Oct 29, 2008 - Tin chloride, Stannous chloride. SEM. Scanning ...... light is used to excite tolonium chloride or methylene blue dyes, respectively, to achieve a.
Middle infrared lasers for endodontic applications
Roy George BDS, MDS
A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland, October 2008
School of Dentistry, The University of Queensland
I
Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material.
Roy George BDS, MDS 29 October 2008
II
Published Works by the Author Incorporated into the Thesis 1. George R, Walsh LJ. Coaxial water mist spray alters the ablation properties of human radicular dentine for the Holmium:YAG laser. Journal of Oral Laser Applications 2007;7(4):225-231. Incorporated as Chapter 9. 2. George R, Walsh LJ. Factors influencing the ablative potential of the Er:YAG laser when used to ablate radicular dentine. Journal of Oral Laser Applications 2008;8(1):33-41. Incorporated as Chapter 2. 3. George R, Walsh LJ. Apical extrusion of root canal irrigants when using Er:YAG and Er,Cr:YSGG lasers with optical fibers: An in vitro dye study. Journal of Endodontics 2008;34(6):706-708. Incorporated as Chapter 7. 4. George R, Rutley EB, Walsh LJ. Evaluation of smear layer: a comparison of automated image analysis versus expert observers. Journal of Endodontics 2008;34:999-1002. Incorporated as Chapter 4. 5. George R, Meyers IA, Walsh LJ. Laser activation of endodontic irrigants using improved conical laser fiber tips for removing smear in the apical third of the root canal. Journal of Endodontics 2008; in press. Incorporated as Chapter 5. List of presentations 1.
George R, Walsh LJ. Differential ablation of radicular dentine with Er:YAG laser radiation under varying water flow rates. Academy of Laser Dentistry. March 2007 Nashville, TN, U.S.A. http://www.laserdentistry.org/scholarship/index.cfm
2.
George R, Walsh LJ. Apical extrusion of root canal irrigants when using Er:YAG and Er,Cr:YSGG lasers with optical fibers: An in vitro dye study. Australian Association for Laser Dentistry. April, 2008. Brisbane.
3.
George R, Walsh LJ. Lasers and optical fibers in endodontics. The Australian society of Endodontology. May 2008. Brisbane Australia.
4.
George R, Walsh LJ. Efficiency of Er:YAG and Er,Cr:YSGG lasers in removing smear layer in the apical third of the root canal using modified optical fibers. Australian Association for Laser Dentistry. August 2008. Brisbane Australia.
5.
George R, Meyers IA, Walsh LJ. Novel Fibers for Smear Layer Removal with Middle Infrared Lasers. International Association for Dental Research, ANZ Division. October 2008, Perth.
III
Acknowledgments I would like to immensely thank Professor Laurence Walsh for having made it possible for me to do my PhD at this university. Also I would like to thank him for his constant support, exceptional guidance, interest in my professional growth and above all being making him self available at short notice or odd times during the length of my project. Thanks are also due to the following: 1
Professor Ian Meyers for his guidance, valuable suggestions, providing me with basic material for my project and also for giving me an opportunity to work in the clinics.
2
Dr Edward Rutley for not only his guidance and taking an active interest in my project, but also for introducing me to the local endodontic community.
3
Dr Fardad Shakibaie for providing me with valuable mathematical hints.
4
Dr Helen Boocock for being a great support during the whole of my program.
5
Bruce Rex and Neil Taylor for providing me with useful hardware that was necessary for my project.
6
Nicky Foxlee, Cathy Hibberd and Thelma Campbell for library assistance.
7
Peter Moeser and Matthew Moncreiff of High Tech Laser Australia for providing me access to Holmium:YAG laser that was used in this project.
8
Eddie Delsorte, Glenda Maher, Catherine Purcell and Jenny Erskine for their assistance within at the Dean’s office.
9
The staff at the UQ Center for Microscopy and Microanalysis for the training and guidance provided in the use of scanning electron microscope
10
The Australian Dental Research Foundation and the Australian Society of Endodontology, who provided funding to support parts of this work.
11
The Faculty of Health Sciences of The University of Queensland, for providing a scholarship to assist in my PhD studies.
Finally and most importantly I would like to thank my family and friends, especially my wife Elby, and my children Steve and Shaun, for being patient, co-operative and a source of constant encouragement during these years of my research. Roy George
IV
Abstract Middle infrared lasers are currently used in clinical dental practice for ablation of dental hard and soft tissues. The use of middle infrared lasers for endodontic applications has not yet been adopted widely, with significant challenges being the limitations of optical delivery systems, the thermal stress developed by laser treatment, and the containment of energy within the confines of the root canal. Against this background, the current study investigated a series of novel approaches designed to address these issues. The study was done in eight phases. Phase 1 explored factors that influenced the ablative potential of the Er:YAG laser when used to ablate radicular dentine. This identified optimal parameters, and revealed that dentine ablated differently from the internal (radicular aspect) than from the external (root aspect). High water flow rates were found to attenuate dentine ablation within the root canal space. Phase 2 involved modifying optical fibers to increase lateral emission of laser energy, using a range of physical and chemical processes both alone and in combination. Three free-running pulsed infrared lasers (Nd:YAG, Er:YAG, and Er,Cr:YSGG) were employed to test the performance of the modified fibers. Compared with conventional fibers, conical ended and honeycomb fibers gave increased lateral emissions, which would be of benefit for ablation of radicular dentine. Methods for treating fibers of different chemical composition were quantified. In Phase 3, Er:YAG and Er,Cr:YSGG lasers were used to treat root canals, with a particular emphasis on the removal of a thick smear layer which was created intentionally in root canals prior to lasing. A novel digital analysis method was developed to assess the extent of smear layer remaining after the various root canal treatments. This image analysis method was validated and then used in Phase 4, in which the effectiveness of the Er:YAG and Er,Cr:YSGG lasers in removing smear layer in the apical third of the root canal was studied, this time using both conventional plain fibers and conical modified fibers. For smear layer removal, conical fibers performed better than plain fibers, when matched for the same laser system and the same irrigant. There was no difference in performance between the two middle infrared laser systems. Lasing was found to improve the action of EDTAC when allowed to remain in the canal for the same treatment time. Either of the laser systems, when V
used with conical tips, could remove thick smear layers. Conversely, if used with plain tips, the overall performance of the laser systems was less than the “gold standard” of rotary nickel titanium files used with EDTA and NaOCl irrigants. Phase 5 of the study showed that minimal temperature effects occurred on the external surface of the root when this laser treatment was undertaken with either plain or modified endodontic laser tips. An additional safety concern with intra-canal laser use is the possibility of extrusion of fluids from the apical foramen. Thus, Phase 6, a novel digital analysis method was developed to quantify extrusion of microdroplets from the apex when Er:YAG or Er,Cr:YSGG lasers were used with plain or conical fiber tips. Both lasers generated sufficient pressure waves to displace small volumes of fluids past the apex, with an effect greater than the conventional “gold standard” treatment of irrigation with a 25-gauge needle. The issue of extrusion should be considered when considering the irrigants used with intra-canal laser treatments in endodontics. In Phase 7, additional variations to optical fiber design were examined, including “safe ended” fibers fabricated using metal deposition methods. Forward emissions were reduced, with no reduction in the lateral emissions. This suggests that tip plating methods may be useful in obtaining safe ended endodontic laser tips. In final phase of the study, the use of an alternative middle infrared laser, the holmium:YAG system, was examined, using methodology similar to that in Phase 1. Based on the work undertaken in Phases 1 it was predicted that the use of coaxial water mist could alter the ablative effect and overcome problems of surface thermal interactions such as carbonization. It was found that use of coaxial water spray altered the ablation effect, and produced craters with smooth outlines indicative of an entirely explosive process without adjacent collateral damage. The ability to ablate dentine under wet lasing conditions, and the ability to be transmitted through glass optical fibers offers promise for the application of the Ho:YAG laser for endodontic procedures, particularly shaping the root canal system with modified quartz glass fibers. This work has established the utility of middle infrared lasers for certain aspects of endodontic therapy, and demonstrated the value of lasing in combination with water-based irrigants. Of particular importance, new designs for optical fiber tips have been developed, VI
with enhanced lateral emissions to address the challenges of irradiating the walls of the root canal.
Keywords Lasers, Endodontics, Smear layer, Rotary NiTi, Holmium lasers, Er:YAG lasers; Digital imaging, Fiber optics.
Australian and New Zealand Standard Research Classification (ANZSRC) 1150503 (Endodontics) 55%, 0903 (Biomedical Engineering) 40%, 110501 (Dental materials and equipment) 5%
VII
List of abbreviations AgNO3
Silver nitrate
ANOVA
Analysis of variance
CMCP
Camphorated paramonochlorophenol
CO2
Carbon dioxide
CEJ
Cemento-enamel junction
DEJ
Dentino-enamel Junction
EBSD
Electron back scatter diffraction
EDTA
Ethylenediaminetetraacetic Acid
Er:YAG
Erbium: Yttrium Aluminum Garnet
Er,Cr:YSGG
Erbium Chromium: Yttrium Scandium Gallium Garnet
GaAlAs
Gallium Aluminum Arsenide
H202
Hydrogen peroxide
HF
Hydrofluoric acid
HLLT
High level laser therapy
HNO3
Nitric acid
Ho:YAG
Holmium: Yttrium Aluminum Garnet
KEY3
KaVo Erbium:YAG 3
KTP
Potassium-titanyl-phosphate
NaOCl
Sodium hypochlorite
NaOH
Sodium hydroxide
NH3
Ammonia
HeNe
Helium Neon
IR
Infrared
InGaAsP
Indium Gallium Aluminum Arsenide Phosphate
VIII
LASER
Light Amplification by Stimulated Emission of Radiation
LDF
Laser Doppler flowmetry
LLLT
Low level laser therapy
Nd:YAG
Neodymium: Yttrium Aluminum Garnet
PAD
Photo Activated Disinfection
PDT
Photodynamic therapy
P-value
Probability Value
Psi
Pounds per square inch
Pps
Pulse per second
RMANOVA
Repeated Measures Analysis of variance
SnCl2
Tin chloride, Stannous chloride
SEM
Scanning electron microscopy
UV
Ultraviolet
W
Watt
IX
List of Figures Chapter 1 Fig.1.1. Absorption of water at different wavelengths. …………………………………...…13 Fig.1.2. Absorption spectra of water. . ………………………………………………………22 Fig.1.3. RCLase laser tip. . …………………………………………………………………..39 Fig.1.4. Conventional etching process using an etchant (HF) and an organic solvent. …..…53 Fig.1.5. The static meniscus on a circular cylinder immersed into a solution…………….... 53 Fig.1.6. Tapered fiber transmission. . ……………………………………………………..…55 Fig.1.7. Large end to small end transmission. . ……………………………………………...56 Fig.1.8. Various shaped optical tips. . …………………………………………………….…56
Chapter 2 Fig. 2.1. Crater from 500mJ laser pulses on the internal dentine surface at 0.5mL/min water flow rate …………………………………………………………….……………..96 Fig. 2.2. Crater from 500mJ laser pulses on the external surface at 0.5mL/min water flow rate……………………………………………………………..………………..….97 Fig. 2.3. Crater from 500mJ laser pulses on the internal dentine surface at 1.5mL/min water flow rate…………………………………………………………………………....98 Fig. 2.4. Crater from 500mJ laser pulses on the external dentine surfaceat 1.5mL/min water flow rate……………………………………………………………………………99 Fig. 2.5. SEM examination of dentine tubules at the bases of craters (500mJ)…………….100 Fig. 2.6. Crater diameters with varying irradiation conditions, dentine topography and water flow rates. …………………………………………………………………..….…101 Fig. 2.7. Crater depths with varying irradiation conditions, dentine topography and water flow rates. ………………………………………………………………………….…..101 Fig. 2.8. Estimated crater volumes with varying irradiation conditions, dentine topography and water flow rates. ……………………………………………………………..102 Fig. 2.9. Effects of various treatments within the apical third of the root canal…………... 103
X
Chapter 3 Fig. 3.1. Angles for testing light transmission of optical fibers……………………….……113 Fig. 3.2. SEM images showing the surface topography of the modified fibers…………….114 Fig. 3.3. Elemental analytic graph of fiber tips. ……………………………………………116 Fig. 3.4. Emission in the forward direction at a fixed distance of 10 mm. ……………...…117 Fig. 3.5. Emission in the lateral direction at a fixed distance of 2 mm………………….….117 Fig. 3.6. Schematic of light propagation from modified optical fibers…………………..…119 Fig. 3.7. Distribution of visible red light (632.8 or 635 nm) from coaxial aiming beams.…120 Fig. 3.8. Conical fiber modification (Group 2) of the Biolitec fiber. ………………………121 Fig. 3.9. Honeycomb fiber modification (Group 6) of the Biolitec fiber. ……………….…122 Fig. 3.10. Spectrophotometer recordings of light acceptance by a plain optical fiber….…..123 Fig. 3.11. Spectrophotometer recordings of light acceptance by a conical ended optical fiber... …………………………………………………………………………..……..….124 Fig. 3.12. Spectrophotometer recordings of light acceptance by a plain optical fiber subjected to abrasion only…………………………………………………….…….…….…125 Fig. 3.13. Spectrophotometer recordings of light acceptance by a honeycomb optical fiber subjected to abrasion only…………………………………………….…….….…126 Fig. 3.14. Distribution of light in excitation and fluorescence. ………………..…….…..…129
Chapter 4 Fig. 4.1. Scanning electron micrograph of a Group 1 specimen after digital image analysis …………………………………………………………………………………………..…..136 Fig. 4.2. Representative SEM images and their related scores by digital assessment ……..138
Chapter 5 Fig. 5.1. Optical fiber tips used in the study……………………………………….…….…149 Fig. 5.2. Apical third of the root canal after treatment in the control groups……….……...154 Fig. 5.3. Apical third of the root canal after treatment using the Er, Cr:YSGG laser……....155 Fig. 5.4. Apical third of the root canal after treatment using the Er:YAG laser …….……..156 Fig. 5.5. Graphical presentation of the percentage of tubules exposed in pixels for the various laser groups vs. control…………………………………………………………...159 XI
Chapter 6 Fig. 6.1 Experimental schematic for temperature study……………………………………171 Fig. 6.2 Experimental set up for the temperature study. ……………………………...……172 Fig. 6.3 Thermal changes during lasing……………………………………………….……175 Chapter 7 Fig. 7.1 Experimental set up for the pilot study to record to fluid movement within a root canal resin block. ……………………………………………………..…….…….184 Fig. 7.2. Luer-lok syringe connected to polyvinylchloride tubing, which in turn is connected via a tap valve to a source of compressed air …………………………………….186 Fig. 7.3. Pressure transducer and power supply………………………………………….…186 Fig. 7.4. Schematic of the experimental setup…………………………………………...…187 Fig. 7.5. Typical conical tip created using tube etching with a KEY3 fiber ………………188 Fig. 7.6. Ophir Nova II ®display and an Ophir® 30A-V1-SH smart head sensor……...…189. Fig. 7.7. Dye extruded onto paper …………………………………………………………191 Fig. 7.8. High speed image recording of Er:YAG laser pulses in water in root canal replicas in epoxy resin blocks with an InLine high speed camera……………………...…193 Fig. 7.9. Total number of pixels for all extruded dye (i.e. summed from all distances) for the various experimental groups at either ISO #15 or ISO #20. ………………….……194 Fig. 7.10. Number of pixels of extruded dye at centimeter intervals from the apex, for KEY3 laser group with laser fibers (bare or modified) placed at a distance of 5 mm from the apex, for apical foramina of either ISO #15. …………………………………195 Fig. 7.11. Number of pixels of extruded dye at centimeter intervals from the apex, for KEY3 laser group with laser fibers (bare or modified) placed at a distance of 10mm from the apex, for apical foramina of either ISO #15. ……………………………...…196 Fig. 7.12. Number of pixels of extruded dye at centimeter intervals from the apex, for Biolase laser group with laser fibers (bare or modified) placed at a distance of 5 mm from the apex, for apical foramina of either ISO # 20………………………..……….197 Fig. 7.13. Number of pixels of extruded dye at centimeter intervals from the apex, for Biolase laser group with laser fibers (bare or modified) placed at a distance of 10mm from the apex, for apical foramina of either ISO #20………………….…198
XII
Chapter 8 Fig. 8.1. Fiber designs…………………………………………………………………....…210 Fig. 8.2. Experimental set up for the pilot study of silver coating capillary tubes………….211 Fig. 8.3. Silver coated glass capillary tube created using the electroless silver plating technique……………………………………………………………....……….…212 Fig. 8.4. Forward emission losses …………………………………………….…..…..…....216 Fig. 8.5. Side emission losses………………………………………………….…..……..…216 Fig. 8.6. Emission profiles from optical fiber designs showing distribution of visible red light beam(632.8 or 635 nm)……………………………………………..…..……..… 217
Chapter 9 Fig. 9.1. Diameter of craters when lasing dentine under dry conditions……………………227 Fig. 9.2. Diameter of craters when lasing dentine under wet conditions………………...…227 Fig. 9.3.Depth of craters when lasing dentine under dry conditions……………………..…228 Fig. 9.4. Depth of craters when lasing dentine under wet conditions………………….…...228 Fig. 9.5. Volume of craters under dry conditions………………………………………..….229 Fig. 9.6. Volume of craters under wet conditions……………………………………….….229 Fig. 9.7. Dry ablation (0.6 J, 2 Hz) …………………………………………………………230 Fig. 9.8. Dry ablation (1.0 J, 6 Hz) ……………………………………………………....…231 Fig. 9.9. Wet ablation (0.6 J, 1 Hz) …………………………………………………..……232 Fig. 9.10. Wet ablation (0.1 J, 6 Hz) ………………………………………………….……233 Fig. 9.11. SEM image of dry ablation (0.6 J, 3 Hz) ……………………………………..…235 Fig. 9.12. SEM image of wet ablation (0.6 J, 3 Hz) ……………………………………..…236 Fig. 9.13. High power SEM images of dry ablation (0.6 J, 3 Hz) ……………………….…237 Fig. 9.14. High power SEM images of wet ablation (0.6 J, 3 Hz) …………………………238
XIII
List of Tables Table.1.1: Bacteria from the root canals of teeth with apical rarefactions ………………..….7 Table.1.2: Selected laser wavelengths and their major absorbing molecules …………….…14 Table.1.3: Selected applications of lasers ………………………………………….………..32 Table.2.1: Dentine tubule patency expressed as a percentage of the total pixel area…...….103 Table.3.1: Angles of divergence……………………………………………………..…..….118 Table.4.1: Hulsmann assessment standard image percentage cutoffs and overall agreement in scores……………………………………………………………………………137 Table.4.2: Inter-examiner differences………………………………………………………140 Table.5.1: Area of dentin tubules……………………………..………………………….…157 Table.5.2: Statistical analyses…………………………………………………………..…..158 Table 6.1: Temperature recordings and effective dentine thickness measurements…….... 175 Table.7.1: Comparison of apical extrusion in the experimental groups……………………194 Table.8.1: Emission profiles of various tip designs…………………………………….......215 Table.9.1: Microscopic effects of Ho:YAG laser treatment of dentine ………………....…234
XIV
Table of Contents Title of the project…………………………………………………………………......……....I Declaration of authorship……………………………………………………………......…... II Published works by the author incorporated into the thesis………………………….…....... III Acknowledgements……………………………………………………………………..…... IV Abstract ……………………………………………………………………………....……....V Key words…………………………………………………………………………………...VII Australian and New Zealand standard research classification………………………............VII List of abbreviations…………………………………………………………………...…...VIII List of figures and tables ………………………………………………………...………..….X List of tables ……………………………………………………………………..….….….XIV Table of contents………………………………………………………………………...….XV
Chapter 1: Literature review: Middle infrared lasers and their applications in endodontics……………………………………………………………………………….…..1 1.1
Introduction……………………………………………………………………………2
1.2
Goals of endodontic …………………………………………………………………...2
1.3
Objectives of Biomechanical preparation……………………………………………..3 1.3.1 Mechanical techniques…………………………………………………..3 1.3.2 Biological techniques……………………………………………………5 1.3.3 Limitations of the present methods of tooth preparation………………..8
1.4
Smear layer and its removal …………………………………………………………..9 1.4.1
Assessment of smear layer removal………………………………………….11
1.5 Lasers in endodontics…………………………………………………………………….12 1.5.1 Laser wave lengths and their absorption characteristics ………………………12 1.5.1.1 Mechanisms of laser action on biological tissues……………………15 1.5.2 Properties of lasers …………………………………………………………….16 1.5.2.1 Diode laser ………………………………………………………..…17 1.5.2.1.1 Properties …………………………………………………..17 1.5.2.1.2 Applications ………………………………………………..17 1.5.2.2 Nd:YAG.……………………………………………………………..19
XV
1.5.2.2.1 Properties………………………………………………..….19 1.5.2.2 2 Applications in dentistry…………………………………...19 1.5.2.3 Holmium lasers……………………………………………………....21 1.5.2.3.1 Properties…………………………………………………..22 1.5.2.3.2 Applications ……………………………………………….23 1.5.2.4 Er,Cr:YSGG & Er:YAG lasers……………………………………...24 1.5.2.4.1 Properties ………………………………………………....24 1.5.2.4.2 Mechanism of ablation…………………………………....25 1.5.2.4.3 Applications……………………………………………....26 1.5.2.4.4 Factors influencing laser ablation………………………..29 1.5.3
Present applications of lasers in endodontics……………………………..…31 1.5.3.1 Laser diagnosis ………………………………………………….….32 1.5.3.1.1 Doppler flowmetry………………………………………...33 1.5.3.1.2 Low level laser therapy (LLLT) for diagnosis………….…33 1.5.3.1.3 Laser fluorescence………………………………………....34 1.5.3.2 Pulpotomy…………………………………………………………....35 1.5.3.3 Pulp capping ………………………………………………………...35 1.5.3.4 Laser assisted widening of the root canal …………………………...36 1.5.3.5 Removal of smear layer from root canal walls..……………………..38 1.5.3.6 Sterilization of the root canal ………………………………………..40 1.5.3.6.1 Photo thermal effects………………………………………40 1.5.3.6.2 Photo activated disinfection (PAD)…..……………………41 1.5.3.6.3 Limitations of lasers for disinfection of root canal………...42 1.5.3. 7 Laser induced analgesia ….………………………………………....42 1.5.3.8 Removal of moisture/drying canal..………………………………….42 1.5.3.9 Removing root canal fillings and fractured instruments……………..43 1.5.3.10 Role of lasers in root fractures and other applications………….…..43
1.5.4 Relevant aspects of laser safety in endodontics……………………………...44 1.5.4.1 Safety issue related to general use of lasers………………………….44 1.5.4.2 Prevention of transmission of infection through contact………….....45 1.5.4.3 Temperature effect of lasers on the dental pulp ……………………..46 1.5.4.4 Temperature effect of lasers on periodontal tissues……………..…...46 1.6
Fiber optics and their modifications………….…………………………………….…47 1.6.1 Articulated Arm ………………………………………………………………..48 XVI
1.6.2 Hollow waveguide ……………………………………………………………..48 1.6.3 Fiber Optics………………………………………………………………...…..48 1.6.3.1 Doped fibers………………………………………………………….49 1.6.3.2 Transmission losses………………………………………………. ...49 1.6.3.3 Methods of modifying fiber tips………………………………… ….51 1.6.3.3.1 Chemical etching …...……………………………………..51 1.6.3.3.2 Etching mechanism………………………………………..52 1.6.3.3.3 Factors effecting etching…………………………………...53 1.6.3. 4 Modified tip profiles …………………………………………….….55 1.6.3.5 Method of use of the tip……………………………………………...57 1.6.3.5.1 Mode of action………………………………………..........57 1.6.3.5.2 Selecting the correct fiber optic……………….…………...58 1.7 Technical issues affecting laser use in endodontics …………………………………….58 1.8 Gap in knowledge ………………………………………………………………………59 1.9 Hypothesis……………………………………………………………………………… 60 1.10 Aims ……………… …………………………………………………………………...61 1.11 References ……………………………………………………………………………...62
Chapter 2: Factors influencing the ablative potential of the Er:YAG laser when used to ablate radicular dentine……………………………………………………………………90 2.1 Abstract………………………………………………………………………………..…91 2.2 Introduction…………………………………………………………………………..…..92 2.3 Materials and methods………………………………………………………………..….93 2.4 Results………………………………………………………………………………..…..96 2.5 Discussion……………………………………………………………………………....104 2.6 Conclusion…………………………………………………………………………...….106 2.7 References…….……………………………………………………………………..….106
Chapter 3: Performance assessment of novel side firing flexible optical fibers for endodontic applications…………………………………………………………………...108 3.1 Abstract……………………………………………………………………………..…..109 3.2 Introduction………………………………………………………………………….…110 XVII
3.3 Materials and methods………………………………………………………………..…111 3.3.1 Lasers and optical fibers……………………………………………….….111 3.3.2 Fiber modifications……………………………………………………..…111 3.3.3 Emission measurements………………………………………………..…112 3.3.4 Transmission………………………………………………………….…..113 3.4 Results……………………………………………………………………………….….114 3.4.1 Fiber topography……………………………………………………….…114 3.4.2 Fiber composition and etching times……………………………………..115 3.4.3 Forward and lateral emissions …………………………………………....115 3.4.4 Angle of divergence………………………………………………………118 3.4.5 Transmission of fibers…………………………………………………….122 3.5 Discussion………………………………………………………………………………127 3.6 Conclusion………………………………………………………………………………129 3.7 References…….…………………………………………………………………..…….130
Chapter 4: Evaluation of smear layer: a comparison of automated image analysis versus expert observers………………………………………………………………..…………..132 4.1 Abstract………………………………………………………………………………....133 4.2 Introduction…………………………………………………………………………..…134 4.3 Materials and methods…………………………………………………………………..135 4.3.1 SEM examination…………………………...………………………….…136 4.3.2 Evaluation of SEM images…………………………………………….…137 4.3.3 Statistical Analysis……………………………………………………..…139 4.4 Results………………………………………………………………………………..…139 4.5 Discussion……………………………………………………………………………....140 4.6 Conclusion………………………………………………………………………………141 4.7 References…….………………………………………………………………………...141
Chapter 5: Efficiency of the Er:YAG and Er,Cr:YSGG lasers in removing smear layer in the apical third of the root canal using modified optical fibers……………………..144 5.1 Abstract……………………………………………………………………………..… .145 5.2 Introduction…………………………………………………………………………..…146 5.3 Materials and methods………………………………………………………………….148 XVIII
5.3.1 Sample selection……………………………………………………….…148 5.3.2 Lasers and optical fibers used………………………………………….…148 5.3.3 Sample preparation …………………………………………………….…150 5.3.4 Sample preparation for SEM and light microscopic examination………..151 5.3.5 Image analysis………………………………………………………….…151 5.3.6 Analysis…………………………………………………………………..152 5.4 Results…………………………………………………………………………….…….152 5.5 Discussion………………………………………………………………………………159 5.6 Conclusion…………………………………………………………………….………...161 5.7 References…….………………………………………………………………….…..…162
Chapter 6: Temperature effect of modified endodontic laser tips on the apical 3rd of root canals when used with Er:YAG and Er,Cr:YSGG lasers………………………....166 6.1 Abstract……………………………………………………………………………..…..167 6.2 Introduction……………………………………………………………………..………168 6.3 Materials and methods………………………………………………………………..…170 6.3.1 Sample selection and preparation…………………………………………170 6.3.2 Lasers and optical fibers………………………………………………. …173 6.3.3 Analysis…………………………………………………………………...174 6.4 Results…………………………………………………………………………………..174 6.5 Discussion………………………………………………………………………………176 6.6 Conclusion………………………………………………………………………….…...177 6.7 References…….………………………………………………………………………...178
Chapter 7: Apical extrusion of root canal irrigants when using Er:YAG and Er,Cr:YSGG lasers with optical fibers: An in vitro dye study……………………..…..180 7.1 Abstract…………………………………………………………………………….…..181 7.2 Introduction…………………………………………………………………………….182 7.3 Materials and methods ………..….…………………………………………………….183 7.3.1 Materials and methods pilot study….…………………………………….183 7.3.2 Materials and methods main study….……………………………………185 7.3.3 Image analysis….……………………………….………………………..190 7.4 Results……………………………………………………………………………..……192 XIX
7.4.1 Results: pilot study………..……………………………………………...192 7.4.1 Results: main study……….……………………………………..………..192 7.5 Discussion……………………………………………………………………….….…..199 7.6 Conclusion……………………………………………………………………….….…..201 7.7 References…….…………………………………………………………………..…….202
Chapter 8: Performance assessment of a safe ended flexible optical fibers for endodontic and periodontal applications……………………………………………………….……..205 8.1 Abstract………………………………………………………………………….….…..206 8.2 Introduction…………………………………………………………………….…….…207 8.3 Materials and methods………………………………………………………….………208 8.3.1 Lasers and optical fibers………………………………………….………208 8.3.2 Sample preparation………………………………………………... …….209 8.3.3 Electroless plating of fiber tip…………………………………………….211 8.3.3.1 Sensitizing solution………………………………………..…….212 8.3.3.2 Silver solution……………………………………………..…….212 8.3.3.3 Reducing solution……………………………………………….212 8.3.3.4 Silvering methods…………………………………………….…213 8.3.4 Emission measurements………………………………………………..…213 8.3.5 Analysis…………………………………………………………….…......214 8.4 Results…………………………………………………………………………………..214 8.5 Discussion……………………………………………………………………………....218 8.6 Conclusion…………………………………………………………………………..…..219 8.7 References…….………………………………………………………………………...219
Chapter 9: An exploration of the use of the Holmium:YAG laser with coaxial water mist spray for ablation of radicular dentine…………………………………………………..222 9.1 Abstract………………………………………………………………………………....223 9.2 Introduction……………………………………………………………………….…….224 9.3 Materials and methods……………………………………………………………….…225 9.3.1 Sample preparation…………………………………………………….…225 9.3.2 Laser treatment………………………………………………….…….….225 9.3.3 Microscopic analysis…………………………………………………..…226 9.4 Results…………………………………………………………………………………..226 XX
9.4.1 Dimensions of laser-induced craters…………………………………..….226 9.4.2 Microscopic findings………………………………………………….….230 9.4.3 SEM observations………………………………………………………...234 9.5 Discussion……………………………………………………………………………....239 9.6 Conclusion……………………………………………………………………………...240 9.7 References…….…………………………………………………………………….…..241
Chapter 10…………………… ….………………………………………………….……..242 10.1 General discussion ……………………………………………….………………..….243 10.2 Directions for future work……………………………………………….………...….246 10.3 Concluding remarks……………………………………………….………………..…247
Appendices Appendix 1: Additional data and statistical analysis for Chapter 2 ……………….………248 Appendix 2: Additional data and statistical analysis for Chapter 3 ………….………….…260 Appendix 3: Additional data and statistical analysis for Chapter 4 ……………………..…270 Appendix 4: Additional data and statistical analysis for Chapter 5 ……………………..…281 Appendix 5: Additional data and statistical analysis for Chapter 6 ……………………….286 Appendix 6: Additional data and statistical analysis for Chapter 7 …………………….….289 Appendix 7: Additional data and statistical analysis for Chapter 8 ……………………..…303 Appendix 8: Additional data and statistical analysis for Chapter 9 ……………………..…312 Appendix 9: Protocol for the ProTaper System…………………………………………….334 Appendix 10: Reagents used……………………………………………………………….336
XXI
Chapter 1 Literature review Middle infrared lasers and their applications in endodontics
Aims and Hypothesis
1
1.1 Introduction As stated by the Commission on Dental Accreditation of the American Dental Association, the discipline of endodontics can be defined as “that branch of dentistry which is concerned with the morphology, physiology and pathology of the human dental pulp and periradicular tissues. Its study and practice encompass the basic and clinical sciences including the biology of the normal pulp, the etiology, diagnosis, prevention and treatment of diseases and injuries of the pulp and associated periradicular conditions”. Root canal treatment involves the separate stages of access cavity preparation, chemomechanical preparation, and obturation. The preparation of the root canal can be accomplished using a wide variety of hand and rotary cutting instruments. Recent advances in the field of rotary cutting instruments have substantially reduced the treatment time and also the fatigue to the operator and patient. At the present time, a number of lasers have been employed in endodontics to augment traditional methods and assist in diagnosis, preparation and sterilisation of the root canal.
1.2 Goals of Endodontics In his seminal paper in 1974, Schilder (1) described the primary goals of endodontics as cleaning organic remnants from the root canal system, and shaping it to receive a three dimensional hermetic (fluid-tight seal) filling of the entire root canal space. In 2005, writing for a contemporary audience, Hulsmann (2) took a biological rather than mechanical focus, and described these goals as the prevention of peri-radicular disease, and/or promotion of healing in cases where disease already exists. Said another way, the goal of modern endodontics is to create a canal that is clean, sterile and well prepared to receive a root canal restorative material (3-5) that prevents both apical and coronal micro leakage (6, 7), as well as to eliminate the periapical inflammatory pathology that impairs oral function. The highly complex and variable nature of the root canal system (8, 9) makes the achievement of these goals difficult, and hence modern endodontics uses a wide range of instruments, techniques, and medicaments to remove debris and bacteria from infected root canals, and shape the canals for later obturation.
2
1.3 Objectives of Biomechanical preparation The preparation of the root canal involves both biological and mechanical objectives, and hence it is commonly called biomechanical preparation (BMP). Schilder (1) listed five design objectives and four biological objectives. The design objectives were to obtain a continuously tapering funnel from the apex to the access cavity, with a narrower crosssectional diameter at every point further apically, to prepare the canal to follow the shape and curvature of the original canal, to maintain the position of the apical foramen, and to keep the apical opening as small as practicable. The four biological objectives were to confine all instrumentation within the root canal, to avoid forcing necrotic debris beyond the foramen, to remove all tissue from the root canal space, and to create sufficient space for intra-canal medicaments. Grossman (10) recommended the widening of the canals, to facilitate the removal of pulp tissue and micro-organisms. Widening also improved access for delivering irrigants, for instrumentation of the apical third of the root canals, and for obturation of the prepared canal. The preparation of the root canal system has also been referred to as chemomechanical preparation (11), as it involves both mechanical components (using hand or rotary instruments) and chemical components (irrigants and medicaments).
1.3.1 Mechanical Techniques Over the years, a number of techniques have evolved in an attempt to meet the objectives of root canal preparation, taking into consideration the design and physical properties of the available endodontic instruments. One of the early techniques for preparation of the canal space was the “conventional technique” (12). This involved the circumferential filing of all canal walls to a size three times greater than the first instrument used, or until the canal was assessed as being clean, as witnessed by white dentinal shavings and a lack of soft tissue remnants on the files. The drawback with this technique was it removed far too much dentine at the apical portion of the root, thus posing a risk of fracture during obturation, but under-prepared the coronal region. 3
Presently, the most commonly recommended techniques for root canal preparation are the step back technique (13-15), the crown-down technique (16, 17), and a combination of the two (the hybrid technique) (18). The step back technique originated in a method described by Clem (19) as “serial root canal preparation”, and was then modified by various authors (20-22). The step back techniques involves establishing the working length, preparing the apex at the working length to a files three size greater than the initial instrument that binds and then stepping back coronally in increments of 1mm till the canal is completely prepared. Other modifications that have been added to this basic technique include starting the step back 3 mm short of the working length, in order to obtain a parallel canal that would provide a better tug back for the master/primary cone (23), and a passive step back technique which requires the use of hand and rotary instruments with minimal force during filing (24, 25). The step back technique is relatively easy to master, and achieves a canal flared in three dimensions, as per Schilder’s criterion. Compared to the “conventional technique”, it produces cleaner canals and better preserves the original canal curvature. The disadvantages of the step back technique include apical extrusion of debris, ineffective irrigation, poor apical control due to coronal binding, loss of working length, and zipping and transportation of the canal, especially when larger files are used at the apex. The crown down technique (also known as the step down technique), involves stepping down the canal length using larger instruments coronally and progressively smaller instruments as the apex is approached. The initial flaring reduces the likelihood that debris is forced apically. The initial flare also gives greater control of the instruments used for the apical third, and thereby lowers the risk of zipping or perforation in this region (2, 26, 27). A useful addition to both step back and crown-down methods when undertaken with hand instruments is the balanced force method(28). This involves inserting files passively into the canal, and then rotating them in a clockwise direction for 90 degrees, to engage the dentine of the root canal walls. While maintaining axial force, the instrument is then rotated counterclockwise, to break loose the engaged dentine, and withdrawn. This method was developed to overcome the problem of zipping of the canals which was caused by instruments failing to remain centered in the canal. An in vitro study has demonstrated the efficiency of this method in preparing curved canals(29), however in a later study comparing balanced force and step-back(30), neither were able to prepare the canals ideally.
4
The introduction of highly flexible super-elastic nickel-titanium (NiTi) hand and rotary instruments in endodontics has led to a proliferation of methods, to allow maximum utilization of the unique design features of individual instruments. Commonly used file systems include ProTaper (Maillifer Dentsply) (31), ProFile (Maillifer Dentsply) (32), K3 (SybronEndo) (33), Pro-system GT (Dentsply Tulsa) (34), Flexmaster (VDW) (35), each with their own sequence of instrument use, but with most file systems following the crown-down technique. Regardless of the NiTi rotary instrument or technique used, stainless steel instruments should be used initially for path finding, because of their greater stiffness. Typically, a size10 to 15 or larger stainless steel K-type file is used for this initial exploration of the canal. These more rigid files can also be pre-curved to bypass any obstructions that may be present, whereas NiTi instruments cannot be pre-curved and is more likely to engage into a ledge or peforation.
1.3.2 Biological techniques Mechanical procedures using instruments can remove debris, necrotic pulp tissue and infected dentine during the process of shaping the walls of the root canal. Contemporary endodontic techniques employ chemical methods involving the use of various medicaments as an adjunct to the mechanical action of files and other instruments. Sundqvist (36-38) described in detail the commonly encountered bacteria in infected root canals (Table.1.1), and identified that poly-microbial infections were the norm in the root canals of untreated non-vital teeth with periapical radiolucencies. Because a range of Gram positive and Gram negative bacterial species and fungi may be present, irrigants and medicaments used within the root canal should have a broad spectrum of activity. Many authors have described the efficiency of irrigants and medicaments in root canal disinfection and debridement. Irrigants in current use include sodium hypochlorite (NaOCl) (39-41), hydrogen peroxide (42-44), chlorhexidine (45), normal saline (46), iodine potassium iodide (IKI) (47), and Ethylenediaminetetraacetic Acid (EDTA) (48) with various additives such as the surfactant Cetrimide. Commonly used medicaments for inter-visit dressings include the antibioticsteroid paste Ledermix ™ (49), camphorated paramonochlorophenol (CMCP) (50, 51), and various preparations of calcium hydroxide (52). 5
A major problem associated with both chemical and mechanical preparation is that microorganisms may be protected in dentine tubules and the most complex parts of the root canal, such as deltas and lateral canals. In these areas, they are inaccessible to the cutting edge of instruments, and they may be more difficult to reach using medicaments, because of surface tension, diffusion and other physical factors. Dentine itself may also partially inactivate medicaments such as calcium hydroxide, which rely upon pH gradients for their antimicrobial actions(53). For these reasons, reliable and complete disinfection of the root canal is a very difficult objective to achieve using contemporary methods alone. The disinfecting actions of irrigants used in the root canal rely upon a combination of direct antibacterial actions as well as a physical flushing action (54, 55). Recently, Hsieh et al. (56) showed that gaining an efficient flushing action with irrigants depended on the gauge of the needle used, the canal diameter, and the distance of the needle tip from the working length. In accordance with this, Sedgley et al. (57) have shown that irrigants are more effective when the needle tip which delivers them is placed closer to the working length. An inherent problem with irrigants is their toxicity when extruded through the apex into the periapical tissues. A number of case reports have documented complications of inadvertent extrusion of NaOCl or hydrogen peroxide beyond the confines of the apical constriction (58). NaOCl has the potential to cause tissue necrosis, haematoma formation, ecchymosis, oedema and pain of considerable duration (58-62). Extrusion of hydrogen peroxide past the apical foramen may lead to air emphysema, swelling, and pain (58, 63). Periapical extrusion of ethylene glycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or EDTA may affect the periapical bone and impair the local immune response by inhibiting phagocytosis by macrophages (64).
6
Table.1.1: Bacteria from the root canals of teeth with apical rarefactions BACTERIA
PERCENTAGE OF INCIDENCE
Fusobacterium nucleatum
48
Streptococcus sp.
40
Bacteroides sp. (non-pigmented)
35
Prevotella intermedia
34
Peptostreptococcus micros
34
Eubacterium alactolyticum
34
Peptostreptococcus anaerobius
31
Lactobacillus sp.
32
Eubacterium lentum
31
Fusobacterium sp.
29
Campylobacter sp.
25
Peptostreptococcus sp.
15
Actinomyces sp.
15
Eubacterium timidum
11
Capnocytophaga ochracea
11
Eubacterium brachy
9
Selenomonas sputigena
9
Veillonella parvula
9
Porphyromonas endodontalis
9
Prevotella buccae
9
Prevotella oralis
8
Propionibacterium propionicum
8
Prevotella denticola
6
Prevotella loescheii
6
Eubacterium nodatum
6
(Adapted from Sundqvist, 1994) (36). * Non-pigmented species
7
Increased hydraulic pressure within the apical third due to binding of the needle walls to the root canal walls, or from pressure placed on the irrigant within the syringe itself, is a significant factor in apical extrusion (65, 66). As shown by Lambrianidis et al. (67), the flow rate of irrigant is an additional important variable. The work of Bradford et al. (68) identified that air pressure from a irrigating needle bound in the canal could damage the apical tissues, or cause emphysema by introducing air through the blood stream. Taken together, these studies indicate that the combination of hydraulic pressure, flow rate and the inherent toxicity of the irrigants used in the canal will determine the extent of extrusion and the degree of symptoms experienced. The use of medicaments in root canal treatment is essential for obtaining and maintaining a sterile root canal environment. Bystrom and Sundqvist (41) noted a rapid increase in the levels of bacteria in the root canal between endodontic appointments when a medicament was not placed in the canal. The efficacy of intracanal medicaments in treating infected endodontic teeth has been reported by a number of authors (49, 69-76). As shown by Haapasalo et al. (77), the antimicrobial activity of calcium hydroxide-based medicaments is reduced because of inactivation by dentine. A further important point is that most medicaments need to be placed in the canal for a suitable length of time to be effective in killing most or all microorganisms within the root canal system. Finally, medicaments containing tetracycline may stain the root (78, 79).
1.3.3 Limitations of the present methods of tooth preparation The success or failure of root canal therapy depends on the complete elimination of bacteria from the root canal followed by a three dimensional fluid tight seal (80). As discussed above, current methods of mechanical preparation using either hand or rotary files are incapable of ensuring sterilization of the root canal, hence requiring the additional use of root canal irrigants and medicaments. Most currently available irrigants and medicaments have varying levels of irritation or toxicity to periapical soft tissues, and hence extrusion of these past the apical foramen would be a concern. For irrigants and medicaments to be effective in sterilization of the canal, they should be able to diffuse into the dentinal tubules, and have a sustained action over time without being inactivated by the surrounding environment. Because of these limitations, it is commonplace that medicaments are used over prolonged treatment times in chronically infected teeth. 8
1.4 Smear layer and its removal Smear layer has been defined as a layer of debris on the surface of dental tissues created by the action of cutting a tooth (81). It varies in thickness, roughness, density, and degree of attachment to the underlying tooth structure, according to the cutting method used. The cutting action of hand or rotary endodontic instrumentation on the walls of the root canal generates a smear layer in the same manner as that produced by rotary instruments such as burs that are used in cavity preparation and caries removal, and in both locations the smear layer consists of both organic and inorganic debris. McComb and Smith (81) suggestion that the smear layer was superficial and only loosely attached to the root canal wall was based on their observed separation of smear layer from the surface of the tooth when subjected to drying prior to SEM. It is now recognized that the smear layer is not just a superficial layer, but can penetrate a distance of some 40-60 µm into dentinal tubules (82, 83). In fact, Halackova and Kukletova (84) described smear layer as having two layers, the outer surface layer of debris being only 2 to 5 μm in thickness, and comprised of debris, while the thicker inner layer penetrated into dentinal tubules. The significance of the smear layer to treatment outcomes has been the subject of considerable debate and controversy, both in endodontics and in restorative dentistry. Several studies have reported that leakage occurs at the interface of the root filling and the root canal wall (85, 86), thus implicating the smear layer as a factor that can prevent close adaptation of sealers and root filling materials to the canal walls. This leads to the notion that if smear layer was present, there may be more rapid microleakage of oral fluids and bacteria through the root canal should the coronal seal break down at a later date. In support of this, Pallares et al. (83) reported that neither softened gutta-percha nor AH-26 sealer (an epoxy resin material) where able to penetrate into the dentinal tubules of the root canal in the presence of a smear layer. Similarly, Cobankara et al. (87), who used a fluid filtration technique to evaluate microleakage, showed that regardless of the sealer used (AH26 sealer or RoekoSeal), the presence of smear layer increased both apical and coronal leakage. In contrast to the above, Shemesh et al. (88) who used a glucose penetration model to evaluate microleakage, did not find any difference in canals obturated with or without smear layer. The interpretation of this result must be done cautiously, since glucose is a low 9
molecular weight tracer, and in this study the samples were under constant pressure for a period of some 8 weeks. In the same study, fluid filtration over a period of 3 hours was also assessed, and once again there was no statistical difference in microleakage with smear layer present or absent, at both the time periods of 1week and 8 weeks, even though there was a trend toward less microleakage in samples that had smear layer removed from the canal walls prior to obturation. Timpawat et al. (89), also using a fluid filtration model, reported greater apical microleakage when smear layer was removed, however in that study the sealer used was Ketac-Endo in a thick layer, and this interacts chemically with dentine. Moreover, thicker sealers show better sealing ability, independent of the presence or absence of smear layer (90). Overall, it appears that some extent of microleakage can occur with all types of root filling materials and sealers, particularly when extended time periods are used, and if the test material (tracer fluids or bacterial suspensions) are applied under pressure. With resin-based sealers, there is evidence that the extent of microleakage would be reduced if smear layer is removed from canal walls prior to obturation (91). An additional argument is the smear layer contains not only bacterial products (such as endotoxins), but also may contain sufficient numbers of viable bacteria to cause re-infection of the root canal. The presence of smear layer will prevent medicaments from diffusing adequately into dentinal tubules, and thus limit their antimicrobial actions (92). Hence, the removal of smear layer is strongly recommended by most authors. Ideally, the agents used to remove smear layer should target both its organic and inorganic components (45). The most widely used agents are preparations based on EDTA, either in plain solution (such as 15% EDTA) or with a surfactant added (such as Cetrimide). Other materials, which have been used to remove smear layer include sodium hypochlorite (39, 40), organic acids (93, 94), and proprietary mixtures such as MTAD (a mixture of a tetracycline, an acid, and a detergent) (95). Ultrasound in the form of endosonics has also been used in combination with various irrigants (93). It is believed that endosonics enhance smear layer removal through their induction of cavitation-related shock waves in a fluid environment. As will be discussed later, shock wave effects can also be induced by some lasers when used in an aqueous medium in the root canal.
10
1.4.1 Assessment of smear layer removal The ability to assess the removal of smear layer consistently and reliably is important in grading the effectiveness of agents, instruments or techniques used in endodontics. Comparing the effectiveness of smear layer removal methods typically involves scoring SEM images of the canal walls. The images are then usually coded and then scored by blinded evaluators using qualitative or semi-quantitative scales, such as those described by Prati et al. (96) and Hulsmann et al. (97), with the latter the most commonly used. Other methods have involved tracing SEM photomicrographs onto graduated tracing paper for subsequent measurement (98), and using resin replicas of the surface under examination (99). There is no universally excepted system of scoring, with some methods using scales with 3, 4, 5, or 7 scoring intervals (96, 97, 100-102). The choice of scoring system is affected by a number of parameters, such as the magnification of the SEM photomicrographs used (since higher magnifications provide better visual information than lower magnifications), the experience of the evaluators (trained or untrained, and whether they are stressed or unstressed), and the presentation mode of the SEM photomicrographs (digital projection versus printed hard copies). A major problem in smear layer evaluation techniques is the selection of the area to be scored. This applies across all techniques that use photomicrographs, where the operator can select representative or non-representative field and thus introduce bias to the outcome. It is preferable that a consistent area of the specimen be photographed in all samples, however there may be a bias towards photographing cleaner fields, which contain more open tubules. The use of a standardized approach that could be used across all specimens would reduce the likelihood of bias. The use of digital image analysis methods in dentistry is becoming more popular, with reports of their use for assessing the curvature of root canals (103), dentine removal during root canal preparation with various techniques (104), and the efficiency of obturation methods (105). In 2007, Ciocca et al. described a computerized automated analysis technique for counting dentinal tubules (106), however the use of this method for characterizing a prepared dentinal surface has not been evaluated. In this thesis, a new digital analysis method for assessing the presence of smear layer and measuring its removal will be described, and its 11
performance compared to the existing “gold standard” method of scoring photomicrographs using panels of expert observers.
1.5 Lasers in endodontics The word laser is the acronym for the process of Light Amplification by Stimulated Emission of Radiation. The principle of stimulated emission was first hypothesized by the physicist Albert Einstein in 1917, however it was not until 1961 that the first laser (the ruby laser) was built by Theodore Maiman. Weichman and Johnson (107) were one of the first teams of investigators to explore the use of lasers in endodontics. They attempted unsuccessfully to seal the apical foramen on extracted teeth by means of a high power far infrared carbon dioxide (CO2) laser. Subsequently, attempts were made to seal the apical foramen using the Nd:YAG laser (108). Lasers used for endodontic applications cover a broad range of procedures, from diagnosis through to obturation of the root canal space (Table1.2). The first laser to obtain formal marketing clearance for use in endodontics in the United States by the US Food and Drug Administration (FDA) was the Er,Cr:YSGG laser (manufactured by Biolase) in 2002.
1.5.1 Laser wavelengths and their absorption characteristics Lasers used in dentistry vary from the ultraviolet region (100-400 nm) through to the infrared region (700 nm and beyond). The visible spectrum lies between these two extremes (i.e. 400-700 nm). The action of the lasers used in endodontics upon the dental hard and soft tissues and other relevant targets such as bacteria is dependent on the absorption of the laser energy into a relevant chromophore, such as water, apatite minerals, and various pigmented substances. As approximately 65% of the volume of bacteria is water, water-absorbing lasers can have a powerful disinfecting action via photothermal effects on bacteria. Greater absorption in water should give a more effective sterilizing action, however this needs to be balanced with the risks of adverse effects such as damage to the roots and their supporting hard and soft tissues (Fig.1.1 a & b).
12
(a)
(b)
Fig.1.1. Absorption of water at different wavelengths. Panel (a) from High Tech Laser, Belgium, 2007 (109). Panel (b) from Hale and Querry (110)
13
Table.1.2: Selected laser wavelengths and their major absorbing molecules Laser type
Wavelength
Region of
Laser Medium
the
Configuration
Delivery system
molecules in
Spectrum
Argon ion
488-514.5 nm
Visible
Major absorbing
tissues
Gas
Optical fiber
Porphyrins, haemoglobin
532 nm
KTP
Solid state
Optical fiber
Porphyrins, haemoglobin
He-Ne
632.8 nm
Visible
Gas
Optical fiber
Melanin
Diode laser
635, 670 nm
Visible
Semiconductor
Optical fiber
Melanin
Diode laser
810, 810 nm
Near infrared
Semiconductor
Optical fiber
Melanin, haemoglobin
Diode laser
980 nm
Near infrared
Semiconductor
Optical fiber
Water, haemoglobin
Nd:YAG
1064 nm
Near infrared
Solid state
Optical fiber
Melanin
Ho:YAG
2100 nm
Mid infrared
Solid state
Optical fiber
Water
Er,Cr:YSGG
2790 nm
Mid infrared
Solid state
Rare earth
Water
element optical fiber Er:YAG
2940 nm
Mid infrared
Solid state
Rare earth
Water
element optical fiber, articulated arm CO2
9300, 9600, 10600 nm
Far infra red
Gas
Waveguide,
Water, apatite
articulated arm
The amount of laser energy absorbed by a target is dependent on the wavelength, the concentration of the absorbing substances, and their absorption coefficients (111) e.g. it has been shown that wavelengths which are absorbed in haemoglobin are absorbed more strongly in fresh whole blood than in diluted blood (112). The available laser energy reduces within the target as absorption events occur. This decrease in intensity has been termed an
14
‘exponential fall off’(112). Absorption of particular materials is typically assessed at a range of different wavelengths by spectrometry. Light of particular wavelengths from a monochromator is passed through a cuvette containing the molecule of interest in an appropriate solvent, and the absorption determined (112). Of particular interest in dentistry is the ability to use the above concept of preferential absorption of tissue components with different wavelengths, for obtaining selective ablation of tissue at exposure settings that do not damage adjacent healthy tissues. 1.5.1.1 Mechanism of laser action on biological tissues A simple classification of the effects that can arise when biological tissues are exposed to laser energy is as follows:
I. Ablation through Photo-physical mechanisms 1. Photo-thermal ablation: This occurs with high powered lasers, when used to vaporization or coagulate tissue through absorption in a major tissue component 2. Photo-mechanical ablation: Disruption of tissue due to a range of phenomena, including (113) •
Shock wave formation
•
Jet formation
•
Cavitation
•
Plasma formation
•
Microstreaming
•
Cleavage of internal chemical bonds (photo-ablation)
II. Photo-chemical effects (114-119) 1. Photo-dynamic activation (Using light-sensitive drugs to treat conditions such as cancer) 2. Photo-activated disinfection (Using light-sensitive dyes to kill bacteria) 3. Low level laser therapy (LLLT): cellular bio-stimulation through activation of mitochondrial energy systems in the cell (114-116)
15
Photo-ablation involves direct breakage of chemical bond in cells or tissues (119) This is possible because of the short (ultraviolet) wavelengths employed and their high photon energies. In contrast, long wavelengths with low photon energies do not directly disrupt chemical bonds, but rather cause electronic activation and vibrational effects at the molecular level. The remaining photo-chemical and photo-thermal effects play a role in irreversible or reversible modification of the physical structure of target tissue, for visible and infrared lasers. Photo-physical events such as boiling of intracellular water can be used to ablate water-containing tissues, in a non-reversible manner (120). On the other hand, photochemical effects such as biostimulation do not cause damage to tissue but acts by causing transient electronic excitation of enzymes within the irradiated tissue. These actions can increase the energy available for normal cellular processes (118) as well as improve blood and lymphatic flow, or suppress firing of nociceptors (114-116). Factors that influence the nature of the effect of lasers on tissue comprise the laser variables of wavelength, pulse energy or power output, exposure time, spot size (and thus energy density), and the tissue variables of physical and chemical composition (e.g. water content, density, thermal conductivity and thermal relaxation) (121).
1.5.2 Properties of lasers The energy emitted from a laser has properties that distinguish it from other sources (sunlight, halogen lamps, etc.). Laser light is monochromatic and coherent, and can be collimated (122). Below is a brief discussion of the properties and applications of selected lasers of interest in endodontics.
16
1.5.2.1 Diode laser Diode lasers are commonly used in consumer and industrial electronic products as well as in medicine and dentistry. The major advantages of diode lasers are their small size and high efficiency, hence enabling units to be compact and of low cost.
1.5.2.1.1 Properties Diode lasers are typically configured as a semiconductor with layers of doped materials. Common combinations are gallium arsenide, aluminium gallium arsenide, indium gallium arsenide, and indium nitride. They have a high efficiency of converting low voltage electrical energy into laser energy. Many diode lasers exist, with wavelengths ranging from ultraviolet (405 nm) through the visible spectrum (470, 635, 655 nm) up to near infrared (730, 780, 810, 905, 980, 1060, 1300 and 1550 nm). Diode lasers can operate in either pulsed or continuous modes, with pulse durations as low as 100 nanoseconds.
1.5.2.1.2 Applications Short wavelength diode lasers in the visible red spectrum are used as a aiming beams for invisible lasers, for profiling tooth surfaces and dental restorations, for scanning of crown preparations for CAD-CAM, and for scanning of models for orthodontic or holographic storage (123). The 655 nm diode laser have been used for detection of dental caries and dental calculus using the principle of fluorescence (3, 4). High power surgical diode lasers are available in wavelengths from 810 to 980 nm (124). These lasers may be used in contact mode for vaporizing oral soft tissues, disinfection of root canals and periodontal pockets, (125) for uncovering implants (126) and for coagulation. These lasers can also be used for photo-thermal bleaching (127). Typically, diode lasers deliver their energy via quartz glass optical fibers. When used in contact mode, the fiber tip needs to be cleaved or polished occasionally, as the tip tends to degrade as a result of heat damage and combustion of adherent tissue debris (128). This problem of degradation of the delivery system does not occur when they are used in a noncontact manner, such as for diagnosis or for scanning (129, 130). Because visible and near
17
infrared wavelengths are poorly absorbed by enamel and dentine, soft tissue surgery with diode lasers can be safely performed in close proximity to teeth. Conversely, both visible and near infrared diode wavelengths are well absorbed by pigmented tissues, and thus they can be used to provide a reasonable level of haemostasis, however the Nd:YAG and the argon lasers have even better haemostatic properties than diode lasers (11). Using the 655 nm diode lasers, fluorescence detection has been shown to be highly specific and reproducible for occlusal caries (131, 132) and proximal caries (133, 134). Several studies have evaluated the use of near infrared diode lasers for disinfection of root canals and periodontal pockets (125, 135, 136). These studies conclude that diode lasers can have a worthwhile disinfecting action; however this needs to be balanced with careful clinical technique to overcome issues of thermal stress. Mortiz et al. (136) reported that there could be a marginal increase of as much as 6 degrees Celsius in temperature on the root surface when using diode lasers in the root canal, albeit at higher powers. Gutknecht et al. (137) reported that an 810 nm diode laser would produce root surface temperatures above 7OC when used for 20 seconds at power settings of 1- 1.5 W, a pulse length of 10 or 20 milliseconds, and a pulse interval of 10 milliseconds. In continuous wave mode at 1-1.5W, a temperature rise above 7OC was noted in 5 seconds. Of particular interest, Wang (102) showed in a feasibility study that smear layer within the root canal could be effectively removed using a 980 nm wavelength diode laser at 5 W for 7 seconds using fibers of 365 and 550 μm, however the recorded maximum temperature rise was some 8.1°C when using the 550μm fiber. A further area of application of diode lasers has been in the field of photo-thermal bleaching. Studies by Dostalova et al. (128) on two diode lasers of wave length 970 and 790nm were used to activate bleaching agents and it was found to have decreased the total bleaching time(approx 5 min). The effect of thermal change due to diode lasers too have been studied(138) and have been in the range of 6 degrees which is lower than that of that produced by some halogen lamps.
18
1.5.2.2 Nd:YAG The Nd:YAG laser was developed in 1964 by Bell Telephone Laboratories. The first pulsed Nd:YAG laser used widely in dentistry was the American Dental Laser, model dLase 300, which was cleared by the United States Food and Drug Administration in 1989 for minor soft tissue procedures (139).
1.5.2.2.1 Properties This is a solid state laser with a wavelength of 1,064 nm in the near infrared spectrum, which can be transmitted using conventional quartz glass optical fibers. The lasing medium is a synthetic cubic garnet crystal doped to 1% with neodymium (Nd:Y3Al5O12). The majority of dental Nd:YAG lasers operate in free-running pulsed mode, and in contact with the tissue, however very short pulse durations can be achieved with this laser by mode-locking and Qswitching, although these methods are not employed with commercially available dental Nd:YAG lasers for clinical applications. The Nd:YAG laser wavelength is highly absorbed by melanin in pigmented tissues, and is absorbed poorly in water. The optical fibers used with this laser may be used bareended in direct contact with the tissue. Such fibers must be cleaved before use, and cleaned during use. 1.5.2.2.2 Applications in dentistry The Nd:YAG laser ablates soft tissue by a photo-thermal mechanism, i.e. it removes tissue by vaporization and superheating of tissue fluids with resultant coagulation and haemostasis (140, 141). A clinical study carried out by White et al. (142) provides the basis for many soft tissue applications using the Nd:YAG laser. When used in a non-contact, defocused mode, this wavelength can penetrate several millimeters into soft tissue, which can be used advantageously for delivering the laser energy to the inner aspects of soft tissue ulcerations (143). Nd:YAG lasers have been used for sulcular debridement in periodontal therapy (144146), as well as for treatment of dental hypersensitivity and for obtaining analgesia. Cobb (147) reported a gain in clinical attachment level with the Nd:YAG laser for treatment of 19
chronic periodontitis, but noted that it would not provide an alternative to scaling and root planning, even though it would assist in reducing levels of subgingival bacteria. The effect of the laser on dentine hypersensitivity is due in part to the laser-induced occlusion or narrowing of the dentinal tubules (148), and to an analgesic effect (149). The Nd:YAG laser has been shown to be 90% effective in reducing symptoms of dentine hypersensitivity (150). Amyra and Walsh (151) have shown that Nd:YAG lasers when used at high power could dry a root canal, however they cautioned against this application because of thermal damage to the radicular dentine and the periodontal apparatus because of the high irradiances required. As with the diode lasers, Nd:YAG laser energy has little interaction with sound tooth structure, allowing tissue surgery adjacent to the tooth to be both safe and precise, however a study done by Lee et al. (152) demonstrated that Nd:YAG laser irradiation could reduce the hardness and elastic modulus of human dentine. Because of its wavelength, the absorption of Nd:YAG laser energy in dentine is very low, however if the dentine is pigmented or coloured, obtaining ablation can be achieved, for example Koba (153) recommended that black Indian ink be painted onto the root canal wall to increase the absorption of Nd:YAG laser energy. The manufacturer of the dLase 300 Nd:YAG laser system (Sunrise Technologies) likewise recommended the use of an initiator (such as Indian ink) to facilitate ablation. Yamada et al. (154) reported that pigmented carious dentine could be removed without using a dye because porphyrins and other chromogens from bacteria absorb the laser energy. The ablation effect of this laser on dentine is due mainly to photothermal processes, i.e. those involving high temperatures, which cause melting, vaporization, and possibly craters at the irradiation site. Such strong thermal processes and their associated high temperatures would necessitate the use of coolants to prevent thermal damage to the supporting periodontal apparatus. Presently, the most popular applications of the Nd:YAG laser in endodontics are for root canal disinfection (155, 156) and removal of smear layer. In 1992, Goodis et al. (157) reported that Nd:YAG laser treatment could produce clean root canals when used after hand files, with a general absence of smear layer and tissue remnants on the root canal walls. Harashima et al. (158) likewise reported that efficient removal of debris and smear layer could be accomplished using the Nd:YAG laser at 2W and 20 Hz with water spray. Depraet 20
et al (159) reported that the affinity of ND:YAG lasers to dark pigments could be used advantageously in the removal of smear layer, they proposed using Indian ink in combination with this laser to enhance smear layer removal. However, Piccolomini et al. (160) despite reporting positively on the ability of Nd:YAG laser treatments to efficiently disinfect root canals, also placed special emphasis on the problem of delivering laser energy with a plain fiber tip, and the challenge of irradiating all walls of the root canal. Other endodontic applications of the Nd:YAG laser include softening of gutta-percha to assist with obturation.(161-163), canal preparation(164), and fusion of smear layer into the dentinal tubules to decrease root canal permeability (165). Additional applications for both Nd:YAG and the various erbium lasers in endodontics include to assist in the removal of root fillings, and the recovery or removal of fractured instruments. The use of the Nd:YAG laser in the latter does not relate to physical removal of the instrument, but rather to bypassing the separated instrument by ablating the dentine surrounding it, after which the instrument is retrieved using conventional means. Matsumoto (166) showed that removal of fractured instruments is difficult if not possible using such an approach in narrow or severely curved canals. Attempts to use lasers in curved canals with conventional fibers could lead to perforation of the root. Although Nd:YAG lasers have been shown to have very good disinfecting actions in endodontics, a major challenge is how to direct this energy directly on the walls of the root canal when using conventional tips. The Nd:YAG laser is not well suited for hard tissue procedures such as shaping the canal because the energy is poorly absorbed by water, and hence to obtain ablation within the root canal the dentine must be coloured, wither naturally or with materials such as Indian ink as initiators. If this was done, a significant risk is that of irreversible thermal damage to the supporting periodontal tissues
1.5.2.3 Holmium:YAG lasers Holmium:YAG lasers were used initially in vascular surgery, neurosurgery, and arthroscopic surgery. Today, they are used in many surgical applications and specialties, including general surgery, urology, laparoscopy, neurosurgery, lithotripsy, and angioplasty.
21
1.5.2.3.1 Properties These lasers have a solid state active medium, a crystal of Yttrium Aluminum Garnet, doped with Holmium. The emitted wavelength of 2100 nm is in the near infrared region, and can be delivered effectively using flexible bare quartz glass optical fibers. These fiber tips can be used in contact with the tissue, with the laser operating in free running pulsed mode. With pulsing, tissue ablation at the surgical site can proceed at an efficient rate, without significant collateral thermal damage. The absorption into water by the Ho:YAG lasers is 100 times greater than for the Nd:YAG (Fig.1.2), which underpins its soft tissue surgical uses. For such procedures, these optical fibers afford good access, precision and a level of tactile feedback. The Ho:YAG lasers has some characteristics of both Nd:YAG and CO2 lasers. Like the CO2 laser, the energy from a Ho:YAG is well absorbed into water, with a shallow depth of penetration, and effective soft tissue ablation. Like the Nd:YAG laser, the Ho:YAG laser offers better haemostasis than the CO2 laser, but less than the Nd:YAG laser (167). Ho:YAG laser energy has less affinity for pigmented components of tissue than Nd:YAG, because of its lower absorbency into haemoglobin and other pigments.
Fig.1.2 Absorption spectra of water. From Hale and Querry (110) Of particular interest is the fact that both enamel and dentine contain significant amounts of water by volume. The shallow depth of penetration by Ho:YAG laser energy within these rigid structures, coupled with its high peak power, should produce a photodisruptive effect similar to ablation, which was termed “spallation” by Mani in 1992. Based 22
on in vitro studies, Ho:YAG lasers should be safe and effective for use on dental hard tissues, although giving much less rapid ablation than the erbium lasers at the same pulse energy(167). Other desirable features of the Ho:YAG laser which makes it useful laser for dental applications include its ability to interact with soft tissues at low powers, and its haemostatic capabilities. Its absorption is not influenced significantly by pigmentation (167). Finally, this pulsed laser can be delivered through quartz glass fiber optics.
1.5.2.3.2 Applications Despite the relatively wide use of the Ho:YAG laser in medicine, its use in dentistry is limited at present because of a lack of substantial research. As already mentioned, because this wavelength is well absorbed by water, it has potential applications for ablation of dental hard tissues. Stevens et al. (168) noted that increasing ablation of dentine occurred with the Ho:YAG laser, with increasing pulse energy from 150 to 1200 mJ. Craters with a maximum depth of 37μm were seen in their 1200 mJ group. Holmium lasers have also been reported to be effective in root canal therapy for shaping the root canal, with Cohen et al. (169) enlarging the root canal using average powers of 0.5, 0.75 and 1.0 Watt, to enlarge the canal from a # 25 ISO instrument size to a #40 ISO instrument size, with an accompanying increase in root surface temperature of less than 5 degrees Celsius. This was dramatically less than the thermal stress reported by Goodis et al. (170) at the level of the dental pulp (32.8 to 43.6 degrees Celsius) when the Ho:YAG laser was used on the root surface, without any coolants, at an average power of 1.0 Watts (67 mJ and 15 Hz) for 120 seconds with 320 to 500μm fibers. In a study of the Ho:YAG laser in endodontics, Cohen et al. (171) observed that an increase in temperature at the root surface can be expected as the canal is enlarged, due to less dentine being available progressively between the canal walls and the outer surface of the root, as treatment progresses. At average power settings of 0.50, 0.75, and 1.00 Watts delivered through fiber optics of 140, 245, 355, and 410 microns in diameter, all recorded temperature differences both apically and coronally were between 0 and 10 degrees Celsius,
23
with the majority (> 98%) being between 0 and 5 degrees. After lasing with the 410 micron fiber, the root canals were widened to at least a size ISO 45 or 50 (i.e 450 or 500 microns). Using the largest fiber of 410 microns, the maximum extent of widening of the canal was 500 microns. In a comparative study, Mortiz et al. (172) reported that no unfavorable temperature increases occurred when using Ho:YAG, Nd:YAG or Er:YAG lasers to disinfect root canals. All three lasers gave antimicrobial actions that would be useful to augment root canal treatment. The antimicrobial actions of the Ho:YAG lasers was also reported by Gutknecht et al. (173), who documented destruction of 99.98% of Enterococci in the root canal. The surface of the Ho:YAG ablated root canal is rougher than when an Er:YAG laser is used (174). Subsequently, Moritz et al. (175) reported the ability of the Ho:YAG laser to remove intra-canal debris and smear layer. Given the useful properties of the Ho:YAG laser (wavelength 2.1 μm) for endodontic surgery, preparation of cavities, and etching of enamel, there is interest in systems of similar wavelength, such as the yttrium lithium fluoride (YLF) lasers based on holmium (Ho:YLF, 2.065 μm) and thulium:YLF (1.908 μm). These would also be able to be delivered through fiber optics, and exploit applications that depend on water for ablation.(176)
1.5.2.4 Er,Cr:YSGG & Er:YAG ( 2780 nm & 2940 nm) In 1988, both Hibst and Paghdiwala were the first to describe in detail the effect of the Er:YAG laser on dental hard tissues (177), however it was not until 1997 that this laser obtained US FDA approval for cavity preparation. One of the earliest companies to release Er:YAG lasers onto the market was KaVo (Germany) in 1992. Subsequently, the second erbium laser hard tissue wavelength (Er:YSGG, 2.78 μm) was developed and marketed by Biolase (USA).
1.5.2.4.1 Properties The Er:YAG laser has an emission wavelength of 2.94 μm, which coincides exactly with the absorption peak of water, giving strong absorption in all biological tissues, including enamel and dentine. In this laser, a solid crystal of Yttrium Aluminum Garnet is doped with
24
Erbium. Er:YAG laser energy can be delivered in different ways, e.g., via a hollow waveguide, through an articulated arm, or in via a fiberoptic bundle. The Erbium, Chromium:YSGG laser has an emission wavelength of 2.78 μm. A solid crystal of Yttrium Scandium Gallium Garnet is doped with both Erbium and Chromium. The laser energy is normally delivered by an optical fiber. This laser also has somewhat lower absorption in water, but better absorption in hydroxyapatite, compared with the Er:YAG lasers. Both lasers are well absorbed in collagen, and can ablate soft tissue because of its high content of water and collagen. In soft tissues, both lasers have an optical penetration depth of only a few micrometers. Reported penetration depths are in the order of 5 μm when using a 300 microsecond duration pulse from an Er:YAG laser (178). The erbium laser wavelengths cannot easily be transmitted along conventional glass fiber optics, meaning that special fibers must be used which are costly, less flexible, more fragile, and physically larger than those fibers used with Ho:YAG or Nd:YAG lasers (177). Erbium lasers are normally delivered through a specialized dental handpiece that transfers the energy via internal reflecting mirrors, to specially adapted fiber optic tips fabricated from quartz, sapphire, doped silica or quartz, or other materials. The fiber tips come in various sizes and shapes depending on their clinical application.
1.5.2.4.2 Mechanism of ablation Several hypotheses have been proposed regarding the possible mechanisms of ablation with Er:YAG and Er,Cr:YSGG lasers. Presently, the accepted mechanism of ablation is that when laser energy is focused onto the tooth, the superficial layer of tooth structure, along with the water contained therein, is heated rapidly because of the large number of photons that are absorbed. The water is vaporized, and the resultant build up of steam causes an expansion, which ultimately over comes or surpasses the crystal strength of the dental structures, and causing fragmentation by micro-explosion (179). The water molecules responsible are between the crystals of mineral in tooth structure, with a larger amount of such water found in dentine than in enamel (180). Physical shock waves are thought to contribute to the ablative process. For example, Loertscher et al. (181) detected acoustic transients at the beginning of the laser pulse, and subsequent expansion and collapse. Carious
25
tooth structure has more water than sound tooth structure, and hence such effects would be more pronounced in carious than healthy tooth structure. For the Er,Cr:YSGG laser, the hypothesized cutting effect includes a hydrokinetic effect due to the effects of laser pulses on water mist spray (182). Rizoiu et al. (183) described the hydrokinetic effect as the process of removing biologic materials through high speed water droplets. These droplets of atomized water absorb laser energy, resulting in a violent yet controlled micro-expansion, inducing strong mechanical forces on the target hard or soft tissue, enhancing tissue removal. This effect was hypothesized based on a report by Kimmel et al. (184, 185) on energized exploding water droplets. Nevertheless, studies by Freiberg and Cozean (186) of the enamel removal mechanism of both the Er:YAG and Er,Cr:YSGG lasers indicate that subsurface expansion and explosion of interstitially trapped water are the most likely mechanism of ablation. These investigations also showed that material devoid of water failed to cut, which the authors concluded was ‘contradictory to the existence of the hydrokinetic phenomenon’(186). The ablation process of Er:YAG and Er,Cr:YSGG lasers on dental hard tissues is accompanied by a characteristic popping sound. This photo-acoustic effect is due to the shock waves created when the laser energy dissipates, creating explosive forces (187). The pitch and intensity of the sound produced varies with the presence or absence of dental caries, with a louder noise with lower frequency and longer duration (a “thud”) generated in caries ablation, compared with the less intense, highly pitched, and short duration “click: of sound tooth structure. This was documented by Walsh (180). The same study (180) also described a loud snapping sound associated with the use of Er,Cr:YSGG lasers when not in contact with any structure in the mouth. This is due to plasma de-coupling of the beam, in which laser energy heats the air and water directly in front of the laser handpiece, delivering energy onto the rear surface of atomized water molecules.
1.5.2.4.3 Applications Erbium lasers have been used for many procedures including caries removal, soft tissue surgery, and bone cutting. In endodontics, erbium lasers have been reported to be used for root canal preparation, smear layer removal, disinfection of the canal, and endodontic surgery. In the latter, erbium lasers have been used for root resection and for removal of 26
surrounding bone during an apicectomy procedure (188). Bone cutting using these lasers is rapid, with an absence of char (189). Walsh et al. (190) reported lateral thermal damage to surrounding bone of only 5-10 μm, while other studies have shown that the adequate use of water spray on a moist surface can prevent a rise in temperature and the formation of char on the laser ablated surface (191-194). With regard to endodontics, Matsuoka et al. (195) reported using an Er:YAG laser to enlarge the root canal using 3 different size conventional fiber tips sequentially, with parameters of 400 mJ/pulse and 2 Hz. They reported that it took approximately 2 minutes to enlarge the canal to the largest size fiber. Similarly, Ali et al. (73) reported that the Er,Cr:YSGG laser could be used to prepare the root canal using a crown-down approach, to widen the apical third to size #30 ISO, and the middle third to #60 ISO, with laser parameters of 2 Watts, with air and water spray. Matsuoka et al. (195) reported the use of erbium lasers with conventional tips could produce a rough and scaly surface of the root canal, as well as formation of artificial root canals (possibly leading to perforations). Matsuoka et al. (196) reported that Er,Cr:YSGG lasers could successfully prepare root canals with up to 10 degree curvatures, when using a step back technique, and laser parameters of 2 Watts and 20 Hz with air and water spray. However, limitations of the method were identified by Jahan et al. (197), who reported that preparation of root canals with a curvature of greater than 5 degrees could lead to zipping, ledge formation, or perforations. The later study of Shoji et al. (198) was one of the first to demonstrate that root canals could be enlarged more rapidly using a conical tip than a plain fiber. In this study, a silica fiber tip reinforced with aluminum was used to irradiate bovine teeth in an experimental model. A further and important cluster of uses of erbium lasers in endodontics is for smear layer removal, debridement and canal sterilization. A number of reports have been published on the efficiency of both the Er:YAG laser (195, 199-202) and the Er,Cr:YSGG laser (202) in removal of smear layer and debridement of the root canal. A study by de Souza et al. (203) reported no statistical different in the coronal leakage of filled canals that had their smear layer removed using either EDTA or an Er:YAG lasers. This result was achieved using a conventional fiber tip, which has limited ability to transfer laser energy directly on the walls
27
of the canal. This would give inconsistent smear layer removal, as has been reported by Altundasar et al. (204). Because erbium lasers are well absorbed by water, they can disinfect the root canal by direct photothermal effects on bacteria, causing denaturation of enzymes and rupture of bacterial cells. Shoop et al. (205) reported that when using a power setting of 1.3 Watts, the Er:YAG laser eliminated most bacteria except Enterococcus faecalis, however in a later study the same group could eliminated all viable E. faecalis bacteria at 1.5 Watts (206). Perin et al. (207) demonstrated showed that canals inoculated with Bacillus subtilis, E. faecalis, Pseudomonas aeruginosa, Staphylococcus aureus, or Candida albicans could be disinfected using an Er:YAG laser at a power setting of 100 mJ and 7 Hz (0.7 Watts), however some 70% of samples that were irradiated 3 mm short of the apex remained infected. This was in contrast to a study by Leonardo et al. (208), which used a different sampling technique, and employed 63 mJ pulses at 15Hz (0.945 Watts), did not show advantage of laser treatment over conventional root canal treatment in eliminating bacteria within the root canal in teeth with apical periodontitis. Most other work was however positive to a variable extent. Wang et al. (209) reported that in canals inoculated with E. faecalis, the Er,Cr:YSGG laser gave a reduction in bacterial count of 77% at 1 Watt, and 96% at 1.5 Watts. At the lower power of 0.5 Watts, Eldeniz et al. (87) reported that canals inoculated with E. faecalis showed reduced levels but not total elimination of bacteria. A significant concern when using erbium and other lasers in the root canal is the risk of thermal insult to peri-radicular tissues. Two studies of the Er,Cr:YSGG laser using power settings of 1 to 6 Watts to remove smear layer and debris from root canals reported a maximum temperature rise of 8.0° C, if cooling was used, and 37° C if cooling was not used(202, 210). When using lower power settings of 0.6 and 0.9 Watts, Shoop et al. (211) reported root surface temperature increases of only 1.3° and 1.6°C, respectively. Similarly, Kimura et al.(212) used an Er:YAG laser at 2 Hz and 136-230mJ/pulse for 1 minute with a water spray, and noted a maximum 6° C rise in temperature at the apex, and 3° C at the mid-root region. Schoop et al. (205) reported a gradual increase in temperature on the root surface, depending on energy used. Temperature increases of 2.6, 3.1, and 4.5° C were observed at average power settings of 0.5, 1.0 and 1.3 Watts, respectively, when the laser was used at a pulse frequency of 15 Hz. 28
With regard to optical fiber design, Lee et al. (213) reported that conical tips produced less temperature increase than conventional bare tips, when used with the Er:YAG laser (30 mJ, 10 Hz, 0.3 Watts average power). The mean temperature increases recorded were 7.19.4° C for the cone-shaped fiber tip, and 6.5-11.0° C for the plain fiber tip, when the laser was used at pulse energies of 20 or 30 mJ, at 10 Hz, without water spray. This is consistent with an energy distribution from the cone-shaped fiber tip being elliptical in nature. The effect of ablation with water and under/through water has been investigated in several studies. A thick layer of water would decrease the ablation achieved by erbium lasers. Mir et al. (214) described the temporary formation of water channels, due to the effect of the initial pulses of laser energy into the water. Such channels would act as gateways for subsequent entry of laser energy directly on the tooth structure. In summary, the use of erbium lasers for preparing the root canal has a number of advantages, but the problem of canal roughness, ledges, zipping, and perforation remain to be addressed. In addition, the important concern of thermal injury to the supporting apparatus, and the critical influence of water on the ablation patterns both require closer examination.
1.5.2.4.4 Factors influencing laser ablation The ablative effect of erbium lasers on tissue may be influenced by a number of factors, including water film thickness (93, 94), pulse energy (214), beam diameter (215), and pulse duration (216, 217). Other factors that have a major influence on laser ablation are the laser delivery system and the properties of the target surface. Several studies indicate that water spray or a moist surface is essential for effective ablation of dentine, as it not only reduces thermal stress but also reduces charring of the ablated surface (191-194). However, dramatically increasing the water flow rate could decrease the efficiency of dentine ablation by giving a thicker surface water layer. Fried et al. (218) reported that thick water films decrease the rate of ablation of enamel with Q-switched and free-running Er:YSGG lasers (2.79 μm micron), Er:YAG (2.94 μm) lasers, free running
29
Ho:YAG lasers, and 9.6 μm TEA CO2 lasers (93, 94). A study by Visuri et al. (219) showed that their optimal water flow rate (4.5 mL/min) only minimally reduced the ablation rates of dentine with an Er:YAG laser, and did not significantly affect the ablation rates of enamel, compared with lasing under dry conditions. In their study, the laser was used to produce linear incisions in enamel or dentine, with or without water. The effect of pulse duration on the ablation process has been described by Apel et al. (216), who described the effect of the four distinctive pulse durations delivered with the Fidelis Er:YAG laser (Fotona, Slovenia): very short pulse (75-100μs), short pulse (250μs), long pulse (450-550μs), and very long pulse (750-950μs). They used this variable pulse duration laser system to ablate dental enamel. Under low radiant exposures, only short pulse durations produced ablation of enamel. No ablation was seen when very long pulses were used, up to 10 J/cm2. The beam diameter can be modified by altering the distance from the target or by using larger diameter tips. Stopp et al.(220) reported that where the beam diameter is modified by moving the delivery system further away from the object, the resulting beam will have a decreased intensity, resulting craters with smaller depths and larger diameters. Beam diameter can also be varied by using fiber optic tips of variable size, in combination with dental laser handpieces. The effect is governed not only by the fiber diameter, but also by collimation, i.e. the extent of the beam that can be accepted by the fiber. An additional factor is the inherent losses associated with the fiber optic element itself (i.e. its transmission factor). As an example, the instruction manual for the KaVo KEY3 laser system states that more energy is delivered through endodontic fibers of larger diameters, when the same panel settings are used. The relationship between ablation rate and pulse energy for both enamel and dentine has been described by Kim et al.(221), when erbium lasers are used in combination with water spray. The ablation rate of dentine has been reported to be almost twice that of enamel (222). Hence, careful consideration of the above factors would be needed to obtain effective and optimum ablation.
30
1.5.3 Present applications of lasers in endodontics The current applications of lasers in endodontics could be classified as follows:
Classification of uses of lasers in endodontics 1. Diagnosis •
Detection of pulp vitality - Doppler flowmetry - Low level laser therapy (LLLT)
•
Laser fluorescence
- Detection of bacteria
2. Pulp therapy- Pulp capping and pulpotomy 3. Canal preparation •
Biomechanical preparation
•
Removal of smear layer
•
Sterilization of the root canal a) High level lasers - Photo thermal b) Low level lasers - Photochemical (PAD)
4. Periapical surgery •
Soft tissue procedures
•
Hard tissue procedures
5. Laser-induced analgesia 6. Other • Removal of root canal filling material and fractured instrument • Softening gutta-percha • Removal of moisture/drying of canal The uses of various lasers in endodontics and some of their more popular applications have been listed in Table.1.3 (overleaf).
31
1.5.3.1 Laser diagnosis Proper and reliable diagnosis of pulp vitality is important for proper treatment planning in dentistry. Tests to determine tooth vitality (sensibility) rely mainly on the response of the dental pulp to hot, cold or electric stimulation. This method does not take into account the presence or absence of blood flow within the tooth, and hence false positive or negative responses could occur. A false negative response could occur in the case of acute trauma, where pulpal blood flow may be intact but the neural elements have been severed or are unresponsive (223). The optimal method to check vitality would be to confirm the presence or absence of blood flow within the tooth. For this purpose, several methods can be used, including laser Doppler flowmetry (LDF) (224) or low level laser therapy (LLLT) (114).
Table.1.3: Selected applications of lasers Laser
Wave length Argon
Reported Uses in endodontics Endodontic disinfection.
Long wave length
Short wave length
488-514.5 nm KTP 532nm
Soft tissue surgery in endodontics, endodontic disinfection
He-Ne 633 nm
Doppler flowmetry, photoactivated disinfection of root
Diode 635 nm
canals
Diode 810-980 nm
Soft tissue surgery in endodontics, endodontic disinfection
Nd:YAG
Soft tissue surgery in endodontics, endodontic disinfection,
1064 nm
biomechanical preparation.
Ho:YAG
Tooth preparation, soft and hard tissue surgery in
2100nm
endodontics, endodontic disinfection, biomechanical preparation
Er,Cr:YSGG
Tooth preparation, soft & hard tissue surgery in endodontics,
2780nm
endodontic disinfection, biomechanical preparation
Er:YAG
Tooth preparation, soft & hard tissue surgery in endodontics,
2940nm
endodontic disinfection, biomechanical preparation
Carbon dioxide
Pulp capping; soft and hard tissue surgery in endodontics
10600nm
32
1.5.3.1.1 Doppler flowmetry LDF was developed to assess blood flow in microvascular systems (224). The basic principle involves directing a beam of laser light onto the tooth, which reaches the dental pulp, and is scattered by moving red cells. This scattering causes a frequency shift. Photons that interact with stationary elements are scattered, but not Doppler shifted. The backscattered and frequency shifted beam is detected and processed to produce a signal. This is an indicator of red cell flux (volume of cells illuminated and their mean velocity). Lasers used for LDF are usually low-power devices of 1 or 2 mW. The He-Ne (632.8 nm) laser were amongst the first laser used for LDF(225, 226) The semiconductor diode lasers of wavelength 780–820 nm(227-230) have a greater ability to penetrate teeth, and have demonstrated improved results using forward scattering detection, as opposed to conventional backward scattering detection. LDF has been used to monitor and follow-up traumatized teeth, in particular to monitor revascularization in incompletely formed teeth that have been subjected to trauma (e.g. avulsed and re implanted), where LDF is superior to traditional methods such as dry ice (231). With regard to the root canal (as opposed to the pulp chamber), the wide variations in shape of the root canal make delivering the laser beam into the radicular pulp tissue difficult, hence making a full analysis of the pulpal blood flow over the length of the tooth impossible. Available probes only allow estimation of coronal blood flow, with the possibility of obtaining a false positive reading, if the recording is made close to the gingival tissues.
1.5.3.1.2 Low level laser therapy (LLLT) for diagnosis LLLT normally operate at powers of 100-200 milliwatts (114), and may be used to check vitality by triggering vasodilatation of blood vessels within the pulp. The increased intra-pulpal pressure elicits a nociceptors response. The point of first response can be recorded, and compared to opposing teeth. Appropriate laser settings (continuous wave or
33
long pulse durations) must be used, otherwise analgesic effects may develop and the nociceptors response might not be elicited (232).
1.5.3.1.3 Laser fluorescence Laser fluorescence is an interesting diagnostic application of lasers that has potential for use in endodontics for detection of bacteria in the root canal, based on the fluorescence emissions of bacteria and their by products or metabolites. According to Hibst et al.(233), the main component responsible for fluorescence in dental caries and dental calculus is porphyrin derivatives. When a fluorophore within a sample is exited, fluorescence will be emitted in all directions, and the intensity of fluorescence will be directly proportional to the intensity of the excitation source (234). Pini et al. (235) used laser fluorescence to detect residual pulp tissue within the root canal, using a 308 nm wavelength ultraviolet laser, while Sarkissian and Le (236) used 366, 405, and 440 nm wavelengths to distinguish remaining pulp tissue and bacteria from normal hard tissue in root canals. Most work using fluorescence in dentistry has employed visible light as the excitation source. In 1993, Koenig et al. (237) used 407nm wave lengths to detect various types of bacteria in culture using fluorescence. Subsequently, Hibst et al. (238) used the 655 nm wavelength for detection of dental plaque and dental caries, and this led to the development of the DIAGNOdent, a device which has become a widely used chair side diagnostic device in dental practice since 2000. Lussi et al. (129) later reported the use of a modified sapphire tip with the DIAGNOdent, for detection of proximal caries. The DIAGNOdent assesses near infrared emissions from porphyrins and other molecules of bacterial origin. Recently, Sainsbury (239) has reported that the DIAGNOdent system could be adapted for the detection of bacteria in the pulp chamber and root canal. He identified that healthy dental pulp soft tissues and healthy dentine give minimal infrared emissions, whilst strong emissions occurred from canals which had been infected with bacteria either in vivo or in vitro.
34
1.5.3.2 Pulpotomy Pulpotomy, the endodontic procedure in which dental pulp tissue is removed from the pulp chamber, is undertaken on teeth where the pulp tissue has been exposed by dental caries or traumatic injuries. The intention is to preserve the vitality of the radicular pulp, whilst removing the infected coronal pulp tissue. A number of materials and techniques have been used for performing this procedure, with reported success rates ranging from as low as 44%, to as high as 97% (224). Materials applied to the dental pulp after removal of pulp tissue include formocresol (240), glutaraldehyde (241, 242), calcium hydroxide (52), and more recently ferric sulphate and mineral trioxide aggregates (243). Some of the lasers used for this procedure are CO2, Nd:YAG, argon ion, laser diodes and Erbium lasers (166, 244-248). The first recorded laser pulpotomy was performed using the CO2 laser in dogs (249). Erbium and CO2 lasers are well absorbed by water, and thus act only on the superficial layer of the dental pulp tissue, with carbonization occurring in the latter. Jukic et al. (248) reported that following pulpotomy, exposed pulp tissue irradiated with either Nd:YAG or CO2 lasers showed carbonization, necrosis, infiltration of inflammation cells, oedema and hemorrhage in the pulp tissue, and a lack of newly formed dentine over the exposed pulp tissue after 45 days. In contrast, an earlier clinical study by Walsh (250) showed that the CO2 laser used alone in single pulse mode was effective for pulp capping and pulpotomy procedures, provided irradiation conditions were carefully controlled.
1.5.3.3 Pulp capping Pulp capping can be divided into indirect and direct approaches; the former is defined as the application of a medicament over a thin layer of remaining carious dentin, after deep excavation, with no exposure of the pulp, while the latter involves the placement of a biocompatible agent on healthy pulp tissue that has been inadvertently exposed during caries excavation or from traumatic injury to the tooth. With proper case selection, success with direct pulp capping is dependent on the ability to prevent bacterial contamination of the exposed site, stimulate reparative dentine formation, and maintain a coronal seal. In a comparative study using 200 teeth and recall period of 12 months, Mortiz et al. (251) concluded that pulp capping with the CO2 laser gave better outcomes in direct pulp
35
capping than calcium hydroxide, while Jayawardena et al. (252) who used the Er:YAG laser demonstrated in a rat animal model that laser-exposed pulp tissue possessed good healing capacity, with the formation of a dentine bridge and reparative dentine. LLLT effects may assist the repair process after pulpotomy. Dabrowska et al. (253) examined the effect of laser biostimulation on teeth treated with direct pulp capping and pulpotomy. In their study, direct pulp capping or pulpotomy had success rates of 53.85% and 82.6% at 12 months, which increased to 100% results at 12 months when LLLT was used after direct pulp capping or pulpotomy. These laser-treated teeth showed dentinal bridge formation within one to two months, on radiographic examination.
1.5.3.4 Laser assisted widening of the root canal One of the earliest explorations of the use of lasers to enlarge the root canal was the study of Levy (254), in which an Nd:YAG laser with water spray was used to widen root canals in the apical zone from ISO #20 to ISO #35, based on the fit of K files. The technique employed was a painting and sweeping action circumferentially, with lateral pressure on the canal walls during withdrawal of the fiber. The procedure took 60 seconds, using of 300 mJ and 1 Hz. Consistent with this, Matsuoka et al. (195) required approximately 2 minutes to enlarge root canals from 0.285 mm to 0.470 mm. Both Ali et al. (255) and Jahan et al. (197) took only 60 seconds of lasing time to prepare the root canal using a crown-down technique. This excludes the time required to change fiber optic tips. It would be predicted that canals with larger tapers would be easier to prepare than those with narrower tapers. With regard to the Ho:YAG laser, Cohen et al. (169) used a 245 μm diameter optical fiber to enlarge canals. The fiber was inserted to the apex, energized and then withdrawn slowly at 4 mm/second. Using this technique, canals with internal dimensions of ISO #25 were widened to an apical size of ISO #40. Using the same laser, Cohen et al. (171) employed a step back technique with four different optical fiber tips (with diameters of 140, 245, 355 and 410 μm) to enlarge canals progressively, whilst Deutsch et al. (256) used six different-sized optical fiber tips for enlarging the root canal with the Ho:YAG laser.
36
With regard to the Er,Cr:YSGG laser, Ali et al. (255) reported the use of fibers of various diameters to prepare root canals using a crown down technique. While noting that this laser wavelength was useful for removal of smear layer and debris, the risk of ledging, zipping, perforation, or over-instrumentation of canals was noted. Matsuoka et al. (196) reported that the Er,Cr:YSGG laser could be used successfully to prepare root canals with curvatures up to 10 degrees, using a step back technique, with an average energy of 2 Watts, a pulse rate of 20 Hz, and air and water spray. In contrast, Jahan et al. (197) reported that preparation of canals with a curvature above 5 degrees could lead to zipping, ledge formation or perforations. There is more limited information regarding use of the Er:YAG laser for enlarging the canal. Matsuoka et al. (195) reported using the Er:YAG lasers to enlarge the root canal using 3 different size conventional optical fiber tips used sequentially, in line with the step back approach. Although several studies have shown the potential for lasers to widen the root canal, it is difficult to attain all of the mechanical objectives of root canal preparation when laser energy is delivered with conventional optical fibers. This relates to their inability to deliver laser energy directly onto the walls of the root canal, as well as the operator challenge of maintaining a constant withdrawal rate. In 2006 Altundasar et al. (257) showed that delivery of laser energy onto the walls of the root canal using a conventional (plain) optical fiber to remove smear layer gives inconsistent ablation. From the standpoint of optics, a beam delivered from a plain fiber (and thus largely parallel to the walls of the root canal surface to be ablated) has low efficiency, and this has been demonstrated in the laboratory setting, by comparing the effects of parallel and perpendicular beams directed onto root canal dentine slices. In an attempt to overcome some of these problems, fiber tips with sculpted polished ends and greater lateral emissions have been developed(198, 256, 258-261). Shoji et al.(198) employed a cone-shaped irradiation tip which could disperse laser energy in an annular pattern. This aluminum reinforced silicate tip was used to deliver Er:YAG laser energy, to enlarge root canals. This tip design produced maximal enlargement when the laser was used at 30 mJ and 10 Hz.
37
1.5.3.5 Removal of smear layer from root canal walls Many laser types have been reported to be useful in removal of smear layer from root canal walls, including the argon fluoride (ArF) and other excimer lasers (262), argon ion lasers (263), KTP laser (532 nm) (264), diode lasers (11, 15), Nd:YAG lasers (158, 199), HoYAG lasers (175), Er:YAG lasers (265, 266), Er,Cr:YSGG lasers (197, 202), and CO2 lasers (101). Diode lasers are cost effective, compact and portable devices. The near infrared laser emissions from these devices (810-980 nm) have penetrating disinfecting actions, which is an additional advantage to being able to remove smear layer. Wang (102) used a 980 nm wavelength diode laser at 5 W for 7 seconds to remove smear layer, however concerns remain in terms of generation and conduction of heat to the supporting apparatus if high irradiances are used (267). Nd:YAG lasers are more effective for disinfecting the root canal, and relatively less effective for removing smear layer, compared to the erbium lasers (268). Goya (269), who investigated the effect of the Nd:YAG laser on smear layer, found that black ink increases the removal of smear layer by enhancing absorption of laser energy. However, Wilder-Smith et al. (270) identified that thermal damage was a concern when using the Nd:YAG laser to remove smear layer. The water absorbing properties of the Er:YAG and Er,Cr:YSGG lasers make these useful both for disinfection of the root canal, and removal of smear layer(199, 202, 271). Takeda et al.(199) undertook a comparative study of the argon ion laser (1 W, 50 mJ, 5 Hz), Nd:YAG laser (2 W, 200 mJ, 20 Hz.) and Er:YAG laser (1 W, 100 mJ, 10 Hz) in terms of removal of smear layer from prepared root canal walls, compared to EDTA. All lasers achieved better smear layer removal than EDTA, and the Er:YAG laser was the most effective of the three lasers used. In a later study, Takeda et al. (101) reported that Er:YAG lasers were better than CO2 lasers and three different acids in removal of smear layer. Ali et al.(255) reported less smear layer or debris when using an Er,Cr:YSGG laser, compared to the conventional root canal techniques, however the mechanical quality of the canal preparation (smoothness, taper, etc) was worse with the laser method. Biedma (272) also reported similar results of that of Ali et al. (255), but using the Er:YAG laser. 38
As already noted, several studies have reported inconsistent or inefficient removal of smear layer when using erbium lasers delivered using conventional optical fibers. Altundasar et al. (204) reported inconsistent smear layer removal of the walls of the root canal when the Er,Cr:YSGG laser (operated at 3W and 20 Hz) was delivered using a conventional tip, whilst Anic et al. (257) reported greater efficiency of a perpendicular beam for ablation when compared to a parallel beam. Kimura et al. (224) stated that it was difficult to evenly irradiate root canal walls using a conventional fiber tip, and advocated an improvement in the fiber tip design or method of irradiation to avoid obtaining an uneven surface. To overcome such problems, several authors have employed sculptured fiber tips that have greater lateral delivery of laser energy (198, 258, 259). Alves et al. (260) used the Er:YAG with forward emitting sapphire tips and hollow fibers, and compared these to modified tips which gave lateral emissions. Shoji et al. (198) used an Er:YAG laser delivered into a cone-shaped tip to enlarge artificial root canals in a block of bovine dentine using Er:YAG laser energy. The cone shaped tip was faster for cavity preparation and smear layer removal, compared with conventional instruments. Likewise, Takeda et al. (101) used a conical tip with the CO2 to remove smear layer from the root canal. Stabholz et al. (127) designed an endodontic side firing spiral tip (RCLase; Lumenis, OpusDent, Israel) (Fig.1.3), which comprised a hollow waveguide with spiral slits along the length of the tube. The end of the tip was sealed to prevent the forward transmission of laser energy. The Er:YAG laser was used at 500 mJ and 12 Hz through this tip to remove smear layer successfully. However, such tips are too large and rigid to be used in narrow, curved root canals. Moreover, if the tip were to bend, more energy would be emitted across those slits that are in a straight line with the beam.
Fig.1.3. RCLase laser tip. Lumenis, OpusDent, Israel. From Stabholz et al. (127)
39
1.5.3.6 Sterilization of root canals The mechanisms by which laser energy can be used to kill bacteria within the root canal depend on wavelength and irradiation parameters employed. Major advantages of using lasers for root canal sterilization are greater penetration than medicaments, and a more rapid action (273). The use of lasers obviates problems of discoloration of root canal dentine caused by medicament containing tetracyclines. Both photothermal and photochemical processes can be used for disinfection of the root canal. Lee et al. (274) classified the action of lasers on living cells as either photothermal, photo-chemical, photo-ablative or photo–mechanical. Photo-thermal disinfection involves local heating of bacteria with high intensity laser radiation, causing thermal denaturation of microbial enzymes, whilst photochemical disinfection uses low intensity laser energy to activate a photosensitizer which generates oxygen free radicals, which in turn kill bacteria through membrane damage. In contrast, photo-ablative disinfecting methods involve direct breaking of chemical bonds in the bacterial cell walls (119). Wilson (119) identified the laser factors which influence the mechanism by which microbial cells are killed, as wavelength, power output, exposure time, beam diameter (energy density), and the microbial factors as their chemical composition and physical attributes (water content, thermal conductivity, etc.). To date, the most common mechanism used to disinfect root canals has been the photothermal mechanism. Most lasers exert a bactericidal effect at high powers, but must be used in pulsed mode for endodontic disinfection, in order to reduce the risk of thermal injury to periodontal ligament cells. If the power is reduced, the possibility of damage to supporting periodontal apparatus is lower, however the bactericidal effects are limited (275).
1.5.3.6.1 Photothermal effects Photothermal disinfection has been documented with the XeCl excimer laser (308 nm) (276), diode lasers (810-980 nm) (135), Nd:YAG laser (172), the Nd:YAP laser (1.34µm) (277), and the erbium lasers (278). With the latter, the bacterial reduction which occurs is due to the high surface temperatures achieved (up to 300 degrees Celsius) (279, 40
280). Thus, the major drawback with photo-thermal disinfection is the amount of heat conducted through the root to the periodontal apparatus. Bahcall et al. (164) reported that such heat could induce collateral damage, including bone and root resorption, root ankylosis, and bone remodeling. Deleterious thermal effects can also occur within the root canal. For example, Turkmen et al. (281) documented undesirable surface effects including carbonization and cracking of radicular dentine when Nd:YAG and CO2 lasers were used for disinfection
1.5.3.6.2 Photo activated disinfection (PAD) PAD can be defined as "a method of disinfecting or sterilizing a hard tissue or soft tissue site by topically applying a photosensitizing compound to the site, and then irradiating this with laser light at a wave length absorbed by the photosensitizing compound, so as to destroy microbes at the site" (282). Much of the early work on this concept was undertaken by Wilson and colleagues in the early 1990’s, who showed that Toluidine Blue O ( TBO), used in conjunction with Helium-Neon laser energy (wavelength of 633 nm) would kill a suspension of 10¹² bacterial colony forming units in nutrient medium, when delivered over a period of 30 seconds (283). Initially Streptococcus mutans, and later other bacteria were shown to be susceptible to inactivation using this approach (275, 283-287). The current applications of PAD in dentistry are broad, and include the treatment of deep carious lesions, periodontal pockets, peri-implant sites, and mucosal wounds, as well as disinfection of root canals(288). For the latter, the advantages of PAD in endodontics include: 1. An increased certainty of single or multi-visit endodontic treatment 2. Killing of more than 99.99% of bacteria 3. Effective against root canal biofilms as well as planktonic bacteria, even though the former are typically more resistant to the action of antimicrobial agents (289, 290) 4. No thermal damage to the periodontal apparatus, since the thermal changes associated with PAD are less than 0.5 degrees Celsius (289) 5. PAD can be applied effectively for killing gram-positive, gram-negative, aerobic and anaerobic bacteria, in fact, all commonly encountered bacteria associated with dental disease (274). 6. Problems of antibiotic resistance are overcome. 41
The killing effect obtained with PAD is even more profound when laser energy is delivered using a flexible endodontic diffuser tip, which gives even irradiation of the root canal system, rather than a conventional optical fiber. Dickers et al (291) reported that the temperature rise recorded on the external root surface with the use of PAD for 150 seconds at 100mW was on an average 0.16 ± 0.08°C , hence making it perfectly safe.
1.5.3.6.3 Limitations of lasers for disinfection of the root canal While the middle infrared erbium lasers exert a bactericidal effect (172, 292), when delivered using conventional fibers their disinfecting action in the root canal can be inconsistent. Several reports have documented the inability of these lasers to sterilize the entire canal(207, 293) In these past studies, the fibers used in most studies have had conventional forward emitting tips, with a small angle of divergence.
1.5.3.7 Laser-induced analgesia Laser-induced analgesia is a low-level laser effect, which can be elicited by near infrared and middle infrared pulse laser emissions. It has been used for the treatment of dentine hypersensitivity, pain associated with temporo-mandibular joint disorders, and relief of orthodontic post-adjustment pain (114). Lasers that have been used for laser-induced analgesia include Nd:YAG, Er:YAG, and Er,Cr:YSGG lasers. The precise mechanism of action of the analgesic effect is still under debate. LLLT may selectively block depolarization of slowly conducting nociceptive afferent nerve fibers, particularly unmyelinated C-fibers (115, 116). It may also act on large diameter myelinated A delta fibers, and thus elicit the gate-control response (294). Simunovic has also postulated other possible mechanisms reasons for the analgesic effect (295, 296), as has Walsh(232) , who proposed that when these lasers are used at 15-20 Hz the laser frequency coincides with the natural "bio-resonance" frequency of the control domain of the Na-K ATPase pump cell in the membranes of nerve fibers, causing temporary disruption.
42
1.5.3.8 Removal of moisture/drying of canal Studies by Amyra et al. (151) showed that dehydration of the root canal could not be done safely using pulsed CO2 or Nd:YAG lasers because of adverse thermal effects, which would cause irreversible thermal damage to the periodontal apparatus. While the CO2 laser used with long pulse durations was effective at dehydrating the canals, thermal effects on the root surface were above the threshold of 5.5 degrees Celsius. Using the Nd:YAG laser gave a greater temperature increase. At higher power settings (up to 150 mJ and 20 Hz), the root canal was dehydrated in 60 seconds, however the temperature increase on the root surface was as much as 25 degrees.
1.5.3.9 Removing root canal fillings and fractured instrument Nd:YAG and erbium lasers can be used to remove gutta percha root canal fillings. Viducic et al. (297) compared the efficiency of Nd:YAG laser to commonly used gutta percha solvents, and reported that the Nd:YAG laser could effectively soften and remove gutta-percha from the root canal, without adverse thermal effects, and without the need for solvents. Anjo et al. (163) also showed that the Nd:YAG laser could remove gutta-percha faster than conventional techniques. Lasers may also be used to assist in removal of fractured instruments, allowing bypassing of the instrument by ablating the surrounding dentine. Yu et al. (298) reported a success rate of 55% for fractured instrument removal using this method. However, Matsumoto (166) showed that removal of fractured instrument is difficult impossible in narrow canals and in canals with severe curvatures. Attempts to use forward emitting fibers in curved canals for this procedure could lead to perforation of the canal.
1.5.3.10 Role of lasers in root fracture and other applications According to Kantola (299), recrystallization of the dentine can be elicited by high power Nd:YAG or CO2 laser irradiation. Simultaneously, growth in the crystal size occurs. This method may have application for repair of fractures.
43
Arakawa et al. (300) induced root fractures, then irradiated these with an Nd:YAG laser with air/water surface cooling, filling the fracture sites with a paste of tri-calcium phosphate (TCP) which was fused with the laser. Levy and Koubi (301) likewise used an Nd:YAG laser to seal vertical root fracture lines, in combination with TCP paste. SEM examination of the repaired sites showed deep fusion of the TCP paste had occurred. Similarly, Lin (302) developed a di-calcium phosphate (DP)-bioactive glass paste which was then used to repair fractures by fusion with a medium power continuous-wave CO2 laser. Lasers have also been used to try to strengthen pulpless teeth by lasing the teeth with 38% silver ammonium solution (166) using pulsed Nd:YAG, CO2 , and argon lasers, with air cooling and average power settings of 2-3 Watts for 20 seconds. The lasing is continued until the root surface becomes silver and mirror like. The lasing is continued until the root surface becomes silver and mirror like.
1.5.4 Relevant aspects of laser safety in endodontics In terms of safety aspects for eye and skin exposure, lasers are classified into several groups: class I (inherently safe); class II and IIIa (where the eye is protected by the blink reflex); class IIIb (where direct viewing is hazardous); and class IV (where the laser power is above 0.5 Watts, and the laser is classed as extremely hazardous). Most dental and medical lasers are class IV, and thus compliance with safety standards is necessary to protect the dentist, patient and support staff.
1.5.4.1 Safety issues related to general use of lasers General safety requirements include a laser warning sign outside the clinic, use of barriers within the operatory, and the use of eyewear to protect against reflected laser light or accidental direct exposure. The selection of the correct eyewear depends on the laser system being used. The potentially damaging effect of lasers on the eye depends on their wavelength and thus absorption characteristics. Er:YAG, Er,Cr:YSGG and Ho:YAG lasers are strongly absorbed by water. Because water is a major constituent of the cornea, direct exposure to the
44
eye would cause corneal burning and ablation. In contrast, lasers that are well absorbed by the pigments of the retina, such as Nd:YAG and KTP, will cause retinal damage (303). Other safety issues include the prevention of infection. Hardee et al. (304) noted the potential for infection to spread via laser plume, and hence high speed dental suction is recommended (303).
1.5.4.2 Prevention of transmission of infection through contact Laser endodontic fibers tips used within the root canal would be expected in many cases to encounter blood or other fluids which could be a source of patient-to-patient transmission of infection, if the fibers are not appropriately disinfected. Disposable tips have become available for some laser systems, however many fiber optic systems are used where the fibers are cleaved after each use (305). Appropriate disinfection and sterilization must be carried out for laser accessories and components that come into direct contact with oral soft and hard tissues. Other relevant recommendations include: 1. Fluid fed through a sleeve around the laser to cool it during surgery must be sterile. 2. Deposits of carbonized tissue residue can reduce the quantity and quality of the light emission. Therefore, it is necessary to wipe the tip after use. It may be necessary to calibrate the tip during the procedure. 3. Sapphire tips that come into contact with sterile tissue must be sterile and need to be cleaned and then sterilized after each use. Piccione (306) further recommended that all controls of the laser should be disinfected or covered with a barrier, in a manner similar to other dental equipment, while smaller laser accessories such as handpiece should be steam sterilized.
45
1.5.4.3 Temperature effects of lasers on the dental pulp Andersen (307) has demonstrated that in the human dental pulp both cold and heat evoked a decrease in pulpal blood flow, when measured using a Doppler flowmetry. There is, therefore, a low potential of pulpal blood flow for cooling. The absorption coefficient and the reflectivity of the laser wavelength used are important in determining the pulpal reaction. Nyborg and Brannstrom (308) determined that a temperature of 150°C on the enamel surface for 30 seconds could cause necrosis of the dental pulp. According to Zach and Cohen (309), an intra-pulpal temperature increase of approximately 5.5°C can promote necrosis of the dental pulp in 15% of cases, while temperature increases of 11 and 17°C will cause necrosis in 60 and 100% of cases (309, 310). Pulpal damage can be avoided or minimized by a suitable choice of laser parameters, and by appropriate use of irrigation or an air/water spray. Armengo (311) studied the effect of water spray on the temperature rise when using an Er:YAG or Nd:YAP laser. Water spray reduced the temperature rise associated with laser treatment, and also helped to clear the ablation site of debris, and keep it moist. The importance of air/water spray is exemplified in the study of Glockner et al. (312), which demonstrated that during coronal cavity preparation with the Er:YAG laser, a temperature reduction occure after a few seconds from 37 °C to 25 °C, because of the cooling effect of the air/water spray.
1.5.4.4 Temperature effect of lasers on periodontal tissues Maintaining the health of the periodontal apparatus is critical for the success or failure of endodontic treatment undertaken with lasers. Modern endodontic rotary instruments produce little or no increase in peri-radicular root surface temperature (313). In contrast, several studies have shown that certain canal preparation techniques (314, 315) and obturation techniques (316-319) can transfer heat to the periodontal tissues. Erbium lasers cause evaporation and expansion of water within the crystals of hard tissue, and this evaporation can have a cooling action. Several authors have studied the thermal effect of lasers on the periodontal ligament and surrounding bone (169, 171, 211, 213). The supporting periodontal apparatus is known to be sensitive to temperatures of 47°C, while temperatures of 60°C and above will permanently 46
stop blood flow and cause bone necrosis (320). On the other hand, periodontal tissues are not damaged if the temperature increase is kept below 5° Celsius (321). A threshold temperature increase of 7°C is commonly considered as the highest thermal change which is biologically acceptable to avoid periodontal damage (322-325). Kimura et al.(212) using the Er:YAG laser noted that the root surface temperature increase was less than 6 °C at the apical third, and 3°C at the middle third. Similarly, Theodoro et al. (279) using the same laser reported temperature increases below 7°C, while in the study of Machida et al. (322) where water spray was used the temperature increase at the apex was less than 2°C. Thus, the use of air or water coolants in combination with lasers will help prevent adverse thermal effects on the periodontal ligament and surrounding bone (311, 312). A further consideration is that of the thermal relaxation time (TR), which is the amount of time required for heat to flow into adjacent regions or otherwise be dissipated (112). The use of pulsed lasers with short pulse durations will minimize the zone of thermal damage, by producing a thermal event that is shorter than the TR of the tissue (326). In case of root canal ablation, the conduction of heat from dentine to periodontal ligament and bone can be reduced by using a continuous stream of water during ablation. On the other hand, a dry root canal is devoid of fluid, and will conduct energy similar to a solid body, which is uniformly in all directions. However, canals that are irrigated with fluids will benefit from transfer of heat into that fluid.
1.6 Fiber optics and their modifications For a laser to be useful in clinical practice, it must be able to effectively deliver laser energy to the target site. Early delivery systems were too bulky or cumbersome to use in the oral cavity, especially in root canals and other areas where access is limited. Fiber optics were introduced into medicine as early as 1954 by Kapany, who developed the endoscope (327), which occurred six years before lasers were invented by Maiman in 1960. Early fiber optic systems had high-energy losses, and were incapable of delivering the mid-infrared laser 47
wavelengths efficiently, and thus most early mid-infrared lasers used alternate delivery systems. The existing range of laser delivery systems includes: Articulated arms (with mirrors at joints) – for UV, visible and infrared lasers Hollow waveguides (flexible tube with reflecting internal surfaces) – for middle and far infrared lasers. Fiber optics – for visible and near infrared lasers The fiberoptic delivery systems are essential for endodontic applications. 1.6.1 Articulated Arms When the laser wavelength does not permit transportation through waveguides or fiber optics, or the peak power is very high, articulated arms are the delivery system of choice. These arms use reflecting mirrors within a rigid closed hollow tube, which direct the laser energy in the required direction (166). Proper alignment is essential for proper beam exit.
1.6.2 Hollow Waveguides Flexible hollow waveguides have an internal reflective coating along the length of the tube. Depending on the coating, they can transmit light in various parts of the infrared range. The hollow tube could be metallic, plastic, carbon fiber, and is coated internally with a metallic or dielectric film (328-330). These waveguide are somewhat flexible.
1.6.3 Fiber Optics The most commonly used material to fabricate fibers is glass [Quartz glass or fused silica (amorphous silicon dioxide = SiO2)], either in pure form or with some dopants added. Fibers can also be fabricated from phosphate or fluoride glasses (331), polymers, or even crystalline materials (such as sapphire).
48
Optical fibers operate by total internal reflection, and in general are comprised of three concentric layers. Light passes only through the central glass core of the fiber. This is surrounded by a cladding, which has a lower refractive index than the core. The cladding layer may be doped with different materials, such as fluoride, to alter its refractive index (332). The outer layer is the buffer layer and is used only for mechanical strength and protection of the fiber. The buffer coating is normally a polymer material such as polyvinylchloride. The advantages of optical fibers over other delivery systems are their small size and high flexibility. Tran (333) noted that while sapphire fibers transmit some light wavelengths better than quartz, sapphire fibers are rigid, often rupture on bending, and can only be polished not cleaved, hence shaping of the tips is difficult. Moreover, unlike quartz fibers, crystalline sapphire cannot be reheated to produce different shapes by drawing out the fiber. Sapphire fibers are more expensive than glass fibers because the grain growth process is much slower than the glass fiber drawing process For the middle infrared region, chalcogenide glasses, fluoride glasses, polycrystalline metal halides, and some germanate oxides transmit well at wavelengths beyond 2.1µm, and have all been fabricated into optical fibers. Unfortunately, these materials tend to be very difficult to process, and have inferior mechanical and durability properties when compared to fused silica (334, 335). Though quartz tips have high transmission losses in the infrared range, their better physical properties make them the most popular tips currently used for delivery of laser energy within the root canal.
1.6.3.1 Doped fibers Dopants may be added to the core fiber to act as transmitters or amplifiers; hence overcoming to some extent the expected losses. Recently, fibers doped with rare earth elements or other dopants have emerged as a promising medium (336).
49
1.6.3.2 Transmission losses Attenuation is defined as reduction in the amplitude and intensity of a signal. Passage of laser energy through fiber optics can suffer from attenuation due to intrinsic or extrinsic causes (337). Intrinsic causes of transmission losses are absorption by the core material and by residual impurities, and by Rayleigh scattering from microscopic inhomogeneities, which are dimensionally smaller than the optical wavelength. Imperfections in the atomic structure induce absorption by the presence of missing molecules or oxygen defects. Silica fibers have low intrinsic absorption at wavelengths from 700 to 1600 nm, and hence are well suited for transmission of lasers within this range. Intrinsic absorption in the ultraviolet region is caused by electronic absorption by silicon-oxygen (Si-O) bonds(338). Extrinsic causes of attenuation include improper fabrication, geometric effects of fiber design (sharp bends and micro bends) and losses occurring when laser energy is coupled into and out of a fiber optic. Extrinsic absorption may also be caused by impurities in the fiber material, particularly traces of metal impurities, such as iron, nickel, and chromium. These metal ions can undergo electronic transition from one energy level to another(338). Extrinsic absorption also occurs when hydroxyl ions (OH-) are introduced into the fiber. Water in silica glass forms a silicon-hydroxyl (Si-OH) bond, which as a fundamental absorption at 2700 nm. The amount of water (OH-) impurities present in a fiber should be less than a few parts per billion. Thus, fiber attenuation caused by extrinsic absorption is highly sensitive to the level of impurities (OH-) present in the fiber. If the amount of these impurities is reduced, fiber attenuation is reduced. In the middle infrared range, quartz glass fibers have a much lower transmissibility than sapphire. Tran (333) reported that quartz fibers transmit very poorly at wavelengths above 2.5 µm, thus for an Er:YAG laser only 30 % of the laser power can be transmitted through a quartz tip which is 12 mm long. Fused silica does not transmit well at near-IR to IR wavelengths (2.1 to 20 µm), due to multiphoton (atomic vibrational) absorbance (335). Robertson et al. (339) stated that multiphoton absorption occurs when two or more photons are absorbed by an atom
50
simultaneously, mimicking the effects of the absorption of a higher energy photon. For example, the simultaneous absorption of two green (516 nm) photons could produce the same effects as a single UV (258 nm) photon. Chalcogenide glasses, fluoride glasses, polycrystalline metal halides, and some germanate oxides perform well beyond 2.1µm, and have all been fabricated into optical fibers. Unfortunately, as noted earlier, these materials tend to be very difficult to process, and have inferior mechanical and durability properties when compared to fused silica (334, 335).
1.6.3.3 Methods of modifying fiber tips Fiber tips are commonly modified by heating and pulling (340, 341), or by chemical etching (342-344). Alternatively the fiber end can be polishing. For example, a flat surface can be polished at an angle to accommodate a totally reflecting surface for a uni-directional side-firing fiber. If the fiber tip is rotated while polishing at a small angle; a tapered tip will result, with multi-directional emissions (345). The tip can also be modified by fixing certain materials to the fiber end to disperse the light across wide angles. Such tips are commonly called isotropic tips and are widely used in photodynamic therapy (346, 347). However, these tips can only be used at relatively low energy levels.
1.6.3.3.1 Chemical etching A typical chemical etching process involves immersing a fiber optic tip into a stock solution of etchant and etchant-insoluble organic solvent. The chemical composition commonly used for etching is 40% to 50% hydrofluoric acid (HF), topped with silicon oil. The oil prevents emissions of HF vapour, modifies the contact angle achieved between the fiber and the etchant, and contributes to the initial meniscus height formed at the interface of the bare quartz tip, the etchant and the inorganic solvent (348). Inorganic solvents including isooctane, 1-bromodecane and 1-octnethiol (349) may be used as alternatives to silicon oil.
51
Etching is typically done in polystyrene (PS) transparent containers, as these are chemically resistant to HF. The chemical etching method is the simplest and most inexpensive method of shaping the tip to obtain a conical end that gives a broad distribution of energy, whilst still allowing for high optical transmission. The different methods of etching fibers include: 1. Static and dynamic etching (342, 343) 2. Tube etching – for polymer coated materials (344) •
Micro convection mechanism for impermeable coatings
•
Gradient and lateral diffusion for permeable coatings
1.6.3.3.2 Etching mechanism The conventional method of etching involves immersing the quartz fiber tip into a suitable etchant, after the protective polyimide coating has been removed. The etchant wets the immersed fiber surface, and forms an initial meniscus height due to surface tension at the glass-liquid interface. As etching proceeds, the upward pulling force resulting from surface tension decreases, due to the reduction of the fiber radius in contact with the etchant (Fig.1.4). Consequently, the meniscus height reduces progressively until the portion of the fiber below the oil is completely etched, forming the conical tip (348). The final profile of the tip depends on the relationship between the fiber radius and meniscus height, and can be obtained by solving the Young-Laplace equation (equation 1) (Fig.1.5, overleaf). However in the tube etching technique the meniscus height is constant as the protective acrylic or polyimide coating is acid resistant, and thus its diameter is constant. In this case, etching occurs either due to diffusion through the coating (350) or via a micro convection mechanism if the coating is impermeable (344). Lambelet et al. (350) reported that the tube etching technique provided a smoother taper than could be obtained with a conventional etching technique.
52
Fig.1.4. Conventional etching process using an etchant (HF) and an organic solvent. Based on Reference (348)
Fig.1.5. The static meniscus on a circular cylinder immersed into a solution. From Reference (348) After etching, the etched fiber should be rinsed successively with water and acetone (349) or otherwise the etchant must be neutralized using other agents such as solutions of sodium hydroxide, sodium bicarbonate or other alkaline materials.
1.6.3.3.3 Factors effecting etching The two important outcomes that will be affected by variations in the etching process are the etching rate and the final shape of the fiber tip. The etching rate is influenced by the temperature of the etchant, the concentration of the etchant, the physical composition of the etchant, and the method of etching. The shape of the fiber tip is affected by the initial diameter of the fiber, the density of the etching solution, the concentration of the etchant, and the temperature of the etchant.
53
Sayah et al. (349) reported that increasing the temperature of the HF solution from room temperature to 60 degrees Celsius decreased the etching time by half and produced a smooth surface etch. Increasing the concentration of HF from 10 to 40% increased the etching rate by four-fold. With regard to the effect of the physical composition of the fiber on the etching rate, Smith et al. (351, 352) reported variations in the etching rate of doped fibers, specifically that Germanium-doped fibers etch faster than fluoride doped fibers. The choice of etching technique (i.e., tube etching or the conventional etching technique) can also influence the etching rate. Etching techniques that do not require removal of the protective coating prior to etching (tube etching) require a longer etching time (344). The shape of the fiber tip will depend on: 1. The diameter of the fiber: a smaller diameter leads to decreased initial meniscus height, leading to shorter cones (349). 2. Differences in density between the two liquid solutions: shorter cones and wider angles are obtained with solvents, which give a lower initial meniscus height. (349) 3. The concentration of etchant: Tips etched at low HF concentration have sharp angles and a long taper. Etching with HF concentrations above 40% produces large cone angles and short tapers. (349) 4. The temperature of the etchant. Other than accelerating the etching process, increasing the temperature of the etchant will lead to short tapers and long cone angles. (349) However, it should be noted that factors that affect the shape of the fiber with conventional etching, by virtue of altering the meniscus height, may not influence the shape of the fiber when using the tube etching technique. Moreover, the etching rate and physical composition of the fiber influence the shape of the fiber when using the tube etching technique.
54
1.6.3.4 Modified tip profiles Two important factors that influence the characteristics of the beam passing through any fiber are its refractive index and the diameter of the fiber. The ability to characterize beam profiles based on the geometry and physical properties of fibers is important in defining their possible application (353). Because fiber optics act as light guides, any modifications in their shape should lead to variations in their emission profile. The ability to modify the emission profile for laser energy by variations in the structural design of fiber optics has allowed new applications in laser medicine and surgery. Using an argon ion laser, Ward (354) showed that the beam profile for a straight-cut (plain, conventional) fiber end was a cone of diverging rays. Royston et al. (355) described the optical properties of a spherical, hemispherical, cone and wedge shaped fiber optic surgical tips when used with an Nd:YAG laser. The passage of light through a tapered fiber is governed by the relationship d1.Sin(ø1)=d2.sin(ø2), where d1 and d2 are the diameters and ø is the angles (Fig.1.6 ) (335). The angle of reflection of a light ray is equal to the angle of incidence. Therefore, light entering the small end of a fiber becomes more collimated as the diameter increases, because the reflecting surface is not parallel to the fiber axis. On the other hand, collimated light entering tapered fibers at the larger end (Fig.1.7) becomes de-collimated. Importantly, if the angle of incidence exceeds the acceptance angle, light will pass through the side of the fiber, giving a lateral emission pattern.
Fig.1.6 Tapered fiber transmission. Based on Reference (335)
55
Fig.1.7 Large end to small end transmission. Based on Reference(335). James et al. (356) have described a wide variety of different modified tips for medical and industrial applications. Verdaasdonk et al. (329)also described various shaped silica tips and their possible emission profiles (Fig.1.8).
Fig.1.8 Various shaped optical tips. From Reference(329).
56
Shoji et al. (198) described a fan shaped emission profile for a conical tip, with 80 percent of the energy directed laterally, and only 20 percent in the forward direction. Tips with a 360 degree emission profile(isotropic round tips) have been used for photoactivated disinfection of root canals (346, 347). Similarly Heisterkamp et al. (357) used cylindrical diffusion tips for coagulation of solid tumors, however these tips are too large (diameter 1.65 mm) for endodontic use. An alternative method of achieving a 360 degree emission profile is the use of embedded titanium dioxide for dispersing Nd:YAG laser energy laterally along the length of the embedded fiber tip (358). Although this tip design is of interest, its cost (due to process of embedding) and large diameter (600 microns) make it unsuitable for use in endodontics. Ideally, for lasers used in endodontics for smear layer removal, canal shaping, and disinfection, fiber optic tips which can deliver laser energy laterally need to be developed, preferably with minimal to modest cost.
1.6.3.5 Method of use of the tip. There are basically two methods by which laser energy is applied to tissues: contact or non-contact mode. The contact mode describes the process of delivering laser energy on the tissue with the fiber or the delivery system in direct contact with tissue; whereas the noncontact mode describes the delivery of laser energy without of the delivery system coming in contact with the tissue. In dentistry, the contact mode is mainly used for soft tissue procedure, where as the non-contact mode is used for both hard and soft tissue procedures.
1.6.3.5.1 Mode of action When the laser tip is in direct contact with the tissue, the effect of the laser energy on that tissue is dependent on the shape of the tip as well as the laser wave length (177, 359). Laser energy can heat a fiber tip to temperatures of several hundred degrees Celsius, enabling vaporization of soft tissue when the tip is held in contact with the tissue. Such tips are
57
described as “hot tips”, and with these tips the shape and diameter of incision is dependent on the shape and size of tip used. Such hot tips have been investigated for both medical and dental surgical applications (360). In the non-contact mode of delivery of laser energy, the effective beam diameter will play a large role in the diameter of ablation or incision. A hot-tip action is not possible with such a delivery system. 1.6.3.5.2 Selecting the correct fiber optic When selecting an optical fiber, the proper fiber material must be used, which transmits the laser wavelength in use. Other factors which must be considered before selecting a fiber include: (361) 1) Numerical aperture 2) Back reflection 3) Attenuation 4) Packing Fraction 5) Minimum Bend Radius 6) Input/Output Phenomenon
1.7 Technical issues affecting laser use in endodontics The following summarizes the current state of knowledge regarding technical issues which affect laser use in endodontics 1. Conventional plain fiber tips deliver laser energy primarily in a forward direction (parallel to the fiber tip) with little lateral emissions. 2. The flexibility of fiber optics reduces as their diameter increases. The flexibility of fibers is over a larger arc than for NiTi endodontic instruments, thus making them stiffer and more difficult to use in highly curved canals. 3. High transmission losses are seen with fiber optics used with erbium lasers.
58
4. There are no fibers available which can ablate along their length of the canal. This technical issue makes available methods for preparing the root canal technique sensitive. 5. Because of attenuation, current fibers are restricted in the amount of energy that can be passed through them. Passing energy greater that the settings recommended by the manufacturer could lead to heating in the fiber and destruction of the fiber tip. 6. Presently available fibers for root canal procedures cannot be used in canals that have an apical size smaller than ISO #20. Hence canals need to be widened to this minimum size before these fibers could be safely used in the root canal. 7. Fibers that have sharp angles tend to restrict the smooth movement of the fiber towards the apex. 8. Fiber tips cannot be pre-curved to the canal shape, and hence there is an inherent risk of ledges or perforation, when withdrawing a flexible bare tip. The flexible tip will straighten past the curve, and its energy will be delivered directly on the wall of the canal that has the least curvature. 9. Conventional plain optical fiber tips, unlike hand or rotary endodontic instruments, have parallel sides, which pose a problem in these being maneuvered to the apex of a tapered canal.
1.8 Gap in knowledge Although lasers have been used successfully to ablate dentine, there is at present insufficient knowledge regarding the ablation characteristics of root canal dentine. Little is known regarding the effect of water flow rates, which would be expected to alter ablation characteristics. The lack of a delivery system that can deliver laser energy directly onto the walls of the root canal has prevented consistent and uniform ablation of root canal dentine. Although lasers tips with various emission profiles have been tried, these have not been assessed within the root canal or compared to the conventional tips. Because shock waves have been shown to propel fluids at high speeds, it is of interest to determine if these pressure waves could force irrigant fluids past the apex. The bulk of previous research on ablation of root canal dentine has used one of the two erbium lasers. Use of these lasers is restricted by the inherent transmission losses of the 59
fibers used. Thus, there is value in examining an alternative infrared wavelength such as the Ho:YAG laser which has high absorption in water and excellent transmission properties in plain optical fibers, for ablation of root canal dentine.
1.9 Hypotheses The overall hypothesis of this project is that fiber optics can be effectively shaped to produce lateral emission profiles that would increase the effectiveness of mid-infrared lasers in various root canal applications. The specific hypotheses are as follows: a.
The morphological variation of external vs. internal dentine and the variation in flow rates will have an influence on ablation of root canal dentine.
b.
The ability to modify optical fibers will create fiber tips with lateral emission profiles that would be of interest for laser irradiation of the walls of the root canal.
c.
The use of digital imaging to determine the boundaries of dentinal tubules can play a useful role in quantifying the efficiency of smear layer removal.
d.
The use of fiber optic shapes with preferential emission laterally rather than in the forward direction can be used to remove smear layer more effectively from the apical third than a conventional plain optical fiber tip.
e.
The use of a laser tips with a shape that produces more lateral emission would scatter energy laterally and hence have reduced thermal effects on the root surface and thus less risk of injury to the safety of periodontal apparatus.
f.
The ability of lasers to produce shock waves that could drive fluids at considerable speeds in the canal could lead to apical extrusion of irrigants when used for root canal therapy.
g.
The ability to electroplate glass optics would be valuable in modifying and controlling the emission patterns of fiber optic delivery systems.
h.
Holmium:YAG lasers can be used to ablate dentine efficiently in the presence of adequate water spray.
60
1.10 Aims In line with the above hypotheses, the aims and objectives are to: 1. Compare the differences in ablation between external and internal root canal dentine when using a Er:YAG laser with different water flow rates. 2. Fabricate fiber optic tips with the ability to deliver infrared laser energy along the length of the modified fiber tip, and record the emission profiles of various fiber tip designs. 3. Use digital analysis to evaluate smear layer removal, and compare this method to the established gold standard (the Hulsmann based ordinal scoring system with three observers). 4. Assess the efficiency of smear layer removal with Er:YAG and Er,Cr:YSGG lasers when used with a conventional plain tip and optically modified conical tips and different irrigant solutions. 5. Measure the temperature effects of Er:YAG and Er,Cr:YSGG lasers when used with different fiber tips. 6. Quantify the extent of apical extrusion of fluid when using Er:YAG and Er,Cr:YSGG lasers with different optical fiber designs 7. Fabricate fiber optics with lateral delivery and a safe tip, and record their emission profiles. 8. Compare the ablative process in human dentine using the Ho:YAG laser with a range of pulse energies and frequencies both in “dry” mode and when accompanied by a coaxial water mist spray (“wet” mode).
61
1.11 References 1.
Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269296.
2.
Hulsmann M, Peters OA, Dummer PMH. Mechanical preparation of root canals: shaping goals, techniques and means. Endod Topics 2005;10:30-76.
3.
Whitworth J. Methods of filling root canals: principles and practices. Endod Topics 2005;12:2-24.
4.
Goldberg F, Gurfinkel J. Analysis of the use of Dycal with gutta-percha points as an endodontic filling technique. Oral Surg Oral Med Oral Pathol 1979;47:78-82.
5.
Welch SE. Gutta percha coated silver cones as root canal filling material. Ill Dent J 1978;47:604-610.
6.
De Moor R, Coppens C, Hommez G. Coronal leakage reconsidered. Revue belge de medecine dentaire. Belgisch tijdschrift voor tandheelkunde 2002;57:161-185.
7.
Taylor JK, Jeansonne BG, Lemon RR. Coronal leakage: effects of smear layer, obturation technique, and sealer. J Endod 1997;23:508-512.
8.
Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589-599.
9.
Sert S, Aslanalp V, Tanalp J. Investigation of the root canal configurations of mandibular permanent teeth in the Turkish population. Int Endod J 2004;37:494499.
10.
Grossman LI. Endodontic practice. 8th ed. Philadelphia: Lea & Febiger; 1974.
11.
Harty FJ, Pitt Ford TR. Harty's endodontics in clinical practice. 5th ed. Edinburgh; New York: Wright; 2004.
12.
Grossman LI. Endodontic practice. 10th ed. Philadelphia: Lea & Febiger; 1981.
13.
Weine FS, Kelly RF, Lio PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endod 1975;1:255-262.
14.
Goodman A, Reader A, Beck M, Melfi R, Meyers W. An in vitro comparison of the efficacy of the step-back technique versus a step-back/ultrasonic technique in human mandibular molars. J Endod 1985;11:249-256.
15.
Lev R, Reader A, Beck M, Meyers W. An in vitro comparison of the step-back technique versus a step-back/ultrasonic technique for 1 and 3 minutes. J Endod 1987;13:523-530.
62
16.
Wu MK, Wesselink PR. Efficacy of three techniques in cleaning the apical portion of curved root canals. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:492-496.
17.
Morgan LF, Montgomery S. An evaluation of the crown-down pressureless technique. J Endod 1984;10:491-498.
18.
Saunders WP, Saunders EM. Effect of noncutting tipped instruments on the quality of root canal preparation using a modified double-flared technique. J Endod 1992;18:32-36.
19.
Clem WH. Endodontics: the adolescent patient. Dent Clin North Am 1969;13:482493.
20.
Weine FS. Endodontic therapy. 3rd ed. St Louis: Mosby; 1972.
21.
Walton RE. Histologic evaluation of different methods of enlarging the pulp canal space. J Endod 1976;2:304-311.
22.
Mullaney TP. Instrumentation of finely curved canals. Dent Clin North Am 1979;23:575-592.
23.
Ingle JI, Bakland LK. Endodontics. 5th ed. Hamilton, Ont. London: B C Decker; 2002.
24.
Torabinejad M. Passive step-back technique. Oral Surg Oral Med Oral Pathol 1994;77:398-401.
25.
Torabinejad M. Passive step-back technique. A sequential use of ultrasonic and hand instruments. Oral Surg Oral Med Oral Pathol 1994;77:402-405.
26.
Marshall FJ, Pappin J. A Crown-Down pressureless preparation root canal enlargement technique. Technique Manual. Portland, OR: Oregon Healthh Sciences University. 1980.
27.
Leeb J. Canal orifice enlargement as related to biomechanical preparation. J Endod 1983;9:463-470.
28.
Roane JB, Sabala CL, Duncanson MG, Jr. The "balanced force" concept for instrumentation of curved canals. J Endod 1985;11:203-211.
29.
Charles TJ, Charles JE. The 'balanced force' concept for instrumentation of curved canals revisited. Int Endod J 1998;31:166-172.
30.
Briseno Marroquin B, Pistorius A, Willershausen-Zonnchen B. Canal transportation caused by a new instrumentation technique and three standard techniques. J Endod 1996;22:406-409.
31.
Ruddle CJ. The ProTaper technique. Endod Topics 2005;10:187-190. 63
32.
Lloyd A. Root canal instrumentation with ProFile instruments. Endod Topics 2005;10:151-154.
33.
Gianluca G. The K3 rotary nickel titanium instrument system. Endod Topics 2005;10:179-182.
34.
Buchanan LS. ProSystem GT: design, technique, and advantages. Endod Topics 2005;10:168-175.
35.
Sonntag D. FlexMaster: a universal system. Endod Topics 2005;10:183-186.
36.
Sundqvist G. Taxonomy, ecology, and pathogenicity of the root canal flora. Oral Surg Oral Med Oral Pathol 1994;78:522-530.
37.
Sundqvist G. Associations between microbial species in dental root canal infections. Oral Microbiol Immunol 1992;7:257-262.
38.
Sundqvist G. Ecology of the root canal flora. J Endod 1992;18:427-430.
39.
Monika CM, Froner IC. A scanning electron microscopic evaluation of different root canal irrigation regimens. Braz. Oral Res 2006;20:235-240.
40.
O'Connell MS, Morgan LA, Beeler WJ, Baumgartner JC. A comparative study of smear layer removal using different salts of EDTA. J Endod 2000;26:739-743.
41.
Bystrom A, Sundqvist G. The antibacterial action of sodium hypochlorite and EDTA in 60 cases of endodontic therapy. Int Endod J 1985;18:35-40.
42.
Ahmed MF, Elseed AI, Ibrahim YE. Root canal treatment in general practice in Sudan. Int Endod J 2000;33:316-319.
43.
Gutierrez JH, Herrera VR, Berg EH, Villena F, Jofre A. The risk of intentional dissolution of the smear layer after mechanical preparation of root canals. Oral Surg Oral Med Oral Pathol 1990;70:96-108.
44.
Yeung SY, Lan WH, Huang CS, Lin CP, Chan CP, Chang MC, et al. Scavenging property of three cresol isomers against H2O2, hypochlorite, superoxide and hydroxyl radicals. Food Chem Toxicol 2002;40:1403-1413.
45.
Stamatova IV, Vladimirov SB. The smear layer in the root canal and its removal. Folia Med (Plovdiv) 2004;46:47-51.
46.
Ghoddusi J, Naghavi N, Zarei M, Rohani E. Mandibular first molar with four distal canals. J Endod 2007;33:1481-1483.
47.
Barnhart BD, Chuang A, Lucca JJ, Roberts S, Liewehr F, Joyce AP. An in vitro evaluation of the cytotoxicity of various endodontic irrigants on human gingival fibroblasts. J Endod 2005;31:613-615.
64
48.
Calt S, Serper A. Time-dependent effects of EDTA on dentin structures. J Endod 2002;28:17-19.
49.
Abbott PV. Systemic release of corticosteroids following intra-dental use. Int Endod J 1992;25:189-191.
50.
Gomes BP, Ferraz CC, Vianna ME, Rosalen PL, Zaia AA, Teixeira FB, et al. In vitro antimicrobial activity of calcium hydroxide pastes and their vehicles against selected microorganisms. Braz Dent J 2002;13:155-161.
51.
Bystrom A, Claesson R, Sundqvist G. The antibacterial effect of camphorated paramonochlorophenol, camphorated phenol and calcium hydroxide in the treatment of infected root canals. Endod Dent Traumatol 1985;1:170-175.
52.
Gatewood RS, Himel VT, Dorn SO. Treatment of the endodontic emergency: a decade later. J Endod 1990;16:284-291.
53.
Athanassiadis B, Abbott PV, Walsh LJ. The use of calcium hydroxide, antibiotics and biocides as antimicrobial medicaments in endodontics. Aust Dent J 2007;52:S64-82.
54.
Gulabivala K, Patel B, Evans G, Ng Y-L. Effects of mechanical and chemical procedures on root canal surfaces. Endod Topics 2005;10:103-122.
55.
Baker NA, Eleazer PD, Averbach RE, Seltzer S. Scanning electron microscopic study of the efficacy of various irrigating solutions. J Endod 1975;1:127-135.
56.
Hsieh YD, Gau CH, Kung Wu SF, Shen EC, Hsu PW, Fu E. Dynamic recording of irrigating fluid distribution in root canals using thermal image analysis. Int Endod J 2007;40:11-17.
57.
Sedgley CM, Nagel AC, Hall D, Applegate B. Influence of irrigant needle depth in removing bioluminescent bacteria inoculated into instrumented root canals using real-time imaging in vitro. Int Endod J 2005;38:97-104.
58.
Hulsmann M, Hahn W. Complications during root canal irrigation--literature review and case reports. Int Endod J 2000;33:186-193.
59.
Witton R, Brennan PA. Severe tissue damage and neurological deficit following extravasation of sodium hypochlorite solution during routine endodontic treatment. Br Dent J 2005;198:749-750.
60.
Kavanagh CP, Taylor J. Inadvertent injection of sodium hypochlorite into the maxillary sinus. Br Dent J 1998;185:336-337.
61.
Joffe E. Complication during root canal therapy following accidental extrusion of sodium hypochlorite through the apical foramen. Gen Dent 1991;39:460-461. 65
62.
Neaverth EJ, Swindle R. A serious complication following the inadvertent injection of sodium hypochlorite outside the root canal system. Compendium 1990;11:474, 476, 478-481.
63.
Kaufman AY. Facial emphysema caused by hydrogen peroxide irrigation: report of a case. J Endod 1981;7:470-472.
64.
Segura-Egea JJ, Jimenez-Rubio A, Rios-Santos JV, Velasco-Ortega E, CalvoGutierrez JR. In vitro inhibitory effect of EGTA on macrophage adhesion: endodontic implications. J Endod 2003;29:211-213.
65.
Gernhardt CR, Eppendorf K, Kozlowski A, Brandt M. Toxicity of concentrated sodium hypochlorite used as an endodontic irrigant. Int Endod J 2004;37:272-280.
66.
Bowden JR, Ethunandan M, Brennan PA. Life-threatening airway obstruction secondary to hypochlorite extrusion during root canal treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:402-404.
67.
Lambrianidis T, Tosounidou E, Tzoanopoulou M. The effect of maintaining apical patency on periapical extrusion. J Endod 2001;27:696-698.
68.
Bradford CE, Eleazer PD, Downs KE, Scheetz JP. Apical pressures developed by needles for canal irrigation. J Endod 2002;28:333-335.
69.
Abbott PV. Medicaments: aids to success in endodontics. Part 1. A review of the literature. Aust Dent J 1990;35:438-448.
70.
Abbott PV. Medicaments: aids to success in endodontics. Part 2. Clinical recommendations. Aust Dent J 1990;35:491-496.
71.
Abbott PV, Hume WR, Pearman JW. Antibiotics and endodontics. Aust Dent J 1990;35:50-60.
72.
Barnard D, Davies J, Figdor D. Susceptibility of Actinomyces israelii to antibiotics, sodium hypochlorite and calcium hydroxide. Int Endod J 1996;29:320-326.
73.
Chong BS, Pitt Ford TR. The role of intracanal medication in root canal treatment. Int Endod J 1992;25:97-106.
74.
Heling I, Sommer M, Steinberg D, Friedman M, Sela MN. Microbiological evaluation of the efficacy of chlorhexidine in a sustained-release device for dentine sterilization. Int Endod J 1992;25:15-19.
75.
Heling I, Steinberg D, Kenig S, Gavrilovich I, Sela MN, Friedman M. Efficacy of a sustained-release device containing chlorhexidine and Ca(OH)2 in preventing secondary infection of dentinal tubules. Int Endod J 1992;25:20-24.
66
76.
Siqueira JF, de Uzeda M. Intracanal medicaments: evaluation of the antibacterial effects of chlorhexidine, metronidazole, and calcium hydroxide associated with three vehicles. J Endod 1997;23:167-169.
77.
Haapasalo HK, Siren EK, Waltimo TM, Orstavik D, Haapasalo MP. Inactivation of local root canal medicaments by dentine: an in vitro study. Int Endod J 2000;33:126-131.
78.
Kim ST, Abbott PV, McGinley P. The effects of Ledermix paste on discolouration of immature teeth. Int Endod J 2000;33:233-237.
79.
Kim ST, Abbott PV, McGinley P. The effects of Ledermix paste on discolouration of mature teeth. Int Endod J 2000;33:227-232.
80.
Siqueira JF, Jr. Aetiology of root canal treatment failure: why well-treated teeth can fail. Int Endod J 2001;34:1-10.
81.
McComb D, Smith DC. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endod 1975;1:238-242.
82.
Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod 1984;10:477-483.
83.
Pallares A, Faus V, Glickman GN. The adaptation of mechanically softened guttapercha to the canal walls in the presence or absence of smear layer: a scanning electron microscopic study. Int Endod J 1995;28:266-269.
84.
Halackova Z, Kukletova M. Rinsing of the root canal. Scr Med (Brno) 2003 76:4954
85.
Hovland EJ, Dumsha TC. Leakage evaluation in vitro of the root canal sealer cement Sealapex. Int Endod J 1985;18:179-182.
86.
Wu MK, Wesselink PR. Endodontic leakage studies reconsidered. Part I. Methodology, application and relevance. Int Endod J 1993;26:37-43.
87.
Cobankara FK, Adanr N, Belli S. Evaluation of the influence of smear layer on the apical and coronal sealing ability of two sealers. J Endod 2004;30:406-409.
88.
Shemesh H, Wu MK, Wesselink PR. Leakage along apical root fillings with and without smear layer using two different leakage models: a two-month longitudinal ex vivo study. Int Endod J 2006;39:968-976.
89.
Timpawat S, Vongsavan N, Messer HH. Effect of removal of the smear layer on apical microleakage. J Endod 2001;27:351-353.
90.
Wu MK, Wesselink PR, Boersma J. A 1-year follow-up study on leakage of four root canal sealers at different thicknesses. Int Endod J 1995;28:185-189. 67
91.
Froes JA, Horta HG, da Silveira AB. Smear layer influence on the apical seal of four different obturation techniques. J Endod 2000;26:351-354.
92.
Fogel HM, Pashley DH. Dentin permeability: effects of endodontic procedures on root slabs. J Endod 1990;16:442-445.
93.
Guerisoli DM, Marchesan MA, Walmsley AD, Lumley PJ, Pecora JD. Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation. Int Endod J 2002;35:418-421.
94.
Torabinejad M, Cho Y, Khademi AA, Bakland LK, Shabahang S. The effect of various concentrations of sodium hypochlorite on the ability of MTAD to remove the smear layer. J Endod 2003;29:233-239.
95.
Torabinejad M, Khademi AA, Babagoli J, Cho Y, Johnson WB, Bozhilov K, et al. A new solution for the removal of the smear layer. J Endod 2003;29:170-175.
96.
Prati C, Foschi F, Nucci C, Montebugnoli L, Marchionni S. Appearance of the root canal walls after preparation with NiTi rotary instruments: a comparative SEM investigation. Clin Oral Investig 2004;8:102-110.
97.
Hulsmann M, Rummelin C, Schafers F. Root canal cleanliness after preparation with different endodontic handpieces and hand instruments: a comparative SEM investigation. J Endod 1997;23:301-306.
98.
Schilke R, Lisson JA, Bauss O, Geurtsen W. Comparison of the number and diameter of dentinal tubules in human and bovine dentine by scanning electron microscopic investigation. Arch Oral Biol 2000;45:355-361.
99.
Absi EG, Addy M, Adams D. Dentine hypersensitivity. The development and evaluation of a replica technique to study sensitive and non-sensitive cervical dentine. J Clin Periodontol 1989;16:190-195.
100.
Teixeira CS, Felippe MCS, Felippe WT. The effect of application time of EDTA and NaOCl on intracanal smear layer removal: an SEM analysis. Int Endod J 2005;38:285-290.
101.
Takeda FH, Harashima T, Kimura Y, Matsumoto K. A comparative study of the removal of smear layer by three endodontic irrigants and two types of laser. Int Endod J 1999;32:32-39.
102.
Wang X, Sun Y, Kimura Y, Kinoshita J, Ishizaki NT, Matsumoto K. Effects of diode laser irradiation on smear layer removal from root canal walls and apical leakage after obturation. Photomed Laser Surg 2005;23:575-581.
68
103.
Nguy D, Sedgley C. The influence of canal curvature on the mechanical efficacy of root canal irrigation in vitro using real-time imaging of bioluminescent bacteria. J Endod 2006;32:1077-1080.
104.
Mikrogeorgis G, Molyvdas I, Lyroudia K, Nikolaidis N, Pitas I. A new methodology for the comparative study of the root canal instrumentation techniques based on digital radiographic image processing and analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;101:e125-131.
105.
De-Deus G, Maniglia-Ferreira CM, Gurgel-Filho ED, Paciornik S, Machado AC, Coutinho-Filho T. Comparison of the percentage of gutta-percha-filled area obtained by Thermafil and System B. Aust Endod J 2007;33:55-61.
106.
Ciocca L, Gallina I, Navacchia E, Baldissara P, Scotti R. A new method for quantitative analysis of dentinal tubules. Comput Biol Med 2007;37:277-286.
107.
Weichman JA, Johnson FM. Laser use in endodontics. A preliminary investigation. Oral Surg Oral Med Oral Pathol 1971;31:416-420.
108.
Weichman JA, Johnson FM, Nitta LK. Laser use in endodontics. II. Oral Surg Oral Med Oral Pathol 1972;34:828-830.
109.
High Tech Laser. Tissue absorption. 2007 [cited 2008 25-Sept]; Available from: http://www.hightechlaser.be/bco/download/en/559132/image/scaletomax-5000/beeld2en.jpg
110.
Hale GM, Querry MR. Optical constants of water in the 200-nm to 200-µm wavelength region. Appl. Opt 1973;12:555-563.
111.
Altshuler GB, Yaroslavsky I. Absorption characteristics of tissues as a basis for the optimal wavelength choice in photodermatology. 2004 [cited 2008 24-Sept]; Available from: http://www.palomarmedical.com/FileUploads/AltshulerAbsorption-4000-0019.pdf
112.
Kane SA. Introduction to physics in modern medicine. London ; New York Talyor & Francis; 2003.
113.
Apostolos Doukas, Lee. S. Transdermal Drug Delivery with Photomechanical Waves.
114.
Tam LE, McComb D. Diagnosis of occlusal caries: Part II. Recent diagnostic technologies. J Can Dent Assoc 2001;67:459-463.
115.
Jimbo K, Noda K, Suzuki K, Yoda K. Suppressive effects of low-power laser irradiation on bradykinin evoked action potentials in cultured murine dorsal root ganglion cells. Neurosci Lett 1998;240:93-96. 69
116.
Wakabayashi H, Hamba M, Matsumoto K, Tachibana H. Effect of irradiation by semiconductor laser on responses evoked in trigeminal caudal neurons by tooth pulp stimulation. Lasers Surg Med 1993;13:605-610.
117.
Masotti L, Muzzi F, Repice F, Paolini C, Fortuna D, Inventors; Devices and methods for biological tissue stimulation by high intensity laser therapy. US patent 20070185552. 2007 Aug.
118.
Poon VK, Huang L, Burd A. Biostimulation of dermal fibroblast by sublethal Qswitched Nd:YAG 532 nm laser: collagen remodeling and pigmentation. J Photochem Photobiol B 2005;81:1-8.
119.
Wilson M. Photolysis of oral bacteria and its potential use in the treatment of caries and periodontal disease. J Appl Bacteriol 1993;75:299-306.
120.
Splinter R, Hooper BA. Light- tissue interaction mechanisms and applications: Photobiology. In: An introduction to biomedical optics. New York: Taylor & Francis; 2007. p. 320-321.
121.
Berlien HP, Müller GJ, Breuer H. Applied laser medicine In: Berlien HP, Müller GJ, editors.: springer; 2003. p. 299.
122.
Stratigos AJ, Alora MB, Urioste S, Dover JS. Cutaneous laser surgery. Curr Probl Dermatol 1998;10:127-172.
123.
Walsh LJ. The current status of laser applications in dentistry. Aust Dent J 2003;48:146-155; quiz 198.
124.
Adams TC, Pang PK. Lasers in aesthetic dentistry. Dent Clin North Am 2004;48:833-860, vi.
125.
Moritz A, Gutknecht N, Doertbudak O, Goharkhay K, Schoop U, Schauer P, et al. Bacterial reduction in periodontal pockets through irradiation with a diode laser: a pilot study. J Clin Laser Med Surg 1997;15:33-37.
126.
Yeh S, Jain K, Andreana S. Using a diode laser to uncover dental implants in second-stage surgery. Gen Dent 2005;53:414-417.
127.
Stabholz A, Zeltser R, Sela M, Peretz B, Moshonov J, Ziskind D, et al. The use of lasers in dentistry: principles of operation and clinical applications. Compend Contin Educ Dent 2003;24:935-948.
128.
Dostalova T, Jelinkova H, Housova D, Sulc J, Nemec M, Miyagi M, et al. Diode laser-activated bleaching. Braz Dent J 2004;15 Spec No:SI3-8.
129.
Lussi A, Hack A, Hug I, Heckenberger H, Megert B, Stich H. Detection of approximal caries with a new laser fluorescence device. Caries Res 2006;40:97-103. 70
130.
Tonioli MB, Bouschlicher MR, Hillis SL. Laser fluorescence detection of occlusal caries. Am J Dent 2002;15:268-273.
131.
Toraman Alkurt M, Peker I, Deniz Arisu H, Bala O, Altunkaynak B. In vivo comparison of laser fluorescence measurements with conventional methods for occlusal caries detection. Lasers Med Sci 2008;23:307-312.
132.
Krause F, Jepsen S, Braun A. Comparison of two laser fluorescence devices for the detection of occlusal caries in vivo. Eur J Oral Sci 2007;115:252-256.
133.
Lussi A, Zimmerli B, Hellwig E, Jaeggi T. Influence of the condition of the adjacent tooth surface on fluorescence measurements for the detection of approximal caries. Eur J Oral Sci 2006;114:478-482.
134.
Virajsilp V, Thearmontree A, Aryatawong S, Paiboonwarachat D. Comparison of proximal caries detection in primary teeth between laser fluorescence and bitewing radiography. Pediatr Dent 2005;27:493-499.
135.
Moritz A, Gutknecht N, Goharkhay K, Schoop U, Wernisch J, Sperr W. In vitro irradiation of infected root canals with a diode laser: results of microbiologic, infrared spectrometric, and stain penetration examinations. Quintessence Int 1997;28:205-209.
136.
Moritz A, Schoop U, Goharkhay K, Schauer P, Doertbudak O, Wernisch J, et al. Treatment of periodontal pockets with a diode laser. Lasers Surg Med 1998;22:302311.
137.
Gutknecht N, Franzen R, Meister J, Vanweersch L, Mir M. Temperature evolution on human teeth root surface after diode laser assisted endodontic treatment. Lasers Med Sci 2005;20:99-103.
138.
Eldeniz AU, Usumez A, Usumez S, Ozturk N. Pulpal temperature rise during lightactivated bleaching. J Biomed Mater Res B Appl Biomater 2005;72:254-259.
139.
van As G. Erbium lasers in dentistry. Dent Clin North Am 2004;48:1017-1059.
140.
Partovi F, Izatt JA, Cothren RM, Kittrell C, Thomas JE, Strikwerda S, et al. A model for thermal ablation of biological tissue using laser radiation. Lasers Surg Med 1987;7:141-154.
141.
Halldorsson T, Langerholc J, Takeda FH. Thermodynamic analysis of laser irradiation of biological tissue. Appl Opt 1978;:39-48.
142.
White JM, Goodis HE, Rose CM. Use of the pulsed Nd:YAG laser for intraoral soft tissue surgery. Lasers Surg Med 1991;11:455-461.
71
143.
Coluzzi DJ. Fundamentals of dental lasers: science and instruments. Dent Clin North Am 2004;48:751-770, v.
144.
Ishikawa I, Sasaki KM, Aoki A, Watanabe H. Effects of Er:YAG laser on periodontal therapy. J Int Acad Periodontol 2003;5:23-28.
145.
Wang Z, Ding Y, Wu Y. [The effect of pulsed Nd:YAG laser used as an adjunct to subgingival scaling and root planning]. Hua Xi Kou Qiang Yi Xue Za Zhi 2003;21:292-294.
146.
Sjostrom L, Friskopp J. Laser treatment as an adjunct to debridement of periodontal pockets. Swed Dent J 2002;26:51-57.
147.
Cobb CM. Lasers in periodontics: a review of the literature. J Periodontol 2006;77:545-564.
148.
Whitters CJ, Hall A, Creanor SL, Moseley H, Gilmour WH, Strang R, et al. A clinical study of pulsed Nd: YAG laser-induced pulpal analgesia. J Dent 1995;23:145-150.
149.
Orchardson R, Peacock JM, Whitters CJ. Effect of pulsed Nd:YAG laser radiation on action potential conduction in isolated mammalian spinal nerves. Lasers Surg Med 1997;21:142-148.
150.
Renton-Harper P, Midda M. Nd:YAG laser treatment of dentinal hypersensitivity. Br Dent J 1992;172:13–16.
151.
Amyra T, Walsh LT, Walsh LJ. An assessment of techniques for dehydrating root canals using infrared laser radiation. Aust Endod J 2000;26:78-80.
152.
Lee BS, Lin CP, Lin FH, Li UM, Lan WH. Effect of Nd:YAG laser irradiation on the hardness and elastic modulus of human dentin. J Clin Laser Med Surg 2003;21:41-46.
153.
Koba K. Pulsed Nd:YAG laser application to one visit treatment of infected root canals-histopathological and clinical examination. Jpn Endodontic assoc 1995;16:20-27.
154.
Yamada Y, Hossain M, Nakamura Y, Suzuki N, Matsumoto K. Comparison between the removal effect of mechanical, Nd:YAG, and Er:YAG laser systems in carious dentin. J Clin Laser Med Surg 2001;19:239-243.
155.
Fegan SE, Steiman HR. Comparative evaluation of the antibacterial effects of intracanal Nd:YAG laser irradiation: an in vitro study. J Endod 1995;21:415-417.
156.
Folwaczny M, Mehl A, Jordan C, Hickel R. Antibacterial effects of pulsed Nd:YAG laser radiation at different energy settings in root canals. J Endod 2002;28:24-29. 72
157.
Goodis H, White JM, Moskowitz E, Marshall S. Root canal system preparation: Conventional versus laser method -in vitro. J Dent Res 1992;71:162.
158.
Harashima T, Takeda FH, Kimura Y, Matsumoto K. Effect of Nd:YAG laser irradiation for removal of intracanal debris and smear layer in extracted human teeth. J Clin Laser Med Surg 1997;15:131-135.
159.
Depraet FJHW, De Bruyne MAA, De Moor RJG. The sealing ability of an epoxy resin root canal sealer after Nd:YAG laser irradiation of the root canal. Int Endod J 2005;38:302-309.
160.
Piccolomini R, D'Arcangelo C, D'Ercole S, Catamo G, Schiaffino G, De Fazio P. Bacteriologic evaluation of the effect of Nd:YAG laser irradiation in experimental infected root canals. J Endod 2002;28:276-278.
161.
Anic I, Matsumoto K. Dentinal heat transmission induced by a laser-softened guttapercha obturation technique. J Endod 1995;21:470-474.
162.
Anic I, Matsumoto K. Comparison of the sealing ability of laser-softened, laterally condensed and low-temperature thermoplasticized gutta-percha. J Endod 1995;21:464-469.
163.
Anjo T, Ebihara A, Takeda A, Takashina M, Sunakawa M, Suda H. Removal of two types of root canal filling material using pulsed Nd:YAG laser irradiation. Photomed Laser Surg 2004;22:470-476.
164.
Bahcall J, Howard P, Miserendino L, Walia H. Preliminary investigation of the histological effects of laser endodontic treatment on the periradicular tissues in dogs. J Endod 1992;18:47-51.
165.
Tani Y, Kawada H. Effects of laser irradiation on dentin. I. Effect on smear layer. Dent Mater J 1987;6:127-134.
166.
Matsumoto K. Lasers in endodontics. Dent Clin North Am 2000;44:889-906, viii.
167.
Leo J Miserendino, Robert MP. Lasers in dentistry. Quintessence’s publication co, Inc; 1995.
168.
Stevens BH, Trowbridge HO, Harrison G, Silverton SF. Dentin ablation by Ho: YAG laser: correlation of energy versus volume using stereophotogrammetry. J Endod 1994;20:246-249.
169.
Cohen BI, Deutsch AS, Musikant BL. Effect of power settings on temperature change at the root surface when using a Holmium YAG laser in enlarging the root canal. J Endod 1996;22:596-599.
73
170.
Goodis HE, White JM, Marshall GW, Jr., Yee K, Fuller N, Gee L, et al. Effects of Nd: and Ho:yttrium-aluminium-garnet lasers on human dentine fluid flow and dental pulp-chamber temperature in vitro. Arch Oral Biol 1997;42:845-854.
171.
Cohen BI, Deutsch AS, Musikant BL, Pagnillo MK. Effect of power settings versus temperature change at the root surface when using multiple fiber sizes with a Holmium YAG laser while enlarging a root canal. J Endod 1998;24:802-806.
172.
Moritz A, Schoop U, Goharkhay K, Jakolitsch S, Kluger W, Wernisch J, et al. The bactericidal effect of Nd:YAG, Ho:YAG, and Er:YAG laser irradiation in the root canal: an in vitro comparison. J Clin Laser Med Surg 1999;17:161-164.
173.
Gutknecht N, Nuebler-Moritz M, Burghardt SF, Lampert F. The efficiency of root canal disinfection using a holmium:yttrium-aluminum-garnet laser in vitro. J Clin Laser Med Surg 1997;15:75-78.
174.
Komori T, Yokoyama K, Matsumoto Y, Matsumoto K. Erbium:YAG and holmium:YAG laser root resection of extracted human teeth. J Clin Laser Med Surg 1997;15:9-13.
175.
Michael Nuebler-Moritz, Norbert G, Hermann FS, Peter H, Wilhelm P. Laboratory investigation of the efficacy of holmium:YAG laser irradiation in removing intracanal debris. In: Harvey A, Wigdor., John D, Featherstone., Peter R, editors. Lasers in Dentistry III. SPIE; 1997 May p. 150-156.
176.
Zezell DM, Cecchini SC, Eduardo CP, Matsumoto K, De Rossi W, Nogueira GE, et al. Experimental studies of the applications of the holmium laser in dentistry. J Clin Laser Med Surg 1995;13:283-289.
177.
Coluzzi DJ. Fundamentals of dental lasers: science and instruments. Dent Clin North Am 2004;48:751-770.
178.
Hibst R, Keller U. Experimental studies of the application of the Er:YAG laser on dental hard substances: I. Measurement of the ablation rate. Lasers Surg Med 1989;9:338-344.
179.
Nelson JS, Yow L, Liaw LH, Macleay L, Zavar RB, Orenstein A, et al. Ablation of bone and methacrylate by a prototype mid-infrared erbium:YAG laser. Lasers Surg Med 1988;8:494-500.
180.
Walsh LJ. The current status of laser applications in dentistry. Aust Dent J 2003;48:146-155.
181.
Loertscher H, Shi WQ, Grundfest WS. Tissue ablation through water with erbium:YAG lasers. IEEE Trans Biomed Eng 1992;39:86-88. 74
182.
Hadley J, Young DA, Eversole LR, Gornbein JA. A laser-powered hydrokinetic system for caries removal and cavity preparation. J Am Dent Assoc 2000;131:777785.
183.
Rizoiu I, Kohanghadosh F, Kimmel AI, Eversole LR. Pulpal thermal responses to an erbium,chromium: YSGG pulsed laser hydrokinetic system. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;86:220-223.
184.
Kimmel AI, Rizoiu IM, Eversole LR. Phase doppler particle analysis of laser energized exploding water droplets. In: International Laser Congress. Athens,Greece: (abstract 67); 1996.
185.
Riziou I, Kimmel A, Inventors; Atomized fluid particles for electromagnetically induced cutting. US patent 5,741,247. 1998.
186.
Freiberg RJ, Cozean C. Pulse erbium laser ablation of hard dental tissue: the effects of atomised water spray vs. water surface film. In; 2002: SPIE; 2002. p. 74-84.
187.
Pelagalli J, Gimbel CB, Hansen RT, Swett A, Winn DW, 2nd. Investigational study of the use of Er:YAG laser versus dental drill for caries removal and cavity preparation--phase I. J Clin Laser Med Surg 1997;15:109-115.
188.
Grgurevic J, Grgurevic L, Miletic I, Karlovic Z, Krmek SJ, Anic I. In vitro study of the variable square pulse Er:YAG laser cutting efficacy for apicectomy. Lasers Surg Med 2005;36:347-350.
189.
Truong M, Majaron B, Pendoh N. Erbium:YAG laser contouring of the nasal sorsum: a preliminary investigation. SPIE 2001;4244:113–120.
190.
Walsh JT, Jr., Flotte TJ, Deutsch TF. Er:YAG laser ablation of tissue: effect of pulse duration and tissue type on thermal damage. Lasers Surg Med 1989;9:314326.
191.
Romano V. Bone microsurgery with IR lasers: a comparative study of the thermal action at different wavelengths. Proc SPIE 1994;2077:87-97.
192.
Shori R, Walston A. Quantification and modeling of the dynamic changes in the absorption coefficient of water at 2.94 lm. . IEEE J Sel Top Quantum Electron 2001;7:959-970.
193.
Sasaki KM, Aoki A, Ichinose S, Yoshino T, Yamada S, Ishikawa I. Scanning electron microscopy and Fourier transformed infrared spectroscopy analysis of bone removal using Er:YAG and CO2 lasers. J Periodontol 2002;73:643-652.
75
194.
Kimura Y, Yu DG, Fujita A, Yamashita A, Murakami Y, Matsumoto K. Effects of erbium,chromium:YSGG laser irradiation on canine mandibular bone. J Periodontol 2001;72:1178-1182.
195.
Matsuoka E, Yonaga K, Kinoshita J, Kimura Y, Matsumoto K. Morphological study on the capability of Er:YAG laser irradiation for root canal preparation. J Clin Laser Med Surg 2000;18:215-219.
196.
Matsuoka E, Jayawardena JA, Matsumoto K. Morphological study of the Er,Cr:YSGG laser for root canal preparation in mandibular incisors with curved root canals. Photomed Laser Surg 2005;23:480-484.
197.
Jahan K, Hossain M, Nakamura Y, Yoshishige Y, Kinoshita J-I, Matsumoto K. An assessment following root canal preparation by Er,Cr:YSGG laser irradiation in straight and curved roots, in vitro. Lasers Med Sci 2006;21:229-234.
198.
Shoji S, Hariu H, Horiuchi H. Canal enlargement by Er:YAG laser using a coneshaped irradiation tip. J Endod 2000;26:454-458.
199.
Takeda FH, Harashima T, Kimura Y, Matsumoto K. Comparative study about the removal of smear layer by three types of laser devices. J Clin Laser Med Surg 1998;16:117-122.
200.
Moshonov J, Sion A, Kasirer J, Rotstein I, Stabholz A. Efficacy of argon laser irradiation in removing intracanal debris. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:221-225.
201.
Matsuoka E, Kimura Y, Matsumoto K. Studies on the removal of debris near the apical seats by Er:YAG laser and assessment with a fiberscope. J Clin Laser Med Surg 1998;16:255-261.
202.
Yamazaki R, Goya C, Yu DG, Kimura Y, Matsumoto K. Effects of erbium,chromium:YSGG laser irradiation on root canal walls: a scanning electron microscopic and thermographic study. J Endod 2001;27:9-12.
203.
De Souza FD, Pecora JD, Silva RG. The effect on coronal leakage of liquid adhesive application over root fillings after smear layer removal with EDTA or Er:YAG laser. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:125128.
204.
Altundasar E, Ozcelik B, Cehreli ZC, Matsumoto K. Ultramorphological and histochemical changes after Er,Cr:YSGG laser irradiation and two different irrigation regimes. J Endod 2006;32:465-468.
76
205.
Schoop U, Moritz A, Kluger W, Patruta S, Goharkhay K, Sperr W, et al. The Er:YAG laser in endodontics: results of an in vitro study. Lasers Surg Med 2002;30:360-364.
206.
Schoop U, Kluger W, Moritz A, Nedjelik N, Georgopoulos A, Sperr W. Bactericidal effect of different laser systems in the deep layers of dentin. Lasers Surg Med 2004;35:111-116.
207.
Perin FM, Franca SC, Silva-Sousa YT, Alfredo E, Saquy PC, Estrela C, et al. Evaluation of the antimicrobial effect of Er:YAG laser irradiation versus 1% sodium hypochlorite irrigation for root canal disinfection. Aust Endod J 2004;30:20-22.
208.
Leonardo MR, Guillen-Carias MG, Pecora JD, Ito IY, Silva LA. Er:YAG laser: antimicrobial effects in the root canals of dogs' teeth with pulp necrosis and chronic periapical lesions. Photomed Laser Surg 2005;23:295-299.
209.
Wang QQ, Zhang CF, Yin XZ. Evaluation of the bactericidal effect of Er,Cr:YSGG, and Nd:YAG lasers in experimentally infected root canals. J Endod 2007;33:830832.
210.
Ishizaki NT, Matsumoto K, Kimura Y, Wang X, Kinoshita J, Okano SM, et al. Thermographical and morphological studies of Er,Cr:YSGG laser irradiation on root canal walls. Photomed Laser Surg 2004;22:291-297.
211.
Schoop U, Barylyak A, Goharkhay K, Beer F, Wernisch J, Georgopoulos A, et al. The impact of an erbium, chromium:yttrium-scandium-gallium-garnet laser with radial-firing tips on endodontic treatment. Lasers Med Sci 2007.
212.
Kimura Y, Yonaga K, Yokoyama K, Kinoshita J, Ogata Y, Matsumoto K. Root surface temperature increase during Er:YAG laser irradiation of root canals. J Endod 2002;28:76-78.
213.
Lee BS, Jeng JH, Lin CP, Shoji S, Lan WH. Thermal effect and morphological changes induced by Er:YAG laser with two kinds of fiber tips to enlarge the root canals. Photomed Laser Surg 2004;22:191-197.
214.
Mir M, Meister J, Franzen R, Sabounchi SS, Lampert F, Gutknecht N. Influence of water-layer thickness on Er:YAG laser ablation of enamel of bovine anterior teeth. Lasers Med Sci 2007.
215.
Meister J, Apel C, Franzen R, Gutknecht N. Influence of the spatial beam profile on hard tissue ablation. Part I: Multimode emitting Er:YAG lasers. Lasers Med Sci 2003;18:112-118.
77
216.
Apel C, Franzen R, Meister J, Sarrafzadegan H, Thelen S, Gutknecht N. Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel. Lasers Med Sci 2002;17:253-257.
217.
Khabbaz MG, Makropoulou MI, Serafetinides AA, Papadopoulos D, Papagiakoumou E. Q-switched versus free-running Er:YAG laser efficacy on the root canal walls of human teeth: a SEM study. J Endod 2004;30:585-588.
218.
Fried D, Ashouri N, Breunig T, Shori R. Mechanism of water augmentation during IR laser ablation of dental enamel. Lasers Surg Med 2002;31:186-193.
219.
Visuri SR, Walsh JT, Jr., Wigdor HA. Erbium laser ablation of dental hard tissue: effect of water cooling. Lasers Surg Med 1996;18:294-300.
220.
Stopp S, Svejdar D, Deppe H, Lueth TC. A new method for optimized laser treatment by laser focus navigation and distance visualization. Conf Proc IEEE Eng Med Biol Soc 2007;2007:1738-1741.
221.
Kim ME, Jeoung DJ, Kim KS. Effects of water flow on dental hard tissue ablation using Er:YAG laser. J Clin Laser Med Surg 2003;21:139-144.
222.
Shigetani Y, Okamoto A, Abu-Bakr N, Iwaku M. A study of cavity preparation by Er:YAG laser--observation of hard tooth structures by laser scanning microscope and examination of the time necessary to remove caries. Dent Mater J 2002;21:2031.
223.
Gopikrishna V, Tinagupta K, Kandaswamy D. Comparison of electrical, thermal, and pulse oximetry methods for assessing pulp vitality in recently traumatized teeth. J Endod 2007;33:531-535.
224.
Kimura Y, Wilder-Smith P, Matsumoto K. Lasers in endodontics: a review. Int Endod J 2000;33:173-185.
225.
Notzli HP, Swiontkowski MF, Thaxter ST, Carpenter GK, 3rd, Wyatt R. Laser Doppler flowmetry for bone blood flow measurements: helium-neon laser light attenuation and depth of perfusion assessment. J Orthop Res 1989;7:413-424.
226.
Micheels J, Alsbjorn B, Sorensen B. Laser doppler flowmetry. A new non-invasive measurement of microcirculation in intensive care? Resuscitation 1984;12:31-39.
227.
Watson AD, Pitt Ford TR, McDonald F. Blood flow changes in the dental pulp during limited exercise measured by laser Doppler flowmetry. Int Endod J 1992;25:82-87.
228.
Vongsavan N, Matthews B. Some aspects of the use of laser Doppler flow meters for recording tissue blood flow. Exp Physiol 1993;78:1-14. 78
229.
Vongsavan N, Matthews B. Experiments on extracted teeth into the validity of using laser Doppler techniques for recording pulpal blood flow. Arch Oral Biol 1993;38:431-439.
230.
Zang D, Millerd J, Wilder-Smith P, Arrastia A. A novel laser Doppler flowmeter for pulpal blood flow measurements. Proceedings SPIE 1996;2672:21-26.
231.
Lee JY, Yanpiset K, Sigurdsson A, Vann WF, Jr. Laser Doppler flowmetry for monitoring traumatized teeth. Dent Traumatol 2001;17:231-235.
232.
Walsh LJ. The current status of low level laser therapy in dentistry. Part 1. Soft tissue applications. Aust Dent J 1997;42:247-254.
233.
Hibst R, Paulus R. Molecular basis of red excited caries fluorescence. Caries Res 2000;34:308-360.
234.
Kishen A, Asundi A. Fundamentals and applications of biophotonics in dentistry,pages 93-121. In: Series on biomaterials and bioengineering London: Imperial College Press; 2007. p. 93-121.
235.
Pini R, Salimbeni R, Vannini M, Cavalieri S, Barone R, Clauser C. Laser dentistry: root canal diagnostic technique based on ultraviolet-induced fluorescence spectroscopy. Lasers Surg Med 1989;9:358-361.
236.
Sarkissian A, Le AN. Fiber optic fluorescence microprobe for endodontic diagnosis. J Dent Educ 2005;69:633-638.
237.
Koenig K, Hibst R, Meyer H, Flemming G, Schnecken-Burger H. Laser induced autofluorescence of carious regions of human teeth and caries-involved bacteria. Proc SPIE 2080. Bellingham, WA:SPIE 1993;2080:170-180.
238.
Hibst R, Gall R, Klafke M, Inventors; Kaltenbach & Voigt GmbH & Co, assignee. Device for the recognition of caries, plaque or bacterial infection on teeth US patent 6024562. 2000 Feb.
239.
Sainsbury AL. Laser fluorescence analysis of the root canal system [Thesis (M D Sc )]. St. Lucia, Qld: University of Queensland; 2005.
240.
Srinivasan V, Patchett CL, Waterhouse PJ. Is there life after Buckley's Formocresol? Part I -- a narrative review of alternative interventions and materials. Int J Paediatr Dent 2006;16:117-127.
241.
Tsai TP, Su HL, Tseng LH. Glutaraldehyde preparations and pulpotomy in primary molars. Oral Surg Oral Med Oral Pathol 1993;76:346-350.
242.
Rusmah M. Glutaraldehyde in dentistry--a review. Singapore Dent J 1993;18:17-21.
79
243.
Ng FK, Messer LB. Mineral trioxide aggregate as a pulpotomy medicament: An evidence-based assessment. Eur Arch Paediatr Dent 2008;9:58-73.
244.
Huth KC, Paschos E, Hajek-Al-Khatar N, Hollweck R, Crispin A, Hickel R, et al. Effectiveness of 4 pulpotomy techniques--randomized controlled trial. J Dent Res 2005;84:1144-1148.
245.
Saltzman B, Sigal M, Clokie C, Rukavina J, Titley K, Kulkarni GV. Assessment of a novel alternative to conventional formocresol-zinc oxide eugenol pulpotomy for the treatment of pulpally involved human primary teeth: diode laser-mineral trioxide aggregate pulpotomy. Int J Paediatr Dent 2005;15:437-447.
246.
Wilkerson MK, Hill SD, Arcoria CJ. Effects of the argon laser on primary tooth pulpotomies in swine. J Clin Laser Med Surg 1996;14:37-42.
247.
Liu JF. Effects of Nd:YAG laser pulpotomy on human primary molars. J Endod 2006;32:404-407.
248.
Jukic S, Anic I, Koba K, Najzar-Fleger D, Matsumoto K. The effect of pulpotomy using CO2 and Nd:YAG lasers on dental pulp tissue. Int Endod J 1997;30:175-180.
249.
Shoji S, Nakamura M, Horiuchi H. Histopathological changes in dental pulps irradiated by CO2 laser: a preliminary report on laser pulpotomy. J Endod 1985;11:379-384.
250.
Walsh LJ. Clinical evaluation of dental hard tissue applications of carbon dioxide lasers. J Clin Laser Med Surg 1994;12:11-15.
251.
Moritz A, Schoop U, Goharkhay K, Sperr W. The CO2 laser as an aid in direct pulp capping. J Endod 1998;24:248-251.
252.
Jayawardena JA, Kato J, Moriya K, Takagi Y. Pulpal response to exposure with Er:YAG laser. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:222229.
253.
Dabrowska E, Zdanowicz-Wiloch J, Pawinska-Magnuszewska M, Stokowska W. Intravital treatment of the pulp with simultaneous laser biostimulation. Rocz Akad Med Bialymst 1997;42:168-176.
254.
Levy G. Cleaning and shaping the root canal with a Nd:YAG laser beam: A comparative study. J Endod 1992;18:123-127.
255.
Ali MN, Hossain M, Nakamura Y, Matsuoka E, Kinoshita J, Matsumoto K. Efficacy of root canal preparation by Er,Cr:YSGG laser irradiation with crowndown technique in vitro. Photomed Laser Surg 2005;23:196-201.
80
256.
Deutsch AS, Cohen BI, Musikant BL. Temperature change at the root surface when enlarging a root canal with a holmium: YAG (Ho:YAG) laser, using six different fiber-optic sizes. Gen Dent 2004;52:222-227.
257.
Anic I, Segovic S, Katanec D, Prskalo K, Najzar-Fleger D. Scanning electron microscopic study of dentin lased with argon, CO2, and Nd:YAG laser. J Endod 1998;24:77-81.
258.
Martin. Comparison of the emission characteristics of three erbium laser systems-A physical case report. J Oral Laser Appl 2004;4 263-269.
259.
Rudolf M Verdaasdonkz, Christiaan F P vanSwol. Laser light delivery systems for medical applications. Phys Med Biol 1997;42:869-894.
260.
Alves PR, Aranha N, Alfredo E, Marchesan MA, Brugnera Junior A, Sousa-Neto MD. Evaluation of hollow fiberoptic tips for the conduction of Er:YAG laser. Photomed Laser Surg 2005;23:410-415.
261.
Shirk GJ, Gimpelson RJ, Krewer K. Comparison of tissue effects with sculptured fiberoptic cables and other Nd:YAG laser and argon laser treatments. Lasers Surg Med 1991;11:563-568.
262.
Stabholz A, Neev J, Liaw LH, Stabholz A, Khayat A, Torabinejad M. Effect of ArF-193 nm excimer laser on human dentinal tubules. A scanning electron microscopic study. Oral Surg Oral Med Oral Pathol 1993;75:90-94.
263.
Harashima T, Takeda FH, Zhang C, Kimura Y, Matsumoto K. Effect of argon laser irradiation on instrumented root canal walls. Endod Dent Traumatol 1998;14:26-30.
264.
Tewfik HM, Pashley DH, Horner JA, Sharawy MM. Structural and functional changes in root dentin following exposure to KTP/532 laser. J Endod 1993;19:492497.
265.
Kesler G, Gal R, Kesler A, Koren R. Histological and scanning electron microscope examination of root canal after preparation with Er:YAG laser microprobe: a preliminary in vitro study. J Clin Laser Med Surg 2002;20:269-277.
266.
Takeda FH, Harashima T, Kimura Y, Matsumoto K. Efficacy of Er:YAG laser irradiation in removing debris and smear layer on root canal walls. J Endod 1998;24:548-551.
267.
da Costa Ribeiro A, Nogueira GE, Antoniazzi JH, Moritz A, Zezell DM. Effects of diode laser (810 nm) irradiation on root canal walls: thermographic and morphological studies. J Endod 2007;33:252-255.
81
268.
Kaitsas V, Signore A, Fonzi L, Benedicenti S, Barone M. Effects of Nd: YAG laser irradiation on the root canal wall dentin of human teeth: a SEM study. Bull Group Int Rech Sci Stomatol Odontol 2001;43:87-92.
269.
Goya C, Yamazaki R, Tomita Y, Kimura Y, Matsumoto K. Effects of pulsed Nd:YAG laser irradiation on smear layer at the apical stop and apical leakage after obturation. Int Endod J 2000;33:266-271.
270.
Wilder-Smith P, Arrastia AM, Schell MJ, Liaw LH, Grill G, Berns MW. Effect of ND:YAG laser irradiation and root planing on the root surface: structural and thermal effects. J Periodontol 1995;66:1032-1039.
271.
Takeda FH, Harashima T, Eto JN, Kimura Y, Matsumoto K. Effect of Er:YAG laser treatment on the root canal walls of human teeth: an SEM study. Endod Dent Traumatol 1998;14:270-273.
272.
Biedma BM, Varela Patino P, Park SA, Barciela Castro N, Magan Munoz F, Gonzalez Bahillo JD, et al. Comparative study of root canals instrumented manually and mechanically, with and without Er:YAG laser. Photomed Laser Surg 2005;23:465-469.
273.
Klinke T, Klimm W, Gutknecht N. Antibacterial effects of Nd:YAG laser irradiation within root canal dentin. J Clin Laser Med Surg 1997;15:29-31.
274.
Lee MT, Bird PS, Walsh LJ. Photo-activated disinfection of the root canal: a new role for lasers in endodontics. Aust Endod J 2004;30:93-98.
275.
Wilson M, Dobson J, Sarkar S. Sensitization of periodontopathogenic bacteria to killing by light from a low-power laser. Oral Microbiol Immunol 1993;8:182-187.
276.
Stabholz A, Kettering J, Neev J, Torabinejad M. Effects of the XeCl excimer laser on Streptococcus mutans. J Endod 1993;19:232-235.
277.
Blum JY, Michailesco P, Abadie MJ. An evaluation of the bactericidal effect of the Nd:YAP laser. J Endod 1997;23:583-585.
278.
Gomi K, Kobayashi S, Nakano M. The effects of Er and Nd-YAG laser on disinfection for infected root canals. Jap. J. Cons. Dent 1997;40:800-806.
279.
Theodoro LH, Haypek P, Bachmann L, Garcia VG, Sampaio JE, Zezell DM, et al. Effect of ER:YAG and diode laser irradiation on the root surface: morphological and thermal analysis. J Periodontol 2003;74:838-843.
280.
Bachmann L, Diebolder R, Hibst R, Zezell DM. Changes in chemical composition and collagen structure of dentine tissue after erbium laser irradiation. Spectrochim Acta A Mol Biomol Spectrosc 2005;61:2634-2639. 82
281.
Turkmen C, Gunday M, Karacorlu M, Basaran B. Effect of CO2, Nd:YAG, and ArF excimer lasers on dentin morphology and pulp chamber temperature: an in vitro study. J Endod 2000;26:644-648.
282.
Wilson M, Wilson H, Inventors; patent number 5,611,793, assignee. Laser treatment. US. 1997.
283.
Burns T, Wilson M, Pearson GJ. Sensitisation of cariogenic bacteria to killing by light from a helium-neon laser. J Med Microbiol 1993;38:401-405.
284.
Wilson M, Burns T, Pearson G. Effects of pH on PDT in bacteria associated with dental caries. J Dent 1994;22:273 - 278.
285.
Wilson M, Burns T, Pratten J, Pearson G. Bacteria in supra-gingival plaque samples can be killed by low power laser light in the presence of photo-sensitiser. J Appl Bacteriol 1995;78:569-574.
286.
Burns T, Wilson M, Pearson GJ. Effect of dentine and collagen on the lethal photosensitization of Streptococcus mutans. Caries Res 1995;29:192-197.
287.
Wilson M, Pratten J. Lethal photosensitisation of Staphylococcus aureus in vitro: effect of growth phase, serum, and pre-irradiation time. Lasers Surg Med 1995;16:272-276.
288.
Bonsor SJ, Pearson GJ. Current clinical applications of photo-activated disinfection in restorative dentistry. Dent Update 2006;33:143-144, 147-150, 153.
289.
Silbert T, Bird P, Milburn G, Walsh L. Disinfection of root canals by laser dye photosensitization. J Dent Res 2000;79 569.
290.
Lee M. Photoactivated disinfection of E. faecalis in root canals using lasers. Brisbane: The University of Queensland, St Lucia; 2003.
291.
Dickers B, Lamard L, Peremans A, Geerts S, Lamy M, Limme M, et al. Temperature rise during photo-activated disinfection of root canals. Lasers Med Sci 2007:1-5.
292.
D'Ercole S, D'Arcangelo C, Catamo G, Prosperi GD, Tripodi D, Pasquantonio G, et al. Microbiological study and scanning electron microscopic analysis of root canal wall dentin following pumped Diodium Nd:YAG laser irradiation. New Microbiol 2004;27:55-63.
293.
Jha D, Guerrero A, Ngo T, Helfer A, Hasselgren G. Inability of laser and rotary instrumentation to eliminate root canal infection. J Am Dent Assoc 2006;137:67-70.
294.
Tam G. Low power laser therapy and analgesic action. J Clin Laser Med Surg 1999;17:29-33. 83
295.
Simunovic Z. Low level laser therapy with trigger points technique: a clinical study on 243 patients. J Clin Laser Med Surg 1996;14:163-167.
296.
Simunovic Z, Trobonjaca T, Trobonjaca Z. Treatment of medial and lateral epicondylitis-tennis and golfer's elbow-with low level laser therapy: a multicenter double blind, placebo-controlled clinical study on 324 patients. J Clin Laser Med Surg 1998;16:145-151.
297.
Viducic D, Jukic S, Karlovic Z, Bozic Z, Miletic I, Anic I. Removal of gutta-percha from root canals using an Nd:YAG laser. Int Endod J 2003;36:670-673.
298.
Yu DG, Kimura Y, Tomita Y, Nakamura Y, Watanabe H, Matsumoto K. Study on removal effects of filling materials and broken files from root canals using pulsed Nd:YAG laser. J Clin Laser Med Surg 2000;18:23-28.
299.
Kantola S. Laser-induced effects on tooth structure. VII. X-ray diffraction study of dentine exposed to a CO2 laser. Acta Odontol Scand 1973;31:381-386.
300.
Arakawa S, Cobb CM, Rapley JW, Killoy WJ, Spencer P. Treatment of root fracture by CO2 and Nd:YAG lasers: an in vitro study. J Endod 1996;22:662-667.
301.
Levy GC, Koubi GF. An experimental technique to repair cracked teeth using calcium phosphate, melted by a laser beam: an in vitro evaluation. Compendium 1993;14:1444, 1446, 1448-1452; quiz 1452.
302.
Lin CP, Lin FH, Tseng YC, Kok SH, Lan WH, Liao JD. Treatment of tooth fracture by medium energy CO2 laser and DP-bioactive glass paste: compositional, structural, and phase changes of DP-bioglass paste after irradiation by CO2 laser. Biomaterials 2000;21:637-643.
303.
Stoker MR. Basic principles of lasers. Anaesthesia & intensive care medicine 2005;6:402-404.
304.
Hardee MW, Miserendino LJ, Kos W, Walia H. Evaluation of the antibacterial effects of intracanal Nd:YAG laser irradiation. J Endod 1994;20:377-380.
305.
Dutch Working party Infection Prevention (WIP). Infection prevention when using laser instruments [website] Dec 2003 [cited 2007 Nov]; WIP:[Available from: www.wip.nl
306.
Piccione PJ. Dental laser safety. Dent Clin North Am 2004;48:795-807, v.
307.
Andersen E, Aars H, Brodin P. Effects of cooling and heating of the tooth on pulpal blood flow in man. Endod Dent Traumatol 1994;10:256-259.
308.
Nyborg H, Brannstrom M. Pulp reaction to heat. J Prosthet Dent 1968;19:605-612.
84
309.
Zach L, Cohen G. Pulp Response to Externally Applied Heat. Oral Surg Oral Med Oral Pathol 1965;19:515-530.
310.
Powell GL, Morton TH, Whisenant BK. Argon laser oral safety parameters for teeth. Lasers Surg Med 1993;13:548-552.
311.
Armengol V, Jean A, Marion D. Temperature rise during Er:YAG and Nd:YAP laser ablation of dentin. J Endod 2000;26:138-141.
312.
Glockner K, Rumpler J, Ebeleseder K, Stadtler P. Intrapulpal temperature during preparation with the Er:YAG laser compared to the conventional burr: an in vitro study. J Clin Laser Med Surg 1998;16:153-157.
313.
Capelli A, Guerisoli DM, Barbin EL, Spano JC, Pecora JD. In vitro evaluation of the thermal alterations on the root surface during preparation with different Ni-Ti rotary instruments. Braz Dent J 2004;15:115-118.
314.
Eriksson JH, Sundstrom F. Temperature rise during root canal preparation--a possible cause of damage to tooth and periodontal tissue. Swed Dent J 1984;8:217223.
315.
Walters JD, Rawal SY. Severe periodontal damage by an ultrasonic endodontic device: a case report. Dent Traumatol 2007;23:123-127.
316.
Barkhordar RA, Goodis HE, Watanabe L, Koumdjian J. Evaluation of temperature rise on the outer surface of teeth during root canal obturation techniques. Quintessence Int 1990;21:585-588.
317.
Bailey GC, Cunnington SA, Ng YL, Gulabivala K, Setchell DJ. Ultrasonic condensation of gutta-percha: the effect of power setting and activation time on temperature rise at the root surface - an in vitro study. Int Endod J 2004;37:447-454.
318.
Lee FS, Van Cura JE, BeGole E. A comparison of root surface temperatures using different obturation heat sources. J Endod 1998;24:617-620.
319.
Weller RN, Koch KA. In vitro radicular temperatures produced by injectable thermoplasticized gutta-percha. Int Endod J 1995;28:86-90.
320.
Eriksson AR, Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury: a vital-microscopic study in the rabbit. J Prosthet Dent 1983;50:101107.
321.
Gutknecht N, Kaiser F, Hassan A, Lampert F. Long-term clinical evaluation of endodontically treated teeth by Nd:YAG lasers. J Clin Laser Med Surg 1996;14:711.
85
322.
Machida T, Mazeki K, Narushima K, Matsumoto K. Study on temperature raising in tooth structure at irradiating Er:YAG laser. J Jpn Endod Assoc 1996;17:38-40.
323.
Machida T, Wilder-Smith P, Arrastia AM, Liaw LH, Berns MW. Root canal preparation using the second harmonic KTP:YAG laser: a thermographic and scanning electron microscopic study. J Endod 1995;21:88-91.
324.
Nammour S, Kowaly K, Powell GL, Van Reck J, Rocca JP. External temperature during KTP-Nd:YAG laser irradiation in root canals: an in vitro study. Lasers Med Sci 2004;19:27-32.
325.
Sauk JJ, Norris K, Foster R, Moehring J, Somerman MJ. Expression of heat stress proteins by human periodontal ligament cells. J Oral Pathol 1988;17:496-499.
326.
Moriyama EH, Zangaro RA, Lobo PD, Villaverde AB, Pacheco MT, Watanabe IS, et al. Optothermal transfer simulation in laser-irradiated human dentin. J Biomed Opt 2003;8:298-302.
327.
Baillie J. The endoscope. Gastrointest Endosc 2007;65:886-893.
328.
Harrington JA. A review of IR transmitting, hollow waveguides. Fiber Integr. Opt. 2000;19:211-227.
329.
Verdaasdonk RM, van Swol CF. Laser light delivery systems for medical applications. Phys Med Biol 1997;42:869-894.
330.
Cossmann PH, Romano V, Sporri S, Altermatt HJ, Croitoru N, Frenz M, et al. Plastic hollow waveguides: properties and possibilities as a flexible radiation delivery system for CO2-laser radiation. Lasers Surg Med 1995;16:66-75.
331.
Poulain M. Fluoride glass fibers: applications and prospects. In: Mohammed S, editor. Infrared Glass Optical Fibers and Their Applications; 1998: SPIE 1998. p. 212.
332.
Gambling WA. The rise and rise of optical fibers. Journal on selected topics in quantum electronics November/December 2000; 6:1084-1093.
333.
Tran D, Inventor Infrared Fiber Systems, Inc, assignee. Biocompatible optical fiber tip for in vivo laser surgery. US patent 5809199. 1998.
334.
Martin G.Cohen, Williams I. Kern, Stephen. Trokel, Inventors; Quantronix Corp, assignee. Infrared lasers for surgical purposes employing compound fiber probes. US patent 4988163. 1991 Jan.
335.
Polymicro Technologies. Infrared Waveguides. 2007 [cited 2008 24-Sept]; Available from: http://polymicro.com/catalog/2_8.htm
86
336.
Shibin J, Robert W K, editors. Rare-Earth-Doped Materials and Devices VI Proceedings of SPIE April 2002.
337.
Pedrotti FL, Pedrotti LM, Pedrotti LS. Fiber Optics. In: Introduction to optics pages. 3rd ed. Upper Saddle River, N.J: Pearson Prentice Hall; 2007. p. 243-260.
338.
Introduction to Fiber Optics. Naval electric engineering training series 2007 [cited 2008 8 Oct]; Available from: http://www.tpub.com/neets/tm/106-14.htm
339.
Robertson J, Marjoribanks RS. Multiphoton absorption and the evolution of green plants. Can. Undergrad Phys. J. 2002;1:13-14.
340.
Burgos P, Lu Z, Ianoul A, Hnatovsky C, Viriot ML, Johnston LJ, et al. Near-field scanning optical microscopy probes: a comparison of pulled and double-etched bent NSOM probes for fluorescence imaging of biological samples. J Microsc 2003;211:37-47.
341.
Haber LH, Schaller RD, Johnson JC, Saykally RJ. Shape control of near-field probes using dynamic meniscus etching. J Microsc 2004;214:27-35.
342.
Pak Kin W, Ulmanella U, Chih-Ming H. Fabrication process of microsurgical tools for single-cell trapping and intracytoplasmic injection. J. Microelectromech. Syst 2004;13:940-946.
343.
Lazarev A, Fang N, Luo Q, Zhang X. Formation of fine near-field scanning optical microscopy tips. Part I. By static and dynamic chemical etching. Rev Sci Instrum 2003;74:3679-3683.
344.
Stockle R, Fokas C, Deckert V, Zenobi R, Sick B, Hecht B, et al. High-quality nearfield optical probes by tube etching. Appl. Phys. Lett. 1999;75:160-162.
345.
Held T, Emonin S, Marti O, Hollricher O. Method to produce high-resolution scanning near-field optical microscope probes by beveling optical fibers. Rev Sci Instrum 2000;71:3118-3122.
346.
Hutson EJ. The development of radio-opaque, isotropic, fibre-optic probes for light dosimetry studies in photodynamic therapy. Phys. Med. Biol 1993;38:1529-1536.
347.
Walsh L, Vlacic J. Photoactivated disinfection. Moritz, A. ed. Berlin: Quintessence; 2004.
348.
Wong PK, Wang T-H, Ho. C-M. Optical fiber tip fabrication by surface tension controlled etching. In: Hilton Head Solid State Sensor, Actuator and Microsystems Workshop; 2002; Los Angeles, CA 2002. p. 94-97.
87
349.
Sayah A, Philipona C, Lambelet P, Pfeffer M, Marquis-Weible F. Fiber tips for scanning near-field optical microscopy fabricated by normal and reverse etching. Ultramicroscopy 1998;71:59-63.
350.
Lambelet P, Sayah A, Pfeffer M, Philipona C, Marquis-Weible F. Chemically etched fiber tips for near-field optical microscopy: a process for smoother tips. Appl Opt 1998;37:7289-7292.
351.
Smith KH, Ipson BL, Lowder TL, Hawkins AR, Selfridge RH, Schultz SM. Surface-relief fiber Bragg gratings for sensing applications. Appl Opt 2006;45:1669-1675.
352.
Smith KH, Ipson BL, Lowder TL, Hawkins AR, Selfridge RH, Schultz SM. D-fiber etching description. 2006 [cited 2008 24-Sept]; Available from: http://www.ee.byu.edu/photonics/etching.phtml?sop-see-all=true
353.
Androsik A, Mirovitskaya S, Fateeva G. Modified refraction-interference method for calculating the geometric and optical parameters of optical waveguides. Measurement Techniques 1996;39:288-293.
354.
Ward H. Molding of laser energy by shaped optic fiber tips. Lasers Surg Med 1987;7:405-413.
355.
David Royston, Ronald Waynant, A Banks, S Ramee, White CJ. Optical properties of fiber optic surgical tips. Appl Opt 1989 28:799-803.
356.
James PC, Richard JT, John H S. Shaped Fiber Tips for Medical and Industrial Applications. In: Gannot I, editor. Optical Fibers and Sensors for Medical Applications IV; June 2004: SPIE Proceedings June 2004. p. 70-80.
357.
Heisterkamp J, Van Hillegersberg R, Sinofsky EL, Ljzermans JNM. Interstitial laser photocoagulation with four cylindrical diffusing fibre tips: Importance of mutual fibre distance. Lasers Med Sci 1999;14:216-220.
358.
Fried NM, Lardo AC, Berger RD, Calkins H, Halperin HR. Linear lesions in myocardium created by Nd:YAG laser using diffusing optical fibers: in vitro and in vivo results. Lasers Surg Med 2000;27:295-304.
359.
Coluzzi DJ. An overview of laser wavelengths used in dentistry. Dent Clin North Am 2000;44:753-765.
360.
Abela GS, Fenech A, Crea F, Conti CR. "Hot tip": another method of laser vascular recanalization. Lasers Surg Med 1985;5:327-335.
88
361.
Optical Building Blocks ™. A reference guide to optical fibers and light guides. [cited 2008 24-Sept]; Available from: http://www.obb1.com/Technotes/OpticalFiberProperties.html
89
Chapter 2† Factors influencing the ablative potential of the Er: YAG laser when used to ablate radicular dentine
† Chapter 2, has been published Journal of Oral Laser Applications. 2008;8:33-41.
90
2.1 Abstract Back ground: The use of Er:YAG lasers for intra-canal ablation of dentine, as part of biomechanical preparation in endodontics, is attracting interest, however this process is yet to be optimized fully in terms of mode of operation, delivery system, and irrigation. The aim of this study was to compare the ablation characteristics of dentine when ablated from the root canal (radicular) aspect compared with the external root (periodontal) aspect, and examine the effect of water mist spray flow rate on the efficiency of ablation. The application of these parameters to direct ablation of smear layer in the root canal environment was then tested, comparing lasing with a 400
m fiber to the passive effects of EDTA during and after rotary
Ni-Ti preparation. Methods: In part 1, single rooted extracted teeth were split into two portions, and the surfaces of the split roots irradiated at 1 Hz for 5 pulses with a KaVo KEY3 Er:YAG laser at pulse energies of 250, 300, 400 or 500 mJ. This was undertaken with either a low (0.5 mL/min) or high (1.5 mL/min) water flow rate. A total of 10 sites were irradiated for each of the 16 unique energy/water flow rate/site combinations, giving 160 sites. Crater depth, diameter and volume were measured, and differences between groups also assessed using light microscopy and SEM. In part 2, root canals prepared using rotary Ni-Ti instruments were irradiated in the presence of water using an optical fiber, and the effects on dentine assessed using image analysis. Results: All dentine sites showed ablation at 250mJ/pulse. There was a consistent increase in crater depth and diameter with increasing energy in all subgroups, with larger craters with low water flow than with high water flow on the external (periodontal aspects). Comparing the effect of location, there was significantly greater ablation on the periodontal aspect in the low water flow group, than on the root canal (radicular) aspect. In contrast, in the high water flow group, there was no significant difference between the two locations. Irradiated surfaces had open dentinal tubules and no carbonization, cracking or other microscopic types of surface thermal injury. Lasing in the canal with an optical fiber in the presence of water had a limited and irregular effect on a thick smear layer, when compared to the passive effect of EDTA. Conclusion: These results indicate that significant interactions occur between dentine ablation and the variables of water spray flow rate and dentine location. This will be useful for developing methods to ensure that sufficient energy can be delivered to radicular dentine to achieve effective ablation for the biomechanical preparation of root canal dentine.
91
2.2 Introduction Many authors have demonstrated the effectiveness of the Er:YAG laser in endodontic applications, particularly for removing intra-canal debris and achieving disinfection.(1-4), 7) Er:YAG lasers have been shown to be effective in preparing straight canals as well as curved canals up to a 10 degree curvature, under ideal laboratory conditions(5). When used in the root canal system without water irrigation, concerns of thermal stress to the periodontium arise, for all laser systems that are strongly absorbed in water. A number of studies have documented this issue. Amyra and Walsh noted thermal stress with Nd:YAG and CO2 lasers used within the root canal under both wet and dry conditions (6), while Yamazaki et al.(4), when using a Er,Cr:YSGG laser at 6W reported a maximum temperature increase of 37°C for lasing without cooling (50% water and 48% air), but only 8°C when cooling was used. For Er:YAG lasers, a water mist spray can reduce thermal insult to hard tissues. Kimura et al. observed that a Er:YAG laser used with water spray (20mL/min) at 2 Hz and an exit energy up to 230 mJ/pulse from the tip for 1 minute gave a temperature rise of less than 6°C on the root surface at the root apex, and 3°C at the middle third of the root(7). Many studies indicate that water spray or a moist surface is essential for effective ablation of dentine, as it not only reduces thermal stress but also reduces charring of the ablated surface (8-11). However, dramatically increasing the water flow rate could decrease the efficiency of dentine ablation by giving a thicker surface water layer (12, 13). Fried et al. (12) reported that thick water films decrease the rate of ablation of enamel with Q-switched and free-running Er:YSGG (2.79 μm micron) and Er:YAG (2.94 μm) lasers, free running Ho:YAG lasers and 9.6 μm TEA CO2 lasers. However a study by Visuri et al. (13)showed that their optimal water flow rate (4.5 mL/min) only minimally reduced the ablation rates of dentine with an Er:YAG laser, and did not significantly affect the ablation rates of enamel, compared with lasing under dry conditions. In their study, the laser was used to produce linear incisions in enamel or dentine with or without water. Obtaining and sustaining a thin water film in the root canal would require a low water flow rate. The ablative process for dentine within the root canal may also be affected by its physical makeup. While external (root surface) and internal (root canal) dentine has a similar overall chemical composition with respect to proteins and minerals, the level of water differs
92
because the external dentine contains dentinal tubules that are smaller in diameter and fewer in number when compared to internal dentine. With more of the dentine volume occupied by tubules it could be expected that internal dentine would ablate at greater efficiency for the same laser parameters. As no previous study has compared the differences in ablation between external and internal root canal dentine, this study was designed to address this question, using different water flow rates as a second major variable.
2.3 Materials and methods In the first part of the study, a standardized exposure method with a non-contact handpiece was used. This approach was based on the methodology previously used by Fried to determine the ablation properties of human enamel with various overlying water films (12, 13), albeit used in this case for the Er:YAG laser rather than for the carbon dioxide laser. While not directly comparable to the clinical situation, it allowed precise control of all ablation parameters. Part 2 of the study examined the effect within root canals per se. A total of 10 extracted human premolar teeth were used in part 1. The surfaces of the roots were debrided with an ultrasonic scaler and hand curettes to ensure complete removal of cementum, as confirmed by microscopic examination. The teeth were then stored in tap water until used. The roots were divided longitudinally using a diamond disk. The cut internal surfaces of the split roots were flattened using a polishing disc to give a flat surface. Samples were then allocated randomly to either the high or low water flow rate groups (1.5 mL/min and 0.5mL/min, respectively). All samples were kept moist and were lased under moist conditions. A free running pulsed Er:YAG laser (KaVo KEY3, Model 1243) was used at the following parameters: 250-500mJ/pulse, fluence 44 - 88 J/cm2, 250 microsecond pulse duration, pulse repetition rate 1Hz) with a model 2060 non-contact sapphire window handpiece in focus (0.85 mm spot size at a working distance of 13 mm) at a frequency of 1Hz for a total of 5 superimposed pulses on the same target spot, either with low or high water flow rates. The optimum working distance was maintained at 13mm with the help of the integral diode aiming beam and a pre-measured endodontic instrument attached to the front surface of the handpiece. 93
The external (periodontal) surface of the split root samples was subjected to pulse energies of 250, 300, 400 and 500mJ, at 1 Hz for 5 pulses, delivered at 90 degrees to the surface. This procedure was repeated on the internal radicular (root canal) samples. A total of 10 replicate sites were irradiated for each of the 16 unique energy/water flow rate/site combinations, giving 160 sites. The diameter of the craters created by lasing were measured with the aid of an Olympus binocular dissecting microscope with a micrometer scale, while the depth of the craters was measured using a contact micrometer with a penetration needle (to an accuracy of 10 microns). The craters were photographed with a 3.34 mega pixel digital camera attached to the microscope (at a final magnification of X30), and the samples dehydrated, mounted on stubs, sputter coated with platinum and examined under low vacuum at 10 kV using a JEOL 6400F SEM system. The volume of dentine ablated was determined taking into account the proportion of the sample occupied by dentine tubules. First, SEM images were used to estimate the diameter of dentine tubules in the sample; next the number of tubules across the crater area was estimated from the SEM images. The tubule number was then multiplied by the mean diameter (per tubule, assuming circular cross sectional profiles) and finally by the crater depth, to give the total tubule volume. Typical tubule densities were 45,000 and 19,000/mm2, with mean diameters of 2.5 and 0.5 μm, for the internal and external dentine surfaces respectively. The corrected volume of the crater was determined by multiplying the crater area by the crater depth, to give the total volume, and then subtracting the volume occupied by the dentine tubules. Using the Kolmogorov-Smirnov normality test, numerical data sets for crater parameters (diameter, depth and volume) were found to be normally distributed in all groups, and thus inter-group differences were analyzed using one way ANOVA, and repeated measures t- tests. In the second part of the study, the effects of the Er:YAG laser on dentine ablation within the root canal were examined using 400 μm endodontic laser fibers (KaVo) attached to the 2062 handpiece of the KEY3 laser. A total of 21 single rooted teeth were used; these were stored in water saturated with thymol until used. Patency of the apical opening was confirmed with an ISO #08 K file passed in a retrograde manner. Access to the root canal
94
space was established using conventional rotary cutting instruments, and the working length establishing by passing a ISO #08 K file to the apex in an anterograde direction, and then backing off the measurement by 1mm. Teeth used had an apical foramen size of either ISO#15 or ISO #20. All root canals were prepared with rotary nickel-titanium instruments to 1 mm short of the apex to size F5 (0.50 mm) using Protaper® (Mallifer, Dentsply) instruments, following the manufactures guidelines. The teeth were then divided into 3 groups, the first of these being the positive control group, in which both 1% sodium hypochlorite and 15% EDTAC were used during endodontic therapy, in order to ensure complete removal of smear layer, and thus allow precise quantification of dentine tubule density. In the remaining two groups, during rotary instrument preparation of the canals, water was used as an irrigant rather than EDTA or sodium hypochlorite, to ensure that a smear layer was present at the end of sample preparation. In the lased group, after preparation, the root canal was filled with water using a syringe before inserting the laser fiber so that the terminus was 2 mm short of the apex (and thus 1 mm short of the working length). The KaVo KEY3 laser system was used at a panel setting of 200 mJ/pulse (4 Watts) and 20 pulses/second for 5 seconds. After placing more water in the canal, lasing was repeated, for a total of 10 cycles of irrigation followed by lasing. Each cycle was spaced by 5 seconds. The measured power output determined with a laser power meter placed at the terminus of the fiber was 1.0 Watt. The 2062 handpiece does not permit additional air or water from the laser system to be delivered, thus the only water present was that added into the canal before inserting the fiber. Each tooth was treated with a new ‘3 ring’ 400 μm fiber. During the time of lasing, the handpiece was moved in a circular motion and simultaneously withdrawn at a rate of 1mm/sec. Only the apical third of the root canal system was treated. The third group had the laser fiber placed (with the aiming beam activated) with EDTA present as the irrigant but without Er:YAG laser energy being delivered (sham irradiation). After treatment, the roots were split to allow examination of the apical third, and the samples dehydrated, mounted on stubs, sputter coated with platinum and examined by SEM, with attention being paid to the effect of lasing on removal of smear layer and ablation of dentine. From the images, the proportions of open tubules in the control and lased groups were determined by image analysis using Image Pro Plus ™ software, using one image per sample at a magnification of X1000, of the apical third of the root canal system. The number of pixels occupied by the openings of dentinal tubules was divided by the total area of pixels
95
in the image to determine a percentage score, as a surrogate measure for dentine tubule “patency”. Group data were pooled from the three groups, and assessed for normality using the Kolmogorov-Smirnov test. Differences between groups were then assessed using one way ANOVA, and a t-test.
2.4 Results In the first part of the study, the light microscopic evaluation of the impact sites showed that the craters were regular in pattern, with no cracks or fissure in the peripheral regions near the crater. Charring was not seen on the surface of craters in either water flow groups. Of note, the margins of the craters on the external root surface had a bevelled surface, while the craters on the internal surface had a sharper perpendicular profile (Insets in Figs. 2.1 – 2.4).
Fig. 2.1. Crater from 500mJ laser pulses on the internal dentine surface at 0.5mL/min water flow rate show no charring, fissures or microfractures of the surrounding dentine. The margins of the crater are perpendicular (SEM 60X magnification; inset: light micrograph with scale bar = 1 mm).
96
Fig. 2.2. Crater from 500mJ laser pulses on the external surface at 0.5mL/min water flow rate ,showing no charring, fissures or microfractures, however the margins of the crater are beveled (SEM 60X magnification; inset: light micrograph with scale bar = 1 mm).
97
Fig. 2.3. Crater from 500mJ laser pulses on the internal dentine surface at 1.5mL/min water flow rate, showing no charring, and perpendicular margins (SEM 60X magnification; inset: light micrograph with scale bar = 1 mm).
98
Fig. 2.4. Crater from 500mJ laser pulses on the external dentine surface at 1.5mL/min water flow rate, showing no charring, but margins of the crater are beveled (SEM 60X magnification; inset: light micrograph with scale bar = 1 mm).
99
SEM examination at low magnification (60X) showed that in all groups the craters had rough and irregular margins (Figs. 1 - 4). At higher magnification (1000X), open tubules, lack of a smear layer, and a scaly surface with no melting or fusing of dentine were seen. Higher magnifications also demonstrated the structural variations between the external and internal dentine; larger numbers of tubules with larger diameters were observed on the internal dentine compared to the external dentine (Figs. 2.5A-D).
Fig. 2.5. SEM examination of dentine tubules at the bases of craters (500mJ), showing internal dentine (A and C) with 0.5mL/min (A) or 1.5mL/min (C), and external dentine (B and D) with 0.5mL/min (B) or 1.5mL/min (D). All views show patent dentinal tubules with no smear layer and no melting or fusing of dentine. Note the larger tubules and greater tubule density in internal dentine. There was an increase in crater diameter, depth and volume with increasing pulse energy (Figs. 2.6-2.8). Under low water flow conditions, when comparing external versus internal dentine, there was a statically significant difference between the crater diameter and volume, with the external surface showing a larger crater diameter at all energy levels, and 100
larger volume mineral loss at higher energy levels. The depth of craters was not statistically different between the two dentine locations. Under high water flow conditions, there was no statistical difference in crater diameters, depths and volumes between internal and external dentine. For external dentine, the diameter and depths of the craters produced were greater in the low water flow group than high water flow group. For internal dentine only depth was significantly larger in the low water flow group when compared to the high water flow group. At a given pulse energy, the total volume of mineral lost was significantly greater in the low water flow group for both internal and external dentine locations.
Fig. 2.6. Crater diameters with varying irradiation conditions, dentine topography and water flow rates.
Fig. 2.7. Crater depths with varying irradiation conditions, dentine topography and water flow rates.
101
Fig. 2.8. Estimated crater volumes with varying irradiation conditions, dentine topography and water flow rates. In the second part of the study, in which the effect of lasing in the canal with fibers was examined, no smear layer was present in the positive control group in which EDTA and sodium hypochlorite were used. A reduction in smear layer occurred during the passive exposure to 15% EDTAC during sham treatment (a total of 2 minutes). Laser treatment in the presence of water in the root canal was only partially effective in removing the smear layer from the walls of the root canal. Isolated areas of dentine ablation were seen, whilst others showed minimal change (Fig. 2.9). There was greatest dentinal tubule patency in the positive control (Ni-Ti + EDTA irrigant) group (P = 0.0051), but no statistically significant difference between the sham irradiated and lased groups (Table 2.1).
102
Fig. 2.9. Effects of various treatments within the apical third of the root canal. A, Positive control of rotary NiTi with EDTA and sodium hypochlorite as irrigants. B, Effect of passive incubation with EDTA and sham irradiation ( no irradiation)on a thick smear layer. C and D, Er:YAG laser with accompanying water in the canal. All images are at the same magnification and are from similar locations in the apical third of the root canal.
Table 2.1. Dentine tubule patency expressed as a percentage of the total pixel area Group
Lased
Sham
NiTi
Mean
0.77
3.01
5.97*
SD
0.61
0.55
4.37
* Significantly greater than the other two groups.
103
2.5 Discussion
Ablation characteristics of radicular dentine have been studied by a number of authors, (14-16) however no previous study has reported the difference in the ablation rates and characteristics of radicular external and internal dentine. Variations in ablation characteristics were expected considering the differences in morphology as well as the content of water within the dentine, in particular the differences in tubule number and diameter, and this was confirmed by the experimental results. There was significantly greater ablation on the external (periodontal) aspect in the low water flow group, than on the root canal (radicular) aspect. In contrast, in the high water flow group, there was no significant difference between the two locations, for the same pulse energy. There are several possible reasons for this. Laser energy could result in the preferential evaporation of water within tubules, rather than inter-crystalline water. The outer radicular surface contains more mineralized tissue and is more solid in nature, with the water found mostly in the dentine matrix rather than in the tubules. Thus, the matrix may disintegrate readily when the water is converted to steam. The internal root surface has, by comparison, more “free” water (i.e. dentinal fluid within tubules), which would be preferentially vaporized, rather than inter-crystalline water. The internal radicular dentine surface also has a different physical structure with minimal peri-tubular dentine and large tubule diameters, which in turn would affect the propagation of photomechanical shock waves which disrupt tissue by their explosive action. Other contributing factors include the effect of the beam profile on the ablation process. The edge of the Gaussian (TEM00) beam profile is less energetic and may not deliver sufficient energy to reach the ablation threshold. This explains why the outer root surface dentine showed a crater with beveled edges. In contrast, on the inner radicular surface, craters had more vertical walls indicating more effective ablation at the periphery. This difference in crater shape contributes to differences in the ablation volume between the two surfaces, under the same irradiation and flow rate conditions. In relation to water flow rates, the depth of the craters in the low water flow group however did not vary significantly. Though we would have accepted a larger depth on the 104
internal surface this is not so and could be due the larger tubules acting as reservoirs of water pooling and hence this thick film of water could be responsible for the decrease depth of the crater. Comparing the effect of location, there was significantly greater ablation on the periodontal aspect in the low water flow group, than on the root canal (radicular) aspect. In contrast, in the high water flow group, there was no significant difference between the two locations in terms of diameter or depth of craters. The latter could be simply be due to the higher water flow rate causing an excess surface water film thickness, which then acts as an intermediary between the incoming laser pulse and the dentine surface. An effect of excess water has been reported previously(12, 13, 17, 18) In the root canal one could expect a constant thickness of water due to pooling of water in the canal and its interaction with the dentine surface because of surface tension effects. Direct evidence for the limited effect of lasing when in the presence of water was gained in the second part of the study, in which delivery of Er:YAG laser energy in the presence of water had, under the parameters used, a limited effect on the thick smear layer deliberately created by not using EDTA during rotary preparation. Of interest, a passive effect of EDTA during sham irradiation (no irradiation) could be seen. While the use of water during rotary preparation is not realistic, it was useful for ensuring a thick smear layer, and thus providing a greater challenge to the laser in terms of ablation. Some areas of ablated dentine were seen whilst other areas were less affected, reflecting the problems of achieving a consistent effect with the delivery system used. This study emphasizes the difference in the ablation patters of both external and internal toot surface. Within the root canal, an irregular ablation pattern would be expected when using a conventional optical fiber with a perpendicular cleave, or a sapphire or quartz tip with a polished perpendicular end. A challenge with this end firing approach, if used for physical preparation of the canal, is to achieve uniform ablation, whilst at the same time limiting heat transfer to the supporting periodontal tissues. Simple beveled ends on fibers used with water spray would likely result in some parts of the canal being ablated more than others. Further studies of fibers for use in the root canal are needed to optimize their design and performance. To achieve a uniform and effective ablation of the root canal walls, factors such as the morphological variations of the radicular dentinal surface, the water flow rate 105
(into the canal and out of the canal [due to evaporation or due to flow]), the fiber tip (shape, transmission profile, angulations to canal walls), the laser pulse energy settings, and the rate withdrawal of fiber from the canal need to be considered carefully.
2.6 Conclusions Based on the present results, the quantity of water both contained within the dentinal tubules as well as the water spray flow rate itself, appear to have a marked influence on the ablation rate of dentine. Precise adjustment of the water spray flow rate needs to be undertaken so as to obtain optimal ablation with the lowest possible pulse energy level.
2.7 References 1.
Takeda FH, Harashima T, Kimura Y, Matsumoto K. Comparative study about the removal of smear layer by three types of laser devices. J Clin Laser Med Surg 1998;16:117-122.
2.
Matsuoka E, Kimura Y, Matsumoto K. Studies on the removal of debris near the apical seats by Er:YAG laser and assessment with a fiberscope. J Clin Laser Med Surg 1998;16:255-261.
3.
Matsuoka E, Yonaga K, Kinoshita J, Kimura Y, Matsumoto K. Morphological study on the capability of Er:YAG laser irradiation for root canal preparation. J Clin Laser Med Surg 2000;18:215-219.
4.
Yamazaki R, Goya C, Yu DG, Kimura Y, Matsumoto K. Effects of erbium,chromium:YSGG laser irradiation on root canal walls: a scanning electron microscopic and thermographic study. J Endod 2001;27:9-12.
5.
Matsuoka E, Jayawardena JA, Matsumoto K. Morphological study of the Er,Cr:YSGG laser for root canal preparation in mandibular incisors with curved root canals. Photomed Laser Surg 2005;23:480-484.
6.
Amyra T, Walsh LT, Walsh LJ. An assessment of techniques for dehydrating root canals using infrared laser radiation. Aust Endod J 2000;26:78-80.
106
7.
Kimura Y, Yonaga K, Yokoyama K, Kinoshita J, Ogata Y, Matsumoto K. Root surface temperature increase during Er:YAG laser irradiation of root canals. J Endod 2002;28:76-78.
8.
Romano V. Bone microsurgery with IR lasers: a comparative study of the thermal action at different wavelengths. Proc SPIE 1994;2077:87-97.
9.
Shori R, Walston A. Quantification and modeling of the dynamic changes in the absorption coefficient of water at 2.94 lm. . IEEE J Sel Top Quantum Electron 2001;7:959-970.
10.
Sasaki KM, Aoki A, Ichinose S, Yoshino T, Yamada S, Ishikawa I. Scanning electron microscopy and Fourier transformed infrared spectroscopy analysis of bone removal using Er:YAG and CO2 lasers. J Periodontol 2002;73:643-652.
11.
Kimura Y, Yu DG, Fujita A, Yamashita A, Murakami Y, Matsumoto K. Effects of erbium,chromium:YSGG laser irradiation on canine mandibular bone. J Periodontol 2001;72:1178-1182.
12.
Fried D, Ashouri N, Breunig T, Shori R. Mechanism of water augmentation during IR laser ablation of dental enamel. Lasers Surg Med 2002;31:186-193.
13.
Visuri SR, Walsh JT, Jr., Wigdor HA. Erbium laser ablation of dental hard tissue: effect of water cooling. Lasers Surg Med 1996;18:294-300.
14.
Brugnera A, Jr., Zanin F, Barbin EL, Spano JC, Santana R, Pecora JD. Effects of Er:YAG and Nd:YAG laser irradiation on radicular dentine permeability using different irrigating solutions. Lasers Surg Med 2003;33:256-259.
15.
Ebihara A, Majaron B, Liaw LH, Krasieva TB, Wilder-Smith P. Er:YAG laser modification of root canal dentine: influence of pulse duration, repetitive irradiation and water spray. Lasers Med Sci 2002;17:198-207.
16.
Cernavin I. A comparison of the effects of Nd:YAG and Ho:YAG laser irradiation on dentine and enamel. Aust Dent J 1995;40:79-84.
17.
Burkes JEJ, Hoke J, Gomes E, Wolbarsht M. Wet versus dry enamel ablation by Er:YAG laser. J Prosthet Dent 1992;67:847-851.
18.
Kim ME, Jeoung DJ, Kim KS. Effects of water flow on dental hard tissue ablation using Er:YAG laser. J Clin Laser Med Surg 2003;21:139-144.
107
Chapter 3† Performance assessment of novel side firing flexible optical fibers for dental applications
† A provisional patent application has been submitted for the technology described in this Chapter.
108
3.1 Abstract Back ground and Objective: Use of lasers in dentistry in root canals of teeth and in periodontal pockets for disinfection would be more effective if energy was delivered laterally. This study examined the energy emission profiles of fibers modified in various ways to enhance their lateral emissions for dental use. Materials and Methods: Commercial optical fibers were altered by tube etching with hydrofluoric acid, modified tube etching (after removing the protective polyimide coating), alumina abrasive particle beams, and by etching and particle beams used in combination. Three free-running pulsed infrared lasers (Nd:YAG, Er:YAG, and Er,Cr:YSGG) were employed to test the modified fibers, with 25 fibers for each laser (modified or unmodified). Surface topography of fibers was examined using SEM. Laser emissions forward and laterally were measured, and thermally sensitive paper used to record the emission profiles. Visible tracing of emissions was undertaken using coaxial He-Ne or InGaAsP diode laser emissions. Results: The etching/abrasion/etching combination gave a unique honeycomb surface configuration with grating-like properties, whilst etching alone gave a conical end. Conical and honeycomb tips showed greater lateral and lower forward emissions compared with plain fibers, with four-fold improvements in lateral emission. The most regular lateral emissions were from the honeycomb configuration. Conclusion: The honeycomb and the conical fiber modifications show dramatic improvements in lateral emissions. The unique emission profile obtained for the honeycomb fibers could play a significant role in increasing the efficiency of laser delivery for endodontic and periodontal applications in dentistry, as well as in other fields.
109
3.2 Introduction In dentistry, lasers are used in endodontics for disinfection of root canals, smear layer removal and root canal preparation, as well as for soft tissue applications such as pulp capping and pulpotomy. For the endodontic hard tissue applications, delivery of laser energy is undertaken using plain optical fibers attached to dental handpieces. Optical fibers in endodontics need to be small and flexible so as to negotiate the complex curved and tortuous anatomy of the root canal. Flexibility of existing optical fibers is less than for the superelastic Ni-Ti instruments used in conventional endodontics. More importantly, existing fibers have plain ends, so the laser energy exits forward with a relatively small divergence, requiring the clinician to move the fiber in a plunging, withdrawing and rotating action to attempt to gain even irradiation of the canal walls. Despite this clinical technique, existing fibers do not give even irradiation of the root canal walls. Fiber optic designs that enable lateral distribution of laser energy would be more appropriate used in root canal preparation, as well as in other dental situations such as laser disinfection of periodontal pockets. A number of modifications for optical fibers for medical(1) or industrial applications(2) have been reported. For dentistry, these include hollow waveguide extensions to optical fibers for Er:YAG lasers(3) and hollow metal conical tips with slits for lateral emission(4). Such metal waveguides have limited clinical use in situations other than in large and straight root canals because of their size and inherent rigidity. For optical fibers, conical ends can be created by grinding and polishing (5, 6). The ends of optical fibers can also be modified by fixing certain materials to the fiber end to disperse the energy, including titanium dioxide. Such isotropic tips may have application for photodynamic therapy (photo-activated disinfection) in endodontics (7-9). In industrial settings, fiber tips may be modified by heating and pulling (10, 11) or by etching with strong acids (12-14). The latter is a simple and inexpensive method of altering the tip to obtain greater lateral distribution of energy. Reported etching methods include static etching, dynamic etching (12, 13), and tube etching(14). These various methods have not been applied to fibers used in dentistry. In this report, we describe the application of tube etching, and novel variations to this technique to create unique fiber optic termini with superior lateral emission characteristics.
110
3.3 Materials and Methods
3.3.1 Lasers and optical fibers Three free-running pulsed lasers were used in the study: an Nd:YAG laser (dLase 300, American Dental Laser, Fremont, CA) at 1.5 mJ/pulse, 20Hz (3.0 W panel) with a 320 µm quartz glass fiber (WF 320 MDF, BioLitec, Winzelaer, Germany), an Er:YAG (KEY3, Model 1243, KaVo, Biberach, Germany) used at 200mJ/pulse and 20 Hz (4 W), with a 400 µm (ISO 40) endodontic fiber, and an Er,Cr:YSGG laser (Waterlase MD, Biolase, Irvine, CA) used at a panel setting of 1.25W and 20 Hz (62.5 mJ/pulse), delivered into a 400 µm endodontic fiber (MZ4).
3.3.2 Fiber modifications A total of 75 fibers (25 for each laser) were used. For each laser group these were further divided into 5 groups of five fibers each. Group 1 fibers were unmodified, as provided by the manufacturer, to serve as controls. Group 2 fibers were etched with 50% hydrofluoric acid (HF) using the tube etching technique(14). A silicon oil layer was placed over the HF to protect the fiber mounts from HF vapors. Etching was undertaken at 25 degrees Celsius, for durations ranging from 45 to 180 min. The appropriate etching times were determined from a pilot study in which the progress of etching was checked at 5 minute intervals using a microscope at a final magnification of 30X. The chosen endpoint was a conical pointed tip. Once etching was complete, the polymer coating was removed either by mechanical stripping or by dissolving it in hot concentrated H2SO4. Fibers in Group 3 were etched similar to Group 2, but had 2 mm of the polyimide coating removed before commencing etching. For Group 4 fibers, a 5 mm length of the polymer coating was stripped off, and the exposed fiber then treated with a particle beam of medical grade 50µm aluminium oxide (Microetcher ERC, Danville Engineering, San Ramon, CA, USA) using compressed air at a pressure of 2.85 bar. The particle beam was applied in 4 bursts of 0.5 sec each whilst rotating the fiber tip 180 degrees during abrasion to achieve a consistent abrasive action. Fibers in Group 5 fibers were modified in a 3-step protocol, beginning with modified tube etching as in Groups 2 and 3, to obtain a conical configuration, then abrading the tip with the alumina particle beam (as in Group 4), and finally etching the fiber end once more. The second etching time was determined from a pilot study, and was 15 minutes for both WF 320 MDF fibers and Biolase 111
fibers, and 10 min for KEY 3 fibers. Before being further examined, the terminal 20 mm of all etched fibers in Groups 2, 3 and 5 was dipped in a saturated sodium bicarbonate solution to neutralize any residues of HF.
3.3.3 Emission measurements Fiber tips were examined using a JEOL 6400 scanning electron microscope at 15 kV after sputtering with platinum. For elemental analysis, the fibers were sputter coated with carbon. Images were taken at a final magnification of 500X using a 6460 JEOL SEM for electron back scatter diffraction (EBSD) analysis at 30 kV. The exit laser energy from the various fibers at fixed points in the forward direction (10 mm in front of the tip) and laterally (2 mm from the side of the tip) was measured with a power meter (Nova II, Ophir Optronics, North Andover, MA). ANOVA and Tukey Kramer post hoc test were used to compare exit powers in forward and lateral directions between bare (Group 1) and modified tips. Thermally sensitive white paper was used to record the emission profiles of the various fiber tips, with the tip kept parallel to and 2 mm above the surface of the thermal paper. To enhance absorption for the Nd: YAG laser, the non-sensitive side of the thermal paper was darkened with black printer ink. No enhancer was necessary with the erbium wavelengths. Tracing the distribution of visible red light was undertaken using coaxial He-Ne laser (632.8 nm) (in the dLase 300 Nd:YAG system) or InGaAsP diode laser (635 nm) emissions (in the erbium systems). The distribution of visible red light was photographed on a grid using a stereomicroscope equipped with a digital camera, holding the fiber in direct contact to the gird. Angles of divergence were measured with aid of Image-J image analysis software (NIH, Bethesda, MD, USA).
112
3.3.4 Transmission The ability of the modified fibers to transmit light was tested using 320 micron diameter optical fibers (Biolitec). The fibers were connected to a spectrometer (Model USB 2000, Ocean Optics, Dunedin, FL, USA) using an SMA connector. The fibers were then placed on a grid under a stereomicroscope, and a 3 mW 670 nm diode laser module (Product code 1250-3590, RS Components, Smithfield, NSW, Australia) with a beam diameter of 1 mm was used to illuminate the fiber at 1 mm intervals along the length of the fiber. This was done in order to evaluate the ability of these fibers to accept and conduct light along their length. The diode laser was driven using a regulated power supply at a constant DC voltage of 2.7 volts. To evaluate the ability of these fibers to receive light over variable angulations, the diode laser beam was aimed at the tip of the plain fiber at angles of 0 degrees (i.e. directly on the tip), 45 degrees (from the tip), 90 degrees (i.e. directly perpendicular), and at 135 and 180 degrees, as shown in Figure 3.1 below.
Fig. 3.1. Angles for testing light transmission of optical fibers.
113
3.4 Results 3.4.1 Fiber topography Simple etching with HF using the tube etching technique (Group 2) or modified tube etching technique (Group 3) both gave similar conical shaped fiber ends, with a typical final diameter of 33 μm (Fig. 2A). Group 4 fibers treated with the particle beam showed a microscopically roughened surface (Fig. 2C). Fibers in Group 5 treated by etching, abrasion and further etching had a multi-faceted surface with a honeycomb-like appearance (Fig. 3.2 B and 3.2 D).
Fig. 3.2. SEM images showing the surface topography of the modified fibers. A. conical tip (Groups 2 and 3), B and D (at higher magnification), honeycomb surface with the combination of etching and abrasion. C, abrasion alone. 114
3.4.2 Fiber composition and etching times Elemental analysis of the three fiber types revealed differences in composition, with the Biolitec and Biolase fibers being a fluoride-doped silica glass and the KEY3 fiber a germanium-doped silica fiber (Fig. 3.3). There was no change in fiber composition when samples were compared before and after etching with HF. The etching time required for Group 2 samples varied according to the fiber composition, with the depending on the type of fiber, with the germanium-doped fibers from the KEY3 laser requiring (mean + SD) 91 min (+9), versus 161 min (+6) and 174 min (+7) for the Biolitec and Biolase (fluoride-doped) fibers, respectively. The difference in etching times between fiber types was significant (P0.05
NiTi vs. Er,Cr:YSGG
20.810
ns
P>0.05
NiTi vs. Unprepared
24.000
ns
P>0.05
NiTi vs. NiTi + water only
53.238
*** P0.05
Er:YAG vs. Unprepared
4.905
ns
P>0.05
Er:YAG vs. NiTi + water only
34.143
**
P0.05
Er,Cr:YSGG vs. NiTi + water only
32.429
**
P0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Bartlett statistic ANOVA assumes that the data are sampled from populations with identical SDs. This assumption is tested using the method of Bartlett. Bartlett statistic (corrected) = 19.462 The P value is 0.1094. Bartlett's test suggests that the differences among the SDs are not significant.
One-way Analysis of Variance (ANOVA) The P value is < 0.0001, considered extremely significant. Variation among column means is significantly greater than expected by chance
284
285
Not significant.
# Post hoc- Tukey Kramer’s test and a test (marked in red) * P0.10
Yes
KEY/Conical Max Temp
0.2198
>0.10
Yes
BioLase/Bare Max Temp
0.1989
>0.10
Yes
BioLase/Conical Max Temp
0.2818
>0.10
Yes
287
Bartlett statistic Bartlett statistic (corrected) = 9.110 The P value is 0.0279. Bartlett's test suggests that the differences among the SDs are significant.
Since ANOVA assumes populations with equal SDs, and Bartlett’s test suggested that the means where not equal, hence though the samples groups followed a Gaussian population a nonparametric test was performed.
Kruskal-Wallis Test (Non-parametric ANOVA)
The P value is 0.4890, considered not significant. Variation among column medians is not significantly greater than expected by chance. The P value is approximate (from chi-square distribution) because at least one column has two or more identical values.
Calculation detail Group
Points
Sum of Ranks
Mean of Ranks
KEY/Bare Max Temp
16
580.00
36.250
KEY/Conical Max Temp
16
523.00
32.688
BioLase/Bare Max Temp
16
547.00
34.188
BioLase/Conical Max Temp
16
430.00
26.875
Kruskal-Wallis Statistic KW = 2.425 (corrected for ties) Post tests were not calculated because the P value was greater than 0.05.
288
Appendix: 6 Additional data and statistical analysis for Chapter 7
Apical extrusion of root canal irrigants when using Er:YAG and Er,Cr:YSGG lasers with optical fibers: An in vitro dye study
289
Statistical analyses 1. Descriptive statistics of apically extruded dye • 15k file group • 20k file group 2. Kolmogorov and Smirnov test: To determine if the data was normally distributed. • 15k file group • 20K File group 3. ANOVA and post hoc multiple comparison test • Significance in 15k group at a distance of 5mm • Significance in 15k group at a distance of 10mm • Significance in 20 k group at a distance of 5mm • Significance in 20k group at a distance of 10mm 4. Paired Two Sample for Means (t-Test) for 20k vs. 15 k file group • Bare Fibers • Modified Fibers • Controls 5. Paired Two Sample for Means (t-Test) for distance from apex 5mm vs. 10mm • Bare Fibers • Modified Fibers • Controls
290
Descriptive statistics of apically extruded dye 15k file group
Bio/Bare 5mm Bio/Bare 10mm Key/Bare 5mm Key/ Bare 10mm Bio/Modified 5mm Bio/Modified 10mm Key/Modified 5mm Key/Modified 10mm Maxi-I Probe/5mm Maxi-I Probe/10mm
Mean * 9236 9342.875 10627.75 10740.13 9681.5 9036.375 10330.63 10563.13 5954.375 0
SD* 4565.959 4789.761 6720.606 6685.859 5164.023 4904.214 7913.235 9590.536 4253.136 0
Max* 18196 16546 23814 22509 17648 16698 23968 26119 12337 0
Min* 4424 4388 5420 3633 3507 3706 3992 2377 1276 0
25G SYRINGE/5mm 25G SYRINGE/10mm
10492.13 5010.625
4471.719 4706.964
15994 13100
5355 0
* Data in pixels
20K File group
BIOLASE/ 5mm BARE BIOLASE/ 10mm BARE KEY/ 5mm BARE KEY/ 10 mm BARE
Mean * 36238.13 32120.5 43328 37204.63
SD* 15375.94 9287.871 16943.87 14571.92
Max* 63324 43540 73634 54903
Min* 16510 16923 24226 20086
Biolase/ 5mm Modified
33051.38
13166.7
52398
20717
Biolase/ 10mm Modified KEY/ 5mm Modified KEY/10 mm Modified 25G SYRINGE/5mm 25G SYRINGE/10mm Maxi-I Probe/5mm Maxi-I Probe/10mm
28512.38 40340.5 34105 33405.63 18034.63 12771.25 592.125
10373.07 14882.21 11958.36 18213.03 11978.78 6462.065 1647.877
47235 59851 56675 58122 35463 19737 4670
11145 21535 13077 13376 3755 5018 0
* Data in pixels
291
Kolmogorov and Smirnov test: To determine if the data was normally distributed. 15k file group Group
KS
Bio/Bare 5mm Bio/Bare 10mm Key/Bare 5mm Key/ Bare 10mm Bio/Modified 5mm Bio/Modified 10mm Key/Modified 5mm Key/Modified 10mm Maxi-I Probe/5mm Maxi-I Probe/10mm 25G SYRINGE/5mm 25G SYRINGE/10mm
0.2327 0.2530 0.3364 0.2000 0.2053 0.2343 0.3705 0.3840 0.2872 0.2917 0.2314
P Value >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Passed normality test? Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes
20k file group Group
KS
Bio/Bare 5mm Bio/Bare 10mm Key/Bare 5mm Key/ Bare 10mm Bio/Modified 5mm Bio/Modified 10mm Key/Modified 5mm Key/Modified 10mm Maxi-I Probe/5mm Maxi-I Probe/10mm 25G SYRINGE/5mm 25G SYRINGE/10mm
0.1745 0.1707 0.2236 0.2337 0.3055 0.2705 0.1698 0.2531 0.2118 0.5000 0.2633 0.1749
P Value >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 0.0366 >0.10 >0.10
Passed normality test? Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes
292
Analysis ANOVA and post hoc multiple comparison tests 1. 2. 3. 4.
Significance in 15k group at a distance of 5mm Significance in 15k group at a distance of 10mm Significance in 20 k group at a distance of 5mm Significance in 20k group at a distance of 10mm
1. Significance in 15k group at a distance of 5mm One-way Analysis of Variance (ANOVA) The P value is 0.5756, considered not significant. Post test Post tests were not calculated because the P value was greater than 0.05.
2. Significance in 15k group at a distance of 10mm One-way Analysis of Variance (ANOVA) The P value is 0.0040, considered very significant. Tukey-Kramer Multiple Comparisons Test Comparison Bio/Bare10mm vs. Key/ Bare 10mm Bio/Bare10mm vs. Bio/Modified 10mm Bio/Bare10mm vs. Key/Modified 10mm Bio/Bare10mm vs. Maxi-I Probe/10mm Bio/Bare10mm vs. 25G Syringe/10mm Key/ Bare10mm vs. Bio/Modified 10mm Key/ Bare10mm vs. Key/Modified 10mm Key/ Bare10mm vs. Maxi-I Probe/10mm Key/ Bare10mm vs. 25G SYRINGE/10mm Bio/Modified10mm vs. Key/Modified10mm Bio/Modified 10mm vs. Maxi-I Probe/10mm Bio/Modified 10mm vs. 25G Syringe/10mm Key/Modified 10mm vs. Maxi-I Probe/10mm Key/Modified 10mm vs. 25G Syringe/10mm Maxi-I Probe/10mm vs. 25G Syringe/10mm
Mean Difference -1397.3 306.50 -1220.3 9342.9 4332.3 1703.8 177.00 10740 5729.5 -1526.8 9036.4 4025.8 10563 5552.5 -5010.6
q
P value
0.6747 0.1480 0.5893 4.512 2.092 0.8228 0.08548 5.187 2.767 0.7373 4.364 1.944 5.101 2.681 2.420
ns ns ns * ns ns ns ** ns ns * ns * ns ns
293
Non parametric - Kruskal-Wallis Test (Nonparametric ANOVA) The P value is 0.0012, considered very significant. Variation among column medians is significantly greater than expected by chance. The P value is approximate (from chi-square distribution) because at least one column has two or more identical values.
Calculation detail Group Bio/Bare 10mm Key/ Bare 10mm Bio/Modified 10mm Key/Modified 10mm Maxi-I Probe/10mm 25G SYRINGE/10mm
Number of Points
Sum of Ranks
Mean of Ranks
8 8 8 8 8 8
239.00 256.00 241.00 225.00 48.000 167.00
29.875 32.000 30.125 28.125 6.000 20.875
Kruskal-Wallis Statistic KW = 20.048 (corrected for ties) Dunn's Multiple Comparisons Test Comparison Bio/Bare 10mm vs. Key/ Bare 10mm Bio/Bare 10mm vs. Bio/Modified 10mm Bio/Bare 10mm vs. Key/Modified 10mm Bio/Bare 10mm vs. Maxi-I Probe/10mm Bio/Bare 10mm vs. 25G SYRINGE/10mm Key/ Bare 10mm vs. Bio/Modified 10mm Key/ Bare 10mm vs. Key/Modified 10mm Key/ Bare 10mm vs. Maxi-I Probe/10mm Key/ Bare 10mm vs. 25G SYRINGE/10mm Bio/Modified 10mm vs. Key/Modified 10mm Bio/Modified 10mm vs. Maxi-I Probe/10mm Bio/Modified 10mm vs. 25G SYRINGE/10mm Key/Modified 10mm vs. Maxi-I Probe/10mm Key/Modified 10mm vs. 25G SYRINGE/10mm Maxi-I Probe/10mm vs. 25G SYRINGE/10mm
Mean Rank Difference -2.125 -0.2500 1.750 23.875 9.000 1.875 3.875 26.000 11.125 2.000 24.125 9.250 22.125 7.250 -14.875
P value ns P>0.05 ns P>0.05 ns P>0.05 ** P0.05 ns P>0.05 ns P>0.05 ** P0.05 ns P>0.05 ** P0.05 * P0.05 ns P>0.05
294
3. Significance in 20 k group at a distance of 5mm One-way Analysis of Variance (ANOVA) The P value is 0.0030, considered very significant.
Tukey-Kramer Multiple Comparisons Test Comparison BioLase/5mm Bare vs. KEY/5mm Bare BioLase/5mm Bare vs. BioLase/5mm Modified BioLase/5mm Bare vs. KEY/5mm Modified BioLase/5mm Bare vs. 25G Syringe/5mm BioLase/5mm Bare vs. Maxi-I Probe/5mm KEY/5mm Bare vs. BioLase/ 5mm Modified KEY/5mm Bare vs. KEY/5MM Modified KEY/5mm Bare vs. 25G SYRINGE/5mm KEY/5mm Bare vs. Maxi-I Probe/5mm BioLase/ 5mm Modified vs. KEY/5mm Modified BioLase/ 5mm Modified vs. 25G Syringe/5mm BioLase/ 5mm Modified vs. Maxi-I Probe/5mm KEY/5MM Modified vs 25G SYRINGE/5mm KEY/5MM Modified vs Maxi-I Probe/5mm 25G SYRINGE/5mm vs Maxi-I Probe/5mm
Mean Difference -7089.9 3186.8 -4102.4 2832.5 23467 10277 2987.5 9922.4 30557 -7289.1 -354.25 20280 6934.9 27569 20634
q
P value
1.367 0.6143 0.7908 0.5460 4.523 1.981 0.5759 1.913 5.890 1.405 0.06829 3.909 1.337 5.314 3.977
ns ns ns ns * ns ns ns ** ns ns ns ns ** ns
ns P>0.05, * P0.05 ns P>0.05 * P0.05 ns P>0.05 ns P>0.05
Bartlett statistic Bartlett statistic (corrected) = 7.593 The P value is 0.0552. Bartlett's test suggests that the differences among the SDs are not quite significant.
311
Appendix 8 Additional data and statistical analysis for Chapter 9
Coaxial water mist spray alters the radicular ablation properties of human radicular dentine for the Holmium:YAG
312
Statistical anlyses
1. Descriptive statistics • Dry diameter • Dry depth • Dry volume • Wet diameter • Wet depth • Wet volume
2- Kolmogorov Smirnov test: To test for normal distribution of data • Dry diameter • Dry depth • Dry volume • Wet diameter • Wet depth • Wet volume
3- ANOVA: Two-Factor with Replication • Dry diameter • Dry depth • Dry volume • Wet diameter • Wet depth • Wet volume
4- t-Test for means: to test the following Dry vs. wet diameter Dry vs. wet depth Dry vs. wet volume
313
Descriptive statistics: Dry diameter
Summary
0.5J
0.6J
0.7J
0.8J
1.0J
1.2J
1.4J
1.6J
Total
1Hz 8
8
8
8
8
8
8
8
64
3.4
3.5
3.625
3.45
3.625
3.65
3.95
4.025
29.2
Average
0.425
0.438
0.453
0.431
0.4531
0.456
0.49
0.503
0.46
Variance
0.002
0.003
1E-03
0.002
0.002
0.001
0
0.002
0
Count Sum
2 Hz 8
8
8
8
8
8
8
8
64
Sum
3.325
3.95
3.95
4.475
5.225
5.25
6.23
6.45
38.9
Average
0.416
0.494
0.494
0.559
0.6531
0.656
0.78
0.806
0.61
Variance
0.002
0.004
1E-04
0.004
0.0029
0.002
0
0.004
0.02
8
8
8
8
64
Count
3 Hz Count
8
8
8
8
4.3
4.5
4.875
4.775
5.375
6.2
6.35
7.425
43.8
Average
0.538
0.563
0.609
0.597
0.6719
0.775
0.79
0.928
0.68
Variance
0.005
0.002
0.002
0.007
0.0038
0.004
0
0.01
0.02
Sum
4 Hz 8
8
8
8
8
8
8
8
64
Sum
4.75
5.275
5.85
5.925
6.175
6.6
8.1
8.7
51.4
Average
0.594
0.659
0.731
0.741
0.7719
0.825
1.01
1.088
0.8
Variance
0.004
7E-04
0.004
0.002
0.0028
0.008
0
0.009
0.03
8
8
8
8
8
8
8
8
64
Sum
5.6
5.875
6.05
6.775
7.525
8.15
8.13
8.975
57.1
Average
0.7
0.734
0.756
0.847
0.9406
1.019
1.02
1.122
0.89
Variance
0.002
0.006
0.004
0.005
0.005
0.007
0.01
0.013
0.03
Count
5 Hz Count
6 Hz 8
8
8
8
8
8
8
8
64
Sum
5.95
6.05
6
6.45
8.95
8.975
8.28
10.03
60.7
Average
0.744
0.756
0.75
0.806
1.1188
1.122
1.03
1.253
0.95
Variance
0.002
0.001
0.002
0.003
0.0008
0.008
0
0.013
0.04
Count
314
Descriptive statistics: Dry depth
Summary
0.5J
0.6J
0.7J
0.8J
1.0J
1.2J
1.4J
1.6J
Total
1Hz Count
8
8
8
8
8
8
8
8
64
Sum
1.4
1.75
1.95
2.3
2.4
2.4
2.5
2.55
17.25
Average
0.175
0.219
0.244
0.288
0.3
0.3
0.313
0.319
0.27
Variance
1E-05
0.001
0.002
1E-03
0.003
0.002
0.002
5E-04
0.004
2 Hz Count
8
8
8
8
8
8
8
8
64
Sum
1.5
2.05
2.5
2.4
2.55
2.7
2.85
3.05
19.6
Average
0.188
0.256
0.313
0.3
0.319
0.338
0.356
0.381
0.306
Variance
2E-04
8E-04
0.002
4E-04
0.002
2E-04
5E-04
0.005
0.005
3 Hz Count
8
8
8
8
8
8
8
8
64
Sum
3
3.25
3.25
3.55
4.15
4.4
4.9
4.7
31.2
Average
0.375
0.406
0.406
0.444
0.519
0.55
0.613
0.588
0.488
Variance
0.002
1E-04
7E-04
0.002
0.001
0.001
0.006
0.009
0.01
4 Hz Count
8
8
8
8
8
8
8
8
64
Sum
3
3.1
3.45
3.7
4.1
4.55
4.8
5.1
31.8
Average
0.375
0.388
0.431
0.463
0.513
0.569
0.6
0.638
0.497
Variance
0.002
9E-04
0.005
0.005
2E-04
0.002
0.002
0.013
0.012
5 Hz Count
8
8
8
8
8
8
8
8
64
Sum
3
3.15
3.55
3.4
4.35
4.4
5.15
5.3
32.3
Average
0.375
0.394
0.444
0.425
0.544
0.55
0.644
0.663
0.505
Variance
4E-04
0.001
4E-04
7E-06
0.003
0.004
0.001
0.002
0.012
6 Hz Count
8
8
8
8
8
8
8
8
64
Sum
3.05
2.4
3.5
2.95
4.8
5
3.95
5.2
30.85
Average
0.381
0.3
0.438
0.369
0.6
0.625
0.494
0.65
0.482
Variance
0.002
0.001
0.02
2E-04
0.026
0.009
0.045
0.023
0.029
315
Descriptive statistics: Dry Volume of dome shaped Oblate Ellipsoid crater
Summary
0.5J
0.6J
0.7J
Count Sum Average Variance
8 0.1334 0.0167 1E-05
8 0.1751 0.0219 3E-05
8 0.2109 0.0264 3E-05
Count Sum Average Variance
8 0.1367 0.0171 1E-05
8 0.2636 0.0329 8E-05
8 0.3187 0.0398 4E-05
Count Sum Average Variance
8 0.4661 0.0583 0.0004
8 0.5406 0.0676 0.0001
8 0.6378 0.0797 0.0002
Count Sum Average Variance
8 0.5576 0.0697 0.0002
8 0.709 0.0886 0.0002
8 0.9586 0.1198 0.0003
Count Sum Average Variance
8 0.7722 0.0965 0.0002
8 0.8885 0.1111 0.0003
8 1.0668 0.1333 0.0004
Count Sum Average Variance
8 0.8863 0.1108 0.0003
8 0.7232 0.0904 0.0002
8 1.0376 0.1297 0.0023
0.8J 1 Hz 8 0.2268 0.0283 5E-05 2 Hz 8 0.3963 0.0495 0.0001 3 Hz 8 0.6627 0.0828 0.0004 4 Hz 8 1.0567 0.1321 0.0003 5 Hz 8 1.2853 0.1607 0.0007 6 Hz 8 1.0098 0.1262 0.0004
1.0J
1.2J
1.4J
1.6J
Total
8 0.2592 0.0324 7E-05
8 0.2634 0.0329 6E-05
8 0.3181 0.0398 4E-05
8 0.3424 0.0428 9E-05
64 1.929 0.03 1E-04
8 0.5721 0.0715 0.0002
8 0.6116 0.0764 0.0001
8 0.908 0.1135 0.0003
8 1.0443 0.1305 0.001
64 4.251 0.066 0.002
8 0.9899 0.1237 0.0007
8 1.3898 0.1737 0.0009
8 1.6235 0.2029 0.0016
8 2.1753 0.2719 0.008
64 8.486 0.133 0.007
8 1.2836 0.1604 0.0005
8 1.6261 0.2033 0.0014
8 2.5748 0.3218 0.0008
8 3.2007 0.4001 0.0141
64 11.97 0.187 0.014
8 2.0142 0.2518 0.0012
8 2.3964 0.2996 0.0026
8 2.8033 0.3504 0.0055
8 3.5111 0.4389 0.0077
64 14.74 0.23 0.016
8 3.1737 0.3967 0.0144
8 3.3587 0.4198 0.0129
8 2.2545 0.2818 0.0186
8 4.3187 0.5398 0.0272
64 16.76 0.262 0.035
316
Descriptive statistics: Wet Diameter
Summary
0.5J
0.6J
0.7J
Count Sum Average Variance
8 2.925 0.366 0.002
8 3.35 0.419 0.002
8
Count Sum Average Variance
8 3.225 0.403 0.005
8 3.75 0.469 0.003
3.8 0.475 0.002
Count Sum Average Variance
8 4.125 0.516 0.011
8 4.25 0.531 0.015
8 4.325 0.541 0.002
Count Sum Average Variance
8 4 0.5 2E-04
8 4.35 0.544 0.004
8 4.55 0.569 0.009
Count Sum Average Variance
8 4.35 0.544 0.005
8 4.7 0.588 0.005
8 4.8 0.6 0.008
Count Sum Average Variance
8 4.275 0.534 0.002
8 4.975 0.622 0.006
8 5.35 0.669 0.003
3.4 0.425 7E-04 8
0.8J 1Hz 8 3.35 0.419 0.001 2 Hz 8 4.375 0.547 0.003 3 Hz 8 4.375 0.547 0.004 4 Hz 8 4.225 0.528 0.003 5 Hz 8 5.175 0.647 0.008 6 Hz 8 5.475 0.684 0.012
1.0J
1.2J
1.4J
1.6J
Total
8 3.525 0.4406 0.0016
8 3.575 0.447 0.002
8 3.75 0.469 8E-04
8 4.075 0.509 3E-04
64 27.95 0.437 0.003
8 4.875 0.6094 0.0095
8 5.75 0.719 0.006
8 5.875 0.734 0.007
6.4 0.8 0.006
64 38.05 0.595 0.023
8 4.4 0.55 0.002
8 5.175 0.647 0.007
8 6.075 0.759 3E-04
8 6.375 0.797 0.005
64 39.1 0.611 0.016
8 5.65 0.7063 0.0098
8 6.15 0.769 0.02
8 6.125 0.766 5E-04
8 5.575 0.697 0.01
64 40.63 0.635 0.017
8 6.275 0.7844 0.0118
8 6.125 0.766 0.008
8 6.3 0.788 0.01
8 6.2 0.775 0.005
64 43.93 0.686 0.016
8 5.875 0.7344 0.0084
8 6.05 0.756 0.02
8 7.5 0.938 0.035
8 7.5 0.938 0.015
64 47 0.734 0.029
8
317
Descriptive statistics: Wet Depth Summary 1Hz Count Sum Average Variance
0.5J
0.6J
0.7J
0.8J
1.0J
1.2J
1.4J
1.6J
Total
8 1.7 0.213 9E-04
8 1.65 0.206 0.002
8 2 0.25 0.0011
8 2.35 0.294 8E-04
8 2.25 0.281 0.002
8 2.6 0.325 4E-04
8 2.85 0.356 5E-04
8 2.65 0.331 0.002
64 18.05 0.282 0.004
2 Hz Count Sum Average Variance
8 1.7 0.213 2E-04
8 1.75 0.219 5E-04
8 2.15 0.2688 0.0001
8 2.35 0.294 0.001
8 2.5 0.313 9E-04
8 2.55 0.319 0.002
8 2.7 0.338 0.003
8 2.65 0.331 0.004
64 18.35 0.287 0.003
3 Hz Count Sum Average Variance
8 1.8 0.225 0.002
8 1.8 0.225 0.002
8 2.4 0.3 0.0054
8 2.65 0.331 0.001
8 2.75 0.344 0.004
8 2.8 0.35 0.003
8 2.95 0.369 0.002
8 2.9 0.363 2E-04
64 20.05 0.313 0.005
4 Hz Count Sum Average Variance
8 1.8 0.225 7E-04
8 1.85 0.231 5E-04
8 2.4 0.3 0.0054
8 2.45 0.306 0.002
8 2.6 0.325 0.002
8 2.65 0.331 0.001
8 2.75 0.344 0.002
8 2.95 0.369 1E-04
64 19.45 0.304 0.004
5 Hz Count Sum Average Variance
8 2.55 0.319 1E-04
8 2.6 0.325 4E-04
8 2.6 0.325 0.0011
8 2.6 0.325 4E-04
8 2.7 0.338 0.007
8 2.7 0.338 0.004
8 2.85 0.356 5E-04
8 2.9 0.363 2E-04
64 21.5 0.336 0.002
6 Hz Count Sum Average Variance
8 1.95 0.244 0.002
8 2.1 0.263 0.003
8 2.55 0.3188 0.0012
8 2.5 0.313 0.002
8 2.45 0.306 0.005
8 2.85 0.356 0.001
8 2.75 0.344 8E-04
8 2.8 0.35 0.001
64 19.95 0.312 0.003
318
Descriptive statistics: Wet Volume Summary
0.5J
0.6J
0.7J
0.8J
1.0J
1.2J
1.4J
1.6J
Total
1 Hz Count
8
8
8
8
8
8
8
8
64
Sum
0.1212
0.1502
0.1893
0.2172
0.2287
0.2739
0.3289
0.3595
1.869
Average
0.0151
0.0188
0.0237
0.0272
0.0286
0.0342
0.0411
0.0449
0.029
Variance
2E-05
1E-05
2E-05
3E-05
3E-05
5E-05
3E-05
3E-05
1E-04
2 Hz Count
8
8
8
8
8
8
8
8
64
Sum
0.1492
0.2039
0.258
0.3699
0.498
0.693
0.7733
0.8958
3.841
Average
0.0186
0.0255
0.0323
0.0462
0.0622
0.0866
0.0967
0.112
0.06
Variance 3 Hz Count Sum Average Variance
5E-05
4E-05
5E-05
1E-04
0.0005
0.0004
0.0008
0.001
0.001
8 0.2628 0.0329 0.0002
8 0.2767 0.0346 0.0003
8 0.3713 0.0464 0.0002
8 0.4391 0.0549 0.0002
8 0.6252 0.0782 0.0006
8 0.8936 0.1117 0.0003
8 0.9715 0.1214 0.0006
64 4.254 0.066 0.001
Count Sum Average
8 0.2364 0.0296
8 0.2905 0.0363
8 0.4111 0.0514
8 0.4139 0.0517 8E-05 4 Hz 8 0.364 0.0455
8 0.6934 0.0867
8 0.8347 0.1043
8 0.8433 0.1054
8 0.765 0.0956
64 4.439 0.069
Variance
2E-05
8E-05
0.0003
0.0007
0.0013
0.0002
0.0006
0.001
Count Sum Average Variance
8 0.4029 0.0504 0.0002
8 0.4773 0.0597 0.0002
8 0.4958 0.062 0.0003
8 0.868 0.1085 0.0011
8 0.8198 0.1025 0.0003
8 0.9414 0.1177 0.001
8 0.9183 0.1148 0.0004
64 5.503 0.086 0.001
Count Sum Average Variance
8 0.2925 0.0366 8E-05
8 0.4371 0.0546 0.0005
8 0.6036 0.0754 0.0003
0.0001 5 Hz 8 0.5792 0.0724 0.0004 6 Hz 8 0.6045 0.0756 0.0002
8 0.6861 0.0858 0.0006
8 0.8776 0.1097 0.0014
8 1.3066 0.1633 0.0043
8 1.2827 0.1603 0.0009
64 6.091 0.095 0.003
319
2. Kolmogorov Smirnov test: To test for normal distribution of data Dry –diameter Group
KS
1 Hz.
0.5J
0.2500
P Value >0.10
Passed normality test? Yes
2 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2734 0.3166 0.2854 0.3108 0.3159 0.4600 0.3447 0.3105
>0.10 >0.10 >0.10 >0.10 >0.10 0.0678 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
3 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3359 0.4554 0.2393 0.3232 0.3095 0.4539 0.2400 0.4520
>0.10 0.0724 >0.10 >0.10 >0.10 0.0740 >0.10 0.0760
Yes Yes Yes Yes Yes Yes Yes Yes
3 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2273 0.3825 0.2579 0.1506 0.2291 0.2881 0.2610 0.3211
0.10 0.10 0.10 0.10 0.10 0.10 0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
5 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2221 0.3739 0.4495 0.2865 0.2373 0.2546 0.2793 0.2253
>0.10 >0.10 0.0789 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
6 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3273 0.3341 0.2760 0.3236 0.3370 0.4345 0.2467 0.3128
>0.10 >0.10 >0.10 >0.10 >0.10 0.0975 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J
0.3273 0.2500 0.2231 0.3350 0.2643 0.2294 0.1517
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes
320
Dry: depth Group 1 Hz.
0.5J
0.2500
P Value >0.10
2 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2851 0.1801 0.1558 0.2108 0.2500 0.1500 0.2387 0.2298
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
3 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3364 0.1506 0.2500 0.2613 0.3205 0.2387 0.2982 0.2500
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
4 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3256 0.3404 0.3008 0.2851 0.1975 0.2827 0.3251 0.2500
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
5 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.1489 0.2982 0.3013 0.2298 0.1887 0.4169 0.2760 0.2500
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J
0.2814 0.2471 0.3750 0.2631 0.2736 0.4035 0.1500 0.1893 0.2730 0.2843 0.4308 0.3252 0.1552 0.2042 0.2879
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
6 Hz.
KS
Passed normality test? Yes
321
Dry Volume 1 Hz
2 Hz
3 Hz
4 Hz
5 Hz
6 Hz
Energy 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 0.5J
KS 0.2110 0.3252 0.1535 0.1599 0.2031 0.2615 0.1555 0.2608 0.2350 0.2603 0.1744 0.2406 0.3466 0.2960 0.3173 0.2563 0.2999 0.2514 0.2571 0.1925 0.1717 0.2056 0.1679 0.1940 0.2058 0.1424 0.2224 0.2856 0.2303 0.1802 0.2023 0.2145 0.1221 0.1517 0.2172 0.2637 0.2357 0.2328 0.2888 0.3055 0.2881 0.2246 0.1801 0.2071 0.2986 0.1910 0.1881 0.1991
P Value >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Passed normality test? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
322
Wet: diameter
1 Hz.
2 Hz.
3 Hz.
4 Hz.
5 Hz.
6 Hz.
Group 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J 0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J
KS 0.1558 0.3074 0.2500 0.3304 0.2771 0.2029 0.2401 0.4429 0.2736 0.3537 0.4481 0.3065 0.2293 0.4086 0.3216 0.2500 0.3145 0.2756 0.2822 0.2811 0.2453 0.1791 0.4429 0.3686 0.3750 0.1888 0.3304 0.3533 0.4209 0.3220 0.3774 0.4517 0.2413 0.1667 0.2589 0.2854 0.2166 0.2038 0.3353 0.2363 0.3052 0.1416 0.3926 0.2215 0.1966 0.2324 0.2272 0.3222
P Value >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 0.0867 >0.10 >0.10 0.0805 >0.10 >0.10 >0.10 >0.10 0.0867 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 0.0867 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 0.0765 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Passed normality test? Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
323
Wet depth Group
KS
P Value
Passed normality test?
1 Hz.
0.5J
0.1621
>0.10
Yes
2 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3067 0.2775 0.3350 0.3204 0.2500 0.3012 0.1872 0.3252
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
3Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3012 0.4554 0.3159 0.1621 0.1872 0.2519 0.3223 0.2229
>0.10 0.0724 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
4Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2229 0.2527 0.3159 0.3610 0.3252 0.3021 0.3252 0.3252
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
5Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.3012 0.2527 0.1872 0.2229 0.3159 0.3204 0.4554 0.4554
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 0.0724 0.0724
Yes Yes Yes Yes Yes Yes Yes Yes
6 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2500 0.2775 0.2500 0.2790 0.2298 0.3012 0.3252 0.3204
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J
0.3350 0.4554 0.3012 0.3232 0.4554 0.3350 0.2500
>0.10 0.0724 >0.10 >0.10 0.0724 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes
324
Wet Volume Group
KS
P Value
Passed normality test?
1 Hz.
0.5J
0.1833
>0.10
Yes
2 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2427 0.2516 0.2648 0.2714 0.1915 0.1711 0.2008 0.2414
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
3Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2950 0.4517 0.1473 0.2457 0.2150 0.1963 0.2397 0.2462
>0.10 0.0764 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
4Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.1316 0.1413 0.2435 0.2051 0.1826 0.2222 0.3086 0.2730
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
5Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2155 0.1850 0.3006 0.1657 0.2006 0.1787 0.3651 0.2202
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
6 Hz.
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J 0.5J
0.2312 0.1929 0.2399 0.1961 0.1928 0.2775 0.2075 0.1328
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes Yes
0.6J 0.7J 0.8J 1.0J 1.2J 1.4J 1.6J
0.2852 0.3253 0.2391 0.1725 0.2580 0.2173 0.1648
>0.10 >0.10 >0.10 >0.10 >0.10 >0.10 >0.10
Yes Yes Yes Yes Yes Yes Yes
325
ANOVA: Two-Factor with Replication 1. Dry diameter- ANOVA Source of Variation Sample Columns Interaction Within Total
SS 10.94 6.07 1.445 1.306 19.76
df 5 7 35 336 383
MS 2.188 0.867 0.041 0.004
F 562.7 223 10.62
P-value 7E-161 4E-122 2E-36
F crit 2.241 2.037 1.458
2. Dry depth – ANOVA Source of Variation
SS
df
MS
F
P-value
F crit
Sample
3.645
5
0.729
164
7E-88
2.241
Columns
2.468
7
0.353
79.34
2E-67
2.037
Interaction
0.563
35
0.016
3.618
5E-10
1.458
Within
1.493
336
0.004
Total
8.168
383
3. Dry Volume of dome shaped Oblate Ellipsoid crater- ANOVA Source of Variation
SS
df
MS
F
P-value
F crit
Sample
2.6866
5
0.5373
202.48
4E-99
2.2409
Columns
2.525
7
0.3607
135.93
5E-94
2.0369
Interaction
1.2083
35
0.0345
13.009
5E-44
1.4583
Within
0.8916
336
0.0027
Total
7.3115
383
326
ANOVA: Two-Factor with Replication
4. Wet diameter – ANOVA Source of Variation
SS
df
MS
F
P-value
F crit
Sample
3.324
5
0.665
101.3
6E-65
2.241
Columns
3.569
7
0.51
77.72
2E-66
2.037
Interaction
0.804
35
0.023
3.502
1E-09
1.458
Within
2.204
336
0.007
Total
9.901
383
SS
df
5. Wet depth –ANOVA Source of Variation
MS
F
P-value
F crit
Sample
0.124
5
0.0247
14
2E-12
2.241
Columns
0.646
7
0.0922
52.21
4E-50
2.037
Interaction
0.107
35
0.003
1.725
0.008
1.458
Within
0.593
336
0.0018
Total
1.469
383
6. Wet volume of dome shaped Oblate Ellipsoid crater- ANOVA
Source of Variation
SS
df
MS
F
P-value
F crit
Sample
0.1686
5
0.0337
76.282
3E-53
2.2409
Columns
0.3014
7
0.0431
97.418
6E-77
2.0369
Interaction
0.0581
35
0.0017
3.7584
1E-10
1.4583
Within
0.1485
336
0.0004
Total
0.6766
383
327
T test: Paired Two Sample for Means- Dry vs. wet diameter 1 Hz 0.5J 8Dry vs. 8Wet
0.6J 8Dry vs. 8Wet
0.7J 8Dry vs. 8Wet
0.8J 8Dry vs. 8Wet
1.0J 8Dry vs. 8Wet
1.2J 8Dry vs. 8Wet
1.4J 8Dry vs. 8Wet
1.6J 8Dry vs. 8Wet
Pearson Correlation Hypothesized Mean Difference
0.283
-0.226
-0.2
0.553
0.019
-0.49
0.37
-0.39
0
0
0
0
0
0
0
0
df
7
7
7
7
7
7
7
7
t Stat
2.967
0.753
1.76
1
0.592
0.406
2.16
-0.34
P(T
