If you’ve been keeping up with COVID-19 news, there’s a good chance you’ve heard the words “aerosol” and “droplet,” but can’t distinguish between the two. Aerosols are small liquid particles that stay suspended in the air for at least a few hours and, when inhaled, are considered to be a cause of airborne transmission. Droplets, on the other hand, are larger liquid particles which fall through the air and land on surfaces and are considered to be the main culprit in spreading disease. The true distinction between aerosol and droplet lies in size; although there’s contention about the exact cutoff, the scientific community generally agrees that anything under 50 microns (μm) is referred to as an aerosol and anything larger is a droplet.

The facts show that the majority of Covid-19 cases are transmitted when humans come in contact with these droplets on surfaces, often referred to as “contact spreading”. It’s posited that aerosols are less feasible routes of transmission because their small size allows them to evaporate out of the air more quickly. In “contact spreading”, on the other hand, someone touches a fallen droplet on a contaminated surface, and then introduces the particles into their body by touching a point of entry. Keep in mind, we touch our eyes, nose or mouth an average of 20 times per hour.

So, what determines if we get infected from an aerosol or droplet? The answer lies in its viral load, or the quantity of viral particles in a given volume of fluid. If a viral load contains higher than an infectious dose, the amount of virus needed to establish an infection, exposure might mean infection. However, not all aerosols and droplets contain a sufficient viral load for COVID-19 transmission.

Now that we’re familiar with some of the Covid-19 terminology, it’s important to understand the kinds of aerosols and droplets that normal respiratory activity generates. As you’ll see in the table below, the biggest spreader of droplets, and therefore the biggest threat of transmission, is sneezing and coughing.

Table: Normal respiratory activities and their respective aerosol generation, (Morawska, 2006)

Depending on our immune response, the droplets we’re exposed to, and their viral loads, we are always at risk of infection from surface contamination transmission. Not touching your face and washing your hands according to CDC guidelines are crucial behaviors that can protect your health. Whether you think you are exposed or want to take proactive action, oral care is an amazing place to start. Adding one of two practices: (1) sodium chloride spray or (2) hydrogen peroxide rinse into your daily routine twice a day can potentially reduce the amount of Covid-19 in the mouth. If you’re looking for a new hydrogen peroxide rinse, we suggest asking your dentist for ECO Balance Gum Health Treatment.

So what does this mean for the dental practice? In dentistry, we perform Aerosol Generating Procedures (AGPs) from a hand piece or an ultrasonic, producing a water spray that you can sometimes see in the air. However, the spray generated from AGP’s is NOT the same as an aerosol from a sneeze or a cough. This is because, as your dental hygienist works through your oral cavity, whatever bacteria or virus that exists in your mouth is being diluted by water. As a result, the spray that comes out holds only a small percentage of the actual viral and bacterial contents of your mouth. 

In addition, from research over the last 30 years, we’ve learned that the high volume evacuation we use in the dental office reduces the production of dental aerosols by 90% on average. To note, most hospitals don’t even have suction that is rated as high volume (Harrel). Since the emergence of Covid-19, we’ve adopted the use of rubber dams, which have already been shown to lower transmission of the disease another 7% on top of the high volume evacuation efficiency. (Peng, X, Xi. X. Li). 

If you are in the office and we put on this rubber dam that protects the patient and our dental team, this is the rationale to spend the extra minute to place it in the mouth.

Between viral load dilution and barrier control, the dentists and hygienists on our team are the most equipped people to treat you during this time. In fact, our dental colleagues in Wuhan, China, Canada, and the EU, give us reason to believe that we can all reopen with a goal of “minimal to zero risk.” From the department of Stomatology in Wuhan, out of 1857 oral health professionals, only .47% of the dentists wearing only basic PPE contracted Covid-19 (Meng et al.). With experienced barrier control to elevated PPE (N-95 masks, face shields, disposable gowns and booties) plus improved air filtration and purification options, there is close to zero chance that our dental teams can come down with Covid-19. 

We are really good at barrier control in dentistry as we have been practicing these safety methods since the AIDS crisis, for the last 30 years.  Today, with Covid-19, we are raising our level of infection control creating the safest environment in all of healthcare with higher PPE standards, air purification, and scheduling that creates a safe haven for everyone. I am very proud of my profession as we reopen our doors  and have chosen to reinvent what we do to a higher standard for our patients with a greater degree of wellness and oral health is a great place to start.

References:

Harrel SK, Molinari J. Aerosols and splatter in dentistry: a brief review of the literature and infection control implications. J Am Dent Assoc. 2004;135(4):429‐437. doi:10.14219/jada.archive.2004.0207

Meng, L et al. “Coronavirus Disease 2019 (COVID-19): Emerging and Future Challenges for Dental and Oral Medicine.” Journal of dental research vol. 99,5 (2020): 481-487. doi:10.1177/0022034520914246

Morawska L. Droplet fate in indoor environments, or can we prevent the spread of infection?. Indoor Air. 2006;16(5):335‐347. doi:10.1111/j.1600-0668.2006.00432.x

Peng, X., Xu, X., Li, Y. et al. Transmission routes of 2019-nCoV and controls in dental practice. Int J Oral Sci 12, 9 (2020). https://doi.org/10.1038/s41368-020-0075-9

Tang J.W Et al. Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises. Journal of Hospital Infection. Journal of Hospital Infection, 2006. 64(2): p. 100-14

Wilson, N.M. et al. Airborne transmission of severe acute respiratory syndrome coronavirus-2 to healthcare workers: a narrative review. Anaesthesia.