a female dentist numbing a female patient

Learn About Local Anesthesia

Sometimes your trip to the dentist results in a numb mouth. Your dentist may have to inject local anesthesia into your cheek and gums. Lidocaine is the most commonly used local anesthetic that dentists use. There are other ingredients alongside lidocaine that are injected too.

The liquid injected has lidocaine and can include some of the following:

  • A Vasoconstrictor – This drug narrows the blood vessels in your cheek and gums to make the numbing effect last longer (another chemical is added to make the vasoconstrictor break down slower).
  • Sodium Hydroxide – This compound assists the lidocaine in effectively numbing you.
  • Sodium Chloride – This compound helps the drug access your blood

Types of Numbing Injections

Local anesthesia at the dentist can be injected in two ways depending on what type of procedure you are having. A block injection is an injection that numbs an entire region of your mouth. This could be one whole side of your lower jaw, for example. The second type of injection is an infiltration injection. An infiltration injection numbs a much smaller area. The area numbed is only where the injection site is.

If your dental procedure requires local anesthesia, your dentist will use air or cotton to dry out the injection site. Some dentists add a topical anesthetic. It is usually in the form of a gel that has similar properties with the local anesthetic but is applied on top of the injection site to numb the area for a needle.

Your dentist will then slowly inject the local anesthetic. Almost everyone feels a little pressure from the local anesthetic entering the tissue, and a mild discomfort that is short-lived.

An injection can last several hours depending on your diet, exercise, metabolism, etc. It varies, but nothing to worry about.

Side Effects

Since local anesthetics are so commonly used in a dental office, the side effects are very rare but could include the following:

  • Hematoma – Swelling caused by blood. This can be the result of the needle hitting a blood vessel.
  • Numbness Outside Target Area – If this happens, it can cause some to worry, but rarely is there something to worry about. It will wear off when the drug wears off.
  • Unable to Blink One Eye – If this happens, you may need to tape your eyelid shut until the drug wears off (again, these are very rare).
  • Nerve Injury – This is the worst (still manageable) and most rare of them all. This can cause numbness and/or pain for several weeks; however, the nerve usually heals with time.


If you have allergic reactions to any drugs, make sure to tell your dentist before you begin. Also, be sure to tell him about any medications you are on. This includes over-the-counter drugs, herbs, supplements, vitamins, etc. If you remember any time you had a reaction to medicines, make sure to let your dentist know.

If you have any questions about the local anesthesia process we use here at Eagle Rock Dental Care in Rexburg, don’t hesitate to call us and/or make an appointment online. We would be happy to inform you and to put your mind at ease.


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