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DMS :( > elastomeric impression materials > Flashcards

elastomeric impression materials Flashcards

1
Q

chemistry

A

polymerisation - cross-linking of polymer chains
- generates elastic properties
- fluid - solid transition
may produce by-products
- H2O, H2, alcohol
- affect dimensional stability and cast compatibility

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2
Q

elastomers

A 
polysulphides
silicones
 - addition curing
 - condensation curing (conventional)
polyethers
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3
Q

conventional silicone e.g. Verone chemistry - base paste

A

silicone prepolymer with terminal hydroxyl groups

filler

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4
Q

conventional silicone e.g. Verone chemistry - catalyst paste (or liquid)

A

cross-linking agents (alkoxyorthosilicate or organohydrogen siloxane)
activator - organo-tin compound

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5
Q

conventional silicone e.g. Verone chemistry - different setting reactions

A

different formulations have different setting reaction depending on cross-linking agents

  • alkoxyl-orthosilicate
  • organohydrogen siloxane
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6
Q

conventional silicone e.g. Verone chemistry - setting reactions

A

silicone polymers + organohydrogensiloxane - cross-linked polymer + H2

silicone polymers + alkoxyorthosilicate - cross-linked polymer + alcohol

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7
Q

addition cured silicone e.g. PVS e.g. extrude chemistry

A

base paste and catalyst paste
no byproducts
hydrophobic

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8
Q

addition cured silicone e.g. PVS e.g. extrude chemistry - base paste

A

polydimethylsiloxane - some methyl groups replaced by hydrogen
filler - variations change viscosity

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9
Q

addition cured silicone e.g. PVS e.g. extrude chemistry - catalyst paste

A

polydimethylsiloxane - some methyl groups replaced by vinyl
filler - variations change viscosity
platinum catalyst e.g. chloroplatinic acid

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10
Q

hydrophillic silicones

A

incorporate non-ionic surfactant

  • wets tooth surface
  • more easily wetted by water-containing die materials
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11
Q

polyethers e.g. Impregum chemistry

A

base paste
catalyst paste
polyether + sulphonate ester = cross-linked material

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12
Q

polyethers e.g. Impregum chemistry - base paste

A

imine terminated pre-polymer - cross-linking

inert filler - viscosity, strength

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13
Q

polyethers e.g. Impregum chemistry - catalyst paste

A

ester derivative of aromatic sulphonic acid - initiates polymerisation
inert oils - form paste
inert fillers - form paste

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14
Q

polyethers setting reactions

A

activation
initiation
propagation

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15
Q

material properties

A 
flow/viscosity
surface detail (reproduction)
contact angle/wettability
elastic recovery (%)
stiffness (flexibility)
tear strength
mixing time (min)
working time (min)
Shore A hardness
thermal contraction
Shark fin test (flow under pressure)
setting shrinkage
dimensional stability
thermal expansion coefficient
biocompatibility
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16
Q

ideal properties

A

quality of surface interaction between material and tooth/soft tissue surfaces
accuracy
dealing with removal and undercuts
dimensional stability

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17
Q

ideal properties - quality of surface interaction between material and tooth/soft tissue surfaces

A

viscosity
surface wetting
contact angle

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18
Q

ideal properties - accuracy

A 
surface reproduction (ISO)
viscoelasticity/elastic recovery
19
Q

ideal properties - dealing with removal and undercuts

A

rigidity
flow under pressure “shark fin test” - flows readily under pressure - large shark fin length
tear/tensile strength
- removing from undercuts
- can have a good shark fin length but if tears easily then not good when you come to remove it
- not too high - if in deep undercut might not be able to remove it

20
Q

ideal properties - dimensional stability

A

setting shrinkage
thermal expansion/contraction
- contraction when you remove it from warmer oral cavity to cooler room temp

21
Q

viscosity

A

measure of a materials ability to flow
determines a material’s potential for making close contact with surfaces
how well it records surface detail

22
Q

contact angle

A

determines how well material envelop the hard/soft tissue surface (to record fine detail)

23
Q

surface wetting

A

must make intimate contact with teeth/mucosa

is material hydrophillic?

24
Q

small contact angle

A

no spaces between globules of impression material so all of surface is replicated

25
Q

large contact angle

A

spaces between globules of impression material, so some of tooth surface not replicated

26
Q

reproduction of surface detail - ISO

A

standard notch dimensions
A - 20um
B - 50um ISO norm
C - 75um

27
Q

elasticity ideal behaviour

A

no permanent deformation - once load (strain) removed material back to original dimensions

28
Q

flow under pressure - shark fin test

A

force - impression material - chamber with slot
high flow = large fin length (will flow rapidly into sulcus, undercuts)
low flow = short fin length

29
Q

tear/tensile strength

A

stress material will withstand before fracturing

30
Q

rigidity

A

stress/strain ratio i.e. stress needed to cause material to change shape
ideally low value i.e. flexible - for ease of removal of material, esp from undercut regions

31
Q

viscoelastic behaviour

A

occurs when after being stretched/compressed a material fails to return to its original dimensions/shape
i.e. there is a permanent deformation

32
Q

minimising permanent deformation with viscoelastic behaviour

A

remove tray quickly with a sharp pull
- if load time is less there is less overall permanent strain (lower deformation)
leave before pouring - recovery takes time
elasticity only develops after material is firm - don’t remove tray too soon

33
Q

setting shrinkage

A

low

34
Q

thermal expansion/contraction

A

a large difference between mouth and room temp may cause a change in shape
ppm/degrees should be low

35
Q

storage

A

some materials absorb/release moisture causing a change in its dimensions

36
Q

extrude

A

PVS addition cured

37
Q

impregum

A

polyether

38
Q

aquasil

A

addition silicone

39
Q

virtual

A

addition silicone

40
Q

flexitime

A

addition silicone

41
Q

best elastic recovery

A

virtual

42
Q

best tear strength

A

virtual

43
Q

viscosity depends on

A

molecular weight of polymer

additives e.g. fillers

44
Q

cross-linking

A

binding chains to form a 3D network

DMS :( (18 decks)

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