Because it gets embedded into the tooth's enamel. Fluorid-enriched enamel is more resistant to acids produced by bacteria. (i.e. fluoride doesn't affect bacteri

Because it gets embedded into the tooth's enamel. Fluorid-enriched enamel is more resistant to acids produced by bacteria. (i.e. fluoride doesn't affect bacteria, it makes teeth more resistant to byproducts of bacteria's feeding on sugars.)