The effectiveness of fluoride in preventing tooth decay is well documented in dental literature and well known by the public. The mechanism of this protection is not, however, common knowledge.
Dental plaque consists mostly of bacteria. These bacteria consume sugar from the diet and produce two main products. These are the acid that destroys the teeth, and bacterial toxins that attack the gums and bone that support the teeth leading to periodontal done loss. The primary function of fluoride is to combine with the enamel of teeth and render this enamel less soluble to the acid produced by the bacteria.
In infancy and early childhood, fluoride taken internally is incorporated into forming dental enamel. This is the stage of development when fluoride in drinking water or dietary supplements is valuable. Later in life, topical fluoride applied to the teeth in conjunction with professional cleaning is absorbed to a lesser degree by the surface enamel for the purpose of decreasing acid solubility.
The result of both systemic and topical fluoride application is the same. That is teeth have an incidence of decay that has been measured to be up to 50% less than treated with fluoride.