## 4 Discussion
Peracetic acid and hydrogen peroxide are some of the most commonly used substances for this procedure. Their efficiency is comparable, while hydrogen peroxide is an environmentally safer agent compared to peracetic acid [40]. Dry fogging has been recommended for use in healthcare facilities and even in severely contaminated spaces like intensive care units treating severely ill SARS-CoV-2 patients [41; 42]. Sanosil, the substance we used for this study, was proven to have the required antiviral and bactericidal effect [43]. Dry fogging, in our study, was the only decontamination technique providing zero CFU on all the employed culture media. The disadvantage of this technique is that the fogging machine presents the highest acquisition costs and it also requires a high quantity of the used substance for each run, which also adds considerable costs. The action and settlement time for this method was 40 min, but national and international guidelines require another 2 to 4 h of natural ventilation to avoid any unwanted effects, which would unfeasibly modify the expected patient flow of a dental practice. The UVC air recirculation unit also proved to be extremely efficient. Among all corresponding Petri dishes, only two CFU were formed throughout the entire duration of the patient's visit and treatment. Confirming our findings, other studies also showed good results for these devices, although these studied other working environments [28; 30]. The initial costs of the device used in this study were high, but not as high as those of the fogging device. In addition, except for electricity, no other consumables were needed in this case. The important advantage of this technique is that it drastically reduces the time gap needed between patients and, most of all, that it prevents patient to doctor or doctor to patient contamination, by an important decrease in air contamination. Another major advantage is the fact that it can also be used with no harmful effects in the direct proximity of humans, thereby ensuring the necessary air decontamination both between and during treatment sessions. Hence, we can recommend the use of such a device in all dental offices. Use of the UVC projector is a validated air decontamination method for bacteria, viruses and fungi. Its effect on Sars-CoV-2 is proven by several older and, especially, more recent studies [44; 45]. A decontamination time of 30 min between patients is not difficult to manage and this method is also efficient from an economic point of view. The air decontamination obtained by using it is not as good as other methods, most likely because of the relevance of the distance between the UVC source and the different parts of a dental office, and even more so because of its inactivity in areas that are positioned in closed spaces or in the shadow of other objects. Another drawback would be the fact that UVC projectors must not be used in the presence of humans, given the health hazards of direct exposure to ultraviolet radiation. Natural ventilation of the office for two hours also showed a drastic decrease in air contamination. The major disadvantage of this method is the fact that it requires long breaks between patients, which is not beneficial from a financial point of view. However, still from a financial point of view, this method is obviously the cheapest to enact, since it requires no financial investment. Reaching a balance between these two economic aspects should be considered by each dental practice individually, in order to evaluate the real economic impact of natural ventilation as a stand-alone decontamination method. Further studies on this subject should be conducted, given that we evaluated bacterial and fungal air-loading by using only 56 dishes and four interventions. Other air decontamination methods are also under consideration as potential candidates for our future studies.