A patient had root canal treatment completed and continues to experience lingering pain in the same tooth. What is the MOST probable cause?

Correct answer: B. An untreated (missed) canal

• A. Normal post-treatment tenderness resolves in days; 'lingering pain' that persists indicates a real problem.
• B. CORRECT. Persistent or lingering PAIN after completed endodontic therapy most often means residual vital or infected tissue remains in a canal that was never located and instrumented — classically MB2 in a maxillary molar or a second canal in a mandibular incisor or premolar. Retreatment with magnification and CBCT is indicated.
• C. A poor coronal seal permits reinfection over time, but that typically presents later with apical periodontitis, not immediate lingering pain.
• D. Overextension causes pain on percussion or a foreign-body response, not lingering thermal-type pain.

Note: Persistent pain after RCT: think missed canal first, vertical root fracture second.