evaluation of gram negative bacterial contamination in dental unit water supplies in a university clinic in tabriz, iran

background and aims. bacterial contamination of dental unit water supplies (duws) has attracted a lot of attention in recent years due to the emergence of serious infections in susceptible dental patients. the aim of the present study was to evaluate the presence of gram-negative bacterial contamination in duws at tabriz university of medical sciences faculty of dentistry. materials and methods. this descriptive study was carried out on 51 active dental units in different departments. contamination was determined by taking samples from the unit's water supply before dental procedures and the use of specific culture media. the cultures were evaluated after 48 hours. results. gram-negative bacterial contamination was identical in all the departments. in the departments on the ground floor, namely departments of periodontics and oral and maxillofacial surgery, pseudomonas contamination was observed in 71% of units; in the departments on the first floor, namely departments of prosthodontics, orthodontics and pedodontics, 46.8% of the units had pseudomonas contamination; and in the departments on the second floor, namely departments of operative dentistry and endodontics, 37.7% of the units demonstrated pseudomonas contamination. conclusion. gram-negative bacterial contamination was evident in the evaluated duws. the contamination type was identical but the number of contaminated units decreased with the increase in the height of the floors.