Studies on the calcification mechanism of dental hard tissue by graded tracing of apatite precursors

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Cation-selective membrane were used as a model cell for tissue cell to get better understanding of calcification mechanism in tooth enamel. Our previous in vitro finding has suggested that hydroxyapatite obtained by hydrolysis of octacalcium phosphate that nucleated on and grew perpendicular to the cation-selective membrane is comparable to human enamel in respect to crystal shape, crystallinity and the degree of orientation.In this report,the influence of pH and initial concentration of calcium, phosphate,carbonate,magnesium and fluoride ions on the morphology and orientation of octacalcium phosphate is studied in the cation-selective membrane system to elucidate the calcification mechanism and growth process in enamel. In order to clarify the reaction that might be taking place in the diffusion layer on the cation-selective membrane, some reactions were carried out in non-membrane system in which precipitation was initiated by adding calcium solution dropwise to phosphate solution.In most cases,these ions suppressed the crystal growth in the c-axis direction of OCP, particularly when they coexisted. The morphology of OCP crystal changed from ribbon-like to flake-like, depending on the inhibitory activity. The inhibitory activity, particularly that F^- ions, was suppressed at pH lower than pH 6.8 . Antagonistic effect of Mg^<++> and F^- ions was observed at pH 6.5 . In the case of F^- ion, OCP crystals showed a unique pattern, which suggests hydrolysis of OCP and subsequent growth of apatite. These findings indicate that inorganic ions, particularly F^- ion, influence the growth of OCP. Although CO_3 Mg^<++> and F^- ions coexisted, extended growth in the c-axis direction of OCP took place at pH 6.0.