Purpose: The biomechanical effects of different strengths of grafted bone, bicortical anchorage, and dimensional alterations of a dental implant with maxillary sinus augmentation were investigated. Materials and Methods: Sixteen finite element (FE) models that included five implant lengths, two implant diameters, and grafted bone with two levels of stiffness were studied. A posterior maxillary model was constructed from computerized tomographic images of a human skull, and the implant models were created via computer-aided design software (SolidWorks 2006). All materials were assumed to be isotropic and linearly elastic. A 45-degree oblique force of 129 N was applied to the buccal cusp of the first molar. Results: The von Mises stress was highest in the 7-mm-long implant. Stresses in cortical and trabecular bone were reduced by at least 50% for all other implants (length≥ 8.5 mm) with bicortical anchorage. Increasing the length of the bicortically anchored implant did not decrease the stress in native bone, but it decreased the stress in sinus grafts by at least 20%. The use of a wide implant decreased the stress by 24% to 42% in cortical bone and 17% to 36% in trabecular bone. Increasing the elastic modulus of grafted bone decreased the stress in native bone by approximately 10%. Conclusions: Bicortical fixation of implants and the presence of grafted bone with greater stiffness reduced the stresses in native bone. Increasing the length of the implant in grafted bone did not reduce the stress in native bone, but it did reduce the stress in grafted bone. The effects of implant diameters on reducing bone stress are primarily a result of the increased contact area between implant and bone. The results of the FE analysis imply that the success of a sinus-augmented dental implant is heavily dependent on the implant design and rigidity of the bone grafts. Int J Oral Maxillofac Implants 2009;24:455–462