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)

The main idea is that enamel demineralization kicks in when the oral environment becomes acidic enough that enamel minerals no longer stay dissolved but begin to dissolve away. Enamel is largely hydroxyapatite, and its dissolution increases as pH drops. There’s a well-established tipping point around pH 5.5: below this, the solution is undersaturated with calcium and phosphate, so minerals leach out of the enamel. Above this pH, remineralization can outpace loss, especially with buffering from saliva and the help of fluoride.

So, when acid challenges bring the local pH down to about 5.5 or lower, demineralization is likely to occur; brief excursions below this threshold can start white spot lesions if cycles persist. The other values are either too neutral or not the usual turning point for initiating mineral loss.