DM - precious and low gold alloys

Question 1

what are the 2 types of alloys with noble metal content of at least 25% but less than 75%?

Answer 1

low gold casting alloys
silver palladium alloys

Question 2

explain the placement of a pure gold restoration?

Answer 2

tiny pieces of gold placed into a cavity which is lined by an oxy phosphate lining material - takes hours

prior to placement must heat to 250 degrees - drives off grease

Question 3

what are the 4 types of casting gold alloys?

Answer 3

type 1 low strength
type 2 medium strength
type 3 high strength
type 4 extra high strength

Question 4

what is the use of type 1 low strength casting gold alloys?

Answer 4

castings subject to slight stress - inlays

Question 5

what is the use of type 2 medium strength casting gold alloys?

Answer 5

castings subject to moderate stress e.g., inlays/ onlays

Question 6

what is the use of type 3 high strength casting gold alloys?

Answer 6

high stress situations e.g., onlays, thin cast backings, pontics, full crowns

Question 7

what is the use of type 4 extra high strength casting gold alloys?

Answer 7

for casting thin in cross section e.g., saddles, bars, clasps, crowns, bridges and partial denture frameworks

Question 8

what is the gold content expressed as in traditional gold casting alloys?

Answer 8

carat - parts by weight of gold in 24 parts of alloy
fineness - parts by weight of gold in 1000 parts of alloy

Question 9

how do you express a gold alloy with 75% gold?

Answer 9

18 carat
750 fine

Question 10

which type of gold alloy has the most gold?

Answer 10

type 1

Question 11

as you move from gold alloy 1 - 4, what properties increase?

Answer 11

hardness
proportional limit
strength

Question 12

as you move from hold alloy 1-4, what properties decrease?

Answer 12

ductility
corrosion resistance

Question 13

why, as gold content decreases, does hardness increase?

Answer 13

solution hardening - formation of solid solutions with gold

Question 14

what are the properties of silver in gold casting alloys?

Answer 14

slight strengthening effect and counteracts reddish copper tint

Question 15

what are the properties of coper in gold casting alloys?

Answer 15

increases strength and lowers MP
if content >16% alloy will tarnish

Question 16

what are the properties of platinum/ palladium in gold casting alloys?

Answer 16

increase both strength and MP

Question 17

what are the properties of zinc in gold casting alloys?

Answer 17

acts as a scavenger - when used up its function taken over by Cu (this is not good as it impairs physical properties of the casting)

Question 18

what is important about zinc in gold casting alloys?

Answer 18

always have fresh alloy as dont want a deficit of zinc

Question 19

what types of gold alloys can have heat treatments?

Answer 19

type 3 and 4 - results in further hardening by precipitation hardening of Ag/ Cu and Au/ Cu systems

Question 20

why is heat treatment not possible for types 1 and 2?

Answer 20

lack of silver and copper that required for the necessary atomic diffusions

Question 21

what is the composition of low gold alloys?

Answer 21

Au 40-50% (but could be down to 10%)
high palladium
“white” in colour

Question 22

what is the composition of silver palladium alloys?

Answer 22

primarily Ag and Pd
little/ no Au