Cyclic fatigue resistance of two reciprocating nickel–titanium instruments after immersion in sodium hypochlorite

Abstract Aim To assess resistance to cyclic fatigue of reciprocating NiTi files (Reciproc and WaveOne) after immersion in NaOCl solution over several time periods. Methodology A total of 90 new Reciproc R25 and WaveOne Primary were tested. The forty-five files of the same brand were randomly assigned to three groups (n=15) and submitted to the following immersion protocol in 5% NaOCl at 37 °C for 16 mm: no immersion (control), 1 or 5 minutes dynamically. The dynamic immersion and the following cyclic fatigue tests were performed using the appropriate preset reciprocation modes (“RECIPROC ALL” or “WAVEONE ALL”) in a specially designed endodontic motor. Resistance to cyclic fatigue was determined by recording time to fracture (TtF) in a stainless steel artificial canal with a 60° angle of curvature and 5-mm radius of curvature. The artificial canal was manufactured reproducing the instrument‟s size and taper. Data were analyzed by 2-way analyses of variance. Results Resistance to cyclic fatigue of the same NiTi file was not significantly affected by immersion in NaOCl. Reciproc R25 was associated with a higher cyclic fatigue resistance in all groups compared to WaveOne Primary (P < .0001). Conclusions Reciprocating dynamic immersion in NaOCl for 1 or 5 minutes did not reduced the cyclic fatigue resistance of nickel-titanium files significantly. However, the type of reciprocating instrument influenced cyclic fatigue resistance with Reciproc R25 being more resistant than WaveOne Primary.