Combining periodic and continuous sodium hypochlorite treatment to controlbiofilms 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 separa te 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 th e effluent coolant water was assayed via mic;microbiologic culture on a wee kly basis, At the end of the study, scanning electron microscopy of the inn er 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 cont amination of less than 1 CFU/mL. Baseline scanning electron microscopy demo nstrated 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 be low Environmental Protection Agency limits for drinking water. Conclusions. Weekly treatment with 5.25 percent NaClO diluted 1:10, and con comitant use of chlorinated treatment water (3 parts per million chlorine) consistently attained the proposed American Dental Association goal of fewe r than 200 CFU/mL, in the unfiltered output. The effects of continuous trea tment on dentin and enamel bond strength may require further evaluation. Clinical Implications, The success of this protocol suggests that optimal a ttainment of dental water quality goals may require a combination of approa ches.