Cyclic fatigue and torsional resistance of heat-treated One Curve compared with different nickel-titanium rotary instruments

Objective: The present study compared the cyclic fatigue and torsional resistance of size 25/0.06 taper of One Curve (OC), 2Shape (TS), ProFile Vortex (PV) and OneShape (OS) instruments. Materials and methods: The cyclic fatigue resistance of instruments was tested in simulated canals with 90-degree angle of curvature until fracture. The number of cycles to fracture (NCF) was recorded. The torsional resistance was determined by counting the number of load applications before instrument fracture. Data were statistically analysed and Weibull analysis was conducted on NCF data. Statistical significance was set at P 0.05. Results: OC had the highest NCF between the tested instruments (P 0.001). Nevertheless, OS showed the highest torsional resistance compared with other instruments (P 0.001). The predicted cycles of OC were 238 cycles for 99% survival. On the other hand, OS instruments had the lowest predicted cycles (60 cycles) compared with other instruments. Conclusion: OC instrument (C-Wire) had a higher cyclic fatigue resistance but a lower torsional resistance. TS and PV heat-treated nickel-titanium (NiTi) alloys enhanced the cyclic fatigue resistance of rotary instruments compared with OS conventional NiTi instruments. OS instruments displayed superior torsional resistance compared with other instruments. Keywords: cyclic fatigue, heat treatment, One Curve, torsional resistance