Valerie Monroe
Photo: Patrik Andersson
Q: Is there any downside to using those at-home teeth-whitening products?

A: Whitening toothpastes can remove some discoloration, but their effect is minimal, says Steven Fox, DDS, a New York City dentist who has served on the faculty of the Harvard School of Dental Medicine. Whitening strips (like Crest 3D White Professional Effects Whitestrips, $50; drugstores) contain a peroxide component and are more effective; if you use them daily you should see results in about 14 days. As for a downside: Serial bleaching can cause tooth sensitivity because the bleach demineralizes the teeth, leaching calcium from the enamel. Let your symptoms be your guide, Fox says; at the first sign of discomfort, stop bleaching.

Keep in mind: Fillings, crowns, and veneers can't be bleached.

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