Master Impressions

Question 1

what are the 3 main classifications of impression materials?

Answer 1

non-elastic, synthetic elastomers, hydrocolloids

Question 2

name a hydrocolloid

Answer 2

alginate

Question 3

name a synthetic elastomer

Answer 3

silicone, polyether, polysulphides

Question 4

name a non-elastic impression material

Answer 4

zine oxide eugenol, compounds, waxes

Question 5

what do you need to consider when requesting for trays to be made for master impressions?

Answer 5

appropriate spacing for the material you plan to use for the master impression which prevents over seating and distortion and allows an even distribution of material

Question 6

why do you produce a master impression?

Answer 6

to produce a master or working cast

Question 7

what is the master cast made of?

Answer 7

100% stone

Question 8

what is the master cast used for?

Answer 8

to build the denture on

Question 9

how do you take a master impression?

Answer 9

special custom tray made from the primary cast which should be spaced appropriately, disinfect the tray before trying it in the patients mouth

Question 10

where do you stand to insert an upper tray?

Answer 10

behind the patient

Question 11

where do you stand to insert a lower tray?

Answer 11

in front of the patient

Question 12

what do you do if the tray is over extended?

Answer 12

trim back the peripheries with a bur

Question 13

what do you do if the tray is underextended?

Answer 13

add to the peripheries using greenstick compound or wax

Question 14

what should you do to prevent tearing and distortion of the impression material?

Answer 14

large interdental spaces beneath contact points should be blocked out in the mouth using soft ribbon wax or other suitable material, prior to completion of the impression

Question 15

how do you use poly vinyl siloxane

Answer 15

apply appropriate adhesive to the tray fit surface and periphery

Question 16

where do you NOT use polyether?

Answer 16

in patients with severe undercuts, periodontal disease too

Question 17

what are the properties of polyether?

Answer 17

good flow and accuracy, dimensionally stable, rigid set

Question 18

what is a good impression material to use for undercuts?

Answer 18

alginate

Question 19

what do you need to be wary of when using alginate?

Answer 19

air blows in key areas and that the stone casts should be poured immediately to minimise dimensional change

Question 20

what are the properties of impression compound

Answer 20

non elastic, sets rigidly

Question 21

when do you not use impression compound

Answer 21

for full arch impressions in dentate patients

Question 22

where is impression compound useful?

Answer 22

in free end saddle areas

Question 23

what must you do to heat up impression compound before use?

Answer 23

for the red one heat in bowl of hot water

for green one use bunsen burner/hot air blower

Question 24

give an example of combining two impression materials?

Answer 24

with a free ended saddle use impression compound to capture detail accurately and then apply flowable material (alginate/silicone) over the top to take whole mouth impression

Question 25

summarise the master impression procedure?

Answer 25

try in special tray and trim peripheries, modify peripheries with greenstick and fit surface for free end saddles, apply adhesive and use alginate/polyether for impression, disinfect place in sealed bag and write instructions to technician

Question 26

what do you do once the impression is complete?

Answer 26

inspect for defects, excess material removed
reflect to see if errors are present and if need to repeat
disinfect with perform before sending to lab

Question 27

what do you need to tell the lab?

Answer 27

whether the denture will be cobalt chrome or acrylic and therefore what to pour the cast in

Question 28

if a cobalt chrome denture is to be made what should you tell the lab?

Answer 28

pour model in improved stone, construct chrome framework per design

Question 29

if an acrylic denture is to be made what should you tell the lab?

Answer 29

pour model in 100% dental stone, construct record blocks