Extrinsic and intrinsic stains are the two types of dental stains. Extrinsic stains occur on your teeth’s surface. Intrinsic stains occur deep in your dentin and between the microcracks in your enamel (the layer of your tooth underneath your enamel). Whitening toothpaste and fluoride mouthwashes can help you get rid of extrinsic stains. Intrinsic stains, on the other hand, require professional teeth whitening.

Teeth whitening agents are rich in peroxide compounds. Peroxide compounds, especially hydrogen peroxide and carbamide peroxide, contain oxygen molecules that are highly volatile. 

When these volatile oxygen molecules come into contact with surface stains on your teeth, they dissolve the chemical connections that hold the stains to your enamel. This whitens your teeth and helps you have a bright smile.