ObjectiveThe 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 methodsEighteen Reciproc R25 (25.08) and Reciproc Blue (25.08) instruments were tested in a cyclic fatigue device at body temperature (37 degrees C) using a stainless steel block with an artificial canal with a curvature angle of 90 degrees and radius of curvature of 2mm. 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.ResultsThe 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).ConclusionsReciproc Blue R25 instruments displayed significantly higher NCF than Reciproc R25.Clinical relevanceThis 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.