dental ceramics 2

Question 1

what is bonding porcelain to metal like?

Answer 1

Strong bond between the porcelain and alloy is essential

Thermal compatibility between the two materials is a requirement. Otherwise, unfavorable stress distribution during cooling will cause crack formation

Bonding can be mechanical and chemical

If fracture occurs, the path can occur:
Through the interaction zone
Along the interface between the porcelain and the interaction
zone, or
Along the interface between the metal and the interface zone

Question 2

what is bonding porcelain to metal using electrodeposited substrates?

Answer 2

Electrodeposition of a thin gold layer on the metal followed by a tin layer

Improves the wetting of the porcelain onto the metal

Reduces the porosity at the porcelain-metal interface

Inhibits excessive diffusion of metal into the porcelain during firing

Yields a light color of oxide film to the porcelain, thus eliminates the use of opacifiers

Question 3

what are the advantages of metal-ceramics over pure cermic prostheses?

Answer 3

Stronger

Resistant to fracture

Superior aesthetics

Less tooth structure needs to be removed to provide the proper bulk for the crown (WON’T BE ASKED THIS POINT ON THE EXAM because people say different things)

Question 4

how are pressable glass-ceramics made?

Answer 4

Produced by pressure molding

Formed into the desired shape as a glass

Heat treated to form a crystalline phase

Crystalline phase obstructs the propagation of cracks under oral stresses. Thus the material is stronger and tougher

Smaller the grain size the more resistant to fatigue, this is how the crystalline phase is.

Question 5

what are stress raisers in ceramic prostheses?

Answer 5

Stress raisers are discontinuities in the structure that cause stress concentration

Surface defects are stress concentration areas

Abrupt changes in shape or thickness can act as stress raisers

Question 6

THIS WILL BE ON FINAL

How do you improve the fracture resistance of ceramic prostheses?

Answer 6

1. Select stronger and tougher ceramics
2. Develop surface residual compressive stresses by thermal tempering
3. Develop residual compressive stress within interfacial regions by matching expansion coefficients
4. Reduce tensile stress by selecting stiffer support
5. Minimizing firing cycles
6. Design broader radii of curvature
7. Adhesively bond ceramic crowns to tooth structure

Zirconia is the strong and tough ceramic
Allumina is another one, titanium oxide is another one.
Silica is another one. Porcelain is another one.

You don’t want to heat and cool too much (I.e. minimize firing cycles)

Question 7

what is the abrasiveness of dental ceramics?

Answer 7

1. Adhesion mechanism (metals and comopsites): Localized bonding of two surfaces occur, resulting in pullout and transfer of matter from one surface to the other

Example of adhesion is a joint with metal and is cupped by high molecular weight polyethylene, the metal as it rubs, the polymer adheres to it.

2. Microfracture (ceramics and enamel): Results from gouging, asperities, impact, and contact stresses that cause cracks or localized fracture

Question 8

how do you reduce the abrasiveness of ceramics?

Answer 8

polishing and glazing