When a cavity becomes too large to fill by a traditional white or silver fillings a slightly different approach is taken because traditional filling materials are not strong under all circumstances. Porcelain (tooth coloured) inlays and onlays are restorations placed on the chewing surfaces of the back teeth after an impression is taken of the cavity either with a traditional mould procedure or by using a dental scanner device.
An inlay fits within the confines of the teeth (as in the picture below). An onlay covers the entire chewing surface of the tooth. These can be made of either a dense and tough polymer, porcelain or gold.
The procedure involves removing decayed tooth structure or old fillings, preparing the tooth cavity, taking an impression or scan of the cavity to fabricate a custom-fit inlay or onlay. Two visits are usually required to complete the treatment. Where possible, inlays and onlays are completed using the CEREC (Ceramic Reconstruction) technique. With this technique an inlay or an onlay is fabricated in one appointment at the surgery using a highly specialised scanner and a milling machine.