A local anesthetic injection was placed correctly in an area of inflammation but anesthesia was inadequate. What is the most likely reason?

Correct answer: C. Low pH of the inflamed tissue

• A. Insufficient volume can contribute, but the question states the injection was successfully placed — pH effect is the primary mechanism.
• B. Wrong technique could cause failure, but the question specifies correct placement.
• C. Inflamed tissue has a LOW pH (acidic) from metabolic byproducts. Local anesthetics (weak bases) must be in their free base (uncharged) form to cross nerve membranes. In an acidic environment, more LA exists in the ionized (cationic) form → reduced membrane penetration → incomplete anesthesia. This is the 'hot tooth' phenomenon.
• D. High pH would favor more free base form (more active) → would IMPROVE anesthesia.