The performance of implant-supported restorations is strongly influenced by both the implant diameter and the surrounding bone density. This research aimed to examine how these two parameters affect stress distribution when subjected to vertical and 30° oblique loading. A finite element analysis was performed using dental implants of a constant length of 6.5 mm, but with different diameters (Ø3.3, Ø3.5, Ø3.75, Ø4.0, Ø4.25, and Ø4.75 mm). Each implant was positioned axially and restored using a 2 mm high straight transepithelial abutment for a single-tooth prosthesis. Four bone density conditions—Type IV, III, II, and 0-I—were modeled based on a simplified mandibular segment. A 200 N force was applied vertically and at a 30° inclination to the occlusal surface, located 11 mm above the implant platform, and the equivalent Von Mises stresses in bone were evaluated. The highest stress value appeared in Type IV bone with the Ø3.3 implant (235 MPa), whereas the lowest was found in Type 0-I bone with the Ø4.75 implant (41 MPa). Across all diameters, improved bone density corresponded with reduced stress levels. Increasing the implant diameter produced a similar, but more pronounced, reduction in bone stress. Implant diameter plays a major role in minimizing bone stress, as wider implants distribute loads more efficiently.
