Dental unit waterline testing practices: an 11-Year retrospective study

OBJECTIVES: This retrospective study examined the dental unit waterline (DUWL) testing practices of Saskatchewan dental clinics over a period of 11 years, with an emphasis on their responses after identification of high microbial levels. MATERIALS AND METHODS: Dental clinics (n = 137) aseptically collected samples of output water from their air/water syringes, handpieces, and ultrasonic scaler lines using Sigma-Aldrich® waterline test kits and delivered them to a quality assurance laboratory. Tests were incubated for seven days at room temperature, and those with heterotrophic plate counts > 500 CFU/mL were reported as failures. Statistical analyses were performed on a database containing 4,093 test results. RESULTS: Participating clinics submitted an average of 11 DUWL tests per year. Overall, 21% of tests failed, and a moderate positive association (r(s)=.52, p < 0.001) was found between clinics’ DUWL testing frequency and failure rate. Only 7% of failed DUWL tests were followed up by collection of a subsequent test within two weeks, of which 47% still exceeded the 500 CFU/mL threshold. CONCLUSIONS: Our findings demonstrate an association between DUWL testing frequency and detection of unacceptable microbial levels, along with infrequent retesting and often-inadequate intervention after a failed test. This suggests the need for further efforts at the regulatory and educational levels to maintain adequate water quality during dental treatment. CLINICAL RELEVANCE: Procedural water can become contaminated in DUWLs and endanger patients. Regular DUWL monitoring and evidence-based interventions to treat contaminated systems are necessary to safeguard patient health.