The eyes may be the window to the soul, but the mouth provides an even better view of the body as a whole.

Some of the earliest signs of diabetes, cancer, pregnancy, immune disorders, hormone imbalances and drug issues show up in the gums, teeth and tongue -- sometimes long before a patient knows anything is wrong.

There's also growing evidence that oral health problems, particularly gum disease, can harm a patient's general health as well, raising the risk of diabetes, heart disease, stroke, pneumonia and pregnancy complications.

'We have lots of data showing a direct correlation between inflammation in the mouth and inflammation in the body,' says Anthony Iacopino, director of the International Centre for Oral-Systemic Health, which opened at the University of Manitoba Faculty of Dentistry in Canada in 2008. Recent studies also show that treating gum disease improves circulation, reduces inflammation and can even reduce the need for insulin in people with diabetes.

Such findings are fueling a push for dentists to play a greater role in patients' overall health. Some 20 million Americans -- including 6% of children and 9% of adults -- saw a dentist but not a doctor in 2008, according to a study in the American Journal of Public Health this month.

'It's an opportunity to tell a patient, 'You know, I'm concerned. I think you really need to see a primary care provider,' so you are moving in the direction of better health,' says the study's lead researcher Shiela Strauss, co-director of statistics and data management for New York University's Colleges of Nursing and Dentistry.

George Kivowitz, a restorative dentist with offices in Manhattan and Newtown, Pa., says he has spotted seven cases of cancer in 32 years of practice, as well as cases of bulimia, due to the telltale erosion of enamel on the back of the upper front teeth, and methamphetamine addiction. 'We call it 'meth mouth,' ' he says. 'The outer surface of teeth just rot in a way that's like nothing else.'

Some of the most distinctive problems come from uncontrolled diabetes, Dr. Kivowitz adds. 'The gum tissue has a glistening, shiny look where it meets the teeth. It bleeds easily and pulls away from the bone -- and it's all throughout the mouth.'

An estimated six million Americans have diabetes but don't know it -- and several studies suggest that dentists could help alert them. A 2009 study from New York University found that 93% of people who have periodontal disease are at risk for diabetes, according to the criteria established by American Diabetes Association.

It's not just that the same lifestyle habits contribute to both gum disease and high blood sugar; the two conditions exacerbate each other, experts say. Inflammation from infected gums makes it more difficult for people with diabetes to control their blood-sugar level, and high blood sugar accelerates tooth decay and gum disease, creating more inflammation.

There's also growing evidence that the link between periodontal disease and cardiovascular problems isn't a coincidence either. Inflammation in the gums raises C-reactive protein, thought to be a culprit in heart disease.

'They've found oral bacteria in the plaques that block arteries. It's moved from a casualrelationship to a risk factor,' says Mark Wolff, chairman of the Department of Cariology and Comprehensive Care at NYU College of Dentistry.

Bacteria from the mouth can travel through the bloodstream and cause problems elsewhere, which is why people contemplating elective surgery are advised to have any needed dental work performed first.

The American Heart Association no longer recommends that people with mitral valve prolapse (in which heart values close abnormally between beats) routinely take antibiotics before dental procedures, since it's now believed that oral bacteria enter the bloodstream all the time, from routine washing, brushing and chewing food.

But the American Heart Association, the American Medical Association and the American Orthopedic Association all urge people who have had a full joint replacement to take an antibiotic one hour before any dental visit for the rest of their lives to reduce the risk of post-surgical infections. 'I have my guidelines taped to the door in my hygienists' room,' Dr. Kivowitz says.

Dentists say they also need to stay up to date with all medications, supplements and over-the-counter drugs their patients are taking. Blood thinners can create excess bleeding in the mouth. Bisphosphonates, often prescribed for osteoporosis, can severelyweaken jaw bones. Both should be stopped temporarily before oral surgery.

Antihypertensive drugs, calcium-channel blockers and some anti-inflammatory drugs can cause painful ulcerations of the gums. Many medications, from antidepressants to chemotherapy drugs, cause dry mouth, which can cause cavities to skyrocket, since saliva typically acts as a protective coating for teeth. Additional fluoride treatments can help.

Some proactive dentists have glucose monitors for another check on blood-sugar levels if they suspect diabetes. Some also take patients' blood pressure and hold off on invasive procedures if it's extremely high.

The Centers for Disease Control and Prevention recommends that dentists offer HIV testing, because some of the first symptoms appear in the mouth, including fungal infections and lesions. Dentists can do the HIV test with a simple mouth swab and get results in 20 minutes.

Breaking the bad news is often more difficult. 'I went into oral surgery because I didn't think I would have to deliver that kind of news to patients,' says Clifford Salm, an oral and maxillofacial surgeon in Manhattan who has found leukemia, lymphoma, AIDS and metastatic breast cancer after performing biopsies on suspicious spots. 'It can be a difficult conversation,' he says, 'but most patients are very grateful.'