Methods: Water samples (20mL) were collected from the water lines for high-speed handpieces, 3-way syringes and drinking water for dental chairs of each type. Samples of tap water were also collected. Water samples (0.5mL) were mixed with tryptic soy-yeast extract medium, incubated and viable counts of colonies made after 24h incubation.
Results: : Initially all samples yielded bacterial counts >105 c.f.u./mL whereas bacterial counts from tap water in were 50-300 c.f.u./mL. E. coli was isolated from the DUWL in one dental chair. Disinfection regimes using either Calbenium® or Citrisil® were adopted following the manufacturers´ instructions. Disinfection of DUWL in the oldest units was not posible. Disinfectants were used twice per week and a policy was established of running water from all dental unit water lines twice per week and drinking water daily. Sampling was repeated and the results demonstrated a significant reduction in bacterial counts, with water samples from 9/21 dental chairs meeting the ADA/ EU criteria.
Conclusions: Water lines of dental units become contaminated, especially in units left unused for long periods. Disinfection policies were successful in reducing bacterial counts to the recommended levels but even regular running of water through lines that could not be disinfected had a beneficial effect on reducing the bacterial count.