The Effect Of Thermocycling On Tensile Bonding

The Effect Of Thermocycling On Tensile Bonding Strength Of Three Different Brands Of Artificial Teeth With Denture Base In vitro study

A Thesis Submitted To The Council Of College Of Dentistry, Hawler Medical University,In Partial Fulfillment Of The Requirements For The Degree Of Master Of Science In Prosthodontics

By Ghalib Rahman Hawrami B.D.S

Supervised by: Prof. Dr. Souza A. Faraj B.D.S. , M.Med.Sci.

October

Galla-Rezan

Thi Al-qaida

2011 A.D.

2711 K.

1432 A.H.

DEDICATION o To my mother and spirit of my father o To my faithful wife o To my lovely children

Parez Padasht o And Pezan

o To my brothers and sister

Ghalib

Declaration of supervisor I certify this thesis was prepared by Ghalib Rahman Hawrami under my supervision at the college of dentistry, hawler medical university in partial fulfillment of the requirements for the degree of Master of Science in prosthodontics.

Supervisor Professor: Dr. Souza Abdul-Aziz Faraj B.D.S. , M.Med.Sci.

In view of the available recommendation, I forward this thesis for debate by the examining committee.

Assistant Professor Dr. Ziwar Ahmad Salh The Dean of the college of dentistry

Committee Certification of Supervisor

We the examining committee, certify that we have read this thesis and have examine the graduate student Ghalib Rahman Hawrami in its content , in our opinion it meets the student of thesis for the master degree of science in prosthodontics.

Professor Dr. Salem Abdul-Latif Salem Chairman of examining committee

Professor

Lecturer

Dr. Widad A. Al-Nakkash

Dr. Rizgar M. Ameen Hasan

Member

Member

Supervisor Professor: Dr. Souza Abdul-Aziz Faraj B.D.S. , M.Med.Sci.

A approved by the council of the college of dentistry. Assistant Professor Dr. Ziwar Ahmad Salh The Dean of the college of dentistry

ACKNOWLEDGEMENT

I Indebted to Allah for always simplifying difficulties of life and helping me to finish what I start where I found it very hard. All respect to the dean of Dentistry College, Hawler medical university

Dr. Ziwar Al-Qasab for his support and to head of

prosthodontics department Dr. Rizgar M. Ameen Hasan and all dentistry colleges staff. All respect to Erbil Medical Technical Institute for allowing the time, and support for this thesis. Great thank to my supervisor Dr. Souza Abdul-Aziz Faraj, for here constant support, patience, gaudiness and encouragement through my work. Special thank to head of dental technical department in Erbil Medical Technical Institute Dr. Jabar Hussain for his valuable advice and support before and during the time of this thesis. I wish to thank Dr. Ibrahim Baqi Hawrami Lecturer in electrical engineering department / college of engineering and to Dr. Idress Izat Chuchani Lecturer in mechanical engineering department / college of engineering, for his great support and help. Finally, the role of my Wonderful wife and my family is observed, all loves and appreciation to them for their kind, support and encouragement.

I

ABSTRACT Present study is designed to evaluate the tensile bonding strength of the teeth were treated with thermocycling. Three different brands of acrylic teeth: (M=MAJOR DENT), (K=KAILI HUGEDENT) and (S= SUPER NEWCLAR IDEAL DENT MAKOO) were subdivided to A=control, B=1000 cycle and B=2000 cycle (n=8). Thermocycling cycle was 30 seconds in 55oC and 30 seconds in 5oC using automatic designed device. Universal testing machine was used to evaluate the tensile bonding strength of teeth with denture base resin. In this study the tensile bonding strength of the group A shows K brands was the highest with (14.288 MPa) while the brand S lowest with (12.777MPa), but in group B it was found that M brand was the highest with (12.01MPa), and K brand was the lowest by (10.167 MPa). While in group C it's obvious that S brand was scored (11.017MPa), and the lowest one was K brand with (8.471MPa). A very high significant difference among the groups of M and K brand (p < 0.0001), with a significant difference among groups of S brand (p < 0.05). It's obvious that all brands were used in this study influenced by thermocycling. All failures which was seen was adhesive or mixed completely, the M brand failed adhesively and the thermocycling process not affect its property while the K and S brands were with mixed failure or adhesive failure and both brands was influenced by thermocycling and the mode of failure change to more adhesive. Previous result give conclusion of that S brand is the best one in relation to K and M because it lost minimum amount of its bonding property after thermocycling, and the worst one was K since it lost maximum bonding properties. Also it was concluded that thermocycling affect all brands in different degree and change the mode of failure from mix to adhesive. II

LIST OF CONTENT Title

Page No.

Dedication Acknowledgment

I

Abstract

II

List of content

III

List of figure

VI

List of table

IX

List of abbreviation

XI

Introduction

1

Objectives

2 Chapter one : Review of literature

1.1.

Polymer

3

1.1.1.

History

3

1.1.2.

Polymerization of methylmethacrylate

5

1.1.3.

Types of polymerizations

5

Polycondensation

5

Polyaddition

5

Reaction of polymerization

6

Activation

6

Initiation

6

Propagation

6

Termination

6

Artificial teeth

7

1.1.4.

1.2.

III

1.2.1.

History

7

1.2.2.

Type of artificial teeth according to material

8

Hard acrylic

8

Visible light cure composite

8

Porcelain vacuum fired

8

Acrylic resin (plastic)

9

Properties of acrylic teeth

9

Advantage of acrylic teeth

9

Disadvantage of acrylic teeth

10

Chemical composition of acrylic teeth

12

1.3.

Denture base

14

1.3.1.

History

14

1.3.2.

Type of denture base polymers

15

1.3.3.

Properties of denture base:

15

1.3.4.

Compositions of acrylic denture base materials

17

1.4.

Thermocycling

19

1.5.

Bonding of artificial teeth to acrylic denture base

25

1.2.3.

Chapter two: Material and Method 2.1.

Equipments and materials

36

2.1.1.

Equipments and instruments

36

2.1.2.

Materials

38

2.2.

Methodology

39

2.2.1.

Sample preparation

39

A. Preparation the ridge lap portion of teeth

39

IV

B-preparation of mold and sample

42

C. Flasking and deflasking

45

D. Finishing and polishing of specimens

47

2.2.2.

Grouping of specimens

49

2.2.3.

Thermocycling

50

2.2.4.

Debonding test

63

2.2.5:

Mode of failure

66

2.2.6.

Statistical analysis and software

68

Chapter three: Result 3.1.

Tensile bonding strength [TBS]

69

3.2.:

Mode of failure

78 Chapter four :Discussion

Discussion

81

4.1.

Thermocycling effect on tensile bonding strength [TBS]

83

4.2.

Thermocycling effect on mode of failure

84

Chapter Five :Conclusions and Suggestions 5.1.

Conclusions

86

5.2.

Suggestions

87

Reference

88

Appendix

100

V

LIST OF FIGURES Fig. No. Title 1.1

Page No.

Two-dimensional schematic representations of

3

linear and cross-linked polymers 1.2

The structural formulas of common methacrylate in

4

dentistry 2.1

Artificial acrylic teeth used, M: MAJOR DENT, K:

39

KAILI HUGEDENT, S: SUPER NEWCLAR IDEAL DENT MAKOO 2.2

Preparation the ridge lap portion of teeth

40

2.3

Surface roughness tester (profelometer)

41

2.4

A: Brass collar, B: Brass bar , C: Tooth attach to

42

brass bar 2.5

Mold to obtain standard attachment, alignment,

42

diameter and length of wax pattern 2.6

Mold of silicone for occlusal third of teeth (3 pairs

44

of mold right and left for each brands) 2.7

Flasking and Deflasking of specimens.

45

2.8

Mixing acrylic cover in jar and Packing of

46

specimens. 2.9

Sample with plaster during finishing and before thermocycling

VI

48

2.10

Diagram illustrated specimens grouping of acrylic

49

artificial teeth 2.11

Skeleton of thermocycling machine

51

2.12

Mechanical part of thermocycling machine

52

2.13

Satellite dish mover with micro switch (break the

53

current cycle at exact point) and Satellite postioner 2.14

Constructed beam to transmit the movements from

54

the dish mover to the pulley (inside to out side). 2.15

Collected piece inside the dish mover and Dish

55

movers after preparing to transmit the movements from inside dish mover to out side pulley with aid of the beam. 2.16

Out side of cylindrical role soldered to original base,

56

Inside of cylindrical role soldered to the beam and pulley 2.17

Vertical floss passing through the ring of horizontal

56

floss and Constructed rack for sample holding 2.18

Mechanical and electrical part of thermocycling

57

machine 2.19

Electro digital part which control path, period and

59

number of cycle. 2.20

Electrical current cycle of device which control: time, period and counting of cycle

VII

61

2.21

Thermocycling device parts after collection

62

2.22

Metal fixture to grasping the specimens the end is

63

adapted to tight with the universal testing machine 2.23

Grasping and debonding test with universal testing

64

machine 2.24

Visual , Digital camera and Microscopic

66

examination 2.25

Type of failure (Cohesive acrylic, cohesive tooth,

67

Mixed and Adhesive). 3.1

Histogram of means Tensile Bonding Strength of

75

groups for brand (MPa) arranged by brands 3.2

Histogram of means Tensile Bonding Strength of

75

groups for brand (MPa) arranged by treatments 3.5

Mode of failure A: adhesive and M: mixed

VIII

78

LIST OF TABLES Table

Title

Page

No.

No.

1.1.

Composition of acrylic denture base materials

19

3.1

Mean, standard deviation, standard error of mean, maximum,

69

minimum of control groups of MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) respectively 3-2

Analysis of variance (ANOVA) of control for (MAJOR DENT,

70

KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) 3-3

Mean, standard deviation, standard error of mean, maximum,

71

minimum of 1000cycle groups of ( MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) respectively 3-4

Analysis of variance (ANOVA) of thermocycling 1000 cycle

71

for (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) 3-5

Mean, standard deviation, standard error of mean, maximum, minimum of 2000 cycle groups of ( MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) respectively

IX

72

3-6

Analysis of variance (ANOVA) of thermocycling 2000 cycle

73

for (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) 3-7

statistical decision between groups (A= control, B= 1000 cycle

73

and C= 2000 cycle) of all three brand artificial teeth (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) 3-8

Statistical decision between control and treat groups (A=

76

control, B= 1000 cycle and C= 2000 cycle) of MAJOR DENT 3-9

Statistical decision between control and treat groups (A=

77

control, B= 1000 cycle and C= 2000 cycle) of KAILI HUGEDENT 3.10

statistical decision between control and treat groups (

77

A=control , B= 1000 cycle and C= 2000 cycle )of SUPER NEWCLAR IDEAL DENT MAKOO 3-11

Mode of failure for control group of all brands

79

3-12

Mode of failure for thermocycling 1000 cycle group of all

80

brands 3-13

Mode of failure for thermocycling 2000 cycle group of all brands

X

80

LIST OF ABBREVIATIONS o

C

Degree centigrade

%

Percentage

µTBS

Microtensile bond strength

4-META

4-Methacryloxyethyl trimellitate anhydride Infinity

ANOVA

Analysis of variance

1BisGMA

Bisphenol -A- glycidyl dimethacrylate

Cm

Centimeter

DCL

Double cross-linking

EGDMA

Ethylene glycol dimethacrylate

GPT

Glossary of prosthodontic terms

HEMA

Hydroxyethyl methacrylate

hr

Hour

Hz

Hertz

IPN

Interpenetrating polymer networks

1ISO

International standard organization

1IUPAC

International union of pure and applied chemistry

Kg

Kilogram

Kg . m . sec

Kilogram .meter. Second

LPR

Polymerized denture base resins

LSD

Least significant difference

m. s2

Meter. Second square

XI

m2

Meter square

MAPR

Metal Adhesive Auto polymerized resin

mm

Millimeter

MMA

Methylmethacrylate

MPa

Mega Pascal

N

Newton

?

diameter

p

Probability of chance

Pa

Pascal

1PMMA

Poly methylmethacrylate

Ra

Roughness

SBS

Shear bond strength

S.D

Standard deviation

SEM

Scanning electron microscope

TBS

Tensile bond strength

TEGDMA

Tri ethylene glycol dimethacrylate

US

United state

VLC

Visible Light Cured Resin

Vt

Volt

X

Magnifications Alpha

CM

Compression molded

IM

Injection molded

XII

Introduction

INTRODUCTION Millions of people throughout the world have lost all of their teeth, and the prevalence increases with age. In the United States, About 30% of 65 years and older are edentulous, compared to 46% in 20 years ago. These figures are higher for those living in poverty (US Department of Health and Human Services, 2002). Edentulous state is considered as a social psychological catastrophe by majority of people. Replacements by artificial substitutes such as dentures are vital. Many materials and techniques for fabrication had been employed for construction of dentures. Materials like Ivory, Wood and various metals like Gold have been used to make teeth. Resin teeth were introduced in 1930 and they are in use till this day in fabrication of majority of prosthesis (Winkler et al, 1992 cited by Mello et al, 2009). Thermal stresses naturally occur in vivo, and these phenomena are often represented in laboratory simulations as thermal cycling regimens, which are the in vitro processes of subjecting both the restoration and the tooth to extreme temperatures. Thermalcycling simulates the entrance of hot and cold substances in the oral cavity, and shows the relationship of linear coefficient of thermal expansion between tooth and denture base material (Nalcai and Ulusoy, 2007). About %80 of prosthetic appliances which have to be repaired one third of these repairs are debonding of the teeth (Cunningham, 1993 cited by Kavrut and Duymus, 2005). Despite efforts to ensure bonding between the artificial teeth and the denture base, it has been reported that 33% of all denture were repaired was be repairs due to debonding of teeth (McCabe and Walls, 2008). The present study is designed to evaluate the tensile bonding strength of three different brands Acrylic artificial teeth with denture base after thermocycling procedure with 1000 and 2000 cycles.

Chapter One

Review of Literature

The aim of study 1- Evaluation the tensile bonding strength of acrylic artificial teeth with denture base material with out and with thermocycling at 1000 cycle and 2000 cycle 2- Evaluation the effect of thermocycling on mode of failure between acrylic artificial teeth with denture base material: at 1000 cycle and 2000 cycle

Chapter One


Chapter One


REVIEW OF LITERATURE

1.1. Polymer 1.1.1. History: Polymers are macromolecules built up by linking together of large numbers of much smaller molecules. The small molecules that combine with each other to form polymer molecules are termed monomers, and the reactions by which they combine are termed polymerizations. There may be hundreds, thousands, tens of thousands, or more monomer molecules linked together in a polymer molecule (George, 2004). The above unique excellent properties of polymer make it play an important role in the all dentistry branch including prosthodontics (Deb, 1998). Polymeric materials in dentistry can be divided into linear polymers (e.g. Poly methylmethacrylate( PMMA) and cross linked polymers (e.g. Bisphenol -A- glycidyl dimethacrylate (BisGMA)). Linear polymers are composed of long carbon chains which are linked together by weak chemical bonds Fig (1. 1) (O Brien, 2008).

Fig (1.1): Two-dimensional schematic representations of linear and cross-linked polymers (O Brien WJ, 2008).

Chapter One


Linear polymers can be heated and reformed and they are also dissolvable to certain solvents. Cross linked polymers are composed of carbon chains which are linked together by strong chemical covalent bonds. Cross linked polymers can not be reformed by heat and it is also more difficult to dissolve them into solvents (O Brien, 2008).

Figure (1.2): The structural formulas of common methacrylates in dentistry (O Brien, 2008). Most polymeric materials used in dentistry Fig (1.2), are based on chemistry of methacrylates (Vuorinen, 2010). Methacrylates are esters of methacrylic acid and they have carbon-carbon double bond which can react in free

radical

polymerization.

A

simple

methacrylate

monomer

is

methylmethacrylate (MMA). MMA is used in its polymerized form,

Chapter One


polymethylmethacrylate (PMMA), e.g. as a denture base material (Garcia et al. 2006 cited by Vuorinen, 2010).

1.1.2. Polymerization of methylmethacrylate: Polymerization is forming of a compound by the joining together of molecules of small molecular weights into a compound of large molecular weight (GPT, 2005).

1.1.3. Types of polymerizations: According to (International union of pure and applied chemistry (IUPAC) Recommendations, 1994) 1- Polycondensation; addition (chain growth): polymerization in which the growth of polymer chains proceeds by condensation reactions between molecules of all degrees of polymerization. Expressed by: Px + Py

Px + y (+ L)

{x and y} are [1, 2 . . . ]

where Px and Py denote chains of degrees of polymerization x and y, respectively, and L a low molar mass by product. 2- Polyaddition: polymerization in which the growth of polymer chains proceeds by addition reactions between molecules of all degrees of polymerization. Expressed by: Px + Py

Px + y

{x and y} are [1, 2 . . . ]

Where Px and Py denote chains of degrees of polymerization x and y, respectively.

Chapter One


The term "addition polymerization" embraced both the current concepts of "polyaddition" and "chain polymerization", but did not include "condensative chain polymerization".

1.1.4. Reaction of polymerization: According to (McCabe and Walls, 2008) polymerization processes follow a well documented pattern which consists of following stages: A- Activation: Activation is a process, usually chemical, that starts the polymerization process or enhances the action of an accelerator (Harper and Petrie, 2003). McCabe and Walls (2008) stated that activation involves decomposition of the peroxide initiator using thermal activation (heat), chemical activators or radiation of a suitable wavelength if a radiation activated initiator is present for benzoyl peroxide. B- Initiation: Initiation is the first step in the free radical polymerization process. During initiation free radicals are generated, usually by the decomposition of an initiator. The free radicals that are formed then react with the monomer to form other free radicals that are capable of chain growth (Harper and Petrie, 2003). C- Propagation: Propagation is the second step in a free radical polymerization process. The chain radicals that are formed in the initiation step are capable of adding successive monomers to propagate the chain. This growth of the chains is known as propagation (Harper and Petrie, 2003). D- Termination: Termination is the final step in the free radical polymerization process. After initiation and propagation of the chain radicals, the termination step stops the chain growth. Generally, this occurs because of the strong tendency of radicals to react in pairs to form a paired electron covalent bond with loss of radical activity (Harper and Petrie, 2003). McCabe

Chapter One


and Walls (2008) stated that it is possible for the propagation reaction to continue until the supply of monomer molecules is exhausted. Factors which have an important influence on the properties of the resulting polymer are molecular weight and the degree of chain branching or cross linking.

1.2. Artificial teeth 1.2.1. History: Around 700 B.C. the Etruscans used bone, teeth of cadavers and ivory to construct artificial teeth (Manappallil, 2006). Costly metals such as silver, gold, agate and mother of pearl were also used. The introduction of fused porcelain for teeth in 1789 was regarded as one of the most important events in the history of dentistry (Craig and Power, 2002). Porcelain teeth made their appearance in 1774 when a French pharmacist named Duchateau and a dentist called Dubois de Chement made them. During the Napoleonic wars, scavengers took the best teeth from dead soldiers (Mooney, 2009). This has been used until the middle of the nineteenth century denture bases were generally made from gold or ivory, but these were supersede by vulcanite (rubber hardened with sulphur), which remained popular until the 1940s, when poly (methylmethacrylate) resin was used to construct teeth and denture bases (Corrado,1990). Methyl methacrylate first came into accepted in dental use under the trade name "Paladon" in about 1937, and it was about 1940 that a specialized product under the trade name 'Portex" first became available for purely conservative procedures, experience with which inspired an article by Leader, (1942), so courageously titled "A Dental Revolution" (Cultle, 1945). There are three options of materials for artificial teeth: porcelain, acrylic resin and metal. In removable prostheses, acrylic resin teeth are used

Chapter One


more frequently than porcelain teeth (Ghazal et al, 2008), recently acrylic teeth have been used commonly and have competed porcelain teeth (Craig et al. , 2004).

1.2.2. Types of artificial teeth according to material 1.2.2. A. Hard acrylic Hard acrylic resin teeth are more wear resistance than regular acrylic teeth (Ogle et al. ,1985). Study prove that hard acrylic is stronger than conventional acrylic and with no staining (Von Fraunhofer et al. ,1988). The new generation of hard acrylic resin teeth and the newer composite resin teeth has reduced use of porcelain teeth during the past decade (Zarb, 1997).

1.2.2. B. Visible light cure composite Visible light cured composite have become popular for many prosthodontic application because of there improved wear properties (Nicholas, 1987). Their application includes replacement of lost or broken denture teeth (Lipkin and Wescott, 1992).

1.2.2. C. Porcelain vacuum fired Artificial porcelain teeth are produced to standard shapes and sizes by using moulds which are approximately 30% larger than required, in order to allow for shrinkage during firing. Small holes or metal pins are incorporated in the base of the porcelain teeth during their production. These are used to give mechanical attachment to the denture base, porcelain is brittle and teeth constructed from this material are more likely to chip and fracture than acrylic teeth (McCabe and Walls, 2008).

Chapter One


1.2.2. D. Acrylic resin (plastic) Acrylic resin artificial teeth are produced in reusable metal moulds using either the dough moulding technique or by injection moulding in which the acrylic powder is softened by heating and forced into the mould under pressure. The resins used are highly cross linked in order to produce artificial teeth which are resistant to crazing. The main difference between these materials and those used for denture base construction is the incorporation of tooth colored pigments rather than pink ones. Some manufacturers encourage bonding process by constructing the base and core of the artificial teeth from uncross linked or only lightly cross linked resin which is more readily softened. The outer enamel layers of the tooth are constructed from highly cross linked resin to prevent crazing. Bonding to heat cured resins is more effective than bonding to autopolymerizing resins (McCabe and Walls, 2008). Acrylic teeth are made of cross linked acrylics and micro filled composite resins. Cross linked acrylic denture teeth have been developed by utilizing

various

polymer

technologies

including

blend

polymer,

interpenetrating polymer networks (IPN), and double cross linking (DCL) to increase the resistance to crazing and wear (Ghazal et al, 2008).

1.2.3. Properties of acrylic teeth 1.2.3. A. Advantage of acrylic teeth 1- Good appearance: the saturation, brilliance, phone, hue and translucency are superior, and these teeth in most instances blend satisfactorily with the natural teeth (Zarb et al 2004). 2- Good attachment between the artificial teeth and the denture base (McCabe and Walls, 2008).

Chapter One


3- Strong and tough in order to resist fracture (McCabe and Walls, 2008). 4- Hard enough to resist abrasive forces in the mouth and during cleaning (McCabe and Walls, 2008). 5- Allow grinding with a dental bur at the chair side, plastic teeth are readily altered in contour by grinding for purpose of lapping (Craig, 1985). 6- Butting against the ridge, these teeth are easily reduced for butting against the edentulous ridges. The cut surface is susceptible to receiving a high polish which makes these teeth more comfortable to the soft tissue than are porcelain teeth (Dirksen, 1952). 7- Adaptation to unusual condition, plastic teeth are ideal for replacing isolated teeth in partial dentures where the occlusogingival or incisogingival space is limited. Also they are readily ground and altered in shape to form the labial surface of plastic jacket crown (Dirksen, 1952).

1.2.3. B. Disadvantage of acrylic teeth 1- Crazing: Crazing is the result of local stresses set up in the resin. It has been shown that crazing in polymethyl methacrylate is caused either by application of external mechanical stresses or by the action of chemical agents on stressed material (solvent crazing). The latter type of crazing may occur in the presence of residual monomer, solvents, or depolymerization products. These substances will produce local strains greater than the material can withstand. Often the simultaneous action of solvents and external stresses produces crazing. It is probable that the crazing of dentures results mainly from solvent action in combination with both internal and external stresses (Sweeney et al, 1955).

Chapter One


2- Wear: Wearing down of plastic teeth may seriously affect vertical dimension, tooth relationship and mastication efficiency. Composite resin denture teeth with inorganic fillers showed less wear than acrylic resin denture teeth without fillers. For composite resin denture teeth, the incorporation of nanofillers resulted in more wear compared to teeth with traditional microfillers. None of the resin materials tested demonstrated the 3-body wear resistance of ceramic teeth or human enamel (Stober et al, 2010). 3- Bleaching: Plastic teeth on occasion, bleach during processing of the denture. Tin foiling the teeth would aid in preventing this failure of material (Skinner, 1951). 4- Distortion: Phenomena happens due to internal or external pressure when the denture close to the glass transition temperature : At which the denture start to flow; if patient wants to clean his denture some time he boil it, may be during boiling he applied a pressure or stress to denture here the internal distortion happen. So the distortion happens if the load applied to denture while it s close to glass transition temperature. When denture teeth have been subjected to temperature changes and then immersed in a monomer solution, teeth must not show any whitening, distortion or crazing in the stereomicroscope (Head of Biomaterials dept., 2010). 5- Rebasing and dublicating: The plastic teeth can not be removed readily from the denture either singly or as a unit and replaced in the mold during rebasing and dublication so on this process influence the plastic teeth properties (Dirksen, 1952).

Chapter One


6- Discoloration: On discoloration, several discoloration media such as coffee, tea, red wine, curry powder

etc, have been used to evaluate discoloration by

colorimetric measurements. However, the components of composite resin teeth that are responsible for discoloration have not been clearly identified and confirmed .Further more, the effects of polishing on discoloration are inconsistent among different studies (Imamura et al, 2008). 7- Fatigue cracks: Happens due to frequent use, loading for many years

1.2.3. C. Chemical composition of acrylic teeth Most synthetic resin teeth are manufactured from acrylic polymer and methyl methacrylate monomer similar to those used in denture base construction. Nevertheless the degree of cross linking is some what greater than that within denture bases. This increase is achieved by elevating the concentration of cross linking agent in denture base monomer. The resultant polymer displays enhanced stability and improved clinical properties (Wollff, 1962). Plastic teeth are prepared from acrylic and modified acrylic materials similar to denture plastics. Different pigments are used to produce the various tooth shades, and usually a cross linking agent is used to improve strength and prevent crazing. Plastic teeth are prepared in layers of different colors so the shade is gradually lightened toward the incisal and occlusal portions to give these areas a translucent appearance. The gingival or body portion may not be as highly cross linked as the incisal or occlusal portion. This is done to improve the chemical bond between the teeth and the denture base. Fillers may be added to increase resistance to wear. Plastic teeth are of a similar

Chapter One


material to the denture base and may be chemically bonded to the base. Highly cross linked acrylic denture teeth may be treated with 4methacryloxyethyl trimellitic anhydride to improve the bond strength to denture base resins (Craig and Powers, 2002). Properties of plastic material can be modified through the use of fillers, reinforcement agent and chemical additive (Chanda and Roy, 2007). In particular inferior wear resistance of acrylic resin artificial teeth is a significant limitation for complete denture therapy. The denture cannot resist parafunctional movements and maintain proper occlusal relationships over time. For this reason acrylic resin teeth have been modified to overcome the disadvantages of acrylic resin by using cross linking agents, different monomers, and the addition of fillers (Loyaga et al, 2007). New types of artificial teeth using to modified acrylic resin that incorporate cross linking agents and composite resin containing filler have become increasingly. Cross linking agents are generally used to improve strength and crazing resistance. However cross linked acrylic resin artificial teeth have been reported to demonstrate lower bond strength to denture base resin when compared to conventional acrylic resin teeth. Therefore, the ridge lap portion of the teeth is expected to be the least cross linked so as to facilitate bonding to the denture base resin (Zarb et al 2004); (Craig et al., 2004). The amounts of filler content, geometry and size of the filler particles and the properties of the polymer matrix have been reported to influence the properties of polymer materials (Condon et al, 1997). Furthermore the bonding of artificial tooth resin to denture base acrylic resin has been related to the ability of monomer to diffuse into the tooth resin, observed by the presence of swelling. The degree of swelling is related to the degree of cross linking of a polymer, if a polymer is highly cross linked it has difficult swelling in organic solvent. However there is a lack of scientific information regarding these new types of

Chapter One


artificial teeth with respect to composition and properties that are important to ensure good clinical performance (Vallittu et al, 1997 cited by Loyaga et al, 2007). Two cross linking agents in common use are: (Allyel methyacrylate and Glycol dimethacrylate), both cross linking compounds are characterized by the reactive

C=C groups at the opposite ends of the molecules together.

The main advantage in using cross linking agent is that the final polymer has greater resistance to minute surface cracking or crazing (Hill, 1981). Cross linking agent may be present in amount of about 2% to 14%, but up to 25% have a little effect on the tensile strength, transverse properties, or hardness of acrylic plastic, through the recovering of the indentation by a ball is some what improved (Craig, 1985).

1.3. Denture base: 1.3.1. History: Denture base is the part of a denture that rests on the oral mucus membrane and to which teeth are attached. It does not include the artificial teeth (McCabe, 1985). Many type of material was been used as a denture base such as wood, bone, ivory, porcelain, metal and Vulcanized rubber or vulcanite was introduced as denture base material in 1855. Vulcanite displayed, questionable, esthetics and the fabrication process was particularly demanding (Rueggeberg, 2002). During subsequent years, the dental profession sought suitable substitutes for vulcanite. In 1937 polymethyl methacrylate was introduced and rapidly replaced vulcanite as the most commonly used denture base material. Polymethyl methacrylate provided enhanced physical properties readily available, inexpensive and easily manipulated. Since the introduction of Chapter One


polymethyl methacrylate additional polymers have been tested for denture base applications. Polystyrenes poly (vinyl acrylic) and polyamides that is nylons have been investigated as potential denture base materials. Although each of these materials displays desirable properties, none has proved superior to polymethyl methacrylate. As a result the poly methyl methacrylate remains the material of choice for denture base construction (Cultle, 1945).

1.3.2. Type of denture base polymers: According to (International standard organization ISO 1567, 1999 cited by Chhnoum, 2008): Type 1: Heat processed polymer a) Class 1: Powder and liquid b) Class 2: Plastic cake Type 2 : Auto polymerized polymers a) Class 1: Powder and liquid b) Class 2: Powder and liquid pour type resins Type 3: Thermoplastic blank or powder to form the denture base Type 4: Light activated materials Type 5: Microwave cured materials

1.3.2. Properties of denture base: Craig and Powers, (2002), McCabe and Walls, (2008) Considered an ideal denture base material are: 1- Should be possess several key physical attributes important in the fabrication of polymeric denture base as the cured polymer.

Chapter One


2- Should be stiff enough to hold the teeth in occlusion during mastication and to minimize uneven loading of mucus. 3- Should be biocompatibility, non toxic and non irritant. 4- Should be unaffected by oral fluid. 5- Should be with good esthetics. 6- Should be had high bonding strength with available denture teeth. 7- Should be had radiopacity, ease of repair. 8- Should possess adequate physical and mechanical properties. 9- Should have thermal expansion which matches oral environment. 10- The denture base must be strong enough to allow the prosthesis to withstand functional and parafunctional masticatory forces. 11- The material should not deteriorate in the aqueous environment of the mouth and should be able to withstand attacks from solvents present in food, drinks, or medications. 12- The cured polymer has to be biologically inert and possess a low rate of foul smell formation. During fabrication of a denture, the curing conditions and choice of materials have great influence on the denture s subsequent physical and mechanical properties. Each curing cycle or fabrication technique is a compromise that attempts to optimize the properties for a given application. For an allergy prone patient, low residual monomer content in denture base has greater priority than stiffness. For a patient requiring a soft lining, stiffness is very important if the reduced cross sectional area of the denture is not to cause stability or loading problems (O Brien, 2002).

Chapter One


1.3.3. Compositions of acrylic denture base materials The most widely used denture products are supplied in a powder and liquid form. The major component of the powder is beads of PMMA with diameters up to 100 m produced by a process of suspension polymerization in which MMA monomer, containing initiator, is suspended as droplets in water. Starch or carboxy methylcellulose can be used as thickeners and suspension stabilizers to the droplet. The temperature is raised in order to decompose the peroxide and bring about polymerization of the MMA to form beads of PMMA, which after drying form a free flowing powder at room temperature. PMMA is a clear, glass like polymer and is occasionally used in this form for denture base construction. Pigments and opacifiers can be incorporated in order to produce a more life like denture base. Pink pigments used in denture base resins are traditionally salts of cadmium. These pigments have good color stability and have been shown to leach cadmium from the denture base in only minute amounts. Fears of toxicity of cadmium compounds, however, have led to the gradual replacement of cadmium salts with other safer substances (McCabe and Walls, 2008). MMA is a clear, colorless, low viscosity liquid with a boiling point of 100.3°C and a distinct odor which is exaggerated by relatively high vapor pressure at room temperature. It contains some cross linking agent, and susceptible to free radical addition polymerization. Following mixing of the powder and liquid components and activation, the curing of denture base is due to the polymerization of MMA monomer to form PMMA. The liquid normally contains some cross liking agent. The substance most widely used is EGDMA. This compound is used to improve the physical properties of the set material. Hydroquinone, an inhibitor, is used to prolong the shelf life of the liquid component. In the absence of this inhibitor, polymerization of monomer and cross linking agent would occur slowly, even at room Chapter One


temperature and below, due to the random occurrence of free radicals within the liquid. The source of these free radicals is uncertain, but once formed they cause a slow increase in viscosity of the liquid and may eventually cause the liquid component to solidify (McCabe and Walls, 2002). The inhibitor works by reacting rapidly with radicals formed within the liquid to form stabilized radicals which are not capable of initiating polymerization. One way of reducing the occurrence of unwanted radicals in the liquid is to store the material in a can or in a dark brown bottle as visible light or ultra violet radiation may activate compounds which are potentially capable of forming radicals. The activator is present only in those products which are described as self curing or auto polymerizing materials and not in heat curing denture base materials. The function of the activator is to react with the peroxide in the powder to create free radicals which can initiate polymerization of the monomer (McCabe and Walls, 2002).

Chapter One


Table 1.1.: Composition of acrylic denture base materials (McCabe and Walls, 2002) Polymer poly (methyl

Polymer poly (methyl methacrylate) beads

Powder

methacrylate) beads Initiator

A peroxide such as benzoyl peroxide (approximately 0.5 % )

Pigments

Salts of cadmium or iron or organic dyes

Monomer

Methyl methacrylate

Cross linking agent

Ethyleneglycoldimethacrylate

Liquid

(approximately 10 % ) Inhibitor

Hydroquinone (trace)

Activator Only in self- N N -dimetheyl-p-toluidine curing materials.

(approximately 1 % )

1.4. Thermocycling: Denture resins are routinely subjected to thermal stresses in the oral cavity, especially during the ingestion of hot and cold foods and beverages (Barclay et al., 2005). Thermocycling samples through hot and cold water baths is further in vitro simulation of the thermal stresses encountered in the oral environment, although thermocycling is modeled on an in vivo setting. It has not been validated as accurate and completely equating to clinical conditions. The recommendation from ISO standard ISO/TR 11405:1994(E) for testing dental materials involves placemat of specimens in a humidifier at Chapter One


100% humidity and 37 C for 24 hour then subsequent thermocycling for 500 cycles between 5 C and 55 C with 20 second dwell time in each water bath and 5-10 second interlude between water baths when one cycle constitutes a combined hot and cold water bath immersion (Dudley, 2008). Intraoral temperature changes are produced from routine eating, drinking and breathing, and can change the interface between the acrylic resin teeth and acrylic resin denture base. Laboratory simulations of clinical service are often performed because clinical trials are costly and time consuming. Thermocycling is an in vitro process used to simulate in vivo, with few exceptions are always proposed without reference to in vivo observations (Barbosa et al, 2008). Many studies have been performed in relation to the effect of thermocycling on the bond of artificial teeth to denture base: Clancy et al, (1989) Studied the bond strengths of heat cured acrylic resin, auto polymerizing acrylic resin and the Triad Visible Light Cured Resin (VLC) bonded to a plastic denture tooth and an interpenetrating polymer network (IPN) abrasion resistant plastic denture tooth after thermo cycling of the specimens were reduced by milling to a diameter of 6 mm in the region of the tooth resin interface and thermo cycled for 24 hours. Specimens were then subjected by grinding grooves on the joint surface of an acrylic resin tooth before it was cured to the PMMA. Inspection of the retention holes showed that neither heat cured nor auto polymerizing PMMA had completely penetrated into the retention hole of the teeth. Clancy et al, (1991) examined the tensile bond strength and failure sites of one heat cured (Microlon) and two visible light cured (Traid and Extoral) denture resins to two types of denture teeth (Trubyte Bioform plastic teeth and Trubyte Bioform interpenetrating network (IPN) abrasion resistant teeth, half of the prepared specimens passing through thermocycling. They concluded Chapter One


that the strongest bonding was with the heat cured resin Microlon bonded to Dentsply standard acrylic resin teeth and to Dentsply IPN abrasion resistant denture teeth. The visible light cured resin Triad displayed stronger bonding than the visible light cured resin Extoral to both types of teeth except the standard acrylic resin teeth in the non thermocycled group. Thermocycling had no effect on the bond strength of Microlon and Triad resins, but decreased the bonding of Extoral resin to both types of teeth. Bonding to the standard acrylic resin denture teeth was stronger or equal to bonding to the IPN abrasion resistant denture teeth, dependent on the base used. The bond was greater with the Microlon and non thermocycled Extoral resin groups, but no difference for the Triad and thermocycled Extoral resin groups. The nature and location of the fracture sites were different among the 3 resins tested. Marchack et al, (1995) investigated adhesion of porcelain teeth to Heat Polymerized Polymethyl Methacrylate denture base resin. They reported that high energy abrasion, hydrofluoric acid etching, and use of a general purpose dentin bonding agent all improved bond strength of heat polymerized denture acrylic resin bonded to denture tooth porcelain. Silane coating did not improve bond strengths, and conventional air abrasion was no more effective than polishing with 600 grit silicon carbide. Artificial aging by water storage and thermocycling dramatically reduced bond strength. The strongest bond strengths were achieved by a high energy abrasion + etching + multiple purpose bonding agent treatment, but a simpler etching + multiple purpose bonding agent treatment also produced reliable results. The bond strength between two types of acrylic resin denture teeth and a denture base resin after thermocycling was examined by Chai et al, (2000) they concluded that thermocycling significantly decreased the bond strength of the two types of resin teeth, the denture teeth were untreated, prepared with diatorics, or treated with a solvent, dichloromethane. The Conventional

Chapter One


denture teeth and cross linked denture teeth were bonded to a pour type denture base resin. Compressive load was applied at 45 degrees on the palatal surface of each tooth until fracture. The teeth were either thermocycled or not thermocycled. Porcelain teeth were also tested for comparison. They found that there was no significant difference in bond strength between the conventional resin teeth and the cross linked denture teeth. However the thermocycling significantly decreased the bond strength of the 2 types of resin teeth but had no effect on porcelain teeth. The application of dichloromethane significantly improved the bond strength of the 2 types of resin teeth either before or after thermocycling. Schneider et al ,(2002) compared the tensile bond strengths of heat polymerized (lucitone 199) and microwave polymerized (Acron MC) acrylic resins among 4 types of acrylic resin denture teeth (IPN, SLM, Vitapan, and SR-Orthotyp-PE). Specimens were thermocycled and tested for strength until fracture with a custom alignment device. They concluded that higher bond strengths to the denture teeth tested were obtained with the conventional heat polymerized acrylic resin rather than the microwave polymerized acrylic resin. Regardless of which denture base acrylic resin was used, bond strengths recorded with Orthotyp PE and IPN denture teeth were significantly higher than those recorded with SLM and Vitapan denture teeth. The heat polymerized groups failed cohesively within the denture base acrylic resin or the denture tooth and the microwave polymerized groups failed adhesively at either the ridge lap or the occlusal surface of the denture tooth. Amin, (2002) investigated the effect of ageing in simulated mouth conditions on bond strength between acrylic teeth and denture base resins which was evaluated. Bonding was tested in tension according to ADA specification No. 15. The ageing effect on bond strength became significant after six months of exposure when bonding of acrylic teeth to heat cured and

Chapter One


auto polymerized resins was significantly reduced. The bond strength value of the auto polymerized resin to acrylic tooth after one year in test environment was half the acceptable value of 31.0 Mega Pascal (MPa) suggested by the ADA specification No. 15, whereas tooth bond strength to heat cured resin was acceptable even after one year of exposure. Saavedra et al, (2007) studied the durability of adhesion between acrylic teeth and denture base acrylic resin. The ridge lap surfaces of 24 acrylic teeth were flatted and submitted to 4 surface treatment methods ,no treatment, application of a methyl methacrylate bonding agent (Vitacol);: air abrasion with 30 micron silicone oxide plus silane; air abrasion with 30 micron silicone oxide plus silane and application of a methyl methacrylate based bonding agent (Vitacol). A heat polymerized acrylic resin was applied to the teeth. Thereafter, bar specimens were produced for the microtensile test at dry and thermocycled conditions (60 days water storage followed by 12,000 cycles). The results showed that bond strength was significantly affected by the surface treatment and storage regimens (dry > thermocycled). The methyl methacrylate based adhesive showed the highest bond strength. Barbosa et al, (2008) concluded that thermocycling and polymerization methods influenced the bond strength between acrylic resin and artificial teeth in {(Microwave polymerized, heat polymerized and auto polymerizing) with resin denture tooth (Biotone). The acrylic resins were polymerized according to the following: (A) microwave microwave

fast cycle; (B) microwave

manufacturer s cycle; (T) water bath

long cycle; (C)

long cycle; and (Q)

bench polymerization cycle}. The 5000 cycle fore 30s period between 4 C and 60 C decreased the bond strength of all polymerization methods. Thermocycling

insignificantly

decreased

the

bond

strength

of

all

polymerization methods, except for microwaveable cycle Q, which was statistically significantly decreased. The polymerization methods affected the

Chapter One


bond strength of the thermocycling and non thermocycling groups. The conventional water bath cycle (T) and microwaveable cycles B and C produced the highest bond strength values. However, only the Q polymerization method exhibited significantly reduced strength values when comparing thermocycling and non thermocycling groups. In addition, the thermocycled group failed adhesively, while the non thermocycled group showed mixed cohesive and adhesive failures. Chaves et al, (2009) state that there was no statistically significant effect of the factors ,acrylic resin, surface treatment, thermocycling, or their interactions on the Tensile bond strength (TBS) of the acrylic teeth to the denture base resins. Marra et al. (2009) evaluated the thermocycling effects and shear bond strength of acrylic resin teeth to denture base resins. Three acrylic teeth (Biotone, Trilux, Ivoclar) were chosen for bonding to four denture base resins: microwave polymerized (Acron MC), heat polymerized (Lucitone 550 and QC-20), and light polymerized (Versyo.bond). Twenty specimens were produced for each denture base acrylic tooth combination and were divided into two groups without thermocycling (control groups) and thermocycled groups submitted to 5000 cycles between 4 C and 60 C. Shear strength tests (MPa) were performed with a universal testing machine at a crosshead speed of 1 mm/min. The shear bond strengths of Lucitone/Biotone, Lucitone/Trilux, and

Versyo/

Ivoclar

specimens

were

significantly

decreased

by

thermocycling, compared with the corresponding control groups the means of Acron/Ivoclar and Lucitone/ Ivoclar specimens increased after thermocycling. The highest mean shear bond strength value was observed with Lucitone/Biotone in the control group and the lowest with QC-20/Trilux in the thermocycled group. So some acrylic tooth denture base resin

Chapter One


combinations can be more affected by thermocycling; effects vary based upon the materials used.

1.5. Bonding of artificial teeth to acrylic denture base: One of the primary advantages of acrylic teeth is their ability to bond chemically to the denture base resin, so it provide better retention than that obtained by the mechanical bonding of porcelain teeth, however failures have been observed in which plastic acrylic teeth break loose from denture, indicating that chemical bonding dose not always occur (Darbar et al 1994 cited by Hatim and hasan, 2010). Acrylic teeth are the most popular artificial teeth for denture construction. Unlike porcelain teeth, they are suitable for a chemical union between the teeth and the denture base resin (Morrow et al, 1978). "Caul et al, (1952) recognized the need to depend on mechanical retention when auto polymerizating acrylic base material is used with acrylic teeth, while Sorensen and Fieldstad (1961) and Rupp et al, (1971) recommended the use of a solution containing a solvent and a polymerizable monomer in order to improve the bond strength of acrylic teeth to autopolymerizing denture base material" (Mohamad RM, 2007). Rupp et al, (1971) cited by Harshavardhan, (2007) stated that the use of a solution containing a solvent and a polymerizable monomer has been advocated for bonding of plastics. This solvent polymerizable system swells the surface and permits the diffusion of the polymerizable material. On polymerization, a network of polymer chains is interwoven that results in a tensile strength of up to 80% that of the parent plastic, the strength of the bond is dependent on the degree of penetration of the solvent and the strength of the interwoven polymer chains.

Chapter One


Huggett et al, (1982) investigated the bond of three types of anterior plastic teeth, each having varying degrees of copolymerization to heat cured and autopolymerizing resin. Teeth as supplied were compared to those where the ridge lap surface were modified by grinding, grinded and repolished, and modified with a retentive groove. It was reported that ridge lap modifications failed to improve the strength of the bond between the teeth and the denture base resin. Also it was concluded that copolymerzation was not a major factor in reducing the bond strength. The failure of the tooth denture bond may be caused by excessive stress failure or by fatigue. The strength of the bond is related to the composition of the material, for example, to the extent of copolymerization of the acrylic denture base, poor laboratory technique including faulty boil out technique and indiscriminate use of separating medium in particular have been held responsible for preventing optimum tooth denture base bond strength, thus causing many failures. Yamauchi et al, (1989) evaluated the bond strength of artificial teeth to microwave curing, conventional heat curing and 4-Methacryloxyethyl trimellitate anhydride (4-META) containing denture base resin. Also the effects of grinding and monomer coating of the tooth ridge lap on the bond strength of artificial teeth to microwave curing denture base resin which was slightly higher than the other two resins. Also, bond strength of artificial teeth to denture base resin was increased by grinding and monomer coating of tooth ridge lap. Plastic teeth act as functional portions with acrylic denture base material. The resin teeth are the integral part of the denture by their chemical bonding with the base, but several factors affect the bonding: faulty wax elimination, residual wax on ridge laps of the teeth, careless application of separating layer during packing the denture, on the other hand, grinding the non crosslinked portion of ridge lap surface, painting the teeth with monomer

Chapter One


or a solvent, preparing retention grooves on the ridge lap portion of the teeth (Can and Kansu, 1990). Geerts and Jooste (1990) evaluated the shear bond strengths between microwaves polymerized and conventional water bath cured polymethyl methacrylate (PMMA) bonded to denture teeth .Besides the effect of surface treatment with MMA and sand blasting. They reported that the bond strength of microwave polymerized PMMA to denture teeth was superior to that of conventional heat polymerized PMMA. Surface treatment by roughening did not enhance bond strength, whereas priming with monomer significantly improved the bond strength of micro waved PMMA. Polyzois and Dahi, (1993) investigated the bond strength of six different brands of acrylic teeth to heat cured and specially designed resin for microwave curing. The specimens were prepared and tested in a tensile shear mode. A superior bonding was found after water bath curing. No statistically significant difference in the fracture load between the two types of curing was found. Chung et al, (1995) concluded that roughening of the tooth surface and the use of a swelling solving in conjunction with methyl methacrylate improves the reliability of the joint between acrylic teeth and acrylic denture base material. Darber, et al. (1995) stated that debonding of teeth might occur at any early or late stage. However the most probable reason for ultimate failure is crack propagation from areas of high stress concentration. Knowledge of the intensity and distribution of these stresses can minimize tooth detachment from the denture base resin Acrylic resin teeth present a problem when they detach unexpectedly from the denture base resin. Detachment is caused by stress concentrations at the tooth denture base resin interface; the finite

Chapter One


element method was used to examine the stress distribution at this interface when a single static force that resembled incisal bite force was applied. The results indicated that irrespective of the type of acrylic resin teeth used, maximum tensile stresses were found at the palatal aspect of the interface. It is suggested that boxing the tooth in the acrylic resin will help redistribute stress concentrations favorably. Cunningham and Benington, (1995) evaluated a significant bond strength variation, both within and between dentures has been reported. In one study, the tensile bond strength of specimens from standardized and anonymously fabricated partial dentures were evaluated. Randomly selected commercial dental laboratories and a university dental laboratory produced the dentures. A wide range of tooth debonding forces was recorded. The results highlighted the need for further investigation to determine a more standardized technique to provide satisfactory denture tooth bond testing. Thean et al, (1996) evaluated the debonding of 3 resin denture teeth (Bioform, Dentacryl, and TNR) from a single base material and found that 93% of specimens exhibited cohesive failure within the body of the tooth rather than adhesive failure at the tooth denture base junction. The influence of placing a diatoric in the denture tooth (using monomer to pre wet the tooth) and of breaking the glaze on the denture tooth also have been evaluated. Cunningham and Benington, (1996) described anew technique for testing the tensile bond between acrylic teeth and denture base, with application of a wax solvent as a control group, second group was abraded to a standard depth of 0.5 mm after dewaxing, third group was retention groove 2mm deep and 3mm wide at the base extended for a distance of 5mm ± 0.5mm mesiodistally was cut, fourth group was sodium alginate mould seal was painted on the tooth bonding surface last group a molten wax was painted to the neck. It was found that there were no significant differences in the Chapter One


mean bonding values between any of the surface preparation condition, with the notable exception of the wax contaminated surface, as highly significant reduction in strength was obtained. Buyukyilmaz and Ruyter, (1997) compared the shear bond Strength of cold cure, heat cure denture base resin to teeth with various polymerization temperatures. High bond strength was resulted when neat cured denture base resin was used. While for cold cure as the temperature of the curing increased the failure was changed from adhesive to cohesive indicating a bond formation. This was due to greater diffusion rates of the monomer into tooth structures and increased with increasing temperature. Vallittu et al, (1997) suggested that, an auto polymerized denture base polymer was cured at 30 C, 50 C, or 70 C, and a heat cured denture base polymer was cured at 100 oC in contact with acrylic resin polymer teeth. The specimens were ground wet and polished to a thickness of 0.21 mm for the examination of the interface with a light microscope. The surface of the specimens was then treated with the solvent tetrahydrofuran, and the specimens were examined with a scanning electron microscope (SEM). Microscopically, the interface between the heat cured denture base polymer and the polymer teeth appeared diffuse in the region of the interpenetrating polymer networks (IPN) and the matrix. The IPN appeared as a separate zone in the outer parts of the beads of the teeth, both with the light microscope and with the SEM. The results suggested that by increasing the polymerization temperature, the monomers of the denture base polymers diffused more effectively into acrylic resin polymer teeth. This increases the bond strength between the polymer teeth and the denture base polymer. Barpal et al, (1998) found that the bonding of highly crosslinked denture teeth to a denture base was influenced by modification of the ridge lap before processing. Chapter One


Hirano et al, (1998) investigated strengths of light polymerized denture base resins (LPR) bonded to all acrylic resin teeth, denture base resins and denture base metals. Acrylic resin posterior denture teeth were selected for the study. A heat polymerized acrylic denture base resin and an auto polymerizing resin were the denture base resins used for study. A cobalt chromium alloy, 18-8 stainless steel, pure titanium and a gold silver palladium alloy were chosen as metals for denture bases. Bonding strength of a metal adhesive denture base resin and a metal adhesive auto polymerized resin were measured to evaluate the adhesive strength of LPR to metals. They concluded that the auto polymerized resin adhered to the heat polymerized resin more firmly than it did to LPR under both dry and wet conditions. When LPR was bonded to resin teeth using a newly developed light activated bonding agent, the adhesive strength improved compared to bond strengths without a bonding agent. However when compared to the bond strength of resin teeth to a heat polymerized resin, the value was less. As the number of thermocycle was increased, the adhesive strength of the heat polymerized resin to resin teeth decreased significantly, while that of the light polymerizing resin remained stable. When adhesive strengths to denture base metals between LPR and Metal Adhesive Auto polymerized resin (MAPR) were compared, LPR had values equal to or significantly greater than MAPR. The adherence of Metal Adhesive Heat Polymerized Resin (MHPR) to pure titanium showed values significantly greater than that of LPR. However, LPR values to the 18-8 stainless steel and cobalt chromium alloy were significantly greater than the MHPR, except for the air abraded cobalt chromium alloy under wet conditions and after 400 thermocycle. Cunningham and Benington, (1999) investigated the variables which may affect the bond between acrylic teeth and different denture base resin as a function of different variables. The result showed a significantly higher bond

Chapter One


was obtained when the resin was packed late in the dough stage and superior bond, in all cases, when light impact resin was use. Tooth surface modification by grooving or grinding made no significant difference when compared with unmodified surfaces. Wax contaminated surfaces produced highly significant weaker bonds. Time of introduction and duration of water bath processing had no significant effect on the bond strength. The effect of surface treatments on shear bond strength of a light activated composite resin bonded to acrylic resin denture teeth were investigated by (Vergani et al, 2000), who found monomer cementing of the tooth surface, especially with high impact monomer, significantly improved the bond strength. The application of resin cements was found to produce the most significant increase in denture tooth bond strength. The study revealed that combined surface treatment on methyl methacrylate monomer followed by application of light cured adhesive resin provided the highest shear bond strength between composite resin and acrylic resin denture teeth. Hasan, (2002) evaluated the bond strength of acrylic resin cured by two different curing techniques, water bath and microwave to different denture teeth as influenced by surface treatment with monomer for 180 second. He concluded that the bond strength of acrylic resin cured by microwave to artificial teeth was significantly higher than that cured by water bath. The monomer application improved the bond strength. Abu-Anzeh, (2003) evaluated the tensile bond strength of water bath and microwave cured acrylic resin to three types of artificial acrylic teeth as a function of different surface treatment, the teeth were allocated into five groups of different surface treatment. The first group received no further treatment, the second groups were treated with monomer, the third groups were treated with acetone, the fourth groups were treated with dichloromethane, and the fifth groups were conditioned with diatoric Chapter One


preparation. Each group was processed by both water bath and micro wave curing resin. The result showed that microwave cured resin has a significant lower tensile bond strength (TBS) means values than water bath cured resin to all artificial acrylic teeth type. All surface treatment application improved the (TBS)

significantly;

however

with

dichloromethane application

the

significantly highest (TBS) mean values were gained. Bragaglia, (2005) concluded that regarding bond strength between teeth and denture base, there were statistically significant differences only between diatoric (worst results) and roughening with an aluminum oxide stone (best results). While the groups roughened with bur, stone or air abrasion showed higher bond strength mean values than other groups. After teeth debonding, most failures were cohesive in the teeth (vestibular portion) associated with cohesive in denture base material (palatal portion). Harshavardhan, (2007) Studied the bond strength of two varieties of acrylic teeth; Premadent and Acry Pan and the conventional denture base resin material of brand name (DPI), using four variables in each group. The following conclusions were made. There was a significant improvement in the bond strength when retentive groove cut, in the form of cingulum ledge lock on the ridge lap area when, compared to the ridge lap area being left unmodified or use of other groove designs. Acry Pan acrylic teeth showed a better bond strength to conventional heat cure denture base resin when compared to Premadent acrylic teeth. Canine teeth had a stronger bond superior to that of central or lateral incisors. Chung et al ,(2008) examined the bond strength between acrylic teeth after various surface treatments and processing with either a heat or microwave polymerized denture base material. Specimens were prepared and tested according to the methods described in American National Standard / American Dental Association, Specification No.15. Three brands of acrylic Chapter One


teeth were used with the following treatments: control (no treatment), grinding and grinding plus sandblasting. Treatment groups were further divided into two denture base processing subgroups: heat polymerized and microwave polymerized methods. Bond strength test was performed using a universal testing machine with five specimens and each specimen is composed of six anterior teeth per experimental group. The mean bond strength values ranged from 33.1 S.D. 4.1 to 51.6 S.D. 2.5 MPa. The bond strength values of sandblasted surfaces were significantly higher than those of the ground surface and control. Combined (acrylic tooth and denture base resin) cohesive failures were disclosed in all tested samples. Acrylic tooth surface preprocessed surface treatment with grinding plus sandblasting and processed with a heat polymerized denture base provided the greatest bond strength between acrylic tooth and denture base. Hatim and Hasan , (2010) stated that the shear bond strength of acrylic teeth to microwave cured denture base resin is significantly higher than that to conventionally water bath cured denture base resin. Cross linked acrylic teeth (FloriDent and MajorDent) show lowest shear bond strength compared to other type of acrylic teeth. Modes of failure are mostly adhesive in all types of untreated acrylic teeth, with monomer treatment, modes of failure are directed toward cohesive tooth (within tooth structure) for cross linked acrylic teeth, mixed (adhesive and cohesive) for acrylic teeth, mixed, cohesive acrylic and cohesive tooth for hard acrylic in his teeth. Stoia et al, (2010) reviewed the factors determining negative or positive influences to the adherence of the teeth to the denture base, the 6 factors are: 1. Teeth and denture base resin manufacturing technology.

Chapter One


2.nFactors involved in the laboratory technological steps of samples manufacturing: wax impurities Spartley, (1987) or gypsum impurities (Ritchie et al, 1983). 3. Physical or chemical ridge lap area treatment agents (such as organic solvents, curing agents, monomers adhesives) (Rupp et al, 1971), (Marrow et al, 1978), (Huggett et al, 1982) and (Cardash et al, 1986). 4. The action time of physical and chemical agents on the acrylic tooth ridge lap area (Yamauchi et al, 1989). 5. Technological methods for dough stage denture base acrylic resin preparation (the amount of monomer and polymer in accordance with the manufacturer indications) (Clancy et al, 1989). 6. Acrylic resin denture base polymerization method (auto polymerization, heat polymerization, , microwave polymerization) (Yamauchi et al, 1989). Stoia et al, (2011) in study demonstrates that the Tensile bond strength mean values were statistically significant among groups ( I: polished , II:polished + methyl methacrylate, III: sandblasting + methyl methacrylate, IV:sandblasting + universal repairing adhesive (Clearfil Repair-Kuraray), V:polished + dichlormethane), was ranging from 13.5 MPa (group IV) to 35.9 MPa , the latter pertaining to group V. Dichlormethane treatment leads to enhanced bond strength to the artificial teeth and may be considered as a laboratory and clinical procedure as well, in order to improve the quality of bonding . Korkmaz et al ,( 2011) compared shear bond strength and type of bond failure between a highly cross linked tooth and different denture base polymers. The results showed that heat cured PMMA groups failed cohesively and demonstrated significantly higher bond strengths than the

Chapter One


other resins used. The application of dichloromethane on the ridge lap areas of teeth resulted in a significant improvement of bond strengths in heat and auto cured resins, the study suggested that type of denture base material and processing methods may have an influence upon the bond strength between interpenetrating polymer network (IPN) denture teeth and base materials. Treatment of denture teeth with dichloromethane could provide substantial improvement in the bond strength of teeth with heat and auto cured denture base resins; however, this finding should be validated in further investigations on the long term effect of such treatment on the bond strength.

Chapter One


Chapter Two

Materials and Methods

MATERIAL AND METHOD 2.1. Equipments and materials: 2.1.1. Equipments and instruments: 1. Auxiliary Contactor ADD ON BLOCK ( TC , TA1DN22 , INDIA) 2. BOIL OUT SYSTEM 2000 3. Brass (ring , grasping )constructed 4. Brush (Italy) 5. Clamps (Hanau engineering comp. U.S.A.). 6. Contactor 220V 50Hz (TC, TC1D1810M5 , INDIA) 7. Cylindrical roller bearing (china) 8. Dental engine Dental Lab MARATHON Handpiece 35K r/m + Micro motor N3 9. Dental flask ( BRODEN , SWEDEN ) 10. Dental hydraulic press (Hydofix Bego , Germany) 11. Dental lathe (Quayle dental, U.K.) 12. Dental polishing lathe (Quayle DENTAL) with (CILA MOTORU B) 13. Dental vibrator (Bego , Germany) 14. Digital caliper Hogetex 0.01(Germany) 15. Digital camera 12.1 Mega Pixels ( Canon, Japan) 16. Disk bur 345-524-060HP (Shangyu Coated Abrasives, China) 17. Electrical generator (TG-max) (220 Vt, 50Hz 15 Am) 18. Electromagnetic Pulse counter (MEM-201 , Maroli Meters Private Limited , India) 19. Finishing burs ( acrylic and stone , Germany) 20. Flash timer (VBR-8X Multifunctional, Double Adjustable Flasher Relay) ( ER-NA , V- Otomat Tipi Flasor Role , Turkey ) 21. Floss polyester (PP, polyester, nylon, cotton , China) Chapter Two

Materials And Method

22. Glass jar (China) 23. Hydraulic press (Hydofix Bego , Germany) 24. Iron (astm , Turkey) 25. Iron beam constructed from (astm , Turkey) 26. Lacron Carver (Germany) 27. Lathe Operator constrictor (Quayle DENTAL 7000-H, Germany ) 28. Light Microscope (Olympus , Japan) 29. Machine curing temperature ( Curing unit) (DEROTOR) 30. Motor (CILA MOTORU B ) 31. Plastic box very small. 6 x 200 x 100mm (china) 32. Postioner satellite mover ( SONYSAT , V-BOX II , GERMANY) 33. Processing unit ( DEROTOR ,MULTICURE) 34. Pullies (china) 35. Rag wheel pumice (China) 36. Rubber bowls with flexible function (Germany) 37. Sand paper (aluminum , oxldecloth No. 240-china ) 38. Satellite dish mover (skyvision, 1-800-500-9275, U.S.A.) 39. Spatula (vista ,dental-11 R, India) 40. Surface roughness tester (Talysurf 10, RPT Ltd, U.K.) 41. Surveyor (Dental farm Type B double joint arm- Italy) 42. thermometer (ertco thermo scientific precision spirit filled glass thermometer , range -20 C- 110 C) 43. Universal testing machine (TERCO MT 3037,Germany) 44. Vibrator (QUAYLE DENTAL, U.K.) 45. Water bath ( TAFESA ,HANNOVER , GERMANNY) 46. Wax

elimination

machine

(BOILE

OUT

SYSTEM

2000,

SKILLBOND, U.K.)

Chapter Two


2.1.2. Materials: 1. Acrylic artificial teeth (MAJOR DENT cross linked - Italian), (KAILI HUGEDENT double cross-linked China) and (SUPER NEWCLAR IDEAL DENT MAKOO non cross-linked - Iran) 2. Acrylic resin (Stellon QC-20. Dentsply, U.K.) 3. Plaster (Wiegelmann dental, European Dental Center) 4. Polywax toughened dental modeling wax (Russia) 5. Sand paper (aluminum, oxldecloth No. 240-china) 6. Separating media (MEDWAY PLASTER COTING SOLUTION, Iran) 7. Silicone rubber (ZetaPlus soft, Zhermack, Italy)

Chapter Two


2.2. Methodology 2.2.1. Sample preparation: 2.2.1. A. Preparation the ridge lap portion of teeth: Specimens collectively were 72 artificial acrylic teeth (24 MAJOR DENT), (24 KAILI HUGEDENT) and (24 SUPER NEWCLAR IDEAL DENT MAKOO) Fig (2.1), 12 pairs of first mandibular molar acrylic artificial teeth in each brand (right and left), the first eight teeth from each brands were tested for debonding with acrylic denture base as control a control group, second group of samples tested after thermocycling with 1000 cycles while the third group of sample tested after 2000 cycle of thermocycling process.

M

K

S

Fig (2.1): Artificial acrylic teeth used, M: MAJOR DENT, K: KAILI HUGEDENT, S: SUPER NEWCLAR IDEAL DENT MAKOO

Chapter Two


A mixture of plaster was prepared according to manufacturer instruction then poured in side a flat rectangular plastic box (6 mm height * 200 mm length and 100 mm width) then each time 6 teeth were embedded 5 mm of them in up down position which was previously determined by a digital caliper Fig (2.2 A), the occlusal surface of tooth was parallel to the floor, Fig (2.2 B).

A

B C Fig (2.2): A: Engine mounting with surveyor B: Digital caliper, C: Grinding of ridge lap portion Chapter Two


The micro engine was fixed on the surveyor Fig (2.2 C), the ridge lap surface was ground in zero tilt position of surveyor plate by engine high speed using disk bur in one way direction, Fig (2.2 C). The disk was changed after the grinding of six teeth, to avoid heat generation water spray was used, then the ridge lap surface was smoothed with sand paper, the teeth ridge lap portion was with the roughness of (Ra= 0.34 ± 0.05 micrometer) were tested by Surface roughness tester (Profilometer) seen in Fig (2.3), this smoothness aid in uniform and excellent attachment between tooth and brass ring and at the same time produce uniform surface area which will be attached to acrylic beam later.

Fig (2.3): Surface roughness tester (Profilometer) Brass ring were constructed by turning operator machine with the dimension of (12mm diameter * 4mm height) with a centered hole were the hole with the dimension of (5mm diameter *4mm height) Fig (2.4 A) (Cunningham and Pennington, 1996). Chapter Two


A

B

C Fig (2.4): A: Brass collar, B: Brass bar, C: Tooth attach to brass bar through brass hole (Cunningham and Benington, 1996)

2.2.1. B. Preparation of mold and sample: Prepared teeth were cleaned with tab water. Uniform mold for brass ring with beam was prepared, cut it vertically at the middle with blade no. 15 allowed to formation of four indexes to excellent repositioning, using two large rings for fixing the mold during the sample preparation as shown in Fig (2.5).

Fig (2.5): Mold to obtain standard attachment, alignment, diameter and length of wax pattern A: Ring to fix the silicone rubber, B: Silicone rubber with indexes, C: Brass bar with brass ring

Chapter Two


However all teeth were chosen with same size from each brand but some difference was present between brands and right to left so that 3 pairs (right and left) of mold was prepared from silicone rubber according to manufacture instruction for occlusal third of teeth to be in the same position and alignment during wax pattern preparation, lift the prepared tooth in up down position in the occlusal mold then put small brass ring over it joining them together by a drop of molten wax Fig (2.6 A), the prepared tooth with the ring lift in the lower large mold Fig (2.6 B). After repositioning of two halves of silicone mold by the aid of indices with two brass rings tight these halves, Fig (2.6 C); molten wax was added to the upper hole of mold Fig (2.6 D) and allowed to cool in cold water for 10 sec., then allowed for bench cool then remove the large rings and separate the two halves of the mold ; finally specimens will be obtained, Fig (2.6 E and F).

Chapter Two


A

B

C

D

E

F

Fig (2.6): A: Mold of silicone for occlusal third of teeth (right and left one for each brands), B: Silicone mold uniform for all specimens (tooth, bras ring and brass bar), C: Reposition two halves of the mold and closing it with two rings, D: melting wax was poured in side the hole, E and F: Open the mold then wax pattern will obtained

Chapter Two


2.2.1. C. Flasking and deflasking: Layers of separating media were painted to inner surface of dental flasks with brush. Mixture of plaster was poured in the lower halves of flasks on the vibrator, then insert the samples vertically until sample ring was embedded in the plaster, Fig (2.7 A).

A

B

Fig (2.7) A: Flasking, B: Deflasking of specimens. Separating media painted on the set plaster, after that repositioning of the upper halves of flask, then on the vibrator fill the flasks with plaster and tight the flasks with dental clamp. After 45 minute the flasks are ready for wax elimination, flasks were immersed in boiling water with (BOIL OUT) machine, after 4 to 6 minutes the flasks were removed from the machine and upper halves separated from lower halves, then the wax washed away with boiling water, finally washed it with clean boiling water, Fig (2.7 B).

Chapter Two


A B Fig (2.8): A: Mixing acrylic cover in jar, B: Packing of specimens. Mixing the hot acrylic powder (polymer) and liquid (monomer) in ratio of 3:1 which was used to pack it into a gypsum mold for curing. The ratio of powder to liquid was important since it controls the workability of it during manipulation of the mixture as well as to avoid dimensional changes during setting time of acrylic. Acrylic resin dough stage was made were the acrylic resins were handled according to the manufacturer's recommendations, and left to polymerize for approximately 10-15 min at 23 C. The mixing should be done in a clean jar which was covered with wax to avoid evaporation of the monomer, Fig (2.8 A). The mixture of acrylic was pushed in to the holes of mold which was left by wax elimination of samples, it was forced through 5 mm diameter of brass and plaster holes of both halves of plaster until the acrylic exuded from the other site of the plaster mold which was performed in second layer of plaster. then the two halves of the flask were closed until they were almost in approximation, this process was done to make the separation of the acrylic evenly throughout the mold then placed it under pressure about 100 Kg/cm² by dental hydraulic press until the excess acrylic flow out was stopped, the flasks

Chapter Two


was change place to clamp and the clamp was closed tightly. Then the flasks immersed in side the curing unit which was used for polymerization at temperature 70 C (slow cycle technique for 7 hour). This technique more preferable than others were make the conversion of monomer to polymer better which occurs during the period at 70 C and during this time the dough it self may approach 100 C were polymerization reaction are exothermic reaction. To avoid boiling of the monomer the acrylic must be kept below 100.3 C temperature; on the other hand rapid curing cycle usually results in some degree of porosity.

2.2.1. D. Finishing and polishing of specimens: The flasks were left to cool at room temperature, If not increased distortion of the acrylic may occur, The whole upper and lower plaster add was removed from the flask Fig (2.9 A), then carefully with the aid of engine, carver, wax knife etc separate the samples, avoiding any excess force. For finishing and polishing the sample using low speed lathe with motor dental polishing lathe Fig (2.9) all time avoiding heat generation, by this procedure the samples were ready for the next step which was the thermocycling step, all samples were stored in (distilled water) a humidifier at 100% humidity and 23 C for 24 hour.

Chapter Two


C Fig (2.9): A: Sample with plaster, B: Lathe used to Finishing of specimens C: Specimens before thermocycling Chapter Two


2.2.2. Grouping of specimens: Seventy two first mandibular molar acrylic artificial teeth Fig (2.10), 24 from each brand prepared with denture base material as it was be explained in section 2.2.1 , then each brand is subdivided randomly to three subgroups (n=8), four teeth right side and four teeth left side, after that tested as follow: A: First group

: Control group with no thermocycling.

B: Second group: Under go 1000 cycle of thermocycling. C: Third group : Under go 2000 cycle of thermocycling. Total sample

SUPER NEWCLAR IDEAL DENT MAKOO

KAILI HUGEDENT Debonding test

MAJOR DENT Debonding test

Debonding test

Control

Control

Control

thermocycling

thermocycling

thermocycling

thermocycling

thermocycling

thermocycling

Fig (2.10): Diagram illustrated sample grouping of the specimens

Chapter Two


2.2.3. Thermocycling: The thermal cycled specimen group was immersed in distilled water and treated in a thermocycle device at 1000 and 2000 cycles at border temperatures ranging 5 C ± 2 C and 55 C ± 2 C with an interval of 30 second (Pinto et al , 2002) and (Pinto et al, 2004). The number of cycles was used to simulate total prosthesis use for approximately 1 and 2 years. The patient wear the prosthesis which eats three times in a day for 1 or 2 years, would have eaten 1095 or 2190 meals at the end of that time (Pinto et al, 2004). This calculation is based on a single thermocycle per meal. The temperature variations were chosen on the basis of the similarity of temperatures of foods ingested during meals and were not damaging to oral tissues (Caio et al, 2008). In order to perform this step two water bath were used one regulated by thermostat at 55 C and the other is regulated by thermostat at 5 C. Automatic device was prepared to change place of the samples between the two water baths. A device was designed and constructed for performing thermocycling technique. This device composed of an external skeleton, mechanical part, electrical part and digital part. The external skeleton of the device consist of original base iron (2cm*2cm) with dimension of (100 cm length* 8 cm width), 4 angled feet (70 cm length) soldered to this base. A secondary metal base (13cm length * 8cm width) was soldered to the center of the original base through 30cm length metal rod (arm), Fig (2.11).

Chapter Two


Secondary base

length

Pulley with cylindrical roller

Original base

Angle feet

Fig (2.11): Skeleton of thermocycling machine The mechanical part was composed of 3 pullies, Fig (2.12 A). On the right and left side of the original base there was two pullies for horizontal movement, were the left one attached to the Cylindrical Roller Bearings Fig (2.12 B) and Fig (2.11) while the right one attached to Satellite dish mover Fig (2.12 C) and the third pullies placed on the secondary base, controls the vertical movement.

Chapter Two


A

B

C Fig (2.12): A: Pullies, B: Cylindrical Roller Bearings, C: Satellite dish mover The magnetic micro switches, Fig (2.13 A) inside the dish movers was adjusted to break the electrical current exactly after the movement has reached 25 Cm distance from the center (right , left , up and down ).

Chapter Two


Roller which control micro switch

Micro switch

A

B Fig (2.13): A: Satellite dish mover with micro switch (break the current cycle at exact point), B: Satellite postioner The electro mechanical part was composed of two Satellite dish movers, Fig (2.12 C) one on the right side of original base and the other one on the secondary base both are connected to the digital part which were two Postioner satellite movers Fig(2.13 B) which direct the dish movers. The movement of dish was transmitted to the pullies by beams which were constructed from iron by turning operator machine Fig (2.14 A) having

Chapter Two


dimension of 150mm length (the head of the beam is 30mm length and 13mm diameters the middle part 50mm length and a 15 mm diameter the last part has the length of 70mm and a diameter of 5 mm with a dais end No. 10), Fig (2.14 B).

A

m with l Diameter with dais end

[

l l

l

l

l

B

l

l

Fig (2.14): Constructed beam A: Turning operator machine, B: Beam to transmit the movements from the dish mover to the pulley (inside to out side). The constructed beam was connected to the helical plastic gear through the small dais end which passes through another hole in the middle dish plate then passes through another hole in the external cover of the dish movers and connected to the pulley, Fig (2.15).

Chapter Two


A

B

C

Fig (2.15): A: 1.Helical plastic gear, 2.pulley, 3.magnetic role, 4.constructed beam, B: Collected piece inside the dish mover, C: Dish movers after preparing to transmit the movements from inside dish mover to out side pulley with beam. One of the dish movers was tightened on the right side of the original base, Fig (2.18). On the left side of the original base there was cylindrical roller bearings soldered to the original base from outside, a beam with the dimension

Chapter Two


of 100mm length and 25mm diameter soldered to the center of the bearings, to give free movement with the pulley that is attached to the beam, Fig (2.16).

C

B A

Cylindrical Pulley

Roller Bearings

Fig (2.16): A: Out side of cylindrical role soldered to original base, B: Inside of cylindrical role soldered to the beam, C: pulley is tightening on the beam. Floss having the length of 210cm tighten around the horizontal pullies (pulley of horizontal dish mover and pulley of Cylindrical Roller Bearings side) Fig (2.18), at the center of this floss a metal ring was present Fig (2.17 A) which moves according to the movement of horizontal dish mover, Fig (2.18).

Vertical floss Horizontal floss

A

B

Fig (2.17): A: Vertical floss passing through the ring of horizontal floss B: Constructed rack for sample holding. Chapter Two


Satellite dish mover

Vertical floss

Horizontal floss

Rack for sample

Water bath

Satellite Postioner

Fig (2.18): Mechanical and electrical part of thermocycling machine; were both flosses are not interfere and they are free in there movements.

The movement of these floss is directed by a satellite postioner to exactly 50cm (25cm right and 25cm left from center ) so that the samples which are hold by the constructed rack Fig (2.17 B) can be transmitted between two positions right and left (horizontal movement of sample),

in side the

secondary base there is a dish mover Fig (2.18), constructed beam with above dimension connect to the third pulley which is moved by vertical satellite postioner so that the samples are moved to up 25 cm and down 25 cm exactly from center, floss with 50 cm length is passed through metal ring

Chapter Two


of the horizontal floss, Fig (2.17 A). Below the iron skeleton exactly at the left side of the water bath which is regulated at (55 C) and at right second water bath which is regulated at (5 C), Fig (2.18). The process of sample movements up and down, right and left with exact 30 second inside each water bath proceeds until 1000 and 2000 cycles was done automatically as describe below: Electrical source of (220 Vt, 50Hz) with additional source diesel generator was used in the present study. This source of electricity is supplied the both water baths (memert ) regulated at temperature 55 C and other water bath ( tafoon ) regulate at 5 C Fig (2.18), regularly remove the water and add ice or frozen water in the (tafoon) if reading of cold water are exceed 5 C using thermometer. The electrical current supply original flash timer Fig (2.19) for regular working (2 minute off and 15 minute on) in order to; first the electrical part is not disposed or burn and secondly to correct electrical current which is delayed from a piece to other few millisecond which collectively be second, minute and so on.

Chapter Two


Auxiliary contactors Direct

Flash timer

backward of dish mover

Determine the period of contactors current

Main contactors Direct only forward of dish mover

Pulse counter

Fig (2.19): Electro digital part which control path, period and number of cycle. From original flasher the current is transmitted to two flasher one of them is regulate the (30 second on and 30 second off) which is supplied contactor with auxiliary Contactor Fig(2.19) to exchange the positive and negative postioner movers so the sample is moved ;30 seconds downward and 30 seconds upward , but the movement on the other hand is controlled by micro switch Fig (2.13 A) there for even the current will continue from the satellite postioner the dish mover is restricted in the first millisecond only so the vertical movement of sample is regulated in each 30 second. Chapter Two


Other flasher regulate the (1 minute on and 1 minute off) which was supplied the contactors with auxiliary contactor to exchange the positive and negative postioner mover so; 1 minute to right side and 1 minute to left side but the movement on the other hand was controlled by micro switch Fig (2.13 A) therefore even the current was continued from the satellite postioner but the dish mover is restricted in the first millisecond only so that the horizontal movement of the sample is done regularly each 1 minute. From the right positive cycle of the horizontal contactor a pulse counter is connected to count the pulse so that we can know the exact number of the cycle, Fig (2.19). The source of electricity of both satellite postioners was from the original flasher but before entrance to the dish mover it regulates by contactors so the direction and period is regulated exactly, Fig (2.20). Since each cycle was consist of ( 30 seconds in the 1st water bath followed by 30 seconds interval then 30 seconds in the 2nd water bath finally 30 second interval ) so each cycle was taken exactly 2 minutes. As thermocycling was 2000 cycles, it has taken 4000 minuets i.e. (67 hr), as the procedure has an interrupted time (every 17 minutes have an interrupted 2 minutes) the over all the process was about 75 hr, however the job was done in cold weather at January where the normal temperature were below 10 C but during this worked period tried the beast to control the temperature of the cold water and observation of the steps of the method, Fig (2.21).

Chapter Two


Chapter Two


Fig (2.20): Electrical current cycle of device which control: period, repetition, direction and counting of cycle

Chapter Two


Fig (2.21): Thermocycling device parts

2.2.4. Debonding test: The specimens were held in a metal fixture which is constructed by turning operator machine to grasp the sample in one side and the end of the machine in the other side, Fig (2.22).

Fig (2.22): Metal fixture to grasping the specimens, the end is adapted to tight with the universal testing machine

Chapter Two


The specimens were tested at speed of 0.5mm/minute and load cell of 49 kg the force of failure was recorded in the (Kg) and converted to (N), Fig (2.23).

Fig (2.23) Grasping and debonding test with universal testing machine At first the data which obtained from Universal testing machine was in Kg (Kilogram), this unit must convert to N (Newton) by multiplying by 9.81 m. s2 (meter. Second2 ) according to Newton s gravitation low. The ? (diameter) also converted from mm (millimeter) to m (meter) by dividing on 1000 to obtain uniform units (Kg. m. sec) according to (International System of Units). In order to find the (T.B.S) the result of force by (Newton) must be divided on the area square m2 (meter

Chapter Two

2

) after this step stress obtained


with Pa (Pascal), also it should be converted to MPa (Mega Pascal) by subdividing on 1000000 (O'Brien, 2002) , (Craig and Powers, 2004). The following equation discusses the debonding force by Mega Pascal:

Surface area of circle =

* r2

were

D (diameter) = 5mm, S= ( 22/7) * (5/2) 2 S= 19.643 mm2 T.S= tensile strength ((Kg. m. s2)/mm2) or (N/mm2) F= force at failure (N) S= area of cross section (O'Brien, 2004). Changing the Kg to N must be multiplied the result by 9.81(m.s2) Newton low of gravitation. At the end application the following equation

In order to Mega Pascal, the Pascal (N/mm2) dividing on 1000000 according to (International System of Units).

Chapter Two


2.2.5: Mode of failure: The failure site was evaluated with visual examination and light microscope (X 16 magnifications) as shown in Fig (2.24).

A

B

C

D

Fig (2.24): A: Visual examination B and C: Digital camera examination and D: Microscopically examination

Chapter Two


The mode of failure was mentioned by (Moffitt et al 2008) who stated that, Adhesive failure occurs if there is no trace of any denture base resin on the tooth surface after the debonding Fig (2.25 A), while Cohesive failure occurs where there is denture base resin on the surface of the denture tooth or remnants of the denture tooth on the denture base, Fig (2.25 B). Denture base Artificial tooth

A

B

C

Fig (2.25): Type of failure (A: Adhesive failure, B: Cohesive failure, C: Mixed failure) (Darvell and Clark, 2000).

Chapter Two


2.2.6. Statistical analysis and software: 2.2.6. A. Statistical analysis methods were used in this study to analyze the result was: 1- statistical table 2- arithmetic mean 3- standard deviation 4- graphical presentation 5- student t-test one sample in two occasion between to set of data 6- ANOVA single factor between three set of data with ( statistical decision) 2.2.6. B. Computer program was used in most of the study steps as: 1- Microsoft windows XP 2- Office 2003 (word , excel , power point ,paint and picture viewer) 3- Office 2007 (word , excel , power point) 4- Crocodile technology 609 5- VLC media player 6- Internet source

Chapter Two


Chapter Three

Results

RESULT 3.1. Tensile bonding strength [T.B.S.]: Measuring the tensile bonding strength (T.B.S.) of artificial teeth (24 MAJOR DENT - Italian), (24 KAILI HUGEDENT –China) and (24 SUPER NEWCLAR IDEAL DENT MAKOO - Iran) was used subdividing on three subgroups; (A= control) with out thermocycling and with thermocycling (B= 1000 cycle and C=2000 cycle) were n=8. Appendix (I - IX) shown the process of converting the data from Kg to MPa for MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO for groups (A, B and C) respectively. Analysis of data and comparison between different brands for control groups was seen in Table (3-1) and Table (3.2). Table (3-1): Mean, standard deviation, standard error of mean, maximum, minimum of control groups of T.B.S. of MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) respectively. Artificial teeth brands MAJOR DENT

Mean

Standard

Standard

Sample

MPa

Deviation

Error

Variance

Minimum Maximum

12.862

1.265

0.447

1.601

10.777

14.246

14.288

2.454

0.868

6.022

11.39

17.995

12.777

1.408

0.498

1.984

10.877

14.556

KAILI HUGEDENT IDEAL DENT MAKOO

Chapter three

69

Result

Table (3.2): Analysis of variance (ANOVA) of control for (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) ANOVA : ANOVA Single Factor Source of Variation

SS

Df

MS

F

P-value

Between Groups

11.53159758

2

5.765799

1.800642

0.189778

Within Groups

67.24368025

21

3.20208

Total

78.77527783 23

Table (3.2) shows that there was no significant difference among brands in control groups (p > 0.05). The result also shows that the strongest one was KAILI HUGEDENT comparing to other in control groups. After 1000 cycle the analysis of data and comparison between different brands (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) was shown in Table (3-3) and Table (3-4).

Chapter three

70

Result

Table (3-3): Mean, standard deviation, standard error of mean, maximum, minimum of 1000cycle groups of T.B.S. of ( MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) respectively. Artificial teeth brands

Mean

Standard

Standard

Sample

MPa

Deviation

Error

Variance

Minimum Maximum

12.01

0.899

0.318

0.808

10.95

13.297

10.167

1.281

0.453

1.64

8.898

12.047

11.436

0.812

0.287

0.659

10.147

12.647

MAJOR DENT KAILI HUGEDENT IDEAL DENT MAKOO

Table (3.4): Analysis of variance (ANOVA) of thermocycling 1000 cycle for (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) ANOVA : ANOVA Single Factor Source of Variation

SS

Df

Between Groups

14.22094375

2

Within Groups

21.75145625 21 1.035783631

Total

Chapter three

MS

F

P-value

7.110471875 6.864823562 0.005080994

35.9724 23

71

Result

In Table (3.4) finding that there was a high significant difference among brands in (1000 cycle) group (p < 0.01). The result also shows that the strongest one was MAJOR DENT among brands. The statistical analysis of data for third groups (2000 cycle of thermocycling) of all brands was seen in (Table 3-5) and Table (3-6). Table (3-5): Mean, standard deviation, standard error of mean, maximum, minimum of 2000 cycle groups of T.B.S. of ( MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) respectively Artificial teeth brands

Mean

Standard

Standard

Sample

MPa

Deviation

Error

Variance

Minimum Maximum

9.973

1.703

0.602

2.9

7.698

12.697

8.471

1.991

0.704

3.962

5.998

11.167

11.017

1.301

0.46

1.692

9.7225

13.547

MAJOR DENT KAILI HUGEDENT IDEAL DENT MAKOO

Chapter three

72

Result

Table (3.6): Analysis of variance (ANOVA) of thermocycling 2000 cycle for (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) ANOVA Source of Variation

SS

Df

MS

F

Between Groups

26.20906608

2

Within Groups

59.88126725 21 2.851488917

Total

86.09033333 23

P-value

13.10453304 4.595680862 0.022107225

In Table (3.6) shows that there was a significant difference among brands in (2000 cycle) group (p < 0.05). The result also shows that the strongest one was SUPER NEWCLAR IDEAL DENT MAKOO among brands after thermocycling process. Table (3-7): statistical decision between groups (A= control, B= 1000 cycle and C= 2000 cycle) of all three brand acrylic artificial teeth (MAJOR DENT, KAILI HUGEDENT and SUPER NEWCLAR IDEAL DENT MAKOO) Between brands

ANOVA p-value

Decision(LSD)

A= Control of brands

0.189731091

NS (P>0.05)

B= 1000 cycle of brands

0.005074326

HS (P