It has been stated that the mouth is a Petri dish and the cavity of the mouth is home to mutliplex, potent, and diversified microbiologic compilations in the human body. Current studies propose that up to 1000 bacterial species exist in the oral cavity, occupying several diverse microbial niches, for example saliva, teeth, gingival sulcus, hard and soft palate, tongue, cheek, lip, and attached gingival.¹,² By now, over 700 microbial species have been detected in saliva, many of which are associated with oral and systemic infections.³ Since saliva can host many distinct viruses including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the transmission risk of viruses through saliva is inevitable in a dental office. The WHO has asserted that the pandemic virus of SARS-CoV-2 could have a profound repercussion on dentistry as it predominantly transmits through droplets and aerosols.⁴ Aerosols can be defined as “suspensions of liquid and/or solid particles in the air generated by coughing, sneezing, or any other act that expels oral fluids into the air.”⁵ Dental procedures can provoke generation of the cross-infection, droplets, aerosols, and spills that are contaminated with saliva, which may specifically infect uncovered skin/conjunctiva/mucosa, or be breathed in by the professional, causing potential cross-contamination. In addition, saliva-infected aerosols and droplets can also contaminate inanimate areas in the dental operatory which too may lead to nosocomial infection.⁶ Dentists are at a high occupational risk of infection; therefore, we have to be proactively vigilant and pursue rigorous infection control protocol. We suspect getting to be another SARS-CoV-2 casualty, being an asymptomatic spreader, and tainting members of our family. Therefore, this review focuses on highlighting the potential sources and factors correlated with the transmission of aerosols, types of pathogens they can harbor, primary properties of aerosols generated during routine human activity and everyday dental procedures, its hazardous effects, and the different techniques to manage aerosol and to decrease the risk of cross-infection to patients and health-care workers.

Literature research

The electronic research was carried out by searching the PubMed and Advanced Search (Basic Search) catalog to search evidence-based clinical trials related to aerosol-generating dental procedures and strategies adopted to prevent aerosol. A Google search was conjointly been undertaken to seek out different recommendations for dental practice and dental guidelines in context to aerosol generating procedures throughout COVID-19 pandemic. The electronic research was complemented with a hand search of the following websites: “Irish Dental Association, American Dental Association, Australian Dental Association, Swiss Dental Association, The Royal Dutch Dental Association, Scottish Dental Clinical Effectiveness Programme, Centers for Disease Control and Prevention, Biosafety Working Group of the São Paulo Regional Dentistry Council, Royal College of Dental Surgeons of Ontario, Chinese Stomatological Association, Croatian Chamber of Dental Medicine, Dental Council of India, Irish Dental Association, Myanmar Dental Association, Norway Dental Health Service – FHI, Philippine Dental Association Science Committee, The Polish Dental Association, Spanish National Dentistry Council.”

Three search strings were run in PubMed from inception to April 01, 2021. Search terms were combined in the search strategy using Boolean operators [Supplementary 1]. In PubMed, the following strings were combined: ([aerosols {Mesh} OR aerosol OR aerosols OR bioaerosol OR bio-aerosol OR “bio aerosol” OR bio-aerosols OR “bio aerosols”] OR [”Aerosol generating procedures”]) AND (COVID-19).

Study Selection

Eligibility assessment of the studies was performed independently in an unblinded standardized manner by three investigators (KR, HR, and PS). After initial search and duplicate removal, titles of the identified studies were reviewed for relevance to the review question. Further, the abstracts and full texts of the eligible studies were evaluated independently and the articles addressing review questions specifically were selected for the review. If any disagreements between reviewers occured regarding the inclusion of studies they were resolved by consensus and discussion with the fourth reviewer (PK).

Aerosols generated during routine activities

During this COVID-19 pandemic, all of us have remained incredibly focused on aerosol-generating procedures (AGPs), but it is crucial to recognize that aerosols are additionally generated via routine human activities (e.g., respiration).⁷ Papineni and Rosenthal have revealed that around 90% of the particles produced by human expiration are <1 μm.⁸ Table 1 shows the outcome of an experiment performed by Duguid,⁹,¹⁰ who concluded that 95% particles were lesser than 100 μm, and the greater number were between 4 and 8 μm. The majority of small droplets emerge from the front of the mouth and a few, from the nose or from the throat.{Table 1}

Aerosol-generating procedures in dentistry

AGPs can be defined as “any medical or patient care procedure that results in the production of airborne particles (aerosols)”¹¹ Table 2.¹²,¹³,¹⁴,¹⁵,¹⁶,¹⁷,¹⁸,¹⁹ According to a review, use of high-speed handpieces and 3-in-1 syringes account for 56% of the AGPs, powered (sonic/ultrasonic) scalers for 43%, slow-speed handpieces for 29%, and surgical handpieces account for 22% AGPs.¹⁷ In spite of the fact that the aerosols do not have a dominant role in the transference of SARS-CoV-2 in the usual everyday functions, the status is dissimilar within the dental operatory. This is because many dental devices need a water splash to cool the operating tip and to restrict heat generation. The water, when combined with compressed air, is used as a coolant, and spraying generates aerosols that become infected with microbes from mouth.¹⁸ A water sprayer is also utilized to lavage the operating site to increase the operator's vision.¹² A COVID-positive patient bears several viruses in his saliva and on tongue.¹⁹ If aerosols generated procedures are performed on these individuals, they are likely to transfer the virus to the dentist.²⁰ The mean level of bioaerosols generated depends on the procedures; greater levels of aerosol are produced during cavity preparation (24–105 CFU/m³) and for ultrasonic scaling (42–71 CFU/m³), and lower levels for extraction (9–66 CFU/m³) and for clinical examination of oral cavity (24–62 CFU/m³).²¹ Most studies have reached the conclusion that bioaerosols return to baseline 2 h after the dental procedure.²² The sites displaying the greatest microbial contamination due to splatter and aerosol are masks of the operator and assistant, a unit lamp, areas close to spittoons, and mobile instruments. A dental surgeon operates from about ≤60 cm from the patient's mouth. Recent research shows that the greatest amount of microbial contamination in the dental operatory takes place not beyond 1 m from the mouth, through both aerosols and splashes.²³{Table 2}

Direct and indirect contact

Cross-transmission of the pathogen Table 3 in dental setups via direct contact can occur through hands, improperly sterilized instruments, or needle stick mishaps.²⁴ The prime contagion route includes inhalation of those pathogens that remain suspended in environment and later descend upon surfaces.²⁵ This happens because even after the treatment is completed, aerosols hover within the dental clinic air, with heavier and bigger particulates descending sooner.²⁰ Settling occurs in almost all areas, after which these can possibly act as a medium for transference of the SARS-CoV-2 virus via indirect contact. Researches prove that the viable virus was still present on plastic surfaces even after 72 h for up to 7 days.²⁶ Recent research has revealed that the COVID causing coronavirus can persist on some surfaces for up to 9 days.²⁷ Indirect transmission is through a fomite, “an object that has been in contact with an infected person and can thus spread the infection to another person.” Irrespective of the route of transference, the minimum dose of SARS-CoV-2 dose that can be contagious has not yet been confirmed. Hence, regardless of the level of infection, all areas that are potentially aerosol contaminated or touched by patients must be considered as a potential source of infection Figure 1.{Table 3}Figure 1

Modes aerosol transmission in dental clinics.

The transference of SARSCoV-2 primarily happens via aerosol and droplets. SARSCoV-2 can stay in aerosol for up to 3 h and has a comparatively longer half-life of almost 1.1–1.2 h.²⁶ Meng et al.³³ revealed the incidence of nine COVID-19 cases amid 169 dental professionals, emphasizing the significant hazard of contagion to professionals.

Saliva as a source of aerosol transmission

WHO has claimed that the novel coronavirus (2019-nCoV) transmits principally through saliva droplets or discharge from the nose.⁴ SARS-CoV-2 has the three different courses to show in saliva. It might enter the oral cavity through the lower and upper respiratory tract; SARS-CoV-2 within the blood may infiltrate the oral cavity through the gingival crevicular fluid; the salivary gland can be infected by this virus, with the particle discharge into the saliva via salivary ducts.³⁴ As SARS-CoV-2 can be identified in saliva,¹⁹ the hazard of transference of viruses that cause respiratory diseases via saliva cannot be overlooked within the dental setup; hence, the transference-based protections ought to be taken within the dental operatory.³³ COVID-19-positive patients without any symptoms may show up for the emergency in dental clinics. These patients are assumed to have infected saliva and are confirmed sources of contamination. Also, the nasolacrimal duct is associated with the conjunctival mucosa and the upper respiratory tract, and they share ACE2 on their cell membranes,³⁵ this endangers the dentist to the possibility of contamination through direct exposure of conjunctiva to splatter/droplets from patients amid the various dental procedures.

ACE2 is the prime host cell receptor of SARS-CoV-2 and plays an integral part in the access of virus into the cell.³⁶ The research laboratory results prove that angiotensin-converting enzyme-2 is expressed highly on oral mucosa epithelial cells, advocating that the mouth is at more risk for SARS-CoV-2 infection.³⁷

Role of particle size in transmission

Aerosols are assorted mostly depending on their particle size Table 4²⁵,³⁸,³⁹: Spatter is more than 50 μm, droplet is <50 μm, and a droplet nucleus is <10 μm. In dental environments, 90% of the aerosols generated are usually <5 μm⁴⁰ There is continuing debate about how to segregate them, the World Health Organization⁴¹ defines that “the particles of more than 5 μm as droplets, and those <5 μm as aerosols or droplet nuclei.” Particles of sizes between 0.5 and 10 μm have the highest potentiality to enter the lungs and respiratory tract, acquiring the probability to spread the infection.⁴² Segregating aerosols by their basic size is relevant in relationship to their dispersion patterns. Outcomes from some research have exhibited that aerosols from microbes such as SARS-CoV-2 can migrate >6 feet.⁴³{Table 4}

As per the present epidemiological research, 2019-nCoV has greater transmissivity as compared to SARS-CoV and MERS-CoV.⁴⁴ Hence, modification of standard safety measure disease control regime focused on 2019-nCoV is indispensable amid this flare-up Table 2. Various dental AGPs as defined in international dental guidelines and the mitigation procedures suggested by them are tabulated in Table 5.{Table 5}

A direct co-relationship between bioaerosols generated during dental procedures and the transference of highly contagious infections not only to the dental professionals but additionally to patients has been confirmed. The probability of SARS-CoV-2 spreading through aerosols even in the absence of aerosol-generating procedures has also been supported by some studies.

Recommendations

The COVID-19 pandemic has had a startling effect on clinical practice. There is a huge gap in our knowledge regarding the role of aerosol in the spreading of COVID-19 and to prevent its transmission. Indeed, it is the appropriate time for dental surgeons to update themselves and be dynamic members of health-care organizations dealing with the pandemic. It is indispensable that in the current scenario, the necessary salience should be given to dental procedures that the WHO labeled as emergencies. This would be a suitable step in an attempt to abridge any transference of COVID-19. Dentists who treat amid the coronavirus pandemic should assume “every” person is potentially infected and mandatorily follows universal infection control protocol, as discussed in the current article.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.

Supplementary 1: Information sources and search strategy

Three search strings were run in PubMed from inception to April 01, 2021. In PubMed the following strings were combined: ((”aerosols”[MeSH Terms] OR (”aerosol s”[All Fields] OR “aerosolization”[All Fields] OR (”bioaerosol”[All Fields] OR “bioaerosols”[All Fields]) OR “Aerosol generating procedures”[All Fields]) AND (”covid 19”[All Fields] OR “covid 19”[MeSH Terms] OR “sars cov 2”[All Fields] OR “sars cov 2”[MeSH Terms] OR “severe acute respiratory syndrome coronavirus 2”[All Fields] OR “ncov”[All Fields] OR “2019 ncov”[All Fields] OR ((”coronavirus”[MeSH Terms] OR “coronavirus”[All Fields] OR “cov”[All Fields]).

PRISMA flow chart

[INLINE:1]