Abstract
OBJECTIVES: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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. CLINICAL SIGNIFICANCE: 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.