FIXED PROS - Materials for Crowns and Bridgework Flashcards
what should the choice of materials ensure with the patient? (4)
- cosmetic expectation
- no excessive removal of sound tissue
- there is no adverse contact with tissue
- meet the relevant standards
what requirements should the material meet? (6)
- accurate fit
- strong to resist occlusal force
- similar thermal expansion as the tooth
- should not attract plaque
- biocompatible
- be rigid to avoid bending
what options are there for crown and bridge materials?
metal
ceramics
metal-ceramics - porcelain+metal
indirect dental composite
what are the two types of metal alloys used?
precious alloys - gold and palladium alloys
non-precious alloys - base metal alloys - nickel and titanium
how do you decide what material to use? (7)
- cost
- corrosion resistance
- strength
- hardeness
- stiffness
- ductility - deform
- location
describe a gold crown from LDI
1 star
medium-gold casting alloy - gold, silver, platinum.
yellow
extra-hard
why is Gold used as an alloy? (4)
tarnish-free
corrosion resistant
adds good malleability to an alloy
increases density
why is Copper used as an alloy? (2)
strengthener
enhances the colour with reddish colour
why is Silver used as an alloy? (3)
- balance reddening from copper
- adds greenish colour
- controls strength and hardness
why may you not use pure gold?
too soft, costs
what is the common alloy used?
Ag-Au-Cu
gold, silver, copper
what if there isn’t enough gold?
density is reduced
what if there is too much palladium or silver?
they absorb oxygen when molten = porous castings
why may base metal alloys be preferred to use over precious alloys? give one con in comparison.
have higher modulus elasticity = more rigid and stiff
- need careful controlled casting conditions, hinders the biocompatibility
define material biocompatibility.
the ability of a material to perform with an appropriate host response in a specific application
what is the biggest downside of having high levels of NICKEL? and one other side effect lol.
its carcinogenic
- well known to cause contact dermatitis
the fumes from grinding and casting alloys can lead to? (3)
conjunctivitis
dermatitis
bronchitis
why may you use porcelain fused to metal?
have the benefits of metal and aesthetic benefits of ceramic
what is the success rate of porcelain fused to metal materials?
95-97% over 7 years
does porcelain bond better to non precious metals, or precious metals?
precious metals
in PFM (porcelain fused to metal) alloys, Indium is a metal which also may be used, why?
it strengthens and hardens gold and palladium
- by raising the thermal expansion
- lowering the melting range
- contributes to bonding oxide
what are gold alloys called? and what are the PFM alloy called?
gold alloy - 1 star casting alloy
PFM - V-Delta SF Alloy
which has higher density? the gold alloy or PFM?
PFM - V-Delta SF Alloy
which has higher melting range? the gold alloy or PFM?
PFM - V-Delta SF Alloy
= 1180-1300
gold = 840-875
