The specifi c structure of dental units favours the presence of biofi lm and microbial
contamination of the dental unit waterlines (DUWL) water. The ability of bacteria
to colonize surfaces and to form biofi lm in water supply tubes, including DUWL, is a
common phenomenon, which has been well documented, just as with diffi culties in biofi
lm removal and prevention of its regrowth. Microorganisms from contaminated DUWL
are transmitted with aerosol and splatter, generated by working unit handpieces. On the
basis of the detailed literature review, the state-of-the art knowledge of the microfl ora of
dental unit waterlines is presented. Most of the microorganisms isolated from DUWL
are of low pathogenicity. Nevertheless, the public health signifi cance of many of the
microorganisms found in DUWL is unknown. According to current knowledge, it is not
the mere presence of bacteria that is important in DUWL contamination monitoring, but
their number, the presence of potential pathogens, and patients’ oral cavity microfl ora.
Numerous studies emphasize the need for effective mechanisms to reduce the microbial
contamination in DUWL and highlight the risk for cross-infection in general practice,
especially in view of the ever-increasing number of immunocompromised persons who
present at outpatient dental clinics.