BOARDS PART 2: IMPRESSION MATERIALS Qs
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