Dental Unit Waterlines and Biofilm Risk

Study Notes

DUWLS contain more bacteria than faucets.
Stagnant water in the lines encourages biofilm growth.
Biofilm is a community of bacterial cells and other microbes.
Biofilm adheres to surfaces and forms a protective slime layer.
Biofilm forms where moisture meets suitable solid surfaces.
Biofilm includes bacteria, fungi, algae, and protozoa.
Viruses do not multiply in biofilm.
Exopolysaccharide slime (EPS) protects biofilm cells.
Water channels within biofilm carry nutrients.
Planktonic organisms can break off from biofilm and contaminate coolant and irrigating solutions.
DUWLS provide suitable conditions for biofilm formation.
Low water pressure, low flow rates, and frequent stagnation promote biofilm.
Output water often has high bacterial contamination despite sterile source water.
Dental personnel can inhale contaminated aerosols from contaminated DUWLS.
Legionellosis (a serious type of pneumonia) is a potential health risk from contaminated water.
Public water supply is the primary source of microorganisms in DUWLS,
Saliva can enter DUWLs during treatment: "suck-back."
Public water often has a low Colony Forming Unit (CFU) count
But CFU counts increase rapidly in the DUWLs.
Biofilm development has stages: initial attachment, irreversible attachment, maturation I & II, dispersion.
Planktonic bacteria adhere to the surface, then form biofilm.

Biofilm regrowth in DUWLS happens within a week.
DUWLs need regular treatment to eliminate biofilm.
Chemical products should be effective, compatible with DUWL components, non-toxic to patients/DHCP, and environmentally friendly.
Introducing chemical agents can be intermittent or continuous.
Intermittent treatment involves placing a chemical agent (in a reservoir) and flushing the water lines.
Chemical should remain in contact with tubing for designated time.
Afterward, the chemical should be thoroughly flushed with water.
Treatment duration depends on the disinfectant type.
If the unit is connected to municipal water, turn off the connection before treatment.
Continuous treatment: mixing the chemical agent with the dental treatment water, or adding agent to a reservoir inside the dental unit for continuous release.

Flushing for 2 minutes in the morning and 20-30 seconds after each patient is a norm.
Longer flushes recommended after weekends.
Flushing at the beginning of the day should be done without connected handpieces.

Bacterial counts of non-pathogenic bacteria in water should be as low as possible without exceeding 500 CFU/mL.
Monitor water quality regularly
Follow manufacturer recommendations for sampling DUWLs.
Steps followed if no recommendations are given; clean air-water/syringe, instrument hose, patient cup filler, waterline, and spittoon rinse waterlines of the dental unit for 2 minutes before collecting samples.
Collect 50 mL of water from each outlet and from independent water reservoir bottles.
Store samples between 2 and 8°C, and return to the microbiology laboratory within 24 hours of collection.
Label samples with details including the sampled waterline, sender's reference, sampler, date, and time of sampling.