The objective of this study was to investigate a bone graft substitute containing carbonate apatite (CO3Ap) 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 CO3Ap, 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 CO3Ap 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 CO3Ap 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 CO3Ap groups. Five days after tooth extraction, osteoclasts were observed near CO3Ap. The bone thickness in the CO3Ap group was significantly increased than that in the control group and the bone formation in the CO3Ap group increased by the same level as that in the AB group. CO3Ap 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.
Keywords: autogenous bone; bone substitute; carbonate apatite; osteoclast.