Inlays and onlays are restorative dental options that are used to fill in gaps in teeth when a filling will not work because there is too much damage to the tooth, and a crown would be too intrusive a solution. An inlay fills in the hollows and cavities in the areas between the cusps, mainly covering the chewing surface of teeth. An onlay is a more substantial reconstruction, doing more than just filling in cavities and areas of the chewing surface. Onlays also extend out and cover one or more of the cusps of the tooth. Both inlays and onlays are made of the same material as crowns are, and serve the same function. The difference is that they do not cover the entire surface of the tooth the way a crown does.