Tooth whitening is a many sitting procedure. If you want the desired brightness for you teeth you have to undergo several sessions of bleaching over a couple of months. Your dentist will use several methods to whiten teeth. Typically, in the in-office bleach, the dentist will use a chemical with carbide per oxide. This breaks down to release hydrogen peroxide that targets the tooth colour in a chemical reaction. The in-office method is considered safe and quick. The whitening effect may also last longer. Dentists can recommend home bleaching in some cases. Your dentist will make custom made trays to fit your mouth. You have to add a gel to the tray and keep it in your mouth for upto I hour for a few weeks to whiten your teeth.