Some 300 kinds of bacteria — millions of individual organisms — live in your mouth.

The late Ed Moore and recently retired Lillian (Peg) Moore, husband and wife and University Distinguished Professors in anaerobic microbiology at Virginia Tech, spent two decades identifying the bacteria involved in periodontal disease. They linked 17 kinds of bacteria to the disease and identified more than 300 kinds that are present in the mouth, more than half of which had not previously been described. The interview for this article was done in 1995, but the findings are still very relevant.

The researchers found that no two mouths are alike. “You seem to have your flora and I have mine,” said Ed Moore.

They started by comparing bacteria in periodontal disease with those of healthy people, and found they are different, and are in different proportions in different people.

The researchers then investigated health and gingivitis and periodontal disease. “There is a progression from health to gingivitis to periodontal disease,” Peg Moore reports. “Flora we find first in gingivitis persist and others appear in periodontal disease.”

Non-pathogenic bacteria normally present in your mouth attach to the surface of teeth and gums first and form a bridge for the pathogenic bacteria. If we do not floss to clean out the small crevice between tooth and gum, bacteria will grow on the tooth surface and in the crevice, and eventually there will be gum tissue destruction and a deeper crevice. If the crevice becomes as deep as four millimeters (slightly more than one-hundredth of an inch), only professional cleaning will succeed in cleaning it, and even that will not lead to a bacteria-free crevice.

Periodontal disease can get its foothold as a result of irritation at the gum line and between the teeth from plaque, which is a mass of bacterial cells. Gingivitis or bleeding of the gums occurs when the waste products of bacterial proliferation irritate the gum. The blood and serum from the gum stimulate growth of other bacteria. Many of the bacteria in periodontal disease are serum-requiring organisms. As this process progresses, the collagen that binds the tissue to the tooth is destroyed.

Gingivitis is reversible, but periodontal disease is not, although it can be slowed or stopped. The problem is knowing when periodontal disease is starting, said Peg Moore.

Of the 17 organisms the Moores have linked to periodontal disease, several are present in gingivitis. “We still have our normal flora, but at lower levels, and the total bacteria mass is greater in the diseased state, meaning a lot more pressure on the body, more toxin, and more bacterial acid products," said Ed Moore.

The presence of disease-causing bacteria does not always lead to disease, however. What does? “One theory is that our bodies develop antibodies to stop the action of bacteria for a time, but another bacterial species may come along later to continue tissue destruction and detachment. Finally, white blood cells enter the battle against bacteria, mobilizing calcium from the bone which surrounds the root of the tooth, doing more harm than good."

The Moores' research told them how bacteria are retained, but not where they come from. "They do not come from meat, vegetables, or soil," said Peg Moore.

“The compositions of the flora of different people are statistically different, and we want to know why," said Ed Moore. “Is it genetic, or environmental, or both?”

To learn where disease-causing bacteria come from and why different people have different flora, the Moores did a study with twin boys aged 11-14. That work demonstrated that both genetic and environmental factors control our personal flora.

Another reason the Moores' work is important is "there are many unknown bacteria that cause disease," said Peg Moore. "Once we describe a bacterium, very often then it is found at other body sites where it was unrecognized before."

Organisms from the mouth that they have described have then been found at the sites of pulmonary disease, brain abscesses, female gynecological diseases, and diseases of other soft tissues. "Periodontal bacteria may enter the blood stream, the lungs, or the brain," she explains.

As a result of the Moores' work, rapid diagnostic tests for progressive periodontal disease were developed using the 17 known organisms, and a great deal more has been learned about the connection between gum disease and other disease, such as heart disease.

(Although this research is no longer being done at Virginia Tech, I decided to leave the article online as an example of how research is done and because it contains interesting information and had important outcomes. — Susan Trulove)