Purpose: The aim of this study was to compare prospective treatment with implant-retained mandibular overdentures (IROs) versus conventional complete dentures (CDs). This paper reports on the study design and 1-year outcomes. Part 2 in this series will report the 7-year outcomes. Materials and Methods: Sixty edentulous patients with severely resorbed mandibles, already using a conventional CD, participated. Thirty patients received an IRO and 30 received a conventional CD. The patients were retrospectively matched for age, gender, and social class. The length of each treatment session was recorded. Both groups provided a subjective assessment of their current dentures, and satisfaction with their new dentures was evaluated using questionnaires focusing on denture-related complaints and a general satisfaction scale. Results: Patients with IROs were more satisfied with the performance of their dentures than those using conventional CDs, especially with regard to subjective fit, looseness, and quality of chewing; however, more clinical treatment was required. The mean time taken by the prosthodontist to construct CDs was 268 minutes, compared to 327 minutes for IROs, to the time of the second review appointment after insertion. Conclusions: Mandibular IROs provided enhanced performance but required more clinical resources.