Dental Radiology and Diagnostic Imaging
What the exam tests
Correct selection of the right image for the clinical question, safe dosing, and interpretation of anatomy and artefacts that mimic disease.
Core rules
- Justification and optimisation: every exposure must change the management. Use paralleling technique with a holder to avoid elongation and foreshortening; bitewings for proximal caries and bone levels, periapicals for individual teeth and apices, panoramic views for gross jaw assessment.
- Panoramic images have lower resolution and geometric distortion; they do not show proximal caries reliably and cannot replace periapicals or bitewings. Ghost images and overlap of the spine are common.
- Cone-beam CT is for three-dimensional questions: canal proximity, root fractures, implant planning, impacted teeth. It carries a higher dose than intraoral films and is not a routine screening tool.
- Anatomical mimics: the mental foramen, incisive canal, submandibular gland fossa (Stafne defect), maxillary sinus, inverted Y of the mandibular canal and the pterygomaxillary fissure can all look like pathology.
- Radiation protection: lead apron and thyroid collar, fastest receptor compatible with the diagnostic need, no routine repeat films. Dose units are gray (absorbed) and sievert (effective).
Worked example
A panoramic radiograph taken for a denture patient shows a well-corticated radiolucency below the mandibular canal in the angle region, and the patient is asymptomatic. Reasoning: a corticated, asymptomatic defect below the canal in the submandibular fossa is likely a Stafne bone cavity. Confirm with occlusal or cone-beam imaging before considering biopsy; blind biopsy of this developmental defect is inappropriate.
Traps that cost marks
- Diagnosing caries from a panoramic image.
- Assuming every radiolucency needs surgery.
- Ignoring distortion when judging working length or canal proximity.