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Root Canal Working Length — MFDS Part 1 MCQ

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ModerateRestorative PrinciplesRoot Canal Working LengthMFDS Part 1

During primary root canal treatment of a mature permanent tooth with a closed apex, which target best defines the working length for cleaning, shaping and obturation?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: C — At the apical constriction, located primarily using an electronic apex locator

The ideal endpoint is the apical constriction. UK specialist guidance recommends using an electronic apex locator as the principal aid to working-length determination, supplemented by radiographic and other clinical information. The radiographic and anatomical apices do not reliably coincide with the constriction, so a universal rule of 0.5–1 mm short of the radiographic apex is only an approximation, not the definition of working length. Terminating at the radiographic or anatomical apex risks over-instrumentation and irritation of periapical tissues, while extending beyond the foramen is inappropriate. Stopping 3 mm short may leave infected or necrotic tissue within the apical canal.

Reference: British Endodontic Society. A Guide to Good Endodontic Practice, Chapter 6: Root canal treatment, 2022. https://www.rcseng.ac.uk/-/media/FDS/The-British-Endodontic-Society-guide-to-Good-Endodontic-Practice.pdf