Combining Periodic and Continuous Sodium Hypochlorite Treatment to Control Biofilms in Dental Unit Water Systems

Background: This study evaluated the efficacy of combined intermittent and continuous treatment with diluted sodium hypochlorite, or NaClO, to improve dental unit water quality in a clinical setting.

Methods: In this prospective study, 10 dental units were fitted with separate water reservoir systems. Dental units were maintained with weekly rinses with 1:10 NaClO. Treatment water consisted of 750 milliliters of tap water and one drop of undiluted commercial bleach. Bacterial contamination in the effluent coolant water was assayed via microbiologic culture on a weekly basis. At the end of the study, scanning electron microscopy of the inner surfaces of the dental unit waterlines corroborated the results.

Results: All 10 dental units consistently delivered water with less than 10 colony-forming units per milliliter, or CFU/mL, with a mean bacterial contamination of less than 1 CFU/mL. Baseline scanning electron microscopy demonstrated biofilm formation. Scanning electron microscopy at the end of the study demonstrated the lack of features consistent with biofilm formation. Although tri-halomethanes were detected in output water, all samples were below Environmental Protection Agency limits for drinking water.

Conclusions: Weekly treatment with 5.25 percent NaClO diluted 1:10, and concomitant use of chlorinated treatment water (3 parts per million chlorine) consistently attained the proposed American Dental Association goal of fewer than 200 CFU/mL in the unfiltered output. The effects of continuous treatment on dentin and enamel bond strength may require further evaluation.

Clinical Implications: The success of this protocol suggests that optimal attainment of dental water quality goals may require a combination of approaches.