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ADA Council on Scientific Affairs

Background: Organized dentistry has traditionally assumed responsibility for assessing and improving the quality of dental care provided to patients. The widespread adoption of enhanced infection control methodologies by dental practitioners is just one example of the profession's commitment to high quality patient care.

In 1995, the American Dental Association Board of Trustees and ADA Council on Scientific Affairs, adopted a statement on dental unit waterlines. This statement was in response to scientific evidence that the microbiologic quality of water used in dental treatment could be improved; and called for the design of dental equipment so that, by the year 2000, water delivered to patients during nonsurgical dental procedures consistently contained no more than 200 colony-forming units per milliliter (cfu/ml) of aerobic mesophilic heterotrophic bacteria at any point in time in the unfiltered output of the dental unit. Since 1995, technological advances have made this goal possible. In addition, the CDC now recommends that coolant water used in non-surgical dental procedures meet EPA regulatory standards for drinking water, which is less than or equal to 500 colony forming units of heterotrophic bacteria per milliliter of water. This CDC recommendation was published in their Guidelines for Infection Control in Dental Health-Care Settings—2003 (CDC has different guidelines about water used in oral surgical procedures). Considering these developments, a statement was adopted in 2004 to update the 1995 ADA statement on dental unit waterlines.

In 2012, a case report was published concerning an 82-year-old otherwise healthy woman who developed Legionnaire's disease after a dental visit.1 The current statement updates the 2004 ADA statement on dental unit waterlines to recognize this case report.

The Council is sensitive to heavy regulatory burden imposed on dentists in recent years by various federal, state and local government agencies. In some cases, the regulations have been based on limited science. The Council reaffirms its strong belief that both the profession and the public are served when recommendations affecting dental practice are based on sound science and take into account their cost in light of their expected benefit. The recommendations that follow are made in light of these considerations.

Dental unit waterlines must be maintained regularly to deliver water of an optimal microbiologic quality. Although infection associated with microbial contamination of waterlines appears to be rare, it has been shown that the level of microorganisms in untreated dental unit waterlines is greater than 500 CFU/mL, which exceeds the drinking water standard. Colonization of microorganisms within the waterlines-while it may not be a concern to healthy individuals-might place elderly or immunocompromised patients at unnecessary risk. 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, in significant numbers, a wide variety of microorganisms including bacteria, fungi, and protozoans. These microorganisms colonize and replicate on the interior surfaces of the waterline tubing, inevitably resulting in adherent heterogenous microbial accumulations termed "biofilms". Biofilms, once formed, serve as a reservoir significantly amplifying the numbers of free-floating microorganisms in the water exiting the waterlines. It has been suggested that heating dental unit water to increase patient comfort, as is the practice in some dental offices, may further augment biofilm formation. In dental unit waterline systems that are not maintained, these microbial accumulations can contribute to occasional objectionable odors and visible particles of biofilm material exiting the system.

Water Quality Improvement: Dental unit water systems designed for general dental practice must be regularly maintained in order to deliver water of an optimal microbiologic quality. Manufacturers of dental equipment are encouraged to continue 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. Further, the ADA urges industry to continue to ensure that all dental units manufactured and marketed in the U.S.A. in the future 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.

In 1993, CDC recommended that dental waterlines be flushed at the beginning of the clinic day to reduce the microbial load. However, studies have demonstrated this practice does not affect biofilm in the waterlines or reliably improve the quality of water used during dental treatment. Dental unit water that remains untreated or unfiltered is unlikely to meet drinking water standards, <500 CFU/mL, therefore, one or more commercial devices and procedures designed to improve the quality of water should be employed. At the present time, commercially available options for improving dental unit water quality include the use of:

  • Independent water reservoirs
  • Chemical treatment regimens 
  • Source water treatment systems
  • Daily draining and air purging regimens 
  • Point-of-use filters

Additionally, strict adherence to maintenance protocols is required to sustain the quality of dental unit water. Industry and independent researchers are strongly encouraged to continue to explore the possible alternatives and adjuncts to the above listed options. Dental practitioners should always consult with the manufacturer of their dental units before initiating any waterline treatment protocol.

Water Quality Monitoring: It is important that waterline treatment schedules include water quality monitoring. Simple and inexpensive methods to estimate the number of free-floating heterotrophic bacteria in dental unit water are available. A well-designed water quality indicator should be self-contained and easy to use in-office; accurately detect a wide concentration range and type of aerobic mesophilic heterotrophic waterborne bacteria within a reasonable incubation time at room temperature; and be relatively inexpensive to use. In addition to in-office testing kits, laboratories across the U.S. also offer mail-in testing services. Cleaning Waterlines (PDF). 

Delivery of Sterile Surgical Irrigation: According to the 2003 CDC Recommendations, "Sterile solutions such as sterile saline or sterile water should be used as a coolant/irrigation in the performance of oral surgical procedures. Oral surgical procedures involve the incision, excision, or reflection of tissue that exposes the normally sterile areas of the oral cavity including biopsy, periodontal surgery, apical surgery, implant surgery, and surgical extractions of teeth (removal of erupted or nonerupted tooth requiring elevation of mucoperiosteal flap). Conventional dental units cannot reliably deliver sterile water even when equipped with independent water reservoirs because the water-bearing pathway cannot be reliably sterilized. Delivery devices (e.g., bulb syringe or sterile, single-use disposable products) should be used to deliver sterile water. Oral surgery and implant handpieces, as well as ultrasonic scalers, are commercially available that bypass the dental unit to deliver sterile water or other solutions by using single-use disposable or sterilizable tubing."

Training and Education: The ADA has resources available to educate dental practitioners regarding microbial contamination and biofilm formation in dental unit waterlines, and improving the quality of water delivered to patients. Additionally, manufacturers should be active in training and educating the profession in the proper use and maintenance of their systems.

In summary, the Council recognizes that the scientific literature supports the need for improvement in dental unit water quality. The Council will continue to work with industry and the research community to address research and development needs that will allow the delivery of water of an optimal microbiological quality to the dental patient. The Council recommends dissemination of this information to dentists as part of the ADA's ongoing service to the profession and the public.

April 2012


  1. Ricci ML, Fontana S, Pinci F, et al. Pneumonia associated with a dental unit waterline. Lancet 2012;379(9816):684.

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