PARTIAL CERAMIC CROWNS. ESTHETIC AND TISSUE CONSERVATIVE
RESTORATIONS – PART I: POSTERIOR TEETH
castable ceramics failure rates for partial crowns
were high. 6
Pressing of ceramic was introduced using leucite
reinforced ceramic (Empress I) in the 90s of
last century with better clinical results. Further
improvements were achieved using lithium disilicate
(IPS e.maxPress) ceramics for the pressing process.
However, again the restorations were fabricated in a
dental laboratory after impression taking.
A basic change in the processing of ceramics
occurred with the introduction of CAD/CAM
techniques, which employed an optical impression
(or scan), and the restorations were constructed by
means of a computer program (CAD – Computer
Aided Design). The restorations were then
fabricated by 3-D-milling (CAM – Computer Aided
Manufacturing) of an industrially prefabricated bloc.
Restorations could be fabricated chairside, but also
in a dental laboratory. This method has gained more
and more importance recently.
Which ceramic to select?
Selection of the suitable ceramic materials/ceramic
processing methods should be based on scientific
data. Here, results from clinical studies over at
least 3-5 years are of special relevance. For leucite
enhanced glass ceramics and for lithium-disilicate
ceramics such studies are available (see above:
longevity). Regarding the aspect of processing of
ceramics, broad and positive clinical experience
exists with pressing techniques and with CAD/
CAM. If the restorations are produced in a dental
laboratory, an experienced technician and a close
communication between dentist and technician are
essential. In our clinic, we have extensive and positive
experience over more than 20 years with leucite
reinforced and lithium disilicate ceramics using the
pressing technique or the CAD/CAM approach.
Fabrication of a ceramic partial crown
In the following series of figures, the fabrication
of a lithium disilicate CAD/CAM partial crown is
shown (Fig. 7a to 7f). After the optical “impression”
the partial crown is constructed with the help of
a computer program. In our clinic we are using
the CEREC 3 system (Cerec Bluecam and Cerec
Omnicam, Software Version SW 4.4.4.139706).
Then, a suitable ceramic bloc is selected matching
best in tooth color. Milling is performed on the blue
bloc with partially crystallized 40% plate-like lithium-
metasilicate crystals (0.2-1.0 µm) in a glass matrix (ca.
130–150 MPa). After try in, the restoration has to be
heat treated to receive its final color, individualization,
Figure 7. Fabrication of a lithium disilicate partial crown
using a CAD/CAM approach: (a) preparation, (b) CAD of the
restoration, (c) t ry-in of the metasilicate restoration, (d)
occlusal adjustment, (e) preparation for final firing, (f) luted
partial crown.
Figure 8. Crack formations on the buccal wall of a tooth with
a PCC without coverage of the functional, buccal cusp.
Table 2. Results from an in vitro study comparing the fracture
rate of ceramic (Vita Mark II) with 0.5 to 1 and 1.5 to 2 mm
thickness; modified according to (Federlin M, et al. Partial
ceramic crowns: influence of ceramic thickness, preparation
design and luting material on fracture resistance and marginal
integrity in vitro. Oper Dent. 2007;32(3):251-260).
Rely X Unicem
Variolink II
274
Ceramic Thickness Fractures (n)
Group 1 (0.5-1 mm) 7
Group 2 (0.5-1 mm) 1
Group 1 (0.5-1 mm) 8
Group 2 (0.5-1 mm) 1
Figure 9. Retentive, semi-retentive and non-retentive
cavity designs for the in vitro study on marginal quality
(Federlin M, et al. Partial ceramic crowns. Influence of
preparation design and luting material on margin integrity-
-a scanning electron microscopic study. Clin Oral Investig.
2005;9(1):8-17).
Stoma Edu J. 2017;4(4): 270-281
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