Effects of abutment screw preload in two implant connection systems: A 3D finite element study

Statement of problem. Finite element analysis (FEA) has been used to evaluate the biomechanical behaviors of dental implants. However, in some FEA studies, the influence of the preload condition has been omitted to simplify the analysis. This might affect the results of biomechanical analysis significantly. The preload condition requires analysis. Purpose. The purpose of this FEA study was to evaluate and verify the effects of the presence of the preload condition on abutment screws under the occlusal load for external and internal hexagonal connection systems. Material and method. The finite element models consisting of bone blocks, 2 different implant systems (Osstem US and GS system; Osstem Implant Co), and crowns were created. With these components, a total of 6 models with different conditions were constructed for FEA: external hexagonal connection system only with preload (E0), external hexagonal connection system with no preload but occlusal load (EN), external hexagonal system with both preload and occlusal load (EP), internal hexagonal system only with preload (10), internal hexagonal system with no preload but occlusal load (IN), and internal hexagonal system with both preload and occlusal load (IP). An 113-degree oblique load (100 N) to the axis of the implant was applied on the occlusal surface of the crown for the models with occlusal load. A preload of 825 N was applied in the abutment screw of the models EO, EP, IO, and IP. The maximum von Mises stress, maximum principal stress, and maximum displacement of the components of the models were evaluated. Results. Both external and internal connection systems resulted in higher maximum von Mises stress and maximum principal stress values in the presence of preload in the abutment screw. The internal connection system showed higher displacement values than the external system with or without occlusal loading, and values tended to increase with the preload condition. Conclusion. The presence of a preload condition significantly affected the biomechanical behaviors of the components of 2 different connection systems. The preload condition should be included in FEA to achieve more realistic results.