Applied Dental Materials Flashcards
what is an alloy ?
a mixture of 2 or more metallic elements
what advantages does an alloy have over pure metals ?
cost, biocompatibility, mechanical properties, ease of casting
what are the fabrication processes of alloys?
forming - plastic deformation e.g. rolling, extrusion
amalgamation
casting
powder metallurgy - sintering, injection moulding, 3D printing
what physical properties should an alloy have for dental application ?
low melting point (flow)
moderately high density (castability)
low coefficient of thermal expansion
what chemical properties should an alloy have for dental application ?
corrosion resistance
electrochemical corrosion resistance
what mechanical properties should an alloy have for dental application ?
high modulus (stiffness) moderately high yield strength (resistance to plastic deformation ) hardenable by heat treatment (retention of polish )
what biological properties should an alloy have for dental application ?
biocompatible - no toxic soluble phases
non-reactive
what are the 2 types of casting metal alloys ?
noble (precious metal)
base metal
which alloys are noble metal alloys ?
gold
silver - palladium
which alloys are base metal alloys ?
cobalt-chromium and nickel - chromium
titanium
what are the properties of noble metals ?
surfaces retain lustre unclean dry air
resist oxidation, tarnish and corrosion during heating casting and soldering
what are the properties of gold ?
malleable, ductile
tarnish resistant in air and water at any temp
insoluble in nitric, sulphuric and hydrochloric acids
low strength
small amounts of impurities e.g. lead, mercury have detrimental effect on its properties
what is the fusion temperature of gold ?
106.3 deg
what is the density of gold ?
19.3g/cm^3
what is the coefficient of thermal expansion of gold ?
14.2x10^-6/degC
what is the MOE of gold ?
80 GPa
what are the properties of platinum ?
tough, malleable, ductile
high corrosion resistance
high cost
higher melting step than porcelain
what is the fusion temperature of platinum ?
1755 deg
what is the density of platinum ?
21.37 g/cm3
what is the coefficient of thermal expansion of platinum ?
8.9x10^-6/degC
what is the MOE of platinum ?
147 GPa
what are the properties of palladium ?
decreased cost
prevents corrosion of silver in oral environment
absorbs hydrogen gas when heated improperly
what is the fusion temperature of palladium ?
1555 deg
what is the density of palladium ?
11.4g/cm3