Radiation Health and Safety practice test, every answer explained

Answer: B. Radiolucent, while the areas recording light on it are called radiopaque

Anatomic landmarks are read by their normal appearance, and the vocabulary for that appearance is one fixed pair: the areas that record dark on a radiograph are radiolucent, and the areas that record light are radiopaque. Less dense structures such as air spaces and areas where bone is thin or absent let more of the beam reach the receptor and so record dark, while enamel, cortical bone and metal restorations absorb more of it and record light. The pair never reverses, neither term covers both appearances, and both describe the structure being imaged rather than the receptor it was recorded on.

Source: Dental Radiography (subcourse MD0512), U.S. Army Medical Department Center and School; section “3-24. GENERAL”. U.S. government work, public domain.

Answer: C. Whether the disease has caused any loss of the bone that supports the teeth

X-ray images of the teeth and mouth are one of the tests a dentist or dental hygienist performs to diagnose gum disease, and what an x-ray can show is whether there is any bone loss as a result of the disease. That is why bone level is read on periapical and bitewing images. The other three answers belong to the rest of the workup rather than to the image: pocket depth is measured with a probe during the gum examination, redness, swelling and easy bleeding are judged by looking at the gums, and tobacco use and diabetes come out of the medical history the dentist takes.

Source: Periodontal (Gum) Disease, National Institute of Dental and Craniofacial Research; section “Diagnosis”. U.S. government work, public domain.

Answer: B. Proximal carious lesions, on the tooth surfaces that face the neighboring teeth

The patient selection criteria state that clinically detectable dental caries may suggest the presence of proximal carious lesions that can only be detected with a radiographic examination, which is why an image is read carefully where two teeth meet. Nothing in the criteria turns a clinical finding of decay into pulpal involvement in every restored tooth. Fusion is a developmental union of two tooth germs, present from the time the teeth form and unrelated to decay, and attrition is tooth substance worn away by tooth grinding against tooth, which decay does not cause.

Source: The Selection of Patients for Dental Radiographic Examinations, U.S. Food and Drug Administration; section “Recall Patient with Clinical Caries or Increased Risk for Caries”. U.S. government work, public domain.

Answer: A. The maxillary sinuses, prominent radiolucent structures

The maxillary sinus is a very prominent radiolucent structure, sometimes recording as overlapping lobes and sometimes as a single dark area with a radiopaque border, and it occupies a large part of the body of the maxilla above the posterior ridge. That is where these two spaces lie. The nasal fossae are a different pair: they sit at the midline, one either side of the nasal septum, rather than out over the back of the ridge. Destroyed bone and empty sockets would both be irregular areas at the ridge itself, not smooth symmetrical spaces above it.

Source: Dental Radiography (subcourse MD0512), U.S. Army Medical Department Center and School; section “3-25. RADIOLUCENT LANDMARKS ON MAXILLARY RADIOGRAPHS”. U.S. government work, public domain.

Answer: C. It shows the tooth's overall position relative to the arch and nearby structures

Among the uses of the panoramic radiograph, a complete survey can be made of the teeth and related structures, and the location and position of impacted teeth may be determined. That is what an unerupted canine calls for: where the tooth lies in relation to the arch, the neighboring roots and the structures around it. The same section is candid about the cost. The definition of a panoramic is not as sharp as a periapical or a bitewing, so it is not the projection for the finest enamel and dentin detail, and magnification, distortion and natural overlapping of some of the teeth are listed among its problems, so it certainly does not record every structure at its true size. Nor does it measure anything: it is described as a continuous view of the lower half of the face, read for disease and abnormalities, not as a source of numeric bone-density values.

Source: Dental Radiography (subcourse MD0512), U.S. Army Medical Department Center and School; section “Section VI. THE PANORAMIC RADIOGRAPH”. U.S. government work, public domain.

Answer: A. In line with the open end of the PID, directly in the path of the primary beam

The primary beam leaves the tubehead through the open end of the PID, so standing anywhere along that axis means direct primary-beam exposure — the highest-risk operator position and never acceptable, however brief the exposure. Every other position applies distance or shielding instead: a structural barrier absorbs the radiation that reaches it, several feet of separation off the beam axis exploits the inverse-square drop in intensity, and a control point outside the operatory removes the operator from the field altogether.

Source: Dental Radiography (subcourse MD0512), U.S. Army Medical Department Center and School; section “1-10. PROTECTIVE MEASURES AND STANDARDS”. U.S. government work, public domain.

Answer: A. A leaded glass window, so the operator can watch the patient during the exposure

Dental radiography guidance recommends that operator barriers ideally contain a leaded glass window so the patient can be observed during the exposure — the operator has to be able to see a patient move, and stop, without stepping out from behind the shielding. Mounting the exposure switch on the barrier serves the same purpose: the exposure can be made without leaving the protected position. Scatter radiation is not a gas or an airborne contaminant, so ventilation does nothing for it.

Source: The Selection of Patients for Dental Radiographic Examinations, U.S. Food and Drug Administration; section “OPERATOR PROTECTION”. U.S. government work, public domain.

Answer: D. Her dose may be assessed from surveys or from other radiation measurements instead

External dose is normally determined by measurement with a personal monitoring device, but the rule anticipates that the device may be missing or its results unavailable. In that case the deep-dose, lens-dose and shallow-dose equivalents may be assessed from surveys or other radiation measurements in order to demonstrate compliance with the occupational limits. Recording a zero would falsify the record, and one worker's badge documents only that worker, so it can never stand in for another's exposure.

Source: 10 CFR 20.1201, Occupational dose limits for adults, U.S. Nuclear Regulatory Commission (CFR 2024, govinfo); section “Occupational dose limits for adults”. U.S. government work, public domain.

Answer: D. Before the plate goes into the read-out unit, so the scanner stays uncontaminated

Only the outside of the barrier envelope is contaminated; the plate sealed inside stays clean. The envelope is therefore opened before the plate goes anywhere near the reader, so the plate drops out untouched and nothing from the mouth enters the scanner. Read-out equipment cannot be barriered or disinfected internally, so contamination carried in is handed on to every plate that follows it. Waiting until after the scan defeats the purpose entirely, and an envelope that has been in the mouth is contaminated whether or not it looks wet.

Source: Guidelines for Infection Control in Dental Health-Care Settings, 2003, Centers for Disease Control and Prevention (MMWR 52, RR-17); section “Radiology”. U.S. government work, public domain.

Answer: B. Touch the mounts, monitor and keyboard only with hands cleaned after glove removal

Exposed receptors are dried, transported in a clean container and handled aseptically so that the processing and viewing areas never become contaminated. The viewing station — mounts, viewer, monitor, keyboard and mouse — is a clean zone entered only with hands washed after glove removal, because any surface a contaminated glove touches must then be cleaned and disinfected. Bringing a just-removed receptor to that counter, or wiping a soiled sleeve there, moves saliva into the one area meant to stay clean. Images and mounts are clean, not sterile, and clean hands are what keeps them that way.

Source: Guidelines for Infection Control in Dental Health-Care Settings, 2003, Centers for Disease Control and Prevention (MMWR 52, RR-17); section “Radiology”. U.S. government work, public domain.