Several studies in various countries have shown that water from dental unit waterlines (dental unitwater) was heavily contaminated with bacteria. Among these bacteria were occasionally detected waterborne human pathogens.
Objectives: Our study was carried out because no information is available about bacterial contamination of dental unitwater in Norway.
Methods: 260 practitioners were randomly selected from the national register of dentists in Norway. Each participant received instructions on how to collect aseptically dental unitwater and potable water samples (40 ml each), sterile tubes, a questionnaire and a postage-paid return packing. Immediately after collection, the water samples and the completed questionnaire were shipped to our laboratory (shipping time: 1-3 days). The numbers of culturable heterotrophic, mesophilic bacteria and of selected pathogens (enterobacteria,
Legionella species,
Pseudomonas aeruginosa and staphylococci), determined as colony forming unites (cfu) in each sample, were assessed by cultivation on nonselective and selective media. PCR was used for detection of
L. pneumophila. Results: Most of the water samples from air rotor showed growth of heterotrophic bacteria with counts that varied between <200 cfu/ml and >10.000 cfu/ml. These counts were highly significant higher (Wilcoxon two-sample test, p=0.0000) than those of water samples from the glass filling tube of the dental units. The potable water samples showed the highly significant lowest (p=0.0000) such counts. 21% of the water samples from air rotor demonstrated growth of one or more of the selected pathogens except
L. pneumophila, which was not detected in any sample. The corresponding figure for samples from glass filling tube and of potable water were 14% and 6%, respectively.
Conclusions: The dental unitwater was heavily contaminated with bacteria compared with potable water. When present, the waterborne pathogens constituted a minor part of the total bacterial counts. Dental unitwater in Norway may represent a potential infection risk to immunocompromised dental patients.