Control of DUWS microbial contamination using tetra-sodium EDTA

Water delivered by dental unit water systems (DUWS) in general dental practices may harbour high numbers of bacteria, including opportunistic pathogens, and increase the risk of cross-infection. Improved methods to control the microbial water quality of DUWS are needed. Objectives: This study evaluated the ability of weekly applications of tetra-sodium EDTA, to control the bacterial loads in DUWS outflow water to below the American Dental Association's (ADA) guideline of 200 (2.30 log CFU/ml) . Methods: DUWS (n=10) in Leeds Dental Institute were treated weekly with a single application of either 4% or 8% (w/v) tetra-sodium EDTA solution. A six week baseline measurement of the microbial load of out-flowing water was followed by four weeks of disinfection with 4% tetra-sodium EDTA solution and 2 weeks of 8% tetra-sodium EDTA solution. Water samples were tested for total viable counts (TVC) and the presence of opportunistic pathogens. Results: Baseline mean TVC before disinfection were 2.31 ± 0.73 and 2.56 ± 0.86 log CFU/ml for the air/water triple syringes and high-speed hand pieces, respectively. One treatment with 4% tetra-sodium EDTA solution reduced these mean TVC to 0.96 ± 0.37 (p <0.01) and 0.98 ± 0.36 (p < 0.01) log CFU/ml. During the week following each treatment counts gradually increased to baseline levels or above. Weekly treatment with 8% tetra-sodium EDTA solution reduced microbial re-growth below base line levels until mid- week, but by the end of the week there were 5/10 DUWS which still exceeded ADA guidelines. Conclusion: Untreated DUWS outflow water had bacterial counts greater than ADA guidelines. A single application of 8% tetra-sodium EDTA solution was highly effective at rapidly reducing these counts and maintaining them at <200 CFU/ml for up to 5 days.

(This work was supported by Aseptica Inc, Washington).