Base Metal Alloy casting

Question 1

What are base metals?

Answer 1

Non-ferrous metals that aren’t precious

Question 2

Why are base metal alloys required?

Answer 2

Price of gold and other precious metals increased so much

Question 3

What base metals make the most successful base metal alloy?

Answer 3

Co, Cr, Ni

Question 4

What is the main base metal in Co/Cr alloys for removable appliances

Answer 4

Mainly Co

Question 5

Why is Cr added to Co/Cr alloys?

Answer 5

Corrosion resistance

Question 6

What is the main constituent of Ni/Cr alloys for removable appliances? Why is the other metal added?

Answer 6

Ni

Cr added for corrosion resistance

Question 7

What 2 alloys are generally used for removable appliances?

Answer 7

Co/Cr

Ni/Cr

Question 8

Safety considerations Ni/Cr

Answer 8

Nickel is a common cause of allergic dermatitis

Contains beryllium = toxic

Question 9

Why is Mo added to Co/Cr and Ni/Cr alloys?

Answer 9

Make smaller grains = improve yield strength

Question 10

Why is C added to Co/Cr and Ni?Cr alloys?

Answer 10

Form carbides in small quantities

Question 11

Why is beryllium added to Ni/Cr alloys?

Answer 11

Make grains smaller

Question 12

Categorization of alloys for fixed restorations

Answer 12

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

Question 13

Increased proportional limit

Answer 13

Withstand greater stress without deformation

Question 14

Decrease in % elongation?

Answer 14

Device much harder to adjust without it breaking

Question 15

How does proportional limit change between Type I and IV base alloys for fixed appliances?

Answer 15

Increase = increased stress without deformation

Question 16

Base alloys have a higher melting range than gold alloys. whta is the effect of this?

Answer 16

Decreased accuracy and more shrinkage

Question 17

base alloys have lower density than alloy, what si the effect fo this?

Answer 17

Reduced accuracy

Question 18

Difference in strength and proportional limit between base and gold alloys

Answer 18

Gold alloys = harder = base alloys resist stress better

Question 19

Difference in stiffness of base and gold alloys?

Answer 19

Gold alloys lower = deform easier

Question 20

Difference in ductility of base and gold alloys?

Answer 20

Base alloys range from 3-18%
Gold alloys range from 10-18%

so some gold alloys are easier to adjust

Question 21

Difference in hardness between base and gold alloys?

Answer 21

Gold alloys softer

Base alloys more difficult t polish but retain polish well

Question 22

Difference in biocompatibility between base and gold alloys

Answer 22

Base = nickel and beryllium
Gold = rare

Question 23

Difference in cost for base and gold alloys

Answer 23

Base = low cost but high manufacture cost

Gold = high cost but low manufacturing cost

Question 24

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

Answer 24

a) gold = higher density, lower shrinkage
b) gold = lower stiffness, lower yield strength
c) base = higher stiffness = resist deformation
d) gold = allergies rare

Question 25

What would be the ideal alloy for

a) connectors of partial dentures
b) clasps of PD

Answer 25

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