Tray whitening is a type of professional whitening that uses custom-made trays and whitening gel only available through your dentist. The whitening gel is placed in custom-fitted trays that fit perfectly over your teeth. As the peroxide in the gel breaks down, hydroxyradicals help whiten stained teeth. Unlike strips, this process whitens all your natural teeth and may contain ingredients intended to provide maximum comfort. At-home professional tray whitening generally takes 10-14 days, although you may notice results in as little as three to five days.