Environmental Disinfection of a Dental Clinic during the Covid-19 Pandemic: A Narrative Insight

Background The control of biological hazard risk in health care and dental clinic environments represents a critical point in relation to the Covid-19 infection outbreak and international public health emergency. The purpose of the present review was to evaluate the scientific literature on the no-touch disinfection procedures in dental clinics aiming to limit transmission via airborne particles or fomites using no-touch procedures for environmental decontamination of dental clinics. Methods An electronic database literature search was performed to retrieve research papers about Covid-19 and no-touch disinfection topics including full-length articles, editorials, commentaries, and outbreak studies. A total of 86 papers were retrieved by the electronic research. Results No clinical article about the decontamination of a dental clinic during the Covid-19 pandemic was detected. About the topic of hospital decontamination, we found different no-touch disinfection procedures used in hospital against highly resistant organisms, but no data were found in the search for such procedures with respect to SARS-CoV-2: (1) aerosolized hydrogen peroxide, (2) H2O2 vapor, (3) ultraviolet C light, (4) pulsed xenon, and (5) gaseous ozone. One paper was retrieved concerning SARS-CoV-2; 32 documents focused on SARS and MERS. The cleaning and disinfection protocol of health care and dental clinic environment surfaces are essential elements of infection prevention programs, especially during the SARS-CoV-2 pandemic. Conclusion The decontamination technique that best suits the needs of the dental clinic is peroxide and hypochlorous which can be sprayed via a device at high turbine speed with the ability of producing small aerosol particles, recommendable also for their low cost.


Background
A new coronavirus emerged in the central Chinese city of Wuhan in late 2019 [1] and spread rapidly around the world [2] causing the World Health Organization to declare pandemic infection on 11 March 2020 [2]. It is a coronavirus (SARS-CoV-2) that causes pneumonia, moderate to serious respiratory failure, septic shock, and higher risk of death in patients with other pathologies, especially in older people with underlying medical problems like chronic respiratory diseases, cancer, cardiovascular disease, and diabetes [1,3]. The Covid-19 disease presents nonspecific symptoms such as conjunctivitis, diarrhea, vomiting, shortness of breath, sore throat, fatigue, and muscular pain, and then, there are also asymptomatic patients [4].
This coronavirus pneumonia has a high percentage mortality rate due to risk factors and mortality predictors such as age ≥ 65 years, concomitant cardiovascular pathologies, CD3 +CD8+ T cell count ≤ 75 cell·μL −1 , and cardiac troponin I ≥ 0:05 ng·mL −1 , [5,6]. In Italy, the number of confirmed cases was 274.644, including 35.518 deaths as of 4 Sept. 2020, while the great spread of the number of infected cases has caused a lockdown of dental clinical activity and poses a significant risk to personnel dental health care (DHCP) and dental patients. Transmission of SARS-CoV-2 occurs mostly by respiratory droplets over a close distance. It is an aerosol-transmissible disease which can spread when infected people talk, cough, sneeze, or disperse mouth and nasal fomite secretions into the air. Droplets exhaled during speech, sneezes, coughs, and exhalations emit mucosalivary droplets with semiballistic trajectories and a multiphase turbulent gas cloud that entrains ambient air and carries within its clusters of droplets with different droplet sizes. In fact, the exhaled air of infected humans is one of the prime sources of ambient contamination by pathogenic microorganisms. Larger droplets may rapidly settle on the ground or transmit disease to individuals in near proximity, while smaller droplets may remain suspended for a long time and can contribute to disease transmission over great distances [7] and for a long time [8]. Today, there is a worldwide pandemic SARS-CoV-2 agent of serious viral pneumonia in course which is being mitigated by lockdown (quarantine and isolation). The transmission routes of the novel coronavirus include direct transmission (aerosol-transmissible) via droplets that "settle" on another individual, while airborne transmission occurs via small droplets in suspension in the air. In particular, airborne transmission can occur without direct contact and at a long distance via air flows (e.g., if an infected person coughs in a room, leaves, and another person enters) as in the restaurant example presented by Lu et al. [9], while the fomite transmission refers to transmission via droplets (usually larger) that settle on surfaces and are then inoculated by contact of the hands with the contaminated surface which then touch nasal, oral, or eye mucous membranes.
Improving ventilation of health spaces will dilute and clear out potentially infectious aerosols [10,11].
Viruses or bacteria take flight and remain in the air so that other people can breathe the airborne pathogenic organisms, or these can land on other surfaces. The locally humid and hot atmosphere within the turbulent gas cloud allows the contained droplets to elude evaporation for longer than occurs with isolated droplets [8].
So, for this reason, it is important to implement respiratory infection control with a good prevention strategy in dental practices and health care offices.
In fact, humans have a high-frequency face-touching habit with an average of 23 times in 1 hour, and hands are a common vector for the transmission of health careassociated infections [12]. When air containing pathogenic airborne microorganisms is inhaled by a human, it can cause tuberculosis or Legionella [13], mycoplasma, or influenza, which are great problems in dentistry practice [14]. In dental practices, droplets from infected patients can contaminate the equipment and surfaces with the risk of transferring microorganisms from contaminated surfaces to other patients through hand contact [14][15][16]. The high-touch equipment surfaces surrounding the patient increase the risk of contamination of these surfaces. Furthermore, aerosolized virus, fungi, or bacteria in health care facilities can cause infection in the dentistry equipe and all health care workers [17].
So, it is very important that we adopt a proactive infection control approach to sanitation in the dental clinic between one patient and another to minimize the risk of transmission. We can use the disinfection agents through contact, but this procedure is too long and ineffective, because it is impossible to reach all hidden surfaces. The aims of this article are to discuss and suggest some of the novel notouch disinfection methods in SARS-CoV-2 infection control and prevention of viral transmission in the dental clinic setting, where droplets can be spread by dental tools that aerosolize particles from the mouth, and where surface disinfection is a priority.
In the present review, the scientific literature on the notouch disinfection procedures in dental clinics aiming to limit transmission via airborne particles or fomites or using no-touch procedures for environmental decontamination of dental clinics was evaluated.

Methods
A 2-stage procedure was followed. The manuscript included for the evaluation was retrieved from PubMed and MED-LINE, and the data were collected on a specially designed Excel database (Microsoft, Redmond, WA, USA). The database search was performed by two expert reviewers (L.F. and A.S.). Moreover, a second step of the manual search was provided to identify manuscripts eligible for descriptive evaluation. The full text and abstract of the papers included were collected and analyzed. Information available from the literature on the no-touch disinfection of dental clinics in the SARS-CoV-2 pandemic era was acquired. A literature search was also performed to retrieve study articles regarding Covid-19 (SARS-CoV-2) and no-touch disinfection in dental clinics. In the present investigation clinical studies, retrospective and prospective trials and reviews in English full-length articles were included. The exclusion criteria were proceedings, short communications, and letters to the editors. Data was then selected by focusing on the documentation of the measures of no-touch disinfection, and the actual situation of managing SARS-CoV-2 diffusion in the dental clinic. Also taken into consideration were the articles on the measures implemented in hospitals. The literature search was from database inception up to April 30, 2020. Editorials, commentaries, and outbreak studies were included. Studies in which no-touch disinfection methods were used to evaluate the efficacy of reducing contamination of surfaces were also included.

Results
A total of 86 papers were retrieved by the electronic research. No data on the clinical experience in the decontamination of dental clinics during the pandemic of Covid-19 were detected.
We found in literature different no-touch disinfection procedures used in hospitals against highly resistant organisms, but no data was found in the search for such procedures with respect to SARS-CoV-2 (Tables 1-9). Different no-touching disinfection systems have been 2 BioMed Research International   Decomposes under the influence of light on warming producing oxygen. Increase of fire hazard and is a strong oxidant. Attacks many organic substances such as textiles and paper 3 BioMed Research International proposed such as aerosolized hydrogen peroxide [18], hydrogen peroxide-producing systems [19], H 2 O 2 vapor [20], hydrogen ultraviolet C light [21], pulsed xenon [22], and gaseous ozone [23].
We found more papers on the efficiency of disinfectant agents on other viruses such as severe acute respiratory syndrome (SARS), Middle East Respiratory Syndrome (MERS), mouse hepatitis virus (MHV), canine coronavirus (CCV), and human coronavirus (HCoV).
Aerosolized hydrogen peroxide systems (aHP) generate a dry-mist hydrogen peroxide aerosol of hydrogen peroxide and use a solution containing 5%-7% hydrogen peroxide with or without <50 ppm silver (Nocospay) (Figures 1 and 2) [24,25]. The generator injects into a room a solution of HP followed by passive aeration and water and is very active against microorganisms.
This device produces a variable particle size of 2-12 μm [26] or of 0.5 μm [27]. Generally, a dosage of 6 mL per m 3 is recommended which, after erogation, should be left to decompose naturally. This technique uses a low concentration of hydrogen peroxide which, for this reason, metabolically inert spore and catalase-negative bacteria are less susceptible. It is able to reduce contamination of MRSA and C. difficile on work surfaces but has not been shown to eradicate pathogens in clinical practice. It is difficult to achieve the saturation of the environment because aHP is introduced via a unidirectional nozzle by gravity [28]. Boyce et al. [92] 2016 No-touch technologies include aerosol and vaporized hydrogen peroxide, mobile devices that emit continuous ultraviolet (UV-C) light, a pulsed-xenon UV light system, and use of high-intensity narrow-spectrum (405 nm) light Environmental departments should consider the use of newer disinfectants and no-touch decontamination technologies to improve disinfection of surfaces in health care There are two types of HPV: condensing HPV technology and noncondensing vaporized hydrogen peroxide (VHP) technology. This technology uses a vaporizer heated to 120°C and circulates the HPV through the environmental chamber via a supply and return hose. Condensing systems inject hydrogen peroxide until the air in the room becomes saturated and HP begins to condense on the surfaces. The condensing of HP on surfaces can cause corrosion [29]. The HPV device injects at 2 mL/min for 1, 2, or 5 min followed by 1.5 mL/min for 15 min equating to three different volumes: 25, 27, and 33 mL.
The level of 1 ppm is the max level of exposure according to the Occupational Safety and Health Administration and International Labour Organisation. This procedure requires a first phase injection and second phase aeration for a total time of approximately 2-3 h, varying with the amount of hydrogen peroxide being vaporized.
Noncondensing systems produce dry gas by a vaporized hydrogen peroxide system that utilizes erogation of 30%-35% aqueous hydrogen/peroxide (VHP) at high-velocity air. VHP systems have a generator which delivers until the air in the enclosure becomes saturated and hydrogen peroxide begins to condense on surfaces, and it is designed to achieve a humidity level set prior to the start of the cycle [30]. This system is noncondensing VHP because the vapor stream is dried as it is returned to the generator [31]. It is virucidal, bactericidal, sporicidal, and active against myco-bacteria including C. difficile spores, MRSA, and a wide range of nosocomial pathogens [32,33]. Its long cycle times have made it difficult to use this system in health care facilities. It is efficient against fungi, viruses, MRSA, VRE, C. difficile, Klebsiella, Serratia, Mycobacterium tuberculosis, and Acinetobacter [34,35].
Dilute hydrogen peroxide (DHP). This technique uses water vapor and oxygen in the ambient air to continuously produce ozone-free hydrogen peroxide [36]. The environmental hydrogen peroxide produced is 0.02 ppm that is well below human safety thresholds. In fact, a level of 1 ppm is the max safety level of exposure according to the Occupational Safety and Health Administration and International Labour Organisation [37,38]. DHP is active against a variety of viruses, bacteria, and fungi. It can be used during routine clinical practice in conjunction with established cleaning and decontamination methods. So, there are no restrictions on the use of a room for a period of time in practices.
Surface disinfection via aerosol (SDVA). The device produces dry fog through a turbine at high speed that atomized and sprays disinfectant. Usually, H 2 O 2 and hypochlorous acid (HOCl) are used as a disinfectant (Figures 1 and 2). The disinfectant is atomized into ultrafine droplets, blown into the air, and, after 10-30 min, settles on all surfaces; these disinfectant droplets quickly begin to take effect. The generator produces on average size 5 μ particles of disinfectant and ensures a slow and completely uniform sedimentation on each square of the treated premises with no humidity. The Clostridium difficile aerobic colony counts were calculated for each of 5 standardized high-touch surfaces in the rooms before and after UV light decontamination (UVLD) The mobile UV-C light unit significantly reduced aerobic colony counts and C. difficile spores on contaminated surfaces in patient rooms Nerandzic et al. [46] 2010  (HOCl) is a weak acid and has a virucidal power 300 times that of chlorine and is widely used for the decontamination of swimming pools. It is safe and used for nasal irrigation in patients affected by chronic sinusitis. A study showed a low (0.85%) concentration HOCl solution can be used as an effective nasal irrigation solution [39]. Hypochlorous acid (HOCl) has demonstrated broadspectrum antimicrobial activity while being suitable for general use [40]. 20 to 200 ppm of HOCl solution resulted in ≥99.9% reduction of noravirus contagion on inanimate surfaces and aqueous suspensions [40], with low potential to damage treated surface materials [41]. The generator produces droplets of size ranging between 20 and 50 μm. The HOCl fogs to concentrations ranging from 20 to 200 ppm and has virucidal effect against human norovirus [42]. Fogging is a mechanical action that produces small particles that can accelerate the interfacial mass transmission of chlorine gas. Low concentrations of hypochlorous acid (HOCl) have been demonstrated to exhibit both anti-influenza virus and antibacterial activity, but HOCl is also used to kill human rhinovirus (HRV) [42]. HOCl is considered by the FDA the agent that has the highest bactericidal activity against a broad range of microorganisms (US FDA, 2015) [43]. Avian influenza (H5N1) virus inactivation through fog applications of HOCl was achieved in 10 seconds [44]. HOCl has a temporary and gentle chlorine smell that dissipates rapidly.
The UV light also inactivates drug-sensitive and multidrug-resistant bacteria and viruses [47].
This technology is very limited because conventional UVC light sources are a human safety hazard, with a carcinogenic effect [48]. For this reason, the power of UVC light has been lowered to 2 mJ/cm 2 and a recent study showed an efficiency when the lamps were positioned in public locations, reducing incidences of transmission of tuberculosis and influenza epidemics [49]. They are very efficient for the disinfection of health care environmental surfaces after manual cleaning has been performed. So, UVC irradiation treatments are effective for inactivating SARS-CoV. A continuous 30 min ultraviolet radiation is required to disinfect target surfaces and air [50]. High-touch surfaces in rooms previously occupied by C. difficile-infected patients were sampled after discharge but before and after cleaning using either bleach or nonbleach cleaning followed by 15 min of PX-UV treatment There is a problem that natural and synthetic polymers are attacked by ultraviolet radiation, materials that make up many parts of a dentist chair, and other medical devices that include polypropylene.
Pulsed-xenon (PX-UV) systems emit high-intensity broad-spectrum UV irradiation in the 200-320 nm range [51] and are a means of quickly producing germicidal UV [51].
Usually, this is a portable device used in empty patient rooms because prolonged exposure to UV-C can cause eye and skin irritation. Fifteen minutes of PPX-UV exposure time can eliminate the pathogenic microorganisms [52] against 45 min required to clean a room with bleach [53].
Gaseous ozone is used for environmental disinfection [54]. It has antimicrobial and antiviral properties inclusive of Ebola although its mechanisms of action are not well understood [55,56]. The device generates ozone and increases the ozone gas peaking at 20-25 ppm and includes ozone's known corrosive properties [20]. This technology is more efficient when there is low relative humidity [23]. It only takes 3-4 ppm to reduce all viruses and bacteria [57], but at 25 ppm, it is a disinfectant, while at 50+ ppm, it sterilizes surfaces. Ozone can damage the lungs when inhaled, a recent study showed in a rat model that increased methylation of the apelin promoter downstream of DNA damages the lungs, causing the development of pulmonary edema [58].
The generators are unable to elevate ozone levels near the required ppm range even in a small or average-sized room (<1-5 ppm). One to two hours of treatment are needed and 10-15 min of reentry after ventilation or open windows.

Discussion
During dentistry activity and the use of high-speed drills, droplets that are contaminated with the virus [59] can spread as far as two meters on to exposed surfaces [60] with environmental contamination and these remain infectious on workstation surfaces, medical instruments, etc. at room temperature for up to 9 days [61].
In fact, dental instruments such as rotating devices or ultrasonic devices use high-speed gas to drive the turbine to rotate at high speed and work with running water, and some dental procedures can cause coughing and, in any case, the patient breathes. The airborne droplets are of different dimensions and contain virus or bacteria pathogens which may survive on inanimate surfaces up to several months, and they may serve as a reservoir for cross-contamination Acute inhalation of ozone induces DNA methylation of apelin in the lungs and if a change in expression is related to altered DNA methylation in the lung Ozone exposure reduced DNA cytosine-5-methyltransferase (DNMT) activity and Dnmt3a/b gene expression. Epigenetic modifications accompanied ozone-induced reduction of apelin expression and development of pulmonary edema Ding et al. [103] 2019 Ozone disinfection of chlorine-resistant bacteria in drinking water The ozone resistance of bacteria Aeromonas jandaei < Vogesella perlucida < Pelomonas < Bacillus cereus < Aeromonas sobria was lower than that of spores Bacillus alvei < Lysinibacillus fusiformis < Bacillus cereus at an ozone concentration of 1.5 mg/L. More than 99.9% of Bacillus cereus spores were inactivated by increasing ozone concentration and treatment duration 7 BioMed Research International with self-inoculation, as contaminated hands are a route for disseminating respiratory infections [62,63].
In addition to the infected patients, there are the asymptomatic ones who can be negative to current health status investigations and/or the presence of risk factors for Covid-19 [64,65]. For this reason, all patients must be treated during dental procedure as being Covid-19 positive. Hence, this is a timely topic, and dental clinics would be interested in the state of the art with respect to sanitization procedures. Several studies have found that hygiene quality management in the dental office may be problematic and surface microbial contamination has been found [66,67]. All environment surfaces can become contaminated with infectious droplets from sprays of oral fluids or from touching them with contaminated fingers. The surfaces most frequently touched are drawer knobs, light handles, unit switches, dental radiograph equipment, reusable containers of dental materials, drawer handles, and dental chairside computers, and when these devices are touched, microbial agents can be transferred to other instruments [15]. General cleaning and disinfection with chemical or physical agents are recommended for device contact surfaces. It is very important to know material compatibility with physical or liquid chemical germicides. When wiping or scrubbing is used to remove microorganisms, any antimicrobial effect provided by the agent is reduced as there can still be a risk of creating another reservoir for microorganisms in the diluted solutions of the disinfectants themselves [68].
Disinfection of instruments and workstation surfaces against microbial contamination and inefficacy of environmental decontamination could be risk factors for crossinfection. Disinfection of surfaces is a method for reducing the risk of contact to viruses and interrupting their spread [69]. In dentistry, conventional manual disinfection of medical device surfaces is used, and this needs a two-stage disinfection procedure which includes surface rehydration followed by disinfection, for effective inactivation of bacteria and viruses on dry surfaces [70]. It is important to improve ventilation of health care spaces to dilute and clear out potentially infectious aerosols [10,11]. Ventilation can reduce virus concentration in the air, limiting airborne transmission, but also the settling of viral particles, causing fomite transmission, for example, in influenza viruses [71]. The use of high ventilation rates during and after aerosol-generating procedures, such as high-speed drills, or piezosurgery [72][73][74][75] or between two patients has the potential to efficiently reduce circulating concentration of viral particles.
Environmental disinfection of the dental clinic is very important because the coronavirus can persist on inanimate surfaces like metal, glass, or plastic for up to 9 days, but fortunately, it is very sensitive to the action of disinfectants [61]. A recent correspondence in The New England Journal of Medicine showed that the stability of SARS-CoV-2 was like that of SARS-CoV-1 and was more stable on plastic and stainless steel than on copper and cardboard, and viable virus was detected up to 72 hours after application on these surfaces [76]. Different disinfectant agents were used against severe acute respiratory syndrome (SARS), Middle East Respiratory Syndrome (MERS), mouse hepatitis virus (MHV), canine coronavirus (CCV), and human coronavirus (HCoV) such as ethanol [77], 2-propanol [78], benzalkonium chloride [79], dodecyl dimethyl ammonium chloride [80,81], chlorhexidine digluconate [80], sodium hypochlorite [82], hydrogen peroxide [83], formaldehyde [78],  [82], and povidone-iodine [84]. The WHO recommends environmental cleaning and disinfection procedures which must be followed correctly. Benzalkonium chloride and chlorhexidine digluconate are not very effective or basically ineffective. The most effective disinfectants are ethanol at strong concentration while sodium hypochlorite and hydrogen peroxide require a minimal concentration to be effective with a low impact on human health. Also, ethanol at 62 and 71% is similarly efficacious against coronavirus but can be used for small surfaces [85]. Ethanol has been widely used for the decontamination of hands based on 80% ethanol or 75% 2-propanol, and these are sufficiently efficacious [86].
For cleaning the workstation surfaces, sodium hypochlorite is suitable at a concentration of 0.05% with efficient and sufficient procedures [85] and when used at a concentration of 0.1%, it is effective in 1 min. Also, hydrogen peroxide is effective with a low concentration of 0.5% and an action time of 1 min. It is used for cleaning and disinfection implant drills because it preserves the drill structure after 50 cycles of decontamination [87][88][89].
Thorough decontamination and disinfection of all workstation surfaces in the hospital are very often difficult to achieve on multiple surfaces and complex equipment with wiping or scrubbing and require a lot of time.
For this reason, systems have been proposed, which offer the potential to improve the efficacy and reliability in hospital disinfection of environment and surfaces such as aerosolized hydrogen peroxide [18], hydrogen peroxide-producing systems [19], H 2 O 2 vapor [20], hydrogen ultraviolet C light [21], pulsed xenon [22], and gaseous ozone [23].
There are differences between these systems in terms of their effectiveness, technological aspects, and microbiological efficacy. No data were found in the Guidelines for Infection Control in Dental Health-Care Settings 2003 and 2016. UV-C activity against viruses and bacteria is strongly influenced by distance and exposure times and has the most critical parameters; for this reason, a mobile ultraviolet-C device has been introduced [90]. A recent study showed that 6 min PX-UV disinfection is required to disinfect target surfaces and air, so it is fast and effective disinfection [91]. PX-UV disinfection is an effective agent for decontaminating the  Figure 1: This is a schematic representation as there is no data referenced here in the present paper. (a) Aerosol generating during piezosurgery procedures. (b) Particles of different sizes. Smaller droplets (5 μ) may remain suspended for a long time and can settle on all environmental surfaces such as drawer knobs, light handles, unit switches, dental radiograph equipment, reusable containers of dental materials, drawer handles, and dental chairside computers and when these devices are touched, microbial agents can be transferred to other instruments. (c) Manual disinfection of medical device surfaces is very difficult. 9 BioMed Research International workroom. However, UV radiation may cause a significant degradation of synthetic polymers such as polystyrene which results in breaking the polymer chains [54].
The performance of different systems must be evaluated for use in dental practice. The UVC light and PX-UV systems are efficacious methods for decontamination of a room, but both systems attack synthetic polymer materials and many parts of dentist chairs and other medical devices can be damaged. The gaseous ozone requires a high concentration and in practice is very difficult to achieve without sealing the doors. So, the most interesting techniques for decontamination in clinical practice are (  10 BioMed Research International VHP and aHP both of which use HP vapor or aerosol and are widely used for environmental decontamination in hospitals [92]. It is desirable that these techniques are also applied to dentistry. Manual disinfection of work surfaces can result in poor disinfection of work stations with the risk of spreading pathogens from one surface to another [93]. However, there are many variables that influence the efficacy of the manual disinfection process such as distribution and contact time of the agent, which further limit the repeatability and reliance for an operator. For example, quarternary ammonium is an efficacious agent but when used with cotton or wipes containing substantial amounts of cellulose, the antimicrobial efficacy of the disinfectant may be reduced [94,95]; therefore, it is recommended to use microfiber [96]. Another error is inappropriate overdilution of disinfectant solutions resulting in inappropriately low concentrations.
Outbreaks and rapid transmission of some viral diseases like rhinovirus, influenza, avian influenza, SARS, and infectious bronchitis, with their elevated morbidity and mortality rates, are generally attributed to infection via aerosol. Droplets produced during the use of high-speed handpieces and air/water syringes with the patient's saliva contaminate the air and floor, all work surface walls, and the objects that are nearby. Then, a no-touch or automatic disinfection approach to disinfection is needed to improve disinfection of surfaces in the dental clinic.
The major problem in clinical practice is that many enteric and respiratory viruses can be shed at great concentrations and contaminate and survive for long periods on environmental and medical device surfaces; this has been shown to play a role in their transmission [97]. HPV is a vapor-phase disinfection method. It is virucidal, including against influenza, and hence can be considered for the environment decontamination and disinfection of viruscontaminated surfaces in the dental clinic.
This technique is also very safe; in fact, it has also been used for the disinfection of N95 respirators with a residual level of H 2 O 2 on the inner facial filter respirator at a very low level, 0.6 ppm at 2 hours and undetectable at 3 hours when the safety limit is actually lower, being <1 ppm [98]. Also, HOCI is a fast and simple technique that can be implemented in the dental clinic, since slightly acidic hypochlorous acid water has very fast and strong efficacy against pathogens [99].
Biosecurity programs have a critical role in the control of all infectious diseases. The main way to control and prevent those diseases that are airborne in the hospital or dental clinic is inactivation of infectious agents by spraying disinfectants in the air. HOCI is very popular for its broad and strong disinfection ability, demonstrating a very fast and strong efficacy against avian influenza and many viruses in a short contact time (5 sec), in vitro [44]. It has shown activity also against many bacteria and other microorganisms such as Staphylococcus aureus and Pseudomonas aeruginosa. Application of HOCI in low concentrations 20-200 ppm, by a spraying system with high turbine speed with the ability of producing aerosol particles (3-10 μ) inside dental clinics, is able to reduce the chances of aerogenic infection causing outbreaks and can limit virus transmission from one site to another. This powerful weapon is 100 percent safe for humans as it occurs naturally in our bodies. Neutrophils are white blood cells that are the first to arrive on site when an invading microorganism is detected. Neutrophils will chase down and engulf the pathogen through phagocytosis. Upon contact, neutrophils release a burst of bactericidal chemicals including its most effective oxidizing agent, HOCl. This inactivates the pathogen by destroying the cell membranes and proteins [100]. All the articles discussed in this review concern the control of infections of very resistant agents (such as norovirus, Ebola, methicillin-resistant Staphylococcus aureus, and C. difficile); for this reason, we can deduce that they are also active against influenza viruses which are much more sensitive to common disinfectants. Very few studies on dental clinics and the identified potential methods to achieve decontamination are detected in literature. So the decontamination technique that best suits the needs of the dental clinic is peroxide and hypochlorous which can be sprayed via a device at high turbine speed with the ability of producing small aerosol particles, recommendable also for their low cost.
These procedures do not replace the correct use of personal protective equipment [101,102]. The lower the shed quantity (via the use of masks and safety glasses to limit shedding), the easiest it is to reach noninfectious doses after disinfection, and the lower the exposure dose, the lower the probability to get infected (via the use of masks to limit inoculation) [103,104]. Although all dentistry procedures cannot be realized with a mask on the patient, it is important for the dentist to wear correctly one, in addition to colleagues entering the room, and patients in the waiting room for instance. We believe that no-touch methods augment manual cleaning but cannot replace it.

Conclusions
Dentists should consider the use of these disinfectants and no-touch decontamination technologies to improve disinfection of surfaces in dental clinics. In conclusion, manual cleaning and disinfection of environmental surfaces in health care facilities (daily and at patient discharge) are essential elements of infection prevention programs, especially during the SARS-CoV-2 pandemic.

Conflicts of Interest
The authors declare that they have no conflicts of interest.