Tooth Whitening is a process of lightening discolored or stained teeth using hydrogen peroxide, or chemicals that can break down into hydrogen peroxide. In recent years it has become popular to whiten the teeth at home using a custom-fitted tray with whitening gel. Patients must be evaluated by their dentist and must be free of cavities or periodontal disease before the whitening. The procedure is safe. It will not cause damage to the teeth. Some patients experience tooth sensitivity. It is usually short term and can be taken care of with desensitizing toothpaste.