Impression material classification and basic requirements:
Classification of impression materials:
Non elastic - used in mouth with no undercuts or no teeth.
Zinc oxide eugenol.
Hydrocolloids (aqueous) - Agar (reversible), Alginate (irreversible).
Polysulfides - lead dioxide catalyst, clean catalyst.
Silicons - condensation, addition.
Classification according consistency:
According viscosity -
Type 0 à very hard, very high viscosity à putty.
Type 1 à hard, high viscosity à putty.
Type 2 à medium viscosity.
Type 3 à low viscosity.
Type 0 & 1 can combined with type 3 for precise.
Mucostatic impression material - less likely to compress soft tissue
Mucocompressive impression material - more viscous.
Requirements for impression material:
Accurate & persise - mainly depend on viscosity of the mixed and the ability of the impression material to adapt closely to both the soft and the hard tissues. Materials that very fluid are called mucostatic impression materials because they are less likely to compress soft tissues. While initially more viscous material called mucocompresive.
Dimensional stability - contraction of material may produce oversized die.
Proper working and setting time.
Non toxic and non-irritating.
Easy to mix.
Pleasant taste and odor.