Inlays and onlays are laboratory-constructed restorations that are made of very strong compressed ceramic. Also, they are a superior alternative to white fillings where the restoration is large and strength is required. Such restorations are also aesthetically superior.
The process for an inlay is twofold. During your first appointment, the tooth is prepared and a scan or impression is taken of the tooth which then has a temporary restoration placed. About a week later, the finished product is bonded into the tooth with a strong resin bonded cement.
An inlay is more expensive than a typical white filling due to the cost of the material, the time and skill involved in its construction. However, ceramic restorations are far more durable and should be seen as an investment.