We make onlays of ceramic, composite resin, gold, titanium or other metals. Onlays are like crowns, in that they afford protection against cracking to the tooth; but they're more conservative in the amount of natural tooth structure that we need to remove to make room for them. They're also similar to inlays, except that they cover at least one of the pointed chewing cusps of the tooth.
Metallic onlays are generally cemented (glued) and ceramic and composite resin onlays are generally bonded (fused with adhesive) onto the tooth, at a separate appointment from the tooth preparation appointment.