This is a building mechanism utilized when there is inadequate tooth structure remaining to support a traditional restoration. A small metal rod, referred to as the post, is inserted into the root canal of the tooth, and left to protrude from the root for about a few millimeters to allow the filling, or core, to be put in place. They are used to retain cores and crowns in place. Posts are only placed in teeth previously root canaled. Build Ups are mostly utilized underneath crowns for support.