Elastomeric Impression Materials
Elastomeric = Rubber-like polymers that show an elastic behavior at the time of load
application
These polymer molecules have weak interaction in
between (Van der Wall forces), although they are tied
together in 3D network.
On stretching (on loading) chains uncoil
At rest (off loading) chains snap backC
hem
ical N
atu
re
Higher tear strength
More stable dimensionally in storage
(No Synersis, Imbibation or Evaporation)
Ability to be electroplated
But, Quite Expensive !!!!But, Quite Expensive !!!!In c
om
pari
son
to
hyd
rocolloid
s
Elastomeric impression materials
Polysulfide(hydrophobic)
SiliconesPolyether
(hydrophilic)
Condensation Silicone
(hydrophobic)
Addition silicone
Hydrophobic type
HydrophilictypeF
ou
r d
iffere
nt
typ
es
Pre
sen
tati
on
fo
rmsMaterials’
Consistency
Light
Medium
Heavy
PuttySilicone materials only
Polysulfide Rubber Polysulfide Rubber Impression MaterialImpression Material
CHEMISTRY A. Composition:
Base paste 1. LMW Polysulfide with two terminal and one pendant
SH groups 2. Fillers (Titanium dioxide) 3. Plasticizer (Dibutyl phethalate)
Catalyst paste1. Lead dioxide (Brown) or organic peroxides (Gray)
reactor2. Fillers (Titanium dioxide) 3. Plasticizer (Dibutyl phethalate)
Poly
su
lfid
e
Ru
bb
er
Poly
su
lfid
e
Ru
bb
er
B. Setting Reaction:
+ Pb +H2o
HS---- R ---- SH HS---- R ---- SH
SH SH+PbO2
HS---- R ---- S S---- R ---- SH
HS---- R ---- S S---- R ---- SH
S
S
S
S + Pb +H2o
HS---- R ---- SH HS---- R ---- SH
SH SH+PbO2
HS---- R ---- SH HS---- R ---- SH
SH SH+PbO2
HS---- R ---- S S---- R ---- SH
HS---- R ---- S S---- R ---- SH
S
S
S
S
Condensation polymerization (exothermic + shrinkage) with releasing of H2O as reaction by-product
It occurs as a series of simple oxidation reactions
Oxidation of terminal SH groups polymer chains
Oxidation of pendent SH groups Cross-linking
Material sets via condensation polymerization reaction
Water is the reaction by-product Evaporation of water + polymerization shrinkage
Dimensional changes in storage Water could cause air bubbles in stone cast Polysulfide is hydrophobic, and can be electroplated
Lead dioxide is toxic and has bad smell, so it has been replaced in recent products by peroxide compoundsP
oly
su
lfid
e
Ru
bb
er
OBVIOUS CHARACTERS
Condensation SiliconeCondensation SiliconeImpression MaterialImpression Material
CHEMISTRY A. Composition:
Base paste 1. LMW silicone polymer with terminal OH groups 2. Fillers (Colloidal silica or titanium dioxide) (white)
Catalyst paste1. Alkyl silicate (Cross linking)2. Tin dilaurate or Stannous octoate (Activator)
Con
den
sati
on
S
ilic
on
e
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
Si
C2H5OC2H5O
C2H5O C2H5O
C2H5OHSi
OO
O O
HO Si - O - Si
CH3
CH3 CH3
CH3
HO Si - O - Si
CH3
CH3 CH3
CH3
Si - O - Si OH
CH3
CH3 CH3
CH3
Si - O - Si OH
CH3
CH3 CH3
CH3
+
HMW Silicon Polymer Ethyl Alcohol
Dimethyl Siloxane Alkyl Silicate
StanousOctoate
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
Si
C2H5OC2H5O
C2H5O C2H5O
C2H5OHSi
OO
O O
HO Si - O - Si
CH3
CH3 CH3
CH3
HO Si - O - Si
CH3
CH3 CH3
CH3
Si - O - Si OH
CH3
CH3 CH3
CH3
Si - O - Si OH
CH3
CH3 CH3
CH3
+
HMW Silicon Polymer Ethyl Alcohol
Dimethyl Siloxane Alkyl Silicate
StanousOctoate
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
HO Si - O - Si OH +
CH3
CH3 CH3
CH3
Si
C2H5OC2H5O
C2H5O C2H5O
Si
C2H5OC2H5O
C2H5O C2H5O
C2H5OHSi
OO
O O
HO Si - O - Si
CH3
CH3 CH3
CH3
HO Si - O - Si
CH3
CH3 CH3
CH3
Si - O - Si OH
CH3
CH3 CH3
CH3
Si - O - Si OH
CH3
CH3 CH3
CH3
+
HMW Silicon Polymer Ethyl Alcohol
Dimethyl Siloxane Alkyl Silicate
StanousOctoate
B. Setting Reaction:
Condensation poly-merization (exothermic + shrinkage) releasing C2H5OH as reaction by-product
It occurs as a series of cross-linkage of siloxane polymer to alkyl silicate in presence of the activator, to form a 3D polymer networkC
on
den
sati
on
S
ilic
on
e
Material sets via condensation polymerization reaction
Ethyl alcohol is the reaction by-product Evaporation of alcohol + polymerization shrinkage
Dimensional changes in storage > that of polysulfide Alcohol could cause air bubbles in stone cast Cond. silicone is hydrophobic, and can be
electroplated either with silver or copper
Con
den
sati
on
S
ilic
on
e OBVIOUS CHARACTERS
Addition SiliconesAddition SiliconesImpression MaterialsImpression Materials
Ad
dit
ion
Silic
on
es
CHEMISTRY A. Composition:
Base paste 1. Poly methyl hydrogen siloxane (Hydried or silane
terminated silicone)
2. Other Siloxane pre-polymers
3. Fillers
Catalyst paste1. Divinyl poly(dimethyl siloxane)
2. Platinum salt activator (Chloroplatinic acid)
3. Siloxane pre-polymers
4. Fillers
B. Setting Reaction:
Addition polymerization (exothermic + shrinkage) with no release of by-product
It occurs as a series of cross-linkage between vinyl-terminated silicon and silane-terminated (hydried) silicon molecules, in presence of the catalyst (platinum salt) to form a 3D polymer network
A side reaction (Releasing hydrogen gas Air bubbles in gypsum cast) may occur if : 1. No balance between vinyl siloxane and the hydried silicone2. Moisture react with hydrides of the base polymer
Adding noble metal (platinum or palladium) to the composition will act as hydrogen absorberA
dd
itio
n S
ilic
on
es
Adding surfactants (surface tension reducing agents) to the composition of add. silicone help turns the material to be hydrophilic (water lover)
Advantages:1. Better wetting of soft tissue registration of better details2. Air bubbles in gypsum cast
Disadvantages:1. Difficult to be electroplated2. Setting reaction could be retarded in presence of sulfur (in latex gloves) or sulfate compounds (in gingival retraction cords)
HYDROPHILIC SILICONEA
dd
itio
n S
ilic
on
es
Material sets via Addition polymerization reaction (No by-product) More dimensionally stable than condensation-polymerized materials
Hydrogen gas may release from a side reaction in presence of moisture or imbalance of the reactants. But, adding noble metal to the composition prevents the release of hydrogen gas no air bubbles in the gypsum cast
Add.silicone is hydrophobic and can be electroplated, however adding of surfactants turns the material hydrophilic
Ad
dit
ion
Silic
on
es
OBVIOUS CHARACTERS
Polyether RubberPolyether RubberImpression MaterialImpression Material
CHEMISTRY A. Composition:
Base paste 1. LMW polyether with terminal imine groups
2. Filler (colloidal silica)
2. Plasticizer (dibutyl phethalate or glycoether)
Catalyst paste1. Aromatic sulfonate reactor (Sulfonic acid ester)
2. Fillers
3. Plasticizer
Poly
eth
er
Ru
bb
er
CHEMISTRY
B. Reaction: (Cont.d) Material sets via ring opening addition poly-
merization reaction (No by-product) of imine- terminated polyether with the aromatic sulfonate
LIGHT-CURED POLYETHER It is based on polyether-urethane dimethacrylate,
photo-initiator, accelerator, and silicone filler (has refractive index similar to resin that helps in maximizing the depth of curing)
This material is no longer be usedPoly
eth
er
Ru
bb
er
Material sets via Addition polymerization reaction (No by-product) More dimensionally stable than condensation polymerized materials
Set material is so stiff (as a result of high rate of crosslinking), so tray adhesive must be used to retain the material within the tray at the time of removing an impression
Polyether is hydrophilic and can absorb water in wet condition (swelling), accordingly Can not be electroplated should be stored in dry environment to preserve its
dimensional accuracy
OBVIOUS CHARACTERSP
oly
eth
er
Ru
bb
er
Comparative Properties Comparative Properties of Elastomeric Impression of Elastomeric Impression
MaterialsMaterials
Biological properties:
1. Lead dioxide (polysulfide) is toxic, but following the manufacturer’s instruction will decrease this risk
2. Alcohol by-product (cond. Silicone) is irritant to oral soft tissues
3. Aromatic sulfonate (polyether) is irritant, but proper mixing will decrease this irritability
Com
para
tive
Pro
pert
ies
Interfacial properties:
1. Hydrophilicity… Polysulfide, cond. Silicone, & add. Silicone are
hydrophobic Hydrophilic silicone and polyether are Hydrophilic
2. Compatibility with model and die materials... Hydrophilic materials can not be electroplated Polysulfide could be electroplated with silver, while
silicones could be electroplated either with silver or copper
hydrophobic materials may cause air bubbles in stone casts
Com
para
tive
Pro
pert
ies
Interfacial properties: (cont.d)
3. Separating media… There is no need (elastic materials) for separating
medium before pouring the cast
4. Detail reproduction… Although, hydrophilic materials show better
registration of details than hydrophobic ones, Polysulfide is the best detail reproducer due to its higher flow rateCom
para
tive
Pro
pert
ies
Mechanical properties:
1. Flexibility... Polysulfide > Cond. Silicone > add. Silicone > polyether
2. Flow...Polysulfide > Cond.silicone > Polyether > Add. Silicone
3. Permanent deformation…Polysulfide > Cond.silicone > Polyether > Add. Silicone
4. Tear strength…Polyether > polysulfide > silicones
5. Recovery…Rubber materials are viscoelastic, so impressions should be poured 30 min after removal from the patient mouth in order to get the whole elastic and delayed recovery of imp.mat.
Com
para
tive
Pro
pert
ies
Chemical properties:
1. Dimensional changes…Cond. silicone > polysulfide > Polyether > add silicone
All materials are associated with setting (polymerization) shrinkage
All condensation polymerized materials are less stable in storage as a result of evaporation of the reaction by-product
2. Odor…Lead dioxide-containing polysulfide has bad smellCom
para
tive
Pro
pert
ies
Practicability:
1. Mixing time... (45 sec.- 1 min.)
2. Working time... (average 5 min.)
3. Setting time... (average 8-12 min)
4. Coast... higher than hydrocolloids
5. Shelf life…storage in refrigerator elongate the shelf life
6. Disinfection… could be done either by spray or short immersion technique using NaOCl, Iodofore or Glutaraldehyde. Care should be expressed with hydrophilic materials (not immersed for long time)
Com
para
tive
Pro
pert
ies
Materials’ ManipulationMaterials’ Manipulation
Man
ipu
lati
on
Mixing:
1. Using paper pad (Glass slab) and SpatulaLight, medium and heavy consistencies
2. Hand KneadingHeavy or putty consistency
3. Automixer and DispenserCartridge form only (Light, medium, heavy)
4. Automatic mixingAll consistencies, special electric mixer + special material form
Man
ipu
lati
on
Man
ipu
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on
Trays:
1. Stock tray... Used with heavy and putty consistency Retention come through; tray perforations, rim locks, or tray
adhesive
2. Special tray… Used with light and medium consistency Retention comes from; tray perforations and tray adhesive
3. Wash impression... Some times heavy or putty impressions act as special tray for
light consistency material
Man
ipu
lati
on
Uses:
1. Impression making... Copper ring impression Monophase impression Double mix single phase impression Double mix double phase impression (over-wash impression) Closed mouth-double arch impression
2. Occlusal bite registration…A specially supplied rubber material is used for this purpose (commonly cartridge form)Man
ipu
lati
on
Your Comments Your Comments are appreciatedare appreciated