Restorative & Materials · single question
Which of the following represents the mechanism of fluoride in caries prevention?
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Correct answer: B. Decrease dissolution of calcium phosphate
Fluoride prevents caries by: (1) Incorporating into hydroxyapatite to form FLUORAPATITE, which is significantly more acid-resistant (less soluble at low pH); (2) Remineralizing early carious lesions; (3) Inhibiting bacterial enzymes (enolase inhibition reduces acid production). The net effect is DECREASED DISSOLUTION of calcium phosphate from enamel in the presence of acid, making the enamel more resistant to demineralization.
- A. INCORRECT. Fluoride REPLACES hydroxyl groups with fluoride ions (forming fluorapatite) — it DECREASES, not increases, the hydroxyl content.
- B. CORRECT. Fluoride DECREASES the dissolution (solubility) of calcium phosphate from enamel. It does this by replacing hydroxyl groups in hydroxyapatite with fluoride to form fluorapatite, which has a much lower critical pH (~4.5 vs. ~5.5 for hydroxyapatite) and is therefore more resistant to acid dissolution.
- C. INCORRECT. Fluoride INCREASES the availability of a more stable form of calcium phosphate (fluorapatite) — it does not decrease it.
- D. INCORRECT. Fluoride does the OPPOSITE — it DECREASES dissolution, not increases it.
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