Effect of movement kinematics on the cyclic fatigue resistance of nickel–titanium instruments

AIM: To compare the cyclic fatigue resistance of new generation OneShape and WaveOne instruments when used with different kinematics. METHODOLOGY: An artificial canal, made of stainless steel with an inner diameter of 1.5 mm, a 60° angle of curvature and a curvature radius of 3 mm, was used for cyclic fatigue test of new generation OneShape and WaveOne instruments. Groups were as follows (n = 20): 150°-30°, 210°-30°, 360°-30° and continuous rotation. The time to fracture was recorded in seconds, and the data were analysed statistically using a two-way anova and LSD tests (P = 0.05). RESULTS: Cyclic fatigue resistance was significantly affected by the movement kinematics (P < 0.001). The cyclic fatigue resistance of the new generation OneShape instruments increased significantly when operated in various reciprocation motions (150° CW-30° CCW, 210° CW-30° CCW and 360° CW-30° CCW) compared with the continuous rotation mode. New generation OneShape instruments had significantly more resistance to fracture under cyclic loading than WaveOne instruments (P < 0.001). CONCLUSIONS: When using new generation OneShape and WaveOne instruments, all the reciprocating motions (150° CW-30° CCW, 210° CW-30° CCW and 360° CW-30° CCW) resulted in extended fatigue life when compared with continuous rotation.