Effects of Heat Treatment and Design on Mechanical Responses of NiTi Endodontic Instruments: a Finite Element Analysis

Heat treatments and geometries have a significant influence on the mechanical behavior of endodontic files. Finite element analyses were performed to verify the effects due to each of these parameters in NiTi files. Two designs and three NiTi atomic structures (resultant from different heat treatments) were selected for this study. The geometries of the ProTaper Next X1 and ProTaper Universal S2 files, and the structures of fully austenitic (conventional superelastic), austenite treated, and fully R-phased were used. The mechanical responses were evaluated under flexion and torsion loading conditions described by ISO 3630-1 specification. According to the results, the design of the X1 file exhibit higher flexibility in comparison to the S2 model. Under torsional loads, S2 showed higher stiffness. The structures of fully austenitic showed the least flexibility under flexion and the highest torsional stiffness. The stress levels reached for the austenitic condition were uppermost. The treated condition that resulted in a fully R-phase file usually presented a higher level of flexibility with lower stress levels, indicating a longer life in fatigue when compared to the other treatments.

Keywords:
NiTi endodontic files; heat treatment; cross-sectional design; finite element analysis; bending and torsional loads