MFDS Radiology and Radiography — Questions and Answers
Question 1: According to the IRMER (Ionising Radiation (Medical Exposure) Regulations 2017) in the UK, what are the three key roles defined in the regulations for dental radiography?
- Patient, radiographer, and consultant
- Referrer (who requests the exposure), practitioner (who justifies the exposure), and operator (who carries out the practical aspects) (Correct answer)
- Dentist, nurse, and technician
- Inspector, supervisor, and operator
Correct answer: Referrer (who requests the exposure), practitioner (who justifies the exposure), and operator (who carries out the practical aspects)
IRMER 2017 defines three key roles: the Referrer is the registered health professional who requests the radiograph with sufficient clinical information; the Practitioner (IR(ME)R practitioner) is entitled to justify the exposure by weighing the clinical benefit against the radiation risk; and the Operator carries out the practical aspects including positioning, exposure, processing, and quality assurance. In dental practice, the dentist may fulfil all three roles, though qualified dental nurses and dental therapists can act as operators.
Question 2: What is the ALARA (or ALARP) principle in dental radiology and how is it applied in practice?
- All Lateral And Rotational Adjustments — it refers to patient positioning
- As Low As Reasonably Achievable (or Practicable) — radiation doses should be kept to the minimum consistent with obtaining diagnostic information, achieved through proper selection criteria, optimal technique, quality assurance, and rectangular collimation (Correct answer)
- Anterior Lateral Anteroposterior Radiograph Assessment — a specific projection technique
- It refers to the storage protocol for radiographic films
Correct answer: As Low As Reasonably Achievable (or Practicable) — radiation doses should be kept to the minimum consistent with obtaining diagnostic information, achieved through proper selection criteria, optimal technique, quality assurance, and rectangular collimation
ALARA/ALARP is the overriding principle of radiation protection requiring that all radiation exposures be kept as low as reasonably achievable while obtaining the necessary diagnostic information. In dental practice, this is achieved through: using selection criteria to justify each exposure, choosing the lowest effective dose (optimal kV, mA, exposure time), using rectangular collimation (reduces dose by up to 60% compared to round collimation), using fast-speed film or digital sensors, proper quality assurance programmes, and avoiding repeat exposures through good technique.
Question 3: On a periapical radiograph, a well-defined radiolucent area is visible at the apex of a vital upper central incisor with a thin radiopaque border. What is the most likely diagnosis?
- Periapical abscess
- Periapical (radicular) cyst
- Nasopalatine duct cyst (incisive canal cyst) (Correct answer)
- Periapical granuloma
Correct answer: Nasopalatine duct cyst (incisive canal cyst)
A nasopalatine duct cyst (incisive canal cyst) is the most common non-odontogenic cyst of the jaws. It presents as a well-defined, round or heart-shaped radiolucency in the midline of the anterior maxilla, often with a corticated (radiopaque) border. Critically, the associated teeth are vital, distinguishing it from periapical pathology. It arises from epithelial remnants of the nasopalatine duct and is typically an incidental radiographic finding or may cause painless swelling of the anterior palate.
Question 4: What radiographic features would suggest a lesion in the jaw is malignant rather than benign?
- Well-defined margins with a corticated border
- Ill-defined, irregular, ragged margins with no corticated border, destruction of adjacent structures (teeth, cortical bone, inferior alveolar canal), and a 'moth-eaten' or permeative pattern of bone destruction (Correct answer)
- A perfectly round radiolucent area with a sclerotic rim
- A mixed radiolucent-radiopaque lesion with a clear capsule
Correct answer: Ill-defined, irregular, ragged margins with no corticated border, destruction of adjacent structures (teeth, cortical bone, inferior alveolar canal), and a 'moth-eaten' or permeative pattern of bone destruction
Malignant lesions typically show: ill-defined, irregular, non-corticated margins (indicating aggressive, uncontrolled growth); ragged or 'moth-eaten' pattern of bone destruction; destruction of adjacent anatomical structures (resorption of tooth roots, erosion of the inferior alveolar canal wall, destruction of cortical bone); 'floating teeth' (teeth appearing to hang in space due to extensive bone loss); sunburst or onion-skin periosteal reaction (in osteosarcoma); and soft tissue mass. In contrast, benign lesions typically have well-defined, corticated margins.
Question 5: What is the maximum recommended dose of radiation for occupational exposure per year for dental professionals in the UK, according to the Ionising Radiations Regulations 2017 (IRR17)?
- 1 mSv per year
- 20 mSv per year (whole body effective dose limit for classified workers) (Correct answer)
- 50 mSv per year
- 100 mSv per year
Correct answer: 20 mSv per year (whole body effective dose limit for classified workers)
Under the Ionising Radiations Regulations 2017 (IRR17), the dose limit for occupational exposure for classified radiation workers is 20 mSv effective dose per year (averaged over 5 years, with no single year exceeding 50 mSv). For non-classified workers (which includes most dental professionals), the practical limit is lower. The dose limit for the general public is 1 mSv per year. In a well-run dental practice, staff doses should be negligible (<0.1 mSv/year) due to appropriate shielding, distance, and time protocols.
Question 6: What is the advantage of a cone beam computed tomography (CBCT) scan over conventional two-dimensional radiography in dentistry, and what are its limitations?
- CBCT uses less radiation than a single periapical radiograph and has no limitations
- CBCT provides three-dimensional imaging allowing assessment of structures in all planes, with higher spatial resolution than medical CT for dental structures; limitations include higher radiation dose than conventional radiographs, limited soft tissue contrast, and motion artefacts (Correct answer)
- CBCT is identical to medical CT in all respects
- CBCT only shows soft tissues and cannot image bone or teeth
Correct answer: CBCT provides three-dimensional imaging allowing assessment of structures in all planes, with higher spatial resolution than medical CT for dental structures; limitations include higher radiation dose than conventional radiographs, limited soft tissue contrast, and motion artefacts
CBCT uses a cone-shaped X-ray beam rotating once around the patient to acquire volumetric data, which is reconstructed into 3D images viewable in axial, coronal, sagittal, and oblique planes. Advantages include true 3D assessment (no superimposition), high spatial resolution for hard tissues, lower radiation dose than medical CT (though 5-100 times more than a panoramic radiograph). Limitations include higher dose than conventional radiographs (must be justified under IRMER), poor soft tissue contrast (compared to medical CT/MRI), metallic artefacts from restorations, and motion artefacts.
MFDS Radiology and Radiography
According to the IRMER (Ionising Radiation (Medical Exposure) Regulations 2017) in the UK, what are the three key roles defined in the regulations for dental radiography?