Abstract
In the first stage of tooth development, enamel crystals are thin, ribbon-like in shape and highly orient in their c-axis direction. Based on a hypothesis with respect to a role of Tomes' process that the cell membrane control not only the concentration of ions necessary to precipitate initial phase but also their diffusing direction to regulate the orientation of growing crystals, a new technique using ion selective membrane has been proposed. In this system nucleation and growth of calcium phosphates were initiated and controlled by allowing calcium (phosphate) ions to diffuse into phosphate (calcium) solution through synthetic ion-selective membranes. Hydroxyapatite thus obtained by hydrolysis of octacalcium phosphate, which has been proposed as a possible precursor involved in the first stage of tooth development, nucleated on and grown perpendicular to the membrane is found to be comparable to mature human enamel in degree of orientation. In this report, the dependence of morphology and orientation on such physiological factors as pH, initial concentrations of calcium, phosphate, and fluoride is studied In order to clarify the raction that might be taking place in the diffusion layer on the ion selective membrane, some reactions were carried out in nonmembrane systems in which precipitation was initiated by adding calcium (phosphate) solution dropwise to phosphate (calcium) solution.
