Radiology · patient case question
The concave defect on the distal root of #18 at the point of contact with the impacted #17 is:
Patient case: Films for a Patient Not Seen in Ten Years
Patient: 48-year-old male
Chief Complaint: “I want a full check-up. I know it's been a while.”
Background: Last dental visit approximately ten years ago. No current symptoms. Reports his gums bleed when he brushes.
Medications: None
Vital Signs: BP 128/80 mmHg · HR 76 bpm · RR 16 · T 98.4°F
Findings: Generalized 5–7 mm pockets with bleeding on probing and visible recession. Several teeth are slightly mobile. On imaging: a horizontally impacted #17 whose crown abuts the distal root of #18, which shows a concave defect at the contact point; a well-defined mixed radiolucent-radiopaque lesion at the apices of the mandibular anteriors, which all test VITAL; and a radiopaque structure superimposed over the mandible on both the panoramic and lateral cephalometric films.
Show answer and explanation
Correct answer: A. External resorption
- A. CORRECT. EXTERNAL resorption. It originates OUTSIDE the tooth, in the periodontal ligament, and is initiated here by chronic PRESSURE from the impacted third molar crown against the root surface. Sustained pressure recruits clastic cells to the root surface. Radiographically the defect is a saucer-shaped concavity on the root outline, and the canal outline remains visible and INTACT through it.
- B. Hypercementosis is excessive cementum DEPOSITION producing a bulbous root, the opposite process.
- C. Attrition is occlusal or incisal wear from tooth-to-tooth contact — a crown phenomenon, not a root one.
- D. Internal resorption originates from the PULP, requires vital pulp tissue and odontoclasts within the canal, and produces a balloon-like expansion of the CANAL itself. The canal outline is lost at the lesion, which is the key radiographic distinction.
Note: Distinguishing the two on film: EXTERNAL — canal outline traceable through the defect, and the lesion MOVES relative to the canal when the horizontal angle is changed. INTERNAL — canal outline lost, lesion stays centred on the canal. Other causes of external resorption: orthodontic force, trauma, periapical inflammation, cysts and tumours.