By Jerry M. Mark and Robyn Gordon

Summary: Often overlooked, water treatment for dental waterlines has its own set of bacterial issues to be confronted. Some factors causing bacteria are outlined here as well as possible technologies available to professional water dealers. Each has its own advantages and drawbacks. In addition, the application of UV and a set of test results are also discussed in detail.

Factors in Bacterial Growth
Based on research, the dental industry has been able to pinpoint many factors that contribute to extremely high bacteria counts. These include:

  • Tubing used to deliver the dental water,
  • Inoperable anti-retraction check valves (designed to prevent patient “suck-back”),
  • Biofilm growth, which occurs when bacteria within the water supply attaches to walls of the dental waterline and begin to multiply, and
  • Improper infection control procedures and/or no infection control procedures.

Dental industry research cites documented dental waterline infection cases. One was reported by the California Board of Examiners regarding the fatality of an orthodontist from Legionella. An English report implicates Pseudomonas aeruginosa from dental waterlines as the cause of oral infection in two medically compromised dental patients.1 Additionally, a significant decrease in lung function in 15 percent of 57 children ages 6 to 18 years old who underwent dental treatment was documented.2

Researchers report that biofilm provides an environment conducive to proliferation of a wide variety of microscopic life, including fungi, algae, protozoa and nematodes.3 Potential pathogens find their way into dental water systems such as P. aeruginosa, L. pneumophila and Mycobacteria.4 Cladosporium is an aquatic fungus, which has been recovered from dental waterline units and is associated with hypersensitivity pneumonitis.5

Both the ADA and Centers for Disease Control (CDC) suggest the best course of action to reduce high bacteria counts is to simply flush the dental waterline with water before, between and after patients. Still, according to Dr. Chris Miller, a well-known infection control expert, “Merely flushing dental waterlines isn’t effective. It’s a well-known fact dental plaque biofilm isn’t removed simply by rinsing the mouth with water. Likewise, dental waterline biofilm isn’t removed by flushing lines with water.”6

The most conclusive article was published in the October 2000 issue of JADA—the Journal of the American Dental Association—by Dr. Shannon Mills, a colonel in the U.S. Air Force Dental Corps, and the dental program manager. Dr. Mills chronologically listed all known published data regarding this matter and was the first to summarize the severity of this national dental “crisis.” He concluded, “Reducing the number of microbes in water from dental units is absolutely consistent with long accepted infection control principles. Does it make sense to sterilize a dental hand piece, store it in an impervious package designed to ensure its sterility, and then use it to introduce into the oral cavity water that fails to meet acceptable microbiological standards for drinking or recreational water?”7

And Dr. Mills warned his colleagues, “Dental unit waterline cleanliness is not a public health crisis. Nevertheless, water that’s unfit to drink as defined by nationally recognized standards is unsuitable for therapeutic use in dentistry. Continued inaction on the part of the dental profession can serve to undermine public confidence in our commitment to quality dental care.”7

The American Dental Association
(ADA) has been aware of contamination problems existing within dental waterline units (DWU) since 1963; however, only in recent years has it caught the public’s attention. Thanks to coverage by national prime-time news programs like “20/20” with Barbara Walters (aired February and August 2000) and CBS’s morning news (aired October 1999), the public is now aware of contaminated dental waterlines found in virtually every untreated dental office across America.

These programs revealed contamination rates as high as 1 million colony-forming units per milliliter (cfu/ml) of bacteria from water exiting dental waterline units. The ADA issued statements to the national media and on its website instructing dentists on how to respond to patients’ questions. The main themes of these “dental responses” centered on the fact “there were no published scientific reports linking serious illness or death due to DWU contamination.”

While the U.S. Environmental Protection Agency (USEPA) established a guidance limit for treatment techniques of 500 cfu/ml of heterotrophic bacteria for public water supplies, the ADA adopted a goal of no more than 200 cfu/ml of bacteria by 2000 (see Factors).

Dental waterline treatment
A number of “solutions” have hit the market claiming to permanently solve the high bacteria counts within dental waterline units. These solutions break down into four different categories:

  1. Chemical treatment,
  2. Submicron filtration,
  3. Self-contained water systems, and
  4. Water purifiers/sterilizers.

All will affect, to some degree, bacteria counts emanating from dental hand pieces. With varying costs and results, the following is a brief overview of each technology.

Chemical treatments
There are several types of chemicals designed to eliminate and/or prevent biofilm approved by the Food and Drug Administration (FDA). One chemical suggests a continuous delivery of chlorhexidine gluconate within dental waterlines. This approach is very expensive when a 10-ounce bottle retails for $10. There also have been questions in the dental industry as to how this chemical would affect different dental procedures. Further, these chemicals must be introduced into the dental waterline, requiring additional hardware and expense.

Another manufacturer offers a hydrogen peroxide-based solution, which must be introduced into dental waterlines on a frequent basis. Again, this requires additional hardware or a means to introduce the chemical into the water supply. This chemical is endorsed by the ADA’s Seal of Acceptance as the organization’s website states: “The Seal on a product is an assurance for consumers and dentists against misleading or untrue statements concerning a product, its use, safety and effectiveness.”

The third most popular chemical treatment introduces a small amount of iodine into the water supply, which is later filtered by a submicron filter located near the dental hand piece. All of these chemicals require constant attention of the dentist and the staff, yet none include any failsafe means of monitoring or testing results. Still, chemical treatment is an effective way of reducing existing biofilm from dental waterlines and should be considered for those purposes.

Submicron filtration
One more popular way to reduce bacteria is submicron filtration (0.02 micron). These small filters are mounted as close to the dental hand piece as possible (dentists are reluctant to slice into the dental waterlines) and require constant changing. Some last a day and others last up to a week. Not only are these filters time-consuming, but they’re expensive. The average dentist has at least two operatories (fully equipped patient care units), which represent between $2,300 and $7,000 in annual filter replacement expenses.

Self-contained water systems
A few dental equipment manufacturers offer a self-contained water bottle delivery system, utilizing small water bottles that must be refilled frequently. According to a research paper presented at an OSAP (Organization for Safety and Asepsis Procedures) Symposium, “Independent reservoirs can be effective in improving quality. Lax hand washing and careless handling of bottles and feeder tubes can result in contamination of the water systems with enteric or skin organisms. The same thing can happen when dental water systems are repaired. A case of coliform contamination in dental units has been reported.”<sup>7</sup>

Water purifiers/sterilizers
There are only a handful of manufacturers offering water purification for the dental industry. Technologies may include large industrial size distillers (capable of providing distilled water to all operatories), water treated with ozone at or near the dental hand piece, and most recently ultraviolet (UV) irradiation to treat water as it enters the dental waterlines.

Two manufacturers serving the dental industry for years have developed what they believe is a true water purification system. One offers a UV system that provides a UV reaction chamber without any prefiltration. Experts within the water treatment industry agree—prefiltration is necessary to prevent bacteria and viruses from being protected by “shadowing,” where suspended solids and other particulate in the water prevent full effectiveness of the UV irradiation. The other manufacturer offers a small unit designed to be installed into each operatory that incorporates both UV irradiation and ozone. This seems to be one of the best solutions, until you read the fine print: It’s recommended that only distilled water be used to refill the reservoirs.

A complete approach to UV
A third company focuses on the belief that once bacteria and biofilm are successfully eliminated from existing dental waterlines, only bacteria-free water should be introduced afterwards. To this end, it offers a comprehensive disinfection protocol that allows the dentist to utilize recommended pretreatment by introducing a chemical disinfectant within the same system, instead of purchasing additional hardware to perform this function. The system also offers an audible alarm to notify the clinician should there be a disinfection failure. It’s backed by five laboratory reports, FDA cleared and NAMA approved, and manufactured with only UL- and NSF-compliant components.

The system produces up to 2 gallons per minute (gpm) of disinfected water (water produced is disinfected by 3 logs), enough for two operatories (depending upon existing plumbing). Water is prefiltered with two different types of filters, then it’s exposed to a high intensity UV lamp where waterborne bacteria and viruses are inactivated.

The two prefilters are a 1-micron sediment filter, followed by a ½-micron carbon block filter. It’s recommended that once installed, the service technician should remove the filter media and then fill the filter housings with a disinfectant as recommended by the Clinical Research Associates (CRA), a not-for-profit dental consumer group. Once the filter housings are filled with either the blue or pink disinfectant, they should be reattached and the water turned on. Then they should go to each dental operatory and open the dental hand piece until the “blue” or “pink” is seen. The disinfectant should remain in the lines overnight (or as directed by the manufacturer) and then flushed out the next morning. Finally, the original filters should be returned to their appropriate filter housings and secured to the unit again.

Dental water dispensing system
This system incorporates both RO and UV into one small system. It’s designed to dispense mineral-free, disinfected water for refilling chair-mounted, water bottle systems. Since the dental water bottle must be refilled usually once a day per operatory, most dental offices simply buy bottled water to refill these dental water bottles, or use tap water. In these scenarios, the unit is generally installed within the breakroom, lab or common area within a dental office. It’s typically installed under a sink area with a “goose-neck” faucet for sterile/mineral-free water dispensing.

Therefore, sterile and mineral-free water is obtained from the system’s faucet and not routed to the individual operatories (when a chair-mounted water bottle system is used, there are no waterlines run into the operatory rooms).

Today, dental equipment manufacturers tend to offer operatory equipment, which is “self-contained” and requires no municipal water connections; however, this isn’t always the solution to dental waterline contamination. Occasionally, proper infection control guidelines are sometimes overlooked or ignored entirely (especially when a patient is in the chair and the water bottle runs dry).

Recently, the Microbiological Department of the University of Tennessee Dental College conducted a laboratory test, comparing a self-contained water bottle system against an RO/UV dental water system. This test revealed the bottle system as having bacteria counts from a low of 1,700 cfu/ml to a high of 3,100 cfu/ml. One particular unit produced 0 cfu/ml, except for one test that had a UV lamp turned off.

The RO/UV system also provides water for use in autoclaves that are used daily to sterilize dental hand pieces (with steam). Until recently, only distilled water was recommended for use within these autoclaves. Several autoclave manufacturers have given this system approval for use with their autoclaves (based on a laboratory analysis by Spectrum Labs). The system can also be modified to deliver enough mineral and bacteria-free water to replace municipal water for up to 16 operatories, as is the case with a dental hygienic college in Pueblo, Colo. This saves hundreds of dollars in dental hand piece repair due to calcium/magnesium scale buildup.

Office line disinfection
This whole building/office point-of-entry (POE) system is one of the more popular dental water disinfectants. It’s designed to operate an entire year before any maintenance is required. Unique to this system is its ability to filter all water (up to 15 gpm) down to 0.5 micron. Afterwards, the filtered water is exposed to high intensity UV light. Unlike filter backwashing, a self-cleaning mechanism also washes the outside of each filter up to six times per day, thereby washing away trapped debris. The self-cleaning filter design has been independently tested, and verified to extend the life of the filters up to six times longer than without the self-cleaning mechanism.

Moreover, one of the features to this system is that it can extend the life span of all dental appliances with which the treated water comes into contact. For a dentist who is either remodeling or moving into a new office, it helps to protect their overall investment.

Considering that water quality regulatory officials generally agree a multi-barrier approach to water treatment is most effective, incorporation of UV with pretreatment filtration (and even RO) as well as self-cleaning systems and auditory alarms offers advantages for dental offices proactive about the care and safety of their clients. The aforementioned dental waterline systems have been reviewed in depth by the FDA, ADA and are currently being “clinically” tested by CRA. The systems are sold through specialized dental dealerships.


  1. Kono, Gary, “Dental Unit Waterlines: Taking the High Road Now,” Dentistry Today, August 1997.
  2. Mathew, P.S., et al., “Effects of dental treatment on the lung function of children with asthma,” Journal of the American Dental Association (JADA), 1998.
  3. Costerton, J.W., et al., “Microbial biofilms,” Annual Review, Microbiology, 1995.
  4. Barbeau, J., R. Tanguary and E. Faucher, “Multiparametic analysis of waterline contamination in dental units,” Microbiology, 1996; CDC: “Legionnaires’ disease and Pontiac fever,”; and Schulze-Robbecke, R., C. Feldmann and Lung Dis Tuber, “Dental units: an environmental study of source of potentially pathogenic mycobacteria,” 1995.
  5. Includes: “Microbial contamination of dental waterlines: prevalence, intensity, and microbiological characteristics,” Williams, J.F., A.M. Johnston, B. Johnson, M.K. Huntington, JADA, 1993; “Reduction of microbial contamination in dental units with povidone-iodine 10%,” Mills, S.E., P.W. Lauderdale, R.B. Mayhew, JADA, 1986; “Microbial aggregate contamination of waterlines in dental equipment and its control,” Kelstrup J, T. Funder-Nielson, J. Theilade, Acta Pathol Microbiol Scand, 1977; “Hypersensitivity pneumontis caused by Cladosporium in an enclosed hot tub area,” Jacobs, R.L., R.E. Thorner, J.R. Holcomb, L.A. Schwietz, F.O. Jacobs, Annals of Internal Medicine, 1986.
  6. Miller, Chris H., “Microbes in Dental Unit Water,” CDA Journal, January 1996.
  7. Mills, S.E., “The dental unit waterline controversy,” JADA, October 2000.
  8. Mills, S.E., and F. McClesky, “Isolation of fecal coliform bacteria from independent dental water systems,” Paper presented at Organization for Safety and Asepsis Procedures Annual Symposium, Las Colinas, Texas, June 1996.

About the authors
Jerry M. Mark is vice president of sales and marketing at O-So-Pure, of Phoenix, with over 20 years of experience in residential and resort sales/marketing worldwide.

Robyn Gordon is O-So-Pure’s operations director, and has over 12 years of experience working with major water treatment manufacturers.

Both can be reached at (602) 944-4635, (602) 944-9897 (fax) or email: [email protected]


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