What is the single best clinical indicator of a vertical root fracture?

Correct answer: B. An isolated, narrow, deep periodontal probing defect

• A. Generalised horizontal bone loss is the pattern of chronic periodontitis, which affects multiple sites rather than one narrow point.
• B. CORRECT. A vertical root fracture creates a direct channel from the canal to the periodontium along the fracture line. Bacteria track down it and produce a NARROW, ISOLATED, DEEP probing defect immediately adjacent to otherwise normal sulcus depths — often 8–10 mm at one point with 2–3 mm on either side. That solitary probing spike is the most reliable clinical sign.
• C. Most vertically fractured roots have already been root-treated and are therefore non-vital and non-responsive to cold.
• D. Apical PDL widening is non-specific and occurs with apical periodontitis of any cause.

Note: Other supporting signs: a J-shaped or halo radiolucency wrapping the root, a sinus tract close to the gingival margin rather than at the apex, and direct visualisation of the fracture on flap reflection. Prognosis is hopeless — extraction, or root resection in a multi-rooted tooth.