elastomeric impression materials Flashcards
chemistry
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
elastomers
polysulphides silicones - addition curing - condensation curing (conventional) polyethers
conventional silicone e.g. Verone chemistry - base paste
silicone prepolymer with terminal hydroxyl groups
filler
conventional silicone e.g. Verone chemistry - catalyst paste (or liquid)
cross-linking agents (alkoxyorthosilicate or organohydrogen siloxane)
activator - organo-tin compound
conventional silicone e.g. Verone chemistry - different setting reactions
different formulations have different setting reaction depending on cross-linking agents
- alkoxyl-orthosilicate
- organohydrogen siloxane
conventional silicone e.g. Verone chemistry - setting reactions
silicone polymers + organohydrogensiloxane - cross-linked polymer + H2
silicone polymers + alkoxyorthosilicate - cross-linked polymer + alcohol
addition cured silicone e.g. PVS e.g. extrude chemistry
base paste and catalyst paste
no byproducts
hydrophobic
addition cured silicone e.g. PVS e.g. extrude chemistry - base paste
polydimethylsiloxane - some methyl groups replaced by hydrogen
filler - variations change viscosity
addition cured silicone e.g. PVS e.g. extrude chemistry - catalyst paste
polydimethylsiloxane - some methyl groups replaced by vinyl
filler - variations change viscosity
platinum catalyst e.g. chloroplatinic acid
hydrophillic silicones
incorporate non-ionic surfactant
- wets tooth surface
- more easily wetted by water-containing die materials
polyethers e.g. Impregum chemistry
base paste
catalyst paste
polyether + sulphonate ester = cross-linked material
polyethers e.g. Impregum chemistry - base paste
imine terminated pre-polymer - cross-linking
inert filler - viscosity, strength
polyethers e.g. Impregum chemistry - catalyst paste
ester derivative of aromatic sulphonic acid - initiates polymerisation
inert oils - form paste
inert fillers - form paste
polyethers setting reactions
activation
initiation
propagation
material properties
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
ideal properties
quality of surface interaction between material and tooth/soft tissue surfaces
accuracy
dealing with removal and undercuts
dimensional stability
ideal properties - quality of surface interaction between material and tooth/soft tissue surfaces
viscosity
surface wetting
contact angle
ideal properties - accuracy
surface reproduction (ISO) viscoelasticity/elastic recovery
ideal properties - dealing with removal and undercuts
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
ideal properties - dimensional stability
setting shrinkage
thermal expansion/contraction
- contraction when you remove it from warmer oral cavity to cooler room temp
viscosity
measure of a materials ability to flow
determines a material’s potential for making close contact with surfaces
how well it records surface detail
contact angle
determines how well material envelop the hard/soft tissue surface (to record fine detail)
surface wetting
must make intimate contact with teeth/mucosa
is material hydrophillic?
small contact angle
no spaces between globules of impression material so all of surface is replicated
