Influence of continuous rotation or reciprocation of Optimum Torque Reverse motion on cyclic fatigue resistance of nickel-titanium rotary instruments.

AIM: To evaluate the resistance to cyclic fatigue of ProTaper Next (PTN; DentsplySirona, Ballaigues, Switzerland), Revo-S (Micro-Mega, Besançon, France), Mtwo(Sweden & Martina, Padova, Italy), Twisted Files (TF, SybronEndo, Orange, CA, USA) and EndoWave (J Morita Corporation, Osaka, Japan) used in continuousrotation or in reciprocation of Optimum Torque Reverse motion (OTR).METHODOLOGY: A total of 120 nickel-titanium files were tested. Twenty-fourinstruments for each brand were divided into 2 groups (n = 12) on the basis ofthe motion tested: continuous rotation (Group 1) or reciprocation of OTR motion(Group 2). 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 TtF data were analysed by using the two-way analysis of variance (ANOVA) and Bonferroni post-hoc tests at 0.05.RESULTS: Mtwo and TF had significantly higher TtF when compared with all otherinstruments, both in continuous rotation and reciprocation of OTR motion (P <0.0001 and P < 0.05, respectively). No difference was observed between Mtwo and TF (P > 0.05), in both motions. PTN was associated with higher cyclic fatigueresistance than Revo-S and EndoWave, both in continuous rotation andreciprocation of OTR motions (P < 0.0001). No difference was observed betweenRevo-S and EndoWave, in both motions (P > 0.05). Reciprocating OTR motionimproved TtF of all instruments (P < 0.0001).CONCLUSIONS: Reciprocation of OTR motion improved significantly cyclic fatigue resistance of all instruments tested compared with continuous rotation. Mtwo and TF had significantly higher cyclic fatigue than the other instruments, in bothcontinuous rotation and reciprocation of OTR motion.