Biomechanical Effects of Platform Diameter and Screw Length in an Abutment-Free Tissue-Level Implant System Compared with a Ti-Base Configuration: 3D Finite Element Analysis

This finite element analysis compared a tissue-level implant with an engaging Ti-base to abutment-free, direct-to-implant, tissue-level configurations (3.7 mm and 4.5 mm platforms; short and long retention screws) to examine how platform width and screw length influence stresses under axial and oblique loads. Five configurations were modeled with identical materials and boundary conditions. Screw preload corresponding to a tightening torque of 35 N·cm was applied in the first step, followed by either a 400 N axial load or a 300 N at 30°. Oblique loading dominated the mechanical response, increasing stresses relative to axial loading and concentrating them at the implant neck and first thread, as well as at the crown screw-access and antirotation regions. Under oblique loads, the 3.7 mm platform implant showed the highest stresses, whereas the 4.5 mm platform implant was comparable to or slightly less stressed than the Ti-base configuration, whose peaks remained confined to a small internal recess. Crown stresses remained localized around the antirotation features, while the composite layer bore negligible load. Within the limitations of this numerical model, abutment-free, direct-to-implant workflows may achieve biomechanical performance comparable to Ti-base solutions if platform and screw selection are aligned with the occlusal scheme, but ISO-style fatigue testing and experimental or clinical validation are required.