Sinus bone formation and implant survival after sinus membrane elevation and implant placement: a 1-to 6-year follow-up study

Objectives: To investigate the long-term clinical and radiographic results of the maxillary sinus membrane elevation technique where implants were inserted in a void space created by the elevation of the sinus membrane without adding any graft material. Materials and methods: A total of 84 patients were subjected to 96 membrane elevation procedures and simultaneous placement of 239 implants. Changes of intra-sinus and marginal bone height in relation to the implants were measured in intraoral radiographs taken at insertion, after 6 months of healing, after 6 months of loading and then annually. Computerized tomography was performed pre-surgically and 6 months post-surgically. Resonance Frequency Analyses measurements were performed at the time of implants placement, at abutment connection and after 6 months of loading. The implant follow-up period ranged from a minimum of one to a maximum of 6 years after implants loading. Results: All implants were stable after 6 months of healing. A total of three implants were lost during the follow-up period giving a survival rate of 98.7%. Radiography demonstrated on average 5.3 +/- 2.1 mm of intra-sinus new bone formation after 6 months of healing. RFA measurements showed adequate primary stability (implant stability quotient 67.4 +/- 6.1) and small changes over time. Conclusion: Maxillary sinus membrane elevation and simultaneous placement of implants without the use of bone grafts or bone substitutes result in predictable bone formation with a high implant survival rate of 98.7% during a follow-up period of up to 6 years. The intra-sinus bone formation remained stable in the long-term follow-up. It is suggested that the secluded compartment allowed for bone formation according to the principle of guided tissue regeneration. The high implant survival rate of 98.7% indicated that the implants sufficiently supported the fixed bridges throughout the study period. This technique reduces the risks for morbidity related to harvesting of bone grafts and eliminates the costs of grafting materials.