After one cartridge of lidocaine 1:100,000, profound numbness occurs, but soon the patient feels pain in an INFECTED tooth. Why is anesthesia lost/ineffective?

Correct answer: A. Acidic environment of infected tissue

• A. Correct. Inflamed/infected tissue is ACIDIC; low pH keeps the anesthetic in its ionized (charged) form, which cannot cross the nerve membrane, reducing efficacy.
• B. Incorrect. Infected tissue is acidic, not basic; the acidic pH is what impairs anesthetic action.