In cases when there is a "large" cavity it may not be possible to restore a tooth with a normal white filling. Porcelain inlays are made by a technician in the dental laboratory and then bonded into the cavity. This means the final filling is stronger and will protect the tooth better.

The process 

Two visits are normally required. At the first visit the tooth is "prepared" an impression taken and a temporary placed. The Inlay is then made, and at the second visit finally placed.