The microbes in this water have evolved mechanisms allowing the microbes to attach to and accumulate on surfaces such as the inside of dental unit waterlines. This accumulation is referred to as biofilm, and is similar in structure to oral biofilm (dental plaque). The microbes from this biofilm are released into the flowing water and become planktonic bacteria that end up in patients’ mouths. These bacteria then are sprayed into your “personal space” and into the operatory environment during the use of handpieces, air/water syringes and ultrasonic scalers.

Although the number of microbes in the incoming water may be low, they are constantly flowing into the dental unit waterlines and serve as a continuous inoculation of those lines.

There are several reasons why these inoculated bacteria form excessive biofilm in dental unit waterlines. First, there is a high ratio of surface area to volume in these small-diameter lines. In other words, there is a large amount of surface compared to the volume of water in the lines. So the bacteria have plenty of sites to attach to and accumulate. Second, the flow rate of water through these lines is relatively slow. (The high pressure spray from a handpiece does not occur until the waterline meets the compressed air inside the handpiece–see Fig. 2). Third, the flow rate of the water near the walls of the lines is even slower because of the drag on the water molecules that results from their contact with the surface. Collectively, these encourage optimal activity from bacterial attachment mechanisms.

Fig. 2 The waterline connects with compressed air inside a handpiece to create high-pressure water spray.

In 1993, the Centers for Disease Control and Prevention (CDC) recommended that dental waterlines be flushed at the beginning of the clinic day to reduce the microbial load.¹ This may temporarily reduce the number of planktonic microbes in the flowing water, and help flush out some patient materials that may have been retracted into the high-speed handpiece. Still, flushing alone does not consistently reduce the level of biofilm in the waterlines. Dental unit waterline biofilm actually forms as water flows through the lines. So, merely flushing more water through the lines in an attempt to clean them does not solve the problem.

In 1995, the American Dental Association (ADA) charged manufacturers to develop units by the year 2000 that would deliver to nonsurgical patients water that consistently contains no more than 200 colony-forming-units per milliliter (CFU/mL) of aerobic heterotrophic bacteria at any point in time in the unfiltered output of the dental unit.³

Since 1995, technological advances have made this goal possible. In addition, the CDC now recommends that coolant water used in non-surgical dental procedures meet EPA regulatory standards for drinking water, which is less than or equal to 500 colony-forming-units of heterotrophic bacteria per milliliter of water. This CDC recommendation was published in their Guidelines for Infection Control in Dental Health-Care Settings –20034 (Note: The CDC has different guidelines about water used in oral surgical procedures). As a result of these developments, the CDC statement, in effect, updates the 1995 ADA statement on dental unit waterlines.

CONTINUED ON NEXT PAGE

1 of 3