MJDF Part 1 - Membership of Joint Dental Faculties Dental Radiology and Imaging 1 — Questions and Answers
Question 1: Which imaging modality provides three-dimensional data and is MOST appropriate for assessing the relationship between an impacted mandibular third molar and the inferior alveolar canal?
- Panoramic radiograph
- Periapical radiograph
- Cone beam computed tomography (CBCT) (Correct answer)
- Oblique lateral radiograph
Correct answer: Cone beam computed tomography (CBCT)
CBCT generates volumetric 3D data that allows precise assessment of the spatial relationship between an impacted third molar and the inferior alveolar canal in all planes, information that cannot be reliably obtained from 2D projections.
Question 2: The paralleling technique for intraoral periapical radiography is preferred over the bisecting angle technique primarily because it:
- Requires a lower radiation dose per exposure
- Produces less geometric distortion of the tooth image (Correct answer)
- Is more easily tolerated in patients with shallow palates
- Eliminates the need for a film-holding device
Correct answer: Produces less geometric distortion of the tooth image
In the paralleling technique the receptor is placed parallel to the tooth's long axis with an increased target-to-receptor distance, minimising foreshortening and elongation and yielding a more dimensionally accurate image than the bisecting angle method.
Question 3: On a periapical radiograph, the lamina dura is correctly described as:
- A radiolucent line surrounding the entire root
- A radiopaque line lining the root canal space
- A radiopaque line of cortical bone lining the tooth socket (Correct answer)
- A radiolucent halo around the cementoenamel junction
Correct answer: A radiopaque line of cortical bone lining the tooth socket
The lamina dura is the compact cortical bone that lines the alveolar socket; it appears as a continuous radiopaque (white) line surrounding the root. Its absence or discontinuity can indicate periapical pathology or systemic bone disease.
Question 4: Which of the following BEST describes the radiographic appearance of an acute periapical abscess?
- A well-defined radiolucent area with a distinct corticated border at the root apex
- A diffuse radiolucent area at the root apex with poorly defined margins (Correct answer)
- A radiopaque mass replacing the periapical bone
- Widening of the periodontal ligament space alone, without apical bone loss
Correct answer: A diffuse radiolucent area at the root apex with poorly defined margins
An acute periapical abscess reflects rapid, active bone destruction and typically presents as a diffuse, ill-defined radiolucency at the apex. A well-corticated border suggests a more chronic, organised lesion such as a radicular cyst or granuloma.
Question 5: The SI unit that expresses effective radiation dose — incorporating both radiation weighting and tissue weighting factors — is the:
- Gray (Gy)
- Roentgen (R)
- Sievert (Sv) (Correct answer)
- Becquerel (Bq)
Correct answer: Sievert (Sv)
The Sievert (Sv) quantifies effective dose by accounting for the biological effectiveness of different radiation types (radiation weighting factor) and the differential radiosensitivity of various tissues (tissue weighting factor). The Gray measures absorbed energy per unit mass only.
Question 6: Which of the following is a recognised inherent limitation of panoramic (orthopantomographic) radiography compared with intraoral periapical radiography?
- It cannot image the full dentition within a single exposure
- It delivers a higher effective radiation dose than a full-mouth periapical series
- It has lower spatial resolution, making fine detail assessment less reliable (Correct answer)
- It requires significantly longer exposure time, increasing motion artefact risk
Correct answer: It has lower spatial resolution, making fine detail assessment less reliable
Panoramic radiography sacrifices spatial resolution compared with intraoral films because of the longer object-to-receptor distance, larger receptor size, and geometric factors inherent in the rotating-beam technique. This makes it less suitable for detecting early interproximal caries or subtle periapical changes.
MJDF Part 1 - Membership of Joint Dental Faculties Dental Radiology and Imaging 1
Which imaging modality provides three-dimensional data and is MOST appropriate for assessing the relationship between an impacted mandibular third molar and the inferior alveolar canal?