What is the BEST method to distinguish a toothache of endodontic origin from one of periodontal origin?

Correct answer: B. Pulp vitality testing (cold or electric pulp test)

• A. Probing depth is informative but not definitive on its own — a draining endodontic lesion can produce a deep isolated probing defect that mimics periodontal disease.
• B. CORRECT. The single defining difference is PULP STATUS. A tooth with an endodontic problem has a compromised or necrotic pulp and responds abnormally or not at all to vitality testing. A tooth with a purely periodontal problem — even with a deep pocket and a periodontal abscess — has a VITAL, normally responding pulp. Combine pulp testing with probing patterns (a narrow isolated defect suggests endodontic drainage; broad generalized pockets suggest periodontal disease), sinus tract tracing with gutta-percha, and radiographs.
• C. Heat testing is one form of pulp testing but is less reliable and less commonly used than cold; it is most useful for reproducing a specific chief complaint.
• D. PERCUSSION indicates inflammation in the periodontal ligament, which occurs with BOTH endodontic and periodontal pathology — it cannot separate them.

Note: ⚠️ The recall marked 'percussion.' Percussion tells you the PDL is inflamed; it does not tell you WHY. Vitality testing is the discriminator.