Fixed Full-Arch Maxillary Prostheses Supported by Four Versus Six Implants: 5-Year Results of a Multicenter Randomized Clinical Trial.

OBJECTIVES: This 5-year multicenter randomized clinical trial assessed the non-inferiority of maxillary implant-supported fixed complete dentures (FCDs) with four (4-I) compared to six implants (6-I) in terms of radiographic marginal bone level (MBL) changes after 5 years in function. MATERIALS AND METHODS: Individuals were randomly assigned to the 4-I or 6-I groups. Follow-ups occurred at 1, 3, and 5 years. At each visit, FCDs were unscrewed, clinical parameters (plaque index, bleeding on probing, pocket depth, and keratinized mucosa width) were recorded using a periodontal probe, periapical radiographs were obtained, and maintenance care was performed. MBL changes, incidence of techincal, prosthetic, and biological complications, treatments costs, and satisfaction were evaluated. RESULTS: Of 47 patients rehabiliated with 233 implants, survival rates were 99.3% for 6-I and 100% for 4-I (one early failure; 6-I group). No significant MBL differences were observed at 5 years between and within the groups. Both groups showed a decrease in keratinized mucosa width and experienced prosthetic and biological complications, but no peri-implantitis. The 4-I exhibited a significantly higher incidence of technical complications (16.6% vs. 0%) Cost analysis favored 4-I for initial and total costs. Clinician and patient satisfaction varied, with 4-I preferred aesthetically and 6-I functionally, particularly in speaking ability at earlier follow-ups. CONCLUSION: The use of FCDs supported by four implants is non-inferior to six implants in terms of radiographic MBL changes after 5 years in function. Both groups demonstrated comparable survival rates and incidence of biological and prosthetic complications. The 4-I was associated with higher technical complications and reduced overall treatment cost. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02405169.