MJDF Part 1 - Membership of Joint Dental Faculties Dental Radiology and Imaging Questions and Answers

Question 1

A dentist reviews a treatment plan with a patient and determines that bitewing radiographs are required. The dentist then asks their qualified and appropriately trained dental nurse to perform the exposure. According to the Ionising Radiation (Medical Exposure) Regulations 2017 (IR(ME)R), who is acting as the 'Practitioner' in this scenario?

Accepted Answer

The dentist who clinically justified the exposure

Answer

Under IR(ME)R 2017, the 'Practitioner' is the registered healthcare professional responsible for the justification of an individual medical exposure. The 'Operator' is the person who carries out the practical aspects, such as positioning the patient and activating the X-ray set. In this case, the dentist performs the justification, making them the Practitioner, while the dental nurse is the Operator.

Question 2

A dental practice is conducting a quality assurance audit of its digital radiographs. According to the 'Guidance Notes for Dental Practitioners on the Safe Use of X-ray Equipment' (Public Health England/FGDP), what is the minimum target percentage for radiographs to be graded as 'diagnostically acceptable'?

Accepted Answer

Not less than 95%

Answer

UK guidance specifies that for digital imaging, the target for 'diagnostically acceptable' radiographs is not less than 95%. For older film-based imaging, the target is slightly lower at 90%. This ensures that patient radiation exposure is consistently optimised to produce images of sufficient diagnostic quality.

Question 3

Two periapical radiographs are taken to determine the bucco-palatal position of an unerupted maxillary canine. The second radiograph is taken with the X-ray tube head shifted mesially compared to the first. On the second image, the unerupted canine appears to have also moved mesially relative to the adjacent central incisor root. According to the parallax principle, what is the position of the canine?

Accepted Answer

It is palatally positioned.

Answer

This scenario uses the SLOB (Same Lingual, Opposite Buccal) rule for parallax. The tube head was shifted mesially, and the object of interest (the canine) appeared to move in the same direction (mesially). Therefore, the object is on the lingual (palatal) side.

Question 4

A dentist is planning an implant in the lower left first molar (LL6) region. A periapical radiograph shows limited bone height above the inferior dental canal. To assess the bucco-lingual bone width and the precise 3D relationship to the canal, which imaging modality is most justified as the next step according to UK selection criteria?

Accepted Answer

A cone beam computed tomography (CBCT) scan

Answer

When 2D imaging cannot provide sufficient information for safe implant placement, particularly regarding the 3D relationship with vital structures like the inferior dental canal, cross-sectional imaging is required. Cone Beam CT (CBCT) is the modality of choice for this, providing detailed 3D information of the dento-alveolar structures at a lower radiation dose than medical CT.

Question 5

What is the primary radiation protection advantage of using a rectangular collimator instead of a circular one for an intraoral periapical radiograph?

Accepted Answer

It significantly reduces the patient's effective dose.

Answer

Rectangular collimation restricts the size of the X-ray beam to more closely match the dimensions of the rectangular image receptor. This reduces the volume of patient tissue irradiated, which can lower the effective radiation dose by 40-60% or more compared to a standard circular collimator. While it may increase the risk of 'cone-cutting' errors if not aligned correctly, its dose-saving potential is a key principle of radiation optimisation (ALARP).

MJDF Part 1 Practice Test

MJDF Part 1 Practice Test

MJDF Part 1 - Membership of Joint Dental Faculties Dental Radiology and Imaging Questions and Answers