L12 : metal and alloys in dentistry

Question 1

what are casting alloys used for ?

Answer 1

restoration of missing teeth, onlays , crowns , fixed dental protheses and for removable partial dentures

Question 2

what are wrought alloys used for ?

Answer 2

to join metal parts together using high heat

Question 3

desirable quality of metals and alloys regarding porcelain bonding :

Answer 3

form a thin oxide layer

Question 4

what are the nobel metals

Answer 4

gold , palladium , platinum

Question 5

categories of noble metal alloys are classed based on ?

high noble casting alloy
noble alloy
predominantly base metal alloy

Answer 5

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)

Question 6

what are base metal alloys used for ?

Answer 6

full-cast and metal ceramic restorations as well as for removable partial denture frameworks

Question 7

describe the physical qualities of base metal alloys:

Answer 7

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

Question 8

Subclasses of base metal alloys :

Answer 8

1.) nichel chromium beryllium
(beryllium improves castability and promotes formation of stable metal oxide for porcelain bonding)
2.) nickel chromium
3.) cobalt -chromium

Question 9

which metals can cause allergic reactions oe even have carcinogenic effects ?

Answer 9

base metals ( beryllium and nickel)

Question 10

titanium melting point and rate of oxidation ?

Answer 10

both are high
1668C

ABOVE 900C

Question 11

WHERE DOES TITANIUM DERIVE ITS CORROSION PROTECTION FROM ?

Answer 11

a thin passivating oxide film which forms spontaneously

Question 12

what is the most bio-compatible metal in dentistry ?

Answer 12

titanium

Question 13

what is the most widely used titanium alloy in dentistry ?

Answer 13

Ti-6AI-4V

Question 14

Alloys that are mechanically worked after casting are called?

Answer 14

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

Question 15

example of wrought alloys ?

Answer 15

orthodontic wire
endodontic files

Question 16

which metal joining techniques join two metallic components with a filler metal along with a flux and a heat source ?

Answer 16

soldering and brazing

Question 17

what makes brazing and soldering different ?

Answer 17

brazing is conducted above 450C while soldering is conducted below 450C

Question 18

which metal joining technique doesn’t require a filler metal because the metal surfaces to be joined melt and fuse locally ?

Answer 18

welding

Question 19

what are solder fluxes ?

Answer 19

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