(PR84) Evaluation of the Fatigue Resistance of Reciprocating Instruments with Different Heat-treatments

This study evaluated the cyclic fatigue resistance of reciprocating instruments manufactured with different heat-treatment processes. Three types of instruments presenting similar cross-sections but different thermal treatments were selected: Pro-R, Reciproc, and Reciproc Blue. A total of thirty-six new instruments size 25 and .06 taper were inspected under magnification and selected for this study (n=12). Artificial canals were milled in zirconia presenting a curvature of 60^o angle and 5 mm radius located 8 mm from the tip. The block containing the artificial canals was mounted in a container filled with distilled water kept at 37^oC. A specially designed device was used to perform controlled axial movements of the handpiece. The endodontic motor X Smart IQ motor (Dentsply Sirona) was used to activate the instruments in the “Reciproc” setting until the fracture was observed. Time to failure was recorded in seconds and the fragment lengths were measured (mm). Statistical analysis was performed with the significance set at 5%. Pro-R and Reciproc Blue instruments presented the highest resistance to fracture, being significantly different from Reciproc (p < 0.05). The fragment length of Pro-R instruments was significantly different from the other files (p < 0.05). Within the limitations of this in vitro study, it can be concluded that post-machining heat treatment improved the cyclic fatigue resistance of reciprocating instruments.