Aerosols in dentistry

[Dr Chetna Bogar]

Aerosols were defined as particles less than 50 micrometers in diameter. Particles of this size are small enough to stay airborne for an extended period before they settle on environmental surfaces or enter the respiratory tract. The smaller particles of an aerosol (0.5 to 10 µm in diameter) have the potential to penetrate and lodge in the smaller passages of the lungs and are thought to carry the greatest potential for transmitting infections. Splatter was defined as airborne particles larger than 50 µm in diameter. These particles behaved in a ballistic manner. This means that these particles or droplets are ejected forcibly from the operating site and arc in a trajectory similar to that of a bullet until they contact a surface or fall to the floor. These particles are too large to become suspended in the air and are airborne for short time. These two definitions of aerosols and splatter were given by Micik and colleagues in their work on aerobiology.
Therefore the greatest airborne infection threat in dentistry comes from aerosols (particles less than 50 µm in diameter) due to their ability to stay airborne and potential to enter respiratory passages. With the emergence of TB, however, splatter droplets also must be considered a potential infection threat. The usual method for transmission of TB is through the formation of droplet nuclei. These form when a droplet of sputum or saliva containing Mycobacterium tuberculosis is projected from the patient by coughing or potentially by splatter from a dental procedure. As the droplet begins to evaporate, the size of the droplet becomes smaller, and it then has the potential to stay airborne or to become reairborne as a dust particle. Thus, splatter droplets also may be a potential source of infection in a dental treatment setting. Splatter and droplet nuclei also have been implicated in the transmission of diseases other than TB, such as SARS, measles and herpetic viruses.
There are at least three potential sources of airborne contamination during dental treatment: dental instrumentation, saliva and respiratory sources, and the operative site. Contamination from dental instrumentation is the result of organisms on instruments and in DUWLs(dental unit waterlines). Routine cleaning and sterilization procedures should eliminate contamination of all dental instruments except those being used with the current patient.
The oral environment is inherently wet with saliva which is grossly contaminated with bacteria and viruses. Dental plaque, both supragingival and in the periodontal pocket, is a major source of organisms. Also the mouth is part of the oronasal pharynx. As part of this complex, the mouth harbors bacteria and viruses from the nose, throat and respiratory tract. Any dental procedure that has the potential to aerosolize saliva will cause airborne contamination with organisms from some or all of these sources.
The most serious potential threat present in aerosols is M. tuberculosis, the organism that causes TB. In the past, TB was viewed as an occupational hazard of dentistry. Patients known to have active TB should be treated using special respiratory precautions so that the aerosols produced during treatment can be controlled. Patients with undiagnosed, active, infectious TB, however, remain a risk for the dental team and other patients. The saliva and nasopharyngeal secretions also may contain other pathogenic organisms like common cold and influenza viruses, herpes viruses, pathogenic streptococci and staphylococci, and the SARS virus. Initially, the precautions taken were based on the assumption that all patients may have an infectious bloodborne disease, such as hepatitis B, hepatitis C and HIV. It also should be assumed that all patients may have an infectious disease that has the potential to be spread by dental aerosols; thus, universal precautions to limit aerosols also should be in place.
Most dental procedures that use mechanical instrumentation will produce airborne particles from the site where the instrument is used. Dental handpieces, ultrasonic scalers, air polishers and air abrasion units produce the most visible aerosols. Each of these instruments removes material from the operative site that becomes aerosolized by the action of the rotary instrument, ultrasonic vibrations or the combined action of water sprays and compressed air. The water spray usually is the portion of the aerosol that is most visible to the naked eye and is noticed by the patient and dental personnel. Figure 1 and Figure 2 show the coolant water aerosol and splatter produced by an ultrasonic scaler and air polisher.

Figure 1. The visible aerosol cloud produced by an ultrasonic scaler using a flow of 17 milliliters per minute of coolant water.

Figure 2. The visible aerosol cloud, made up of water and abrasive at the levels recommended by the manufacturer, produced by an air polisher

METHODS OF REDUCING AIRBORNE CONTAMINATION
The use of personal barrier protection such as masks, gloves and eye protection will eliminate much of the danger inherent in splatter droplets arising from the operative site. However, any infectious material that is present in a true aerosol form (particles less than 50 µm in diameter) or splatter that becomes reairborne as droplet nuclei has the potential to enter the respiratory tract through leaks in masks and contact mucus membranes by going around protective devices such as safety glasses. A true aerosol or droplet nuclei may be present in the air of the operatory for up to 30 minutes after a procedure. This means that after a dental procedure, if the operator removes a protective barrier such as a face mask to talk to a patient when a procedure is completed, the potential for contact with airborne contaminated material remains. Also, there is a potential for an airborne contaminant to enter the ventilation system and spread to areas of the facility where barrier protection is not used.
One method of reducing overall bacterial counts produced during dental procedures is the use of a preprocedural rinse. The use of a .01 percent chlorhexidine or essential oil–containing mouthwash for one minute before a dental procedure has been shown to significantly reduce the bacterial count in the air of the operatory. Chlorhexidine is an effective antiseptic for free-floating oral bacteria such as those found in the saliva and those loosely adhering to mucus membranes. Chlorhexidine, however, does not affect bacteria in a biofilm such as established dental plaque, does not penetrate subgingivally, will not affect blood coming directly from the operative site and is unlikely to affect viruses and bacteria harbored in the nasopharynx.
During many dental procedures, the use of a rubber dam will eliminate virtually all contamination arising from saliva or blood. If a rubber dam can be used, the only remaining source for airborne contamination is from the tooth that is undergoing treatment. This will be limited to airborne tooth material and any organisms contained within the tooth itself.
It must be emphasized that no single approach or device can minimize the risk of infection to dental personnel and other patients completely. The dental team should not rely on a single precautionary strategy. In the reduction of dental aerosols, the first step of defense is personal protection barriers such as masks, gloves and safety glasses. The second step of defense is the routine use of an antiseptic preprocedural rinse with a mouthwash such as chlorhexedine. The third step of defense is the routine use of an HVE (high volume evacuation) either by an assistant or attached to the instrument being used. An additional step of defense may be the use of a device to reduce aerosol contamination that escapes the operating area, such as a HEPA filter. The first three steps of defense are found routinely in most dental operatories, are inexpensive and can be made part of routine infection control practices easily. Unfortunately, many operators appear to use only the first step of defense (personal protection barriers) without following the other simple steps. All three simple and inexpensive steps should be followed routinely for adequate protection.

        

[drmittal]

An apparatus to aid in isolating a medical practitioner from infectious materials found in a patient. The apparatus includes a collector for providing a vacuum barrier around the mouth of a patient to trap aerosols and the like emanating from the patient during a dental procedure. The collector is flow connected to a vacuum source for drawing a vacuum, and gases drawn in by the source are passed through a filter. The collector is ring-shaped to surround the mouth and to allow the practitioner to see into the site of the procedure and is disposable after each operation.

        

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