Dental Material Science Flashcards
What is porcelain prone to?
Mechanical failure due to microcracks formed at fitting surface
What is elastic modulus also called?
Young’s modulus
what is elastic modulus a measure of?
rigidity
what ratio is a measure of elastic modulus?
stress/strain ratio
stress required is to cause a change in what?
shape
what is brittleness/ductility?
dimensional change experienced before fracture
what is hardness?
resistance of surface to indentation or abrasion
What are the porcelain characteristics?
Rigid, Hard, Strong, tendency to form surface defects, brittle
what does tendency to form surface defects mean?
Leads to fracture at low stress
For porcelain-metal restorations bonding of what to porcelain? and what does it help eliminate?
bonding of metal oxide to porcelain helps eliminate defects/cracks on porcelain surface
what is function of alloy in a porcelain metal restoration?
Alloy acts as support and limits the strain that porcelain experiences
when forming a porcelain fused alloy restoration what does it have to be fired in?
furnace
after raising the temp of a porcelain fused alloy restoration what do you have to do?
cooling them without developing any thermal stresses that could cause either material or the metal oxide layer to develop defects or micro-cracks
what must porcelain and alloy have similar of?
thermal expansion coefficents
what is indium and tin role in high gold alloy’s
they enable a metal oxide layer to firm which enables bonding to porcelain
what has better mechanical properties high or low gold?
low gold
what are properties of silver palladium?
high mp, care needed in casting
what are properties of nickel chromium?
high melting point, high young modulus, high casting shrinkage, low-ish bond strength
what are advantage of cobalt chromium in porcelain fused metal restorations
high elastic modulus, hard, high tensile strength
what is the only alloy satisfactory in each criteria for porcelain fused to metal alloys?
low gold
what is the big disadvantage of high gold?
tendency to undergo creep
which is the only alloy to have a bicompatibility concern for porcelain fused to metal alloys?
nickel chromium due to allergic responses attributed to nickel
what are the required properties of a porcelain fused to metal alloy?
form good bond to porcelain, similar thermal expansion coefficient, avoid discolouration of porcelain, adequate material props (bond strength, hardness, elastic modulus), good melting recrystallisation temp of alloy
what is form good bond to porcelain also known as?
good wetting