Tooth Whitening brightens teeth and helps to remove stains and discoloration. Whitening is among the most popular cosmetic dental procedures because it can greatly improve how your teeth look. Tooth whitening can be done in the dentist's office or at home. In-office whitening allows your dentist to use a more powerful whitening gel. A specialized light or laser activates the gel and allows bleaching to happen. Usually it takes 30 to 90 minutes. Different types of stains respond differently to the treatment.