Impact of metallurgical and geometric characteristics on cyclic fatigue resistance of three thermally treated NiTi rotary instruments

Background This study aimed to evaluate the cyclic fatigue resistance and metallurgical characteristics of thermally treated NiTi rotary instruments: ProDesign Logic, Solla Purple, and Solla Colors. Material and Methods Cyclic fatigue testing was conducted at room temperature (20°C ± 1°C) and simulated body temperature (36°C ± 1°C) using a standardized artificial canal with a 60° curvature and 5 mm radius. Ten instruments per group (25.06) were tested at each temperature. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) were employed to assess phase transformation behavior and fracture topography, respectively. Results ProDesign Logic exhibited the highest cyclic fatigue resistance at room temperature compared to Solla systems (p<0.0001). Temperature variations did not significantly affect cyclic fatigue resistance (p>0.05). ProDesign Logic had the highest austenite finish temperature (Af = 53.0°C). SEM confirmed typical fatigue fracture patterns in all groups. Conclusions ProDesign Logic demonstrated greater cyclic fatigue resistance, attributed to its high Af temperature and cross-sectional design.