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As a primary source of reinfection, biofilm control is a vital but often overlooked aspect of ‘best practice’ in dental surgeries. The focus needs to switch to biofilm formation, suggests the latest independent research on the treatment of dental waterlines from Amsterdam’s world famous dental school- ACTA. Simon Davies, founder of CleanCert Hygiene discusses these findings and shows how easy it is to implement these recommendations.

Latest research shows hidden risks  


New findings released from a top European University in September 2022 – involving research into hundreds of dental unit waterlines (DUWLs) – articulate the vital need for dental surgeries to take steps to control biofilm formation as well as using antimicrobials.

The dental profession has been aware of the need to address biofilm formation for years, however there is still some confusion and “a lack of clarity regarding the process of disinfection and maintenance of Dental Unit Water Lines” and other situations in the dental surgery where biofilm can grow.

You may have seen disinfection product manufacturers claiming that their use of their antimicrobial is unlikely to result in biofilm growth. But such claims do not correlate with independently conducted science. These studies conclude that optimising DUWL cleaning protocols is especially important because outside of normal working hours, water in the lines stagnate and offers the micro-organisms present many opportunities to build up a strong matrix-encapsulated biofilm that can resist antimicrobial treatments.

Dental professionals need to understand what biofilms are, how they form, and how to eliminate them through adoption of best practice behaviours and procedures. Both dental unit manufacturers and dental practitioners have a legal obligation to ensure the water in dental units is safe.


Shocking new findings from ACTA

Recent research led by Michel Hoogenkamp at the University of Amsterdam (ACTA) reinforces the need to focus on biofilm control. The research found that the vast majority (over 60%) of 226 DUWS sampled exceeded the recommended microbiological guidelines. Detailed analysis of biofilm samples from the units saw Legionella, amoebae, and fungi in 71%, 43% and 98% of units, respectively.


What is biofilm?

A specific and persistent issue is biofilm formation in DUWLs.

Biofilms can cause plaque, endodontic disease, periodontal disease and peri-implantitis. Biofilms in DUWS can dislodge, be incorporated in aerosols, and subsequently inhaled by staff and patients with a potential to cause oral and other infections.

When biofilm forms, free-floating bacteria, fungi, or protists clump together and colonise damp or submerged surfaces to form sticky, slimy coatings. The organisms in the biofilm can then grow and reproduce, rapidly forming a multi-layered microcolony.

As this ecosystem matures, it secretes a protective, slimy extracellular matrix of protein and polysaccharides. Eventually, individual microorganisms or clumps of cells burst out of the biofilm and disperse to contaminate new surfaces.

The main challenges of dealing with biofilms are their invasive nature, their unpredictable formation and their ‘hard to control’ nature – all of which can leads to the opportunity for human error in assessing and eradicating them.

Waterline biofilm

The study also indicated that the use of generic disinfection protocols is unlikely to be effective in guaranteeing safe dental unit water and it suggests that infection control guidelines should focus on the presence and control of biofilm formation as this is the key source of reinfection in the effluent water.
Current waterline treatment procedures focus on disinfecting (ie killing free floating bacteria as per continuous dosing), but removal of the biofilm is required to prevent subsequent recolonization. The study recommends using disinfectant products that can remove the whole biofilm as the ‘dead’ biofilm still can serve as a nutrient source for amoebae and a growth media for opportunistic pathogens.

The Dutch research also looked at the most effective methods to remove biofilm using model systems. Simple flushing of treatment water through the open ports of DUWS may remove unwanted fluids but does not reliably remove attached biofilms. A weekly ‘shock’ treatment is widely used in dental surgeries. Shock treatment uses high concentrations of effective cleaning products that can that detach biofilm from the internal surfaces of DUWS water lines. Shock treatment is effective and resulted in a 60% pass rate in the Dutch research.

However, the research highlighted the importance of also monitoring and maintaining bacteria-free water for the rest of the week following shock treatment. The study found that water from dental units that received a daily low dose of disinfectant in combination with the normal weekly shock dose generally contained a lower microbial load. These new results from the University of Amsterdam reflect and reinforce other research that surveyed infection control in DUWS associated with more than 22,000 dental ‘chairs’.

The Dutch study also looked at differences between mains water-fed and closed loop (i.e., fed from self-contained bottled water) DUWS. Water samples from both types of units were analysed, and significantly higher amounts of Legionella DNA were found in mains fed units. The study concluded that a closed, bottle-fed system is the better alternative as such DUWS allow for a better, more controlled use of biocide cleaning products and therefore have a higher impact on the prevention of biofilm growth.


Start preventing biofilm growth today

Clearly, as this latest independent Dutch research shows, better prevention of biofilm growth in DUWS is essential to ensure the continuing health and well-being of dental staff and patients and to enable good hygiene practice. Infection control guidelines “should focus on the presence of biofilm formation as this is a primary source of reinfection,” concludes this important study. This is an important shift in focus for dental staff from eliminating free floating planktonic bacteria in dental waterlines (with continuous dosing), to eliminating the biofilm that those bacteria form into.

CleanCert Hygiene provides a range of solutions that make the dental surgery a safer place whilst supporting sustainable dentistry. We understand the risks presented by biofilms in waterlines, which is why CleanCert is able to do both protocols in the one bottle. CleanCert is the only 2-in-1 dental waterline disinfectant that is non-cytotoxic and 100% eco friendly, whilst offering exceptional value per dose. Contact us for a free sample via sales@cleancert-hygiene.co.uk or visit www.cleancert-hygiene.co.uk.



[1] Umer F, Khan M, Khan FR, et al. Managing dental unit waterlines: a quality improvement programme
BMJ Open Quality 2022;11: e001685. doi: 10.1136/bmjoq-2021-001685. Available from:https://bmjopenquality.bmj.com/content/11/2/e001685

[2] Hoogenkamp M.A., Brandt B.W., de Soet J.J., Crielaard W. An in-vitro dynamic flow model for translational research into dental unit water system biofilms. J. Microbiol. Methods. 2020;171:105879. doi: 10.1016/j.mimet.2020.105879. Available from: https://pubmed.ncbi.nlm.nih.gov/32105699/

[3] Walker J.T., Marsh P.D. Microbial biofilm formation in DUWS and their control using disinfectants. J. Dent. 2007;35:721–730. doi: 10.1016/j.jdent.2007.07.005. Available from: https://pubmed.ncbi.nlm.nih.gov/17714847/

[4] Garg S.K., Mittal S., Kaur P. Dental unit waterline management: Historical perspectives and current trends. J. Investig. Clin. Dent. 2012;3:247–252. doi: 10.1111/j.2041-1626.2012.00135.x. Available from: https://pubmed.ncbi.nlm.nih.gov/22927105/

[5] Barbeau J., Nadeau C. Dental unit waterline microbiology: A cautionary tale. J. Can. Dent. Assoc. 1997;63:775–779. Available from: https://pubmed.ncbi.nlm.nih.gov/9401300/

[6] Shajahan I.F., Kandaswamy D., Lakshminarayanan L., Selvarajan R. Substantivity of hypochlorous acid-based disinfectant against biofilm formation in the dental unit waterlines. J. Conserv. Dent. 2017;20:2–5. doi: 10.4103/0972-0707.209076. Available from: https://pubmed.ncbi.nlm.nih.gov/28761244/

[7] Sedlata Juraskova E., Sedlackova H., Janska J., Holy O., Lalova I., Matouskova I. Legionella spp. in dental unit waterlines. Bratisl. Lek. Listy. 2017;118:310–314. doi: 10.4149/BLL_2017_060. Available from: https://pubmed.ncbi.nlm.nih.gov/28516796/

[8] Hoogenkamp, M.A. (2021). PhD thesis: Challenging dental unit water biofilms: Clean, treat, repeat. Available from: https://dare.uva.nl/search?identifier=fa425356-009b-4d24-a399-b876ea364387

[9] Dewhirst, N., and Molinari, J.A. Treating and Monitoring Dental Water in Current Topics in Infection Control (2018). Available from: https://cleancert-hygiene.co.uk/wp-content/uploads/2021/11/GREAT-Molinari-Dewhirst-Article-12-pages-COMPENDIUM-May-2018.pdf