Elastomeric Impression Materials
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What are the two impression materials?
Polyether Addition silicone
What are the desirable qualities of an impression material?
Accurate detail reproduction Elastic recovery High tear strength Dimensionally stable Ease of use Speed of setting
What are the ISO standards?
Dental Standard – designed to assess relevant properties of a product to see whether it meets acceptable requirements for safe and effective use
What is the ISO standard for impressions materials?
• grooves/indentations of either 20um or 50um (depending on material viscosity) are replicated
What components in addition silicone ensure exceptional precision and excellent reproduction of anatomical details?
The combination of the polymer and spheroid silicon microfillers
What does a good wetability mean?
Material spreads easily and adapts smoothly to denture and moist oral tissue
What is the purpose of the ISO standards?
“Standards are NOT designed to establish which is the “best performing” material for a given clinical application ……(instead) they are designed to exclude unsafe and poorly performing materials from the market”
What are the ideal properties of impression materials?
Viscosity – must be able to flow readily Surface wetting – must make intimate contact with teeth/mucosa close to 0 degrees is best Accuracy - surface reproduction and viscosity-elasticity/ elastic recovery Tear Strength - stress material will withstand before fracturing Low rigidity - ideally impression material is FLEXIBLE ie has low rigidity, to ease its removal from undercut /interdental regions
What is viscosity and what is the different ranges?
• a measure of material’s ability to flow • determines a material’s potential for making close contact with hard/soft tissue surfaces (how well it records surface detail) - range: low, medium, high
What is the ideal elasticity of a material?
100% elastic recovery Recovery from deformation, no permanent strain
What should be done to reduce permanent strain/deformation?
If LOAD time is less - and impression removed with a sharp pull, there is less overall permanent strain (ie lower deformation)
What is the ideal viscoelasticity?
when impression material, having been stretched/compressed on removal from mouth, fails to return to its original dimensions/shape ie there is permanent deformation (permanent strain) IDEAL – low viscoelasticity (small deformation)
What type of material has a shorter working and setting time?
Polyether