RPD-Alloys-PPT MODIFIED

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Assalamaa aleh kum

DENTURE BASE MATERIALS for RPD’s : 

DENTURE BASE MATERIALS for RPD’s Prof. Dr. S. Venugopal. MDS.

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RPD CASTING ALLOYS

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ADVANTAGES OF METALLIC DENTURE BASE

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HISTORICAL BACKGROUND 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 CLASSIFICATION Classification by RPD components: Frameworks (major and minor connectors) Clasps; Wrought retention wires Rests 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 (Fe-Cr) Dentillium P-D (Ti-6Al-4V) (cp-Ti) h. (Ni-Ti)

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RPD ALLOY PROPERTIES 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 bleach Image source: Steve Bayne, University of Michigan, 2008

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3. 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 RPD ALLOY PROPERTIES Image and graph source: Steve Bayne, University of Michigan, 2008

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Moduli 3. Mechanical Properties: (continued) …… f. Fatigue much more important for clasps than connectors RPD ALLOY PROPERTIES Graph source: Steve Bayne, University of Michigan, 2008

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4. 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) RPD ALLOY PROPERTIES

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COMPARISON OF ALLOY MECHANICAL PROPERTIES

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BIOMECHANICAL ANALYSIS Clinical Lifetime of RPDs (5-8 years) RPD must resist 4 degrees of freedom = x, y, z, rotation General categories of failure: Biologic = bone resorption; tooth mobility; tissue irritation (2) Physiologic = PDL overload; toth wear (3) Materials = materials defects; lab problems; adjustments Image source: Steve Bayne, University of Michigan, 2008

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THANK YOU My sir… with your preaching I am here and sharing the knowledge with the world of new dental doctors…