The Role of Flushing Dental Water Lines for the Removal of Microbial Contaminants

Objectives: This study was designed to determine the role of flushing dental water lines for the removal of heterotrophic plate count bacteria, Legionella spp., and free-living protozoa. Methods: Forty dental offices were surveyed in the study. An initial sample and a sample taken after three minutes of flushing were obtained from the air/water syringe at each location. All samples were quantitatively analyzed for heterotrophic bacteria using three bacteriological procedures. The samples were analyzed for the presence of Legionella spp. using cultura, immunological, and molecular procedures and for the occurrence of free-living protozoa using a killed bacteria plate procedure. Results: The flushing process reduced the level of heterotrophic plate count bacteria by 1.1 to 1.5$\text{log}_{10}$CFU/ml. Compliance with recommendations for bacterial levels varied depending on the methodology employed in the analysis. The flushing process did not reduce the occurrence of Legionella spp. or free-living protozoa. Conclusion: The results support recent U.S. Centers for Disease Control and Prevention recommendations that the process of flushing dental water lines cannot be relied upon as a sole means of reliably improving the quality of water used in dental treatment.