Aim: To evaluate the cyclic fatigue resistance of Reciproc blue (RB) 40/0.06 instruments tested at room temperature (20° ± 0.5°C) and at body temperature (37° ± 0.5°C) in a simulated stainless steel canal. Materials and methods: Twenty-four new RB 40/0.06 instruments were randomly divided into two groups (n = 12) according to the temperature used. Dynamic fatigue testing was performed using an artificial stainless steel canal with a 60° curvature angle and a 5-mm radius of curvature. The temperature was controlled throughout the experiment with an underwater thermometer and a thermostat. The data were analyzed descriptively using the IBM SPSS 23.0 program, considering p < 0.05. Results: The time to fracture of the RB instruments differed significantly between the two temperatures (1083.82 seconds at 20°C and 403.80 seconds at 37°C). No significant differences were found in fragment size. Conclusion:An increase in temperature reduces the cyclic fatigue resistance of RB 40/0.06 instruments. The results of the study suggest that an intracanal cooling system can be favorable to the fracture resistance of the tested instruments. Clinical significance: A cooling system of the root canal system is important in endodontic as it favors the cyclic fatigue resistance of Ni-Ti instruments.

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