Impression material (Elastic) Quiz 2 Flashcards
Why did we come up with elastic impression materials?
want a flexible gel which deforms elastically around undercuts and springs back into position without distortion
colloids
There two phases?
represent a molecular distribution of solute dispersed uniformly in a solvent; sugar in water. TWO separate phases can be IDed:
1) dispersed phase -sugar
2) dispersion phase h2O
The ______ ____ of the dispersed phase is used to classify dispersed systems
particle size
Colloids 1) small dispersed molecules are considered to be ______ 2) macro-sized solid molecules visible to the eye are ________ 3) what is the intermediate called?
1) in solution
2) in suspension
3) sol
sol
particle size for colloids is in between a true solution and a suspension
Lyosol
a type of sol that combines multiple states of matter: gas, liquid or solid dispersed in a liquid
hydrocolloid
hydrocolloid
formed when a gelatin or agar is dissolved in H2O and the gelatin attracts water, causeing it to swell
gel
semi solid state; happens when concentration of dispered particles exceeds a critical amount at a given temperature
The dispersed phase can agglomerate to form? When these combine to form a brush heap structure you get?
Fibrils, combined to make impression materials
Are primary or secondary bonds irreversible?
primary, secondary can be changed with heat
gel strength strain rate sensitivity means?
the gel can support shear stress without flow IF the stress is applied rapidly. If removed slowly, the fibril network will be ruined
higher brush heap density of fibrils results in higher?
stiffness
How does temperature affect gel?
low temp= stronger gel
high temp= lower cohesion
HIGHER temp= reversion to sol ONLY for reversible gels (irreversible gels are formed by a chemical rxn that isn’t susceptible to temp)
A large part of hydrocolloids is? This means?
water.
Loss of water= shrinkage
Gain of water= expansion
What does syneresis mean?
evaporation of water off surface
