Master Impressions Flashcards
what are the 3 main classifications of impression materials?
non-elastic, synthetic elastomers, hydrocolloids
name a hydrocolloid
alginate
name a synthetic elastomer
silicone, polyether, polysulphides
name a non-elastic impression material
zine oxide eugenol, compounds, waxes
what do you need to consider when requesting for trays to be made for master impressions?
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
why do you produce a master impression?
to produce a master or working cast
what is the master cast made of?
100% stone
what is the master cast used for?
to build the denture on
how do you take a master impression?
special custom tray made from the primary cast which should be spaced appropriately, disinfect the tray before trying it in the patients mouth
where do you stand to insert an upper tray?
behind the patient
where do you stand to insert a lower tray?
in front of the patient
what do you do if the tray is over extended?
trim back the peripheries with a bur
what do you do if the tray is underextended?
add to the peripheries using greenstick compound or wax
what should you do to prevent tearing and distortion of the impression material?
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
how do you use poly vinyl siloxane
apply appropriate adhesive to the tray fit surface and periphery
where do you NOT use polyether?
in patients with severe undercuts, periodontal disease too
what are the properties of polyether?
good flow and accuracy, dimensionally stable, rigid set
what is a good impression material to use for undercuts?
alginate
what do you need to be wary of when using alginate?
air blows in key areas and that the stone casts should be poured immediately to minimise dimensional change
what are the properties of impression compound
non elastic, sets rigidly
when do you not use impression compound
for full arch impressions in dentate patients
where is impression compound useful?
in free end saddle areas
what must you do to heat up impression compound before use?
for the red one heat in bowl of hot water
for green one use bunsen burner/hot air blower
give an example of combining two impression materials?
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
summarise the master impression procedure?
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
what do you do once the impression is complete?
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
what do you need to tell the lab?
whether the denture will be cobalt chrome or acrylic and therefore what to pour the cast in
if a cobalt chrome denture is to be made what should you tell the lab?
pour model in improved stone, construct chrome framework per design
if an acrylic denture is to be made what should you tell the lab?
pour model in 100% dental stone, construct record blocks
