Let the Water Flow Forth: Disinfection of Water Systems
The water systems of a dental clinic can be heavily contaminated. The two ways that this can occur are through an intake of germs through tap water or through a reflux of spray water from transmission instruments when turning off the micromotor. Although this contamination at first seems minor, the hoses and pipes provide germs an ideal habitat for reproduction and growth, creating a serious danger not only for the patients but the dental team as well.
Tap water treated in accordance with the Drinking Water Ordinance still can contain some germs. If the standing water of the dental water systems is at temperatures of 30ºC –40ºC and is consistently being supplied with more contaminated water, this can result in a serious contamination of colony building units (CBU). The development of this contamination is similar to the quick development of a stable biofilm in a suction unit, which works like a magnet to attract and bind to more pathogens and calcium carbonate particles. A biofilm can form within eight hours after a dental unit has been connected to the water system. Particularly at risk are the commonly used plastic pipes as their structure and components encourage the development of a biofilm layer.
The following are parts of the water system in a dental clinic:
- transmission instruments
- multifunction spray
- devices for the removal of plaque (ultrasonic)
- glass filler
Water Contaminated with Bacteria
Legionella, Pseudomonas aeruginosa, and E. coli are just some of the pathogens that have been proven to reproduce and inhabit contaminated water supplies.
Legionella serves as a possible route of transmission for the nosocomial legionellosis. The most favorable conditions for the bacteria are standing water, an ample food supply from the biofilm, and a temperature of 25ºC –45ºC (optimally 35ºC). Drinking water that has been contaminated with legionella is normally not dangerous. A disease can only be caused if the germs are inhaled through contaminated aerosol. This could occur, for example, when filling the mouth rinsing cup.
Pseudomonas aeruginosa is a Gram-negative bacteria that is not very dangerous for patients with normal immune systems. It is, however, problematic in that it has the capacity to create a large amount of biofilm in water systems, which encourages the colonization of other types of pathogens.
Recent water samples have shown that Escherichia coli can be found in high concentrations in many water systems. This pathogen is particularly at home in aqueous environments and can cause diarrhea and urinary tract infections.
Clean Water Means Safety
The Robert Koch Institute recommends that the contamination of water must never exceed 100 CBU/ml (for legionella: 1 CBU/ml). Any higher number of colonies suggests the presence of a biofilm colony, which requires intensive disinfection measures.
A technical contraption that helps prevent contamination are tiny valves that can be built into the micromotors of transmission instruments. Almost all modern dental units possess such valves that prohibit the reflux of bacteria from the oral cavity.
A regular flushing of the unit with water (after every patient, every morning, and during lunch break) raises the water exchange and disposes the water possibly contaminated by a patient. Freely floating bacteria are washed away. Studies have shown that this practice can lower the germ contamination of the water by up to 99 percent. However, the number of germs often rises considerably after this flushing. This is due to a biofilm contamination that has not been eliminated.
Reduction and Control of Germ Contamination
| Frequency | Measure |
|---|---|
| After every patient | Flush the used treatment unit for 20 to 30 seconds. |
| Every morning After the lunch break | Flush all points-of-use (without attached instruments) for 2 minutes. |
| Once daily at the end of the workday or before the weekend (depending on the system). Review instructions of the manufacturer. | Additionally use a disinfectant for long-term disinfection of units, then flush with tap water. |
| At least once every year | Microbiological testing of the water:
|
Disinfection Units in Water Systems
The Drinking Water Ordinance requires the absence of pathogens in concentrations that can have a negative health impact. If this health standard cannot be guaranteed, then disinfection measures must be carried out. There are a variety of disinfection possibilities for water systems. Most modern dental units already have disinfection units installed. This should be a strong consideration when purchasing new units.
An often-utilized procedure is the long-term disinfection. This method involves adding a disinfectant to the water supply for a long period of time, such as overnight, during the weekend, or during vacation. This procedure helps avoid the formation of a biofilm and reduces or destroys an existing biofilm. Older dental units that do not have this capacity can be retrofitted with add-on disinfection units.
The disinfectant that is used for this disinfection of the water system should have the following characteristics:
- must possess as wide a spectrum of effectiveness as possible
- may be neither toxic nor pollutant to the environment
- may not result in damages of the materials (e.g., corrosion or calcification)
- should be able to target both freely floating bacteria as well as those enclosed in biofilm.
Another method is the continual disinfection, which entails the constant adding of a disinfectant to the water supply. These units also have an intensive cleaning program that should be used after longer periods of time. The disinfectant that is used for the continual disinfection of water systems must meet the requirements of the Drinking Water Ordinance. For both the long-term disinfection and the continual disinfection, it is essential to use the disinfectant only according to the manufacturer's instructions.
Another disinfection procedure that does not used chemicals is the UV disinfection. This procedure disinfects the water by subjecting it to ultraviolet light with a wavelength of 254 nanometers. Organic materials in the water are quickly destroyed by the ultraviolet light; pathogens are either destroyed or deactivated. Required for this procedure are flow rate devices that can be retrofitted onto the disinfection unit.
Long-term, Continual, and UV Disinfection Methods
| Advantage | Disadvantage | |
|---|---|---|
| Long-term Disinfection | does not pollute the water with disinfectant while the patient is being treated | additional workload: filling of the disinfection unit |
| Continual Disinfection | no additional workload during the workday | the water is polluted by disinfectant |
| UV Disinfection | disinfectants are not required |
|
Use of Sterile Washing Solutions
When treating immunodeficient patients as well as during comprehensive surgical procedures, the Robert Koch Institute recommends the use of a physiological salt solution. This sterile solution should be inserted into the units through tubes that are either disposable or can be sterilized in an autoclave. The entire system must first be disinfected.
