Purpose: This study aimed to compare the in vitro effects of Nd:YAG and Er:YAG laser irradiation on root canal walls using scanning electron microscopy (SEM), and evaluate apical leakage and temperature changes in external root surfaces. Materials and Methods: Seventy-four recently extracted human teeth with single, straight roots were used. The teeth were prepared to 1 mm short of the apical foramen by a conventional technique using K-files and assigned to different groups: G1) no laser irradiation/control; G2) Nd:YAG laser/helicoidal technique; G3) Nd:YAG laser/vertical technique; G4) Er:YAG laser/helicoidal technique; G5) Er:YAG laser/vertical technique; G6) Er:YAG and Nd:YAG laser/helicoidal technique; G7) Er:YAG and Nd:YAG laser/vertical technique. The Nd:YAG laser parameters were 100 mJ, 15 Hz, 0.5 J/cm2, and those of the Er:YAG laser were 160 mJ, 10 Hz, 0.9 J/cm2, for four times at 2 mm/s, with 20-s intervals. Temperature changes were recorded thermographically. All teeth were examined by light microscopy or scanning electron microscopy (SEM). Results: No apical leakage was observed in the teeth irradiated with Nd:YAG laser alone or in association with Er:YAG laser. However, in the teeth irradiated with Er:YAG laser, more pronounced leakage was observed. SEM observation showed that Nd:YAG laser irradiation caused melting and crystallization on dentin surfaces. Er:YAG laser samples showed a clean, debris-free surface with opened dentinal tubules. Specimens irradiated by the combination of the two lasers showed a melted layer covering the dentinal tubules. The temperature increase did not exceed 6°C. Conclusions: This study demonstrated that Nd:YAG laser irradiation with or without adjunct Er:YAG laser irradiation is a potentially suitable means of root canal treatment, since morphological alterations are desirable and it did not cause thermal damage to adjacent tissues.
Keywords: apical leakage, dentin, dentinal tubules, endodontics, Er:YAG, Nd:YAG, scanning electron microscopy, thermographic evaluation