ABSTRACT
Objective To compare the effect of different ways of water supply and whether or not drain water from waterlines for overnight on bacterial counts in dental unit waterlines(DUWLs).Methods In the first phase,6 sets of DUWLs were randomly divided into 2 groups (external storage tank water supply group and municipal water sup-ply group);in the second phase,6 sets of DUWLs were all changed to use external storage tank and randomly di-vided into 2 groups (draining water for overnight group and without draining water for overnight group),bacterial count before and within one week of disinfection between two groups at two phases were compared respectively. Results In the first phase,handpiece water of DUWLs was most seriously contaminated by bacteria,the average colony count was 4117 CFU/mL,qualified rate was 15.38%.Before disinfection,no significant difference in bacte-rial count were found among each groups (all P>0.05),bacterial count of DUWLs of all groups severely exceeded the standard(all >3000 CFU/mL).Comparison of bacterial count in DUWLs from different water supply routes after disinfection was not significantly different on day 1(P>0.05),but were significantly different at day 2-7(all P0.05),but were significantly different on day 2-7(all P100 CFU/mL.Conclusion Use of external storage tank,daily change of sterile distilled water,and daily emptying water for overnight can effectively reduce bacterial count in DUWLs.