The next time you kiss someone, think about this: in your mouth, and in the mouth of every adult, live more than 400 different species of microorganisms, mostly bacteria. Billions and billions of them grow in layers, crowded together and wrapped cozily around each other, on every slimy surface, dark nook, and inviting cranny. It’s enough to make a body want to keep lips permanently pursed.
With an average temperature of about 95 degrees, a saliva-induced humidity of 100 percent, and regular stoking with sugar and other simple carbohydrates-manna from bacterial heaven-the mouth provides a home for such a diversity of species that it could be called the tropical rainforest of the body. “In one mouth, the number of bacteria can easily exceed the number of people who live on earth,” says Sigmund Socransky, a dental researcher at the Forsyth Dental Center in Boston, Mass. “In a clean mouth, 1,000 to 100,000 bacteria live on each tooth surface. A person who doesn’t have a terribly clean mouth can have 100 million to 1 billion bacteria growing on each tooth.”
These facts are more useful than fodder for cocktail party chatter. An entire branch of dental research has grown up around “oral ecology”-the study of the relationships among the inhabitants of this minute jungle ecosystem-to develop the next generation of weapons in the fight against tooth and gum disease.
Since 1959, when scientists isolated a species of infectious bacteria that causes most cavities, a national campaign to reduce tooth decay has focused on brushing, flossing, and adding fluoride to water supplies, toothpaste, and mouthwashes. Fluoride, a chemical that appears naturally in groundwater in many areas of the world, quickly bonds with the tooth’s enamel to maintain its smooth crystalline surface and deter bacteria from gaining a toehold.
These dental hygiene methods have worked so well that today 51 percent of U.S. children under 12 have no tooth decay. However, many of the remaining 49 percent have severe forms of cavities that are difficult to control, even with the best dental hygiene. And other problems challenge dental researchers. Periodontal disease-infection of the gums that is caused by about a half-dozen bacterial species-affects millions of adults and children. People with Sjogren’s syndrome, an auto-immune disease of unknown origin that causes severe drying of the mouth, eyes, and other mucosal surfaces, have serious problems with tooth decay, as do many people whose saliva glands stop functioning after certain medical procedures.
Over the last 20 years, modern biotechnology, including genetic engineering and techniques to study anaerobic bacteria-those that live without oxygen and cause most periodontal disease-have enabled oral ecologists such as Socransky to identify some of the organisms. They have not only pinpointed about a dozen species of bacteria living in the mouth that can cause infections in the teeth and gums, but they also have made significant strides in understanding how these organisms colonize the mouth and how they are transmitted from one person to another.
Researchers are now applying their new knowledge to develop techniques that prevent the organisms from gaining residence in the first place, or to force them out using innocuous strains or new antibiotics once they’ve already settled in. They are also attempting to create artificial saliva for people with compromised saliva glands to sluice harmful germs out of the mouth and into the digestive system before they can stick to the teeth and gums.