Dental unit water: bacterial decontamination of old and new dental units by flushing water

: Objective: To evaluate by means of Petrifilm™ system (3M, St Paul, MN, USA) the level of bacterial contamination in water from old and new dental units (air–water syringes and high‐speed turbines) before and after flushing water through waterlines. The old dental units had been used for 13 years and the new dental units for 1 year. A fast method named Petrifilm™ AC (3M) was employed to evaluate the level of water contamination with total aerobic bacteria and Petrifilm™ EC for Escherichia coli and coliforms. Methods: Dental unit water were collected before and after flushing of 4 (air–water syringes) and 2 min (high‐speed turbines) from 24 old and new dental units. Thereafter, samples were diluted, inoculated onto Petrifilm™ plates and incubated. Results: The filtered tap water that filled up dental unit reservoirs showed a low level of bacterial contamination (4 and 15 CFU ml−1). However, all water samples from old and new dental units were highly contaminated. The flushing of dental unit waterlines reduced the bacterial count in all dental unit water, but the reduction was better in water from new dental units than from old dental units. E. coli and coliforms were not detected in any water samples analysed. Conclusion: Flushing water is a simple measure that should do part of dental routine, because it was able to reduce the level of total aerobic bacteria in water from old and new dental units.