Cyclic fatigue resistance and metallurgic comparison of rotary endodontic file systems

The aim of this study was to compare, in pairs, the cyclic fatigue resistance, scanning electron microscopic (SEM) appearance, and energy-dispersive X-ray (EDX) profiles of 6 rotary files: ProTaper Gold vs EdgeTaper Platinum; ProTaper Universal vs EdgeTaper; and Vortex Blue vs EdgeSequel Sapphire. Six types of rotary file were tested in 2 sizes of each type. A 3-point cyclic fatigue apparatus imparting a 60-degree angle of curvature and a 3-mm radius of curvature was used to evaluate 30 files of each type and size. The cyclic fatigue testing results from similar file types and sizes were paired for statistical analysis. After fatigue testing was completed, 36 files (3 of each type and size) were randomly selected for SEM imaging and EDX analysis. When similar file types and sizes were paired in independent-samples t tests, statistically significant differences (P < 0.0001) in cyclic fatigue resistance were established. For both tested sizes, EdgeTaper Platinum exhibited significantly greater fatigue resistance than ProTaper Gold. ProTaper Universal and EdgeTaper each demonstrated significantly greater fatigue resistance than the other system in 1 size pairing. Vortex Blue exhibited significantly greater fatigue resistance than EdgeSequel Sapphire in both size pairings. In general, the heat-treated files demonstrated greater cyclic fatigue resistance than the non-heat-treated files. The SEM images verified that fracture patterns were consistent with cyclic fatigue failure. Differences in file design between the matched pairs were noted, particularly at the tips. The EDX comparisons showed that nickel and titanium were present in similar percentages (1:1 atomic ratio) for all file types. The disparities in cyclic fatigue results and tip design indicate that clinicians should not expect identical clinical performance from different files.