Background and objectives: the fracturing of nickel-titanium rotary instruments during endodontic treatment because of the cyclic fatigue remains a common incidence. This study evaluated the effect of temperature on the cyclic fatigue of various nickel-titanium rotary files and compare between them. Methods: Three types of rotary instruments with tip size 0.25 were used: HyFlex EDM (OneFile, variable taper, Colten/Whaledent), ProTaper Gold (F2, 0.08 taper, Dentsply) and 2Shape (TS2, 0.06 taper, Micro-Mega). Twenty files for each instrument were tested for cyclic fatigue at (20°C and 37°C) temperatures and rotated until fracture occurred in a simulated canal with an angle curvature of about 60°, a radius curvature of 5 mm, and a canal width of 1.5 mm. Six groups were formed for all instruments (total number = 60), with ten files in each group. The number of cycles to fracture was recorded, and statistical analysis was completed using analysis of variance and independent t-test with significance at a (P<0.05). Results: HyFlex EDM OneFile registered no differences in fatigue life between the 2 temperatures tested (P > .05), whereas ProTaper Gold F2 and 2Shape TS2 showed a statistically significant reduction in fatigue life at body temperature compared with room temperature (P <0.05). HyFlex EDM OneFile exhibited statistically higher resistance to cyclic fatigue than ProTaper Gold F2 and 2Shape TS2 both at room and body temperatures (P<0.05). Conclusions: Within the limitations of this study, body temperature influenced the cyclic fatigue resistance of ProTaper Gold F2 and 2Shape TS2 files, whereas it did not influence the fatigue life of HyFlex EDM OneFile. The HyFlex EDM OneFile was more resistant to cyclic fatigue than the ProTaper Gold F2 and 2Shape TS2 files at room and body temperatures.

Introduction: The purpose of this study was to compare the cyclic fatigue of different types of nickeltitanium rotary files at body temperature. Methods: Four types of rotary instruments with tip size 0.25 were used: HyFlex EDM (OneFile, variable taper, Colten/Whaledent), ProTaper Gold (F2, 0.08 taper, Dentsply), XP-endo Finisher (zero tapers, FKG Dentaire) and 2Shape (TS2, 0.06 taper, Micro-Mega). Ten files for each instrument were tested for cyclic fatigue at body temperature and rotated until fracture occurred in a simulated canal with an angle curvature of 60°, a radius curvature of 5 mm, and a canal width of 1.5 mm. Four groups were formed for all instruments (total number = 40). The number of cycles to fracture and the length of fractured fragment were recorded, and statistical analysis was completed using analysis of variance with significance at a (p-value < 0.05). Results: The cyclic fatigue resistance of the HyFlex EDM OneFile was significantly greater than the other instruments, while that of the 2Shape TS2 was significantly lower (p < 0.05). Conclusion: Within the limitations of this study, the HyFlex EDM OneFile was more resistant to cyclic fatigue than the XP-endo Finisher, ProTaper Gold F2 and 2Shape TS2 files.