A histological evaluation on self-setting alpha-tricalcium phosphate applied in the rat bone cavity

This study aimed to elucidate the biological effects of a self-setting tricalcium phosphate bone substitute (BIOPEX) applied in rat femoral cortical bone cavities. Narrow penetrations through the cavity and bone marrow were prepared to obtain cellular sources. In the experimental group at day 1, a thin cell layer intruded into a narrow space between the grafted BIOPEX and the bottom of the cavity. From days 5 to 10, a range of tartrate-resistant acid phosphatase (TRAPase)-reactive osteoclasts accumulated on the surface of the BIOPEX facing the bottom of the cavity, whilst many alkaline phosphatase (ALPase)-positive osteoblasts were localized on the bone surface opposing the BIOPEX. However, at day 20, osteoblasts were localized neighboring the osteoclasts on the BIOPEX, and deposited bone matrices onto this material, implying a coupling between osteoclasts and osteoblasts. At days 30 and 40 post-operation, small remnants of BIOPEX particles were present in the new bone with a profile of compact bone. Thus, BIOPEX is resorbed by osteoclasts, and succeeded by osteoblastic bone apposition with a coupling of osteoclasts and osteoblasts at the later stage. In conclusion, the use of BIOPEX provides adequate bone regeneration with the profile of compact bone.