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QUARTER 2 | 2014 | CERECDOCTORS.COM | 55
focusing more on materials. Before we
can understand that, we need to look
at a cross-section of the tooth (Fig. 4).
Enamel thickness is a critical component
to take into consideration when plan-
ning how you are going to prep a case.
Enamel contains the translucency, value
and opalescence of the natural tooth.
The Dentin transmits the hue, chroma
and fluorescence (Fig. 5). This is very
important to understand when one starts
to think about prepping the tooth. If the
preparation can be ultra-conservative
and remain in the enamel, we can use a
lot of the natural properties of the tooth.
If the preparation is more aggressive,
now we have to depend on the material
Fig. 5: The enamel
contains the
translucency,
value and
opalescence
of the natural
tooth; the dentin
transmits the
hue, chroma and
fluorescence
Fig. 6: Light
Transmissions
through different
thicknesses of
material
itself to create the natural properties of
the tooth, which is inherently more diffi-
cult to achievewithmonolithicmaterials.
In short, the preparation is the single-
most important determining factor when
choosing materials.
The main concepts to understand
when planning for the restoration are:
• We want to keep opacity at deepest
internal level
• 0.5 mm to 0.7mm of enamel thickness
is ideal
• High-valueopaciouscoreisanadvantage
• There are diminishing returns with
excessive restoration thickness
The concept that is the most impor-
tant is the last one. That is: the more you
prepare a tooth, the more difficult your
task is going to be. If you have an aggres-
sive preparation, the thickness of the
material will lower the value of the resto-
ration. Remember, the natural value of the
tooth is contained in the enamel. If you
remove all the enamel, you must depend
on the restoration itself for the value.
To further emphasize thispoint,wecan
examine the light transmission of e.max
CAD LT and HT at different thicknesses
(Fig. 6). You can see how light transmis-
sion of thematerial is not only affected by
the translucence of thematerial itself, but
also the thickness of thematerial. This, in
turn, will affect the overall value of the
restoration. Therefore, when preparing a
tooth, only prepare based on the overall
outcome you are trying to achieve, the
degree and location of any discoloration
and the overall space requirements of
the restorative material. Less is most
certainly better.
Knowing this, we can now go into
case planning with a general idea of
how we would like to prep. Of course,
there are always going to be surprises,
but knowledge of the properties of teeth
helps guide us. If we look at three very
different cases, we will likely plan on
very different preparation plans.
Fig. 4: Average
enamel thickness
.3 - .4 mm
.8 - 1.0 mm
1.1 - 1.3 mm
In short, the
preparation is
the single-most
important
determining factor
when choosing
materials.
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