UGROŽENOST STOMATOLOŠKOG OSOBLJA SARS-CoV-2 VIRUSOM TOKOM STOMATOLOŠKIH INTERVENCIJA OCCUPATIONAL HAZARD FOR DENTAL STAFF EXPOSED TO THE SARS-CoV-2 VIRUS DURING DENTAL PROCEDURES

Uvod: Stomatološka profesija je visokorizična profesija, sa aspekta mogućeg inficiranja, od skoro 100% u toku stomatoloških intervencija, od strane pacijenata koji su nosioci bakterijskih, virusnih i gljivičnih bolesti. Cilj rada: Analiza svih podataka koji objašnjavaju mogućnost inficiranja SARS-CoV-2 virusom u stomatološkoj praksi. Materijal i metode: Analizirana je literaturna o zastupljenosti SARS-CoV-2 virusa, njegove karakteristike i ponašanje u spoljašnjoj sredini i u živim tkivima. Korišćene su baze podtaka iz biblioteka Medline, Cochrane Library, Science-Direct, EMBASE, and Google scholar, kao i drugi izvori informacija o ovom virusu. Rezultati:. SARS-CoV-2 je RNK virus, koji ima submikronsku veličinu i mogućnost da opstane u raznim sredinama. Zadržavanje virusa SARS-CoV-2 u vazduhu/aerosolu traje prosečno 3 sata, dok je poluživot ovog virusa 5 do 6 sati na nerđajućem čeliku i 6 do 8 sati na plastici. Inficirani pacijenti SARS-CoV-2 virusom razvijaju COVID-19 bolest, koja se manifestuje kroz presimptomatski, simptomatski i postsimptomatski period bolesti. Zaključak:SARS-CoV-2 virus moguće je identifikovati u aerosolu, koji stvaraju stomatološke mašine, korišćenjem kompresorskog vazduh u radu. Zaštita stomatologa i osoblja od inficiranja virusom je moguća, košćenjem N95 respiratorne maske sa stepenom zaštite 2 i 3, koje imaju efikasnost filtracije,tj. zadržavanja submikronskih čestica sa efikasnošću od ≥ 98%. Treba koristiti vodonepropusne zaštitne naočare sa zaštitnim vizirom ili industrijski posebno dizajnirani facijalni vizir u vidu maske za celo lice, koji ima sopstveni motor za dotok filtriranog vazduha u masku i koji sprečava kontaminaciju mukoze oka, nosa i usta putem stvorenog tečnog ili čvrstog aerosola u vazduhu. Ostala jednokratna zaštitna oprema takođe treba da bude vodonepropusna.


Introduction
The dental profession is a high-risk profession, considering the aspect of a possible 100% infection from patients who are carriers of bacterial, viral and fungal diseases, and who are undergoing a dental procedure 1 . The dental staff may standardly be exposed to and jeopardized by the following pathogenic microorganisms and viruses: mycobacterium tuberculosis, streptococcus and staphylococcus bacteria, cytomegalovirus (CMV), herpesvirus types 1 and 2, hepatitis B and C virus, as well as other pathogens which cause various diseases 2 .
The transmission mode of these microorganisms and infection of dental staff by the patient who carries the disease occur through: direct contact with blood, saliva or through another infectious biological source; indirectly through contaminated instruments, equipment or work surfaces of the furniture in the office; contact with infectious droplets from the conjunctiva of the eye, oral and nasal mucosa containing pathogenic microorganisms and viruses which are released into the external environment (over a short distance), talking, sneezing or coughing; by inhaling pathogens residing in the air over an extended period of time 3 .
At this moment, it is of special interest to consider some facts related to the pandemic with the new coronavirus declared by the World Health Organization at the end of last year 4 , as well as the mass infection of the population with the new coronavirus. Considering these dramatic health events, the decision to declare a state of emergency in the Republic of Serbia owing to the coronavirus epidemic has contributed to dental interventions being performed in specific and highly aggravating circumstances for dental health workers and patients in need of dental care.

Biology of the coronavirus
In people, the coronavirus causes colds which have the usual symptoms of a cold of the upper respiratory tract, affecting the nasal cavity, and sometimes spreading to the pharynx, larynx and the sinuses 5,6,7 .
On the other hand, the current coronavirus, which has caused a mass/global viral infection, is similar to two other viruses: the beta-coronavirus (SARS-CoV 1).
The current new type of coronavirus, which has the ability to cause severe acute respiratory syndrome with a possible fatal outcome, was given the initial name 2019-nCoV 8 , and soon received the official name of: "SEVERE ACUTE RESPIRATORY SYNDROME CORONAVIRUS 2" / CORONA VIRUS 2 (SARS-CoV-2) 8 , which causes the coronavirus disease (COVID-19) 9 . It is important to note that SARS-CoV-2 belongs to RNA viruses 10 and that it is similar to the coronavirus SARS-CoV-1.
The size of the SARS-CoV-2 virus is less than 1 micron, and is 125 nm or 0.125 µm 11,12 , and this submicron size of the SARS-CoV-2 virus significantly reduces the possibility of protection against virus transmission in dental staff during their daily work.

Ways of coronavirus transmission
Coronavirus (SARS-CoV-1) is a type of virus that can infect bats, civets of the genus viverida that are similar to mongooses, and people, in whom it causes severe acute respiratory syndrome (SARS) 13,14 . This virus attacks human epithelial cells in the lungs 15,16 , which it enters by binding to ACE2 receptors (angiotensin-converting enzyme) 15,16 . ACE 2 receptors are also found in the kidneys, heart and endothelial cells, and their main role is the regulation of the renin-angitensin system (RAS) 17 . Recent findings indicate that ACE2 reacts with transmembrane protease-serine 2 (TMPRSS2), responsible for the activation of the viral "S" protein SARS-CoV-2, which reacts with the surface ACE2 enzyme almost identically to the SARS virus; activated viral material SARS-CoV-2 enters the cytoplasm of an infected person, and the process of virus replication takes place through cellular host mechanisms 16,18,19,20 .
There are still disagreements over how the current coronavirus (SARS-CoV-2) is transmitted; through large respiratory droplets as an influenza virus, or through a fine water mist called aerosol, as in the case of rubella 21 . However, the SARS-CoV-2 virus is thought to spread to humans primarily through respiratory droplets which occur when a person infected with the SARS-CoV-2 virus SARS-CoV-2 virusom energično govori, kašlje ili kija i na taj način izbacuje sekret, tj. respiratorne kapljice u vazduh i to nekoliko metara u daljinu; smatra se da je minimalna sigurna razdaljina, koja otežava zaražavanje ≥ 1,8 m -2m.
A worrying fact is that it has been proven that it is possible to isolate SARS-CoV-2 RNA from blood and feces; its presence has also been proven on cardboard, plastic and stainless steel 23,24 .
Recent studies have shown that the SARS-CoV-2 virus remains in the air / aerosol for an average of 3 hours; the half-life of this virus was 5.6 h on stainless steel and 6.8 h on plastic 23 .
The presence of the SARS-CoV-2 RNA virus has been proven in some other inanimate organisms as well 22,25 , which has led to caution in professional circles and the consideration of this way of spreading the virus.

Impact of the clinical manifestations of the covid-19 disease on dental treatment
In everyday dental work, there is a great possibility for the transmission of the SARS-CoV-2 virus, considering the fact that the dental instruments and equipment used, such as handpieces (turbines, contra-angle handpieces and straight handpieces), ultrasonic dental plaque removers, ultrasound devices for bone tissue surgery, etc., create a barely visible, fine water cloud or haze, which may contain infectious particles. When using these instruments, an inevitable consequence is the creation of large droplets of water, saliva, blood, microorganisms, viruses and other possible infectious material. During the performance of dental interventions, not only is the dentist who performs the intervention at 30-40 cm from the patient's oral cavity threatened, but also the dental assistant, the dental nurse who is involved in the process and possibly the assistant nurse. Spraying possible infectious particles into the immediate environment around the patient and the dentist allows these infectious particles to fall onto the team performing the dental intervention, onto the floor, the workbench of the dental machine and onto the desk or furniture in the office.
Sadašnja saznanja o COVID-19 bolesti nam govore da postoje tri nivoa kliničkog stanja zaraženog pacijenta, koji može da bude istovremeno i stomatološki pacijent. Standardizovane su faze razvoja COVID-19 bolesti, koja se razvija kroz presimptomatski period, simptomatski period i postsimptomatski period 27 . Najveća opasnost od transmisije i zaražavanja SARS-CoV-2 virusom stomatološkog osoblja, tokom izvođenja stomatoloških intervencija, su pacijenti sa SARS-CoV-2 virusom, koji su u asimptomatskoj i/ili presimptomatskoj fazi razvoja bolesti COVID-19 28  An even greater danger is the possible appearance of an aerosol that may contain an infectious pathogenic microorganism. It is a well-known fact that surgical masks worn by staff during the described interventions generally protect the mucosa of the oral cavity and nose from the droplets reaching the protective mask; the medical problem is that there is problematic protection against inhalation from the formed contaminated clouds in the air or aerosols that potentially contain the virus 26 .
Current knowledge of the COVID-19 disease tells us that there are three levels of clinical conditions of an infected patient who may be a dental patient at the same time. The stages of development of the COVID-19 disease that develops through the presymptomatic period, symptomatic period and post-symptomatic period are standardized 27 . Patients with the SARS-CoV-2 virus that are in the asymptomatic and/or presymptomatic development phase of the COVID-19 disease represent the greatest threat of transmission and infection with the SARS-CoV-2 virus to dental staff during dental interventions 28 . The incubation period of the COVID-19 disease lasts an average of 5-6 days, although there are data that it lasts 14 days. 29 The virulence of the SARS-CoV-2 virus allows the patient to be infectious 1-3 days before the manifestation of all symptoms of the COVID-19 disease, and 40-50% of the virus transmission from an infected person to a healthy person occurs in this first silent phase of the disease, i.e. in the asymptomatic or presymptomatic phase of the disease 22,30 . It is believed that 97.5% of the patients who are in the symptomatic phase of the COVID-19 disease develop symptoms 11.5 days after the SARS-CoV-2 infection 31 .
The symptoms of the COVID-19 disease are: fever, cough, painful and sore throat, muscle weakness and pain, loss of appetite, nausea, vomiting, loss of smell and taste, shortness of breath 32,33,34,35,36 . Laboratory analyses of individual blood and biochemical values are characterized by specific deviations, such as: elevated d-dimer value, lactate dehydrogenase, C-reactive protein, ferritin and lymphopenia presence; it is not uncommon for patients to have normal procalcitonin levels; severe cases of the Covid-19 disease involve the occurrence of leukocytosis with lymphopenia, prolonged prothrombin time and a significant increase in liver enzymes, lactate dehydrogenase, C-reactive protein, ddimer, interleukin-6, C reactive protein and procalcitonin 32,37,38,39,40 .

Possible transmission mode of the SARS-CoV-2 virus in the dental practice
Waiting rooms are the first places where there is a risk of transmitting the virus from an infected patient to the dental staff. Therefore, it is recommended that there be a minimum number of patients in the waiting room with a mandatory distance greater than 1.8 to 2m. There should be a minimum number of unnecessary things in the waiting room, and magazines, toys, books, etc. should be removed from the office. If necessary, patients should first be interviewed by telephone to determine if they have been in contact with potentially infected persons, if they have or have had symptoms and signs of the COVID-19 disease, i.e. patients are required to provide such information upon their arrival at the dental office 26 .
The staff of the dental institution must wear clean clothes intended for work during the working day even if they are not in contact with the patients, and the clothes intended for work are to be changed daily. During the entire working hours, the dental staff in the office must wear a face mask, i.e. a surgical mask. If it is necessary to touch the mask for any reason, hands are to be washed with an antiseptic with diluted alcohol in a concentration of 70-75% before and after such manipulation. Protection of the hands from virus contamination is usually performed with 2 pairs of disposable gloves; when, for any reason, the outer gloves are potentially contaminated or damaged, such gloves are first decontaminated with diluted alcohol in a concentration of 70-75%, then the outer (second) gloves are removed, and the decontamination is done again with alcohol on the inner (first) gloves. Finally, new disposable the outer (second) gloves are put on again. Protective disposable shoe cover can also be worn over the shoes worn at work. Furthermore, dental staff who first come into contact with patients must keep a safety distance of 1.8 to 2 m from the patient, and must wear goggles or a protective visor to prevent the contamination of the conjunctiva or mucosa from droplet transmission > 5 μm, which may contain a virus that can be released into the air by an infected patient. With the described measures, the prevention of virus transmission from a known or unknown virus carrier is ensured, i.e. possible direct contact or droplet transmission of the virus, or indirect transmission of the virus from things is prevented 26 .
Dental patients should be divided into 2 groups: Group 1 -patients for whom there will be no machine-generated aerosol, and Group 2 -patients for whom there will be a machine-generated aerosol.

Group 1 -patients for whom there will be no machine-generated aerosol
For patients in Group 1, where dental interventions are performed that do not require the use of handpieces, which cannot produce aerosol through the use of compressed air for their work, the following protective measures are applied: wearing a respiratory face mask that has the ability to stop particles the size of 0.3 µ with an filtration efficiency of 95%; these masks are marked differently (although they are the same in characteristics), dependent on the country of origin: N95 (USA code), KN95 (China code), KF94 (Korea code), and FFP2 (EU code and UK code) 41,42 . These masks are disposable and changed every 20-30 minutes if exposed to intense spraying with liquids, aerosols, etc., or after 1 hour in normal "dry" working conditions 43, 44 . This type of mask also has the ability to protect against aerosols and large droplets of fluid, which are created in dental work 2,45,46,47 .The effectiveness of protection with these masks is reflected in the fact that they retain particles the size of 1-5 µ with 95% success 2,48 , and indicates that they can provide protection for dental staff. It should be noted that they do not provide such protection if placed incorrectly, if not applied close-fitting to the face and if worn by a person with a beard 49 . The use of protective visors and goggles are mandatory parts of the personal protective equipment of dentists and other staff. It is desirable that the goggles be waterproof and the visor ergonomically shaped, because the dentist is in very close contact with the patient's face in the course of their work, so the inadequate dimensions of the visor and its shape interfere with dental work. Combinations of waterproof glasses and face-shaped visors are the most functional ( Figure 1).
Other disposable protective materials include a disposable protective coat, a protective cap, 2 pairs of disposable gloves 51 , as well as protective disposable shoe covers (overshoes).

Slika 2.
Vodonepropusna zaštitna maska celog lica sa posebnim filterom za vazduh i mikromotorom za ubacivanje filtriranog vazduha u masku 52 Figure 2. Specially designed facial visor in the form of a mask for the whole face with a special air filter and a motor for inserting filtered air into the mask 52

Group 2 -patients for whom there will be a machine-generated aerosol
Dental procedures, such as: tooth preparation (tooth grinding) in prosthetic interventions, tooth cavity preparation, restorative dentistry, endodontic therapy of tooth root canals, use of ultrasonic dental plaque removers, machine tooth polishing, periodontal surgery, implant surgery, complex oral and maxillofacial surgeries, represent high-risk interventions. During the performance of the described procedures, an abundance of liquid and aerosol or blood in aerosol is formed, which, aided by compressed air from dental handpieces and equipment, under pressure, spreads into the air around the dental team, onto the dental equipment workbench, onto the interior in the office, filling the working space of the office. For this reason, N95 respiratory masks with the highest degree of protection, protection levels 2 and 3, which have filtration efficiency, i.e. retention of submicron particles with an efficiency of ≥ 98%, need to be used 42 . Face masks are changed after each patient, after extended procedures and after each 20 minutes in highly aerosolized environments 42 . Protection of the eyes and face, i.e. mucous membranes of the eyes and nose must be done with waterproof goggles and additionally with a protective visor. It is possible to protect the mucous membranes of the eyes, nose and mouth, i.e. the entire face of the dentist with a special industrially designed facial visor in the form of a full face mask, which has its own motor for filtering Poželjna je i upotreba koferdama 26 , u cilju smanjenja mogućnosti transmisije virusa, kao i jačih stomatoloških usisnih aspiratora 26 . Ostali zaštitni materijali za jednokratnu upotrebu obuhvataju vodonepropusni zaštitni mantil, vodonepropusnu kapu, 2 para rukavica za jednokratnu upotrebu 51 , kao i zaštitne jednokratne kaljače (nazuvice), koje su takođe vodonepropusne.
The use of rubber dams 26 , as well as stronger dental suction aspirators 26 , is also desirable in order to reduce the possibility of virus transmission. Other disposable protective materials include a waterproof protective coat, a waterproof cap, 2 pairs of disposable gloves 51 , as well as protective disposable shoecover that need to be water resistant.
All these protective measures also apply to assistants, nurses and other staff who are in the office while working with patients. It is advisable to arrange several interventions with patients during one visit to the dentist, whenever possible 9,26 .

Removal of protective equipment
After finishing the work with the patient, the procedure of removing the protective equipment follows, which needs to be carried out in a disciplined manner and in a certain order. During this procedure, there must be a person who is responsible only for this procedure. Firstly, the outer gloves of the nurse who participated in the work are sprayed with disinfectant (alcohol 70-75%, 0.5%, freshly made sodiumhypochlorite -bleach, benzalkonium chlorideasepsol ≥ 1%), then the back of the protective coat is unbuttoned and fully taken off with outer gloves, and outer shoe cover and disposed of into a container for contaminated material. The protective visor and goggles are then removed, sprayed with disinfectant and placed into a disinfection container. This is followed by spraying the inner gloves with disinfectant. In the end, the mask is removed by taking the tape of the mask behind the ear, removing it from the face and placing it into a waste container. This is followed by a re-disinfection procedure by spraying the inner gloves, removing the inner shoecover, and disposing of them into a container for contaminated material. This is followed by re-spraying the inner gloves with disinfectant, putting on new uncontaminated gloves, going to the locker room, removing the gloves, antiseptic hand washing and changing into a new, clean work blouse and pants for the health worker involved in the work, while the used work clothes are to be stored in the medical laundry container. It should be noted that health workers who work with high-risk
patients need to change their work clothes every day. The same procedure applies to the dentist, and to each of the staff members who participated in the work. What follows is a complete disinfection of the office and instruments according to the usual procedure for preventing the transmission of microbes, viruses and fungi in healthcare facilities 26 .

Conclusion
It is extremely important to implement a unique doctrine for the protection of dental staff from possible infection with the SARS-CoV-2 virus, as well as the prevention of infection with other pathogens that cause diseases during dental interventions. This procedure is extremely delicate, considering the fact that the dental profession is the most endangered profession with the possibility of infection of 100%. The main protective measures of the dental staff are related to the protection against machine-generated aerosols that may contain the SARS-CoV-2 virus of an infected patient. The use of waterproof disposable protective equipment, along with waterproof goggles, protective visors, N95 face respirators with a submicron particle retention rate of ≥ 98%, and the use of a full-face waterproof mask are possible safety measures for preventing the SARS-CoV-2 transmission to the dental staff.