Comparative reduction of enamel demineralization by calcium and phosphate in vitro

In theory, calcium and phosphate in the plaque fluid exert a large influenc e on the demineralization of enamel surface. In order to know the effect of increasing the concentration of either of these factors, the following in vitro experiment was conducted, Three thin sections, about 150 mu m thick, were cut out from each of 13 human premolars. All surfaces of the sections, except for the original enamel surface, were coated with nail varnish. The se sections were immersed into one of two sets of demineralizing solutions for 1 week at 25 degrees C, Each set, the 'calcium set' and the 'phosphate set', contained three solutions. The composition of these solutions differe d mainly in calcium or phosphate concentrations. After 1 week, the degree o f demineralization was determined by image analysis of contact microradiogr ams from each section. The subsurface demineralization in enamel was reduce d by 95% by increasing the calcium concentration of the demineralizing solu tion from 7 to 21 mmol/l, A similar reduction (87%) was observed by increas ing the phosphate concentration. However, the amount of phosphate needed wa s approximately 20 times more than that of calcium. The larger inhibitory e ffect that calcium has on enamel demineralization was related to the larger effect it has on the degree of saturation of the solution. Even though no statistically significant difference was found between the effect of calciu m and phosphate on the demineralization of enamel (when the solutions had t he same degree of saturation), the difference in the standard deviation of demineralization suggests the existence of so me other facto rs wh ich have an influence on the demineralization reaction. Copyright (C) 2000 S. Karge r AG, Basel.