Base Metal Alloy casting Flashcards
What are base metals?
Non-ferrous metals that aren’t precious
Why are base metal alloys required?
Price of gold and other precious metals increased so much
What base metals make the most successful base metal alloy?
Co, Cr, Ni
What is the main base metal in Co/Cr alloys for removable appliances
Mainly Co
Why is Cr added to Co/Cr alloys?
Corrosion resistance
What is the main constituent of Ni/Cr alloys for removable appliances? Why is the other metal added?
Ni
Cr added for corrosion resistance
What 2 alloys are generally used for removable appliances?
Co/Cr
Ni/Cr
Safety considerations Ni/Cr
Nickel is a common cause of allergic dermatitis
Contains beryllium = toxic
Why is Mo added to Co/Cr and Ni/Cr alloys?
Make smaller grains = improve yield strength
Why is C added to Co/Cr and Ni?Cr alloys?
Form carbides in small quantities
Why is beryllium added to Ni/Cr alloys?
Make grains smaller
Categorization of alloys for fixed restorations
Type I - low stress applications e.g. inlays
Type II - moderate stress applications e.g. large inlays, onlays and full crowns
Type III - high stress applications including bridge and implant superstructures
Type IV = very high stress applications including long span bridges and implant superstructures
Increased proportional limit
Withstand greater stress without deformation
Decrease in % elongation?
Device much harder to adjust without it breaking
How does proportional limit change between Type I and IV base alloys for fixed appliances?
Increase = increased stress without deformation
Base alloys have a higher melting range than gold alloys. whta is the effect of this?
Decreased accuracy and more shrinkage
base alloys have lower density than alloy, what si the effect fo this?
Reduced accuracy
Difference in strength and proportional limit between base and gold alloys
Gold alloys = harder = base alloys resist stress better
Difference in stiffness of base and gold alloys?
Gold alloys lower = deform easier
Difference in ductility of base and gold alloys?
Base alloys range from 3-18%
Gold alloys range from 10-18%
so some gold alloys are easier to adjust
Difference in hardness between base and gold alloys?
Gold alloys softer
Base alloys more difficult t polish but retain polish well
Difference in biocompatibility between base and gold alloys
Base = nickel and beryllium Gold = rare
Difference in cost for base and gold alloys
Base = low cost but high manufacture cost
Gold = high cost but low manufacturing cost
What would be the ideal alloy for
a) casting crown and bridges
b) adjusting crown and bridges
c) function of crown and bridges
d) safety of crown and briges
a) gold = higher density, lower shrinkage
b) gold = lower stiffness, lower yield strength
c) base = higher stiffness = resist deformation
d) gold = allergies rare
What would be the ideal alloy for
a) connectors of partial dentures
b) clasps of PD
a) must be rigid, resist deformation = base = higher stiffness
b) must be flexible to engage undercuts = gold = lower stiffness
Must resist deformation = base = higher yield strength
Allow for adjustments = gold
