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
how do you achieve a good bond between metal and ceramic? (3)
- mechanical retention - roughen the metal
- direct chemical bond - add Indium
- mismatch the coefficient of thermal expansion - metal higher then ceramic = creates a compressive stress
why may PFM alloys not be ideal? (4)
- absence of light transmission - light doesnt pass through metal
- reduced depth of translucency
- so grey line at gingival margin
- can have sensitivity or allergies
what can be the downside of non-precious metal alloys?
discolouration over time
for aesthetics, what is the gold standard?
all ceramic material and no metal
what property do ceramic materials posses?
brittleness - need to be very careful
breaking point is 0.1% of strain
- they dont bend, they break
what is the Griffith Equation?
the failure stress = fracture toughness/flaw size
using the Griffith Equation, how may you increase the fracture toughness?
increase the failure stress
reduce the flaw size
why is it better to use ceramic rather than glass?
more resistant to cracks leading to complete failure due to crystalline domains
what is Alumina Porcelain?
porcelain containing up to 50% fused alumina crystals
what is the benefit of adding alumina crystals to porcelain?
it acts as a crack stopper
adding strength
what is the con of alumina porcelain?
it is opaque, need to build on more translucent shades
what are glass ceramics?
fine grained polycrystalline materials obtained from a glass phase following a heat treatment
pro of glass ceramic.
large number of fine crystals
= limit the development of flaws
what is an example of a glass silicate? what is it made of?
IPS E.Max
- 60% Lithium Disilicate
- Lithium Orthophosphate
layering material = fluoroapatite
what are the 2 production routes in making glass ceramic materials?
- grind into fine power, melt, cast into mould
- crystallise, brings the tooth shapes
what are the uses for glass ceramics?
veneers
inlays
onlays
posterior and anterior crown
what ceramic has the best aesthetic?
glass
instead of alumina, what can you use? why and how?
zirconia
- strong due to transformation toughening
what is the property of zirconia when heating above 1000 degrees?
goes from monoclinic to tetragonal
- opposite way when cooling down
what does adding magnesium to Zirconia do? aka transformation toughening explained.
- retains the tetragonal structure at low temps
- energy from cracks is converted into converting tetragonal into monoclinic crystals
= compressive forces = oppose tensile forces causing crack
= suppresses crack propagation
in order, what’s the order of toughness for ceramics?
- porcelain
- glass ceramic
- glass ceramic with alumina
- zirconia high-tech
