Written by Thomas E. DeLopez, DDS Sunday, 31 March 2002 19:00
The purpose of this article is to help the clinician categorize and differentiate anterior cases with potential problems from those that are more routine, by presenting guidelines for the predictable and profitable use of pressable ceramics. When complications are foreseen before the case is presented, treatment can be economically planned.
BACKGROUND: PRESSABLE CERAMICS
Pressed ceramic restorations are an invaluable part of an aesthetic practice. Each restorative material has its own advantages. These are some of the advantages the author attributes to pressed ceramic restorations:
- Restorations made from pressed ceramics have better margins and are much stronger than feldspathic porcelain restorations.
- Compared with porcelain-fused-to-gold crowns or ceramic crowns with milled cores, pressed ceramic crowns have greater translucency and generally blend better with adjacent teeth.
- Uncomplicated cases are easy for the laboratory to restore.
Pressed ceramic restorations are fabricated by a sophisticated lost wax technique. A pattern is waxed onto a die, which is then invested and burned out. Small ceramic discs called ingots are melted to a honey-like consistency and then pressed into that pattern (Figure 1).
Figure 1. Five different shade 110 ceramic ingots.
Figure 2. Note opaque PFM crown with exposed margin.
Figure 3. A single Empress I crown greatly improves the patient’s smile.
Figure 4. Tooth No. 8 is darker than the adjacent teeth.
Figure 5. Note the volume of porcelain that will be required.
Figure 6. Completed restoration.
Figure 7. Pre-op.
|Figure 8. Note the prep size and the volume of porcelain that will be required.|
Figure 9. Completed restoration.
Figure 10. Two discolored composites.
The dentist selects the desired tooth shade and the shade of the prepared tooth, the “stump shade.” Using this information, the lab makes a die from the appropriately colored stump material and selects the opacity level of the ingot that will produce the desired hue and intensity in the restoration. The ceramic ingots not only come in different shades, but also in different levels of opacity. The selection of the opacity of the ingot used to fabricate the restoration is equally important as the shade selection. The opacity level is generally selected by the lab technician.
The most common variables that affect the aesthetic outcome of proposed restorations include the color and the volume of remaining tooth structure following preparation and the position of the gingival margin relative to the lip and adjacent teeth.
COLOR MATCHING AND COMPLICATIONS
You are essentially replacing the enamel with a material that refracts the reflected dentin color and draws color from the adjacent teeth as light passes through the incisal and interproximal areas, which are translucent and opalescent. This creates the illusion of a natural tooth when the laboratory technician has matched the surface texture and contour of the adjacent teeth.
RESTORING SINGLE CENTRAL INCISORS IS UNPREDICTABLE
In the first case presented, when this old PFM crown was removed there was an adequate amount of tooth structure remaining, and the dentin color was good. An Empress I crown was fabricated from a translucent, 25% opacified ingot, and an ideal shade match was achieved. However, prior to removing the old crown there was no way to predict the difficulty of this restoration (Figures 2 and 3).
Figure 11. Two 50% opacified Empress veneers.
Figure 12. Diastema with a PFM crown.
|Figure 13. Two Empress II crowns.||Figure 14. Six chipped and stained composites.|
|Figure 15. Six Empress I veneers.||Figure 16. Discolored composites with an angled incisal plane.|
|Figure 17. Six teeth prepared for modified 3/4 crowns.||Figure 18. Patient’s smile with six Empress II 3/4 crowns.|
|Figure 19. Often peg lateral incisors require minimal preparation.||Figure 20. Empress I veneer at day of insertion.|
In the next example, crowning a single central incisor, which was slightly darker because of a degenerated pulp, seemed ideal for a pressed ceramic crown, as shown in Figure 4. The tooth was slightly rotated, thus requiring more tooth structure to be removed from the distal than in an ideal preparation, as shown in Figure 5. A layered, 25% opacified crown was fabricated, but discarded at try-in as it was too translucent and thus low in value. A second crown using a more opaque, 50% opacified core with glass-ceramic layering was seated as the final restoration, as shown in Figure 6.
Adjacent teeth may be identical in color, but one tooth can be shorter because of a traumatic fracture. One tooth may have undergone more reduction to correct misalignment, or from a previous crown. Often, these teeth will look totally different when restored with Empress crowns pressed from the same ingot. This is because of the translucency and opalescence of Empress I. The beauty of this porcelain is that light passes through it. However, if there is not enough dentin to reflect some light back, that translucency which creates the illusion of a healthy vital tooth when present on the incisal and interproximal causes the entire crown to appear gray.
PREDICTABLE PROCEDURES ARE PROFITABLE
When teeth are in the correct position, the color is good, and there is minimal tooth reduction, dental laboratories can easily produce an exceptional aesthetic restoration with the most translucent pressable ceramic materials. Ceramic cores with varying levels of opacity should be used for more complicated cases. This material requires significantly more skill and effort by the laboratory technician.
The author would like to thank Ken Rockwell of Rockwell Laboratories for the high-quality laboratory work and his technical advice.
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