3.2 metal alloys and metal framework fabrication

what type of metal alloys are used in fabrication of RPD framework?

noble metals: gold and platinum group AND base metals

what are the noble metals?

gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os)

metals that are highly resistant to oxidation and dissolution in inorganic acids

noble metal

metal that readily oxidizes or dissolves to release ions

base metal

what are the base metals?

cobalt-chromium, cobalt-chromium-nickel, nickel-chromium (w or w/o beryllium), titanium

what are six desired properties/characteristics of base metal alloys?

• corrosion resistant

• lighter weight

• high strength

• high modulus of elasticity 

• low density

• low cost

what are the principal materials used in RPD fabrication?

chromium type alloys

what material does an alloy contain to prevent corrosion and tarnish?

chromium Cr (Cr₂O₃)

what is passivation?

the conditions under which a metal is resistant to corrosion

vitallium

• cobalt-chromium

• vitallium 2000: improved physical properties and handling characteristics

what is the difference in elongation and brittleness of vitallium?

Cr alloys 2-3% elongation & quite brittle; vitallium more elongation & less brittle 

which base metal alloy?

• cobalt: 60%

• chromium: 25-30%

• molybdenum, aluminum, tungsten, iron, gallium, copper, manganese, silicon, carbon, platinum 

cobalt-chromium 

which component of cobalt chromium: hardness?

cobalt

which component of cobalt chromium: corrosion resistance?

chromium

which component of cobalt chromium: hardening and strengthening?

molybdenum, tungsten, carbon

which component of cobalt chromium: fluidity?

manganese and silicon

which base metal alloy?

• Co: 50%

• Cr: 25%

• Ni: 19%

• Other: 6%

  • molybdenum and carbon levels significantly lower than Co-Cr

cobalt-chromium-nickel

what does beryllium do for nickel-chromium?

• lowers melting temp

• enhances fluidity 

• improves grain structure of alloy 

• molybdenum, tungsten, manganese, cobalt, silicon, carbon,

what base metal alloy is lighter than chromium but just as strong?

titanium 

which base metal alloy is the strongest, but the most expensive, heavy, and is the softer metal so it makes it less durable and wear resistant?

type IV gold alloy

physical properties of base metal alloys: melting temp is significantly (lower/higher) than those of gold alloys

higher

physical properties of base metal alloys: temp ranges of base metal alloy

1,399-1,454 ℃

physical properties of base metal alloys:polished Co-Cr and Ni-Cr are lustrous and (gold/silvery white)

silvery white

physical properties of base metal alloys:Cr alloys are (lighter/heavier) than gold alloys

lighter

physical properties of base metal alloys:linear casting shrinkage is relatively (low/high) 2.05-2.33%

high

physical properties of base metal alloys: (heavier/lighter) weight materials are especially useful for the construction of large and bulky maxillary removable appliances 

lighter

mechanical properties of base metal alloys: 30% (harder/softer) than type IV gold alloys; there are special equipments for finishing and polishing 

harder

mechanical properties of base metal alloys: (ultimate tensile strength/yield strength) is 621-828 MPa making it fracture resistant 

ultimate tensile strength

mechanical properties of base metal alloys: (ultimate tensile strength/yield strength) is 414-621 MPa making it resistant to permanent deformation

yield strength

mechanical properties of base metal alloys: the modulus of elasticity (stiffness) of cast based metal alloys is approximately (2x/3x) of cast dental gold alloys 

2x

mechanical properties of base metal alloys: Co-Cr alloys exhibit (shortening/elongation) of 2-3%

elongation

mechanical properties of base metal alloys: Co-Cr-Ni elongates 10% because (higher/lesser) amount of molybdenum and carbon

lesser

mechanical properties of base metal alloys: which base metal alloy can be neither controlled by heat Tx

Co-Cr

mechanical properties of base metal alloys: which base metal alloy is strength and ductility can be altered by high temp heat Tx

Ni-Cr

chemical properties of base metal alloys: alloys containing (greater than/less than) 85% by weight Cr, Co, Ni exhibit a reasonable degree of intraoral corrosion resistance 

greater than 

chemical properties of base metal alloys: surfaces made passive in air by the spontaneous developmental of thin, transparent and contiguous (Cr₂O₃/cobalt) film, passivation

Cr₂O₃

chemical properties of base metal alloys: chemical coating w zirconium oxide …

• reduces Cr release levels in artificial saliva

• provides better corrosion resistance 

repair or modification of a Co-Cr-Mo rpd framework should be accomplished with (the same/a different) alloy to avoid galvanic corrosion

the same

why do we tell pts that a Cr-type alloy is attacked by chlorine?

bc pt may use household bleach to clean them which will ruin it

lab manipulation: what material is used as investment materials?

phosphate bonded or ethyl silicate; necessary to withstand the extremely high casting temperatures required for these alloys

lab manipulation: what compensate for high linear casting shrinkage of Co-Cr alloys

investment materials

high linear casting shrinkage: the tendency of a metal casting to significantly decrease in length as it cools and solidifies after being poured into a mold

lab manipulation: what can entrapped gases produce in large casting?

voids