- more filler=thicker viscosity - more filler= lesser contraction (more accurate) - more filler= less detail

Impression Materials Flashcards by Rachel Walker

2 major categories of impression material:

inelastic (rigid)
elastic (flexibile)

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When did we use to use inelastic impressions specifically plaster?

for edentulous patients
ZOE is still used for cement
compound is still used for border molding

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What are the 2 types of elastic impression materials?

hydrocolloids (mainly use irreversible)
elastomers (polysulfide, condensation silicone, addition silicone, polyether)

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What are the 2 elastomers impression material that don’t have byproducts?

addition silicone
polyether

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Do you dispense by equal lengths of equal volumes of impression material?

equal lengths

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Polysulfide chemistry reaction:

condensation reaction
- byproduct: water

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Benefit of Polysulfide impression material:

manipulation time is long
it sets in 10-20 minutes

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Composition of Polysulfide:

base paste: polysulfide polymer, fillers
accelerator paste:lead dioxide, sulfur (made bad smelling)

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Lead free options of Polysulfide:

omniflex and coe flex

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Composition of condensation silicones:

base paste: dimethyl siloxane with reactive terminal hydroxyl groups (byproduct produced), fillers
accelerator paste: tin octoate and an alkyl silicate

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Properties of Polysulfide:

unpleasant odor (from sulfur)
stains clothing
extremely viscous/sticky
hydrophobic

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Properties of condensation silicones:

almost odorless
variety of colors
hydrophobic

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Chemistry of condensation silicones:

condensation rxn
- byproduct: alcohol

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Another name for addition silicones:

polyvinyl siloxane or vinyl polysiloxane

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What dental material has a composition with a base that has low molecular weight polymer with silane groups (-Si-H)?

addition silicones

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What do fillers do?

more filler=thicker viscosity
more filler= lesser contraction (more accurate)
more filler= less detail

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Accelerator/catalyst for addition silicones:

chloroplatini acid catalyst

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What is seen in addition silicones to help with less bubble formation?

palladium= it is a hydrogen absorber and hydrogen is what causes the bubbles

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Are addition silicones hydrophilic or phobic?

hydrophilic!
- different than polysulfudes and condensation silicones

which consistency has the least and most filler?

light (least amount of filler) < regular< heavy < putty (most amount of filler)

How is addition silicones dispensed and mixed?

mixed in cartridge and dispenses in gun
more accurate and not wasting much material (only waste in mixing tube)

How does the heavy wash/1 stage impression work?

heavy body in tray
wash material or light body around tooth

How does putty wash/2 stage impression work?

first, putty impression before prepping teeth
then add heavy body in tray and light body around teeth
better detail in all the teeth

Addition silicone properties:

almost odorless
naturally hydrophobic (catalyst inside to change it though)

Addition silicone setting reaction:

- rapid working time: 1-2 minutes setting time: 4-5 minutes

Chain lengthen increases

viscosity

Chain cross-linking increases

elasticity

Which impression material used to have a catalyst that would cause a reaction?

Polyether- benzene was in it that caused reaction. eliminated now

Which impression materials have an addition reaction with no by product?

- addition silicones - polyether

A newer material that gets good properties from both addition silicone and polyether

vinyl polyether silicone

Properties of vinyl polyether silicone:

- intrinsically hydrophilic - good flow - low contact angle (10 degrees/ polyether is 70 degrees) - working time: 2 minutes - setting time: 3.5 minutes - easier removal than polyether with increased flexibility - high tear strength (stretches out rather than tears)

Which material are easier to mix due to low initial viscosity?

silicones - but means they set quicker

Which have the most rapid setting function of time?

- addition silicone -polyether (due to low viscosity)

Decreasing viscosity will _______ shear rate

increase

Words for impression material thinning out when applying force:

shear thinning, pseudo plastic, thixotropic

Working/setting times in order:

polysulfide (longest) > silicones > polyethers (shortest)

Working/setting times are shortened by:

increasing temp and humidity - so will set faster in patients mouth

Shrinkage of impression material due to:

- evaporation of byproducts - thermal contraction - rearrangement of bonds during polymerization

Dimensional changes/shrinkage in order of material:

addition silicone (smallest) < polyethers and polysulfide < condensation silicone (largest)

Shrinkage occurs towards the ____

tray

Which materials can affect the dimensional change by absorbing water?

- polyether and hydrophilic addition silicone - don't wrap up in wet paper towel because then it will swell and cast will be smaller

Order of permanent deformation/elastic recovery of impression material:

addition silicone (best recovery)> condensation silicone> polyether> polysulfide

Order of flexibility/strain of impression materials:

polyether (stiffest) > addition silicone> condensation silicone> polysulfide (more flexible)

Which material have the lowest flow?

silicones and polyether

Order of hardness of impression materials:

polyether (hardest > addition silicone > condensation silicone > polysulfide

Order of tear strength of impression materials:

polysulfide (highest resistance) > silicones > polyether