The effect of frequent clinical use of dental unit waterlines on contamination.

Three dental units with self-contained water systems in an outpatient teaching dental clinic were treated with a proprietary chlorine dioxide waterline cleaner. Three similar units were used as controls. After four weeks, test and control units were crossed over. Water samples were taken from each line on each unit and from the sink faucets at six time periods; and the frequency of use of each line was recorded. Statistical analysis showed that increased frequency of use of waterlines did not affect lines that were chemically treated, but was associated with less contamination of untreated lines.