week 4: Gold Alloys Flashcards
Why are metals electrically conductive
The e- don’t bond to a specific atom, but float freely around in the metal
What is a dislocation
a defect in the attic structure in which few ions in a layer are missing
what characteristics about grains control the mechanical properties of a metal
Grain size and shape
How does Grain boundaries impact the slipping or dislocation of a crystal lattice
They stop the progression of dislocations
Describe the impact of a high concentration of grain boundaries will have on the metals physical properties
increase the hardness
increase the yield strength
increase stiffness
increase brittleness (less Ductile)
How will heat and rapid cooling impact the grain boundaries produced in metals
Heat will increase the size, but decrease the number of grain boundaries
Rapid cooling will increase the # but decrease the size of boundaries.
Provide an example of a noble and base metal
Noble: gold, palladium, platinum
Base: titanium, nickle, copper, silver, zinc
What are the advantages and disadvantages of pure gold
Advantages
- Corrosion resistant
- No cement needed
Disadvantages
- Low rigidity and elastic limit
- High cost
Indications for pure gold
Class 1 Restoration in (low) occlusal load
Sandwich gold-titanium foils are used for class 2 restorations
What are the 6 Alloy metals/ combinations that are added with gold
- Copper/silver
- zinc
- iron
- indium
- Nickel and cobalt
What are the benefits/reasons they are alloyed with gold (everyone take one)
Copper/silver: Hardens and strengthens noble metals
Zinc: low melting point so hardness gold base and prevents oxidation during casting
iron: enhances bonding between ceramic and gold alloys
Indium: encourages small grains
Nickle & Cobalt: used in low cast alloys
what is the minimum gold percentage needed for an alloy.
75%
What is the risks associated, if any, with the previous alloy metals
Nickle can cause allergic reactions
What are Type 1 Gold Castings used for
Inlays
low stress bearing rests with lots of supportive tooth structure.
What are Type 2 Gold Castings used for
Inlays or inlays
moderate stress bearing restos
Most common inlay gold material
What are Type 3 Gold Castings used for
Inlays, poetics, crown, saddles
high stress bearing restos
What are Type 4 Gold Castings used for
saddle, crown, bridge, clasps
very high stress bearing restos
partial denture framework
Describe palladium
excellent corrosion resistance,
Higher melting point than gold
harder then gold
Describe platinum
higher melting point then palladium
poor mixing capability with gold
high cost
what are the 5 important properties of casting metals
Solidus(setting temp)
Liquidus(melting temp)
density
yield strength
hardness
Describe Solidus, liquids, density and yield strength
solidus: important in soldering metal elements and porcelain+metals
liquidus: important in casting procedure
Density: Amount of mass in volume G/mm3
- higher the density the better casting
- noble metals >base metals
yield strengthmaximum stress applied with no plastic deformation
- Base metals>noble metals
Hardness: 125-380 kg/mm3
-enamel = 343kg/mm3
what is the highest corrosive alloy combination and its allergy rates
nickle+beryllium
8-15%
what are wrought alloys and give an example used in dentistry
mechanically shaped after the metal is made into a block (endo files, orthodoxy wires, prosto wires)
Describe the reaction involved with ceramic and metal bonding
Cemical reaction that occurs due to formation of an oxide layer
