HISTOLOGICAL, CHEMICAL, AND CRYSTALLOGRAPHIC ANALYSIS OF 4 CALCIUM-PHOSPHATE CEMENTS IN DIFFERENT RABBIT OSSEOUS SITES

Four calcium phosphate cement formulations were implanted in the rabbi t distal femoral metaphysis and middiaphysis. Chemical, crystallograph ic, and histological analyses were made at 2, 4, and 8 weeks after imp lantation. When implanted into the metaphysis, part of the brushite ce ment was converted into carbonated apatite by 2 weeks. Some of the bru shite cement was removed by mononuclear macrophages prior to its conve rsion into apatite. Osteoclastlike cell mediated remodeling was predom inant at 8 weeks after brushite had converted to apatite. The same his tological results were seen for brushite plus calcite aggregate cement , except with calcite aggregates still present at 8 weeks. However, wh en implanted in the diaphysis, brushite and brushite plus calcite aggr egate did not convert to another calcium phosphate phase by 4 weeks. C arbonated apatite cement implanted in the metaphysis did not transform to another calcium phosphate phase. There was no evidence of adverse foreign body reaction. Osteoclastlike cell mediated remodeling was pre dominant at 8 weeks. The apatite plus calcite aggregate cement implant ed in the metaphysis that was not remodeled remained as poorly crystal line apatite. Calcite aggregates were still present at 8 weeks. There was no evidence of foreign body reaction. Osteoclastlike cell remodeli ng was predominant at 8 weeks. Response to brushite cements prior to c onversion to apatite was macrophage dominated, and response to apatite cements was osteoclast dominated. Mineralogy, chemical composition, a nd osseous implantation site of these calcium phosphates significantly affected their in vivo host response. (C) 1998 John Wiley & Sons, Inc .