Water Quality in Dental Healthcare Delivery
Maintaining a clean water supply is one of the most crucial aspects of a successful infection control strategy.
Eve J. Cuny, RDA, MS
The dental scientific literature leaves no doubt that many factors encourage the development of biofilm in the lines that carry water to dental devices such as handpieces, sonic scalers, and air/water syringes.1-3 This biofilm, which is similar to biofilm in many wet environments, harbors microorganisms that have the potential to cause disease or infections among dental patients and dental personnel. Complex forces work to provide a protective environment for these microorganisms, making the removal and control of dental waterline biofilm a process that requires rigorous compliance with product-use instructions. It may also be necessary to monitor the water output to verify that the office protocols are sufficient to maintain a level of water quality suitable for use in healthcare settings.
In the early 1960s reports of water contamination associated with dental units and attached devices began to appear in the dental literature.4 Numerous studies since that time identify the colonization of bacteria in the dental waterlines in addition to other waterborne microorganisms and, in some cases, oral flora.1-3 Microbial contamination of the water resulting from contact with the biofilm that lines dental tubing reaches levels as high as 200,000 colony-forming units per milliliter (CFU/mL) within days of installation of the dental unit. These findings led to the adoption of a statement on dental water quality by the American Dental Association (ADA) in 1995. The statement, published in the The Journal of the American Dental Association in 1996, encouraged the design of equipment that would lead to dental water quality that would consistently contain no more than 200 CFU/mL of aerobic mesophilic heterotrophic bacteria.5 The ADA recommended that practitioners use independent water reservoirs on dental units, institute chemical treatment, and perform daily water-draining and air-purging regimens and/or use point-of-use filters. Before the ADA statement, the only recommendation from any public agency or organization was to flush lines with water on a routine basis. This method of reducing contamination is not effective in producing or sustaining water quality control. Since the ADA publication of the waterline statement in 1996, there have been numerous advances in the control of dental treatment water contamination.
The Centers for Disease Control and Prevention (CDC) published its latest guidelines for infection control in dentistry in 2003, which established a recommendation that water quality for routine dental procedures not exceed Environmental Protection Agency (EPA) drinking-water standards of not more than 500 CFU/mL. In addition to delivering an irrigant that meets drinking water quality for routine procedures, the CDC recommends the use of sterile irrigants during surgical procedures. Those irrigants should be delivered using a device specifically designed for sterile water/irrigant delivery.6 Today, many options allow the dental team to achieve these goals.
Water Line Treatment Options
The treatment options available to individual offices rely heavily upon the system present for delivery of water to the dental unit. Offices that have units connected directly to the municipal water supply have three main options. All rely on interruption of the water supply before it reaches the patient. It is important to use a "shock" treatment as the initial step in the use of these devices. Treatment with a disinfectant alone when there is an existing biofilm may well destroy a majority of the organisms, but if the biofilm architecture is allowed to remain it provides a pre-formed matrix in which the biofilm can renew.7 A properly applied, EPA-registered shock treatment will effectively remove biofilm. This, followed by routine treatment according to manufacturer’s instructions, should enable a dental practice to maintain a high quality of dental treatment water.
At least two companies offer systems that consist of a canister that attaches to the water line before it enters the dental unit (Figure 1). These canisters contain filter beds impregnated with either silver ion or iodine to act as a disinfectant or mechanism to disrupt and treat the biofilm. The cartridges require replacement on a routine schedule, usually between 3 and 12 months. The other type of filter interrupts the waterline close to where it exits the dental devices. Often called a point-of-use filter, this device does not improve water quality in the dental unit but relies upon a filter membrane to remove solid contaminants before the water reaches the patient. These filters require daily maintenance or replacement. Finally, there are centralized devices that treat and deliver water to a single or multiple units within a dental office. These devices require installation and maintenance and involve methods including nanofiltration, reverse osmosis, ultraviolet light irradiation, and possibly the addition of a chemical agent to control biofilm formation.
Most dental units manufactured in the past decade contain independent water reservoirs (bottles) rather than a direct connection to the municipal water supply (Figure 2). Early attempts at reducing water contamination included diluting the water with bleach solutions. Although effective, these solutions tend to corrode the dental unit’s internal metal components and can damage rubber gaskets. Currently, a large selection of waterline treatment products and devices are available to the dental professional (Table 1). Many of these products and devices are cost-efficient and relatively easy to use. The products available to control water quality in dental units with independent water reservoirs fall into two broad categories: those that provide a continuous treatment and those that provide intermittent treatment. Both of these treatments may require an initial and periodic "shock" treatment with a separate product intended for that purpose. Most manufacturers provide guidance regarding the initial treatment.
Continuous treatment products remain in the water reservoir even during patient treatment. The manufacturers of these products must demonstrate that they are safe for patient consumption before they can sell them in the US dental market. As medical devices these product must receive Food and Drug Administration (FDA) clearance before marketing in the United States. As disinfectants or germicides, they must receive EPA registration. However, demonstrating biocompatibility with the ever-growing selection of dental restorative materials is not part of the FDA clearance or EPA registration process for any waterline treatment products.
Continuous-use products are tablets, tubes that insert into the water reservoir bottle, or powder or liquid that personnel mix with the water in the reservoir or add to the reservoir in place of water. There are also products that are ready-to-use and do not require the addition of water. It may be necessary to include a schedule of shock treatments to ensure that the biofilm does not reform on the dental lines. Even with the use of continuous or intermittent chemical treatment, biofilm can return and the chemical treatment regimens do not necessarily eliminate heavy growth of biofilm.
Intermittent treatment products require a routine chemical treatment of waterlines either in combination with or in place of continuous-use products. The intermittent-treatment products typically require that personnel introduce a chemical product, either ready-to-use or mixed with water, to the water reservoir and flush the entire bottle of product through all of the lines that deliver water. Some products may need to be left in the lines overnight or over the weekend. The cleaning process often requires additional flushing of water through the lines to remove the chemicals before adding dental treatment water.
How To Ensure Quality Assurance
Because dental waterline treatment products must clear the FDA or have EPA registration, it is not necessary for the dental office to test the performance of the products or devices to validate the manufacturer’s claims. The manufacturer must demonstrate safety and efficacy before selling products to US dental offices. Still, there is a benefit to testing the water output to ensure that the office protocols are producing the desired outcome. Many protocols are technique sensitive and some reports in the dental literature indicate that over time, some treatment methods may not sustain favorable results.8 There is also the possibility of user error in applying the manufacturer’s recommended protocols. Setting a routine for testing the water output quality will ensure early identification in lapses in protocol that may result in reformation of biofilm and an increase in water contamination.
There are two choices when it comes to water quality monitoring in the dental office. One method allows to test and record results by office personnel, while the other requires collection of samples for shipment to a laboratory for analysis. Testing should provide results that indicate the number of CFU/mL of heterotrophic bacteria. The results can be too numerous to count, in which the biofilm treatment should be initiated or modified and the water retested to ensure it meets the drinking-water standard of not more than 500 CFU/mL.
Other important considerations to ensure the efficacy of treatment include ensuring that there are no lines within the dental unit attached to unused ports, such as extra air/water or handpiece lines not in use. The treatment of dental lines requires the water to pass through the lines to ensure efficacy. If these so-called "dead legs" are present in the dental unit, clamp them off to prevent recontamination of the lines that are in use.
Some products require the use of distilled water in combination with a chemical agent. Others indicate that tap water is sufficient. The characteristics of tap water can vary greatly from one location to another. Therefore, it would be even more important to perform quality assurance testing of protocols to ensure the water in a specific location does not interfere with the efficacy of a given product. Carefully follow the manufacturer’s instructions for mixing, purging, and treatment schedule.
1. Gaudie WM. Contamination of dental unit waterlines: a re-evaluation. J N Z Soc Periodontol. 2006;89:12-16.
2. Meiller TF, Depaola LG, Kelley JI et al. Dental waterline units: biofilms, disinfection and recurrence. J Am Dent Assoc. 1999;130(1):65-72.
3. Szymanska J. Microbiological risk factors in dentistry. Current status of knowledge. Ann Agric Environ Med. 2005;12(2):157-163.
4. ADA statement on dental unit waterlines. J Am Dent Assoc. 1996;127:185-186.
5. Blake GC. The incidence and control of bacterial infection of dental units and ultrasonic scalers. Br Dent J. 1963;115:413-416.
6. Centers for Disease Control and Prevention. Guidelines for Infection Control in Dental Health-Care Settings–2003. Morbidity and Mortality Weekly Report. 2003;52(RR17);1-61.
7. Kumar S, Atray D, Paiwal D, et al. Dental unit waterlines: source of contamination and cross-infection. J Hosp Infect. 2010;74:99-111.
8. Porteous NB, Cooley RL, Lau CA. The efficacy of a continuous-use stabilized chlorine dioxide dental unit waterline cleaner and the evaluation of two water sampling methods. Gen Dent. 2003;51(5):472-476.
About the Author
Eve J. Cuny, RDA, MS
Assistant Professor, Dental Practice
Director, Environmental Health and Safety
University of the Pacific
Arthur A. Dugoni School of Dentistry
San Francisco, California