Water from dental unit water delivery systems may pose a risk particularly to immune compromised patients. Contaminated water caused through biofilm within the dental water system is a risk that can be avoided.
Dental unit water lines are an ideal environment for bactericidal bio-film
formation due to the high surface to volume ratio utalised within the dental
water delivery system, this regardless of water continuously moving through
the working dental unit a now all too common concern regarding the quality of water at the point of delivery.
Micro-organisms proliferate on surfaces exposed to moisture they form bio-films that are resistant to most disinfectants and not always detected. This is a microbial community contained in a matrix of polymers and water forming a layer anything from micrometers to several millimeters thick that adheres to the internal surfaces of water lines.
Although the first scientific study devoted to biofilms dates from the 1940s, it was not until the 1970s that there abundance in natural environments was known. Biofilms form on all submerged surfaces be it in soft water or sea water or any surface frequently moistened from floors to teeth and of course water pipes.
In certain environments the presence of biofilms is not harmful as the polymers of the matrix can trap organic molecules or minerals. These substances can be broken down by the bacteria, thus contributing to the purification of natural water environments or to that of used water in treatment sites. In the medical environment however biofilms can contribute to a real danger through sheltering harmful bacteria including respiratory pathogens Legionella, Pneumophila and Mycobacterium.
Rinsing of the dental water lines and/or adding disinfectant additives to the reservoir is not necessarily the answer as one of the prime factors which explains the resistance of biofilms to disinfection is their powerful adhesion to surfaces, this results from a complex process, physical forces determine the attachment of the molecules of the bacteria to the surface.
This contact stimulates the secretion of glucidic organic molecules which adhere to the surface while remaining connected to the bacterial walls. The biofilm forms, multiplication then causes the film to thicken, consequently the matrix anchors biofilms to the surface.
The cells of the superficial layer are aerated and fed on each contact with water, the products of their metabolism result in a continual shredding into the water supply. Disinfection is made extremely difficult as the matrix anchoring the biofilms limit the penetration of disinfectants.
Contamination of the DUWL is reversible, particularly in the early stages as the adhesion to the surface is not strong. However, if untreated the inner surface of the water system will become over colonised and adding a disinfectant and/or flushing alone may only have limited effect on reducing the bactericidal count within water supplied at the point of delivery.
There are several products targeted specifically for the disinfection of dental water delivery systems however careful consideration should be given to using a product with specific stated ability to thoroughly clean and remove
biofilms.
Cleaning of the system must be carried out routinely and in accordance with the specific product manufactures recommendations, routine weekly or even daily cleaning may be the requirement together with regular purging of the water lines following each patient treated.