Study about Biodegradation of Hydroxyapatite and beta-tricalcium Phosphate Coating Layer

ABSTRACT

OBJECTIVE: Biodegradation of synthetic calcium phosphate depends on two mechanisms; dissolution in body fluid and a cellular reaction. The chemical dissolution process is well understood, but details of the cellular reaction are not yet fully understood. Thus, we investigated whether the resorption mechanisms of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) coating layer were identical, and, if not, what differences were observed. METHODS: Titanium discs, 12 mm in diameter and 2 mm in thickness, were coated with HA (n = 40) or beta-TCP (n = 40) by a dip and spin method. In each group, specimens were divided into two subgroups; the Dissolution group (D) and the Osteoclast Culture group (C). Discs in the D group were immersed in the distilled water or cell culture medium for 5 days, whereas, in the C group, osteoclast-like cells, which were obtained from giant cell tumor of bone, were seeded onto specimens and cultured for 5 days. The degradation characteristics of the surface coating were observed by light microscopy and scanning electron microscopy. RESULTS: Extent of the cracks and denudations were much greater in the beta-TCP coating than the HA coating after dissolution. In the C groups, the mean area fraction of resorption lacunae in the HA-C group was 11.62%, which was significantly higher than the 0.73% noted in the beta-TCP-C group (P = 0.001). CONCLUSION: The resorption mechanism of HA and beta-TCP coating was different and the beta-TCP coating was degraded principally by dissolution and separation from the implant, but the HA coating was resorbed by osteoclastic activity.