Elastic Limits in Torsion of Reciprocating Nickel-Titanium Instruments

Abstract Introduction Reciprocating angle and torsional load at the superelastic limit were investigated for nickel-titanium (NiTi) instruments used with reciprocating movements. Methods Two reciprocating NiTi instruments (Reciproc R25 [VDW, Munich, Germany] and WaveOne Primary [Dentsply Maillefer, Ballaigues, Switzerland]) and ProTaper F2 (Dentsply Maillefer) were tested for 2 torsional conditions using a custom-designed testing device. Rotational angles were applied, and generated torque values were recorded. The first test condition fixed the files at 5 mm and repetitively rotated them with gradually increasing angles up to 250° ( n = 10). The second test subjected the files to a single continuous rotation until fracture ( n = 10). The superelastic limits of the instruments were determined from their torque-rotation curves. Statistical analysis was performed (Kruskal-Wallis) at a 95% significance level. The tested specimens were examined under a scanning electron microscope. Results It was found that the angle at the superelastic limit was higher for R25 and Primary files than the ProTaper file ( P