Conversion of octacalcium phosphate in calcium phosphate cements

This study investigated the in vitro conversion reaction in calcium phospha te cements (CPCs) containing octacalcium phosphate (OCP) as one of the reag ents. OCP is known to be a precursor for apatite formation in vivo. The rea ction products were characterized using infrared spectroscopy and X-ray dif fraction. Although the conversion of OCP into hydroxyapatite is thermodynam ically favorable, OCP only yields apatite formation in CPC provided it is c ombined with a highly soluble Ca2+ and OH releasing reaction partner. In th is respect, tetracalcium phosphate is a promising compound. Adding small am ounts of monocalcium phosphate monohydrate can stimulate the setting throug h intermediate brushite formation. The preparation method of OCP might dras tically affect the performance of the cement. The reaction path of the sett ing of these CPC probably does not conform to the singular point principle described in the literature, and an in situ hydrolysis of OCP to apatite is conceivable. Simulation of apatite formation using OCP as the precursor an d/or seed in CPC might be beneficial for some biomedical applications. (C) 2000 John Wiley & Sons, Inc.