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Op dent 2 > Dental Alloys - End first unit > Flashcards

Dental Alloys - End first unit Flashcards

1
Q

Gold is too

A

weak for dental restorations unless other alloying elements are used.

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2
Q

Gold melts at

A

1063 degC

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3
Q

Gold not

A

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

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4
Q

Gold can be etched by

A

aqua regia

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5
Q

Noble metals do not form

A

stable oxides at RT

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6
Q

Noble metals have the lowest tendency to

A

lose electrons and become +

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7
Q

Noble metals

A

gold, palladium, iridium, ruthenium, rhodium, osmium

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8
Q

Noble metal content on dental packaging

A

Au+Pt+Pd

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9
Q

Silver is not a

A

noble metal in oral environment (silver sulfide)

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10
Q

Precious metals classified by

A

price. HIgh purity = high price

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11
Q

Carat =

A

parts in 24 of pure gold.

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12
Q

Fineness =

A

parts in 1000 with pure gold (decimal sometimes)

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13
Q

1 lb Avoirdupois =

A

16 oz

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14
Q

1 lb troy =

A

12 oz

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15
Q

1 troy oz =

A

20 pennyweights (dwt)

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16
Q

1 dwt =

A

1.555 gm

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17
Q

Current standard for detnal casting alloys is

A

ISO 22674 - universal.

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18
Q

0.2% offset

A

yield strength minimum - resistance to deformation

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19
Q

Minimum percentage

A

elongation after fracture

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20
Q

Minimum young’s modulus only specified for

A

type 5

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21
Q

Stiffness =

A

young’s mod

22
Q

other alloy selection factors

A

cost, burnishability, solderability, experience of dental lab

23
Q

Type 0

A

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

24
Q

Type 1

A

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

25
Q

Type 2

A

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

26
Q

Type 3

A

Multiple unit fixed restorations - eg bridges

27
Q

Type 4

A

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

28
Q

Type 5

A

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

29
Q

Gold provides

A

ductility, tarnish and corrosion resistance

30
Q

Copper

A

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

31
Q

Silver

A

Coutneracts effects of copper on color and substitutes for gold economically

32
Q

Platinum and palladium

A

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

33
Q

Zinc -

A

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

34
Q

Grain =

A

microscopic single crystal.

35
Q

Top line

A

liquidus

36
Q

bottom line

A

solidus

37
Q

Gold alloys freeze with disordered

A

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

38
Q

Gold alloys freeze with disordered

A

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

39
Q

Disordered alpha structure at high t is

A

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

40
Q

Very small amounts of iridium are incorporated to provide

A

desired small grain size or refinement.

41
Q

Increase yield strength and hardness, and you

A

decrease in ductility

42
Q

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

A

gold is expected.

43
Q

Decreases occur in ease of adjustment and

A

burnishability for casting

44
Q

For gold, decrease in melting temp is

A

expected

45
Q

Solid solution hardening

A

provided by copper, platinum, palladium, silver, zinc

46
Q

Order hardening

A

provided by copper (sufficient amount must be present)

47
Q

Grain size refinement

A

iridium usually

48
Q

Slow cooling through appropriate temp range enables

A

ordering to occur

49
Q

Quenching of casting gives

A

softened condition- cooling rate is too rapid for ordering transformation

50
Q

Bench cool or furnace heat-treat casting for

A

hardened condition as result of ordering transformation

51
Q

Ordered phase is

A

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

Op dent 2 (6 decks)

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