Impression Materials Flashcards
What properties are desirable for an elastomeric impression material?
Low viscosity
Good surface detail
Wettability- high
High elasticity (elastic recovery)
Flexibility
Tear strength
Mixing time
Working time
Low viscoelasticity
Flow under pressure
Low setting shrinkage
What is meant by wettability?
Surface wetting is the surfaces that the material contacts
High gettability means that it makes an intimate contact with teeth and mucosa.
What type of elastomers are present?
Polyether
Addition silicones (polyvinylsiloxanes).
What is the ideal scenario for an impression material?
As the impression material is placed over the tooth, it should undergo maximum strain.
Once removed from the mouth, it should go back to its original dimensions (100% elastic recovery) and no permanent strain.
What is the contact angle?
Determines how well a material envelopes the hard/soft tissue surface.
You want a small contact angle.
What is meant by viscosity?
A measure of a material’s ability to flow.
What two aspects determine accuracy?
Surface reproduction
Elastic recovery.
How does tray removal method influence viscoelastic behaviour?
The quicker the tray is removed from the mouth, the less permanent strain the material undergoes.
What is tear strength?
Stress material will withstand before fracturing.
What type of impression material is alginate?
Elastic, irreversible hydrocolloid.
What materials are non-elastic impression materials?
Impression compounds- red impression compound and green stick.
Waxes- red ribbon wax.
Why is it important that alginate impressions are covered in damp gauze?
It undergoes syneresis (released water) and therefore, shrinks.
What is the function of an impression material?
To produce an accurate replica of the surface and shape of hard and soft oral tissue.
Creates a negative reproduction of tissues.
Give examples of elastic impression materials
Hydrocolloids
Elastomers
What is meant by a hydrocolloid?
Colloid is a two phase system of fine particles that are dispersed in water.
