Comparative study about the removal of smear layer by three types of laser devices.

Abstract

The aim of this study was to analyze the effectiveness of three types of laser, argon, Nd:YAG, and Er:YAG, to remove the smear layer from the prepared root canal walls in vitro. After cleaning and shaping by step-back preparation, 32 human extracted maxillary molar teeth were divided randomly into four groups. Root canals in group 1 (G1) were unlased and were irrigated by 17% EDTA. In group (G2), root canals were irradiated by argon laser at the parameters of 1 W, 50 mJ, and 5 Hz. In group 3 (G3) root canals received Nd:YAG laser irradiation at 2 W, 200 mJ and 20 Hz. Teeth in group 4 (G4) were irradiated by Er:YAG laser at the following parameters: 1 W, 100 mJ and 10 Hz. Then these teeth were bisected longitudinally, observed using SEM, and evaluated. The middle third of the teeth from G1 showed clean wall surfaces with open dentinal tubules. In G2, at the middle third, the smear layer was free and vaporized pulpal tissue remnants were observed. In G3, most of the specimens showed very clean walls with the smear layer evaporated, melted, fused, and recrystallized in both the middle and apical thirds. The walls of G4 revealed the evaporated smear layer and open dentinal tubules in the middle and apical thirds. Statistical analysis showed significant differences between G1 and G2, G1 and G3, and G1 and G4. These results show that the argon laser and Nd:YAG laser are useful to remove the smear layer and that the Er:YAG laser irradiation is the most effective to remove the smear layer on root canal walls.