The goal of the proposed research is to improve understanding of mineralization and demineralization at synthetic calcium phosphate and tooth surfaces by determining the physical mechanisms at both kinetic and molecular levels and the influence of simple ions and proteins and their sub-segments including those of enamel, dentin, and saliva. The Dual Constant Composition (DCC) method using multiple ion specific electrodes to control the concentrations in the reaction solutions will provide kinetics data in the presence and absence of the modulating simple ions such as Mg2+, F-, and CO32- and macromolecules. Parallel in situ atomic force microscopic (AFM) investigations will be made under identical conditions to those of DCC studies, to investigate molecular events such as the spatial relationship between the adsorbed modulating molecules and growth features such as atomic steps in DCPD and OCP nucleation and growth. Growth rates calculated from AFM step movement over the crystal surfaces will be correlated with DCC reaction inhibition by both simple ions and proteins and their sub-segments. A new model for dissolution involving the formation of surface pits of critical size will be tested both in the absence and presence of simple ions, proteins, and their synthesized sub-segments. In the light of the demonstrated importance of interfacial energy in determining the ability of surfaces to nucleate biominerals, we will make surface tension measurements by sessile drop and thin layer wicking on synthetic calcium phosphates and enamel and dentin surfaces both in the absence and presence of modulating additives. Solid phases will be investigated by scanning electron and field emission microscopy, X-ray, EDX, ESCA, SIMS, differential scanning calorimetry, zeta potential, and laser scattering size distribution measurements. DCC dissolution kinetics measurements will be made at small (4x4mm) enamel windows to examine the influence of temperature and macromolecular modulators on the rates of erosion as a function of depth. A new DCC procedure to examine the concomitant rates of growth and dissolution of minerals at dentin surfaces will address the problem of dentin hypersensitivity.
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