The purpose of this study was to compare the stress distributions of NiTi rotary instruments based on their cross-sectional geometries of triangular shape-based cross-sectional design, S-shaped cross-sectional design and modified rectangular shape-based one using 3D FE models.

NiTi rotary files of S-shaped and modified rectangular design of cross-section such as Mtwo or NRT showed larger stress change while file rotation during simulated shaping.

The stress of files with rectangular cross-section design such as Mtwo, NRT was distributed as an intermittent pattern along the long axis of file. On the other hand, the stress of files with triangular cross-section design was distributed continuously.

When the residual stresses which could increase the risk of file fatigue fracture were analyzed after their withdrawal, the NRT and Mtwo model also presented higher residual stresses.

From this result, it can be inferred that S-shaped and modified rectangular shape-based files were more susceptible to file fracture than the files having triangular shape-based one.

Flexibility and fracture properties determine the performance of NiTi rotary instruments. The purpose of this study was to evaluate how geometrical differences between three NiTi instruments affect the deformation and stress distributions under bending and torsional conditions using finite element analysis.

Three NiTi files (ProFile .06 / #30, F3 of ProTaper and ProTaper Universal) were scanned using a Micro-CT. The obtained structural geometries were meshed with linear, eight-noded hexahedral elements. The mechanical behavior (deformation and von Mises equivalent stress) of the three endodontic instruments were analyzed under four bending and rotational conditions using ABAQUS finite element analysis software. The nonlinear mechanical behavior of the NiTi was taken into account.

The U-shaped cross sectional geometry of ProFile showed the highest flexibility of the three file models. The ProTaper, which has a convex triangular cross-section, was the most stiff file model. For the same deflection, the ProTaper required more force to reach the same deflection as the other models, and needed more torque than other models for the same amount of rotation. The highest von Mises stress value was found at the groove area in the cross-section of the ProTaper Universal.

Under torsion, all files showed highest stresses at their groove area. The ProFile showed highest von Mises stress value under the same torsional moment while the ProTaper Universal showed the highest value under same rotational angle.