Bone level alterations at implants placed in the posterior segments of the dentition: outcome of submerged/non-submerged healing - A 5-year multicenter, randomized, controlled clinical trial

Objective: To determine if longitudinal bone level change at Astra Tech (TM) implants placed in the posterior part of the dentition was influenced by the healing conditions provided following implant placement, i.e., submerged or non-submerged healing. Material and methods: Eighty-four patients and 115 fixed partial dentures (FPDs or cases) entered the study. The cases were randomized into two implant installation groups: initially non-submerged (group A) or initially submerged (group B) implants. Three hundred and twenty-four implants were installed (group A = 153; group B = 171): 145 in the maxilla and 179 in the mandible. Radiographs from the implant sites were obtained at FPD insertion (baseline) and subsequently every 12 months. In the radiographs, the position of the marginal bone at the mesial and distal aspects of the implants was determined and the radiographic (Rx) bone level change over time was calculated. Results: Seven implants failed to integrate (four in group A and three in group B). During the 5 years of monitoring, three implants had to be removed and 35 implants were lost to follow-up. The Rx bone level alteration that occurred during year 1 was 0.02 +/- 0.38 mm in group A and 0.17 +/- 0.51 mm in group B. During the subsequent 4 years there was some further Rx bone loss in group B (0.02 +/- 0.62 mm), while in group A there was some gain of bone (0.07 +/- 0.5 mm). Conclusion: The peri-implant bone level change and number of biological complications that took place during the 5 years was small and unrelated to the surgical protocol used for implant placement.