Impression Materials Flashcards
What do dimensional changes need to add up to?
zero
What are the three types of impression materials?
rigid, plastic and (visco)elastic
Viscoelastic impression materials are found as reversible (agar) or irreversible (alginate) ___.
hydrocolloids
Viscoelastic impression materials can also be found as synthetic ___. These are ___ that polymerize into ___.
elastomers; oligomers; elastomers
What are the different forms of synthetic elastomers?
polysulfide, silicone, polyether, and new product
Which is the most common for of synthetic elastomer?q
addition silicone
T/F. Light and heavy body impression materials are used separately to enhance the accuracy of the final impression.
False, they are used together.
T/F. The light impression material is used for detail while the heavy is used in the other areas.
True.
Define hydrocolloid.
Water is bound within a colloid matrix
Both Alginate (___)(reversible/irreversible) and Agar (___) (reversible/irreversible) lack dimensional stability with time and require ___ pouring of models.
irreversible; reversible; immediate
What type of polymer has no cross-linking and its physical state is reversibly controlled by temperature? For example, when heated it is fluid and when cooled it can be removed from the patient.
Thermoplastic
A ___ polymer is transformed from monomer to polymer and involves irreversible ___.
Thermoset; cross-linking
T/F. Condensation polymerization releases no by products.
False, addition polymerization releases no by-products whereas, condensation does.
During the change from liquid or paste into a solid, advantageous final properties are ___ (increased/decreased).
increased.
During the change from liquid/paste into a solid, the inherent density increase causes a volumetric ___ (shrinkage).
contraction
During the change from liquid/paste into a solid, heat of reaction causes material to ___ ___, but this is usually minor.
heat up.
During the change from liquid/paste into a solid, there is a ___ on cooling.
contraction
Polysulfide low molecular weight oligomers containing reactive ___ groups.
mercaptan
Polysulfide oxidized by lead dioxide or copper hydroxide to form a polysulfide ___ with a ___ condensate. This stains and does not taste good.
rubber; water
T/F. For polysulfides to be accurate, this material requires a rigid custom tray for minimal thickness of impression materials.
True.
T/F. Polysulfides recover from permenant deformation.
False, they do not recover from permanent deformation.
T/F. Polysulfides should be poured as quickly as possible.
True.
Silicones (Polysiloxanes) are inherently ___ but the addition type can be made more ___.
hydrophobic; hydophilic
What was the first type of silicone introduced?
condensation
How do you make the addition type of silicone more hydrophilic?
simple addition of surfactant or chemical incorporation of hydrophilic moieties into the silicone backbone.
Fluid material needs a ___ contact angle, therefore you want it to be ___.
low; hydrophilic
Why are contact angles important?
unset impression material over wet oral structures
unset gypsum-water mix into set impression
Condensation silicone have low molecular weight oligomers containing reactive terminal ___ groups which react with ortho-ethyl silicate and stannous octoate to form the three dimensional network rubber with the liberation of ___ ___.
hydroxyl; ethyl alcohol
With addition silicone, in the presence of ___ acid, ionic polymerization produces chain-lengthening and cross linking.
chloroplatinic
With addition silicone, if there is residual ___ groups present from the mucosa, a secondary reaction occurs which produces ___ gas.
hydroxyl; hydrogen
T/F. Pouring of addition silicone should be delayed.
True. It should be delayed until all of the hydrogen is liberated.
What can contaminate addition silicone impression materials?
latex rubber gloves because of the sulfur
If unmixed polyether contacts the skin or mucous membranes, this will cause contact ___.
dermatitis
What are the four requirements of an ideal impression material?
- low cost
- long shelf life
- biocompatibility
- pleasant to patient
What are the properties before setting?
ease of manipulation
control over working time
good wetting (low contact angle) on moist oral structures
What are the properties during setting?
no dimensional change
short setting time
What are the properties after setting?
- high flexibility
- high tear strength (a function of rate of strain)
- no dimensional change
- high elastic recovery
- from applied stress
- upon standing - compatibility with disinfectants
- compatibility with die and cast materials
- contact angle of gypsum-water mix
- chemical interference
- reproduction of fine detail
