BOARDS PART 2: IMPRESSION MATERIALS Qs

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what are the disadvantages of condensation silicone?

- must be poured immediately, poor dimension stability due to evaporation of ethanol, hydrophobic, and low tear strength

which material tolerates moisture the most? - polyether, addition silicon, polysulfide or hydrocolloid

hydrocolloid

for gypsum, increases trituration time will _____ compressive strength and ____ setting and expansion

increase decrease

for alginate, increased water:powder ratio ____ setting time and ____ expansion

increases decreases

alginate is an _____ hydrocolloid

irreversible

what is the most inaccurate impression material?

irreversible hydrocolloid

which is not recommended for a final FPD cast impression? - irreversible hydrocolloid, reversible hydrocolloid, PVS or polyether

irreversible hydrocolloid

which material can't be used to get cast impressions? - reversible hydrocolloid, irreversible hydrocolloid, polysulfide, or PVS

irreversible hydrocolloid

why is elastomer not a good interocclusal record?

it rebounds when mounting

what is condensation silicone?

it's an elastomeric impression material that sets in a cross-linking polymerization reaction and gives off ethanol as a by-product

what's wrong with polyethers?

it's hard and engages undercuts

when compared to other materials, which of the following is the main disadvantage of using polyether elastomeric impression material i

it's much stiffer

catalyst of polysulfide impression is

lead dioxide

what happens if you increase water in gypsum stone?

less expansion and strength (b/c particles are farther apart)

what are the disadvantages of polysulfide

long setting time, very unpleasant odor and taste, and highest permanent deformation

what are the advantages of polysulfide

long work time, flexible, and tear resistant

what is the property of interocclusal recording material

low resistance to jaw closure

if you decrease water temp, you have _____ working time for an irreversible hydrocolloid

more

what is the hardest material to remove from the oral cavity (stiffest)

polyether

what is the most rigid impression material

polyether

which impression material is most likely to get stuck in the mouth?

polyether

which material would you not use for a single crown? - polyether, polysulfide or PVS

polysulfide

which of the following is the best for tear strength - polysulfide or polyether

polysulfide

imbibition and syneresis affect which one the most? - impression compound, polysulfide, reversible hydrocolloid, or silicone

reversible hydrocolloid

syneresis and imbibition applies to which impression material?

reversible hydrocolloid

when pouring gypsum material into an impression, which material will cause the least amount of bubbles? - polysulfide, polyether, silicone, or irreversible hydrocolloid

silicone

why will an alginate impression shrink in 100% humidity - imbibement, syneresis, or historgysm

syneresis (extraction or expulsion of a liquid from a gel -> leads to shrinkage)

polysulfide gives out what

water

what happens when you taken an impression and the lip immediately swells?

angioedema (allergic reaction)

condensation silicone releases what as it's by product

ethyl alcohol

polysulfide (rubber base) is an elastomeric impression material that has an ____ setting reaction with water as a by-product

exothermic

in gypsum, longer spatulation, increase water temp, use of slurry water, less water:powder ratio leads to ____ expansion and ___ setting time

greater shorter

additional silicon (PVS) releases what

H2 (as secondary reaction)

what are the disadvantages of PVS (addition silicone)

- hydrophobic and temperature sensitive

what are the advantage of PVS (or addition silicone)

- excellent dimensional stability (up to 2 weeks), excellent surface detail, and low permanent deformation

what of the following systems is thought to malfunction in the hereditary form of angioneurotic edema? - C1 esterase, c-1q inhibitor, CH50 consumption, serine phosphatase or complement synthetase

C1 esterase

what are used in angioedema to inhibit the complement system

C1 inhibitors

what is addition silicone

PVS - it's become one of the most popular crown and bridge impression material. there are no by-products compared to condensation silicones

what is imbibition?

a special type of diffusion when water is absorbed by solids-colloids and leads to an enormous increase in volume

what is the most stable elastic impression in moisture environment - polyether, additional silicone, condensation silicone or polysulfide

additional silicone

which impression material is least distorted by water?

additional silicone (condensation silicone is a better answer if it's available)

what is the most stable impression material or provides the best dimensional quality?

additional silicones (aka PVS)

for gypsum if you increase water to power ratio, then you ____ expansion

decrease

in gypsum, older investment = ____ expansion

decrease

for gypsum if you decrease spatula/mixing, you _____ expansion

decrease ***true vice versa as well

in gypsum, increasing water:powder ratio leads to ____ expansion and ____ setting time

decrease longer

what happens to thermal expansion when you increase water/powder ratio of an investment gypsum?

decrease thermal expansion

what decreases setting time of gypsum

decrease water:powder ratio

for alginate, mixing faster and increasing water temperate ____ setting time

decreases


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