Development of Evidence-Based COVID-19 Safety Protocols for Practice in Dental Schools and Their Application for Future General Practice

When the first reports of an unknown clustering of respiratory signs and symptoms in Wuhan, China, started circulating in late 2019,¹ little if any information about the nature and modes of transmission of SARS-CoV-2 was readily available. As the transmission crossed borders and spread worldwide, including in the United States,² the dental community became highly anxious about the possible risk of transmission in dental settings. Moreover, there was a lack of evidence-based guidance on modes of transmission, how to prevent transmission, and the infectivity of SARS-CoV-2.

In response to COVID-19, which is caused by the coronavirus SARS-CoV-2, in March 2020 the American Dental Association (ADA) called for dentists to pause non-emergency care. Two months later, in May, the ADA released guidelines based on the best available evidence for reopening practices amid the pandemic, advising dentists on how to keep both themselves and their patients safe. In late July 2020, the ADA's Board of Trustees adopted an ad interim policy stating that oral health is an integral component of systemic health and that dentistry is an essential healthcare service.³ The Centers for Disease Control and Prevention (CDC) published and then subsequently updated its guidance on infection prevention and control for dental practices delivering care during the pandemic.⁴ These recommendations helped dentists (where permissible by federal, state, and local authority) safely resume the provision of non-emergent care and treat patients safely amid the pandemic.

Due to the pandemic and the uncertainties regarding safety measures needed to practice safely, clinical operations at many dental schools were reduced to emergency services only. Some clinics reopened for expanded services in the late spring or summer of 2020 after COVID-19 safety protocols were put into place. This article reviews the evidence that was used to develop COVID-19 safety protocols at two dental schools: University of California San Francisco in San Francisco, and Temple University in Philadelphia. The policies were developed to ensure safety of all dental personnel and patients receiving dental care at the schools. The article also comments on any reports of occupational transmission at these academic dental institutions and the applicability of COVID-19 safety protocols for future dental practice.

The sudden and rapid spread of COVID-19 and the risk of transmission of SARS-CoV-2 in dental settings required rapid synthesis of information on this virus and similar families of viruses. Developing the required safety protocols to prevent cross-infection with spread of salivary droplets and aerosol in a close patient-dentist working proximity presented a major challenge, similar to that experienced in the early 1980s during the emergency of the human immunodeficiency virus.

Dental schools were faced with the dilemma of ensuring safety of dental personnel, learners, and patients. During initial shelter-in-place or lockdowns, dental schools were reduced to emergency services or total closure of all operations in some states. Anxiety among learners, faculty, and staff was palpable. Information was very limited regarding the transmissibility of the virus as well as what protection measures, such as enhanced personal protective equipment (PPE), would be required to practice safely.

Following the evolving guidance from the CDC, ADA, and state local public health departments, dental schools were prepared to start operations again in staggered and varying approaches, keeping the needs and safety of patients and dental personnel, as well as PPE availability, at the forefront. The CDC interim recommendations for infection control in dental settings offered a multilayered strategy for safe reopening.⁴ New COVID-19 safety protocols were created to include standard and transmission-based precautions. COVID-19 education and training resources were generated to educate personnel and made readily available for reference at dental schools.

The ADA has defined the term "evidence-based dental practice" as "an approach to oral healthcare that requires the judicious integration of systematic assessments of clinically relevant scientific evidence, relating to the patient's oral and medical condition and history, with the dentist's clinical expertise and the patient's treatment."⁵  In early 2020, the evidence on COVID-19 was based mostly on case reports from Wuhan⁶and other health centers in China as well as laboratory studies. The major breakthrough in understanding SARS-CoV-2 was the deciphering of the genetic code of the virus, which helped to home in on the family of viruses from which SARS-CoV-2 originated.

The authors reviewed the literature on SARS-CoV-2 (including the outbreak in Wuhan, China, the progression of the pandemic, and modes of transmission), aerosols in dentistry, and evidence-based protocols for preventing SARS-CoV-2 transmission in dental settings. The dental schools at UCSF and Temple used pragmatic approaches to define the precautions necessary to resume patient care.

Over the past year the COVID-19 pandemic has progressed with varying intensity in different geographic locations. Dental professionals have continued to provide dental services to patients with appropriate safety protocols in place. According to the CDC interim guidance for infection control in dental settings, currently no data is available to assess the risk of SARS-CoV-2 transmission during dental practice.⁴ However, after operating for several months since reopening, it appears that dental care practiced under proper precautions has been safe and has not yet resulted in any clusters of COVID-19 cases.

This conclusion is supported by a recent study that reported a low prevalence of COVID-19 rates among practicing US dentists,⁷ indicating that current infection control recommendations may be sufficient to prevent infection in dental settings. Another study involving dental hygienists also reported low prevalence.⁸ These studies reflect the report from Wuhan's Hospital of Stomatology that documented only eight infected staff and residents during the height of the COVID-19 spread in that city.⁹

In dental settings, SARS-CoV-2 can be transmitted through several routes: (1) direct contact, via droplet transmission (cough, sneeze, droplet inhalation) or contact transmission (contact with oral, nasal, or eye mucous membranes)¹⁰; (2) indirect contact with contaminated surfaces or instruments and transferring the virus to mucosal surfaces; (3) contact with contaminated spatter (particles composed of a mixture of air, water, and solid substances larger than 50 μm in diameter) and aerosols (solid or liquid particles generally smaller than 50 μm)^11,12 generated during dental treatment performed on suspected or known COVID-19-positive patients.

It has been estimated and generally accepted that dental healthcare providers and dental patients may have an increased risk from airborne diseases associated with close proximity and/or aerosol generation in the course of dental practice. The major pathways of transmission of the SARS-CoV-2 virus in dental settings are by aerosol or droplet transmission routes. The source of these infectious aerosols may include salivary and/or respiratory secretions.¹²

The practice of dentistry involves the use of rotary dental and surgical instruments, such as handpieces or ultrasonic scalers, and air-water syringes. These instruments create a visible spray that can contain particle droplets of water, saliva, blood, microorganisms, and other debris, and they also aerosolize this biomaterial. Harrel et al found that an ultrasonic scaler produced aerosols that transmitted at least 18 inches from the operative site.^12,13 Dental literature shows that many dental procedures produce aerosols and droplets that are contaminated with bacteria and blood. It is also well established that aerosol particles of 10 μm or smaller pose a significant health concern, as they are likely to remain airborne for a longer period and enter the nasal passages and serve as carriers of respiratory diseases.¹² In addition, particles in the range of 10 μm to 20 μm may also evaporate, leaving droplet nuclei-contaminated material with a potential for viral transmission.¹³ In the past, spatter and droplet nuclei have been implicated in the transmission of diseases such as SARS, measles, and herpetic viruses.¹²

Contamination from spatter and aerosol dissemination poses a significant hazard to dental personnel when high-speed dental equipment is used.¹⁴ Thus, aerosol mitigation techniques that either reduce the production of aerosols or clear the aerosols quickly at the source are necessary for safe practice. The aerosol mitigation procedures employed at UCSF School of Dentistry and Temple Dental include the use of four-handed dentistry, rubber dams, intraoral high-volume evacuation (HVE), Isovac^®/Isolite^® systems, and extraoral HVE devices. HVE usage has been shown to reduce the contamination arising from the operative site by more than 90%.^11,12 Use of a dental dam with HVE or Isolite has been shown to significantly reduce spatter overall compared with the use of HVE alone.¹⁵

Dental aerosols may remain in the operatory for 30 minutes after the dental procedure.¹⁶ Therefore, it is important to catch and clear these aerosols at their source before they circulate in ambient air. SARS-CoV-2 has been shown to remain vital in aerosols for at least 3 hours, and it was more stable on plastic and stainless-steel surfaces than copper and cardboard surfaces.^14,17 On inanimate surfaces, human coronaviruses can remain infectious for up to 9 days.¹⁸ Therefore, dental operatories, including cabinets, doors, etc, must be disinfected thoroughly following the completion of each dental procedure. According to a study on coronaviruses on inanimate surfaces and their inactivation with biocidal agents, surface disinfection with 0.1% sodium hypochlorite or 62% to 71% ethanol significantly reduced coronavirus infectivity on surfaces within 1 minute exposure time, and the authors expected a similar effect against SARS-CoV-2.¹⁸

SARS-CoV-2 can also become airborne and spread through air currents and ventilation systems indoors.¹⁹ Droplet transmission can occur at a distance greater than even 2 meters (6.5 feet) if there is direct airflow from an infected person.²⁰ This emerging evidence forced dental practices to carefully assess their ventilation systems to mitigate airborne transmission of SARS-CoV-2.

Mitigating Transmission of SARS-CoV-2 in Dental School Settings

UCSF School of Dentistry and Temple Dental employed multilayered strategies in efforts to prevent transmission of SARS-CoV-2 in the dental school settings. The schools instituted combinations of the following safety protocols.

Engineering Controls

Engineering controls included the following:

Physical barriers in the form of sneeze guards were installed to create a partition between the staff and patients. The open floor plans in the dental clinics posed a challenge for adequate separation among patients. To increase safety in these clinic areas, the height of the partitions between the operatories were increased, leaving enough space from the ceiling for adequate ventilation.

Evaluation of ventilation systems was performed. It was confirmed that buildings had "once through" or 100% outside air and code-required airflows with six or more air changes per hour.²¹ The direction of air clearance was studied and approved for safe operations. Practice areas that had recirculating air were assessed for installation of high-efficiency particulate air (HEPA) filters, minimum efficiency reporting value (MERV) 13 filters, and ultraviolet C (UVC) light to disinfect ambient air.

Physical distancing measures were also put in place to enable adequate distancing between people in all areas of the buildings.

Administrative Measures

Steps were taken administratively to limit SARS-CoV-2 transmission at the dental schools. Foremost, COVID-19 screenings were implemented, whereby prior to arrival at the dental school patients are prescreened via telephone at the time of confirmation of their appointment. Upon arrival, all patients are screened at the building entrance using a COVID-19 screening questionnaire. This questionnaire takes into account symptoms related to COVID-19, recent travel history, and any recent unprotected close contact with COVID-positive persons, including family. Providers also document a negative COVID-19 screening in the patient's electronic health record. The patient's temperature reading is taken and documented as well.

All staff, faculty, and learners are screened via a screening app from Conversa Health. This screening questionnaire is taken within 4 hours prior to the beginning of the shift.

Other administrative measures taken to mitigate transmission of the virus are listed in Table 1.

Work Practice Controls

A number of work practice controls have been implemented and include recommendations for minimizing or, if possible, completely avoiding aerosol-generating procedures, as well as minimizing use of rotary instruments like ultrasonic instruments, dental handpieces, and air-water syringes. Minimally invasive/atraumatic restorative techniques, with hand instruments only, have been prioritized. Aerosol mitigation techniques, as described earlier, have been employed.^12,17

Asymptomatic preprocedural COVID-19 testing has been implemented. Patients undergoing aerosol-generating procedures are tested for COVID-19 prior to the procedure through administration of a nasopharyngeal and oropharyngeal swab RT-PCR (real-time polymerase chain reaction) test at the dental school testing site. This measure has ruled out performing any aerosol-generating procedures on asymptomatic or pre-symptomatic COVID-19-positive individuals.

Other work practice control measures include disinfection of high-touch surfaces like door handles and elevator buttons multiple times throughout the day and disinfection of any shared items such as pens and signature pads after each use.

Clinical Infection Control

Infection control measures have included the use of preprocedural mouthrinses prior to performing any oral examination or treatment.^12,22 Also, strict adherence to hand hygiene, as well as hygienic clinic spaces, has been recommended for staff, providers, and patients. All operatories and clinic spaces have been cleared of any clean or bulk items that may become exposed to infectious spatter or aerosols during treatment. Additionally, use of US Environmental Protection Agency (EPA)-registered disinfectants that have qualified under EPA's emerging viral pathogens program for use against SARS-CoV-2 (List N on the EPA website²³) has been instituted for clinical disinfection.

Personal Protective Equipment

PPE measures have been enhanced, especially for aerosol-generating procedures. PPE required for patient care includes isolation gowns, N95 respirators or powered air-purifying respirators for aerosol-generating procedures, surgical masks, protective eyewear, faceshields, bouffant caps, and exam gloves.²⁴ Guidance and education have been provided to personnel on appropriate PPE usage and donning and doffing procedures to minimize self-contamination. Visible signage and reminders have been posted in the clinics to aid in PPE compliance.

The year 2020 was challenging, to say the least. Dental practices had to quickly pivot to ensure dental care was safely provided to patients while keeping dental team members safe. Dental professionals traditionally have been trained well in infection prevention practices, including appropriate use of PPE. The studies indicating low COVID-19 prevalence rates among dental professionals further bolster the assertion that dentists are adequately trained and skilled in infection prevention practices. This demonstrates that providing dental care during the pandemic has been safe when COVID-19 safety protocols are followed meticulously.

During the past year, the two academic dental institutions examined in this article have had no reports of SARS-CoV-2 transmission due to exposure while providing, or while patients were receiving, dental care. Any reported cases among personnel have all been community acquired, and none could be traced to occupational exposure. This is a testament to the COVID-19 safety protocols in place, including appropriate use of recommended PPE.

As COVID-19 vaccinations continue to be administered widely and the prevalence of the virus declines further, the risk of SARS-CoV-2 transmission in dental settings can be expected to reduce further. It is too soon, however, to relax the COVID-19 safety protocols. There is hope that in coming months some of these protocols will evolve and become less restrictive.

Dental aerosols as possible vectors of disease in dental settings will continue to be further studied. Enhanced respiratory protection, including the use of N95 respirators or powered air-purifying respirators worn by dental professionals during aerosolizing procedures, may be relaxed as the threat from aerosol-transmissible diseases like COVID-19 becomes less prevalent. Decision-making will be steered by existing and emerging evidence and definitive guidance from the CDC and regulatory agencies.

Going forward, dental practices will likely be designed and constructed with consideration given to future threats from similar respiratory pathogens. Quality of ambient air in dental practices has also garnered due attention and will continue to be at the forefront for ensuring health of dental professionals and patients.

The dental clinics at UCSF and Temple dental schools have operated safely with evidence-based aerosol mitigation techniques in place, providing care to patients in clinics with open floor plans. Patient screening and testing measures have proved to be adequate to rule out performing dental aerosolizing treatment on asymptomatic or pre-symptomatic COVID-19-positive individuals. Based on the evaluation of the risk of aerosol transmissible diseases in dental school settings, negative pressure rooms were not required. Alternate strategies were developed to refer any emergency dental procedures on COVID-19-suspected or -positive patients to a hospital setting where treatment could take place in designated negative pressure rooms.

Throughout this pandemic, healthcare professionals, including those in the dental community, have learned how to deal with an exceedingly impactful crisis in a swift but evidence-based manner. Lessons gleaned during the pandemic and research performed on SARS-CoV-2 will provide a valuable resource for future challenges.

Ramneek Rai, DDS
Director of Health and Safety and Assistant Clinical Professor, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, San Franscisco, California

Amid Ismail, BDS, MPH, MBA, DrPH
Dean and Laura H. Carnell Professor, Temple University Maurice H. Kornberg School of Dentistry, Philadelphia, Pennsylvania