## 2 Materials and Methods  
The present study was conducted in a private dental office in Cluj-Napoca, Romania. The treatment room in which the aerial bacterial load was measured had a surface of 18 m\({}^{2}\) (193 ft\({}^{2}\)) and a volume of 72 m\({}^{3}\) (2542 ft\({}^{3}\)). It hosted a single dental unit and was connected, by separate access points, to a sterilization area and to a waiting room. The UVC projector, UVC air recirculating unit and nebulizer (fogging machine) were placed as depicted in Figure 1. The window that was used for ventilation was 220 cm by 80 cm. The UVC projector (Biocomp, Iasi, Romania) was a 55 W, single fluorescent tube germicidal lamp, with the dominant wavelength of 253 nm. It was placed at 1.2 m above ground level, on a pivotal support (Figure 2). Figure 1: Treatment room layout. Figure 2: The Ultraviolet C (UVC) lamp. The fogging machine (COX, Bucharest, Romania) had a 650 W turbine, producing particles of less than 5 \(\upmu\)m, projecting them at a 220 km/h speed. For this study, we used Sanosil (Sanosil Ltd. International, Hombrechitikon, Switzerland), a substance containing 5 g/100 g H\({}_{2}\)O\({}_{2}\) and 0.005 g/100g Ag\({}^{+}\) (silver ions) that is supposed to effectively inactivate bacterial spores, bacteria, yeasts, fungi and viruses (all types), including enveloped viruses (Influenza, Corona). Hydrogen peroxide is an effective yet environmentally friendly substance and the traces of silver that remain on various surfaces are supposed to have an extended antibacterial effect, even after the fogging procedure has finished (Figure 3). The UVC air recirculation unit (UVC box)--Sterybox (TISSIMedica, S. Giuliano Milanese, Italy) is a device with a total power of 350 W, with five 25 W lamps and a minimum air flow of at least 50 m\({}^{3}\)/h. The device was designed to cover a room floor size of 20 m\({}^{2}\) or a total room volume of 50 m\({}^{3}\). A total of 56 Petri dishes were used for the present test as follows: 8 during the treatment and 8 after the disinfection method application for ventilation, fogging and UVC, respectively. While using the Sterybox, 8 dishes were used, since there was no separate decontamination phase for this method. The experiments were conducted in 4 stages: Stage 1 entailed the collection of airborne bacteria during the 30 min of patient treatment by using sedimentation plates (Petri dishes), followed by 2 h of natural ventilation (open window, no forced ventilation, door of cabinet remained closed), after which a new set of bacterial sedimentation on Petri dishes was collected for 30 min. Stage 2 was similar to stage 1, but the decontamination of the air was performed by using the UVC for 30 min. Stage 3 included the same steps, but the air was disinfected by using the fogging machine (6 mL/m\({}^{3}\)), followed by 40 min of settlement and action time for the airborne substance. Stage 4 was different, since we used the UVC box for 15 min before patient admission, during patient treatment and for 15 min after the patient had left the treatment room. Before every patient entered the office, current national guidelines (UVC, ventilation and fogging, with a total of 5 h gap between patients) for disinfection were applied, to ensure maximum patient safety. This also provides a constant disinfection guideline. For every measurement performed during patient treatments, we used a total of 8 Petri dishes: 2 xNA-Nutrient-Agar, 2 xYPD - YPD-Agar, 2 xGPY-Glucose-Peptone-Yeast-Agar and 2x MHA-Mueller-Hinton-Agar (Table 1). Figure 3: Fogging machine. Four Petri dishes, one for each culture medium, were placed in position 1 of the dental office and a second such set of 4 Petri dishes was placed in position 2 of the dental office (Figure 1). Position 1 was situated at a distance of 1 m from the patient's oral cavity, with no obstacles in between, while position 2 was located at a distance of 3.5 m from the patient's oral cavity, in an area where it was not directly exposed to treatment-related airflow. A total of 56 dishes were used (Figure 4).