Why can a person still move their jaw after receiving a local anesthetic for dental work?

The ability to move your jaw after receiving a local anesthetic for dental work is due to the selective nature of how these drugs block nerve impulses.1

Local anesthetics work by blocking conduction in nerve fibers, but their effectiveness depends on the diameter of the fibers and the length of the fiber that must be affected. In general, thinner fibers are blocked first. The fibers responsible for transmitting dull, aching pain are among the thinnest and most susceptible to the anesthetic.1

While local anesthetics are capable of blocking both sensory and motor nerve fibers, normal clinical dosages are typically sufficient to block pain sensation without impairing motor function. Consequently, while the sensory nerves in the area are numbed to prevent pain, the motor nerves controlling the jaw remain functional, allowing you to continue moving it during the procedure.1