Cariostatic efficacy of the combined use of fluorides

There is ample evidence documenting that simultaneous use of several fluoride application techniques results in an enhanced cariostatic effect. A formula is presented which estimates the combined cariostatic efficacy of such multiple usage. For simultaneously applied topical fluorides, the formula seems to overestimate the combined efficacy. Both higher frequency of use and higher concentration result in increased topical fluoride efficacy. Within narrower limits, higher concentrations of fluoride in water or salt also enhance efficacy. The rapid and substantial decline of caries prevalence in some highly industrialized countries may, in part, be attributed to multiple fluoride usage, but other factors must also have exerted a beneficial effect.