Shaping ability of two nickel–titanium instruments activated by continuous rotation or adaptive motion:a micro-computed tomography study

Objectives: The objective of the study was to evaluate the shaping ability of curved root canals using Twisted File Adaptive (TFA) files (SybronEndo, Orange, CA) and Mtwo (Sweden & Martina, Padova, Italy) activated by continuous rotation or adaptive motion. Materials and methods: Thirty-two mandibular molars with two separate mesial canals and severe angles of curvature were selected. Each canal was randomly assigned to one of the four experimental groups (n = 16): TFA and Mtwo files used in continuous rotation (groups 1 and 3) or in adaptive motion (groups 2 and 4). Root canals before and after preparation were assessed by micro-computed tomography. Volume, surface area, canal transportation, and centering ability were recorded and analyzed using two-way analyses of variance. Results: Volume and surface area increased less with TFA files in continuous rotation than in other groups (P <0.001 and P <0.01, respectively, for each comparison) that were not different (P > 0.05). TFA files had significantly less transportation and higher centering ability than Mtwo both in continuous and adaptive motion (P <0.0001). Centering ratio, but not canal transportation, was improved by adaptive motion compared with continuous rotation for both instruments (P <0.01). However, no differences were found in canal transportation and centering ability in the apical third for both instruments and motions (P > 0.05). Conclusions: No difference between the devices and kinematics was found in the apical third; TFA performed significantly better in the middle and coronal parts of the root canal. Clinical relevance: The use of NiTi files made by heat-treated alloy and/or adaptive motion could improve the qualities of root canal shaping rather than the use of conventional NiTi instruments and/or continuous rotation in the coronal and middle thirds of the root canals, but not in the apical one. Moreover, these findings encourage the use of adaptive motion with conventional NiTi files to improve centering ability without affecting other preparation qualities of root canals.