Purpose: This study aimed to evaluate the 10-year prosthodontic outcomes with splinted and unsplinted designs for maxillary overdentures on three implants opposing mandibular two-implant overdentures. Materials and Methods: Using two similar implant systems, 40 edentulous participants with existing mandibular two-implant overdentures were randomly allocated to two prosthodontic treatment groups (splinted design with bar units; unsplinted design with ball attachments). Participants had three narrow-diameter implants placed in their edentulous maxillae using a one-stage surgical procedure, and they were conventionally loaded with overdentures. Prosthodontic maintenance events were documented at 1-, 2-, 5-, 7-, and 10-year recalls. Results: Progressive attrition of the cohort resulted in 36 participants being seen for the 1-year recall, 31 participants for the 2-year recall, 30 participants for the 3-year recall, 28 participants for the 5-year recall, 26 participants for the 7-year recall, and 23 participants (nearly 60%) for the 10-year recall. Data showed no significant differences in prosthodontic maintenance or success associated with patrices, matrices, or other aspects of the overdentures using the different attachment systems and designs. Conclusion: Maxillary three-implant overdentures are a viable treatment option for edentulous patients wearing opposing mandibular two-implant overdentures. There were no differences in prosthodontic maintenance and success between the splinted (bar) and unsplinted (ball) designs.