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In 1963 a short paper was published in the British Dental Journal concerning the finding that high concentration of waterborne bacteria was expelled from the small-bore tubing connected to dentist’s handpieces. At that time the information went virtually unnoticed: an anecdotal report of low concern? Before the 1980s, gloving in dentistry was not universally used (I remember the taste of my dentist’s fingers in the 1970s and early 1980s), sterilization of instruments was done only for surgical instruments, and disinfection was a matter cleanliness. I can say without a doubt that the quality of water used to cool my dentist’s high-speed drill was far from being of any concern to me back then. It was not until the mid-90s that the old problem of dental unit waterlines "contamination" reared its ugly head and became one of the dentistry’s most troublesome concerns.

Water is considered potable when fecal coliform levels are less than 1 per 100 ml and a total of less than 500 CFU/ml is present in a given water sample. Furthermore, opportunistic waterborne pathogens are found in very low concentrations in drinking water. Water delivered through dental handpieces does not meet potable water standards because it contains too many bacteria: mean counts of 200,000 CFU/ml can be obtained. Waterborne biofilms that form inside waterlines tend to increase the baseline level of opportunistic pathogens. Pseudomonas aeruginosa can be isolated from 15 to 24% of dental unit water at concentrations up to 2 x 10⁵ CFU/ml and may account for 75 to 100% of the cultivated flora in these units. Legionella spp. can regularly be isolated from dental unit waterlines where they can reach 10²-10⁴ CFU/liter. Non-tuberculous mycobacteria reach concentrations in dental water that are 400 times greater than in tap water. Waterborne biofilms that hide inside our dentist’s dental unit can be looked at as reservoir for opportunistic pathogens (Barbeau et al., Can. J. Microbiol 44:1019--28, 1998).

Most of the research on the subject has been published in dental journals, and therefore I hardly can find any input from my esteemed microbiologists colleagues. The reason for this is not a lack of opinion on the subject but a simple lack of interest. Those who possess a certain grasp of the problem often smile mockingly and quickly express their wish to discuss "more groundbreaking" microbiological research. This is indeed an opinion, however it is an unserviceable embryonic argument to serve to public and mass media.

There are more than 10,000 Canadian and 130,000 American dentists out there struggling with something that does represent a real big problem: a significant increase in the cost of infection control program that will be inevitably be assumed by the patient or the health system in the end. We are talking about thousands of patients that are convinced they will get sick (eye and mucosal infections, gastrointestinal disorders, respiratory disease, brain abscess) because of "dirty" dental water. We are talking about lawsuits and possible class action in North America. We see TV programs (20/20, February 2000) where questionable "scientists" plunge their hands in clean urinary and toilet bowls and look stunned when CFU level are lower than those of dental unit water. Just imagine the understandable public perception and the proliferation of products designed to disinfect waterlines.

Dental unit waterline disinfection is a potential market of more than $300 million per year: an equivalent of some 30 million liters of disinfectants flushed in the environment each year to mitigate a problem that certain people feel is imaginary or artificially inflated. Dental companies push hard on the problem; the field is free and the dental community is short of arguments. The problem has gone wild and almost nothing can stop the wheel.

The objective of this letter is to solicit some input from the microbiologist’s community. If we don’t think dental unit waterline is a serious problem then we should write it somewhere, but most of all we have to say why. We need scientific and logical arguments. I strongly believe that it is time for microbiologists to speak out. If we do not do it, who will?

As a dental microbiologist, I do not know the risk that dental unit waterborne microorganisms represents for the patient if we consider the huge number of oral bacteria, but I cannot say there is no risk at all (can you?). If as scientists, microbiologists can present facts that prove the absence of risks (or at least explain why a negligible risk should be ignored), I would be glad to hear and read their point of view and to use their arguments to support my struggle (and the one of some of my Canadian and American colleagues) with mass media, dental companies and worried patients. Many thanks for your input.

Jean Barbeau
University of Montreal
Montreal, Ontario, Canada
Barbeauj@medent.umontreal.ca