Case Study: What is the real risk of dental treatments spreading COVID-19?

During the COVID-19 pandemic, dental practices across the world closed down for months. There was a concern that dental procedures would generate aerosols, transferring tiny virus particles from the mouth into the air. Yet there was not any rigorous research on this matter to back up this theory. As a result, Professor Emad Moeendarbary and Professor Ian Eames – experts in biomedical engineering and fluid mechanics – collaborated with a team of dentists at the UCL Eastman Dental Institute.

The main purpose of this research was to analyse flow physics during dental procedures and to understand the interaction between dental instruments, biomaterials and biofluids within the mouth. To evaluate the risk of infection spread associated with dental drilling, they also studied biofluid films. The biofluid film is the layer of saliva in the mouth that can contain viruses or bacteria. In particular, they investigated whether and how the potentially infectious biofluid film is actually dispersed via dental instruments and procedures. This research was supported by the UCL COVID-19 Rapid Response Fund.

Mechanical engineers collaborating with dentists

The UCL Mechanical Engineering team started the project by visiting a team of dentists led by Dr Jeanie Suvan and Professor Francesco D'Aiuto working at the UCL Eastman Dental Institute, to gain an understanding of the dental tools, procedures and general dentistry environment. Based on this, they designed a series of lab experiments, using dye, high-speed cameras (that can capture photos hundreds of times faster than smartphone cameras) and a 1,000-watt projector to illuminate the trajectory of the aerosols, which were a mixture of water and saliva.

The team also used mannequins with false teeth to try to understand what happens when a dental instrument makes contact with teeth. “It doesn’t do what you would think,” says Professor Eames. “There are a lot of different elements of physics at play that need to be unpicked. When physical contact is made between the tip of a dental instrument and the teeth, the resulting aerosols don’t just go into the air and flow; they move along surfaces and other things in a room. It was a shock because it told us that a lot of the studies that have been performed in the past didn’t take account of what actually happens when contact is made.”

Low-risk procedures for spreading disease

Although the research confirmed that aerosols do travel outside the mouth when dental instruments are used, the type of aerosol that is released in dental procedures is actually unlikely to carry diseases such as COVID-19. “The question is not what is in the air, but the question is, where does it come from?” Professor Eames explains. “The risk of infection being spread through dental treatments is small. The risk is not the one that was described early on in the pandemic.”

The risk of disease being carried from the mouth and infecting other people rests in the biofluid film. As well as containing COVID-19 when someone is infected, biofluid film can also carry diseases such as Mycobacterium tuberculosis and Herpes simplex. But the measures dentists have been using for decades to clean the mouth – such as mouthwash before a procedure, the use of water to flush the teeth and suction to constantly remove excess fluid from the mouth – are actually largely removing the potentially infectious biofluid film.

When the usual procedures are used, including mouthwash and flushing, the majority of fluid that comes from the mouth during dental procedures are these other fluids and not the biofluid film. “We showed that changing the viscosity of the fluid is important,” says Professor Eames. “Using pre-mouthwash that has antiviral properties could even limit the risk of disease spread to zero.”

"I think the policy needs to be changed," says Professor Moeendarbary. “If there’s another pandemic, or something else happens, policy for dental procedures needs to reflect evidence-based research such as this.”

As a result of this research, the team has been awarded further funding from the Engineering and Physical Sciences Research Council (EPSRC), so they can continue related research activities.