根管象牙質の疲労強度に対するEr:YAG、Er,Cr:YSGGおよび半導体レーザー照射の影響の評価（改良型根管治療用レーザーチップを使用）

Laser-assisted endodontic treatments have gained popularity over the last decade. This study evaluated the flexural strength (FS), fatigue resistance, and surface characteristics of root dentine after laser-assisted endodontic protocols. Forty extracted, caries-free canines were used to prepare root dentine beams (n = 37/group). Beams were irradiated with (1) Er:YAG 2,940 nm (20 mJ, 0.3W, 15 Hz, 50 ms), (2) Er,Cr:YSGG 2,780 nm (2.25W, 50 Hz, 140 ms), and (3) 940 nm diode laser (1W, CW). The non-irradiated beams served as control group. Both erbium groups were treated with laser-activated irrigation with radial firing tips (RFTs); meanwhile, the diode group irradiation protocol, using RFT, was dry. Specimens underwent quasi-static loading (n = 12) and cyclic loading for fatigue behaviour (n = 25) using 4-point flexure test. Scanning electron microscopy analysis was performed. Data were analysed using analysis of variance and Kruskal-Wallis tests (α = 0.05). No significant difference was found in FS or fatigue resistance after laser-assisted treatment (p > 0.05), but endurance limits improved by 18% (Er:YAG) and 19% (Er,Cr:YSGG) compared to controls. These findings suggest that Er:YAG, Er,Cr:YSGG, and 940 nm diode lasers, when applied with recommended parameters, do not compromise dentine fatigue strength. Therefore, they may be safely integrated into root canal treatment protocols.