Nowadays, due to high quality and efficiency of dental implants, implantation is considered as the best method for replacing missing teeth. However, challenges such as the stress-shielding phenomenon can affect the success of this approach. This phenomenon, which occurs due to the mismatch in mechanical properties between the implant fixture and the surrounding bone, prevents the natural stimulation of the bone for necessary densification and regeneration. As a result, it reduces the quality of the osseointegration process and delays healing. In this study, the effect of a bidirectional functionally graded titanium-hydroxyapatite structure on the mechanical properties and fatigue life of a dental implant screw was investigated using finite element simulation. Since this structure provides better control over variations in both radial and height directions, it offers more optimization potential compared to homogeneous as well as unidirectional functionally graded structures in implant screws. Therefore, the primary objective of this study is to compare the performance of the bidirectional functionally graded implant screw with homogeneousas well as unidirectional graded screws, to reduce the stress-shielding phenomenon and eva‎luate its fatigue life. For this purpose, the ABAQUS software and the USDFLD subroutine were utilized for simulating the implant and functionally graded structure, while the FE-Safe software was employed for fatigue life analysis. Some simplifying assumptions, such as isotropic linear elastic behavior for the jaw bone, were employed. The implant screw and the abutment were modeled as an integrated unit. A rigid ceramic crown with simplified geometry was modeled tied to the abutment. For modeling the jawbone geometry, the section of the lower jaw in the molar teeth area was adopted. The influence of adjacent teeth was ignored, and a single tooth was modeled within the jawbone. The results indicate that the bidirectional functionally graded structure for the screw may reduce the stress-shielding effect. Moreover, compared to unidirectional functionally graded case, the displacements experienced by the jawbone decrease, and hence, prevent damaging the adjacent teeth and jawbone. It is worth mentioning that the proposed bidirectional functionally graded screw satisfy the infinite fatigue life condition, as it should be.

مهدي سلماني تهراني

محمدرضا فروزان , مهدي جوان بخت