ceramics Flashcards
1
Q
ceramic/porcelain
A
all porcelain is ceramic but not all ceramic is porcelain
2
Q
difference between decorative and dental ceramics
A
decorative contain kaolin - clay - hydrated aluminium silicate - opaque dental need to be translucent so kaolin removed - feldspar and silica replace it
3
Q
dental ceramic constituents
A
kaolin <5% quartz (silica) 12-25% feldspar 70-80% metal oxides 1% glass up to 15%
4
Q
decorative ceramic constituents
A
kaolin 50+% quartz (silica) 15-25% feldspar 15-25% metal oxides <1% glass 0
5
Q
are ceramics glasses?
A
yes
6
Q
feldspar
A
potash feldspar (KAl silicate)
soda feldspar (Na, Al silicate)
flux - melts and embeds other particles, increases viscosity
lowers the fusion and softening temp of the glass
lowest fusing component and flows during firing forming a solid mass around the other components
7
Q
borax
A
lowers fusing temp
8
Q
metallic oxides
A
strengtheners
colour to ceramic
9
Q
chromium
A
green
10
Q
cobalt
A
blue
11
Q
copper
A
green
12
Q
iron
A
brown
13
Q
manganese
A
lavender
14
Q
nickel
A
brown
15
Q
ceramic powder
A
dentine pink
enamel blue
16
Q
conventional ceramics - making the powder
A
heat constituents to >1000 degrees
cool rapidly (fritting) in H2O - creates cracks and crazing of the ceramic mass
mill frit - fine powder
add binder - often starch
17
Q
conventional ceramics - building up the Rx
A
powder and distilled water built up
apply to die with brush
different porcelains for E and D
no further chemical reaction required - powder melts together to form crown
- crown heated in a furnace to coalesce the powder into ceramic
heating leads to sintering
18
Q
what do feldspathic ceramics form when heated to 1150-1500 degrees?
A
leucite (potassium aluminium silicate)
forms around glass phase
gives powder of known physical and thermal properties
19
Q
overall properties
A
aesthetics chemical stability biocompatibility thermal properties dimensional stability mechanical properties
20
Q
sintering
A
occurs just above the glass transition temp
when the ceramic particles begin to fuse into a single mass
glass phase softens - coalesce
over time controlled diffusion - form solid ceramic mass
20% contraction - skilled technician to judge contraction in 3D
21
Q
chemical stability
A
v stable
generally unaffected by the wide pH range in mouth
don’t take up stain from food/drink
22
Q
biocompatibility
A
good
minimal adverse effects on biological tissues
23
Q
thermal properties
A
similar to tooth TEC similar to dentine - low stresses to Rx in mouth during use thermal diffusivity low - protective of remaining tooth
24
Q
aesthetics
A
best of any Rx material colour stable v smooth surface retain surface better - less staining long-term optical properties - reflectance - translucency - opacity - transparency - opalescence
25
dimensional stability
once fully fired v stable
during fabrication - shrinkage - must be accommodated for by technician
- 20% normal for a conventional feldspathic ceramic crown
26
compressive strength
high
27
hardness
too high
| can lead to abrasion of opposing teeth esp if not glazed
28
tensile strength
v low
29
flexural strength
v low
30
fracture toughness
v low
31
result of mechanical properties
lead to failure during loading
32
static fatigue
cracking over time, but over v long period and less than you would get from hydrolysis of composite
time dependent decrease in strength even in the absence of any applied load
probably due to hydrolysis of Si-O group within material, over time in an aq env
33
surface microcracks
during manufacture, finishing or due to occlusal wear
| areas where fractures can initiate
34
slow crack growth
cyclic fatigue under occlusal forces in a wet env over time
35
where can conventional ceramics be used?
only in low stress areas
- anterior crowns - not in all pts - if deep OB/Bruxist
too brittle for use elsewhere
36
overcoming problems with conventional ceramics
aesthetics good but need to be stronger
produce a strong coping resistant to fracture, and cover it in conventional porcelain
cast/press a block of harder ceramic
mill a lab prepared block of ceramic
37
strong coping
metal coping
alumina core
zirconia core
38
why can alumina only be used as a core?
because it is opaque
39
alumina core increased strength
flex strength double porcelain >120MPa
alumina particles act as crack stoppers - prevent propagation
- necessitates more energy to propagate a crack so more resilient
40
alumina core uses
prev first choice for anterior crowns, not strong enough for posteriors
aesthetics could be excellent but need enough room for Al core and feldspathic layers
possibly more palatal reduction required than MCC, but less labially
41
alumina core advantages
cheap
| no specialist equipment - just need a furnace
42
conventional alumina core
max 50% Al
43
increasing the Al content and so strength
new techniques
- INCERAM
- PROCERA
44
INCERAM alumina content
around 85%
45
INCERAM flexural strength
high >400MPa
46
In-ceram spinel
```
has Spinel (MgAl2O4) rather than alumina as its core material
- better aesthetics but lower flex strength
```
47
In-ceram zirconia
33% zirconia replacing alumina in core
| - higher strength but poorer aesthetics
48
INCERAM slip casting (complicated)
ceramic core formed onto a refractory model
apply fine slurry of alumina
heat to 1120 degrees for 10 hours
- below glass transition temp for alumina
- partial sintering
- porous core produced
core infiltrated with lanthanum glass at 1100 degrees
49
PROCERA
pure alumina core >99% pure
50
PROCERA properties
high flexural strength >700MPa
possibly better translucency than glass infiltrated core
strong enough for posterior teeth, might be strong enough for bridges
51
PROCERA manufacture
even more complicated process
core is made centrally not in every lab
a fully densified alumina core is produced at around 1700 degrees
52
PROCERA and INCERAM clinical uses
both cores can be veneered with conventional feldspathic porcelain to produce the final crown
both probably suitable for single posterior crowns
not often used as bridge materials
53
zirconia core and bonding
difficult to bond to
54
most popular ceramic core material
probably zirconia
55
zirconia naturally occurring mineral
zirconium dioxide
in different forms at diff temps
v hard
56
when couldn't zirconia be used as a core until?
CAD-CAM
| powder doesn't sinter unless heated >1600 degrees
57
what type of zirconia should be used and why?
Yttria-stabilised zirconia
| pure zirconia can crack on cooling
58
% of yttria
<1%
59
normal zirconia structure
monoclinic crystal at room temp
60
Yttria structure
tetragonal crystal structure
61
how does Yttria zirconia stabilisation work?
if a crack begins - when the stress at the crack tip reaches a critical level the crystal structure transforms to the monoclinic structure
causes slight expansion of material and closes crack tip
like a self-healing crack - goes from one crystal structure to a bigger crystal structure which fixes the crack
62
Yttria stabilised zirconia properties
hard
strong (1000MPa flexural strength)
tough
strong enough to use as a bridge framework
63
zirconia cored crowns fabrication
impression of prep - send to lab
case model then scan digitally
software unit creates a bridge substructure on virtual prep
min thickness of connectors are determined and fabricated
raw zirconia block selected for milling
pre-sintered block much easier to mill
milling for a 3 unit bridge around 1hr
cut framework heat treated 850 degrees to achieve its final physical properties
causes 20% shrinkage but computer deals with this during milling
stain
veneer it with feldspathic porcelain to produce final Rx
64
manufacturers of zirconia systems
```
LAVA from 3m
IPS e.max Zir CAD
Opalite
Zerion
Everest ZH
```
65
problems with zirconia cored crowns
£££ 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 MCC?
inert fitting surface - can't etch or bond
- use conventional cement
66
advantages of zirconia cored crowns
once you have the equipment they are cheaper
- cost of metal is increasing
fit generally excellent
- work at least as well as MCCs
67
milled core crowns and bridges
```
zirconia
lithium disilicate
precious metal
non-precious metal
titanium
```
all have a sintered surface layer for best aesthetics
- but ones milled from a single block are stronger than if you put the layer of sinter on
68
milled core crowns and bridges prep
need to round internal angles in prep as sharp shoulder can't be replicated in a milled Rx
69
sintered vs milled
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
as aesthetics of 'blocks' of ceramic improve these will become most commonly used crown
- probably already acceptable in posterior teeth
70
milled fabrication
```
cast into scanner
scanned image of cast
lower cast is scanned and articulated
select crown margin
adjust crown margin
select crown type and place on 'model'
adjust shape and size of selected crown
save file
send to milling machine
30-40mins have crown
still requires final finishing
```
71
truly digital workflow
don't need models and impressions
- scan in mouth
- design on CAD machine
- mill
- polish
- cement
72
lithium disilicate glasses crystals
have unique needle-like crystals
crack propagation v difficult - good flexural strength
?maybe use for bridges
73
why are cast and pressed becoming a bit redundant?
because of the milled ceramics
74
cast and pressed ceramics technique
like casting a metal Rx
wax up Rx
invest
cast from a heated ingot of ceramic (1100 degrees)
no sintering - ceramic ingot is already fully condensed prior to firing
once devested and cleaned, Rx heated to improve its crystal structure producing crack inhibiting crystals - ceraming
can stain - comes out as single colour on cast
most often is cut back labially and veneered with feldspathic porcelains
75
ceramic used for cast and pressed
glass ceramics
- lithium disilicate glass
- leucite reinforced glass
76
ceraming
heat to improve its crystal structure producing crack inhibiting crystals
stage 1 - crystal formation. max no of crystal nuclei are formed
stage 2 - crystal growth to maximise physical properties
crystal phase of the ceramic can approach 100%
77
strong cast and pressed ceramics
small crystal size and high vol fraction of crystals
78
luting silica containing ceramics
etch with HF acid - retentive surface
- can bond to it using a silane coupling agent
- bond to tooth w bonding agent
79
luting zirconia cored crowns
don't contain silica - not affected by acid
strong enough to be self-supporting, can be luted with conventional dental cement
difficult to bond to
80
lithium disilicate ceramic material advantages
better aesthetics than zirconia - translucency
contains silica so can etch surface to provide a reliable bond to composite luting agents, with the use of a silane coupling agent
stronger - crystalline structure
81
lithium disilicate ceramic material occlusal reduction
min 1.5mm
82
lithium disilicate ceramic material name
Emax
83
cementing lithium disilicate ceramic material
silane coupling agent - give chemical bond to onlay surface
dual curing composite resin luting cement
- reduced light penetration through onlay
DBA - to allow composite resin to bond to tooth
84
reinforcing ceramics
dispersion strengthening - alumina often used
monolithic e.g. milled from ceramic block
core (coping)
