all ceramic materials part 2

Question 1

what do flaws in ceramics lead to

Answer 1

Stress concentrations (magnifiers)

Question 2

strength of ceramics

Answer 2

strong theoretical strength

weak actual strength due to flaws

Question 3

why do ceramics have more flaws than metals

Answer 3

Cuz they cant reform cracks

Question 4

where does stress appear when placing glass on a complicent surface

Answer 4

tensile strength on the bottom side of the glass

Question 5

how does chemical strengthing work

Answer 5

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

Question 6

where is the sorse of stress in an anterior crown

Answer 6

directly under contact

Question 7

what is the source of hoop stress

Answer 7

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

Question 8

what teeth are likely to have hoop stress

Answer 8

posterior crowns

Question 9

what does polishing and glazing due for a crown

Answer 9

removal of flaws from the surface

Question 10

does glass normally react with water

Answer 10

no

Question 11

how does water lead to cracking

Answer 11

Comes in and forms hydrogen bonds breaking the glass bonds

Question 12

steps of crack propogation with water

Answer 12

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

Question 13

the most common way to strengthen a ceramic

Answer 13

Crystalline reinforcement

Question 14

what is dental porcelain made of

Answer 14

Noncrystalline/amorphous silica based glass

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

Question 15

how does crystalline reinforcement work

Answer 15

deflects cracks

Question 16

examples of crystalline reinforcement

Answer 16

Leucity-reinforced glass ceramics

Lithium disilicate glass ceramic

Question 17

Characteristics of glass ceramics

Answer 17

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

Question 18

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

Answer 18

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

Question 19

downside of crystalline reinforcement( greater crystallines)

Answer 19

Poor translucency

Question 20

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

Answer 20

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

Question 21

characteristics of Dense sintered zirconia (100 zirconia)

Answer 21

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

Question 22

ranking of ceramic strengths(weakest first)

Answer 22

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

Question 23

stregnth of zirconia crowns

Answer 23

1200 – 1400mPa

Question 24

how does zirconia do transformation toughening

Answer 24

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

Question 25

What is LDP (aging)

Answer 25

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

Question 26

problem with LDP (aging)

Answer 26

may lead to long term weakness?

Question 27

ways to make a All-ceramic crowns

Answer 27

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

Question 28

benifit of full contour crowns with surface strains

Answer 28

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

Question 29

characteristics of minimal cutback with layered porcelain

Answer 29

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

Question 30

characteristics of full cutback with layered porcellain

Answer 30

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

Question 31

what crown type cannot be pressed

Answer 31

zirconia(must be milled)

Question 32

how does one get zirconia

Answer 32

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

Question 33

what does heat processing zirconia do to it

Answer 33

20% shrinkage

Question 34

what have zirconia developments done

Answer 34

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