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PASSIVE RETRACTION

Passive retraction is when water flow in air-water dental syringes becomes bi-directional while a handpiece is running – that is, a small amount of fluid flowing out of dental units is drawn back, or aspirated, upstream into the waterlines/unit, carrying with it oral fluids and microscopic, microbial-laden aerosols generated while cutting and drilling.

This debris often contains blood and saliva-borne pathogens which is actively drawn back into waterlines. These pathogens collect in waterlines, grow and propagate to form biofilm.

When microbial particles from biofilm growth are sloughed off into the water stream, they are dispensed into an unsuspecting patient’s mouth. Dental workers are also exposed with every patient treatment.

LAMINAR FLOW

Passive retraction can be explained by Laminar Flow – when the fluid velocity adjacent to the wall is theoretically zero and increases to a maximum velocity in the center.

This sets in motion a “turbulent boundary layer” in which fluid revolves in concentric circles (or vortices similar to spinning smoke rings). These constantly form and dissipate due to high velocity flow through the center of the pipe and correspondingly low pressure on the outside flow, creating pressure gradients opposite to the flow direction.

Under the influence of pressure gradients opposite to the direction of motion, the flow within the boundary layer tends to reverse and flow in an upstream direction.

The Risk of BioFilm?

For decades, researchers have known that water delivered by dental units often contains high levels of bacteria and other micro-organisms.

Biofilm in water systems was identified as a serious problem in the 1990s, when media reports on dental unit waterline contamination spurred patients to ask, “Is visiting my dentist safe?”

For the most part, dentistry is perceived as safe. But how safe is safe — especially when more patients are immune-suppressed and exposure to new highly adaptive, life-threatening pathogens increases daily?

What is the risk to patients, doctors and their staff? The primary benefit of the AquaSept System is that it allows for the microbial separation of Patient A from Patient B. This applies to surgical and non-surgical procedures, using either sterile or potable water.

AquaSept™ is the only system that provides complete sterilization of equipment and waterlines used in dental procedures. AquaSept is the ultimate protection against microbial infection between patients. By sterilizing the tubing, too, AquaSept is the best methodology to manage risk of infection and preventing waterline contamination from spreading.

Time Bomb:

Why Biofilm is Becoming More Dangerous

Back On The Radar

Serious public health outbreaks in dentistry and concerns over dental unit waterlines (DUWLs) as possible sources of infection continue to rise. In “Dental Unit Waterlines: Check Your Dental Unit Water IQ,” published in Access (1997), by the American
Dental Hygienists’ Association, the authors noted:

  • Greater awareness by oral healthcare workers and clients regarding infection control issues in dentistry.

  • Increased numbers of scientific and public media reports of relatively high levels of pathogenic micro-organisms in dental treatment water has increased.

  • Case reports have been published associating illness with dental water contamination.

In fact, lethal drug-resistant strains are spreading in this country and around the world.

Consider this: the number of bacteria in water from dental handpieces and air-water syringes can be hundreds or thousands of times beyond the 500 colony forming units (CFUs) per milliliter of heterotrophic bacteria permitted in municipal water by the Environmental Protection Agency. A CFU is a colony of bacterial cells that will form on an agar growth plate when cultured. As these clump together, a biofilm is formed.

Current Infection Controls in Dentistry

The U.S. Food and Drug Administration (FDA) has given marketing clearance for a number of products for infection control, including chemical agents, independent water reservoirs, automated metering devices and microfiltration technology. Sterile water delivery systems, which employ either heat sterilizable or sterile disposable components, also are available.

The dental industry has advanced tools to minimize CFU levels in dental water. Scientific literature supports the need for improvement in dental unit water quality, which comes about only through intervention.

Anti-retraction Valves
While anti-retraction valves are used on most older dental units, they only work when the unit is shut off. Because of passive retraction, contamination will occur while water is flowing.

Filtering
Microfilters can reduce the number of microbes in output water, however, retracted patient-borne bacterial microbes will accumulate on the patient side of a filter.

Viruses are smaller than bacterial microbes and can pass through filtration. They are not identified in standard tests for potable water, and serious viruses such as HIV may be present in blood and saliva exposed to coolants.

Flushing
The daily flushing of waterlines will reduce, but cannot eliminate, microbial levels in the dental unit water supply. Concentrations will fall after two minutes of flushing, but are quickly restored to pre-flush levels 30 minutes later. Flushing must be done before
every patient.

Chemical Germicides
A number of chemical germicides are in use and are effective in reducing CFU/mL levels below guidelines set by CDC and the ADA. However, they may not necessarily remove all biofilm from tubing surfaces. And there is question as to whether the AIDS virus is sufficiently controlled by disinfecting agents.

Additionally, chemical germicides must be safe and leave only safe levels of residues. Some may have corrosive effects on dental restorative materials, and materials used in construction of dental water delivery systems. They may also produce potentially hazardous disinfectant byproducts*. Also, patients may experience chemical after-taste from lines that have not been adequately rinsed.

*(Organization for Safety and Asepsis Procedures: Statements on the Responsibilities of Manufacturers of Devices and Chemical Agents for Improving the Quality of Dental Treatment Water).

Autoclaving/Steam Sterilization Autoclaving – sterilizing under high pressure and steam at high temperatures for a minimum of 10 minutes — is the only way to assure 100% sterilization of dental equipment.