PARTIAL CERAMIC CROWNS. ESTHETIC AND TISSUE CONSERVATIVE
RESTORATIONS – PART I: POSTERIOR TEETH
Figure 3. Chipping fracture of a partial ceramic crown.
a
Figure 4. Bulk fracture of a partial ceramic crown due to
too little thickness of the ceramic.
b
Figure 5. Scanning electron picture of a crack propagation in a ceramic restoration: (a) at baseliine (b) after 4 years (Friedl KH,
et al. Clinical and quantitative marginal analysis of feldspathic ceramic inlays at 4 years. Clin Oral Investig. 1997;1(4):163-168).
5. Which Ceramic?
A large variety of different ceramic materials for
partial crowns are available. They can be classified
according to their composition or to the way they
are processed. A survey of ceramics based on the
composition is presented in Fig. 6.
Material
Ceramic materials differ e.g. in their mechanical and
esthetic properties. In comparison to metals/alloys,
which undergo some plastic deformation after the
application of load, ceramics are considered to be
brittle with no/very little plastic deformation, which
can absorb energy. 17,18 The strength of ceramics is
usually assessed by means of classic flexural strength
tests using bar- or disk-shaped specimens 19 reflecting
sudden application of a heavy load. Additionally,
fracture toughness is a measure of resistance to
crack propagation. 19 Esthetic properties are mainly
related to the translucency of ceramics, 18 the higher
the translucency, the better the esthetics.
Dental ceramics materials can be subdivided into
three groups: 18
a. primarily glass containing (feldspatic) ceramics
based on silicate (also termed silica, SiO 2 )
b. leucite reinforced silicate ceramics, lithium
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disilicate ceramics, or zirconium oxide reinforced
lithiumsilicate ceramics
c. Mainly crystalline oxide ceramics (aluminum
oxide, zirconium oxide) (Table 1).
Feltspatic ceramics in general show very good
esthetics, but comparatively low mechanical strength
(Table 1). Therefore, these materials were either
reinforced with leucite, or are based on lithium
disilicate; additionally, zirconium oxide reinforced
lithiumsilicate ceramics have been introduced.
All silicate based ceramic materials need to be
adhesively luted to the tooth substrate. Examples for
materials with long clinical experiences are leucite
reinforced silicate ceramic (e.g. Empress I, formerly
named Empress) or lithium disilicate ceramic, which
contains 70% needlelike Lithium disilicate crystals
(3-6 µm long) in a glass matrix ( IPS e.max Press for
labside fabrication and IPS.max CAD for chairside,
CAD/CAM fabrication). This material shows better
mechanical properties than leucite reinforced
ceramics but still adhesive luting is recommended.
At least 1.5 mm thickness is recommended for
restorations made from these ceramics (see also
preparation). 18 Recently, zircon oxide reinforced
lithium silicate ceramics containing 10 wt.% 0,5 µm
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