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BDS2 CDS DMS > partial denture alloys > Flashcards

partial denture alloys Flashcards

1
Q

what are the ideal properties of a partial denture alloy?

A 
rigid
strong
hard
ductile
precise casting (shrink)
melting point
density
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2
Q

what are the 4 partial denture alloys?

A

type IV gold
CoCr
white gold
titanium

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3
Q

what properties should a denture base have?

A

rigid to maintain shape

high EL to avoid plastic deformation

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4
Q

what properties should a clasp have?

A

less rigid to flex over tooth

high EL maintain elasticity over wide range of movement

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5
Q

what are the 4 types of gold used for?

A

I-simple alloys
II - larger inlays
III - crown & bridge alloys
IV partial dentures

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6
Q

what are the effects of copper as the alloying element in gold?

A 
solid solution in all proportions
solution hardening
order hardening (40-80% gold)
reduced melting point
little/no coring
imparts red colout
reduces density
base metal can corrode if too much
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7
Q

what are the effects of silver as the alloying element in gold?

A 
solid solution in all proportions
solution hardening
precipitation hardening with copper & heat tx
can allow tarnishing
molten silver absorbs gas
whitens alloy-compensates for copper
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8
Q

what are the effects of platinum as the alloying element in gold?

A

solid solution w/ gold
solution hardening
fine grain structure
coring can occur

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9
Q

what are the effects of palladium as the alloying element in gold?

A

similar to platinum but less expensive
less coring
coarser grains
absorbs gases when molten-porous casting

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10
Q

what is the effect of zinc as the alloying element in gold?

A

scavenger=preferentially oxidising during casting process

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11
Q

what is the effects of nickel as the alloying element in gold?

A

increase hardness & strength

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12
Q

what is the effect of indium as the alloying element in gold?

A

fine grain structure

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13
Q

what heat tx can be done on type IV gold alloys?

A 
quench after casing
-gives fine grains causes coring
homogenising anneal
-eliminates coring
stress relief anneal
-if cold worked
heat harden
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14
Q

CoCr uses

A

wires
surgical implants
cast partial dentures
-connectors

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15
Q

what is the composition of CoCr

A 
Co-54%
Cr-25%
Ni-15%
Mo-5%
C-0.4%
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16
Q

what are the effects of cobalt as the alloy in CoCr

A

forms solid solution with Cr
increased strength, hardness, rigidity
coring possible

17
Q

what are the effects of chromium as the alloy in CoCr?

A

forms solid solution with Co
increased strength, hardness, rigidity
coring possible
forms passive layer-corrosion resistance

18
Q

what are the effects of nickel in CoCr?

A

replaces some Co
improves ductility
slight reduction in strength
sensitivity (6% f, 2%m)

19
Q

what are the CoCr techniques?

A 
investment method
-high temp
-silica/phosphate added
melting
-electric induction preferred
casting
-centrifugal force required
-overheating -> coarse grains
-cooling too fast/slow =brittle
20
Q

how is CoCr finished?

A

sandblast
electroplate
abrasive wheel
polishing buff

21
Q

describe the properties of CoCr

A 
harder than gold
(resists) wear in mouth better
finishing/polishing time consuming
low ductility
work hardens rapidly
adjustment difficult
precision casting
22
Q

what are the uses of titanium?

A

implants
crown & bridge
maxillo-facial skull plates
partial dentures

23
Q

describe titanium

A 
good biocompatibility
good corrosion resistance
parts joined by laser welding
electric arc melting
absorbs gases
-specialised investment & casting
24
Q

which partial denture alloy has the greatest elongation?

A

titanium

25
Q

which partial denture alloy has the greatest UTS? (tensile strength)

A

S. steel

26
Q

which partial denture alloy has the greatest density?

A

gold

lighter alloy more comfortable & unobtrusive

27
Q

which partial denture alloy has the greatest rigidity?

A

Co-Cr
2x stiffness of gold
much less flexing

28
Q

which partial denture alloy has the greatest hardness?

A

Co-Cr

S. steel close

29
Q

which partial denture alloy has the greatest shrinkage?

A

Co-Cr
always some
shrinks double gold
processing more difficult

BDS2 CDS DMS (16 decks)

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