At what pH level does enamel demineralisation occur?

• A. 5.0
• B. 5.5
• C. 6.5
• D. 7.0

Answer: (B)

The amount of mineral loss from enamel depends on the pH of the mouth. Enamel demineralises when the oral environment becomes acidic enough that hydroxyapatite starts to dissolve faster than minerals can be redeposited. The commonly cited critical pH for enamel is about 5.5, which is the tipping point where demineralisation begins to occur with frequent acid exposure. Below this level, acids from plaque and diet drive mineral loss; above it, saliva and fluoride help remineralisation and keep enamel intact. So 5.5 is the best answer because it represents the threshold at which demineralisation is triggered. Higher pH values, like 6.5 or 7.0, are less conducive to demineralisation, while a pH as low as 5.0 would be more acidic than the threshold, but the stated critical level is 5.5.