How does teeth whitening work?

How does teeth whitening work?
There are two types of tooth stains “extrinsic,” those stains that are on the surface of the tooth, and “intrinsic,” those stains that are on the inside of the tooth and show through the enamel as discoloration. While whitening toothpaste and chewing gums may be effective for removing extrinsic stains, they are not designed to work inside the tooth to remove the darker, more challenging instrinsic stains.

Some form of hydrogen peroxide gel, either hydrogen peroxide itself or a more stable version, carbamide peroxide, is the most effective material for removing the internal stains. When applied to the tooth, the hydrogen peroxide breaks down into water and radical hydroxyl ions. As these ions work their way through the dentinal tubules and into the tooth, they attach themselves to stain particles and effectively break the stains apart. With the stains removed the teeth appear whiter and brighter.