The problem of biofilm in dental unit waterlines

Recognising and eliminating the hidden danger of biofilm in your practice.

With the increasing awareness of decontamination and cross infection control procedures, all equipment within a practice that uses water requires constant monitoring and has strict protocols to adhere to. The need to monitor, control and record procedures to meet the requirements of HTM 01-05 means that DCPs in general now have much more involvement in regulatory procedures. It is essential that all staff, not just the infection control lead, have a clear appreciation of matters that might affect water hygiene and safety.

With so much attention on water quality throughout the practice, it is of no surprise that the water actually entering patients’ mouths via dental unit water lines (DUWLs) must also be closely monitored. It is universally accepted in dentistry, and underlined in HTM 01-05, that the water entering a patient’s mouth, by whatever method, must be of an acceptable quality. According to HTM 01-05 section 6.79: “Where monitoring is carried out the microbiological contamination expressed as TVC (total viable count, the number of viable bacteria per millilitre of water [cfu/ml]) should be expected to lie in the range 100 to 200 cfu/ml.”

Current market testing, however, is indicating that levels in some DUWLs are as high as several thousand cfu/ml and the need for an effective solution for both the removal and control of biofilm is clear.

The issue of biofilm

The term ‘biofilm’ refers to a collection of microorganisms that adhere to a surface and are surrounded by a protective and adherent slime, known as the extracellular matrix, which is secreted by the bacteria. Biofilms are particularly prevalent in water containing low concentrations of solids and low levels of nutrients, including streams and rivers, cooling towers, piped water systems and U-bends in domestic sinks. Even the plaque that readily forms on our teeth causing tooth decay and periodontal disease is actually a type of biofilm.

Biofilms form when a few individual bacteria in the planktonic state in water adhere to a solid surface such as the wall of a pipe or tube. The initial attraction to the surface is weak, but subsequent bacteria continue to adhere directly to those already attached. This increases the adhesion and enables more planktonic bacteria to then adhere to the film, building up the level of biofilm and causing water quality levels to fall below acceptable standards.

Biofilm is a hidden problem that is difficult to identify, remove or control because the susceptibility of biofilms to external agents such as detergents and disinfectants is quite small when compared with that of individual planktonic organisms and each biofilm bacterium requires only small amounts of nutrients in order to survive and flourish.

Why does biofilm grow so readily in DUWLs?

DUWLs provide an ideal environment for the growth of bacterial biofilms for a variety of reasons:

• The water in DUWLs has a low flow rate, typically 30ml/min, which favours bacterial adhesion.
• The water flow is intermittent, causing minimal disruption to the growing biofilm, and fresh liquid flowing through the system when using a handpiece or when the system is flushed, brings with it nutrients and planktonic bacteria that encourages the growth of new biofilm. The liquid moving towards the distal end of the system carries bacteria released by the maturing film along with excreted matter.
• The materials used for their tubing are non-toxic, and low toxicity to humans also means low toxicity to bacteria.
• The warm surgery environment provides an ideal temperature range for bacterial growth.

If biofilm is left untreated, the build-up can damage surgery equipment by causing a reduction in water flow and even tube blockage, leading to unit downtime and additional repair costs.

HTM 01-05 compliance

HTM 01-05 guidelines state that the disinfection of DUWLs should be carried out ‘periodically’, but no definition of ‘periodically’ is provided. Other measures to reduce contamination include the emptying and storage of water bottles at the end of the working day and the flushing of water lines “for 2 minutes at the beginning and end of the working day and after breaks. They should also be flushed for 20–30 seconds between patients.” Despite this recommendation, however, the guidance acknowledges that flushing only has a small effect on biofilm build-up.

The guidelines also state that sodium hypochlorite and isopropanol and a number of other agents have been shown to be effective in the removal of biofilm and the reduction of microbacterial contamination. However, these agents should only be used where recommended by manufacturers. If they are used, great care must be taken to ensure DUWLs are thoroughly flushed after disinfection and before being returned to clinical use.

Ensure compliance

The problem of biofilm has been an issue in dentistry for many years. The challenge for the dental team is to control and prevent biofilm, using proven and reliable solutions at regular intervals as stated by the manufacturer, making DUWL decontamination a thing of the past and ensuring compliance with HTM 01-05 and other local guidelines.