Effects of pulsed Nd:YAG laser irradiation on smear layer at the apical stop and apical leakage after obturation

AIM: This study evaluated the removal of smear layer at the apical stop by pulsed Nd:YAG laser irradiation with or without black ink, and the degree of apical leakage after obturation in vitro. METHODOLOGY: Sixty extracted human single-rooted teeth were used in this study. The teeth were instrumented up to a size 40 K-file, and then divided into three groups of 20 teeth each: group 1 was unlased as a control group; group 2 was treated with a laser; group 3 was treated with a laser and black ink. The laser was operated at 2 W and 20 pp for 2 s, and irradiation was performed twice with a 30-s interval. In each group, 10 teeth for the leakage study were obturated and immersed in rhodamine B solution for 48 h at 37 degrees C, and the others were used for evaluation of remaining smear layer. All teeth were bisected longitudinally and observed by stereoscopy or scanning electron microscopy. RESULTS: The smear layer in the laser-treated groups almost melted or evaporated, and was removed significantly compared with the control group (P < 0.05). Leakage was observed in 60% of samples in group 1 and in 20% of samples in group 2. No leakage was observed in group 3, which was significantly different from the control (P < 0.05). CONCLUSIONS: These results suggest that pulsed Nd:YAG laser irradiation with black ink increases the removal of smear layer compared with that without black ink, and reduces apical leakage after obturation significantly.