A review of biofilms and their role in microbial contamination of dental unit water systems (DUWS)

Biofilms are heterogeneous functional consortia of microbial cells that grow on surfaces. This review discusses how biofilms form and why dental unit water systems (DUWS) are susceptible to biofilms composed of environmental (e.g. Moraxella spp. and Flavobacterium spp.) and opportunistic pathogens (e.g. Pseudomonas aeruginosa, Legionella pneumophila and Mycobacterium spp.). DUWS have narrow-bore tubing, slow flow and long stagnant periods that encourage biofilm growth. To control the microbial loading of DUWS, surgeries have used filtration, ultraviolet light and flushing. Dental practitioners are now being encouraged to retrofit independent water supplies that enable the practitioner to apply control strategies using chemicals such as sodium hypochlorite, chlorine dioxide, peroxides, peracetic acid and citric acid. Owing to the recognition of the public health significance of microbially contaminated DUWS, a vast range of chemical and non-chemical products have been developed in the last 3 years. With an increasing number of immuno-compromised dental patients presenting at dental surgeries, practitioners are now being given the mechanisms with which to control biofilms and maintain microbial numbers below the European Union drinking water guidelines and American Dental Association DUWS standard of 100 and 200 CFU ml^-1, respectively.