Dental ceramics part1 - Minia
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Dental ceramics part1 1
Transcript of Dental ceramics part1 - Minia
Dental ceramics part1
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• Keramikos = Burn stuff
i.e. All desirable properties are achieved by Firing
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• General properties:
• Affected by
Ionic bonding Covalent bonding
Both types
atomic bonding
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1. High melting temperature.
2. Thermal & electrical insulators.
3. Transparent unless porous Translucent.
4. Mechanical properties: a) Brittle
b) Low fracture toughness.
c) Hard.
5. Chemically inert due to: a) Formed by oxidation Maximally reacted No free electrons.
b) Strongly bonded No leaching out of constituents.
6. Chemically indestructible Dissolves in strong acids as HF
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• Important terms for silica based ceramics:
Gt (Fictive temperature) Rigid & hard porcelain < Gt< Viscous & soft
Ceraming
Vetrification (Glass forming) Devetrification (Crystallization)
Glass ceramics
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Uses: Denture teeth.
Jacket crowns.
PFM.
Inlays.
Advantages Disadvantages
1. Satisfactory aesthetic.
2. Glazed surface compatible with soft tissue.
3. Resist sudden thermal changes.
4. Adequate strength.
1. Different optical properties than En. & Dn.
2. Additional tooth preparation.
3. Wear of opposing natural teeth.
4. Brittle.
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Composition: (generally vitreous ceramic based on silica network and feldspar)
1.Feldspars:
(75-85%)
Anhydrated aluminum silicate Potassium aluminum silicate (orthoclase)
(K2O. Al2O3.6SiO2) + Sodium aluminum silicate (albite) (Na2O. Al2O3.6SiO2)
1290ºC Glassy phase that gives the form of the restoration.
Potasium feldspar + metal oxides Firing Leucite (Crystalline mineral with α)
2. Silica:
(12-22%)
Quartz Crystalline dispersion in glassy phase Strengthening agent.
3. Kaolin:
(3-5%)
Hydrated aluminum silicate (Al2O.2SiO2 2H2O) With water Sticky Workable mass
Molding of unfired porcelain.
On heating Framework as feldspars Shrinkage and opacity.
4. Others:
a) Glass modifier: Metal ions: Na+,K+ or Ca+ Associated with O atoms Bond strength
Softening temp.
Effects Viscosity of glass.
Softening temp.
Thermal expansion.
↑↑ Conc. Chemical durability of glass Resistance to attack by water,
alkalis and acids.
Crystallization of glass during firing.
b) Fluxes: In low fusion glasses Fusion temp.
c) Pigments:
(< 1%)
As metal oxides Required color.
d) Sugar&Starch: Help manipulation of powder. 7
Manufacturing:
1. Pyrochemical reaction:
All components Blending Melting at temp.
2. Quenching:
The red hot material Quenching Porcelain powder (Frits)
supplied to dental lab.
The frits are composed of
Vitreous (glassy) phase (Feldspars & Kaolin)
Crystalline phase (Silica & Metal oxides)
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a) General classification of
porcelain restorations:
All ceramic
restorations
PFM - Feldspar
1. Core reinforced ceramics: -Aluminous porcelain.
-Hi – Ceram.
-In – Ceram.
-In – Ceram spinell.
-Magnesia core porcelain.
2. Feldspar: -Low – leucite.
-High – leucite (Optec).
3. Cast glass ceramic: -Mica (Dicor).
-Leucite Injection molded glass (Empress).
4. Milled ceramic restorations -CAD/CAM (Cerec).
-Copy milling (Celay).
Classifications of dental porcelain
b) Acc. to fusion temp.
-High fusing 1300ºC denture teeth
-Medium fusing 1100 - 1300ºC
-Low fusing 850 - 1100ºC Cr & Br
-Ultra-low fusing < 850ºC
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Classifications of dental porcelain
I. According to their application:
Core porcelain it must have adequate mechanical
Properties.
Dentin porcelain it gives the shape and color.
Enamel porcelain it is quite translucent
II. According to the method of firing:
At atmospheric pressure.
At reduced pressure (under vacuum).
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III. Accoording to fusion temp.
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High fusing 1300ºC Denture teeth
Medium fusing 1100 - 1300ºC
Low fusing 850 - 1100ºC Cr & Br
Ultra-low fusing < 850ºC
Methods of fabricating ceramic restorations:
- Condensation and sintering (Conventional technique).
- Pressure molding and sintering.
- Casting and ceraming.
- slip- - casting.
- Sintering and glass infiltration.
- Milling by computer control.
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Porcelain manipulation (Technique):
Conventional condensation and sintering for PJC:
Procedures:
Dentist
(In the clinic)
Technician
(In the lab)
1. Tooth preparation
2. Impression
3. Model or Die
4. Platinum foil matrix (0.025 mm)
5. Application of porcelain layers:
-Opaque shade.
-Dentin shade.
-Enamel shade.
Stages of porcelain application:
-Compaction. •Vibration.
•Spatula pressure.
•Sprinkling dry powder
-Firing in electric oven (muffle) Loss of water & Sintering
-Glazing Shiny impervious surface.
Done by Self-Glaze
Applied Glaze
-Cooling Slow cooling Avoid Crazing 13
Tooth preparation Impression Die preparation
Platinum foil matrix
Opaque layer application Porcelain application
& Compaction Firing
Glazing Cooling
Correction and
adjustment
Fired restoration
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Properties:
1. Firing shrinkage: Linear shrinkage = Low fusing 14% , High Fusing 11.5%.
Volumetric Shrinkage = Low fusing 32 -37% , High Fusing 28-34%.
Cause Loss of water Voids Sintering Voids Shrinkage.
2. Porosity:
(1.3 – 4.8%)
Effect Strength & Opacity.
To reduce to 1.3% 1. Firing under vacuum
2. Use powder with different particle size
3. Chemical prop.: Chemically stable Dissolved by strong acids (HF).
4. Mechanical
prop.:
Brittle
% Elong.
Shear St.
0.1%
110 MPa
Tens. St. Diam. Com.
Trans. St.
Comp. St.
34 MPa
62-90 MPa
172 MPa
E.
KHN
69 GPa
460 kg/mm2
5. Specific gravity: 2.2 – 2.3
6. Esthetic & color: Excellent but not perfect
Affected by Nature of incident light.
Porcelain translucency, reflectance, fluorescence.
Lanthamide earth Fluorescence.
7. Biological effect: Very inert No adverse effect to surrounding tissues.
But It is a very bulky restoration Needs excessive tooth reduction.
May produce stresses on the gingiva.
It is very hard Attrition of opposing natural dentition.
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Denture porcelain teeth: Made from high and medium fusing temperature.
Anterior teeth Retained in denture by Pins.
Posterior teeth Retained in denture by Diatoric Channels.
Advantages Disadvantages
1. Aesthetic > Acrylic.
2. More resistance to wear.
3. Allow denture rebasing.
1. Brittle.
2. Clicking sound with opposing.
3. Needs high interarch space
They can not be ground.
4. Very rigid and not resilient
Transmit stresses to bone
Excessive bone resorption.
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I. PROPERTY Acrylic T. Porcelain T.
Mechanical properties Not brittle not resistant to
abrasion
Brittle resistance to a abrasion much
lower than denture base
aesthetics Reasonable More aesthetics
Thermal expansion A teeth similar to denture
base
Have a large difference between the
acrylic base and it So, crazing occur
Density 1.2 gm/C3 2.4 gm/cm3
Retention to denture
base
Chemical bonding Mechanical bonding to dentate base
under cut or pins
Adjustment Can be ground and replaced Cannot ground cannot replaced
Inter ridge space Require smaller space Require larger space
Performance in service • Highly resilient
• Less force transmit to
underling mucosa
• No clicking on contact
with giving natural feeling
• Least resilient
• Low resilience transmits moor
force to underling mucosa.
• Clicking sound occurs on contact.
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Ceramics strength values are much lower than the
predicted values based on their primary intratomic bond.
Why do ceramics fail at
stresses far below their
theoretical strengths?
Scratches and surface defects
Stress concentration and crack propagation
Stress concentration at the tip
Exceeding of theoretic strength
Bond breakage
Crack propagation
Failure
F
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F
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F
STRESS
RAISERS
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