Local Injections

Sometimes your dentist needs to numb a part of your mouth. He or she injects numbing drugs into your gum or inner cheek. This is called local anesthesia. It numbs only the area near the injection.

Lidocaine is the most common local anesthetic that dentists use. There are many others. They all have names ending in "-caine." Many people think of Novocain as the classic numbing drug. But Novocain actually is not used anymore. Other drugs last longer and work better than Novocain. These drugs also are less likely to cause allergic reactions.

The numbing drug is only one part of what's injected. The liquid in the shot also can include:

A type of drug called a vasoconstrictor. This drug narrows your blood vessels. This makes the numbness last longer.

A chemical that keeps the vasoconstrictor from breaking down

Sodium hydroxide, which helps the numbing drug work

Sodium chloride, which helps the drugs get into your blood

There are two kinds of numbing shots. A block injection numbs an entire region of your mouth, such as one side of your lower jaw. An infiltration injection numbs a smaller area.

If you need a numbing shot, your dentist will dry part of your mouth with air or cotton. Many dentists then swab the area with a gel to numb the skin.

Then, your dentist will slowly inject the numbing drug. The needle can sting. However, most people don't feel the needle itself. Instead, the sting they feel is caused by the liquid moving into the tissue.

A numbing shot can last up to several hours. After you leave the dentist's office, you may find it difficult to speak clearly or eat. Drinking from a straw can be messy. Be careful not to bite down on the numb area. You could hurt yourself without realizing it.

Local anesthetics are the most common drugs used in the dental office. Side effects are very rare.

One possible side effect is a hematoma. This is a blood-filled swelling. It can form when the injection needle hits a blood vessel.

The numbing drug sometimes causes numbness outside of the targeted area. If this happens, your eyelid or mouth can droop. You will recover when the drug wears off.

Sometimes, the vasoconstrictor drug can cause your heart to beat faster. This lasts only a minute or two.

Finally, the needle can injure a nerve. This can lead to numbness and pain for several weeks or months. The nerve usually heals over time.

It is rare to have an allergic reaction to a local anesthetic. Tell your dentist about any allergies you have. Also tell him or her about all the medications—both prescription and over-the-counter —you are taking. Some drugs can interact with local anesthetic solutions.