## 1 Introduction
Moreover, the in vitro study by [PERSON] et al., 2021 stated that 99.99% of HCoV-OC43, a surrogate for SARS-CoV-2 [29] and of A/H1N1 virus, was inactivated by dry steam within 4 s of its use [23]. Overheated dry-saturated steam is currently used as an effective disinfection system in both healthcare and non-healthcare environments due to its easy and rapid use and high ability to inactivate pathogenic microorganisms, overcoming the disadvantages of chemicals [21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34]. In healthcare facilities, it is mainly used for surfaces and medical devices' disinfection, such as e.g., during the COVID-19 pandemic for filtering facepiece respirators' decontamination [21; 22; 31; 32]. In non-health fields, its major applications include cleaning textile materials with no risk of damage and disinfection of surfaces in domestic, educational and food service settings [25; 30; 33]. The characteristics of the steam to be dispensed in terms of temperature, pressure, distance and time of application depend both on the features as well as on the type of the material and/or surface to be disinfected and on the chosen device that has to be used by following the manufactures' instructions. In general, the steam jet has to be vertically maintained above the surface to be disinfected without touching it and in continuous motion during its application. For instance, in real-life settings, using a 99 \({}^{\circ}\)C steam jet at a pressure of 83 to 138 kPa for 90 s is reported to be effective in the disinfection of carpets against human norovirus (HuNoV) [27]. To the best of our knowledge, to date, scant literature discusses studies evaluating the efficacy of overheated dry-saturated steam in the disinfection of surfaces in dental practice [21]. For this reason, the present study aimed to deepen the knowledge of using an overheated dry-saturated steam system to disinfect dental chair surfaces after performing AGDPs through Adenosine triphosphate (ATP) bioluminescence analysis. ATP bioluminescence analysis is a rapid method used to evaluate the surfaces' cleanliness by measuring the cellular ATP amount. ATP levels on environmental surfaces provide a measure of the total organic matter present, including not only microorganisms, but also potential blood and saliva traces and tissue debris, which frequently contaminate the work surfaces. ATP bioluminescence analysis is based on an enzyme-substrate (luciferin-luciferase) chemical, which uses the ATP released by cells to generate a bioluminescent signal that is detected by a luminometer and expressed in Relative Light Unit (RLU). The RLU value provided by the luminometer is proportional to the ATP concentration on the tested surface. RLU reference values vary depending on the device used, but an ATP amount of 100 RLU/100 cm\({}^{3}\) is usually considered a threshold level [28; 34; 35]. This study aimed to decrease the superficial microbial contamination of the evaluated surfaces, reducing the risk of cross-infections for patients and DHCPs in dental practice. The primary hypothesis tested was that using the overheated dry-saturated steam disinfection system after performing AGDPs would reduce the superficial microbial contamination on the dental chair's surfaces. The secondary hypothesis tested was that after performing AGDPs, the microbial contamination on the dental chair's surfaces would not differ among the different surfaces.