Background and Aim: Dental staff are exposed to aerosols. Water supply of dental units has insignificant bacterial count but the exiting water in the waterlines has over 100,000 microorganisms per milliliter. Various types of microorganisms exist in the waterline of dental units. Legionella pneumophila (L. pneumophila), Pseudomonas aeruginosa (P. aeruginosa) and Gram-positive cocci are among the most important ones. Scaling and root planning is a dental procedure carrying a high risk of bacterial contamination. This study aimed to assess water contamination in private dental offices in Isfahan city.

Materials and Methods: In this descriptive study, water sampling was done in 50 private offices 10 mL samples of dental unit water were collected from each scaler and a sample from the city tap water as control. We used 3-step polymerase chain reaction (PCR) for detection of L. pneumophila. The extracted DNA was evaluated for presence of mip gene sequence using spectrophotometry. For detection of P. aeruginosa, samples were cultured in Brilliant Green Bile broth. To confirm P. aeruginosa, the grown colonies were cultured in Cetrimide agar medium and presence of P. aeruginosa was re-confirmed with oxidase test. For evaluation of Gram-positive cocci, multiple smears were prepared and after Gram staining, Gram-positive specimens were cultured in blood agar medium. Data were analyzed using SPSS version 20 and reported in tables and diagrams as number and percentage.

Results: None of the control samples were positive for any bacterium. Thirty-two test samples were also negative for the understudy bacteria but 18 offices tested positive for these bacteria.

Conclusion: Our results shows that hazardous bacteria may be present in dental unit bio-film. Special attention must be paid to the cleanliness of water used in dental procedures.