For instance, information is limited on how best to manage air flow and filtration in dental settings to mitigate risk.
"All we can say is that air flow control can help play a role, and even for that, we don't have any concrete evidence," said Dr. Purnima Kumar, Ph.D., professor of periodontology at Ohio State University, who participated in an American Dental Association webinar on aerosol and the transmission of coronavirus. "We only have evidence from medicine, where infectious disease units and isolation rooms have air flow controls based on principles of laminar flow. That's all the evidence we have right now, so everything else at this point is conjecture."
The Centers for Disease Control and Prevention suggests dentists consider using a portable air filter that meets the high-efficiency particulate air standard while performing aerosol-generating procedures and immediately afterwards. In its Interim Infection Prevention and Control Guidance for Dental Settings During the COVID-19 Response, updated May 19, the CDC states using a filter will reduce the particle count in the room, including droplets, as well as the air turnover time provided by the building HVAC system alone.
There are additional factors dentists need to consider when using air filters, however. These include the direction of the air flow in their operatories and the capacity of the filters, Dr. Kumar told the ADA News.
Ideally, air would flow from a vent behind the head of the patient, where aerosols are produced, down to a filter at the patient's feet, with dentists and their staff on either side of the patient so they don't come between the aerosol and the filter, she said. That is easier said than done, however, because in some operatories, air may be flowing from a vent on the ceiling or from other sources, such as windows.
Also, while some practices may have portable filters dentists can place in different parts of the operatory, others may have filters that are part of their ventilation system. Comparing the two is hard to do because both come with their own specifications, Dr. Kumar said. While portable filters allow dentists to control their placement, their capacity may not be as large as the ones that are built into the ventilation system.
"It's doing the math of your room size versus the system capacity," she said.
Regarding how effective they are at trapping the coronavirus, filters that meet the high-efficiency particulate air standard have a 95% chance of trapping particles that are 0.3 microns or greater, Dr. Kumar said. The virus is 0.06 to 0.14 microns in size, but as long as it is traveling on a large enough particle in the aerosol, it would be caught by the filter.
Another array of products dentists may be considering to help sanitize the air in their practices are ultraviolet lights with wavelengths between 200 and 280 nanometers, known as UVC lights. The CDC states dentists may consider using upper-room ultraviolet germicidal irradiation as an adjunct to higher ventilation and air cleaning rates.
While UVC lights are germicidal, many factors can impact their effectiveness, including the amount of organic matter in the air, the intensity and wavelength of the light, the type of suspension generated by the procedure that is performed, the ambient temperature in the room, the microorganism to be killed, the distance between the light and target and the cleanliness of the light tube, Dr. Kumar said during the ADA webinar.
Safety is another consideration.
"There are still questions regarding what is a safe wavelength for human exposure," she told the ADA News.
When it comes to suction devices, the ADA states in its Return to Work Interim Guidance Toolkit that dentists should use high-velocity evacuation whenever possible. Dr. Kumar also advises that dentists reduce aerosols at the source, but information about potential issues or best practices when using high-volume evacuators and extra-oral vacuum aspirators is limited.
"The work to generate the evidence has not been done, so those would be entirely reliant on what the manufacturers have done for product safety and product efficacy," she said. "Yes, we know that high-volume evacuators can reduce aerosols by anything up to 93% and they have to be close to the instrument source, and that’s all we know at this point."
When using suction devices, dentists should hold high-volume evacuators about 2-5 inches from the instrument being used in the procedure and place extra-oral vacuum aspirators 6-12 inches from the patient, Dr. Kumar said during the webinar.
Suction devices also require regular maintenance, she told the ADA News.
"Everyday cleaning, routine maintenance after each procedure is important," Dr. Kumar said. "The tubing has to be clear, and the filters have to be clear."
Overall, research on dental aerosols is lacking. No studies have identified viruses in dental aerosols because researchers weren’t looking for them, she said during the webinar.
"When we look at dental aerosols, at this point, there’s nothing that we can nail down and say that this virus or salivary organisms spread through dental aerosols, but again, absence of evidence is not evidence of absence, and therefore, use precautionary prevention protocols," Dr. Kumar said.
For all of the ADA's resources on COVID-19, visit the Coronavirus (COVID-19) Resource Center for Dentists.