The management of dental unit waterlines (DUWL) has become a key focus for infection control, as they can easily become contaminated with microorganisms, which rapidly lead to biofilm development. However, technological advances in disinfectants designed for use with DUWL mean the potential threat posed by biofilms could be
virtually eradicated if best practice is followed.
Dental unit waterlines are an integral part of dental surgery equipment, supplying water to irrigate the oral cavity during treatment. The water is not sterile and contains high numbers of bacteria. Although the large volumes of water
produced are mainly removed by high volume aspiration, some is almost certainly swallowed by the patient and droplets may be inhaled by staff.
A study of water obtained from DUW systems from 55 dental surgeries showed that in 95 per cent of water samples, microbial loading exceeded European Union drinking water guidelines. The study authors believe that these “values probably underestimate the true microbial load to which a patient is exposed”. The most common pathogen detected was Pseudomonas spp; Legionellosis, Mycobacterium spp and Candida spp were also detected.
A major concern is contamination of the water supply with Legionella species, in particular L. pneumophila, which can cause Legionella pneumonia. Transmission of Legionellae occurs when water containing the bacterium is aerosolised in droplets and inhaled. Dental staff have a higher prevalence of Legionella antibodies compared to the general public, suggesting that aerosols generated by dental equipment are a potential source of infection.
Water from dental lines can be heavily contaminated due to microorganisms proliferating on the inner surface of the water lines. Frequent periods of water stagnation in DUWLs together with the properties of the plastics from which they are manufactured promote the attachment and colonisation of biofilm-forming microorganisms.
Biofilms are adherent colonies of bacteria, fungi and protozoa embedded in a matrix of extracellular polymeric substances that form along the inner surface of DUWLs and are responsible for high levels of contamination. The nature of DUWLs is such that they will develop a biofilm and water flowing down the biofilm coated waterlines
will contribute to microbial load in the water as it exits the tubing. Biofilms protect organisms from the effects of heat and chemicals, which reduces their susceptibility to the disinfection process.
HTM 01-05 Section 6.76 states that “the use of water in dentistry must comply with a series of regulations which are designed to ensure the safety of patients, staff and the public.” The guidelines clearly state that the acceptable maximum level of microbial contamination “should be expected to lie in the range 100 to 200 colony forming units per millilitre (cfu/ml).” This is similar to the quality expected for mains supplied drinking water. The EU Directive 98/83 states that the European standard for drinking water should be less than 100 CFU (colony forming units). Once water enters the DUWLS the number of bacteria begins to increase with numbers as high as 1.6 x 10 CFU/ml having been recovered in the outflow.
Although flushing of water lines is recommended by HTM 01-05, studies have shown that flushing alone results in only a small reduction in biofilm TVC (9.1 per cent) and an even smaller reduction in biofilm coverage (only 0.5 per cent).
A study evaluating a range of disinfectants to control biofilm contamination in DUWLs states that the disinfectant should kill bacteria in the water phase, kill biofilm bacteria and remove biofilm from surfaces.
Biofilms need to be removed as well as ‘killed’ as a ‘killed’ biofilm may still act as a source of endotoxins allowing rapid recolonisation of new biofilm. Any disinfectant selected should meet these three criteria.
A study evaluating a range of disinfectants found that most did not meet all three of the above criteria. However a product such as schülke watersafe (previously known as schülke DUWL) provides complete elimination of viable bacteria and 100 per cent reduction of biofilm coverage.
The safety of dental treatment requires that good quality water is used. Understanding the nature, formation and ways to eliminate biofilm is a major step towards reducing health risks for both patients and dental personnel.
Case Study
Monitoring programme to ensure water quality
As part of its ongoing infection prevention and control policy, a large dental practice in Surrey has instigated regular testing of the water quality of its dental unit waterlines. The aim is to ensure microbial levels do not exceed those
of EU drinking water standards. Says practice manager Jo: “We know that even with regular flushing, DUWLs become contaminated, so we have instigated a complete biofilm eradication system. This included a one-off procedure to completely eliminate viable bacteria and biofilm coverage. We now use a cleaning solution for continuous protection against biofilm reforming. Every quarter we use dip slides to check that the water quality never falls below standard – which it never has!”
References available on request.