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Indications and clinical technology of manufacture of artificial crowns.
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Indications and clinical technology of manufacture of artificial crowns
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
Partial Crown • 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
Complete Crown • A complete crown covers the entire anatomy of a tooth’s clinical crown. There are several types of complete crowns
Fig. 2-1. The optimum restoration should satisfy biologic, mechanical, and esthetic requirements.
Fig. 2-2. Damage to adjacent teeth is prevented by making a thin "lip" of enamel as the bur passes through a proximal contact.
Fig. 2-3. Mouth mirror protecting the soft tissues during tooth preparation
Fig. 2- 4. a considerable amount of care is needed when preparing a tooth for a complete crown because of the extensive nature of the reduction, with many dentinal tubules sectioned. Each tubule communicates directly with the dental pulp.
Fig. 2-5. Conservation of tooth structure by using partial-coverage restorations. In this case, they are used as FPD abutments to replace con-genitally missing lateral incisors.
Fig. 2-6. Excessive taper results in considerable loss of tooth structure (shaded area).
Fig. 2-7. An anatomically prepared occlusal surface results in adequate clearance without excessive tooth reduction. A flat occlusal preparation will result in either (1) insufficient clearance or (2) an excessive amount of reduction
Fig. 2-9. Examples where subgingival margins are indicated. A, To include an existing restoration. B, To extend apical to the proximal contact (adequate proximal clearance). C and D, To hide the metal collar of metal-ceramic crowns.
Fig. 2-10. A and B, Poor preparation design, leading to increased margin length. C, A rough, irregular margin will make the fabrication of an accurately fitted restoration almost impossible. D, An accurately fitting margin is possible only if it is prepared smoothly.
Fig. 2-11. Precise control of the orientation of the diamond is very important. A, Tilting away from the tooth creates an undercut. B, Tilting toward the tooth results in excessive convergence.
All unsupported enamel must be removed. Fig. 2-12. A chamfer should not be wider than half the bur used to form it. Otherwise, a lip of unsupported enamel will be left.