Detection of Failure and Measurement of Number of Cycles to Failure of Nickel–Titanium Rotary files in Bending Fatigue Testing

Objectives: This study aimed to (1) develop a novel method for fabricating simulated root canals, (2) introduce a reliable approach for detecting file fractures, and (3) establish a direct measurement technique for determining the number of cycles to failure (NCF) in bending fatigue tests of rotary files. Materials and Methods: Bending fatigue tests were conducted using a custom setup consisting of a simulated root canal, a handpiece-controller unit, and a signal extraction module for monitoring motor current and encoder signals. The simulated canals were fabricated to match the geometry of 25.06 ZenFlex rotary files, and included five configurations with varying radii (2, 5, and 8 mm) and angle of curvature (30°, 45°, and 60°). Tests were performed at room and body temperatures. File fracture was identified by an abrupt drop in motor current, and the NCF was directly determined from encoder-derived revolution counts. To verify accuracy, encoder-based revolution counts were compared with those measured with a mechanical counter. In addition, the proposed method was benchmarked against the conventional time-based calculation of NCF. Results: > 0.05). Conclusions: fatigue testing of files. The signal extraction method provided accurate revolution counts and a more realistic estimation of NCF than conventional time-to-failure methods, which overestimated actual values by 1.85 to 6.28% in this study.