Elastomeric Impression Material

Question 1

what are the two types of elastomers

Answer 1

polyether
addition silicones

Question 2

how are elastomers formed

Answer 2

polymerisation and cross-linking of polymer chains

Question 3

what does cross linking of polymer chains in elastomers generate

Answer 3

elastic properties and causes fluid to solid transition

Question 4

what are the two forms of elastomer silicones available

Answer 4

addition cured
conventional

Question 5

what characteristics of elastomers affect the accuracy by which the surface details are recorded

Answer 5

surface detail
flow/ viscosity
contact angle/ wettability

Question 6

what three characteristics affect the accuracy of dimensions and final strength of the impression

Answer 6

elastic recovery
stiffness
tear strength

Question 7

what is the shark fin test

Answer 7

the ability of an impression material to deal with undercuts

Question 8

what is dimensional stability critical for

Answer 8

producing an accurate positive replica using gypsum

Question 9

what are the four categories to assess impression materials

Answer 9

how the material interacts with hard and soft dental tissues
how accurate the impression material is
how well the impression material copes with the removal stage and can it record undercuts
is the material dimensionally stable after the removal

Question 10

what does the contact angle indicate

Answer 10

how readily the impression material wets the tooth surface

Question 11

what does a low contact angle suggest

Answer 11

a large percentage of the volume of the impression material will make contact with the target surface = ideal

Question 12

what does a high contact angle mean

Answer 12

more likely to have gaps between each globule of material - the impression material wont replicate the whole tooth surface

Question 13

what are the two aspects of seeing how accurate an impression material is

Answer 13

how accurately the surface detail is replicated
how elastic the material is

Question 14

what is the way to measure surface reproduction of an impression material

Answer 14

place the impression material along a surface which has grooves of specified width (20,50 and 75) – an IM that records the 20 niche will give the most accurate surface detail

Question 15

is any impression material truly elastic

Answer 15

no - they are all visco-elastic

Question 16

for elastic recovery also depends on clinical technique, how would you ensure reducing permanent deformation

Answer 16

remove the tray quickly

Question 17

what does more fin length in the shark fin test mean

Answer 17

the more the impression material is able to flow under pressure and records deeper undercuts more readily

Question 18

what type of impression material is impregum

Answer 18

polyether

Question 19

do polyethers or addition silicones set quicker

Answer 19

polyethers

Question 20

are addition silicones or polyethers better with elastic recovery

Answer 20

addition silicones

Question 21

what type of impression material is better at recording deep undercuts

Answer 21

polyethers

Question 22

what type of impression material is better for tear strength

Answer 22

addition silicone