partial denture alloys Flashcards
what are the ideal properties of a partial denture alloy?
rigid strong hard ductile precise casting (shrink) melting point density
what are the 4 partial denture alloys?
type IV gold
CoCr
white gold
titanium
what properties should a denture base have?
rigid to maintain shape
high EL to avoid plastic deformation
what properties should a clasp have?
less rigid to flex over tooth
high EL maintain elasticity over wide range of movement
what are the 4 types of gold used for?
I-simple alloys
II - larger inlays
III - crown & bridge alloys
IV partial dentures
what are the effects of copper as the alloying element in gold?
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
what are the effects of silver as the alloying element in gold?
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
what are the effects of platinum as the alloying element in gold?
solid solution w/ gold
solution hardening
fine grain structure
coring can occur
what are the effects of palladium as the alloying element in gold?
similar to platinum but less expensive
less coring
coarser grains
absorbs gases when molten-porous casting
what is the effect of zinc as the alloying element in gold?
scavenger=preferentially oxidising during casting process
what is the effects of nickel as the alloying element in gold?
increase hardness & strength
what is the effect of indium as the alloying element in gold?
fine grain structure
what heat tx can be done on type IV gold alloys?
quench after casing -gives fine grains causes coring homogenising anneal -eliminates coring stress relief anneal -if cold worked heat harden
CoCr uses
wires
surgical implants
cast partial dentures
-connectors
what is the composition of CoCr
Co-54% Cr-25% Ni-15% Mo-5% C-0.4%
what are the effects of cobalt as the alloy in CoCr
forms solid solution with Cr
increased strength, hardness, rigidity
coring possible
what are the effects of chromium as the alloy in CoCr?
forms solid solution with Co
increased strength, hardness, rigidity
coring possible
forms passive layer-corrosion resistance
what are the effects of nickel in CoCr?
replaces some Co
improves ductility
slight reduction in strength
sensitivity (6% f, 2%m)
what are the CoCr techniques?
investment method -high temp -silica/phosphate added melting -electric induction preferred casting -centrifugal force required -overheating -> coarse grains -cooling too fast/slow =brittle
how is CoCr finished?
sandblast
electroplate
abrasive wheel
polishing buff
describe the properties of CoCr
harder than gold (resists) wear in mouth better finishing/polishing time consuming low ductility work hardens rapidly adjustment difficult precision casting
what are the uses of titanium?
implants
crown & bridge
maxillo-facial skull plates
partial dentures
describe titanium
good biocompatibility good corrosion resistance parts joined by laser welding electric arc melting absorbs gases -specialised investment & casting
which partial denture alloy has the greatest elongation?
titanium
which partial denture alloy has the greatest UTS? (tensile strength)
S. steel
which partial denture alloy has the greatest density?
gold
lighter alloy more comfortable & unobtrusive
which partial denture alloy has the greatest rigidity?
Co-Cr
2x stiffness of gold
much less flexing
which partial denture alloy has the greatest hardness?
Co-Cr
S. steel close
which partial denture alloy has the greatest shrinkage?
Co-Cr
always some
shrinks double gold
processing more difficult
