Which sensation is lost first after a dental local anesthetic injection?

Which sensation is lost first after a dental local anesthetic injection?

• A. Pain
• B. Temperature
• C. Touch
• D. Proprioception

Answer: (A)

Pain is lost first because local anesthetics preferentially block the small-diameter nerve fibers that carry nociception. These fibers (A-delta and C) are more susceptible to sodium channel blockade, so conduction ceases in them before larger fibers are affected. Temperature is carried by some of the same small fibers and may follow, but clinically the earliest loss is pain. Larger fibers responsible for touch and proprioception (and motor fibers) require more drug to block and thus lose function later. Therefore, pain is the first sensation to disappear after a dental local anesthetic injection.

Pain is lost first because local anesthetics preferentially block the small-diameter nerve fibers that carry nociception. These fibers (A-delta and C) are more susceptible to sodium channel blockade, so conduction ceases in them before larger fibers are affected. Temperature is carried by some of the same small fibers and may follow, but clinically the earliest loss is pain. Larger fibers responsible for touch and proprioception (and motor fibers) require more drug to block and thus lose function later. Therefore, pain is the first sensation to disappear after a dental local anesthetic injection.