Purpose: The aims of this study were to (1) establish a biomechanical model that simulates the full-arch restoration supported by immediately loaded implants, which is customized for individual patients, and (2) clarify the effect of the implant placement and rigidity of a provisional restoration on the biomechanical response at the bone-implant interface. Materials and Methods: Three-dimensional finite element analysis models of a maxillary full-arch prosthesis supported by four immediately loaded implants were created from computed tomography data of maxillary edentulous patients. Displacements of the implants and equivalent stress on the bone around the implants under the loading conditions that simulated sleep bruxism were then calculated for these models. The effects of the implant placement angle (vertical or inclined), the reinforcement of the provisional restoration (with or without reinforcement), and the implant length on the maximum displacements of each implant were investigated, in addition to the average equivalent stress of the bone around the implant. Results: A longer implant and rigid restoration with reinforcement have the potential to reduce implant displacements and associated bone stress; however, the rigidity of the restoration had a much more significant effect on these parameters. Conclusions: The rigidity of full-arch provisional restorations supported by four immediately loaded implants should be improved by reinforcements, which could ensure the successful achievement of osseointegration by reducing load-induced micromovements of the implants.