Biomimetic Remineralization Of Gallic Acid Stabilized Amorphous Calcium Phosphonate Induced By Glycine On Early Enamel Caries

Objective:Gallic acid（GA）is a natural polyphenol derived from Chinese traditional medicine gallnut.The carboxylic acid radical produced by ionization in aqueous solution can exchange anion with hydroxyapatite（HAP）to combine with HAP.GA can also form and stabilize amorphous calcium phosphate（ACP）through phenol hydroxyl chelating calcium ion.Glycine（Gly）can significantly reduce the（001）interface energy of HAP,resulting in the orderly assembly of HAP crystals along the c-axis.Based on the nonclassical theory and amelogenesis,this study formed stable ACP through GA in order to make the remineralized enamel have the structure and surface hardness similar to natural enamel under the action of Gly.Methods:GA-ACP was prepared by chemical precipitation.Add Gly to GA-ACP to obtain GA-Gly-ACP.The characteristics of the formed ACP were observed by transmission electron microscopy and selected area electron diffraction.The early enamel caries model of Ekstrand Grade 2 was obtained by etching the enamel surface with a surface microhardness of 320 ～ 340 VHN with 37% phosphoric acid.GA-ACP and GA-GlyACP were applied to the surface of early enamel caries model for 30 min/day to promote remineralization.The surface morphology of enamel before demineralization,after demineralization and after remineralization was observed by scanning electron microscope.The orientation and crystallinity of enamel surface crystals after remineralization were observed by X-ray diffraction.The changes of enamel surface hardness before demineralization,after demineralization and after remineralization were detected by surface microhardness.Results:1.ACP was formed under the stable action of GA and linearly arranged ACP was formed under the action of Gly.2.Compared with the enamel after demineralization,the prisms and interrods of GA-Gly-ACP remineralized enamel were significantly mineralized,and retain the basic structure of enamel,which were similar to natural enamel.3.The orientation and crystallinity of hydroxyapatite formed on the enamel surface after GA-Gly-ACP remineralization were similar to those of natural enamel.4.The surface hardness of enamel after GA-Gly-ACP remineralization was significantly higher than that after demineralization and the control group.Although it did not completely return to the level before demineralization,it reached the level of normal enamel.Concluded:1.ACP bands formed under the joint action of Gly and GA in our research was similar to ACP bands in the secretory phase of enamel.2.Under the action of Gly,GA stabilized ACP successfully promoted the remineralization of prisms and interrods on the surface of demineralized enamel.The remineralized enamel surface had a structure and surface hardness similar to natural enamel.