## 4 Discussion  
It is known that FFP2 masks can provide an efficient filter against droplets responsible for the transmission of the COVID-19 infection. The more the FFP2 is securely adapted to the face, the better the seal, thereby preventing the spread of infection. Fit testing is mandatory in some countries e.g., in the United Kingdom and has been employed to ensure masks (FFP2 and FFP3) fit adequately to ensure a good seal for people working in public health systems. In dentistry, great attention has been directed towards Aerosol Generating Procedures (AGP) such as ultrasonic scaling and use of a high-speed air turbine handpiece with water. During these procedures, aerosols are generated, and the possibility to be infected is high. The \"Mask Fitter\" is an attempt to help dental professionals wearing masks in clinical environments to improve the seal of the mask. Concerning the Survey, Section 1, questions 1, 2 and 3 reported demographic data. Of the 20 dental staff participants, 30% were aged 30-39 years, 45% were aged 40-49 years and 55% were 50+ years old; and 75% were female. The dental staff comprised Dentists 35%, Hygienists 10%, and Dental Nurses 55%. The dental staff who participated in the study came from 4 different general dental practices. Section 2 concerned the use of PPE prior to the COVID-19 pandemic. In question 4, 95% of the dental staff declared that they already routinely used a protection system with only one exception. All of the dental staff used the surgical face mask, 45% a shield with or without the surgical mask. In question 5, before COVID-19, 20% wore a mask all the time, another 20% only when having clinical contact with patients, 35% when treating patients and only 25% wore a mask all the time. As expected, the situation changed substantially after the COVID-19 health emergency (Section 3). Dental staff declared the use of a wide range of protection, with FFP2 adopted by 100% of the participants. Face shields were also widely used in combination with FFP2 masks. Surgical masks were still used but mostly overlaying the FFP2 as an additional layer of protection, with a view to replacing the surgical mask between patients, retaining the FFP2 mask which has a higher cost and at least early in the pandemic were much harder to source. Only one operator reported using a FFP3 mask (with valve and surgical mask overlying) and 2 reported using alternative systems such as an open helmet and special glasses resembling a scuba diver mask, both used with FFP2. Fitting and ease of use of the FFP2 (question 9) was reported to be medium to very high for all the staff members involved, showing that this PPE is now routinely used in daily practice. However, the wearing of FFP2 masks is considered to be tiring. In questions 10, 11 and 12 dental staff reported that wearing the mask is comfortable for up to 1 h (rating 3, 4 or 5 out of 5), reducing between 1 to 4 h (rating 2, 3 and 4 out of 5), and further reduced comfort over a full day of use (rating 1 to 4 out of 5 with 45% rating 2). Confidence in obtaining a proper seal (question 13) was widely reported, with 15% rating 2 out of 5, 40% rating 3, 35% rating 4 and only 2% rating 5 out of 5. This means that dental staff were wearing the FFP2, but they still had some concerns regarding its efficacy. Interest in a system designed to improve this efficacy (question 14) was 75% with only 1 staff member answering no (Figure 7). Section 4 evaluated the Mask Fitter. Concerning the ease of wearing the Mask Fitter (question 15), the outcome was widespread, with 10% of dental staff rating 1 out of 5, 5% rating 2, 25% rating 3, 35% rating 4 and 25% rating 5. In total 85% rated the ease of wearing from medium to very high. Wearing (questions 16, 17 and 18) was reported to be comfortable over time, within one hour (3 out of 5 for 30%, 4 for 30%, 5 for 20%). The percentage decreased when worn 1 to 4 h, as well as all day long, with only 10% still rating 4 and no one rating 5 at the end of the working day.