Nickel-titanium rotary instruments: an in vitro comparison (Torsional resistance of two heat-treated reciprocating files)

Aim and objective: The present study aims to evaluate the difference in torsional resistance of two reciprocating nickel–titanium (Ni–Ti) rotary files: WaveOne Gold and EdgeOne Fire. Materials and methods: A total of 40 nickel–titanium rotary instruments (n = 40): 20 WaveOne Gold Small (WOGS) and 20 EdgeOne Fire Small (EOFS) were divided into two groups. Each instrument was tested using a torsional resistance device already validated in previous studies to evaluate and compare torsional resistance. The static torsional test was implemented by blocking each instrument at 3 mm from the tip and rotating it until fracture with a reciprocating motion. Torque to fracture (TtF) and fragment length (FL) were measured and statistically analyzed. Results: Statistical analysis of TtF found significant differences between the two groups (p <0.05). The EOFS showed higher TtF if compared to WOGS, with a mean value and a standard deviation of 3.05±0.07 (Ncm) against 2.97±0.08 (Ncm). Data for FL showed no significant differences (p >0.05) between the two groups. Conclusion: According to the results of this study, it is reasonable to assert that EOFS instruments showed a higher torsional resistance if compared to the WOGS. Clinical significance: As evidenced by this study, EOFS should be considered as a safer solution, in terms of torsional resistance, if compared to WOGS, reducing the risk of intracanal separation due to excessive torsional load.