There are two popular teeth whitening options available through your dentist. The first, in-office teeth whitening, produces a significant color change in your teeth in a short amount of time, usually within an hour. The procedure is done at the dentist's office by applying a high-concentration peroxide gel on the teeth after they have been protected with a special shield.
The second method, involves the use of take home whitening kits. These whitening kits are purchased from your doctor for use at home. The strength of the gel used in these kits is lower than that used for in-office bleaching, and thus the gel can be applied for longer periods of time. Usually the trays are worn a couple hours a day or overnight for a few days or weeks depending on the product.
Its best to consult your dentist to understand which whitening option is best for you.