Effectiveness of Dental-Unit-Waterline Decontamination by Combining Shock and Continuous Treatment

Objective:  To compare the effectiveness of dental unit waterline (DUWL) decontamination by combining shock treatment with sodium hypochlorite followed by continuous treatment with chlorhexidine gluconate or ICX^TM

Materials and methods:  Thirteen dental units were first treated with 0.005% NaOCl for 1 hour as Shock treatment. The units were then randomly divided into three group: continuous treatment with 0.005% chlorohexidine gluconate or ICX^TM and control group respectively. Water from each DUWL was sampled daily for 2 weeks using aerobic heterotropic plate count. The percent reduction of CFUs in each groups were evaluated. Samples of colonies in each group were randomly selected to examine by gram stain. The data was analyzed by using Mann-Whitney U Test.

Results:  After Shock treatment with NaOCl, the average numbers of microorganisms in water samples were reduced to nearly undetectable level in all dental units. The bacterial count in control group has returned to the level equivalent to or even higher than that of the pre-treatment by day 5.  On day 5, the average numbers of microorganisms in chlorhexidine and ICX^TM groups were still as low as those of day 0 post-treatment. Despite the gradual increase in bacterial count in these two groups, the CFUs are still below the pre-treatment levels by day 12. Percent reduction of CFUs recovered from chlorhexidine gluconate and ICX^TM groups were significantly higher than the control group by day 5 and 12 (p = 0.05). Interestingly, in contrast to the heterogenic gram stain species observed in control group, we found that most of bacterial stained after continuous treatment with chlorhexidine or ICX^TM were predominantly gram negative bacilli.

Conclusion: This data shows that combining shock treatment with NaOCl followed by continuous treatment with 0.005% chlorohexidine gluconate or ICX^TM were more effective in inhibiting recoverable numbers of microorganisms from DUWL than shock treatment alone.