Flashcards in Impression materials Deck (63)
What is the purpose of using impression materials and gypsum materials?
fabricate diagnostic cast
What is the purpose of impression materials?
makes NEGATIVE mold of dental structures
What is the synonymous term for irreversible hydrocolloid?
alginate for impression
What are the characteristics of ideal impression materials?
low cost, long self life, bio-compatible, stable, good handling, pleasant to patient
What are two rigid impression materials?
zinc oxide eugenol and plaster
What are two plastic impression materials?
wax and compound
What are two elastic impression materials?
hydrocolloids and elastomers
What are the limitations of alginate?
not used for crown or bridge impression because of the lack of accuracy
resembles a solution but is made of colloidal particles dispersed in liquid
What is the product of alginic acid in water?
How can sol transform into gel?
through control of temperature and chemical
entangles network of solid colloidal particles in which liquid is trapped in the interstices and held by capillary forces
When transforming from sol to gel, which control is reversible
temperature is reversible
chemically is irreversible
What is the purpose of a reactant in impression material?
allows for cross linking
What is the purpose of a retarder in impression material?
it controls the reaction
What is the purpose of a reinforced filler in impression material?
adds body and strength
What is the purpose of potassium sulfate or alkani zinc fluorides in impression material?
provides good surfaces on gypsum dies
What is the affect of increasing the powder and decreasing the water in alginate?
Lowering the W/P ratio causes an increase in strength, increase tear resistance, decreases working/setting time
How does lowering the temperature affect alignate?
increasing working/setting time
What is mixing time a measure of?
how long it takes to form uniform blend
What is working time a measure of?
how long from the beginning of the reaction until the setting begins
What is setting time a measure of?
how long from the beginning of the mix until the setting reaction is over
Is syneresis the gain or loss of eater to the surrounding?
Is imbibition the gain or loss of water into the surrounding?
What are the advantages of alginate?
economical, easy to use, quick setting, quick setting, fair tasting, hydrophilic, displace saliva/blood, stick trays
What are the disadvantages of alginate?
limited detail reproduction, low tear resistance, single pour only, quick pouring required, low dimensional stability
What are three well known hydrophobic impression materials?
Doe hydrophobic materials have a high or low contact angle?
high angle because the water beads up
How are polysiloxanes made less hydrophobic?
use of a surfactant or incoperating moieties into the silicone backbone