Chris Miller, PHD
The water coming out of most dental units is contaminated with potentially pathogenic bacteria. While this has apparently not caused any recognized public health problem, some lines of indirect and anecdotal evidence suggest that a few people may be susceptible to the water microbes.
This information, along with the microbial characteristics of dental-unit water, will be discussed in upcoming issues of RDH. This column describes the most recent actions taken in this area by the American Dental Association (ADA).
Involvement of the ADA
The ADA has been active in monitoring information on water quality in dental units for quite some time. The organization, for example, made a recommendation in 1978 to:
- Consider disinfecting dental unit waterlines.
- Conduct several workshops on this topic involving equipment manufacturers, researchers, educators, clinicians, and regulators.
- Publishing research articles in their journal.
Last fall, the ADA Division of Science convened a panel of experts to again review the current status of the microbial quality of dental-unit water. The panel emphasized that the number of bacteria in dental unit water that exits the air/water syringe, high-speed handpiece, and ultrasonic scaler needs to be better controlled. Recommendations were made to the Council on Scientific Affairs, and the ADA Board of Trustees approved them in December 1995.
Approaches for improvement
The ADA will take the following approaches to further encourage the improvement of dental unit water quality:
- To encourage industry and the research community to improve the design of dental equipment so that by the year 2000, water delivered to patients during nonsurgical dental procedures consistently contains no more than 200 colony-forming-units (cells) per milliliter (CFU/mL) of aerobic mesophilic heterotrophic bacteria at any point in time in the unfiltered output of the dental unit.
The inside of the dental-unit waterlines become colonized with a microbial biofilm that releases bacteria into the flowing water. Controlling the number of microbes in the water that passes through these lines involves controlling the development of this biofilm.
The stated approach of maintaining no more than 200 CFU/mL in the exiting water will indicate that the lines have not become colonized with a biofilm. This goal is currently used as an indicator that hemodialysis units have not become colonized with water-borne microbes.
- To encourage dental unit manufacturers to develop accessories that can be retrofitted to dental units currently in use, whatever the water source (public or independent), to aid in achieving the water quality goal.
If current dental units can be modified in a reasonably simple manner to deliver the appropriate quality of water, the cost of this improvement can be better controlled.
- To urge industry to ensure that all dental units manufactured and marketed in the United States in the future have the capability of being equipped with a separate water reservoir independent of the public water supply.
This can allow better control of the type of water that enters the dental unit. This also can provide an alternative source of water when local health agencies issue "boil water" notices resulting from problems with municipal water supplies.
To encourage the development of simple and inexpensive methods to estimate the number of free-floating heterotrophic bacteria in dental unit water to test the effectiveness of control measures.
This can provide a means of routinely monitoring the microbial quality of the water, which will help determine the success of whatever control measures are being used. The monitoring methods serve as a quality assessment procedure for the safety of patients much like that of administering spore tests to the office sterilizers.
To enhance efforts to educate dental practitioners regarding microbial contamination and biofilm formation in dental unit waterlines and the need for improvement in the quality of water delivered to patients. Additionally, manufacturers should maintain an active approach in training and educating the profession in the proper use and maintenance of their systems.
With any actual change in technology or procedures, appropriate information must be distributed so that informed decisions can be made. As is true for most aspects of infection control in the office, routine repetitive efforts are required to assure continued success in reducing the numbers of microbes shared among people.
To encourage research:
- Define the natural history of biofilms, specifically to more clearly determine the relationship of the numbers and types of microorganisms in the fixed population (sessile) to their free-floating (planktonic) counterparts;
- Develop research-based methods to effectively eliminate existing biofilm and prevent or control formation of new biofilm in dental unit waterlines;
- Develop alternative devices for monitoring the microbial quality of water used during dental care that are simple, reliable, and cost-effective.
Discussion on this topic continues next month.
Chris Miller is director of Infection Control Research and Services and professor of oral biology at Indiana University.