Chapter 20 Ceramics
Porcelain-fused-to-metal restorations provide the opportunity to restore damaged, nonfunctional teeth to proper function and esthetics (Figure 20-1). These restorations have been among the most popular and most heavily used restorations in dentistry over the last 50 years. Porcelain-fused-to-metal restorations have a long history of clinical success and provide the opportunity to give patients an esthetic option to rehabilitate damaged teeth. Any tooth can be restored with porcelain fused to metal.
For an esthetic approach to restoring a tooth, the dentist needs to consider the patient’s concerns and desires. Most often the anterior teeth and those that are visible when a patient speaks or smiles are chosen for esthetic restorations. This not only includes the anterior teeth but in many patients includes teeth as far back as the maxillary first molar, which is still a tooth to be considered when overall smile esthetics are evaluated. Molar teeth, even mandibular second molars, are often considered for porcelain-fused-to-metal restorations. These restorations are more frequently requested and done than any other indirect restorations.
Initially in dentistry, full-coverage restorations were performed using cast metals. About 50 years ago, as the demand for more esthetic restorations was developing, dentists started using acrylics and placing acrylic facings onto the cast metal restorations. For a period of time this provided a full-coverage restoration with some esthetic value. About 15 years later, new techniques were developed so it was possible to fuse porcelain to a metal casting and thereby provide a far superior, more esthetic full-coverage restoration. This began the advent of the porcelain-fused-to-metal restorations available today. As ceramics and techniques have improved, the porcelain-fused-to-metal restorations have become more and more esthetic.
When a tooth has been damaged to the point that it requires a full-coverage restoration, it is of primary importance that the tooth be returned to proper function. For patients who desire an esthetic final restoration, the use of porcelain fused to metal allows the dentist to create a final esthetic restoration that achieves the return to full function. The function of the crown is to protect the tooth from further damage and to restore proper anatomy so that the lost structure is restored. By using the porcelain-fused-to-metal restoration, the dentist can restore function with a tooth-colored esthetic replacement.
In some situations, proper restoration of function is difficult to achieve in an esthetic manner. For example, a patient who has a history of bruxing or clenching may demonstrate a lot of tooth wear. Some of these patients have the potential to fracture porcelain. With such patients, a full-coverage restoration in full cast metal is more appropriate because of the increased risk of fracturing a porcelain structure.
In addition, depending on the patient’s occlusion, porcelain may be in the functional pathway and, because of porcelain’s abrasive nature, can cause wear on the opposing dentition. In these situations the dentist may be inclined to place metal as opposed to porcelain in the functional pathway.
Any time teeth have been damaged by trauma, decay, or tooth fracture and/or heavily restored, those teeth are structurally compromised (Figure 20-2). These are good candidates for porcelain-fused-to-metal restorations. In addition, patients who have high esthetic demands or requirements may be treated with a porcelain-fused-to-metal restoration. This choice allows the dentist to create a restoration that can visually restore the tooth to its proper esthetics.
The primary contraindication would be if the crown preparation cannot achieve sufficient occlusal clearance. This means 2 mm for the porcelain-fused-to-metal restoration. Another contraindication would be concern about porcelain wearing the opposing dentition when functional occlusion is restored. Porcelain would not be appropriate in a functional pathway. Instead cast metal would be more desirable.
There are a number of different material options for the metal substrate of the porcelain-fused-to-metal restoration. The major classes are base cast metals, high noble metals, and semi-precious metals. The advantages of each are partially based on cost. Base metals are inherently lower in price and tend to provide the structural integrity needed. These lower-cost restorations still provide for the patient’s functional and esthetic needs. However, the dentist must carefully select patients in whom base metals are to be used. Dentists must be concerned about the biocompatibility of the metals. Base metals frequently contain nickel, which is associated with a high incidence of allergic reactions in patient populations.
The semi-precious metals contain high percentages of gold, platinum, and palladium, all of which are even more biocompatible (Figure 20-3). These metals also tend to have a slightly better fit and even the potential for the margins to be burnished, which provides an enhanced clinical result.
Many different types of porcelain can be used. The industry standard for years has been the use of stacked porcelains, where a powder and liquid are mixed together on top of the metal to provide the final esthetic result (Figure 20-4).
Recently techniques have been developed wherein ceramics are actually pressed on top of metal. This provides another ceramic option to the dentist in obtaining an ideal end result. The pressed ceramics offer the advantages of ease of fabrication and slightly better strength.
The dentist must carefully consider the different options available for full-coverage restorations. Porcelain-fused-to-metal restorations are one of several different types of restorations available. Based on the patient’s clinical needs, the dentist’s experience, and the labo/>