Cyclic fatigue of ProTaper rotary nickel-titanium instruments in artificial canals with 2 different radii of curvature

Objective. This study compared the cyclic fatigue resistance of ProTaper rotary nickel-titanium (NiTi) files in artificial canals with 2 different radii of curvature. Study design. One hundred ProTaper rotary instruments were used in this study. Twenty files of each size (S1, S2, F1, F2, and F3) were tested. Cyclic fatigue testing was performed using a device that allowed the instruments to rotate freely inside stainless steel artificial canals with radii of curvature of 5 and 10 mm. The number of cycles to fracture was recorded for each file and the data were analyzed using a t-test. Results. The 5-mm radius group had significantly fewer cycles to fracture than the 10-mm radius group for all file sizes. For sizes F2 and F3, the difference between the 5 and 10-mm radius groups was highly significant (P < .001). For the 10-mm group, the difference between S1 and F3 was significant (P < .05). For the more abrupt 5-mm radius group, the difference between S1-F2, S2-F2, and F1-F2 was statistically significant. The difference between S1-F3, S2-F3, and F1-F3 was highly significant (P < .001). Conclusion. Cyclic fatigue resistance of ProTaper instruments was dependent on both instrument size and radius of curvature. Especially larger-size instruments should be used with great care in curved canals.