Immunohistochemical study of rat parietal bone defect repair with β-tricalcium phosphate and carbonate apatite

In order to examine effects of β-tricalcium phosphate (TCP) or carbonate apatite particles (CAP) in bone repair, we studied bone healing processes histopathologically and immunohistochemically in rat parietal bone defects filled with TCP or CAP. Without TCP or CAP filling, the bone repair was carried out by osteoblasts derived from the edge of the bone defect but did not occur at the center area of the defect. However, with TCP or CAP filling, conductive bone formation occurred along the surfaces of both particles, indicating that those ceramics definitely induced osteoblastic differentiation, which was confirmed by immunohistochemical expressions of such osteoblastic differentiation markers as BMP2/4, Runx2 and Osterix. The expressions of BMP2/4 preceding those of the other osteoblastic markers seemed to be essential for the conductive bone formation by calcium phosphate ceramics. Osteoblastic cells on these particles were derived from resting osteoblasts on the remaining bone surface. Type I collagen, dentin matrix protein 1, and osteocalcin were also expressed in osteoblastic cells as well as in the bone matrix, suggesting that these molecules participated in both bone formation and regulation of osteoblastic differentiation.