Cyclic fatigue resistance of two variable-taper rotary file systems: ProTaper universal and V-Taper

The cyclic fatigue resistance of ProTaper Universal (Dentsply Tulsa Dental Specialties, Tulsa, OK) and V-Taper (Guidance Endo, Albuquerque, NM) files was measured while rotating files around a 5-mm radius curve with 90 degrees of maximum flexure. The files were rotated at 250 rpm with a continuous axial oscillation of 4 mm at 1 Hz. The number of cycles to failure was calculated and analyzed by using univariate analysis of variance and the Tukey HSD posthoc test with results confirmed by nonparametric Kruskal-Wallis and Mann-Whitney U tests with a Bonferroni correction. The fracture faces of representative files were imaged with a scanning electron microscope to confirm cyclic fatigue as the mode of fracture. For the instruments tested, the ProTaper files appeared to resist fracture better than the V-Taper files. At each tip size tested, the ProTaper files either outperformed or were not statistically different than V-Taper files.