IAN Injury Predictor — MFDS Part 1 MCQ

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ModerateOral Surgery PrinciplesIAN Injury PredictorMFDS Part 1

During preoperative assessment of a mandibular third molar on a panoramic radiograph, which finding is a recognised high-risk sign associated with inferior alveolar nerve injury following extraction?

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Correct answer: E — Darkening of the root where it overlaps the inferior alveolar canal

The correct answer is E. Darkening of a mandibular third-molar root where it overlaps the inferior alveolar canal is a recognised high-risk panoramic-radiographic sign for postoperative IAN injury. UK Royal College guidance places it among the three most significant signs, alongside diversion of the canal and interruption of its cortical white line. Root dilaceration or the number of roots may affect operative difficulty, but without an associated alteration in the canal-root relationship they are not equivalent predictors of IAN injury. Crown width and coronal caries may influence extraction planning or indication for treatment, but they do not indicate close anatomical proximity to the IAN. Darkening is relatively specific but not sufficiently sensitive to exclude risk when absent.

Reference: Faculty of Dental Surgery, Royal College of Surgeons of England. Parameters of Care for Patients Undergoing Mandibular Third Molar Surgery, Appendix 5: Radiological considerations. 2021. https://www.rcseng.ac.uk/-/media/Files/RCS/FDS/Guidelines/3rd-molar-guidelines--April-2021-v4.pdf