Methods: A long-term investigation evaluating biofilms in DUWL with a continuous chlorine dioxide product versus tap water was determined by colony forming units (CFU) in the effluent and scanning electron microscopy (SEM) of the sessile colonies. At the end of the first day, 150mL of the ClO2 concentrate was put into the test unit's reservoirs and allowed to remain overnight. For 6 months, 8 control units were treated with tap water and 16 test units used continuous 10:1 dilution ClO2 waterline cleaner.
All units were sampled weekly with the Millipore Heterotrophic Plate Count (HPC) Sampler plates, incubated 7 days and counted at 10.5X by two independent investigators, and reported as CFU/ml.
SEM was used to analyze the characteristics of the % biofilm coverage and texture (thickness). A 5 mm section of new tubing, and 5 mm sections of tubing from the junction box under the chair were excised from each of the 24 units at baseline and 6-months. The geometric center of tubing was imaged at 5000X. Coverage % was determined by overlay grid counts.
Results: The weekly mean HPC count for test units always adhered to American Dental Association recommendations of <200 CFU/ml. Control units exceeded 3x104 CFU/ml. Chlorine dioxide use resulted in an overall 113-fold biofilm reduction (P<.0001) compared to tap water. The fitted probability of a count <200 from a logistic regression model of treated units was 90.6% overall. SEM exhibited a reduction in % test unit biofilm coverage (P<.001) and texture (P<.001).
Conclusion: Continuous use of a stabilized chlorine dioxide DUWL cleaner showed significant reduction of microbial effluent counts and biofilm coverage.