L07: Impression Materials Flashcards
What is dimensional accuracy?
Key properties of material upon mixing/activation (prior to setting), and after setting
What is considered under dimensional accuracy?
Rheological properties, viscosity, hydrophobicity, wettability, shrinkage, tray adhesion, mechanical properties
What are rheological properties?
How it flows (before and after it comes into contact with the dental arch)
What do you have to consider in viscosity in dentistry?
Too viscous might not conform to small fine details, too low viscosity means it might make patient gag and flow down throat.
Edentulous patients - are soft tissues going to be influenced by the material? Less viscous are less likely to compress soft tissue whereas more viscous means there might be displacement of soft tissues. Problematic in denture design.
What is the relevance of hydrophobicity of impression materials in dentistry?
The mouth is a moist environment. Alginate is a hydrolytic reaction so is hydrophilic whereas silicones and elastomeric materials are hydrophobic (but have optimal mechanical properties.
What is wettability?
How a liquid wets a solid surface - how well a liquid spreads out over the surface of the material. Surface energy of the solid and surface tension of the liquid.
How does shrinkage affect impression materials?
Alginate has a cross-linking reaction. May be associated with change in volume, affecting accuracy.
How does tray adhesion affect impression materials?
Tray adhesion is important so there is no distortion of impression as it sets or is removed from the mouth. E.g., adhesive and perforated trays creating a mechanical interlock.
What mechanical properties of impression materials should we consider?
Tear resistance, tensile strength
What is dimensional stability?
Maintenance of the original accuracy.
It needs to last within the time of the impression being taken away
Does alginate have good dimensional stability?
No, alginates are bad in terms of stability due to hydraulic based, and water evaporates. If leaving it, it’ll shrink. Needs to be placed in damp cloth to stop evaporation/absorption of water.
What properties are part of dimensional stability?
Elastic recovery (time implication of returning back to its original dimension)
Residual stresses on cooling
Volatile components (water evaporation)
Tray adhesion
How are hard and soft tissue impressions affected by the viscosity of the impression material?
Hard tissue impressions - fine detail may be influenced
Soft tissue impressions - degree of tissue compression
What does mucostatic mean?
More fluid, so less likely to compress soft tissue
What does mucocompressive mean?
More viscous, more likely to compress soft tissue
What materials have high viscosity?
Putty elastomers (heavy-body)
Impression compound
What materials have medium viscosity?
Regular body elastomers
What materials have low viscosity?
Light body elastomers (wash)
Impression plaster
ZnO-eug paste
Hydrocolloid - agar (reversible) and alginate (irreversible)
How can you measure wettability?
Can measure by measuring the angle with which the liquid forms against the solid interface.