In the summer of 1999's issue of the Palette, expert
ceramist Bill Zanin explained his
"Theory of Encapsulation" and how it relates to anterior teeth.
Bill takes his theory a step further by discussing the concept as
it applies to posterior teeth in this second part of his study.
Encapsulation refers to the internal, anatomical structure
of the tooth and how we ceramists can most easily replicate it. In
simple terms, the internal coloration of the tooth is dentin, which
is surrounded by a grayish translucent layer. Finally, the translucency
is "encapsulated" by a more opacious enamel layer on the outside of
the tooth that regulates the value. (See diagram 1)
Although
this theory seems easy enough to practice, with posteriors, the building
process is a bit more involved than with anteriors. Posteriors simply
can not be thought of as a singular form, but rather the fusing of
multiple forms - the cusps. Each cusp is itself an entity of dentin,
translucency/transparency, and enamel. When each cusp is treated as
an individual three-dimensional form and then fused to the other cusps
in a restoration, we begin to step away from the mediocrity of "units"
and begin to embrace the idea of restoring "dentition."
There is no reason that beautiful posteriors cannot
be anatomically built-up in a relatively simple and efficient manner.
The first step is to form the internal structure of each cusp in a
dentin material. Do not over build dentin out to the cusp tips. The
dentin formations should be distinct, sharp and 3-dimensional, but
out of centric occlusion. Follow this step with a generous surrounding
of highly translucent/transparent material such as Creation's CL-O,
NT, HT's or TI's. (See diagram 2)
At this point, the restoration should be very close to full contour,
but not beyond its anticipated finished contour.
Centric occlusion should be established with the final layers of
enamel. Try Creation's PS's, TI-2 and the SI's for the final occlusion.
(See diagram 3)
Resist the temptation to over build the occlusion.
"Squashing" the porcelain with the articulator will merely destroy
the layering, and disturb the condensing of the porcelain particles.
With an eye for detail, the restoration can be fired and glazed
with a minimum adjustment to the porcelain. Because the restoration
is anatomically built up, any adjustments necessary due to unforeseen
lateral or protrusive excursions will result in a very natural appearing
wear facet (See diagram 4).
By learning and incorporating the "Theory of Encapsulation"
and using an anatomically esthetic porcelain like Creation, you'll
be well on your way to creating some truly vital "teeth."
Revision 0, 6/19/00