Tooth #19 has had RCT and a post placed. The patient shows 9 mm probing depths on the distobuccal and distolingual surfaces, while all other surfaces probe normally. What is the MOST likely cause?

Correct answer: B. Vertical root fracture

• A. Incorrect. Furcation involvement would show probe readings in the furcation itself and affect the area more broadly.
• B. Correct. A vertical root fracture (VRF) after post placement classically presents with a narrow, isolated deep probing on ONE or TWO surfaces of the fractured root. The isolated 9 mm DB/DL probing on a post-restored RCT tooth is the hallmark VRF presentation.
• C. Incorrect. Localized aggressive periodontitis affects multiple sites in young patients — not isolated to two surfaces of one post-restored tooth.
• D. Incorrect. Secondary caries causes sensitivity and marginal breakdown — not selective deep probing consistent with a root fracture.