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After performing the laboratory/clinical exercises in this chapter, the student will be able to do the following:
1. List at least three reasons for placing a temporary crown.
2. Describe the materials used to construct temporary crowns.
3. Describe a method to make a temporary crown with acrylic resin.
preformed shell crown
A crown is a restoration that provides complete coverage of the coronal portion of a tooth. It may be composed of a variety of materials. Steps in the construction of a crown are shown in Figure 1.10. After diagnosis and treatment planning, the tooth is prepared. A temporary crown is made and then “worn” between the preparation appointment and the cementation appointment. Temporary crowns are made for patient comfort and esthetics. The temporary crown will protect the pulp from temperature extremes and other irritants. Temporary crowns are cemented with temporary cement and are removed when the permanent crown is ready to be placed. Temporary restorations are also used while making other indirect restorations, such as an inlay or bridge. The terms “interim” and “provisional” are replacing the term “temporary” in some dental circles; however, they basically mean the same thing. Necessary items for constructing a temporary crown are listed in Table 35.1.
TABLE 35.1. Armamentarium for Constructing a Temporary Crown
A. Aspects to Consider
Three aspects must be considered when making a temporary crown (Fig. 35.1).
FIGURE 35.1. Cross section of a crown. Dark arrows point toward the mesial (M) and distal (D) contacts. Light arrows point toward the margins.
1. The outer surface of the crown should reproduce the anatomy of the tooth that is being restored. The shape of the crown includes occlusal contacts, proximal contacts, and side contours. The occlusal contacts must not be heavy (high), or the tooth will become sore from excessive biting forces. However, if the temporary crown has no occlusal contact, the tooth may drift occlusally or “supererupt.” Supereruption of the tooth will require excess occlusal adjustment of the permanent crown. Proximal contacts (dark arrows in Fig. 35.1) are also important. If the proximal contacts are too tight, the excessive force may push (orthodontically move) the adjacent teeth in a mesial or distal direction. The permanent crown will not have good contact, and food will impact between the teeth, causing periodontal problems. If the interproximal contacts of the temporary crown are open, food will again impact and cause periodontal problems. Proper interproximal contacts and side contours will facilitate periodontal health.
2. The inner surface of the temporary crown must closely follow the shape of the prepared tooth for retention. As with a permanent crown, the preparation should be covered by the temporary crown to prevent postoperative sensitivity. The margins of the temporary crown (light arrows in Fig. 35.1) should be smooth and properly contoured to promote periodontal health and esthetics.
3. The temporary crown material must be thick enough and strong enough to withstand occlusal forces for several weeks.
B. Temporary Crown Surfaces
The outer surface of a temporary crown can be made in several ways. It is either part of a preformed shell crown, as shown in Figure 35.2, or it is constructed with use of a “mold” (negative shape). The mold can be made in the mouth before the tooth is prepared, or it can be made on a cast. The inner surface of the temporary crown conforms to the preparation because the temporary crown is typically made in the mouth, directly on the prepared tooth. Chemically activated acrylic resins were the most popular material for the construction of temporary crowns but have been replaced by resin systems called “bis-acryl” materials (see Fig. 35.3A). Bis-acryl materials can be described as having a chemical structure that is intermediate between that of acrylic resin and those of dental composite materials. They often contain some filler. Both acrylic resin and bis-acryl resins are available in a variety of shades (see Fig. 35.3B).
FIGURE 35.2. Types of preformed crowns, a celluloid crown form (left), a polycarbonate shell crown (middle), and an aluminum shell crown (right).
FIGURE 35.3. A. A bis-acryl resin automix product. B. A sample of shade A3 material next to a shade guide.
The various techniques for construction of a temporary crown use a variety of materials and products. Each patient is unique, and he or she presents specific challenges to the dentist. Each clinician also has favorite materials and techniques, several of which are presented in this chapter.
One popular technique uses a disposable triple tray impression (Fig. 8.5B). The impression is taken before preparing the tooth. After preparing the tooth, the impression of the unprepared tooth of interest is filled with the temporary material in a doughy state. The impression is replaced in the patient’s mouth. The patient closes into the normal bite, seating the impression (the form for the temporary crown) into place. The material sets. The patient opens, and the impression is removed. The temporary crown is removed from the impression or tooth and trimmed. Because the form is precisely seated by the opposing arch, the occlusion of the temporary crown is nearly perfect.
II. Preformed Temporary Crowns
Preformed crowns are shown in Figure 35.2. The preformed crown becomes the outer surface of the temporary crown.
Tips for the Clinician
- Mix the acrylic material, and wait for the doughy stage before seating the material on the prepared tooth. If the material is too runny, it will flow excessively.
- Remove and replace the temporary crown several times during the setting process to prevent the material from becoming locked in the interproximal undercuts.