Influence of continuous or reciprocating motion on cyclic fatigue resistance of 4 different nickel-titanium rotary instruments.

INTRODUCTION The aim of this study was to evaluate the resistance to flexural fatigue of Reciproc R25 (VDW, Munich, Germany), WaveOne Primary (VDW, Munich, Germany), Mtwo (Sweden & Martina, Padova, Italy), and Twisted File (TF; SybronEndo, Orange, CA) instruments used in continuous rotation or in 2 different reciprocating motions. METHODS A total of 180 nickel-titanium files from 4 brands marketed, 2 for use in reciprocating motion (ie, Reciproc R25 and WaveOne Primary) and 2 for use in continuous rotation (ie, Mtwo and TF both taper .06/0.25 tip diameter), were tested. Forty-five instruments for each brand were divided into 3 groups (n = 15) on the basis of the motion tested: continuous rotation (group 1: 300 rpm) and reciprocal motion (group 2: "RECIPROC ALL" mode and group 3: "WAVEONE ALL" mode). The resistance to cyclic fatigue was determined by counting the number of cycles to failure in a 60° curve with a 5-mm radius. Data were analyzed through 2-way analyses of variance. RESULTS The cyclic fatigue resistance of the 2 reciprocating motion instruments (ie, "RECIPROC ALL" and "WAVEONE ALL") was significantly higher than the continuous rotation in each brand (P < .001). No significant difference was observed in cyclic fatigue between the 2 different reciprocal motions tested in each brand (P > .05). When considering the appropriate clinical motion for each brand, no significant difference in cyclic fatigue was found between TF, Mtwo, and Reciproc R25 instruments, whereas the cyclic fatigue resistance of WaveOne files was less than the other 3 brands (P < .05). CONCLUSIONS Reciprocal motion showed a significantly higher cyclic fatigue resistance in all brands compared with continuous rotation. No differences were found between the 2 reciprocating motions.