Justin Phillips, age 9, of Enid, Okla., for his question:

WHAT DID MY DENTIST DO TO NUMB MY JAW?

A drug used to bring about a state of painlessness termed anesthesia is called an anesthetic. There are two main groups of anesthetics: local and general.

The local anesthetics are usually chemical relatives of procaine, which dentists use to deaden a tooth before they repair it. Local anesthetics block conduction in the nerves in a certain area and keep them from carrying the pain impulse to the spinal cord and brain.

These local anesthetics are usually injected with a needle and syringe directly into the skin and underlying tissues to deaden the region.

The brand name for preparations of procaine hydrochloride is Novocaine, and the product is used as a local anesthetic during minor surgery. It is this product, most likely, that your dentist used to numb your jaw.