Comparison of carbonate apatite and β-tricalcium phosphate (resorbable calcium phosphates) implanted subcutaneously into the back of rats

Abstract

Bioresorption and biocompatibility of carbonate apatites, both sintered and non-sintered (S-CAP and N-CAP), and of sintered β-tricalcium phosphate (β-TCP) were compared by implanting particles of these materials into the back of adult rats. Bioresorption - when evaluated non-destructively with non-decalcified tissues using microfocus X-ray tomography -was essentially the same for N-CAP and β-TCP, while S-CAP exhibited statistically lower bioresorption at 2, 4, and 12 weeks postoperatively. Biocompatibility - when evaluated by ED1 immunostaining - was in the order of β-TCP > N-CAP > S-CAP. The intensity of ED1 immunostaining decreased with time, but persisted longer in β-TCP than in S-CAP and N-CAP, indicating that β-TCP produced the strongest and most enduring stimulation of macrophages. Although no statistical differences were found in tartrate-resistant acid phosphatase (TRAP) staining among the materials at each implantation period, the degree of TRAP staining for S-CAP was statistically greater at 12 weeks than at 2 and 4 weeks, indicating that osteoclast-like cells were in part responsible for the resorption of the carbonate apatite.