WASHINGTON — Equipment used during routine visits to the dentist can harbor and possibly transmit the AIDS virus if rigorous sterilization procedures are not followed, according to a study released Friday by researchers at the University of Georgia.
The scientists, writing in the British medical journal The Lancet, said they used DNA techniques to identify evidence of the human immunodeficiency virus in two types of frequently used dental tools, the drill and the prophylaxis angle, an instrument used for cleaning and polishing teeth.
Researchers used a dozen high-speed drills and 40 prophylaxis angles from a range of manufacturers to clean the teeth of infected patients and said "in all cases" they found material containing the virus trapped in the equipment. They said the substances "were blown out" when the tools were used again, even after disinfection with chemical germicide--suggesting that this might pose a risk of the material being deposited in the next patient's mouth.
They conducted similar tests with the hepatitis B virus and found the same results.
"It truly poses a risk, just like a contaminated needle does to a health care worker," said the study's author, Dr. David Lewis, a microbiologist with the university's ecology department. "The risk from a needle stick is small, but it does happen."
Lewis said the risk of transmission virtually can be eliminated if dentists sterilize their instruments between each patient using an autoclave--which produces steam heat--or chemicals and heat, rather than disinfection with cold chemicals alone.
Dr. June Osborn, a virologist who chairs the National Commission on AIDS, said the public should not become alarmed over this issue.
"I don't think people should be concerned at all," she said. "Clearly, dentists have been doing this (sterilization) very well all along. Otherwise, we would have had a vastly broadened epidemic--because we all go to the dentist."
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief of the federal AIDS research effort, agreed.
"The epidemiological surveys that have gone on clearly argue against there being a significant risk (of dental transmission) because there was only . . . one known case," he said.
The issue of AIDS transmission in the dental office was first raised more than two years ago by the case of a Florida dentist with AIDS who apparently infected five patients, although the mode of transmission remains unknown. These are the only known HIV transmissions in a dental procedure.
The best-known of those patients, Kimberly Bergalis, waged an unrelenting campaign for mandatory HIV testing of health care professionals before she died of the disease.
Most public health officials, however, place a greater emphasis on strict adherence to infection control procedures--known as universal precautions--as the most effective way to prevent transmission of HIV and other diseases in the health care setting.
"HIV escapes the typical chemical disinfection process," Lewis said. "It is usually applied to the outside of the equipment, which is not enough. Also, an additional problem is that this kind of equipment is lubricated with greases and oils that repel water and the germicides that are used are dissolved in water."
Heat, on the other hand, is effective against HIV and a range of other live viruses, he said, including hepatitis B, which is considered a greater threat in the health care environment.
Osborn said that HIV is "extraordinarily fragile," particularly on flat surfaces where it can be easily killed by chemical disinfectant. She said the virus could survive longer in the crevices of dental equipment, however, where it can be shielded from disinfectant by other biological material, such as blood and tissue. But even in those circumstances, she said, "heat will kill it easily."
Lewis said "there's an average of 15 to 20 minutes between (dental) patients most times." An official with the American Dental Assn. said the ADA has recommended heat sterilization for many years.
Until recently, however, many of these hand-held dental instruments could not withstand heat treatment, and cold disinfection was used instead.
But since 1988, all dental hand pieces manufactured in the United States can tolerate heat treatment. Technology is also available to retrofit older equipment so that it can withstand heat sterilization, the ADA said.
The ADA said a survey conducted last May showed that 84% of all general practice dentists have heat hand pieces that can be sterilized, which is "a 300% increase in those who heat sterilize between patients since 1989," the organization said. The ADA represents 150,000 practicing dentists and dental students in the United States.
The Food and Drug Administration, in a letter mailed to all dentists in September, urged them to heat sterilize their equipment between patients or have their tools retrofitted to attain heat tolerance.
"Hand pieces that cannot be retrofitted and thus not heat sterilized should not be used," wrote James S. Benson, director of the FDA's center for devices and radiological health.
Lewis said he does not intend the study "to scare patients away from the dental office," because "patients are more likely to get serious and even fatal infections from lack of routine dental care than they ever would from cross infection with something like the AIDS virus." Nevertheless, he said, "we don't want to overlook this risk."