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AU14 Fixed Restorative III > All-Ceramics II > Flashcards

All-Ceramics II Flashcards

1
Q

The actual strength of a ceramic is always what

A

lower than its theoretical strength

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2
Q

What is the differences of the theoretical strength and the actual strength of ceramics

A

theoretical strength = 7000MPa

actual strength = 35-50MPa

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3
Q

What two things contribute to strengthening mechanisms of ceramics

A

fabrication defects

surface flaws

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4
Q

Who proposed that flaws act as a stress concentrator (magnifiers)

A

Griffiths

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5
Q

What does stress concentration apply

A

low locally applies stresses can result in very high effecting local stresses

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6
Q

What are two fabrication defects of ceramics

A

sintered powders introduce voids

casting and pressing result in potentially less flaws

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7
Q

What are two surface flaws of ceramics

A

grinding can introduce flaws (this is why polishing or re-glazing is critical)
usually failure occurs from the largest flaws

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8
Q

What are two aspects of chemical strengthening of ceramics

A

puts surface of ceramic in compression (pre-stress)

not commonly used in dentistry

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9
Q

What are two aspects in glazing of ceramics

A

self-glazing; tends to heal flaws

surface glazing can be designed to cool so they are under surface compression to improve strength

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10
Q

What are two characteristics of preventing stress corrosion of ceramics

A

ceramics are weaker when fracture occurs in water; water reacts with ceramics
ceramics fused to metal foil (captek) can reduce this

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11
Q

This is used to strength the ceramics

A

crystalline reinforcement

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12
Q

What is crystalline reinforcement

A

introduce increased crystal content in the glassy matrix to deflect cracks

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13
Q

What are two examples of glass ceramics crystalline reinforcement

A

glass ceramics; both silica based
leucite-reinforces (Empress)
lithium disillicate (eMax)

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14
Q

What is the strength of glass ceramics

A

moderate

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15
Q

What is the translucency of glass ceramics

A

good translucency

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16
Q

In which type of restorations can glass ceramics be used

A

full thickness restorations

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17
Q

In which three ways can glass ceramics be formed

A

pressing
machining
sintered powders

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18
Q

How is the shrinkage/fit of glass ceramics

A

no shrinkage/good fit

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19
Q

What is the strength of crystalline reinforced glass infiltrated alumina (InCeram)

A

high strength

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20
Q

What is the translucency of crystalline reinforced glass infiltrated alumina (InCeram)

A

poor

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21
Q

What is the shrinkage of crystalline reinforced glass infiltrated alumina (InCeram)

A

no shrinkage

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22
Q

What is crystalline reinforced glass infiltrated alumina (InCeram) used for

A

a core

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23
Q

How can you fabricate crystalline reinforced glass infiltrated alumina (InCeram)

A

it can be fabricated without special equipment

24
Q

What is the strength of crystalline reinforced dense sintered alumina

A

high

25
Q

What is the translucency of crystalline reinforced dense sintered alumina

A

low

26
Q

What is crystalline reinforced dense sintered alumina used as

A

a core only

27
Q

How can you fabricate crystalline reinforced dense sintered alumina

A

special equipment machine (CAD)

high temp ovens

28
Q

What is the strength of stress-induced transformation dense sintered zirconia

A

high

29
Q

What is the translucency of stress-induced transformation dense sintered zirconia

A

variable

30
Q

What is stress-induced transformation dense sintered zirconia used as

A

a core or full thickness restoration

31
Q

How can you fabricate stress-induced transformation dense sintered zirconia

A

special equipment machining (CAD)

high temp ovens

32
Q

What steps happen when stress-induced transformation dense sintered zirconia undergoes stress

A

it leads to cracks
the lack of crystal constraint leads to crystals expanding (transformation)
resulting in reduced stress at crack tip

33
Q

What are the four all ceramic systems available at OSU

A

Leucite reinforced glass-ceramic
lithium di-silicate glass-ceramic
full contour zirconia
porcelain fused to zirconia

34
Q

What are two characterics of forming empress and eMax press

A

lost wax technique

hot-pressed

35
Q

In which two ways an Empress and eMax be used

A

full contour with surface stain and glaze

minimal cutback with porcelain veneer

36
Q

This type of fabrication technique is less labor intensive (less expensive), excellent outcomes, and has the full contour strength of material

A

surface staining

37
Q

This fabrication technique is more labor intensive and expensive, excellent outcomes, full counter strength of material in high stress areas like the lingual or occlusal surfaces

A

minimal cutback with layered porcelain

38
Q

This fabrication technique is the most labor intensive and expensive, has excellent outcomes, and the strength of material is reduced because thickness is reduced

A

full cutback with layered porcelain

39
Q

How is zirconia supplies

A

isostatically pressed powders, stronger than chalk in this state but easy to mill

40
Q

How much shrinkage does zirconia undergo

A

20%

41
Q

What is the strength of zirconia

A

> 1000MPa

42
Q

What is the crystalline structure of zirconia at room temperature

A

largest; monolinic

43
Q

What is the crystalline structure of zirconia at 1170℃

A

intermediate; tetragonal

44
Q

What is the crystalline structure of zirconia at 2370℃

A

smallest; cubic

45
Q

Adding small amounts of this will cause the powders to stabilize in the tetragonal phase

A

yttrium (3%)

46
Q

What is transformation toughening

A

crack causes local crystals to be unconstrained in some area
lack of crystal constraint allows phase transformation
phase transformation results in increase in crystal size
increase in crystal size closes crack

47
Q

What are some unknowns of zirconia

A

it is still a ceramic and not a metal, so long term failure mechanism is still unknown for single crowns

48
Q

What the low-temperature degradation of zirconia

A

because its metastable there is concern about transforming over time and creating flaws that lead to failures

49
Q

How long has zirconia been used as a substructure and what has been found with fractures

A

10-15 years

minimal fracture

50
Q

How long has zirconia been used for FCZ and what has been found with fractures

A

about 4 years

few reported issues

51
Q

What are the steps to cement LDS and LRGC (leucite and lithium based)

A

etch ceramic with HF acid
apply silane
dual cure resin cement
apply adhesive to tooth

52
Q

This step in cementation of LDS and LRGC preferentially removes glassy phase and leaves a rough surface

A

acid etch

53
Q

This step in cementation of LDS and LRGC chemically bonds to hydrophilic glass surface to make the surface hydrophobic

A

silane

54
Q

This step in cementation of LDS and LRGC bonds to silane surface and adhesive on tooth site

A

dual cure resin cement

55
Q

What is the characteristic of zirconia cementation

A

zirconia is cemented similar to metal but the inner surface is not rough

56
Q

Why not you etch zirconia to tooth structure

A

to keep the minerals in

AU14 Fixed Restorative III (10 decks)

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