Investigation of the behavior of different Ni-Ti dental files and chemical-mechanical behavior using finite element analysis

Rotary files with superelastic qualities have received attention in dentistry field with gold standard for endodontic procedures such as root canal preparation and shaping. Despite their high flexibility, files within root canals can fracture. The most common causes of file fractures are bending and torsional forces. Therefore, manufacturers attempt to enhance the mechanical properties in order to resist such forces and pressures. Many factors, including the instrument-making process, alloy's characteristics, as well as file geometry and features like pitch length and taper may impact the mechanical performance of the files. The aim of the present study was to investigate the effect of file geometry on file resistance to flexural and torsional stresses. This work was conducted as an experimental analysis using finite element analysis (FEA). The NiTi file was characterized using X-ray diffraction (XRD) analysis. Four different endodontic files including Vortex Blue, Edge File, One Curve and Hyflex-EDM with the same tip and diameter, and different geometric features were designed using SolidWorks software. These models were then transferred to ANSYS, a three-dimensional (3D) modeling program, and examined under torsional and flexural forces. In order to simulate rotational stress, the file shank was fixed and rotated at θ = 22°. In additon, a 3.8 mm file was bent on the Y axis for simulating flexural stresses. The Edge File and Vortex Blue file had the highest and lowest amounts of flexural and torsional stress, respectively. Further, in all the samples the highest amount of torsional stress was observed at 2 to 3 mm of the file tip while the highest amount of flexural stress was seen in the depth of the flutes and near the winning edges. The four examined endodontic instruments had different mechanical properties due to their different geometry. For a good and longer-lasting root canal treatment, dentists should utilize an appropriate file based on manufacturing instructions and clinical conditions.