Plastic materials (e.g., silver amalgam or composite resin) are the most commonly used dental restoratives. They allow simple and conservative restoration of damaged teeth. However, their mechanical properties are inferior to cast metal or metal-ceramic restorations. Their continued service depends on the strength and integrity of the remaining tooth structure. When the remaining tooth substance needs reinforcement, a cast metal restoration should be fabricated, usually with amalgam as the foundation or core (see Chapter 6).
Large amalgam restorations (Fig. 3-2, A) are shaped or carved directly in the mouth. The great degree of difficulty associated with this direct approach often results in defective contours and poor
sion resistance of the gold casting alloy; in a tooth with a minimal proximal carious lesion, however, it usually requires greater removal of tooth structure than an amalgam preparation. Inlays do not have sufficient resistance or retention to be used as abutment retainers for fixed partial dentures.
Extracoronal Restorations (Fig. 3-4). An extra-coronal cast metal restoration or crown encircles all or part of the remaining tooth structure. As such, it can strengthen and protect a tooth weakened by caries or trauma. To provide the necessary bulk of material for strength, considerably more tooth structure must be removed than for an intracoronal
restoration. The margins of an extracoronal restoration often must be near the free gingiva, which can make maintenance of tissue health difficult. Tooth preparation for an extracoronal restoration may be combined with intracoronal features (e.g., grooves and pinholes) to gain resistance and retention.
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