Medical Emergencies · single question
At which critical pH value does ENAMEL demineralization begin to occur?
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Correct answer: B. 5.5
pH 5.5 (B) is the critical pH for enamel demineralization (the 'critical pH of enamel'). Below this pH, the hydroxyapatite in enamel begins to dissolve. This is why maintaining oral pH above 5.5 is essential for caries prevention.
• Dental caries process: Bacteria (S. mutans) ferment dietary sugars → produce organic acids → pH drops below 5.5 → enamel dissolves.
• Critical pH for dentin/cementum: ~6.0-6.5 (lower mineral content and more organic matrix → more susceptible). This is why root caries initiates at higher pH than coronal caries.
• Stephan curve: shows pH drop after sugar exposure, falls below 5.5 within 2-5 min of sugar intake, recovers to neutral in ~20-30 min with saliva buffering.
• Fluoride lowers critical pH to ~4.5 by converting HA to fluorapatite.
• Dental caries process: Bacteria (S. mutans) ferment dietary sugars → produce organic acids → pH drops below 5.5 → enamel dissolves.
• Critical pH for dentin/cementum: ~6.0-6.5 (lower mineral content and more organic matrix → more susceptible). This is why root caries initiates at higher pH than coronal caries.
• Stephan curve: shows pH drop after sugar exposure, falls below 5.5 within 2-5 min of sugar intake, recovers to neutral in ~20-30 min with saliva buffering.
• Fluoride lowers critical pH to ~4.5 by converting HA to fluorapatite.
- A. pH 6.5 is the critical threshold for DENTIN demineralization — not enamel. Enamel's threshold is 5.5.
- B. pH 4.5 is below the critical pH for enamel. Demineralization does occur here, but it is not the THRESHOLD at which it begins. The critical pH for enamel is 5.5.
- C. pH 9.5 is alkaline — no demineralization occurs at this pH. Demineralization requires an acidic environment below the critical pH.
- D. The critical pH for ENAMEL demineralization is 5.5. When plaque pH drops below 5.5, the environment becomes undersaturated with respect to hydroxyapatite, and enamel dissolution begins. The critical pH for DENTIN/CEMENTUM is higher (~6.0-6.5) due to less mineral content.
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