Managing Biofilms in Waterlines: Is Your Choice Chemical or Physical?

April 1, 2002
Managing these organisms ideally involves a combination of approaches.

Managing these organisms ideally involves a combination of approaches.

by Nancy Andrews, RDH, BS

Research reveals a persistent and pervasive tendency of bacteria to form protective, slimy layers inside the water tubing of our dental equipment, contaminating the water we use to do dentistry. The waterline organisms also can form biofilms, which may cause infections in susceptible people with mild to very serious – or even fatal – results. For ethical reasons, it is important to understand and manage this potential threat to clinicians and patients.

Once we understand the nature of biofilm organisms, as well as the potential risks, the next step is to look creatively at dental equipment. Dental units and most stand-alone devices (such as ultrasonic scalers) involve many feet of hidden (or difficult to reach), narrow (1 to 1.5 mm) diameter tubing and complex chambers or dead-end lines where water stagnates. Until dental equipment is radically redesigned, we must "manage" biofilm in three ways:

•Remove the biofilm matrix
•Remove or destroy the organisms
•Prevent the biofilm

These three goals can be accomplished using two basic approaches – physical and chemical – which sometimes are combined.

Physical methods of managing biofilm in waterlines include the following:

o Filtration, or the physical removal of biofilm-related contaminants from waterlines
o Antiretraction devices to prevent contaminants from being "sucked back

Chemical cleaning and disinfection of waterlines and equipment includes these steps:

•The use of equipment that allows chemicals to be added or generated, meaning disconnection with the public water supply
•Periodic "shock" treatments with caustic or corrosive chemicals aimed at killing microbes and, perhaps, biofilm removal and slowing the regrowth of biofilm (these harsh chemicals must be removed prior to treating patients)
•Adding low amounts of chemicals to dental water to inhibit biofilms and floating organisms (these chemicals remain in the water while patients are treated)

With any system, it is important to remember that pathogens enter dental equipment from different sources and can defeat your efforts. All of these sources must be managed. The source water, for example, may be contaminated. Municipal water, while it is stored in open reservoirs, can pick up mycobacterium Avium from birds, E coli from animal feces, and many other organisms. Water sources such as bottled or distilled water can have surprisingly high numbers of contaminants. For example, tabletop distillers grow biofilm and must be cleaned.

Secondly, clinicians may introduce contamination by handling the system. If pathogens enter the system between chemical treatments, they may grow wildly until the next treatment.

Thirdly, dental units might be sucking back contaminated fluids each time the water or handpiece is stopped due to unnoticeable fatigue and failure of antiretraction devices hidden within the equipment. These equipment parts have a limited life, and many dental handpieces and air/water syringes retract without detection. There is one check valve, the BackStop, which comes with the ClearLine Plus filter that is easy to find and change – a great advantage over this common weak link in our dental setup. You can use the BackStop with filters, or alone without a filter in place.

Finally, some designs of equipment promote biofilm. All irregularities inside the water pathway – especially "control blocks" with their hidden "nooks and crannies" and hidden dead-end lengths of tubing – serve as constant reservoirs of biofilm. In these places, water collects and is not flushed freely or treated effectively by even the harshest chemicals. Water heaters also encourage types of organisms that prefer human body temperatures. Avoid dental units with heated water, because dangerous organisms might be growing and sloughing imperceptibly.

Chemical waterline treatment

You may have reservoir systems (the bottles attached to dental units), which offer the advantage of control over the water source and the ability to access the system to disinfect the waterlines. Research shows that bottle systems can be maintained at or below the 200 CFU level, but not without rigorous maintenance. In addition, biofilm can develop in the lines and reservoirs without you noticing it.

One main drawback of chemical waterline protocol is human error and poor compliance. Many hours and dollars can be saved if the person in charge understands the hazards and weak points of chemical waterline maintenance.

To use chemicals to manage biofilms successfully, strong waterline disinfectants and cleaners can be used as periodic "shock" treatments. These caustic chemicals pose a danger to patients and possibly dental personnel, and must be purged out of the lines completely before treating patients. Immediately after periodic chemical treatments, floating bacteria may drop to very low levels. But buildup will occur again and may exceed safe levels before you treat the lines again, especially if the chemical treatment fails to penetrate and remove the biofilm.

Another approach is to add low levels of chemicals to the treatment water. In this case, the chemicals are always present. The occupational hazards of constant exposure to biocides are unknown, and the development of resistant bacteria with long-term use of low levels of antimicrobials is a potential problem. Studies showing that DUWL biocides decrease the bond strength of dental materials raises another concern about chemicals present in dental treatment water. Lastly, there is concern that irritation and allergic reactions to chemical-laden water will be a problem for both patients and clinicians. Symptoms include respiratory complications, nasal irritation, headache, runny nose, tearing, stinging eyes, and skin rashes.

The chemical methods we use for treating biofilm in waterlines often are time-consuming, give us unpredictable results, often damage or age the equipment, and pose risks of chemical injury or exposure to dental personnel. We are putting caustic chemicals into equipment not originally designed to withstand corrosives under pressure. In reality, most offices have great difficulty in regularly performing the chemical DUWL treatments. Most biofilm grows back because people don't have time or don?t want to use the chemicals.

If you use fewer chemicals, your equipment will last longer ... but how will you control water contamination? You might consider combining physical and chemical approaches. If chemicals are used less frequently, you can expect biofilm and microbial buildup between chemical shock treatments. If bacterial filters are installed near the handpiece, you can filter out bacterial contaminants before they pass out of your waterlines into your patient's mouth or your face by 99.9 percent. If you control upstream levels of contamination by treating the system chemically – or by other methods such as UV or ozone – fewer contaminants will build up on your filter.

Think of it this way: Use the chemicals more rarely with the goal of reducing biofilm, keeping the system clear of gross contamination. Between chemical treatments, use a filter to be sure that the bacteriological contaminants in your treatment water are predictably under control.

Several filters are available. Some filters, though, release chemicals such as iodine, introducing the possibility of toxic and allergic reactions, adverse effects on dental materials, and the usual drawbacks of chemicals. Choose a filter with an antiretraction valve, which gives you the additional piece of the puzzle: control of retraction from the patient.

This approach may seem like belts and suspenders, but it relies on the physics of filtration and allows you to treat patients using water with nearly zero CFUs of bacteria per mL.

To get the best results, be sure to change your filter as recommended. Biofilm organisms eventually will clog or grow through your filters if you do not maintain them. Maintaining your filters is easy. Just remove and discard the old filter.

So, what does it take to use filters?

First, either adapters or removable connectors must be installed in your lines. The purpose is to connect the filters and antiretraction valves about six inches from your handpiece. Removable connectors are an option if the dental unit is not designed for installation of luer connectors in the tubing. The connectors are available with or without fiber-optic fibers, and there is a special European adapter. The connectors are autoclavable. The tubing can be chemically treated and should be replaced periodically. (Remember, these filters do a far better job than the 50 micron or 100 micron filters already installed in your unit. Those are for larger particles and also should be changed periodically.)

DUWL biofilm formation is virtually inevitable despite chemical treatments, raising liability issues. We cannot afford to approach this in a hit-and-miss way, wondering if we have a little, some, or a lot of heavy bacterial contamination in the water. We all want to practice at the highest professional standard of asepsis and be done with it! Unfortunately, it will require some time and effort – but hopefully as little as possible with as few risks as possible.

It is unknown just how many patients or practitioners have become ill from contaminated dental water. The research has not been done. As doctors, lawyers, and the public learn about the potential for infection from dental waterlines, it's logical to expect more legal claims against dentists for not eliminating this unacceptable risk.

To choose the best solution for your office, determine your tolerance for water contamination by the type of procedures you do, the degree of invasiveness, and the susceptibility of both patients and clinicians/staff.

We have some professional and legal minimum guidelines: The CDC recommends that sterile fluids be used for surgical procedures and that nonsurgical procedures be performed with fluids at least as clean as drinking water.

Considering the care dentistry takes to ensure the safety of patients and employees, it is inconsistent and unethical to practice dentistry with water that fails to meet the minimum safety levels of drinking water and has a high probability of containing large numbers of pathogens.

We know about it; equipment alternatives are available; and, so, we are morally, legally, and professionally compelled to solve the problem. Next time you see a patient with a weak immune system, ask yourself: Is it OK to use our dental unit water on him? If you have to stop and think about your answer, it's time to look carefully at your waterline management program.

Benefits of filters

•Controlled retraction of patients' pathogens
•Precise control of waterline organisms
•Reduced exposure to, and damage from, chemical waterline treatments
•Time savings

Nancy Andrews, RDH, BS, is currently a product manager for new product development at Kerr/Metrex. She has had numerous articles published on infection prevention in peer-reviewed professional journals. She also is a member of OSAP, an infection prevention association. A graduate of the University of Southern California, Andrews