It is now a question of drawing up and implementing protocols that are effective in protecting doctors and medical staff, but also in preventing cross-contamination and consequent infection of patients, once they will be allowed to reopen practices.
We do not think it is useful to focus here on the general and consensual measures in the waiting room (social distance, 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...).
Rather, we would like to highlight two points that are rarely mentioned in the protocols currently in circulation:
- The simplest 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 that 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 flu. But with potentially much more serious consequences.
For the German Hospital Hygiene Association, coughing, singing or simply talking are the main sources of virus spread. This suspicion is confirmed by a letter from the American National Academy of Science to the White House, which suggests that the coronavirus could remain in the mist formed during breathing.
Furthermore, the 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 is viable for several hours in experimental aerosols. The same paper describes the survival of the virus for up to 3 days on hard 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, and 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 obviously 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 the use of ultrasonic scalers, air/water spraying and 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 a very special situation: Not only does the patient is obviously not wearing 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 a behaviour 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 metres.
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 ( https://www.youtube.com/watch?v=LLzMDvzWeV8&feature=youtu.be ) on these microdroplet clouds shows that they remain suspended for long periods of time 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 cloud of micro-droplets 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:
1. Reduction of the risk of cross-contamination by aerosols
2. Reduction of aerosol formation/contamination during treatment
Aerosols are only produced during treatments with ultrasonic scalers, air/water spraying or air/water-cooled rotating instruments. Manual scaling/root gouging, tooth extraction, implant placement, for example, are less at risk. It has been shown (Kampf et al., 2020) that hydrogen peroxide (H2O2) with 0.5% for 1 minute effectively kills the virus, as does poviodone-iodine. A mouth rinse with a 1% solution of H2O2 for 1 minute or with isobetadine can therefore be recommended before the start of a dental procedure.
Note that chlorhexidine has little or no effect on the 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 are effective in reducing the virucidal load in the air (SARS-CoV-2 has a size of 0.1 µm, but since it is carried by micro-droplets, it is effectively stopped by HEPA filters with a pore diameter of 0.3 µm), but 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 in decontaminating the atmosphere. Several articles (see below) have shown that UV in sufficient doses is very effective in destroying the RNA of viruses, including corona viruses.
UV-FAN Air and Surface DisinfectionNote 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 is capable of decontaminating surfaces (lighting system, surgical unit, radio, equipment rack, instrument whips...) and the floor!
Decontaminate surfaces/floors with Hydrogen peroxide + colloidal silver spray (Nocospray) can be effective in disinfecting surfaces, but :
- it does not decontaminate the air;
- 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 for daily disinfection,
> 60 minutes for a curative treatment (i.e. after the last aerosol)!
- The staff cannot stay in the room.
Therefore, this system does not seem to be 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 manpower. However, it can be carried out while the ventilation decontamination systems are in operation.
- 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, aldehydes... the most commonly used surface disinfectants will be effective. The instructions for use of the product used should be followed.
Sterilizing air and surfaces
At present, the only method for decontaminating or even sterilizing air and surfaces (including soil) appears to be direct exposure to UV light.
This is the method of choice, if available, for the disinfection of hospital rooms according to Covid patients and of public transport. It can be combined with continuously ventilated decontamination systems. There is ample evidence that UV irradiation is effective in denaturing coronavirus RNA.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), with the exception of some UV robots at a very high price. If UV devices designed for dental practices are available at an affordable price, they could become the benchmark for the fastest (5-10 minutes) complete decontamination (air/surface/floor) of the operating room after aerosol formation.
Additional points on safety
- Air Compressors: Practitioners should check whether their 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.
- Suction systems: 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!
- When the air is discharged to the outside: OK.
- If the air inside the building is blown out Either 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.
If air is sucked in (negative pressure) and expelled to the outside, this is fine.
When positive pressure is applied, the air is usually expelled from the dental office into the common rooms.
This can mean that the dental aerosol is distributed in the practice.
- Practice architecture: This can lead to very difficult or even impossible problems. For example, an open architecture without physical separation of the individual offices allows infectious dental aerosols from one dental chair to enter the entire open structure. This is sometimes the case in modern dental practices, where solutions can be found on a case-by-case basis. This is even more common in some dental clinics or hospitals, where several dental chairs are sometimes grouped in open spaces. Controlling the flow of the microdroplet clouds seems impossible in these open areas.
The continuation of dental treatment is such that large open spaces should be discussed or questioned during the current Covid 19 pandemic.
- Par Eric Rompen , Souheil Salem , Publié le 24.04.2020. Paru dans L'Information Dentaire
- https://www.information-dentaire.fr/actualites/covid-19-et-gestion-des-arosols-dans-les-cabinets-dentaires/