Moderate heating of waterline improves dental unit water quality by activating bactericidal properties of tap water

Daily flushing of dental unit waterlines (DUWLs) with fresh tap water for an adequate duration each morning before dental procedures is essential to prevent healthcare-associated infections. However, the bacterial reduction achieved by flushing alone is often temporary and may be insufficient. The purpose of this study was to evaluate the management practices of clinically used DUWLs and identify effective measures for improving water quality.

The bactericidal free residual chlorine concentration (FRCC) and heterotrophic plate counts (HPCs) in air turbine handpiece DUWLs with or without chemical disinfectants and/or heating apparatus were evaluated before and after flushing, based on legal standards and target values for water quality assessment.

Residual water in the DUWL consistently exhibited lower FRCC and higher HPCs than the legal standard and target values, respectively. Extended flushing in water discharged from conventional dental units increased FRCC beyond the legal standard value; however, HPCs did not consistently decrease below the legal target value. Flushing DUWLs equipped with a chemical disinfectant apparatus reduced HPCs to below the legal target value but did not always restore FRCC completely. Notably, heating of DUWLs at 65 °C improved both FRCC and HPCs through flushing, regardless of the type of dental unit.

Flushing plays a crucial role in maintaining the water quality of dental units. Moderate heating of DUWL can ensure compliance with legal standards for water quality management by enhancing the effectiveness of flushing.