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10 June 2020

Which masks do we have to use to prevent the risk of Coronavirus infection?

Lara Figini

In these times, during Coronavirus emergency, there is a lot of talk about masks and what would be the safest for dentists.
First of all, between surgical and respiratory masks FFP2 and FFP3 (N95) (which would seem to be the only ones to guarantee adequate protection against Covid-19) there are important differences:  
- surgical masks do not adhere closely to the contours of the face and therefore can only prevent that larger droplets of respiratory secretions (droplets) come into contact with the wearer's mouth or nose;
- FFP2 and FFP3, also called facial filters, instead are made in such a way as to adhere closely to the wearer's face, thus filtering even the finest aerosols with the smallest particles, such as viruses.  

A respirator perfectly adapted to the face can filter the aerosols containing viruses generated by infected people, but compared to surgical masks it has the drawback of not being tolerated for long periods due to the difficulty of breathing through it. Respirators, for example, are not recommended for those with small heads or for people with beards (due to the impossibility of perfect adaptation to the contours of the face).    The respiratory problems are:
-      the high level of protection is real only if they are worn correctly;
-      the respirators make the passage of air flows more difficult, therefore they are annoying or problematic to wear for long periods and for those with respiratory dysfunctions.  
Cough and respiratory distress can in fact be aggravated by the use of FFP2 or FFP3 masks. To overcome respiratory fatigue, given by prolonged use of respirators, the valve is useful, which can be present on both FFP3 and FFP2 respirators and which has the purpose of facilitating the escape of fumes. However, this entails an important disadvantage, namely that of not filtering the exhalation of the wearer of the respirator, which can consequently infect the patient in the event of operator infections.   In the literature, clinical studies are inconclusive on the effectiveness of N95 respirators in comparison with that of surgical masks in preventing viral respiratory infections of healthcare personnel (HCP) in the workplace. 

Materials and Methods
    In a study, published on JAMA in September 2019, the effect of N95 respirators was compared to surgical masks for the prevention of influenza (virus very similar to Covid-19) and other viral respiratory infections among health professionals. This randomized cluster study was conducted in 137 clinics at 7 US medical centers between September 2011 and May 2015, with final follow-up in June 2016. Every year for 4 years, during the 12-week period of the viral flu peak, the pairs of outpatient sites (clusters) within each center were randomly matched and assigned to the N95 respirator group or surgical mask group. Overall, 1993 participants in 189 groups were randomly assigned to wear N95 respirators and 2058 in 191 groups were randomly assigned to wear surgical masks when in contact with respiratory disease patients.      

 The results of this study did not reveal any significant differences in the incidence of influenza, confirmed in the laboratory, between the outpatient healthcare staff who wore N95 respirators  compared to the staff who wore surgical masks. Another systematic review of 2017 confirms the results, showing greater effectiveness of the N95 masks only in the case of pathologies of bacterial origin, while it did not find any performance differences for viral diseases.    

The performance of respirators is comparable to that of surgical masks with a much higher cost, however.  The real problem, therefore, is the resulting clinical efficacy of the mask that the dentist wears, because if the mask or respirator are not well adapted to the face or create continuous discomfort or difficulty in breathing, they continuously cause instinctive reaction from the wearer to touch them to fix them and this increases the risk of contagion significantly.   Therefore, it is fundamental to reduce the contagion is how the masks are positioned, but also how they are removed.    

For additional information:  N95 respirators vs medical masks for preventing influenza among health care personnel - A randomized clinical trial.

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