de Oliveira DJF, et al. - Researchers matched 32 mesial roots of mandibular molars with severe curvature to assess the shaping ability of 4 different nickel-titanium systems (reflecting their variation in alloy treatment, kinematics, and design) used to prepare canals with severe curvature using micro-computed tomographic analysis. Following were the 4 experimental groups (n = 8) according to the canal preparation: ProTaper Next (PTN; Dentsply Maillefer, Ballaigues, Switzerland), Reciproc (RC; VDW GmbH, Munich, Germany), Reciproc Blue (RCB, VDW GmbH), and TRUShape (TRU; Dentsply Tulsa Dental Specialties, Tulsa, OK) systems. A significant increase due to preparation in all analyzed parameters was noted. They did not observe statistically significant differences between RC and RCB or between PTN and TRS in any of the investigated parameters. RC and RCB presented higher mean increases in the cervical third when compared to PTN and TRU. The instruments of greater taper seemed to promote greater morphologic modifications.