What happens when the local anesthetic (LA) solution is buffered?

Correct answer: C. Increase the pH of the LA solution

• A. Buffering actually DECREASES (speeds up) the time for pulpal anesthesia onset — the opposite of this answer.
• B. Buffering does not significantly decrease duration. Duration is primarily determined by the specific anesthetic agent and the presence/absence of vasoconstrictor.
• C. Buffering LA (adding sodium bicarbonate to commercial LA carpules) INCREASES the pH from ~3.5-4.0 to approximately physiologic pH (7.0-7.4). This increases the proportion of the uncharged free-base form (non-ionized), which crosses nerve membranes more rapidly, resulting in FASTER onset of anesthesia and reduced burning/stinging upon injection. Commercial buffers include Onset (Anutra Medical).
• D. Buffering affects pH but does not enhance the vasoconstrictive effect of epinephrine in the LA solution.