Inlays and Onlays are a type of a dental treatment that blends the benefits of both a filling and a crown.  It takes the conservative removal a filling and couples it with the strength of crown material.  It means less shaping of a tooth and the final restoration is far stronger than a routine resin filling.  The cost is about equal to that of a crown, since it uses the same materials and techniques, but it leaves much more of the natural tooth intact.