If a root canal becomes infected again after a root canal has been done, it's often because of a problem near the apex of the root. Your dentist can do an apicoectomy to fix the problem so the tooth doesn't need to be extracted. An apicoectomy is done only after a tooth has had at least one root canal procedure.
 
In many cases, a second root canal treatment is considered before an apicoectomy. With advances in technology, dentists often can detect additional canals that were not adequately treated and can clear up the infection by doing a second root canal procedure, thus avoiding the need for an apicoectomy.

An apicoectomy is not the same as a root resection. In a root resection, an entire root is removed, rather than just the tip.