Since the development of the ruby laser by Maiman in 1960 and the application of the laser in the endodontic field by Weichman in 1971, many papers on the use of lasers have been published and much information has been accumulated. Although research on new devices and methods of using lasers in endodontics has continued, there have been few review articles on this area. Accordingly, this study aimed to summarize the latest information on the use of lasers in endodontics. This paper examines the following: diagnosis of dental pulp, treatment of dentinal hypersensitivity, applications for the treatment of pulp capping and pulpotomy, effects of lasers on root canal walls, root canal preparation by lasers, effects of lasers on periodontal tissues, application for apicoectomy, and other applications for endodontic treatment. The key question is whether laser treatment can provide equal or better treatment than conventional care. This article reviews the role of lasers in endodontics since the early 1970s, summarizes many research reports over the last half century, and considers the possible future of lasers in endodontics. With the potential availability and future development of lasers of different wavelength and method of pulsing, interest is growing in this promising field.

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In recent years, antimicrobial photodynamic therapy （a-PDT） has been used in the dental field. In particular, it has many applications for periodontal treatment. It has been reported that the combined use of a-PDT during SRP improves clinical parameters such as periodontal pocket depth, attachment level and BOP, and reduces the number of periodontal pathogenic bacteria. We studied the antimicrobial properties of a-PDT against various dental disease-related bacteria, effects on the root surface, and the resolution of organic matter. This review outlines a-PDT and then introduces our research.

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Photobiomodulation of low-level laser therapy （LLLT） has favorable biological effects on periodontal tissue. We reviewed basic studies on the cytological responses of cells in periodontal tissue for LLLT by Er:YAG laser in vitro. Low-level Er:YAG laser irradiation has been reported to affect proliferation and gene expression in osteoblasts, osteocytes, fibroblasts, and periodontal ligament cells.

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Various types of laser have been developed and put to use in dental procedures in recent years. One of such lasers, called the Erbium, Chromium: Yttrium Scandium Gallium Garnet （Er,Cr:YSGG） laser, can be used to cut hard tissue. In this study, we examined the bond strength of resin composites of 1-bottle 1-step bonding systems to the enamel and dentin after Er,Cr:YSGG laser irradiation, and the effects of removing the denatured dentin with clinical tools on the bond strength. The study was performed after obtaining approval from the Animal Care and Use Committee, Osaka Dental University （Approval No.: 16-09004）. As the 1-bottle 1-step bonding systems, we used G-BOND PLUS （GC, GP）, and AdperTM EASY BOND （3M, EB）. We used bovine teeth, and measured the bond strength to tooth substances with laser irradiation （LI）, in which the laser was uniformly irradiated on the enamel and dentin, and without laser irradiation （Control）. Furthermore, for dentin that was used as the specimen, we measured the bond strength and conducted Scanning Electron Microscope （SEM） observation on the fractured surface under five conditions intended to remove the dentin denatured by laser: phosphoric acid etching for 20 sec after laser irradiation （LI＋PA）, cutting with a round-shaped steel bur or spoon excavator for 20 sec after laser irradiation （RB, SE）, and phosphoric acid etching for 20 sec after cutting with either tool （RB＋PA, SE＋PA） （n＝5）. We conducted statistical analysis on the measurement results according to two-way analysis of variance and Tukey’s test （P＜0.05）. As a result of two-way analysis of variance on the effects of Er,Cr:YSGG laser irradiation on the bond strength to enamel and dentin, we found that neither the bonding system nor the use of laser irradiation affected the tensile bond strength to enamel, and observed no interactions between the two factors. However, we found that the bonding system and the use of laser irradiation significantly affected the tensile bond strength to dentin, and observed interactions between the two factors. As to the effects of removing denatured dentin on the bond strength to dentin, the tensile bond strength of the RB group was significantly higher than LI, LI＋PA or SE＋PA with GP, and higher than LI or SE＋PA with EB. Based on the results of these experiments on the bond strength of the 1-bottle 1-step bonding systems to the tooth substances after Er,Cr:YSGG laser irradiation, we found that the bond strength to the enamel was favorable after Er,Cr:YSGG laser, but that the bond strength to the dentin was problematic, indicating that further examination on the recovery of bond strength is needed. In addition, removing the denatured layer from the Er,Cr:YSGG laser-irradiated dentin with a round-shaped steel bur effectively recovered the bond strength of the resin composite.

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