Middle infrared lasers for endodontic applications

Roy George (2008). Middle infrared lasers for endodontic applications PhD Thesis, School of Dentistry, The University of Queensland.

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s41063307_PhD_abstract.pdf Middle infrared lasers for endodontic applications, Abstract application/pdf 11.84KB 6
s41063307_PhD_totalthesis.pdf Middle infrared lasers for endodontic applications, Total thesis application/pdf 11.89MB 20
Author Roy George
Thesis Title Middle infrared lasers for endodontic applications
School, Centre or Institute School of Dentistry
Institution The University of Queensland
Publication date 2008-10
Thesis type PhD Thesis
Total pages 357
Total colour pages 50
Total black and white pages 307
Subjects 11 Medical and Health Sciences
Abstract/Summary 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 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, with enhanced lateral emissions to address the challenges of irradiating the walls of the root canal.
Keyword Lasers
Smear layer
Rotary NiTi
Holmium lasers
Er:YAG lasers
Digital imaging
Fiber optics.
Additional Notes 13 22 39 55 96 97 98 99 101 115 119 120 121 122 123 124 125 128 136 138 149 159 171 172 175 184 186 187 188 189 191 194 210 211 212 216 217 227 228 229 130 231 232 233 272 273 274 275 276 277

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Created: Mon, 18 May 2009, 11:55:02 EST by Mr Roy George on behalf of Library - Information Access Service