Dental procedures present a potential for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission due to the extensive generation of droplets and aerosols during the use of power-driven instruments.

Researchers at the University of Ljubljana have demonstrated how a virus can spread by droplets during ultrasonic scaler (USS) operation and how this spread can be mitigated by merely substituting the irrigant with clinical virucidal agents, namely sodium hypochlorite and EOW (Electrolyzed Oxidizing Water). The study is currently available on the bioRxiv* preprint server.

Background

Dental procedures are a potential way of infection transmission. Power-driven instruments, such as ultrasonic scaler (USS), high-speed rotary instruments, and air-and-water syringes, generate extensive droplets and aerosol. It is reported that contamination occurs up to 3 meters from the patient's mouth.

This contamination is generally reduced by way of mouth-rinsing before the procedure or using povidone-iodine and chlorhexidine gluconate as an ultrasonic liquid compared with distilled water.

During the COVID-19 (coronavirus disease 2019) pandemic, caused by SARS-CoV-2, the focus of dental procedure-associated transmission has rapidly changed from bacteria to viruses. However, to date, there is no research on virus transmissions associated with dental procedures.

The study

The researchers developed an experimental model to study virus transmission during the USS instrumentation and examined the prevention of spreading by replacing the coolant with an antiviral agent. The researchers observed that the virus was transmitted mainly by droplets and up to the distance of 45 cm by USS activity. The tests with aerosol produced inconclusive results.

This study used the Equine Arteritis Virus (EAV) – a non-human viral pathogen resembling SARS CoV-2 in structure and genome. EAV is an animal pathogen, species-restricted to Equidae members. EAV is an enveloped virus with a single-stranded, positive-sense RNA genome and is transmitted in aerosols through the respiratory route.

The researchers designed an experimental setup to demonstrate the EAV spread by USS action. It is well established that the contaminants during the operation settle primarily on the operator's dominant arm, eyewear, and chest of the patient. It was observed to a lesser extent on the nondominant arm and chest of the operator and assistant. Likewise, the EAV predominantly spread via larger droplets (splatter) that reached the immediate surrounding area on the plates up to the distance of 45 cm from the USS tip.

"To the best of our knowledge, this is the first proof of the contribution of a USS action to the spread of the virus via droplets to the environment."

While the researchers were able to detect the EAV in low concentrations in the air sample, they did not achieve a reproducible collection of the infectious virus from the air-sampler.

This is consistent with reports from hospital settings where the air samples tested positive for SARS-CoV-2 RNA and the viable virus in small percentages (17.4% and 8.6%, respectively). The researchers attribute the reason to this: 1) by calculating the virus concentration per aerosol, which was a small fraction of particles harboring a virus, and 2) by explaining possible virion damage during sampling.

To prevent the droplet spread of the virus to the surroundings, the researchers changed the saline coolant with EOW or hypochlorite. They noted that both the virus inactivation and absence of cytotoxicity were achieved at 0.25% hypochlorite.

The researchers looked for a specific cytopathic effect (CPE) – with the cells rounding and degeneration of the cell monolayer occurring. In the control, where they used saline, they observed the virus infection even at a greater distance from the tip.

Compared to the practical results from using the hypochlorite, the researchers observed that EOW produced no cytotoxicity and no infection at all. The researchers claim that this is the first study that has clearly shown the possibility of disinfecting the virus in droplets generated by USS by replacing inert coolant with antiseptic irrigant.

Significance

Because the SARS-CoV-2 is present in the saliva, gingival crevicular fluid, nasopharyngeal, oropharyngeal and bronchial excretions, the dental procedures represent a high risk of SARS CoV-2 virus transmission. Here, the researchers present the first dental procedure virus transmission study, performed with a viable virus evaluation.

Importantly, this study shows that the virus droplet transmission could be prevented by a simple saline replacement with a virucidal agent that has already been tested as mouth-rinse for home oral care.

This study has shown EOW as an effective virucidal tool in dental procedures in a huge leap for disinfection in dental settings during this pandemic. The approach addresses both direct and indirect contamination of surfaces – effectively preventing transmission of the virus.

*Important Notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Dr. Ramya Dwivedi

Ramya has a Ph.D. in Biotechnology from the National Chemical Laboratories (CSIR-NCL), in Pune. Her work consisted of functionalizing nanoparticles with different molecules of biological interest, studying the reaction system and establishing useful applications.