the purpose of an impression is to make a _________ reproduction of teeth and tissues then once poured in gypsum is to make a _______ reproduction of teeth and tissues
negative
positive
what are the two hydrocolloids, give examples
reverisble: Agar
irreversible: Alginate
what are three types of elastomers
polysulfides
silicone rubber
polyethers
what are the two categories of elastic impressions
hydrocolloids and elastomers
what are three types of inelastic materials?
plaster-type I gypsum
compound
zinc-oxide/ eugenol
reversible hydrocolloid unergoes what type of reaction?
physical only
the solid to gel state of a reversible hydrocolloid is temperautre dependent?
yes
temp solidifies but not temp liquifies
hysteresis
absorbs moisture
imbibition
contract and squeeze out liquid
syneresis
reversible hydrocolloid (agar) is popular for ______ preparations but ______
multiple
unstable
solidification by called is called?
gelation
______ ______ is needed for proper set gypsum for the reversible hydrocolloid
potassium sulfate
what is the gel strengthener for reversible hydrocolloid?
borax
what is the antifungal for the reversible hydrocolloid?
alkyl benzoate
_____ and _____ retard set of gypsum products
borax and agar
what cancels the effect of borax and agar?
potassium sulfate
what are three advanatages to the reversible hydrocolloid (agar)
moist field
accuracy
inexpensive
an example of irreversible hydrocolloid is?
alginate
what type of reaction does irreversible hydrocolloid undergo?d
chemical
t/f irreversible hydrocolloid is temperature dependent by
false not temperature dependent
how can you delay or accelerate the setting up of irreversible hydrocolloid (alginate)
delay-cold water
accelerate-warm water
t/firreversible hydrocolloids are susceptible to imbibition but not syneresis
false susceptible to both
what is the most widely used impression material?
irreversible hydrocolloid (alginate)
what is added to keep alginate from interfering with set of gypsum products?
potassium sulfate
what is the mixing time for regular set alginate?
2-3 min
what ist he workingtime for fast set alginate?
1.25-2 min
what is not recommended with preparing alginate to affect the setting time?
adjusting water to powder ration
how long do you rinse and disinfect an impression
10 minutes
you must pour an impression within _____ hour of taking the impression, why?
1 hour
looses moisture and changes shape
why does an impression change shape over time?
due to water loss (shrinkage)
what must be covered on the maxillary of an impression? mandibular?
max-hamular notch
man-retromolar pad
when loading a tray you load ____ increments and load ____
large
quickly
a right handed clinician must stand _____ pt at ____oclock position
behind
11
a left handed clinician must stand _____ pt at ___oclock position
behind
1
hydrocolloids are _____ and elastomers are ___ _____
aqueous
nonaqueous
t/f elastomers are hydrophobic
true
silicone rubber is a ______ reaction silicion
condensation
polyvinyl siloxane (PVS) is ______ reaction silicion
addition
what type of material has the smallest dimensional change?
polyvinyl siloxane PVS
when must you pour a PVS impression
within one week
what type of gloves must be worn when mixing PVS? why?
vinyl
latex interferes with set
what type disinfectants are appropriate for alginate and silicone