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H. Ralph Rawls Biomaterials
UTHSCSA Dental School
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Uses of Ceramics in
Dentistry
PFM crowns, bridges & fixedpartial dentures
All-ceramic crowns, inlays,
onlays and veneers
Ceramic denture teeth
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UTHSCSA Biomaterials 3
Other Ceramic Materials
- Grinding Wheels
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Ceramic Highly reacted Inert compounds Oxides such as SiO2, MgO,
Al2O3, Gypsum
Glass Ceramic Amorphous
Non-crystalline Single phase
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UTHSCSA Biomaterials 5
CERAMICS
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UTHSCSA Biomaterials 6
PORCELAIN
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UTHSCSA Biomaterials 7
Porcelain - Raw Ingredients
Feldspar the main raw ingredient K2O
Al2O3 6SiO 2
K2OPotash
Al2O3 Alumina
SiO2Silica
(potash feldspar )
Na 2O
Al2O3 6SiO 2
(soda feldspar or albite )
Na 2O Soda
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UTHSCSA Biomaterials 9
AmorphousCrystalline
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COMPOSITION
Various ions canreplace Si : Mg, Al, Ca Na, B, KFor example,replacing with: Na reduces meltrange Al increasesmelting range
2-DimensionalSilicate Structure
Glass
Si
Quartz
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Dental CeramicsProcessing Methods
SINTERING OF PORCELAIN
Richard Van Noort: Introduction to Dental Materials, 2nd edition Dental Ceramics http://www.fleshandbones.com/readingroom/
The thermochemical reactionsbetween the porcelain powder components are virtually completedduring the original manufacturing
process
The purpose of firing is to
sinter - FUSE TOGETHER -the particles of powder toform the prosthesis
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High- (1200-1400C) & Medium- (1050 1200C) Low-fusing (800 1050C)
porcelains
Opaque, dentine & enamelporcelains Compaction Firing sintering
Glazing
Production of porcelain jacket crowns
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PFM - Fabrication
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Castable glass
ceramic
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Indications Crowns Inlays Onlays Veneers
Leucite-reinforced ceram ic Based on a glass containing
latent nucleating agent
Pressing heated ceramic material
Permits precise
reproduction of full-contour waxed restorations
IPS Empress :
Hot PressingLeucite-reinforced glass ceramic
Empress
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Mechanical Performance
Metals usually undergoplastic deformation
Ceramics exhibit brittle fracture
Brittle behaviour
Necked region
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Surface Defects Theoretical strength of a glass isapproximately 100 times greater thanits measured strength. This is due to surface defects
voids scratches microcracks
Known as Griffith's flaws.
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Glass
Load
Griffith flaws
When a tensile load is applied . Flaws act as stress concentrators This produces cracks
Propagationof cracks
Cracks propagate and cause fracture failure
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Fracture of ceramics
and glasses Maxstrain that glass can withstand is 0.1%
Glass is extremely sensitive to thepresence of surface microcracks
Tiny flawsin the interior of thecrown act as initiating sites forcatastrophic failure
Two solutions provide support using astronger substrate Produce ceramics that arestronger and tougher
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Methods of strengtheningporcelains
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Stronger substrates tosupport the porcelain
Reinforced ceramiccore systems support is provided
by another ceramicmaterial
Metal-ceramics theceramic is supportedby a strong and toughmetal
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Crack propagation in an non-reinforced glass
Crack propagation
Crack propagation in a reinforced glass
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Strengthening Mechanisms
Glazing/overglazing
Application to metal Dispersion strengthening
Ion exchange Transformation toughening
Glazing/overglazing
Dispersion strengthening
Ion exchange Transformation toughening
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Glazing/Overglazing Glazed porcelain is significantly
stronger than unglazed porcelain. Glazing minimizes the number and
size of surface flaws. This limits crack propagation within
the porcelain.
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FiringAtmosphere
SurfaceCondition
Modulus of Rupture (psi)
Porcelain Air
Vacuum
Ground
Glazed
Ground Glazed
11,000
20,465
11,547 19,187
Material
Surface Glaze and Vacuum
Removal of Defects
Glazing almost doubles strength
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Application of
Porcelain to Metal
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Na+
Na+
Na+
Na+ Na+
Na+
Na+ Na+ Na+
K+
K+ K+
K+
Na+ Na+
Na+
Na+
Na+Na+
Na+
Na+Na+ Na+K+ K+ K+ K+
Compression
Na+
Small ions are replaced by large ions
Introduces compressive stress into the surface Closes surface defects and increases strength
Ion Exchange
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Type of ceramic Flexuralstrength(MPa)
Feldspathic porcelain Alumina coreGlass-ceramic DICOR Non-shrink alumina ceramic Cerestore Leucite-reinforced ceramic Optec
Aluminous core porcelain Hi-Ceram Heat-pressed reinforced ceramic Empress Glass-infiltrated alumina ceramic In-Ceram High alumina, 98% purityGold alloy (yield strength)
65-8592-12490-124
105-114105-120
140-141160-180400-446420-520350-600
Brand name
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CAD/CAM Ceramics that can be milled(machined) to form inlays,onlays , and veneers.
The CEREC [ chair-side ]system
CAD/CAM C omputer Assisted Design /C omputer Assisted Machining
Can produce restorations in oneoffice visit.
Quick turn-around from a lab (Craig, Robert G.. Restorative Dental Materials, 11th Edition .
Elsevier, 2002. 18.5.3).
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Computer-ControlledMilling Machine
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All-Porcelain Application
Pure Alumina Core Procera AllCeram 99.5% sintered alumina Digitized scan of die sent to Sweden Coping returned usually w/in 24 hrs
Veneered with feldspathic Flexural Strengtharound 700 MPa
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All-Porcelain ApplicationGlass-Infiltrated Ceramic Core
In-Ceram Spinel / Alumina / Zirconia
Not Slip-castdry-pressed into blocks
Machined / CAD-CAM Cerec or Celay Flexural Strength
even >700 MPa!
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Other Advantages of
CAD/CAM Systems Bonding ceramic restorations withresin cement helps to compensate for
the problems of poor marginal fit. Fracture of ceramic restorations can
be prevented if the preparation hasadequate thickness to resist occlusalforces.
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Disa dvantages of
CAD/CAM Systems Marginal accuracy can be poor , with values of 100to 150 m
Longevity less than PFM crowns . Durability excellent for inlays; however, full posterior
crowns tend to break within 4 years.
Color match limited Ceramic blocks difficult tocolor match
Technically challenging : Assistants oftenintimidated by CEREC technology High cost CEREC System is ~ $100,000.
This cost is transferred to the patient making the cost of aCEREC inlay $500 - $1,500.
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Translucency Transmission of light via an indirect path through a material Pores or crystalline regions reflect and refract a light beam
Causing it to be scattered in manydirections as it passes through
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Opacity Zero light transmission.A large amount of scattering can
cause opacity . Color (hue ): Blue and violet arescattered more than yellow and red.
Therefore scattering results in a weakchange in color shade (hue).
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ABSORPTION Removal of a portion of light (at certain wavelengths) passing
through a material by electron interaction Principal cause of color Portion not absorbed is perceived ascolor
reflected
scatteredor transmitted
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Color Space Has three dimensions: HUE Dominant wavelength (blue, etc.)
VALUE Grey scale ( black )(high value low value)
CHROMA - Color saturation, or color intensity
Pastels have low chroma:
is low in chroma
but
is high in chroma. Figure 2.A color wheel showing complementary colors.HUE
Component of Color Space
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Questions?