Tissue response to titanium implants in the rat maxilla: Ultrastructural and histochemical observations of the bone-titanium interface

Background: The detailed mechanism of osseointegration, the most appropriate implant-bone interface, remains unclear in jaw tissues at the ultrastructural level in contrast to the many reports using long bones. The present study reports on tissue response to titanium-implantation on an animal model using rat maxilla. Methods: Animals were sacrificed at 1 to 28 days postimplantation and prepared tissue specimens, freed from implants by a cryofracture technique, were processed for transmission electron microscopy and histochemistry for tartrate resistant acid phosphatase activity (TRAPase). Results: Different patterns in bone formation were recognized between lateral and base areas of implant cavities. In the lateral area with narrow gaps, bone deposition took place from the pre-existing bone towards the implant after active bone resorption by osteoclasts reactive to TRAPase. However, no distinct bone formation appeared in the lateral area where the implant had been installed close to the osteotomy margin. On the other hand, new bone formation was found at the base area without any apparent bone resorption. Interestingly, mononuclear cells reactive to TRAPase, presumably preosteoblasts, frequently occurred near preosteoblasts. Osseointegration around the implants was obtained in this model by 28 days post-implantation except for the lateral area with complete contact with implants, where the thin layer remained in contact with the implant surface. Conclusions: These findings indicate that ossification proceeds at different modes around the titanium implant in rat maxilla, depending on the nature of the recipient bones and the dimension of the gap between the implant and osteotomy margin.