ORE Part 1 Dental Radiology 2 — Questions and Answers
Question 1: Which radiographic technique is most appropriate for detecting proximal caries in posterior teeth?
- Periapical radiograph with paralleling technique
- Horizontal bitewing radiograph (Correct answer)
- Dental panoramic tomograph
- Lateral cephalogram
Correct answer: Horizontal bitewing radiograph
Horizontal bitewing radiographs are the gold standard for detecting proximal (interproximal) caries in posterior teeth. They show the crowns of upper and lower teeth and the crestal bone level with minimal geometric distortion, making early enamel lesions visible that cannot be detected clinically.
Question 2: What is the most common cause of a radiopaque (white) artefact on a digital dental radiograph?
- Metallic restoration or prosthesis (Correct answer)
- Air bubble in processing chemicals
- Light leak in the darkroom
- Software malfunction
Correct answer: Metallic restoration or prosthesis
Metallic restorations (amalgam, crowns, posts) and prosthetic components are the most common cause of radiopaque artefacts on dental radiographs. They appear intensely white due to their high atomic number and density, which attenuates the X-ray beam almost completely.
Question 3: The paralleling technique for periapical radiography requires a minimum focus-to-film distance of:
- 10 cm
- 20 cm
- 30 cm (Correct answer)
- 40 cm
Correct answer: 30 cm
The paralleling (long cone) technique requires a minimum focus-to-receptor distance of 30 cm (using a long cone/spacer) to produce near-parallel X-rays that minimise geometric distortion and magnification. Some systems use 40 cm for even better image geometry. The bisecting angle technique uses a shorter distance of 20 cm.
Question 4: Which structure appears as a radiolucent band across the roots of maxillary teeth on a DPT (OPG)?
- Maxillary sinus floor
- Hard palate shadow
- Air shadow of the oropharynx (Correct answer)
- Nasal septum
Correct answer: Air shadow of the oropharynx
The oropharyngeal airway creates a characteristic radiolucent (dark) band that is superimposed across the roots of the anterior teeth on a DPT. This is a normal anatomical shadow and should not be confused with pathology. Asking the patient to place their tongue against the palate during exposure helps reduce this artefact.
Question 5: A cone-cut error on a periapical radiograph appears as:
- A blurred image across the entire film
- A clear unexposed area on part of the image (Correct answer)
- Double exposure of teeth
- Excessive darkness of the entire image
Correct answer: A clear unexposed area on part of the image
A cone-cut occurs when the X-ray beam does not fully cover the receptor, resulting in a clear (unexposed) area on part of the image. It is caused by misalignment between the beam and the sensor/film and is more common with rectangular collimation. Film holders with beam-aiming devices help prevent this error.
Question 6: What is the effective dose of a single digital periapical radiograph approximately equivalent to?
- 1 day of UK background radiation (Correct answer)
- 1 week of UK background radiation
- 1 month of UK background radiation
- 1 year of UK background radiation
Correct answer: 1 day of UK background radiation
A single digital intraoral periapical radiograph delivers an effective dose of approximately 1–5 microsieverts, which is roughly equivalent to less than one day of natural background radiation in the UK (approximately 7 microsieverts per day). This helps put the risk in perspective when discussing radiography with patients.
ORE Part 1 Dental Radiology 2
Which radiographic technique is most appropriate for detecting proximal caries in posterior teeth?