Reduction of intra-oral demineralization of enamel after single exposures to sodium fluoride.

Studies demonstrated the effects of single rinses with low concentrations of NaF on the intra-oral demineralization of enamel. Blocks of bovine enamel were covered with Streptococcus mutans IB1600, mounted in palatal appliances, and worn in the mouths of volunteers for specified times. Subjects rinsed with solutions of NaF, with or without sucrose. Demineralization was determined as changes in iodide penetrability (delta Ip) of the enamel, while the pH and F of the streptococcal plaque, and enamel F, were determined with ion-specific electrodes. Delta Ip was reduced by about 80% (from 14.5 +/- 2.7 to 2.8 +/- 2.3 units) when 250 micrograms F/mL was added to the sucrose rinse. Corresponding plaque pH's were 4.1 +/- 0.5 and 4.2 +/- 0.3, consistent with a lack of effect on bacterial acidogenesis. Protection against mineral loss was concentration-dependent. Administration of sucrose at different times after NaF revealed that the effect of F persisted for at least 60 min. Analyses of plaque F demonstrated an initial elevation and concentration within the cells, followed by a drop to stable, baseline values. Enamel F increased slowly to almost 500 micrograms/g enamel after 105 min. The protective effect of F appeared to be manifested in two stages, the first related to a high plaque F and the second to F that became incorporated into the enamel. Analysis of the data suggested that F was transferred from plaque to enamel during the experimental period.