Two points must be emphasized, rarely put forward in the protocols currently in circulation: 

• the simplest method of considerably reducing the risk of cross-contamination, as taught in all good dental schools, is to increase the average duration of appointments: if this average duration is doubled, the risk of cross-contamination of patients and dental staff are cut in half.
  At the same time, the negative financial impact of time-consuming cleaning / disinfection procedures is also reduced by two;
• the second point concerns dental aerosols. On the one hand, SARS-CoV-2 is a respiratory virus, very different from the viruses that we are used to managing, such as HIV, hepatitis B and C This means that, for cross-contamination to occur, the virus does not need to enter a wound; simple airborne transmission is possible, just like with viruses that cause colds (nasopharyngitis) or flu. 

But with potentially much more serious consequences. 

For the German Hospital Hygiene Association, coughing, singing or simply speaking are the main sources of viral spread. This suspicion is confirmed by a letter from the American National Academy of Science to the White House suggesting that the coronavirus may remain in the mist formed during respiration. 

In addition, soil contaminated by patients in Chinese hospitals may be the source of new aerosols due to cleaning or staff movement. 

In an article in the New England Journal of Medicine (March 2020), the virus was found to be viable in experimental aerosols for several hours. The same document describes the survival of the virus up to 3 days on hard surfaces, such as metal or plastic. 

U-VCs 

The human eye is able to visualize light with a wavelength between 780nm, or red light, and 400nm, or purple light. At lower wavelengths, we will speak of ultraviolet up to 100nm, and still below, we will speak of X-rays. 

Ultraviolet light is itself divided into 4 categories, type A (UV-A), type B (UV-B), type C (UV-C) and finally extreme ultraviolet (VUV or Vacuum UV in English). Part of this UV, and more particularly UV-C and even more specifically, UV-C with a wavelength of 254nm, will be efficiently absorbed by DNA and will lead to its damage, even destruction. This mechanism supports the biocidal effect of UV. 

To emit UV-C radiation, there are essentially two technologies since LEDs capable of emitting this type of radiation do not yet offer attractive yields. Both of these technologies are based on the ionization of mercury vapors at medium or low pressure. The UV spectrum emitted by these two technologies varies greatly. For medium pressure lamps, the spectrum is narrow and almost entirely in the UV-C spectrum and centered on 254 nm. For medium pressure lamps, the spectrum covers a wider wavelength range from UV-C to UV-A. 

The very numerous studies on adenoviruses have shown that to reach 99.99% disinfection, the UV doses required vary between 803 and 2004 mJ / cm2. An extrapolation from the study by Walker & amp; Ko would suggest that a dose of 20 to 30 mJ / cm2 could allow such an efficient abatement for a coronavirus. 

The table on the left shows two references of the doses required to degrade from 90 (1 log) to 99.99% (4 log) of 3 single-stranded RNA viruses with positive polarity. This table is extracted from the synthesis database of the international association of Ultraviolets 

Malayeri A.H., Mohseni M., Cairns B. and Bolton J.R. (2016). Fluence (UV dose) required to achieve incremental Log inactivation of bacteria, protozoa, viruses and algae. www.iuva.org 

Walker C.M. and Ko G. (2007). Effect of Ultraviolet germicidal irradiation on viral aerosols. About. Sci. Technol. 41, 5460-5465.