The purpose of this study was to examine the influence of reinforcing the structure of an overdenture on stress distribution in the residual ridge using the three-dimensional finite element method. Four models of mandibular overdentures with various reinforcement methods were analyzed, including (1) without reinforcement, (2) with chrome-cobalt reinforcing wire, (3) with a reinforcing structure (a cast metal framework) and no reinforcement on the coping top, and (4) with a reinforcing structure and reinforcement on the coping top. The reinforcement adjacent to the top of the coping and the medial part reduces the stress beneath the loading side of dentures and widely and evenly distributes the stress of the residual alveolar ridge.