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fixed 2 > all ceramic materials part 2 > Flashcards

all ceramic materials part 2 Flashcards

1
Q

what do flaws in ceramics lead to

A

Stress concentrations (magnifiers)

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2
Q

strength of ceramics

A

strong theoretical strength

weak actual strength due to flaws

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3
Q

why do ceramics have more flaws than metals

A

Cuz they cant reform cracks

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4
Q

where does stress appear when placing glass on a complicent surface

A

tensile strength on the bottom side of the glass

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5
Q

how does chemical strengthing work

A

add larger attoms that press the crack togethre to create compressive strength

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6
Q

where is the sorse of stress in an anterior crown

A

directly under contact

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7
Q

what is the source of hoop stress

A

due to tooth squat leading to expansion on the base of the crown

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8
Q

what teeth are likely to have hoop stress

A

posterior crowns

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9
Q

what does polishing and glazing due for a crown

A

removal of flaws from the surface

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10
Q

does glass normally react with water

A

no

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11
Q

how does water lead to cracking

A

Comes in and forms hydrogen bonds breaking the glass bonds

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12
Q

steps of crack propogation with water

A 
functional load applied
stress on the bottom of the crown
existing cracks strained
water enters
crack extends
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13
Q

the most common way to strengthen a ceramic

A

Crystalline reinforcement

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14
Q

what is dental porcelain made of

A

Noncrystalline/amorphous silica based glass

minor components of crystalline silicates (quartz or crystobilite, leucite (NOT lucite)

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15
Q

how does crystalline reinforcement work

A

deflects cracks

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16
Q

examples of crystalline reinforcement

A

Leucity-reinforced glass ceramics

Lithium disilicate glass ceramic

17
Q

Characteristics of glass ceramics

A 
Moderate strength
Good translucency
used in full thickness restorations
formed by pressing, machining or sintered powders
no shrinkage/good fit
18
Q

Characteristics of crystalline reinforced ceramics (85%) alumia)- glass inflitrated alumina

A

High strength
Poor translucency
no shrinkage
can be fabricated without special equipment

19
Q

downside of crystalline reinforcement( greater crystallines)

A

Poor translucency

20
Q

characteristics of crystalline reinforced ceramics (100% alumina)- dense sintered alumina

A

high sttrength
low translucency (core only)
need special quiment (CAD and high temp ovens)

21
Q

characteristics of Dense sintered zirconia (100 zirconia)

A

high strength
Variable translucency
core and full thickness restorations
Special equipent (CAD and high temp ovens)

22
Q

ranking of ceramic strengths(weakest first)

A 
silicate glasses:
Porcelain
LRGC
LDS
Non-silicate ceramic:
Inceram
AlO
ZrO
23
Q

stregnth of zirconia crowns

A

1200 – 1400mPa

24
Q

how does zirconia do transformation toughening

A

Crack causes local crystals to go from cubic to tetragonal to monoclinic shape filling the void not allowing water in(phase transformation)

25
Q

What is LDP (aging)

A

the spontaneous t-m transformation occurring over time at low temperatures, when the t-m transformation is not triggered by local stress from an advantage

26
Q

problem with LDP (aging)

A

may lead to long term weakness?

27
Q

ways to make a All-ceramic crowns

A 
MEtalceramic like (high strength opaque substructure)
minimal curback (porcelain only in critial esthetic areas)
monolithiic (moderate strength translucent ceramics)
28
Q

benifit of full contour crowns with surface strains

A

Less labor intense (less expensive)
good outcome
full contour strength of material

29
Q

characteristics of minimal cutback with layered porcelain

A

Labor intense (expensive)
excellent outcome
full contour strenth in high stress areas

30
Q

characteristics of full cutback with layered porcellain

A

most labor intense (expensive)
excelled outcome
strength reduced due to increased thinness

31
Q

what crown type cannot be pressed

A

zirconia(must be milled)

32
Q

how does one get zirconia

A

isostatically pressed powders like strong chalk to be machined
heat processed at 1500 c

33
Q

what does heat processing zirconia do to it

A

20% shrinkage

34
Q

what have zirconia developments done

A

make the structure translucent (at the expense of stength with less stable tetragonal zirconia)

fixed 2 (8 decks)

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