Inlays, onlays and crowns are known as indirect restorations, this is because the restoration is fabricated outside of the mouth. Unlike a filling, which is built in layers that are applied directly into the tooth/teeth. The dentist takes impressions of the teeth and creates the restoration shaped to match the part of the tooth/teeth it will be replacing. The restoration is attached using an effective dental cement.
An indirect restoration is an inlay if it covers part of a tooth, without extending to a cusp (pointed tip of tooth). It is an onlay if it extends to replace a tooth’s cusp. And if it complete covers the top surface of the tooth, it is called a crown or cap.
Inlays, onlays and crowns are more effective than fillings in reinforcing teeth to withstand biting forces, and more resistant to further decay. If a tooth’s original structure is too compromised to support a filling, these indirect restorations can provide fantastic, long-lasting, beautiful results.