Radiography questions split into two halves: the legal and safety framework, and reading images well enough to spot what has gone wrong. Fault recognition comes up a lot — foreshortening, elongation, cone cut, overlapped contacts — and each has a specific cause you are expected to name.
What radiography covers in the Knowledge Test
- IR(ME)R duties and who holds them
- Justification: why an exposure must be worth taking
- Intraoral views — periapical, bitewing, occlusal — and when each is used
- Panoramic imaging and its limitations
- Positioning faults and the error that produced each
- Quality assurance and when a retake is genuinely justified
Where candidates lose marks
Justifying a retake on preference rather than diagnostic need — under IR(ME)R that is the wrong answer.
Mixing up foreshortening and elongation. One is too much vertical angulation, the other too little.
Assuming overlapped contacts are a vertical problem. They are horizontal.
Who does what under IR(ME)R
The Ionising Radiation (Medical Exposure) Regulations define named duty holders, and exam questions routinely ask which one is responsible for a given decision. A dental nurse with a radiography qualification is usually the operator; the dentist is normally the practitioner who justifies the exposure.
| Role | Responsible for |
|---|---|
| Employer | Procedures, protocols, training records and equipment |
| Referrer | Providing enough clinical information to justify the exposure |
| Practitioner | Justifying the exposure — deciding it is worth the dose |
| Operator | Any practical aspect: positioning, exposure, processing, QA |
Reading the faults
Fault recognition is the most reliably examined part of this topic, because each fault has one cause. Learn the cause and the question answers itself.
| What you see | Cause |
|---|---|
| Roots look shorter, anatomy compressed | Foreshortening — too much vertical angulation |
| Roots look longer than expected | Elongation — too little vertical angulation |
| Contacts overlapped | Horizontal angulation error |
| Clear unexposed curve across the image | Cone cut — beam not centred on the receptor |
| Apices missing | Receptor positioned too far coronally |
| Image too pale or too dark | Exposure factors, or a processing fault |
| Blurring | Patient or receptor movement during exposure |
When a retake is justified
Under IR(ME)R every exposure must be justified, and that includes repeats. A retake is justified when the image cannot answer the clinical question — multiple overlapped contacts hiding interproximal caries, for example. It is not justified because the image is slightly dark but still diagnostic, because the patient dislikes it, or because you want a better teaching example. This is a values question as much as a technical one, and the exam tests it directly.
Worked examples
Real questions from our bank, with the reasoning. No sign-in needed.
Several lower molar periapicals in one session all show missing apices. What is the most likely cause?
- AExposure time consistently too long
- BThe receptor is repeatedly placed too coronallyCorrect
- CThe patient keeps swallowing
- DHorizontal angulation is too distal
Why: A fault repeating identically points to consistent positioning, not a one-off. Placing the receptor too high fails to cover the root ends.
Both free mocks draw from this topic in the same proportion as the real paper — 65 questions in 90 minutes, with an explanation for every answer and a per-topic breakdown at the end.
Start a free mock examRadiography questions, answered
Can a dental nurse take radiographs?
Only with an appropriate post-registration qualification, such as the NEBDN Certificate in Dental Radiography, and working within the practice's IR(ME)R procedures. Taking radiographs without that qualification is outside a dental nurse's scope of practice.
What causes foreshortening on a periapical radiograph?
Excessive vertical angulation of the beam. The roots appear shorter than they are and the anatomy looks compressed. Too little vertical angulation produces the opposite — elongation.
Why are contacts overlapped?
Horizontal angulation error: the beam has not passed through the contact points at right angles. It is a horizontal problem, not a vertical one, which is a distinction exam questions rely on.
When is a repeat radiograph justified under IR(ME)R?
When the original cannot answer the clinical question. Preference, minor density variation, or wanting a cleaner image for teaching are not sufficient justification for an additional radiation dose.
What is a cone cut?
A clear, unexposed curved area where the beam missed part of the receptor, because the tube head was not centred on it.
The other nine topics
Independent study material, not affiliated with or endorsed by NEBDN. Always check the official NEBDN website for the current syllabus. NEBDN does not publish a pass mark for the Knowledge Test.