In vitro assessment of integrated apex locator systems: working length accuracy, operational parameter deviations, and mechanical effects on NiTi instruments

OBJECTIVES This study aimed to evaluate the accuracy of four hybrid endodontic motors—VDW Gold (GOLD), iRoot Pro (IRP), E-Connect S (ECS), and TriAuto ZX2 (TZX)—in maintaining length, speed, and angulation during alternating and continuous rotation kinematics and the influence of these parameters on instrument fatigue. MATERIAL AND METHODS Forty-eight mandibular incisors (n = 12 per group) were used to assess apex locator accuracy during glide path procedures with alternating rotation and auto apical stop (AAS) set to the apical foramen (AF: 0.0). Positioning precision was evaluated using micro-CT, while torsional resistance of instruments was tested per ISO 3630-1. Actual speed and angulation were measured using a tachometer and Arduino system. Cyclic fatigue testing was conducted with Only One File 25.08 instruments in an artificial curved canal (60°, 5 mm radius). Data were statistically analyzed with a significance level of 5%. RESULTS The evaluated devices exhibited similar precision (p > 0.05). The TZX showed the lowest number of determinations beyond the AF (p < 0.05). Regarding torsional testing, no significant differences were observed between groups (p > 0.05). The equipment showed substantial differences compared to the values displayed on the screen (p < 0.05). The OGP motion provided significantly higher resistance to cyclic fatigue (p < 0.05). CONCLUSIONS All hybrid motors were accurate in length control, with TZX being the most conservative. Kinematics did not influence torsional resistance, but significant differences were found between programmed and real parameters. CLINICAL RELEVANCE: Hybrid motors exhibited similar and accurate length control. OGP motion provided significantly higher resistance to cyclic fatigue.