MJDF Radiology & IRMER 4 — Questions and Answers
Question 1: What is the effective dose from a dental bitewing radiograph (digital) compared to background radiation?
- Approximately 1–8 µSv per image; background radiation is approximately 2,700 µSv/year in UK (Correct answer)
- Identical to a chest X-ray (~20 µSv)
- 100 µSv per image
- No radiation from digital sensors
Correct answer: Approximately 1–8 µSv per image; background radiation is approximately 2,700 µSv/year in UK
A digital bitewing delivers approximately 1–8 µSv (depending on technique), representing a very small fraction of the average UK background radiation of approximately 2.7 mSv/year; this context aids risk communication with patients.
Question 2: What is the definition of 'radiation weighting factor' (wR)?
- A factor applied to absorbed dose to account for the biological effectiveness of different radiation types (X-rays: wR=1) (Correct answer)
- The ratio of radiation dose to image quality
- The number of X-rays absorbed per kg
- The distance factor for X-ray beams
Correct answer: A factor applied to absorbed dose to account for the biological effectiveness of different radiation types (X-rays: wR=1)
The radiation weighting factor (wR) converts absorbed dose (Gy) to equivalent dose (Sv), accounting for the biological damage potential of different radiation types; for X-rays and gamma rays, wR = 1 (alpha particles wR = 20).
Question 3: Under IRR 2017, what is the role of the Radiation Protection Supervisor (RPS) in a dental practice?
- Ensures day-to-day compliance with local radiation protection rules and supervises radiation workers in practice (Correct answer)
- Performs dosimetry for all patients
- Prescribes radiographs for all patients
- Only responsible if an incident occurs
Correct answer: Ensures day-to-day compliance with local radiation protection rules and supervises radiation workers in practice
The RPS (usually a trained senior team member in the practice) ensures that the local rules for radiation protection are followed in daily practice and acts as the first point of contact for radiation protection matters.
Question 4: What is the clinical significance of a 'J-shaped' root canal on a periapical radiograph?
- Suggests a lateral canal or missed additional root — important for endodontic planning (Correct answer)
- Normal root anatomy always
- Indicates external resorption
- Caused by radiographic positioning error
Correct answer: Suggests a lateral canal or missed additional root — important for endodontic planning
A J-shaped radiolucency at the root apex suggests the possibility of a missed lateral or accessory canal, an untreated additional root, or a strip perforation during endodontic treatment.
Question 5: What is the appearance of hypercementosis on a periapical radiograph?
- Bulbous enlargement of the root apex surrounded by normal PDL space and lamina dura (Correct answer)
- Absence of PDL space
- Radiolucency at the apex
- Short blunted root
Correct answer: Bulbous enlargement of the root apex surrounded by normal PDL space and lamina dura
Hypercementosis appears as excessive cementum deposition around the root, giving a club-shaped or bulbous root appearance with an intact (widened) PDL space and lamina dura, distinguishing it from periapical pathology.
Question 6: What is the purpose of the lead thyroid collar in dental radiography?
- Protect the radiosensitive thyroid gland from scatter radiation — important especially in children and young adults (Correct answer)
- Replace the lead apron
- Required only for panoramic radiographs
- Only used in CBCT
Correct answer: Protect the radiosensitive thyroid gland from scatter radiation — important especially in children and young adults
The thyroid is highly radiosensitive (especially in children); the thyroid collar attenuates scatter radiation reaching this gland during dental radiographic procedures, reducing the dose to this at-risk tissue.
MJDF Radiology & IRMER 4
What is the effective dose from a dental bitewing radiograph (digital) compared to background radiation?