Impression Materials Flashcards
What different situations would result in different ideal properties for an impression material?
Single tooth
Whole dentition
Edentulous mouth
What is the function of an impression?
To produce an accurate replica of the surface & shape of hard and soft oral tissues
What are the classifications of impression materials?
Clinical - mucostatic, mucocompressive
Properties - elastic, non elastic
What is a mucostatic impression material?
Fluid material that displaces the soft tissue slightly - giving an impression of the undisplaced mucosa.
e.g. zinc oxide eugenol, low viscosity alginates
What is a mucocompressive impression material?
Viscous materials that record an impression of the mucosa under load - giving an impression of displaced mucosa.
e.g. impression compound, high viscosity alginates/elastomers
What are the elastic impression materials?
Hydrocolloids - alginate (irreversible)
Elastomers - polyethers, silicones (conventional & addition cured)
What are the non-elastic impression materials?
Impression compound
Impression paste
What is impression compound?
Combination of resins, wax, stearic acid and filler pigments
What are the properties of impression compound?
High thermal expansion Poor fine detail Plastic deformation during removal Stability OK Non toxic, non irritant Setting time OK Sterilisation difficult Long shelf life Compatible with die materials
What is impression paste?
Two pastes
- ZnO powder + oil
- eugenol + inert filler
\+ accelerator
\+ hydrogenised resin
a.k.a. ZOE pasteWhat are the properties of impression paste?
Setting time OK (3-8 mins) Fine details OK Setting changes OK Not elastic Storage OK Compatibility with stone OK Non toxic, non irritant (eugenol may cause allergies) Adheres to tissues (must coat lips with petroleum jelly) Shelf life OK Expensive
What are hydrocolloids?
2 phase system of fine particles (1-200nm) of one phase dispersed in another phase
States - SOL (viscous liquid state), GEL (jelly like consistency)
e.g. alginate & agar (not used anymore)
What are the properties of alginate?
Flow fine detail ok Setting changes ok Nearly elastic (viscoelastic) Poor tear strength Non toxic, non irritant Acceptable taste and smell Setting time OK Relatively easy to use Must be prepared ASAP as it changes shape
What is an elastomer?
A polymer with viscoelasticity & very weak intermolecular forces
What properties should you assess in an impression material?
Flow/viscosity Surface detail reproduction Contact angle/wettability Elastic recovery (%) Stiffness Tear strength Mixing time (min) Working time (min)
