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7 Cards in this Set
- Front
- Back
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Classification of commercial high Au alloys? Also provide Au percentages
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1. Soft (1,2 surface inlays) 80 - 90%
2. Medium (inlays, MODs, Crowns) 75 - 78% 3. Hard (Inlays, crowns, post n cores, short span bridges) 62 - 78% 4. Extra hard (Post n cores, thin crowns, long span bridges) 60 - 70% |
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Purposes of alloying elements
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Au - Tarnish resistance and with Cu gives hardness
Ag - lightens colour and some strengthening thru solution hardening Cu - Reduces melting temperature Pt and Pd - Increase strength and MP Zn - Scavenges for O2 during casting Other noble elements eg Indium - grain refinement |
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Desirable properties of dental casting alloy?
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1. biocompatible
2. corrosion resistant 3. tarnish resistant 4. non-allergenic 5. aesthetics 6. thermal properties 7. ease of melting 8. castability 9. bond to porcelain 10. economically viable |
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What are the desirable thermal properties of dental casting alloy?
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MP has to be higher than firing temp of prcelain
Metal must have a thermal expansion/contraction coeff similar to porcelain |
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How are metals classified in dentistry?
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Precious
Semiprecious Base metals |
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1 – How do we use metals in dentistry? Name some of the appliances that we can fabricate with them and explain how we categorise the metals used. [5]
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Metals have many uses in dentistry. They can be used in their pure form such as in Ti implants, or alloyed together for various purposes. Some appliances include RPD frameworks, crowns, inlays, onlays, post & cores, and bridges. Metals are categorised by rarity and cost which relates to their properties.
- Precious – high noble - Semiprecious – noble - Base metals Gold casting alloys can be also classified according to harden-ability - Non-hardenable – for inlays and some crowns - Hardenable - fore bridges and crowns under greater load |
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1 – How may dental casting alloys be generally classified? Give an example of an alloy in each classification and what it might be used for. [6]
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- Precious: Pd-Cu-Au-Pt used in bridges and crowns under load
- Semiprecious: Ag-Pd-Au-Cu used in bridges and crowns under lesser stress - Base metals: Cr-Co-Mo used in RPD frames, stainless steel wire, Ti implants Alloys containing gold can be further classified into hardenable (containing Cu) and non-hardenable (no Cu). Non-hardenable are used for inlays and some crowns, and hardenable is used for bridges crowns. Extra notes: Pt and Pd are used to increase the melting point and help create oxide layers for better bonding, Cu is for age hardening, Au is inert. |
