Purpose: The aim of the present study was to evaluate the prosthodontic maintenance required for mandibular overdentures supported by 4 implants and splinted with either a round bar and resilient overdenture anchorage or a milled bar with rigid anchorage over a 5-year period. Materials and Methods: In a randomized prospective trial, 51 edentulous patients received 4 mandibular interforaminal implants to support an overdenture and maxillary complete dentures. For the implant-supported overdentures (IODs), bar architecture and denture stabilization were chosen randomly; 25 patients received round bars (group 1) and resilient anchorage and 26 patients received milled bars (group 2) and rigid anchorage. The prosthodontic maintenance required for the IODs and opposing dentures were evaluated during a 5-year follow-up period and compared between the 2 retention modalities used for IODs. Results: Forty-six patients (22 in group 1, 24 in group 2) were available for a 5-year follow-up (dropout rate: 9.8%). Prosthodontic maintenance efforts were significantly greater (P .01) with the round bar design (group 1) than with the overdentures stabilized with milled bars (group 2). In group 1, prosthodontic maintenance efforts were more frequent in the early phase of use (1 to 2 years), as compared with an evenly distributed incidence over the 5-year period with the rigid milled bar system. Major prosthetic complications (IOD remaking, bar fracture) were only seen in cases without metal-reinforced frameworks (group 1). Conclusion: When 4 interforaminal implants are used to anchor mandibular overdentures, the design of the anchorage system will significantly affect prosthodontic maintenance efforts and complication rates. Rigid anchorage using milled bars and a metal-reinforced denture framework required less prosthodontic maintenance, ie, for clip activation/fracture, than resilient denture stabilization using multiple round bars without a rigid denture framework.