Partial Denture Alloys
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what are the alloy hardening processes?
work, solution, order, precipitation
what are the alloy annealing processes?
homogenisation, stress relief
what are the ideal properties for partial denture alloys?
rigid, strong, hard, ductile, precise casting, melting point, density
what are the different types of partial denture alloys?
ADA type 4 gold, CoCr, white gold, titanium
what does the youngs modulus and elastic limit need to be for the base of a denture?
high YM to maintain shape in use and high EL to avoid plastic deformation
what does the youngs modulus and elastic limit need to be for the clasp of a denture?
low YM to allow flexure over tooth and high EL to maintain elasticity over the wide range of movement
what are the uses for pure gold?
class 3 and 4 cavities
what are the effects of copper in an alloy?
solid solution in all proportions, solution hardening, order hardening, reduced melting point, little/no coring, imparts red colour, reduces density, base metal
what are the effects of adding silver to an alloy?
solid solution in all proportions, solution hardening, precipitation hardening with copper and heat treatment, can allow tarnishing, molten silver absorbs gas, whitens alloy
what are the effects of adding platinum to an alloy?
solid solution with gold, solution hardening, fine grain structure, coring can occur
what are the effects of adding palladium to an alloy?
less coring than platinum, coarser grains than platinum, absorbs gas when molten (porous casting)
what does zinc do in an alloy?
it is a scavenger
what does nickel do in an alloy?
increases hardness and strength
what does indium do in an alloy?
fine grain structure
what heat treatments are used for type 4 gold alloys?
quench after casting, homogenising anneal, if cold worked then stress relief anneal, heat harden
what would type 4 gold alloy be used for on a denture?
clasp
what is CoCr used for?
wires, surgical implants, cast partial dentures, connectors
what does cobalt do in CoCr?
forms solid solution with Cr, increased strength, hardness, rigidity, coring possible
what does chromium do in CoCr?
forms solid solution with Co, increased strength, hardness, rigidity, coring possible, forms passive layer
what are the effects of nickel in CoCr?
replaces some Co, improves ductility, slight reduction in strength, sensitivity
what techniques are used for CoCr finishing?
soundblast, electroplate, abrasive wheel, polishing buff
what is the hardness of CoCr compared to gold?
it is harder so you can wear it in the mouth better although finishing and polishing time is consuming
what is the ductility of CoCr?
low
what are the uses of titanium?
implants, crown and bridge, maxillo-facial skull plates, partial dentures