Dental aerosols, mixed with bioaerosols, pose a risk of transmission of SARS-CoV-2 among dental workers and patients. The size of a single COVID-19 virus is 70–90 nm , however, the virus does not exist individually but in droplets of > 0.3 µm. Several critical questions need to be addressed: first, how long does aerosol remain in the dental operatory? Studies showed that dental aerosol remains in the operatory 30 min after the dental procedure . Second, how long does SARS-CoV-2 remain vital in aerosol after the dental procedure is completed? A study demonstrated it remains vital in aerosols for at least 3 h, and it was more stable on plastic and stainless steel surfaces than copper and cardboard surfaces . Therefore, the disinfection of the dental operatories, cabinets, and floors must be conducted within several minutes following the completion of dental procedures for each patient. Third, how far does aerosol spread in the dental operatory? Harrel et al. found that an ultrasonic scaler produced aerosols that transmit at least 18 inches from the operative site . Another study found that the maximum contamination was seen in 2 feet away and 1foot above from the site of operation . Fourth, since aerosols may spread to different locations in the dental operatory with different concentrations, it would be interesting to detect the difference among these locations and assess which location(s) exhibit higher concentration of aerosol. In present study, we focused on the fourth question. Veena et al. reported that maximum contamination was found on the right arm of the dentist and left arm of the assistant, in addition to the head, chest and inner surface of the face mask of the dentist and of the assistant . To control dental aerosols, the American Dental Association (ADA) recommended using SE + HSS as a standard in the dental operatory. The present study found SE + HSS had a significant role in the control of aerosol spreading. Only the chest area of the dentist had an elevated level of aerosol, and other 3 locations (3′ above the patient center, 3′ above the patient right and chest of the patient) had slightly elevated levels. Our results support the use of SE + HSS in the dental operatory as recommended by the ADA.
Although several studies intended to assess the dissemination of aerosol by measuring bacterial contamination in the dental operatory [9, 17, 18], only a handful of studies directly measured the aerosol’s dissemination [19,20,21]. However, these studies either measured the aerosol level in the whole area of dental office which includes multiple dental chairs/operatories, or measured the generation of aerosols in a long period of time (ranged from a day to a week) [20, 21]. In addition, some studies used manikin or extracted teeth instead of patients [12, 19], which failed to simulate dental aerosols that contains a mixture of patient’s saliva and fluid with compressed air and water. To the best of our knowledge, there is no published quantitative evidence on the distribution of size and concentration of aerosols in an individual dental operatory during a specific dental procedure. In the present study, the dentist, assistant, and patient were all positioned in the clinic dental operatory, and the aerosols were tracked and captured in real time while the mock dental procedures were performed. The aerosols were measured by three meters to capture various mass and particle concentrations. This is the first study providing evidence on the generation of different sizes of dental aerosol during a dental procedure.
The highest level of aerosol was found in a triangle area between the chest area of the dentist, of the dental assistant, and of the patient. Current protocol of engineering control, using advanced personal protective equipment (PPE) such as the surgical gown, N95 mask or level 3 surgical mask, eye goggles, face shield, head cover and shoe cover, play a critical role to prevent the spread of pathogenic microorganisms from this area. Dental personnel should strictly follow current guidelines to protect themselves and patients from potential disease transmission. This study also showed that extraoral suction system HVS, as a supplement to SE + HSS, was an effective way to further control of aerosols. HSH + SE + HSS generated the highest level of aerosol in the chest area of the dentist, and HVS was able to reduce it to the baseline level. It was interesting to note that the assistant side had a relatively lower level of aerosol than the dentist's side. This may be due to the fact that both HSS and HVS was approached to patient from the assistant side, and the tilted angle of HSS tip and HVS suction mouth led to a slightly different power of suction.
In the US + SE + HSS group, using HVS increased aerosol at the patient chest area. This was possibly due to the fact that the HVS suction hood was placed further away from the patient’s mouth (more than 4 inches) when this location was measured. The HVS by itself can be a multiplier of aerosol as measured. Exhaust suction provided added velocity to the aerosol stream, and any deflection by the HVS (moved further away from patient mouth) can jettison this stream downward to the patients’ chest area.
Three limitations of the present studies are: (1) when the HSH was used, the bur did not cut the teeth. In clinical scenario, cutting teeth with rotating bur at 400,00 rpm will generate more aerosols. However, compared previous studies that only used a manikin or extracted teeth, the advantage of the present study using a volunteer patient is that we measured the aerosols generated from the human oral cavity, which contains a mixture of patient’s saliva and fluid with compressed air and water. We believe it is a better simulation than those that used a manikin. (2) the present study only measured the aerosol with size smaller than 10 µm. In fact, the aerosol with particle size larger than 10 µm and the splatters (> 50 µm) also contribute to the disease transmission. (3) it is a proof-of-concept study with only 1 volunteer patient. We plan to perform future study with more real patients with actual dental procedures, and measure aerosols with a wider range of particle size.
Finally, to the best of our knowledge, there is no report about COVID-19 infection among dental workers in the dental office since the pandemic started, and most of the transmissions occur due to community interactions and not in institutions following PPE standards. The results of the present study indicated that with SE + HSS, aerosols with size smaller than 10 µm generated in the dental operatory were only at a slightly elevated level compared to baseline, this could partially contribute to the fact that the lack of report about COVID-19 infection among dental workers in a dental office who are strictly following guideline and donning PPE. However, the importance of infection control protocols should not be diminished. In addition to the upgraded PPE, the CDC guidance for dental settings includes preprocedural mouth rinses, and wiping patient’s nostrils and mouth areas with alcohol gauze before dental procedures. Some aerosol generating procedures such as endodontic treatment requires placing an additional rubber dam barrier. The strict compliance with these guidelines will help effectively control aerosol in dental settings. The present study has found that aerosol (with size smaller than 10 µm) generation was minimal for dental procedures relative to the baseline readings. Using the ES + HSS with HVS further reduced aerosol in the dental operatory. This study increases the understanding of the significance of aerosol transmission in the dental operatory and eases the unnecessary levels of anxiety in daily dental practice.