The problem with having the treatment in those unenlightened years was that your neighborhood barber-surgeon would file down your teeth and then soak them in a concentrated solution of nitric acid. The procedure would turn them pearly white, all right, but it also destroyed the tooth enamel and led to massive tooth decay, says the weekly magazine, published by the American Chemical Society, the world's largest scientific society.
It may have taken some time, but 21st century dentists with their latex gloves and rubber face masks are using far safer and more effective whitening techniques than their barber-surgeon predecessors. Among their tools are gels, strips and pastes.
The main cause of most tooth discoloration lies just at the surface of the enamel, where red wine, coffee and tea are the culprits, says C&EN. Colored molecules such as tannins and polyphenols, found in these beverages, become absorbed by the enamel's surface. Dark pigments in cigarettes, blueberries and other foods also can be deposited on your tooth enamel. Much of this staining can be brushed away, but over time these compounds can seep into the enamel, where you can't reach them with your brush.
Aging is another major culprit. As we grow older, our teeth gradually turn more yellow. On the other hand, the antibiotic tetracycline can turn children's teeth gray if taken during the early childhood, when tooth enamel has yet to harden completely, C&EN explains. Over time the antibiotic mixes with light and oxygen and gives teeth a grayish-blue tint that's hard to remove. All toothpastes depend on abrasives to scrub stains from the tooth surface. The first "toothpowder," invented in England in the late 1700s, like the first whiteners, was a bit harsh. It contained brick dust and ground-up cuttlefish as abrasives. Today toothpastes contain milder polishing agents such as silica, aluminum oxide, calcium phosphates and calcium carbonate.
If the stains are below the surface, however, you'll likely need whitening agents containing hydrogen peroxide, according to the news magazine. The tooth-whitening power of peroxide was first recognized by dentists in the early 1970s. They had been using an oral antiseptic containing peroxide to heal mouth sores when they realized it also brightened teeth. Today peroxide-based teeth-whiting gels are in millions of bathrooms across the nation.
Hydrogen peroxide whitens by forming radical intermediates (extremely unstable and destructive molecules) that then break down into water and oxygen. Researchers believe these radical intermediates react with pigments that stain teeth, at least in part by destroying the double-bond network that gives such compounds as polyphenols their color.
As so often is the case, if the usual whiteners don't work for your teeth, you can look to the beautiful people in Hollywood for one more option: tooth veneers. These thin coverings made of porcelain are bonded to your teeth. They won't last as long as your pearly whites, but they won't stain.
For more stories on the chemistry of everyday objects, go to http://www.cen-online.org and click on "What's That Stuff?", winner of a Scientific American Sci Tech Web Award for one of the best science websites for the public.
Journal
Chemical & Engineering News