What do they inject in your gum to numb tooth pain?

Anesthetic: One of many local anesthetics is chosen, depending on your need, spread of infection, etc. You can't do this yourself at home. If you have tooth pain, you have a badly infected or damaged tooth. Even if numbed, the infection will spread into the surrounding tissues and your blood stream. You need to have the infection treated. Please call your dentist now.

Usually: It is usually lidocaine.. But other medications are also used. It is usually mixed with a little Epinephrine and a preservative. Ask your dentist what he or she uses.

Solution needed...: Dental pain exists because there is a problem, and requires and/or healing to go away. It sounds like you need a dental appointment. During a dental procedure a local anesthetic may be injected by your provider; this would be specific to each case and you can discuss it at you appointment. Good luck ;).

Local anesthetics: The most commonly used local anesthetics used in dentistry are lidocaine, mepivacaine, articaine, bupivacaine, prilocaine and etidocaine... There are others, too...