An "inlay" is a form of dental restoration used to repair a decayed, chipped, cracked, or otherwise damaged tooth. In contrast to an "onlay," which is used to correct damage extending to a "cusp" (the raised points on the biting surface), an inlay is used to repair only that portion of the tooth between these cusps.
Generally speaking, there are two different types of dental restorations: "direct" and "indirect." For example, a "filling" is a type of direct restoration, because the material used to repair the tooth undergoes its hardening process while in "direct" contact with the tooth and *inside* the mouth.
Unlike a filling, where a malleable material is placed into the tooth, and allowed to harden, an inlay is an *already* hardened material (like a crown) that is joined to the tooth by bonding or cement. Because the material used to repair the tooth is created *outside the mouth*, either in a lab by a dental technician, or via a computer-controlled milling machine, the process is referred to as an "indirect" restoration.
In all, there are five surfaces of the tooth eligible for restoration: the distal, occlusal, buccal, mesial, and lingual/palatal surfaces. With this dental procedure code, an inlay is made from either porcelain or ceramic, and placed on one of those surfaces. An inlay constructed of either of these materials yields positive cosmetic results, with porcelain creating a more natural look than the "heavier" look of full ceramic. For this reason, an all porcelain inlay is typically used to repair decay on teeth within the "smile-zone," whereas a fully ceramic inlay is most often used in the rear of the mouth.
To prepare for a single surface inlay, a dentist will first remove any decayed or weakened areas of the tooth. Then, depending on the process used by your dentist, either a physical impression of the tooth will be made, or 3D imaging will be used to render a digital impression. Next, you may be fitted with a temporary inlay until the custom version is completed, or if your inlay can be fabricated on-site your dentist will proceed with the installation.