Comparative analysis of torsional resistance among single-file nickel-titanium systems

Purpose: To evaluate the torsional fatigue resistance of One Curve Mini (OCM), HyFlex EDM (HEDM), WaveOne Gold Primary (WOG), and Reciproc Blue R25 (RPB) rotary and reciprocating nickel-titanium (NiTi) single-file systems.
Methods: Eighty NiTi instruments were tested: OCM (25/.06), HEDM (25/.08), WOG (25/.07), and RPB (25/.08) (n=20 per group). The instruments were fixed at apical 3 mm along their long axis and constant rotation of 2 rpm were applied until fracture occured. Ultimate strength at maximum torque and distortional angle for each file were measured using torsiometer. Statistical analysis was performed with one-way analysis of variance followed by Tukey’s post-hoc test, using a 5% significance level (p<0.05). All the fractured instruments were scanned using scanning electron microscope to confirm that the instruments were fractured due to torsional fatigue.
Results: Maximum torque values were observed in HEDM and RPB (p<0.05) and the minimum values were in OCM (p<0.05) files. The torque values of WOG were not statistically different from the other three files (p>0.05). The distortion angle was highest in OCM and HEDM and the lowest values were in WOG files (p<0.05). RPB files have a similar distortion angle with the other three files (p>0.05).
Conclusion: HEDM and RPB were highest and OCM was the least resistant to torsional stress among the tested NiTi file systems.

Keywords: Instrument fracture, nickel-titanium, resiprocating file, rotary file; torsional resistance.