All-Ceramics I

Question 1

What is the main indication of an ACC

Answer 1

optimize esthetics

Question 2

What are five contraindications of an ACC

Answer 2

parafunctional activity
insufficient support from tooth preparation
insufficient porcelain thickness in lingual aspect
opposing teeth that occlude with cervical fifth of crown
short cervical crowns

Question 3

What are three advantages of an ACC

Answer 3

best esthetics
best color stability
some ACC systems can be bonded to natural tooth structure

Question 4

What is a main disadvantage of an ACC

Answer 4

CATASTROPHIC FAILURE due to weak strength and brittle nature of ceramics

Question 5

What are four disadvantages of an ACC

Answer 5

higher laboratory costs (more so 10 years ago)
more tooth reduction is required
cementation can be complicated
may have poorer marginal adaptation

Question 6

What are the two silica based ceramics

Answer 6

feldspathic ceramics

hot-pressed glass ceramics

Question 7

What are two types of hot-pressed glass ceramics

Answer 7

leucite reinforced glass ceramic

lithium dislocate reinforced glass ceramic

Question 8

What are two non-sillica based ceramics

Answer 8

slip-cast, glass infiltrated ceramic (alumina, alumina/zirconia and magnesium alumina)
polycrystalline “densely sintered” alumina and zirconia

Question 9

What are the characteristics of bonding silica based ceramics

Answer 9

can AND must bond with resin to improve strength

Question 10

What are the characteristics of bonding non-silica based ceramics

Answer 10

difficult to bond but strong enough to use conventional cements

Question 11

What are the four components of dental feldspathic porcelain

Answer 11

feldspar; potassium and sodium aluminosilicates
quartz
ceramic oxides (color and shade)
20% leucite crystals

Question 12

Dental feldspathic porcelain is headed to a glassy molten mass (around 2000℉) and quenched to form what

Answer 12

a “frit” and ground into a fine powder

Question 13

Dental porcelain is mostly what

Answer 13

glassy with a small amount of leucite crystals (12%)

Question 14

Leucite has a much higher what than glass

Answer 14

thermal expansion

Question 15

Why is leucite need to make the bonding to metal possible

Answer 15

leucite has a much high coefficient of thermal expansion (CTE) than glass, the addition of the crystals raises the CTE of the porcelain so that it is slightly lower than that of metal in order to place the ceramic under slight compression; enhancing the durability of the porcelain to metal bond

Question 16

Ceramic materials are susceptible to what kind of fracture

Answer 16

brittle

Question 17

What happens to the properties of ceramics under tension and compression

Answer 17

ceramics are weaker when in tension and stronger when under compression

Question 18

Leucite crystalline reinforcement strengthens the ceramic how

Answer 18

by resisting crack propagation via deflection of the advancing crack

Question 19

How does the leucite crystal cause crack deflection to occur

Answer 19

the higher CTE (and contraction) of the leucite crystals compared to the glassy matrix results in a layer of glass under compression immediately adjacent to the crystal; the stronger layer within the glassy matrix deflects the advancing matrix

Question 20

This type of dental porcelain is the high concentration of ceramic and metal oxides that block out metal substructure

Answer 20

opaque

Question 21

This type of dental porcelain is more translucent, with some oxide pigments

Answer 21

body or dentin

Question 22

This type of dental porcelain is very translucent, no oxides

Answer 22

enamel or incisal

Question 23

What is the composition of modern dental feldspathic porcelain

Answer 23

feldspathic glass containing 20% leucite

Question 24

dental feldspathic porcelain offers great esthetics, why?

Answer 24

it is very translucent due to high glass content

Question 25

What is the strength of dental feldspathic porcelain

Answer 25

relatively low, (60-80MPa) due to lower crystalline phase

Question 26

Recently, lower-fusing dental feldspathic porcelains containing <10% leucite with smaller particle size have been developed and have shown what

Answer 26

low enamel wear and higher strength

Question 27

What is the size of leucite particles of conventional feldspathic porcelain

Answer 27

20-30μm

Question 28

What is the translucency of stacked dental feldspathic porcelain

Answer 28

highest translucent (superior esthetics) of any dental ceramic

Question 29

What are two indications for stacked dental feldspathic porcelain

Answer 29

layering porcelain for metal and ACCs | feldspathic porcelain veneers

Question 30

What are two disadvantages of stacked dental feldspathic porcelain

Answer 30

low strength | translucency prevents masking of discolored teeth

Question 31

What are four reasons that ceramics fail

Answer 31

brittle fracture initiated from internal surface cyclic fatigue (low loads, many cycles) stress corrosion

Question 32

What is the difference between brittle fracture in metals vs. ceramics

Answer 32

in metals, the atoms slide past each other (dislocation slip) in ceramics, the bonds between atoms break (Griffiths flaws)

Question 33

Where does the propagation of a fracture of ceramic initiate

Answer 33

from the interior to the exterior (inside → out) due to tension

Question 34

You can strengthen porcelain with this but interface initiated fractures are difficult but contact fractures are still present

Answer 34

metal substructure

Question 35

What are the two development strategies of ACCs

Answer 35

develop stronger materials to substitute for metal and veneer with feldspathic porcelain develop high strength translucent materials that can be used in full thickness or minimal reduction

Question 36

Always do this to porcelain, or it will crack

Answer 36

polish, do not leave it rough

Question 37

Which type of ACC, monolithic, minimal cutback, or layered substructure, has the most feldspathic porcelain

Answer 37

layered substructure