Wrought Dental Alloys and Dental Wire

1
Wrought Dental Alloys and Dental Wire
2
(No Transcript)
3
Wrought Alloys

• alloys that have been worked or shaped and
  fashioned into a serviceable form for an
  appliance.
• Examples dental wire, orthodontic brackets,
  endodontic instruments, .etc.

4
Microstructure

• fibrous , results from the cold work applied
  curing the shaping operation.
• Wrought forms normally have a measurable increase
  in tensile strength and hardness but decrease in
  ductility and resistance to corrosion when
  compared with corresponding cast structures.
• Results from the entangled, fibrous internal
  structure created by the cold work.

5
A cast gold alloy
Same alloy in wire form
6

• Wrought forms will recrystallize during heating
  operations.
• ? The fibrous microstructure is converted to a
  grained structure similar to the structure of a
  cast form.
• Recrystallization results in a reduction in
  mechanical properties in proportion to the amount
  of recrystallization.

Fibrous structure
Grained structure
7
Fibrous structure
Grained structure
8
Wrought Stainless Steel Alloy

• Steel iron and carbon alloy
• Stainless Steel Alloys of iron and carbon
  that contain chromium, nickel, manganese, and
  other metals.
• Applications Orthodontic appliances, Endodontic
  instruments, Stainless steel crown, Denture
  clasp, etc.

9
Stainless steel orthodontic wire
10

• Chromium amount must be between 13 and 28 for
  optimal corrosion resistance.
• Crlt13 ? no adhere chromium oxide layer
• Crgt28 ? chromium-carbides form ? embrittle the
  steel
• Cr resists corrosion well because of the
  formation of a strongly adherent coating of oxide
  on the surface which prevents further reaction
  with the metal below the surface.
• The formation of such oxide layer is called
  passivation.

11

• Heat treatment above 650oC ? recrystallization,
  compositional change, and formation of
  chromium-carbides. ? ?mechanical properties and
  corrosion resistance.
• Stress-relieving treatments
• To remove the effects of cold working during
  fabrication and increase ductility
• 400oC to 500oC for 5 to 120 seconds

12
Wrought Cobalt-Chromium-Nickel Alloy

• Elgiloy
• 40 Co, 20 Cr, 15 Ni, 7 Mo, 2 Mn, 0.4 Be,
  0.15 C, 15.4 Fe, 0.05 other
• Applications orthodontic wire (soft, ductile,
  semispring temper, and spring temper)

13
Wrought Nickel-Titanium Alloy

• Nitinol
• 55 Ni and 45 Ti
• High resiliency, limited formability, and thermal
  memory
• Shape-Memory Effect will return to its
  original shape when heated from below to above a
  temperature transitional range (TTR).
• The term Shape Memory Alloys (SMA) is applied to
  that group of metallic  materials that
  demonstrate the ability to return to some
  previously defined shape or size when subjected
  to the appropriate thermal procedure. Generally, 
  these materials can be plastically deformed at
  some relatively low temperature, and upon
  exposure to some higher temperature will return
  to their shape prior to the deformation.

14
Wrought Beta-Titanium Alloy

• 78 Ti, 11.5 Mo, 6 Zr and 4.5 Sn
• Can be shaped easily.
• Can be soldered and welded.