Replacement Process of Carbonate Apatite by Alveolar Bone in a Rat Extraction Socket.

The objective of this study was to investigate a bone graft substitute containing carbonate apatite (COAp) to analyze bone replacement and the state of bone formation in vitro and in vivo compared with autogenous bone (AB) or control. An osteoclast precursor cell line was cultured with AB or COAp, and morphological analysis using scanning electron microscopy and a tartrate-resistant acid phosphatase activity assay were performed. The right maxillary first and second molars of Wistar rats were extracted and compensated by AB or COAp granules. Following implantation, the bone formation state was evaluated after 3, 5, 7, 14, and 28 days of surgery by micro-computed tomography and immunohistostaining. The osteoclast-like cell morphology was typical with many cell protrusions in the AB and COAp groups. Additionally, the number of osteoclast-like cells formed in the culture increased in each group; however, there was no significant difference between the AB and COAp groups. Five days after tooth extraction, osteoclasts were observed near COAp. The bone thickness in the COAp group was significantly increased than that in the control group and the bone formation in the COAp group increased by the same level as that in the AB group. COAp is gradually absorbed by osteoclasts in the extraction socket and is easily replaced by alveolar bone. The process of bone replacement by osteoclasts is similar to that of autologous bone. By observing the process of bone replacement in more detail, it may be possible to gain a better understanding of the bone formation and control the amount of bone after surgery.