OBJECTIVES: The aim of this study was to investigate the efficacy of three newly introduced rotary endodontic systems: Genius ProFlex (Medidenta), TruNatomy (Dentsply Maillefer), and ZenFlex (Kerr). METHODS: Forty-five mandibular molars with root canal curvatures <
5° were utilized. Micro-computed tomography scans were performed pre- and post-preparation to assess apical transportation, centralization, percentage of dentin wear, and canal volume alterations. Eight instruments of each diameter underwent cyclic fatigue testing. RESULTS: The percentage of dentin wear on mesial and distal walls showed no significant differences among ZenFlex, TruNatomy, and Genius ProFlex at 1, 2, 3, and 4 mm from the apical foramen and root canal orifice (p >
0.05). Centering ability varied in the mesiolingual canal (p <
0.05). No notable differences were observed in transportation (p >
0.05). Genius ProFlex demonstrated lower volumetric changes (p <
0.05). There were significant differences in cyclic fatigue, with higher values for Genius ProFlex and lower values for TruNatomy (p <
0.05). CONCLUSIONS: The three nickel-titanium rotary instruments are safe and efficient for root canal preparation, with Genius ProFlex exhibiting superior cyclic fatigue resistance.