Challenging dental unit water biofilms: Clean, treat, repeat

Research output: PhD ThesisPhD-Thesis - Research and graduation internal


Biofilm formation within dental unit waterlines and subsequent microbial contamination could be a potential health-risk for immune-compromised and elderly patients. In this thesis the degree of microbial contamination and which microbes are present in the dental unit waterlines in the Netherlands was examined. Furthermore, an in-vitro dynamic flow model was developed to be able to study treatment regimens and antimicrobial products.
Results from a field study revealed that of 213 dental units tested only 39% complied with hygiene standards based on heterotrophic plate counts. Molecular DNA techniques, however, revealed that 43%, 71%, 98% of the units tested positive for the presence of amoebae, Legionella spp. and fungi. Analysis of confounding factors indicated that units, treated daily with a low concentration of hydrogen peroxide in combination with a weekly high dose disinfectant were acceptably low in the microbial load. This result was validated and confirmed by testing four different treatment regimens in the newly developed in-vitro dynamic flow model. Further evaluation of commercially available high-dose disinfectants revealed that most products were unable to clean a biofilm-contaminated surface within a single treatment.
To control biofilm formation within the dental unit waterlines and safe-guard the patients’ health, these units should be redesigned, dental staff to be educated on the reasons why strict adherence to infection control measures is important and to frequently test the dental unit water. Additionally, the current method of testing the dental unit water and how to control microbial contamination in the dental unit water is discussed.
Original languageEnglish
Awarding Institution
  • University of Amsterdam
  • Crielaard, W., Supervisor
  • de Soet, J.J., Supervisor
  • Laheij, AMGA, Co-supervisor
  • Brandt, Bernd, Co-supervisor
Award date17 Sept 2021
Print ISBNs9789464214376
Publication statusPublished - 2021


Dive into the research topics of 'Challenging dental unit water biofilms: Clean, treat, repeat'. Together they form a unique fingerprint.

Cite this