Influence of artificially simulated pulpal temperature on cyclic fatigue resistance of heat treated NiTi files

INTRODUCTION. NiTi rotary files, which have been heat-treated, have shown an increase in the flexibility and cyclic fatigue resistance. But the effect of the changes of intracanal temperature during clinical instrumentation on file performance is not well known.

MATERIALS AND METHODS. NiTi files with heat treatment (n = 108) were used (ProTaper Gold, WaveOne Gold, and Reciproc Blue, n = 60 each) in a standardized artificial canal (angled at 60 and radius of curvature = 5 mm). The files were randomly selected into three temperature conditions (n = 20 / group): Group A (20°C – room temperature), Group B (37°C – normal body temperature) and Group C (45°C – higher inflammatory temperature). Fatigue test was carried out in a cyclic manner until file fracture. Fracture time (TTF) and cycles to failure (NCF) were measured. One-way ANOVA and Tukey post-hoc tests (0.05) were used in statistical analysis.

RESULTS. A major difference in cyclic fatigue resistance was found across temperature groups in each file system (p < 0.001). ProTaper Gold showed 412 ± 68 NCF at 45°C relative to 584 ± 92 at room temperature (20°C) (p < 0.001). WaveOne Gold was found to have 738 + 114 NCF at 45°C compared to 1024 + 156 NCF at 20°C (p < 0.001). Reciproc Blue used showed 896 ± 128 NCF at 45°C unlike 1246 ± 182 NCF at 20°C (p > 0.001). High temperature (45°C) decreased the cyclic fatigue resistance by 28929.5 percent in all the systems subjected to it.

CONCLUSIONS. Artificially reproduced elevated pulpal temperatures have a great influence in reducing cyclic fatigue resistance of heat-treated NiTi files. Endodontic practice requires the clinical awareness of temperature-dependent mechanical behavior to avoid instrument separation and complicate endodontic practice especially in inflamed teeth.

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