Purpose: To evaluate the effect of laser irradiation (Nd:YAG and Er:YAG) after conventional endodontic treatment on the cleaness of root canal walls. Materials and Methods: The roots of 9 extracted single-rooted human teeth were conventionally prepared and randomly divided into 3 groups (n = 3 per group): 1. control, not irradiated; 2. Nd:YAG laser irradiation (100 mJ; 1.5 W; 15 Hz, 124.4 J/cm2); 3. Er:YAG laser irradiation (120 mJ, 15 Hz, 1.8 W, 108.7 J/cm2). The teeth were irradiated 3 times with rotational movements in the apical-coronal direction, at a speed of 2 mm of root canal per second. The teeth were bisected longitudinally and prepared for scanning electron microscopy (SEM). Results: Independent of the experimental group, both clean and smear-layer-covered areas were observed in the same sample and the same root canal third. The samples treated with Er:YAG laser mostly presented clean areas. The Nd:YAG laser apparently removed less smear layer than the Er:YAG laser, and left areas completely covered by debris and smear layer. The control root canal walls predominantly exhibited areas covered by smear layer. Conclusion: Complete cleaning of root canal walls with Nd:YAG and Er:YAG laser radiation with the power settings used here was not possible. Although the cleaning capacity of laser could improve conventional endodontic treatment, there is still a need to develop devices which can irradiate root canal walls in their entirety.

Keywords: Er:YAG laser, Nd:YAG laser, root canal, scanning electron microscopy