Microbial contamination in dental unit waterlines with different flushing volume

Pingping XU; Xiaochun CHEN; Xiaoqing SHEN

ABSTRACT

BACKGROUND:

Daily flushing of dental unit waterlines (DUWLs) is believed to be the least expensive and simplest method for reducing the level of microbial contamination in DUWLs.Authorities' guidelines suggest that high-speed handpieces should be run to discharge water for 30 seconds after use on each patient.However,the guideline is inaccurate for clinicians according to the time-dependent flushing since the maximum flow rate of flushing water varied from dental chair units (DCUs).

OBJECTIVE:

To assess the level of microbial contamination in water effluent from the air-water syringe and the high-speed handpiece line of DCUs and prevalence of three species of bacteria detected in DUWLs at each flushing volume.Thus,practical water flushing measures could be proposed according to the effect of volume-dependent dental unit waterline flushing on the microbial contamination in DUWLs.DESIGN,TIME AND

SETTING:

A cross-sectional investigation was designed and conducted in Guangdong Provincial Stomatological Hospital and Laboratory of Microbiology,School of Public Health and Tropical Medicine,Southern Medical University between May 2007 and March 2008.MATERIALSThe materials used in this investigation including nutrient agar,blood plates,biochemical testing kit,agglutination testing kit and Gram staining agents.These materials were supported by Guangdong Huankai Microbiological Science and Technology Ltd.

METHODS:

Water sampling was conducted at 80 DCUs in a stomatologicel hospital.A total of 6 mL,2 mL for once sampling,of continuous water flushing from the air-water syringe and the high-speed handpiece line of each DCU respectively were collected aseptically after the finish of the daily clinical work on every second Friday,between May 2007 and October 2007.Standard isolation and identification technique of bacteria was adopted.MAIN OUTCOME

MEASURES:

Concentration of bacteria and prevalence of three species of bacteria in water effluent from the air-water syringe and the high-speed handpiece line of DCUs at each flushing volume were evaluated.

RESULTS:

The median concentration of bacteria in water effluent from either the air-water syringe or the high-speed handpiece line of DCUs was 5.67×10~2 cfu/mL,and there were no statistical differences among microbial concentrations of first three 2-mL flushing water samples (P>0.05).Prevalence of Staphylococcus spp.from the third 2-mL flushing water sample demonstrated an obviously higher level than that of Staphylococcus spp.from the first two 2-mL (P < 0.05),while prevalence of Streptococcus spp.and Actinomycete spp.kept at a relative stable level (P > 0.05) at each flushing volume.

CONCLUSION:

Volume-dependent water flushing procedure stays a more practical measure for reducing microbial contamination in DUWLs rather than time-dependent flushing,but the volume of flushing water needs to be further evaluated.