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32 Cards in this Set
- Front
- Back
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1. What were the most common findings for clinical longevity of metal-ceramic restorations?
Three things... What was the success of M-C restorations? What was the survival? |
1. Supragingival crown margins due to recession
2. Gingival bleeding on probing 3. Occlusal wear of opposing teeth 75% success 78% survival |
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2. What are some of the most important properties for clinical performance of prosthodontic alloys?
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1. Strength
2. Hardness 3. Modulus of elasticity 4. Proportional limit 5. Corrosion |
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3. What does gold do?
(two things) What is the most common type of gold used? |
1. Increases resistant to tarnish and corrosion
2. Increases ductility and malleability Type III gold |
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4. What is copper used for?
When is it necessary? What is the main purpose of silver? What other two things does silver do? |
Principal hardener
Necessary for heat treatment Modify the red color produced by gold and copper 1. Reduces melting temperature 2. Increase ductility & malleability |
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5. What does platinum do?
Four things.... |
1. Raised melting temp
2. Increases tensile strength 3. Decreased coefficient of thermal expansion 4. Reduces tarnish and corrosion |
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6. What does palladium do?
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1. Raises melting temperature
2. Increased hardness 3. Absorbs H gas *cause porosity in casting 4. Prevents tarnish and corrosion 5. Strong whitening effect on gold |
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7. What does zinc do?
How does zinc improve castability? |
Acts as a scavenger and prevents oxidation of the other metals during the manufacturing process
Increases fluidity and decreases surface tension |
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8. What main things does indium do?
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Contributes to oxide layer
**oxide layer bond is very strong |
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9. How do alloys for M-C restoration differ from the gold-based alloys?
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1. Have higher melting temp to accommodate temperature required for porcelain application
2. Contain little if any silver which could cause porcelain to turn green 3. Contain little if any copper b/c could cause alloy to sag during porcelain firing |
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10. What causes M-C alloys to have a higher melting temperature?
What are the six types of alloys used for M-C crowns? How is the coefficient of thermal expansion for titanium? What does leucite do? |
Greater palladium content
Four are gold (or palladium) based and two are nickel or cobalt based Titanium has a low coefficient of thermal expansion *like zirconia Raises coefficient so can bond with porcelain |
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11. What are the disadvantages of metal-ceramic alloys for porcelain bonding?
Three things |
1. Higher casting temperature
2. Higher hardness **makes fabrication, finishing and polishing difficult 3. Low ductility |
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12. What three characteristics determine porcelain-metal compatibility?
What amount of residual stress is desirable for porcelain in the final restoration? How is such a state achieved? |
1. Thermal expansion
2. Bond strength 3. Composition State of 0 residual stress Total expansion and contractions of the porcelain and metal are matched bwt the porcelain firing temp and room temp **thermal expansion is important |
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13. What does porcelain to metal bond strength ensure?
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Retention of porcelain both in oral environment and during thermal processing when induced thermal stresses can be quite high
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14. What is the classification of alloys based upon composition?
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1. High-Noble
-gold content > 40& -noble metal content > 60% 2. Noble -noble metal content > 25% 3. Primarily Base Metal -noble metal content < 25% |
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15. What additives help in the oxide layer formation?
By how much do they increase the alloy's bond strength to porcelain by? What are two disadvantages of these alloys? |
1. Tin
2. Indium 3. Iron Factor of three 1. Lower rigidity 2. Poor sag resistance during porcelain firing |
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16. What are the three subclasses of high-noble alloys?
Why is the vicks hardness important? What alloys have a hardness # near that of enamel? |
1. Gold-platinum
2. Gold-palladium 3. Gold-palladium-silver Important factor for how it abrades b/c if too high then it abrades contacting enamel Gold-palladium and high gold Use them for occlusal contact |
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17. What are the requirements for a ceramic metal system?
Four things.. |
1. Alloy must have high melting temp
2. Ceramic must be able to we alloy readily when applies as a slurry 3. Good bone bwt metal & ceramic 4. Coefficient of thermal expansion between ceramic & metal must be compatible so ceramic doesn't crack during fabrication |
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18. What are requirements for a ceramic metal system?
Four things... |
5. Adequate stiffness and strength of alloy
*if not stiff enough get flexing and cracking 6. High sag resistance 7. High accuracy 8. Adequate design |
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19. What are the principal disadvantages of the high-gold alloys?
What are gold-platinum alloys used for? Why should they be limited to short-span fixed partial dentures? What do they contain for hardeners? |
1. Low elastic modulus
2. Poor sag resistance Full cast and M-C restorations B/c they are subject to sag Silver and zinc |
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20. What are three good characteristics of gold-palladium-silver alloys?
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1. Elastic modulus is higher
2. Less susceptible to dimensional changes 3. Corrosion resistant |
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21. What is the principle disadvantage of gold-palladium-silver alloys?
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Tendency to induce color changes in porcelain b/c of their silver content
**silver results in yellow-green color change |
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22. What is necessary when using palladium-silver or silver-palladium alloys?
What are three good characteristics of Pa-Ad and Ag-Pa? How is the elastic modulus for Pa-Ag alloys? |
Should use a "non-greening" porcelain
1. Low sag tendency 2. High rigidity 3. Easy to solder Have most favorable elastic modulus of all the precious metal alloys **results in least flexible castings |
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23. Why are indium, gallium or tin added to gold-palladium alloys?
What else does gallium help improve? |
Promote oxide layer formation for better bonding to porcelain
Improves castability |
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24. What are the advantages of gold-palladium alloys?
Five things... |
1. Favorable yield strength & hardness
2. Increased elastic modulus 3. Improved rigidity *important w/ partial dentures 4. Corrosion resistance 5. Good sag resistance |
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25. What is the only recognized disadvantages of gold-palladium alloys?
How do the coefficients of thermal expansion compare between silver containing and silver free alloys? What has been done recently to correct this? |
Thermal expansion is incompatible with some of the higher-expansion porcelains
Silver free have lower thermal expansion Silver has been added but at low amounts **less than 5% so there are no porcelain color problems |
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26. What are the characteristics of Palladium-Copper alloys?
Five things... |
1. Heavy oxide
*difficult to cover w/ opaque porcelain 2. High hardness *offset by low elastic modulus 3. Strength is good 4. Lower sag resistance 5. Do not melt or cast as easily |
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27. What does gallium do in palladium-copper-gallium alloys?
What is the role of gallium then? |
Lowers the melting temperature
Enhances bonding of porcelain to the metal and increases strength |
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28. What is the hardness of Ultima Lite like?
How much expansion does it have? |
300 HV
**high hardness so always put porcelain over it 15% **use phosphate investment |
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29. What is the main advantages of palladium-cobalt alloys?
What is the main disadvantage? |
Higher coefficient of thermal expansion
Formation of dark oxide that may be difficult to mask at thin margins |
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30. In selecting alloys for fixed partial dentures what characteristics become increasingly important as the span increases?
Four things |
1. Solder and joining behavior
2. Sag resistance 3. Strength 4. Elastic modulus |
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31. What characteristics are equally important when selecting an alloy for either a single crown or fixed partial denture?
Five things... |
1. Castability
2. Biocompatibility 3. Tarnish & corrosion resistance 4. Porcelain color 5. Hardness |
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32. How are palladium-silver alloys?
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1. Excellent clinical working characteristics
2. No real disadvantage **provided porcelain is not one susceptible to discoloration in the presence of silver |
