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It's is Thursday morning, which is when we talk about your health. And this morning we'll talk about your teeth - bleaching them. If you're willing to pay, techniques such as BriteSmile and Zoom are marketed as a breakthrough.

NPR's Allison Aubrey reports on whether they work any better than less expensive bleaching gels or over-the-counter white strips.

ALLISON AUBREY: The Center for Dental Health in Washington, D.C.'s toney Spring Valley neighborhood has the feel of a spa and offers many high-end procedures. But one thing you won't find here is a Zoom light or any other kind of light for teeth whitening.

Dentist Eric Morrison says the jury's still out on whether the light is effective.

Dr. ERIC MORRISON (Dentist): That's very true. What they're showing is, is that it isn't providing a significant difference in the result.

AUBREY: Meaning if you want to whiten your teeth, bleaching gels used alone can be just as effective as sitting in your dentist's office under a light. The first bit of evidence that light-activated systems may not enhance the results of bleaching was published in a dentistry journal back in 2003.

Researcher Lee Hansen explains there was an assumption that heat from the light served as a catalyst to decompose the bleaching gel.

Professor LEE HANSEN (Brigham Young University): That's the theory behind it. But it's incorrect for two reasons.

AUBREY: Hansen, who's a retired chemistry professor, explains in order to accelerate the chemical reaction of the gel, you'd need a decent amount of ultraviolet light and heat. But most of the UV light is filtered out of the whitening lamps because the exposure would sunburn people's gums.

Professor HANSEN: So all you have in the light is visible light, and so none of that light is absorbed. It's all simply reflected back out so it can't do anything.

AUBREY: To test his theory, Hansen's colleagues at Clinical Research Associates - considered to be the Consumer Reports of dentistry - tried a combination of bleach and light on a small group of patients. On one side of their mouths they used bleaching gel alone, and on the other side they added the light. At the end of the study all the teeth were whiter, but there was no difference between the two sides.

Dentist Gerry Kugel of Tufts University says this one study was by no means a final word on light-activated bleaching.

He says a lot of patients do seem to like the procedure. When they leave the dentist chair after an hour-long session, many can see the difference - and they may assume it's all from the light.

Dr. GERRY KUGEL (Dentist): You've got to remember, they're getting peroxide on their teeth. You know, with the Zoom it's 25 percent. Some of the other ones it's even higher. And so they do leave with a whitening effect.

AUBREY: But within about seven days, when the teeth rehydrate, studies show there's a rebound in the color. That's why most patients are sent home with more bleaching gel that they can apply at home.

Kugel says jump-starting the process with an in-office light bleaching, which typically costs about $500, does seem to offer a time advantage.

Dr. KUGEL: My argument is it's so minimal that I don't see it being worth what, you know, people are being charged for this. I just don't get it.

Lots of dentists may disagree with Kugel. About 20,000 of them offer Zoom, and another few thousand use BriteSmile. Both are owned by Discus Dental. Dentist Marilyn Ward directs training for the company.

Dr. MARILYN WARD (Discus Dental): We have strong clinical studies showing that you do have statistical significance in light versus no light.

AUBREY: Zoom started to take off as a brand several years ago, after company founder Bill Dorfman began appearing on the hit TV show "Extreme Makeover." As the program's aesthetic dentist, he repeatedly touted Zoom.

All the consumer interest piqued the curiosity of researcher Joe Ontiveros. He's a dentist at the University of Texas. He's just finished a study, partly funded by Discus Dental, analyzing the effects of bleach alone compared to the Zoom light on a small group of patients.

Dr. JOE ONTIVEROS (Dentist): For some people it was dramatic, and some people you could barely tell the difference.

AUBREY: Ontiveros says for his patients he still recommends at-home tray-bleachings first.

Dr. ONTIVEROS: Because it's just got a long track record and it's very predictable.

AUBREY: At the end of the day, experts who study bleaching do agree on one fact; that is that hydrogen peroxide works.

Professor HARALD HEYMANN (University of North Carolina): I've always said in my lectures, bleach is bleach is bleach.

AUBREY: Researcher Harald Heymann says there's a pretty simple formula here. If you want quick results, go for a high concentration of peroxide. If you've got more time or you're more sensitive to the chemicals, tray-bleachings or Crest Whitestrips can work just as well.

Allison Aubrey, NPR News, Washington.

INSKEEP: And that's your health on this Thursday morning. Should remind you that teeth, even in babies, come in all sorts of shades, and you can find out what determines tooth color and why we have wisdom teeth by going to npr.org/yourhealth.

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