classified as an extracoronal. An intracoronal replacement like an inlay fits into a tooth. An extracoronal restoration fits around what remains of a tooth.
An artificial crown is a fixed prosthetic restoration that covers more than half of the coronal portions of the tooth. There are several types of crowns. They may be made of gold, porcelain, acrylic, or a combination of these materials. Along with onlays, which are classified as extracoronal restorations, are the various kinds of crowns that make up the balance of the extracoronal category.
A partial crown is a cast restoration made entirely from metal and covers more than half but not all of the tooth's clinical crown. A partial crown is named according to the fractional amount of the clinical crown it covers. Examples are the half, three-quarters (see fig. 8-2(A)), four-fifths, and seven-eighths crowns (see fig. 8-2 (B)). In most instances, the facial surface of the tooth is not disturbed for esthetic reasons.
A complete crown covers the entire anatomy of a tooth's clinical crown. There are several types of complete crowns. A complete metal crown is constructed entirely of a noncorrosive metal, such as gold (see fig. 8-2(C)). A complete veneered crown consists of complete coronal coverage of the tooth with a metal substructure overlaid with porcelain or resin for esthetic effect (see fig. 8-2(D)). A complete crown constructed of cast metal with a fused porcelain (ceramic) veneer is commonly called a PFM (porcelain-fused-to-metal) crown.
A post crown is a complete crown of any kind (complete metal, veneer), supported by a metal extension (post) into a tooth's root canal. Because the pulp is removed from teeth that are endodontically treated, the teeth eventually become brittle and are prone to fracture. In many instances, the teeth are also destroyed by caries or previous restorations and very little clinical crown is left. Often, only the root portion is left to retain the crown. To maintain an endodontically treated tooth as an abutment (anchor) capable of supporting and retaining a crown, it is common practice to cement a post about two-thirds of the way into a root canal. To do this, a gold casting
Figure 8-2. - Types of artificial crowns.
called a post and core, must be constructed. The part of the post that protrudes from the root canal is called the core. The core, combined with the remains of the coronal part of the tooth, is built to resemble a complete crown preparation. After the post and core are cemented into the root, a complete crown is fabricated on top of this foundation (fig. 8-3). Post and core castings are most often associated with endodontically treated anterior teeth, but they may also be used on posterior teeth as well (fig. 8-4).
A fixed partial denture (FPD) (fig. 8-5) is a restoration designed to replace more than one missing natural tooth. In contrast to a removable partial denture, the dentist attaches an FPD to natural teeth (abutments) or roots by cementation. An FPD consists of two types of units: retainers and pontics. The unit castings are joined together by connectors. The overall size of the FPD is measured in units. Each pontic or retainer counts as one unit. For example, an FPD with three retainers and two pontics has a total of five units. The units of an FPD may be made entirely from metal, combination of metal or resin, or from a combination of metal and porcelain. Next, we will discuss the retainers, pontics, connectors, and abutments that make up the FPD (fig. 8-5). 8-2