Sometimes a cavity can become so big that it infects the nerve inside of the tooth. This causes pain and swelling, and you’ll need a root canal to fix it. First, we give you a numbing agent so that you don’t feel any pain. Then, we remove the decayed portion of the tooth and clean out the infected nerve. We then use a material called “gutta percha” to fill the space where the nerve used to be in order to keep bacteria from attacking the tooth again. You’ll usually need a crown after a root canal, as the tooth usually loses a lot of strength.