Other new research is aimed at ridding the mouth of harmful organisms that have already found comfortable habitats. At the University of Florida at Gainesville, molecular biologist and dentist Jeffrey Hillman has been using genetic engineering to develop a harmless strain of S. mutans that will replace the acid-producing varieties that occupy and cause cavities in most mouths.In the early 1980s, Hillman and his research team isolated a type of S. mutans that metabolizes sugar but doesn’t produce acid as a waste product. But no matter what he and his colleagues tried-for example, eliminating the original strain with antibiotics and painting the teeth with iodine-the S. mutans that already occupied a person’s mouth would not be budged. “They have hiding places,” he says. “Nobody found a way to wipe them out entirely.”
So Hillman examined hundreds more strains of S. mutans to find one that produced an antibiotic-like molecule that killed all other strains of S. mutans. Using genetic engineering, he modified it so that it would no longer produce acid. This so-called effector strain can colonize tooth surfaces, he says, and wipe out native S. mutans.
Within the next few months, Hillman will begin trials on laboratory rats, infecting their mouths with the bacteria. If the bacteria perform as intended, he will then conduct trials on humans. He anticipates that, eventually, dentists will apply the bacteria during a typical cleaning. “In theory, the new strain should stay with people the rest of their lives,” says Hillman. “And since S. mutans normally is transmitted from mother to child, this effector strain will also be transmitted, and will prevent tooth decay in the children of those treated.”
Other attempts to oust offensive germs from their comfortable dwellings are taking aim at the bacteria, yeast, and protozoa that dive down tiny cracks in a tooth to infect the blood- and nerve-rich tooth roots and cause ice-pick-like stabbing pain. If root infections in certain teeth in the upper jaw are not treated, the bacteria can cause serious eye infections, even blindness. “That’s why they’re called eye teeth,” says Kathleen Olender, an endodontist at the University of California-San Francisco Dental School.
Similarly, if a tooth in the lower jaw becomes severely diseased, the bacteria can travel to the throat and cause a condition called Ludwig’s angina in which the larynx can swell so much that the person can’t breathe, says Craig Baumgartner, chair of the Department of Endodontology at Oregon Health Sciences University in Portland. Bacteria from a tooth in an upper jaw can also spread into the pterygoid plexus, a locus of nerves and blood vessels in the face. “The bacteria can back up the veins into the brain,” he says, and even cause dementia.
Baumgartner says that while endodontists see these severe infections only occasionally in the United States, they are still common in developing countries where people don’t have access to antibiotics and aggressive care to surgically remove infected roots. Moreover, although root-canal procedures have been performed for hundreds of years, and today about 10 million teeth a year undergo endodontic procedures, it was not until antibiotics were developed after World War II that dentists were allowed to perform root canals in the United States because the bacterial infection in the root was often difficult to contain.
Researchers aiming to control these infections have recently identified eight species of bacteria that seem to cause most of the infections that occur in tooth roots. Their goal is to eliminate all of the bacteria in an infected root, since it is normally sterile. But because there seems to be a complex interplay among the species of infecting bacteria-a byproduct of one is used as a nutrient by another-researchers such as Baumgartner at the Oregon Health Sciences University believe that identifying and focusing on killing one or two species would upset the ecosystem to such a degree that the rest would die off. Toward that end, he and other researchers are now testing the effectiveness of individual antibiotics on targeted bacteria species.