Abstract:

Objective

To evaluate the difference of the species and quantity of microorganisms in dental unit water lines （DUWL） before and after disinfecting with sodium hypochlorite solution.

Methods

The water supplied with 20 separate sources were collected and divided into two experimental groups， each comprising ten DUWL. The microorganisms were quantified with nutrient agar after incubated for 48 h， recorded as colony forming unit （CFU/ml）. The species of microorganisms were studied. Pseudomonades， Legionella and E.coli were determined with National Standard Methods. The sodium hypochlorite at concentration of 525 mg/L was used in this study for disinfection of DUWL. The data were analyzed by ＂two-sample t-test for independent samples＂， ＂paired t-test for independent samples＂ and ＂one-way ANOVA＂ with SPSS 10.0 software， α=0.05.

Results

（1）The number of bacteria in water at the baseline was 2.23×10³ CFU/ml before disinfection with sodium hypochlorite solution， whereas it was 0 CFU/ml（P ＜0.05） after disinfection. （2）Eight species of bacteria were identified from the separate water，and three species were identified after disinfection. Before disinfection Pseudomonas were positive in 7 samples （out of 20）（35%） of the separate water， and E.coli and Legionella were not found in water. The three opportunistic pathogens were not detected after disinfection.

Conclusions

This study confirmed that DUWLS has been contaminated heavily with a number of microbes，including some opportunistic pathogens like Pseudomonas. The high concentration of microbes in DUWL brings high risk of cross infection to both dental professionals and patients. Sodium hypochlorite at the concentration of 525 mg/L may be used as a disinfection solution for DUWL infection control contributing its satisfying disinfection effect.

Key words: Dental unit water lines, Sodium hypochlorite, Disinfection