SOLUBILITY RATE AND NATURAL FLUORIDE CONTENT OF SURFACE AND SUBSURFACE ENAMEL

¹ Eastman Dental Dispensary, University of Rochester, Rochester, N. Y.

1. Solubility in buffers of pH 4.0, 4.5, and 5.0, and fluoride concentrations were determined for successive layers of enamel from deciduous teeth, unerupted permanent teeth, and erupted permanent teeth from persons under 20 years of age, and from persons over 50 years of age. The teeth were obtained from persons who were born and had lived continuously in cities where the water supply contains 0.1, 1.0, or 5.0 ppm fluoride.

2. Solubility increased from the first (outermost) to the sixth (innermost) layer in all teeth at each pH level, and increased most markedly from the first to the second layer.

3. Within each group of teeth the fluoride concentration of successive layers decreased as the solubility of the respective layers increased. However, enamels with comparable concentrations of fluoride showed different solubilities.

4. Mottled enamel, with the highest fluoride concentration, was more resistant to acid than was enamel from the other groups; deciduous enamel with the lowest fluoride concentration was the least resistant.

5. The difference in solubility between surface and subsurface layers was shown not to be related to the organic content of enamel.

6. There appeared to be no relation between age and solubility of enamel in acid.

7. Only small amounts of fluoride were lost from enamel during exposure to acid under the conditions of our experiment.

8. In addition to fluoride concentration, other factors also must affect the resistance of enamel to the decalcifying action of acids. Due consideration must be given to accumulation of trace elements other than fluoride, and other changes which may occur in enamel during its pre- and posteruptive history.