Cyclic Fatigue Resistance of RaCe and Mtwo Rotary Files in Continuous Rotation and Reciprocating Motion

Introduction: The purpose of this study was to evaluate and compare the cyclic fatigue resistance of RaCe (FKG Dentaire, La Chaux-de-Fonds, Switzerland) and Mtwo (VDW, Munich, Germany) rotary files in continuous rotation and reciprocating motion. Methods: A total of 60 new rotary Mtwo and RaCe files (ISO size = 25, taper = 0.06, length = 25 mm) were selected and randomly divided into 4 groups (n = 15 each): Mt(c) (Mtwo NiTi files in continuous rotation), R-c (RaCe NiTi files in continuous rotation), Mt(r) (Mtwo NiTi files in reciprocating motion), and 13, (R.aCe NiTi files in reciprocating motion). A cyclic fatigue testing device was fabricated with a 60 degrees angle of curvature and a 5-mm radius. All instruments were rotated or reciprocated until fracture occurred. The time taken for each instrument to fracture and the length of the broken fragments were recorded. All the fractured files were analyzed under a scanning electron microscope to detect the mode of fracture. The Kolmogorov-Smirnov test was used to assess the normality of samples distribution, and statistical analysis was performed using the independent sample t test. Results: The time taken for the instruments of the Mt(r) and R-r groups to fail under cyclic loading was significantly longer compared with the Mt(c) and R-c groups (P<.001). Scanning electron microscopic observations showed that the instruments of all groups had undergone a ductile mode of fracture. The length of the fractured segments was between 5 and 6 mm, which was not statistically significant among the experimental groups. Conclusions: Mtwo and RaCe rotary instruments showed a significantly higher cyclic fatigue resistance in reciprocating motion compared with continuous rotation motion.