Dear A Moment of Science,
My best friend says that sugar causes cavities. Is this right? -Pain-in-the-mouth
Well, Pain, your friend is right and wrong. Technically speaking, sugar does not cause cavities alone-they are caused by an interaction between plaque bacteria and your diet known as "dental caries." Ninety-seven percent of people everywhere have this problem.
The Tooth of the Matter
Imagine a thin layer of microorganisms living on your teeth. Again, these are micro-organisms, far too small for you to see or feel until they build up and form "dental plaque."
These microorganisms are capable of producing acid which lowers the pH level next to your teeth. "pH level" means how much acid, how much base. If the pH level around your teeth goes below around 5.5, acids dominate and your tooth enamel starts to break apart. Above the 5.5 mark teeth stay okay.
Cavities aren't caused by microorganisms eating your teeth, as some folks say. They're caused by microorganisms living their own lives on your teeth, and as a by-product, changing the pH balance. But guess what those microorganisms do eat? They eat sugar.
See the problem now? When you eat sugar, and don't scrub it off your teeth by brushing afterwards, the little guys have a feast. And that means pH levels will drop. And that means tooth decay, which is cavities.
So while sugar itself doesn't hurt teeth, it indirectly causes cavities. There's no getting around it. Eat fewer sweets and brush more often, and cavities will be less likely to form.
"Ask the Experts." (Scientific American)