When we eat or drink, stains are left on the enamel of our teeth. By immediately brushing we can remove these stains, but very few people do this. As a result, a layer can form on top of the enamel. Since enamel, which is made up of a tightly packed mass of hydroxyapatite crystals, is porous, the stains penetrate through and become deeper.
To remove the stains, hydrogen peroxide or carbamide peroxide is used. Home whitening kits involve placing the bleach into whitening trays, which are then slid on to the teeth. The bleaching agent is broken down on the tooth, allowing oxygen to enter the enamel, breaking apart the staining compounds. It also permeates to a layer beneath the enamel called dentin, allowing for deeper bleaching.
Dentists can use a whitening lamp to aid the process. A high-concentration gel containing hydrogen peroxide is placed on the teeth and a light is shone on them for about an hour. The energy
produced leads to faster chemical reactions and speedier whitening.