22 Infection Control Practice Questions & Answers

1. 1. Contaminated instruments used on one patient are cleaned, packaged and heat-sterilized before they are used on anyone else. Which link in the chain of infection is broken by this step?

   • A.The mode of transmission (indirect contact)✓ Answer
   • B.The portal of entry
   • C.The reservoir
   • D.The susceptible host

   A contaminated instrument is a vehicle that carries an infectious agent from one person to the next, which is indirect contact transmission. Heat sterilization destroys the organisms on that vehicle, so the agent can no longer travel from the reservoir to a new host, while the host's susceptibility, the portals and the reservoir itself are unchanged.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Infection-Control Principles: chain of infection and modes of transmission in dentistryReport a problem with this question

2. 2. A patient's medical history is reviewed and updated at the start of the appointment and lists no illnesses and no medications, and the assistant asks whether lighter protection may be used for this visit. What is the correct practice?

   • A.Reduce personal protective equipment to gloves only, since the history is negative
   • B.Use full precautions only for patients who disclose an infectious disease
   • C.Follow the same Standard Precautions that are used for every patient✓ Answer
   • D.Postpone treatment until the patient is tested for bloodborne pathogens

   Standard Precautions apply to blood, to all body fluids, secretions and excretions except sweat, to non-intact skin and to mucous membranes, regardless of the patient's known or suspected diagnosis. A health history cannot identify patients who are undiagnosed, asymptomatic or unwilling to disclose an infection, so in dentistry saliva is always treated as potentially infectious and the same precautions are used for every patient.

   Source: CDC Summary of Infection Prevention Practices in Dental Settings, Standard Precautions; OSHA Bloodborne Pathogens Standard 29 CFR 1910.1030(d)(1)Report a problem with this question

3. 3. After removing her gloves at the end of a procedure, an assistant sees that blood leaked through a small tear and her hands are visibly contaminated. What must she do?

   • A.Wipe the hands with a surface disinfectant wipe and re-glove
   • B.Apply an alcohol-based hand rub containing 60-95% alcohol
   • C.Put on new gloves immediately, since gloves were worn during the procedure
   • D.Wash the hands with soap and running water✓ Answer

   Alcohol-based hand rubs do not remove organic material; blood and other soil block the alcohol from reaching microorganisms, so they are only appropriate when hands are not visibly soiled. Soap and running water are required whenever hands are visibly soiled or contaminated with blood or other potentially infectious material, and after using the restroom, and surface disinfectants are never used on skin.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Hand Hygiene: soap and water required when hands are visibly soiled or contaminated with blood/OPIMReport a problem with this question

4. 4. Before assisting with an aerosol-generating restorative procedure, in what order should the assistant put on personal protective equipment?

   • A.Gloves, gown, mask, eye protection
   • B.Gown, mask, eye protection, gloves✓ Answer
   • C.Eye protection, gloves, gown, mask
   • D.Mask, gloves, gown, eye protection

   PPE is donned gown first, then mask or respirator, then eye protection, and gloves last, so that gloves are the outermost and cleanest-handled item and can be pulled over the gown cuffs without contaminating anything already in place. When PPE is removed, the reverse principle applies: the most contaminated item, the gloves, comes off first and the mask or respirator comes off last, followed immediately by hand hygiene.

   Source: CDC Summary of Infection Prevention Practices in Dental Settings, Personal Protective Equipment (sequence for donning and removing PPE)Report a problem with this question

5. 5. At the end of the day an assistant asks how the operatory floor, walls and sink, which are housekeeping surfaces, should be handled. Which practice is correct?

   • A.Cover them with impervious barriers that are changed between patients
   • B.Clean them with detergent and water on a routine schedule✓ Answer
   • C.Spray them with an intermediate-level disinfectant after every patient
   • D.Disinfect them with an FDA-cleared high-level disinfectant

   Housekeeping surfaces are not touched during patient care and carry little risk of disease transmission, so routine cleaning with detergent and water is sufficient; a disinfectant is added only when the surface is visibly soiled or after a spill of blood or other potentially infectious material. High-level disinfectants are regulated for heat-sensitive semicritical devices and must never be used on environmental surfaces, and barriers are reserved for hard-to-clean clinical contact surfaces.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Environmental Infection Control: housekeeping surfacesReport a problem with this question

6. 6. A curing light handle was not barrier-protected and is now visibly spattered with blood. What is the correct way to process this clinical contact surface before the next patient?

   • A.Clean the surface first, then disinfect with an EPA-registered hospital disinfectant that carries a tuberculocidal claim✓ Answer
   • B.Wipe it once with 70% isopropyl alcohol
   • C.Wipe it with an FDA-cleared glutaraldehyde solution
   • D.Apply a low-level disinfectant with an HIV/HBV claim without cleaning first

   Organic material physically shields microorganisms and inactivates many chemistries, so cleaning must always precede disinfection. When a clinical contact surface is visibly contaminated with blood, an intermediate-level product, meaning an EPA-registered hospital disinfectant with a tuberculocidal claim, is required; plain alcohol evaporates too quickly, cleans poorly and fixes protein, and FDA-cleared glutaraldehyde is a liquid sterilant/high-level disinfectant that is never used on environmental surfaces.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Environmental Infection Control: clinical contact surfaces and use of EPA-registered hospital disinfectantsReport a problem with this question

7. 7. The label of the operatory surface disinfectant states a contact time of several minutes. Which practice ensures the product actually achieves the kill claimed on that label?

   • A.Wipe the surface dry immediately after application to prevent residue
   • B.Apply the product once, because a single wipe kills microorganisms on contact
   • C.Keep the surface visibly wet for the entire contact time stated on the label✓ Answer
   • D.Allow 30 seconds, which is adequate for any hospital disinfectant

   A disinfectant kills microorganisms only while it is in wet contact with the surface, so the surface must remain visibly wet for the full contact time on the label; if it dries early the product must be reapplied. The label directions are the legally enforceable instructions for an EPA-registered disinfectant, and contact times differ by product, so no single fixed time can be assumed.

   Source: EPA-registered hospital disinfectant label directions (contact/wet time); CDC Guidelines for Infection Control in Dental Health-Care Settings, Environmental Infection ControlReport a problem with this question

8. 8. A patient has just been dismissed and the assistant, still gloved, begins turning over the operatory, where the light handle, chair controls and air-water syringe are covered with plastic barriers. Which sequence is correct?

   • A.Place fresh barriers on top of the used ones to save time
   • B.Spray disinfectant over the barriers before removing them
   • C.While still gloved, remove and discard the barriers, then remove the gloves and perform hand hygiene before placing fresh barriers with clean hands✓ Answer
   • D.Remove the gloves first, then pull off the barriers with bare hands

   Used barriers are contaminated, so they are removed while the hands are still protected, which keeps the contamination off bare hands and off the clean surface underneath. Gloves are then removed and hand hygiene is performed so that fresh barriers are placed with clean hands; the surface beneath is cleaned and disinfected if a barrier was compromised and at the end of the day.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Environmental Infection Control: surface barriersReport a problem with this question

9. 9. Water delivered from the dental unit to handpieces and air-water syringes during routine, nonsurgical dental treatment must meet which microbiologic standard?

   • A.Untreated municipal tap water is acceptable with no treatment or monitoring
   • B.It must contain no more than 100 CFU/mL of heterotrophic bacteria
   • C.It must contain no more than 500 CFU/mL of heterotrophic bacteria✓ Answer
   • D.It must be sterile, as verified by a biological indicator

   Narrow-bore waterline tubing and low flow rates let biofilm form on the tubing walls and shed bacteria into the water, so untreated lines routinely exceed safe counts. Water used for nonsurgical dental procedures must meet the drinking-water standard of no more than 500 CFU/mL of heterotrophic bacteria, achieved by treating and monitoring the lines according to the device or product manufacturer's instructions for use.

   Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Dental Unit Waterlines, Biofilm, and Water Quality (EPA drinking water standard of <=500 CFU/mL heterotrophic bacteria)Report a problem with this question

10. 10. During a surgical extraction in which bone will be removed and the surgical flap is reflected, what must be used to irrigate the surgical site?

    • A.An antimicrobial mouthrinse delivered through the air-water syringe
    • B.Sterile water drawn into a clean but non-sterile syringe
    • C.Water from a treated dental unit waterline that was flushed for two minutes
    • D.Sterile saline or sterile water delivered through a sterile delivery device✓ Answer

    Surgical procedures that cut bone or expose normally sterile tissue bypass the body's protective barriers, so the irrigant itself and everything it passes through must be sterile. A treated dental unit waterline meets only the drinking-water standard for nonsurgical care and can still harbor biofilm organisms, and drawing sterile solution into a non-sterile syringe contaminates it before it reaches the wound.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Dental Unit Waterlines: sterile irrigating solutions and sterile delivery devices for oral surgical proceduresReport a problem with this question

11. 11. At the end of an appointment, which item from the treatment room must be discarded as regulated (biohazardous) waste rather than as general waste?

    • A.Gauze saturated with blood that would release blood if compressed✓ Answer
    • B.A disposable saliva ejector
    • C.Used examination gloves
    • D.A patient bib lightly spotted with saliva

    Regulated waste is limited to liquid or semi-liquid blood or other potentially infectious material, items so caked or soaked with blood that they would release it if compressed, contaminated sharps, and pathologic and microbiologic waste. The great majority of dental waste, including gloves, bibs and lightly soiled gauze, does not meet that definition and is handled as general waste under applicable disposal rules.

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

12. 12. While changing the chairside solids collector, the assistant finds amalgam particles among the trapped debris. How should those contents be handled?

    • A.Autoclave the contents and then place them in the regular trash
    • B.Rinse the contents down the sink drain
    • C.Place the contents in a labeled, closed container and recycle them through a licensed amalgam waste handler✓ Answer
    • D.Place the contents in a red biohazard bag for infectious waste pickup

    Amalgam contains mercury, so its waste is a hazardous chemical waste rather than infectious waste; heating it in an autoclave or incinerator volatilizes mercury vapor and creates an inhalation hazard. Amalgam-containing trap contents and scrap are stored in a labeled, closed container and recycled through a licensed handler, wastewater discharge is controlled by an amalgam separator, and chlorine-containing line cleaners are not run through lines holding amalgam because they can release mercury.

    Source: EPA Dental Office Point Source Category rule, 40 CFR Part 441 (amalgam separators and prohibited discharges); ADA Best Management Practices for Amalgam WasteReport a problem with this question

13. 13. A high-speed handpiece was used for a restorative procedure and its exterior looks clean. How must it be processed before it is used on the next patient?

    • A.Flush its waterline for 30 seconds and use it on the next patient
    • B.Wipe the exterior with an EPA-registered intermediate-level disinfectant
    • C.Clean it and then heat-sterilize it according to the manufacturer's instructions for use✓ Answer
    • D.Immerse it in a high-level disinfectant for 20 minutes

    Handpieces and other devices attached to the air and water lines, including low-speed motors, prophy angles, ultrasonic scaler tips and air-water syringe tips, can retract and retain patient material internally, so a clean-looking exterior proves nothing about the internal surfaces. These are semicritical devices that must be cleaned and then heat-sterilized between patients following the manufacturer's instructions; surface disinfection or liquid immersion cannot reach or sterilize the internal components.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Dental Handpieces and Other Devices Attached to Air and WaterlinesReport a problem with this question

14. 14. In the decontamination area, what is the preferred method for cleaning a cassette of contaminated instruments before packaging?

    • A.Use an ultrasonic cleaner or instrument washer, keeping the lid or door closed during the cycle✓ Answer
    • B.Soak the instruments in a surface disinfectant until the end of the day
    • C.Place the instruments directly into pouches and run the sterilizer without cleaning
    • D.Scrub each instrument individually by hand at the sink

    Automated cleaning is preferred because it removes debris without workers handling sharp contaminated instruments, which directly lowers the risk of percutaneous injury; ultrasonic units clean by cavitation and the lid stays closed to contain contaminated aerosols. If instruments cannot be cleaned promptly they are held in a presoak or holding solution, which is a cleaning or enzymatic product rather than a disinfectant, and debris left on an instrument will shield microorganisms and cause sterilization to fail.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Instrument Processing: cleaning (automated cleaning preferred to reduce handling of contaminated sharp instruments)Report a problem with this question

15. 15. After a steam cycle, the external chemical indicator printed on a sterilization pouch has changed color. What does that color change establish?

    • A.That the package was exposed to the sterilization process, but not that sterilization was achieved✓ Answer
    • B.That the instruments inside are sterile and ready to use
    • C.That all spores in the load were killed
    • D.That the required time, temperature and pressure were maintained inside the chamber

    An external chemical indicator, also called a process indicator, responds to one parameter such as heat and only distinguishes processed from unprocessed packages, so a color change cannot confirm that lethal conditions were held long enough. Time, temperature and pressure are verified by mechanical monitoring of the gauges or printout for every load, an internal chemical indicator is placed inside each package to show the agent penetrated it, and only a biological indicator, which challenges the cycle with highly resistant spores, directly verifies that sterilization was achieved.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Sterilization Monitoring: mechanical, chemical, and biological indicatorsReport a problem with this question

16. 16. The weekly spore test for the office steam sterilizer shows growth in the processed biological indicator, and the unprocessed control from the same lot also shows growth. What should be done?

    • A.Discard only the packages from that one load and leave the sterilizer in service
    • B.Continue using the sterilizer, because a single failure is usually a laboratory error
    • C.Take the sterilizer out of service immediately, and recall and reprocess items back to the last negative spore test✓ Answer
    • D.Repeat the cycle and keep using the sterilizer while waiting for the new result

    Growth in the unprocessed control proves the spores were viable, so growth in the processed indicator means the cycle failed to kill highly resistant spores and every load since the last negative test is suspect. The sterilizer is removed from service at once, those items are recalled and reprocessed, and the test is repeated with a new indicator and control after checking for operator error or mechanical fault; if the repeat is also positive the unit stays out of use until it is inspected or repaired and three consecutive negative results are obtained.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Sterilization Monitoring: biological monitoring and response to a positive spore testReport a problem with this question

17. 17. A practice wants a heat sterilization method for carbon steel instruments that will not rust the instruments or dull their cutting edges. Which choice meets that requirement?

    • A.A steam autoclave operated at 121 C
    • B.Unsaturated chemical vapor✓ Answer
    • C.Immersion in 2% glutaraldehyde for 45 minutes
    • D.Wiping the instruments with an EPA-registered intermediate-level disinfectant

    Unsaturated chemical vapor sterilizes with a heated chemical solution that contains very little water, and without enough moisture the electrochemical corrosion that rusts and dulls carbon steel cannot occur, although instruments must be dried before processing and the room must be adequately ventilated. Saturated steam corrodes carbon steel, a 45-minute glutaraldehyde immersion achieves only high-level disinfection rather than sterilization, and wiping with a surface disinfectant never sterilizes an instrument.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Sterilization of Patient-Care Items: unsaturated chemical vapor sterilizationReport a problem with this question

18. 18. Two weeks after it was processed, a wrapped instrument cassette on the sterile storage shelf is found with a tear in the wrap. What should the assistant do?

    • A.Use it, because the package is still within its shelf life
    • B.Consider the package contaminated and reprocess it, regardless of the processing date✓ Answer
    • C.Put the torn package back into the sterilizer without rewrapping and use it after the cycle
    • D.Tape the tear closed and use the instruments the same day

    Sterility is event-related, not time-related: a package stays sterile until an event such as a tear, wetness, dropping or other compromise of the packaging lets microorganisms in. Because the barrier has failed, the date is irrelevant, and the instruments must be cleaned as needed, repackaged in intact packaging with a new internal indicator, and sterilized again before use.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (MMWR 52/RR-17), Storage Area for Sterilized Items and Clean Supplies (event-related sterility)Report a problem with this question

19. 19. A newly hired dental assistant whose duties involve reasonably anticipated exposure to blood has completed her bloodborne pathogens training. Under the OSHA Bloodborne Pathogens Standard, when and how must the employer make hepatitis B vaccination available?

    • A.Only after the employee has an exposure incident
    • B.Within 30 days of hire, with the employee paying part of the cost
    • C.Only if the employee submits a written request before starting work
    • D.Within 10 working days of initial assignment, at no cost to the employee✓ Answer

    The standard requires the employer to offer the hepatitis B vaccination series after training and within 10 working days of initial assignment to work with occupational exposure, and all costs are borne by the employer. Hepatitis B is the most readily transmitted bloodborne pathogen in dentistry, so protection must be in place before exposure occurs; an employee who declines signs the standard's declination statement and may still accept the vaccine later at any time while still covered.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030(f)(2) — hepatitis B vaccination made available within 10 working days of initial assignment at no cost to the employeeReport a problem with this question

20. 20. While transferring a contaminated instrument, an assistant sustains a puncture wound to her finger from a used needle. What is the FIRST action she should take?

    • A.Wash the wound with soap and running water, then report it immediately to the designated person✓ Answer
    • B.Squeeze the puncture site to express as much blood as possible
    • C.Finish the procedure and report the injury at the end of the workday
    • D.Pour household bleach on the wound to disinfect it

    Washing with soap and running water removes contaminated material without damaging tissue; squeezing the wound and applying bleach or other caustic agents are not recommended because they injure tissue and have no proven benefit. Reporting must be immediate rather than at the end of the day because the confidential medical evaluation, source testing where legally permitted, baseline testing and any post-exposure prophylaxis are most effective when started as soon as possible after the exposure.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030(f)(3) (post-exposure evaluation and follow-up); CDC recommendations for management of occupational exposures to bloodborne pathogensReport a problem with this question

21. 21. The dentist will need to give a second injection later in the same appointment, so the anesthetic needle must be recapped between injections. Which practice complies with the OSHA Bloodborne Pathogens Standard?

    • A.Recap the needle using a one-handed scoop technique or a mechanical recapping device✓ Answer
    • B.Leave the uncapped syringe on the tray until the appointment is finished
    • C.Recap it by holding the cap steady with the other hand
    • D.Bend the needle before recapping so that it cannot be reused

    Recapping is permitted only when there is no feasible alternative, such as between injections with the same syringe, and it must be done with a one-handed scoop technique or a mechanical device so that no hand is ever placed in the path of the needle. Two-handed recapping, and bending, shearing or breaking a contaminated needle, are prohibited work practices, and leaving an uncapped needle on the tray creates a sharps hazard for everyone in the room.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030(d)(2)(vii) — contaminated needles shall not be recapped except by a one-handed technique or mechanical deviceReport a problem with this question

22. 22. A concentrated disinfectant is diluted and transferred into a spray bottle that will be used by other staff members on later shifts. What does the OSHA Hazard Communication Standard require for that spray bottle?

    • A.No label is needed as long as the original container is stored nearby
    • B.Labeling it simply 'disinfectant' is enough if the safety data sheet is kept in a locked office
    • C.It must be labeled with the product identifier and the hazard information for that chemical✓ Answer
    • D.It must be labeled with the date it was filled and the initials of the person who filled it

    A secondary or workplace container must carry the product identifier and the hazard information, so that any employee who picks it up knows what the chemical is and what protection it requires; the only exemption is a container filled and used up entirely during the same shift by the person who transferred it. The standard also requires a written hazard communication program, an inventory of hazardous chemicals, training, and safety data sheets that are readily accessible to employees during all work shifts, which a locked office would not satisfy.

    Source: OSHA Hazard Communication Standard, 29 CFR 1910.1200(f)(6) (workplace/secondary container labeling) and 1910.1200(g)(8) (safety data sheets readily accessible)Report a problem with this question

Practice questions based on the DANB Radiation Health and Safety (RHS), Infection Control (ICE), and General Chairside Assisting (GC) content outlines, CDC dental infection-prevention guidance, the OSHA Bloodborne Pathogens Standard, and ADA/FDA radiographic selection criteria. DANB, CDA, RHS, ICE, and GC are marks of the Dental Assisting National Board; this site is not affiliated with or endorsed by DANB. The duties a dental assistant may legally perform — and any radiography permit or certification required — are set by your own state dental board. Confirm current requirements with that board and with DANB before testing. About the DANB exams →