key points dental ceramics

Question 1

what is a ceramic?

Answer 1

crystalline minerals and a glass matrix

Question 2

what do decorative ceramics contain?

Answer 2

kaolin - opaque

Question 3

dental ceramic constituents

Answer 3

kaolin <5%
silica 12-25%
feldspar 70-80%
metal oxides 1%
glass up to 15%

Question 4

feldspar

Answer 4

flux - melts and embeds other particles

Question 5

borax

Answer 5

lowers fusing temp

Question 6

metallic oxides

Answer 6

strengtheners

Question 7

making powder

Answer 7

heat
cool rapidly (fritting)
mill frit
add binder

powder and distilled water built up into restoration

Question 8

sintering

Answer 8

heat
glass phase softens - coalesce
form solid ceramic mass
20% contraction

Question 9

aesthetics

Answer 9

best
colour stable
v smooth surface

Question 10

reflectance

Answer 10

% of light striking a surface which is reflected off it

Question 11

translucency

Answer 11

allows light to pass through, objects behind can’t be seen

Question 12

opacity

Answer 12

lacking transparency/translucence

Question 13

transparency

Answer 13

allows light to pass through, objects behind can be seen

Question 14

opalescence

Answer 14

scattering of visible light wavelengths, bluish appearance in reflected colour and orange/brown in transmitted colour

Question 15

chemical stability

Answer 15

v stable

Question 16

thermal properties

Answer 16

similar to tooth
TEC similar to D
thermal diffusivity low

Question 17

dimensional stability

Answer 17

once fired fully v stable

Question 18

mechanical properties

Answer 18

high compressive strength
high hardness - too high
tensile strength v low
flexural strength v low
fracture toughness v low
static fatigue
surface microcracks
slow crack growth - cyclic fatigue

Question 19

high hardness

Answer 19

abrasion of opposing teeth esp if not glazed

Question 20

static fatigue

Answer 20

time dependent decrease in strength even in the absence of any applied load

Question 21

layers

Answer 21

opaque porcelain - provides porcelain metal bond and masks dark oxide colour
body/dentine porcelain
incisal/enamel porcelain

Question 22

alumina core - why can it only be used as a core?

Answer 22

opaque

Question 23

alumina core - mechanism

Answer 23

alumina particles act as crack stoppers - prevent propagation
- necessitates more energy to propagate a crack so more resilient

Question 24

alumina core - strength

Answer 24

flex strength double porcelain >120 MPa

not strong enough for posteriors

Question 25

INCERAM

Answer 25

Spinel and Zi increased alumina content single posterior crowns

Question 26

PROCERA

Answer 26

increased alumina content | single posterior crowns

Question 27

overcoming problems with conventional ceramics

Answer 27

``` strong coping resistant to fracture, cover in conventional porcelain - metal coping - alumina core - zirconia core cast/press a block of harder ceramic mill a lab prepared block of ceramic ```

Question 28

Zi core and bonding

Answer 28

difficult to bond to

Question 29

Zi core

Answer 29

probably most popular ceramic core material v hard use Yttria-stabilised zirconia - <1% Yttria tetragonal crystal to monoclinic structure - slight expansion of the material and closes crack tip - like a self-healing crack strong enough to use as bridge framework

Question 30

problems with zirconia cored crowns

Answer 30

£££ equipment potential for veneering porcelain to debond from core - can inbuild stresses between the 2 materials on manufacture opaque core - are aesthetics much better than metal ceramic? inert fitting surface, can't etch or bond - use conventional cement

Question 31

milled core crowns and bridges

Answer 31

zirconia lithium disilicate precious metal non-precious metal Ti = all have scintered surface layer for best aesthetics - but ones milled from a single block are stronger than if you put the layer of sinter on

Question 32

milled Rx design feature

Answer 32

need to round internal angles in prep as sharp shoulder can't be replicated in a milled Rx

Question 33

all ceramic crowns

Answer 33

``` 1 - glass infiltrated ceramics - etched with HF acid and treated with silane coupling agent, bonds to tooth 2 - no glass content (Zi and alumina) - luted with cement - stronger but less aesthetic ```

Question 34

sintered vs milled

Answer 34

for the same material milled stronger than built up/pressed | block has had ideal heat txs to maximise its properties and all blocks will be consistent

Question 35

lithium disilicate glasses e.g. Emax

Answer 35

``` have unique needle-like crystals - crack propagation v difficult - good flexural strength better aesthetics than Zi - translucency stronger - crystalline structure 2nd gen need 1.5mm occ reduction contains silica heat pressed ```

Question 36

what structure do strong materials have?

Answer 36

small crystal size and high vol fraction of crystals

Question 37

cast and pressed

Answer 37

most often cut back labially and veneered with feldspathic porcelains ceramic used - glass ceramics - lithium disilicate glass - leucite reinforced glass = becoming a bit redundant due to milled ceramics

Question 38

reinforcing ceramics

Answer 38

dispersion strengthening: alumina often used monolithic e.g. milled from a ceramic block core (coping)

Question 39

leucite

Answer 39

``` 1st gen crystalline reinforcing phase v good aesthetics raises TEC - good for MCCs heat pressed weaker than lithium disilicate ```

Question 40

design features

Answer 40

rounding internal line angles | occlusal contacts at least 1.5mm away from porcelain metal jct

Question 41

bonding to metal

Answer 41

needs to be a mononuclear oxide layer

Question 42

adhesive failures

Answer 42

between different materials

Question 43

cohesive failures

Answer 43

between same material

Question 44

luting any silica-containing ceramic

Answer 44

can etch with HF acid - retentive surface - can bond to it using a silane coupling agent - bond to tooth with bonding agent

Question 45

luting Zi-cored crowns

Answer 45

don't contain silica - not affected by acid - strong enough to be self-supporting, can be luted with conventional cement difficult to bond to