ORTHODONTIC WIRES
Arch Wire Materials
There are four main types of material compositions for arch wires:
1) Stainless Steel;
2) Nickel-Titanium (Ni-Ti);
3) Beta-Titanium; and
4) Cobalt-Chromium
A comprehensive orthodontic treatment is usually divided into three phases:
(1) leveling and aligning,
(2) space closure and anterior/posterior correction, and
(3) detailing and finishing.
A variety of alloy wires are used to generate the biomechanical forces associated
with tooth movement. Once the wire is activated or bent, it is the unloading or
deactivating forces that produce orthodontic tooth movement. With current
orthodontic treatment, super elastic nickel-titanium wire is often used for phase 1,
with beta titanium and stainless steel (SS) wires most frequently used for phases 2
and 3. As a result, beta titanium and SS wires tend to be reused more often, leaving
them exposed to the aqueous oral environment for a longer period of time.
Nickel-Titanium (Ni-Ti) wires:
Nitinol was invented by William R.
Buchler and was introduced to the orthodontic community by Andersan in 1971.
They are elastic and can return to their original shape when deformed (shape
memory). Therefore, in the beginning stages of orthodontic treatment, Ni-Ti wires
are frequently used to put gentle forces on the crooked teeth to align them. A
variation of Ni-Ti wires are heat-activated Ni-Ti (Copper Ni-Ti) wires. Heat-activated
Ni-Ti wires can hold the deformed configuration at room temperate, but when the
wire reaches the temperature of a patient’s mouth, the wire will return to its original
shape. Heat-activated Ni-Ti wires are useful in the beginning stages of treatment. If
the teeth are extremely crooked, the wire can be cooled so it can be tied into the
brackets easier. Then after a few minutes, it will reach the temperature of the
patient’s mouth, displaying its Ni-Ti elastic properties. The warm wire will want to
assume its original U-shape and carry the teeth to their new, straighter positions.
Beta-Titanium wires
were introduced by Jon Goldberg and C.J.
Burnstone. They were developed after Ni-Ti wires and offer an intermediate range of
elasticity and strength, while also being able to be permanently deformed. This wire
serves as a good intermediary wire between Ni-Ti and stainless steel. Some
orthodontists will use this wire starting in the middle of treatment while other
orthodontists do not use this type of wire at all.
Composition
Tin – 80%
Molybdenum – 11.5%
Zirconium – 6%
Tin – 4.5%
Titanium molybdenum alloy (TMA) is also used for archwires and
has properties midway between SS and nitinol
Stainless steel wires (entered dentistry -1919)
have been
used for decades due to their high strength. In addition, stainless steel wires do not
rust and can be adjusted many different ways by the orthodontist without breaking.
However, stainless steel wires are not very elastic, meaning that if you bend these
wires too much, they will assume the new position and will not return to their
original position.
3 major types are present:-Ferretic SS
- Martensitic SS
- Austenitic SS
Composition
Chromium (11-26%)–improves the corrosion
resistance
Nickel(0-22%) – austenitic stabilizer
copper, manganese and nitrogen – similar to the amount of nickel added to
the alloy
Carbon (0.08-1.2%)– provides strength
Silicon – (low concentrations) improves the resistance to oxidation and
carburization at high temperatures.
Sulfur (0.015%) increases ease of machining
Phosphorous – allows sintering at lower temperatures.
.
Cobalt chromium nickel (Elgiloy) has the advantage that it can be
hardened by heat treatment after being formed.
Various tempers
Red – hard & resilient
green – semi-resilient
Yellow – slightly less formable but ductile
Blue – soft & formable
Composition
Chromium – 15-22%
Nickel – for strength and ductility
Iron, molybdenum, tungsten and titanium to form stable carbides and
enhance hardness.
Cobalt – 40-45%
Optiflex arch wires
It is a new type of arch wire developed by M.F. Talass
in 1992.these arch wires are made of clear optical fiber and are therefore highly
aesthetic. In addition, they exhibit high resilience. The drawback of this wire is that it
cannot accept a sharp bend.
Shape
1) Round
– .014 up to .020
2) Rectangular
– .021 x .025
3) Square
–
.016 x .016
4) Multi-stranded wires- 2 or more wires of smaller diameter are twisted
together/coiled around a core wire.
-- 0.016 or 0.017
* Dimension is in inches
Round wires have higher ductility than square or rectangular wires.
If both, 1st & 2nd order corrections are required to the same extent, then square or
round wires?
The square wires have advantage. They simultaneously control torque and result in
better orientation into a rectangular slot.
(do not turn and no unwanted forces are created).
 In US - thousandths of an inch
0.016 “ =16 mils
 In Europe and many other areas – millimeters
 CONVERSION
Divide the dimensions in mils by 4 and place a decimal point behind it.
eg – 16 mils = 0.4mm
Applications
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Adams clasp is made in stainless steel in either 0.7 mm (for permanent
molars) or 0.6 mm (for premolars and primary molars) wire.
Labial bow is constructed using 0.7mm hard round stainless steel wire.
Robert`s retractor is a labial bow made in stainless steel wire in 0.5mm.
High labial bow with apron springs- It consists of a heavy wire bow of 0.9mm
thickness and apron spring made of 0.4mm is attached to the high labial bow.
Palatal finger springs are fabricated in 0.5 mm or 0.6 mm hard round
stainless steel wire.
Z spring is made of 0.5mm wire.
T spring is made of 0.5 mm wire.
Coffin spring is made of 1.2mm wire.
U loop canine retractor is made of 0.6mm or 0.7mm wire.
Helical canine retractor is made of 0.6mm wire.
Palatal canine retractor is made of 0.6mm wire.