Only one type of electric toothbrush clearly does a better job of cleaning teeth than the old-fashioned manual kind, according to the first comprehensive attempt to evaluate the devices used by an estimated 55 million Americans.

Electric brushes with bristles that spin in both directions are the sole kind offering sufficient proof of any advantage over regular toothbrushes, according to the report from the Cochrane Collaboration, an independent nonprofit group based in Oxford, England, that evaluates medical practices.

"The others were not worse, but they were just not any better" than manual brushes, said William Shaw, a professor of orthodontics at the University of Manchester in England, who helped coordinate the report of the Cochrane Collaboration's Oral Health Group.

The report is the latest in a series being issued by the Cochrane Collaboration on various aspects of medicine and dentistry that have never been subjected to careful evaluation.

As part of a growing movement toward "evidence-based medicine," the Cochrane organization and others are beginning to evaluate many long-accepted and widely used procedures and treatments that have never been proven effective. Shaw thinks that's an especially important issue in dentistry.

"Many dentists work in isolation in their own small, private offices, and they tend to be bombarded by the manufacturers that make products that are used in dentistry," said Shaw, who was to release his report Saturday at a conference sponsored by the Forsyth Center for Evidence-Based Dentistry in Boston.

"Dentistry needs more evidence in general, and the best source of that is these kinds of unbiased syntheses," he said. "There are literally hundreds of questions that we don't know the answer to."

To evaluate electric toothbrushes, six reviewers combed through every published study on the devices and asked manufacturers for any unpublished results they had. The team then combined 29 studies it considered to be well designed, yielding data involving 2,547 people in North America, Europe and Israel.

Of five types of brushes examined, only the "rotational oscillation" design of the Braun Oral-B device was clearly more effective than manual toothbrushes, the researchers concluded. Compared to manual brushes, that design removed about 11 percent more of the build-up on teeth known as plaque, and reduced by about 17 percent the development of gum disease, or gingivitis.

None of the other brushes evaluated -- the Philips Sonicare, the Interplak, the Teledyne Aqua Tech, the Ultrasonex, the Rowenta Dentiphant and the Rowenta Plaque Dentacontrol Plus -- performed better than manual brushes, Shaw said.

Michele Szynal, a spokeswoman for Gillette Co., which makes the Braun Oral-B, said the company is "thrilled" by the findings. "This basically confirms four decades of our own research," she said.

The Braun product is the choice of 41 percent of Americans who use electric toothbrushes, according to Gillette.

Christopher McInnes, principal scientist for clinical affairs at Philips Oral Healthcare Inc. in Snoqualmie, Wash., which makes the Sonicare electric toothbrush, disputed the findings. The Sonicare brush has an up-and-down sweeping motion that is just as effective and gentler on the gums, he said.

"We have evidence, with Sonicare, that indeed the plaque removal and gingivitis reduction is substantial," he said.

Consumers in North America spend an estimated $1.5 billion a year on toothbrushes, including about $850 million on manual brushes and about $700 million on electric versions, according to Gillette. Prices range from as little as about $7 for a simple battery-operated model to more than $80 for a more sophisticated rechargeable type.

Toothbrush manufacturers are not required to submit evidence of their device's effectiveness to the Food and Drug Administration before putting them on the market, because they are considered low-risk devices, said Susan Runner, chief of the FDA branch overseeing dental devices.

As a result, "these kinds of reviews are very helpful in trying to sort out the literature," said Isabel Garcia, special assistant for science transfer at the National Institute of Dental and Craniofacial Research, part of the National Institutes of Health. "I think that's needed, both for the clinician and for the public."

Kenneth Burrell, senior director of the American Dental Association's Council on Scientific Affairs, said his group will "make sure our members know this study exists."

"The ADA is doing a lot . . . educating its members about this new concept of evidence-based dentistry," he said.

Eugene Giannini, a dentist in the District, said he tends to recommend the Braun Oral-B toothbrush to most of his patients but will likely continue to recommend other brands as well -- despite the new findings.

"Electric toothbrushes generally are better than conventional toothbrushes. Patients tend to brush longer. And since they invested in this toothbrush, they tend to be more committed to their oral hygiene," he said.

But one of Giannini's patients, Dorothy O'Neill, 34, an accountant who lives in the District, said she switched from a Braun Oral-B brush to a Sonicare because she didn't like the way the Braun felt on her gums.

"It seemed like it was a little too rough. It seemed like it must have been wearing away on my gums," she said.

She found the new findings surprising but didn't think she would switch back from the Sonicare.

"It seems like it's got to be better than the regular toothbrush, and it doesn't seem like you're sanding . . . away at your gums," she said.