Comparison of Endotoxin Contamination in Dental Unit waterlines

Objective: To compare endotoxin level and its relationship with microbial contamination in dental unit waterlines (DUWLs) with and without treatment using three dental water disinfection devices. Methods: Water samples were collected aseptically from DUWLs without (N=2) or with PureTube, PureTube PLUS or PureLine50 (N=5 each) (Sterisil, Castle Rock, CO) at the baseline, day 1, week 2 and week 5 for microbial (CFU) and endotoxin unit (EU) evaluation. The CFU/mL was determined using the membrane filter method. The content of EU was analyzed using the Chromogenic Limulus Method. Results: The baseline EU ranged from 0.4 to 471.2, with an average of 77.7 for the three treated groups and 23.0 for the control. Only three samples (17.6%) had the EU lower than 1.0, which is the limit for purified water set by US regulations. All three Sterisil devices effectively reduced CFU in the DUWLs after one day treatment and remained effective at weeks 2 and 5. Compared to the baseline, the EU levels were reduced in PureTube group at day 1 (-52%) and week 2 (-88%), while an increase was observed in the PureTube PLUS group at the same time points (112% and 319%, respectively). For PureLine50, there was an increase (245%) on day 1, but a decrease (-37%) at week 2. The EU levels were reduced dramatically (-92% to -99%) at week 5, but the values remained to be above the US regulatory limit. Conclusion: 1) Unacceptable endotoxin levels exist in DUWLs that are not disinfected. 2) Initial disinfection processes appear to elevate endotoxin levels. 3) CFU counts alone may not be adequate to judge the safety of the dental water supply. 4) Continuous DUWL disinfection controls microbial contamination and reduces endotoxins in dental water. Sponsored by Sterisil Inc.