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Local Anesthesia

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Sometimes your dentist needs to numb a part of your mouth. He or she injects medicine into your gum or inner cheek. This medicine is called local anesthesia.

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 injection 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 injections. 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. This is the area near where the injection was given.

If you need local anesthesia in order to have your dental treatment done, 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 local anesthetic. Most people don't feel the needle. Instead, the sting they feel is caused by the anesthetic moving into the tissue.

An injection of local anesthesia 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.

Side Effects

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 medicine 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.

If you are unable to blink, you may need to have your eye taped shut until the numbness wears off. The anesthetic usually lasts for only a couple of hours. In some people, the vasoconstrictor drug can cause the heart to beat faster. This lasts only a minute or two. Tell your doctor if this has ever happened to you.

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. Be sure to tell your dentist about all of the medicines you take. This should include over-the-counter drugs and also any herbs or vitamins you take. Also, tell your dentist about any reactions you have had with medicines, no matter how minor the reaction was. Some drugs can interact with local anesthetics.

Local anesthesia can lead to a short-term problem with operation of wheelchairs that use "sip and puff" technology. If your mouth is numb, you may not be able to create a tight seal around the straw that controls your wheelchair. Make sure that you have someone with you who knows how to use the manual controls on your wheelchair until your numbness wears off.


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