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Good morning. Prof. Dr. Manal A. El Ebiary Dental Bio- Materials Department Faculty of Dentistry Tanta & MUST Universities. How do you contact with me?. manalahmed727@yahoo.com. Dental Casting Alloys. Definition Construction of indirect metallic restoration

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  1. Good morning

  2. Prof. Dr. Manal A. El Ebiary Dental Bio- Materials Department Faculty of Dentistry Tanta & MUST Universities

  3. How do you contact with me? manalahmed727@yahoo.com Assoc. Prof. Manal El-Ebiary Gold & Gold Alloys

  4. Dental Casting Alloys Definition Construction of indirect metallic restoration e.g. inlays, onlays, crowns, bridges, endodontic post and core, and removable partial denture

  5. Desirable Properties of Dental Casting Alloys Assoc. Prof. Manal El-Ebiary Gold & Gold Alloys

  6. General Ideal Requirements Functional requirements Working requirements

  7. Functional Requirements • Stiffness • It is the resistance to elastic deformation Metals • can be constructed in thin section. • Equal stress distribution

  8. Resilience • It is the ability to absorb energy without plastic deformation • Then the stress not transmitted to the under lying supporting tissue • High yield stress High yield stress is required to resist permanent deformation under the masticatory stresses in the mouth.

  9. Fatigue Resistance High to resist cyclic loading. • High ductility Allows for burnishing of restorations • High sag resistance ability of the alloy to resist plastic flow at high temperature, useful during soldering. • High tarnish and corrosion resistance

  10. Compatibility with porcelain

  11. Compatibility with porcelain • The melting temp. of metal should be higher than the firing temp. of porcelain to have high sag resistance • The coefficient of thermal expansion and contraction should be slightly higher than that of porcelain to obtain compressive bond

  12. The metal should have high modulus of elasticity ( rigidity= stiffness) and strength to avoid cracking of porcelain • Not produce discoloration of porcelain

  13. B) Working Requirements: 1- Ease of casting 2- Ease of soldering 3- Ease of burnishability

  14. Classification of Dental Casting Alloys Noble metals Base metals

  15. Gold and Alloys of Noble Metals Assoc. Prof. Manal El-Ebiary Gold & Gold Alloys

  16. Gold Restorations Indirect Direct Pure Gold Foil Gold Alloys

  17. Noble metals and their effect on properties: 1)Gold: • a high noble resists tarnish and corrosion. • It has low strength, hardness • high ductility • Melting temp 1063 C • Specific gravity =19.3

  18. 2) Platinum: • a noble metal • It increases strength and hardness of goldalloy • Tough • Ductile • Melting temp. 1755 C • Specific gravity = 21.37 which increase weight

  19. 3) Palladium: • cheaper than platinum • used as a replacement for platinum. • Specific gravity 11.4 • Malleable and ductile • Palladium as low as 5% have a pronounced effect on:- • Whitening the color of gold alloy, • Decreases the greening effect of silver • Decreases the red color of copper. • Preventing corrosion of silver in the oral cavity.

  20. 4) Silver: • Malleable and ductile • strong and harder than gold • Whitest than any other metals • Melting temp . 960 C • Specific gravity 10.4 • Pure silver occludes oxygen in the molten alloy & causes small pits, porosity and rough casting surface develop. • This tendency is reduced when 5 to 10% Cu is added to Ag.

  21. 5) Irridium, Ruthenium, and Rhodium: iridium is more commonly used in dentistry thanRuthenium, and Rhodium, all have the same effect; As little as 0.005% is effective inrefiningthe grain size of gold alloy.

  22. B) Base metals: • Copper: • malleable and ductile metal • red color • High strength and hardness • Melting temp. 1083 C • It is an important factor in heat treatment. .

  23. 2) Zinc: • acts as a scavenger (deoxidizing agent) during melting and casting • Improve castability and fluidity 3) Indium • soft and grey metal with • low melting points (156 C) • used in some gold alloys as replacement of zinc. • Produce oxides in porcelain alloys, which help bonding with porcelain

  24. 4) Tin • White metal • Melting temp. 232 C • Produce oxide layer which help bonding with porcelain • Combine with platinum and palladium producing hardening effect

  25. 5- Iron • Added in very small ration (1%) in order to precipitated hardening

  26. Classification of gold alloys

  27. White yellow

  28. 1- According to gold content

  29. Carat • indicates the parts of pure gold in 24 parts of alloy. • Thus 24 carat indicate pure gold • 12 carat indicate 50% gold. • !8 carat gold = 18 parts of pure gold + 6 parts of other metals

  30. Fineness • Is the parts of pure gold in 1000 parts of alloy • 1000 fine = pure gold • 750 fine = 750 parts pure gold + 250 parts other metals

  31. 2- According to mechanical properties

  32. Assoc. Prof. Manal El-Ebiary Gold & Gold Alloys

  33. Traditional casting gold alloys Type 1:- Low strength – for castings subject to very slight stress, e.g. inlays. Type 2 :- Medium strength – for castings subject to moderate stress, e.g., inlays and onlays. Type 3 :- High strength – for castings subject to high stress, e.g. full crowns . Type 4:- Extra high strength – for castings subject to very high stress and thin in cross section, e.g. crowns, bridges and partial denture frameworks.

  34. 3- According to alloy description

  35. By Color A- White gold alloy: Predominantly gold in composition but are whitened with platinum , palladium and silver B- Yellow gold alloys:- High gold and copper ratio with decrease in platinum , palladium and silver

  36. By price • The noble metals in gold alloy should be not less than 75% • As the price of gold increase the % of gold can decrease to 55% • The reduction of gold % should be replace by palladium & silver

  37. Silver & copper & palladium are very critical • Tarnish of silver occur in oral cavity then 1% palladium is required for every 3% silver to control tarnish • The ratio of silver & copper should be carefully balanced to avoid tarnish

  38. Heat treatment Assoc. Prof. Manal El-Ebiary Gold & Gold Alloys

  39. The typeIII(hard) and type IV (extra hard) casting gold alloys can be further hardened by heat treatments. There must be at least 11% copper in the gold alloys for heat treatment. Hardening heat treatments are not beneficial for the types I and II alloys because they contain insufficient quantities of copper and silver

  40. Soft heat treatment ( solution heat treatment) 10 minutes at 700 °C quenched rapidly in water. All intermediate phases in the alloy are changed to a disordered solid solution at 700 °C, and the rapid quenching prevents ordering from occurring during cooling. • Decrease strength • Decrease hardness • Increase ductility

  41. Hard heat treatment (age hardening) the temperature of the furnace is set between 200 °C and 450 °C and the casting is heated for 15 to 30 minutes before it is quenched in water.During this long period of time the lattice structure arranged in ordered solid solution • Increase strength • Increase hardness • Decrease ductility

  42. Thank you

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