NITINOL WIRE DESCRIPTION
Nitinol is a nickel-titanium alloy with super elasticity and shape memory properties. Shape memory refers to the ability of Nitinol to undergo deformation at one temperature, then recover its original, under formed shape upon heating above its transformation temperature. Super elasticity occurs at a narrow temperature range just above its transformation temperature; in this case, no heating is necessary to cause the under formed shape to recover, and the material exhibits enormous elasticity, some 10-30 times that of ordinary metal.We offer a variety of surface finishes so you can tailor our Nitinol wire to your exact needs.
Nitinol, an alloy that consists of approximately 55 per cent nickel and up to 45 per cent titanium. It is this specific combination that provides the material its pseudo-elastic deformation properties. Another outstanding feature is the option of giving the material a shape memory. The largely tension-free behaviour of this new generation Nitinol file was well received as previously it was almost impossible to manually bend NiTi files.
In dentistry, the differentiation between elastic, transient deformation and irreversible, plastic deformation is equally important. A plastically deformed NiTi file will break easily due to material fatigue, and plastic deformation can usually not be detected (even under magnification let alone with the naked eye), due to the high bounce back effect of conventional NiTi material. Minute and invisible microfractures which occur during the metal cutting manufacturing process can increase the risk of unexpected instrument failure. Unfortunately, the pseudo elasticity of conventional NiTi files often masks existing plastic deformation: visibly, the damaged file does not differ from an unused file, but the consequences during endodontic preparation can be serious. Until now, the dentist had no prospect of verifying the clinical condition of the used instrument. Even disposable files offer no guarantees, althoughthey do increase safety somewhat.
Shape Memory Increases Safety
The development of a new generation of NiTi files finally solved this problem. It is possible to differentiate between the elastic and plastic deformation of nickel-titanium alloys. To achieve this, the material used must possess a true shape memory. Ultimately, shape memory is no more than “training” the material to “memorise” a certain shape under different conditions. After deforming the material (by bending or other forces), its shape memory automatically returns it to its original shape as soon as the external conditions change. Temperature or pressure changes are examples of such changed parameters. Alternatively, magnetism or simple chemical processes can induce a return to the original shape.
For endodontic instruments, the practical advantages of this principle are evident: a NiTi file with “controlled memory” adapts to the anatomical shape of the root canal during the entire treatment procedure. In case of resistance or a block in the canal, the file bypasses this stress situation by changing their cross-sectional shape. After use, the file is subjected to a thermal change during autoclaving; the heat returns the instrument to its original shape.
If the uniform spiral structure of the file can no longer be reattained, the file is plastically deformed and should no longer be used. For the first time it is possible to visually differentiate between elastic and plastic deformation in the file with the naked eye, considerably increasing clinical safety, even when faced with short set-up times or inexperienced personnel.
The reason why Nitinol can be trained so reliably lies in its inner structure. Nickel-titanium alloys display two crystallographic phases: the austenite phase at high temperatures and the martensite phase at lower temperatures. In the martensite phase, Nitinol can be bent into complicated shapes without effort. Without further external influences, the bent NiTi file with “controlled memory” remains in this position at room temperature. In the austenite phase, (higher temperatures), the material adopts its original structure and the molecules form a cubic face-centred lattice structure. Heat induces the phase transformation and the file returns to its original condition during sterilisation. This controlled bounce back effect can be demonstrated with a conventional lighter. When placed over the flame, the bent instrument changes to its original straight file shape within a few seconds
The dental file is composed of a working part and a handle. The working part is made of nickel-titanium alloy memory alloy, and the handle is made of copper alloy.
The nickel-titanium alloy part of the working part is generally made of nickel-titanium wire with a diameter of 1.3mm. There are requirements for the elasticity, smoothness, phase transition temperature and mechanical properties of the product.
If there is no corresponding heat treatment after processing the dental file, there is a risk of product breakage
In the process of dental treatment, dental files are mostly disposable products
XOT’s nitinol wire supports the most complex of component designs requiring intricate geometric shapes. By fine-tuning the wire’s chemical composition and thermal processing, XOT has achieved wire with the flexibility and kink-resistance central to medical device applications, including stents, catheters, endodontic files, needles, trocars, mandrels, baskets, surgical instruments, snares and guidewires.
Precautions
Nitinol, like other materials, has limitations. If a helix of wire is stretched too much, it will be permanently damages. If it is subjected to too great a force during thermal shape-memory recovery, it will lose its shape-memory. Specifically, if Nitinol is subjected to a cycle in which it is cooled, elongated by stretching, and heated without being allowed to contract (e.g., held at a constant length) the ability to do work will diminish in just a few cycles. If, on the other hand, the sample (e.g., a Nitinol wire in tension) is allowed to contract against a constant force during heating, the ability of the wire to do work may be enhanced with cycling, and the wire will quickly stabilize so that succeeding cycles are repeated.
At XOT, all incoming Nitinol raw materials are inspected to ensure they meet proprietary internal specifications for chemistry, ingot transformation temperature, material homogeneity, and microstructure. Optimized to promote an exceptionally smooth and uniform surface finish quality, all wire products utilize a proprietary single and multi crystalline diamond drawing die technology. After the correct super-elastic heat treatment, medical grade Nitinol will accommodate strain up to 8% without permanent kinking at body temperature.
We provide nitinol wire in their “as drawn” condition for experimenters who wish to form and train their own shapes. They must be “cooked” (formed and annealed) in order to exhibit their shape memory properties, and the many parameters of time, temperature and processing can give wide-ranging results.
If you have any need for niti products,please contact us. Our Nitinol application sales engineers will be glad to help.