Flexible alloy used in orthodontics and endodontics
Flexible Alloys Used in Orthodontics and
Done by :Dr.MohamadGhazi Kassem
ID NO :201202738
Supervised By: DR. ESSAM OSMAN
DR.MOSTAFA ABOU SHELIB
Flexible Alloy Used in Orthodontics and
Phase transformation in Flexible Alloys. The unique behavior of Flexible Alloys is based on a
thermoelastic(i.e., thermal and mechanical) phase (or crystal structure) transformation. The
shape memory and superelasticity are essential in Orthodontics and Endodontics treatment.
Flexible Alloys that can Used in Orthodontics and Endodontics:
Nickel Titanium alloy.(Used in endodontic & orthodontic)
Copper Nickel Titanium.(Used orthodontic)
Beta-Titanium.(Used in orthodontic)
Stainless steel multi strand.(Used in orthodontic)
Introduction to NiTi:
It is a nickel- titanium metal alloy with some unique properties. It is also known as
Nickel titanium. This alloy exhibits the superelasticity or pseudoelasticity and the shape
memory properties. It means this unique metal can remember its original shape and
shows great elasticity under stress.
The term nitinol is derived from its composition and its place of discovery: (Nickel
Titanium-Naval Ordnance Laboratory). WilliamJ. Buehler along with Frederick Wang,
discovered its properties during research at the Naval Ordnance Laboratory in 1962.
While the potential applications for nitinol were realized immediately, practical efforts to
commercialize the alloy did not take place until a decade later. This delay was largely
because of the extraordinary difficulty of melting, processing and machining the alloy.
Even these efforts encountered financial challenges that were not really overcome until
the 1990s, when these practical difficulties finally began to be resolved.
The discovery of the shape-memory effect in general dates back to 1932 when Swedish
researcher Arne Olander first observed the property in gold-cadmium alloys. The same
effect was observed in Cu-Zn in the early 1950s.
Properties of NiTi
One of nickel titanium's more unusual properties is its "shape memory." In
austenite form, the alloy is fairly rigid and has a particular shape. When it changes
tomartensite after exposure to lowered temperatures, nickel titanium becomes
more elastic and flexible. However, if the alloy is heated again and reverts to
austenite, the alloy will take on the shape it had before cooling, regardless of what
shape it had as martensite. This phenomenon of "remembering" its former shape
is called "shape memory."
Nickel titanium at cooler temperatures -- below -4°F -- is known as martensite,
and its molecules have a rhomboid crystal structure, meaning that its shape has six
sides and each side has four edges, but it's not a cube because the angles and sides
are not symmetrical. On one side of the molecule, the angles measure 98.8° and
81.2°, and its edges measure 0.46 nanometers (nm) and 0.30 nm. The edges of
adjacent faces measure 0.30 nm and 0.41 nm.
Austenite Start Temperature
As nickel titanium is heated above a certain temperature, it begins to transition
from martensite into austenite. This temperature ranges from -4°F to 140°F,
depending on the amount of nickel in the compound. Specifically, the complex
molecular structure of martensite begins to shift into a simpler cubic structure.
The distance between the atoms along the edges of the cubic structure is 0.3 nm.
The angles at any given corner of the cube measure 90°.
Appearance: this is a bright silvery metal.
Density: The density of this alloy is 6.45 gm/ cm3
Melting Point: Its melting point is around 1310 °C.
Resistivity: It has a resistivity of 82 ohm-cm in higher temperatures and 76 ohmcm in lower temperatures.
Thermal Conductivity: The thermal conductivity of this metal is 0.1 W/ cm-°C.
Heat Capacity: Its heat capacity is 0.077 cal/ gm-°C.
Latent Heat: this material has a latent heat of 5.78 cal/ gm.
Magnetic Susceptibility: Its magnetic susceptibility is 3.8 emu- gm in high
temperatures and 2.5 in low temperatures.
Ultimate Tensile Strength: The ultimate tensile strength of this material ranges
between 754 and 960 MPa.
Typical Elongation to Fracture: 15.5 percent
Typical Yield Strength: 560 MPa in high temperature; 100 MPa in low
Approximate Elastic Modulus: 75 GPa in high temperature; 28 GPa in low
Advantages of NiTiarchwiresin Orthodontics:
Constant forces over large wire deflection.
Which make the NiTiarchwires one of the best material Used in Orthodontics to
arrange the teeth and move them.
Disadvantages of NiTiarchwires:
Very sensitive to manufacturing process.
Offer little advantages in small diameters.
Very sensitive to temperature changes in the oral cavity.
Fraction between the archwire and the brackets.
The composition of Nitinol used to construct in orthodonticsarchwires55 Ni:45 Ti
The Use of NiTi in Endodontic Hand Files:
Walia, Brantley, and Gerstein conducted the first reported investigation of the NiTi alloy
in endodontics in 1988.Testing concluded that the NiTi had two to three times the elastic
flexibility and greater resistance to torsion fractures. By 1991 Quality Dental (Johnson
City, TN), developed a process for grinding NiTi alloy files for NiTi Co. (Chattanooga,
TN).It was reported to be 500% more flexible than conventional stainless steel and said
to be capable of withstanding 1000% more stress than conventional stainless steel.
University of South Carolina conducted a study in 1992 with their pre-doctoral students.
Fewer cases of broken instruments, perforations, and ledges occurred in the group using
NiTi hand files University of Tennessee conducted a similar study in 1993 with their predoctoral students. Students using NiTi hand files had significantly higher grades,
instrumented the canals significantly faster, and had overall superior results. NiTi files
seemed to work more efficiently in a reaming motion rather than a filing motion.
The composition of Nitinol used to construct endodontic instruments is 56% (wt)
nickel and 44% (wt) titanium.
Copper NiTi “CuNiTi”:
The composition ofCopper NiTiis 5% Copper, 0.2-0.5%.
Chromium.The addition of Cu:
Increase strength, reduce energy loss and allows greater control of TTR.
-Long force plateau
-Better manufacturing consistency
-Tolerate repeated loading better
-3 Types 27°, 35°, 40°.
CuNiTi 35 °
CuNiTi 40 °
CuNiTi 27˚It is Superelasticwire Used where rapid tooth movement is required.
CuNiTi 35˚It is Thermoelastic wire Used where relative low forces are required.
CuNiTi 40˚It is Thermoelastic wire it is good as initial rectangular wire.
Beta-Titanium Alloy (TMA)
The Contains of Beta-Titanium Alloy is 80% Ti, 11% Mo, 7% Zr and 4% Sn.
Medium stiffness ( 1/3 of SS and twice of Nitinol).
Produce gentler linear forces than SS.
Has more range and greater springback.
Has rough surface.
Stiffness ( Young's Modulus) GPa
Multi-strand stainless steel wire provides greater flexibility and fracture resistance than equivalent single strand wire
Multi-strand wire have various types:
Three Strand Wire
Will not unravel when cut.
Moderate force , but drops quickly as teethmoves.
Excellent for gentle - constant force for alignment.
Six strand Coaxial wire/Seven strand
Coaxial six stand wire is a super resilientwire that can be bent to a greater degree than ordinary twist wire
without taking a set.
Coaxial Wire is an excellent initial archwire.
Eight Strand Braided wire
Wire will not fray when cut.
Rectangular shape completely fills bracketslot to archive torque control and levelingwith one archwire .
Flexible enough to engage every bracket,yet rigid enough for settling and finishing.
Here this table shows the difference between the orthodontic wires Springback and stiffness ratios
of different materials:
Flexible alloys are very important for Orthodontic treatment especially in the first phase of orthodontic
treatment (Leveling and Alignment) and this will improve the esthetics by providing light continuous force
with long range of action and shape memory.
In EndodonticsFlexible alloys can make the magic which it allows the dentist to shape and clean the carved
canals without fracturing the endodontic instrument in the canal.
W.J. Buehler, J.W. Gilfrich& R.C. Wiley, "Effects of low-temperature phase
changes on the mechanical properties of alloys near composition TiNi," Journal
of Applied Physics34 (1963) p 475. doi:10.1063/1.1729603.
F.E. Wang, W.J. Buehler & S.J. Pickart, "Crystal structure and a unique
martensitic transition of TiNi," Journal of Applied Physics36 (1965) p 3232-3239.
"The Alloy That Remembers", Time, 1968-09-13.
Kauffman, George B.; Mayo, Isaac (1997), "The Story of Nitinol: The
Serendipitous Discovery of the Memory Metal and Its Applications", The
Chemical Educator2: 1, DOI:10.1007/s00897970111a.
Olander, A (1932), J. Amer. Chem. Soc.54: 3819
Hornbogen, E. (1956), Z. Metallkunde47: 47