What is the critical pH range for enamel?

• A. 4.5 to 4.7
• B. 5.5 to 5.7
• C. 6.2 to 6.4
• D. 7.0 to 7.2

Answer: (B)

The critical idea is the pH at which enamel begins to demineralize faster than it can remineralize. For enamel, that threshold is about 5.5. When plaque acids drop the local pH to around 5.5 (and sometimes slightly lower), hydroxyapatite dissolves and minerals are lost from the enamel. This is why after sugar intake, the acid attack can start demineralization unless saliva and fluoride help raise pH and promote remineralization. Therefore, the best answer is the range around 5.5 to 5.7, which reflects natural variability among people and conditions in the mouth. The lower ranges (4.5–4.7) are more acidic than the established threshold, and the higher ranges (6.2–6.4 or 7.0–7.2) are above the threshold, where enamel remains stable or remineralization is favored.