METHODS OF REDUCING AIRBORNE CONTAMINATION

As noted previously, if the ADA's recommendations for sterilization of instruments and treatment of DUWLs are followed, these major sources of potentially contaminated dental aerosols can be controlled. However, it should be recognized that the aerosol created by the interaction of coolant water and ultrasonic vibrations or by compressed air and a rotary motion are visible to patients and dental personnel. It is important that this aerosol cloud be controlled to the greatest extent possible to reassure patients and dental personnel. It also should be recognized that contaminated aerosols are produced during dental procedures when there are little or no visible aerosols. As has been shown in the study of aerosol production by ultrasonic scalers when no coolant water was used, even in the complete absence of coolant water there is aerosolization of material from the operative site.²⁰ During routine dental treatment, there is a strong likelihood that aerosolized material will include viruses, blood, and supra- and subgingival plaque organisms.

At this time, it is impossible to determine the exact infection risk represented by aerosolized material. The potential for the spread of infection via an almost invisible aerosol, however, must be recognized and minimized or eliminated to the greatest extent feasible within a clinical situation.

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.²⁹ 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 masks³⁰ 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.¹³ 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.^{31, 32} 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. While preprocedural rinses will reduce the extent of contamination within dental aerosols as routinely measured on agar plates, they do not eliminate the infectious potential of dental aerosols.

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. In certain restorative procedures such as subgingival restorations and the final steps of crown preparation, it often is impossible to use a rubber dam. The use of a rubber dam also is not feasible for periodontal and hygiene procedures such as root planing, periodontal surgery and routine prophylaxis. This is of particular concern owing to the fact that periodontal procedures always are performed in the presence of blood and instruments such as the ultrasonic scaler, which has been shown to create the greatest amount of aerosol contamination, are used.

Two methods are available to reduce airborne contamination arising from the operative site. One method involves using devices that remove the contaminated material from the air of the treatment area after it has become airborne. The other is to remove the airborne contamination before it leaves the immediate area surrounding the operative site. The most frequently mentioned methods of removing airborne contamination from the air of the treatment room are the use of a high efficiency particulate air, or HEPA, filter and the use of ultraviolet, or UV, chambers in the ventilation system. While both of these systems appear to reduce airborne contamination, they are somewhat expensive; the UV system is cost-prohibitive for most dental offices at this time. Both approaches also have the problem that it takes an extended period for the air in the treatment room to cycle through the filter or UV treatment system.

From a practical point of view, it is easiest to remove as much airborne contamination as possible before it escapes the immediate treatment site. The use of a high-volume evacuator, or HVE, has been shown to reduce the contamination arising from the operative site by more than 90 percent.^{8, 23, 33, 34, 35} It should be emphasized that for a suction system to be classified as an HVE, it must remove a large volume of air within a short period. An evacuator that pulls a high vacuum but does not remove a large volume of air, such as is used routinely for hospital suction, is not considered an HVE. The usual HVE used in dentistry has a large opening (usually 8 millimeters or greater) and is attached to an evacuation system that will remove a large volume of air (up to 100 cubic feet of air per minute). The small opening of a saliva ejector does not remove a large enough volume of air to be classified as an HVE.

During restorative dentistry, the HVE often will be used by an assistant who is able to guide and aim the vacuum in a manner that eliminates or greatly reduces the visible water spray produced during dental procedures. It has been shown that the number of CFUs produced during dental procedures is reduced greatly when an assistant uses an HVE.⁸ A problem arises when the operator is working without an assistant. This often is the case during delivery of periodontal treatment by a dental hygienist. Several options are available to operators working without an assistant. They include using the operating instrument in one hand and the HVE in the other hand, HVE devices that attach to the operating instrument and various “dry field” devices that attach to an HVE. For air polishing and air abrasion, devices are available that combine a barrier device to help contain the abrasive material and a vacuum to remove the abrasive material and the airborne particles created by the procedures.^{28, 36} All of these instruments are available commercially from multiple sources.

It must be emphasized that no single approach or device can minimize the risk of infection to dental personnel and other patients completely. A single step will reduce the risk of infection by a certain percentage, another step added to the first step will reduce the remaining risk, until such time as the risk is minimal. This can be described as a layering of protective procedures. This layering of infection control steps needs to be followed in reducing the potential danger from dental aerosols.

The dental team should not rely on a single precautionary strategy. In the reduction of dental aerosols, the first layer of defense is personal protection barriers such as masks, gloves and safety glasses. The second layer of defense is the routine use of an antiseptic preprocedural rinse with a mouthwash such as chlorhexadine. The third layer of defense is the routine use of an HVE either by an assistant or attached to the instrument being used. An additional layer 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 layers 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 layer of defense (personal protection barriers) without following the other simple steps. All three simple and inexpensive steps should be followed routinely for adequate protection. Table 3 lists the available methods of reducing aerosols and splatter contamination, as well as their relative effectiveness and costs.