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

为了更好地了解牙釉质中的钙化机制，采用阳离子选择膜作为组织细胞的模型细胞。我们先前的体外研究表明，在阳离子选择膜上成核并垂直于牙釉质生长的八钙磷灰石在晶体形状、结晶度和取向度方面与人牙釉质相似。本文研究了在阳离子选择膜体系中，pH和钙、磷、碳酸盐、镁和氟离子的初始浓度对磷酸八钙形态和取向的影响，以阐明牙釉质中的钙化机理和生长过程。为了弄清阳离子选择性膜上扩散层中可能发生的反应，在非膜体系中通过向磷酸盐溶液中滴加钙溶液来引发沉淀反应，在大多数情况下，这些离子抑制了OCP沿c轴方向的晶体生长，特别是当它们共存时。OCP晶体的形貌随缓蚀活性的不同而由带状向片状转变。当pH低于6.8时，抑制活性受到抑制，尤其是F~(2-)离子。在pH为6.5的条件下，观察到了镁离子和氟离子的拮抗作用。在F离子的情况下，OCP晶体表现出独特的图案，这表明OCP的水解和随后的磷灰石生长。这些发现表明，无机离子，特别是F~-离子，对OCP的生长有影响。虽然CO_3镁离子和F~+离子共存，但在pH为6.0时，OCP发生了沿c轴方向的延伸生长。

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.