Nowadays;
all-ceramic prostheses are considered as the alternative materials
compared with metal-ceramics. They offered increasingly great feel by
emulating so normally the optical properties of teeth. Another later
factor influencing the choice of dental ceramic materials is the high cost
of precious metals such as gold. The common disadvantage of the first introduced ceramics
production as feldspathic ones were the mechanical stability that limited the
indication for all dental ceramic materials to anterior regions and to
single units fixed prostheses for their higher esthetic properties.
In the last years, numerous new dental ceramic
materials were developed to increase the mechanical stability and also
keeping their esthetic properties. Among those materials: leucite/
lithium-disilicate, glass ceramics, and oxide ceramic, for
example, alumina and zirconia that gave off an impression of being
promising for different indications (1,2). The first
method of manufacturing the ordinary crown is lost wax-technique which is
considered a technique sensitive as it requires several steps. In
addition, it requires the therapeutic procedure to happen in numerous
visits, expanding treatment time and potential complications .
However, using
computer-aided design /computer-aided manufacturing which is a recent technique
helped to produce (CAD/CAM) frameworks which allowed the dental professional
to easily make ceramic crowns in one visit, without the necessity of
forming temporary crowns that may lead to decrease postoperative
complications and reduce treatment time
Organization
Grouping and Clinical Application
Esthetic
materials are shaped through at least two particular stages on a glass
framework and crystalline filler particles (5). The improvement of
higher properties of ceramics is result of the in wrinkled utilization of
crystalline material and filler particles that are included in the glass
lattice planned for improving the ceramic’s mechanical properties by
decreasing less glass stage and, at long last, no glass content. Based on
the micro-structural level, dental ceramic can be characterized by their
organization of glass-to-crystalline proportion in three fundamental
classes:
•
Prevalent smooth materials with high glass content. • Molecule filled
glasses with variable measures of glass content. • Poly crystalline
ceramic production without glass content. The glass-based structures used
in dental ceramic start from feldspar minerals that contain transcendently
silicon dioxide (silica or quartz), which have various proportions of
alumina (aluminum oxide); they are in like manner called aluminosilicate
glasses. Feldspathic glasses contain sodium and potassium, which can alter
critical properties of the glass, for instance, decreasing ending
temperatures or growing warm turn of events and withdrawal lead
Lithium-disilicate
glass esthetic
Glass
ceramic production improved with lithium-disilicate precious metals (SiO2-
Li2O) were created by Ivoclar Vivadent to be utilized with the lost wax
heat pressed technique (IPS Empress® 2 and IPS e.max® Press) and later on
with the Computer Aided Design/CAM innovation (IPS e.max® Computer aided
design). The esthetic microstructure comprises of exceptionally
interlocked lithium-disilicate precious stones, 0.6 mm long and 0.8 mm in
distance across (7). Because of the
moderately low refractive record of the lithium-disilicate gems,
this material has high translucency shows disdain toward its high
crystalline substance.
The
IPS e.max lithium-disilicate ceramic can be utilized in solid application
for esthetics, onlays, and posterior crowns or as a center material for
crowns and three-unit FDPs in the anterior area.
Machinable lithium-disilicate squares (IPS e.max computer aided design)
were recently developed to be utilized with computer- aided design CAD/CAM
handling innovation. These squares are exposed to a two-phase
crystallization process. During the last crystallization process, 70% of
precious stone volume is incorporate-evaluated in a glass framework,
expanding its last opposition. Furthermore, in this stage the blue shade
of the recrystallized square is changed to the chosen tooth conceal.
The last restoration has a flexural quality of 360 MPa; these are demonstrated
for foremost or back crowns, embed crowns, trims, onlays, and facade.
ompletely
Polycrystalline or Polycrystalline ceramic production/No Glass Content
The
advancement of high-quality polycrystalline ceramic production resulted from
the expanded utilization of crystalline material with ensuing diminished
measures of the glass stage, until no glass was present in the material
microstructure (8). These ceramic
productions are framed by legitimately sintering gems together, bringing
about a thick, glass-free polycrystalline structure.
• Composed of: - Alumina; Nobel BioCare grasped the idea of computer
aided design/CAM innovation to manufacture every single ceramic crown made
out of a thickly sintered, high-virtue aluminumoxide coping joined with a
low-melding all-ceramic veneering porcelain. Copings contain 99.5% to
99.9% high-immaculateness aluminum oxide. - Zirconia; is a polymorphic
material that happens in three crystalline structures that
are temperature-subordinate: monoclinic, tetragonal, and cubic. The
zirconia ceramic production is described as a thick, monocrystalline
homogeneity, and have low warm conductivity, low erosion potential, great
radiopacity, high biocompatibility, low bacterial surface grip, and positive
optical properties. Contrasted and high-quality alumina ceramics, zirconia
has twice the flexural quality.
Classification according to techniques:
Fabricating All- Ceramic Crown Restoration Currently,
special structures are utilized to fabricate metal-free prosthesis:
powder condensation, pressing, slip casting, and CAD/CAM milling of
ceramics (12).
Powder Condensation Powder condensation is considered to be the
gold popular approach of fabricating allceramic crowns (13).
Moist porcelain powder is utilized to construct up the crown and then
extra humidity is eradicated to condense the powder particles. Then
the porcelain is fired below a vacuum however, a massive quantity of
residual porosity is found. Although all-ceramic crowns fabricated through
this method have low strength, they are extra esthetic than crowns which
have been made by the way of the other methods due to their higher
translucency .
Heat Press Technique The misplaced wax approach is used to produce all-ceramic crowns by means of the heat press technique. It consists of heating pressable ceramics ingots to an excessive temperature, at which they flip out to be extraordinarily viscous liquid and then are pressed progressively into the shaped misplaced wax mold. All-ceramic crowns fabricated by this method have decreased porosity and top accuracy of fit (1 3). All pressable ceramic substances are supplied in the structure of ingots. The first generation of the heat-pressed ceramics used to be composed of 35-45% leucite by the way of volume as crystalline segment whilst the 2d technology comprised approximately 65% lithium disilicate by the way of extent as the major crystalline phase (1 4).
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