Purpose: This prospective study evaluated the prosthodontic maintenance requirements during the first year of service of mandibular overdentures supported by two unsplinted implants using three different implant systems. Materials and Methods: Seventy-two patients randomly allocated to three equal groups were each provided with a conventional complete maxillary denture and a mandibular overdenture supported by two unsplinted implants. A different implant system was used for each group (Steri-Oss, ITI, or Southern Implants), and their prosthodontic maintenance requirements were compared, primarily for the patrix and matrix. Additional maintenance categories recorded included any type of overdenture fracture, reline or remake of the overdenture, and maintenance of the maxillary denture. Results: Sixty-eight percent of the patients, regardless of implant system, required prosthodontic maintenance in the first year, most commonly for the matrices. The Southern Implants matrices required less maintenance than those of Steri-Oss or ITI (P .05). Additional overdenture maintenance was required by 28% of patients, irrespective of implant system. When all categories of prosthodontic maintenance were combined, there were no differences between implant groups. Evaluation of overall prosthodontic success using six-field tables revealed statistically significant differences between the three implant systems, with more ITI and Steri-Oss patients than Southern Implants patients requiring overdenture retreatment (repair). Conclusion: During the first year of service, the matrix maintenance requirements of Southern Implants were significantly lower than those of the ITI or Steri-Oss groups; this was reflected in the number of retreatment (repair) categories recorded. Although the three systems did not differ significantly for overall prosthodontic maintenance, both the Steri-Oss and the ITI titanium matrices showed problems of clinical significance.