Objective: Reuse of endodontic files remains an open issue in clinical practice. This study was designed to evaluate the fracture strength of WaveOne Gold (Dentsply Maillefer, Ballaigues, Switzerland) and Reciproc Blue (VDW, Munich, Germany) files with successive reuse for root canal shaping in up to three molars. Material and Methods: Prospective clinical study carried out by five calibrated endodontists who treated 384 molars (1291 canals) with a curvature <45° over a 12-month period. A total of 128 instruments were used (64 Reciproc Blue and 64 WaveOne Gold). Each instrument was used to treat three posterior teeth. After each use, the instruments were observed under an operating microscope at 8× magnification. Data were tabulated and a chi-square test was applied. Significance was accepted at the 5% level. Results: Two instruments (one from each group) separated, both on the third use and during instrumentation of a mandibular first molar. In other words, instrument separation occurred in 0.52% of teeth and 0.16% of treated root canals. Conclusions: There was a low incidence of instrument fracture when reciprocating files were used for up to three endodontic treatments in molars.