INLAYS AND ONLAYS
Traditionally, inlays were used instead of fillings to replace a small amount of tooth structure loss due to decay. Like fillings, inlays fit inside the tooth and were made only of gold.
Today, inlays are still used in the same situations, but the inlays can be made of a tooth-colored material such as ceramic/porcelain or special dental composite. Defective or unsightly "fillings" can be replaced by tooth-colored inlays and bonded to the tooth. This bonding process may actually improve the strength of the tooth and help seal the inlay to the tooth.
Onlays also fit inside the tooth, but extend onto the chewing surface of a back tooth to replace one or more cusps. In the past, onlays were made only of gold, but like inlays, more and more patients request a tooth-colored onlay. Making the onlay of ceramic/porcelain allows the restoration to be bonded to the tooth. This bonding process may actually improve the strength of the tooth and help seal the onlay to the tooth.