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Master Apical File Size — MFDS Part 1 MCQ

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ModerateRestorative PrinciplesMaster Apical File SizeMFDS Part 1

During preparation of a mature root canal, after coronal preflaring and determination of working length, which statement best describes selection of the final apical preparation size?

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

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Correct answer: D — Slightly enlarge the natural apical canal to a known size, adapting the preparation to its anatomy

The correct answer is D. Contemporary UK guidance describes apical preparation as slight enlargement of the natural canal to produce a terminal preparation of known size. The extent must reflect canal anatomy, dimensions, curvature and procedural safety; naturally wide or immature canals may require little or no enlargement. The first file to bind is only an estimate and may bind coronally despite preflaring, so it does not justify an invariant numerical rule. Finishing at or below that file size may provide inadequate apical preparation. Conversely, enlarging exactly three ISO sizes in every canal is a traditional teaching convention rather than a universal minimum. Using the largest available instrument disregards anatomy and risks transportation, ledging or perforation.

Reference: British Endodontic Society, A guide to Good Endodontic Practice, section on apical preparation, 2022. https://www.rcseng.ac.uk/-/media/FDS/The-British-Endodontic-Society-guide-to-Good-Endodontic-Practice.pdf