Alloys for Cast Metal Restorations
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what is compressive strength
stress required to cause fracture
what is elastic modulus
stress/strain ratio
what is brittleness/ductility
dimensional change experienced before fracture
what is hardness
resistance of surface to indentation or abrasion
what information does the stress strain curve give
rigidity, ductility, and strength
what are the characteristics of porcelain
rigid hard strong - high compressive, low tensile forms surface defects leads to fracture at low stress brittle
what does bonding of metal oxide to porcelain help to eliminate
defects/cracks on porcelain surface
what do alloys do for porcelain
acts as a support and limits the strain that porcelain experiences
what are the required property of an alloy to bond to porcelain
form good bond to porcelain thermal expansion co-efficient similar avoid discolouration of porcelain bond strength hardness elastic modulus - high to prevent fracture melting point higher than fusion temperature of porcelain
what is creep
gradual increase in STRAIN experienced under prolonged application of stress
what metal causes green discolouration
silver in silver palladium copper
what is the problem with high gold alloys
melting range may be too low youngs modulus too low
what are the advantages of low gold alloys
increased melting temperature slightly better mechanical properties
what are the advantages of silver palladium alloys
high melting point
what are the advantages of nickel chromium alloys
high melting point high youngs modulus high casting shrinkage low-ish bond strength
what are the advantages of cobalt chromium alloys
high melting point high youngs modulus high tensile strength high hardness
what is the stressed skin effect
slight differences in thermal contraction coefficients which lead to compressive forces which aid bonding
what is the chemical bonding of metal and porcelain
porcelain flows and oxides in the metal oxide coating migrate