Part of a dental chair unit (DCU) used to provide water to cool and irrigate a variety of DCU-supplied instruments (i.e. turbine and conventional handpieces, ultrasonic scalers, and three-in-one air/water syringes), and tooth surfaces during dental procedures, as the heat generated during instrument operation can be harmful to teeth. DUWLs also supply water used by patients for oral rinsing during and following dental procedures and to rinse the DCU cuspidor after oral rinsing. Water supplied by DUWLs is frequently contaminated with high densities of micro-organisms, especially bacterial species, due to the formation of biofilm on the internal surfaces of the waterlines. The waterline network in a DCU consists of several meters of narrow-bore (i.e. a few mm) plastic tubing in which water stagnates when the DCU is not being used. Micro-organisms, in the DCU supply water, attach to the internal surfaces and form microcolonies that eventually give rise to multi-species biofilm. Water at the internal surface of DUWLs flows more slowly than water at the centre and thus there is little disturbance to any micro-organisms present. This allows the micro-organisms to multiply and disperse throughout the waterline network as planktonic forms. Micro-organisms from DUWLs can be transferred directly into the mouths of patients during dental procedures and can be aerosolized during the operation of high-speed handpieces and ultrasonic scalers. The most common micro-organisms recovered from DUWL output water are aerobic heterotrophic Gram-negative environmental bacterial species, although pathogenic organisms such as Pseudomonas aeruginosa, Legionella pneumophila, and non-tuberculosis Mycobacterium species can also be present. The presence of high densities of micro-organisms in DUWL output water provides a potential risk of infection of dental patients and healthcare staff and is contrary to good cross-infection control and prevention practices. Exposure to bacterial endotoxin in DUWL output water poses additional potential adverse health effects. Biofilm in DUWLs can be effectively controlled by regular disinfection with disinfectants or biocides that effectively remove biofilm. A wide range of such agents are available commercially but only some have been shown to be effective in long-term studies.
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