Dental Unit Water Lines
Most dental professionals are aware that dental unit water lines (DUWL) harbor bacterial biofilms if not treated routinely. Several years ago the ADA recommended a goal of 200 colony forming units per ml (CFU) as the upper limit for bacterial contamination in water used for general dentistry procedures. We have examined hundreds of operatories that do not do any biofilm preventive measures and none of them meet this goal. Typically, we recover 10,000 to 100,000 CFU from DUWL. The organisms isolated are usually naturally occurring soil bacteria; although, we frequently isolate strains of Legionella and Pseudomonas which are significant human pathogens. We also isolate numerous strains of oral streptococci including the cariogenic mutans strains. Thus, DUWL harbor microorganisms originating from both the water supply and from the patient.
Biofilms form on the interior of DUWL because of the plastic tubing required for flexibility. Bacteria tend to adhere to hydrophobic surfaces such as plastic and there are no naturally inhibitory ions released as with copper piping. In addition, there are nutrients available in the water to support the growth of microorganisms, albeit slowly. The picture above is a scanning electron micrograph of the interior of a DUWL biofilms. The organisms detected in the water supply are those that have broken away from the biofilms and are referred to as planktonic or free floating bacteria. The CDC is preparing guidelines for DUWL to be released in late 2003. The preliminary proposal called for an upper limit of 500 CFU in general dentistry treatment water which is the same standard as potable municipal water supplies. There are several approaches that can be taken to clean and maintain your DUWL; although, many questions remain to be answered.
For more information, contact Dr. Staat's laboratory:
Sterilizer Monitoring Program
Dr. Robert Staat, Director
School of Dentistry
University of Louisville
Louisville, KY 40292