I.  Classification by Amount of Tooth Structure Restored

A.  Inlays

Inlays are intracoronal (inside the crown) restorations that replace small to medium amounts of tooth structure, as shown in Figure 1.3. They are most commonly used to restore pits, fissures, and grooves (class I) as well as proximal surfaces (class II) of posterior teeth. They do not restore the cusps. They are retained by luting cements.

B.  Onlays

Onlays (or overlays) involve replacing more tooth structure than inlays. In addition to the pits, fissures, and proximal surfaces of an inlay, onlays restore one or more cusps and, at times, the entire occlusal surface of a tooth. Onlays are used when the likelihood of cusp fracture is high. The onlay protects the cusps from occlusal forces. Onlays, like inlays, are retained with intracoronal retention and luting cements. An onlay is shown in Figure 10.1.

C.  Veneers

A veneer is a thin layer of material that covers another material (like the shell of a hard-boiled egg). In dentistry, veneers are restorations that are placed on the facial surface of anterior teeth to treat an esthetic problem, such as discolorations, rotations, or spaces (diastemata) (Fig. 10.2). Veneers are often used in conjunction with orthodontic or periodontal treatment. Two types of veneers are used.

D.  Crowns

Crowns are used to restore teeth that have lost a significant amount of tooth structure. They are used when intracoronal retention is unavailable or when the tooth needs to be surrounded and held together by the restoration. A full gold crown is shown in Figure 1.4. A porcelain crown is shown in Figure 1.10F. Ceramometal crowns are shown in Figure 10.3.

E.  Complex Restorations

Complex restorations combine the features of inlay, onlay, and crown restorations, as shown in tooth #4 of Figure 10.1. A complex restoration is designed by the dentist after caries, and the loss of tooth structure has been assessed.

F.  Dental Bridge

A bridge replaces missing teeth. Typically, a bridge has a crown, called a retainer, at each end. The retainers are supported by teeth called abutments. The replacement teeth are called pontics. A bridge may replace one tooth or several teeth, as shown in Figure 1.5.

II.  Classification by Material

A.  Metals

A variety of metals are used to restore teeth, as shown in Figures 10.1 and 10.4. Most metallic indirect restorations are made by a casting procedure. Casting involves melting the metal and then pouring or forcing the liquid metal into a mold. The casting process allows custom, complex shapes to be easily produced. Metals are very tough and work well in high-stress situations, but their esthetics are poor.

B.  Ceramic Materials

Ceramic materials are used when esthetics are important, as shown in Figure 1.10. Ceramic materials can simulate the natural colors and translucency of teeth. Porcelain is the ceramic material most commonly used in dentistry to obtain a variety of colors or shades for a single crown. A variety of materials and processing techniques are employed. Most ceramic materials lack the toughness and fracture resistance required by bridges, but their esthetics can be excellent.

C.  Ceramometal

A metal–ceramic combination was developed for dentistry in the 1950s. This material is made by using the same process to bake enamel (porcelain) on metal as that was used to make old-fashioned pots and pans or sinks and bathtubs. The tough, strong metal supports the weak but esthetic ceramic material. The restorations are called ceramometal restorations (or porcelain-bonded-to-metal or porcelain-fused-to-metal crowns) and are considered to be an important “workhorse” in modern restorative dentistry. Ceramometal restorations are shown in Figure 10.3.

D.  Composite Materials—Optional

Particle-reinforced composite materials (very similar to those discussed in Chapter 5, Direct Polymeric Restorative Materials) have been adapted for use as fixed indirect restorations. These materials are polymers reinforced by irregularly shaped particles, as shown in Figure 5.8C. They are cured at elevated temperatures, pressures, or both in the dental laboratory. Particle-reinforced composites have seen only limited success because their strength and toughness do not meet those required by crown and bridge materials.

Recently, fiber-reinforced composites have been developed for dentistry. These composites are similar to materials that have been developed for many other industries in which glass fibers are used to reinforce polymeric materials. Imagine a bowl of frozen, leftover spaghetti with sauce. The spaghetti represents the glass fibers; the frozen sauce represents the polymer matrix. The long fibers transfer stresses over a larger area than particles do. Automotive, aerospace, and sports equipment companies use fiber-reinforced composites to manufacture strong, lightweight products. Fiber-reinforced composites are much tougher and stronger than particle-reinforced composites. Clinical results are promising, but these materials are not commonly used.

III.  Procedures for Constructing an Indirect Restoration

A.  Diagnosis, Treatment Planning, and Designing the Restoration

1.  Diagnosis

Lost tooth structure and missing teeth result from a variety of causes. Caries and periodontal disease are the most common. An extreme case involving caries and periodontal disease is shown in Figure 11.10. Trauma or fracture (Fig. 10.4A), esthetic concerns (Fig. 1.10), and congenital deficiencies (Fig. 10.2A) are other reasons to restore or replace teeth. Often, teeth are lost as the result of restoration and re-restoration and multiple dental treatments (Fig. 10.4B).

2.  Treatment Planning

A variety of factors affect the success of a restoration. These factors must be assessed during treatment planning.

3.  Restoration Design

Many factors influence the design of a restoration.

B.  Preparation

The tooth or teeth are prepared with specific restorative materials in mind. Different materials require different amounts of tooth reduction and shapes of the margins. Amalgam and inlay preparations are shown in Figure 1.3. Crown preparations are shown in Figures 1.10B and 8.1A.

C.  Impressions

After the preparation is complete, an impression of the preparation, adjacent teeth, and opposing teeth is taken. Full-arch impressions result in more accurate articulation of models and less adjustment of a complex restoration before cementation. Several impressions were shown in Figure 1.8A and in Chapter 8.

D.  Fabrication of a Temporary Restoration

The patient will not like the appearance and feel of the prepared tooth. In addition, exposed dentin can be very sensitive to heat, cold, and air. A temporary restoration (also called a provisional restoration) is constructed and cemented at the time of preparation, as shown in Figure 1.10C. The temporary restoration is left in place until the final restoration is received from the lab and permanently cemented. Chapter 35 presents techniques for the fabrication of a temporary crown.

E.  Laboratory Procedures

The description and design of the restoration is written on a laboratory prescription (Fig. 10.5). This prescription becomes a part of the patient record. Impressions are disinfected and then poured in the dental office or a commercial laboratory. The laboratory constructs the final restoration according to the dentist’s instructions. A variety of restorations and prostheses are shown in Chapters 1, 10, and 11.

F.  Cementation of the Restoration

At a second appointment, the temporary crown is removed, and the temporary cement is cleaned from the prepared tooth. Scaling instruments or pumice and a prophy cup are used. “Try-in” of the restoration is next. The restoration is seated on the preparation and carefully evaluated. The proximal contacts are checked with floss. The margins are examined with an explorer. The occlusion is evaluated with articulation paper, and the esthetics are examined with the patient’s input. If all is acceptable, the restoration is cemented (see Fig. 7.1). Completed crowns are shown in Figures 1.4 and 1.10E.

G.  Completion of the Treatment Plan

After the restoration is cemented, the remaining treatment plan is completed. The final step in the treatment plan should be to determine the recall status of the patient based on periodontal concerns, caries risk, chronic problems, and oral hygiene home care practices.

IV.  Casting Process—Optional

Dentistry has used the “lost-wax casting technique” for a century to produce metal restorations. This process first constructs the restoration in wax. The wax is then replaced with metal in the same shape and size as the original wax pattern. The lost-wax casting technique is shown in Figure 10.6.

A.  Wax and Waxing

1.  Waxing

Wax is easy to mold and shape. All that is required is a heat source and a few simple instruments. Creating the shape of the restoration in wax (wax pattern) requires skill and involves both the art and the science of dentistry, as shown in Figure 10.6A. The art is creating a reproduction of the shape of the lost tooth structure. The science is the requirement for the shape to function as the original tooth structure did (or should).

2.  Dental Waxes

Dentistry uses a variety of waxes with different melting, working, and handling properties. Several are shown in Figure 10.7. The composition of a wax product is usually proprietary and is typically a combination of natural and synthetic waxes. Wax is very soft compared to other dental materials. Distortion of wax is not typically visible to the unaided eye, but wax is unstable. A wax pattern can distort over time to a degree sufficient to affect the fit of restorations.

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