What is the mechanism by which INTRAPULPAL anesthesia produces its effect?

Correct answer: D. Pressure — the solution is forced under back-pressure into the pulp chamber

• A. Dentinal tubule diffusion is the proposed basis of topical desensitizers, not of intrapulpal injection, which requires direct access to an exposed pulp.
• B. PDL fibers are not the target — that describes the intraligamentary (PDL) injection, a different technique entering through the gingival sulcus.
• C. Systemic absorption plays no role; the effect is immediate and entirely local.
• D. CORRECT. The essential requirement for intrapulpal anesthesia is BACK-PRESSURE. The needle is wedged into the exposure so the opening is snug, and the solution is expressed against firm resistance. It is the pressure of the injection — not the pharmacology of the drug — that produces the profound and immediate effect. Studies show plain saline injected under the same pressure works nearly as well. Onset is immediate but duration is short (roughly 15–20 minutes), so work must proceed at once.

Note: Warn the patient: intrapulpal injection is briefly but sharply painful. It is a rescue technique for a hot tooth after block and infiltration have failed, and the short duration means you must be ready to work immediately.