Cyclic fatigue of NiTi instruments used in complex curvatures with continuous or reciprocating rotation

AimThe aim of present study was to compare cyclic fatigue resistance of Twisted files (TF, Sybron Endo, Glendora, CA) instrument used with continuous rotation and the new Motion (TFAdaptive rotating reciprocation), to evaluate if the new reciprocating motion could affect the lifespan of tested instruments.Methodology30 new TF instruments were submitted to cyclic fatigue tests. Group 1 instruments were tested using a TFA motion (TFA) while group 2 instruments were used in continuous rotation at 500rpm (CR). The cyclic fatigue testing device used in the present study has been used for studies on cyclic fatigue resistance previously. The artificial canal was manufactured to provide the instrument with a very challenging trajectory 60° curvature, with a 2mm radius.All instruments were rotated or reciprocated until fracture occurred. The time to fracture was recorded. All data were subjected to statistical evaluation with analysis of variance test.ResultsTFA reciprocating motion showed a significant increase (p<0.05) in the time to failure when compared to continuous rotation. Mean time to failure was 131s (SD ±25.2) for group 1 (TFA), and was 68s (SD ±14.8) for continuous rotation group (CR).ConclusionsIn accordance with those findings, the results of the present study showed a significant increase of cyclic fatigue resistance of instruments used with the TFA motion. This can be explained by the alternance of engaging/disengaging movements, since the motion can be defined as a non-continuous rotation, while the traditional continuous rotation movement continuously engages and stresses the instruments