NiTi (in endodontics)

basic metallurgy and advaces in wire manufacturring used in endodontic files .
almustansiriyah university/college of dentistry.M.cs student .

1. Nickle Titanium in endodontics Shadan sahib hameed Ann dirgham Shadan sahib hameed Ann Dhirgham

2. I ntroduction the introduction of nickel-titanium ( NiTi ) rotary files to endodontics has changed the way root canal preparations are performed, enabling more complicated root canal systems to be shaped with fewer procedural errors

3. Background Nickel-titanium alloy was developed in the 1960s , initially for military purposes, but it soon became apparent that NiTi was also useful for other applications, such as orthodontic wires and dental burs . the first NiTi rotary files appeared on the market around 1993. These early rotary files were designed with cross-sections that did not have cutting edges but rather broad radial lands(which reduces the tendency of screwing).

4. Clearly, not all root canals lend themselves to rotary preparation, due to varying degrees of clinician skill and case complexity. Furthermore, rotary files may fracture or create procedural errors. Therefore, knowledge of several clinical “ Golden Rules ” and basic understanding of metallurgical properties of NiTi rotary files are critical for successful use.

5. Structure of NiTi Crystals Have specific geometry Atoms are arranged in unit cells Repeated again to form lattice Lattice Three dimensional network connecting the atoms of undisturbed crystals .

6. What makes NiTi alloy so special? It is an alloy that exists in two crystal structures, austenite and martensite ; transitions from one crystal lattice to the other make NiTi superelastic and give it a shape memory. Its high flexibility is critical for rotary endodontic files because With highly elastic instruments, forces between the file and the canal wall during instrumentation are reduced. This results in the file remaining centered in the root canal space, and in a lower propensity towards canal straightening or other preparation errors

7. Austenite phase

8. Martensite phase At low temperatures,NiTi spontaneously transforms to a more complicated monoclinic crystal structure known as martensite (daughter phase ). Martensite's crystal structure (known as a monoclinic, or B19' structure) ( closely packed hexagonal lattice )has the unique ability to undergo limited deformation in some ways without breaking atomic bonds. This type of deformation is known as twinning .

9. Twining Is the deformation that divide lattice into two symmetric parts at an angle( the rearrangement of atomic planes without causing slip, or permanent deformation. It is able to undergo about 6–8% strain in this manner )

10. Characteristics of martensite and austenite When the material in its martensite form it is soft and ductile ,can be easily deformed and has excellent fatigue resistance While austenitic NiTi is quite strong and hard Stress induced martensite (super elastic) is highly elastic like a rubber band.

11. The R-phase The R-phase is essentially a rhombohedral distortion of the cubic austenite phase The R-phase it is an intermediate transition between austenite and martensite (occur on a narrow temperature range) The R-phase often appearing during cooling before martensite then giving way to martensite upon further cooling. Similarly, it can be observed during heating prior to reversion to austenite, or may be completely absent.

12. Twisting Nickle titanium wire is only possible in R-phase (such as R-phase file or twisted file) Youngs modulus is lower than austenite , thus the instrument made from R-phase more flexible . R-phase shows good super elasticity .

13. Ways of transmission between austenite and martensite There are three ways Nitinol can transform between the austenite and martensite phases 1. Direct transformation , with no evidence of R-phase during the forward or reverse transformation (cooling or heating), occurs in titanium-rich alloys .

14. 2.The "symmetric R-phase transformation" occurs when the R-phase intervenes between austenite and martensite on both heating and cooling

15. 3.The "asymmetric R-phase transformation" is by far the more common transformational route. Here the R-phase occurs during cooling, but not upon heating ,by the time one reaches a sufficiently high temperature to revert martensite , the R-phase is no longer more stable than austenite, and thus the martensite reverts directly to austenite

16. The shape memory effect the name "shape memory" refers to the fact that the shape of the high temperature austenite phase is "remembered," even though the alloy is severely deformed at a lower temperature

17. In term of endodontology ,this phenomenon may transalate to the ability to remove any deformation w ithin NiTi instruments by heating them above 125 c.

18. Superelasticity refers to the ability of NiTi to return to its original shape upon unloading after substantial deformation, similar to stretching a rubber band This phenomenon is based on stress-induced martensite formation. NiTi exhibit super elastic behaveor between 10-125 c

19. Transision temperature The transmission temperature range (TTR) for each Nickle Titanium alloy depends on its composition. The TTR of a 1:1 ratio of Nickle and Titanium is -50 to +100 C.  Reduction of TTR can be achieved in several ways ; In the manufacturing process both cold working and thermal treatment. Altering nickle:titanium ratio in favoring of access Nickle ( such as in Hyflex wire ) By substituting of nickle by cobalt

20. There are four transition temperatures associated to the austenite-to- martensite and martensite -to-austenite transformations. Starting from full austenite, martensite begins to form as the alloy is cooled to the so-called martensite start temperature, or Ms , and the temperature at which the transformation is complete is called the martensite finish temperature, or Mf. When the alloy is fully martensite and is subjected to heating, austenite starts to form at the austenite start temperature, As, and finishes at the austenite finish temperature, Af .

21. it is common practice to refer to a NiTi formulation as " superelastic " or "austenitic" if Af is higher than a reference temperature, while as "shape memory" or "martensitic" if lower . The reference temperature is usually defined as the room temperature or the human body temperature (37 °C; 98 °F).

22. Advances in NiTi alloy ;

23. M-wire Introduced at 2007( by dentsply tulsa ) Ex ; profile GT series , profile vortex , vortex blue

24. A hybride microstructure ( austenite to martensite ) with certain proportion of martensite is more likely to have favorable fatique resistance(400%) than the fully austenitic structure .

25. CM-wire

26. CM-wire has lower percentage of nickle 52% (instead of the conventional 54-57 %) that gave it the controlled memory effect (stay bent) Maximum strain of CM wire before fracture is more than three times higher than that of super elastic NiTi wire and have greater flexibility . Ex; HyFlex CM .

27. CM-wire The controlled memory of CM wire and its flexibility allow it to follow the anatomy of the canal and prevent ledge formation or canal transportation. Respod to excessive resistance by straightening of the spiral to avoid binding to the canal wall and decrease fracture ( reversed by heating) 300% more resistant to cyclic fatigue thus decrease file seperation ( Hyflex CM)

28. The file made of CM wire have the ability of bending just like the stainless steel files to allow it to follow the curvature of the canal , and ruturn to the original shape after heating by autoclave.

29. R-phase alloy Developed by S ybronEndo in 2008 Formed by transforming a raw NiTi wire in the austenite phase into the R-phase through a thermal process . Af 17c .

30. MAX wire the NiTi MaxWire ® ( Martensite-Austeniteelectropolish-fleX ).( by FKG) This material reacts at different temperature levels and is highly flexible and incredible fatigue resistance Ex; XP endo finisher and shaper .

31. Surface treatment NiTi Why? 1- To enhance cleaning surface of ni ti instrument 2- Minimize defect , increase surface hardness and flexibility 3- Enhance cutting efficiency 4- Increase resistance to cyclic fatigue

32. Strategies of surface treatment

33. 1- Plasma immersion ion implantation – To reduce released of ni ions - Create continous interface between the bulk and surface 2- Cryogenic treatment -submersion of metal in super cooled path containing liquid (196ْ) & then allow to warm at room temp. The effect include all cross section not only the surface Increase cutting efficiency as well as strength of metal ( inexpensive) Change properties by two mechanism 1- More complete transformation of martiensite phase from austenite 2- Precipitation of carbide particles on crystalline structure

34. 3-electropolish treatment - method used for surface polish of ni ti instrument -instrument connect to anode immersed with other electrode in temperature path of electrolyte followed by passing direct current in the solution - this process alter the surface texture and composition and make it more homogeneous .

35. 4 – EDM :- ELECTRICALLY DISCHARGE MACHINE IS the process of machining electrically conductive material by using precisely controlled sparks that occur between electrode and work piece in the presence of fluid , the electrode may be considered the cutting tool.