Cyclic Fatigue of Nickel-Titanium Rotary Instruments in a Double (S-shaped) Simulated Curvature

Introduction: The goal of the present study was to test the fatigue resistance of nickel-titanium rotary files in a double curvature (S-shaped) artificial root canal and to compare those results with single curvature artificial root canals. Methods: Two nickel-titanium endodontic instruments consisting of identical instrument sizes (constant .06 taper and 0.25 tip diameter) were tested, Pro File instruments and Vortex instruments. Both instruments were tested for fatigue inside an artificial canal with a double curvature and inside a curved artificial canal with a single curvature. Ten instruments for each group were tested to fracture in continuous rotary motion at 300 rpm. Number of cycles to failure (NCF) was calculated to the nearest whole number, and the length of the fractured fragment was measured in millimeters. Data were statistically analyzed with a level of significance set at 95% confidence level. Results: The NCF value was always statistically lower in the double curved artificial canal when compared with the single curve (P < .05) in both the apical and coronal curvatures. Statistically significant differences (P < .05) were noted between instruments of the same size of different brand only in the single curve; Pro File registered a mean of 633.5 +/- 75.1 NCF, whereas Vortex registered a mean of 548 +/- 48.9 NCF. Conclusions: Regardless of the differences between the instruments used in the present study, the results suggest. that the more complex is the root canal, the more adverse are the effects on the cyclic fatigue resistance of the instruments. (J Endod 2012;38:987-989)