Test 1 Review Flashcards
which two impression materials can be poured multiple times and maintain reasonable accuracy?
PVS and polyether
what 3 things can create distortion in impression material?
time, compression, and temperature extremes
___ is the ability of an impression material to rebound back to its original accuracy
elastic recovery
how long does alginate take for full elastic recovery?
about 10 minutes
between polymethylmethacrilate and polyethylmethacrilate, which has a higher exotherm upon polymerization?
polymethylmethacrilate
between polymethylmethacrilate and polyethylmethacrilate, which one shrinks more upon polymerization?
polymethylmethacrilate
between polymethylmethacrilate and polyethylmethacrilate, which has a higher fracture toughness?
polymethylmethacrilate
between polymethylmethacrilate and polyethylmethacrilate, which one is easier to add to?
polymethylmethacrilate
between polymethylmethacrilate and polyethylmethacrilate, which would you only want to use for a single unit and why?
polyethylmethacrilate because it is quite soft, even in its set form
when taking an impression, what can happen if you allow the light body to start setting before you add the heavy body?
the bite record will be open
when taking an impression, what can happen if the heavy body material starts to polymerize before it is inserted?
the die will be smaller
what are the two biggest drawbacks to hydrocolloids and why?
syneresis and imbibition, because they make the hydrocolloids unstable
what is syneresis?
the expression of fluid from hydrocolloid impression material over time, resulting in dimensional change and distortion
what is imbibition?
the uptake of water by hydrocolloid when immersed in water
what is the modulus of elasticity, and which impression materials has the highest modulus of elasticity?
stiffness of a material
polyether
why shouldn’t you use plastic posterior impression trays in the clinic?
because they can bend - this is why you should use metal
___ can interfere with the setting of PVS
latex gloves
why is it important to capture the area apical to the prepared margin when taking an impression of crown prep?
it is easier to trim and easier to help with contours
when taking indirect crown prep impressions, what 3 things are absolutely necessary for you to capture?
you want to capture the die, the opposing anatomy, and the adjacent teeth
what are some ways that impression material can be kept adherent to impression trays?
adhesive spray, rim lock, and perforated trays
how can gypsum be reinforced, and what does the reinforcement do?
it can be reinforced by adding low viscosity cyanoacrylate, which makes the gypsum stronger and more abrasian-resistant
how many ADA recognized types of gypsum materials are there?
5 types (I-V)
___ is the term used to describe taking water away from gypsum
calcination
dental stone casts reach maximum strength how long after being poured? about what percent of the setting expansion occurs within the first hour of setting?
24 hours (typically, over 75% of the setting expansion occurs within the first hour of setting)

