Investigation of the Bacterial Contamination of Dental Unit Waterlines and the Effectiveness of Flushing on the Contamination Level in Rafsanjan, Southeastern Iran

Introduction: Dental unit water lines (DUWLs) are potential sources of microbial contamination that threaten patients and dental personnel. This study aimed to determine the bacterial quantity and quality of DUWLs in Dental School in Rafsanjan and to determine the effect of flushing on the contamination rate. Materials and Methods: In this cross-sectional study, 124 water samples were collected from 20 active units in five departments (endodontics, periodontics, pediatrics, prosthetics, and restorations) at Rafsanjan Dental School (July 2024). Sampling was carried out using a standard method from the water inlet and the connection point of the turbine and scaler in three stages: before work, after 30-second flushing, and after work. To identify the bacterial contamination load, heterotrophic plate counting (HPC), Gram staining, and standard biochemical tests for each bacterial species were used. Kruskal-Wallis and Mann-Whitney tests were used to analyze the data. Results: The results showed that the contamination level in 53.2% of the samples was above the permissible limit. The highest contamination level was observed in the periodontics department (890 CFU/mL), and the lowest was in the endodontics department (380 CFU/mL). 30-second flushing significantly reduced contamination and the number of bacteria (p ≤ 0.001), while the difference between contamination levels in different departments and components of the dental units was not significant (p ˃ 0.05). Conclusion: Given the contamination of DUWLs, continuous water disinfection, cleaning of water lines, and flushing before and during work in dental units are recommended.