Purpose <p>This systematic review evaluated the implant survival rate and prosthetic complications of single implant-supported mandibular overdentures (1-IOD) and compared them with those of traditionally recommended two implant-supported mandibular overdentures (2-IOD).</p> Methods <p>The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used as a reference for reporting this systematic review. The study protocol was prospectively registered in the PROSPERO database (registration number: CRD420250644169). This review included 17 randomized controlled trials that compared 1-IOD and 2-IOD, with a follow-up period of at least 12 months after denture placement. The assessed outcomes included implant survival rate, denture fractures, denture relining, O-ring replacement, and metal housing reattachment. The risk of bias in the included studies was assessed using the Cochrane Risk-of-Bias 2 tool.</p> Results <p>This meta-analysis revealed no difference in implant survival rates between the 1- and 2-IOD groups over a 5-year period. In the subgroup analysis, overdenture fractures, denture remakes, and metal housing reattachments were more frequently observed in the 1-IOD group, whereas no statistically significant differences were found in the need for relining or O-ring replacement.</p> Conclusions <p>Although 1-IOD may be a less invasive alternative to 2-IOD, careful consideration is necessary because of its increased incidence of prosthetic complications.</p>