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QUARTER 1 | 2014 | CERECDOCTORS.COM | 13
to add stains to mimic these effects:
violet or black on the incisal edges of
anteriors, white on the marginal ridges
and cuspal inclines of posterior teeth.
Darker chroma for the gingival one-
third and the occlusal table can give the
depth and relief we desire. If we milled
thin margins we could, as we experi-
ment and gain experience, create very
life-like illusions in the restorations for
our patients.
Now, this newer class of materials
has physical properties that allow us to
change the way we approach creating
esthetics for our restorations. We can
start to think about getting the effect we
desire by replacing what was lost with
a semi-transparent material — not by
placing amaterial thatwe have tomodify
with stains to create an “illusion.”
The fracture resistance of these mate-
rials has been shown to be much better
than those ceramics of the past and
present. If we look at the performance of
the materials when subjected to the
Vickers test, we can see some dramatic
results. A Vickers test is a test of the
surface hardness of a material, and it is
done by applying a measured force on a
pyramid-shaped stylus until it pene-
trates into the material of a standard
thickness. The test stylus can be seen in
Figure 1. It is not the value that is of great
interest with our materials, but the
effect of the stylus penetration (much
like a plunging cusp’s effect on the denti-
tion). In Figure 2 we can see that there is
an imprint of pyramid in the surface of
the material, but more important is the
effect on the area around the material.
From the SEM pictures taken of the
materials after being subjected to the
Vickers test, we can see how the perfor-
mance of the tested materials differs.
On the left is the all-ceramic, which has
cracks radiating very far from the point
of penetration. In themiddle, the sample
is Enamic, which has cracks extending
out in a disjointed manner. The ceramic
framework has cracks, but the infil-
trated resin helps stops the fractures
from propagating out. The Lava Ulti-
mate samples, due to the nano-ceramic
hybrid technology, have no propagation
from the point of penetration.
The question that arises from this test
is: if we do not see crack propagation, do
the same constraints limit us now when
designing our restorations?
The milling performance of the new
hybrid materials has also been fantastic.
There has always been a fear that if our
restorations get too thin we may see
a fracture or chipping of the ceramic.
A heavy chamfer or a shoulder was
probably not clinically significant, it
does demonstrate the brittleness of
the material. Figure 4 is an SEM picture
of a Lava Ultimate restoration milled
with the CEREC system, and it is very
easy to see the difference in the margin.
Far less chipping is evident since it
can tolerate the torture of the milling
process much better.
So, canwe start to think aboutwhatwe
are replacing? Do we have to continue
to think of ways to fool the eye? With
the superior fracture strength, fracture
resistance and the milling performance
of the hybrid material, I think our
approach can evolve.
These new materials can help
simplify our lives; we can place in
natural contours that reflect what natu-
rally occurs. We don’t have to think as
the illusionist does; we can think like a
naturalist. These new materials have
removed the need for stain and glaze,
and the need to fire these restorations
in the oven. The superior milling perfor-
mance offers the ability to create smooth
tapers down to a minimal shoulder,
allowing us to use the translucent prop-
erties to our advantage. The cervical
one-third and the center of the occlusal
table can be influenced by the warmth
of the dentin as it is in a natural tooth.
Tertiary anatomy can be placed into the
restorations, enhancing the depth of our
restorations and the way light reflects
off of them.
The CEREC system can be a utilized
in more ways than just a crown
machine; its role can be increased only
when we realize that it is very efficient
at fabricating partial-coverage restora-
tions. These CEREC-fabricated inlay
restorations save us the stress and time
of placing matrix bands and stacking
composite. Fabricating restorations in
this manner can reduce the stresses in
our restorative materials by minimizing
those stresses that occur in the curing
our composites.
Fig. 3: SEM of all-ceramic after being
milled in an MCXL
Fig. 4: SEM of Lava Ultimate after
being milled in an MCXL
necessary to help ensure the successful
milling of a block. We didn’t want
to push the material to the point of
breakage, slowing our appointment and
adding to the material cost of a case.
Figure 3 is an SEM picture of a ceramic
restoration milled with the CEREC
system — the chipping of the margin is
easy to see at this magnification. While
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