Smear layer and debris remaining after instrumentation with Mtwo and Alpha Kite rotary files: a scanning electron microscopy study.

Aim To evaluate the presence of smear layer (SL) and debris on the walls of canals shaped with two NiTi sys- tems with or without EDTA final irrigation. Methodology Thirty-two single-rooted freshly extracted teeth were divided into four experimental groups (G1–G4, n = 8) and cut transversally to obtain 12-mm-long roots. Two longitudinal specular grooves were made on their external surfaces with a cutting disc. The canals were shaped with Mtwo (G1 and G2) or Alpha Kite (G3 and G4) rotary files. In all groups, irrigation was performed with 2.4% sodium hypochlorite during instru- mentation; additionally, a 17% EDTA solution was used as a final rinse in G2 and G4. The roots were split, sput- ter-coated with gold and subjected to scanning electron microscope (SEM) examination. Ten micrographs per root third were acquired and scored according to the Hulsmann’s scales for SL and debris. The median value of the 10 scores of each third was regarded as statistical unit, and differences among groups were assessed by means of a Kruskal–Wallis test and a Conover test for pairwise comparisons (a = 0.05). Results There was significantly better SL removal in relation to EDTA irrigation after instrumentation with both NiTi systems, obtaining similarly low SL scores in G2 and G4. When EDTA was not used, Mtwo produced lower SL deposits than Alpha Kite. Regardless of the group, the apical third was poorly cleaned. Limited debris was detected in all groups. Conclusions The best results with the two considered NiTi systems in terms of SL removal were obtained with a 17% EDTA final rinse, which did not affect the remaining debris amount, which was already low. With- out EDTA final rinse, the use of Mtwo rotary files generated a lower SL amount than Alpha Kite, but similar debris.