Impression Materials Flashcards
What is the function of an impression materials
produce an accurate replica of the surface and shape of hard and soft oral tissues
What is an impression
a negative reproduction of tissues
What is a mucostatic impression material
Fluid that displace the tissues only slightly - give a impression of displaced soft tissue (e.g low viscosity alginates)
What is a mucocompressive impression material
Viscous materials that record an impression of the mucosa under load i.e give impression of displaced soft tissue (e.g impression compound elastomers)
What are requirements of an impression material
Accuracy - low viscosity and wetting ability (liquids ability to maintain contact with solid surface)
Dimensional Stability - on setting and removal, long term
Handling characteristics- strength and tear resistance
Miscellanous factors - cost, taste, colour
What is viscoelasticity
a material exhibiting both viscous and elastic properties, i.e will deform but will return to original shape unless stress is maintained or increased beyond elastic limit
What are the two main groups of elastic materials
Hydrocolloids (2 phase system made of fine particles dispersed using water)
- alginate (irreversible)
- agar (reversible)
Elastomers
- Polysulphides (hydrophobic)
- Polyethers e.g impregum (hydrophilic)
- Silicone (addition or condensation)
What are the main two kinds of non-elastic impression materials
- Impression compound (thermoplastic)
- Impression paste
used in edentulous patients as the undercuts of teeth cause the material to fracture
Describe the components of alginate
- sodium alginate (reacts w/calcium ions)
- calcium sulphate (provides the calcium ions)
- trisodium sulphate (slows down the gelation process)
- Filler (increases cohesion and strength)
- Modifiers (taste, colour pH etc)
