Dental Waterline Biofilms — MFDS Part 1 MCQ
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Correct answer: D — It can act as a reservoir for opportunistic pathogens such as Legionella and Pseudomonas, which may be released into treatment water and aerosols.
Explanation lettering: E = shown as A · A = shown as D · D = shown as E
A is correct. Narrow-bore dental unit waterlines, periods of stagnation and a high surface-area-to-volume ratio favour adherent microbial biofilm. These biofilms may contain opportunistic environmental pathogens, including Legionella and Pseudomonas species, which can be shed into treatment water or generated aerosols. Exposure is particularly important for medically susceptible or immunocompromised patients. Routine flushing may reduce free-floating organisms temporarily but does not reliably eliminate an established adherent biofilm, so B is incorrect. The organisms are not exclusively oral commensals, excluding C. Biofilm does not provide a beneficial anti-corrosion or infection-control lining, excluding D. Potable incoming water is not sterile, and residual disinfectant does not necessarily penetrate and eradicate mature biofilm, excluding E.
Reference: Umer F, Khan M, Khan FR, Tejani K. Managing dental unit waterlines: a quality improvement programme. BMJ Open Quality. 2022;11:e001685. https://assets.publishing.service.gov.uk/media/67e673f78ac59d1882eadda1/Hospital_FWE_Microbiology_Guidelines.pdf