Microbial quality of closed- and open-circuit dental unit water systems

ABSTRACT

This study was undertaken to compare microbial levels of dental units with independent water . source [closed-circuit] to dental units directly linked to municipal water system [open-circuit]. Ten dental units with a closed-circuit and ten dental units with open-circuit water systems were randomly selected for this study. Both dental unit types were supplied by municipal water and subjected to the same disinfection protocol. Water samples were collected from the distal outlet of 'the 3-in-l syringe and from the cup filler. The samples were cultured on yeast extract agar medium >.H;'for 48 hours at 37°C. The total number of colony forming units [CPU] was counted using a Darkfield Quebec Colony Counter. The results were compared using analysis of variance [ANOVA] with significance level set to p < 0.05. The mean total viable count [TVC] for the 3-in-l syringe water samples was 619 CPU ml'1 for closed-circuit water system units and 496 CPU ml'1 for open-circuit system units the difference was not statistically significant [p= 0.565]. The mean TVC for the cup filler water samples was 466 CPU ml'1 for closed-circuit system units, and 336 CPU ml-1 for open circuit system units, the difference was not statistically significant [p=0.534]. Over 50% of all the collected samples contained TVC exceeding the ADA recommended level of < 200 CPU ml[-1]. It was concluded that both dental unit types were similar in containing unacceptably high levels of microorganisms