There’s a good chance that thousands—if not millions—of microorganisms are present in the water dental practitioners use with their patients every day. Even very low levels of bacteria commonly present in treated city water can increase exponentially in dental unit waterlines.
But don’t just take our word for it:
“Elevated microbe counts in handpiece, air/water syringe, and automated scaler waterlines are the result of very small diameter lines used in dental equipment… Although most of these microbes are not frank pathogens, capability to cause disease in permanently or temporarily compromised patients and clinicians is a definite possibility.”
Clinical Research Associates Newsletter, Volume 21, Issue 3 (March 1997)
As our friends at Clinicians Report pointed out more than 20 years ago, the problem of microbial contamination in dental unit waterlines is compounded by the design of the dental equipment itself. And the use of small-diameter waterlines is only one part of the problem. Other factors—including low flow rates, long periods of stagnation, waterline termination (“dead legs”), and even occasional “suck back” from patients—all contribute to creating a “perfect storm” of microbial contamination.
Even though municipal water typically arrives at a dental practice relatively microbe-free, the more narrow pipes and tubing within the building create a higher surface-to-water ratio that facilitates microbial growth. The lower volume of water in the smaller-diameter tubing also warms to room temperature fairly rapidly, incubating any viable organisms.
This narrow tubing also creates a laminar flow of water, which describes the fluid’s tendency to flow freely only through the center of the tubing—allowing the flow along the edges of the tubing to become stagnant. This stagnation allows microorganisms present in the water to attach to the surface of the tubing and grow virtually undisrupted. Organic and inorganic substances present in the water provide nutrients that “feed” the organisms. This provides building blocks for creating what’s known as biofilm, which can multiply rapidly along the length of the tubing.
Biofilm can be stubborn. Through an amazing process called quorum sensing, these interconnected microorganisms form an “emergency phone network” of sorts that helps to protect and preserve the biofilm. This phenomenon transmits warning signals and instructions “downstream” to other microorganisms, which can change their DNA to resist chemicals (such as chlorine, silver, iodine and antibiotics) that might have killed all but a few survivors upstream.
If you’ve ever seen biofilm discharged from a waterline, you know that it’s pretty gross. But does the presence of these microorganisms really affect patients or clinicians?
Well, sometimes. In order to answer that question it’s important to distinguish between common (and typically harmless) varieties of environmental bacteria and more “serious” types of pathogenic microorganisms. Let’s start with a few of the more well-known “bad guys.”
Pathogenic, or potentially disease-causing, microorganisms commonly found in water include bacteria (such as E. Coli and Salmonella), viruses (such as norovirus and rotaviruses), and protozoans (such as Giardia and Cryptosporidium). Many of these microorganisms spread from the fecal waste of animals and humans, which can contaminate streams and lakes, or enter the public water supply through cracks in old city pipelines. These types of pathogens can cause symptoms like nausea, abdominal pain, vomiting and diarrhea, even in healthy individuals.
Another category of waterborne microorganisms includes more “normal” environmental bacteria that typically pose very little threat to the health of patients and practitioners. However, at the high levels of contamination often seen in dental unit waterlines, even these organisms can pose the risk of infection, especially for immunocompromised individuals.
The only “good news” about these waterborne microorganisms is that they’re typically fairly easily managed by city water treatment facilities. Giardia, for example, is actually rather large by microbiological standards and is fairly easily removed by most microfilters. Chlorination of city water supplies also kills the vast majority of microorganisms that might otherwise be viable.
But remember what we just learned about the “perfect storm” of factors that enable even a single microorganism that survives filtration and chemical treatment to grow (and protect itself) in waterlines. These factors make waterline contamination a very serious issue that must be addressed rigorously. When neglected, the unthinkable can (and occasionally does) happen.
As reported by many major news outlets, in September and October 2016, 68 children were hospitalized after undergoing pulpotomy procedures at a facility in Anaheim, California earlier that year. These children were all diagnosed with severe infections of the mouth and jaw from an environmental bacteria called Mycobacterium abscessus. The children had to receive antibiotics intravenously for several months, and many lost adult teeth or even underwent partial removal of their jaw bones as a result of the infections.
The first instinct in a situation like this is often to blame infections on a disregard for sanitation and surgical protocols. In fact, in this case the practice was using tap water instead of what they should have used for a surgical procedure: packaged sterile water delivered by sterile means. That said, I share this example only to underscore the seriousness of the issue.
Even the ideal-quality input water can quickly become contaminated in dental unit waterlines. That's because even a single microorganism that survives filtration and chemical treatment can grow exponentially (and protect itself) in the dental delivery system. These factors make microbiological contamination of dental unit waterlines a very serious issue that must be addressed rigorously. Read on to learn more about the standards in place for microbial content of dental water, and the steps necessary to measure and combat waterline contamination.