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Stephen C. BayneStephen C. BayneUniversity of MichiganSchool of DentistryAnn Arbor, [email protected]
RPDRPDCASTING ALLOYSCASTING ALLOYS
HISTORICAL BACKGROUNDHISTORICAL BACKGROUND1.1. Cr-alloysCr-alloys used in dentistry since 1930s -- widely used since 1970s used in dentistry since 1930s -- widely used since 1970s2.2. Corrosion resistance; high strength and E; low density; low $$$Corrosion resistance; high strength and E; low density; low $$$3.3. Compositions similar to ones for C&B, MF, and orthopedic implants Compositions similar to ones for C&B, MF, and orthopedic implants
RPD ALLOYS CLASSIFICATION1.1. Classification by RPD components:Classification by RPD components:
a.a. Frameworks (major and minor connectors)Frameworks (major and minor connectors)b.b. Clasps; Wrought retention wiresClasps; Wrought retention wiresc.c. RestsRestsd.d. SoldersSolders
2.2. Framework casting alloys:Framework casting alloys:a.a. (Gold Alloys, Type IV)(Gold Alloys, Type IV)b.b. Co-CrCo-Cr Vitallium (60Co-31.5Cr-6Mo)Vitallium (60Co-31.5Cr-6Mo); Nobillium; Nobilliumc.c. Co-Cr-Ni Co-Cr-Ni d.d. Ni-CrNi-Cr (and Ni-Cr-Be) (and Ni-Cr-Be) Ticoncium (74Ni-15Cr)Ticoncium (74Ni-15Cr); Howmedica II; Howmedica IIe.e. (Fe-Cr)(Fe-Cr) Dentillium P-DDentillium P-Dg.g. (Ti-6Al-4V) (cp-Ti)(Ti-6Al-4V) (cp-Ti)h.h. (Ni-Ti)(Ni-Ti)
RPD ALLOYRPD ALLOY PROPERTIESPROPERTIES
1.1. Physical PropertiesPhysical Properties::a.a. Typical fusion temperatures = 1400 to 1454 Typical fusion temperatures = 1400 to 1454 CCb.b. Color = lustrous silvery whiteColor = lustrous silvery whitec.c. Density (lighter weight than gold counterparts) = typically 8-9 gm/cm3Density (lighter weight than gold counterparts) = typically 8-9 gm/cm3d.d. Linear casting shrinkage = 2.05 to 2.33% (vs 1.4 to 1.7% for gold alloys)Linear casting shrinkage = 2.05 to 2.33% (vs 1.4 to 1.7% for gold alloys)e.e. Thermal conductivity = highThermal conductivity = high
2.2. Chemical PropertiesChemical Properties::a.a. Electrochemical corrosion = good passivation by CrElectrochemical corrosion = good passivation by Cr22OO33 if Ni-Cr-Co >85% if Ni-Cr-Co >85%b.b. Passive film attacked vigorously by chlorine -- do not use household bleachPassive film attacked vigorously by chlorine -- do not use household bleach
Image source: Steve Bayne, University of Michigan, 2008
3.3. Mechanical PropertiesMechanical Properties::a.a. E = 200-240 GPa (about 2X that of comparable cast dental gold) E = 200-240 GPa (about 2X that of comparable cast dental gold) b.b. Hardness (typically 30% harder than Type IV golds) = R30N (or VHN) = 370;Hardness (typically 30% harder than Type IV golds) = R30N (or VHN) = 370;
YS = 414-621 MPa, YS = 414-621 MPa, c.c. UTS = 621-828 MPaUTS = 621-828 MPad.d. % Elongation (Cr alloys are quite brittle) = 1-2%% Elongation (Cr alloys are quite brittle) = 1-2%e.e. Co-Cr alloys not affected by HT; Ni-Cr alloys can be affected by high temp HTCo-Cr alloys not affected by HT; Ni-Cr alloys can be affected by high temp HT
Co-Crx
STRAIN
ST
RE
SS
x Ni-Cr
x Au Alloy
RPD ALLOYRPD ALLOY PROPERTIESPROPERTIES
Moduli
Rigidity:(1) geometry of component(2) thickness(3) modulus
Image and graph source: Steve Bayne, University of Michigan, 2008
ClaspStrain
FatigueResistance
Log CYCLES
ST
RE
SS
Co-Cr
x
STRAIN
x
x
ST
RE
SS
Ni-Cr
Au Alloy
Moduli
3.3. Mechanical PropertiesMechanical Properties: (continued): (continued)…………f.f. Fatigue much more important for clasps than connectorsFatigue much more important for clasps than connectors
RPD ALLOYRPD ALLOY PROPERTIESPROPERTIES
Graph source: Steve Bayne, University of Michigan, 2008
4.4. Laboratory ManipulationLaboratory Manipulation::a.a. InvestmentInvestment (requires high temperature investments) = PBI or SBI (requires high temperature investments) = PBI or SBIb.b. SpruingSpruing (entrapped gases may produce voids) = careful venting (entrapped gases may produce voids) = careful ventingc.c. Melting methodsMelting methods = oxyacetylene, oxygen-gas, or electric induction = oxyacetylene, oxygen-gas, or electric inductiond.d. CastingCasting (broken-arm casting machines not recommended) = (broken-arm casting machines not recommended) =
use vacuum and/or pressure castinguse vacuum and/or pressure castinge.e. Sprue removal and finishing/polishing = special lab equipment due to high HSprue removal and finishing/polishing = special lab equipment due to high Hf.f. SolderingSoldering = use care in fluxing, soldering, and = use care in fluxing, soldering, and
heat control (electric soldering)heat control (electric soldering)g.g. Solders = usually >800 fine Ag-solders (good corrosion resistance)Solders = usually >800 fine Ag-solders (good corrosion resistance)f.f. SterilizationSterilization = dilute bleach solutions = dilute bleach solutions
5.5. Clinical propertiesClinical properties::a.a. AdjustmentsAdjustments (casts, etc.) = difficult due to high hardness and E (casts, etc.) = difficult due to high hardness and Eb.b. Ni sensitivity = sometimes but probably due to misfit or improper designNi sensitivity = sometimes but probably due to misfit or improper designc.c. Wear = low (but may contribute to excessive wear of teeth or restorations)Wear = low (but may contribute to excessive wear of teeth or restorations)d.d. HygieneHygiene = clean with soap and water or very dilute solutions = clean with soap and water or very dilute solutions
avoiding chlorine (Use stiff bristle brush; Avoid abrasive dentifrices)avoiding chlorine (Use stiff bristle brush; Avoid abrasive dentifrices)
RPD ALLOYRPD ALLOY PROPERTIESPROPERTIES
Alloy TypeAlloy Type YieldYieldStrengthStrength(MPa)(MPa)
TensileTensileStrength Strength (MPa)(MPa)
Percent (%)Percent (%)ElongationElongation
HardnessHardness(VHN)(VHN)
ModulusModulus(GPa)(GPa)
ADA Spec #14, Min 500 ----- 1.5 ----- 172
Type IV Gold AlloyType IV Gold Alloy 493493 776776 7.7. 264264 9090
Fe-CrFe-Cr 703703 841841 9.9. 309309 202202
Co-Cr-NiCo-Cr-Ni 470470 685685 8.8. 264264 198198
Co-CrCo-Cr 710710 870870 1.61.6 432432 224224
Ni-CrNi-Cr 690690 800800 3.83.8 300300 182182
Ti-6Al-4VTi-6Al-4V ---------- 930930 5.5. 320320 117117
Others (cp-Ti, Ni-Ti)Others (cp-Ti, Ni-Ti)
COMPARISON OF ALLOYCOMPARISON OF ALLOYMECHANICAL PROPERTIESMECHANICAL PROPERTIES
BIOMECHANICAL ANALYSISBIOMECHANICAL ANALYSISClinical Lifetime of RPDs (5-8 years)Clinical Lifetime of RPDs (5-8 years)
RPD must resist 4 degrees of freedom = x, y, z, rotationRPD must resist 4 degrees of freedom = x, y, z, rotation
General categories of failure:General categories of failure:(1)(1) Biologic = bone resorption; tooth mobility; tissue irritationBiologic = bone resorption; tooth mobility; tissue irritation(2) (2) Physiologic = PDL overload; toth wearPhysiologic = PDL overload; toth wear(3)(3) Materials = materials defects; lab problems; adjustmentsMaterials = materials defects; lab problems; adjustments
11
2233
44
55
Image source: Steve Bayne, University of Michigan, 2008