Indirect Ceramics

Question 1

What material is used in porcelain laminate veneers AND

Ceramic onlays/inlays

Answer 1

• Dental Porcelain

- Glass ceramics

Question 2

What material for glass ceramic crowns and bridges

Answer 2

Glass ceramics: Lithium disilicate or Leucite

Question 3

What material in a high strength core/veneer crown and bridges

Answer 3

Aluminium
Or Zircona

Veneer = dental porcelain

Question 4

What material in a monolithic high strength crown and bridge

Answer 4

-Zirconia

Question 5

What material in a PFM

Answer 5

precious or non precious alloy metal+ Dental porcelain

Question 6

What do true porcelains contain

Answer 6

Kaolin

Question 7

What is low fusing temperature dental porcelain used for?

Answer 7

Veneer

Question 8

Why do we condense the dental porcelain in manufactre

Answer 8

To maximise packing factor

Eliminate shrinkage

Question 9

What state is the porcelain in at the end of condensation

Answer 9

Green state

Question 10

What is the purpose of opaque powder in the porcelain manufactre

Answer 10

To mask the discoloured core of tooth

Question 11

After condensation, Porcelain is fired, but slowly why?

Answer 11

To drive off the excess water as quick steam can cause cracks

Question 12

What is the bisque state

Answer 12

Where the initial porcelain has fused and holds its shape

Question 13

What happens as the glass becomes molten of porcelain

Answer 13

Draws particles closer together, eliminating voids and eliminating porosity in material

Question 14

Why do we need slow cooling after sintering

Answer 14

To avoid thermal residual stress as this can cause fracture

Question 15

Why do we glaze porcelain

Answer 15

To get a smooth finish so biofilms cannot adhere easily

-To fill in porosity

Question 16

Why do MCCs fail

Answer 16

Breakdown at the interface between metal and ceramic–> Chipping + Delamination

Question 17

3 factors that lead to good MCC bond

Answer 17

• 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

Question 18

Why do we need the metal to have a higher coefficient?

Answer 18

The metal cools down quicker and so this puts compressive stress in ceramic (as the ceramic restricts the metal shrinking)

Question 19

Why is the compressive tension the ceramic put under good?

Answer 19

The compressive tension the ceramic is put under reinforces it and so we would need more energy for a crack to propogate within it

Question 20

What metal alloy is good for long span bridge

Answer 20

Co-Cro or Ni-Cro

Question 21

What did porcelain with 40% weight alumina crystals give?

Answer 21

Increased strength
-BUT decreased aesthetics and loss of translucnecy

-Lead to development of all ceramic crowns

Question 22

What is high strength alumina/zirconia core

Answer 22

Core made of alumina/zirconia and then dental porcelain bonded to it.

Question 23

How is alumina made that helps overcome shrinkage?

Answer 23

• Uses a die
• The restoration is made oversized
• When it is sintered, the shrinkage gives predicted shape

Question 24

What is the strength of Zirconia influenced by?

Answer 24

Dominant phase (monoclinic, cubic etc)

Question 25

What phase of zirconia has the largest volume?

Answer 25

Monoclinic

Question 26

Post sintering, when there is cooling of Zirconia, what happens?

Answer 26

Transformation from tetragonal to monoclinic phase at around 670-1070 degrees

Question 27

Why cant we use pure zirconia to sinter?

Answer 27

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

Question 28

What does the stabiliser help maintain

Answer 28

Tetragonal phase at oral temp

Question 29

Why do we partially stabilise Zirconia?

Answer 29

We end up with cubic phase

Question 30

What is cool about Y(TZP)

Answer 30

• 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