Powder suspension method for critically re-examining the two-site model for hydroxyapatite dissolution kinetics.
A powder dissolution method has been developed, and experiments with the hydroxyapatite suspensions confirm earlier conclusions based on dissolution from hydroxyapatite disks. Although a quantitative assessment of the properties of site 1 was not possible from the data obtained in the present study, a rather accurate and independent evaluation of the properties and the behavior of site 2 of the two-site model for hydroxyapatite dissolution was possible, and the results clearly validate the original two-site model. The present work together with the earlier disk studies show that dissolution from site 2 is well described by a first-order expression, rate = kc2 (Cs2-C), where kc2 is a first-order rate constant, Cs2 is the apparent solubility for site 2 (defined by an ion activity product, KHAP, of the form a10Ca2+PO43-a2OH-, and the solution conditions), and C is the microenvironmental solution concentration of hydroxyapatite. For four different precipitated hydroxyapatite preparations, a single KHAP value of 1 X 10(-128) +/- 1 was found to be consistent with experiments using solutions covering wide ranges of partial saturation and calcium-phosphate ratios. The hydroxyapatite powder and pellet methods (including the data evaluation procedures) now offer a powerful combination for investigating the complex kinetics associated with dental enamel dissolution in particular and enamel chemistry in general.
D002118:Calcium / Q000032:analysis; D055598:Chemical Phenomena; D002621:Chemistry; D002845:Chromatography / Q000379:methods; D006863:Hydrogen-Ion Concentration; D006882:Hydroxyapatites; D007700:Kinetics; D008956:Models, Chemical; D010710:Phosphates / Q000032:analysis; D012995:Solubility; D013535:Suspensions
D006882:Hydroxyapatites; D010710:Phosphates; D013535:Suspensions; D002118:Calcium