SARS-CoV-2 spreads mainly through respiratory droplets, and dental procedures are known to produce an abundance of aerosols - leading to fears that flying saliva during a cleaning or a restorative procedure could make the dentist's chair a high-transmission location.
Ohio State University researchers set out to determine whether saliva is the main source of the spray, collecting samples from personnel, equipment and other surfaces reached by aerosols during a range of dental procedures.
By analyzing the genetic makeup of the organisms detected in those samples, the researchers determined that watery solution from irrigation tools, not saliva, was the main source of any bacteria or viruses present in the spatter and spurts from patients' mouths.
Even when low levels of the SARS-CoV-2 virus were detected in the saliva of asymptomatic patients, the aerosols generated during their procedures showed no signs of the coronavirus. In essence, from a microbial standpoint, the contents of the spray mirrored what was in the office environment.
"Getting your teeth cleaned does not increase your risk for COVID-19 infection any more than drinking a glass of water from the dentist's office does," said lead author Purnima Kumar, professor of periodontology at Ohio State.
"These findings should help us open up our practices, make ourselves feel safe about our environment and, for patients, get their oral and dental problems treated - there is so much evidence emerging that if you have poor oral health, you are more susceptible to COVID," Kumar said.
The study was published Wednesday, May 12, in the Journal of Dental Research.
Previous research has shown that dental-procedure aerosols tend to land on providers' faces and the patient's chest, and can travel as far as 11 feet. But the studies, catching the spray in petri dishes placed on people, equipment and around the room, found only that bacteria existed - they rarely identified the organisms and never determined where they came from. Saliva has been the presumptive source for a long time.
When saliva was considered potentially deadly at the start of the pandemic, Kumar decided a long-term answer was needed to settle the question of whether saliva is the source of dental aerosols.
For the study, the team enrolled 28 patients receiving dental implants and restorations using high-speed drills or ultrasonic scaling procedures in Ohio State's College of Dentistry between May 4 and July 10, 2020. Researchers collected samples of saliva and irrigant (the water-based cleaning solutions used to flush out the mouth) before each procedure and, 30 minutes after the procedure, aerosol remnants - condensate - from providers' face shields, the patient's bib and an area 6 feet away from the chair.
Kumar and colleagues then put genome sequencing technology to use that wasn't available in the petri-dish days. This allowed them to first characterize the microbial mix in pre-procedure saliva and irrigants, which they could then compare to organisms in the aerosol samples collected later.
With the analytical method they used, the researchers did not need to characterize the microbes - they instead looked for variations in sequences that provided enough information to identify the family of bacteria or viruses to which they belonged.
"Some species that live in your mouth can closely resemble those in water and the environment. Using this method, we don't even have to know the names of these organisms - you can tell whether they are exactly genetically identical or genetically different," Kumar said. "If you use this granular approach to see these very nuanced differences in the genetic code, you can very accurately identify where they're coming from."
No matter the procedure or where the condensate had landed, microbes from irrigants contributed to about 78% of the organisms in aerosols while saliva, if present, accounted for 0.1% to 1.2% of the microbes distributed around the room.
Salivary bacteria were detected in condensate from only eight cases and of those, five patients had not used a pre-procedural mouth rinse. The SARS-CoV-2 virus was identified in the saliva of 19 patients, but was undetectable in aerosols in any of the cases.
The findings are reassuring, but also make sense, Kumar said: Irrigant dilutes saliva - a "thick, viscous" substance - by an estimated 20- to 200-fold, and the research is validated by a 2020 study that reported a less than 1% COVID-19 positivity rate among dentists.
Kumar noted that dentistry has long been at the forefront of infection-control practices in health care. During the pandemic, new protocols have included strengthened ventilation systems, extra aerosol suction equipment, N95 masks and face shields on top of goggles, and extended downtime between patients. She is hopeful this study's findings will make practitioners and patients feel at ease about being in the dentist's office - with continued stringent protection in place.
"Dental surgeons and hygienists are always at the forefront of the war against bacteria in the mouth, and they of course did not feel safe because they are front-line workers surrounded by aerosol," said Kumar, who has a periodontology practice of her own and was one of the procedure operators in the study.
"Hopefully this will set their mind at rest because when you do procedures, it is the water from the ultrasonic equipment that's causing bacteria to be there. It's not saliva. So the risk of spreading infection is not high," she said. "However, we should not lose sight of the fact that this virus spreads through aerosol, and speaking, coughing or sneezing in the dental office can still carry a high risk of disease transmission."
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