1. Chapter 24 Dental Unit Waterlines
Copyright 2003, Elsevier Science (USA).
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2. Introduction
Outbreaks of waterborne disease have occurred in a broad range of facilities. Although there is no evidence of a widespread public health problem, published reports have associated illness with exposure to water from dental units. The fact that there are bacteria capable of causing disease in humans found in dental unit waterlines is reason for concern.

3. Introduction- cont’d
In community water, the number of waterborne bacteria is kept below 500 colony-forming units (CFU) per milliliter.
The water from air-water syringes and dental handpieces frequently has bacteria levels that are hundreds or thousands of times greater than is permissible in drinking water.
The types of bacteria that are found in dental unit water are frequently the same types as those found in community water, but the levels of bacteria found in the dental units are almost always higher.

4. Background
Dental health care workers are exposed to Legionella bacteria at a much higher rate than the general public.
Dental personnel are exposed to contaminated dental unit waterlines by inhaling the aerosol generated by the handpiece and the air-water syringe.
There is at least one suspected fatality of a dentist from legionellosis.
Case reports have been published of immunocompromised patients who developed postoperative infections caused by contaminated dental water.

5. Microorganisms in Waterlines
The primary source of microorganisms in dental waterlines is the public water supply.
It is possible that saliva may be retracted back into the waterlines during treatment. This process is also called “suck back.”
Antiretraction valves on dental units and thorough flushing of the dental lines between patients minimize the chance of this occurring.
Entering public water source has a colony forming units (CFU) count of less than 500; once that water enters the dental waterlines and colonizes within the biofilm, the CFU count skyrockets.

6. Communities of Bacteria
There are two “communities” of bacteria in dental unit waterlines:
One bacterial community exists in the water itself and is referred to as planktonic (free floating).
The other exists in the biofilm attached to the walls of the waterlines.

7. Fig 24-1 Close up of dental tube opening.

8. Fig A cross-section of a dental unit waterline illustrating the formation of biofilm on the inside wall of a dental tube.
Fig. 24-2

9. Fig 24-4 Maze of dental unit lines.

10. Biofilm
Biofilm exists in all places where moisture and a suitable solid surface exist.
Biofilm consists of bacterial cells and other microbes that adhere to surfaces and form a protective slime layer.
Biofilm can contain many types of bacteria, as well as fungi, algae, and protozoa.
Viruses, such as the human immunodeficiency virus (HIV), cannot multiply in the dental unit waterline.

11. Fig. 24-3 Magnification of biofilm formation on the walls of the tube.

12. Fig. 24-5 Bacteria in biofilm dropping into waterlines.

13. Methods to Reduce Contamination
It is not yet possible to totally eliminate biofilm, but it can be minimized by:
Self-contained water reservoirs
Chemical treatment regimens
Microfiltration
Daily draining and drying of lines

14. Self-Contained Water Reservoirs
These systems supply air pressure to the water bottle (reservoir).
The air pressure in the bottle forces the water from the bottle up into the dental unit water lines (DUWL) and out to the handpiece and air-water syringe.
Self-contained water systems have two advantages:
The dental personnel can select the quality of water to be used, such as distilled, tap, or sterile.
Maintenance of the water system (between the reservoir bottle and the handpieces and syringes) is under the control of the dentist and staff.

15. Fig 24-6 Self-contained dental water unit.

16. Microfiltration Cartridge
A disposable inline microfiltration cartridge also can dramatically reduce the bacterial contamination in the dental unit water.
This device must be inserted as close to the handpiece or air-water syringe as possible.
It should be replaced at least daily on each line. The use of filtration cartridges combined with water reservoirs can ensure improved water quality.

17. Fig. 24-8 Disposable microfiltration filter in place near the handpiece at the end of the waterline.

18. Chemical Agents
Chemicals can be used to help control biofilm in two ways:
Periodic or “shock” treatment with biocidal levels (levels that will kill microorganisms) of chemicals.
Continuous application of chemicals to the system (at the level to kill the microorganisms but not harm humans).
Always check with the manufacturer of the dental equipment to determine which chemical product and maintenance protocol they recommend.

19. Water for Surgical Procedures
Dental unit water should not be used as an irrigant for surgery involving the exposure of bone.
Only use sterile water from special sterile water delivery systems or hand irrigation using sterile water in a sterile disposable syringe.

20. Flushing Waterlines
All dental waterlines and handpieces should be flushed in the mornings and between patients.
Although this will not remove biofilms from the lines, it may temporarily reduce the microbial count in the water.
It will help clean the handpiece waterlines of materials that may have entered from the patient’s mouth.
Flushing also brings a fresh supply of chlorinated water from the main waterlines into the dental unit.

21. Minimize Aerosol
Always use the high-volume evacuator when using the high-speed handpiece, ultrasonic scaler, and air-water syringe.
The high-volume evacuation may also reduce exposure of the patient to these waterborne microorganisms.

22. Use Protective Barriers
The dental dam greatly reduces direct contact.
The dam also greatly reduces the aerosolizing and spattering of the patient’s oral microorganisms onto the dental team.
Protective barriers, including masks, eyewear, and face shields, also serve as barriers for the dental team.