Dental onlays fall somewhere in between dental fillings and dental crowns. Like dental inlays, onlays restore large cavities without having to use a crown. Dental inlays and onlays are the same kind of restoration, but they cover different proportions of the tooth. A dental inlay fills the space in between the cusps, or rounded edges, at the center of the tooth’s surface. The dental onlay works like an inlay but covers one or more cusps or the entire biting surface of the tooth. Because of their extensive coverage, dental onlays are sometimes referred to as “partial crowns.” Dental onlays are more durable and usually last longer than dental fillings but, like any restoration, can still weaken the tooth’s structure.