How they work: In a half-hour appointment, a dentist takes impressions of your top and bottom teeth, then creates soft plastic molds for you to wear at home. He’ll also prescribe a hydrogen peroxide gel (containing up to a 22.5 percent concentration) to squeeze into the trays before use.
The whitening effect: Five to eight shades, when used for 30 minutes twice a day for two weeks. Lasts 6 to 12 months.
Good to know: Prescription hydrogen peroxide can cause tooth sensitivity in some people. To minimize the chances, brush with a desensitizing paste. (Try Sensodyne toothpaste; $6 at drugstores.) And rinse with a nonalcoholic mouthwash that has a high fluoride content. (Try ACT Total Care Sensitive Formula mouthwash; $5 at drugstores.)
Average cost: $250 to $500 for a set of trays; $25 to $50 for the whitening solution.