This study investigated the thermal effects and the morphological changes after diode laser irradiation (810 nm) of root canals. Samples were irradiated at 2.5 W, 1,989 W/cm2 (group 2) and 1.25 W, 10 Hz, 994 W/cm2 (group 3), with group 1 being the control group of nonirradiated samples. The temperature rise was evaluated using an infrared thermographic camera, and the morphological changes were assayed by scanning electron microscopy (SEM). The SEM images revealed closed dentinal tubules, especially at the apical regions when compared with the control samples. The maximum temperature variations at the apical region were analyzed, and the resulting 95% confidence intervals of the medians (Wilcoxon) ranged from 1.6 to 8.6 degrees C (group 2) and from 1.2 to 3.3 degrees C (group 3). The results suggest that the diode laser can be used for endodontic purposes and show that the method is safe for periodontal tissues at the investigated parameters.