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BDS2 - dental material science > partial denture alloys > Flashcards

partial denture alloys Flashcards

(62 cards)

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1
Q

what are the mechanical properties of partial denture alloys like

A
  • good
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2
Q

what are the important mechanical properties to consider for partial denture alloys

A
  • stress, rigidity, elastic limit, hardness and ductility
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3
Q

what are the alloy processes of hardening

A
  • work hardening
  • solution hardening
  • order hardening
  • precipitation hardening
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4
Q

what are the alloy processes of annealing

A
  • homogenisation annealing

- stress relied annealing

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5
Q

what are the ideal properties of partial denture alloys

A
  • rigid = YM
  • strong = UTS, EL
  • hard
  • ductile
  • precise casting = shrinkage
  • melting point
  • density
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6
Q

why is melting point important for partial denture alloys

A
  • for the investment material

- can be issues with the melting point = determines what investment material to use

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7
Q

why is density important for partial denture alloys

A
  • want as lightweight as possible for patient comfort
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8
Q

what are the types of partial denture alloys

A
  • ADA type IV gold
  • white gold = Ag-Pd
  • Co-Cr
  • titanium
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9
Q

what is the problem with one piece casting for partial denture alloys

A
  • base and clasps need different properties
  • base = want a high YM to maintain shape in use, and what a high EL to avoid plastic deformation
  • clasp = want a lower YM to allow flexure over tooth, and a high EL to maintain elasticity over wider range of movement/strian
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10
Q

how are the issues of one piece casting resolved

A
  • compromise
  • use thick section of alloy for base = rigid
  • use thin section of alloy for clasp = flexible
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11
Q

what is the carat for pure gold

A
  • 24 carat
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12
Q

what is the fineness for 100% gold

A
  • 1000
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13
Q

what is pure gold used for

A
  • class III and class IV cavities
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14
Q

what are the 4 types of gold alloys used for

A
  • type 1 = simple alloys
  • type 2 = larger (2-3 surface) inlays
  • type 3 = crown and bridge alloys
  • type 4 = partial dentures = has particular composition
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15
Q

how many other metals are in type IV gold

A
  • 5 other metals
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16
Q

what is the composition of type IV gold

A
  • Au = 65% but can be between 60-70%
  • Zn = 2% but can be between 1-2%
  • Cu = 14% but can be between 11-16%
  • Ag = 14% but can be between 4-20%
  • Pd = 3% but can be between 0-5%
  • Pt = 2% but can be between 0-4%
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17
Q

what does the phase diagram of order hardening of Au-Cu show

A
  • liquidus and solidus are continuous so means can have lots of different compositions = solid solution in all properties
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18
Q

how can Au-Cu benefit from solidus and liquidus being close together

A
  • as if it undergoes some type of heat treatment it forms an ordered solution
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19
Q

what are the effects of using copper as an alloying element with gold

A
  • solution hardening
  • solid solution in all proportions
  • order hardening = if 40-80% gold and correct heat treatment
  • reduced melting point
  • no coring = solidus close to liquidus
  • can impart a red colour = not ideal
  • reduces density = good for patient comfort
  • base metal = can corrode if too much
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20
Q

what does the phase diagram of complete solubility of Au-Ag show

A
  • liquidus and solidus are close tougher so any combo of Au and Ag can co-exist together
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21
Q

what are the effects of using silver as an alloying element with gold

A
  • solid solution in all proportions
  • solution hardening
  • precipitation hardening with copper and heat treatment = related to Ag and Cu in combo and if heat treat it can undergo precipitation hardening
  • can allow tarnishing
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22
Q

what happens if silver and copper in type IV gold

A
  • molten silver absorbs gas such as CO2

- whitens alloy = compensated for red form copper

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23
Q

what does the phase diagram of partial solubility of Ag-Cu in type IV gold show

A
  • there are 2 solid phases = alpha and beta
  • can only have material in these areas
  • with partial solid, get benefit of precipitation hardening
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24
Q

what does the phase diagram of complete solubility of AuPt show

A
  • get a degree of separation between liquidus and solidus = coring occurs
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25
what are the effects of using platinum as an alloying element with gold
- solid solution with gold - solution hardening - fine grain structure = better mechanical properties - coring can occur = wide liquidus to solidus gap
26
what are the effects of using palladium as an alloying element
- similar to platinum but less coring occurs - less expensive than platinum - coarser grains than platinum - absorbs gases when molten = means porous casting = weaker material
27
what are the effect of using zinc as an alloying element
- scavenger
28
what are the effects of using nickel as an alloying element
- increases hardness and strength = wrought alloys
29
what are the effects of using indium as an alloying element
- fine grain structure
30
what is the process of heat treatment for type IV gold
- quench after casting = pour molten alloy into cast then cool quickly which makes it under of coring so then have to undergo annealing - homogenising anneal = raise temp to 700oC for 10 mins after quenching - if need to cold work to manipulate to fit into patient then need to do stress-relief annealing - heat harden = order and precipitation hardening = raise temp to 450oC then cool slowly (15-30mins) down to 200oC then quench
31
what does quenching after casting produce
- fine grains
32
what are the heat treatment process done for
- improve partial denture or reduce negative consequences
33
what is CoCr used for
- wires - surgical implants - cast partial dentures = connectors - want high EL and high YM for thick sections, and high EL and low YM for thin sections
34
what is the composition of CoCr alloy
- Co = 54% but can be between 35-65% - Cr = 25% but can be between 25-30% - Ni = 15% but can be between 0-30% - Mo = 5% but can be between 5-6% - C = 0.4% but can be between 0.2-0.4%
35
what is Mo
- molibdium
36
what are the effects of using cobalt as an alloy
- forms solid solution with Cr = 2 metals co-exist across lattices - increased strength, hardness, rigidity - coring is possible
37
what are the effects of using chromium as an alloy
- forms a solid solution with Co - increased strength, hardness, rigidity - coring possible - forms passive layer = key role in corrosion resistance
38
what are the effects of using nickel as an alloy
- replaces some Co = improves CoCr - improves ductility - slight reduction in strength - sensitivity for patients = 6% in women and 2% in males
39
what is the effect of carbon on CoCr alloy
- undesirable, carbide grain boundaries are hard and brittle - ideally don't want any but it is inevitable
40
what is the effect of Mo on CoCr alloy
- reduces grain size, hence increases strength
41
what is the effect of W (tungsten) on CoCr alloy
- increases strength - Al = increases Pl - others = scavengers
42
what is the investment material for CoCr
- needs to be high temperature = 1200-1400oC | - so need to use silica or phosphate bonded instead of gypsum
43
how is CoCr melted
- electric induction preferred | - oxyacetylene = avoid carbon pickup
44
how is CoCr casted
- centrifugal force required - avoid overheating = coarse grains - cooling too fast or slow = carbides = brittle - challenging material to produce casts of
45
how is CoCr finished
- sandblast - electroplate - abrasive wheel - polishing buff
46
is CoCr easy to polish
- no | - difficult material to polish, but means as it shard to polish it is hard to roughen up again after polishing
47
what is the hardness of CoCr
- BHN = 370 - much harder then gold = lasts longer - wear in mouth better - finishing/polishing is time consuming
48
what is the elongation of CoCr
- means ductility - low ductility - 4% - work hardens rapidly - adjustment difficult - precision casting = if casting is not precise then 4% is not enough ductility
49
how much pure metal is titanium
- 99.5%
50
what are the used of titanium
- uses of pure titanium have developed recently and show promise - several commercial labs provide titanium casts - implants, partial dentures, crown and bridge, maxilla-facial skull plates
51
what are the properties of titanium
- good biocompatibility | - good corrosion resistance = passive oxide layer
52
how are parts of titanium joined together
- laser welding | - electric arc melting
53
what is done because titanium absorbs gas
- specialised investment and casting
54
when comparing partial denture alloys which has best elongation
- titanium but it is expensive so often go for type IV gold or CoCr
55
when comparing partial denture alloys which has the best UTS (MPa)
- stainless steel
56
why is UTS important
- because don't want partial denture to fracture
57
when comparing partial denture alloys which has the best density
- important for patient comfort | - CoCr is better then Au as it is lower
58
when comparing partial denture alloys which has the best rigidity
- also known as Young's modulus | - CoCr is best by quite a lot
59
when comparing partial denture alloys which has the best hardness
- gold is easier to polish but means it will wear easier | - CoCr highest
60
when comparing partial denture alloys which has the best shrinkage
- CoCr is highest so need to use different investment material to reduce it
61
why do you need precision casting for CoCr
- work hardens quickly
62
what are the properties to know about for type IV gold and CoCr
- shrink = gold is 1.3 %, CoCr is 2.3% - density = gold is 15, CoCr is 8 - Young's modulus = gold is 100, CoCr is 250 - UTS = gold is 790, CoCr is 690 - elongation = gold is 15 or 10, CoCr is 4 - hardness = gold is 210-230, CoCr is 370

BDS2 - dental material science (13 decks)

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