Clinical Insights: What We Know and Don’t Know About Dental Aerosols

With the current COVID-19 pandemic, there is a great deal of commentary about the airborne spread of disease. All of us who practice clinical dentistry know that dental procedures tend to produce copious airborne materials. The potential for these airborne particles to carry the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from an infected patient to dental personnel—including dentists, dental hygienists, dental assistants, and office staff—is a major concern. Transmission from dental team members to patients is also a possibility.

As of this writing, dental offices are opening for elective procedures in most states, while a few remain closed except for emergency cases. In both circumstances, the provision of care will have to change in order to deliver effective and safe treatment. There is no question new protective procedures will be necessary, but, at this point, no one knows exactly what those will be. This commentary explores what we know about the airborne materials produced during dental procedures, and what we need to find out to make reasonable recommendation to safeguard personnel and patients.

What is in the cloud we see when using a handpiece or an ultrasonic scaler?

This question is best answered with a series of definitions.

Spatter (Splatter). All the material we see comes under the heading of spatter. By definition, if the airborne particle is large enough that it can be seen, it is spatter.¹ Because of its relative large size, spatter will behave in a ballistic fashion. Simplistically, this means it will act like a bullet and rise to a certain point, depending on trajectory and energy, and fall to the floor, environmental surfaces, or the clothing of dental personnel and patients. During treatment, the main component of spatter is coolant water—yet within the water is potentially infectious material that originates from the patient’s mouth. With restorative procedures, this will include debris from the tooth or possibly restorative material that is being removed. During dental hygiene and periodontal procedures, this will encompass plaque, calculus debris, and blood. In both instances, the spatter will contain saliva. The salivary glands and saliva have been shown to have high concentrations of SARS-CoV-2, so it can be assumed that spatter will contain the virus if the patient has an active or asymptomatic infection.

Aerosols. By definition, aerosols are too small to be seen with the naked eye.¹ Most industrial hygiene professionals define aerosols as particles less than 50 microns (about the diameter of a human hair). Some infection control groups have defined aerosols as particles less than 10 microns.² In both instances, aerosolized particles are small enough they can float in the air for a period of time and settle on environmental surfaces. How long these particles will stay in the air and how far they will float depends on size, weight, and other factors, such as air currents. Information on the behavior of aerosols that test positive for SARS-CoV-2 has been wide ranging; reports suggest distances of a few to many feet from the source, and time in the air from less than an hour to many hours.

Droplet Nuclei. Beginning as spatter but, as the water component of the spatter starts to evaporate and particle size and weight diminish, droplet nuclei become light enough to become aerosols. This may be the greatest concern with dental infection control, as droplet nuclei exit the mouth as relatively large particles and therefore are able to contain more biological material from the patient. As the water evaporates and they become small enough to become aerosols, the biological—and possibly infectious—material becomes more concentrated.

What do we know about the novel coronavirus and what remains unknown?

The simple answer is that we don’t know enough about the virus, and the information available and recommendations for healthcare providers are changing daily. We do know SARS-CoV-2 will concentrate in certain body parts and secretions. Those of greatest interest to the dental profession are nasopharyngeal secretions and saliva. It is a given that working in the mouth of a patient with COVID-19 will potentially expose clinicians to the virus. As many have recommended, providers should avoid treating a patient with a known, active case of COVID-19. Emergency treatment for those with a known COVID-19 infection ideally should be performed in a specially equipped operatory with negative pressure ventilation and full face masks, and closed ventilation for the operators. For the moment, this means referring these patients to a hospital, assuming hospital-based dental care is available.

The most likely danger will come from the asymptomatic individual with COVID-19 who is shedding the virus. The news media has reported on studies that indicate approximately 30% to 50% of many populations are asymptomatic carriers of the virus. The best approach would be to test all patients for the virus when they arrive at the office. While point-of-care testing is not possible at this time, there is a high probability this will become possible and perhaps mandatory in the near future. The American Dental Association has petitioned the US Food and Drug Administration and Centers for Disease Control and Prevention to make dental offices part of a primary care system, which will allow dental offices to perform diagnostic testing. As of this writing, many state boards have rules against dental offices performing these types of tests, so this will be subject to both federal and state rules. How the eventual regulations are stated will likely be a factor as to whether insurance will cover these tests in a dental setting.

What can we do now?

These recommendations are presented in very general terms and are based on equipment and technologies that currently exist. None of the recommendations are official federal or state regulations or recommendations. They are based on common sense and my understanding of infection control in both hospital and dental environments.

Drape the Operatory. Most dental settings have many flat surfaces and cabinets. In addition, various pieces of equipment are often stored in treatment rooms. Dental teams should drape this equipment, as is routinely done in a medical operating room. Only the items that will be used on the current patient should be exposed to aerosols and spatter. The fronts of cabinets, flat surfaces (such as tray tables and Mayo stands), and equipment (such as radiography units and scanning devices) should be draped. It would be best if these drapes were replaced after each patient, but plastic drapes could be wiped down with disinfectants. This is a major departure from current infection control practices in many offices, but until dental teams can check each patient for COVID-19, this will be a mandatory addition and added expense in patient care.

Preprocedural Mouthrinses. In many offices, it is routine to have the patient rinse with chlorhexidine (CHX) prior to treatment. Early studies have indicated that while CHX will reduce the viral load of SARS-CoV-2, a diluted hydrogen peroxide or diluted bleach mouthrinse is more effective in killing the virus. The currently recommended dilution for hydrogen peroxide is 1% to 1.5%. Commercially available hydrogen peroxide is 3%, so a 1:1 dilution with water will yield the recommended rinse. The dilution of bleach varies considerably, with a capful of bleach to 1 liter of water as one of the recommendations. Care should be taken with bleach solutions, as bleach will corrode stainless steel. Hydrogen peroxide is mildly acidic but, to my knowledge, does not corrode stainless steel.

While preprocedural rinses will reduce the amount of bacteria and virus in a patient’s mouth, the nasopharynx and salivary glands have been shown to be reservoirs of SARS-CoV-2, so the reduction of viral load from preprocedural rinses will be transitory. When possible, it may be beneficial to have the patient rinse several times throughout the procedure. This would be particularly relevant during routine prophylaxis and nonsurgical periodontal procedures.

Use of High-Volume Evacuation. Almost all dental offices have an evacuator system that is capable of removing a high volume of air/droplets/aerosols from the operating field. High-volume evacuation is usually performed by an assistant using a large-bore, disposable evacuation tip. The inside diameter of a large-bore evacuator tip is 13 mm or greater. This large internal size allows for a high volume of material to be removed from the treatment area, and has been shown to reduce the number of bacteria produced during various procedures by 90% to 95%.^3,4 Various high-volume vacuum devices that fit in the patient’s mouth and fit around an ultrasonic tip are available that allow for high-volume evacuation without the need for a dental assistant.

It needs to be strongly emphasized the routinely used disposable saliva ejector tip is not a high-volume evacuator. Even if the system is capable of removing a high volume of material, the small inside diameter of a saliva ejector is not capable of removing spatter and aerosols. In order to obtain the necessary spatter and aerosol reduction, the use of a saliva ejector as the only means of vacuum evacuation should be avoided. This will greatly impact the routine practice of dental hygiene. Whenever a handpiece or ultrasonic scaler is used, the procedure will require a high-volume evacuator. Again, a saliva ejector is inadequate.

Reduction of Material From the Nasopharynx. An important risk of aerosols and spatter that is not directly associated with the dental procedure comes from the patient’s normal respiration. During care, the patient is breathing directly in the practitioners’ faces. While high-filtration (eg, N95) masks will filter out a large amount of viral particles, as the name implies, they will only filter 95% of the potentially infectious material. I recommend the use of a facial surgical drape for the patient. These are commonly used in oral surgeries, but are rarely used in other dental procedures. These drapes consist of a disposable sheet that covers the patient’s nose, eyes, and hair, while having an opening that allows access to the oral cavity. This drape will “put a mask” on the patient’s nose and help block any particles exhaled through the nose. This drape will also act to absorb much of the spatter that originates from the mouth and, as a disposable item, will be thrown away after the procedure.

Personal Protective Equipment. As of this writing, the recommendations for personal protective equipment (PPE) are rapidly changing. Some are recommending full environmental protection, such as gowns with masks and independent filtered breathing equipment. While ideal, this level of protection is impractical at this time. It is likely the universal use of existing protective gear, with the addition of high-filtration masks (eg, N95) will be the norm for the foreseeable future. As a minimum, these must include a high-filtration mask, goggles or safety glasses with side shields, face shield, hair covering, and a disposable gown. Many clinicians currently practice in short-sleeved scrubs with a standard surgical mask and their routinely used glasses. This is inadequate to protect against SARS-CoV-2 infection. All of the items previously listed are necessary during treatment of every patient; in addition, all disposable items should be changed between each patient and nondisposable items wiped down with disinfectant.

What does the future hold?

The steps and recommendations outlined in this article are my opinion based on long-term experience in many areas of epidemiology and infection control, as well as the private practice of dentistry. Instituting these safeguards will be burdensome; it will also be expensive and slow the delivery of care. Under the current circumstances, it does not appear these steps can be safely avoided.

In the long term, two factors will probably come into play to allow the return of a more routine method of care. The first will be point-of-care testing for COVID-19. As mentioned earlier, such testing appears to be something that may transpire in a matter of a few months. If this happens, patients who test negative can be treated with minimal changes in office procedures. Those who test positive will need to have their treatment delayed, or, if emergency treatment is necessary, be treated in a specialized setting.

The longer-term solution will be an adequate vaccine similar to what we now have for influenza. With an adequate vaccine, the numbers of patients presenting with COVID-19 will be greatly diminished, and the immunity of treatment personnel will be greatly enhanced. Until this occurs, dental teams need to take precautions and infection control steps far beyond what the profession routinely used prior to this pandemic.

REFERENCES

1. Hinds WC. Aerosol Technology, Properties, Behavior, and Measurement of Airborne Particles. New York: John Wiley and Sons; 1982:6–8.
2. Cottone JA, Terezhalmy GT, Molinari JA. Practical Infection Control in Dentistry. Baltimore, Maryland: Williams and Wilkins; 1996:139–140.
3. Harrel SK. Use of an aerosol reduction device with ultrasonic scalers. Compend Contin Educ Dent. 1996,17:1185–1193.
4. King TB, Muzzin KB, Berry CW, Anders LM. The effectiveness of an aerosol reduction device for ultrasonic scalers. J Periodontol. 1997;68:45–49.

From Dimensions of Dental Hygiene. May 2020;18(5):16-18.