Advertisements for special toothpastes, powders and gums suggest that it’s possible. Here’s what dental experts say.

By Sean Dong

Most of us know that the best defense against tooth decay — or damage to the surface, or enamel, of your teeth — is to limit sugary foods and to brush and floss regularly. But once that damage has begun, or even progressed into a cavity, can you reverse it?

Online advertisements for products like cavity-undoing chewing gums and enamel-rebuilding toothpastes and tooth powders suggest that you can.

We asked experts if they work, and if it’s possible to backtrack on tooth decay in the first place.

Your mouth is home to both good and bad bacteria, which adhere to your teeth in a sticky layer called plaque.

The bad bacteria love to snack on sugary, starchy foods — like sweetened sodas, gummy candies, pastries and fruit juices — and then turn them into acids that, over time, may pull important minerals from your teeth.

The more these bad bacteria eat, the more acids they produce that dissolve essential minerals like calcium and phosphate, said John Featherstone, a professor emeritus of preventive and restorative dental sciences at the University of California, San Francisco, School of Dentistry.

This dissolution is called demineralization, Dr. Featherstone said, and it can weaken your enamel over months to years until it eventually caves in and forms a cavity.

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