A root canal is a dental restoration used to fill in the hollow central chamber (or chambers) within a tooth. Root canal treatment is recommended when a tooth problem has extended to the very depth of a tooth. Problems that sometimes make root canal treatment necessary include: deep tooth decay, badly broken teeth, infected teeth, badly worn teeth. Patients who have teeth requiring root canal treatment are occasionally (but not always) in discomfort when they arrive. In the vast majority of cases, root canal treatment completely takes that pain away. Usually teeth that have had root canal treatment require crowns afterward.