Purpose: To investigate the influence of splinted vs unsplinted designs for a maxillary overdenture supported by four implants in terms of the outcome measures implant survival, overdenture longevity, and patient satisfaction. Materials and Methods: A systematic search, complemented by a handsearch, was carried out in the Embase, MEDLINE (PubMed), and Web of Science databases from 2000 to 2018. The PRISMA statement and a PICO approach were adopted. Free-text words were used in the strategy search, including "4-implantretained overdenture," "4-implant-supported overdenture," "implant-supported overdenture," "implantretained overdenture," "maxillary overdenture," "splinted design," "un-splinted design," and their combinations. All selected articles provided at least a 1-year follow-up, 10 fully edentulous patients, and at least one of the following clinical outcomes: survival rate of implants, survival rate of overdentures, and/or patient satisfaction scores. Nonparametric Fisher test for unpaired data was adopted in order to analyze data deriving from the survival rates of implants and overdentures. Results: The initial electronic search produced a total of 2,922 articles. After applying the inclusion criteria, 14 articles were included. The mean follow-up time after implant placement ranged from 1 to 10 years. No statistical difference was detected in the survival rate of implants between the splinted implant group and the unsplinted implant group (P = .1). Only 4 included studies reported an overdenture survival rate of lower than 95%. It is interesting to note that among these 4 studies, 3 employed four splinted implants with a bar anchorage; however, no statistical difference was detected in the survival rate of overdentures between the splinted and unsplinted groups (P = .47). High scores were reported by all studies investigating patient satisfaction. Conclusion: Within the limits of this systematic review, it can be concluded that the survival rates of implants and overdentures and patient satisfaction with a maxillary overdenture supported by four implants were not influenced by the overdenture design, and no statistical difference was detected between the splinted and unsplinted groups.