Hesperian Health Guides

How to Inject

In this chapter:

For a good, safe injection, remember these 5 things! Local anesthetics are the only injections given in the mouth. Learn more about injecting antibiotics.

swollen gum near the teeth.
  1. Do not inject local anesthetic into an area that is swollen. This can spread the infection. Also, pus inside the swelling stops the local anesthetic from working properly. Instead, treat the swelling first and take out the tooth later.
  2. If the person has a heart problem, do not inject more than 2 times in one visit. Also, it is best not to use an anesthetic with epinephrine on persons with heart problems. Use lidocaine only, or bupivacaine only.
  3. Before you push the needle under the skin, be sure its pointed end and opening are facing in the correct direction.
  4. a needle with the pointed end on top for injecting above an upper tooth.
    The local
    anesthetic must
    come out against
    the bone, where
    the nerve is.
    a needle with the pointed end down.

  5. Before you inject the local anesthetic, wait a moment to see if any blood enters the syringe. (Note: only an aspirating syringe will do this.)

    a syringe with some blood in it.

    Pull back on the plunger. If blood comes inside, it means you have poked a blood vessel.

    Pull the needle part way out and gently move it over to a different place.

    If you inject local anesthetic into the blood vessel, there will be more swelling afterward, and the person may faint. If the person faints:

    • Lay him on his back.
    • Loosen his shirt collar.
    • Lift his legs so they are higher than his head.

  6. Clean and sterilize or dispose of syringes and needles..
    Do not pass an infection from one person to another by using unsterilized needles.
    DENT Ch9 Page 138-4.png


    Sterilize the syringe and needle by baking or pressure steaming. When using a metal syringe, also use a new cartridge of anesthetic for each person. Do not use local anesthetic from a cartridge that you have already used on another person.


injecting near the roots of a back tooth.

Injecting the upper teeth

Inject local anesthetic near the root of the tooth you want to treat.

Front teeth have one root. Back teeth have more than one.

For a tooth to become completely numb, the local anesthetic must touch the small nerve going to each one of its roots.

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  1. First decide where to inject. Lift the lip or cheek. See the line that forms when it joins the gum. The needle enters at the line where the lip or cheek meets the gum.
  2. Push the needle in, aiming at the root of the tooth. Stop when the needle hits bone. Inject about 1 ml of local anesthetic (½ of a cartridge). Pull the needle part way out and move it over to the next root. Inject again.

    If the tooth is to be taken out, leave .25 ml for the next step.

  3. If you are taking out a tooth, also inject the gums on the inside.
    Ask the person to open wide. Inject the remaining anesthetic (.25 ml) directly behind the back tooth that must come out.
    DENT Ch9 Page 139-3.png
    DENT Ch9 Page 139-4.png

    One injection can numb the gum behind the 6 front teeth. Inject into the lump of gum behind the middle front teeth.

    (Note: This injection hurts! It may help to use "pressure anesthesia.")

  4. Wait 5 minutes for the tooth to become numb.

Injecting the lower teeth

When you block the nerve, it affects all of the teeth as well as gums on that side. However, it takes practice to do this successfully. Ask an experienced dental worker to help you learn how to give this injection properly.

Stand in such a way that you can see clearly where you need to inject. Ask the person to open wide.

standing in front of person in a chair while injecting inside his mouth.
standing beside the person while injecting.

  1. First feel for the place to be injected.
    Put your thumb beside the last molar tooth. (Wash your hands first!) Feel the jawbone as it turns up towards the head. Rest your thumb in the depression there.
  2. Press against the skin with the end of your thumb.
    The skin forms a “v” shape. Your needle must go into the “v.” Hold the syringe on top of tooth number 4 and aim the needle at the “v.”
    DENT Ch9 Page 140-3.png

    Push the needle in until it hits the jawbone, (about ¾ of the length of a long needle). Pull back on the plunger of the aspirating syringe to check for blood.

    Inject 1.5 ml of local anesthetic (¾ of a cartridge).

    Try to feel your way: If you hit bone too early, pull the needle part way out and move it over so that it points more toward the back of the mouth. Try again.

    If you do not hit bone, the needle is too far back. Pull it part way out, and point it more toward the front. Push it in again.

  3. Give a second injection BESIDE the back teeth.
    DENT Ch9 Page 141-1.png

    If you are going to fill or remove a back tooth, inject beside that tooth, where the cheek joins the gum.

    Inject .5 ml of local anesthetic (¼ of a cartridge).

    This injection is not needed for front teeth. It is enough to block the main nerve.

  4. Wait 5 minutes for the tooth to become numb.

This page was updated:17 May 2024