Elimination of contaminants in waterlines may be guesswork, but several options help

Chris Miller, PHD

A universally accepted, well-documented procedure to eliminate dental-unit waterline contamination in all dental settings is not available. Several approaches, however, are being considered. Some are currently available, but most of the approaches still need further study to determine or confirm their effectiveness and/or safety. Several approaches will be briefly described here.

In the past two issues of RDH, microbial contamination of dental-unit water has been discussed. The Infection Control columns described:

- What is known about the extent of the contamination.

- The types of microbes present in dental-unit water.

- The formation of biofilm in waterlines as the continuing source of contaminants of the water.

- Recent statements on waterline contamination from the American Dental Association.

Flushing of the lines

The current CDC recommendations for infection control in dentistry were derived in 1993. The recommendations state sterile water or saline (rather than dental-unit water) should be used as a coolant or for irrigation when surgical procedures involving the cutting of bone are performed.

The CDC recommendations also include flushing the dental-unit lines with water for several minutes at the beginning of the day and flushing high-speed handpieces 20 to 30 seconds with air and water between patients. The recommendations should be followed. Flushing handpieces aids in the removal of patient material that may have entered the handpiece. Flushing the waterlines may temporarily reduce the number of microbes in the exiting water and brings in small amounts of chlorinated water from the main waterlines.

It must be recognized, however, that flushing with water will not eliminate the biofilm in the lines.

One approach to reducing dental-unit water contamination is to use a source of water other than that which is plumbed through the unit. Separate water systems are available, and they consist of a separate bottle for treatment water - or one bottle for treatment water and another for disinfectant.

The alternative sources of water are pressurized from air in the unit. This clean water then passes through the lines and into the handpieces and three-way syringes.

These alternatives eliminate municipal or well-water as the source of contaminants. The separate water systems are also particularly beneficial when local health authorities issue "boil water" notices as a result of some contamination problem with the municipal water supply (water main break, for example). With one of these systems in place, the dental office would not have to "shut down," because municipal water is not being used.

The bottles and lines associated with these separate water systems must be regularly maintained by cleaning and flushing with a disinfectant, followed by rinsing.

Other separate systems provide for the delivery of sterile water to the patient, completely bypassing the waterlines of the dental unit. Another source of water which would completely bypass the dental unit would be a disposable plastic syringe filled with the appropriate treatment water. This can be used for hand irrigation.

Chemical disinfection and air purging

As described above, regular disinfection of the dental-unit waterlines is a necessary part of using separate sources of water for the dental unit. Some evidence indicates that regularly flushing the lines with an anti-microbial solution (an appropriate disinfectant, for example) may work in controlling water contamination.

More studies are needed, though, to better define the optimal conditions for killing microbes while ensuring minimal damage to the unit. One concern is that some disinfectants may enhance corrosion of dental-unit waterline fittings. In addition, the disinfectant may enter patient`s mouths, if not thoroughly rinsed from the lines.The solutions may cause internal damage to attachments - particularly handpieces.

Draining the lines and then purging them with air on a daily basis may also help kill microbes in biofilm. But, again, more studies are needed to demonstrate the extent of biofilm destruction that can be achieved. Before attempting to disinfect dental-unit waterlines, call the manufacturer of the dental unit for advice.

Replacement of the waterlines

Replacing the waterlines would be a way to eliminate the biofilm that continually contaminates the flowing water. However, this approach would be of little value unless procedures were instituted that eliminate any return of the biofilm. The biofilm will return if microbes are allowed to re-enter the system and grow unchallenged.

One way to manage contaminated dental-unit water is to pass the water through an appropriate filter that removes bacteria. Such a filter system is available for insertion into the dental-unit waterline just before the water enters the handpiece or three-way syringe.

Studies are needed to further characterize:

- How such filters function in different dental settings to determine optimal times to change the filters.

- The effect of concentration of microbes or other materials in the water being filtered.

- Adequacy of procedures for eliminating any cross-contamination of the line between the filter and the patient.

Filtering the dental-unit water just before it enters the patient`s mouth can certainly reduce this type of exposure for patients. However, such filters do not effect the waterline biofilm - the continuing source of the water contamination. While filters may be present in waterlines entering some dental units, such "pre-filters" usually retain only larger particles and are not of sufficiently small pore size to retain bacteria.

The rubber dam serves as a barrier that reduces patient contact with dental-unit water. Alternatively, eyeglasses, masks, faceshields, protective clothing, and gloves reduce dental team contact with this water.

Several additional approaches to preventing or managing dental-unit water contamination are being designed or are in early testing phases. It appears that offices will eventually have a large number of weapons with which to battle water contamination.

Chris Miller is director of Infection Control Research and Services and professor of oral biology at Indiana University.

ADA statement on waterlines

The statement released by the American Dental Association in December 1995 includes the following:

"...Although there is no evidence of a public health risk due to this phenomenon, steps should be taken to improve the quality of water used in patient care as soon as feasible. Dental unit waterlines (the tubes that connect the high-speed handpiece, air/water syringe, and ultrasonic scaler to the water supply) have been shown to harbor a wide variety of microorganisms.

"Dental unit water systems currently designed for general dental practice are incapable of delivering water of an optimal microbiologic quality ... the design of dental equipment [needs to be improved] so that by the year 2000, water delivered to patients during nonsurgical dental procedures consistently contains no more than 200 colony forming units per milliliter of aerobic mesophilic heterotrophic bacteria at any point in time in the unfiltered output of the dental unit.

"Manufacturers of dental equipment are encouraged to develop accessory components that can be retrofitted to dental units currently in use, whatever the water source (public or independent), to aid in achieving this goal. [Equipment] in the future [should] have the capability to be equipped with a separate water reservoir independent of the public water supply. In this way, dentists not only will have better control over the quality of the source water used in patient care, but also will be able to avoid interruptions in dental care when `boil water` notices are issued by local health authorities.

"At the present time, commercially available options for improving dental unit water quality are limited and will involve some additional expense. They include the use of:

- Independent water reservoirs

- Chemical treatment regimens

- Daily draining and air purging regimens

- Point-of-use filters

"...some combination of the above strategies will be necessary to control biofilm formation and to achieve the desired level of water quality. To date, however, there are insufficient data to establish the effectiveness of available methods ... Dental practitioners should always consult with the manufacturer of their dental units before initiating any waterline treatment protocol.

"A well-designed water quality indicator (WQI) should be self-contained and easy to use in-office ... The Council [on Scientific Affairs] is aware that technology meeting these criteria is available and could possibly be adapted for use in dentistry with minimal developmental cost."