Bone Formation Around Immediately Loaded and Submerged Dental Implants with a Modified Sandblasted and Acid-Etched Surface After 4 and 8 Weeks: A Human Histologic and Histomorphometric Analysis

Purpose: A high clinical and radiographic level of osseointegration has been reported for early and immediately loaded (IL) implants. The aim of this study was to analyze, histologically and histomorphometrically, the bone-titanium interface of IL and submerged titanium implants that were retrieved at 4 and 8 weeks after placement. Materials and Methods: Four patients underwent rehabilitation of the posterior mandible with fixed prostheses, and an additional implant was inserted distally in the mandible. In two patients, the additional implants were put into nonfunctional immediate loading with a fixed provisional prosthesis on the same day of the implant surgery, whereas in the other two patients, the implants were left submerged. The implant stability quotients at implant insertion were 70 and 67 for the submerged implants and 69 and 77 for the IL implants. Before retrieval, the IL implants were clinically osseointegrated and were not mobile. After 4 and 8 weeks, the four implants (two IL and two submerged) were retrieved with a 5-mm trephine and processed for histologic examination. Results: After 4 weeks, the IL implant showed a bone-implant contact percentage (BIC) of 65.6%, while the BIC for the submerged implant was 54.7%. After 8 weeks, the BIC was 76.2% for the IL implant, while for the submerged implant it was 62.3%. Conclusions: Very high BICs were present after 4 and 8 weeks around both submerged and IL implants, with the latter showing a higher quantity of bone. IL did not impede bone formation in the early healing periods. Keywords: histology, immediate loading, implant surfaces, loading conditions, retrieved dental implants