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

β-Tricalcium Phosphate(β-TCP),one of the most used bone graft substitutes,may contain up to 5 wt%foreign phase according to standards.Typical foreign phases includeβ-calcium pyrophosphate(β-CPP)and hydroxyapatite(HA).Currently,the effect of small amounts of impurities on β-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 β-CPP fractions(<1 wt%)on the in vitro osteoclastic resorption of β-TCP.A minor aim was to examine the effect of β-CPP and HA impurities on the physico-chemical properties of β-TCP powders and sintered cylinders.Twenty-six batches of β-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 β-TCP cylinders.Finally,six of them,with a Ca/P molar ratio varying between 1.496(1 wt% β-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 β-CPP fraction in a linear manner.The presence of 1% β-CPP reduced β-TCP resorption by 40%,which underlines the importance of controllingβ-CPP content when assessing β-TCP biological performance.