DMS summary - investment materials Flashcards
What are the types of investment material
dental stone/plaster
gypsum bonded materials
phosphate bonded materials
silica bonded materials
What is dental stone/plaster used for
acrylic dentures
What are gypsum bonded materials used for
gold casting alloys
What is the composition of gypsum bonded materials
Silica
Calcium sulphate hemihydrate
Reducing agent
Chemicals to inhibit heat shrinkage and control setting time e.g boric acid/nacl
What is the setting reaction of gypsum bonded materials
Hemihydrate → dihydrate
Undergoes hygroscopic expansion
What is phosphate bonded materials used for
Used for base metals/cast ceramics
What is the composition of phosphate bonded materirals powder
Silica
Magnesium oxide
Ammonium phosphate
What is the composition of phosphate bonded materials liquid
Water / colloidal silica
What are the ideal properties of an investment material
Able to expand (thermal, hygroscopic and inversion)
Porous
Strong
Stable
What components make up an investment material
binder
refractory
What are the different binders
Gypsum
Phosphate
Silica
What is the function of binder
forms solid mass
What is the function of refractory
gives expansion and ability to withstand high temp
What is the refractory
silica
What is the composition of dental ceramics
