Comparative Study of Torsional and Bending Properties for Six Models of Nickel-titanium Root Canal Instruments with Different Cross-sections

This study investigated the influence of cross-section profile on the mechanical behaviors of six commercial nickel-titanium (NiTi) root canal instruments using the finite element method. The nonlinear mechanical characteristics of the NiTi alloy were taken into account. The six root canal instruments studied were ProTaper, Hero642, Mtwo, ProFile, Quantec, and NiTiflex. Mathematical models for these instruments were constructed and their performances were analyzed under equal torque conditions. The ProTaper and Hero642 models achieved the lowest stress levels that made them the most torque-resistant while the NiTiflex model was the poorest. The maximum stress value and the stress distribution in a model were found strongly influenced by the cross-section profile. Factors affecting the stress distribution include the cross-sectional inertia, depth of the flute, area of the inner core, radial land, and peripheral surface ground. As the area of the inner core of the cross-section increased, the model was more torque-resistant.