By Christian Millman
Special to ABCNEWS.com

Farmers, cowboys and other sensible men always examine a horse’s mouth before buying the animal. One good look can sum up the horse’s health history and predict how long the old boy will live. A human mouth isn’t much different exhibit A: John Elway

"This horse test is based on the old ‘focal-infection theory,’ which says that an oral infection affects the whole body," says Dr. Raul G. Caffesse of the University of Texas, Houston Health Science Center. That used to be the excuse for lots of tooth pulling until dentists abandoned the theory 40 years ago.

But the focal-infection theory is making a big comeback — minus the fun of the extractions. And now it’s supported by more than frontier hunches. In fact, there’s growing clinical evidence that small infections in your kisser may be a contributing factor to several diseases.

Although the theories are still controversial, dentists and other physicians think that the following five afflictions may have their roots in your mouth. And that makes five excellent reasons to buy some floss — now.

HEART ATTACKS
Dr. Robert J. Genco of the University of Buffalo studied 1,372 people at the Gila River Indian community in Arizona and found that those with gum disease had triple the risk of heart attacks in a 10-year period.  He believes that oral bacteria — there are 350 different types in your mouth — enter your bloodstream through small tears in your gums. The bacteria, Genco suggests, may infect your liver and cause it to produce artery-clogging proteins, or they may directly infect your heart arteries and somehow cause blockages. The exact mode of attack is still a mystery, he says, but Porphyromonas gingivalis bacteria have been found in fatty arterial blockages that cause heart failure. And, you’ve probably heard, that oral bacteria can be especially dangerous to people who have heart disease. If you have an ailment involving the heart valves, such as mitral valve prolapse or a heart murmur, you may need to take antibiotics before receiving dental treatment, says Dr. Mark V. Thomas of the University of Kentucky College of Dentistry. Dental work dislodges bacteria and nicks your gums, sending a rush of germs into your bloodstream. That can cause bacterial endocarditis, an often fatal infection that strikes about 20,000 people each year.

STROKES
Men with gum disease could be destined for the drooling-and-Depends years that sometimes follow a massive stroke. University of Buffalo researchers surveyed the health histories of 9,982 people from 25 to 75 and found that the 35 percent with severe gum disease were twice as likely to have had a stroke. Oral bacteria may cause fatty accumulations in the carotid arteries in your neck, which can result in blockages, says Dr. John Marler of the National Institute of Neurological Disorders and Stroke. These little logjams often break apart, float upstream and lodge in your brain. And if a tiny chunk dams up a blood vessel in your gray matter, your dancing days are over.

DIABETES
When a person with diabetes is fighting a bacterial infection, his insulin works less efficiently. That can raise his blood-sugar level, says Dr. Perry R. Klokkevold of the UCLA School of Dentistry. If you’re battling diabetes — and about one in 17 Americans is — a gum infection can make managing the disease much tougher. When University of Buffalo researchers examined 168 diabetics, they found those with periodontitis (severe gum disease) had the most trouble controlling their blood-sugar levels. That’s what eventually causes the kidney disease, heart disease and blindness that plague many diabetics. Though gum disease probably doesn’t directly cause diabetes, Klokkevold says. "This is a relatively new field of research, but we know that having gum disease will worsen diabetes," says Dr. Christopher Saudek, a diabetes specialist at Johns Hopkins University in Maryland. "People with diabetes should be careful to keep their gums healthy." And if you have both a gum infection and a family history of diabetes, get checked for diabetes immediately.

ULCERS
Some evidence suggests that the Helicobacter pylori bacterium that can cause stomach ulcers resides in dental plaque, says Dr. Sherie Dowsett of the Indiana University School of Dentistry. She and her colleagues found that among 242 study subjects, 210 of them carried the bacteria in their mouths. H. pylori may migrate to your stomach and proceed to eat painful little holes, which is why we think every bottle of Pepto-Bismol should come with a free toothbrush.

PNEUMONIA
With every breath, your lungs suck down a stew of bacteria, including Chlamydia pneumoniae and Pseudomonas aeruginosa, two bugs that cause respiratory diseases. Careful readers will have guessed one source: the plaque buildup around your teeth. Your immune system usually destroys these invaders. But when your resistance is low, such as during an illness or after surgery, they can infect your lungs and cause bacterial pneumonia, Caffesse says. This infection kills about 83,000 people a year.