Change in Crown-to-Implant Ratio of Implants Placed in Grafted and Nongrafted Posterior Maxillary Sites: A 5-year Prospective Randomized Study

Purpose: The aim of this study was to evaluate the performance of implants placed for 5 years in grafted vs nongrafted sinuses in relation to crown-to-implant ratio. The measurements of crown and implant lengths took into account changes in both endo-sinus and crestal bone levels over 5 years. Materials and Methods: Enrolled patients required one or two implants in at least one sinus and presented a residual bone height of posterior maxilla ≤ 4 mm. Individual sinuses were randomly allocated either to be grafted or not before surgery. Implants of 8 mm in length were placed using osteotome sinus floor elevation (OSFE). After 10 weeks of healing, they were loaded functionally using definitive single crowns. Radiographic measurements were made on periapical radiographs taken at surgery, prosthetic steps, and 5 years. The implant length was measured between the most apical and coronal contact of bone and implant, and the crown length was measured between the most occlusal point of the crown and the crestal bone. Data were analyzed using mixed linear models. Results: Twenty implants were placed in grafted sinuses and 17 in native bone (12 patients). One of the 35 restored implants failed. Immediately after surgery, the mean lengths of the implants placed in grafted and nongrafted sites were 2.4 ± 0.8 and 2.7 ± 0.9 mm, respectively (P = .351). At loading, the mean crown-to-implant ratios were 3.8 ± 0.8 and 4.6 ± 2.0 (P = .033), respectively, whereas at 5 years, they were 2.0 ± 0.8 and 2.1 ± 0.4, respectively (P = .341). Conclusion: The use of grafting material is not necessary to restore posterior maxilla ≤ 4 mm with OSFE and simultaneous implant placement. Over 5 years, all restored implants but one were functional. Despite unfavorable conditions in terms of initial bone anchorage and height of single crown restoration, a high initial crown-to-implant ratio did not compromise the long-term survival of implants placed in grafted or nongrafted sinuses. Keywords: atrophic posterior maxilla, crown-to-implant ratio, dental implants, grafting material, osteotome sinus floor elevation, proximal bone-to-implant contact