To whiten your teeth, dentists use trays, lasers or a combination of both. "In-office bleaching will give you the best results," says Jan Linhart, D.D.S., an NYC based cosmetic dentist responsible for many celebrity chops. "Since we do everything in the office, there's much less margin for error."

Trays: The most popular whitening method involves your dentist taking an impression of your teeth and making a plastic mouthpiece for you to take home. Also, you'll be supplied with bleaching gel to fill in the tray. Duration: You wear the trays anywhere from two hours per day to all night, for about two weeks. Cost: $400 to $800. Pros: You control how white you want to go, and when you've reached your desired shade, you can store the kit in the fridge for touch-ups. Cons: A slight chance of tooth and gum sensitivity, and you don't get the instant gratification of a laser treatment.

Laser Bleaching: Your dentist coats your teeth with a peroxide gel and activates it with a laser or a high intensity lamp. Duration: One hour. Cost: $600 to $1,500. Pros:Lasers are super quick, and you don't have to deal with trays. Cons: Well, there's that price! (Whitening is not covered by insurance.) Also, the method can be inexact-you can't totally predict what shade your teeth will end up. -L.K.