Ceramics

Question 1

Give some properties of conventional ceramics

Answer 1

Good aesthetics - colour stable and smooth

Chemically stable - inert

Biocompatible - inert

Thermal properties are good - similar thermal expansion to dentine

Dimensionally stable - very stable but 20% shrinkage during firing

Good mechanics - high compressive strength, hardness

Question 2

What are some poor properties of ceramics? What does this mean?

Answer 2

Static fatigue

Surface micro-cracks

Slow crack growth

Ceramics only used in low stress areas

Question 3

What is sintering?

Answer 3

Fusing of ceramic particles above a threshold temperature

Question 4

What zirconia is used in dentistry? Why? What des yttria do?

Answer 4

Yttria stabilised zirconia, As pure zirconia can crack on cooling

Yttria increased translucency

If a crack forms, yttria goes from tetragonal structure back to monoclinic structure (that of normal zirconia) and covers the gap

Question 5

Some drawbacks of the zirconia production procedure?

Answer 5

CAD/CAM is expensive, cheaper crowns once these bought though

Inert fitting surface so no etch or bond

Question 6

Which crown to use where?

Answer 6

Posterior teeth
- monolithic zirconia

Anterior teeth single crowns
- LiDiSi as very translucent so good aesthetics

Anterior bridge
- LiDiSi

Longer spanning bridges with heavier occlusion
- zirconia cored with zirconia where occlusal contacts meet

Question 7

Difference between decorative and dental ceramic

Answer 7

Decorative ceramic has higher percentage of

Kaolin

Dental ceramics have more

Feldspar and glass particles

Question 8

What are the optical properties of dental ceramics

Answer 8

Reflectance

Translucency

Opacity

Transparency

Opalescence

Opacity

Question 9

How can ceramic be modified to make it more retentive using silane?

Answer 9

Etch with hydrofluorid acid