The same sticky compounds in the small, hard red fruit -- which is boiled into a jelly that is a staple at American winter holiday meals -- that help keep bacteria at bay in the bladder also appear to help prevent bacteria from clinging to teeth, according to the researchers.

They also found it seemed to help ward off plaque, a gooey substance formed from bits of food, saliva, and acid that can harbor bacteria and eventually irritate the gums.

"There's potential to find compounds there that prevent dental cavities," said Hyun Koo, an oral biologist at the University of Rochester Medical Center in New York.

The ultimate goal is to extract the berry's protective properties and add them to toothpaste or mouthwash, he said, but it is still unclear exactly why the fruit is so effective.

In the meantime, Koo warned people against drinking or eating excessive amounts of cranberry-containing products.

"The biggest problem with any cranberry product is the (food) industry -- they add sugar," he said in an interview. "Sugar is the main enemy in causing cavities."

The fruit is also loaded with natural acid that can strip away essential minerals in teeth, he added.

"At this stage you have the other negative factors ... that prevent us from saying 'go ahead and swish with cranberry juice,"' Koo said.

During the study, researchers coated a synthetic material that acts like tooth enamel, called hydroxyapatite, with cranberry juice. They then applied the cavity-causing bacteria streptococcus mutans, plaque, or glucan -- a type of enzyme that builds plaque.

The results, which took about seven months to obtain, showed cranberries were about 80 percent effective in protecting teeth, Koo said. More laboratory tests are needed to try to isolate the active compounds before clinical trials with patients can be considered, he added.

Koo's study is part of series of projects sponsored by the National Institutes of Health to study cranberries' health benefits. The agency is also studying the fruit's impact on urinary tract infections and how it is processed by the body.

Tooth decay is one of the most common conditions among Americans, second only to the common cold, according to the NIH.

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