The complex anatomy of the root canal system has required endodontists to use intelligent materials with surprising properties to manufacture their files, such as nickel-titanium alloys: NiTi.
In this blog we will tell you everything about them, their characteristics, their advantages, their types and how their properties evolve even more over time. Are you ready to find out everything about this material that seems to have been brought from the future?
Image: HyFlex EDM - Coltene
We owe the use of NiTi alloys in dentistry to William J. Buehler, a metallurgical engineer from the United States Navy, who in 1958 set out to find an alloy with low density, impact and fatigue, heat resistant to make stronger missile cones. It was not until the late 70s that NiTi found its application in dentistry and particularly in orthodontics due to its shape memory, which It means that it has the ability to "remember" and recover its original shape after being deformed. This occurs because the atoms that make up the alloy can have different crystallographic phases, these are:
- Austenite
- Phase R
- Martensite
The martensite phase is induced by stress and temperature; and is responsible for the incredible shape memory property of nickel-titanium alloys. When the stress is removed and the martensite is heated, it transforms back into austenite, recovering its shape.
The nickel-titanium alloy turned out to be an ideal material in the field of endodontics, as it is easily deformable, soft and ductile, and best of all: superelastic and highly resistant to bending stress, which is particularly useful for instrumentation in the complex anatomy of the root canal system.
The NiTi alloy that we use in endodontics contains 51% nickel and 49% titanium and the martensitic transformation occurs due to the stress imposed by the curvature present in the root canal. In the case of NiTi rotary files, at room temperature they are completely in the austenite phase and their behavior is superelastic during clinical use. The imposition of the stress caused by root curvature results in cycles of martensitic and inverse transformation, due to its rotary movement.
NiTi Alloy vs. Stainless Steel
The most considerable advantage of NiTi instruments over instruments made of stainless steel is their superelastic behaviour. Those made of stainless steel, when subjected to the same deformation, would not be able to return to their original shape.
The rotary files made in Niti also have the great advantage of having surprising flexibility which allows them to rotate 360° in curved canals, facilitating fast and efficient preparation.
But not only rotary files are made of NiTi, there are also manual instruments and these follow a predetermined pattern as a rule, respecting the 2% taper principle. Some examples are the H files (Hedstrom files), the streachers or also called reamers, Nitiflex files (Dentsply Maillefer) and ProTaper manual (Dentsply Maillefer).
Types of NiTi alloy in endodontic files
Phase R Nickel Titanium Alloy
The NiTi Phase R alloy was discovered from a NiTi wire subjected to cooling and heating thermal treatments, thus maintaining the R crystallographic phase (rhombohedral crystalline structure), which that enables the manufacture of NiTi files by twisting.
Endodontic files obtained using the NiTi Phase R alloy have less resistance to elastic deformation, greater flexibility and less rigidity, but at the same time they have a longer useful life in rotary bending, that is, they are more resistant to fatigue fractures.
Nickel Titanium Alloy M-Wire
The NiTi M-Wire alloy is obtained with a special thermomechanical process in which the M-Wire wire causes the martensite to be in the microstructure of the alloy. The presence of martensite is essential to improve the results in terms of flexibility and resistance to fatigue fracture, compared to instruments obtained with the conventional NiTi alloy.
Memory Controlled Nickel Titanium Alloy
Endodontic files with controlled shape memory are manufactured through a process that allows the material to control shape memory. This process allows the file to follow the anatomical trajectory of the canal, reducing the risk of step formation, apical transport of the canal and root perforations. These files undergo a thermomechanical treatment that controls memory making the files extremely flexible, but without the classic memory of conventional NiTi instruments.
Endodontic files obtained from NiTi metallic wires with controlled shape memory, compared to files obtained from conventional NiTi, are more flexible, resistant to fracture due to rotational bending (fatigue fracture) and torsion.
Discover the most purchased NiTi files for endodontic treatments:
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