A 35-year-old patient has pain on biting on tooth #19, which had prior RCT. A gutta-percha cone was traced through a sinus tract to reveal an abscess above the tooth at the furcation area. What is the most likely diagnosis?

Correct answer: C. Vertical root fracture at the furcation

• A. Periodontal furcation involvement is possible but the sinus tract traced to the furcation from above and pain on biting is more specific for fracture.
• B. External cervical resorption presents as a radiolucency in the cervical region, not at the furcation with a sinus tract.
• C. Correct. A sinus tract traced by gutta-percha to the furcation area of a root canal-treated tooth with pain on biting strongly suggests a vertical root fracture at the furcation level. This is the classic presentation: RCT-treated molar, furcation-level sinus tract, pain on biting.
• D. Failed RCT causing apical periodontitis would show a lesion at the apex, not at the furcation.