Examine the radiograph: a tooth was obturated with a silver point and the patient still has pain with a persistent periapical lesion. Among the offered choices, the most likely cause of failure is:

Correct answer: A. A missed/extra (untreated) canal

• A. Correct. Among the offered options, an untreated/missed canal best explains persistent symptoms and apical pathology. (Silver-point corrosion is a classic cause but was NOT an option.)
• B. The radiograph does not show gross overfill as the cause.
• C. A vertical fracture would more likely show a J-shaped lesion and was not the intended answer.
• D. A cracked cusp is a coronal problem, not the persistent apical lesion.

Note: The recall noted that 'silver-point corrosion' — the classic textbook cause of late failure — was not among the answer choices, so 'missed canal' was selected.