Dentigerous Cyst — ORE Part 1 MCQ

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ModerateRadiology & ImagingDentigerous CystORE Part 1

A panoramic radiograph (OPG) shows a well-defined unilocular radiolucency associated with the crown of an unerupted lower third molar. The radiolucency extends more than 2.5 mm from the enamel-cementum junction. What is the most likely diagnosis?

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Correct answer: B — Dentigerous cyst

The answer is B: Dentigerous cyst. The diagnostic features are pathognomonic: a unilocular radiolucency surrounding the crown of an unerupted tooth, attached at the neck, is the defining radiographic presentation of dentigerous cyst. The crucial measurement is the >2.5 mm pericoronal space. Normal dental follicles measure ≤2–3 mm; when the follicular space exceeds 2.5 mm, it is considered pathological and consistent with cyst formation. Radicular cyst requires a non-vital tooth with periapical pathology, not an unerupted crown. Odontogenic keratocyst and ameloblastoma typically present with different radiographic patterns and are less commonly associated with a simple unilocular presentation around the crown of an unerupted tooth. Option E (normal follicle) is excluded by the measurement criterion itself.

Reference: An Analysis of Dentigerous Cysts Developed around a Mandibular Third Molar by Panoramic Radiographs. PMC National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6473924/ (2019); International odontogenic radiology criteria consistent with UK dental school curricula and SDCEP guidance on odontogenic pathology.