Inlays and Onlays are laboratory-produced restorations made of ceramics. To that end, they are mainly composed of glass, with some crystals added to increase the strength of the porcelain ceramic. These procedures are typically indicated where the diagnosis or treatment of tooth decay is performed at a later stage and more tooth structure is lost in the process.
Inlays
Inlays are alternative Intra-coronal restorations (placed within a cavity prepared in the crown of a tooth) using an indirect technique. In contrast to other intra-coronal restorations (fillings – restorations performed when the loss of tooth substance due to decay is minor), an impression of the cavity is taken and a laboratory constructed inlay is produced and subsequently cemented into the prepared cavity.
Onlays
Onlays (or partial crowns) are a form of extra-coronal restoration placed around the tooth. Onlay restorations are indicated when decay or lost tooth structure extends to the cusps (biting surfaces) of the teeth. Onlays preserve more of your natural tooth structure in comparison to full crowns, whereas crowns essentially cover the entirety of the circumference and the biting surfaces of the tooth. Similar to Inlays and crowns, Onlays are constructed by a dental laboratory, necessitating a subsequent visit for cementation of the restoration.