Cyclic fatigue of Reciproc and Reciproc Blue nickel-titanium reciprocating files at different environmental temperatures

Introduction: The aim of the present study was to investigate the impact of ambient temperature on the life span of nickel-titanium (NiTi) files. Methods: Cyclic fatigue testing of NiTi instruments was performed in a stainless steel artificial canal. During the experiment, 4 different temperatures (0°C, 20°C, 35°C, and 39°C) were used in a thermostatic bath controlled using electronic and infrared controls. Eighty R25 Reciproc Blue (VDW, Munich, Germany) and 80 R25 Reciproc (VDW) instruments were reciprocated in the artificial canal until fracture occurred, and the time to fracture and the length of the fractured fragment were recorded. The phase transformation temperature for 3 instruments of each type was analyzed by differential scanning calorimetry. One-way analysis of variance and Bonferroni tests were used to statistically analyze the data at a 5% significance level (P <.05). Results: Reciproc Blue instruments were significantly more resistant to cyclic fatigue than Reciproc at all the temperatures tested (P <.05). Fatigue resistance was proportionally higher as the environmental temperature decreased (0°C > 20°C > 35°C > 39°C). No significant difference was registered for the length of the fractured fragment of both instruments tested at all temperatures tested (P >.05). Conclusions: Blue alloy significantly increases the cyclic fatigue resistance of Reciproc files compared with M-Wire alloy. Temperature significantly affects the life span of NiTi files. When the ambient temperature increases between 0°C and 35°C, the fatigue resistance of the files statistically decreases.