Inlays, onlays and crowns are called indirect restorations, because they are fabricated in a laboratory, instead of being built in layers directly into the teeth like a filling. The dentist takes an impression of the teeth and then the restoration is shaped to match the part of the tooth it will replace. The restoration is attached with dental cement.
An indirect restoration is an inlay if it covers part of a tooth, without extending to a cusp (pointed tip of tooth), whereas, it is an onlay if it extends to replace a tooth’s cusp. If the entire tooth is covered by the restoration, it is called a crown or cap.
Inlays, onlays and crowns are more effective than fillings in reinforcing teeth to withstand biting forces and strengthen. If a tooth’s original structure is too compromised to support a filling, these indirect restorations can provide strong, long-lasting results.