Inlays and onlays are indirect dental restorations that reinforce an existing tooth that is too damaged to support a filling, but not damaged enough to require a crown. Inlays and onlays are known as indirect fillings because, unlike a standard filling, both are made in a laboratory and cemented or bonded to the surface of the tooth during a second visit. Unlike standard fillings, inlays and onlays do not weaken the tooth structure, but actually strengthen it. After the procedure, the tooth can bear up to 50-75% more chewing force.
Because both are fabricated in a dental laboratory, it usually takes two or more appointments to restore a tooth with a porcelain inlay or onlay.