What pH threshold is commonly considered critical for enamel demineralization?

What pH threshold is commonly considered critical for enamel demineralization?

• A. Approximately pH 7.5
• B. Approximately pH 5.5
• C. Approximately pH 4.5
• D. Approximately pH 6.0

Answer: (B)

When the mouth becomes acidic, enamel begins to dissolve because hydroxyapatite minerals lose solubility in low pH environments. The commonly cited threshold for enamel demineralization is about pH 5.5. Below this pH, the balance shifts toward mineral loss as calcium and phosphate diffuse out of the enamel. Fluoride helps counteract this by promoting the formation of fluorapatite, which is less soluble, and by supporting remineralization, so the net effect can be reduced demineralization under mild acid challenges. If the pH stays above around 5.5, buffering from saliva and the remineralization processes keep enamel largely intact. A pH around 7.5 is not acidic enough to drive demineralization, a pH around 6.0 is still above the critical point, and a pH around 4.5 represents a stronger acid challenge but is not the standard threshold used to define onset.