Radiology · patient case question
On the periapical of the mandibular premolars, a round radiolucency roughly 4 mm across sits near the apex of tooth #29. The tooth responds normally to cold and is caries-free. What is this structure?
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: D. The mental foramen
- A. A traumatic (simple) bone cyst is a larger, irregular lucency that characteristically scallops upward between the roots of vital teeth. It is not a small round apical radiolucency.
- B. A lateral periodontal cyst sits along the LATERAL root surface, most often between mandibular canine and premolar, and is typically a well-corticated teardrop shape rather than a round apical lucency.
- C. A periapical granuloma requires a NON-VITAL pulp. This tooth is vital and caries-free, so an inflammatory periapical lesion cannot be the explanation.
- D. CORRECT. The mental foramen is a normal anatomic radiolucency projected in the mandibular premolar region, usually between or near the apices of #28 and #29. It can convincingly mimic periapical pathosis. The two things that settle it are PULP VITALITY — normal response to cold excludes a lesion of endodontic origin — and shifting the horizontal angulation, which moves the foramen relative to the apex while a true periapical lesion stays attached.