## 4 Discussion
Interestingly, even if slightly differently distributed, the percentage from medium to very high levels of comfort at the end of the day were globally very similar both without and with the Mask Fitter (respectively 40% and 35%), showing a good acceptance of this extra item (Figure 8). Figure 8: Wearing comfort over full working day, without and with Mask Fitter. Figure 7: Interest for a customized device. A remarkable outcome from this service evaluation was question 19 where dental staff declared, when wearing the Mask Fitter, to have reached a higher confidence on obtaining a proper seal with 75% rating 5 out of 5. The difference with the same data without the Mask Fitter (only 10% rating 5 out of 5) was impressive (Figure 9). In question 20, 75% of the dental staff rated 5 out of 5 the ease of cleaning the face mask (performed by immersion in disinfectant). When asked (question 21) if they would introduce the Mask Fitter routinely, 25% of the staff stated that they would use it all the time, while 65 % declared that they would use it for selected patients, or procedures, or both. Only 10% reported that they would not use the Mask Fitter (Figure 10). Question (22) invited free text feedback from the participants on the reasons for their responses to question 21. The reasons for not adopting the routine use of the Mask Fitter were that people feel sufficiently safe with the FFP2 alone. The most frequent reason for not adopting the Mask Fitter for continuous use, but more likely for patients and/or selected procedures, was that wearing the Mask Fitter all the time was firing. Therefore, its use for limited situations such as aerosol generating procedures or for those occasions when patients declare no symptoms at the COVID-19 triage stage, with the absence of a fever, but there may be some uncertainty due to a sporadic cough and/or the need to occasionally blow their nose, might be the appropriate indication for the Mask Fitter. Section 5 focused on the effect of wearing the Mask Fitter on the fogging of glasses or loupes. From questions 23 and 24 it was reported that only 15% of the participants used loupes, while 65% wore glasses. A total of 25% of the participants wore neither loupes nor glasses, thus they did not answer the following two questions (25 and 26). Even if the distribution of the fifteen answers related to fogging was quite widespread, the effect of  
Figure 10: Interest in wearing the Mask Fitter routinely. Figure 9: Confidence in achieving an appropriate seal with and without Mask Fitter. the Mask Fitter looked beneficial. Without the Mask Fitter (question 25), the participants reported a total of 73% medium (3 out of 5) to very high (5 of 5) fogging problems, that decreased to a total of 27% (question 26) when wearing the Mask Fitter, thus showing a high capability to reduce fogging problems (Figure 11). The last question of the survey (question 27) invited free text answers on the use of the Mask Fitter. There were some reported problems in obtaining the proper adaptation using a trial-and-error procedure for obtaining an appropriate tightening with or without the use of an additional rubber band on the back of the head. Staff reported that once a good adaptation was obtained, it was easy to be reproduced when worn again. They commented on a sense of constriction on the nose and consequent oral breathing. Some participants reported that due to the position of the nasal arch, even light pressure immediately made it difficult to breathe through the nose. This might be due to a possible slight deformation on the face scan in the nasal area, as reported by [PERSON] et al. [23]. Participants generally agreed that this is the main aspect requiring improvement, even if none of the participants reported any sores and/or scars.