An "onlay" is a form of dental restoration used to repair a decayed, chipped, cracked, or otherwise damaged tooth. An onlay corrects damage extending to a "cusp" (the raised points on the biting surface), in contrast to an inlay, which 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 onlay 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 considered 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 onlay is made from composite synthetic resin, and placed on four or more of those surfaces. Synthetic resins are liquid materials that can be converted into a permanent hardened material, and in dentistry are most commonly acrylic polymer or polymethyl methacrylate. An onlay constructed of resin yields positive cosmetic results, since the material used can be matched exactly to the color of your natural teeth. As a result, this type of onlay is typically used to repair decay on teeth within the "smile-zone."
To prepare for an onlay for four or more surfaces, 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 onlay until the custom version is completed, or if your onlay can be fabricated on-site your dentist will proceed with the installation.
Once the onlay has been prepared and is ready for installation, it will be laid into the excavated area of the tooth and bonded or cemented (luted) in place.
To look up and find more cdt dental codes from the American Dental Association, please visit our complete Dental Procedure Code Library.