A “bridge” is a form of dental prosthetic that allows for the placement of an artificial tooth in an area where a healthy tooth used to exist.
When an entire tooth is lost, a bridge acts as a unifying device that supports the artificial tooth (called a pontic), and eliminates the gap between adjacent teeth. To accomplish this, however, the pontic needs to be joined to these adjacent teeth in order to stay in place. This is accomplished through the use of either an inlay or onlay.
Inlays and onlays are a type of tooth-colored filling made in a lab, and when used as support for a bridge, they act as connecting anchors for the artificial tooth. An onlay is used when support is needed along a "cusp" (the raised points on the biting surface), and an inlay is used when support is required between these cusps. To visualize how the function of these fillings change when used as an abutment for a bridge, it might help to think of them as the raised pins on upside-down version of a Lego® block – they help to keep the bridge secure once cemented to your healthy teeth.
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 two 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 two-surface bridge inlay, a dentist will first remove the portion of your healthy tooth that will act as an abutment. 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, your dentist will likely fit you with a temporary inlay until your bridge completed.
Once the bridge with its extending inlay 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.