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The
following preparation forms are suitable:
- Pronounced
chamfer (90°)
- Shoulder
preparation with rounded axio-cervical line
angle.
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| To
effectively perform all-ceramic preparations in
the anterior and posterior region, a preparation
set comprising six diamond instruments was assembled
(Ergo Prep Set, TD 1275, Gebr. Brasseler, Lemgo). |
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Cylindrical
diamond instruments with a rounded tip (e.g. 8881.314.016,
Gebr. Brasseler, Lemgo) are suitable for a chamfer
preparation. Conical diamond instruments with rounded
edge (e.g. 8951KR.314.017, Gebr. Braseler, Lemgo)
are especially suitable for the shoulder preparation
with a rounded axio-cervical line angle. |
| The use of rotary instruments
with an average grit size 30ùm is recommended
for finishing the preparation. The minimum wall
thickness of the zirconia frameworks is 0.4mm, while
the minimum amount of space required in the cervical
region for veneering is 0.6mm, meaning that a circular
marginal cutting depth of 1.0mm should be the aim. |
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Posterior
Restorations
For the restorations in the posterior region, a
minimum occlusal layer thickness of 1.0mm must be
guaranteed for the veneer ceramic. Based on the
minimum frame work wall thickness of 0.4mm, a substance
removal of 1.5mm should be aimed for in the occlusal
surface region. The cone angle of the corresponding
axial walls occlusal surfaces should be rounded |
| When
determining the path of insertion it is important
- particularly for FPD's - that all corresponding
axial surfaces of the bridge abutments have a cone
angle of at least 6°. In the scanning process,
very steep slopes appear as vertical objects which
cannot be shown precisely by the software. |
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The
occlusal relief should reproduce a simplified form
of the occlusal surface. A 120-140° opening
angle os the occlusal surfaces guarantees an exact
reproduction of the inner surfaces during the million
process and thus a good internal fit. |
| A
rhomboid diamond instrument (e.g. 8899.314.027,
[palatal contouring instrument] Gebr. Brasseler,
Lemgo), which is guided vertically to the tooth
axis, has proven especially suitable for preparing
occlusal portions. |
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Anterior
Restorations
The preparation for anterior restorations
is geared towards the aforementioned general preparation
instruction. Along with a circular cutting depth
of 1.0mm at the preparation limit, a cone angle
of 6-8° must be guaranteed for the axial walls.
The junctions between the axial and palatal surfaces
must bust be rounded, as should the incisal surfaces
(minimum radius: 0.4mm). |
| From
an aesthetic standpoint expecially, incisal removal
should be 2.0mm. The minimum width of the incisal
edge must be 0.9mm in a vestibular-oral direction
to guarantee an exact reproduction of the internal
framework surfaces by the mailing unit. |
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The
use of the aforementioned palatal contouring instrument
(8899.314.027, Gebr. Brasseler, Lemgo) is recommended
for shaping the palatal contour of upper anterior
teeth and canines. |
The
same instrument is also available for rounding
the transfers between the axial walls and incisal
edge. Cercon restorations can also be fabricated
with a vestibular or circular ceramic shoulder.
There are corresponding shoulder ceramics for
the veneer material (Cercon ceram S). With the
design of a ceramic shoulder preparation offers
advantages over the chamfer.
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