MJDF Radiology & IRMER 2 — Questions and Answers
Question 1: What is the classic radiographic appearance of a periapical granuloma?
- Diffuse periapical radiolucency (1–2 mm) without corticated margin at the apex of a non-vital tooth (Correct answer)
- Well-defined corticated radiolucency > 10 mm
- Radiopaque periapical lesion
- Floating tooth appearance
Correct answer: Diffuse periapical radiolucency (1–2 mm) without corticated margin at the apex of a non-vital tooth
Periapical granulomas appear as small (usually <10 mm), diffuse radiolucencies without a distinct sclerotic (corticated) border at the root apex, associated with a non-vital tooth.
Question 2: What is a 'ghost image' on a panoramic radiograph and how is it formed?
- An inverted, blurred image of a radiopaque object on the contralateral side, formed when the object passes through the X-ray beam twice (above and below the rotation centre) (Correct answer)
- A duplicate of the real image at the same position
- An artefact from film processing only
- Only occurs with digital systems
Correct answer: An inverted, blurred image of a radiopaque object on the contralateral side, formed when the object passes through the X-ray beam twice (above and below the rotation centre)
Ghost images appear on the contralateral and superior side to a radiopaque object (e.g., earring, spine of the mandible); they form because the object passes through the beam twice during panoramic rotation.
Question 3: What are the FGDP(UK) radiographic selection criteria guidelines based on?
- Evidence-based clinical indicators — radiographs should only be taken when the clinical information gained changes patient management (Correct answer)
- All patients should receive annual OPGs
- Radiographs should be taken at every appointment regardless of history
- CBCT should be used routinely for all assessments
Correct answer: Evidence-based clinical indicators — radiographs should only be taken when the clinical information gained changes patient management
FGDP(UK) selection criteria are evidence-based, specifying clinical indications (caries risk, signs and symptoms, monitoring) that justify each type of radiograph to ensure benefit outweighs radiation risk.
Question 4: What is the cause of a 'radiopaque' appearance on a dental radiograph?
- Dense structures (bone, enamel, metallic restorations) absorb more X-rays, allowing fewer photons to reach the detector, appearing white (Correct answer)
- Low-density tissue allowing many photons through
- Processing errors
- X-ray beam overexposure
Correct answer: Dense structures (bone, enamel, metallic restorations) absorb more X-rays, allowing fewer photons to reach the detector, appearing white
Radiopaque structures (metals, enamel, bone) absorb X-ray photons strongly, reducing the beam reaching the image receptor; this results in white areas on the radiograph where fewer photons were recorded.
Question 5: What is the recommended kV range for dental bitewing radiographs to reduce patient dose?
- 60–70 kVp (increasing to 65–70 kVp with rectangular collimation to minimise dose) (Correct answer)
- 30–40 kVp
- 90–120 kVp
- 50 kVp always
Correct answer: 60–70 kVp (increasing to 65–70 kVp with rectangular collimation to minimise dose)
Increasing kVp (to 65–70 kVp) with rectangular collimation reduces patient dose by improving beam penetration and reducing scatter, while maintaining diagnostic image quality for bitewing radiographs.
Question 6: What does 'rectangular collimation' achieve in periapical radiography?
- Restricts the X-ray beam to closely match the film/sensor size, dramatically reducing dose and scatter (Correct answer)
- Improves focal spot clarity
- Increases field size for better coverage
- Reduces exposure time only
Correct answer: Restricts the X-ray beam to closely match the film/sensor size, dramatically reducing dose and scatter
Rectangular collimation reduces the irradiated field to match the film/sensor dimensions, reducing patient dose by up to 60% compared to round collimation and reducing scatter that degrades image quality.
MJDF Radiology & IRMER 2
What is the classic radiographic appearance of a periapical granuloma?