Dental Water Line Contamination -- an Overview

Dental unit water lines carry water from the plumbing system (or other water supply) to high-speed handpieces, ultrasonic scalers, and air-water syringes.

Microbial contamination is common in dental water lines. The lines are conducive to the growth of bacteria, including Legionella bacteria, the cause of Legionnaires’ disease. Heterotrophic plate counts (total colonies of all types of bacteria) up to 10,000,000 colony forming units per milliliter (cfu/ml) have been detected in dental lines. For comparison, the US Environmental Protection Agency (EPA) has established a heterotrophic plate count (HPC) limit of 500 cfu/ml for drinking water. The American Dental Association (ADA) set a goal to have bacteria levels in dental water below 200 cfu/ml by the year 2000, but the goal was not attained.

The handheld devices attached to the dental water lines can efficiently transmit bacteria from the water to patients. The risk of contracting disease from contaminated water is greatest for the elderly, young children, pregnant women, alcoholics, smokers, or individuals who are immunocompromised either because of illness (e.g., cancer, diabetes, AIDS) or medical treatment.

Biofilm allows bacteria to thrive in dental water lines. Biofilm is a slimy coating composed of microbes that attach to underwater surfaces (e.g., the inside of a pipe). As the outer layer of biofilm flakes off from the inside of a pipe or tube, potentially high doses of microbes are released into the water.

Dental water lines are conducive to biofilm build-up. Biofilm grows well on most types of plastic tubing. In addition, the tubing is small in diameter, so its surface area is large relative to the volume of water that flows through it. The build-up rate is faster too because microbes suspended in the water have a shorter distance to fall before contacting the tubing surface. Stagnation and low-flow rates also contribute to biofilm build-up. Even when water is flowing through the lines, stagnation occurs at the inner surface of the tubing due to a phenomenon called laminar flow.

For more information, refer to Dental Water Line Contamination.