gold alloys-ppt
TRANSCRIPT
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Copyright 2008, Dr. Stephen Bayne.
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GOLD CASTING ALLOYSGOLD CASTING ALLOYS
Stephen C. BayneStephen C. Bayne
University of MichiganUniversity of MichiganSchool of DentistrySchool of DentistryAnn Arbor, MichiganAnn Arbor, [email protected]@umich.edu
INDIRECT RESTORATIONSINDIRECT RESTORATIONSOverview 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 m / 10,000 m = 0.5%
*Image source: Steve Bayne, University of Michigan, 2008**Image source: Undetermined
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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 ())
2.2. Chemical Properties:Chemical Properties:a.a. Chemical corrosion (tarnish) resistanceChemical corrosion (tarnish) resistanceb.b. Electrochemical corrosion resistanceElectrochemical corrosion resistancec.c. Solubility (solderability)Solubility (solderability)
GENERAL REQUIREMENTSGENERAL REQUIREMENTS
PlatinumPlatinum = 12.45 gms/cm= 12.45 gms/cm33 CobaltCobalt = 8.90= 8.90GoldGold = 18.88= 18.88 NickelNickel = 8.90= 8.90PalladiumPalladium = 12.02= 12.02 IronIron = 7.87= 7.87SilverSilver = 10.50= 10.50 ChromiumChromium = 7.17= 7.17CopperCopper = 8.96= 8.96
ToothTooth = 9-11 ppm/= 9-11 ppm/CC Amalgam Amalgam = 25= 25PFM alloysPFM alloys = 14= 14 Composite Composite = 35-45= 35-45Gold alloysGold alloys = 18= 18
3.3. Mechanical Properties:Mechanical Properties:a.a. High E (stiffness)High E (stiffness)b.b. Moderately high YS and H (resistance to plastic Moderately high YS and H (resistance to plastic
deformation)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 phasesb.b. Non-reactive in the oral environmentNon-reactive in the oral environment
GENERAL REQUIREMENTSGENERAL REQUIREMENTS(continued)(continued)
ST
RE
SS
ST
RE
SS
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
REVIEW OF CORROSIONREVIEW OF CORROSION1.1. 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
CLASSIFICATION OF ALLOYSCLASSIFICATION OF ALLOYS1.1. 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 I 83% Au+ 83% Au+ (Non-heat hardenable)(Non-heat hardenable) -- inlay-- inlay(2)(2) Type IIType II 78% Au+ 78% Au+ (Non-heat hardenable)(Non-heat hardenable) -- inlay, onlay, …-- inlay, onlay, …(3)(3) Type IIIType III 78% Au+ 78% Au+ (Heat hardenable)(Heat hardenable) -- onlay, crown-- onlay, crown(4)(4) Type IVType IV 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 resistanceHardnessHardnessCounteract orange color of copperCounteract orange color of copperIncrease MP and hardnessIncrease MP and hardnessIncrease MPIncrease MPPrevent oxidation during melting (OPrevent oxidation during melting (O22 getter) getter)
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.
ATOMIC PERCENT GOLDATOMIC PERCENT GOLDCUCU AUAU
100
600
700
800
900
1000
500
400
300
200
10 70 80 90 10030 40 50 60200
1100
WEIGHT PERCENT GOLDWEIGHT PERCENT GOLD3010 70 80 90 10040 50 6020 75 85 95
LIQUIDUSLIQUIDUS
SOLIDUSSOLIDUS
DENTALDENTALALLOYSALLOYS
TE
MP
ER
AT
UR
E (
T
EM
PE
RA
TU
RE
( C
)C
)
Low Gold AlloysLow Gold Alloys High Gold AlloysHigh Gold Alloys
RandomRandomSolidSolid
SolutionSolution
OrderedOrderedSolidSolid
SolutionSolutionGraph source: Steve Bayne, University of Michigan, 2008
AGAG CUCU
AUAU
+
5
10
15
20
25
30
35
40
50
45
AU-AG-CUAU-AG-CUTenaryTenary
Phase DiagramPhase DiagramType IType IType IIType IIType IIIType III
Type IVIType IVI
T
Graph source: Steve Bayne, University of Michigan, 2008
COMMERCIAL EXAMPLESCOMMERCIAL EXAMPLES
Graph source: Steve Bayne, University of Michigan, 2008
PROCESSING CYCLESPROCESSING CYCLES
inve
stm
ent
all
oy
TIME
Alloy LCTE = 16-18 ppm/C
CASTCASTGOLDGOLDALLOYSALLOYS
Tm 890C
Trt
Graph source: Steve Bayne, University of Michigan, 2008
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 PROBLEMSfor Gold Alloysfor Gold Alloys
ab
c
Image source: Steve Bayne, University of Michigan, 2008
B.B. Surface IrregularitiesSurface Irregularities::
1.1. Fine Surface Roughness:Fine Surface Roughness: Inherent particle size of investment Inherent particle size of investmenta.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
SurfaceSurfaceroughnessroughness
CASTING PROBLEMSCASTING PROBLEMSfor Gold Alloysfor Gold Alloys
Image source: Steve Bayne, University of Michigan, 2008
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.
InternalInternalporosityporosity
IncompleteIncompletemarginmargin
GasGasbubblebubble
CASTING PROBLEMSCASTING PROBLEMSfor Gold Alloysfor Gold Alloys
Image source: Steve Bayne, University of Michigan, 2008