Alloy Denture Base Materials

Question 1

Name 3 noble metals which are resistant to corrosion in the mouth

Answer 1

1. Gold
2. Platinum
3. Palladium

Question 2

Describe 3 parts of the classifications of alloys according to American Dental Association

Answer 2

1. High-noble
2. Noble
3. Base metal

Question 3

Describe the gold content and noble metal content of a high-noble alloy

Answer 3

Gold content of 40% + and noble metal content of 60% +

Question 4

Describe the gold content and noble metal content of a noble alloy

Answer 4

No requirement of gold content and noble metal content of 25%+

Question 5

Describe the gold content and noble metal content of a base alloy

Answer 5

No requirement of gold content and noble metal content of less than 25%

Question 6

What 4 things does adding base materials to noble metals cause?

Answer 6

1. Increased strength
2. Decreased flexibility
3. Better wear resistance
4. Cheaper

Question 7

Describe Gold alloys as a material

Answer 7

• High density
• Expensive
• Very stable in oral condition
• Excellent biocompatibility

Question 8

Describe cobalt-chromium compared with gold as a denture base material

Answer 8

• Harder
• x2 MoE
• Half as dense
• Proportional limit is reduced (brittle)
• Shrinks more on cooling

Question 9

Name 4 main constituents of cobalt chromium

Answer 9

1. Cobalt (60-65%)
2. Chromium (25-30%)
3. Molybdenum (4-6%)
4. Carbon (0-0.4%)

Question 10

Name 3 functions of cobalt in CoCr

Answer 10

1. Strength
2. Rigidity
3. Hardness

Question 11

Name 2 functions of chromium in CoCr

Answer 11

1. Corrosion resistance

2. Tarnish resistance

Question 12

Name 2 functions of molybdenum in CoCr

Answer 12

1. Add strength

2. Reduce grain size

Question 13

Name the function of carbon in CoCr

Answer 13

Raise strength and hardness but too much carbon can weaken the alloy

Question 14

Name 5 materials where traces are found in CoCr to add strength

Answer 14

1. Tungsten
2. Boron
3. Manganese
4. Iron
5. Silicon

Question 15

Describe the properties of CoCr

Answer 15

• Good biocompatibility
• Casting shrinkage of around 2%
• Must use phosphate bonded investment material
• High MoE makes rigid in thin section
• Low ductility makes clasps prone to fracture
• Low density makes RPD light

Question 16

Name 3 ways to form metals in dentistry

Answer 16

1. Cast
2. Wrought
3. CAD-CAM

Question 17

Describe casting materials in dentistry

Answer 17

Molten alloy poured into mould e.g crowns and RPD bases

Question 18

Describe wrought alloys in dentistry

Answer 18

Alloy shaped by mechanical force (hot or cold pressing, drawing, milling) e.g NiCr for ortho wires, RPD clasps, endo files

Question 19

Describe CAD-CAM as a method for shaping metals in dentistry

Answer 19

Reductive (formed from a block of material) or by addition (built up in thin layers)

Question 20

Describe investing and casting procedures - Lost Wax Technique

Answer 20

• Pattern laid onto model duplicated in refractory model
• Sprues added and model invested
• Placed in a furnace and temperature raised
• Allow melted and cast into mould using centrifugal force
• Casting is sandblasted
• Fitted to master model and polished

Question 21

Name 3 requirements of sprues in the lost wax technique

Answer 21

1. Channel which allows molten alloy to flow into the pattern
2. Sprue acts as a reservoir
3. Sprue should be thicker than thickest section of casting

Question 22

Name 2 methods of sprues

Answer 22

1. Direct (on top)

2. Indirect (or inverted)

Question 23

Describe titanium based alloys as a denture base material

Answer 23

• Good biocompatibility
• Rigid
• Low density
• Excellent corrosion resistance
• Very high casting temperatures
• Reactive with oxygen (must be cast in vacuum)