To determine the shaping ability, the amount of accumulated hard tissue debris (AHTD) and untouched area is generated by different kinematics through micro-CT. Thirty-two mesial roots of mandibular molars with Vertucci type IV were pre-scanned through micro-CT evaluation and randomized to one of the four experimental groups according to the kinematics tested: Continuous Rotation (CR), Reciprocation (REC), Optimum Torque Reverse (OTR) and Jeni motion. The root canal preparation was performed with HyFlex EDM (Coltène/Whaledent AG) up to OneFile. After each file used, irrigation was performed with 2 mL 5.25% NaOCl for 1 min. The final rinse was performed with 1 ml of 5.25% NaOCl followed by a 1 ml of 17% EDTA and, 1 ml of distilled water. Then, the samples were scanned and the images, before and after preparation, were superimposed and analyzed to determine the AHTD, untouched areas, canal transportation, centering ability, and shaping time. Data were statistically analyzed using Kruskal–Wallis test and Dunn post hoc with p < 0.05. No significant differences were detected among the tested kinematics in terms of untouched areas, AHTD, canal transportation and shaping time (p > 0.05). Significantly more untouched areas were detected in the coronal third compared to the middle (p = 0.0301) and apical ones (p = 0.0399) under continuous rotation. Moreover, a significantly higher centering ratio in the middle third compared to the apical was observed for Jeni motion (p = 0.0207). The tested kinematics showed similar untouched areas, AHTD, shaping ability and shaping time. All motions determined an appropriate mechanical preparation; yet, none of them was able to prepare all canal walls and keep the root canals completely free from hard tissue debris.
