22 Radiation Health & Safety Practice Questions & Answers

1. 1. Electrons from the filament strike the tungsten target inside the dental x-ray tube. What happens to the energy those electrons carry?

   • A.Most of it converts to x-radiation, and only a small fraction becomes heat.
   • B.All of it converts to x-radiation, because the tungsten target cannot absorb heat.
   • C.Most of it converts to heat, and only a small fraction becomes x-radiation.✓ Answer
   • D.It becomes visible light first, which the aluminum filter then converts to x-rays.

   At the anode the kinetic energy of the incoming electrons is overwhelmingly converted to heat, and only a very small fraction becomes x-ray photons. That is why the target is tungsten, which has a high melting point, and why it is embedded in a copper stem surrounded by oil to carry heat away. Nothing in the tube converts light into x-rays.

   Source: NCRP guidance on radiation protection in dentistry, x-ray production at the anode targetReport a problem with this question

2. 2. Which part of the dental x-ray tube supplies the electrons that are then accelerated toward the target?

   • A.The tungsten target in the anode, heated so it releases electrons.
   • B.The tungsten filament in the cathode, heated so it releases electrons.✓ Answer
   • C.The copper stem behind the anode, which conducts electrons forward.
   • D.The aluminum filter in the tube port, which strips electrons from photons.

   Heating the cathode filament gives its surface electrons enough energy to escape, a process called thermionic emission; the high voltage across the tube then drives that electron cloud toward the anode. The anode receives the electrons rather than producing them, and neither the copper stem nor the filter has any role in generating them.

   Source: NCRP guidance on radiation protection in dentistry, x-ray tube components and thermionic emissionReport a problem with this question

3. 3. During an intraoral exposure, where does most of the scattered radiation that reaches the operator come from?

   • A.The patient's tissues, which deflect photons out of the primary beam.✓ Answer
   • B.The tubehead housing, which leaks photons around the insert.
   • C.The position-indicating device, which reflects photons off its wall.
   • D.The operatory walls, which re-emit photons stored during exposure.

   Photons entering the patient interact with tissue and change direction, mainly by Compton interactions, so the patient becomes the principal source of scattered radiation in the room. That is why operator protection is built around distance from the patient and staying clear of the primary beam; leakage through the housing is limited by design and walls do not store radiation.

   Source: NCRP guidance on radiation protection in dentistry, scattered radiation and operator positionReport a problem with this question

4. 4. An operatory has no protective wall or barrier to stand behind. What principle governs where the operator stands during the exposure?

   • A.Stand close to the tubehead, since its housing blocks scatter from the patient.
   • B.Stand well away from the patient and outside the path of the primary beam.✓ Answer
   • C.Stand facing the open end of the beam so that the exposure can be watched.
   • D.Stand at arm's length to the side, since the beam stops inside the receptor.

   Two things protect an unshielded operator: distance, because intensity falls off sharply with the square of the distance from the source, and position, because the primary beam must never pass through any part of the operator. Standing near the tubehead keeps the operator close to the patient, the main scatter source, and the beam is not stopped by the receptor.

   Source: NCRP guidance on radiation protection in dentistry, operator position and distance during exposuresReport a problem with this question

5. 5. The extension arm of an x-ray unit drifts, so the tubehead sags slowly after it has been positioned. What should the assistant do?

   • A.Hold the tubehead steady by hand through each exposure until it is repaired.
   • B.Take the unit out of service and report it so the arm can be repaired.✓ Answer
   • C.Ask the patient to hold the tubehead in place while the exposure is made.
   • D.Aim slightly high so that the drift brings the beam onto the receptor in time.

   A drifting tubehead is a malfunction that causes misaligned beams and retakes, so the unit is tagged out of service and serviced by a qualified person. Nobody may hold the tubehead during an exposure: a hand on the tubehead places the operator beside the patient and within reach of the primary beam and scatter, and a patient cannot steady it either.

   Source: NCRP guidance on radiation protection in dentistry, equipment malfunction and the prohibition on hand-holding tubeheads or receptorsReport a problem with this question

6. 6. What makes the radiation used in dental imaging ionizing?

   • A.Its photons carry a negative charge that they pass on to atoms.
   • B.Its photons heat the tissue until chemical bonds break in cells.
   • C.Its photons travel in waves that shake atoms out of position.
   • D.Its photons can eject electrons from atoms, leaving those atoms charged.✓ Answer

   Ionization means removing an electron from a neutral atom, which leaves an ion pair behind; x-ray photons have enough energy per photon to do this. The photons themselves have no mass and no charge, and the energy deposited by a diagnostic exposure is far too little to injure tissue by heating it.

   Source: NCRP guidance on radiation protection in dentistry, properties of ionizing radiationReport a problem with this question

7. 7. Most of the radiation damage that occurs in soft tissue happens indirectly. What is the mechanism?

   • A.Photons strike the DNA itself, breaking both strands at the point of impact.
   • B.Photons pull calcium out of the cell membrane, which then loses its integrity.
   • C.Photons raise the cell temperature, denaturing enzymes throughout the cytoplasm.
   • D.Photons ionize water in the cell, forming free radicals that attack molecules.✓ Answer

   Cells are mostly water, so a photon is far more likely to ionize a water molecule than to hit DNA. Radiolysis of water yields highly reactive free radicals that diffuse a short distance and damage nearby molecules, including DNA; the direct hit on DNA does occur but is much less common.

   Source: DANB Radiation Health and Safety exam outline, radiation biology: direct and indirect effectsReport a problem with this question

8. 8. Which pairing of tissue with its relative radiosensitivity is correct?

   • A.Lymphocytes are relatively resistant; mature nerve tissue is highly sensitive.
   • B.Skeletal muscle is highly sensitive; blood-forming marrow is relatively resistant.
   • C.Lymphocytes are highly sensitive; mature nerve tissue is relatively resistant.✓ Answer
   • D.Mature bone is highly sensitive; the lining of the intestine is relatively resistant.

   Radiosensitivity rises with the rate of cell division and falls with the degree of differentiation. Lymphocytes, marrow and intestinal lining cells divide rapidly and are among the most sensitive, while highly differentiated tissues that divide rarely, such as mature nerve and muscle, are among the most resistant.

   Source: DANB Radiation Health and Safety exam outline, radiation biology: cell radiosensitivityReport a problem with this question

9. 9. Radiation damages a chromosome in a reproductive cell of a patient. How is that effect classified?

   • A.A somatic effect, because the damage stays within the exposed patient's body.
   • B.A genetic effect, because the damage may be passed to the patient's offspring.✓ Answer
   • C.An acute effect, because reproductive cells show visible injury within hours.
   • D.A threshold effect, because it appears only above a set whole-body dose.

   Damage to germ cells is classified as genetic because the altered chromosome can be carried into a future generation, while damage to any other cell of the body is somatic and ends with that individual. The classification depends on which cell line was hit, not on how soon or at what dose an effect appears.

   Source: DANB Radiation Health and Safety exam outline, radiation biology: somatic and genetic effectsReport a problem with this question

10. 10. How does rectangular collimation reduce the dose a patient receives during an intraoral exposure?

    • A.It absorbs the low-energy photons that would otherwise be stopped by skin.
    • B.It shapes the beam closer to the receptor size, so less tissue is irradiated.✓ Answer
    • C.It shortens the needed exposure by packing photons into a smaller area.
    • D.It turns stray photons back toward the tubehead before they reach the face.

    A rectangular collimator restricts the beam to roughly the shape and size of the intraoral receptor, so the volume of the patient's face in the beam is far smaller than with a round beam, and less scatter is produced as well. Removing low-energy photons is the job of filtration, and collimation does not change the exposure factors needed.

    Source: NCRP guidance on radiation protection in dentistry, rectangular collimation for intraoral radiographyReport a problem with this question

11. 11. An aluminum filter sits in the path of the beam inside the tubehead. What does it accomplish?

    • A.It removes low-energy photons that skin absorbs without reaching the receptor.✓ Answer
    • B.It removes high-energy photons that pass through without being absorbed at all.
    • C.It narrows the beam so it covers no more than the face of the image receptor.
    • D.It slows the photons so that more of them are captured by the receptor surface.

    The beam leaving the target contains a spread of photon energies. The weakest photons cannot pass through the patient to reach the receptor, so they add dose to skin and superficial tissue while contributing nothing to the image; aluminum filtration absorbs them preferentially. Restricting beam size is collimation, not filtration.

    Source: FDA performance standards for diagnostic x-ray systems, beam filtration for dental unitsReport a problem with this question

12. 12. An office replaces a short position-indicating device with a longer one and changes nothing else. What is the radiation-safety advantage?

    • A.The beam is more divergent, so the photons spread thinly over the skin.
    • B.The beam is filtered further, so fewer weak photons leave the tubehead.
    • C.The beam is less divergent, so a smaller volume of tissue is exposed.✓ Answer
    • D.The beam is slowed on the way out, so less energy is deposited in bone.

    A longer position-indicating device increases the distance from the focal spot to the patient, so the part of the cone of radiation that reaches the face is less divergent and covers a smaller area of tissue. The same geometry also reduces magnification and improves sharpness; filtration and photon speed are unchanged.

    Source: NCRP guidance on radiation protection in dentistry, source-to-skin distance and position-indicating devicesReport a problem with this question

13. 13. A dentist asks for images that show many shades of gray between the lightest and darkest areas. Which control should be changed, and in which direction?

    • A.Increase the kilovoltage, which lowers contrast and adds more shades of gray.✓ Answer
    • B.Decrease the kilovoltage, which lowers contrast and adds shades of gray.
    • C.Increase the milliamperage, which lowers contrast and adds shades of gray.
    • D.Decrease the exposure time, which lowers contrast and adds shades of gray.

    Kilovoltage sets the penetrating quality of the beam and therefore controls contrast: a higher setting produces a more uniformly penetrating beam and a long-scale, low-contrast image with many intermediate grays, while a lower setting gives short-scale, high-contrast black and white. Milliamperage and time control the quantity of radiation and therefore density.

    Source: DANB Radiation Health and Safety exam outline, factors affecting x-ray production and image qualityReport a problem with this question

14. 14. A digital sensor still yields an acceptable-looking image when the exposure setting is higher than the image needs. Why does that matter?

    • A.The patient absorbs dose that the diagnostic image never required.✓ Answer
    • B.The extra exposure raises contrast until enamel and dentin look alike.
    • C.The sensor stores the excess charge and fails earlier than expected.
    • D.The software compensates, so the added exposure changes nothing at all.

    Digital receptors have a wide exposure latitude and the software normalizes the displayed image, so overexposure is not obvious on screen. The dose is still delivered to the patient, which is why exposure factors must be set to the lowest value that answers the diagnostic question rather than left where the image merely looks fine.

    Source: NCRP guidance on radiation protection in dentistry, optimization of exposure factors with digital receptorsReport a problem with this question

15. 15. How should a personal radiation monitoring badge be handled by the staff member it is assigned to?

    • A.Worn only by that person and kept away from heat and radiation sources.✓ Answer
    • B.Shared with whoever works the next shift so the office needs fewer badges.
    • C.Stored in the operatory beside the x-ray unit so it is never forgotten.
    • D.Taken home and worn off duty so that total yearly dose can be tracked.

    A monitoring badge is a legal record of one named individual's occupational exposure, so sharing it makes the record meaningless. Leaving it near the x-ray unit or in heat or sunlight adds readings the wearer never received or damages the detector, and wearing it away from work mixes in non-occupational exposure.

    Source: NCRP guidance on radiation protection in dentistry, personnel monitoringReport a problem with this question

16. 16. An office policy calls for a full mouth series on every new adult patient before the dentist has examined them. What is wrong with that policy?

    • A.Images must be prescribed by the assistant who exposes them, not the dentist.
    • B.Images must be limited to bitewings until the patient has been seen twice.
    • C.Images must be repeated every year for the record whether needed or not.
    • D.Images must be prescribed from the history and examination, not routinely.✓ Answer

    Selection criteria require that each exposure be justified for that patient: the dentist reviews the health and dental history, performs the clinical examination and assesses risk, then prescribes only the images expected to change diagnosis or treatment. Radiographic screening of everyone before an examination exposes patients for whom no clinical question has been asked.

    Source: ADA and FDA recommendations for patient selection and limiting radiation exposure in dental radiographic examinationsReport a problem with this question

17. 17. Every posterior bitewing in a set shows the proximal surfaces superimposed, so the contacts cannot be read. What must be corrected on the retake?

    • A.The receptor placement, so the contacts sit nearer the center of the plate.
    • B.The vertical angulation, so the central ray passes through the contacts.
    • C.The exposure time, so the contact areas are recorded with more density.
    • D.The horizontal angulation, so the central ray passes through the contacts.✓ Answer

    Overlap is a horizontal problem: the central ray must enter perpendicular to the plane of the proximal contacts, and when it enters obliquely the adjacent surfaces are cast on top of one another. Vertical angulation errors change the recorded length of the teeth instead, producing elongation or foreshortening.

    Source: DANB Radiation Health and Safety exam outline, identification and correction of intraoral technique errorsReport a problem with this question

18. 18. A periapical shows the teeth recorded shorter and stubbier than they actually are. What caused it?

    • A.Insufficient vertical angulation of the central ray toward the receptor.
    • B.Excessive horizontal angulation of the central ray across the arch.
    • C.Excessive vertical angulation of the central ray toward the image receptor.✓ Answer
    • D.Insufficient exposure, which cut short the recorded root outlines.

    Foreshortening comes from too much vertical angulation, because the central ray is no longer perpendicular to the imaginary bisector and the tooth is projected onto the receptor as a shorter image. Too little vertical angulation does the opposite and elongates the teeth; horizontal errors overlap contacts without changing length.

    Source: DANB Radiation Health and Safety exam outline, identification and correction of intraoral technique errorsReport a problem with this question

19. 19. A panoramic image shows a flat, reversed occlusal plane with the hard palate superimposed over the maxillary roots. What positioning error occurred?

    • A.The chin was tipped too low, angling the plane of the head downward.
    • B.The chin was raised too high, tipping the plane of the head upward.✓ Answer
    • C.The patient stood too far forward, ahead of the focal trough of the unit.
    • D.The patient's spine was slumped rather than held straight during the scan.

    Raising the chin lifts the posterior of the occlusal plane relative to the anterior, so the smile line flattens or reverses, and it brings the hard palate into the path of the beam over the maxillary apices. A chin that is too low exaggerates the smile line instead and blurs the mandibular incisors.

    Source: DANB Radiation Health and Safety exam outline, panoramic patient positioning errorsReport a problem with this question

20. 20. Which statement about ghost images on panoramic radiographs is correct?

    • A.They appear on the same side, lower down, reduced in size and sharp.
    • B.They appear only over the midline and disappear if exposure is raised.
    • C.They appear along the lower border and are erased by tilting the chin.
    • D.They appear on the opposite side, higher up, magnified and blurred.✓ Answer

    A radiodense object between the source and the receptor is imaged twice: once in its true position and once as a ghost projected on the opposite side, higher and magnified because it sat closer to the source and the beam is angled upward. This is why a thyroid collar is not placed for a panoramic exposure, since it would throw a ghost across the diagnostic area.

    Source: DANB Radiation Health and Safety exam outline, panoramic imaging artifacts and ghost imagesReport a problem with this question

21. 21. A bitewing shows a wedge-shaped radiolucency on the root just below the enamel edge, between the contact and the bone crest. The area is hard to the explorer. What is it?

    • A.Cervical burnout, an optical effect where less tissue absorbs the beam.✓ Answer
    • B.Root caries, a demineralized lesion that will progress without treatment.
    • C.An abrasion notch, worn into the root surface by hard toothbrushing.
    • D.A resorption defect, where cells have removed part of the root surface.

    Between the edge of the enamel and the crest of bone the root is thin and unsupported, so the beam passes through less absorbing tissue there and the area records darker without any loss of tooth structure. The tell is that the surface is intact and hard on examination, whereas a carious or abraded surface is defective to the explorer.

    Source: DANB Radiation Health and Safety exam outline, recognition of normal landmarks and conditions on dental imagesReport a problem with this question

22. 22. A newly hired dental assistant will expose radiographs and handle contaminated receptors. What does the bloodborne pathogens standard require the employer to provide?

    • A.Hepatitis B vaccination billed to the employee's own health insurance.
    • B.Proof of hepatitis B immunity submitted before the employee is hired.
    • C.Hepatitis B vaccination offered at no cost after the employee is trained.✓ Answer
    • D.Hepatitis B testing repeated each year, paid by the employee.

    The standard treats saliva in dental procedures as a potential source of infection, so staff who handle contaminated receptors and holders fall under it. The employer must offer the hepatitis B vaccine series at no cost to the employee after training and shortly after assignment, and an employee who declines signs a declination form.

    Source: OSHA Bloodborne Pathogens Standard, 29 CFR 1910.1030, hepatitis B vaccination and post-exposure follow-upReport 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 →