Dental Unit Waterlines
Learning Outcomes
On completion of this chapter, the student will be able to achieve the following objectives:
• Pronounce, define, and spell the Key Terms.
• Explain why dental unit waterlines (DUWLs) contain more bacteria than faucets.
• Explain the role of biofilm in DUWL contamination.
• Discuss why there is a renewed interest in DUWL contamination.
• List the factors involved in bacterial contamination of dental unit water.
• Identify the primary source of microorganisms in dental unit water.
• Describe methods used to reduce bacterial contamination in DUWLs.
• Explain the CDC recommendation for the use of saliva ejectors.
Performance Outcome
Upon completion of this chapter, the student will be able to meet competency standards in the following skill:
Electronic Resources
Additional information related to content in Chapter 24 can be found on the companion Evolve Web site.
Key Terms
Antiretraction device A mechanism that prevents entry of fluids and microorganisms into waterlines as a result of negative water pressure; also called “suck back.”
Biofilm (BYE-oe-film) Slime-producing bacterial communities that may also harbor fungi, algae, and protozoa.
Colony-forming units (CFUs) A number of separable cells on the surface of a semisolid agar medium that create a visible colony.
Dental unit waterline (DUWL) Small-bore tubing usually made of plastic, used to deliver dental treatment water through a dental unit.
Heterotrophic (het-ur-oe-TROF-ik) bacteria Bacteria that use organic carbon as a source of nutrients. Protozoa, fungi, and most bacteria fall into this category.
Immunocompromised Having an immune system that is weakened.
Legionella (lee-juh-NEL-uh) Genus of bacteria responsible for the disease legionellosis.
Microfiltration Use of membrane filters to trap microorganisms suspended in water.
Planktonic (plank-TON-ik) Describes bacteria that are freely floating in water.
Self-contained water reservoir Container attached to a dental unit that is used to hold and supply water or other solutions to handpieces and air-water syringes.
Outbreaks of waterborne disease have occurred in a broad range of facilities, including hospitals, nursing homes, schools, restaurants, community water supplies, swimming pools, and spas. Although no evidence suggests a widespread public health problem, published reports have associated illness with exposure to water from dental units. Bacteria capable of causing disease in some humans are found in dental unit waterlines (DUWLs); this is reason for concern (Fig. 24-1). In addition, exposing patients or dental professionals to water with extremely high bacterial counts is not in line with currently accepted infection control principles.
In community water, the number of waterborne bacteria is kept below 500 colony-forming units (CFUs) per milliliter (ml). Water from air-water syringes and dental handpieces frequently has levels that are hundreds or thousands of times greater than are permissible in drinking water. The types of bacteria found in dental unit water are frequently the same as those found in community water, but the quantity of bacteria found in dental units is almost always higher. Research has shown that microbial counts in DUWLs can reach 200,000 CFUs/ml within 5 days of installation of new lines. Counts greater than 1,000,000 CFUs/ml have been reported.
This chapter provides an overview of the problem of dental unit waterline (DUWL) contamination, the potential health risks to patients and dental personnel, and the steps that you can take to lower the risk for DUWL contamination. You will also learn how to comply with Centers for Disease Control and Prevention (CDC) recommendations related to DUWLs, biofilm, and water quality.
Background
The presence of bacteria in DUWLs was first reported more than 30 years ago. This issue is now attracting renewed attention because of increased awareness of occupational hazards in the dental office, as well as concern about the increasing number of dental patients who have a weakened immune system. Elderly patients, and those who smoke or who are alcoholic, and those who have received organ transplants or blood transfusions are among the types of patients with weakened immune systems.
Studies have demonstrated that DUWLs (i.e., tubing that carries water to the high-speed handpiece, air-water syringe, and ultrasonic scaler) can become colonized with microorganisms, including bacteria, fungi, and protozoa. These microorganisms colonize and multiply on the interior surfaces of the waterline tubing and form a biofilm. (Biofilms are discussed later in this chapter.)
Several studies reveal that dental healthcare workers are exposed to Legionella bacteria at a much higher rate than the general public. Legionella species are harmful bacteria often found in water and moist places that are responsible for the disease legionellosis. Dental personnel are exposed to Legionella by inhaling the contaminated aerosol generated by the handpiece and the air-water syringe.
Fortunately, most dental healthcare workers are healthy and do not develop the disease. However, one dentist’s death has been linked to legionellosis. Immunocompromised patients have also developed postoperative infection caused by contaminated dental water.
Microorganisms in Dental Unit Water
Waterborne and human oral microorganisms have been found in dental unit water. This indicates that both incoming community water and the patient’s mouth are sources of these microorganisms.
The primary source of microorganisms in DUWLs is the public water supply. However, saliva may be retracted back into the waterlines during treatment, a process called “backflow.” The installation of antiretraction devices on dental units and thorough flushing of DUWLs between patients minimize this risk. The risk for backflow from saliva ejectors is discussed later in this chapter.
When community water enters the dental office, it contains fewer than 500 CFUs/ml. However, once that water enters DUWLs, and existing bacteria colonize and multiply within the biofilm, the CFU count greatly increases (Table 24-1).
TABLE 24-1
Sample Amounts of Bacteria in Dental Unit Water at Various U.S. Sites
| Source | CFUs/ml* |
| 10 dental units from three offices | 180,000 |
| Tap water from three offices above | 15 |
| 54 air-water syringe hoses | 165,000 |
| 22 high-speed handpiece hoses | 739,000 |
| 10 faucets | <30 |
| 4 water coolers | <30 |
| 11 rivers and streams | 28,200 |
| 8 dental units | 110,000 |
*Colony-forming units per milliliter.
Modified from Miller C, Palenik C: Infection control and management of hazardous materials for the dental team, ed 4, St Louis, 2010, Mosby.
Two “communities” of bacteria have been detected in DUWLs. The bacterial community in the water itself is referred to as planktonic. The other community exists in the biofilm attached to DUWL walls.
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