Radiation Health and Safety (RHS) Exam

1. Question 1 · Radiation Physics and Image Formation

   An exposure produces a diagnostic image at 7 mA and 0.50 second. The unit is changed to 10 mA. Which exposure time keeps the image density the same?
   • A.0.35 second
   • B.0.70 second
   • C.0.50 second
   • D.0.25 second
   Show answer and explanation

   Answer: A. 0.35 second

   Density depends on mAs: 7 mA x 0.50 s = 3.5 mAs, and 3.5 mAs / 10 mA = 0.35 s. Keeping 0.50 second would raise the mAs to 5.0 and darken the image, and 0.70 second comes from multiplying instead of dividing.

2. Question 2 · Radiation Health and Protection

   An office replaces its round PIDs with rectangular collimation. What is the main benefit for patients?
   • A.A longer source-to-skin distance that sharpens the image
   • B.Removal of the low-energy photons that only add to skin dose
   • C.Elimination of the need for beam-alignment devices
   • D.A substantial reduction in the volume of tissue irradiated
   Show answer and explanation

   Answer: D. A substantial reduction in the volume of tissue irradiated

   Rectangular collimation restricts the beam to about the size of the receptor, reducing the irradiated tissue and patient dose by up to about 60% compared with round collimation. Removing low-energy photons is the job of filtration, and rectangular collimation actually makes beam-alignment devices more important.

3. Question 3 · Special Problems

   A patient has large bilateral mandibular tori. Where should the assistant place the receptor for a mandibular premolar periapical image?
   • A.Between the torus and the teeth, close to the lingual surfaces
   • B.On the buccal side of the teeth, next to the patient's cheek
   • C.Directly on top of the torus, pressed against the bony growth
   • D.Between the torus and the tongue, on the far side of the torus
   Show answer and explanation

   Answer: D. Between the torus and the tongue, on the far side of the torus

   For mandibular tori, the receptor is placed between the torus and the tongue (on the far side of the torus) so it does not rest on the sensitive tissue and the teeth can still be imaged. Placing it on top of or tight against the torus is painful and tilts the receptor, and a buccal placement would not image the teeth correctly.

4. Question 4 · Intraoral Technique, Error Correction and Mounting

   On a premolar bitewing, the contacts between the first and second premolars overlap so the interproximal enamel cannot be evaluated for caries. The occlusal plane and arch coverage are correct. What is the MOST likely cause?
   • A.The bitewing tab was not centered between the two arches
   • B.The central ray missed the interproximal spaces
   • C.The receptor was positioned too far toward the midline
   • D.The vertical angulation was set well above +10 degrees
   Show answer and explanation

   Answer: B. The central ray missed the interproximal spaces

   Overlapped contacts are a horizontal angulation error in which the central ray is not directed perpendicular to the receptor through the interproximal spaces. Excessive vertical angulation distorts tooth length and arch proportions, and an off-center bitewing tab changes how much of each arch is shown, not whether the contacts are open.

5. Question 5 · Infection Prevention and Control

   During an FMX, the gloved assistant presses the exposure button, adjusts the headrest lever, and repositions the tubehead by its yoke. Which surface in the room is a housekeeping surface that needs only routine cleaning rather than barriers or disinfection between patients?
   • A.The exposure button on the control panel
   • B.The tubehead yoke used to position the PID
   • C.The headrest adjustment lever
   • D.The floor under the dental chair
   Show answer and explanation

   Answer: D. The floor under the dental chair

   Housekeeping surfaces such as floors, walls, and sinks are not touched during patient care and carry little risk of disease transmission, so routine cleaning is enough. The headrest lever, exposure button, and tubehead yoke were all touched with contaminated gloves, which makes them clinical contact surfaces. Clinical contact surfaces must be barrier protected or cleaned and disinfected between patients.

6. Question 6 · Radiation Physics and Image Formation

   A diagnostic image is made with an 8-inch PID at 0.20 second. The office switches to a 16-inch PID with the same mA and kVp. Which exposure time gives the same density?
   • A.0.80 second
   • B.0.05 second
   • C.0.40 second
   • D.0.10 second
   Show answer and explanation

   Answer: A. 0.80 second

   By the inverse square law, doubling the distance reduces intensity to one-fourth, so the exposure must be increased four times: 0.20 s x 4 = 0.80 s. Doubling the time to 0.40 second ignores the squared relationship, and shorter times would further underexpose the image.

7. Question 7 · Radiation Health and Protection

   An assistant is preparing to take bitewings on a small 7-year-old patient. Which adjustment to the exposure is MOST appropriate?
   • A.Increase the mA because children move more often
   • B.Reduce the exposure time below the adult setting
   • C.Use the adult setting to avoid any risk of retakes
   • D.Increase the kVp to penetrate the developing teeth
   Show answer and explanation

   Answer: B. Reduce the exposure time below the adult setting

   Children's smaller, less dense tissues need less radiation, so the exposure time is reduced to lower the dose while producing a diagnostic image. Using adult settings or increasing kVp or mA would overexpose a child, and the risk of movement is handled with patient management, not more radiation.

8. Question 8 · Special Problems

   A patient has a large maxillary (palatal) torus. Which receptor placement is MOST appropriate for a maxillary molar periapical image?
   • A.Between the torus and the teeth, against the lingual gingiva
   • B.Directly over the torus, centered on the bony growth
   • C.On the far side of the torus, toward the midline
   • D.Against the buccal surfaces of the teeth, next to the cheek
   Show answer and explanation

   Answer: C. On the far side of the torus, toward the midline

   With a palatal torus, the receptor is placed on the far side of the torus (toward the midline, beyond the bony growth) so it is not resting on or tilted by it, and the vertical angulation is adjusted as needed. Placing the receptor directly over the torus tilts it and is uncomfortable, and a buccal placement does not image the teeth correctly.

9. Question 9 · Intraoral Technique, Error Correction and Mounting

   A premolar bitewing does not show the distal surface of the mandibular canine. The rest of the image is acceptable. Which correction is needed on the retake?
   • A.Move the front edge of the receptor forward to the mid-canine
   • B.Move the front edge of the receptor back to the second premolar
   • C.Increase the vertical angulation of the PID to about +20 degrees
   • D.Redirect the central ray through the contacts of the first molar
   Show answer and explanation

   Answer: A. Move the front edge of the receptor forward to the mid-canine

   A premolar bitewing must include the distal surface of the canine, so the anterior edge of the receptor is moved forward to about the middle of the mandibular canine. Moving the receptor farther back would cut off even more of the canine, and changing vertical or horizontal angulation does not correct receptor placement.

10. Question 10 · Infection Prevention and Control

    An office manager wants the main evidence-based recommendations for infection control in dental settings, such as when to use surface barriers and how to reprocess semicritical items. Which agency publishes these guidelines?
    • A.Food and Drug Administration
    • B.Environmental Protection Agency
    • C.Centers for Disease Control and Prevention
    • D.Occupational Safety and Health Administration
    Show answer and explanation

    Answer: C. Centers for Disease Control and Prevention

    The CDC publishes the infection control guidelines for dental health-care settings, which the ADA supports and many states adopt as the standard of care. OSHA's regulations focus on protecting employees from bloodborne pathogens rather than covering all patient-care practices. The EPA registers disinfectants and the FDA clears devices, but neither writes these clinical guidelines.

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