UV Water Disinfection

UV-C in Healthcare: Reducing the risk of Covid-19 infection in Dental Offices


Throughout the world, the global crisis caused by the spread of SARS-CoV-2 Coronavirus has brought all dental activities outside the emergency sector to a standstill.

It is now a question of drawing up and implementing protocols that protect doctors and medical staff and prevent cross-contamination and consequent infection of patients once they are allowed to reopen practices. We do not think it is helpful to focus here on the general and consensual measures in the waiting room (social distancing, limiting the number of patients, wearing masks, avoiding shaking hands…) and to protect the staff (frequent hand washing/disinfection, FFP2/FFP3 masks and face protection during clinical procedures…).

Instead, we would like to highlight two points that are rarely mentioned in the protocols currently in circulation. The most straightforward way to significantly reduce the risk of cross-contamination, as taught in all good dental schools, is to increase the average time of treatment: if this average time is doubled, the risk of cross-contamination of patients and dental staff is halved. At the same time, the negative financial impact of time-consuming cleaning/disinfection procedures is halved.

The second point concerns dental aerosols. On the one hand, SARS-CoV-2 is a respiratory virus that is very different from the viruses we are used to dealing with, such as HIV, hepatitis B, and C. This means the virus does not need to enter a wound for cross-contamination; simple airborne transmission is possible, as with viruses that cause colds (rhinopharyngitis) or the flu. But with potentially much more severe consequences.For the German Hospital Hygiene Association, coughing, singing, or simply talking are the primary sources of virus spread. This suspicion is confirmed by a letter from the American National Academy of Science to the White House. This letter suggests that Coronavirus could remain in the mist formed during breathing.

Furthermore, soil contaminated by patients in Chinese hospitals could be the source of new aerosols due to cleaning or staff relocation. An article in the New England Journal of Medicine (March 2020) found that the virus was viable for several hours in experimental aerosols. The same paper describes the survival of the virus for up to 3 days on metal surfaces like metal or plastic. Since a high proportion of patients who are positive for SARS-CoV-2 will be symptom-free or with very mild effects, symptomatic patients are infectious a few days before the onset of symptoms and possibly long enough after symptoms have subsided, all patients should be considered potentially infectious. For this reason, the use of masks in the waiting room is recommended for patients and secretarial staff.

Once dental treatment begins, the mask is removed, and the patient may become the source of a cloud of microdroplets. In addition, dentistry is characterized by the generation of very powerful aerosols through ultrasonic scalers, air/water spraying, air/water cooled, or air/water-cooled rotary instruments. The resulting cloud of microdroplets is contaminated with microflora from the patient’s mouth and upper airways. This is an extraordinary situation: Not only does the patient not wear a mask and has a wide open mouth, but his oropharyngeal microflora is strongly scattered outwards by some dental treatments.

It has been shown (Micik et al., 1969; Graetz C et al., 2014) that dental aerosols produce splashes with particles > 50 µm, which exhibit behavior that can be described as “ballistic” and directly contaminate the surfaces facing the patient (equipment carrier, floor) over a distance of 0.5 to 2 meters.

However, dental aerosols also produce a cloud of micro-droplets < 1 µm, which remain suspended in the air and may penetrate directly into the lungs. This microdroplet cloud is highly contaminated with oropharyngeal microflora (Dutil et al., 2009; Hallier et al., 2010; Kobza et al., 2018), and recent studies have shown that SARS-CoV-2 can remain viable for up to 3 hours in comparable aerosols (van Doremalen et al., 2020). 

Recent work on these microdroplet clouds shows that they remain suspended for long periods and can spread over long distances. For dental practices, this means that after generating an aerosol in a Coronavirus-positive patient (often not symptomatic, see above), the ambient air can be potentially infectious for staff and the next patient.

This micro-droplet cloud will gradually settle on all surfaces in the dental office, including the floor. To reduce the risk of cross-contamination, significant measures should therefore be taken to decontaminate the atmosphere and all surfaces before treating the next patient such as reducing the risk of cross-contamination by aerosols and reducing aerosol formation/contamination during treatment. 

Aerosols are only produced during treatments with ultrasonic scalers, air/water spraying, or air/water-cooled rotating instruments. For example, manual scaling/root gouging, tooth extraction, and implant placement are less at risk. It has been shown (Kampf et al., 2020) that hydrogen peroxide (H2O2) at 0.5% for 1 minute effectively kills the virus, as does povidone-iodine. A mouth rinse with 1% H2O2 or betadine can therefore be recommended before dental work begins. Note that chlorhexidine has a negligible or no effect on Coronavirus!

High performance vacuuming during aerosol generation processes can significantly reduce (up to 90%) the power of aerosols but not eliminate them. Caution: Check where the aspirated air is discharged (see below). The use of a rubber dam, when clinically indicated, can increase the strength of the aerosol but reduce microbial contamination. Reduction of air pollution. There are various methods of continuous air disinfection/cleaning:

Ventilation systems with HEPA filters effectively reduce the virucidal load in the air (SARS-CoV-2 has a size of 0.1 µm, but since micro-droplets carry it, it is effectively stopped by HEPA filters with a pore diameter of 0.3 µm). However, the filters themselves can be highly infectious. Ventilation systems that combine filters (ideally HEPA filters) with UV disinfection of the filtered air appear to be most effective at decontaminating the atmosphere. Several articles (see below) have shown that UV in sufficient doses effectively destroys the RNA of viruses, including Coronaviruses.

UV-FAN Air and Surface Disinfection

Note 1: Ventilation systems have no immediate effect and require some time to decontaminate.

All air in a room (15 to 30 minutes) after the last aerosol production, which varies according to the flow rate (m3/h) of the device and the volume of the room (the time required is always longer than the simple calculation of the room volume/flow rate of the device, as clean air is reinjected into the room and mixes with unclean air)

Note 2: No ventilation system can decontaminate surfaces (lighting system, surgical unit, radio, equipment rack, instrument whips…) and the floor!

Decontaminating surfaces/floors with hydrogen peroxide + colloidal silver spray (Nocospray) can be effective at disinfecting surfaces, but it does not decontaminate the air and it cannot be used in connection with air purification systems by ventilation + filter/UV; if the diffusion time is only 3 minutes, the contact time required is 30 minutes per day for cleaning and > 60 minutes for curative treatment (i.e., after the last aerosol)! The staff cannot stay in the room.

Therefore, this system is not easily integrated into a routine protocol to reduce cross-contamination of Covid-19. Manual cleaning and disinfection of all surfaces A strict checklist must be used to ensure that no surface is overlooked. This procedure takes a long time (at least 10 to 15 minutes) and consumes a lot of time. However, it can be carried out while the ventilation and decontamination systems operate. Floors are contaminated with aerosols, and it was suspected that staff movement could stir up infectious particles in the air. They are now rarely (ever?) cleaned between patients.

Since SARS-CoV-2 is sensitive to soap, detergents, ethanol, and aldehydes, the most commonly used surface disinfectants will be effective. The instructions for the use of the product must be followed. The only method for decontaminating or sterilizing air and surfaces (including soil) is direct exposure to UV light. There is ample evidence that UV irradiation is effective at denaturing Coronavirus RNA. This is the method of choice, if available, for the disinfection of hospital rooms according to Covid patients and public transport. It can be combined with continuously ventilated decontamination systems. Unfortunately, our market research has not yet identified any UV sterilization systems that are well-suited for dental practices (the presence of central dental chairs requires at least two UV lamps on each side or a mobile UV unit), except for some UV robots at a very high price. 

Suppose UV devices designed for dental practices are available at an affordable price. In that case, they could become the benchmark for the fastest (5-10 minutes) complete decontamination (air/surface/floor) of the operating room after aerosol formation.

Practitioners should check whether their air compressor is pumping fresh air from outside or room air. In the latter case, a HEPA filter should be fitted to the compressor to prevent contaminated air from entering the dental office. The air sucked in by the high-speed suction system to reduce the spread of potentially infectious aerosols is then discharged by the suction machine elsewhere. Practitioners should, therefore, carefully consider the design of their system.

If the air inside the building is blown out, an air decontamination system (UV ventilation) must be installed in the room where the air is blown out, or a HEPA filter must be attached to the air outlet hose. HVAC (reversible air conditioning) systems: Clinicians should check how the building ventilation system has been set up, as it is known (Li et al., 2007) that micro-droplets of aerosols can be transported through ventilation systems. This is fine if the air is sucked in (negative pressure) and expelled to the outside. When positive pressure is applied, air is typically expelled from the dental office into standard rooms.

Dental aerosols can be distributed in practice in this way.Practice architecture can lead to very difficult or even impossible problems. If the individual dental offices are not physically separated, for instance, infectious bacteria aerosols can spread from one dental chair to another. This is sometimes the case in modern dentistry practices, where solutions can be found on a case-by-case basis. This is even more common in dental clinics or hospitals, where several dental chairs are sometimes grouped in large spaces. Controlling the flow of microdroplet clouds seems impossible in these open areas.

As dental treatment continues, large open spaces should be discussed or questioned during the current Covid 19 pandemic.