alloys for cast metal restorations Flashcards
what is the compressive strength
stress required to fracture a material
what is the elastic modulus
measure of rigidity
stress/strain ratio
what is brittleness/ductility
dimensional change experienced before fracture
what is material hardness
resistance of surface to indentation or abrasion
what properties can you ascertain from a material stress strain curve
strength
ductility
elastic modulus
give a property that you can’t ascertain from a stress strain curve
hardness
what property does the separation of proportional limit and fracture stress on the strain axis of stress strain curve relate to
ductility/brittleness
mechanical properties of alloy
ductile
hard
rigid
strong
mechanical properties of porcelain
brittle
hard
rigid
high compressive strength
low tensile strength
how does fusing porcelain to an alloy decrease the strain porcelain experiences
act as a support and limit the strain porcelain experiences as it is more rigid than porcelain
alloy limits the strain porcelain is exposed to so that it is less than what would fracture porcelain
alloy options to bond to porcelain - 3
high gold alloy
low gold alloy - best properties
silver palladium
cobalt chromium - most used in GDH
what does porcelain bond to on the alloy surface
bonds to metal oxides on alloy surface
required properties of an alloy for PFM restoration
bonds to porcelain
similar thermal expansion coefficient to porcelain
avoid discolouration of porcelain
rigid to support porcelain - high EM
why must melting and recrystallisation temperature of alloy be higher than porcelain
creep will occur if not
what is creep
gradual increase in strain experienced under prolonged application of stress that is less than EL
