Congratulations to Dr. Shannon Mills on a very detailed description of the causes, possible pathogenicity and potential treatments in the dental unit waterline issue ("The Dental Unit Waterline Controversy: Defusing the Myths, Defining the Solutions," October JADA). Unfortunately, the report did not give the readers the full perspective of the many sources of colonized water humans ingest, inhale and bathe and play in.
This omission could leave the reader with the impression that dental units are alone in possessing biofilms, suckback and colonization by potentially pathogenic species. In truth, microorganisms are everywhere in our world, coating and inhabiting every surface, including all external and many internal surfaces of the human body, and biofilms are present throughout the body and nature. In addition, it is important to point out that most microorganisms are either not harmful or actively helpful to humans.
It also is important to note that the maximum 500 colony-forming units per milliliter of heterotrophic bacteria specified in the Safe Drinking Water Act is actually only sporadically met in the many contacts the U.S. population has with water designated as "fit for drinking." Clinical Research Associates, or CRA, tests of water from many sources from all over the United States indicate that 38 percent of water taps in homes tested exceeded this limit, and some exceeded it by as much as 16 times the 500 CFU/mL specified.
Bottled water purchased for as much as $5 or more a pint and perceived as "pure" and "health promoting" was found to contain counts up to 86,500 CFU/mL, and 30 percent of 30 different brands tested were colonized beyond the 500 CFU/mL specified in the Safe Drinking Water Act.
Water coolers of the type found in offices and homes throughout the United States were found to contain organisms exceeding 100,000 CFU/mL, and water from refrigerated drinking fountains had counts that exceeded 10,000 CFU/mL.
All of the above are common sources of water used multiple times a day by most people in the United States, in quantities far exceeding dental patients’ exposure to dental unit water. For most people, dental visits occur only periodically. These visits involve low quantities of water measured by CRA at 60 mL and 100 mL for dentists and hygienists, respectively.
In addition, dental treatment water is almost always suctioned, expectorated, absorbed and/or blocked by a rubber dam. In other words, the potential for human contact with waterborne organisms is many times greater outside the dental office—and the species encountered are identical, including the Pseudomonas, Legionella, nontuberculous Mycobacterium, Staphylococcus, Streptococcus and many varieties of yeasts and molds mentioned by Dr. Mills in dental unit waterlines.
To focus on the dental unit and ignore all other human contact with waterborne organisms is like worrying about a dripping faucet in a house uprooted by floodwaters! And to hold dentists responsible for correcting a problem so obviously caused by the dental unit manufacturers’ design flaw is like allowing Fire-stone to sue Ford Explorer crash victims for using their tires!
Truly this issue is a dental unit manufacturers’ problem. They built a flaw into the dental unit (many feet of very small diameter waterlines); now it is their responsibility to fix the problem. The current treatments mentioned by Dr. Mills place all the responsibility, time commitment, costs and ethical and legal responsibility onto dental clinicians.
In my opinion, it is not reasonable to rely on people to forever take on the responsibility for disinfecting and servicing dental units to merely treat the symptoms if a design change can eliminate the problem. In my opinion, I believe dental unit manufacturers should step forward, take ownership for the problem and solve it, using methods that eliminate the "people factor."
