SAN ANTONIO (The San Antonio Express-News)- A growing body of evidence suggests that oral infections, particularly periodontal disease, may play a role in chronic medical problems.

Commonly known as gum disease, periodontal disease is increasingly being blamed for raising the risk of heart disease, stroke, diabetes and preterm and low birth-weight babies.

One study of heart-attack patients found that 85 percent also had periodontal disease. In another, pregnant women with the severest form of periodontal disease had an eightfold risk of giving birth prematurely and a threefold risk if they had a milder infection.

And a third study, published in the Archives of Internal Medicine, concluded that periodontal disease increases stroke risk 15 percent to 18 percent in whites, 38 percent in African-Americans.

Despite such numbers, researchers caution that they have yet to prove specifically that oral infections cause disease. "This is what's called "emerging data,"' said Marjorie Jeffcoat, a dental researcher at the University of Alabama at Birmingham and the first-ever female editor of the Journal of the American Dental Association. "There could be other causes at work that we're unaware of."

Still, most dentists take special precautions when treating patients who have heart problems or other ailments. This includes prescribing preventive antibiotics to kill bacteria.

Although other chronic infections - such as urinary tract infections and sexually transmitted diseases - also have been linked to problems such as heart disease, periodontal disease poses special risks because it is so commonplace.

Seventy-five percent of adult Americans have degree of gum disease, according to the American Dental Hygienists' Association. In a report released last year, U.S. Surgeon General David Satcher wrote simply, "You cannot be healthy without oral health."

Periodontal disease is a bacterial infection of the gums and teeth. It is caused by a buildup of plaque, the colorless film that forms on teeth. Over time it can destroy the fibers and bone that anchor teeth in the jaw, leading to tooth loss.

Mouth infections are particularly dangerous because the gums are so vascular, meaning they contain a lot of blood vessels very close to the surface. So they serve as a convenient expressway to the heart and other organs for havoc-causing byproducts of the infection.

Researchers are still unsure exactly how gum disease might cause chronic illness. One theory holds that byproducts of the infection, called c-reactive proteins, travel to the heart where they bind to damaged cells in the coronary arteries, triggering inflammation. This inflammation can lead to clotting. It's also suspected that certain types of oral bacteria may find their way to the heart, where they trigger blood clots.

There also is the fear that any dental work, even something as benign as cleaning the teeth, can trigger the release of massive amounts of these bacteria and byproducts into the system. In people who already have heart problems, this is thought to increase risk of heart attack.

"I've heard many anecdotal reports of people with heart conditions who suddenly die shortly after having dental work done," said Michael P. Bonner, a San Antonio dentist who runs the Web site gumhealth.net.

Periodontal disease is particularly insidious because the low-grade infection can smolder for years, even decades, before symptoms become apparent.

Unknown at this point is whether clearing up the infection will have a beneficial impact on overall health.

"We do know that diabetics whose periodontal disease is treated have a 10 percent reduction in glycated hemoglobin," a measure of long-term blood sugar levels, said Robert J. Genco, chairman of the department of oral biology at the University of Buffalo in New York. This can reduce the incidence of diabetes-related side effects.

Genco is also the lead investigator in a $7 million study recently funded by the National Institutes of Health.

The study is designed to determine the best way to treat periodontal disease to lower blood levels of c-reactive proteins in patients who have had a first heart attack while at the same time see if such treatments successfully lower risk of a second attack. Genco said results should be available in six to seven years.