Aerosol Management Using High-Volume Evacuation

Dental aerosols are generated by a variety of procedures, and while oral health professionals have always been aware of aerosols and related pathogens, the COVID-19 pandemic brought the issue to the forefront. Industry stakeholders published several guidance documents at the beginning of the pandemic that recommended a variety of safety strategies for dental settings. These included prescreening patients with questions and temperature checks, staggering appointment times, decreasing the number of patients in the facility, changes to personal protective equipment (PPE) recommendations, and aerosol mitigation strategies, such as high-volume evacuation (HVE), also known as high-velocity evacuation.^1,2 

The Occupational Safety and Health Administration (OSHA) is a federal agency tasked with protecting the safety of all workers. Several OSHA standards exist to protect dental personnel from blood and chemicals, such as the bloodborne pathogens standard³ (BBP), hazard communication standard,⁴ and respiratory protection standard.⁵ ­Additional OSHA standards exist for dentistry, but these three are the most commonly discussed. Oral healthcare personnel are familiar with the BBP standard, as it has been a part of routine practice since the 1980s.⁶ The respiratory standard was lesser known until the COVID-19 pandemic, when it became widely cited in guidance documents.^1,2 Until that point, most dental teams were focused on BBP, rather than respiratory pathogens. 

The OSHA respiratory standard 1910.134 protects workers from respiratory hazards.⁵ Employers must have a written, worksite-specific protocol that outlines procedures for assessing and protecting against respiratory hazards, including the selection and provision of appropriate respirators based on these hazards. Common respiratory exposure hazards in dentistry include aerosol generating procedures (AGPs); examples include the use of high-speed handpieces, ultrasonic scalers, air powder polishers, and air-water syringes.^6,7 According to OSHA, AGPs are defined as a “medical procedure that generates aerosols that can be infectious and are of respirable size.”^2,7 The OSHA risk pyramid considers AGPs “very high risk” activities, as sprays from these procedures can aerosolize microorganisms and blood.^7,8 Visible spray from AGPs contains large particle droplets that travel quickly and settle on surfaces, whereas smaller, microorganism-containing aerosols ≤ 10 microns (µm) can remain airborne for long periods, which can then be inhaled.^6,9 

Aerosol Mitigation Strategies

Potentially contaminated patient bodily fluids can become airborne during dental procedures in the form of spatter and aerosols. Spatter is large droplet spray (larger than 50 µm) that follows a forceful trajectory until it contacts a surface or settles on the floor, not staying airborne for long.⁶ Aerosols are generally 0.5 to 10 µm in diameter, and, as noted, can remain airborne for extended periods.⁶ These smaller particles can penetrate the filters of surgical masks and enter the respiratory tract.⁹ For comparison, a human hair is roughly 50 to 70 µm in diameter, which is approximately 2000 times the size of an aerosol particle.^10,11 

Aerosol mitigation strategies include the use of dental dams, HVE, preprocedural mouthrinses, appropriate PPE (e.g., respirator, goggles, face shield, gown and gloves), staggering of patients, air purification devices, positive pressure ventilation, and possibly fallow time (leaving the operatory empty to allow the clearance/settling of aerosols).^1,2 Frequently used in medical settings, positive pressure ventilation is an engineering control that eliminates aerosols by continuous fresh air intake and venting air to the outside.¹² 

In dental settings, HVE has been recommended for AGPs even before the U.S. Centers for Disease Control and Prevention’s (CDC) Guidelines for Infection Control in Dental Health Care Settings was published in 2003.⁶ Four-handed dentistry involves procedures in which clinicians use handpieces with the help of a dental assistant utilizing HVE. Yet because dental hygienists typically work by themselves, use of HVE in this field has been slow to become routine practice.

Ultrasonic instrumentation is considered an AGP that requires HVE^2,6 because potentially infectious material from the operative site can form a spray that can be ejected up to 18 inches from the scaler tip.¹³ Although some clinicians use saliva ejectors in an attempt to control these emissions, Harrel¹⁴ states that a saliva ejector is “inadequate” for this purpose. In light of this shortcoming, and because most dental hygiene procedures do not lend themselves to the use of a dental dam, reliance on HVE and proper PPE is necessary.

Many new HVE devices are available. While each clinician should determine which product best suits his or her needs, suction devices must meet specified criteria to be considered HVE — which is something to bear in mind when selecting a system.

Criteria for High-Volume Evacuation

Several research studies indicate that HVE reduces aerosols by up to 90%.^9,13,14 The evacuation device must have an opening of at least 8 mm, and be capable of quickly removing a large amount of air — up to 100 cubic feet of air per minute — to be considered HVE⁹ (Table 1). Typical HVE devices feature an opening ≥ 8 mm (Figure 1) or multiple bore holes equivalent to 8 mm.⁹ Any device with an opening less than 8 mm (or openings totaling < 8 mm) is considered low-volume evacuation (LVE), which is adequate for fluid control, but not for aerosol control, as the diameter of the opening/s is too small⁹ (Figure 2). Saliva ejectors are LVE devices.⁹ There are several fluid control devices that fall into the LVE category, so clinicians should be aware of the differences. 

Asserting that it is best to capture aerosols in the oral cavity before they have an opportunity to become airborne, Harrel¹³ states this can be achieved by holding the HVE within 2 cm of the ultrasonic tip, which can be difficult as a solo operator. Yet, whether working alone or using a dental assistant, it is imperative to keep the HVE within the 2 cm distance to achieve optimal aerosol reduction.¹³

Multiple studies indicate HVE is still the gold standard for use during AGPs, which is in alignment with prior and current CDC guidance.^{1,6,9,11,13–18} A 2021 study by Ehtezazi et al¹⁵ tested fallow time after six AGPs were performed on mannequin heads with a combination of HVE devices. They found that each device tested significantly reduced aerosols, but did not completely eliminate them — so use of proper PPE, along with HVE, remains a prudent strategy. Also in 2021, Shahad et al¹⁶ reported similar results and suggested HVE as a primary aerosol mitigation strategy. A recent study by Li et al¹⁷ showed that HVE reduced aerosols by 60% as compared to LVE. Research by Suprono et al¹⁸ also noted significant aerosol reduction with ultrasonic scaling and HVE. These studies are consistent with previous findings in the literature dating back to 2003.^6,9

Types of Devices

Important factors to consider when selecting HVE devices include ergonomics, efficiency and design. For proper ergonomics, HVE devices must be lightweight and easily managed by a solo clinician. Long, heavy or coiled hoses cause tension on the wrist and arm, which can lead to musculoskeletal issues.¹⁹ Gupta et al¹⁹ recommend devices that swivel and utilize flexible hoses for better ergonomics.

Clinicians can choose from a variety of ergonomically sound HVE devices, and these fall into four general categories. One type attaches to the finger of the nondominant hand and provides a lightweight variable tip that rotates 360° — making it easy to maintain the recommended 2 cm distance.²⁰ Featuring an 11-mm-bore opening, this fingertip device allows the operator to maintain a neutral wrist position. 

A second type combines a mouth mirror and HVE that either has a 10 mm opening or several bore holes (alongside the mirror’s back and sides) totaling greater than 8 mm.^21,22 These mirror suction devices allow retraction, vision, fluid management and aerosol control (Figure 3). 

The third type serves as a mouth prop or bite block that also offers evacuation. These tools, known as dry field devices, provide excellent fluid and aerosol control while simultaneously helping patients keep their mouth open.²³ They increase clinical efficiency because an entire side can be completed without stopping or readjusting the bite block. While these devices are convenient, they may not be compatible for all patients, as the bite block device can be large and covers the oropharynx. This could be problematic for patients who gag, have difficulty breathing through the nose, have a small mouth, must swallow frequently, or need to feel a sense of control. 

A fourth device is a flexible, autoclavable suction tube that attaches to an ultrasonic scaler with a small clamp, capturing aerosols near the source at the tip and freeing up the nondominant hand for mirror use. This device was shown to reduce aerosols by 93%.²⁴ 

Shortened or curved HVE tips can be used alone or with an assistant, but the tip should be angled to avoid suctioning the lips, buccal mucosa or tongue.²⁵ 

Clinicians can also choose extraoral suction units — called extraoral local extractors — that utilize an arm ending with a cone or cup shape that is placed near the patient’s mouth to capture aerosols.²⁶ While these devices tend to be large and costly, Noordien et al²⁶ reported up to a 50% reduction in dental aerosols when such units are used, as compared to HVE plus LVE. While these extraoral devices may serve as a useful hands-free adjunct to HVE, this area needs further study.²⁷ An extraoral local extractor could be a potential solution for high-volume practices with an open-bay design.²⁸

Future Research Needs

Although much of the literature suggests HVE as the primary method for dental aerosol management, three general themes merit further study: 

1. Black-and-white categorization of therapies into AGP or non-AGP is overly simplistic,^29,30 as a range of procedures may not fall exclusively into either classification. This is an area that needs further definition and investigation; for example, future research might consider stratifying risk.³⁰ 
2. The transmission of viruses, such SARS-CoV-2, through dental aerosols also needs additional study.^29–31 So far, there have been no documented cases of SARS-CoV-2 transmission related to AGPs in dentistry³² — yet clearly a better understanding of the potential infectivity of pathogenic aerosols is needed.^29–32 
3. Current research methodologies in this area also have limitations, as most AGP studies use settle plates to detect droplets that have fallen.^29,33 However, droplets settle quickly, while aerosols persist for longer periods — so settle plates may not be capturing accurate data.^29,33 New approaches for measuring the transmissibility of viruses and other pathogens via dental aerosols would shore up scientific understanding of transmission risk.

Conclusion

Although HVE is widely regarded as a prudent and practical approach to controlling aerosols in the dental setting, no single device works best for everyone. When choosing HVE technologies, clinicians should exercise clinical judgement based on efficacy, evidence, ergonomics and preference. 

In addition, Harrel and Molinari⁹ suggest adopting a layered approach to aerosol management. This includes the use of appropriate PPE, preprocedural mouthrinses, HVE, and operatory high efficiency particulate air filtration technology — recommendations which are consistent with current infection control guidance. 

References

1. U.S. Centers for Disease Control and Prevention. Interim Infection Prevention Control Guidance for Dental Settings During the Coronavirus Disease 2019 (COVID 19) Pandemic. Available at: https:/​/​www.cdc.gov/​coronavirus/떓-ncov/​hcp/​infection-control-recommendations.html?CDC_​AA_​refVal=https%3A%2F%2Fwww.cdc.gov%2Fcoronavirus%2F2019-ncov%2Fhcp%2Fdental-settings.html. Accessed April 29, 2022.
2. American Dental Hygienists’ Association. ADHA Interim Guidance on Returning to Work. Available at: https:/​/​www.adha.org/​resources-docs/​ADHA_​TaskForceReport_著_​C.pdf. Accessed April 29, 2022.
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From Decisions in Dentistry. June 2022;8(6)42-45.