NBDHE Dental Radiography and Interpretation 2 — Questions and Answers

Question 1: Which radiographic technique uses a horizontal angulation of 0° and a vertical angulation of +8° to +10° for mandibular premolars in the paralleling technique?

The beam is directed perpendicular to the long axis of the teeth and the film/sensor, with specific vertical angulation per region (Correct answer)
A bisecting angle approach with steeper vertical angles
An occlusal projection technique
A panoramic technique

Correct answer: The beam is directed perpendicular to the long axis of the teeth and the film/sensor, with specific vertical angulation per region

The paralleling technique directs the central beam perpendicular to both the long axis of the teeth and the image receptor, with regional vertical angulations (mandibular premolars ~+8° to +10°).

In the paralleling technique, the image receptor is placed parallel to the long axes of the teeth, and the central ray is directed perpendicular to both the teeth and the receptor. A positioning device (XCP, Rinn) is used to stabilize the film/sensor at a distance from the teeth. Regional positive vertical angulations for mandibular teeth: incisors −15° to −20°, canines −20°, premolars −10°, molars −5°. The technique produces minimal geometric distortion and is the standard of care for periapical radiography. Film-to-tooth separation requires increased vertical angulation for the bisecting angle technique to avoid elongation.

Question 2: A periapical radiograph showing a well-defined radiolucency with a sclerotic border at the apex of a vital tooth is MOST likely:

Periapical cemento-osseous dysplasia (early stage) (Correct answer)
Periapical abscess
Periapical granuloma
Periapical cyst

Correct answer: Periapical cemento-osseous dysplasia (early stage)

Early-stage cemento-osseous dysplasia around the apices of vital anterior teeth appears as a well-defined radiolucency; vitality testing differentiates it from endodontically involved lesions.

Periapical cemento-osseous dysplasia (formerly cementoma) progresses through three stages: (1) osteolytic — well-defined radiolucency; (2) cementoblastic — mixed radiolucent/radiopaque; (3) mature — dense radiopaque mass with lucent halo. It occurs most often in Black women over 40, near the apices of vital mandibular anterior teeth, and requires no treatment. Vitality testing is essential: periapical granuloma, abscess, and cyst arise from non-vital teeth with periapical periodontitis, and would be associated with a non-vital pulp response. Cone-beam CT can help characterize these lesions further.

Question 3: The maximum permissible dose (MPD) of ionizing radiation for an occupationally exposed dental worker per year in the U.S. is:

50 mSv (5 rem) per year (Correct answer)
100 mSv (10 rem) per year
20 mSv (2 rem) per year
5 mSv (0.5 rem) per year

Correct answer: 50 mSv (5 rem) per year

The National Council on Radiation Protection sets the MPD for occupationally exposed persons at 50 mSv (5 rem) per year, with a cumulative lifetime limit of 10 mSv × age.

The NCRP Report No. 116 establishes the effective dose limit for occupationally exposed individuals at 50 mSv (5 rem) per year, with a cumulative lifetime limit of 10 mSv (1 rem) × age in years. For members of the general public, the limit is 1 mSv (0.1 rem) per year. For pregnant workers, the dose equivalent to the embryo/fetus should not exceed 5 mSv during the entire pregnancy, with no more than 0.5 mSv in any month. These limits are above what dental workers actually receive when proper technique and shielding are used; ALARA (As Low As Reasonably Achievable) is the guiding principle.

Question 4: Elongation on a periapical radiograph using the bisecting angle technique is caused by:

Insufficient vertical angulation (too flat/shallow) (Correct answer)
Excessive vertical angulation (too steep)
Incorrect horizontal angulation
Film/sensor placement too close to the teeth

Correct answer: Insufficient vertical angulation (too flat/shallow)

Elongation occurs when the vertical angulation is too shallow (not enough) — the beam does not bisect the angle properly and the image appears stretched/lengthened.

In the bisecting angle technique, the central ray must be directed perpendicular to the imaginary bisector of the angle formed between the long axis of the tooth and the image receptor. If the vertical angulation is too low (insufficient), the projection captures the tooth at an oblique angle that makes the image appear longer than the actual tooth (elongation). If the angulation is excessive (too steep), the image appears shorter (foreshortening). Horizontal angulation errors cause overlapping of proximal surfaces. The paralleling technique, which uses a positioning device, eliminates this source of angulation error.

Question 5: On a panoramic radiograph, the 'ghost image' artifact is caused by:

A radiopaque structure on the contralateral side projecting across the midline at a higher and more blurred level (Correct answer)
Metallic objects left on the patient's body
Movement of the patient during the exposure
Film/sensor placement outside the focal trough

Correct answer: A radiopaque structure on the contralateral side projecting across the midline at a higher and more blurred level

Ghost images in panoramic radiography are reversed, magnified, blurred secondary images of radiopaque structures located on the opposite side of the beam path that appear above and blurred compared to the primary image.

In panoramic radiography, the x-ray beam passes through the patient and the image receptor rotates around the head. Radiopaque structures on the far side of the beam path (contralateral) can produce secondary (ghost) images that appear on the same side as the original, displaced superiorly and more blurred because they are farther from the image receptor and magnified. Common ghost images include the cervical spine, ramus of the mandible, and the hyoid bone. Lead aprons with cervical collars are not recommended for panoramic radiography as they create ghost artifacts. Patient preparation (removing earrings, glasses, removable prostheses) minimizes artifacts.

Question 6: Which type of dental radiograph is BEST for evaluating the crestal bone height in a periodontal patient?

Vertical bitewing radiograph (Correct answer)
Horizontal bitewing radiograph
Periapical radiograph
Panoramic radiograph

Correct answer: Vertical bitewing radiograph

Vertical bitewing radiographs show both the maxillary and mandibular alveolar crests on the same image with minimal distortion, making them ideal for assessing crestal bone levels in periodontally involved patients.

Standard horizontal bitewing radiographs show only a portion of the alveolar bone; in patients with moderate to severe bone loss, the mandibular crestal bone may not be visible. Vertical bitewing radiographs (with the film/sensor placed vertically in the patient's mouth) reveal more of the alveolar bone apically, allowing better visualization of bone loss patterns (horizontal vs. vertical), furcation involvement, and the remaining crestal bone level. The American Academy of Periodontology recommends vertical bitewings for periodontal patients. Periapical radiographs capture the full root length and periapical region but cannot show adjacent teeth as efficiently as bitewings.

NBDHE Dental Radiography and Interpretation 2

Which radiographic technique uses a horizontal angulation of 0° and a vertical angulation of +8° to +10° for mandibular premolars in the paralleling technique?