Onlays or overlays are partial reconstructions of teeth and are often indicated when the tooth/teeth need(s) some coverage or protection when getting chewed away. This partial coverage devise will provide the sufficient strength to the tooth / teeth to be kept together and will preserve the tooth structure. Inlays are often referred to indirect resin, porcelain or gold fillings that will provide way more sturdy restorations that can last slighlty more.