partial denture alloys
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what are the mechanical properties of partial denture alloys like
• good
what are the important mechanical properties to consider for partial denture alloys
• stress, rigidity, elastic limit, hardness and ductility
what are the alloy processes of hardening
• work hardening • solution hardening • order hardening • precipitation hardening
what are the alloy processes of annealing
• homogenisation annealing - stress relied annealing
what are the ideal properties of partial denture alloys
• rigid = YM • strong = UTS, EL • hard • ductile • precise casting = shrinkage • melting point • density
why is melting point important for partial denture alloys
• for the investment material - can be issues with the melting point = determines what investment material to use
why is density important for partial denture alloys
• want as lightweight as possible for patient comfort
what are the types of partial denture alloys
• ADA type IV gold • white gold = Ag-Pd • Co-Cr • titanium
what is the problem with one piece casting for partial denture alloys
• base and clasps need different properties • base = want a high YM to maintain shape in use, and what a high EL to avoid plastic deformation • clasp = want a lower YM to allow flexure over tooth, and a high EL to maintain elasticity over wider range of movement/strian
how are the issues of one piece casting resolved
• compromise • use thick section of alloy for base = rigid • use thin section of alloy for clasp = flexible
what is the carat for pure gold
• 24 carat
what is the fineness for 100% gold
• 1000
what is pure gold used for
• class III and class IV cavities
what are the 4 types of gold alloys used for
• type 1 = simple alloys • type 2 = larger (2-3 surface) inlays • type 3 = crown and bridge alloys • type 4 = partial dentures = has particular composition
how many other metals are in type IV gold
• 5 other metals
what is the composition of type IV gold
• Au = 65% but can be between 60-70% • Zn = 2% but can be between 1-2% • Cu = 14% but can be between 11-16% • Ag = 14% but can be between 4-20% • Pd = 3% but can be between 0-5% • Pt = 2% but can be between 0-4%
what does the phase diagram of order hardening of Au-Cu show
• liquidus and solidus are continuous so means can have lots of different compositions = solid solution in all properties
how can Au-Cu benefit from solidus and liquidus being close together
• as if it undergoes some type of heat treatment it forms an ordered solution
what are the effects of using copper as an alloying element with gold
• solution hardening • solid solution in all proportions • order hardening = if 40-80% gold and correct heat treatment • reduced melting point • no coring = solidus close to liquidus • can impart a red colour = not ideal • reduces density = good for patient comfort • base metal = can corrode if too much
what does the phase diagram of complete solubility of Au-Ag show
• liquidus and solidus are close tougher so any combo of Au and Ag can co-exist together
what are the effects of using silver as an alloying element with gold
• solid solution in all proportions • solution hardening • precipitation hardening with copper and heat treatment = related to Ag and Cu in combo and if heat treat it can undergo precipitation hardening • can allow tarnishing
what happens if silver and copper in type IV gold
• molten silver absorbs gas such as CO2 - whitens alloy = compensated for red form copper
what does the phase diagram of partial solubility of Ag-Cu in type IV gold show
• there are 2 solid phases = alpha and beta • can only have material in these areas • with partial solid, get benefit of precipitation hardening
what does the phase diagram of complete solubility of AuPt show
• get a degree of separation between liquidus and solidus = coring occurs