Inlays and onlays are used to replace large fillings or restore large cavities. They are usually made from, porcelain. In the past, the only option for large broken down fillings were full coverage crowns where sound tooth structure was removed along with damaged tooth structure. With conservative inlay and onlay preparations, only damaged tooth structure is removed and the inlay is bonded into place. Usually, the margins are above the gum line and are accessible in case there is recurrent decay and can be repaired easily without redoing the restoration. Once placed, they are virtually undetectable in the mouth and conserve much of your natural tooth structure.