Which test is MOST reliable for assessing the pulp status of a newly erupted tooth with an OPEN APEX?

Correct answer: C. Cold test

• A. Percussion tests the PERIODONTAL LIGAMENT, not the pulp. It indicates apical periodontitis but says nothing directly about pulp vitality.
• B. The ELECTRIC PULP TEST is notoriously UNRELIABLE in immature teeth. The plexus of Raschkow is not fully developed until root formation is complete (roughly 3-4 years after eruption), so an EPT commonly gives FALSE NEGATIVES in a perfectly healthy young tooth. It also gives false readings through metallic restorations and in partially necrotic pulps.
• C. CORRECT. In an immature tooth with an OPEN APEX, the COLD test is the most reliable of the available options. Cold produces a rapid hydrodynamic movement of dentinal tubule fluid that stimulates A-delta fibres, and this response is preserved even in an incompletely innervated pulp. Refrigerant spray on a cotton pellet is the standard method.
• D. Heat testing is the LEAST reliable routine vitality test in any tooth. It has a slow onset, is uncomfortable, and is chiefly reserved for identifying a symptomatic tooth in a patient whose complaint is specifically provoked by heat.

Note: Always test a matched CONTRALATERAL control tooth and an adjacent tooth first, so the patient's normal response is established before the suspect tooth is tested. Remember that vitality tests measure INNERVATION (sensibility), not blood supply — which is why a recently traumatised tooth may not respond for weeks yet remain vital.