Twenty-somethings who keep their wisdom teeth may be at risk for gum disease and other health risks even if they show no symptoms or signs, new data from a series of clinical trials suggests.

Periodontal disease is a chronic bacterial infection that can destroy the gums, teeth and bone.

The disease starts when bacteria colonize the space between the teeth and gums, creating pockets around the roots.

It rarely affects people under 30, but researchers from the University of North Carolina and the University of Kentucky found that 60 percent of study subjects in their 20s showed signs of infection around their wisdom teeth, the four rear-most teeth, also known as third molars.

Two years later, 25 percent of those patients' pockets deepened, signaling that the disease progressed.

And when pockets of bacteria deepen, it can lead to loosened teeth and bacteria entering the bloodstream, which can promote inflammation elsewhere in the body.

"That was a huge surprise to find this much periodontal disease with people of this age," said lead researcher Raymond White, a professor at North Carolina's School of Dentistry. "We're recommending that everybody with wisdom teeth should have them evaluated."

The results of the Third Molar Clinical Trials were presented late last month in Boston at the American Association of Oral and Maxillofacial Surgeons annual meeting. More than 50 studies have been finished or are underway concerning third molars, Mr. White said.

The findings are significant because they show that young adults with wisdom teeth may be at risk for oral inflammatory disease, chronic body inflammation and pregnancy risks, he said.

Data from another study presented at the conference found that young women with third molar periodontal disease were twice as likely to give birth prematurely.

Mr. White said he wasn't recommending that everyone have their wisdom teeth removed, since some people have no complications, but if wisdom teeth are kept, they should be evaluated by the age of 25.

"Just because you have no symptoms," he said, "doesn't mean you have no problems."