Fluoride does seem to harden enamel, but how does it do it? All the research concludes that the mechanism is topical, as with the application of toothpaste, mouthwash, or gels, not through drinking fluoridated water or eating fluoride pills or fluoridated salt. This article is from Caries Research, Systemic vs. Topical Fluoride, 2004, 38:258–262, DOI: 10.1159/000077764.