Ceramics for Dental Restorations , Ceramic-Metal Restorations ,All-CeramicRestorations dental material

Ceramics for Dental
Restorations

Definitions
• The term Ceramic is defined as any product
made essentially from a nonmetallic material
by firing at a high temperature to achieve
desirable properties
• The term Porcelain refers to a family of
ceramic materials composed essentially of
Kaolin, Quartz, and Feldspar, also fired at
high temperature

Classification of
Dental Ceramics

Classification of Dental Ceramics
Dental ceramics can be classified according to:
1. Fusion Temperature
2. Application
3. Fabrication Technique
4. Crystalline Phase

Fusion temperature can be classified to:
1. High-fusing ceramics (1315° to 1370° C)
2. Medium-fusing ceramics (1090° to 1260° C)
3. Low-fusing ceramics (870° to 1065° C)
4. Ultra-low-fusing ceramics (below 870° C)

• The medium- and high-fusing ceramics are
used for denture teeth
• Dental ceramics for ceramic-metal or all-
ceramic fixed restorations belong to the low-
or medium-fusing categories

2. Application
Ceramics have three major applications in
dentistry:
1. Ceramics for metal crowns and fixed partial
dentures
2. All-ceramic crowns, inlays, onlays, and
veneers, when esthetics is a priority
3. Ceramic denture teeth

3. Fabrication Technique
• One of the most common fabrication
techniques for dental ceramics is called
Sintering
• Sintering is the process of heating the
ceramic to ensure densification. This occurs
by viscous flow when the firing temperature
is reached

4. Crystalline Phase
• After firing, dental ceramics are composed of two
phases: a glassy (or vitreous) phase surrounding a
crystalline phase
• Increasing the amount of glassy phase lowers the
resistance to crack propagation but increases
translucency
• Materials for all-ceramic restorations have
increased amounts of crystalline phase (between
35% and 90%) for better mechanical properties

Ceramic-Metal Restorations
(or)
Porcelain Fused to Metal (PFM)

Ceramic-metal restorations consist of:
1. Cast metallic framework (or core)
2. Opaque layer, consisting of ceramic rich in
opacifying oxides (esthetics & bond)
3. Dentin and enamel ceramics (translucent)

Composition:
1. In its mineral state, feldspar, the main raw ingredient of
dental porcelains, is crystalline and opaque with an
indefinite color between gray and pink. Chemically it is
designated as Potassium Aluminum Silicate, with a
composition of K2O . Al2O3 . 6SiO2. The fusion
temperature of feldspar varies between 1125° & 1170° C,
depending on its purity

Composition:
2. Pure Quartz (SiO2) crystals are used in dental porcelain
and ground to the finest grain size possible. Silica is
added, and contributes stability to the mass during
heating by providing a glassy framework for the other
ingredients

Manufacture:
1. Feldspathic dental porcelains in recent years
are made mainly with potash feldspar (K2O,
Al2O3, 6SiO2) and small additions of Quartz
(SiO2)

Manufacture:
2. After the manufacturing process is
completed, feldspathic dental porcelain
consists of two phases. One is the vitreous
(or glass) phase, and the other is the
crystalline (or mineral) phase

Processing:
1. Porcelain Application & Condensation
2. Drying
3. Firing/Sintering
4. Glazing
5. Cooling

All-Ceramic Restorations
Several processing techniques are available for
fabricating all-ceramic crowns:
1. Sintering
2. Heat-pressing
3. Slip-casting
4. Machining

1. Sintering:
Two main types of all-ceramic materials are
available for the sintering technique:
A. Alumina-based ceramic
B. Leucite-reinforced ceramic

1. Sintering:
A. Alumina-based ceramic:
• Aluminous core ceramic is a typical example of
strengthening by dispersion of a crystalline phase.
Alumina has a high modulus of elasticity (350 GPa) and
high fracture toughness (3.5 to 4 MPa . m 0.5)
• Aluminous core porcelains have flexural strengths of
about 138 MPa and shear strengths of 145 MPa

1. Sintering:
B. Leucite-reinforced ceramic:
• Leucite acts as a reinforcing phase; the greater leucite
content (compared with conventional feldspathic
porcelain for ceramic-metal applications) leads to
higher flexural strength (104 MPa) and compressive
strength

2. Heat-pressed:
• Heat-pressing relies on the application of external
pressure to sinter and shape the ceramic at high
temperature. Heat-pressing is also called high-
temperature injection molding. The advantages of heat-
pressed ceramics include good esthetics, high strength
(but higher opacity). Processing times are short and
margin accuracy is within an acceptable range

3. Slip-casting:
• Slip-casting involves the condensation of an aqueous
porcelain slip on a refractory die
• Materials processed by slip-casting tend to exhibit
reduced porosity, fewer defects from processing, and
higher toughness than conventional feldspathic
porcelains

4. Machinable:
• Machinable ceramics can be milled to form inlays,
onlays, and veneers using special equipment. One
system uses CAD/CAM (computer assisted
design/computer assisted machining) technology to
produce restorations in one office visit

General Applications
of Ceramics in
Restorative Dentistry

Ceramics for Dental Restorations , Ceramic-Metal Restorations ,All-CeramicRestorations dental material

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