VIDEO TRANSCRIPT: Onlays are indicated when there is not enough natural tooth structure to support a chair-side filling, but conservative enough that you do not have to remove as much tooth structure as a crown. It is essentially an indirect puzzle piece that is nicely bonded into your tooth. Like crowns, onlays require two appointments. In the first appointment, the diseased tooth structure is removed and an impression is obtained so that the lab can fabricate a custom-fit porcelain restoration unique to your tooth. In the second appointment, the onlay is cemented in and it will blend very naturally to your tooth.