A radiograph of a previously root-canal-treated tooth #18 shows a short GP fill and a periapical radiolucency. What is the most likely explanation?

Correct answer: A. Short GP fill (inadequate obturation to the apex)

• A. ✅ Correct. Visible short GP fill + periapical radiolucency = INADEQUATE OBTURATION. The canal was not sealed to the apex, allowing continued bacterial irritation and persistent periapical pathology. This is the most common cause of RCT failure.
• B. ❌ A periapical radiolucency after RCT is NOT normal — it indicates failure or persistent infection.
• C. ❌ Vertical root fracture would show a J-shaped radiolucency or periodontal defect pattern — not simply correlating with a short GP fill.
• D. ❌ Lateral canal communication is a possibility but would not typically cause a classic periapical radiolucency correlated with a visibly short fill.