COVID-19 and saliva: Risk of direct transmission in Dental H
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Direct contact by respiratory droplets or aerosols is the most widely accepted mode of COVID-19 transmission. The use of rotary or surgical instruments such as handpieces, ultrasonic scalers, or air-water syringes in routine dental practice generates visible spatter and droplets of saliva and blood13. The distance the droplets travel depends on the size with larger droplets tending to settle quickly. Very small droplets (<5 µM) may evaporate, become droplet nuclei or aerosol, and could contribute to the airborne transmission of infections14. The number and size of saliva droplets generated not only vary with the dental procedure but also among people, suggesting heterogeneous transmission potential. Contamination of clinical gowns and inner surfaces of masks worn by dental hygienists with salivary droplets has been reported following ultrasonic cleaning. Although the surgical masks protect the mucous membrane of the mouth and nose from the spatter, they do not provide complete protection from airborne infections.

Positive airborne transmission is dependent on the duration of stability of the infectious agent in aerosols and the susceptibility of the individual in the path of the aerosols. The observed stability of airborne SARS-CoV-1 by RT-PCR and in viable cultures suggests transmission of coronaviruses by short-and long range aerosols15, 16. As of now, little is known about the stability of COVID-19 virus in saliva droplets or aerosols. A study from the University of Nebraska Medical Center demonstrated that the SARS-CoV-2 genome was not only detectable in air samples from rooms of COVID-19 patients, but also in 66.7% of air samples obtained from hallways outside the patients’ rooms. Using the Bayesian regression model van Doremalen et al.16 compared the stability of the COVID-19 virus and SARS-CoV-1 in aerosols. They found that much like the SARS-CoV-1, the COVID-19 virus remained viable in aerosols throughout the 3 hour period of experimental duration. Taken together, these observations substantiate the high risk for direct airborne transmission of the COVID-19 virus to dental healthcare professionals.