Purpose: To investigate in vitro the removal of smear layer, plug, debris, and pulp tissue by Nd:YAG irradiation with different potencies and times, with or without black ink on the apical root canal wall. Materials and Methods: Twenty-five extracted human teeth were divided into 5 groups after endodontic treatment. G1: no laser irradiation, control; G2: Nd:YAG laser 1 W, 1 s, 20 pps, 50 mJ; G3: Nd:YAG laser 2 W, 1 s, 20 pps, 50 mJ; G4: Nd:YAG laser 1 W, 2 s, 20 pps, 50 mJ, black ink; G5: Nd:YAG laser 2 W, 1 s, 20 pps, 50 mJ, black ink. All teeth were sectioned and analyzed under light microscope and SEM. Results: Statistically significant differences were observed among the 5 groups, p = 0. 0027(p < 0.05). No significant difference was found between G1 (control) and G2 (1 W, 1 s), p = 0.8345 (p > 0.05), nor between G3 (2 W, 1 s) and G5 (2 W, 1 s, black ink), p = 0.0758 (p > 0.05). However, a marked difference was seen between G4 (1 W, 2 s, black ink) and G5 (2 W, 1 s, black ink), p = 0.0367 (p < 0.05). A statistically significant difference (p < 0.05) was found between G3 (no black ink) and G5 (black ink) regarding carbonization. Conclusion: Nd:YAG irradiation was effective in the removal of smear layer, plug, debris, and pulp tissue, even without an initiator (black ink) in the potencies of 1 W, 2 s and 2 W, 1 s, but the use of black ink caused less carbonization in the potency of 2 W and 1 s, which may suggests it is safer. However, the treatment with 1 W, 2 s was considered more efficient than the treatment with 2 W, 1 s. Nevertheless, Nd:YAG laser treatment was not sufficiently effective with 1 W, 1 s.

Keywords: Nd:YAG laser, black ink, smear layer, plug, debris, carbonization