18 Waterlines, Evacuation & Waste Practice Questions & Answers

1. 1. A newly installed dental unit was left with untreated municipal water standing in its waterlines. Why does biofilm form so readily on the inner surface of that narrow-bore tubing?

   • A.Heat from the handpiece and the unit's motor warms the water enough to multiply bacteria along the whole length of the line.
   • B.Oral fluids retracted into the line after each patient are the material that seeds and feeds the colonies growing on the wall.
   • C.Fungi carried in by the compressed air that mixes with the water at the syringe settle out and colonize the wall of the tubing.
   • D.Narrow tubing and long stagnant periods let waterborne bacteria settle on the wall and grow in a protective slime layer.✓ Answer

   Waterline tubing has a very small internal diameter and a high surface-to-volume ratio, and water sits still in it for most of the day. Free-floating water bacteria attach to the wall and secrete a polysaccharide glycocalyx that shields them, so the population multiplies steadily and sheds organisms into the water delivered to the patient.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), Dental Unit Waterlines, Biofilm, and Water QualityReport a problem with this question

2. 2. An assistant flushes every waterline for two minutes at the start of the clinic day and says this is how the office keeps biofilm under control. Which statement is correct?

   • A.Filling a self-contained reservoir with distilled water ends the biofilm problem, so the lines then need no chemical treatment.
   • B.Flushing at the start of the day strips biofilm from the tubing wall, so a chemical product is added only after a failed test.
   • C.Purging the lines with air at the end of each day keeps biofilm from forming, so chemical treatment is used only for surgery.
   • D.Biofilm is controlled by treating the lines with a chemical germicide on the manufacturer's schedule; flushing does not remove it.✓ Answer

   Flushing moves water through the lumen but does not detach the glycocalyx-protected colonies bonded to the tubing wall, so it cannot bring the delivered water into compliance on its own. Removing and inactivating biofilm requires a chemical germicide protocol, used with the equipment and on the schedule the dental unit or product manufacturer specifies.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), recommendations on dental unit water quality; CDC Summary of Infection Prevention Practices in Dental Settings (2016), Dental Unit Water QualityReport a problem with this question

3. 3. Between patients, water and air are discharged for a short period from the handpieces, the ultrasonic scaler and the air-water syringe. What does this discharge accomplish?

   • A.It sterilizes the water-bearing pathway, so the same lines may be used to irrigate a surgical site later in the day.
   • B.It flushes out patient material that may have been drawn into the handpiece, air line or waterline during treatment.✓ Answer
   • C.It strips the biofilm that has built up on the inner wall of the tubing since the previous patient was treated.
   • D.It confirms the antiretraction valve is working, since fluid would otherwise be seen moving back up the clear line.

   The purpose of the between-patient discharge is mechanical: it expels patient material that may have entered the turbine, air line or waterline during the procedure, so it is not carried forward to the next patient. It is a separate duty from biofilm control, which depends on chemical treatment of the lines.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), recommendation to discharge water and air from devices that enter the patient's mouth after each patientReport a problem with this question

4. 4. An office is setting a schedule for testing the water its dental units deliver during routine, nonsurgical treatment. What should that schedule be based on?

   • A.Sampling only after a patient reports an infection, since lines under chemical treatment need no set monitoring.
   • B.Quarterly cultures for Legionella and Pseudomonas, since those are the organisms that line treatment is aimed at.
   • C.The monitoring recommendations of the dental unit manufacturer and of the maker of the water treatment product.✓ Answer
   • D.Monthly sampling until two consecutive acceptable results are obtained, after which quarterly sampling is enough.

   No national guideline sets a universal testing interval, because the right frequency depends on the treatment chemistry, the equipment and the water source. The defensible answer is to follow the monitoring recommendations of the dental unit manufacturer or of the maker of the waterline treatment product, using an in-office test kit or a commercial water-testing laboratory.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), recommendation to follow the manufacturer's water-quality monitoring instructionsReport a problem with this question

5. 5. The local water utility has issued a boil-water advisory that is in effect this morning. How should the office proceed with patient care?

   • A.Boil tap water in the sterilization area, let it cool, and use it to fill the unit reservoirs for the day's treatment.
   • B.Deliver treatment and rinse water from an alternative source, and use an alcohol-based hand rub for hand hygiene.✓ Answer
   • C.Continue using public water for patient rinsing and for handwashing, since the risk applies only to water that is drunk.
   • D.Flush every line and faucet for several minutes before the first patient, after which public water may be used.

   While an advisory is in force, water from the public system must not reach the patient through the dental unit or any equipment connected to it, and must not be used for treatment, patient rinsing or handwashing, because the utility cannot vouch for its microbiologic quality. Hand hygiene is performed with an alcohol-based rub, or with bottled water and soap when hands are visibly soiled.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), boil-water advisory recommendationsReport a problem with this question

6. 6. The utility has just cancelled the boil-water advisory. What should the office do before treating patients again?

   • A.Submit a water sample for testing and take no other step, letting the result decide whether any flushing is needed.
   • B.Replace the waterline tubing and the reservoir bottles, since contamination taken on during the advisory cannot be removed.
   • C.Flush the waterlines and faucets as the utility directs, then disinfect the lines the way the unit manufacturer specifies.✓ Answer
   • D.Resume normal use at once, since the utility would not cancel the advisory unless building plumbing were also clear.

   Cancellation clears the public supply, not the plumbing inside the building or the dental unit, where contaminated water has been sitting. The published sequence is to flush waterlines and faucets according to the utility's instructions and then disinfect the dental waterlines as the unit manufacturer recommends.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), actions after a boil-water advisory is cancelledReport a problem with this question

7. 7. At the end of the clinic day the evacuation lines are to be cleaned. Which practice follows accepted procedure?

   • A.Draw a foaming cleaner through both lines so the foam expands and reaches the tubing surface above the fluid level.
   • B.Draw a nonfoaming, nonresidue-producing evacuation system cleaner through both lines as the manufacturer directs.✓ Answer
   • C.Draw clear water through both lines, saving the evacuation cleaner for days when the suction has noticeably weakened.
   • D.Draw a diluted chlorine bleach solution through both lines, since contaminated tubing needs a tuberculocidal product.

   Evacuation lines are maintained with a cleaner formulated for the system and run on the manufacturer's schedule, typically at the end of each clinic day. The product must be nonfoaming and nonresidue-producing, because foam is drawn into and coats the pump, and residue narrows the lumen and reduces suction over time.

   Source: Miller, Infection Control and Management of Hazardous Materials for the Dental Team; evacuation system manufacturers' instructions for useReport a problem with this question

8. 8. An office that places and removes amalgam has an amalgam separator on its vacuum system. Why must chlorine bleach and other oxidizing or acidic cleaners be kept out of those lines?

   • A.They dissolve mercury out of the amalgam particles in the wastewater and can damage the separator meant to capture it.✓ Answer
   • B.They are inactivated by the blood and saliva already in the lines, so the tubing is left essentially untreated.
   • C.They leave a chlorine residue in the tubing that can later reach a patient's mouth through saliva ejector backflow.
   • D.They corrode the metal of the high-volume evacuation tips and shorten the service life of the tips and their handles.

   Oxidizing and strongly acidic or alkaline products chemically mobilize mercury from amalgam particles suspended in the vacuum wastewater, converting captured solids into dissolved mercury that passes through to the sewer, and they can corrode the separator itself. Best management practice is to use only line cleaners the separator manufacturer accepts.

   Source: EPA Dental Office Point Source Category, 40 CFR Part 441, best management practices for amalgam process wastewaterReport a problem with this question

9. 9. A patient closes their lips tightly around the saliva ejector tip while the high-volume evacuator is also running. What is the concern with this?

   • A.The seal has been the documented source of hepatitis transmission in offices and calls for an exposure report.
   • B.The seal drops the pressure in the mouth below the pressure in the evacuator, so fluid in the tubing can flow back.✓ Answer
   • C.The seal pulls the mucosa against the tip and produces a hematoma where the tip rests on the soft tissue.
   • D.The seal blocks the vent opening of the tip, so aerosol from the handpiece is no longer captured where it forms.

   Backflow through a low-volume saliva ejector happens whenever pressure in the patient's mouth falls below pressure in the evacuator line, and a lip seal creates exactly that partial vacuum; simultaneous high-volume evacuation and tubing held above the mouth make it more likely. No adverse health effects have actually been reported from this, but staff must know it can occur and must not ask patients to close their lips on the tip.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), recommendation on saliva ejectors and backflowReport a problem with this question

10. 10. The chairside solids collector on an operatory's evacuation line is being changed at the end of the day. Which practice is correct?

    • A.Wear gloves, mask, eyewear and gown, and treat what is trapped in the collector as contaminated material as it is removed.✓ Answer
    • B.Wait to change the collector until suction weakens noticeably, since a partly loaded collector still filters the line.
    • C.Wear gloves only, since the collector is enclosed, and rinse what it holds down the operatory sink with running water.
    • D.Soak the loaded collector in a chlorine solution before reinstalling it so the trapped debris is disinfected in place.

    Collector contents are saturated with blood, saliva and debris drawn from patients' mouths, so the person servicing the trap wears full personal protective equipment and handles the contents as contaminated. The collector is changed on the manufacturer's schedule or when full, and the contents are never rinsed into a sink, both because of the bioburden and because trapped amalgam must go to a recycler.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), personal protective equipment; EPA 40 CFR Part 441 best management practices for chairside trapsReport a problem with this question

11. 11. An impression has just been removed from a patient's mouth and will be carried to the in-office laboratory. What is the correct handling?

    • A.Rinse it under running water to remove blood and saliva, disinfect it with an intermediate-level product, then rinse again.✓ Answer
    • B.Place it straight into the disinfectant without rinsing, so blood and saliva are not spread onto the sink and counter.
    • C.Wrap it in a moistened towel and send it on, since the laboratory decontaminates every case before a technician handles it.
    • D.Pour the cast right away and disinfect the set cast instead, since gypsum sets before oral microorganisms transfer to it.

    The sequence is clean, disinfect, then rinse, carried out as soon as possible after the impression leaves the mouth and before blood or bioburden dries on it. Rinsing first removes the organic material that would otherwise bind and neutralize the disinfectant, and the final rinse removes chemical residue before the case is poured or handled.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), Dental Laboratory recommendations on impressions and prosthodontic materialsReport a problem with this question

12. 12. Which product must be used to disinfect impressions, bite registrations and removable appliances before they are handled in the laboratory?

    • A.A high-level disinfectant and chemical sterilant used for heat-sensitive semicritical items.
    • B.An EPA-registered hospital disinfectant carrying only an HIV and HBV, low-level claim.
    • C.An alcohol-based skin antiseptic of the type supplied at chairside for routine hand hygiene.
    • D.An EPA-registered hospital disinfectant carrying a tuberculocidal, intermediate-level claim.✓ Answer

    Items that have been in the patient's mouth and will be handled by another person must be processed with an EPA-registered hospital disinfectant whose label carries a tuberculocidal claim, which identifies it as intermediate level. A low-level product does not cover the required range, and a high-level sterilant is neither required nor compatible with most impression materials.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), Dental Laboratory recommendations; EPA product registration categoriesReport a problem with this question

13. 13. Before immersing an impression in a disinfectant solution, what determines whether that solution and that contact time may be used on that impression?

    • A.Information from the impression material's manufacturer on how the material holds up in that solution for that time.✓ Answer
    • B.The longest immersion time printed on the disinfectant label, since a longer contact time is always the safer choice.
    • C.An office policy of spraying and wrapping every case, since spray disinfection cannot alter an impression's dimensions.
    • D.Whether the impression can still be poured afterward, since distortion appears only once the material begins to dry.

    Impression materials differ in how they tolerate immersion: some hydrophilic materials absorb solution and distort, while others are stable, so dimensional accuracy and the disinfection outcome both depend on matching the product and time to the material. The guidance is to consult the material manufacturer about stability in the chosen disinfectant.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), recommendation to consult manufacturers on the stability of specific materials during disinfectionReport a problem with this question

14. 14. An office sends cases to an off-site laboratory and receives finished cases back from it. What does infection control require for those cases?

    • A.The disinfection solution and contact time are recorded for cases leaving the office and again for cases coming back.✓ Answer
    • B.Returning cases are handled without personal protective equipment, since the laboratory disinfects each case before shipping.
    • C.The disinfection is recorded for outgoing cases only, since the case becomes the laboratory's responsibility on pickup.
    • D.A signed standing agreement with the laboratory is kept on file, which takes the place of records on the individual cases.

    Neither party can tell by looking whether a case has been decontaminated, so the disinfection technique used, meaning the solution and the duration, is documented when the case is sent and again when it is returned. Without that communication the receiving side must clean and disinfect the case itself before handling it, and personal protective equipment is worn until it has been decontaminated.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), Dental Laboratory recommendations on documenting disinfection of cases sent off site and returnedReport a problem with this question

15. 15. Under the OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030, what makes a contaminated nonsharp item regulated waste rather than general waste?

    • A.It carries saliva because it entered the patient's mouth during treatment, whether or not blood is visible on it.
    • B.It was in the treatment room while an aerosol-generating procedure was performed and has settled spatter on its surface.
    • C.It was touched by the clinician's gloves after those gloves had contacted the patient's mucosa during the procedure.
    • D.It is soaked or caked with blood or other infectious material and would release that material if compressed or handled.✓ Answer

    The standard's definition of regulated waste turns on release, not on contact: liquid or semi-liquid blood or other potentially infectious material, items that would release such material in a liquid or semi-liquid state if compressed, and items caked with dried blood that can release it during handling. That is why saturated gauze is regulated while gloves, masks, gowns and lightly soiled gauze are general waste.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030(b), definition of Regulated WasteReport a problem with this question

16. 16. A used scalpel blade, a segment of orthodontic wire and a broken bur must be discarded at the end of an appointment. Which practice is correct?

    • A.Put them in the operatory container and press the contents down when it fills so its capacity is fully used.
    • B.Put them in a closable, puncture-resistant, leakproof container that is labeled or color-coded and kept at the point of use.✓ Answer
    • C.Put them in a labeled biohazard bag, which is adequate here because none of these items holds liquid blood.
    • D.Carry them to the sterilization area and put them in the container kept there, so no sharps container sits chairside.

    All three items are contaminated sharps, so the standard requires a container that is closable, puncture-resistant and leakproof on the sides and bottom, and labeled or color-coded. Keeping it at the point of use shortens the distance a sharp is carried, and it is closed before removal and replaced at the fill line rather than pressed down or overfilled.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030(d)(4)(iii)(A), containers for contaminated sharpsReport a problem with this question

17. 17. A dental hygiene program has asked the office for extracted teeth for student use, and one of the available teeth has a large amalgam restoration. How should that tooth be handled?

    • A.Immerse it in a chemical sterilant for half an hour, which is accepted in place of heat for teeth that contain amalgam.
    • B.Autoclave it with the other teeth, since a steam cycle handles restorative materials and the mercury without difficulty.
    • C.Send teeth without amalgam instead, since a tooth with amalgam cannot be heat-sterilized because of the mercury vapor.✓ Answer
    • D.Remove the amalgam with a handpiece at the chairside, then autoclave the tooth along with the rest of the teeth being sent.

    Heating amalgam vaporizes mercury, so a tooth with an amalgam restoration must not be put through a heat sterilizer, and teeth free of amalgam are preferred for educational use. Teeth sent to an institution are cleaned, kept hydrated and transported in a leakproof container labeled with the biohazard symbol, and standard precautions still apply to students handling them.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), Handling of Extracted TeethReport a problem with this question

18. 18. An office is writing the waste management portion of its infection control program. Which statement describes the regulatory framework correctly?

    • A.The FDA decides which dental wastes count as regulated and how long an office may hold them before they are collected.
    • B.One federal rule sets both the handling and the final disposal requirements, and it applies the same way everywhere.
    • C.OSHA governs how contaminated waste is contained, labeled and handled by staff, while state and local rules govern disposal.✓ Answer
    • D.The EPA sets the containment and labeling rules for dental regulated waste and licenses the offices that generate it.

    The Bloodborne Pathogens Standard is a workplace rule: it tells the employer how contaminated waste must be contained, labeled or color-coded, and handled by employees, and it requires training for the staff who do that work. Final disposal is not federally uniform, so the program must also follow the state and local requirements that apply to the practice.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030(d)(4)(iii); CDC Guidelines for Infection Control in Dental Health-Care Settings — 2003, MMWR 52(RR-17), medical waste management programReport a problem with this question

Practice questions only — not real exam items, and not affiliated with or endorsed by the Dental Assisting National Board. Questions are written to the domains published in DANB's current RHS and ICE exam outlines, and cover digital radiography only, matching DANB's statement that film-based concepts are no longer tested. This bank does not cover the chairside assisting or dental anatomy component exams. What a dental assistant is legally allowed to do — including who may expose radiographs and what training a state requires first — is set by each state's dental board and is deliberately out of scope here. Exam format, eligibility, and scoring are set by DANB and change from time to time; confirm the current requirements with DANB and your state board before you register. Official DANB exam outlines →