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Inside Dentistry
October 2014
Volume 10, Issue 10

Maintaining Dental Unit Waterlines

Best practices to minimize patient exposure to harmful microorganisms

Marie T. Fluent, DDS

Patients assume that water that enters their oral cavity during dental procedures is as clean as clean and safe as drinking water from a tap. Yet water expressed from an air/water syringe or generated in the form of aerosols in a high-speed handpiece or ultrasonic scaler may be significantly contaminated with microorganisms if waterlines are not properly maintained. Common sense may suggest that the quality of water that flows into the dental unit would be similar to quality of water expressed through the output. However, conditions of the lumens of these waterlines, such as small diameter, low flow rates, and frequent periods of stagnation, can actually promote bacterial growth and the development of biofilm.

Looking at the Numbers

The Environmental Protection Agency (EPA) and other governmental organizations have established standards for safe drinking water quality. These groups mandate that drinking water contain 500 or less colony forming units (CFU) of heterotrophic bacteria per milliliter. The American Dental Association has recommended even lower levels at 200 CFU or less. Meanwhile, studies have demonstrated that microbial counts can reach 200,000 CFU/mL and higher very quickly in dental waterlines and levels of contamination up to 1,000,000 have been documented.1

Microorganism Origins and Health Implications

Most of the microbes that have been isolated from waterlines originate from the public water supply, but some originate from oral fluids retracted through air/water syringes and handpieces. The majority of these microorganisms are considered opportunistic and do not pose a disease risk for healthy persons.2 However, more patients with weakened immune systems are seeking dental care. Patients with AIDS, those undergoing chemotherapy, or those following organ or bone marrow transplantation may seek dental care and would be exposed to high microbial counts in contaminated water. It is difficult to document cases of illnesses due to contaminated dental unit waterlines since most dentists practice in outpatient facilities and patients are not monitored for post-treatment illnesses. However, in 2012, the first documented infection (Legionnaires disease) and death from contaminated dental unit waterlines was reported and highly publicized. In this landmark case, bacteria isolated from the dental handpiece and the patient’s sputum were found to be of the same bacterial serogroup.

Strategies to Improve Water Quality

The Centers for Disease Control and Prevention (CDC) has made several recommendations to improve the quality of dental unit water. It is recommended to flush waterlines for 20 to 30 seconds after each patient. While flushing the waterlines can reduce the microbial load, the effects are temporary. Bacterial counts can quickly rise to levels that equal or exceed pre-flush levels as biofilm grows or is dislodged by flowing water. Simply using self-contained water systems with the use of tap, distilled, or sterile water along with in-line microfilters will not eliminate contamination if biofilms are not controlled. For these reasons, it is recommended that sterile water should be used for surgical procedures. Also, removal or inactivation of biofilms requires the use of chemical germicides to ensure water of acceptable quality for general dental procedures.1

Disinfection of Dental Unit Water

Clinicians have the option to remove or prevent biofilms through periodic “shock” treatments or the continuous presence of chemicals in the waterlines. Shock treatments involve purging the lines, adding a chemical to the reservoir, filling the waterlines, and flushing. Continuous chemical treatment may involve a metering device to slowly release chemical germicides into the treatment water to lower microbial counts and control biofilms or placing several drops into an independent water bottle system about once a week. Some products may require both shock treatments and continuous line treatments to maintain water quality. Most water treatment products require strict compliance with manufacturer’s instructions to maintain consistent water quality and some products are more technique sensitive and time consuming than others. All antimicrobials used for dental waterline maintenance must be registered with the EPA.

Ideal Properties of Waterline Disinfectants

Before introducing any chemical into a dental unit, clinicians must consult with the manufacturer that the germicide is compatible with the dental unit and that it will not harm the patient or dental healthcare professional. Properties of an ideal dental unit waterline germicide include:

• Tasteless and odorless

• Non-toxic and non-allergenic to patient

• Compatible with dental unit and equipment

• Broad spectrum of antimicrobial activity

• Fast-acting/time efficient

• Removes existing biofilm

• Minimizes/prevents biofilm attachment

• Does not interfere with use of bonding agents or other dental materials

• Inexpensive

• Minimal technique sensitivity/easy to implement

• Easy to implement

Although no ideal products exist at this time, products claiming many of the attributes of the ideal are now being marketed.

Monitoring of Dental Unit Water

It is recommended that dental personnel be trained regarding water quality, treatment methods, and maintenance protocol. Noncompliance with water treatment regimens has been associated with contaminated dental unit water. For this reason, the CDC recommends monitoring of water quality to ensure that waterline protocol is being correctly performed and that devices are working. The CDC recommends consulting with the manufacturer of their dental unit or the water delivery system to determine the best method and the frequency of monitoring. As the CDC updates guidelines for infection control in the dental setting in 2015, maintenance and waterline maintenance will be addressed. Proposed changes will emerge from consultation with the EPA and US Food and Drug Administration and a literature review to address the optimal frequency of monitoring for each type of maintenance system.3 After new guidelines are implemented, clinicians will still be advised to adhere to manufacturer’s instructions for waterline maintenance protocol; however, the CDC may offer specific recommendations with regard to frequency and record keeping of dental waterline monitoring.

To ensure that waterline maintenance systems are performing adequately, dental unit water should be tested to detect a wide range of bacteria. There is no need to identify specific organisms unless investigating a specific waterborne illness or dental unit. Testing of dental unit water may help identify compliance or performance issues and documentation.4 The ideal monitoring procedures should be inexpensive and simple to perform and evaluate. Self-contained test kits or commercial water-testing laboratories are among the options available.

Tips for Dental Unit Water Maintenance

Clinicians can share the following with their dental teams:

• Discharge water for 20 to 30 seconds after each patient all devices connected to the dental water system that enters the patient’s mouth (eg, handpieces, ultrasonic scalers, and air/water syringes).

• Do not use water heaters on dental units.

• Read instructions of dental waterline treatment system. Know whether your system requires a shock treatment to remove existing biofilm.

• Use sterile solutions as a coolant/irrigant.

• In case of a boil-water advisory, do not use municipal water in dental operative unit or other equipment that uses public water systems.

• Always consult with dental unit manufacturer before introducing any chemical into the water system.


1. Kohn WG, Collins AS, Cleveland JL, et al; Centers for Disease Control and Prevention (CDC). Guidelines for infection control in dental health-care settings—2003. MMWR Recomm Rep. 2003;52(RR-17):1-61.

2. Molinari JA, Harte JA, eds. Practical Infection Control in Dentistry, 3rd ed. Baltimore, MD: Lippincott Williams & Wilkins; 2010:64-69.

3. Cleveland, J, Gray, S. Update of CDC’s Infection Prevention Guidelines for Dental Healthcare Settings. OSAP Symposium Proceedings 2013. Accessed August 14, 2014.

4. Molinari J, Nelson P. Dental waterline infection control. The Dental Advisor. 2014;31(5).

About the Author

Marie T. Fluent, DDS
Editorial Assistant, The Dental Advisor
Ann Arbor, Michigan

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