Effect of minor amounts of ß-calcium pyrophosphate and hydroxyapatite on the physico-chemical properties and osteoclastic resorption of ß-tricalcium phosphate cylinders.

ABSTRACT

ß-Tricalcium Phosphate (ß-TCP), one of the most used bone graft substitutes, may contain up to 5 wt% foreign phase according to standards. Typical foreign phases include ß-calcium pyrophosphate (ß-CPP) and hydroxyapatite (HA). Currently, the effect of small amounts of impurities on ß-TCP resorption is unknown. This is surprising since pyrophosphate is a very potent osteoclast inhibitor. The main aim of this study was to assess the effect of small ß-CPP fractions (<1 wt%) on the in vitro osteoclastic resorption of ß-TCP. A minor aim was to examine the effect of ß-CPP and HA impurities on the physico-chemical properties of ß-TCP powders and sintered cylinders. Twenty-six batches of ß-TCP powder were produced with a Ca/P molar ratio varying between 1.440 and 1.550. Fifteen were further processed to obtain dense and polished ß-TCP cylinders. Finally, six of them, with a Ca/P molar ratio varying between 1.496 (1 wt% ß-CPP) and 1.502 (1 wt% HA), were incubated in the presence of osteoclasts. Resorption was quantified by white-light interferometry. Osteoclastic resorption was significantly inhibited by ß-CPP fraction in a linear manner. The presence of 1% ß-CPP reduced ß-TCP resorption by 40%, which underlines the importance of controlling ß-CPP content when assessing ß-TCP biological performance.