Outer Enamel Surface Research Articles

Membrane potential in human teeth: The effect of some common organic anions

The membrane potentials across the enamel caps of six sound human teeth at 25 °C with 0.1M and 0.01 KCl solutions on the inner and outer enamel surfaces respectively were measured with a high-impedance potentiometric pen-recorder using calomel half-cells. The effect of five organic potassium salts applied separately to the outer enamel surfaces for a fixed period of 30 min and at 0.1M concentration was studied. In general, on replacing a test solution with 0.01M KCl the potential was initially depressed and then rose above its original value. The order in which the salts elevated the potential was approximately the same for all teeth. Relating these results to the effects produced by six inorganic salts previously investigated gave the following order for the magnitude of the rise in the potential: Citrate > tartrate > fluoride > oxalate > sulphate > lactate > acetate > dihydrogen phosphate > ▪

A film transfer method for determining solution rate of human enamel surfaces

The method requires first the preparation of an enamel “mosaic” from twenty-four pieces of human enamel embedded in plastic. The pieces are rectangles at least 1.2 mm on a side, embedded as six groups of four pieces, with the outer enamel surface exposed. The surface of the mosaic is ground with mild abrasive until the enamel pieces are uniformly soluble in acidic buffer. Cellophane film, moistened with lactate buffer and blotted in a standard manner, is rolled into intimate contact with the mosaic and allowed to remain for 2 min or less. The film is then lifted from the mosaic with adhesive tape and transferred to a “reagent” film of cellophane which has been soaked in molybdate solution and blotted. After 2 min contact between the strips, phosphate diffuses into the reagent strip, producing localized phosphomolybdate precipitation. The precipitate is reduced with stannous chloride until maximum colour is reached, rinsed with dilute ammonia water, blotted and cemented to a glass slide. The rate of solution of enamel from each of the twenty-four pieces can be obtained by reading the optical density of the spots individually on a micro-densitometer. The technique permits comparison of the solubility-reducing action of dentifrices brushed onto various parts of the mosaic. The precision is sufficient to show statistical significance with a 10 per cent change in solution rate.