Elastomeric Impression Materials
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what are examples of elastomer materials used in dentistry?
• polyethers - addition silicone
what is an essential property of elastomeric materials required in dentistry?
must have elastic recovery as close to 100% as possible
what are some essential properties an elastomer impression material must have in order to record accurate surface detail?
• low viscosity (ability to flow over tooth surface) - good wettability/contact angle between the tooth and material
how might the stiffness of an elastomeric impression material affect its use in practise?
stiffness will determine how readily removed the material is from the mouth
what is the ISO dental standard for impression materials?
grooves/indentations of either 20um or 50um (depending on material viscosity) are replicated
what are the ideal properties of an elastomeric impression material when dealing with removal & undercuts within the mouth?
• high tear/tensile strength - low rigidity (flexible) so it is able to disengage easily & overcome bulbous part of tooth
what is meant by viscosity? how does this property determine a materials use as an impression material?
• a measure of a materials ability to flow - determines a materials potential for making close contact with hard/soft tissue surfaces
why is surface wetting important in an elastomeric impression material?
impression material must make intimate contact with teeth/mucosa surfaces (so all of surface is replicated)
what would 100% elastic recovery in an impression material mean?
NO permanent strain on removal from mouth
when removing an impression from the mouth, why is it done in a quick and hard manner?
if LOAD TIME is less, and impression is removed with a sharp pull, there is less overall permanent strain
what is the tear strength of a material?
the stress a material will withstand before fracturing
if a material is rigid, what is meant by this?
a large stress is needed to cause material to change shape