A histological investigation on tissue responses to titanium implants in cortical bone of the rat femur.

Implant materials are placed under various sites-including cortical bone, spongy bone, and bone marrow-at the same time according to the depth at implantation. Although cortical bone is an important site for the prognosis of implantation, detailed reports on tissue responses to implantation have been meager. The present study aims to reveal tissue responses to pure titanium implantation in rat femoris cortical bone. The rats received titanium bars surgically in their femurs and were sacrificed 1 day to 40 weeks post-implantation. The prepared tissue specimens were processed for light and transmission electron microscopy (TEM). Further histochemical detections were performed. One day post-implantation, empty osteocytic lacunae indicating degeneration of osteocytes were found in pre-existing cortical bone around the implant. Such pre-existing bone was replaced by new bone, but remained in part even 40 weeks post-implantation. Light microscopy showed that direct contact between the implant and new bone was identified 12 weeks post-implantation. Chronological and ultrastructural observation showed that new bone deposition appeared to proceed toward the implant, and that the intervening layer at the interface was derived from the degenerated debris of multinucleated giant cells and/or osteoblasts. Furthermore, it seemed that the width of intervening layer varied in relation to the distance from the blood vessels. The cells showing tartrate resistant acid phosphatase activity possessed cytological features of osteoclasts under TEM; they were frequently observed in perivascular sites near the implants even after osseointegration, suggesting that bone remodeling took place steadily around the implant.