Histopathological study of the effects of Er:YAG laser irradiation on root canals in rats

The thermal effects of Er:YAG laser irradiation on the periodontal region during root canal preparation were evaluated using rats histopathologically. One hundred mesial root canals of mandibular first molars in rats were divided into four groups. In three of these groups, root canals were irradiated using an Er:YAG laser at 2 Hz and 34, 68, and 102 mJ/pulse for 30 s. Nonirradiated canals served as controls. The effects of laser irradiation on the periodontal tissues along the root surface and apical area were evaluated at 0, 2 days, 1, 2, and 4 weeks after irradiation under light microscopy. At 4 weeks after treatment, no inflammation or resorption was observed in any case in the control or 34 mJ/pulse-irradiated groups. However, moderate to severe inflammation with resorption of root surface was observed in four of five cases (80%) in the 102 mJ/pulse-irradiated group, which was significantly different from the control (P < 0.01). These results suggest that thermal effects on periodontal tissues during root canal preparation by Er:YAG laser irradiation after pulpectomy are minimal, if appropriate parameters are selected. (C) 2002 Elsevier Science B.V. All rights reserved.