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Nitinol arch wire in a simulated oral environment: changes in mechanical properties
E F Harris1, S M Newman, J A Nicholson
1Department of Orthodontics, College of Dentistry, University of Tennessee, Memphis.
Summary
Nitinol orthodontic wires degrade over time in simulated oral conditions, showing reduced elasticity and increased susceptibility to permanent deformation. Long-term use may impact performance due to these mechanical property changes.
Area of Science:
- Biomaterials Science
- Orthodontic Materials Engineering
Background:
- Nitinol (nickel-titanium) is a widely used orthodontic alloy.
- Understanding its long-term mechanical behavior in the oral environment is crucial for clinical efficacy.
Purpose of the Study:
- To investigate the changes in mechanical properties of nitinol arch wires.
- To assess the influence of time, acidity, and static deflection on nitinol performance.
Main Methods:
- Nitinol arch wires (0.016-inch) were incubated in a simulated oral environment.
- Mechanical properties including ultimate tensile strain, modulus of elasticity, and 0.2% yield strength were measured over time.
- Wires were subjected to varying levels of acidity (pH 3-7) and static deflection (0-4 mm).
Main Results:
- Incubated nitinol wires showed significant decreases in mechanical properties compared to dry, unstressed controls.
- Yield strength decreased monotonically with time, increasing susceptibility to permanent deformation by 15% at 4 months.
- Acidity and static deflection did not significantly affect wire properties within the tested ranges.
Conclusions:
- Long-term use or reuse of nitinol wires in the oral environment leads to a statistically significant degradation in performance.
- The primary degradation observed is a reduction in the wire's elastic limit, affecting its clinical reliability.