The dentist starts by preparing the mouth by isolating the teeth using cheek retractors and covering the gums with a liquid or rubber dam. This extra precaution helps prevent unnecessary contact between the whitening product and the surrounding soft tissue. Next, a whitening gel is applied. This professional bleaching solution often contains a high dose of hydrogen peroxide that is absorbed by the porous enamel of the tooth to break down stains both on the surface and deep inside. A laser is then directed on each tooth to expedite the whitening process. The energy from the laser is designed to instigate a chemical reaction that causes the bleaching agent to foam and remove discoloration.