Partial Denture Alloys

Question 1

what are the ideal properties of a partial denture alloy?

Answer 1

• rigid
• strong
• hard
• ductile
• precise casting
• low density

Question 2

what are the most common partial denture alloys used ?

Answer 2

• cobalt chromium

- type IV gold

Question 3

for a partial denture alloy base what is the ideal YM and EL?

Answer 3

High YM = to maintain shape in use

High EL = to avoid plastic deformation

Question 4

in a partial denture alloy clasp what is the ideal YM and EL values?

Answer 4

Lower YM = to allow flexure over tooth

High EL = maintain elasticity over a wide range of movement

Question 5

what type of cavities can pure gold be used for?

Answer 5

• Class III

- Class IV

Question 6

what occurs to the melting point of gold alloys if copper is the alloying element?

Answer 6

reduced melting point

Question 7

how does alloying with copper affect the density of gold?

Answer 7

reduced density

Question 8

what may occur to gold alloys if too much copper is added?

Answer 8

corrosion

Question 9

what is an alloy used that is similar to platinum?

Answer 9

palladium (less expensive)

Question 10

what are some uses for CoCr?

Answer 10

• cast partial dentures
• wires
• surgical implants

Question 11

for CoCr partial denture connectors, explain the desirable EL & YM for the palatal/bulky section of connector?

Answer 11

• high EL

- high YM

Question 12

if CoCr is being used in partial denture clasps, explain the desirable EL & YM?

Answer 12

• high EL

- low YM

Question 13

what is the composition of CoCr?

Answer 13

• Co (54%)
• Cr (25%)
• Ni (15%)
• Mo (5%)
• C (0.4%)

Question 14

what is a positive reason to use Cobalt in alloys?

Answer 14

• increased strength, hardness, rigidity

- coring is possible

Question 15

in CoCr, what is the function of the chromium?

Answer 15

• increased strength, hardness, rigidity
• coring possible
• corrosion resistance

Question 16

how does chromium in CoCr allow for corrosion resistance?

Answer 16

forms a passive layer on the surface of the alloy

Question 17

what is the purpose of addition of Nickel to CoCr (used in partial dentures)? what is a negative of using this also?

Answer 17

• improves ductility

- slight reduction in strength & people may be sensitive/allergic

Question 18

what are the different casting techniques used for CoCr?

Answer 18

• investment material
• melting
• casting

Question 19

how hard is CoCr?

Answer 19

BHN 370

Question 20

what are some positive reasons to use titanium in partial dentures?

Answer 20

• good biocompatibility
• good corrosion resistance
• parts can be joined by laser welding

Question 21

what is a disadvantage of using gold in partial dentures compared to cobalt chromium?

Answer 21

gold is much denser (less comfortable)

Question 22

what is an advantage of using gold for RPD clasps over cobalt chromium?

Answer 22

gold is less rigid & can therefor flex into undercuts easier