The process of amelogenesis comprises several well-defined stages culminating in highly mineralized mature enamel. Disturbances (e.g., ingestion of fluoride at higher than optimum doses) at any of those stages result in a defective enamel structure which may be aesthetically undesirable, less resistant to physical wearing, or more susceptible to caries formation. The present proposal attempts to gain information on the following points: 1) Characterization of the physical chemical properties of the medium in which enamel crystallites are formed. Of particular importance is the determination of the calcium, phosphate and pH values of the fluid in the initial (cheese-like) stage of enamel formation. Special microanalytical techniques will be used for that purpose in conjunction with bovine and porcine enamel. The proteins associated with the enamel will be examined electrophoretically. 2) The surface pools of Ca and P of the enamel crystals from the secretory, transitional and maturing stages will be determined by isotopic exchange with 45Ca and 33P to obtain information on the nature (and possible transformations) of the growing mineral. Further characterization of the enamel surface will be done through adsorption experiments using small synthetic peptides as adsorbates and, also, through crystal growth experiments using the deproteinated enamel as seeds in solutions supersaturated with respect to calcium hydroxyapatite. 3) The interaction of amelogenins and enamelins with apatitic surfaces will be investigated using model systems, i.e., determining their adsorption isotherms onto hydroxyapatite. 4) The possible orientation of apatitic crystals by permselective membranes. This kind of experimentation is a first approximation to a postulated mechanism in which the orientation of the enamel crystallites (perpendicular to the Tomes processes) is determined by the electrochemical properties of the membrane and the direction of flow of one limiting ion, i.e., calcium. It is proposed to study the aspects described above first with bovine and porcine enamel and then with rats. With the rat model, the investigation will cover animal under various fluoride regimes.
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