Dr. Brantley (Metal Structures and Gold Alloys)

Question 1

type of unit cell used by gold and most other alloy materials

Answer 1

face-centered

Question 2

what is responsible for permanent deformation?

Answer 2

schematic movement of edge location

• dislocations move along slip planes under stress
• blocked at grain boundaries

Question 3

what should be done to strengthen materials?

Answer 3

• dec grain size
• incorporate other materials to form alloys
• work hardening (deform at room temp)
• form precipitates
• regions of ordered structure

Question 4

when a strategy is put in place to strengthen a metal it generally increases ____ and decreases _____

Answer 4

• hardness

- ductility

Question 5

what are some notable properties of gold?

Answer 5

• not tarnished by air or water (most corrosive resistant)

- most malleable and ductile

Question 6

what metal is NOT a noble metal in the oral environment?

Answer 6

silver

Question 7

what are precious metals?

Answer 7

based on unit metal price not electrochemistry

common metals can become precious in high purities

Question 8

part in 24 with pure gold

Answer 8

carat(k)

Question 9

part in 1000 with pure gold

Answer 9

fineness

*used for specification of dental solders

Question 10

1 lb Troy = ___ oz (used for gold)
1 lb Avoirdupois = ____ oz
1 oz Troy = ____ dwt = 31.1 grams

Answer 10

• 12 (used for gold)
• 16
• 20 dwt

Question 11

while coin gold and 22k gold were formerly used for dental restorations, what is the current standard for dental casting alloy?

Answer 11

ISO 22674 from types 0-5

• 0.2% offset yeild strength minimum
• minimum % elongation after fracture

Question 12

what are the 4 main alloy selection factors?

Answer 12

• cost
• burnishability
• solderability
• experience of the dental lab

Question 13

ISO classification that is very low stress-bearing restoration for small veneered one-surface inlays

Answer 13

type 0

Question 14

ISO classification that is low stress-bearing single tooth restoration for veneered or unveneered one-surface inlays

Answer 14

type 1

Question 15

ISO classification that is single tooth fixed restoration (crowns)

Answer 15

type 2

Question 16

ISO classification that is multiple fixed restorations (bridges)

Answer 16

type 3

Question 17

ISO classification that is composed of thin sections subjected to very high forces (RPDs, thin veneered crowns)

Answer 17

type 4

Question 18

ISO classification that is appliances requiring combination of high stiffness and strength (thin RPDs)

Answer 18

type 5

Question 19

element that provides ductility, tarnish (discolor), and corrosion resistance

Answer 19

gold

Question 20

element that is the PRINCIPLE ELEMENT FOR HARDENING AND STRENGTHENING

Answer 20

copper

Question 21

element that counteracts effects of copper on color and substitutes economically for gold w/o degrading mechanical properties

Answer 21

silver

Question 22

element that is an oxygen scavenger during melting to minimize oxidation of other elements, and considered to improve cast ability or fluidity of molten alloy

Answer 22

zinc

Question 23

type of unit cell for ordered AuCu3

Answer 23

simple cubic

Question 24

type of unit cells for disordered AuCu3

Answer 24

face-centered

Question 25

very small amounts of ____ give grain refinements of gold

Answer 25

iridium

Question 26

what are the three trends going from ISO type 1 - 5

Answer 26

• inc in yield strength and dec in percentage elongation after fracture (inc hardness)
• increase in total other element besides gold
• dec ease of adjustment and burnish ability (makes sense bc less gold)

Question 27

what is needed for proper ordering transformation to occur

Answer 27

slow cooling through temperature range

if it happens to fast (quenching) it will be too soft