Investigation of the Presence of Opportunistic Bacteria in Dental Unit Waterlines and the Impact of Flushing

Aims: Water used in dental settings plays a critical role in patient care, and its microbiological safety is essential for protecting both patients and dental staff. This study aimed to investigate the presence of Pseudomonas aeruginosa and Aeromonas hydrophila in dental unit waterlines (DUWLs). Methods: In this cross-sectional study, 140 water samples were collected from different points of DUWLs at Gorgan Dental School, northern Iran, as well as from municipal water supplies, between August 2022 and May 2023. The presence of P . aerugin osa and A . hydrophila was detected using polymerase chain reaction. Associations between physicochemical parameters and bacterial presence were analyzed using the Chi-squared test, with P < 0.05 considered statistically significant. Results: P . aeruginosa and A . hydrophila were detected in 66.4% (93/140) and 32.1% (45/140) of the samples, respectively. A statistically significant association was observed between bacterial prevalence and sampling points ( P < 0.05). The highest prevalence of both bacteria was found in dental handpieces before flushing, whereas the lowest prevalence was observed in municipal water supply points. Flushing did not significantly reduce bacterial prevalence. Mean values of pH, residual chlorine, and temperature ranged from 7.20 to 7.50, 0.0 to 0.3 mg/L, and 19.30°C to 23.80°C, respectively. Residual chlorine levels in contaminated samples were generally low. Conclusion: The presence of opportunistic bacteria in DUWLs indicates potential health risks, particularly for immunocompromised patients. Implementing effective water safety plans and improving dental staff training are essential to enhance DUWL microbiological quality and reduce infection risks in dental clinics.