RESUMO
OBJECTIVE: The aim of this study was to evaluate the cyclic fatigue resistance of Reciproc and Reciproc Blue by testing in a severe apical curvature at intracanal temperature. MATERIALS AND METHODS: Eighteen Reciproc R25 (25.08) and Reciproc Blue (25.08) instruments were tested in a cyclic fatigue device at body temperature (37 °C) using a stainless steel block with an artificial canal with a curvature angle of 90° and radius of curvature of 2 mm. The number of cycles to fracture (NCF) was calculated. The instruments were examined by differential scanning calorimetry (DSC). The data were analyzed using both Student's t tests and Weibull analysis. RESULTS: The NCF values of Reciproc R25 were significantly lower than Reciproc Blue R25 (P < 0.05). There was no significant difference between the instruments regarding the length of fractured fragments (P > 0.05). CONCLUSIONS: Reciproc Blue R25 instruments displayed significantly higher NCF than Reciproc R25. CLINICAL RELEVANCE: This study reported that novel reciprocating blue wire instruments exhibited higher cyclic fatigue resistance than its precedence M-wire instrument when tested in severely curvatured canals.