Of the inorganic constituents different from calcium and phosphorus, carbonate in the enamel fluid seems to be high enough to affect the mineralization process during amelogenesis. Carbonate is incorporated in substantial amounts into the crystalline lattice of the enamel crystals; this incorporation results in defects which function as reactive sites for demineralization or caries formation. The present proposal, intends to elucidate the mechanisms of carbonato apatite formation during amelogenesis and the chemical properties of enamel mineral, includes the following aspects: 1) Determination of the solubility and solubility product of enamel apatites separated at specific developmental stages of amelogenesis. The enamel samples will be obtained from the permanent dentitions of piglets. Equilibration of the mineral in acidic solutions will be conducted under partial pressures of CO2 similar to those in the enamel fluid. The analytical results of the equilibrating solutions will be used to test several models with respect to the stoichiometry and the type of the carbonate substitution in the lattice of the enamel crystals. 2) Assignment of the location of carbonate ions (adsorption onto enamel apatites and/or substitutions in the PO4 or OH sites of the lattice). Special interest will be focused on the carbonate associated with the initially forming crystals. The proposed approach will combine chemical, IR, EM, and ion chromatography techniques. 3) Investigation of adsorption of enamel matrix proteins onto carbonato apatites. Batches of the adsorbents will be prepared in aqueous systems and characterized with respect to chemical composition, carbonate substitution, specific surface area and crystal morphology. The adsorbates will be obtained from secretory porcine enamel. Adsorbate-adsorbent equilibrations will be conducted in solutions having partial CO2 pressures and ionic strength similar to those of enamel fluid. 4) The possible mechanism of carbonate incorporation into the forming enamel apatite. The experimentation will be conducted using synthesized carbonato apatites as seen in supersaturated solutions having similar composition to that of enamel fluid. The proposed research will give basic information about the developmental maturation of enamel crystals, the formation of crystal defects, and the effect that pertinent biological parameters have on the stability of dental enamel in normal and cariogenic environments.
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