Elastomeric Impression Materials
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what are the two types of elastomer?
polyether and addition silicone
what do you consider when assessing materials for use?
source, product, evidence, reliability
what material properties do you consider when assessing materials for use?
flow/viscosity, surface detail, wettability, elastic recovery, stiffness, tear strength, mixing time, working time
what is the ISO standard for impression materials?
grooves/indentations of either 20um or 50um are replicated
what factors influence the quality of surface interaction between material and tooth/soft tissue surfaces
viscosity, surface wetting
what factors influence accuracy of impression materials?
surface reproduction, visco-elasticity
what factors are important when thinking about removal of impression materials and undercuts?
tear/tensile strength, rigidity
what are the ISO standards designed to do?
exclude unsafe and poorly performing materials from the market
what is viscosity?
a measure of materials ability to flow
what does viscosity determine?
a materials potential for making close contact with hard/soft tissue surfaces so how well it records surface detail
what does surface wetting mean?
impression material must make intimate contact with teeth/mucosa surfaces
what is the ideal elasticity?
no permanent strain
as the materials are viscoelastic, was is the ideal amount of viscoelasticity?
low so small deformation
what is a materials tear strength?
the stress a material will withstand before fracturing
what s the ideal rigidity for impression material?
low rigidity to ease its removal from undercut/interdentla regions
which elastomer has higher setting time and working time?
polyethers
what should you do when decision making about materials?
know the key properties of the material, review the product specification, know typical values expected for specific properties, identify properties not mentioned, reject claims not supported with scientific and/or clinical data