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25 Cards in this Set
- Front
- Back
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Ceramics
make up? Bonding? Structure? |
metal/non metal
ionic/covalent crystalline/amorphus |
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Esthetic Restorations
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translucent
low corrosion/wear high modulus Veneers, inlays/onlays, crowns bridges brittle susepctible to fracture |
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Composition: Porcelains
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Mixtures of 3 ingred:
1. feldspar 2. Quartz 3. Kaolin Dental porcelains only quartz and feldspar, household = 50% kaolin |
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Kaolin
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hydrated aluminosilicates ( al2O-2siO2-2H2O)
binder increading molding opaque |
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Quartz
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Strengthening agent
Fine crystalline dispersion through glassy phase |
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Feldspars
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Mixtures of potassium aluminosilicate(K2O-Al2O3-6SiO2)
potash(K2O) increase viscosity of molten glass Soda(Na2O) lowers fusion temp |
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Liquid phase-Sintering Process
process? Tglass vs. Tsinter vs. Tmelting? Driving force? size effect? |
heat closely packed ceramic particles to cause borders of particles to melt and fuse
Tglass transition<Tsinter<melting reduced surface energy from reduced surface area shrinkage during sintering |
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Fritting
Process? Particle distribution? |
Fire mixed components, rapid cooling, ground into fine powder=frit
Tightly packed to minimize shrinking, multimodal particle size distribution to increase packing density |
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Why do we need glass modifers?
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Silica Glass: too high sintering temp
too low thermal contract coefficient Add Na/K to: Decrease viscosity, increase softening temp, increase thermal EXP |
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Addition of glass modifers
what are they? fxn? Product? |
Alkali metal ions(Na,K,Ca)
Interupt oxygen silicon bonds 3D-silica network-tetrahedra |
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What do glass modifiers do?
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easy movement of chains
lowers viscosity, softenting temp, increases thermal expansion but can reduce chemical durability |
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Classificaiton of Dental Porcelain firing temperatures
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high fusing 1300
med fusing 1101-1300 low-850-1100 Ultra low- <850 |
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Other additives+ fxns
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Boric Oxide-mechanical thermal shock
Pigmenting: simulate natural teeth Opacity-cerium, zirconium, titatnnum, tin oxides flurescence-lanthanide earth Binder-easy manipulation of powders |
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Processing Porcelain:
Jacket Crown Procedure |
Opaque shade
Dentin Shade Enamel Shade condense, fire, glaze/shading |
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Condensation
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slurry to die
compaction-remove water Particle size/shape-degree of shrinkage/handling characteristics Binder- hold particles together |
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Firing
1. 2. 3. 4. |
1. Sinter particles-->prosthesis
2. Cooling-slowly to avoid cracking 3. Air firing- formation from residual air, alter transluceny, exposure of voids after grinding 4. Vacuum-air withdrawn, less voids, denser stronger crown |
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Glazing
1. 2. |
Fill exposed air void on surface
Reduce cracking Final firing after glaze- controlled-->fuse glaze to superficial layer |
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Properties of Dental Porcelains
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1. good aesthetics
2. thermal conducvity and coefficeint of thermal expansion-similar to enamel/dentin 3. Mechanical-high comp. strength, low tensile strength and toughness, brittle |
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Fractures of dental porcelains:
Sensitive to cracks |
rapid outer cooling
higher outer contraction compressive load outside residual tensile stress inside Internal surface cracks early porcelainL low stress bearing |
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Classifications of Dental Ceramics
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1. Early porcelains
2. Metal Ceramics-supported by metal 3. Reinforced ceramic core systems-supposrted by other ceramics, high strength+tough, lack aesthetics 4. Resin-bonded ceramics supported by tooth structure, bonding directly with enamel and dentine |
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Metal Bonded Ceramics
Problems: Aestheitcs Bonding Failure modes |
Aesthetics: lack strength, micro cracks
Bonding: high fracture toughness, metal =prop. crackks breakdown b/w metal ceramic bond mismatch b/w coefficients of expansion-->stress during cooling-->crazing/cracking |
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Problems:
Interlocking Intimate contact |
interlocking: ceramic flows into space on surface of metal-->grinding/abrasive
gas bubbles degrade bond strength -->degassing-burns of impurities and reduces formation of bubbles |
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Compression Fitting
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-mismatch coefficient of thermal expansion, Metal>ceramic
-Procelain shrinks after firing temp with bond |
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Chemical Bonding
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Bonding b/w ceramix and oxide coating of metal
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Thermally Induced Stress
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Coefficient of expansion:
Metal>procelain-->compressive Porcelain > metal-->tensile(outwards) Best combo: M slightly larger than P |
