PRECIPITATION OF OCTACALCIUM PHOSPHATE AT 37-DEGREES-C AND AT PH 7.4 - IN RELATION TO ENAMEL FORMATION

Octacalcium phosphate (OCP) has been proposed to be an important precursor of enamel apatite, but the question remains whether OCP crystals grow in the physiological milieu or not. In this study, the conditions under which OCP precipitates in preference to hydroxyapatite (HAp) were studied at 37-degrees-C and pH 7.40 in connection with the effects of the degree of supersaturation with OCP, initial Ca/P of solution, and stirring. Reactions were carried out both in a pH-stat system and in a buffer solution system. In the pH-stat system, OCP precipitated preferentially from a solution with small Ca/P, when Ca solution was supplied during reaction. Without Ca solution supply, OCP was not obtained. In the stationary buffer solution, OCP precipitated over a wide range of Ca/P (0.025-1.67). The thermodynamical analysis of the precipitation condition indicates that OCP crystals can grow in a basic solution at 37-degrees-C, so long as the driving force to precipitate OCP is larger than that to form HAp.