How whiteners work

All bleaching methods use peroxide--whether in gel, strip, or liquid form--to dissolve surface stains, explains Debra Glassman, D.D.S., a cosmetic dentist in New York City. Teeth surfaces are made up of thousands of tiny dentinal tubules--hollow structures stacked horizontally, like thin straws. They're extremely porous and absorb pigments from food and drink. (Anything that can stain a white T-shirt can discolor your teeth, Glassman says.) Peroxide bubbles into the tubules and lightens those pigments.