Bacterial hazard in dental practice.
How clean is the water in your dental unit?
We talk to Professor Walsh about the current problems with water quality in DUWL and new recommendations from ADA guidelines.
Article by Alpro / Biodegree Pty Ltd, the specialists in clean water solutions and Biofilm Removing Systems.
Professor Laurence Walsh
Q & A
Q. Professor Walsh, what is biofilm?
A. Biofilm is a very well structured layer of different microorganisms such as bacteria and fungi that forms in wet places. Mould or slime in your shower is biofilms, as is dental plaque. We all know how difficult it is to remove these. The tubing inside dental units is a great environment for the growth of complex biofilms.
Q. How does biofilm affect human health?
A. There are several conditions linked to dental unit waterline biofilms. Legionella pneumophila can cause Legionaire’s disease, as well as a milder condition called Pontiac fever, that many people mistake for a viral influenza. The most at-risk patients for these infections have a compromised immune system. They could be elderly, diabetics or smokers. They are more prone to infections from aerosols that are generated by ultrasonic scalers and high speed handpieces. These aerosols transmit the microorganisms from the dental unit waterlines into the air. Both patients and staff breathe this aerosol, and potentially can get infected.
Q. What are the findings from research into water quality in dental unit waterlines?
A. In the last 25 years we have done a range of studies around the topic of dental unit waterline exit water quality. What we have found is very consistent with reports from UK, USA and Europe. All these studies confirm that if there is no flushing and no chemical additives used, the level of bacteria will be very high, and certainly above the 200 CFU/mL threshold limit recommended by the ADA. This is the same threshold used for dialysis water. We also have found variations between the exit water-quality in different brands of dental chairs. On the other hand, we have seen that when continuous chemical treatment of water is taking place, combined with periodic shock treatments and water testing, the levels of bacteria are very low. Unfortunately, only about 1 in 5 of the dental practices would comply with the current threshold level and most surgeries do not even realise that they have a problem.
Q. Is the water coming out of the dental unit the same quality as the water being fed in?
A. No, this is not the case at all. Inside the dental chair are several meters of very narrow dental tubing, where the water flows very slowly and has a tendency to stagnate. If there is no active chemical treatment of the water treatment, the quality of the exit water is never as good as the input. This has led to the statement, “It’s no wonder, when your patients rinse or drink from the dental cup, that you then tell them to spit that water out into the spittoon.”
Q. Why is it important to test the exit water from waterlines on regular basis?
A. With different types of tubing and internal designs of dental chairs, as well as water of different quality being fed in the chair, plus different locations and climates, this all gives a very complex system, so each chair needs to be individually measured. If you actually never test your exit water and simply rely on speculation, you will never know how your water is performing according to the guidelines
Q. Why is it important to do shock treatments?
A. A shock treatment is different from continuous water disinfection. It is designed to detach and break down the biofilm, rather than just suppress the growth of bacteria. Once microorganisms have formed into biofilm, they are much more difficult to kill with externally applied chemical agents. A shock treatment is a specific intervention to detach and break down the biofilm. Those fragments can then be rinsed through, leaving the surface of the tubing clean.
Q. Can domestic bleach solution be considered a suitable shock treatment?
A. I have concerns regarding using household bleach as a shock treatment. There are many problems with the stability of bleach (sodium hypochlorite), for example, it degrades with time, elevated temperature and on exposure to light. Unless you test the level of free available chlorine in domestic bleach, you do not know if it is active at all. It could have been sitting in the warehouse for a long time, and lack potency. When we use a designated product designed specifically to break down waterline biofilm, it has stabilisers added, so it is chemically active, and its efficacy is predictable. Domestic bleach can also interact with the control blocks in some brands of dental chair, and cause severe corrosion. You would never just try and see, without knowing from the manufacturer that it was safe to use.
Q. Once the waterlines are clean, how do maintain a clean system?
A. Once the system and clean and tested, we need to use an antimicrobial chemical to stop bacteria from replicating. There are different products that can do this function. They differ in terms of how quickly they work against bacteria, and how stable they are over a longer period of time. Sometimes the best solution is to combine the best and most effective agents, and put them together to achieve optimal efficacy and stability.
Q. Are we going to see some changes in terms of water testing in the new ADA guidelines?
A. The ADA guidelines are based on evidence. When they are reviewed and updated, we take the latest studies and research into consideration. There has been a lot of recent evidence around the problems from bacteria in waterlines. In ADA publications and webinars over recent years, we have been recommending that dental surgeries start water testing on a regular basis. If they find out that the bacterial levels are higher than those recommended by the ADA, they will have to intervene with a shock treatment, and retest the water again. In the new ADA guidelines, there is more information about this approach of water testing, shock treatment and retesting. This is an important addition to the recommendations in Australia, with a level of detail not found in previous editions.
Q. Are there any issues with dropping white tablets into the bottle attached to the chair without wearing gloves?
A. There are issues. If it is done without gloves, that can contaminate the system with organisms from the skin. As a matter of fact, there is a need for a hygiene protocol around the chair bottle. Rinsing and cleaning them, and leaving them to dry overnight will prevent from the regrowth of microorganisms. It is very important to carefully read and follow the manufacturer’s instructions. Often surgeries use a tablet system, but the staff completely ignores the instructions which indicate the need for a shock treatment and a follow up water test. Some staff do not realise that by putting a tablet into the bottle, they are not following just one of several instruction steps – and because of missing the others they end up with a non-compliant system.
Q. If the dental unit is plumbed into the mains, how does one perform a shock treatment?
A. Some chairs come with internal dosing bottles, while others have external bottles attached to them. If the dental unit does not have a bottle, a retrofit to add one on is normally easy to do. Ask your service technician about it. This very simple addition will allow you to use chemical additives for daily disinfection, as well as chemical agents for periodic shock treatment.
Professor Laurence Walsh AO
Laurie is a clinically active specialist in special needs dentistry who is based at the University of Queensland in Brisbane. His research group members have undertaken extensive research in infection control and clinical microbiology, and Laurie has been teaching these subjects for over 25 years at postgraduate level, including as chief examiner in microbiology for the RACDS for the past 20 years.
He has presented invited courses and lectures on infection control across Australia and internationally. Laurie has written well over 60 articles on infection control in ADA publications and in addition published over 320 journal papers and a further 190 technical reports and literature reviews. He has served on the ADA Infection Control Committee since 1998, including six years as a former chair. He has contributed extensively to the development of infection control guidelines in Australia.