Effect of endodontic motor battery levels on the cyclic fatigue resistance of NiTi Files: an in vitro study using the X-Smart plus motor

Abstract Background Nickel–titanium (NiTi) rotary and reciprocating instruments have significantly improved the efficiency and predictability of root canal shaping; however, unexpected instrument fracture due to cyclic fatigue remains a major clinical concern. Although the effects of instrument design and kinematic motion on cyclic fatigue resistance have been extensively investigated, the potential influence of endodontic motor battery indicator level on instrument performance has not yet been evaluated. Therefore, this study aimed to assess the effect of different endodontic motor battery indicator levels on the cyclic fatigue resistance of rotary and reciprocating NiTi instruments. Methods Two NiTi instrument systems, WaveOne Primary (reciprocating motion) and VDW ROTATE (continuous rotational motion), were tested using an X-Smart Plus endodontic motor under three battery charge levels (full, half, and low). A total of 180 instruments ( n = 30 per group) were evaluated in standardized stainless steel artificial canals with a 60° curvature angle and 5-mm radius. Time to fracture was recorded using high-speed video imaging, and cyclic fatigue resistance was calculated as the number of cycles to failure (NCF). Fracture surfaces were examined using scanning electron microscopy (SEM). Statistical analyses included two-way analysis of variance (ANOVA), within-instrument one-way ANOVA with Tukey post-hoc comparisons, effect size estimation, and post-hoc power analysis. Results VDW ROTATE instruments demonstrated significantly higher NCF values than WaveOne Primary instruments across all battery indicator levels ( p < 0.001). Low-battery groups showed lower mean NCF values than the full- and half-battery groups in both instrument systems. Two-way ANOVA showed significant main effects of instrument system and battery indicator level, whereas the instrument system × battery level interaction was not statistically significant. In the additional E-Connect S validation experiment, no significant difference in NCF was observed among battery indicator levels ( p = 0.844). SEM analysis confirmed typical fracture patterns consistent with cyclic fatigue in all groups. Conclusion Within the limitations of this in vitro study using the X-Smart Plus motor, low battery indicator level was associated with lower nominal NCF values in both tested NiTi instrument systems. VDW ROTATE instruments showed higher cyclic fatigue resistance than WaveOne Primary instruments across all battery indicator levels. Direct voltage measurements confirmed progressively lower operating voltages across the battery-indicator levels, whereas no statistically significant difference in actual rotational speed was observed in continuous-rotation mode. However, torque output and reciprocating motion were not directly measured, and no statistically significant battery-level effect was detected in the additional E-Connect S validation experiment.