Dynamic Cyclic Fatigue Resistance of Heat-treated Nickel Titanium Instruments in Reciprocating Motion

Objective: To compare the fatigue resistance of different heat-treated reciprocating instruments tested in a dynamic cyclic fatigue model. Methods: Forty-eight new instruments were inspected under magnification and selected for this study, and then divided as follows (n=12): X1 Blue (MK Life, Porto Alegre, RS, Brazil), Pro-R (MK Life), Reciproc (VDW, Munich, Germany), and Reciproc Blue (VDW). Artificial canals presenting a curvature of 60° angle and 5 mm radius were milled in zirconia. The block containing the artificial canals was mounted in a container filled with water kept at 37°C. A specially designed device was used to perform controlled axial movements while the instruments were activated inside the canals. Time to failure was recorded in seconds, and fragment lengths were measured (mm). Data were analyzed statistically with the significance level set at 5% (One-Way ANOVA and Tukey test). Results: Pro-R and Reciproc Blue instruments presented the highest fatigue resistance, being significantly different from the other tested files (p<0.05). Reciproc presented intermediate results, significantly different X1 Blue (p<0.05). The fractographic analysis showed typical features of cyclic fatigue for all instruments. Conclusion: Pro-R and Reciproc Blue instruments are more resistant to dynamic cyclic fatigue than the Reciproc and X1 Blue.