Nickel-titanium alloy wire is a type of shape-memory metal.
Release Date:
05 Dec,2022
Nickel-titanium alloy wire is a type of shape-memory metal—special alloys capable of spontaneously recovering their original shape from plastic deformation at a specific temperature, while maintaining excellent ductility. In addition to their unique shape-memory properties, these alloys also exhibit outstanding characteristics such as wear resistance, corrosion resistance, high damping performance, and superelasticity.
To put it plainly, nickel-titanium alloy wire is made by forming a binary alloy of nickel and titanium. Due to temperature-induced mechanical stress, it can exist in two distinct molecular structures—namely, the martensite phase and the austenite phase. After cooling, the transformation sequence of the nickel-titanium alloy proceeds as follows: parent phase → R phase → martensite phase. The R phase has a rhombohedral structure, while the martensite phase appears as a cubic shape under relatively high temperatures or when no external load is applied—it’s hard, rigid, and relatively stable. In contrast, the martensite phase adopts a hexagonal structure at lower temperatures or under applied stress, making it highly ductile, resilient, yet extremely unstable and prone to deformation.
Shape memory properties: When the parent phase, which has a specific shape, is cooled from above the Af temperature down to below the Mf temperature, martensite is formed. If this martensitic structure is subsequently deformed at temperatures below Mf, upon reheating back to near the Af temperature, the material will spontaneously revert to its original shape as it existed in the parent phase due to the reverse transformation process.
Superelasticity: So-called superelasticity refers to the phenomenon where a specimen undergoes strain far exceeding its elastic limit under external force, yet spontaneously recovers upon removal of the force.
Oral temperature sensitivity: Stainless steel wires and CoCr aluminum alloy orthodontic archwires exhibit virtually no change in corrective force due to temperature variations inside the mouth.
Corrosion resistance: Studies have found that nickel-titanium wires exhibit corrosion resistance comparable to that of stainless steel wires.
Anti-toxicity and side effects: The special chemical composition of nickel-titanium memory metal—a nickel-titanium-based molecular aluminum alloy containing approximately 50% nickel—raises concerns, as nickel is known to have carcinogenic and cancer-promoting properties.
Soft corrective force: Currently, the orthodontic wires used in commercial dental services include low-alloy steel wires, cobalt-chromium-nickel alloy wires, nickel-chromium alloy wires, Australian alloy wires, gold alloy wires, and nickel-titanium alloy strands.
Better shock-absorbing properties: The more vibration generated by occlusion and nighttime teeth grinding on the archwire, the greater the adverse effects on the tooth roots and periodontal tissues.
Clinical Treatment with Nickel-Titanium Alloy Wires:
1. Nickel-titanium alloy arch wires are currently widely used in medicine as the initial arch wires in orthodontic treatment systems, thanks to their superelasticity, shape-memory properties, and relatively low stress-strain curve, which help gently align and straighten misaligned teeth in the early stages of treatment.
2. Nickel-Titanium Torque Springs: Nickel-titanium push and tension springs are torque springs used in orthodontic treatment, featuring the unique superelasticity of nickel-titanium. They are ideal for expanding interdental spaces and pulling teeth in various directions during orthodontic correction.
Keywords:
Nickel-titanium alloy rope
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