elastomeric impression

• محاضرة مادة سنيةد.رائدElastomeric Impression Materials

• Dr. Raied Al-Attar
• 2017-2018
• 6th lecture

Elastomeric =

Rubber-like polymers that show an elastic behavior at the time of load application
Higher tear strength

More stable dimensionally in storage

(No Synersis, Imbibation or Evaporation)

In comparison to hydrocolloids

• Elastomeric
• impression
• Materials
• (chemical)
• Polysulfide
• (hydrophobic)
• Silicones
• Polyether
• (hydrophilic)
• Condensation
• Silicone
• (hydrophobic)
• Addition
• silicone
• Hydrophobic
• type
• Hydrophilic
• type
Four different types

Presentation forms

• Materials’
• Consistency
• Light
• Medium
• Heavy
• Putty
• Silicone materials only

Polysulfide Rubber Impression Material

• CHEMISTRY

• A. Composition:
• Base paste
• 1. LMW Polysulfide
• 2. Fillers (Titanium dioxide)
• 3. Plasticizer (Dibutyl phethalate)
• Catalyst paste
• 1. Lead dioxide (Brown) or organic peroxides (Gray) reactor
• 2. Fillers (Titanium dioxide)
• 3. Plasticizer (Dibutyl phethalate)
Polysulfide Rubber

• 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,
• Lead dioxide is toxic and has bad smell, so it has been replaced in recent products by peroxide compounds
Polysulfide Rubber
OBVIOUS CHARACTERS

Condensation SiliconeImpression Material

• CHEMISTRY
• A. Composition:
• Base paste
• 1. LMW silicone polymer with terminal OH groups
• 2. Fillers (Colloidal silica or titanium dioxide) (white)
• Catalyst paste
• 1. Alkyl silicate (Cross linking)
• 2. Tin dilaurate or Stannous octoate (Activator)
Condensation Silicone

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


Condensation Silicone
OBVIOUS CHARACTERS

Addition SiliconesImpression Materials

Addition Silicones

• CHEMISTRY
• A. Composition:
• Base paste
• 1. Poly methyl hydrogen siloxane (Hydried or silane terminated silicone)
• 2. Other Siloxane pre-polymers
• 3. Fillers
• Catalyst paste
• 1. Divinyl poly(dimethyl siloxane)
• 2. Platinum salt activator (Chloroplatinic acid)
• 3. Siloxane pre-polymers
• 4. Fillers

• 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 details
• 2.  Air bubbles in gypsum cast
• Disadvantages:
• 1. Setting reaction could be retarded in presence of sulfur (in latex gloves) or sulfate compounds (in gingival retraction cords)
• HYDROPHILIC SILICONE
Addition Silicones


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

Addition Silicones

OBVIOUS CHARACTERS

Polyether RubberImpression Material

• CHEMISTRY
• A. Composition:
• Base paste
• 1. LMW polyether with terminal imine groups
• 2. Filler (colloidal silica)
• 2. Plasticizer (dibutyl phethalate or glycoether)
• Catalyst paste
• 1. Aromatic sulfonate reactor (Sulfonic acid ester)
• 2. Fillers
• 3. Plasticizer
Polyether Rubber


• 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 used
Polyether Rubber

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

should be stored in dry environment to preserve its dimensional accuracy
OBVIOUS CHARACTERS
Polyether Rubber

• Comparative Properties of Elastomeric Impression Materials

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
Comparative Properties

Interfacial properties:

1. Hydrophilicity…
Polysulfide, cond. Silicone, & add. Silicone are hydrophobic
Hydrophilic silicone and polyether are Hydrophilic

2. Compatibility with model and die materials...

hydrophobic materials may cause air bubbles in stone casts

Comparative Properties

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 rate


Comparative Properties

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.

Comparative Properties

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 smell
Comparative Properties

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)
Comparative Properties