Partial denture alloys

ADA Type IV Gold​ ​ Co-Cr​ ​ White Gold (Ag-Pd)​ ​ Titanium

Base : high rigidity - to maintain shape in use high strength - to avoid plastic deformation​ Clasp : lower rigidity - to allow flexure over tooth high strength - maintain elasticity over wide range of movement (ie strain)​

Type I : simple alloys​ Type II : larger (2-3 surface) inlays​ Type III : Crown & Bridge alloys​ Type IV : Partial Dentures

Au - 65% Ag - 14% Cu - 14% Zn - 2% Pd - 3% Pt - 2%

1) solid solution in all proportions​ 2) solution hardening​ 3) order hardening - if 40-80% Gold and correct heat treatment​ 4) reduced melting point 5) little/no coring - solidus close to liquidus​ 6) imparts red colour (if sufficient quantity)​ 7) reduces density​ 8) base metal - can corrode if too much ​

1) solid solution in all proportions​ 2) solution hardening​ 3) precipitation hardening with COPPER & heat treatment​ 4) can allow tarnishing​ 5) molten silver absorbs gas (e.g. CO2) ​ 6) whitens alloy - compensates for copper

1) solid solution with Gold​ 2) solution hardening​ 3) fine grain structure​ 4) coring can occur (wide Liquidus - Solidus gap)

similar to Pt - less expensive​ • less coring than Pt ​ • coarser grains than Pt​ • absorbs gases when molten - porous casting​

1) Quench after casting (fine grains)​ 2) Homogenising anneal (700oC, 10 mins)​ 3) If cold worked - stress relief anneal​ 4) Heat harden - (order & precipitation)​ –> 450oC cool slowly (15 - 30 mins) to 200oC then quench​

Co - 54% Cr - 25% Ni - 15% Mo - 5% C - 0.4%

Solid

Improves ductility while slightly reduces strength

C:- avoid including too much - as carbides will form at the grain boundaries making the alloy too hard & brittle​ Mo:- reduces grain size,​ hence increases strength​ W:- increases strength​ Al:- increases PL​ others:- scavengers

Investment Material : ​ High temp. 1200-1400oC​ Hence - silica or phosphate bonded ​ Melting : ​ Electric Induction preferred ​ Oxyacetylene - avoid carbon pickup Casting : Centrifugal force required​ Avoid overheating - coarse grains​ Cooling too fast or slow - carbides - brittle

sandblast​ electroplate​ abrasive wheel​ polishing buff

Harder than gold, time consuming to finish/polish Low ductility - adjustment difficult work hardens rapidly

Implants​ Crown & Bridge (Cast)​ Maxillo-Facial Skull Plates​ Partial Dentures (Cast)

Good biocompatibility Good corrosion resistance (passive oxide layer) Parts joined by laser welding

Titanium

Stainless steel

Gold

Co - Cr, followed by stainless steel

Co-Cr, then steel

Co-Cr - most shrinkage then gold and silver