L12 : metal and alloys in dentistry Flashcards
what are casting alloys used for ?
restoration of missing teeth, onlays , crowns , fixed dental protheses and for removable partial dentures
what are wrought alloys used for ?
to join metal parts together using high heat
desirable quality of metals and alloys regarding porcelain bonding :
form a thin oxide layer
what are the nobel metals
gold , palladium , platinum
categories of noble metal alloys are classed based on ?
high noble casting alloy
noble alloy
predominantly base metal alloy
high noble casting alloy :
> 40% gold and >60% noble metal
noble alloy:
>25%noble metal
predominantly base metal alloy :
<25% noble metal ( most contain no noble metal at all)
what are base metal alloys used for ?
full-cast and metal ceramic restorations as well as for removable partial denture frameworks
describe the physical qualities of base metal alloys:
they are much harder , stronger and have twice the elastic modulus as the high noble metal alloys . they also have good corrosion resistance
-more difficult to cast
-greater casting shrinkage (2.3%)
-lesh burnishable and more difficult to finish and polish
-more corrosion in acidic conditions
Subclasses of base metal alloys :
1.) nichel chromium beryllium
(beryllium improves castability and promotes formation of stable metal oxide for porcelain bonding)
2.) nickel chromium
3.) cobalt -chromium
which metals can cause allergic reactions oe even have carcinogenic effects ?
base metals ( beryllium and nickel)
titanium melting point and rate of oxidation ?
both are high
1668C
ABOVE 900C
WHERE DOES TITANIUM DERIVE ITS CORROSION PROTECTION FROM ?
a thin passivating oxide film which forms spontaneously
what is the most bio-compatible metal in dentistry ?
titanium
what is the most widely used titanium alloy in dentistry ?
Ti-6AI-4V
Alloys that are mechanically worked after casting are called?
wrought alloys , once casted , an alloy can be shaped into another form by mechanical force and high yield strength and hardness compared to cast alloys
example of wrought alloys ?
orthodontic wire
endodontic files
which metal joining techniques join two metallic components with a filler metal along with a flux and a heat source ?
soldering and brazing
what makes brazing and soldering different ?
brazing is conducted above 450C while soldering is conducted below 450C
which metal joining technique doesn’t require a filler metal because the metal surfaces to be joined melt and fuse locally ?
welding
what are solder fluxes ?
special metals used to join metals
a solder flux must melt before the alloy and must flow freely and wet the soldering alloy
has a risk of corrosion
they come in pastes , powders , or liquids
