Er:YAGレーザーによる根管内殺菌効果の検討

抄録

One important goal of root canal treatment is the elimination of bacteria from the root canal. The disinfection of root canals involves mechanical enlargement using reamers and files, and chemical cleaning with irrigants such as sodium hypochlorite (NaClO) and ethylene diaminetetra-acetic acid (EDTA). Following that, intracanal medicaments such as formalin cresol and calcium hydroxide are applied in the root canal. However, it is very difficult to completely eliminate bacteria from the root canal due to bacterial invasion of the dentinal tubules, biofilm formation in the accessory canals, bifurcation, and the anatomical complexity of root canal systems such as isthmus and fin. Recently, applications of an Er:YAG laser, including its antibacterial effects, for use in root canal preparation, and in retrograde cavity preparation, have been investigated in endodontics. The effects of an Er:YAG laser on bacteria in the root canal are not known in detail. The purpose of this study was to evaluate the effects of 2.94-μm Er:YAG laser radiation on bacteria and lipopolysaccharides (LPS).
An Er:YAG laser with an R200T irradiation tip was used to irradiate root canals containing suspensions of S. mutans, E. faecalis, or C. albicans and root dentin which LPS penetrates. The output energy was standardized at 30 mJ, and the pulse frequency was 25 pps. We evaluated the bactericidal effects based on the morphological changes of bacteria and the reduction rates of viable bacterial numbers. To confirm the bactericidal effects of the Er:YAG laser, live and dead bacteria invading the root dentin were stained with the LIVE/DEAD^® stain method and observed by fluorescence microscopy. The effects of Er:YAG laser irradiation on LPS-invaded root dentin were evaluated. All statistical evaluations were performed using Student's t-test or two-way ANOVA.
The denaturation of proteins and the destruction of bacteria due to laser irradiation were observed by scanning electron microscopy. The reduction rates of viable bacterial numbers were about 97.4 to 100% for the three bacterial species. A red layer indicating dead bacteria with the LIVE/DEAD^® stain method was observed at 400 μm from the inner dentin surface. The LPS content was significantly lower in the samples from the pulpal surface to 100 μm (p < 0.05).
These results indicate that Er:YAG laser irradiation may be an effective method for intracanal disinfection.