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 β-tricalcium
phosphate (β-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 β-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 β-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 β-TCP-C group (P = 0.001).
Conclusion
The resorption mechanism of HA and β-TCP coating was different and the β-TCP coating was degraded
principally by dissolution and separation from the implant, but the HA coating was resorbed by osteoclastic activity.
