Mechanical behavior of three nickel-titanium rotary files: A comparison of numerical simulation with bending and torsion tests

• The mechanical behavior of three NiTi endodontic files was simulated using finite element analysis.
• Standard bending and torsion tests performed on the instruments defined the boundary conditions.
• The stress distribution along the files was influenced by their cross-sectional design.
• The agreement found between simulation and experiment confirmed the efficiency of the method.

AimTo assess the flexibility and torsional stiffness of three nickel-titanium rotary instruments by finite element analysis and compare the numerical results with the experiment.MethodologyMtwo (VDW, Munich, Germany) and RaCe (FKG Dentaire, La-Chaux-de-Fonds, Switzerland) size 25, .06 taper (0.25-mm tip diameter, 0.06% conicity) and PTU F1 (Dentsply Maillefer, Ballaigues, Switzerland) instruments were selected for this study. Experimental tests to assess the flexibility and torsional stiffness of the files were performed according to specification ISO 3630-1. Geometric models for finite element analysis were obtained by micro-CT scanning. Boundary conditions for the numerical analysis were based on the specification ISO 3630-1.ResultsA good agreement between the simulation and the experiment moment–displacement curves was found for the three types of instruments studied. RaCe exhibited the highest flexibility and PTU presented the highest torsional stiffness. Maximum values of von Mises stress were found for the PTU F1 file (1185 MPa) under bending, whereas the values of von Mises stress for the three instruments were quite similar under torsion. The stress patterns proved to be different in Mtwo under bending, according to the displacement orientation.ConclusionsThe favorable agreement found between simulation and experiment for the three types of instruments studied confirmed the potential of the numerical method to assess the mechanical behavior of endodontic instruments. Thus, a methodology is established to predict the failure of the instruments under bending and torsion.