Dental Alloys - End first unit

Question 1

Gold is too

Answer 1

weak for dental restorations unless other alloying elements are used.

Question 2

Gold melts at

Answer 2

1063 degC

Question 3

Gold not

Answer 3

tarnished by air, H20, doesn’t dissolve in acids.

Question 4

Gold can be etched by

Answer 4

aqua regia

Question 5

Noble metals do not form

Answer 5

stable oxides at RT

Question 6

Noble metals have the lowest tendency to

Answer 6

lose electrons and become +

Question 7

Noble metals

Answer 7

gold, palladium, iridium, ruthenium, rhodium, osmium

Question 8

Noble metal content on dental packaging

Answer 8

Au+Pt+Pd

Question 9

Silver is not a

Answer 9

noble metal in oral environment (silver sulfide)

Question 10

Precious metals classified by

Answer 10

price. HIgh purity = high price

Question 11

Carat =

Answer 11

parts in 24 of pure gold.

Question 12

Fineness =

Answer 12

parts in 1000 with pure gold (decimal sometimes)

Question 13

1 lb Avoirdupois =

Answer 13

16 oz

Question 14

1 lb troy =

Answer 14

12 oz

Question 15

1 troy oz =

Answer 15

20 pennyweights (dwt)

Question 16

1 dwt =

Answer 16

1.555 gm

Question 17

Current standard for detnal casting alloys is

Answer 17

ISO 22674 - universal.

Question 18

0.2% offset

Answer 18

yield strength minimum - resistance to deformation

Question 19

Minimum percentage

Answer 19

elongation after fracture

Question 20

Minimum young’s modulus only specified for

Answer 20

type 5

Question 21

Stiffness =

Answer 21

young’s mod

Question 22

other alloy selection factors

Answer 22

cost, burnishability, solderability, experience of dental lab

Question 23

Type 0

Answer 23

very low stress bearing restorations (small veneered one surrface inlays, veneered crowns.

Question 24

Type 1

Answer 24

low stress bearing single tooth restorations. EX veneered or unveneered one surface inlays, veneered crowns

Question 25

Type 2

Answer 25

Single tooth fixed restorations. Ex. crowns or inlays without restriction on number of surfaces

Question 26

Type 3

Answer 26

Multiple unit fixed restorations - eg bridges

Question 27

Type 4

Answer 27

Thin sections subjected to very high forces (clasps, thin veneered crowns)

Question 28

Type 5

Answer 28

appliances requiring combination of high stiffness and strength - thin RDPs, clasps

Question 29

Gold provides

Answer 29

ductility, tarnish and corrosion resistance

Question 30

Copper

Answer 30

principle element of hardening and strengthening (exceeding ~12%)

Question 31

Silver

Answer 31

Coutneracts effects of copper on color and substitutes for gold economically

Question 32

Platinum and palladium

Answer 32

also tarnish, corrosion resisstance, strenghtening (limited amounts because small percentages substantially raise alloy melting temp)

Question 33

Zinc -

Answer 33

oxygen scavenger during melting to minimize oxidizing of other elemnents. Improves castability and fluidity of molten alloy

Question 34

Grain =

Answer 34

microscopic single crystal.

Question 35

Top line

Answer 35

liquidus

Question 36

bottom line

Answer 36

solidus

Question 37

Gold alloys freeze with disordered

Answer 37

alpha structure (random location of Au and Cu atoms). Ordered alpha structure forms below 400 deg C with at least 50% gold

Question 38

Gold alloys freeze with disordered

Answer 38

alpha structure (random location of Au and Cu atoms). Ordered alpha structure forms below 400 deg C with at least 50% gold

Question 39

Disordered alpha structure at high t is

Answer 39

fcc - relevant for traditional high gold alloys - >70% Au

Question 40

Very small amounts of iridium are incorporated to provide

Answer 40

desired small grain size or refinement.

Question 41

Increase yield strength and hardness, and you

Answer 41

decrease in ductility

Question 42

For gold alloys, increase in total amounts of elements other than

Answer 42

gold is expected.

Question 43

Decreases occur in ease of adjustment and

Answer 43

burnishability for casting

Question 44

For gold, decrease in melting temp is

Answer 44

expected

Question 45

Solid solution hardening

Answer 45

provided by copper, platinum, palladium, silver, zinc

Question 46

Order hardening

Answer 46

provided by copper (sufficient amount must be present)

Question 47

Grain size refinement

Answer 47

iridium usually

Question 48

Slow cooling through appropriate temp range enables

Answer 48

ordering to occur

Question 49

Quenching of casting gives

Answer 49

softened condition- cooling rate is too rapid for ordering transformation

Question 50

Bench cool or furnace heat-treat casting for

Answer 50

hardened condition as result of ordering transformation

Question 51

Ordered phase is

Answer 51

AuCu for high gold alloys, AuCu3 for lower gold such as midas