Everyone wants pearly whites. And carbamide peroxide can deliver the goods. You’ll find it in most tooth-whitening products for the simple reason that it can deliver hydrogen peroxide, H2O2, to the tooth surface. Hydrogen peroxide itself is a liquid and difficult to apply to teeth, but when it’s mixed with urea it forms a gel of carbamide peroxide that can easily be painted on teeth, placed into trays fitted to the teeth, or incorporated into whitening strips. Thickeners such as carbopol and glycerin are often used to achieve the right consistency. Actually, hydrogen peroxide isn’t the real active ingredient. It is the hydroxyl free radical that it yields that can break down colored molecules.
Tooth discoloration is mostly the result of colored substances in foods and drinks that embed themselves over time in the calcium phosphate that makes up the tooth’s outer coating, the enamel. Tannins in tea and coffee, anthocyanins in blueberries, and polyphenols in red wine are just some of the compounds that can discolor teeth. A further complication is that dentin, the mix of proteins and calcium phosphate that lies beneath the enamel, yellows naturally with age. The molecules responsible for tooth discoloration tend to have a network of carbon-carbon double bonds. Such unsaturated systems, as they are called, absorb all colors but reflect yellow. Hydroxyl radicals are highly reactive and can disrupt these double bonds, leading to whitened teeth.
Applying various peroxide products to the teeth is generally quite a safe and simple procedure, although some people experience heightened sensitivity to cold after their dentist applies products containing high concentrations of hydrogen peroxide. Products developed for home use generally contain only 3 to 6 percent hydrogen peroxide and do not cause sensitivity, but they may take weeks to lighten discolored teeth. We may not yet have an ideal system for treating stained teeth, but carbamide peroxide is surely a great improvement over historical methods, including gargling with urine or rubbing the teeth with a mixture of chalk and ground rabbit skull.