Influence of Abutment Screw Preload on Stress Distribution in Marginal Bone

Changes in an implant assembly after abutment connection might possibly cause deformation in the implant/abutment joint and even in the marginal bone. Purpose: The aim of this study was to evaluate the influence of abutment screw preload through the implant collar on marginal bone stress without external load application. Materials and Methods: Models of three implant parts made of titanium (implant, abutment, and abutment screw) and cortical bone were built and positioned with computer-aided design software. Meshing and generation of boundary conditions, loads, and interactions were performed. Each part was meshed independently. The sole load applied to the model was a torque of 32 Ncm on the abutment screw about its axis of rotation. Results: The implant collar was deformed axially after the screw was tightened (3 µm). This deformation resulted in 60 MPa of stress in the marginal bone. Moreover, pressure on the marginal bone in a radial direction was observed. Conclusions: It can be concluded that, without any external load application, abutment screw preload exerts stresses on the implant collar and the marginal bone. These findings should help guide the development of new implant/abutment joint designs that exert less stress on the marginal bone. Keywords: bone stress, dental implants, finite element analysis, implant/abutment joint, marginal bone, preload