evaluation of bacterial contamination in dental unit waterlines of qazvin’ dental school ,iran

conclusions flushing dental unit waterlines are an effective measure in reducing the number of bacterial contaminants. results bacterial contamination was found in all 24 units at the beginning of daily activity with a mean colony count of 17850. the number of colonies decreased to 3250 following 30 seconds of flushing in 16 units and later to 1837 after flushing for two minutes in 13 units. in addition, the number of contaminated units at the end of daily activity was 19 with a mean colony number of 11170. objectives this study was designed to evaluate contamination of dental unit waterlines by common gram positive and negative bacteria in qazvin’s dental school during the year 2012. materials and methods this survey was performed on 24 dental units routinely used in the dental school of the city of qazvin. four samples of 100 ml were obtained in sterile bottles from each unit at different work stages as follows: the beginning of daily activity, after flushing for 30 seconds, following two minutes of flushing, and after the end of daily practice. the number of bacterial colonies was determined for each sample and the mean colony number was calculated. background contamination of dental unit waterlines is a well-known issue in the field of dentistry.