Teeth whitening is a simple yet effective process. Teeth Whitening products contain one of two chemical agents hydrogen peroxide or carbamide peroxide. These chemical agents called bleach break yellow brownish stains into smaller pieces, which makes the teeth color less and your teeth turn to be brighter. In-Office teeth whitening, dentists will firstly apply either a protective gel to your gums or a rubber shield to protect your gums from the chemical formulation. Bleach is then applied to the teeth and brushed well. It usually requires one office visit.