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

Background: This study aimed to evaluate the accuracy of four hybrid endodontic motors-VDW Gold (VDW), 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.

Materials 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 Optimum Glide Path (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.