Elastomers Flashcards
The process of changing the rubber
base product or liquid polymer to a rubber-like material.
Vulcanization/Curing
Classification of Elastomers based on chemical composition
- Polyether
- Polysulfides
- Silicones
a. Addition
b. Condensation
Types of consistency/viscosity for rubber impressions
- Light bodied impression
- Regular/medium bodied
- Heavy bodied
A group of flexible chemical polymers that are either chemically
or physically cross-linked.
Elastomeric Impression Materials
T or F
Elastomeric impression materials can be easily stretched and rapidly recover their original dimensions when applied stresses are released
True
Introduced in Germany in late 1960’s and first elastomer to be developed as impression material.
Polyether
Polyether Base and Catalyst
Base
- polyether polymer
- colloidal silica (filler)
- glycol ether or phthalate
Catalyst
- alkyl aromatic sulfonate
Advantages of polyether
- Fast working and setting time
- Less hydrophobic (better wetting)
- Long shelf life
- Proven accuracy
- Adequate tear strength
Disadvantages of polyether
- Clean but tastes bad
- Slightly more expensive
- Stiffness requires blocking undercuts
First non-aqueous elastomeric impression material often called “rubber” or “rubber base”
Polysulfide
Polysulfide Base and Catalyst
Base
- Lithopone and titanium
dioxide (filler)
- Dibutyl phthalate (plasticizer)
- Sulfur (0.5%)
Catalyst
- Lead dioxide (dark
brown color)
- Oleic and stearic acid
(retarders)
Polysulfide disadvantages
- Requires a custom tray
- Odor (unpleasant)
- Messy and stains
clothes - Second pour is less
accurate - Potential for significant
distortion
It was the first type of silicone impression material, and also known as conventional silicones.
Condensation silicone
supplied as a base paste and a low-viscosity liquid catalyst, a two-paste system, or a two-putty system
Condensation silicone
Condensation silicones advantages
- Adequate working and
setting time - Pleasant odor and no
staining - Adequate tear strength
- Better elastic properties
on removal
Condensation silicone base and catalyst
Base
- Colloidal silica
- Metal oxide (filler)
- Colorants (homogenous
mix)
Catalyst
- Alkyl silicate and organo-tin compounds
Condensation silicones disadvantages
- Poor dimensional
stability - Slightly more expensive
- Putty wash method is
technique sensitive. - Potential for significant
distortion
Frequently called as polyvinyl siloxane, and introduced after condensation silicones.
Addition silicone
Commonly used in complete denture.
Addition silicone
Advantages of Addition silicones
- Shorter setting time.
- Easy to mix (automatic mixing devices)
Addition silicones disadvantages
- More expensive (automatic mixing
device) - Hydrogen gas evolution
in some materials
Suspension of fine particles within a liquid.
Colloids
Colloids in water
hydrocolloid
Types of Colloids (2)
Lyophilic - liquid loving sols
Lyophobic - liquid hating
Any solution in which the unit of the
solute are sufficiently large so that it will not dialyze through a suitable
membrane.
Colloids
A substance that forms a gel with water.
Hydrocolloid
Tis is made up of submicroscopic fibrils, with spaces in between called _____
Micelles
Particles in a solution.
Dispersed particles
solution containing a suspension of
particles.
Dispersed Medium
Suspension
The dispersed phase and the dispersion medium are not of like phase.
Tendency to demonstrate a strong
aversion to water.
Hydrophilic
The dispersed phase is of the same
phase as of the dispersion medium.
Emulsion
Tendency to demonstrate a strong
affinity for water.
Hydrophilic
(agar) a colloid that contains water as the dispersion phase.
Hydrocolloid
Agar impression material.
Reversible Hydrocolloid
Alginate impression material.
Irreversible Hydrocolloid
The transformation from a hydrocolloidnsol to gel.
Gelation
The time needed to transform sol to gel.
Gelation time
the temperature in which the sol is
transformed into gel.
Gelation temperature
The transformation from gel to sol.
Liquefaction
Time needed to transform gel to sol
Liquefaction time
the temperature at which the gel is
transformed to sol at a higher
temperature. (60-70C)
Liquefaction temperature
the difference between gelation
and liquefaction temperature.
Hysteresis
Process of water sorption
Imbibition
expression of fluid onto the surface of gel structures.
Syneresis
expression of fluid onto the surface of gel structures.
Setting time
The total time from the start of mixing to the final time at which an impression tray can be fully seated without distortion.
Working time
