May 2008

Illustration: Lee Wolf

Ask The Professor

How do teeth whiteners work-and are any methods better than others?

This month's faculty expert, Gerard Kugel, professor of dentistry, responds:

Many studies have been conducted to test the effectiveness of teeth-whitening materials and techniques, says Dr. Gerard Kugel, D85, L93, professor of prosthodontics and operative dentistry and associate dean for research. By using carbamide peroxide, hydrogen peroxide or a combination of the two, teeth do become whiter, but exactly how that happens is still not completely understood.

When applied to teeth, hydrogen peroxide diffuses through the enamel and dentin. It produces free radicals-atoms with unpaired electrons-which are "extremely unstable and attack most other organic molecules to achieve stability, generating other radicals," says Kugel.

What causes teeth to appear yellow are double-carbon bonds, which absorb light and trap chemicals that add color to molecules, says Kugel. When these double-bonds are broken by the radicals, single-carbon bonds are formed that reflect light, making the teeth appear brighter.

Whitening toothpaste tends to work by removing superficial stains, he adds, but has little effect on pigmentation in the tooth enamel. On the other hand, all peroxide-containing products seem to work, and the effectiveness is related to the concentration levels and time applied. "Higher concentrations, such as 15 percent carbamide peroxide, work faster than lower concentrations," Kugel says. "The results are cumulative, meaning if you bleach every other day, it will take twice as long to whiten the teeth versus whitening every day. Tray systems, white strips and preloaded trays all work." On the other hand, a new treatment option that involves shining a bright light at the teeth, he adds, seems to confer only minimal benefit, according to the research literature.

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