Four or six implants in the maxillary posterior region to support an overdenture: 5-year results from a randomized controlled trial.

OBJECTIVE: To compare clinical and patient-reported outcomes when providing maxillary overdentures on four bar- and six bar-connected implants placed in the posterior region during a 5-year follow-up period. MATERIALS AND METHODS: Sixty-six fully edentulous patients with functional maxillary denture complaints and insufficient bone volume to allow implant placement were scheduled for a maxillary sinus floor elevation procedure with bone from the anterior iliac crest and randomized to receive either four or six implants in the posterior maxilla and four implants in the mandible. After 3 months of osseointegration, a bar-supported overdenture was constructed. Maxillary implant survival, overdenture survival, clinical scores, peri-implant bone height changes and patient satisfaction were assessed. RESULTS: Sixty patients completed the 5-year follow-up. Implant survival was 100% in the four-implant group and 99.5% in the six-implant group. No new overdentures had to be made in the four-implant group, and three new overdentures were made in the six-implant group due to excessive wear of the denture base and teeth (90.9% overdenture survival). Clinical parameters did not differ significantly between groups. Mean marginal bone loss compared to baseline was 0.58 +/- 0.51 mm in the four-implant group and 0.60 +/- 0.58 mm in the six-implant group, respectively. Overall, patient satisfaction improved significantly, but did not differ between groups. CONCLUSION: Following a bilateral maxillary sinus floor elevation procedure, a bar-supported overdenture on four implants in the posterior maxillary region is not inferior to an overdenture supported by six implants after a 5-year evaluation period in patients with functional maxillary denture complaints and marked posterior resorption (Clinical trial registration number: NTR2969).