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Orthodontics
Wire Characteristics
- Resilience: Area under stress-strain curve up to proportional limit; energy storage capacity
- Formability: Permanent deformation before failure
- Ideal wire properties: High strength, low stiffness, high range, high formability
- Nomograms: Developed by Kusy for wire comparison
- Shape memory & superelasticity: Unique to NiTi alloys
Wire Types & Inventors
| Wire Type | Inventor/Details |
|---|---|
| NiTi | William F. Buehler (1962), George Andreasen (1970) |
| Cu-NiTi | Rohit Sachdeva; quaternary alloy |
| Beta Titanium (TMA) | Charles Burstone; Titanium-Molybdenum-Aluminium |
| Stainless Steel | Bearley; 18-8 composition |
| Elgiloy | Cobalt-Chromium alloy; heat-treated for strength |
Elgiloy Color Coding
| Type | Color |
|---|---|
| Soft | Blue |
| Ductile | Yellow |
| Semi-resilient | Green |
| Resilient | Red |
Metallurgical Concepts
- Passivation: Cr₂O₃ layer from chromium prevents corrosion
- Sensitization: Loss of passivation due to chromium carbide formation (400 – 900° C)
- Cold working: Increases hardness/strength, decreases elongation
- Annealing: Reverses strain hardening; temp = 1/2 melting point