lecture 9 (copy)

What are the key properties of metals in their solid state?

• Aggregate state

• Solid state properties

• Crystallization

• Solid state crystals

• Melting point and melting range

• Diffusion

  • Processes related to diffusion:

    1. Annealing

    2. Recrystallisation

zirconia 3/4/5 - what is each type

what is their primary usage? (each of them)

secondary usage of zirconia 3?

contraindications of each - (reasons no to have this treatment)

How is an alloy defined?

• When two or more metals form a solution in the liquid state where their atoms mix randomly.

• The type of mixing of the atoms in the solid state determines the presence of a solid solution or mechanical mixture.

• When two elements are mixed, the alloy is defined as a binary alloy.

• Alloys are named by ordering the elements of which they are composed according to their percentage ratio.

How are alloys classified based on noble metal content?

• High noble metal content: At least 40% gold and 60% noble metals.

• Noble alloys: Contain more than 25% precious metals.

• Non-noble alloys: Contain less than 25% noble metals.

What are the four types of alloys based on mechanical properties?

• Type 1 alloys: Soft, used for restorations subjected to low loads (e.g., inlays).

• Type 2 alloys: Medium-hard, used for restorations that handle higher loads (e.g., onlays, overlays, crowns).

• Type 3 alloys: Hard, used for restorations enduring greater loads (e.g., crowns, bridges up to three units).

• Type 4 alloys: Extremely hard or rigid, used for restorations facing high masticatory loads (e.g., multi-unit bridges, partial dentures).

What are the classifications of alloys based on their use?

• Alloys for all-metal restorations:

  • Used when restoration requires full-metal composition.

  • Chosen for strength and durability.

• Alloys for metal-ceramic restorations:

  • Designed for use with both metal and ceramic materials.

  • Metal provides strength, ceramic offers aesthetic appeal.

• Alloys for partial denture substructures:

  • Used for the framework supporting artificial teeth.

  • Selected for strength and compatibility with the oral environment.

noble alloys - gold, platinum, palladium, iridium and silver melting point

their relative density?

their colour?

properties?

strength/hardness?

purpose?

What is the carat scale and how does it express gold content in an alloy?

• Carat scale: Expresses the relative amount of gold in an alloy.

  • Examples:

    • 24 carat: pure gold

    • 21 carat: 21 parts gold and 3 parts other metals

    • 12 carat: 50% gold

    • 18 carat: 75% gold

conversion from carat to fineness and vice versa

What is the fineness of gold and how is it represented?

• Fineness: Represents the percentage of gold content multiplied by a factor of 10.

  • Example:

    • 18 carat gold is 75% pure gold, so its fineness is 750.

• Usage:

  • Carat scale: specifies gold content.

  • Fineness: used with dental gold solders (carat scale not used in dentistry).

How are gold alloys classified based on hardness?

How are gold alloys classified based on color?

• yellow gold alloys: Contain insufficient palladium to hide gold color.

• White gold alloys: Palladium content above 5%, turning the alloy white; gold remains the main ingredient.

soft, medium hard, hard, extremely hard composostion of gold, silver, copper etc

What are the characteristics of pale gold or economic gold alloys?

• Gold content: 42-58% - cheaper

• Gold replacement: Usually replaced by silver.

• Silver-palladium ratio: 3:1 to reduce alloy corrosion.

• Mechanical properties: Comparable to Type 3 and 4 gold alloys.

What are the features of precious alloys with minimal or no gold content?

• Cost: Cheaper than gold alloys.

• Density: Lower, making casting process more difficult.

• Silver-palladium alloys: More silver than palladium, 10-15% or no gold, mechanical properties similar to Type 3 and 4 gold alloys.

• Palladium-silver alloys: More palladium than silver, 60-80%, some with no gold.

gold copper alloy