Comparison of Cyclic Fatigue Resistance of Three Ni-Ti Rotary Files

: Objective: To compare the cyclic fatigue resistance of three Ni-Ti rotary files. Materials and Methods: A number of forty-five different nickel titanium rotary instruments (n = 15) were used in this study. All files were used according to their manufacturers' instructions. A specially designed, custom-made cyclic fatigue testing device was used in this study. The device had a simulated curved root canal within a stainless-steel block with a 45° angle of curvature and 5 mm radius of curvature. The time to fracture (TtF) in seconds was recorded visually using stopwatch. To characterize fracture mode, fractured fragments from each group were examined using a scanning electron microscope (SEM). The collected data were analyzed using one-way analysis of variance (one-way ANOVA) and post-hoc Tukey multiple comparison test with a statistical significance at p < 0.05 to compare the values of time to fracture (TtF) between the tested groups. Results: When comparing the time to fracture among the tested instruments, One-way ANOVA test revealed that there was a statistically significant difference among the three NiTi instruments (p < 0.05). HyFlex EDM had the highest resistance to cyclic fatigue resistance. Scanning electron microscopy analysis showed that the fracture type of all instruments was ductile fracture. Conclusions: According to the results of this study, HyFlex EDM had the highest cyclic fatigue resistance among the Ni-Ti instruments.