COVID-19 Transmission Risk in Dentistry: A Review and Protective Protocols


 Among several potential sources of transmission for the spreading of the COVID-19, dental services have received a high volume of attention. Several reports, papers, guidelines, and suggestions have been released on how this infection could be transmitted through dental services, and what should be done. This study has systematically reviewed the published literature on dentistry and COVID-19 in order to develop a practically feasible protocol for re-opening and reorientation of dental services. The recommendations identified were tested with a convenience sample of experienced practitioners, and a practical step-by-step protocol is presented in this paper.

Introduction COVID-19, the newly discovered coronavirus disease rst diagnosed in China in 2019, has become pandemic across the world in a relatively short period. It has affected almost all aspects of human life worldwide. Many protocols have been established to minimize the number of infected people, yet this virus has already spread to all ve continents, affecting all communities regardless of borders, nationalities, or climate conditions (1,2). Up to May 31, 2020, the number of people who have been o cially reported to be infected by COVID-19 around the globe was more than 5,934,936 individuals, among which 367,166 deaths have been reported (3). It seems that the real numbers might be much higher than those gures.
COVID-19 has transmission pathways similar, but not identical, to those of other SARS-CoV infections, mainly through the respiratory system (4,5). Many considerations about the possible hazardous activities or workplaces have risen based on both our experience from previous SARS-CoV infections and our observation of the transmission pattern of the SARS-CoV-2 itself in this short time of its appearance. Among them, the potential transmission of the virus through dental procedures and dental settings has attracted much attention leading to either mandatory or voluntary suspension of routine dental care (6,7).
The concern about dental practice coronavirus transmission has been widely recognized around the world.
Recently, The New York Times noted that dentistry was the most at-risk profession for nCoV-19 among various occupations (8). Based on the nature of the dental procedures, and the close proximity of the dental team with patients, the disease could readily spread from infected patients to the dental team, and vice versa, and subsequently to other patients, if appropriate protective infection control measurements are not undertaken (9,10).
Dental teams, led by the dentist, are very familiar with universal personal protective equipment and other cross infection control measures and risk assessment. Whilst these issues have become prominent during the pandemic; there has been uncertainty regarding the most appropriate Personal Protective Equipment (PPE) and way of working. Each country of the world has been required to develop policy very rapidly and has interpreted medical and scienti c evidence and advice from the WHO in very different ways. Similarly, the guidelines written for COVID-19 and advice published for the safe and effective practice of dentistry have shown much variation around the world and also within countries. Perhaps this is due to the lack of evidence-based. It is likely to take some time to develop an effective vaccine and implement widespread immunization, and so it is critical that nd new ways of working so that we can offer much-needed care for patients with oral health issues. The long term consequences of this pandemic are currently unknown but undoubtedly will result in a 'new normal' for the provision of dental care.
Many suggestions and protocols have been issued for re-opening or reorientation of dental clinics in a short period of time. However, many of the protocols have been produced quickly (for understandable reasons) with a focus on the ideal rather than a realistic point of view (11)(12)(13). This systematic review focuses on the risk of the transmission of the COVID-19 during dental treatments and provides pathways and protective protocols to minimize them, bearing in mind the long-term necessity of actions and realistic, practical measures.

Method
In this rapid systematic review of the literature, we searched Pubmed, ISI, and SCOPUS electronic databases using MESH terms and the following keywords: ("Covid-19" OR "Covid19" OR "Corona" OR "Coronavirus" OR "SARS-CoV-2") AND ("Dentistry" OR "Dental"). All articles from the 01.01.2020 until 10.05.2020 that satis ed our selection criteria of being recommendations or guidelines for dental practice during the COVID-19 pandemic were retrieved. Articles were excluded if they were not found to be relevant, produced before the COVID-19 pandemic, or opinion-based without any supporting evidence. Some clinical organizations for example; The World Health Organization (WHO), The Centers for Disease Control and Prevention (CDC), The National Health Service (NHS), The American Dental Association (ADA) and, American Dental Hygienists' Association(AHDA) had also published recommendations and guidelines through their websites. We therefore also undertook a Google search for these and used the English, German, and Farsi languages. These were reviewed by two authors independently and who have experience of infection control in dentistry and medical study methodology. Articles were critically appraised and data extracted to compile a summary clinical protocol for dental practice during the COVID-91 pandemic. The extracted statements of recommendation, both from the published articles and the clinical organization's publications, were formed into grouped items. We also informed this grouping by including the views of ten dentists with more than ve years of clinical in addition to the views of the two authors who had undertaken the data extraction. These additional dentists were selected conveniently based on clinical experience from Iran.

Main Results
This review found 38 articles, of which 9 satis ed our inclusion criteria. The key feature of the nine included studies are summarised in (Table 1). We noted that some researchers had preferred to publish their work rapidly and in alternate ways to using peer-reviewed journals.
Also, some of the guidelines provided by some clinical organizations were reviewed. Since these protocols were very long, these protocols were summarized, and the key elements have extracted from these published guidelines. The recommendations and guidelines identi ed are shown in Table 2 (3, 22-28).

Discussion
A large number of articles were identi ed considering the short duration of the search period. Due to the rapid development of the COVID-19 pandemic and the short publication timeframe, some published articles have subsequently been retracted or rejected with newer information. The publication of unreliable papers has several negative consequences that increase the chance of incorrect treatment for patients (29). In this study, we tried to use more valid and practical articles and protocols.

Possible Risk of Transmission of COVID-19 in Dentistry
Whilst it may be di cult to identify the particular mechanism of infection for the individual patients, we are aware of the common routes of transmission. Droplet spread and fomites are the main modes of transmission by the respiratory system in intrapersonal contacts and especially during sneezing, dry coughing, or even talking (30). We also know that COVID-19 is present in saliva, but transmission through this route has not been conclusively con rmed (31). Considering the main path of transmission of COVID-19 disease, dental procedures that lead to the spray of saliva particles into air (which means almost all dental procedures) could higher the possibility of contamination (21). Much effort has been made in the literature to de ne droplets and aerosols and to distinguish between their ability to carry COVID-19 virus. Knowing which dental procedures produce aerosols that could carry the virus is important to help de ne the level of risk that these procedures create. This then helps to de ne what Personal protective equipment (PPE) is appropriate. As a result, both kinds of particles, or better to say, anything that comes out of the patient should be considered hazardous (32)(33)(34). Given the fact that the majority of dental instruments are composed of metal and polymers, the COVID-19 could adhere and persist on these surfaces for several days. Consequently, they could present a risk of virus transmission if they are not properly decontaminated (30,35). Fundamentally, COVID-19 in dentistry may be transmitted through air, droplets, and contact (19,36). Not only the professionals could act as transmitters, but also, they could become infected during human-to-human transmission, through non-invasive salivary secretions like patients cough or sneeze, or treatment procedures, such as using a high-speed handpiece or ultrasonic instruments which release aerosols which may contain saliva, or blood bacteria and viruses into the environment. Therefore, using appropriate protective wearing is critical, given the fact that the salvia and dental uids spreading have the potential of virus transmission because of the close distance between patients and professionals (18,37).

Special Precautions in Dental Procedure
PPE and hand hygiene should be given very serious attention in a dental clinic at all times, even when no patient is attending (18,38). Regular hand hygiene could be regarded as a critical element in any controlling protocol to reduce the infection outbreak (38). Due to the fact that dentists have close contact with the patients and their hands are exposed to the mouth uids and aerosols, using an antiseptic solution before treatment of each patient is urgent. Although broad types of antiseptic solutions are available, the ethanolic solutions (above 70% concentration) are suitable for this process because of the non-toxic entity, While ethanolic solutions are useful to hand hygiene using soap and water is also effective (36). Using masks with pores less than 50μ m is necessary for dental professionals (37,39,40). On the other hand, these particles could be transmitted from the eyes, thereby, using appropriate goggles or face shields could decrease the risk of the infections (25).
As the aerosols spread from the mouth, suggesting patients use antiseptic oxidative mouth rinse would be protective prior to and after treatment. Currently, ADB and CDC only recommend peroxide to eradicate the virus. Moreover, public health authorities have advised 0.2% chlorhexidine mouthwash (CHX), 1% povidoneiodine (PI), 1.5% hydrogen peroxide (H2O2), or 0.05% hypochlorous acid (HOCl). CHX is weak in terms of virucidal, and the other three (PI, H2O2, HOCl) all have excellent virucidal properties but are weak in substantivity, because saliva ow can potentially replace the virus. Clinically, the most acceptable in terms of virucidal and taste is 1.5% hydrogen peroxide (36,(41)(42)(43)(44)(45).

Speci c Therapeutic Considerations in Dentistry:
The results of a study on 2,537 patients showed that the nCoV-19 pandemic led to a decrease in the emergency dental treatments in Beijing, China because those patients were reluctant to have dental treatment because of the potential risk of infection by going outside(46). Oral hygiene and preventive practices have always been very important, but now, in the current condition, they are more critical than ever. Higher levels of oral hygiene could decrease the need for a person to attend a dental clinic for urgent matters; and at the same time, could signi cantly help the person to remove the virus from the body at the early contamination phase in day to day life (47) and also to reduce the bacterial load in the mouth and the risk of bacterial superinfection especially in patients who are prone to altered bio lms due to diabetes, high blood pressure or cardiovascular disease (48).
The COVID-19 epidemic has led to the closure of dental o ces around the world. Some countries are currently re-opening or planning to re-open dental services. There are many protocols that need to be considered and integrated into a comprehensive and concise protocol (Table 1 & 2). Smart appointment systems and generally avoiding crowding in dental clinics are vital (49). Adequate time should be given between appointments so that appropriate decontamination procedures can be carried out (49).
If emergency treatment is necessary, the ADA COVID-19 Dental Emergency document (40), recommends that chemomechanical caries removal and hand instrumentation should be prioritized over rotary systems.
In the case of symptomatic irreversible pulpitis, reducing pain with a pulpotomy and pulpectomy or vital pulp therapy is recommended over conventional root canal therapies, if possible (18,50,51). For periodontal treatments, priority should be given to manual scaling and polishing instead of ultrasonic techniques. In the case of tooth extraction, the use of high-volume saliva ejectors is crucial, preferably in a supine position of the patient. If a suture is required, using absorbable material is advocated (35). For the patients suffering extreme toothache and extensive caries, extraction of the pathogenic teeth could be considered instead of a restorative treatment as this could reduce the time of treatment and subsequently decrease the risk of infection (50, 51). For prosthodontic treatments, enhanced disinfection techniques of prosthetic materials and impressions are highly emphasized to minimize the risk of cross-contamination to prosthodontic laboratories. To avoid gag stimulation, salivary suction is recommended. Finally, for diagnosis purposes, using extraoral radiographic such as Dental panoramic radiographs (DPRs) or Cone-beam computed tomography (CBCT) are endorsed over the intraoral radiographs (18,50).
Because reducing face-to-face visits is necessary to reduce the risk of infection. The teledentistry provides an opportunity for many patients to access uninterrupted clinical and supportive care and the chance to triage increasingly critical conditions needing face-to-face clinic visits. Furthermore, teledentistry allows for the continuing clinical training of Dental practitioners (52-54). COVID-19 epidemic may cause enduring transformation in dentistry with the advancement of teledentistry(55), the characteristically visual nature of dentistry makes it perfect for the act of telemedicine(56).

Conclusion
This review focused on the methods, protocols, and recent reports regarding the nCoV-19 infection and the transmission process, which could occur during routine dental treatments and surgeries. While the currently available evidence has not demonstrated a clear and direct relationship between the dental treatment or surgery and the possibility of the transmission of COVID-19, there is clearly the potential for transmission to occur. This could result in either because of contaminated dental uids, saliva, or aerosol spread during close human-to-human contact during dental treatments or by contact with contaminated instruments or surfaces. While the currently available evidence has not demonstrated a clear and direct relationship between the dental treatment or surgery and the possibility of the transmission of COVID-19, there is clearly the potential for transmission to occur. This could result in either because of contaminated dental uids, saliva, or aerosol spread during close human-to-human contact during dental treatments or by contact with

Availability of data and materials
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

IX)
Dental unit water quality -Lack of a precise guideline on the management of pediatric patients at various stages of the disease, from positive to asymptomatic to healed ones. 6 Meng and Hua (2020)/ China

I)
In areas where COVID-19 spreads, non-emergency dental practices should be postponed.

II)
Pulp exposure in symptomatic irreversible pulpitis could be made with chemomechanical caries removal.

III)
If a tooth needs to be extracted, an absorbable suture is preferred.

IV)
For patients with facial soft tissue contusion, debridement, and suturing should be performed.

V)
Life-threatening cases with oral and maxillofacial compound

II)
If a patient replies "yes" to screening questions, and body temperature is no less than 37.3 °C, the patient should be immediately quarantined and reported to the infection control department.

III)
If a patient replies "no" to all screening questions, and his/her body temperature is below 37.3 °C, the dentist can treat the patient with extra-protection measures and avoids spatter or aerosol-generating procedures.

IV)
If a patient replies "no" to all screening questions, but his/her body temperature is no less than 37.3 °C, the patient should be instructed to specialized clinics for COVID-19. The study provides a guideline for dental school; however, more precise guides on the management of patients at various stages of the disease, from positive to asymptomatic to healed ones, are required. IX) Decontamination of equipment, surgeries/ operatories after reach patients. 9 Spagnuolo et al. Avoid or minimize operations that can produce droplets or aerosols

IV)
Use of saliva ejectors with a low volume or high volume -Lack of a precise guideline as to which dental Tx should be considered as urgent dental disease Table 2 Guidelines that should be adopted in a dental setting during Covid-19 Prior to dental treatment Before entering a dental o ce -Delay non-urgent dental and cosmetic services. -Hand hygiene should be performed before and after all patient contact, contact with potentially infectious material, and before putting on and after removing PPE.
-Use alcohol-based hand rub (ABHR) with 60-95% alcohol. If hands are visibly soiled, use soap and water for at least 20 seconds before returning to ABHR.

CDC
-Preoperative antimicrobial mouth rinse like peroxide could reduce the number of microbes in the oral cavity. Since SARS-CoV-2 may be vulnerable to oxidation, use 1.5% hydrogen peroxide or 0.2% povidone as a preprocedural mouth rinse.
ADA -Rubber dams and high-volume saliva ejectors can help minimize aerosol or spatter in dental procedures.
CDC, NHS, ADA -use extraoral dental radiographs, such as panoramic radiographs or cone-beam CT, as appropriate alternatives of intraoral radiography ADA -If aerosol-generating procedures are inevitable for emergency care, use 4-handed dentistry.