A study by researchers at Imperial College London and King’s College London measured and analysed the generation of aerosols during dental procedures. (Image: Imperial College London/King’s College London)
Researchers suggest slower drill rotation to make dental practices safer in pandemic
LONDON, UK: Dental procedures were flagged early on in the SARS-CoV-2 pandemic as posing a high risk for the spread of the virus. The strict infection control measures in place at dental clinics have helped to prevent the spread of the virus in dental settings; however, researchers from Imperial College London and King’s College London have found that careful selection and operation of dental drills could lower the risk of transmission even further.
Researchers at the universities measured and analysed the generation of aerosols during dental procedures and suggested changes in the use of dental drills in order to prevent transmission of SARS-CoV-2 and contamination in dental clinics.
According to a joint press release, the suggestions include carefully selecting and controlling the rotation speeds of drills that only use water as a coolant, and avoiding the use of dental drills that use a mixture of water and air as abrasion coolants. The study identified parameters that would allow dental procedures such as tooth reconstructions to be carried out with 60 times fewer aerosol droplets being produced.
The researchers found that using air turbine drill types—the most common type of dental drill—creates dense clouds of aerosol droplets that spread as fast as 12 m/s and can quickly contaminate an entire treatment room. Just 1 ml of saliva from infected patients contains up to 120 million copies of the virus, each having the capacity to infect.
Images of “the spray formed by an air turbine unobstructed running in a steady state (A), the probability distribution of the spray droplet concentration based on >2000 images (B) and its standard deviation (C). For interpretation in (B) pixels that are red indicated a 100% chance of encountering a droplet at any point in time, pixels that are black 0%. In (C) standard deviation is plotted on an equivalent scale.” (Image: Imperial College London/King’s College London)
They tested a high-torque electric micromotor drill both with and without the use of water and air streams. They found that using this type of drill without air streams at speeds lower than 100,000 rpm produced 60 times fewer droplets than air turbine drill types did. In addition to factors such as the positioning of the patient and the presence of ventilation systems, they found that the type of cutting instrument and the amount and type of cooling water being used affected the spread of aerosol concentration in treatment rooms.
The researchers pointed out that the fallow time required between dental treatments limits patient access and commented that the study could help dentists to understand how to reduce the amount of aerosol that is being generated, potentially allowing them to treat more patients.
“This important work describes the basic mechanisms that lead to the features of dental aerosols that we currently consider to be high risk,” Prof. Owen Addison of King’s College London’s Faculty of Dentistry, Oral and Craniofacial Sciences, co-author of the study, was quoted as saying. “This has enabled us to choose drill parameters to keep our patients and the dental team safe at this difficult time. Although we cannot provide every procedure, because slowing our drills is much less efficient, we now have the basis to do more than we have done in the last six months.”
Addison added: “Because of the COVID-19 pandemic, dentistry has become a high-risk practice—but the need for treatments hasn’t gone away. Our suggestions could help begin to open up dentistry to patients once again.”
The study, titled “Mechanisms of atomization from rotary dental instruments and its mitigation”, was published online on 16 December 2020 in the Journal of Dental Research, ahead of inclusion in an issue. Suggestions made by the researchers were included in the evidence appraisal document Rapid Review of Aerosol Generating Procedures in Dentistry, published on 25 September 2020 by the Scottish Dental Clinical Effectiveness Programme.