Cyclic fatigue resistance of three different nickel-titanium rotary instruments in continuous or reciprocating rotation

Aim To investigate the cyclic fatigue resistance of three different endodontic rotary instruments produced by M-wire nickel titanium (NiTi) or traditional NiTi tested in continuous or two reciprocating rotation. Methodology A total of 135 new Reciproc R25; Waveone Primary; Mtwo size 25.06 were tested for cyclic fatigue resistance. Fourty-flve files of the same brand were randomly assigned to three difl'erent groups of 15 each. On the basis of the type of rotation, flles of group 1 were tested in continuous rotation; group 2 in reciprocating motion 'Reciproc ALL'; group 3 in reciprocating motion 'Waveone ALL'. Continuous rotation was performed at 300 rpm and torque at maximum value as in clinical practice, while reciprocating motions 'Reciproc ALL' and 'WaveOne ALL' are preset, unchangeable and patented by the manufacturer. Resistance to cyclic latigue was determined by counting the numbers of cycles to failure (NCF) in a 60° curve with a 5-mm radius. A two-way analysis of variance and Bonferroni multiple comparison post-hoc tests at 0.05 were used to evaluate the data. Results Cyclic fatigue resistance of the two reciprocating motion 'Reciproc ALL' and 'WaveOne ALL' was significantly higher than continuous rotation in every brand (P < O.001). Instead, no significant difference was found in cyclic fatigue between the two different reciprocal motions tested in every brand (P > 0.05). When using the same type of rotation Mtwo 25.06 had the best resistance to cyclic fatigue. However, when considering the appropriate clinical motion for every brand (Reciproc with 'Reciproc ALL'; Waveone with 'WaveOne ALL' and Mtwo with continuous rotation) no significant difference was found in cyclic fatigue between Mtwo and Reciproc R25, while the cyclic fatigue resistance of WaveOne was less than other two brands (P < 0.05) Conclusions Reciprocating movements enhanced the NCF of all instruments tested compared to continuous rotation. No differences were found between the two reciprocating motions. In these experimental conditions, testing the same type of rotation Mtwo 25.06 had the best resistance to cyclic fatigue followed by Reciproc R25 and WaveOne Primary.