Biting down on the culprit causing gum disease.

Biting down on the culprit causing gum disease 

About 10.sup.10 bacteria are found in each site of periodontal, or gum, disease. Among those are about 300 different species of bacteria. And among those species about 12 are considered nasty; they are suspected of being involved in the progression of periodontal disease in adults, which destroys the tissue and bone that support teeth.

But because scientists have not been able to determine which ones are the key types, dentists are forced to use a variety of procedures, including antibiotics (SN: 10/24/87, p.268), to halt the progression of the disease. This course of treatment can pose problems because bacteria can develop a resistance to medication. In addition, antibiotics break down bacteria into their component parts, some of which may infect the mouth.

Now, new work is pointing to a specific bacterium, Bacteroides gingivalis, as at least one cause of periodontal disease. Dental researchers hope that by pinning down specific bacteria, they eventually may be able to interfere with the progression of periodontal disease, perhaps by preventing the key types from colonizing or by cutting off their food supply, which consists primarily of the by-products of other bacteria.

In recent years, scientists have repeatedly isolated B. gingivalis from diseased gums in adults and have linked it to the progression of periodontal disease in humans and monkeys. But they have not been able to say that it is a cause of periodontal disease. For example, when researchers tried to implant it in the mouths of rodents, they did not observe any resulting disease.

However, a group of researchers reports in the Jan. 1 SCIENCE that B. gingivalis does cause a burst of periodontal disease in monkeys, whose mouths have a microbiology and immunology similar to humans'. Currently, the group is trying to determine whether other types of bacteria have a similar effect.

"Periodontal disease has a complex etiology. More than one type of bacteria is involved," says Stanley C. Holt of the University of Texas at San Antonio, where the research, funded by the National Institute of Dental Research (NIDR), was done.

In the experiment, the researchers injected four monkeys with the antibiotic rifampin to kill most of the periodontal-disease-causing bacteria. Another four monkeys were given placebos and served as controls. After eight weeks, the researchers placed silk strings around the base of four teeth in each monkey--a process called ligation, which is supposed to lead to periodontal disease.

Eight weeks later, they detected periodontal disease in 10 of 16 control sites and in 4 of 16 sites in monkeys given rifampin. At this time, they implanted rifampin-resistant B. gingivalis into two of the ligated sites in each monkey. Twenty weeks later, 6 of the 8 sites in the controls and all 8 sites in rifampin animals bled when touched gently with a probe--a standard sign of periodontal disease.

The researchers then isolated rifampin-resistant B. gingivalis itself from 10 of the 16 sites. These numbers agree with the 60 to 80 percent figure usually associated with the prevalence of B. gingivalis in adult cases of periodontal disease.

Says Robert Genco, director of one of five NIDR centers for periodontal disease at the State University of New York at Buffalo: "It appears B. gingivalis is getting support as a periodontal pathogen."

Holt and his colleagues Jeffrey Ebersole and Kenneth S. Kornman now are determining how to interfere with the progression of periodontal disease and are examining which other bacteria are involved.