The quality of dental unit water is critical to the safe provision of oral health care. Practitioners and patients are exposed to water from these lines, as well as to aerosols produced by dental instruments — leading to concerns stemming from dental waterline colonization by potentially harmful biofilm microbes.1–5 In order to minimize this possible source of contamination, clinicians must implement appropriate strategies for waterline cleaning and maintenance.
Waterlines should be aseptically maintained with the same detail as the other environmental surfaces within the operatory. This presents sales professionals with a consultative opportunity to help their clients understand recommended protocols and select appropriate treatment products.
Biofilms are well-organized aggregates of microorganisms that include bacteria, algae, protozoa, nematodes and fungi. Forming on most surfaces in contact with water, biofilms thrive on plastic tubing and dental unit waterlines (DUWLs).6 Frequently embedded within a protective matrix (or slime), biofilms tightly adhere to the surface, making them difficult to destroy.7,8
Community water supplies delivered to the dental unit contain substantially lower numbers of microorganisms than the water that comes out of the dental unit because DUWLs encourage biofilm growth. There are three basic factors involved in this phenomenon: surface area, surface chemistry and flow rates.9,10 The small plastic tubing used in dental operatories plays a prominent role because the high surface-area-to-volume ratio increases the area accessible to biofilm formation.9 In addition, most plastic dental tubing has an inside diameter of 1/16 to 1/8 inch and is made of polyurethane — a form of plastic that provides a hydrophobic carbon source that promotes and sustains bacterial proliferation.
GO WITH THE FLOW
Laminar flow within DUWLs (in which water moves in parallel layers, with no movement between the layers11,12) also promotes biofilm growth. As a result, stagnant conditions still exist even when water is flowing, allowing biofilms to easily form. Intermittent use of water between patients — with typically no use during evenings and weekends — also cf conditions that favor microbial colonization.
These active biofilms now become the primary reservoir for continued contamination because, as pieces of biofilm detach, they seed biofilm growth elsewhere in the system. This also means that microorganisms from the biofilm can be flushed into the mouth — putting patients at risk.11 Aerosols and spatter stemming from contaminated waterlines may also contain pieces of biofilm and planktonic microorganisms that can be inhaled into patients’ and clinicians’ lungs.11
The microbes found in DUWLs are usually benign. On the other hand, Pseduomonas, Mycobacterium and Legionella have been isolated in DUWLs, and these respiratory-opportunistic pathogens can cause serious disease in the immunocompromised.7 This scenario underscores the need for dental teams and sales personnel to work in concert to ensure asepsis in dental water systems.
For routine dental treatment, the U.S. Centers for Disease Control and Prevention (CDC) recommend that DUWLs contain fewer than 500 colony-forming units per milliliter (CFU/mL) of heterotrophic bacteria.13 When managing waterlines to ensure compliance, clinicians and sales pros should consult instructions provided by the dental unit manufacturer. Waterline management consists of three parts: biofilm eradication, control of free-floating planktonic microorganisms, and periodic water quality monitoring.
Flushing the system was first recommended by the American Dental Association (ADA) in 1995, but, while still advised, flushing does not remove biofilm.13 It does serve a helpful purpose, however, as the CDC asserts that waterlines should be flushed for a minimum of 20 to 30 seconds between patients to discharge oral fluids that may have bypassed anti – retraction valves14 designed to combat an exchange of fluids between patients caused by “suck-back” in dental devices such as handpieces.
Sales consultants can offer numerous options for improving the microbial quality of water used in practice, including filters, independent reservoirs, chemical treatments, slow-release cartridge devices, sterile water delivery systems, and antimicrobial agents incorporated into tubing.9–12,15 Furthermore, these options can be divided into two categories: those that treat water entering the dental unit, and independent water systems.
Dental unit waterlines must be maintained with stringent infection control protocols so as to ensure the quality of water used in practice. Aerosols generated using contaminated water supplies, for example, can linger in operatories — posing risks for practitioners and patients not involved in the original aerosol-producing procedure. Sales pros can help dental teams implement effective waterline management strategies.
Although there is no universally accepted protocol for DUWL decontamination, the use of microbial filters may be a smart approach for practices that use community water supplies. These water treatment devices are placed on each waterline and are designed to remove freefloating microorganisms before they can enter a handpiece or air/water syringe. Unfortunately, filters have a limited effect on biofilm and endotoxins. 13 Filters also require upkeep, and practices likewise incur the ongoing expense of replacement. In addition, this approach does not provide a means for sterile water delivery15 indicated for certain surgical procedures.
For practices that seek a more centralized approach, water purifiers and centralized systems are available. These are placed at the junction box connected to the municipal water system. Used for decontaminating DUWLs at the point of entry, nanofiltration, deionization, heat and ultraviolet germicidal irradiation are used to kill and/or remove organisms from the source water.9 These devices may be plumbed directly into the dental unit or they may use holding tanks placed in a centralized location.
This approach improves the source water and can be used in multiple operatories, but it has no residual effect on biofilms within the dental unit. As a result, waterlines must also be treated with a chemical agent designed to eliminate biofilms — and there are systems designed to introduce chemicals for this purpose. One potential upside is that water purifiers may inhibit and delay biofilm formation, while increasing the effectiveness of other decontamination methods.15
Another option is a self-contained water system that isolates the dental unit from community water, allowing for chemical treatment. Older units can be easily and inexpensively retrofitted with a bottle system. But unless the biofilm in the lines is controlled and treated, changing the water source from municipal to distilled or sterile in the independent reservoir will not ensure that water standards of fewer than 500 CFU/mL will be met.
For more information about dental unit waterlines, including maintenance suggestions and a helpful FAQ, search “waterline cleaning” on the Organization for Safety, Asepsis and Prevention’s website (OSAP.org). Additional resources are available through the United States Centers for Disease Control and Prevention (CDC.gov).
Many agents are available to prevent, inactivate and remove biofilms, as well as reduce endotoxins. The technique and frequency of adding these products varies depending on manufacturer instructions. Table 1 provides a list of chemicals used for waterline cleaning. Chemical treatments may be periodically added to the waterline or continuously released. The chemicals come in tablets, cartridges, powders, drops and liquids,16–21 and compliance with recommended procedures is critical to ensure optimal water quality and prevent potentially harmful effects.
Some of your clients may prefer the convenience of an automated cartridge system that slowly releases antimicrobial agents, but while these setups are less dependent on compliance than other products, they may require specially conditioned water to achieve the best results.
The first step of DUWL treatment is to implement a “shocking” process (intermittent use of high-concentration chemicals) to remove the biofilm masses that have built up.9,10,22 These germicides are typically placed in the water bottle, flushed into the waterlines, and held in the line for an extended period before being flushed out.8–10,22 Shocking treatments should be performed on a weekly or monthly basis.
Daily maintenance with low-dose chemical treatments is also needed to maintain low levels of microbes in the lines. These agents are added to the water bottle with each filling. To ensure chemical compatibility, it may be prudent for sales reps to recommend that the office select the same type of agent for both daily use and intermittent shock treatments. Objections to the use of chemical products include risk of exposure to patients and clinicians; interference in the adhesion of dental resins to enamel and dentin; damage to the dental unit; and, over time, microbial resistance to the chemicals.20,21,23,24
An emerging technology in biofilm control is the incorporation of antimicrobial materials into dental tubing and water bottles. Some dental unit manufacturers impregnate tubing with silver ions or iodine. The silver ions interfere with the metabolism of microorganisms and, to some extent, discourage biofilm colonization. The periodic addition of an antimicrobial agent (such as tin ions) is needed, however, to recharge the active ingredient. In addition, hard water may deposit minerals on the tubing, blocking its effectiveness.19 Other agents, such as N-halamine, are being researched — and with promising results. One study showed that grafting N-halamine onto the inner surface of polyurethane tubing prevented bacterial adhesion for up to four weeks.25 The study also found that the introduction of diluted chlorine bleach regenerated N-halamine’s positive effects.
Sterile water delivery systems can effectively prevent the formation of biofilms, but this method is costly and inconvenient for routine dental treatment. These systems are best reserved for certain surgical procedures — such as biopsies or periodontal surgeries — that require sterile water13 to prevent waterborne pathogens from entering the vascular system and increasing the chance of localized infection.12 Designed to completely bypass the dental unit, autoclavable and singleuse tubing are available to deliver sterile water. And for occasional use, sterile bottled water can be delivered with a handheld, bulb-type syringe.
Regardless of what approach is used, the efficacy of the DUWL disinfection system must be monitored. This is critical to assess how well the product is functioning and to determine whether waterline infection control procedures are being performed properly. The manufacturer of the dental unit or asepsis product determines the monitoring interval.
Your clients can test their systems via in-office test kits or outside testing services. Although in-office tests are convenient, some studies report they may underestimate the number of CFUs present in the water,26–28 thus, these tests might be better used as screening tools. If test results reveal high CFU counts, the office’s protocols should be reviewed to ensure compliance. Additionally, shock treatment is warranted to improve overall water quality. If a problem persists, sales reps might suggest the practice consider switching to a different agent or product. As with other forms of office testing, test dates and results should be stringently logged.
When officials have issued a boil-water advisory, water from municipal water supplies cannot be used for patient treatment.29 These advisories are typically associated with bacterial contamination — perhaps stemming from floods that compromise water supplies or power outages that interfere with purification systems. The CDC recommends having patients rinse with bottled water or distilled water as long as the advisory is in effect.29
Units equipped with an independent water reservoir that bypasses the municipal water system are not affected. If the bottled water was disseminated through a DUWL previously connected to the affected water supply, however, flushing and disinfecting the lines are imperative before use. Once the advisory is cancelled, all DUWLs should be flushed for 5 minutes, followed by disinfection.29
Waterline maintenance is an essential component of any infection control program, and dental sales professionals can play a critical role by helping practitioners ensure that the water delivered during patient care is safe.
Susan Lynn Tolle, BSDH, MS, is a professor and director of clinical affairs in the School of Dental Hygiene at Old Dominion University in Norfolk, Va.
- Atlas RM, Williams JF, Huntington MK. Legionella contamination of dental-unit waters. Appl Environ Microbiol. 1995;61:1208–1213.
- Pankhurst CL, Philpott–Howard JN. The microbiological quality of water in dental chair units. J Hosp Infect. 1993;23:167–174.
- Costerton JW, Stewart PS, Greenberg EP. Bacterial biofilms: a common cause of persistent infections. Science. 1999;284:1318–1322.
- Williams HN, Baer ML, Kelley JI. Contribution of biofilm bacteria to the contamination of the dental unit water supply. J Am Dent Assoc. 1995;126:1255–1260.
- Depaola LG, Mangan D, Mills SE, et al. A review of the science regarding dental unit waterlines. J Am Dent Assoc. 2002;133:1199–1206.
- Szymanska J, Sitkowska J, Dutkiewicz J. Microbial contamination of dental unit waterlines. Ann Agric Environ Med. 2008;15:173–179.
- Coleman DC, O’Donnell MJ, Boyle M, Russell R Microbial biofilm control within the dental clinic: reducing multiple risks. Journal of Infection Prevention. 2010;11:192–198.
- Szymanska J. Biofilm and dental unit waterlines. Ann Agric Environ Med. 2003;10:151–157.
- Mollarni JA, Harte JA. Cottone’s Practical Infection Control in Dentistry. 3rd ed. Baltimore, Md: Walters Kluwer/Lippincott, Williams and Wilkins; 2010.
- Mills SE. The dental unit waterline controversy — defusing the myths, defining the solution. J Am Dent Assoc. 2000;131:1427–1441.
- Coleman DC, O’Donnell MJ, Shore AC, Russell RJ. Biofilm problems in dental unit water systems and its practical control. J Appl Microbiol. 2009;106:1424–1437.
- American Dental Association Council of Scientific Affairs. ADA Statement on Dental Unit Waterlines 2012. Available at: www.ada.org/1856.aspx. Accessed December 5, 2012.
- Kohn WG, Collins AS, Cleveland JL, Harte JA, Eklund KJ, Malvitz DM; CDC. Guidelines for infection control in dental health-care settings 2003. MMWR Recomm Rep. 2003;52:1–61.
- Pankhurst CL, Coulter W, Philpott-Howard JN, Surman-Lee S, Warburton F, Challacombe S.Evaluation of the potential risk of occupational asthma in dentists exposed to contaminated dental unit waterlines. Prim Dent Care. 2005;12:53–59.
- American Dental Association Council of Scientific Affairs. Dental Unit Water Quality. Available at: www.ada.org/sections/professionalResources/pdfs/cleaning_waterlines.pdf. Accessed December 5, 2012.
- Organization for Safety, Asepsis, and Prevention (OSAP). Dental unit waterlines. Available at www.osap.org/?page=Issues_DUWL. Accessed December 5, 2012.
- Cobb CM, Martel CR, McKnight SA, Pasley–Mowry C, Ferguson BL. How does time-dependent dental unit waterline flushing affect planktonic bacteria levels? J Dent Educ. 2002;66:549–555.
- Walker JT, Bradshaw DJ, Fulford MR, Marsh PD. Microbiological evaluation of a range of disinfectant products to control mixed-species biofilm contamination in a laboratory model of a dental unit water system; Appl Environ Microbiol, 2003;69:3327–3332.
- Schel AJ, Marsh PD, Bradshaw DJ, Finney M, Fulford MR, Frandsen E, Ostergaard E, Ten Cate, JM, Moorer WR, Mavridou A, Kamma JJ, Mandilara G,et al. Comparison of the Efficacies of Disinfectants To Control Microbial Contamination in Dental Unit Water Systems in General Dental Practices across the European Union. Appl. Environ. Microbiol. 2006;72:1380–1387.
- Mills SE. Dental waterlines: a decade in review. Inside Dentistry 2(3), 2006. Available at http://www.dentalaegis.com/id/2006/04/dental-waterlines-a-decade-in-review. Accessed December 5, 2012.
- Knight JS, Davis SB, McRoberts JG. The effect of a dental unit waterline treatment regimen on the shear bond strength of resin-based composite. J Am Dent Assoc. 2001;13:615–619.
- Walker JT, Marsh PD. Microbial biofilm formation in DUWLs and their control using disinfectants. J Dent. 2007;35:721–730.
- Ritter AV, Leonard RH, Ghaname E. The influence of dental unit waterline cleaners on composite-to-dentin bond strengths. J Am Dent Assoc. 2007;138:985–991.
- von Fraunhofer JA, DePaola LG, Kelley JI, Meiller TF. Effect of a dental unit waterline additive on resin bond strengths. Gen Dent. 2004;52:502–504.
- Luo J, Porteous N, Rechargeable biofilm-controlling tubing materials for use in dental unit waterlines. ACS Appl Mater Interfaces. 2011;24;3:2895–2903.
- Walker J. Decontamination in dentistry — the times they are a changing. British Journal of Infection Control. 2010;11:188–191.
- Bartoloni JA, Porteous NB, Zarzabal LA. Measuring the validity of two in-office water test kits. J Am Dent Assoc. 2006;137:363–371.
- Morris BF, Vandewalle KS, Hensley DM, Bartoloni JA. Comparison of in-office dental unit waterline test kits. Mil Med. 2010;175:901–906.
- CDC. Infection Control in the Dental Settings. Boil-water advisories and the dental office. Available at: www.cdc.gov/oralhealth/infectioncontrol/factsheets/boilwater.htm. Accessed December 5, 2012.