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33 Cards in this Set
- Front
- Back
1. What are some requirements of a ceramic-metal bonding system?
Three things... |
1. High melting temperature alloy
(100 deg C higher than ceramic or solders) 2. Low fusing temperature (metal coping distortion) 3. Adequate stiffness, strength, and sag resistance of the metal |
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2. In a ceramic metal bonding system what must the ceramic slurry do?
What is essential between the ceramic and metal? |
Ceramic slurry must wet the alloy readily when applied
**<60 degrees contact angle A good, stable bond is essential |
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3. How must the coefficient of thermal expansions be in a ceramic-metal bonding system?
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CTEs of ceramic and metal must be compatible
CTE for the metal coping should be slightly higher than that for the ceramic to place the ceramic in slight compression (where it is stronger) as PFM temp decreases from firing temp to room tem |
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4. What are some tests the evaluate the ceramic-metal bonding?
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1. Planar shear test
2. Flexural test -requires layers of ceramic to be bonded to a strip or plate of metal -coated metal plate is flexed in a controlled manner until the ceramic fractures 3. Three-points flexure test -ceramic is fired to one side of a rectangular strip of metal |
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5. What are usual levels of adequate bonding?
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When fracture stress is above 25 MPa
**with may ceramic-metal systems values of 40 to 60 MPa are common |
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6. What are three locations of possible ceramic-metal failures?
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1. Metal-metal oxide
2. Metal oxide-metal oxide 3. Ceramic-ceramic **highest strength ceramic-metal specimens will fracture in ceramic when tested **fractures through the oxide and metal-metal oxide fractures are observed w/ poor bonding |
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7. What are the five requirements for ceramics used in ceramic-metal restorations?
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1. Esthetic (stimulate appearance of natural teeth)
2. Fuse at relatively low temperature (but can range from high to low fusing porcelains) 3. Compatible CTEs w/ metal substructures (leucite content - higher content means higher CTE for porcelains so can match that of dental alloys) 4. Stable in oral environment (solubility, "chemical corrosion") 5. Not abrasive to opposing enamel |
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8. What are the various "functional" porcelains?
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1. Opaque
2. Dentin 3. Enamel 4. Translucent porcelains |
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9. How are opaque porcelains?
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1. Have higher levels of opacifying agents
-TiO2, ZrO2 and SnO2 2. Have a lower viscosity and film thickness |
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10. What are gold-platinum-palladium classified as?
Why are platinum and palladium added? Why are indium, tin, and oxides present? |
Classed as high noble alloys (ADA)
Added to increase the casting temperature to approximately 1150 C Present to form oxides for ceramic-metal bond |
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11. What is hardening of Au-Pt-Pd alloys a result of?
What is the optimum heat treatment? How is the Vickers hardness of Au-Pt-Pd? |
Result from solid solution hardening and the formation of a FePt3 precipitate
Optimum heat treatment is 30 minutes **practically, hardening occurs during firing of the ceramic VHN is close to that of enamel therefore occlusal coverage w/ metal is appropriate |
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12. What are the characteristics of Au-Pt-Pd alloys?
What color are they? |
High:
-stiffness -strength Reasonable elongation Low sag resistance Yellow in color |
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13. What are gold-palladium alloys?
How is their hardening achieved? What additional elements do these alloys contain and why? What color are they? |
High noble alloy
Contains no palladium or iron so have solution rather than precipitation hardening Contain: 1. Indium for bonding 2. Gallium to decrease fusion temp 3. Rhenium for grain refining 4. Ruthenium for castability White color (silver like) |
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14. How do Au-Pd alloys compare to Au-Pt-Pd alloys?
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1. Stronger, stiffer, and harder
2. have higher elongation (more ductile) 3. Higher casting temperatures (easier to solder) **improves castability and soldering 4. Lower density **requires more care in casting due to decreased force entering the investment material |
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15. What are gold-palladium-silver alloys?
How is the palladium content? How is hardening achieved? What are the properties similar to? What is the color? |
High noble alloy
Reduced Pd that is made up by adding silver Solution hardening Properties similar to Au-Pd alloys White color (silver-like) |
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16. What other elements are added to Au-Pd-silver alloys and why?
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1. Indium and tine for ceramic bonding
2. Ruthenium for castability 3. Rhenium for grain refining |
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17. What is palladium-silver classified as?
How much silver does it contain? What color are they? What can the higher silver content result in? |
Noble alloy
Contains a moderate amount of silver (30-37%) White color (silver-like) Sometimes result in porcelain "greening" discoloration |
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18. What other elements are in palladium-silver alloys and why?
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1. Indium and tin for ceramic bonding
2. Ruthenium for castability |
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19. What are palladium-copper alloys classified as?
How much palladium and copper do they contain? What are their properties? |
High Pd content (74-79%)
Contain 10% to 15% copper Can contain up to 2% gold High strength and hardness Moderate stiffness and elongation Low density |
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20. What additional properties do palladium-copper alloys contain and why?
Why is a porcelain opaque layer used? |
1. Indium for ceramic bonding
2. Gallium for reducing-controlling casting temperature Dark oxide layer that must be masked by porcelain opaque layer |
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21. What are high palladium without silver or copper called?
What is the palladium content? Trace amounts of which elements are found? |
Noble alloy-ultima lite
High Pd content (78.4%) Trace amounts of -Zinc -Indium -Gallium -Ruthenium |
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22. What is the thermal expansion like for high Pd w/o silver or copper?
What is the VHN? What is the melting range? What does the dark oxide layer require? |
Mid-range thermal expansion - 15%
(broad compatibility w/ various ceramics) Hardness approx 300 1175 - 1255 C Requires adequate masking w/ ceramic opaquer |
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23. What is nickel-chromium classified as?
What percent chromium does it contain? What does the chromium provide? How are alloys containing Al strengthened? |
Base metal
13%-16% chromium Provides tarnish and corrosion resistance Strengthened by formation of a coherent precipitate of an intermetallic compound, Ni3Al |
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24. What does molybdenum (Mo) doe in nickel-chromium alloys?
What doe beryllium doe? |
Mo reduces the CTE
Beryllium improves castability by decreasing the melting range and hardening **use of beryllium may raise some toxicity issues |
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25. How does nickel-chromium compare to noble alloys?
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1. Higher casting temperatures
2. Harder 3. Lower yield strength 4. Higher elastic modulus |
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26. What percent of chromium is in cobalt chromium base metal alloys and what does it provide?
How are Co-Cr ceramic metal restorations strengthened? What does molybdenum do? What does ruthenium do? |
15%-25% and provides tarnish and corrosion resistance
Strengthened by solution hardening rather than carbide formation Molybdenum lowers CTE Ruthenium improves castibility |
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27. How do Co-Cr alloys compare to noble and Ni-Cr alloys?
How does casting and soldering of Co-Cr and Ni-Cr alloys compare to that of noble alloys? |
Stronger and harder
Have roughly the same densities and casting temps as Ni-Cr alloys Casting and soldering of Co-Cr and Ni-Cr alloys is more difficult than noble alloys as is obtaining a high degree of accuracy in these alloys |
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28. What are some surface treatment considerations of metal coping prior to ceramic application?
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1. Surface roughening (air abrading w/ 25 to 50 micron alumina)
2. Heat treatment in air or partial vacuum to enhance oxide layer formation 3. Use of proper opaque layer w/ good wetting and acceptable CTE 4. Proper matching of thermal expansion 5. Ceramic firing temp must be low enough to prevent alloy sagging |
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29. What do early failure modes in ceramic-metal restorations involve?
What do late failure modes involve? |
Early failures involve defects in the metal-oxide or opaque layer
Defect or stresses in bulk of porcelain or at the porcelain surface |
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30. What are some reasons for late failure modes in ceramic-metal restorations?
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1. Internal stress areas within the porcelain
2. Porosity within the porcelain 3. Surface cracks or crazing which can propagate under stress 4. Improper design considerations |
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31. What are some improper design considerations?
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1. Sharp angles on metal substructure
2. Non-uniform porcelain thickness 3. Localized thin metal areas which may distort under stress |
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32. What is a critical element in adequate bonding of a ceramic material to metal?
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Formation of a mixed oxide layer containing metal and porcelain (ceramic) oxides
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33. As the CTE of a crown and bridge metal (or any substructure) decreases what happens to the leucite content of the veneering porcelain?
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It also has to decrease to lower the CTE of the ceramic
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