Stress-Controlled Torsional Fatigue Assessment of Selected Contemporary Endodontic Instruments

To compare stress-controlled torsional fatigue resistance of TruNatomy (TN), ProTaper Next (PTN), and ProTaper Ultimate (PTUL) instruments of comparable sizes at both room and body temperature. Torsional strength and related twist angles were determined at both temperatures in a torque testing fixture. Stress-controlled torsional fatigue resistance (TFR) was determined by cycling instruments in a custom fixture to pre-set twist angles corresponding to 90% torsional strength until fracture. Data were analyzed using two-way ANOVA and Tukey post-hoc tests with the significance level set at 0.05. Overall, mean (± standard deviation) TFR ranged from 192 (± 66) to 841 (± 201) cycles; PTUL had the highest TFR and TN the lowest; the differences among the three instruments were statistically significant. At 37 °C compared to room temperature, PTUL had a similar TFR, while PTN had a higher and TN a lower one. Applying customized stress-controlled conditions resulted in differences in TFR among the 3 instrument types. Different environmental temperatures had varying effects on the tested instruments manufactured from differently heat-treated nickel-titanium (NiTi) alloy. Understanding TFR is relevant for clinical use of NiTi instruments for continuous rotation and reciprocation, specifically for motor settings. Within the limitations and specific testing parameters of this study, stress-controlled TFR varied among the three tested instruments. Different environmental temperatures had varying effects on the tested instruments manufactured from differently heat-treated nickel-titanium (NiTi) alloy. Variations in instrument design and the NiTi alloy type used may account for different torsional fatigue performance and suggest specific clinical usage parameters. During canal preparation, instruments are stressed under cyclic load, a condition which is replicated in this experiment. The data is relevant for motor presets for continuous rotation and reciprocating motion as well as handling of contemporary heat-treated Nickel-titanium instruments.