BILL ZANIN developed an exciting theory on how teeth are structured. He calls this theory, "encapsulation." Encapsulation means that the center of the tooth is composed of dentin coloring, covered by an internal transparent or translucent layer. Finally, the translucency is encapsulated by a more opacious enamel layer on the outside of the tooth. Understanding this phenomenon may have a dramatic effect on how a restoration is fabricated.

MY THEORY of encapsulation began to develop in the early to mid 1980's. After taking numerous custom shades and observing many worn and aged incisal edges, I began to question the previous methods of using transparent and translucent materials in dental restorations.

Technicians have a tendency to put these porcelains into their restorations without regard for the replication of natural teeth. In reality, worn lower anteriors clearly show no translucency at the contact zones. These teeth have transparency and translucency, but these phenomena are found in different parts of the teeth.

When looking down on the incisal edge one can usually see dentin colors in the central areas of the teeth, which are surrounded by a translucent layer. However, the final surface layers are usually much more opacious and of higher value. This seems to have an effect of controlling the value or amount of light which is allowed to pass directly through the teeth, as well as affecting the amount of light which is reflected back. This also causes a significant amount of light that is ordinarily lost to scatter throughout the teeth, illuminating them. In essence, the transparent or translucent layers are "encapsulated" by more opacious layers.

When layering porcelain for anterior teeth, it is possible to achieve the same optical effects that replicate these anatomical features. Willi Geller's Creation and Surprise porcelains were developed with this logical approach in mind.

To create these effects follow these simple steps:

1. Place dentin to form the internal base shade of the restoration.
2. Add a translucent/transparent layer on top of the dentin layer and extend 1/3 to half of the way to the gingival margin, i.e., CL-O, NT, TI's or HT's.
3. Encapsulate the translucency with enamels/incisals to control value and chroma, i.e., S-O Incisals, SI's or Pearl Enamels. This will create a natural halo effect.

For example, when building an anterior restoration, on your first opaque, proceed as you ordinarily would with your basic Creapast shade. On the second opaque, modify the base shade if you prefer with some Ochre at the marginal area, on the occlusal table, etc. Violet can be placed at the incisal edges as well to give the illusion of depth.

After the opaque firing, proceed with the dentin build-up using your usual choices of modifiers and effects. Complete the dentin cut-back as you usually do, but instead of adding incisal back to complete the original contours, use internal translucency. For light colored, high value shades, use Neutral Transparent (NT) or Neck Translucent (HT-51, 52, or 53). Feel free to use the Neck Translucent in the incisal areas! The Translucent Incisals (TI-1, TI-2) can be used in the same manner as well. For darker, low value shades, Transparent (CL-O) porcelain can be used along with the darker Neck Translucent (HT-53, 54, or 55) and the darker Translucent Incisals (TI-3, TI-4, or TI-5). Use these translucent /transparent materials to restore the build-up to the original full contour before the cutback. Allow for a small amount of incisal edge shrinkage by adding about 1 mm to the incisal edge's length.

Now simply apply a thin "skin" of Incisal (S-O Incisals or the SI Incisals) to the surface of the crown to allow for shrinkage during the firing cycle. Again, use a high value Incisal (S-057, 058 or SI-01, 02 or 03) for the lighter shades. Use the lower value Incisals (S-059, 060, or SI-04 , 05 or 06) for the darker shades. Remember to also add a small amount of Incisal (not CL-O) to the contact areas to complete the encapsulation of the internal translucency.

Keep in mind the purpose is to sandwich the translucent layer (CL-O, NT, etc.) between two more opacious layers (the Dentin and the Incisals). Remember to exercise caution when building and grinding, so that surface layers remain intact and are not removed. By following the above-mentioned steps, while keeping the theory of encapsulation in mind, you should be well on your way to creating some aesthetically pleasing restorations.