ORE Part 1 Radiology & Radiation Protection 4 — Questions and Answers
Question 1: What is the annual occupational dose limit for whole body radiation exposure for a classified dental worker?
- 20 mSv per year (whole body effective dose limit under IRR17) (Correct answer)
- 100 mSv per year
- 1 mSv per year
- 50 mSv in any single year with 100 mSv over 5 years
Correct answer: 20 mSv per year (whole body effective dose limit under IRR17)
IRR17 sets the annual occupational whole-body effective dose limit at 20 mSv. Classified workers are those whose dose exceeds 6 mSv/year or 3/10 of the dose limit. In dental practice, doses are typically well below this limit.
Question 2: What is the 'justification' principle in radiation protection and how does it apply to dental radiography?
- Every radiation exposure must produce more benefit than detriment — exposures with no net benefit are unjustified and must not be taken (Correct answer)
- All radiographs are automatically justified if taken by a dentist
- Justification only applies to CT scanning
- Routine radiographs on new patients are automatically justified regardless of clinical need
Correct answer: Every radiation exposure must produce more benefit than detriment — exposures with no net benefit are unjustified and must not be taken
Justification requires that every radiographic exposure must produce a net benefit (diagnostic information improving patient management) that outweighs the radiation risk. Exposures taken for administrative or routine purposes without clinical indication are unjustified.
Question 3: Why is intraoral radiography preferable to panoramic radiography for diagnosing periapical pathology?
- Intraoral periapical radiographs provide higher resolution of periapical bone changes and root morphology with less geometric distortion than panoramic radiographs (Correct answer)
- Panoramic radiographs always provide better periapical detail
- Both are equivalent for periapical assessment
- Periapical pathology can only be diagnosed on CT scan
Correct answer: Intraoral periapical radiographs provide higher resolution of periapical bone changes and root morphology with less geometric distortion than panoramic radiographs
Periapical radiographs use film/sensor placed close to the tooth with minimal magnification, providing superior sharpness and resolution for periapical bone changes compared to panoramic radiographs which have more inherent distortion and geometric magnification.
Question 4: What is 'foreshortening' on a periapical radiograph and what causes it?
- An image error where the tooth appears shorter than actual — caused by excessive vertical angulation (X-ray beam too steep relative to the long axis of the tooth) (Correct answer)
- An image error caused by insufficient vertical angulation — teeth appear elongated
- An error caused by incorrect horizontal angulation
- A normal feature of all intraoral radiographs
Correct answer: An image error where the tooth appears shorter than actual — caused by excessive vertical angulation (X-ray beam too steep relative to the long axis of the tooth)
Foreshortening occurs when the X-ray beam is directed at too steep a vertical angle relative to the tooth long axis, causing the image to appear compressed/shorter than the actual tooth. Elongation is the opposite (insufficient angle).
Question 5: How should a pregnant dental worker's radiation exposure be managed?
- Once pregnancy is declared, dose to the abdomen/foetus must not exceed 1 mSv for the remainder of pregnancy; reassign to limit exposure if workplace assessment indicates significant risk (Correct answer)
- Pregnant workers must stop all radiography work immediately
- No special precautions are needed during pregnancy for dental radiography
- Pregnant workers must wear double lead aprons
Correct answer: Once pregnancy is declared, dose to the abdomen/foetus must not exceed 1 mSv for the remainder of pregnancy; reassign to limit exposure if workplace assessment indicates significant risk
IRR17 requires that once pregnancy is declared, the employer must ensure the dose to the foetus does not exceed 1 mSv for the remainder of pregnancy. Given typical dental X-ray scatter levels, this is rarely an issue, but a risk assessment must be carried out.
Question 6: What is a 'controlled area' in a dental radiography suite?
- An area where the instantaneous dose rate could exceed 7.5 µSv/hour — typically the area within 1.5 m of the primary beam and tube head, requiring restricted access during exposure (Correct answer)
- The entire dental practice
- Only the darkroom
- Only required for panoramic equipment
Correct answer: An area where the instantaneous dose rate could exceed 7.5 µSv/hour — typically the area within 1.5 m of the primary beam and tube head, requiring restricted access during exposure
Under IRR17, a controlled area is where doses could exceed 3/10 of an occupational dose limit, or where specific working procedures are required to control radiation. In dental radiography this is typically within 1.5–2 m of the tube head.
ORE Part 1 Radiology & Radiation Protection 4
What is the annual occupational dose limit for whole body radiation exposure for a classified dental worker?