Due to the nature and complex design of dental delivery units, the periodic use of waterline cleaners and antimicrobial agents is extremely important for proper dental waterline care. As mentioned earlier, even sterile water introduced to dental delivery systems can become contaminated very quickly and exceed CDC and ADA-recommended guidelines for maximum microbiological contaminant levels of 500 CFU/mL.
At a minimum, practices should use a strong, antimicrobial “shock” treatment in waterlines as recommended by the manufacturer, or as needed, as indicated by HPC test. This type of powerful antimicrobial treatment, conducted only when patients are not being treated, should be performed if bacteria count ever exceeds the 500 CFU/mL threshold.
In addition to periodic “shock” treatments, some practices find it beneficial to use residual chemical waterline treatments on a daily basis, during the normal course of patient care. Most of these products utilize compounds of chlorine, silver, or iodine—each of which has its own pros and cons that should be taken into account considering the total office environment, and in consultation with knowledgeable dental dealers and equipment representatives.
These are the most commonly used chemicals that are safe for maintenance when used as residual treatments:
Chlorine is the most commonly used antimicrobial agent. It’s added to city water supplies to keep bacteria levels at bay as the water is pumped through contaminated piping to its points of use. Chlorine is good at its job, and very affordable relative to other antimicrobial agents. But it’s not the best choice for the low flow rates and small diameter waterlines of dental delivery units.
Chlorine is not especially effective against the biofilms that plague delivery systems. And chlorine levels can be difficult to manage in dental equipment. You need a level high enough to kill bacteria, but not so high as to leave chlorine residue in the tubing and delivery system. Chlorine residual, sodium hypochlorite, can attack equipment surfaces and be offensive during patient care.
Similar to chlorine, chloramine is a chemical compound created by mixing chlorine and ammonia. Chloramine does a fairly good job of killing microorganisms, and is often preferred to chlorine for its lack of carcinogens known as trihalomethanes (THMs).
Much like chlorine, however, chloramine can be a nuisance in dental delivery systems. It, too, can leave a stubborn residue inside the equipment that can block and ultimately destroy parts of the dental delivery unit.
Chlorhexidine gluconate is a chemical compound commonly seen in antiseptic mouthwashes. It has also been been approved for waterline cleaning. This chemical can disrupt and kill bacteria, as well as prohibit further microbial growth. Due to its high potency and quick antibacterial action, bacterial resistance to chlorhexidine gluconate has not been discovered.
Despite its effectiveness against “swimming” bacteria, however, chlorhexidine gluconate does not destroy biofilms. Although this chemical is effective in many different applications, some service technicians have reported that chlorhexidine gluconate can leave behind a sticky residue inside dental delivery units that can plug ports and tubing, depending on what else is present in the water.
Chlorine dioxide is one of the most effective antimicrobials in the world. It it less corrosive than chlorine, works quickly and efficiently, and is not susceptible to the phenomenon known as “quorum sensing” that enables bacteria to change its DNA to become resistant to antimicrobials like chlorine. Chlorine dioxide is effective against free-floating (planktonic) and “attached” (sessile) bacteria (biofilms). Despite its many benefits, chlorine dioxide is not as commonly used as other antimicrobial agents because of its higher cost.
Both elemental silver and silver nitrate have been used for their antimicrobial properties for hundreds of years. Several dental unit waterline products use silver nitrate, while others use different forms of silver compounds. Silver-based antimicrobials were especially popular in years past for their accessibility, although these treatments are generally not as potent as other chemical options. While generally an effective antimicrobial agent, silver has several potential drawbacks when used in dentistry.
Silver can combine with certain dissolved solids in the water to form precipitates commonly known as “silver salts.” These salts look like pepper and can clog the tiny valves and ports inside the delivery system. Silver-based products can also stain dental delivery unit bottles.
Along with mercury, which must be removed by an amalgam separator, silver must be controlled in wastewater due to its potentially harmful effects on the environment. In fact, the EPA states that water treated with silver as a pesticide cannot be discharged into sewage systems without notifying the sewage plant authority.
Recent studies in Europe and elsewhere investigating the possible long-term health effects of exposure to silver-based products have not yet been conclusive. However, several wound and burn-care studies have suggested that bacteria may become resistant to silver, possibly inhibiting its ability to kill these silver-resistant microorganisms over time.
Although silver-based products can be effective residual treatments for dental unit waterlines, the potential tradeoffs involved with using silver should be weighed carefully.
Iodine is a naturally occurring element with tremendous antimicrobial attributes. Although it can be beneficial to the human body in small amounts, consumption of extremely high levels of iodine have been shown to cause thyroid problems and allergic reactions in some individuals. However, it’s very important to note that the type of iodine typically used in dentistry does not cause allergic reactions.
Other relatively minor downsides to iodine include its distinct, astringent taste and odor—sometimes slightly noticeable in iodine-treated water—as well as its tendency to stain tubing and dental bottles. Iodine can be more expensive than other forms of chemical treatment. Despite these minor downsides, we highly recommend iodine-based residual treatments because iodine is a very effective antimicrobial agent.
Even the ideal-quality input water can quickly become contaminated in dental unit waterlines. That's why the periodic use of waterline cleaners and antimicrobial agents is extremely important for proper dental waterline care.