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Introduction
Water from dental unit water lines (DUWL) usually contains higher levels of bacteria than municipal water supplies, which are the primary sources of microorganisms for the DUWLs. But no widespread health problems have been associated with this water. Concern over DUWL contamination has been fueled by an increase in awareness of infection control issues, media reports of contaminated water from dental units, and case reports associating illness with dental water contamination.
Water from dental handpieces, sonic and ultrasonic scalers, and air water syringes continues to be the target of a program to reduce pathogens delivered to the patient during treatment.
Dental unit water contains approximately the same types of bacteria found in drinking water, but in a higher concentration. Municipal water is normally maintained with below 500 colony forming units of heterotrophic (uses complex organic compounds) bacteria per milliliter of water (CFU/mL). Several studies show water from dental handpieces and air-water syringes contaminated at levels exceeding 100,000 CFU/mLs.xv For routine dental treatment, meet the regulatory standards for drinking water, which is less than 500 CFU/ml of heterotrophic water bacteria. The ADA has recommended a goal of 200 CFU/mL.
The microorganisms in DUWL are bacteria, protozoa, and fungi. These microorganisms are found in the water as well as attached to the inside walls (biofilm) of the small bore tubing of waterlines . Microbes enter the tubing from incoming water and a very small proportion from dental patients during treatment. These microbes adhere to the walls of the tubing and begin to multiply. The biofilms serve as a microbial reservoir. The microbes produce a slime layer and more microbes from the water attach to the slime. The flow of the water can dislodge the microbes from the slime layer and release them into the flowing water. The tubing is constantly replenished with more microbes, stagnation of the water facilitates growth of the slime layer, and the small diameter of the tubing results in a large surface-area-to-volume ratio.xvi
Water heating systems in dental units are designed to heat the water to human body temperature. This may increase the numbers of microorganisms adapted to growth in human hosts and encourage bacterial growth in the waterlines.xvii Water heating systems should not be used.
Dental unit water lines shall be anti-retractive. Waterlines should be flushed after each patient for a minimum of twenty (20) to thirty (30) seconds.
Sterile coolant and irrigating solutions should be used for surgical dental procedures involving bone and incision of mucosa. Sterile coolants/irrigants must be delivered using a sterile delivery system. Conventional dental units cannot reliably deliver sterile water even when equipped with independent water reservoirs because the water-bearing pathway cannot be reliably sterilized. Oral surgery and implant handpieces, as well as ultrasonic scalers, are commercially available that bypass the dental unit to deliver sterile water or other solutions by using single-use disposable or sterilizable tubing.
Water with less than 200 CFU/mL of heterotrophic mesophilic (grows between 10 to 45° C) bacteria is acceptable for non-surgical procedures including those involving the sulcus or initial access into dental pulp. xviii
The US Food and Drug Administration (as specified in Section 510(k) of the Federal Food, Drug, and Cosmetic Act) classify dental water treatment and delivery systems as medical devices. They are subject to pre-market standards and must have a 510(k) clearance.
In the past, the CDC recommended that dental waterlines be flushed at the beginning of the clinic day to reduce the microbial load. However, studies have demonstrated this practice does not affect the biofilm in the waterlines or reliably improve the quality of water used during dental treatment. Because the recommended value of = 500 CFU/mL cannot be achieved by using this method, other strategies should be employed.
Separate water reservoir systems in cooperation with chemical treatment are safe and effective.xviii Technologies for waterline treatment include: independent reservoirs, chemical treatment (either continuous or intermittent), filtration, sterile water delivery systems, and combined approaches. A universal treatment protocol has not been published because dental units and water systems vary. Practitioners should consult their dental unit manufacturer for safe, acceptable methods of providing treatment water with fewer than 200 CFU/mL of heterotrophic mesophilic bacteria.
As for filtration, membrane filters are used to trap microorganisms suspended in water. Filters are usually installed on dental unit waterlines as a retrofit device. Microfiltration commonly occurs at a filter pore size of 0.03-10 µm. Sediment filters commonly found in dental unit water regulators have pore sizes of 20-90 µm and do not function as microbiological filters.
Water unfit to drink (or swim in) is unfit for therapeutic use in dentistry. ADA's 200 CFU/mL goal is achievable now. Prudence dictates reasonable action to protect dental professionals and dental patients.xix
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