Cyclic fatigue resistance of three heat-treated nickel-titanium instruments at simulated body temperature

Abstract

<b>Introduction:</b> The aim of this study was to evaluate the cyclic fatigue resistance of three heat-treated nickel–titanium (NiTi) systems at simulated body temperature.<br><b>Materials and Methods:</b> Twelve instruments of similar apical diameter (#25) from three engine-driven NiTi instruments; WaveOne Gold (WOG), Hyflex EDM (HEDM), and M Pro system were tested for cyclic fatigue resistance at 37°C in simulated root canals with 60° angle of curvature and 5 mm curvature radius. All instruments were operated until fracture occurred. Mean and standard deviation of the time to fracture and fragment length were calculated, and statistical significance was set at 5%. The morphological characteristics of the fractured instruments were observed through scanning electron microscopy, and their chemical composition was determined using energy dispersive X-ray analysis (EDXA).<br><b>Results:</b> HEDM showed the highest resistance to cyclic fatigue at 37°C followed by WOG and M Pro instruments with a statistically significant difference. Scanning electron micrographs confirmed a predominantly ductile mode of fracture for all instruments. EDXA showed that WOG was composed of Ni (45.1 wt%) and Ti (37.0 wt%), HEDM was composed of Ni (52.9 wt%) and Ti (42.4 wt%), and M Pro was composed of Ni (49.7 wt%) and Ti (40.4 wt%).<br><b>Conclusions:</b> M Pro instrument showed the least cyclic fatigue resistance at 37°C compared to HEDM and WOG.