Metals Flashcards
What are the noble metals?
Gold, rhodium, iridium, platinum, palladium, osmium, ruthenium
Sometimes silver, but it can corrode intraorally
What are the types of gold alloys?
- Low, 80 Mpa, inlays
- Medium, 180 Mpa, inlays and onlays
- Hard, 270 Mpa, onlay, crowns, pontics
- Extra hard, 360 MPa, crown, bridge, bars, RPD frameworks
Define elastic modulus
Proportional constant between stress and strain during elastic deformation
Yield Strength
Proportional limit
Elastic limit
Amount of stress needed to cause 0.2% plastic deformation
Elastic stress above which the linear relationship between stress and strain no longer exist on the stress-strain plot
Greatest stress to which the alloy can be subjected, such that it will return to its original dimension when force is removed.
What does platinum do for alloys?
Increase hardness, elasticity, melting temperature
Copper?
Silver?
Copper: Renders alloy heat treatable
Silver: Neutralizes red color of copper and makes palladium alloys white
Palladium
Zinc
Indium
Hard, Good tarnish/corrosion resistance
Oxygen scavenger
Acts like Zinc and promotes gold color
Iridium
Rhodium
Ruthenium
All are grain refiner (improves yield strength due to smaller grains)
Rhodium - Soft
Ruthenium - Hard
Four ways that porcelain bonds to metal?
- Mechanical bonding (roughness)
- Chemical (covalent bonding)
- Compression (due to metal having slightly greater CTE)
- Van der waals
2007 Revised ADA Classification of Pros Alloys
High noble alloys: 60% required noble content, 40% required gold content
Noble: 25% required noble
Base metal: Less than 25% noble metal
What is a grain refiner?
They do not melt during the casting of the alloy and serve as nucleating centers for the melt as it cools, resulting in a fine grained alloy
