Objectives: The aim of the present study was to investigate differences in the amount of dentin microcracking caused by the use of a 970-nm diode laser with different parameters for endodontic disinfection procedures. Materials and methods: Forty dental roots underwent mechanical endodontic preparation in a standardized manner. Each sample was randomly allocated to 4 groups receiving constant or interval laser irradiation time, calcium hydroxide disinfection, or a control group, with 10 samples per group. Transmission microscopy of all samples was performed at T0, before preparation; T1, immediately after endodontic preparation; and T2, after laser application in the laser groups and after 1 week of storage in the control and calcium hydroxide groups. The microcracks at each measurement point were color labeled, layered, and compared. Results: No significant differences were noted at T0 and T1 (p>0.05). Statistically significant differences in the overall amount of microcracking were observed between the constant laser group and all other groups at T2 (p<0.05). There were no statistically significant differences between the interval laser group, the calcium hydroxide group, and the control group at T2 in relation to the overall amount of microcracking (p>0.05). When the root sections were analyzed separately, the coronal section did not show any statistically significant differences between the constant laser and interval laser groups (p>0.05). The middle and apical root sections in the constant laser group showed the significantly largest amount of crack formation in comparison with the other groups (p<0.05). The statistically significantly smallest amount of crack formation was observed in the apical third for all groups (p<0.05). Conclusions: Clinically proposed laser protocol seems to be able to prevent side effects to the tissue, such as microcracks of the root canal dentine.
