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Unless otherwise noted, the content of this course material is licensed under a Creative Commons Attribution 3.0 License.Copyright 2008, Dr. Stephen Bayne.The following information is intended to inform and educate and is not a tool for self-diagnosis or a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. You should speak to your physician or make an appointment to be seen if you have questions or concerns about this information or your medical condition. You assume all responsibility for use and potential liability associated with any use of the material. Material contains copyrighted content, used in accordance with U.S. law. Copyright holders of content included in this material should contact open.michigan@umich.edu with any questions, corrections, or clarifications regarding the use of content. The Regents of the University of Michigan do not license the use of third party content posted to this site unless such a license is specifically granted in connection with particular content objects. Users of content are responsible for their compliance with applicable law. See http://www.dent.umich.edu/license/ for more information. Mention of specific products in this recording solely represents the opinion of the speaker and does not represent an endorsement by the University of Michigan. Viewer discretion advised: Material may contain medical images that may be disturbing to some viewers.

RPD CASTING ALLOYSStephen C. BayneUniversity of Michigan School of Dentistry Ann Arbor, Michigan Sbayne@umich.edu

HISTORICAL BACKGROUND1. 2. 3. Cr-alloys used in dentistry since 1930s -- widely used since 1970s Corrosion resistance; high strength and E; low density; low $$$ Compositions similar to ones for C&B, MF, and orthopedic implants

RPD ALLOYS CLASSIFICATION1. Classification by RPD components: a. Frameworks (major and minor connectors) b. Clasps; Wrought retention wires c. Rests d. Solders Framework casting alloys: a. (Gold Alloys, Type IV) b. Co-Cr Vitallium (60Co-31.5Cr-6Mo); Nobillium c. Co-Cr-Ni d. Ni-Cr (and Ni-Cr-Be) Ticoncium (74Ni-15Cr); Howmedica II e. (Fe-Cr) Dentillium P-D g. (Ti-6Al-4V) (cp-Ti) h. (Ni-Ti)



1. Physical Properties: a. Typical fusion temperatures = 1400 to 1454 C b. Color = lustrous silvery white c. Density (lighter weight than gold counterparts) = typically 8-9 gm/cm3 d. Linear casting shrinkage = 2.05 to 2.33% (vs 1.4 to 1.7% for gold alloys) e. Thermal conductivity = high 2. Chemical Properties: a. Electrochemical corrosion = good passivation by Cr2O3 if Ni-Cr-Co >85% b. Passive film attacked vigorously by chlorine -- do not use household bleachImage source: Steve Bayne, University of Michigan, 2008

RPD ALLOY PROPERTIES3. Mechanical Properties: a. E = 200-240 GPa (about 2X that of comparable cast dental gold) b. Hardness (typically 30% harder than Type IV golds) = R30N (or VHN) = 370; YS = 414-621 MPa, c. UTS = 621-828 MPa d. % Elongation (Cr alloys are quite brittle) = 1-2% e. Co-Cr alloys not affected by HT; Ni-Cr alloys can be affected by high temp HT


x Co-Cr x Ni-Cr STRESS x Au Alloy Rigidity: (1) geometry of component (2) thickness (3) modulus STRAINImage and graph source: Steve Bayne, University of Michigan, 2008

RPD ALLOY PROPERTIES3. Mechanical Properties: (continued) f. Fatigue much more important for clasps than connectorsModuli

x Co-Cr x Ni-Cr STRESS x Au Alloy STRESS

Fatigue Resistance

STRAINClasp Strain


Graph source: Steve Bayne, University of Michigan, 2008

RPD ALLOY PROPERTIES4. Laboratory Manipulation: a. Investment (requires high temperature investments) = PBI or SBI b. Spruing (entrapped gases may produce voids) = careful venting c. Melting methods = oxyacetylene, oxygen-gas, or electric induction d. Casting (broken-arm casting machines not recommended) = use vacuum and/or pressure casting e. Sprue removal and finishing/polishing = special lab equipment due to high H f. Soldering = use care in fluxing, soldering, and heat control (electric soldering) g. Solders = usually >800 fine Ag-solders (good corrosion resistance) f. Sterilization = dilute bleach solutions 5. Clinical properties: a. Adjustments (casts, etc.) = difficult due to high hardness and E b. Ni sensitivity = sometimes but probably due to misfit or improper design c. Wear = low (but may contribute to excessive wear of teeth or restorations) d. Hygiene = clean with soap and water or very dilute solutions avoiding chlorine (Use stiff bristle brush; Avoid abrasive dentifrices)

COMPARISON OF ALLOY MECHANICAL PROPERTIESAlloy Type Yield Strength (MPa) 500 493 703 470 Tensile Strength (MPa) ----776 841 685 Percent (%) Elongation 1.5 7. 9. 8. Hardness (VHN) ----264 309 264 Modulus (GPa) 172 90 202 198

ADA Spec #14, Min Type IV Gold Alloy Fe-Cr Co-Cr-Ni

Co-CrNi-Cr Ti-6Al-4V Others (cp-Ti, Ni-Ti)

710690 -----

870800 930

1.63.8 5.

432300 320

224182 117

BIOMECHANICAL ANALYSISClinical Lifetime of RPDs (5-8 years) RPD must resist 4 degrees of freedom = x, y, z, rotation

General categories of failure: (1) Biologic = bone resorption; tooth mobility; tissue irritation (2) Physiologic = PDL overload; toth wear (3) Materials = materials defects; lab problems; adjustments3 2 4

1 5

Image source: Steve Bayne, University of Michigan, 2008