A panoramic radiograph is taken of a patient who had root canal treatment on tooth #18. The image shows a periapical radiolucency at the apex of tooth #18. What is the most likely explanation?

Correct answer: B. Short obturation (inadequate GP length)

• A. Bone loss from periodontal disease typically appears as horizontal bone loss following the contour of the alveolar crest or as angular/vertical defects along the root surfaces — not specifically at the root APEX in a pattern consistent with periapical pathology following RCT.
• B. CORRECT. A periapical radiolucency at the apex of a previously root-canal-treated tooth that shows the GP (gutta-percha) not extending to the radiographic apex is most consistent with short obturation. Under-filled canals leave residual bacteria and space at the apex that cannot heal, resulting in a persistent or developing periapical lesion. This is the most common endodontic failure reason visible radiographically.