Dental Unit Water Line Treatment with Sodium Hypochlorite and Acetic Acid

A private clinic's dental unit water lines (DUWLs) were treated with a solution of 0.525% sodium hypochlorite (5000 ppm active chlorine) in 1% acetic acid or a 0.525% sodium hypochlorite solution in distilled water over 4 weeks to determine its effect on biofilms and planktonic bacteria. At the start of the project the previously untreated DUWL exhibited heterotropic bacterial counts in excess of 106colony-forming units (CFU) per milliliter. The initial chlorine profile curves for the private clinic's DUWLs resulting from the plots of accumulative volume of solution versus chlorine concentration were in accordance with previous studies for contaminated units (>103CFU). After the third hypochlorite:acetic acid treatment, distilled water replaced the acetic acid in the disinfecting solution. Four treatments over a 35-day period were ineffective in reducing biofilm contamination to an acceptable American Dental Association (ADA) level of 200 CFU, possibly because commercial distilled water was used in the separate water system rather than sterile deionized water. Use of acetic acid:chlorine to eliminate established biofilm produced unacceptable levels of trihalomethanes and metal corrosion in the system. Furthermore, the chlorine:acid combination did not enhance the removal of biofilm or reduce the planktonic bacteria to an acceptable ADA level when contrasted with use of hypochlorite alone. A further 25 weeks of cleaning the system according to the established protocol (using distilled water produced on the premises) produced units that were within acceptable ADA levels (