Partial denture alloys

• rigid (high YM) • strong (high UTS, EL) • hard • ductile • precise casting (shrinkagae) • melting point (investment material) • density

• ADA type IV gold • CoCr • white gold (AuPt) • titanium

• high YM (rigid) - to maintain shape in use • high EL - to avoid plastic deformation • thick material

• low YM (ductile) - to allow flexture over the tooth • high EL - to maintain elasticity over a wide range of movement i.e. strain • thin material

• liquidus and solidus are close together so there will be little coring when quenched • the area under the graph shows the two possible ordered solid solutions that can form after annealing (order hardening)

• solid solutions of all proportions possible - both metals are completely soluble in one another • benefits from solution hardening - forms common lattice to impede dislocations (increased EL, UTS, hardness) • benefits from order hardening - as long as 40-80% Au then ordered solution is created when quenched • reduced melting point • little/no coring - solidus close to liquidus • imparts red colour - if sufficient quantity added • reduces density • can cause corrosion if too much added

• solid solutions of all proportions - both completely soluble in one another • benefits from solution hardening • benefits from precipitation hardening with copper - after annealing as Ag and Cu are partially soluble • can allow tarnishing • molten silver absorbs gas - care when casting or alloy may become porous and less robust • whitens the alloy - compensates for the redness α-grains (high Ag%) β-grains (high Cu%)

• solid solution of all proportions - both completely soluble in each other • benefits from solution hardening • fine grain structure • coring can occur - big difference between liquidus and solidus

• similar to Pt but less expensive • less coring than Pt • coarser, large grains than with Pt • absorbs gases when molten - care when casting as alloy may become porous

• zinc: acts as scavenger, oxidising during the process • nickel: increases hardness and strength • indium: encourages smaller/finer grains

• quenching after casting - causes coring of AuPt and AuCu (fine grains produced) • homogenous anneal - eliminates coring by removing the concentration gradient (700degrees, 10 mins) • cold working - pushes dislocations to grain boundaries but induces residual stress within the alloy • stress-relieving annealing - alleviates residual stress • order hardening between Au and Cu • precipitation hardening between Ag and Cu • heated to 450 degrees then cooled slowly to 200 degrees then quenched * all increases alloy’s strength and hardness so is more robust (EL, UTS, hardness)

• wires • surgical implants • casat partial dentures

• forms solid solution with Cr - both co-exist in same lattice network • increases strength, hardness and rigidity • allows coring

• forms solid solution with Co - both co-exist in same lattice network • increases strength, hardness and rigidity • allows coring • forms a passive layer on the alloy on the alloy surface - increases corrosion resistance

• replaces some Co • improves ductility • slight reduction in strength • patients may have allergic reaction

• carbon: small quantities - too much can make the alloy extremely brittle • molybdenum: reduces grain size, increases strength • tungsten: increases strength • aluminium: increases PL - Polymer Laminate

• investment material used when casting CoCr has to cope with** high temperatures: 1200-1400 degrees** • melting the alloy can be done by electric conduction or oxyacetylene • casting requires centrifugal force - avoid overheating (coarse grains) and cooling too fast or slow may induce carbides and make framework brittle

• sandblast • electroplate • abrasive wheel • polishing buff

• hard - resists wear in mouth • low ductility • work hardens rapidly

• implants • crown and bridge (cast) • maxillo-facial skull plates • partial dentures (cast)

• good biocompatability • good corrosion resistance (passive oxide layer) • parts can be joined by laser welding

• required electric arc melting • absorbs gases so needs specialised investment and casting equipment