Impacted Third Molar — ORE Part 1 MCQ

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ModerateOral SurgeryImpacted Third MolarORE Part 1

A 32-year-old man requires extraction of a horizontally impacted lower left third molar. The root apices are in close proximity to the inferior alveolar nerve canal on the OPG. Which radiographic feature on the OPG is most predictive of a direct relationship between the roots and the nerve canal?

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Correct answer: C — Interruption of the white line of the canal

Interruption of the white line of the canal is the most statistically significant and reliable OPG sign for predicting direct anatomical contact between third molar roots and the inferior alveolar nerve canal. The white line represents the cortical boundary of the mandibular canal on panoramic radiography; interruption of this line indicates loss of cortical bone and direct contact between the root and nerve. Evidence from panoramic radiographic studies identifies interruption of the white line as the only statistically significant predictor (p = 0.006) of close proximity/direct contact. Although darkening of the root is the most common sign (52% prevalence), prevalence does not equal predictivity; it has lower specificity than interruption of white line. Narrowing of the canal, deflection of the canal, and narrowing of the root lack comparable statistical support for predicting direct contact. The Rood and Shehab classification framework identifies multiple signs of nerve proximity, but the question requires the single most predictive feature, which the evidence clearly establishes as interruption of the white line.

Reference: Proximity of impacted mandibular third molars to the inferior alveolar canal and its radiographic predictors: a panoramic radiographic study. Int J Oral Maxillofac Surg. 2013. https://pubmed.ncbi.nlm.nih.gov/24431832/