There are two types of teeth whitening:
Bleaching your teeth changes the color of the tooth enamel and removes both surface stains and those deeper in the teeth. Your dentist can bleach your teeth at his or her office, or you can do it yourself with a kit your dentist gives you or with a kit you buy over the counter (OTC). The chemical used to bleach teeth is generally carbamide peroxide. Different products use different concentrations of this chemical.
Whitening toothpastes use a rough (abrasive) material that "scrapes" off surface stains and polishes the teeth.
Bleaching
For in-office bleaching, the dentist often combines bleach with a laser or light to speed up the process. A visit usually takes from 30 minutes to 1 hour, and you may need more than one treatment. Your dentist will protect your gums with a gel or shield and then put the bleaching agent on your teeth. The bleach concentrate used for the in-office process is generally stronger than that used in other methods, because the dentist can watch how it is used.
Your dentist may also give you a kit with a mouthpiece and gel containing the bleach. Your dentist may make a custom mouthpiece to fit your teeth. These kits usually use a lower concentration of bleach than an in-office process. Your dentist will tell you how often to wear the mouthpiece and for how long.
