What is the primary mechanism of action of fluoride in preventing dental caries?

Fluoride prevents dental caries primarily through three mechanisms, the most important of which is the formation of fluorapatite. When fluoride is present during demineralization, it incorporates into hydroxyapatite to form fluorapatite, which is significantly less soluble than hydroxyapatite at acidic pH levels. Fluorapatite is more resistant to acid dissolution, raising the critical pH at which enamel demineralizes from 5.5 to approximately 4.5. Fluoride also enhances remineralization of early caries lesions, and at high concentrations it has bacteriostatic effects by inhibiting bacterial enolase. The net effect is a reduction in demineralization and promotion of remineralization, decreasing caries progression.