Assessment of Microbial Contamination in Dental-Unit Water Lines: An Analytical Study

Introduction: Dental-unit water line (DUWL) contains various microorganisms. American Dental Association and the Centers for Disease Control and Prevention have suggested a standard for dental-unit water system water as water not having more than 200 cfu/ml. Aim: To assess the microbial contamination in DUWLs. Materials and Methods: Two dental chairs, each from four clinical departments, were randomly selected in this study. A total of 31 water samples were collected from each chair containing airotor line, scaler unit, 2-way syringe and oral rinse unit. In one dental chair in the Department of Periodontics, the sample from airotor point was not assessed, as it was not functional at the time of assessment. The samples were inoculated into blood agar, MacConkey agar and peptone water and cultured at 37°C overnight. Result: Colony-forming units were above 500 cfu/ml. The organisms identified were mostly gram-negative bacilli particularly Escherichia coli, Pseudomonas and Klebsiella, as well as gram-positive bacteria such as Enterococci. Conclusion: DUWLs are heavily contaminated with waterborne organisms from biofilm within the tubes as well as human pathogens as a result of the back-siphonage from oral cavity of patients. These organisms may cause serious systemic infections to patients, especially the children, the elderly and the immunocompromised. Periodic checking of anti-retraction valves and disinfecting within the dental water unit system are mandatory.