The clinical finding most indicative of pulp necrosis is a negative response to thermal and electric pulp tests.

- Pulp necrosis occurs when the pulp tissue inside a tooth dies, typically due to infection or trauma. The vital pulp responds to stimuli like cold, heat, and electric pulp testing.
- In a healthy or inflamed pulp, these tests produce a positive response, such as pain or sensitivity.

- Option 1: Prolonged response to cold stimuli usually indicates irreversible pulpitis, where the pulp is inflamed but still vital.
- Option 3: Sharp pain on biting is commonly associated with conditions affecting the periodontal ligament or cracked tooth syndrome, not specifically necrosis.
- Option 4: Spontaneous throbbing pain often signifies pulpitis, particularly symptomatic irreversible pulpitis, due to inflammation rather than necrosis.

In contrast, pulp necrosis results in the loss of pulp vitality, so the pulp will not respond to thermal or electric pulp testing. This absence of response is a critical diagnostic feature distinguishing necrotic pulp from inflamed but still vital pulp tissue.

In summary:
- Necrotic pulp → Negative response to thermal and electric pulp tests
- Inflamed but viable pulp → Positive response (often heightened or prolonged)

This diagnostic approach is essential for determining treatment plans, including root canal therapy.

Reference: *Hargreaves KM, Berman LH. Cohen’s Pathways of the Pulp. 12th edition, Volume 1, Chapter 5, p. 193-197.*