Dental Water Quality: Is It Time to Take Action? By: Shannon E. Mills, DDS, FAGD, FICD

A recent Dentaltown.com Townie Poll queried online readers about the issue of dental unit water lines. Nine hundred thirty-one dental professionals replied with about half of the respondents indicating they currently disinfect their dental water lines. One hundred eighty-seven of the individuals who indicated they did not disinfect their systems indicated their reasons for not doing so. Among these respondents, only six percent were concerned about cost, with another 14 percent citing it requires too much time. Nearly 40 percent indicated they felt it was not important. The remaining 40 percent cited lack of requirements or enforcement.

When Dentaltown asked me to provide an editorial as a companion piece to the poll, I leapt at the opportunity. As a researcher who has spent much of the last two decades trying to better understand the nature of microbial contamination of dental water, and as an author and lecturer on infection control issues, the subject was irresistible. Moreover, the timing was perfect! In December of 2003, the Centers for Disease Control and Prevention (CDC) published the revised “Guidelines for Infection Control in Dental Healthcare Settings—2003” in Morbidity and Mortality Weekly Report. The updated guidelines contain much more comprehensive recommendations for improving the quality of water used for both restorative dentistry and for surgical procedures than the version issued in 1993.

I was not surprised to find the poll reflects the profession’s ambivalence about the issue and the results tend to corroborate the impressions I have formed as I lecture on the topic at various venues across the country. It has been some time since anyone has asked me; “Where are the dead bodies?” Nevertheless, there are still many dentists who remain unconvinced that water lines constitute a problem meriting the expenditure of their time or resources. Still, I am encouraged when, instead of asking about “dead bodies”, I am asked about the best ways to improve dental water quality or how to troubleshoot a problem they have encountered in managing dental water in their practice.

How do I feel about the results of the poll? A good analogy may be the way I’ve felt when my favorite team ends up with a tie score with an archrival (which a famous football coach once said is “a lot like kissing your sister”). In equal measure, I am encouraged that many dental practices are opting to improve dental water quality; while I’m disheartened to learn a fair number of poll respondents were either unaware of the new CDC guidelines or did not consider them to be important.

What does the CDC recommend as far as standards and practices for dental water quality? The guideline recommends water used for restorative dental treatment have no more than 500 colony forming units per milliliter of water (CFU/mL). This standard is consistent with Environmental Protection Agency (EPA) standards for drinking water as well as the American Water Works Association’s recommendations for spas and swimming pools. The guideline further recommends only sterile solutions be used for oral surgical procedures. In contrast, untreated dental units connected to municipal water supplies will typically contain thousands or even millions of colony forming units.

Without some form of intervention to remove or suppress the microbial biofilms that colonize dental unit water lines, there is no plausible way to provide water that complies with the new CDC recommendations.

The CDC’s decision to strengthen the recommendations on dental water quality beyond the minimal guidance provided in 1993 was based on a number of considerations. Perhaps most importantly, the number of papers published in peer-reviewed journals on the topic had nearly doubled over the intervening decade. These inquiries confirmed the presence of high numbers of organisms, including some with documented pathogenic potential, in dental unit water. Moreover, studies of methods intended to improve dental water quality demonstrated that simple flushing of water lines—even for several minutes as recommended in the 1993 guideline––could not dislodge attached biofilms or reliably improve dental water quality. Studies of various methodologies to inactivate or remove biofilms showed that chemical treatment, filtration and combination technologies could improve water quality and could be practically employed in clinical settings.

The development of commercially available, manufacturer-validated products and techniques to improve water quality provided the final and enabling consideration. Unless such options were available, dentists were no more able to improve water quality from their dental units than motorists driving smoke-belching 1970s cars could reduce air pollution without changes to the design of the internal combustion engine. Motivated by the American Dental Association’s 1996 statement on dental water lines which encouraged the dental industry to produce products and techniques that could produce dental water containing fewer than 200 CFU/mL by the year 2000, dental manufacturers developed new technologies and even re-designed their dental equipment to reduce the potential for biofilm formation and facilitate water quality management procedures.

In recent years, a number of new products have been developed and marketed to remove and prevent re-establishment of biofilm in dental equipment. Most currently available approaches use antimicrobial chemicals either intermittently to kill and remove the biofilms or at lower concentrations to prevent their formation. These products are either delivered using separate water reservoirs, or by devices that automatically introduce the chemicals into the water system. Separate water reservoirs now come as standard equipment on many new dental units. Alternatively, some manufacturers are installing devices to treat incoming municipal water and prevent the formation of biofilm. Passive or automated approaches can decrease the time spent on water line management and decrease the likelihood of treatment failures.

In spite the evidence of potential hazards and the availability of devices and procedures to improve dental water quality, many dentists still have not followed the new CDC recommendations. I suspect this may be due at least in part to an important missing piece of the puzzle: Where exactly are those dead bodies? Lacking disease surveillance programs such as those employed in US hospitals, it is very difficult to detect an individual case of disease transmission related to contaminated dental water in the dental office. This is particularly true if the infection involves a pulmonary condition such as Legionnaire’s disease or gastroenteritis that would not normally be associated with dental treatment. Localized post-operative infections, even if associated with contaminated dental water, are usually treated with antibiotics on an empiric basis without culturing of the wound to identify the organisms involved.

In addition to bacteria, fungi and sometimes protozoa, water from dental units may also contain relatively high levels of bacterial endotoxin, a component contained in the cell walls of many water bacteria. Endotoxin (also called lipopolysaccharide or LPS) can have potent physiological effects in susceptible individuals. The poll results suggest that awareness of elevated endotoxin levels in dental water among dental healthcare professionals is limited. In addition to being a trigger for asthma, endotoxin can cause chronic respiratory conditions such as granulomatous pneumonitis following chronic exposure. Workers who are chronically exposed to endotoxin in agricultural and manufacturing trades have been found to exhibit higher incidence of some chronic respiratory diseases. While no link between endotoxin exposure by patients or staff and respiratory disease has been identified, acute exposures may explain research findings that showed decreased lung function in asthmatic children undergoing dental treatment. The effect of long-term exposure of dental healthcare professionals to endotoxin from dental sprays has yet to be investigated.

Does the scarcity of case reports of disease associated with contaminated dental water mean there is no reason dental offices should improve dental water quality? I would argue to the contrary and base my opinion on several fundamental principles of dental practice.

The first are the principles associated with the classic “Chain of Infection”––a symbolic representation of the conditions that must exist for an infection to occur. Healthcare associated infections result when sufficient numbers of pathogenic organisms gain entry to a susceptible host via a portal of entry and begin to replicate. Since two of the major links in the chain (the susceptibility of patients and the pathogenicity of organisms) are typically not under control of the healthcare professional, most infection control procedures focus either on blocking the portal of entry (masks, eyewear, barriers) or by reducing the numbers of potential pathogens in the clinical environment. In fact, healthcare professionals expend considerable effort to prevent disease transmission by reducing the numbers of potentially infectious organisms in the clinical environment through handwashing, instrument cleaning, sterilization and surface disinfection. I find it very difficult to rationalize the use of water heavily contaminated with microorganisms, through dental handpieces that have been carefully cleaned, sterilized and stored aseptically until the time of use.

A second important principle is the doctrine of informed consent. Before beginning any treatment on a patient, the dentist has an obligation to ascertain that the patient comprehends both the risks and benefits of the procedure. This doctrine applies to both procedures with higher risks of complications, where written informed consent must be obtained, as well as for more routine procedures where the patient’s understanding of risks and benefits is often assumed. I suspect many patients would have serious reservations about providing consent to treatment with dental water if they were informed it did not meet standards for drinking or recreational water.

Although dental water line contamination does not appear to pose a serious and immediate health crisis for the dental profession, I believe the available evidence supports a call to action. The new CDC guidelines provide a framework for implementing water quality management procedures and products are now available to provide dentists with safe, effective and affordable options to improve dental water quality. The results of this poll reassure me dental water lines are beginning to lose their aura of controversy and clean water will soon join gloves, barriers and autoclaves as a routine element of infection control practice in the dental office.

To learn more about dental water line contamination and methods to improve the quality of dental water as well as other useful information about dental office safety and infection control, I recommend the following websites:

For general information on dental water lines and a list of currently available products designed to improve the quality of dental water, go to the Organization for Safety and Asepsis Procedures (OSAP) website at http://www.osap.org/issues/pages/water/index.htm.

To download a copy of the 2004 CDC dental infection control guidelines, go to http://www.cdc.gov/mmwr/indrr_2003.html and download the issue entitled December 19, 2003 / Vol. 52 / No. RR—17.

Shannon E. Mills, DDS is a military dental officer who has conducted research on dental water quality issues and is a former consultant for dental infection control to the US Air Force Surgeon General. He is the current Chairman of the American Dental Association Standards Committee for Dental Products and has served as Chair of the Board of Directors of the Organization for Safety and Asepsis Procedures, Dentistry’s Resource for Infection Control and Safety.