Off-Centered Geometry and Influence on NiTi Endodontic File Performance Evaluated by Finite Element Analysis

The influence of cross-sectional eccentricity on the flexibility, torsional stiffness, and stress distribution in NiTi endodontic files was studied by finite element modeling. Three-dimensional (3D) models were built in order to reproduce commercial ProTaper Next X1 and X2 off-centered geometry instruments. Additionally, other 3D models with geometries similar to X1 and X2, but with concentric cross-sections, were created to isolate the eccentricity variable. The material properties and boundary conditions used in this study were the same for all instruments. The mechanical responses of each concentric/eccentric pair were evaluated under flexion and torsion loading conditions described by ISO 3630-1 specification. According to the results, off-centered files exhibit lower flexibility in comparison with their concentric counterparts. However, the eccentricity promoted a change in the stress distribution pattern so that the off-centered instruments showed lower maximum stress values under bending. Under torsional loads, no significant differences were observed. It is concluded that the mechanical and clinical advantages of an offset cross-section are not related to the increase of flexibility but rather to the optimization of the final diameter of the formatted root canal using instruments with lower mass. Also, there is a reduction in stress levels, increasing fatigue life, and improving the performance of the endodontic files.