Indirect Ceramics Flashcards
What material is used in porcelain laminate veneers AND
Ceramic onlays/inlays
- Dental Porcelain
- Glass ceramics
What material for glass ceramic crowns and bridges
Glass ceramics: Lithium disilicate or Leucite
What material in a high strength core/veneer crown and bridges
Aluminium
Or Zircona
Veneer = dental porcelain
What material in a monolithic high strength crown and bridge
-Zirconia
What material in a PFM
precious or non precious alloy metal+ Dental porcelain
What do true porcelains contain
Kaolin
What is low fusing temperature dental porcelain used for?
Veneer
Why do we condense the dental porcelain in manufactre
To maximise packing factor
Eliminate shrinkage
What state is the porcelain in at the end of condensation
Green state
What is the purpose of opaque powder in the porcelain manufactre
To mask the discoloured core of tooth
After condensation, Porcelain is fired, but slowly why?
To drive off the excess water as quick steam can cause cracks
What is the bisque state
Where the initial porcelain has fused and holds its shape
What happens as the glass becomes molten of porcelain
Draws particles closer together, eliminating voids and eliminating porosity in material
Why do we need slow cooling after sintering
To avoid thermal residual stress as this can cause fracture
Why do we glaze porcelain
To get a smooth finish so biofilms cannot adhere easily
-To fill in porosity
Why do MCCs fail
Breakdown at the interface between metal and ceramic–> Chipping + Delamination
3 factors that lead to good MCC bond
- Mechanical retention( roughen surface of metal before bonding)
- Chemical bonding (Metal oxides bond with the Oxisdes in ceramic)
- metal has higher thermal coefficient of expansion than ceramic
Why do we need the metal to have a higher coefficient?
The metal cools down quicker and so this puts compressive stress in ceramic (as the ceramic restricts the metal shrinking)
Why is the compressive tension the ceramic put under good?
The compressive tension the ceramic is put under reinforces it and so we would need more energy for a crack to propogate within it
What metal alloy is good for long span bridge
Co-Cro or Ni-Cro
What did porcelain with 40% weight alumina crystals give?
Increased strength
-BUT decreased aesthetics and loss of translucnecy
-Lead to development of all ceramic crowns
What is high strength alumina/zirconia core
Core made of alumina/zirconia and then dental porcelain bonded to it.
How is alumina made that helps overcome shrinkage?
- Uses a die
- The restoration is made oversized
- When it is sintered, the shrinkage gives predicted shape
What is the strength of Zirconia influenced by?
Dominant phase (monoclinic, cubic etc)
What phase of zirconia has the largest volume?
Monoclinic
Post sintering, when there is cooling of Zirconia, what happens?
Transformation from tetragonal to monoclinic phase at around 670-1070 degrees
Why cant we use pure zirconia to sinter?
Because as there is phase transoformation, there is expansion by 3-4% in volume going from tetragonal to monoclinic and this can cause the structure to crack
What does the stabiliser help maintain
Tetragonal phase at oral temp
Why do we partially stabilise Zirconia?
We end up with cubic phase
What is cool about Y(TZP)
- as we heat the material (goes from monoclinic to tetragonal) there is shrinkage of 4% but as it cools the material expands (goes from tetragonal to monoclinic) and this chances by 3% so overall change of 1% and his closes cracks and increases toughness
