability of enamel damage is greater if the integrity of tooth structure is already compromised by presence of developmental defects, enamel cracks, large restorations and nonvital teeth.


Before attempting to grind a ceramic bracket protective glasses should be taken by the operator and his assistant. Patient can also be given protective glasses or asked to keep his eyes shut while the ceramic bracket is being grinded. Grinding of ceramic bracket produce ceramic dust which has been associated with skin and eye irritation 20.


CHAPTER 6. More time is required to debond ceramic brackets mechanically as compared to metal brackets as extra time is required to remove flash either with burs or with the debonding instruments. 7. Extra cost is involved to buy the manufacturer recommended special instruments, protective goggles and to replace tips of pliers. Clinical Notes 1 Enamel fracture or cracks can occur with ceramic brackets debonding. This can due to: 1. Poor selection of cases. Non-vital teeth, teeth with enamel cracks, large restoration, hypoplastic and hypocalcified teeth shouldn't be bonded with ceramic brackets 21,22. 2. Improper debonding technique This happen if clinician fails to follow manufacturer recommended methods or apply wing method of debonding on ceramic brackets with non-collapsible base. Rotation or tensile forces increases chances of enamel fracture. Debonding brackets from small teeth (mandibular incisor) pose more risk and extra care should be used while debonding on such teeth. 3. Increased bond strength Increased bond strength is associated with ceramic brackets having chemical retention bases or if the clinician uses a highly filled adhesives. Ceramic brackets with chemical retention bases should be avoided in clinical practice. Clinical Notes 2

9

strength, debonding brackets after doing aggressive tooth movement (especially doing pure tipping movement on light rectangular wires) and pain threshold of the patient. Pain can be avoided during debonding by asking the patient to bite on cotton or gauze pack. Gauze or cotton pack will also help to stop swallowing or aspiration of ceramic bracket. Ideally in patient having low pain threshold and mobile teeth, mechanical debonding methods and ultrasonic debonding technique should be avoided. Using thermal, laser and solvent debonding techniques are an optimum solution. Debonding by solvents Various composite softening agents are used in dentistry such as 75% ethanol, polyacrylic acid, acetone , acetic acid and peppermint oil. These softening agents have also been used in orthodontics as debonding agent for ceramic brackets. In orthodontics to aid mechanical debonding of ceramic brackets debonding agents usually used are derivatives of peppermint oil. The debonding agent can be applied at bracket base and left around the base of the bracket for 60 seconds to 2 minutes to facilitate debonding. The bracket is then debonded by mechanical method. Application of debonding agent facilitates bond failure at the adhesive enamel interference without damaging the enamel 20,23. The most commonly used debonding agent is post-debonding agent by GAC, International, Inc. However, a similar agent P-de-A, Oradent Ltd. was not found to be very effective 24, 25 in facilitating easy debonding.

Pain during mechanical debonding of ceramic brackets is related to high bond

222

Notching of composite resin is done to aid easy mechanical debonding of ceramic brackets. Notching can be done at the time of bonding orthodontic brackets or at the time of bracket debonding.

easy and firm grip of debonding pliers or side cutters during debonding. As there are greater chances of enamel damage associated with this method, so this method has been abandoned in clinical settings (Figure 9.38).

Notching at time of bracket bonding This method is used only in an experimental study25 and has practical limitations so it not a recommended method in clinical practice (Figure 9.37).

A

B

Figure 9.37 Notched bracket and matrix strips. Notching is done by placing matrix strip at time of bonding between the enamel and bracket. Both enamel and bracket has a thin coating of adhesive when the strip is placed. After curing of adhesive the strip is removed thus leaving a notch below the bonded bracket.

Notching at the time of bracket debonding Notching at the time of debonding is done with the help of a fissure bur during the process of flash removal. Nothing is done both at incisor and gingival ends of bracket. Notching helps in

223

C Figure 9.38 A. Purchase point created on occlusal side to facilitate grip of the plier in base method. B. Enamel surface after debonding. Using a high speed handpiece to create purchase area will result in enamel damage. A groove is visible in the enamel on the occlusal side. C. A damaged bracket. There are greater chances of bracket damage by the bur in this method.


Debonding by Notching


CHAPTER Ultrasonic debonding Conventional mechanical debonding techniques for ceramic brackets recommended by manufacturers are associated with 10-35 % of brackets fracture 26. To avoid ceramic brackets fracture during debonding use of ultrasonic devices have been advocated. Ultrasonic devices can also be used to debond metal and plastic brackets. How it works In ultrasonic method, ultrasonic scalers are used to debond orthodontic brackets. The scaling tip vibrates in the ultrasonic range of 18-50 kHz i.e. 18000 to 50000 times per second, with an optimum frequency between 18 kHz to 32kHz.The scaler tip vibrates in a linear or elliptical fashion depending upon the type of ultrasonic scaler used. Vibrating metal tip erodes adhesive and creates a purchase point 27 underneath the bracket base. Ultrasonic tip can cause cohesive bond failure within the adhesive or bond failure occurs at enamel adhesive interference. So bracket damage is avoided. Choice of Ultrasonic Scalers Two different types of ultrasonic scalers are commercially available. These are piezoelectric and magnetostrictive scalers (figure 9.39). The difference between them is how they generate energy for vibration or oscillation of their tips. The vibration pattern of the tip between these two types of scalers is also different. Piezoelectric scaler tip vibrate in a linear back and forth fashion while magnetostrictive tip can vibrate in long ellipse or rotatory fashion depending upon its further subdivisions. In terms of clinical significance the difference in vibration pattern result in generation of different cavitation bubbles which might matters in periodontal health but not for orthodontic bracket removal. So theoretically both these types of scalers can be used for bracket debonding. In literature 27, 28

9

only magnetostrictive scalers with special tips have been used to debond ceramic brackets but in some case reports in non-index journals piezoelectric scalers have also been used. Also piezoelectric scalers can work at greater frequency than magnetostrictive scalers and the final enamel surface is also smooth 29. In magnetostrictive scalers usually 30 KHz scalers are preferred over 25 KHz scalers as they are less noisy and of course have a greater vibration speed. Choice of the scaler tip In literature 27, 28 ultrasonic scalers with specialized tips (KJS, KJC) have been used for debonding ceramic brackets. Contrary to conventional ultrasonic tips which are curved these tips are straight and are sharp at working end. In clinical practice if debonding by ultrasonic scalers is intended then the tips used for interdental area are best suited for debonding because they have a narrow and pointed working end which make it easy to create a purchase point under the bracket (Figure 9.40).

Figure 9.39

A magnetostrictive and piezoelectric scaler

224

Debonding time Debonding time by ultrasonic scaler reported in literature 26, 28, 30 ranges between 16.6 to 50 seconds. Advantages Using ultrasonic debonding has the following advantages: Figure 9.40 brackets.

Different scaler tip used to debond ceramic

1. No bracket fracture occurs while using ultrasonic debonding. 2. Site of bond failure is at enamel adhesive interference but decrease enamel fracture as debonding force is lower 27,30. Site of bond failure is also influenced by type of cement used for bonding. 3. The same ultrasonic tips can be used to remove adhesive remnants on enamel. Disadvantages 1. More time is required26, 27 to debond bracket as compared to mechanical and thermal debonding.

Figure 9.41 A scaler tip engaged underneath bracket to cause fatigue failure of bracket.

Method of Ultrasonic debonding 1. Remove composite flash around the bracket periphery before debonding ideally with a slow speed 12 fluted carbide bur using a water coolant. 2. Create a 0.5 to 1mm purchase point 27 under the bracket by moving the scaler tip in the mesiodistal direction (Figure 9.41).The tip is directed towards the bracket to prevent damage to the enamel. 3. A rocking or pushing force is then applied on the bracket by engaging the vibrating scaler tip in the purchase point between the

225

2. Vibration of ultrasonic tip used for debonding is uncomfortable for the patient as moderate forces are applied. 3. Wear of ultrasonic tip as the ceramic brackets are harder than stainless steel tip. Scaler tip get blunt with time and needed to be replaced so it is not cost effective (Figure 9.42). 4. Soft tissue injury can occur as sudden debonding of bracket occurs. 5. The need for water sprays to avoid heat buildup which may cause enamel or pulp damage. 6. Enamel damage can occur during creation


bracket and the enamel to break the bond and facilitate bracket removal.


CHAPTER of purchase point. 7. The bracket can dislodge in oral cavity as it is not gripped during debonding procedure.

9

recycled and reused. Impulse debonding shouldn't be used with ceramic brackets as it will cause bracket fracture. How it works The theory behind impulse debonding is to give a sudden impact shear type force to the bracket base that is strong enough to debond the bracket. The idea has been inspired from crown removal in prosthodontics.

Figure 9.42 brackets.

Wear of scaler tip by debonding of ceramic

Clinical notes Sharp pointed tips should be used. Ideally select tips which are used to remove hard calculus in interdental area. Always direct the instrument toward the bracket and apply moderate force on the scaler handle. Selection of ultrasonic method As ultrasonic debonding is not cost effective and is time consuming so it is clinically useful when fractured bracket is needed to be debonded. Instead of grinding the bracket ultrasonic scaler can be used because it has fewer chances to cause iatrogenic damage and leaves a smoother enamel surface26 than a high speed handpiece. It is a personal finding that ultrasonic debonding is more successful with weak adhesive such as low filled composites and GIC. Ultrasonic scalers are usually not used with metal brackets because of other better options available. In metal bracket ultrasonic scalers can be used in cases of amelogenesis and dentinogenesis imperfect.

Device Air pressure pulse device used in the studies31 for debonding metal brackets is Corona Flex by Kavo (Figure 9.43). A traditional crown remover can also be used (Figure 9.44).

Figure 9.43 Air pulse device recommended in experimental studies for metal bracket removal. The knob on back control the amount of force and trigger button at front is used to initiate the debonding process. It usually takes less than a second to debond a bracket by this method.

Impulse debonding Impulse debonding have been proposed 6, 31 to debond metal brackets without distorting their base and slot characteristics so that they can be

Figure 9.44 A traditional crown removing plier used for bracket removing. Bond failure occurs at bracket adhesive interference.

226

Selection of impulse debonding

These appliances give a sudden shear type of force with no control over the brackets so brackets usually fly out of the oral cavity. To gain better control over bracket during debonding usually a finger is placed over the bracket (Figure 9.45).

Impulse debonding has bond failure at bracket adhesive interference so it can safely be used for debonding of metal brackets if bracket recycling is intended. But this technique is more painful for the patient than wing and base method of mechanical debonding. Extra time is required to remove flash around the brackets with carbide burs. So this technique should be used only when mechanical debonding technique is not available. This technique should be avoided in mobile or sensitive teeth as greater amount of debonding force is required.

Thermal Debonding Figure 9.45 As an upward shear force is applied with this type of debonding and the bracket fly in upward direction so it is better to keep finger over the bracket.

Clinical Notes In impulse debonding more force is applied than mechanical debonding of brackets. The amount of force is greater from the impact side where the instrument toggle is applied so it is better to remove flash from that side (Figure 9.46).

As ultrasonic debonding is associated with increase time and cost thermal debonding is used as a time efficient and safe way to debond brackets. Because of the potential risk of iatrogenic damage associated with ceramic brackets debonding, thermal debonding is usually reserved for these brackets. Metal brackets can also be debonded by this method but mechanical debonding is preferred for these brackets .Thermal debonding is contraindicated for plastic brackets. Principles of Thermal debonding

Figure 9.46 Instrument was engaged from incisor side without removing the flash. Failure to remove flash on the impact side usually result in some flash being attached on the bracket thus increasing chances of enamel damage.

227

Thermal debonding of orthodontic brackets is based on the principle of application of heat. Polymers have a glass transition temperature range 32 in which their physical properties can change from rigid solids to viscous liquid. So heating the polymer based composite materials result in change in their structural properties because when heat is applied van der Waals forces that hold the polymers together are weaken by vibration of polymer chains which gain kinetic energy due to high temperature. The glass transition temperature 33 of BisGMA/HEMA composite resins is around 103


Clinical Notes


CHAPTER °C -159 °C depending upon the photoinitiator used and the water contents. So when BisGMA/ HEMA composite resins are heated above this temperature the solid cement become a viscous liquid 34. For successful debonding, iatrogenic damages to tooth structures should be avoided. Effects of Thermal debonding on Enamel Thermal debonding of orthodontic brackets can damage tooth enamel directly or indirectly. Direct damage can occur either by contact of hot instrument tip with enamel or laser irradiation of enamel. Both these iatrogenic damages can be avoided by using small thermal or laser tips and following the recommended instructions. Indirect damage to enamel occurs by conduction of heat from bracket to adhesive resin and eventually to enamel. It has been proposed35, 36 that if temperature of enamel is kept below 300 °C then its crystal structure will remain stable. As tensile strength of the resin is temperature dependent and is significantly reduced 37,38 above 150°C so heating the resin at this temperature won't affect the enamel as the temperature range is well below 300 °C. Effects of thermal debonding on dental pulp Because heat application is involved in thermal debonding, there is a potential risk that these procedures may lead to increase in pulp temperature and eventually pulp damage. In an experimental study on Mecaca rhesus monkeys on the effects of externally applied heat on dental pulp Zach and Cohen39 showed that an intrapulpal temperature increase of 4° F (1.8° C) did not cause any pulpal damage in their sample. However, an increase in pulpal temperature of 10° F (5.5° C) causes pulpal necrosis in 15% of the teeth. As the temperature increase from this limit chances of pulp damage increases. As Mecaca rhesus monkey teeth are

9

smaller than human teeth and have less dentine than human teeth so it is generally presumed that primate teeth show more increase in intrapulpal temperature than human teeth. So 5.5 °C is taken in dentistry as a benchmark for safe maximum increase in pulp temperature. Apart from the temperature of the heating element of thermal debonder, some other factors also play important role to effect pulp temperature. 1. Type of Bracket 2. Thickness of resin 3. Thickness of enamel 4. Thickness of dentine 5. Presence of any restorations in the teeth Type of bracket Type of bracket is important in thermal debonding. Metal brackets are good conductor of heat and electricity while ceramic brackets are good insulators. Plastic brackets will simply deform and melt on thermal application. Metal brackets require 32 less heat and half time to debond than ceramic brackets so there are greater chances of pulp damage in debonding metal brackets by thermal debonding. Type of resin The type of filler in composite cement also affects thermal debonding. More the polymer cross linking in the filler after curing of the resin more would be the debonding time and so there would be greater increase in pulp temperature. Powder liquid resin system resulted in a lower temperature change 32, 40 than the two-paste, no-mix products and the light-cured materials. No mix system is preferred 32 over two paste system for thermal debonding as it requires less heat.

228

1. Hot instruments Tips

Resin under the bracket also act as a heat insulating zone for dental pulp. Greater the thickness of resin under the bracket less would be the temperature change at the dental pulp. So a thin resin layer 40 will cause more buccal surface and pulpal temperature change than thick resin.

2. Electrothermal method

Thickness of Enamel Enamel provide outer protective barrier for pulp. With increased thickness of enamel less heat would be dissipated to tooth pulp. Teeth with attrition, erosion, abfraction and amelogenesis imperfect are at increased risk of pulp damage in thermal debonding. Thickness of dentine Dentine has low thermal conductivity and acts as an insulating zone for the dental pulp both for cold and hot temperature. So greater the thickness of dentine 41 less would be the temperature change in the pulp. Tissue fluid in the dentinal tubules also dissipates the heat generated during thermal debonding. Presence of any restoration in the teeth Patients with compromised teeth that have large restorations or a questionable pulpal status could behave adversely to amount of heat applied during thermal debonding. More heat is transferred to the dental pulp in case of restoration and if there is resin filling it will also become weaken by thermal debonding. In compromised cases performing pulp vitality tests before thermal debonding would inform the operator about the status of the pulp and thereby prevent the potential for pulpal damage 42 . Thermal debonding should be avoided in patient having dental restorations. Methods of thermal debonding It is done by three methods

229

3. Laser debonding Hot instrument tips In this method the temperature of resin is increased by placing a sharp hot instrument within the bracket slot or saddle for less than 5 seconds and simultaneously giving a torsional force to bracket by the same instrument. Conventionally the instrument used was backside of bracket holder after heating it on a flame gun. This method went into disuse because of following disadvantages 1. The clinician has no way to control the amount of heat that is transferred to the bracket and eventually to enamel and pulp. So it poses a greater risk of iatrogenic damage. 2. Brackets may fall in the mouth and hot bracket may cause soft tissue burn. 3. Hot instrument may cause soft or hard tissue damage on slippage due to sudden debonding of brackets. 4. Debonding instrument usually gets discolored after it is heated red hot. Thermal debonding by hot instruments tips have been abandoned in orthodontic practice. Electrothermal debonding Electrothermal debonding as the name indicates uses electric energy to transfer heat to the bracket for debonding. Electrothermal debonders (ETD) usually uses 15 to 50 watts of electric power 37,43 and its heating element is warmed28,44 to 370 to 450 °F (188-232 °C) . Usually 130+15 °C of heat is transferred to the bracket by the ETD instrument 43 .This temperature is within glass transition temperature of adhesive. So the adhesive


Thickness of resin


CHAPTER transform from solid to viscous liquid and debonding occurs. For ETD instrument the manufacturer recommended that tip or blade shouldn't be placed within bracket slot or saddle for more than 5 seconds. After the heating cycle, brackets are debonded by the tip of debonder giving a torsional force by rotation movement of the wrist. Various elctrothermal debonders were made for commercial use in 1980s and 90s. They were quite useful for chemical retention base of ceramic brackets. With improvement in design of bracket base and other methods available these instrument went into disuse.

9

LASER Debonding The term LASER stands for Light Amplification by the Stimulated Emission of Radiation. LASER was first introduced to the public in 1959 by Gordon Gould. The light emitted by a laser has three major characteristics 1. The light is of single wavelength. So it is monochromatic light. 2. The light beam waves are in the same phase or are coherent. 3. The light beams travel in parallel fashion, so light is collimated.

A

B Figure 9.47 A. Electromagnetic spectrum .B. Magnified view of the near ultraviolet, visible, near and mid infrared part of the spectrum at which lasers exist.

230

Amplitude

How Lasers Work?

It is the height of the wave from the zero axis to its peak. Amplitude shows the amount of energy for each photon. Larger the amplitude greater would be the energy of photon. The energy of photon is measured in joules.

Different tissues in the body preferentially absorb different wavelengths. In order for a wavelength to have a therapeutic effect, it must be well-absorbed by the target tissue. A wavelength that is poorly absorbed by its target tissue will have very little effects. A chart for absorption of wavelengths by various tissues chromophores is given (Figure 9.48). Depending upon wavelength lasers in dentistry can be classified as hard tissue lasers and soft tissue lasers. Some lasers fall in both categories because of diverse composition of hard and soft tissue. For example as water is present in both hard and soft tissues CO2 lasers can be used for both hard and soft tissues. On the other hand diode lasers are used only for soft tissues while Er: YAG laser are used for hard tissues.

The main particle of light is photon. Photon is a tiny particle of energy which travels in waves.

Wavelength It is the horizontal distance between any two corresponding points on the wave and is measured in meters, microns (10−6 meters) or nanometers (10−9 meters). Frequency Frequency is the number of oscillations per second, measured in hertz. As waves travel, they oscillate several times per second. Frequency is inversely proportional to wavelength. The shorter the wavelength, the higher would be the frequency. The electromagnetic spectrum is given in figure (Figure 9.47). On left side of this spectrum is the ultraviolet part which consists of very short wavelengths including gamma rays and x-rays. As wavelength is inversely proportional to energy, therefore these ultra-short wavelengths c o n t a i n m o s t e n e rg y o f t h e e n t i r e electromagnetic spectrum. That's why gamma rays and x-rays are potentially carcinogenic and mutagenic. Next to ultraviolet part of the spectrum from left to right is the visible part of the spectrum, the part of the spectrum that is visible to the human eye. These wavelengths, in increasing length and therefore in decreasing energy are violet, blue, green, yellow, orange, and red.

231

How laser debond brackets? As explained above all lasers have a certain wavelength and they carry energy at that wavelength. Some lasers heat the brackets and the hot brackets causes the adhesive to fail while other laser passes through the brackets and directly affect the adhesive by burning its liquid (water or monomer) contents or effecting its composition. Apart from wavelength other factors must be kept in mind to avoid iatrogenic damages to tooth structures. These are power density of lasers mentioned in Watts, time period in seconds, mode of operation of lasers that is continuous or pulse, mode of application which can either be point application or scanning mode application. Composition of adhesive and geometry of brackets also play crucial role during debonding. It is claimed that laser debond brackets by three


A wave has three basic properties.

Next to visible red part of the spectrum on the right side is the infrared part of the spectrum. This part of the spectrum includes very long wavelengths including radio, television, shortwave, and microwave radiation.

Basic concepts


CHAPTER

Figure 9.48 Absorption of wavelength by various tissues.

mechanism 45. 1) Thermal softening When the power density of laser is low, less energy is transferred by it to the brackets and eventually to the resin. This less energy will cause slow heat up of the resin or bracket depending on laser and bracket type. Monocrystalline brackets transmit laser energy directly to resin while polycrystalline brackets having multiple grain boundaries heats up and transmit less heat energy to the resin. As tensile strength of the resin is temperature dependent and is significantly reduced above 150°C, this slow heating of the resin will cause softening of resin once this temperature is reached and bracket slides over the tooth. Usually a debonding force is applied to the bracket after thermal softening. The amount of that debonding force is fraction of a mechanical debonding force. Ceramic brackets won't distort under such heat as its thermal expansion coefficient is twice than resin. Thermal Ablation Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. Thermal ablation occurs when the heating is fast enough to raise the temperature of the resin into its vaporization range before debonding by thermal softening occur. Thermal ablation result in bracket being blown off the tooth.

9

Thermal ablation occurs at higher power density than thermal softening. The higher energy of the laser will cause evaporation of liquid contents of resin and buildup of gases below the bracket. This gas pressure will blow off the bracket from the tooth without any debonding force. Bracket geometry will affect maximum transmittance of laser light and therefore ablation. As ablation proceeds rapidly there are little diffusion of heat to bracket so the bracket remains cool. Thermal ablation can occur even after a single pulse if pulse energy is high enough. 2) Photoablation Photoablation occur when very high laser energy is absorbed by the resin atoms. This absorbed energy is greater than resin atom dissociation energy levels. High gas pressure will buildup below the bracket due to decomposition of material and bracket will be blown off from the tooth. Like thermal ablation photoablation don't need any external debonding force and occur after a single pulse of high energy. Thermal softening is a slow process and occurs at low power density of laser while thermal ablation and photoablation occur very rapidly and at high energy density. Thermal softening can result in increase in both bracket and tooth temperature while in photoablation and thermal ablation little heat diffusion occur so bracket and tooth temperature remain near physiological level. The difference between the above processes can be made on how the bracket comes off from the tooth e.g. sliding or blown off. A brief review of some of lasers used to debond ceramic brackets is given: Excimer Lasers Excimer laser are used in wavelengths of 248

232

Debonding force is applied to the bracket during laser application. Tocchio45 recommend this force to be 0.8 MPa . Using 3 Watt for 3 second seems to be a reasonable approach.

Excimer laser uses pulse energy of 111 milli joule with power density of 17 w/cm2 for debonding. Debonding is done with less than 5 seconds of bracket exposure by laser. A continuous debonding force is placed on the bracket during application of laser. Uses of excimer lasers have only anecdotal evidence and these lasers are not used for bracket debonding in contemporary orthodontics. Nd:YAG Laser The Nd:YAG laser has a wavelength of approximately 1064 nm, in the invisible nearinfrared portion of the electromagnetic spectrum (Figure 9.49). The Nd:YAG wavelength is highly absorbed by pigmented tissue and little by dental hard tissue so this laser is usually used as a soft tissue laser. Strobl et al37 showed that the transmission of Nd: YAG laser was greater for monocrystalline brackets than polycrystalline brackets. So greater incidence light reaches enamel surface in case of monocrystalline brackets. Also greater heat up of adhesive occurs in case of monocrystalline brackets. Different power densities have been proposed for safe debonding of ceramic brackets with this laser without causing enamel or pulp damage. These are: 1. 3 to 33 watts for 3seconds for monocrystalline brackets to a maximum of 24 seconds for polycrystalline brackets 45. 2. 3 Watts for 3 seconds 46. 3. High-peak power Nd:YAG laser at 2.0 J for 1.2-ms pulse duration with one pulse per second shot and two points application on the brackets47.

233

Figure 9.49

Dental Nd:YAG laser system

Erbium Lasers Within the erbium lasers, there are two different wavelengths. These are Er,Cr:YSGG having a wavelength of 2790 nm and Er:YAG laser with a wavelength of approximately 2940 nm. Both wavelengths are in the near to mid-infrared portion of the electromagnetic spectrum and these lasers are emitted in a pulsed mode. The Erbium wavelengths have a high affinity for hydroxyapatite and also for water. Er:YAG lasers is usually used for ceramic bracket debonding as it has less thermal effect than the Nd:YAG or CO2 laser. The most popular method 48, 49 of debonding by Er:YAG laser on polycrystalline brackets is using a 4.2 Watt laser which is moved over the surface of bracket in a scanning fashion for 6 to 9 seconds (Figure 9.50). Debonding force is applied on bracket after 45 seconds. Debonding force after laser irradiation is usually fraction of the mechanical debonding force. Carbon dioxide lasers


nm to 308 nm in ultraviolet region of electromagnetic spectrum 45. Ultraviolet light (200 to 300 nm) can readily transmit through the ceramic material.


CHAPTER

9

Strobl et al.37 showed that CO2 laser debonding significantly reduced debonding force by thermal softening of the resin. Following settings have been recommended for CO2 lasers in the literature. 1.Continuous mode at 18 W for 2 seconds 50.

2. Continuous mode at 14 W for 2 seconds 37.

A

B

Figure 9.50 A. Erbium based laser machine. B. Scanning method is done by moving tip of laser instrument from one end of bracket to another.

Carbon dioxide laser is one of the earliest gas lasers to be developed and is invented by Kumar Patel of Bell Labs in 1964. CO2 laser has an active medium of carbon dioxide gas and typically produces an invisible laser wavelength of approximately 10,600 nm in the mid-infrared portion of the electromagnetic spectrum ( Figure 9.51).

3. Continuous mode 4 W or less with 5 seconds irradiation 36. 4. Normal pulse laser for 3 seconds at 3 W or Super pulse laser at 2 Wfor 3 seconds 50. 5. CO2 lasers using 188 W, 400 Hz with 5 seconds scanning movement over the bracket.

As water and hydroxyapatite absorbs CO2 wavelength very well it is used as both a hard and soft tissue laser. In most studies in orthodontic literature, carbon dioxide lasers have been preferred for debonding because their wavelength is more easily absorbed by the ceramic brackets. The CO2 laser offers the option of operating continuously or in a wide variety of pulse repetition frequencies, from few hertz to well over 100kHz.It can be in continuous mode, super pulse mode ( short duration lasers with gated pulse width of 1-500 millisecond ),normal pulse CO2 laser (gated pulse width of 5-500 millisecond) or ultra-pulse. Super pulse CO2 laser are superior to normal pulse laser as they are separated by sufficient time to allow the tissue to cool between pulses thus allow minimum thermal damage and carbonization.

Figure 9.51 A CO2 laser machine .Main disadvantage of CO2 lasers are the increased bulk of machine and cost.

Choice of Brackets Most commonly used ceramic brackets in contemporary orthodontics are monocrystalline and polycrystalline. Both these brackets have different structure. Polycrystalline brackets have multiple grain boundaries and that makes difference in laser deboning because these grain boundaries cause

234

Lasers are able to debond both monocrystalline and polycrystalline brackets. Because of suitable structural properties monocrystalline brackets 37,45require less power density and less time for debonding which is usually by thermal ablation or photoablation. Monocrystalline brackets remain cold after debonding. On the other hand polycrystalline brackets need more power densities of laser light and more time to debond. Polycrystalline brackets usually heat up under such power densities and debonding usually occurs by thermal softening. Polycrystalline brackets can also be debonded by ablation of adhesive if the laser emitting radiation is 4 to 7 µm range45. But there are more chances of enamel or pulp damage in this range if debonding of polycrystalline brackets is attempted.

Safety with lasers When operating a dental laser, safety of all the people working in dental office should be the first and foremost consideration. Anyone in the vicinity of the laser should use protective eyewear and high volume suction should be used to evacuate vapor plums. Protective eyewear can also be used with dental or surgical loupes (Figure 9.52). These protective eyewear are wavelength specific. Safety signs should be put in place while doing laser debonding.

A

As monocrystalline bracket take less time and less power density for laser irradiation it is recommended 52 that they should be preferred over polycrystalline brackets for laser debonding.

B

Choice of Adhesive

Selection of Lasers for debonding

Mimura and colleagues 53 investigated suitable resin for laser debonding (CO2) and found that MMA containing 4-META resins requires less laser energy of up to 3W and less debonding force than Bis-GMA which require up to 7W of laser energy. It was recommended52 that if laser debonding was intended in clinical use MMA containing 4-META resins should be used for orthodontic bonding.

Lasers for orthodontic debonding of brackets still remains a novel approach as laser system is not routine part of the dental office and it takes more time to debond bracket by this method. Laser should only be used in cases where bracket fracture or risk of enamel damage is too great like cracked enamel, root canal treated teeth.A personal non evidence based opinion for polycrystalline brackets is to use scanning m e t h o d w i t h E r : YA G l a s e r. F o r monocrystalline brackets low power settings can be used with same method.

In an in vitro study54 it was concluded that orthodontic adhesive containing thermal expansion microcapsules can be used with CO2 laser for debonding with no reported

235

iatrogenic damage to tooth structures.

Figure 9.52 A. Laser goggles for specific wavelength. B. Dental loupes with laser filters.


lateral spreading of laser light. Because of lateral spreading of laser light less light reaches the adhesive below the bracket. In monocrystalline brackets up to 80 % of laser light reaches the adhesive surface.


CHAPTER Reference 1. Arhun N, Arman A. Effects of orthodontic mechanics on tooth enamel: a review. Seminars in Orthod. 2007 Dec; 13(4):281–91. 2. Zachrisson, B.U. and Büyükyilmaz, T.: Bonding in orthodontics. In: Orthodontics Current Principles and Techniques. T.M. Graber, R.L. Vanarsdall and K.W.L. Wig (eds.), pp. 579-653. Philadelphia, Elsevier, 2005. 3. Artun J, Bergland S. Clinical trials with crystal growth conditioning as an alternative to acid-etch enamel pretreatment. Am J Orthod. 1984 Apr; 85(4):333-40. 4. Brosh T, Kaufman A, Balabanovsky A, Vardimon AD. In vivo debonding strength and enamel damage in two orthodontic debonding methods. J Biomech. 2005 May;38(5):1107-13. 5. Bishara SE, Fonseca JM, Boyer DB. The use of debonding pliers in the removal of ceramic brackets: Force levels and enamel cracks. Am J Orthod Dentofacial Orthop 1995; 108:242-8. 6. Knösel M et al. Impulse debracketing compared to conventional debonding. Angle Orthod. 2010 Nov; 80(6):1036-44. 7. Su MZ, Lai EH, Chang JZ, Chen HJ, Chang FH, Chiang YC, Lin CP. Effect of simulated debracketing on enamel damage. J Formos Med Assoc. 2012 Oct; 111(10):560-6. 8. Coley-Smith A, Rock WP. Distortion of metallic orthodontic brackets after clinical use and debond by two methods. Br J Orthod. 1999 Jun; 26(2):1359. 9. Oliver RG. The effect of different methods of bracket removal on the amount of residual adhesive. Am J Orthod Dentofacial Orthop. 1988 Mar; 93(3):196-200. 10. Parrish BC, Katona TR, Isikbay SC, Stewart KT, Kula KS. The effects of application time of a selfetching primer and debonding methods on bracket

9

bond strength. Angle Orthod. 2012 Jan; 82(1):1316. 11. Normando TS, Calçada FS, Ursi WJ, Normando D. Patients' report of discomfort and pain during debonding of orthodontic brackets: a comparative study of two methods. World J Orthod. 2010 Winter; 11(4):e29-34. 12. Lee-Knight CT, Wylie SG, Major PW, Glover KE, Grace M. Mechanical and electrothermal debonding: effect on ceramic veneers and dental pulp.Am J Orthod Dentofacial Orthop. 1997 Sep; 112(3):263-70. 13. Bowen RL, Rodriguez MS. Tensile strength and modulus of elasticity of tooth structure and several restorative materials. J Am Dent Assoc. 1962 Mar; 64:378-87. 14. Retief DH. Failure at the dental adhesive-etched enamel interface. J Oral Rehabil. 1974 Jul; 1(3):265-84. 15. Reynolds IR. A review of direct orthodontic bonding. British J of Orthod 1975; 2:171-178. 16. Flores DA, Caruso JM, Scott GE, Jeiroudi MT. The fracture strength of ceramic brackets: a comparative study. Angle Orthod. 1990 Winter; 60(4):269-76. 17. Swartz ML. Ceramic brackets. J Clin Orthod. 1988 Feb; 22(2):82-8. 18. Bishara SE, Olsen ME, Von Wald L. Evaluation of debonding characteristics of a new collapsible ceramic bracket. Am J Orthod Dentofacial Orthop. 1997 Nov; 112(5):552-9. 19. Bishara SE, Fehr DE. Comparisons of the effectiveness of pliers with narrow and wide blades in debonding ceramic brackets. Am J Orthod Dentofacial Orthop. 1993 Mar; 103(3):253-7. 20. Winchester LJ. Methods of debonding ceramic brackets. Br J Orthod 1992; 19: 233–7. 21. Ghafari J. Problems associated with ceramic

236

ultrasonic instrumentation. Am J Orthod Dentfacial Orthop. 1995 Sep; 108(3):262-6.

22. Joseph VP, Rossouw E. The shear pond strengths of stainless steel and ceramic brackets used with chemically and light-activated composit resins. Am J Orthod Dentofacial Orthop 1990; 97:121-125.

31. Knösel M, Mattysek S, Jung K, KubeinMeesenburg D, Sadat-Khonsari R, Ziebolz D. Suitability of orthodontic brackets for rebonding and reworking following removal by air pressure pulses and conventional debracketing techniques. Angle Orthod. 2010 Jul;80(4):461-7.

23. Waldren M. An introduction into the fracture toughness of a light cured orthodontic adhesive. MSc Thesis, University of London, 1991. 24. Karamouzos A, Athanasiou, A, Papadopoulos, MA. Clinical characteristics and properties of ceramic brackets: A comprehensive review. Am J Orthod Dentofac Orthop 1997; 112:34-40. 25. Larmour CJ, Chadwick RG. Effects of a commercial orthodontic debonding agent upon the surface microhardness of two orthodontic bonding resins. J Dent. 1995 Feb; 23(1):37-40. 26. Bishara SE, Trulove TS. Comparisons of different debonding techniques for ceramic brackets: an in vitro study. Part II; findings and clinical implications. Am J Orthod Dentofacial Orthop.1990; 98:263-73. 27. Krell KV, Courey JM, Bishara SE. Orthodontic bracket removal using conventional and ultrasonic debonding techniques, enamel loss, and time requirements. Am J Orthod Dentofacial Orthop 1993; 103:258-66. 28. Bishara SE, Trulove TS. Comparisons of different debonding techniques for ceramic brackets: an in vitro study. Part I. Background and methods. Am J Orthod Dentofacial Orthop. 1990 Aug; 98(2):145-53.

237

32. Rueggeberg FA, Maher FT, Kelly MT. Thermal properties of a methyl methacrylate-based orthodontic bonding adhesive. Am J Orthod Dentofacial Orthop 1992; 101:342-9. 33. Park HS, Ye Q, Topp EM, Misra A, Kieweg SL, Spencer P. Effect of photoinitiator system and water content on dynamic mechanical properties of a light-cured bisgma/hema dental resin. J Biomed Mater Res A 2009;93:1245-51. 34. Walter R, Swift EJ Jr,Sheikh H, Ferracane JL. Effects of temperature on composite resin shrinkage. Quintessence Int 2009; 40:843-7. 35. He LH, Swain MV. Influence of environment on the mechanical behavior of mature human enamel. Biomaterials. 2007 Oct; 28(30):4512-20. 36. Iijima M, Yasuda Y, Muguruma T, Mizoguchi I. Effects of CO(2) laser debonding of a ceramic bracket on the mechanical properties of enamel. Angle Orthod. 2010 Nov;80(6):1029-35. 37. Strobl K, Bahns TL, Willham L, Bishara SE, Stwalley WC. Laser-aided debonding of orthodontic ceramic brackets. Am J Orthod Dentofacial Orthop. 1992 Feb;101(2):152-8. 38. Obata A. Effectiveness of CO2 laser irradiation on ceramic bracket debonding. J Jpn Orthod Soc 1995;54:285-95.

29. Yousefimanesh H, Robati M, Kadkhodazadeh M, Molla R. A comparison of magnetostrictive and piezoelectric ultrasonic scaling devices: an in vitro study. J Periodontal Implant Sci. 2012 Dec; 42(6):243-7.

39. Zach L, Cohen G. Pulp response to externally applied heat.Oral Surg Oral Med Oral Pathol. 1965 Apr; 19:515-30.

30. Boyer DB, Engelhardt G, Bishara SE. Debonding orthodontic ceramic brackets by

40. Crooks M, Hood J, Harkness M. Thermal debonding of ceramic brackets: an in vitro study.


brackets suggest limiting use to selected teeth. Angle Orthod. 1992 Summer; 62 (2): 145-52.


CHAPTER

9

Am J Orthod Dentofacial Orthop. 1997 Feb; 111(2):163-72.

bonding and debonding. Eur J Orthod. 1999 Apr;21(2):193-8.

41. Lisanti VF, Zander HA. Thermal injury to normal dog teeth: in vivo measurements of pulp temperature increases and their effect on the pulp tissue. J Dent Res. 1952 Aug; 31(4):548-58.

51. Ahrari F, Heravi F, Fekrazad R, Farzanegan F, Nakhaei S. Does ultra-pulse CO2 laser reduce the risk of enamel damage during debonding of ceramic brackets? Lasers Med Sci. 2012 May;27(3):567-74.

42. Takla PM, Shivapuja PK. Pulpal response in electrothermal debonding. Am J Orthod Dentofacial Orthop. 1995 Dec; 108(6):623-9.

52. Azzeh E, Feldon PJ. Laser debonding of ceramic brackets: a comprehensive review. Am J Orthod Dentofacial Orthop. 2003 Jan;123(1):79-83.

43. Sheridan JJ, Brawley G, Hastings J. Electrothermal debracketing. Part I. An in vitro study. Am J Orthod. 1986 Jan; 89(1) :21-7.

53. Mimura H, Deguchi T, Obata A, Yamagishi T, Ito M. Comparison of different bonding materials for laser debonding. Am J Orthod Dentofacial Orthop. 1995 Sep;108(3):267-73.

44. Zarrinnia K, Eid NM, Kehoe MJ. The effect of different debonding techniques on the enamel surface: An in vitro qualitative study. Am J Orthod Dentofacial Orthop 1995; 108:284-93. 45. Tocchio RM, Williams PT, Mayer FJ, Standing KG. Laser debonding of ceramic orthodontic brackets. Am J Orthod Dentofacial Orthop. 1993 Feb; 103(2):155-62.

54. Saito A, Namura Y, Isokawa K, Shimizu N. CO2 laser debonding of a ceramic bracket bonded with orthodontic adhesive containing thermal expansion microcapsules. Lasers Med Sci. 2013 Nov 13.

46. Liu XL, Wang LH, Wang MF, Liu L, Wang Q, Zhai JH. [Histomorphological effects of Nd:YAG laser for debonding ceramic brackets on rabbit pulp]. Hua Xi Kou Qiang Yi Xue Za Zhi. 2009 Aug;27(4):413-6. 47. Hayakawa K. Nd: YAG laser for debonding ceramic orthodontic brackets. Am J Orthod Dentofacial Orthop. 2005 Nov;128(5):638-47. 48. Oztoprak MO, Nalbantgil D, Erdem AS, Tozlu M, Arun T. Debonding of ceramic brackets by a new scanning laser method. Am J Orthod Dentofacial Orthop. 2010 Aug; 138(2):195-200. 49. Nalbantgil D, Oztoprak MO, Tozlu M, Arun T. Effects of different application durations of ER:YAG laser on intrapulpal temperature change during debonding. Lasers Med Sci. 2011 Nov;26(6):735-40. 50. Obata A, Tsumura T, Niwa K, Ashizawa Y, Deguchi T, Ito M. Super pulse CO2 laser for bracket

238

CHAPTER

10

Adhesive Remnants Removal In this Chapter

Hand instrumentation for adhesive removal Adhesive removing pliers Ligature wire cutters Hand Scalers

Discs Finishing and polishing auxiliaries Ultrasonic scalers Sandblasting or air abrasion Adhesive remnants removal by Lasers

Rotatory instruments Burs Carbide burs Diamond burs Steel burs Brown and green stones Composite burs

After orthodontic brackets removal, adhesive remnants needed to be removed from the tooth so that enamel can be returned to its pretreatment condition. These residual adhesive if remained attached to the teeth will be a potential plaque retentive area and may get discolored with time. The amount of these adhesive remnants depends upon the type of bond failure. If bond failure during debonding occurs at bracket adhesive interference, more adhesive needed to be removed as compared to a bond failure at enamel adhesive interference (Figure 10.1).

239

Removal of these adhesive remnants should be done without causing any damage to enamel.

Figure 10.1 Adhesive remnants on the tooth after debonding. Bond failure occur at the bracket adhesive interference. Such bond failure require more time to clean adhesive from the tooth enamel.

Adhesive Remnants Removal

CHAPTER It has been reported 1 that the highest concentration of fluoride is found in the outermost 20 µm of enamel and it rapidly decrease as the enamel proceeds towards dentin. Also apart from high mineral contents, this outermost layer of the enamel contributes in hardness of the enamel. Loss of this outermost enamel surface may lead to decrease resistance of enamel to acids produced in plaque and make it more prone to decalcification 2. So loss of this outermost layer of enamel should be avoided. But unfortunately this is not possible clinically. It is shown that (Table10.1) in almost all processes that requires cleaning of enamel some degree of enamel damage is inevitable. As the adhesive used for orthodontic bonding have microretention within the enamel because of etching process or chemical composition of adhesive, some enamel loss during this adhesive removal stage is inevitable 3, 4. `Table 10.1 procedures. Procedure

Enamel Loss from different Enamel loss in micron(µm) 4.97 + 1.49 µm

Manual tooth brushing5 20 or 80 linear strokes/min Pumicing with bristle 10.7+5.2 µm brush6 Pumicing with rubber 5.01+2.8 µm 6 cups 90 second etching with 10 µm phosphoric acid6 Enamel loss during 2.9 or