The objective of this study is to propose a new mandibular advancement device (MAD) design by applying optimal design techniques. The new MAD is designed to improve the instability that can occur when a partial denture patient uses a conventional MAD. The MAD is a convenient way to artificially move the mandible forward to treat obstructive sleep apnea (OSA), which is common in middle-aged people. The artificially moving the mandible forward may result in jaw joint disorders or unintentional tooth movement. Particularly, it is suspected that patients with partial dentures will need to pay more attention to the use of MAD, but no objective results were reported. In this study, we compared the stability of the mandibular and dental components when using conventional MAD for normal and partial denture models. In the case of the partial denture model, a higher stress was applied to the bone than in the normal case, which was in the range of risk that could lead to bone resorption. Topology optimization tasks were performed to minimize the strain energy and volume of the MAD compared to the conventional MAD, as well as to reduce bone stress into the biomechanically stable range.