*Alloys for PFM Restorations

What role do alloys play in PFM restorations?

Serve as a substructure/coping

What is an alloy?

A mixture of metals

What are the main categories of PFM alloys?

Base and Noble

List the ADA alloy classifications

High-noble, Noble, Predominantely base-metal

How much gold content is in a high-noble alloy?

>= 40%

How much noble metal content is in a noble alloy?

>= 25%

How much noble metal content is in a high-noble alloy?

>= 60%

How much noble metal content is in a predominately base-metal alloy?

<25%

What are considered noble metals?

Au, Ag, Pt, Pd

List characteristics of gold

Resistance to corrosion, good malleability, low melting point

List characteristics of palladium

Higher melting point, harder than gold, not used in pure form, most expensive

List characteristic of platinum

Highest melting point, does not mix as freely with gold 

How many carats is pure gold?

24

If an alloy is 50% gold, how many carats is it?

12

What is the fineness rating of pure gold?

1000

What is the fineness rating of 18 carat gold?

750

What base metals are commonly used in PFMs?

Copper, silver, and zinc

How does copper and silver impact gold-based alloys?

Increase the hardness of gold based alloys

How does zinc impact gold-based alloys?

Decreases oxidation and increases hardness

If you want to decrease oxidation and increase hardness of a gold based alloy, what would you add?

Zinc

Grains are formed by a _______ .

Crystal lattice

Why are noble and high-noble alloys more resistant to corrosion?

They have smaller grains, and thus more uniform properties

What are wrought alloys?

Drawn into wire with grain structure in a fibrous appearance

Describe the organization of cast noble alloys

Ordered crystal structure

What determines the crystal structure of cast noble alloys?

How it is heated and cooled

List important physical/chemical properties for PFM restorations

Color, noble metal content (corrosion resistance), hardness, lab recommendation, modulus of elasticity, yield strength, elongation, thermal properties, density, span length/sag resistance, metal/procelain occlusal

What is the hardness of enamel?

343 kg/mm²

Definition: Modulus of elasticity

Stiffness of the material

Definition: Yield strength

Plastic deformation, force required to permanently distort alloy

What is the significance of thermal creep?

Distortion

List some biocompatibility properties for metal alloys

Cytotoxicity, tissue irritation, nickel & beryllium

List some lab workability properties for metal alloys

Casting accuracy, ease of cutting/finishing

List some porcelain compatibility properties for metal alloys

Composition, thermal expansion, bond strength

List adherence controlling elements (in the context of oxidation)

Fe, Sn, In

What color is Au-Pd-Pt once it oxidizes?

Medium-gray

What color is Pd-Cu once it oxidizes?

Dark brown to black oxide

What color is Pd-Ag once it oxidizes?

Light gray

How does porcelain bond to PFM alloys?

Oxides on metal surface bond chemically to oxides on porcelain

What is a common color change seen on PFM restorations?

Greening

What is the composition of Au-Pt-Pd high noble alloys?

84-86% Au, 4-10% Pt, 5-7% Pd, 1-4% Ag, 203% base metals (Fe, Sn, In)

What are general features of Au-Pt-Pd?

Costly, yellow color, high density, good handling, solid/liquidus 1040-1190 C, low modulus/tensile strength, low sag resistance, hardness mau be low for occlusal wear resistance, high cost, good corrosion resistance, good porcelain bond strength, ideal harness for finishing, indium grain refining element

What is the maximum span of a Au-Pt-Pd restoration?

3 unit

If a patient bruxes, what PFM alloy should you avoid?

Au-Pt-Pd

What is the composition of Au-Pd-Ag high noble alloy?

51-54% Au, 26-31% Pd, 14-16% Ag with base elements (Fe, Sn, In)

What are general features of Au-Pd-Ag PFM alloys?

Lower cost, gray color, good mechanical properties, high sag resistance, good for long-span bridges, solidus/liquidus 1200-1300 C, good porcelain bond, good corrosion resistance, Ag may cause greening

If you are planning for a long span bridge using PFM restorations, what is the ideal material?

Au-Pd-Ag

Thermal expansion of metal must be _______ to that of the porcelain

nearly identical

If metal shrinks a lot less than the porcelain during cooling ______ occurs.

Crazing

If metal shrinks a lot more than the porcelain during cooling ______ occurs.

Shiver or puckering

How do you ensure the porcelain does not crack

Alloy must contract slightly more than porcelain during cooling

What is the composition of Pd-Ag noble alloy?

53-60% Pd, 30-37% Ag, 10% base element (Sn, In)

What are general features of Pd-Ag alloys?

Low cost, low density, high thermal expansion (not suitable for Vita porcelain), high modulus, high sag resistance, solidus/liquidus 1230-1300 C, good porcelain bond strength, good tarnish and corrosion resistance, potential for greening of porcelain

______ do not discolor in Pd-Ag alloys

Non greening porcelains

What is the composition of Au-Pd high noble alloy?

45-42% Au. 38-45% Pd, with In, Sn, sometimes gallium

What are general features of Au-Pd alloys?

White alloy (no discernable oxide), easily cast, good sag resistance, good porcelain bond strength, solidus/liquidus 1270-1304 C, higher strength/modulus/hardness/elongation after heating treatment, low thermal expansion

What are general concerns of base metal alloys?

Corrosion resistance, physical properties, hardness, casting problems, nickel allergy, beryllium castability and toxicity, sag resistance, unreliable soldering, thin sections

What is the corrosion resistance concern of base metal alloys?

Chromium oxide passivating layer (less reactive)

What is the hardness of porcelain?

420 kg/mm²

What is the composition of Ni-Cr base metal alloy?

65-80% Ni, 16-24% Cr, 3-6% Mo, 0-2% Be

What are general features of Ni-Cr base metal alloy?

If no Be may be difficult to cast, green or black oxides, variation in alloy composition, solidus/liquidus 1230-1350 C

______ expansion is more suitable for Authentic porcelain systems

High

_____ expansion is more suitable for Vita or Ceramco porcelain systems

Low

What is the composition of Co-Cr base metal alloy?

60% Co, 30% Cr, with Ga and Nb

What is the most common composition of implants?

Ti Grade 5 (Ti 90%, Al 6%, Vanadium 4%)

What are general features of titanium alloys?

Casting temperature 2000 C, investment reactions, passivity limits based on content

What kind of die is used for sintered alloy?

Refractory die