Failure of anti-retraction valves and the procedure for between patient flushing: a rationale for chemical control of dental unit waterline contamination.

PURPOSE: To evaluate the efficacy of anti-retraction valves; and to compare between-patient flushing with water and with using a chemical treatment to control patient-to-patient contamination through dental unit waterlines (DUWL).
METHODS: For the first aim, nine new antiretraction valves from three different manufacturers were utilized. Each valve was installed along the water line connecting the high-speed handpiece to the dental unit. The handpieces were made to run and stop in a container filled with a solution of about 7 log10/mL of Bacillus subtilis spores (used as a marker) and retraction of spores was measured. Subsequently, all nine valves were installed in dental units in use in private offices, and all tests repeated after 15, 30 and 60 working days. For the second aim, the efficacy of mechanical flushing (30 seconds for each instrument) was compared with that of mechanical flushing in combination with pressurized air and of a between-patient disinfecting procedure (2 minutes contact with TAED and persalt utilizing an "autosteril" system). Before each test (10 tests for each procedure), known concentrations of Pseudomonas aeruginosa (ATCC 27853) suspension (4 to 7 log10cfu/mL) was loaded in the DUWL and let sit for 20 minutes.
RESULTS: In the anti-retraction valve experiment, at baseline only one anti-retraction valve showed a failure in opposing fluid retraction. After 15 days, three valves, after 30 days, six valves, and after 60 days, eight valves showed failure. In the flushing experiment, a highly significant linear correlation (r =.9178) was found between values before and after mechanical flushing. Post flush log10cfu/mL values showed the removal of about only 1 log10cfu/mL of the microorganisms (only about 10% in absolute counts). On the other hand, no cfu/mL was detected in waterlines after the "autosteril" disinfecting cycles.