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Aerosols and splatter in dentistry
SOURCES OF AIRBORNE CONTAMINATION DURING DENTAL TREATMENT
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 water lines]. Routine cleaning and sterilization procedures should eliminate contamination of all dental instruments except those being used with the current patient. The use of ADA-recommended methods to treat the DUWL also should minimize or eliminate airborne contamination from the DUWL. Because contamination from these sources is controlled relatively easily by following standard procedures, we do not discuss them in detail.16
SALIVA AND RESPIRATORY SOURCES OF CONTAMINATION
The oral environment is inherently wet with saliva that continuously replenishes the fluid in the mouth. The fluids in the mouth are grossly contaminated with bacteria and viruses. Dental plaque, both supragingival and in the periodontal pocket, is a major source of these organisms. It should not, however, be overlooked that the mouth also is part of the oronasal pharynx. As part of this complex, the mouth harbors bacteria and viruses from the nose, throat and respiratory tract. These may included various pathogenic viruses and bacteria that are present in the saliva and oral fluids. 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.17, 18 While the number of active TB cases in the United States is relatively small, certain populations such as the homeless, prisoners and recent immigrants have a higher percentage of TB infection.19 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. These may include common cold and influenza viruses, herpes viruses, pathogenic streptococci and staphylococci, and the SARS virus. The use of universal precautions with all patients initially was based on the assumption that all patients may have an infectious bloodborne infection, such as with hepatitis B virus, hepatitis C virus 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.
CONTAMINATION FROM THE OPERATIVE SITE
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.
One study, however, showed that when an ultrasonic scaler was used in vitro without any coolant water, there still was a large amount of aerosol and splatter formed from small amounts of liquid placed at the operative site to simulate blood and saliva.20This airborne material was spread for a distance of at least 18 inches from the operative site. Despite the amount of splatter and the distance it was spread, no visible aerosol was detected during the use of the ultrasonic scaler, and it could only be detected as settled droplets on the environmental surfaces. Figure 3 shows that aerosols and splatter from an ultrasonic scaler can arise both from a coolant water source and directly from the patient.