Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BDS2 Dental Materials Sciences > Partial Denture Alloys > Flashcards

Partial Denture Alloys Flashcards

(89 cards)

Start Studying
1
Q

what are 5 good mechanical properties of alloys to remember

A

Stress

Rigidity

elastic limit

hardness

ductility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

4 ways an alloy can be hardened

A

work hardening

solution hardening

order hardening

precipitation hardening

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

2 types of alloy annealing

A

homogenisation annealing

stress relief annealing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

7 ideal properties of partial denture alloys

A

rigid (YM)

strong (UTS, EL)

hard

ductile

precise casting (shrinkage)

melting point (investment material)

density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

4 types of partial denture alloys

A

ADA Type IV Gold

White Gold (Ag-Pd)

Co-Cr

Titanium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what technique is used in partial denture manufacture

A

one piece casting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

YM and EL of base for one piece casting

A

high YM - to maintain shape in use
- withstand large stresses and not change shape greatly

high EL - to avoid plastic deformation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

YM and EL of clasp for one piece casting

A

lower YM - to allow flexure over tooth
- flex easily and disengage readily

high EL - maintain elasticity over wide range of movement (i.e. strain)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

why do both the clasp and base need a high EL

A

avoid any permanent/plastic deformation even if apply large stress to material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the compromise that is needed in one-piece manufacture to benefit both the base and clasp

A

thick section - rigid base;

thin section - flexible clasp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

2 ways to describe Pure Gold

A

Carat : 24 - pure gold

Fineness : 1000 fine - 100% Au

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

example use of pure gold

A

class III and IV cavities in some situations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

uses of different types of gold

A

Type I : simple alloys

Type II : larger (2-3 surface) inlays

Type III : Crown & Bridge alloys

Type IV : Partial Dentures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

uses of Type IV gold

A

partial dentures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what metals are in type IV gold

A

Au gold

Zn zinc

Cu cooper

Ag silver

Pd palladium

Pt platinum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

type IV gold % composition of gold

A

60-70% (65)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

type IV gold % composition zinc

A

1-2% (1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

type IV gold % composition cooper

A

11-16% (14)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

type IV gold % composition of silver

A

4-20% (14)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

type IV gold % composition palladium

A

0-5% (3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

type IV gold % composition platinium

A

0-4% (2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what are the liquidous and solidus line like for Au-Cu phase diagram

A

Continuous

  • Have all sorts of combination of gold and cooper
  • All the way through
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

8 effects of adding cooper to gold alloy

A

solid solution in all proportions

solution hardening

order hardening

reduced melting point

no coring

imparts red colour
- due to cooper if sufficient quantity

reduces density
- more cooper leads to lower density

base metal - can corrode if too much

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

how can you tell if there will be little to no coring

A

solidus relatively close to liquidus

so little to none coring on quenching

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
what is order hardening
if 40-80% Gold and correct heat treatment - Once taken alloy quenched to room temp and then heat treat - Undergoes some form of heat treatment forms an ordered solid solution (Row of Au row of Cu) - Little peak in phase diagram
26
6 effects of adding silver to gold alloy
solid solution in all proportions solution hardening precipitation hardening with COPPER & heat treatment - silver and cooper can benefit from precipitation hardening, utilise to improve mechanical properties can allow tarnishing molten silver absorbs gas e.g. CO2 - can lead to porosity in casting process whitens alloy – compensates for copper
27
describe the phase diagram for Ag-Au
Simple Close together Any value an coexist in same grain structure
28
describe the phase diagram for Ag-Cu (in type IV Gold)
have solubility limit lines - Partially soluble solid solution End up with potential precipitation hardening
29
describe the phase diagram of AgPt
Simple Reasonable degree of separation - Coring can occur on Rapid cooling - Grains have concentration gradient Have to further process
30
what feature does a partially soluble solid have on phase diagram
have solubility limit lines
31
4 effects of adding platinum to gold alloy
solid solution with Gold solution hardening fine grain structure - greater mechanical properties coring can occur - wide Liquidus - Solidus gap
32
4 effects of adding pallidium to gold alloy
similar to Pt less expensive less coring than Pt coarser grains than Pt absorbs gases when molten porous casting – weaken end RPD
33
contribution of zinc to alloy
scavenger
34
contribution of nickel to alloy
increase hardness and strength (wrought alloys)
35
contribution of indium to alloys
fine grain structure
36
why would you use heat treatment on partial denture alloys
All to improve properties of RPD and minimise negatives
37
4 types of heat treatment on gold alloys
Quench after casting fine grains – good mechanical properties Homogenising anneal (700C, 10 mins) If cold worked - stress relief anneal - Homogenous grain composition - Raise temperature for some time but not to melting point, cool Cold working to manipulate – if doesn’t fit the pt exactly Heat harden - (order & precipitation) - 450C cool slowly (15 - 30 mins) to 200C then quench - ---After cold work, raise temperature then quench
38
role of stress relief annealing of type IV gold
Homogenous grain composition - Raise temperature for some time but not to melting point, cool Cold working to manipulate – if doesn’t fit the pt exactly
39
role of heat hardening type IV gold
order and precipitation 450C cool slowly (15 - 30 mins) to 200C then quench ----After cold work, raise temperature then quench
40
advantage and disadvantage for partial denture of heat treated type IV gold alloy
Properties more suitable for clasp Need thickness for base (expense)
41
3 uses for CoCr
Wires Surgical Implants Cast Partial Dentures Connectors : - High EL, High YM - thick section - High EL, Low YM - thin section
42
metals in CoCr
cobalt chromium nickle molybdenum carbon
43
% composition in CoCr of cobalt
35-65% (54)
44
% composition in CoCr of chromium
25-30% (25)
45
% composition in CoCr of nickle
0-30% (15)
46
% composition in CoCr of molybdenum
5-6% (5)
47
% composition in CoCr of carbon
0.2-0.4%
48
3 effects of cobalt in CoCr
Forms solid solution with Cr Increase strength, hardness, rigidity Coring possible
49
solid solution alloy arrangement
2 metals coexist in normal lattice arrangement | - Across whole spectrum of compositions
50
4 effects of chromium in solid CoCr alloy
Forms solid solution with Co Increase strength, hardness, rigidity Coring possible Forms passive layer – corrosion resistance - Passive oxide layer to resist corrosion – KEY
51
4 effects of nickel in CoCr alloy
Replaces some Co Improves ductility COMPROMISE Slight reduction in strength Sensitivity - 6% females; 2% males
52
2 effects of carbon in CoCr alloy
Undesirable - Ideally not have any, but inevitable to make in casting Carbide grain boundaries hard & brittle
53
role of molybdenum in CoCr
Reduces grain size | - increase strength
54
role of tungsten (W) in CoCr alloy
Al: increases PL Other: scavengers
55
what is the point of having a range of metals of varying compositions in an alloy
Multiple ingredient – best mix for greater properties
56
investment material for CoCr
High temp. 1200-1400C Hence - silica or phosphate bonded - NOT GYPSUM
57
2 melting techniques for CoCr
Electric Induction (preferred) Oxyacetylene - avoid carbon pickup (too many problems to be used now)
58
what is the preferred melting technique for CoCr
electric induction
59
technique for casting CoCr
Centrifugal force required - Avoid overheating ----Risk coarse grains Cooling too fast or slow - carbides - brittle
60
techniques for finishing CoCr (4)
sandblast electroplate abrasive wheel polishing buff
61
why is CoCr hard to polish
very hard material - but then equally hard to roughen up in use - -- so maintains surface longer
62
hardness of CoCr
BHN 370
63
why is the high hardness of CoCr good (2)
Much harder than Gold Wear in mouth better - Experience less wear
64
downside of high hardness of CoCr
Finishing/polishing time consuming
65
elongation/ductility value for CoCr
4% | low
66
what is elongation/ductility
Ability of material to be stretched, change shape
67
effect of CoCr having low elongation value
Work hardens rapidly Adjustment difficult, thus precision casting - Only small amount can be done to fit pt - Casting needs to be really precise so 4% is adequate
68
uses of pure titanium (4)
Implants Partial Dentures (Cast) Crown & Bridge (Cast) Maxillo-Facial Skull Plates
69
3 advantages of titanium
Good biocompatibility Good corrosion resistance (passive oxide layer ) Individual parts joined by laser welding - Casting process less of a challenge
70
why is good biocompatibility key to pure titanium use
Can be used in more demanding situations than RPD e.g. maxilla-facial skull plates
71
% of titanium in pure titanium
99.5%
72
how is titanium melted
Electric Arc Melting Specialised investment and casting – not in GDH Can buy in from commercial outlets
73
why is electric arc melting used for titianium
As titanium absorbs gases
74
what alloy has the highest elongation/ductility value
Titanium easy engage and disengage in pt dentition Expensive - generally between Type IV or CoCr
75
UTS is
fracture strength (MPa)
76
compare UTS of type IV gold, CoCr and titanium
Not identical | - But not tremendous difference in fracture strength
77
why is density (g/cm3) important for partial denture alloys
Pt comfort
78
compare densities of type IV Au and CoCr
Pt comfort Au is the most dense CoCr is half - favoured for pt as lighter
79
compare the rigidity (young's/elastic modulus (GPa)) of CoCr, type IV Au and Titanium
CoCr 250 Au 100 Titanium 110 CoCr is least likely to undergo dimension change due to stress
80
compare the hardness between CoCr and Au and explain this effect on finsihing
CoCr 370 Au 220 Au not as hard to polish but wears down easier
81
what does shrinkage of partial denture alloys impact on
investment material used large shrinkage is a challenge
82
which is more difficult to produce a defect free casting CoCr or gold
CoCr
83
can you use conventional gypsum bonded investment material with CoCr
no
84
is polishing CoCr easy
no as its surface is harder than gold | - but due to this retains polish longer
85
why is precise casting needed for CoCr
``` work hardens (cold hardens) rapidly - casting process is harder to avoid defects ```
86
Au Vs CoCr rigidity
Au less than half rigidity of CoCr
87
Au Vs CoCr fracture strength UTS
Fracture strength is similar
88
Au Vs CoCr ductility
Ductility Au exceeds CoCr
89
AU VS CoCr hardness
CoCr hardness is significantly more than type IV Au

BDS2 Dental Materials Sciences (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions