Root fillings are the 'last-ditch-stand' to save a tooth. Imagine a tooth is like an ice-cream cone, with the part of the tooth visible above the gum being the ice-cream and the tooth root being just like the ice-cream cone - tapered and hollow. The nerve and blood vessels that keep the tooth alive are inside the hollow section of the ice-cream cone (the root canal). Sometimes the root canal becomes infected and causes tooth-ache or an abscess. The purpose of a root canal filling is to clean out the root canal and fill it preventing any further infection. Normally, the root-filled tooth is weakened by this procedure and crown would be recommended to strengthen the remaining tooth. Although a root-filled tooth is dead (no nerve supply) it should function normally for many more years.