Inlays are similar to fillings, except that they are made in lab. The objective is repair of chipped or decayed teeth. Indirect fabrication means that the tooth is prepared for the inlay, an impression (mold) of the prepared tooth is made and poured in dental stone, and the restoration for the tooth is made in a laboratory on the stone replica rather than the tooth itself.
An onlay is a type of cusp-covering dental restoration that is made in a laboratory by a skilled technician, or by a computer controlled milling machine. Onlays can be made of ceramic, composite resin, gold, titanium or other metals. Metallic onlays are generally cemented (glued) onto the tooth, at a separate appointment from the tooth preparation appointment.