Early Trabecular Bone Healing Around Titanium Implants: A Histologic Study in Rabbits

BACKGROUND: A detailed insight into the early healing response of trabecular bone to unloaded titanium implants is lacking. METHODS: Cylindrical implants were inserted in the tibial epiphysis of rabbits and left to heal for 1 to 42 days. Samples were processed into paraffin or methylmethacrylate sections and histomorphometrically analyzed. RESULTS: A hematoma was observed after 1 and 3 days of implant placement. In addition, small fragments of bone trabeculae were detected around the implant as a result of the implant installment procedure. Soon, osteoclasts were observed resorbing these fragments, whereas osteoblasts incorporated them in strands of new bone, thereby making them difficult to distinguish from day 7 onward. At that time, osteoblasts were detected at the edges of the preexisting bone, actively depositing new bone, resulting in maximal osteoid deposition around the implant after 28 days (58%). After 7 days of healing, the presence of basic remodeling units in the surrounding bone was already maximal (P <0.05 versus t = 1 and 3 days). This remodeling activity, together with the new bone formation, provided a firm anchoring of the implant in the trabecular bone. CONCLUSIONS: This study evaluated the early cellular events in trabecular bone surrounding titanium implants. The insertion of an implant into bone initiates a series of biologic processes, including the formation of a hematoma, shattered bone fragments adjacent to the implantation site, intensive bone remodeling, and the formation of new bone, eventually leading to the osseointegration of the implant.