Overdentures are dentures which derive their support from one or abutment teeth by completely enveloping them beneath the fitting surface. The abutment teeth are usually root filled and either simply reduced or used in conjunction with stud or bar precision attachments. For both of these situations two techniques of impression taking are used. When the teeth are already root filled and will later be reduced it is termed an immediate overdenture. An impression of the root filled teeth, prior to reduction, is taken in alginate or elastomer in a special tray. The impression is cast and the abutment teeth on the model are reduced in height by 4mm and the dentures are constructed around this. When the processed denture is fitted, it is relined with cold cured acrylic in the areas around the abutment teeth to make it fit as well as possible. Overdentures can also be implant supported