How does whitening work?

Tooth whitening works by using hydrogen peroxide (or carbamide peroxide) in the whitening agent to oxidize and break down pigment molecules that have built up on the surface and inside of the tooth, making the tooth look brighter. It does not shave the tooth or coat its surface — it is a chemical reaction that breaks down the pigments themselves. Professional in-office whitening uses higher-concentration agents along with a light to speed up the reaction, completed in 1 to 3 sessions, while at-home whitening uses lower-concentration agents consistently over 2 to 4 weeks. However, whitening has no effect on restorations such as composite resin or crowns.