An orthodontic shape-memory alloy archwire for ligating to orthodontic appliances is heat treated, so that different sections of the archwire each exhibit a predetermined modulus of elasticity, and therefore impart a predetermined range of force when deflected. The distal ends of the archwire are further heat treated, or are treated with a dopant, to exhibit substantially diminished superelastic properties in comparison to the other sections of the archwire. The distal ends can therefore be deformed into shapes when ligated to orthodontic appliances to secure them to the appliances, and thus prevent them from slipping therethrough.

FIELD OF THE INVENTION 
The present invention relates to orthodontic archwires and, in particular, 
to orthodontic archwires made of shape-memory alloy wires. 
BACKGROUND INFORMATION 
A variable force archwire made from a nickel-titanium (Ni-Ti) alloy wire is 
shown in Japanese utility model publication SHOO 63-34650 (1988). 
Different sections of the archwire are treated to develop different moduli 
of elasticity, thus imparting different forces when deflected. Typically, 
the sections corresponding to the front teeth, the bicuspids, and the 
molars are heat treated differently so that each section exhibits a unique 
modulus of elasticity. As a result, when the archwire is mounted to a 
patient's teeth, it imparts different forces to different sections of the 
dental arch. 
A typical variable force archwire is heat treated so that its section 
corresponding to the molars imparts a greater force when deflected than 
its section corresponding to the bicuspids. The section corresponding to 
the bicuspids is typically heat treated to impart a greater force when 
deflected than the section corresponding to the front teeth. 
One problem with non-variable force archwires is that the entire length of 
such an archwire exerts substantially the same force when deflected. 
Therefore, because it is necessary to impart different forces to different 
sections of a patient's dental arch, more than one archwire must be 
employed during the course of treatment. Typically, 7 to 8 different 
archwires may be used to treat a single patient. With variable force 
archwires, however, fewer archwires are required. 
In FIG. 1, the teeth T of a typical dental arch are illustrated. An 
orthodontic archwire W is ligated to several orthodontic brackets B 
mounted to the teeth T. The bending and resultant tension within the 
archwire W creates forces that are imparted to the brackets B and thus the 
teeth T. The distal ends WA of the archwire W are secured to the brackets 
B mounted to the anterior molars, to prevent the archwire from slipping in 
the mesial direction. 
With known stainless steel orthodontic archwires, the distal ends are 
typically bent into appropriate shapes to prevent them from slipping 
through the orthodontic brackets B. Typical stainless steel archwires are 
illustrated in FIGS. 2 and 3. As shown in FIG. 2, the distal end WA of the 
archwire W is formed into a triangular shape. In FIG. 3, the distal end WA 
is formed into a hook shape. The bent distal ends are often referred to as 
"stops". 
One problem with shape-memory alloy archwires, such as Ni-Ti archwires, is 
that it has not been possible to bend their distal ends to form stops. 
Because of the properties of shape-memory alloy wires, when their distal 
ends are bent to form stops, the bent shapes are not retained because the 
archwires tend to return to their original shapes. It has been necessary 
therefore to attach fastening accessories to their distal ends to prevent 
them from slipping through the orthodontic appliances. For example, stop 
tubes are typically mechanically fastened to the distal ends of 
shape-memory alloy archwires. The procedure of attaching fastening 
accessories, however, has proven to be relatively complicated and time 
consuming. 
It is an object of the present invention, therefore, to overcome the 
problems and disadvantages of known shape-memory alloy archwires. 
SUMMARY OF THE INVENTION 
The present invention is directed to an orthodontic shape-memory alloy 
archwire for ligating to orthodontic appliances. The archwire comprises a 
shape-memory alloy wire formed into an arch shape and heat treated so that 
at least one section of the archwire exhibits a predetermined modulus of 
elasticity and thus imparts a predetermined range of force when deflected. 
The distal ends of the archwire are treated to exhibit diminished 
superelastic properties in comparison to the at least one other section of 
the archwire. The distal ends are therefore deformable into shapes to 
prevent them from slipping through orthodontic appliances when mounted 
thereto. 
The distal ends of one orthodontic shape-memory alloy archwire of the 
present invention are heat treated to exhibit diminished superelastic 
properties. A dopant is applied to the distal ends of another orthodontic 
shape-memory alloy archwire of the present invention. The dopant permits 
each distal end to be deformed and to retain the deformed shape, to 
prevent them from slipping through orthodontic appliances when mounted 
thereto. Preferably, the shape-memory alloy wire includes nickel titanium 
and the dopant includes iron. 
The present invention is also directed to another orthodontic shape-memory 
alloy archwire. The archwire comprises a nickel titanium alloy wire formed 
into an arch shape. The section of the archwire corresponding to the front 
teeth is heat treated to exhibit a first predetermined modulus of 
elasticity. The sections corresponding to the bicuspids are heat treated 
to exhibit a second predetermined modulus of elasticity. The sections 
corresponding to the molars are heat treated to exhibit a third 
predetermined modulus of elasticity. 
Each section of the archwire thus imparts a predetermined range of force 
when deflected. The distal ends of the archwire are heat treated to 
substantially diminish their superelastic properties in comparison to the 
other sections of the archwire. The distal ends are therefore deformable 
into shapes to secure them to orthodontic appliances when mounted thereto. 
The present invention is also directed to a method of making an orthodontic 
shape-memory alloy archwire for mounting to orthodontic appliances. The 
method includes the following steps: forming a shape-memory alloy wire 
into an arch shape; heat treating the shape-memory alloy wire so that at 
least one section thereof exhibits a predetermined modulus of elasticity; 
and treating the distal ends of the archwire so that they no longer 
exhibit superelastic properties, or exhibit diminished superelastic 
properties in comparison to the at least one other section of the 
archwire. The distal ends are thus deformable into shapes to prevent them 
from slipping through orthodontic appliances when mounted thereto. 
In one method of the present invention, the distal ends of the archwire are 
heat treated. The distal ends are preferably heat treated at a temperature 
within the range of about 600.degree. C. to 900.degree. C. In another 
method of the present invention, a dopant is applied to the distal ends of 
the archwire. The dopant preferably includes iron. 
The present invention is also directed to another method of making an 
orthodontic shape-memory alloy archwire. The method comprises the 
following steps: heat treating the section of the archwire corresponding 
to the front teeth to impart a first predetermined range of force when 
deflected; heat treating the sections of the archwire corresponding to the 
bicuspids to impart a second predetermined range of force when deflected; 
heat treating the sections of the archwire corresponding to the molars to 
impart a third predetermined range of force when deflected; and heat 
treating the distal ends of the archwire to lose their superelastic 
properties, or to exhibit substantially diminished superelastic properties 
in comparison to the other sections of the archwire. The distal ends can 
therefore be deformed into shapes to secure them to orthodontic 
appliances. 
In one method of the present invention, the distal ends of the archwire are 
heat treated at a temperature within the range of about 600.degree. to 
900.degree. C. The section of the archwire corresponding to the front 
teeth is heat treated at a temperature within the range of about 
400.degree. C. to 600.degree. C. for a time period within the range of 
about 1 hour to about 2.5 hours. The sections of the archwire 
corresponding to the bicuspids are heat treated at a temperature within 
the range of about 400.degree. C. to 600.degree. C. for a time period 
within the range of about 15 minutes to 1 hour. The sections of the 
archwire corresponding to the molars are heat treated at a temperature 
within the range of about 400.degree. C. to 600.degree. C. for a time 
period within the range of about 0 to 10 minutes. 
One advantage of the present invention is that the distal ends of the 
archwire are treated so that they no longer exhibit superelastic 
properties, or exhibit substantially diminished superelastic properties. 
Therefore, the distal ends can be shaped to form stops in the same way as 
with stainless steel archwires. As a result, there is no need to fasten 
additional accessories to the distal ends of shape-memory alloy archwires, 
as previously done to prevent them from slipping through the orthodontic 
appliances. 
Other advantages of the apparatus and method of the present invention will 
become apparent in view of the following detailed description and drawings 
taken in connection therewith.

DETAILED DESCRIPTION 
In FIG. 4, an orthodontic archwire embodying the present invention is 
indicated generally by the reference numeral 10. The archwire 10 is made 
of a shape-memory alloy wire, preferably a Ni-Ti alloy wire. The archwire 
10 is heat treated so that different sections of the archwire exhibit 
unique moduli of elasticity. Each section therefore imparts a 
substantially predetermined force to the corresponding teeth of a dental 
arch. 
The section X1 of the archwire 10 corresponds to the front teeth; the 
sections X2 correspond to the bicuspids; and the sections X3 correspond to 
the molars of a typical dental arch. The sections X4 are not used to 
impart forces, but are formed into stops to prevent the archwire from 
slipping through orthodontic appliances mounted to a patient's teeth, as 
described further below. 
The archwire 10 is a variable force archwire, and therefore each of the 
sections X1 through X3 is heat treated to exhibit a unique modulus of 
elasticity. Each respective modulus of elasticity is selected so that the 
respective section of the archwire imparts a substantially predetermined 
force to the corresponding teeth of a dental arch. The section X1 is heat 
treated to impart an optimal range of force to the front teeth; the 
sections X2 are heat treated to impart an optimal range of force to the 
bicuspids; and the sections X3 are heat treated to impart an optimal range 
of force to the molars. 
In accordance with one embodiment of the present invention, the archwire 10 
is made of a Ni-Ti alloy wire having a 0.016 inch wire diameter. Sections 
X1, X2 and X3 of the archwire are each heat treated to exhibit a unique 
modulus of elasticity. Sections X4, on the other hand, are initially heat 
treated in the same way as sections X3, so that they exhibit substantially 
the same modulus of elasticity. 
The section X1 is heat treated in a conventional heating solution at about 
500.degree. C. for a time period within the range of about 60 to 80 
minutes. While the section X1 is heat treated, the other sections of the 
archwire, X2 through X4, are not immersed in the heating solution but are 
maintained at a lower temperature. Then, both sections X1 and X2 are 
immersed in the heating solution, which is again maintained at about 
500.degree. C., for a time period within the range of about 25 to 35 
minutes. The entire archwire 10 is then immersed in the heating solution, 
which is still maintained at about 500.degree. C., for approximately 5 
minutes. The archwire 10 is then removed from the heating solution and 
permitted to cool to room temperature. 
Thus, the section X1 of the archwire 10, which corresponds to the front 
teeth, is heat treated at about 500.degree. C. for a total time period 
within the range of about 90 minutes to about 2 hours. The sections X2, 
which correspond to the bicuspids, are heat treated at about 500.degree. 
C. for a time period within the range of about 30 minutes to about 40 
minutes. The sections X3, which correspond to the molars, and the sections 
X4, which are used to form stops, are heat treated at about 500.degree. C. 
for about 5 minutes. Therefore, sections X1, X2 and X3 of the archwire 10 
are each heat treated to exhibit a unique modulus of elasticity. Sections 
X4, on the other hand, are heat treated in the same way as sections X3, 
and thus should exhibit about the same modulus of elasticity. 
The different sections of the archwire 10 exhibited the following loads 
when deflected about 2 mm: section X1 imparted loads within the range of 
about 30 grams ("G") to 70 G; sections X2 imparted loads within the range 
of about 140 G to 170 G; and sections X3 imparted loads within the range 
of about 250 G to 280 G. 
The sections X4 are then treated again so that they no longer exhibit 
superelastic properties, or exhibit substantially diminished superelastic 
properties. Once the sections X4 lose their superelastic properties, or 
exhibit only negligible superelastic properties, they can be formed into 
stops in the same way as with stainless steel archwires. 
There are various methods for finally treating the sections X4. One method 
is to immerse them into a conventional heating solution, maintained within 
a temperature range of about 700.degree. C. to 800.degree. C. The other 
sections of the archwire 10 are not immersed in the heating solution, but 
are maintained at substantially lower temperatures. The sections X4 are 
maintained in the heating solution for a time period so that they no 
longer exhibit superelastic properties, or exhibit substantially 
diminished superelastic properties. 
Another method is to heat treat the sections X4 by using a pair of electric 
pliers (not shown). The electrodes of the pliers are gripped on either end 
of each section X4, so that the electric current can pass through each 
section. The level of electric current is selected so that each section X4 
is heated to a temperature within the range of about 700.degree. C. to 
800.degree. C. The sections X4 are heated for a period of time so that 
they no longer exhibit superelastic properties, or exhibit significantly 
diminished superelastic properties. 
Another method is to treat each section X4 with a dopant, such as iron ions 
(Fe). The iron permits the sections X4 to be bent and to maintain the bent 
shape, by preventing the shape-memory alloy wire from returning to its 
original shape. Once the sections X4 are finally treated, they can be 
formed into stops in the same manner as with stainless steel archwires. 
For example, the finally treated sections X4 can be formed into the shapes 
shown in either FIGS. 2 or 3. 
One advantage of the present invention, is that there is no need to fasten 
additional accessories to the distal ends of shape-memory alloy archwires, 
as previously done to prevent them from slipping through the orthodontic 
appliances. Because the sections X4 of the archwire 10 are treated so that 
they no longer exhibit superelastic properties, or exhibit substantially 
diminished superelastic properties, they can be shaped to form stops in 
the same way as with stainless steel archwires.