A root canal becomes necessary if the pulp tissue or nerve inside the tooth becomes inflamed or infected. This can be caused from several things. The most common cause is tooth decay progressing down into the tooth that allows harmful bacteria to reach the soft tissue. Other causes are trauma or an accidental blow to the tooth, multiple fillings over the years, or a broken down tooth needing a crown (cap). All these things can cause the pulp to become inflamed or infected. The inflammation and infection can also spread into the surrounding bone at the end of the tooth. The tooth and surrounding area may become very painful and swelling may occur. Once this happens a root canal procedure must be performed in order to save the tooth. The only alternative is having the tooth extracted.