Artificial crowns. Clinical and technological aspects.

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

sectioned. Each tubule communicates directly with the dental pulp. 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 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.

Fig. 7-31. The recommended convergence angle is 6 degrees Fig. 7-31. The recommended convergence angle is 6 degrees. This is a very slight taper. (The angle between the hands of a clock showing 12:01 is 5 1/2, degrees.)

Internal features effectively increase resistance. Fiji- 7-33. Retention form of an excessively tapered preparation can be increased by adding grooves or pin­holes, because these will limit the paths of withdrawal.

Fig. 7-47. Recommended tooth preparation for a metal-ceramic restoration. The facial reduction has two distinct planes.