pouring study casts Flashcards
what are the 6 clinical stages of denture contruction?
exam secondary impressions/jaw registration/tooth position jaw registration trian/base or tooth position tooth trial delivery
what are the 5 lab stages of denture construction?
pouring impressions/special trays/occlusal rims/tooth set up pour impressions, occlusal rims tooth trial or co-cr base tooth trial on base finish dentures
describe the structure of dental plaster
large, irregular particle
describe the structure of dental stone
small, regular
describe the structure of improved dental stone
small regular particle with chemicals added for reduced expansion
why are adequate flow properties important?
fill impression
reproduction of surface detail
why is the water to powder ratio important?
dimensional accuracy
=no expansion or contraction on setting
why is strength important?
hardness and abrasion resistance
no flaking or chipping thin section
what is the powder to water ration for plaster?
100g to 50ml
what is the powder to water ration for stone?
100g to 25ml
what is the powder to water ration for improved stone?
100g to 20ml
what properties does hand mixed alginate give?
air in mix
more expansion
less sense
low strength cast
what properties does mechanically mixed give?
less expansion
greater accuracy
dense mix
harder cast
how does mechanical mixing work?
vacuum pump removes air while mixing
when is hand mixed appropriate?
when precision is not paramount eg primary impressions
