Negating the risk

Bacterial biofilms are complex, surface-attached communities of bacteria held together by self-produced polymer matrices mainly composed of polysaccharides, secreted proteins and extracellular DNAs[i]. Bacteria are able to colonise and form biofilms on virtually all kinds of surfaces, including natural and synthetic surfaces[ii] and wherever water and nutrients are available, including living tissues, indwelling medical devices, industrial or potable water system piping, or natural aquatic systems[iii] (i.e. rivers and streams).

Biofilms are of particular concern in healthcare settings, including in dental surgeries, where microbial contamination of dental unit water lines (DUWLs) is a significant infection prevention issue.

Dental chair units (DCUs) use water to cool and irrigate DCU-supplied instruments and tooth surfaces, and provide rinse water during dental treatment. A complex network of interconnected narrow-bore plastic tubes (DUWLs) supply water to these instruments[iv], which include conventional dental handpieces, high speed turbines, three-way air/water syringes and ultrasonic scalers.

Many studies have demonstrated that DUWL output water is often contaminated with high densities of micro-organisms, predominately Gram-negative aerobic heterotopic environmental bacteria, including Legionella and Pseudomonas species. Untreated DUWLs host biofilms that permit micro-organisms to multiply and disperse through the water network, exposing patients and staff to micro-organisms, to fragments of biofilm and to bacterial endotoxins[v].

Bacterial endotoxins are a major concern in periodontal health and diseases owing to their structure and biological activity[vi]. And because biofilms thicken as they mature, left untreated they can cause damage to surgery equipment by causing a reduction in water flow, creating the potential for tube and instrument blockage.

Preventing biofilm

The challenge for dental teams is to control and inhibit biofilm formation on a continual basis using effective cleaning, disinfection and preventive maintenance strategies along with regular monitoring. However, in a recent Dentisan survey 3.8% of respondents admitted that their practice does not treat DUWLs, while 13.2% of respondents who are using waterline treatment are not monitoring, which means this cohort has no way of knowing if the treatment is effective[vii].

If biofilm formation is not strictly controlled in DUWLs, the water quality will quickly deteriorate, resulting in a failure to comply with guidelines and posing a health risk to patients and staff. For water used in DUWLs, the current recommended standard for England, Wales and Northern Ireland is 100 to 200 colony forming units (CFUs) per millilitre of water [cfu/ml], as detailed in HTM 01-05 section 6.79.

HTM 01-05 in England, WHTM 01-05 in Wales and SDCEP in Scotland all issue similar guidance as to the ways in which water should be treated and stored in DUWLs to minimise the issues of biofilm. The advice includes:

• Flush lines for at least 2 minutes at the beginning and end of the day.
• Flush lines for 30 seconds between patients.
• Flush lines after prolonged disuse/inactivity, such as lunch breaks, weekends, staff holidays and in part-time surgeries.
• Use chemical water treatments (following manufacturer’s instructions) to minimise biofilm formation in DUWLs.
• Continually monitor all DUWLs within the practice.

Continual monitoring

Apart from situations in which there are taste or odour problems, it is not a requirement to carry out routine microbiological monitoring for total viable counts (TVCs) in DUWLs[viii]. However, as stated in HTM 01-05 6.78: “some companies and other institutions offer comprehensive water-purification services that include periodic microbiological sample monitoring. Such services, provided they are quality-controlled, may contribute usefully to risk reduction in this area”.

It should be noted that if taste or odour have become obvious the biofilm problem would be significant. Biofilm contamination that is undetectable to the human senses is likely to result in water quality that does not comply with regulations and hence practices should be controlling and monitoring water quality consistently.

Biological dip slides are a straightforward, cost-effective method of identifying microbial contamination within dental water systems. According to the Dentisan Survey, 83% of respondents regularly use dip slides to monitor DUWLs.

It is recommended biological dip slides should be used on a quarterly basis to test both input and output water in each treatment centre to ensure water quality is maintained. A dip slide is immersed in a sample of input water, allowed to briefly drain then placed in a clear tube provided. This is repeated with a second dip slide sprayed with a sample of output water (i.e. from the 3-in-one line). The slides should immediately be incubated at 30°-35° for 48 hours or at room temperature for 72 hours. Any red spots that are visible on the slides, immediately after the incubation period has lapsed, indicate there is contamination in the waterline and highlight where contamination is most prominent.

There are a number of methods of monitoring water quality including in-house monitoring. If the dip slides can be assessed independently in a laboratory environment that supplies reports and certificates of compliance for each surgery that passes the criteria for clean water, an element of credibility is added to the practice’s infection control protocols.

Legionella monitoring

All UK dental practices are required to have both a written waterline management scheme and a separate Legionella risk assessment (LRA) for controlling any identified risks in accordance with the Health and Safety Commission’s (2000) Approved Code of Practice L8[ix]. While statistically the overall risk from legionella in dental surgeries and from dental equipment is low, there is still a perceived and possible risk to be assessed.

While it is known that legionella and other opportunist bacteria can be amplified in the biofilm that forms in DUWLs, the objective for a LRA as opposed to a waterline management scheme is to identify all water systems where Legionella bacteria could potentially grow and to assess the risk of people being exposed to contaminated aerosols as a result. This includes standard domestic hot and cold facilities throughout the practice, including surgeries, decontamination rooms and reception areas.

Manage, monitor and maintain

Regular testing and monitoring of DUWLs to recognise signs of biofilm build-up within dental chair units and the use of products specifically designed to control and prevent biofilm formation means the risk of contamination can be negated and possibly eliminated. By following official guidance as stated in HTM 01-05 in England, WHTM 01-05 in Wales and SDCEP in Scotland, practices can safeguard the well-being of both patients and staff and remain compliant with local regulations.

To find out more about how to take dip slide water samples from DUWLs watch the video here.