Gold alloys-ppt

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Copyright 2008, Dr. Stephen Bayne.

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2. GOLD CASTING ALLOYSGOLD CASTING ALLOYS
Stephen C. BayneStephen C. Bayne
University of MichiganUniversity of Michigan
School of DentistrySchool of Dentistry
Ann Arbor, MichiganAnn Arbor, Michigan
[email protected]@umich.edu

3. INDIRECT RESTORATIONSINDIRECT RESTORATIONS
Overview of ErrorsOverview of Errors
ERRORS:ERRORS:
•ImpressionsImpressions
•Models/CastsModels/Casts
•WaxingWaxing
•InvestingInvesting
•CastingCasting
•Finishing/PolishingFinishing/Polishing
•CementingCementing
0.1 to 0.2%
------
------
+1.5 to 1.7%
-1.5 to 1.7%
------
------
Calculation of ideal permissible error:
2 x 25 mm / 10,000 mm = 0.5%
*Image source: Steve Bayne, University of Michigan, 2008
**Image source: Undetermined
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4. 0.0.Fabrication requirements vs final properties:Fabrication requirements vs final properties:
1.1.Physical Properties:Physical Properties:
a.a.Reasonably low MP (flow)Reasonably low MP (flow)
b.b.Moderately high density (castability) Moderately high density (castability) ®®
c.c.Low coefficient of thermal expansion (Low coefficient of thermal expansion (aa))®®
2.2.Chemical Properties:Chemical Properties:
a.a.Chemical corrosion (tarnish) resistanceChemical corrosion (tarnish) resistance
b.b.Electrochemical corrosion resistanceElectrochemical corrosion resistance
c.c.Solubility (solderability)Solubility (solderability)
GENERAL REQUIREMENTSGENERAL REQUIREMENTS
PlatinumPlatinum = 12.45 gms/cm= 12.45 gms/cm
33
CobaltCobalt = 8.90= 8.90
GoldGold = 18.88= 18.88 NickelNickel = 8.90= 8.90
PalladiumPalladium= 12.02= 12.02 IronIron = 7.87= 7.87
SilverSilver = 10.50= 10.50 ChromiumChromium = 7.17= 7.17
CopperCopper = 8.96= 8.96
ToothTooth = 9-11 ppm/= 9-11 ppm/°°CC Amalgam Amalgam = 25= 25
PFM alloysPFM alloys = 14= 14 Composite Composite = 35-45= 35-45
Gold alloysGold alloys = 18= 18

5. 3.3.Mechanical Properties:Mechanical Properties:
a.a.High E (stiffness)High E (stiffness)
b.b.Moderately high YS and H (resistance to plastic deformation)Moderately high YS and H (resistance to plastic deformation)
c.c.Hardenable by heat treatment (retention of polish)Hardenable by heat treatment (retention of polish)
4.4.Biological Properties:Biological Properties:
a.a.Biocompatible: no toxic soluble phasesBiocompatible: no toxic soluble phases
b.b.Non-reactive in the oral environmentNon-reactive in the oral environment
GENERAL REQUIREMENTSGENERAL REQUIREMENTS
(continued)(continued)
S
T
R
E
S
S
S
T
R
E
S
S
STRAINSTRAIN
x
Yield Strength (or Hardness)Yield Strength (or Hardness)
Modulus (Stiffness, Slope of Line)Modulus (Stiffness, Slope of Line)
x
Graph source: Steve Bayne, University of Michigan, 2008

6. REVIEW OF CORROSIONREVIEW OF CORROSION
1.1.Types: Types: Chemical CorrosionChemical Corrosion, , Electrochemical CorrosionElectrochemical Corrosion
2.2.Requirements for Electrochemical Corrosion: Requirements for Electrochemical Corrosion:
Anode, Cathode, Circuit, ElectrolyteAnode, Cathode, Circuit, Electrolyte
3.3.Electrochemical Corrosion Categories:Electrochemical Corrosion Categories:
a.a.Galvanic CorrosionGalvanic Corrosion (macro-galvanic) (macro-galvanic)
b.b.Local Galvanic CorrosionLocal Galvanic Corrosion (structure-selective corrosion) (structure-selective corrosion)
c.c.Concentration Cell Corrosion (Concentration Cell Corrosion (crevice corrosioncrevice corrosion))
d.d.Stress CorrosionStress Corrosion
Images source: Steve Bayne, University of Michigan, 2008

7. CLASSIFICATION OF ALLOYSCLASSIFICATION OF ALLOYS
1.1.Full Gold Crown and Bridge Alloys (based on precious metals)Full Gold Crown and Bridge Alloys (based on precious metals)
a.a.ADA Classification System (see phase diagrams)ADA Classification System (see phase diagrams)
(1)(1)Type IType I³³ 83% Au+ 83% Au+(Non-heat hardenable)(Non-heat hardenable)-- inlay-- inlay
(2)(2)Type IIType II³³ 78% Au+ 78% Au+(Non-heat hardenable)(Non-heat hardenable)-- inlay, onlay, …-- inlay, onlay, …
(3)(3)Type IIIType III³³ 78% Au+ 78% Au+(Heat hardenable)(Heat hardenable) -- onlay, crown-- onlay, crown
(4)(4)Type IVType IV³³ 75% Au+ 75% Au+(Heat hardenable)(Heat hardenable) -- crown, bridge-- crown, bridge
b.b.Effects of Alloys Components:Effects of Alloys Components:
(1)(1)GoldGold (Au) (Au) ®®
(2)(2)CopperCopper (Cu) (Cu) ®®
(3)(3)SilverSilver (Ag) (Ag) ®®
(4)(4)Palladium Palladium (Pd) (Pd) ®®
(5)(5)Platinum Platinum (Pt) (Pt) ®®
(6)(6)Zinc Zinc (Zn) (Zn) ®®
Corrosion resistanceCorrosion resistance
HardnessHardness
Counteract orange color of copperCounteract orange color of copper
Increase MP and hardnessIncrease MP and hardness
Increase MPIncrease MP
Prevent oxidation during melting (OPrevent oxidation during melting (O
22 getter) getter)

8. TERMINOLOGYTERMINOLOGY
1.1.Precious MetalPrecious Metal = containing metals of high economic value such as = containing metals of high economic value such as
gold, platinum, palladium, silver, (rhodium), (iridium), (rhuthenium), gold, platinum, palladium, silver, (rhodium), (iridium), (rhuthenium),
and (osmium).and (osmium).
2.2.Noble MetalNoble Metal = a precious metal that is resistant to tarnish. This = a precious metal that is resistant to tarnish. This
excludes “silver” by definition.excludes “silver” by definition.
3.3.Low Gold AlloysLow Gold Alloys = Alloys containing <75% gold (less than 50 a/o gold) = Alloys containing <75% gold (less than 50 a/o gold)
which means that gold atoms represent less than every other atom.which means that gold atoms represent less than every other atom.
4.4.Gold-substitute AlloysGold-substitute Alloys = precious metal alloys not containing gold. = precious metal alloys not containing gold.
5.5.Base-Metal AlloysBase-Metal Alloys = alloys not containing precious metals to impart = alloys not containing precious metals to impart
their corrosion resistance.their corrosion resistance.

9. ATOMIC PERCENT GOLDATOMIC PERCENT GOLDCUCU AUAU
100
600
700
800
900
1000
500
400
300
200
10 70809010030405060200
1100
WEIGHT PERCENT GOLDWEIGHT PERCENT GOLD
3010 70 80 90 10040506020 75 85 95
LIQUIDUSLIQUIDUS
SOLIDUSSOLIDUS
DENTALDENTAL
ALLOYSALLOYS
T
E
M
P
E
R
A
T
U
R
E

(

T
E
M
P
E
R
A
T
U
R
E

(
°°
C

)
C

)
Low Gold AlloysLow Gold Alloys High Gold AlloysHigh Gold Alloys
RandomRandom
SolidSolid
SolutionSolution
OrderedOrdered
SolidSolid
SolutionSolution
Graph source: Steve Bayne,
University of Michigan, 2008

10. AGAG CUCU
AUAU
a
a + b
5
10
15
20
25
30
35
40
50
45
AU-AG-CUAU-AG-CU
TenaryTenary
Phase DiagramPhase Diagram
Type IType I
Type IIType II
Type IIIType III
Type IVIType IVI
T
Graph source: Steve Bayne,
University of Michigan, 2008

11. COMMERCIAL EXAMPLESCOMMERCIAL EXAMPLES
Graph source: Steve Bayne, University of Michigan, 2008

12. PROCESSING CYCLESPROCESSING CYCLES
in
v
e
s
t
m
e
n
t
a
l
l
o
y
TIME
Alloy LCTE = 16-18 ppm/°C
CASTCAST
GOLDGOLD
ALLOYSALLOYS
T
m
890°C
T
rt
Graph source: Steve Bayne, University of Michigan, 2008

13. A.A.DistortionDistortion::
1.1.Margins:Margins: Probability highest in thinner portions of pattern. Probability highest in thinner portions of pattern.
a.a.Wax Deformation:Wax Deformation: improper removal or handling of pattern. improper removal or handling of pattern.
b.b.Premature Quenching:Premature Quenching: wait until button loses red color. wait until button loses red color.
c.c.Investment Expansion/Contraction:Investment Expansion/Contraction:
CASTING PROBLEMSCASTING PROBLEMS
for Gold Alloysfor Gold Alloys
a
b
c
Image source: Steve Bayne, University of Michigan, 2008

14. B.B.Surface IrregularitiesSurface Irregularities::
1.1.Fine Surface Roughness:Fine Surface Roughness: Inherent particle size of investment Inherent particle size of investment
a.a.High W/P ratio increases surface roughness.High W/P ratio increases surface roughness.
b.b.Low W/P ratio decreases investment adaptation or flow.Low W/P ratio decreases investment adaptation or flow.
c.c.Prolonged burnout encourages investment decomposition.Prolonged burnout encourages investment decomposition.
d.d.Overheating alloy encourages investment decomposition.Overheating alloy encourages investment decomposition.
e.e.Overheating alloy encourages reaction with investment.Overheating alloy encourages reaction with investment.
2.2.Surface Defects:Surface Defects:
a.a.Nodules: air bubbles trapped on the pattern during investing.Nodules: air bubbles trapped on the pattern during investing.
(Use surfactant; paint pattern; vacuum invest; vibrate)(Use surfactant; paint pattern; vacuum invest; vibrate)
b.b.Ridges or Veins: poor wetting causing water films on pattern. Ridges or Veins: poor wetting causing water films on pattern.
(Use surfactant; vacuum invest; vibrate investment carefully).(Use surfactant; vacuum invest; vibrate investment carefully).
3.3.Gross Surface Defects:Gross Surface Defects:
a.a.Fins: cracked investment (from overheating)Fins: cracked investment (from overheating)
INVESTMENTALLOY
NodulesNodules
Ridges or veinsRidges or veins
FinsFins
SurfaceSurface
roughnessroughness
CASTING PROBLEMSCASTING PROBLEMS
for Gold Alloysfor Gold Alloys
Image source: Steve Bayne, University of Michigan, 2008

15. C.C.Incomplete CastingsIncomplete Castings::
1.1.Internal Porosity:Internal Porosity: due to improper solidification. due to improper solidification.
a.a.Improper Spruing: Diameter too small or too long.Improper Spruing: Diameter too small or too long.
b.b.Low Temperature: Investment or metal too cold.Low Temperature: Investment or metal too cold.
c.c.Included Gases: Contaminated gold or oxidized old gold.Included Gases: Contaminated gold or oxidized old gold.
d.d.Occluded Gases: Improper burnout of pattern.Occluded Gases: Improper burnout of pattern.
2.2.Incomplete External Shape:Incomplete External Shape:
a.a.Insufficient casting pressure.Insufficient casting pressure.
b.b.Excessive back pressure from investment.Excessive back pressure from investment.
c.c.Suck back into sprue.Suck back into sprue.
InternalInternal
porosityporosity
IncompleteIncomplete
marginmargin
GasGas
bubblebubble
CASTING PROBLEMSCASTING PROBLEMS
for Gold Alloysfor Gold Alloys
Image source: Steve Bayne, University of Michigan, 2008