FLUORIDE UPTAKE BY HYDROXYAPATITE FORMED BY THE HYDROLYSIS OF ALPHA-TRICALCIUM PHOSPHATE

Although there is interest in forming synthetic analogs of hard tissue s at physiologic temperature, significant gaps in knowledge exist with respect to the mechanisms by which precursor solids convert to apatit es and also with respect to the apatite compositions that may be forme d. In this study calcium-deficient HAp [Ca-9(HPO4)(PO4)(5)OH] was prep ared by hydrolysis of tricalcium phosphate (TCP), alpha-Ca-3(PO4)(2). The kinetics of HAp formation were studied as a function of temperatur e by isothermal calorimetry. TCP hydrolyzed completely within about 12 h, and the hydrolysis reaction evolved 133 kJ/mol of HAp formed. Alth ough the kinetics of hydrolysis exhibited a strong temperature depende nce, the mechanistic path taken appeared independent of temperature. T he fluoridation of hydroxyapatite compositions having Ca/P ratios high er than 1.59 previously has been investigated. However, little work ha s been done on the fluoridation of more calcium-deficient hydroxyapati te. Ca-9(HPO4)(PO4)(5)OH was formed at temperatures between 37.4 degre es and 55 degrees C to vary its morphology. These preparations then we re reacted in NaF solution and the kinetics of fluoride incorporation studied. Solution chemical analyses were used to determine the amounts of fluoride incorporated. The extent of hydroxyl replacement by fluor ide ranged from 17 to 72% and correlated with the surface area of the parent HAp. (C) 1998 John Wiley & Sons, Inc.