Porcelain inlays and onlays have a high degree of strength and are excellent for restoring weakened back teeth. Inlays and onlays protect and restore large portions of decayed or extensively filled teeth, or teeth under very heavy function (i.e. back teeth). Unlike crowns, they only cover a portion of the tooth and are therefore more conservative on the amount of tooth preparation required.
Porcelain inlays and onlays are made from the same strong, tooth-colored porcelain that is used for crowns and bridges. The main difference between fillings and inlay/onlays is that they are laboratory fabricated.