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Dental Unit Waterlines

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Dental Unit Waterlines: Questions and Answers






To assist dentists and staff in understanding and addressing the issues surrounding dental unit waterline contamination, OSAP has prepared a series of questions and answers.

 

1.   What is biofilm?
2.   What are the health implications of waterline biofilm?
3.   If the health implications are not clear, why should we be concerned?
4.   How do we know if our waterlines are contaminated? Should we check our water quality?

5.   We've just implemented a waterline treatment device or protocol. How and when should we monitor?

6.   What is "acceptable quality" for treatment water?   
7.   What can we do to improve the quality of treatment water in our practice?  
8.   Does flushing lower microbial counts in dental unit water?  
9.   What are the advantages of self-contained water systems?   
10.  What about chemical agents? Should we disinfect our waterlines?   
11.   What types of chemicals can we use to treat and maintain our waterlines?   
12.   Are filters effective in controlling water quality?   
13.   Should we invest in a sterile water delivery system?
14.   What are the benefits of source water treatments ("water purifiers")?
15.   Summary






What is biofilm?

"Biofilm" is a community of bacterial cells and other microbes that adhere to surfaces and form a protective slime layer. Found in virtually all places where moisture meets a suitable solid surface, biofilm can contain many types of bacteria as well as fungi, algae, protozoa, and nematodes. The polysaccharide slime produced by many microbial inhabitants protects the cells from physical and chemical challenges, while water channels within the biofilm carry nutrients to the cells inside the film. Individual organisms, or even portions of the biofilm near the surface, break off into flowing water. In dental waterlines, this can result in contaminated coolant and irrigating solutions.

Although biofilm can form in all non-sterile fluid environments, dental waterlines provide particularly well-suited conditions. The tubing has a very narrow bore (1/8- to 1/16-inch), which provides a high internal surface-area-to-volume ratio. Low water pressure, low flow rates, and frequent periods of stagnation also encourage any bacteria introduced from the public water supply to accumulate within the tubing. The result is output water that is often many times more contaminated than tap water from the faucet in the same treatment room.

Water heaters and prefilters in dental units further exacerbate bacterial proliferation and colonization of dental unit waterlines. Heating water to near body temperature may enhance the number of microorganisms adapted for growth within a warm-blooded human host. Although they are intended to remove particles from municipal water as it enters the dental unit, prefilters have pores that are too large to trap bacteria. They not only slow the flow of water but also may provide additional surface area for microbial colonization.

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What are the health implications of waterline biofilm?

Since the first report in 1963, dozens of researchers have investigated dental waterline contamination. Despite the high levels of organisms found in dental unit water, no outbreaks of disease have been reported. In fact, few clinical case reports have been associated with waterline contamination. To date, no published scientific evidence confirms a risk of serious health problems for patients or dental personnel from contact with dental water.

However, numerous studies conducted over the past 30-plus years have identified the presence of waterborne opportunistic pathogens in dental unit water, and these findings provide reason for cautious concern. Many environmental organisms identified in dental treatment water have been associated with opportunistic infections in hospitalized or immunocompromised patients. For example, Pseudomonas species, non-tuberculous mycobacteria, and Legionella species all have been isolated from dental unit water. Legionella, the causative agent of Legionnaires' disease, may pose a particular concern, as it appears to be transmitted by inhaling aerosols or aspirating water contaminated with the bacteria.

One study suggests that aerosols produced by contaminated water from highspeed handpieces were associated with altered nasal flora in 14 of the 30 dentists studied. Nine of the dentists with altered nasal flora were positive for the same species of waterborne Pseudomonas isolated from the dental units. Several other studies have found higher titers of Legionella antibodies among dental personnel than in control populations, likely due to chronic exposure to Legionella-contaminated aerosols of dental unit water. Despite the higher antibody titers, however, no cases of Legionella pneumonia among the exposed workers have been documented.

A recent paper discussed the finding that high levels of the bacterial byproduct known as endotoxin may be present in dental unit water. Exposure is known to exacerbate respiratory conditions such as asthma and may effect wound healing.

Some local news reports have suggested that bloodborne pathogens may be transmissible through dental treatment water. In properly functioning units, however, the volumes of patient material needed for disease transmission are unlikely to be retracted into waterlines. Even if minute quantities of virus-contaminated material were to enter waterlines, experts state that there is no risk of colonization, as viruses require animal cells for replication, and they cannot survive long outside of a host organism. Although researchers have found evidence of oral flora in dental water systems, there is little evidence to suggest that these organisms form a significant part of the waterline biofilm community.

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If the health implications are not clear, why should we be concerned?

Exposing patients or personnel to water of poor microbiological quality simply is inconsistent with universally accepted infection control principles. As Dr. Shannon Mills notes in his 2000 Journal of the American Dental Association article "The dental unit waterline controversy: defusing the myths, defining the solutions," infection control procedures concentrate on breaking the chain of infection that consists of potential pathogens in sufficient numbers, a susceptible host, and a portal of entry. The susceptibility of the patient or healthcare worker and the pathogenicity of the organisms are the links over which we have the least control. As such, most efforts to break the chain concentrate on reducing the number of organisms in the clinical environment.

"Most dental practices expend considerable effort and expense to accomplish this goal as an everyday matter through surface disinfection, instrument sterilization, handwashing, and use of antimicrobial mouthrinses," he writes. "As with recommendations to improve the quality of dental treatment water, few of the aforementioned procedures are based on strong epidemiologic evidence. Nevertheless, reducing the number of microbes in water from dental units is absolutely consistent with long-accepted infection control principles.

Dr. Jennifer Cleveland with the Centers for Disease Control and Prevention (CDC) agrees. It is extremely difficult to establish an epidemiologic association between infection and recent exposure to dental unit water, she notes. Because dentistry is typically performed in an outpatient setting, patients are not monitored for post-treatment illness. Furthermore, the variability of individual patients, coupled with their various activities of daily living, make a cause-and-effect relationship between dental treatment and any subsequent illness difficult, if not impossible, to ascertain. Ethical, legal, and cost considerations prevent prospective studies from being performed to establish an association between dental treatment water and clinical illness.

In cases where definitive epidemiologic evidence is lacking, says Dr. Cleveland, practices and policymakers must look at intermediate outcomes. "For example, with percutaneous injuries," she explains, "we don't have any data that say one-handed recapping decreases infections, but it decreases injuries. That's a positive intermediate outcome.
"With waterline contamination, the science clearly shows that water from untreated dental units is contaminated with bacteria. In implementing control measures, the [positive] intermediate outcome is the reduction of bacteria or reduction of biofilm," she states.

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How do we know if our waterlines are contaminated? Should we check our water quality?

Bacterial biofilm is virtually universal in untreated dental unit waterlines. It can begin forming in a new dental unit within a few days. Unless procedures specifically designed to eliminate, trap, or kill biofilm are performed, there is little reason to believe that any dental unit can avoid being colonized by bacteria. In fact, bacterial counts numbering in the hundreds of thousands, even millions, per milliliter of dental unit water have been recovered from dental units across the country.

According to the American Dental Association (ADA) Council on Scientific Affairs' 1999 report to the profession on dental unit waterlines, evaluating water quality before a treatment protocol is implemented is controversial. Because the scientific literature suggests that all units are highly contaminated, pre-testing to confirm contamination is of questionable value. However, testing water quality after initiation of a treatment regimen ascertains whether a waterline product or protocol achieves the desired outcome. Monitoring water quality according to an established schedule can help identify problems in performance or compliance and provide documentation of water quality.

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We've just implemented a waterline treatment device or protocol. How and when should we monitor?

In the clinical setting, monitoring procedures have to be inexpensive and simple to perform and evaluate. Both in-office monitoring devices and commercial testing services are available. Some laboratories provide specialized service to the dental profession, but any commercial water-testing lab can enumerate heterogenic water bacteria present in a sample. Whether to use an outside laboratory or an in-office test is a matter of choice.

The type and frequency of water quality monitoring varies by device and protocol. Consult with the manufacturer or distributor of the dental unit and water treatment device(s) for information on evaluating equipment or protocol performance. Establish a schedule so water samples are collected during the "worst case scenario." When testing units that are chemically treated or equipped with microfilters, take the sample immediately prior to the chemical treatment or filter replacement. If testing water undergoing continuous chemical treatment, first neutralize the agent to ensure accurate colony counts.

The U.S. Air Force Dental Investigation Service has prepared a list of troubleshooting tips that can be applied when monitoring demonstrates a recommended device or protocol's failure to produce water of acceptable quality.

Maintain testing records according to the usual office protocol for similar documents (e.g., sterilizer monitoring). The ADA also recommends consulting the dentist's personal attorney for guidance.

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What is "acceptable quality" for treatment water?

According to the 2003 Guidlines for Infection Control in Dentistry:

DHCP should be trained regarding water quality, biofilm formation, water treatment methods, and appropriate maintenance protocols for water delivery systems. Water treatment and monitoring products require strict adherence to maintenance protocols, and noncompliance with treatment regimens has been associated with persistence of microbial contamination in treated systems (345). Clinical monitoring of water quality can ensure that procedures are correctly performed and that devices are working in accordance with the manufacturer's previously validated protocol.

Dentists should consult with the manufacturer of their dental unit or water delivery system to determine the best method for maintaining acceptable water quality (i.e., <500 CFU/mL) and the recommended frequency of monitoring. Monitoring of dental water quality can be performed by using commercial self-contained test kits or commercial water-testing laboratories. Because methods used to treat dental water systems target the entire biofilm, no rationale exists for routine testing for such specific organisms as Legionella or Pseudomonas, except when investigating a suspected waterborne disease outbreak (244).

 

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What can we do to improve the quality of treatment water in our practice?

 

According to the 2003 Guidlines for Infection Control in Dentistry:

DHCP should be trained regarding water quality, biofilm formation, water treatment methods, and appropriate maintenance protocols for water delivery systems. Water treatment and monitoring products require strict adherence to maintenance protocols, and noncompliance with treatment regimens has been associated with persistence of microbial contamination in treated systems (345). Clinical monitoring of water quality can ensure that procedures are correctly performed and that devices are working in accordance with the manufacturer's previously validated protocol.

Dentists should consult with the manufacturer of their dental unit or water delivery system to determine the best method for maintaining acceptable water quality (i.e., <500 CFU/mL) and the recommended frequency of monitoring. Monitoring of dental water quality can be performed by using commercial self-contained test kits or commercial water-testing laboratories. Because methods used to treat dental water systems target the entire biofilm, no rationale exists for routine testing for such specific organisms as Legionella or Pseudomonas, except when investigating a suspected waterborne disease outbreak (244).

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Does flushing lower microbial counts in dental unit water?

Mechanical flushing alone does little to control contamination in waterlines. Although it can temporarily reduce the number of microbes in the water delivered to patients by clearing away many of the free-floating organisms in the waterline, biofilm bacteria continually break free and recontaminate dental unit water during the course of clinical treatment. Flushing for several minutes between patients, however, may be valuable in removing contaminants that can enter the water system during patient treatment.

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What are the advantages of self-contained water systems?

Self-contained water systems, also referred to as independent water systems or reservoirs, isolate the dental unit from the municipal water supplies, instead providing water or treatment solution from reservoirs filled and maintained by office staff. They allow the practice to control the quality of water that is used in the unit.

Self-contained water systems provide a means for introducing chemical agents to waterlines and permit the use of water of known microbiologic quality. Without chemical or mechanical treatment to remove or inactivate biofilm within the unit, however, self-contained water systems cannot reliably improve the microbial quality of dental unit water. In fact, if the reservoir is allowed to become and remain contaminated, the effluent water may be of worse quality than if it had been drawn from a municipal source.

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What about chemical agents? Should we disinfect our waterlines?

A number of chemicals are reported to inactivate or prevent biofilm, whether through periodic (intermittent or "shock" treatment) or continuous presence in the waterline. Periodic disinfection involves purging the waterlines, adding a chemical to the water reservoir, filling the lines for the recommended time period, and flushing. Continuous chemical treatment refers to waterline treatment via an irrigant/coolant solution or the use of automated metering devices. Metering devices release low levels of chemical germicide into the treatment water to control biofilm to lower bacterial counts in the water. Some products may require both intermittent and continuous line treatments to maintain water quality, and many chemical protocols are technique-sensitive. Strict compliance with the recommended treatment regimen is the key to consistent water quality.

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What types of chemicals can we use to treat and maintain our waterlines?

Chlorine compounds have been fairly extensively studied, with published reports on the efficacy of dilute sodium hypochlorite, chlorine dioxide, chloramine T, and elemental chlorine. In fact, several manufacturers (e.g., A-dec, DCI International, DentalEZ, Dentsply Cavitron, and Proma) authorize weekly water system treatment with a 1:10 solution of household bleach.

Some other active agents scientifically evaluated for treatment of dental unit waterlines include hydrogen peroxide, chlorhexidine gluconate, and iodophors. Commercial products employing hydrogen peroxide, chlorhexidine gluconate, iodine, or citrus botanicals also are being marketed. Active ingredients in currently available continuous chemical treatments include chlorhexidine gluconate, citric acid, hydrogen peroxide, iodine, and ozone and silver.

Although waterline antimicrobials now must also be registered with the Environmental Protection Agency (EPA), the agency has not yet formulated regulatory guidance for intermediate- and low-level germicides used in dental waterlines. The ADA and the American National Standards Institute currently are developing a national specification for waterline antimicrobials that is expected to serve as the basis for EPA evaluation.

Because of concern over compatibility with equipment components, always consult the dental unit manufacturer before introducing any chemical into the water system. Issues of waterline chemical compatibility with various dental materials (for example, dental adhesives) also have recently come to light, and questions regarding disinfectant byproducts and their effects on oral tissues have been raised.

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Are filters effective in controlling water quality?

Usually positioned on each water-bearing line near the handpiece or air-water syringe, microfilters typically use a 0.2-micron membrane to trap free-floating microorganisms before they can be released in the effluent. One currently marketed product also releases small quantities of iodine intended to discourage biofilm formation; another is purported to trap bacterial endotoxin. Some filters incorporate antiretraction features.

The few studies conducted to date suggest that in-line microfilters can produce water that meets or exceeds water-quality goals. In fact, results of independent studies report that 80% of the filtered water samples tested were bacteria-free. Although in-line filters can improve dental water quality, they have no effect on the biofilm within the waterlines. Without treating the biofilm, waterlines are at risk of biofouling, clogging, and release of bacterial byproducts into treatment water. As such, it may be necessary, at minimum, to periodically treat the post-filter segment of the waterlines to control biofilm.

In its 1995 Statement on Dental Unit Waterlines, the ADA specifically set its water quality goal for "unfiltered output water." Nonetheless, filters can be a valuable adjunct to other waterline treatments in controlling the quality of water delivered to patients.

Currently marketed waterline filters have a use life ranging from one to seven days. To maintain efficacy, they must be replaced according to the manufacturer's recommendation.

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Should we invest in a sterile water delivery system?

Sterile water delivery systems address the issue of biofilm by offering disposable or autoclavable waterline tubing that bypasses the dental unit's water supply. Although many systems of this type are oral-surgery and implantology handpieces, ultrasonic scalers and retrofit devices for restorative handpieces also are available.

Sterile water cannot be delivered through a standard dental unit. For practices that perform surgery with instruments that are connected to the dental unit water system, a sterile water delivery system would be a worthwhile investment.

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What are the benefits of source water treatments ("water purifiers")?

No dental unit can provide water that is cleaner than the water that enters it. However, unless source water treatment systems also address the colonized tubing (i.e., the biofilm) within the dental unit, they will provide little improvement in water quality.

Currently available water purifiers treat source water with ultraviolet germicidal irradiation (UVGI), filtration, or both to remove or inactivate planktonic microorganisms. One currently marketed device uses UVGI and a silver electrode to produce ozone and silver ions that are said to discourage the growth of waterline biofilm.

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With so little published research on control mechanisms, what should we, as clinicians, be doing with regard to waterline contamination?

Research is underway to validate some proposed water treatment methods and water-quality monitoring indicators. In the interim, OSAP recommends a number of steps that oral healthcare providers can take to improve the quality of water from their dental units.

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In summary...

Careful compliance with treatment protocols appears to be a critical factor for long-term success. As with other clinical infection control practices, successful control of biofilm in dental unit waterlines depends on technique factors, effective personnel training, and an established standard operating procedure. Failure to establish consistent, rational office procedures could result in damaged equipment as well as harm to patients and dental healthcare workers.

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