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DMS :( > key points dental ceramics > Flashcards

key points dental ceramics Flashcards

1
Q

what is a ceramic?

A

crystalline minerals and a glass matrix

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2
Q

what do decorative ceramics contain?

A

kaolin - opaque

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3
Q

dental ceramic constituents

A 
kaolin <5%
silica 12-25%
feldspar 70-80%
metal oxides 1%
glass up to 15%
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4
Q

feldspar

A

flux - melts and embeds other particles

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5
Q

borax

A

lowers fusing temp

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6
Q

metallic oxides

A

strengtheners

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7
Q

making powder

A

heat
cool rapidly (fritting)
mill frit
add binder

powder and distilled water built up into restoration

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8
Q

sintering

A

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

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9
Q

aesthetics

A

best
colour stable
v smooth surface

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10
Q

reflectance

A

% of light striking a surface which is reflected off it

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11
Q

translucency

A

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

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12
Q

opacity

A

lacking transparency/translucence

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13
Q

transparency

A

allows light to pass through, objects behind can be seen

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14
Q

opalescence

A

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

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15
Q

chemical stability

A

v stable

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16
Q

thermal properties

A

similar to tooth
TEC similar to D
thermal diffusivity low

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17
Q

dimensional stability

A

once fired fully v stable

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18
Q

mechanical properties

A 
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
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19
Q

high hardness

A

abrasion of opposing teeth esp if not glazed

20
Q

static fatigue

A

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

21
Q

layers

A

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

22
Q

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

A

opaque

23
Q

alumina core - mechanism

A

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

24
Q

alumina core - strength

A

flex strength double porcelain >120 MPa

not strong enough for posteriors

25
Q

INCERAM

A

Spinel and Zi
increased alumina content
single posterior crowns

26
Q

PROCERA

A

increased alumina content

single posterior crowns

27
Q

overcoming problems with conventional ceramics

A 
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
28
Q

Zi core and bonding

A

difficult to bond to

29
Q

Zi core

A

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

30
Q

problems with zirconia cored crowns

A

£££ 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

31
Q

milled core crowns and bridges

A

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

32
Q

milled Rx design feature

A

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

33
Q

all ceramic crowns

A 
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
34
Q

sintered vs milled

A

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

35
Q

lithium disilicate glasses e.g. Emax

A 
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
36
Q

what structure do strong materials have?

A

small crystal size and high vol fraction of crystals

37
Q

cast and pressed

A

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

38
Q

reinforcing ceramics

A

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

39
Q

leucite

A 
1st gen
crystalline reinforcing phase
v good aesthetics
raises TEC - good for MCCs
heat pressed
weaker than lithium disilicate
40
Q

design features

A

rounding internal line angles

occlusal contacts at least 1.5mm away from porcelain metal jct

41
Q

bonding to metal

A

needs to be a mononuclear oxide layer

42
Q

adhesive failures

A

between different materials

43
Q

cohesive failures

A

between same material

44
Q

luting any silica-containing ceramic

A

can etch with HF acid - retentive surface

  • can bond to it using a silane coupling agent
  • bond to tooth with bonding agent
45
Q

luting Zi-cored crowns

A

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

DMS :( (18 decks)

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