Elastomers
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What are the benefits of Alginate: Rapide 105
Speed set alginate - high levels of patient comfort are maintained due to speed of setting coupled with a pleasant taste. Unique alginate polymer and excellent water solubility gives greater ease of mixing. Enhanced thixotrophy gives greater accuracy of impression without excessive flow Resultant high elasticity copes with the most severe undercuts. The dimensional stability controlled by pH balance in the formula limits syneresis of the final impression. A perfect unblemished surface finishes off the cast model.
What depth of grooves must be replicated to meet the ISO standard for impression materials
20um or 50um depending on viscosity
What are the properties of Virtual
High tear strength Superior elastic recovery Accurate recording of surface detail Excellent wettability Good contrasting colours (caramel/blue) Convenient to work with - flexible setting times
What is viscosity
• a measure of material’s ability to flow • determines a material’s potential for making close contact with hard/soft tissue surfaces…….so how well it records surface detail
What is surface wetting
– impression material must make intimate contact with teeth/mucosa surfaces – so all of surface is replicated
What is the ideal elasticity behaviour of an impression material
Complete 100% elastic recovery No permanent strain
What reduces the amount of permanent strain
Removing the material quickly with a sharp pull
Is the ideal viscoelasticity high or low
Low viscoelasticity (small deformation)
Which are better impression materials - polyethers or addition silicones
The combination of the polymer and innovative spheroid silicon micro-fillers ensures exceptional precision and excellent reproduction of anatomical details
What are types of elastomers
Polyethers Addition silicones
How are elastomes formed
Polymerisation with cross-linking of polymer chains
What type of material is virtual
Polyvinylsiloxane - addition silicone
What are the benefits of virtual
Hydrophilic Spreads easily and adapts smoothly to most oral tissues Ideal colour combination producing margins that are easy to read and percision impressions Dimensional stability for up to 2 weeks (time to pour models) Elastic recovery Good final hardness Sets quickly (flexible)
What is viscosity
A measure of material’s ability to flow
What does a large contact angle mean
Spaces between the globules of impression material so some of the tooth surface is not replicated
Why is a small contact angle desirable
All of the surface is replacated
What is permanent deformation
After being stretched a material fails to return to its original dimensions/shape
What does a short fin length when compressed indicate about a material
Low flow
What value should an elastomers rigidity be
Low for ease of removal from undercuts
What should setting shrinkage and thermal expansion co-efficient values be for impression materials
Low
Why are addition silicones better than polyethers
Greater working time - slightly greater setting time
What material has the best elastic recovery
Virtual
What material has the best tear strength
Virtual
When should a material be purchased
When there is sufficient evidence showing the new material is better