Determination of the effect of Nd:YAG laser irradiation through dentinal tubules on several oral pathogens.

The effects of Nd:YAG laser irradiations at different power settings on several oral pathogens were evaluated. A total of 252 dentin samples were divided into seven groups consisting of 36 dentin specimens each. In each group, 9 of the 36 specimens were used as controls, thereby including a control in every group. The remaining 27 specimens were divided into three subgroups consisting of nine specimens according to different Nd:YAG laser settings (1.5, 1.8, and 2 W). Each group was inoculated on the nonpulpal side with one of the following microorganisms: Candida glabrata, Candida tropicalis, Candida krusei, Candida sake, Candida lusitaniae, Candida kefyr, and Rhodotorula mucilaginosa. The following irradiation procedure was used: the specimens were irradiated on the bacteria-free side (the side consisting of the pulpal wall) using contact mode under the constant scanning movement of the optical fiber at an angle of 10°. One lasing cycle consisted of four irradiation cycles of 10 s each, with 15-s intervals in between each irradiation cycle. The remainder of the controls and the lased specimens of each group were prepared for the microbiological investigation. After incubation for 24 h at 37 °C, the colonies were counted, and the total number of surviving microorganisms was statistically assessed. Microorganisms irradiated with Nd:YAG laser at power settings 2 W, 15 pps did not survive. Although there was a significant reduction of microorganisms at 1.5 and 1.8 W, when comparing Nd:YAG laser irradiation with the control group, sterilization did not occur.