Inlays and onlays are used when a cavity is large but the surrounding tooth is healthy. Instead of reducing the healthy tooth to fit a crown, an inlay sits in the hole in the tooth and an onlay can replace the cusp of a tooth which maintains the shape of the tooth. Inlays are generally made out of porcelain which is tooth coloured but they can be made out of gold or resin.
The tooth is prepared and impressions are taken, which are sent to the technician who makes models on which the inlay is designed and manufactured. A temporary filling material is placed in the tooth until the permanent inlay/onlay is cemented into position.