Dental Materials Ii

Front 1

1. What is a ceramic?

Back 1

Any product made essentially from a non-metallic inorganic material usually processes by firing at high temperature to achieve its final state or form

Front 2

2. What is a porcelain?

Back 2

A specific form of ceramics

A specific fange of ceramic materials made by mixing kaolin, quartz, and feldspar fired at a high temperature

Ceramics for metal-ceramic restorations are considered dental porcelains

Front 3

3. How can dental ceramics be classified?

Back 3

By...

1. Fusion temperature

2. Crystalline phase (degree of crystalline content)

3. Application

4. Fabrication technique

Front 4

4. Why did PFMs (porcelain-fused-to-metal) succeed?

Back 4

Succeeded by increasing the coefficient of thermal expansion of the veneering porcelain

This was done by mixing controlled amounts of high-expansion leucite w/ feldspar glass at the manufacturing stage

Front 5

5. How is the fusion temperature of a dental porcelain controlled?

Back 5

By the relative proportion of the three major ingredients:

Quarts
Feldspar
Clay (kaolin)

**termed triaxial composition

Front 6

6. How are medium and low fusing porcelains devised?

Back 6

By modifying the powders w/ chemicals of fluxes

**boron oxide/alkaline carbonates of low melting temperature

Front 7

7. What are the three major applications of dental ceramics?

Back 7

1. Ceramic materials for ceramo-metal crowns and fixed partial dentures (bridges)

2. All-ceramic crowns, inlays, onlays, and veneers

2. Ceramic denture teeth

Front 8

8. What are the fabrication techniques?

Back 8

1. Sintering
**ceramics fired to metals (where "stacked" or "pressed") are processed by sintering

2. Heat-presssing

3. Slip-cast

4. Machining

Front 9

9. What are the two distinct phases of dental ceramics?

What ceramics are an exception?

Back 9

1. Glassy or vitreous phase

2. Surrounded by a crystalline phase

**Except dense, polycrystalline ceramics like alumina or all-zirconia

Front 10

10. What does increasing the amount of glassy phase result in?

Back 10

1. Lowers resistance to crack propagation

2. Increased translucency (improved esthetics)

Front 11

11. What amount of crystalline phase do all-ceramic restorations have?

What does this cause?

Back 11

Between 35% to 99%

Better mechanical properties

Front 12

12. What are the two layers of ceramic which are applied and baked to ceramic-metal restorations?

Back 12

First layer in the opaque layer which is rich in opacify-oxides

**also provides the direct bond to the metal surface

Next porcelain layers applied after the opaque layers are the dentin and enamel (most translucent) layers

Front 13

13. What happens after building-up ("stacking") and modeling the porcelain powders?

What is added to noble-metal PFM alloys and why?

Back 13

Ceramo-metal crown is sintered in an oven (Bisque or Biscuit bake)

Tin and indium to enhance the formation of the metal oxide layer for porcelain-metal bonding

Front 14

14. What is the main ingredient of classical, high-fusing dental porcelains?

What is this?

What does it melt at and form?

Back 14

Feldspar

Chemically defined as potassium aluminum silicate

1150 C forming leucite and molten glass

Front 15

15. What are other added components to classical, high-fusing dental porcelains?

Back 15

Various forms of silicon oxide and alumina/hydrated alumina

and

alkali and alkaline earth carbonates as ceramic fluxes

Front 16

16. How is the mix of leucite and the glassy in a molten form cooled?

What is a frit?

What provides the fluorescence in dental porcelains?

Back 16

Quenched in water very rapidly

The scattered fragments that result are called a frit

Provided by the addition of lanthanide oxides (such as cerium oxide)

Front 17

17. What is the crystalline structure of leucite (a potassium alumino silicate)?

What are used as opacifers in dental porcelains?

What controls the CTE of the porcelain?

Back 17

Tetragonal

Tin oxides
Titanium oxides
Zirconium oxides

Amount of leucite present due to its high coefficient of thermal expansion

Front 18

18. Why must all sharp angles on the metal framework by avoided?

What is done after careful cleaning of the metal framework and heat treatment for metal oxide formation?

Back 18

Avoid stress concentrations and wedge effects in the fired porcelain

**this would ultimately lead to crack initiation and propagation

A thin layer of opaque porcelain is applied and baked

Front 19

19. How is the dental porcelain powder mixed?

What is it applied over?

What is critical to minimize porcelain shrinkage and optimize strength?

Back 19

With a modeling solution to a creamy consistency

Over the opaque layer

Proper condensation of the dentin and enamel porcelain powders

Front 20

20. What are three techniques for porcelain condensation?

What is done after application and condensation?

Why is this step critical?

Back 20

1. Vibration method
2. Spaluation
3. Brush tenchnique

Restoration is placed in an open preheated porcelain furnace to be dried

This step is critical to remove any excess water from the porcelain mix in a controlled (not too rapid) fashion

Front 21

21. What are two firing/sintering methods?

What is sintering?

Why are a minimum of three firing operations needed in the fabrication of a ceramo-metal restoration?

Back 21

1. Temperature control
2. Temperature and time control

Process in which the porcelain particles undergo fusion to form a continuous mass of higher density (densification)

One for the opaque portion
One for the dentin and enamel portion
One for the stain and glaze

Front 22

22. Why is it necessary to oversize the porcelain build-up?

What is the biscuit or bisque bake?

Back 22

Compensate for volume shrinkage which can range from 28% to 37% for various types of low and high fusing porcelain

Initial firing of the dentin and enamel portions (second firing)

Front 23

23. At what temperature is the biscuit bake done at?

What occurs during this firing?

Back 23

Temperature 56 degrees C below the fusing temp of the porcelain being used

Virtually all of the shirnkage

Front 24

24. After the biscake firing what is done?

What happens when the glazing temperature is reached?

Why is slow cooling of porcelain critical?

Back 24

The porcelain is cleaned, any stains are applied, and short glaze firing is done

A thin glassy film (glaze) is formed by viscous flow on the porcelain surfaces

Prevents surface crazing or cracking (thermal shock)

Front 25

25. What are the two types of sintered all-ceramic materials?

What can sintered feldpathic porcelain (w/ up to 45% leucite) be used for?

What type of phase is the leucite?

Back 25

1. Alumina based ceramics
2. Leucite reinforced ceramics

All ceramic restorations

Reinforcing phase - provides higher flexural and compressive strength

Front 26

26. How does leucite toughen the porcelian?

What does leucite also contribute to?

Back 26

Internal tangential stresses in the glass around the leucite crystals act as crack defectors

Ability to be etched w/ HF acid and be bonded to tooth structure

Front 27

27. How are contemporary leucite reinforced all ceramic materials heat pressed?

What is this technique used to produce?

What does heat pressing do?

Back 27

Via high temperature injection molding

Used to produce all ceramic crowns, inlays, onlays, and anterior veneers

Reduces large pores and promotes good dispersion of the crystalline phase in the glassy structure

Front 28

28. What are the two techniques for the leucite based, hot pressed ceramic systems?

Back 28

1. Bulk injection to a complete tooth form w/ surface staining

2. Injection of a core or partial tooth form w/ porcelain layering to complete the restoration

Front 29

29. What does the newer form of heat pressed all ceramics contain?

Back 29

Contain lithium disilicate as a major crystalline phase

Lithium disilicate materials are heat pressed at a lower temperature of 890 to 920 degrees C

**use similar equipment as the leucite heat pressed materials

Front 30

30. How are ceramics?

What are ceramics two basic populations of flaws?

Back 30

Brittle

Fabrication defects and surface cracks

**the fracture mechanisms involve crack propagation from these flaws

Front 31

31. In a slip cast all-ceramic material why is alumina partially sintered on a refractory die?

What happens next?

How is the molten glass drawn into the pores of the core material?

Back 31

Produce a porous sub-structure

The fired, partially-sintered porous core material is then infiltrated w/ a molten glass

By capillary action leading to a reinforces, higher toughness ceramic material

Front 32

32. What is the flexure strength of these materials?

What is an example?

Other than alumina what can the core material be?

Back 32

400-500 MPa

In-ceram

Zirconia or a spinel (magensium spinel)

Front 33

33. How is a machinable all ceramic material made?

Back 33

Use a conventional or intra-oral digital impressions

Digital model can be created and a restoration or framework milled to fit that digital mode

Front 34

34. How can milling blocks be made?

Back 34

1. From potassium feldspar in a glassy matrix

2. Lithium disillicate in a glassy matrix

3. Pre-sintered alumina slip-cast blocks

4. Aluminum oxide powder compressed and sintered on an enlarged die (procera)

5. Yttrium-stabilized, tetragonia polycrystalline zirconia blocks (i.e. Cercon, Lava)

Front 35

35. What are some toughening methods of dental crowns?

Back 35

1. Intrinsic methods of toughening dental ceramics
-crystalline reinforcement
-transformation toughening

2. Extrinsic methods of toughening dental ceramics

Front 36

36. In what material does transformation toughening occur?

What occurs?

What else is this called?

What is this accompanied by?

Back 36

Occurs in zirconia

Under stress, the transformation from the metastable tetragonal phase to the stable monoclinic phase

Also called stress-induced

Accompanied by volume increase leading to the closing of cracks in the transformed zone

Front 37

37. How can glazing of the final ceramic restoration occur?

Back 37

Through both a self-glazing process as well as through the application of a low expansion glass material glaze applied at the surface of the final restoration and fired at a high temperature

Front 38

38. What does this glazing layer do?

Back 38

Places the surface in compression on cooling (slight surface strengthening effect)

**Also reduces the depth and width of surface flaws, thus increasing the resistance to crack propagation