Disinfection of dental unit waterlines with an oral antiseptic.

The problem of potential pathogens in biofilm within dental unit waterlines is real. Even though some chemical agents can disinfect biofilms, there remains concern that all remnants of the biofilm matrix are not eliminated, even with periodic treatments, and the bacterial populations in dental unit waterlines recur rapidly. Toxic and caustic residual chemicals are also a concern. In multiple trials following overnight treatment of dental unit waterlines with Listerine Antiseptic (LA), recurrence was investigated by evaluating effluent and biofilm specimens by plate culture. The presence or absence of biofilm within the dental unit waterlines was evaluated, pre- and post-treatment, by scanning electron microscopy. Baseline evaluations of dental unit waterlines determined the effluent and biofilm to harbor an average of 1 x 10(5) CFU per ml and 1 x 10(4) CFU per cm2, respectively, prior to treatment. Overnight, 18-hour treatment with LA rendered effluent and biofilm samples free of recoverable bacteria in all cases immediately following treatment. Viable bacteria in the effluent of treated dental unit waterlines recurred to near pre-treatment levels by Day 7. The minimum inhibitory concentrations for each of the recovered isolates did not change following overnight treatment. Repeated overnight treatments at the beginning of a one-week study were effective in inhibiting recurrence of viable bacteria in the biofilm and effluent indefinitely, but still failed to completely remove the biofilm matrix. New tubing treated prior to use and then daily with LA did not develop a detectable biofilm by scanning electron microscopy during the study. One-month long follow-up clinical trials have demonstrated that a maintenance solution of a 1:50 concentration of LA and sterile distilled water in self-contained dental units with new tubing is effective for prolonged periods in maintaining the effluent within the American Dental Association's recommendation for the year 2000 of < 200 CFU per ml. The clinical significance of these findings is that a solution to the problem of dental unit waterline contamination may be currently available. Since antimicrobial LA is safe for patient use, it may be one of the most viable options suggested to date.