How whitening actually works

Every whitening product — professional or over-the-counter — works the same chemical way. It contains hydrogen peroxide or carbamide peroxide (which breaks down into roughly one-third hydrogen peroxide once it's on the tooth). The peroxide diffuses into the enamel, and through a process called oxidation it breaks the large, deeply colored stain molecules into smaller, lighter-colored pieces. Nothing is removed from the tooth; the stain molecules themselves are chemically changed.

Why teeth stain, and why the cause changes the fix

Not all discoloration lives in the same layer of the tooth, and whitening only reaches one of them. That's the single most useful thing to know before choosing a treatment — and the most common reason a patient tries whitening and is disappointed by the result.

Extrinsic stains are chromogens — colored compounds from food, drink and tobacco — that attach to the outer enamel. They respond well to polishing and to whitening.¹ Intrinsic stains sit deeper, inside the dentin that gives a tooth its underlying color: enamel naturally thins with age and lets more of that yellow dentin show through, an old injury can darken a tooth from the inside, and antibiotics like tetracycline taken during tooth development can cause banding that whitening handles poorly.