Influence of different motions on the cyclic fatigue resistance of Reciproc and Reciproc Blue endodontic instruments

The aim of this study was to evaluate the cyclic fatigue resistance of Reciproc (RCP) and RPC Blue (RCPB) instruments used in continuous rotation, RECIPROC mode, and WAVEONE mode. Materials and Methods: Sixty RCP and 60 RCPB R25 files were used. For each file type, three groups (n = 20) were defined depending on the used kinematics: continuous rotation, RECIPROC mode, and WAVEONE mode. A stainless-steel artificial canal with 60 angle and 5-mm radius of curvature was milled reproducing the size and taper of the used files. The test device was electrically heated to 35C to simulate the clinical environment. All files were reciprocated or rotated until fracture. The time to failure and the length of the fractured fragments were measured. A fractographic examination was performed by scanning the electron microscopy to confirm the cause of fracture. Collected data underwent a two-way analysis of variance (a = 0.05). Results: RCPB files exhibited better cyclic fatigue resistance than RCP. The RECIPROC motion yielded greater cyclic fatigue resistance than the WAVEONE movement; the least resistance was observed in the continuous rotation groups. No significant differences were found among groups in terms of length of the fractured fragment. The fractographic analysis confirmed that all scanned samples separated due to cyclic fatigue. Conclusions: Within the limitation of the present study, the RECIPROC mode increased the cyclic fatigue resistance of the tested instruments compared to WAVEONE mode and continuous rotation. To prevent RCP and RCPB file separation, motion kinematics other than the native RECIPROC movement should be discouraged in the clinical setting.