Cyclic fatigue resistance of two nickel-titanium rotary instruments in interrupted rotation

AIM: To investigate the influence of interrupted rotation on cyclic fatigue oftwo nickel-titanium rotary instruments.METHODOLOGY: Cyclic fatigue of 300 new ProTaper Next size X1; X2 and Mtwo size 10, .04 taper; size 15, .05 taper; size 20, .06 taper and size 25, .06 taperinstruments was tested in continuous or interrupted rotation. Fifty files of the same brand and size were randomly assigned to five groups (n = 10). Group 1instruments were tested in continuous rotation; groups 2 and 3 in paused rotationfor 1 s every 10 or 20 s, respectively; groups 4 and 5 in interrupted rotationfor 5 s every 10 or 20 s, respectively. Cyclic fatigue was expressed in time tofracture (TtF) in an artificial canal with 60° angle and 5 mm radius of curvature. The fracture surface was examined with a scanning electron microscope (SEM). Data were evaluated by two-way analysis of variance.RESULTS: Cyclic fatigue of groups 2 and 4 of ProTaper Next X2 and Mtwo size 25,.06 taper was significantly lower than that of group 1 of the same instruments(P < 0.01). ProTaper Next X2 had significantly reduced cyclic fatigue in groups 3 and 5 (P < 0.05). No differences were found by interrupting the rotation for 1 or 5 s in all instruments (P > 0.05). Fatigue of other instruments was not affected by interrupted rotation (P > 0.05).CONCLUSIONS: Interrupted rotation reduced cyclic fatigue resistance of ProTaper Next X2 and Mtwo size 25, .06 taper, especially when a higher number ofinterruptions was performed.