Fluoride's MAIN mechanism of action in preventing dental caries is:

Correct answer: C. Decreasing calcium dissolution from enamel (reduces demineralization by incorporating into hydroxyapatite as fluorapatite)

• A. Fluoride inhibits bacterial enzymes (including enolase) at high concentrations, but the primary mechanism is enamel stabilization through fluorapatite formation.
• B. Fluoride does not stimulate salivary gland secretion.
• C. Correct. Fluoride's primary mechanism is incorporating into enamel hydroxyapatite to form fluorapatite (FAP), which is significantly more resistant to acid dissolution than hydroxyapatite. FAP is stable at a lower pH (4.5) compared to hydroxyapatite (5.5), reducing the critical pH at which demineralization occurs. Fluoride also enhances remineralization.
• D. While fluoride does have antimicrobial effects at high concentrations (inhibits enolase enzyme in bacteria), this is secondary to its main anticaries mechanism.