Radiology · patient case question
The panoramic radiograph shows loss of root substance on the impacted mandibular third molar, with the defect open to the follicular space. What type of resorption is this?
Patient case: Routine radiographic survey
Patient: Male, 34 years old
Chief complaint: “I'm just here for my check-up.”
History: No significant medical history. No medications. Last radiographs five years ago.
Findings: A panoramic radiograph and a full-mouth periapical series are taken today. Several incidental findings are noted for discussion.
Show answer and explanation
Correct answer: C. External resorption
- A. Physiologic resorption is the programmed loss of primary tooth roots preceding exfoliation. It is not applicable to a permanent third molar.
- B. Idiopathic cervical (invasive) resorption starts just apical to the epithelial attachment at the CEJ, not along the mid-root against a follicle.
- C. CORRECT. The defect originates on the OUTER root surface, at the interface with the follicle and adjacent tooth, and eats inward. External resorption is clast-cell activity initiated in the periodontal ligament or follicle, most often driven by pressure — impaction against a neighbouring tooth, an expanding cyst, or an orthodontic force. Radiographically the outline of the root is ragged and the canal remains a normally-traceable line running THROUGH the defect.
- D. Internal resorption begins in the PULP and balloons outward. Its signature is a smooth, oval, well-circumscribed radiolucency that is CONTINUOUS with the canal, with the canal outline lost at the level of the lesion. It requires vital, chronically inflamed pulp tissue.
Note: The quick discriminator: trace the canal. If you can follow it through the lesion, the resorption is EXTERNAL. If the canal outline disappears into the lesion, it is INTERNAL.