Source: American Dental Association
Teeth Whitening products contain peroxide(s), which actually bleach the tooth enamel. These products typically rely on percent carbamide peroxide as the bleaching agent, carbamide peroxide comes in several different concentrations (10%, 16%, 22%).
Peroxide-containing whiteners typically come in a gel and are placed in a mouthguard. Usage regimens vary. Some products are used for about twice a day for 2 weeks, and others are intended for overnight use for 1-2 weeks. If you obtain the bleaching solution from your dentist, he or she can make a custom-fitted mouthguard for you that will fit your teeth precisely. Currently, only dentist-dispensed home-use 10% carbamide peroxide tray-applied gels carry the ADA Seal.
You also may want to speak with your dentist should any side effects become bothersome. For example, teeth can become sensitive during the period when you are using the bleaching solution. In many cases, this sensitivity is temporary and should lessen once the treatment is finished. Some people also experience soft tissue irritation-either from a tray that doesn't fit properly or from solution that may come in contact with the tissues. If you have concerns about such side effects, you should discuss them with your dentist.