The Dental Unit Waterline Controversy: Defusing the Myths, Defining the Solutions
Source: American Dental Association
Background and Overview. This article reviews the literature on the subject of dental unit
waterline contamination. It has been expanded from the text of a lecture given at the Scientific Frontiers in
Dentistry program sponsored by the National Institute for Dental and Craniofacial Research in Bethesda, Md., in
July 1999. The author examines the underlying biological causes of waterline colonization by microorganisms, the
evidence of potential health consequences and possible means of improving the quality of dental water. He also
describes examples of devices currently marketed to improve and maintain the quality of dental treatment water.
Conclusions. Microorganisms colonize dental units and contaminate dental treatment water. While documented
instances of related illness are few, water that does not meet potable-water standards is inappropriate for use in
dentistry.
Clinical Implications. Exposure to water containing high numbers of bacteria violates basic principles
of clinical infection control. Dentists should consider available options for improving the quality of water used
in dental treatment.
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The effect of disinfectants and line cleaners on the release of mercury from amalgam
Source: American Dental Association
Background. Dental practices use disinfectants or line cleaners to flush dental unit wastewater lines
to minimize odor generation, remove solid waste particles and remove biofilms in dental unit water lines (DUWLs).
Methods. The authors evaluated 47 disinfectants or line cleaners for their potential to release mercury
from amalgam waste. They prepared each product concentration according to the manufacturer's recommendations and
gently agitated it along with one amalgam specimen for 24 hours. They filtered the combined decanted liquid and
rinse and analyzed it for mercury using modified U.S. Environmental Protection Agency method 245.1.
Results. Six preparations released significantly more mercury from amalgam (about 17 to 340 times) than did
the deionized water control (P < .001). The amount of mercury released by the other disinfectants/line
cleaners was not statistically different from that released by the control. The pH values of all preparations ranged
from 1.76 to 12.35.
Conclusion and Clinical Implications. This study and other published reports have demonstrated that preparations
containing chlorine release more mercury from amalgam than did some other products and the deionized water control.
As a result, the use of these products is not recommended for treating dental office wastewater lines or DUWLs.
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Dental Unit Waterline Antimicrobial Agents' Effect on Dentin Bond Strength
Source: American Dental Association
Background. In response to concerns of bacterial biofilm colonization of dental unit waterlines, a
wide range of commercial intermittent and continuous chemical treatments for dental unit waterlines have
been developed and marketed. There has been little research on the possible effect of continuous chemical
treatment regimens on dentin-bonding agents. The authors evaluate the effect of four proposed antimicrobial
agents used in dental unit waterlines on dentin bond strength.
Methods. The authors used a fifth-generation dentin-bonding agent to bond composite cylinders to
molar dentin surfaces. They then used selected antimicrobial agents as rinsing agents after conditioning. The
composite cylinders were shear tested, and their fracture strengths were compared statistically.
Results. All proposed antimicrobial agents reduced dentin bond strength. Proposed waterline
treatment regimens of a diluted mouthrinse and chlorhexidine significantly reduced dentin bond
strength compared with sodium hypochlorite and citric acid regimens.
Conclusion. Dental professionals should be aware of potential interactions between dental unit
waterline antimicrobial agents and dentin-bonding agents. Further research in this area is warranted, as
the clinical implications are uncertain at this time.
Clinical Implications. Dental unit waterline antimicrobial agents may adversely affect dentin bonding strength.
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Biofilm and the Dental Office
Source: American Dental Association
The presence of adherent microbial biofilms in dental unit waterlines was first reported more than 30 years ago.
Recently, interest in these biofilms has reawakened. This can be attributed to increased awareness of potential
occupational hazards in the dental office and concern about increasing numbers of dental patients
considered to have diminished resistance to overt and opportunistic microbial pathogens (for example, elderly people,
smokers, people with alcoholism, organ transplant and blood transfusion recipients, AIDS and cancer patients, people
with diabetes, people with autoimmune diseases and people with chronic organic disorders). Although no definable
health effects have been associated with exposure to dental unit water, there have been documented reports of waterborne
disease outbreaks in a broad range of other facilities, including hospitals, nursing homes, prisons, schools, restaurants,
community waterworks and swimming pools. Responsible waterborne agents include significant bacterial human
pathogens such as Pseudomonas aeruginosa, Escherichia coli and Legionella species, as well as species of
the highly resistant protozoan Cryptosporidium.
This article provides a brief overview of the fundamental processes leading to biofilm formation and the significance
these biofilms have in health care facilities, particularly hospital and dental settings. A statement adopted by the
American Dental Association relating to dental unit waterlines appears as a sidebar. The ADA's statement encourages
a consolidated effort to improve water quality in the dental office and sets out an aggressive, proactive research
agenda for the control and prevention of biofilm formation in dental unit waterlines.
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Detecting Legionella Pneumophila in Water Systems: A Comparison of Various Dental Units
Source: American Dental Association
Legionella species may be present in a variety of water systems, including cooling towers, spas, water storage tanks
and shower heads. Legionella pneumophila is the most common cause of legionella pneumonia, with serogroups 1
through 6 being the most frequently implicated in infections of the respiratory tract.
The bacteria enter the respiratory tract by means of fine aerosols' and any water system containing legionellae or other
bacteria that liberates aerosols into the atmosphere could be considered a potential source of infection. Dental units fall into
this category, as the high-speed outlets emit water to cool the dental bur and tooth during drilling procedures.
This creates fine aerosols that could be inhaled by patients, dental surgeons, nurses or hygienists.
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