A minimally invasive method for a few implant placement and restoration can be considered in a patient with severe mandibular defect. A 59-year-old man had a severe defect in the left mandibular body, and implant installation was difficult. The patient preferred fixed prosthetic therapy rather than removable prosthesis and did not want extensive reconstructive surgery such as bone grafting. Therefore, four implants were installed, and a fixed hybrid denture with an all-on-4 cantilever was planned. During the treatment, osseointegration of #34i failed, and a fixed hybrid cantilever prosthesis was supported by three implants. Prosthetic complications such as repetitive screw loosening and fracture have occurred; however, the function is well maintained up to 7 years and 4 months. In patients with severe mandibular atrophy, minimally invasive implant placement with a small number of implants may be considered as an alternative.