Orthodontic force module with fracture-resistant coupling

An orthodontic force module for correcting Class II malocclusions includes a resilient body and a coupling connected to the body for connecting the body to a selected orthodontic appliance located on the patient's upper jaw. The coupling includes an opening that extends in a reference plane substantially parallel to and preferably containing the longitudinal axis of the body. The orientation of the opening provides enhanced freedom of movement of the force module when the patient's jaws are opened or closed and significantly reduces the likelihood of fracture of the coupling.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an intra-oral force module used in orthodontic 
treatment. More specifically, the present invention relates to an 
orthodontic force module for correcting Class II malocclusions. 
2. Description of the Related Art 
Orthodontic treatment involves movement of malpositioned teeth to 
orthodontically correct positions. During treatment, tiny orthodontic 
appliances known as brackets are connected to anterior, cuspid and 
bicuspid teeth, and an archwire is placed in a slot of each bracket. The 
archwire forms a track to guide movement of the brackets and the 
associated teeth to desired positions for correct occlusion. Typically, 
the ends of the archwire are held by appliances known as buccal tubes that 
are secured to molar teeth. 
Various types of elastomeric devices, also known as force modules, are 
commonly used in orthodontic treatment. The resilient force of such 
modules in tension or compression is typically used to move a tooth or an 
orthodontic appliance relative to other teeth or orthodontic appliances. 
As one example, tiny O-ring devices are used as ligatures to secure the 
archwire in slots of the brackets. As another example, elongated devices, 
including chain-like modules having a number of interconnected O-ring 
portions, are sometimes stretched between selected brackets in order to 
move certain teeth relative to other teeth. Other devices are especially 
adapted to separate adjacent teeth or to rotate a tooth about its long 
axis. 
Examples of known elastomeric devices are found in U.S. Pat. Nos. 
3,530,583, 3,758,947, 4,038,753, 4,950,158 and 5,044,946. U.S. Pat. No. 
5,317,074 describes improved elastomeric orthodontic force modules that 
are made of a material resistant to staining when exposed to foods or 
beverages such as mustard, tea and coffee. 
The orthodontic treatment of some patients includes correction of the 
alignment of the upper dental arch with the lower dental arch. For 
example, certain patients have a condition referred to as a Class II 
malocclusion wherein the lower dental arch is located an excessive 
distance rearward of the upper dental arch when the jaws are closed. Other 
patients may have an opposite condition referred to as a Class III 
malocclusion wherein the lower dental arch is located forward of the upper 
dental arch when the jaws are closed. 
Orthodontic treatment of Class II and Class III malocclusions are commonly 
corrected by movement of the upper dental arch as single unit relative to 
movement of the lower dental arch as a single unit. To this end, pressure 
is often applied to each dental arch as a unit by applying pressure to the 
brackets, archwires or attachments connected to the brackets or archwires. 
In this manner, the Class II or Class III malocclusion can be corrected at 
the same time that the archwires and brackets are used to move individual 
teeth to desired positions. 
Orthodontic force modules made of an elastomeric material have been used in 
the past to treat a Class II malocclusion by connecting a pair of such 
force modules to both arches on opposite sides of the oral cavity. In such 
instances, the force module may be used in tension to pull the jaws 
together in a direction along reference lines that extend between the 
points of attachment of each force module. Examples of such force modules 
include an O-ring or a chain-type module made of a number of integrally 
connected O-rings. 
Conventional elastomeric force modules used in treatment of a Class II or 
Class III malocclusion are often removable by the patient for replacement 
when necessary and for cleaning of the teeth. Unfortunately, neglect of 
the patient to reinstall the force modules seriously retards the progress 
of treatment. Poor cooperation from the patient can defeat timely 
achievement of the goals of an otherwise well-planned treatment program, 
resulting in an additional expenditure of time for both the patient and 
the orthodontist. Patient cooperation is often a problem with adolescent 
patients. 
A number of devices that are fixed in place in the oral cavity during 
orthodontic treatment have been proposed in the past to overcome the 
problems of patient cooperation associated with removable force modules. 
For example, U.S. Pat. Nos. 3,798,773, 4,462,800 and 4,551,095 disclose a 
telescoping tube assembly that urges the jaws toward positions of improved 
alignment. The assemblies are fixed to other orthodontic appliances by the 
orthodontist, and thus problems of patient non-compliance are avoided. The 
device shown in U.S. Pat. No. 3,798,773 includes an internal coil 
compression spring to exert force on the dental arches as the mouth is 
closed. 
A coiled wire spring device used in tension for applying corrective forces 
between the dental arches is shown in U.S. Pat. No. 3,618,214 and 
includes, in one embodiment, a pair of fasteners such as eyelets secured 
to opposite ends of the coiled wire spring. A protective sheath is 
disposed around the spring. The spring produces a restoring force upon 
elongation that urges the jaws toward an improved alignment. 
Other orthodontic devices for correcting Class II and Class III 
malocclusions are described in U.S. Pat. Nos. 4,708,646 and 5,352,116. 
Such patents describe flexible members with swivel end attachments for 
connection to the upper and lower jaws of a patient. The length of the 
members is selected such that the member is curved in an arc when the 
patient's jaws are closed. The inherent bias of the members toward a 
normally straight orientation provides a force that pushes one jaw 
forwardly or rearwardly relative to the other jaw. 
The commercial embodiments of the devices described in U.S. Pat. Nos. 
4,708,646 and 5,352,116 include internal coil spring that are surrounded 
by a plastic sheath. It has been observed in some instances that the coil 
spring may break during use after a period of time. Unfortunately, the 
plastic sheath often hides the broken portion of the spring, such that it 
is difficult to confirm that the device is working as intended. 
Other types of force modules are described in U.S. Pat. Nos. 5,435,721, 
5,651,672 and 5,897,313. However, there is a continuing need to improve 
the state of the art so that a force module can be constructed that 
provides reliable corrective force as desired by the orthodontist over the 
expected lifetime of its use. More specifically, there is a desire to 
reduce as much as possible the likelihood that the force module will 
fracture after extended periods of use in the oral cavity, so that the 
treatment program is not interrupted and replacement of the module during 
the course of treatment is unnecessary. 
SUMMARY OF THE INVENTION 
The present invention is directed in one embodiment toward an orthodontic 
force module for correcting Class II malocclusions. The force module 
comprises a resilient body having a longitudinal axis. The body has a 
first end section, a second end section and a middle section located 
between the first end section and the second end section. A first coupling 
is connected to the first end section for connecting the first end section 
to a selected orthodontic appliance located on the patient's upper jaw. A 
second coupling is connected to the second end section for connecting the 
second end section to a selected orthodontic appliance located on the 
patient's lower jaw. The body has a length such that the middle section is 
bent in a curve when the patient's jaws are closed. At least one of the 
couplings includes an opening that extends in a reference plane 
substantially parallel to the longitudinal axis of the body. 
Another embodiment of the invention is also directed toward an orthodontic 
force module for correcting Class II malocclusions. In this embodiment, 
the force module includes a resilient body having longitudinal axis, and 
the body has a first end section, a second end section and a middle 
section located between the first end section and the second end section. 
A first coupling is connected to the first end section for connecting the 
first end section to a selected orthodontic appliance located on the 
patient's upper jaw. A second coupling is connected to the second end 
section for connecting the second end section to a selected orthodontic 
appliance located on the patient's lower jaw. The first coupling includes 
an opening. The force module also includes a pin having a generally 
"L"-shaped configuration with a first leg extending in a generally lingual 
direction through the opening and a second leg extending in a generally 
mesial direction for connection to the selected orthodontic appliance 
located on the patient's upper jaw. 
The force module in its various embodiments provides a reliable corrective 
force to treat Class II malocclusions, and yet also has been found to be 
less likely to fracture over extended periods of time in cycle testing. 
Advantageously, the force module in certain embodiments of the invention 
may be used on either the right or the left side of the oral cavity, so 
that two different force modules need not be manufactured, kept in 
inventory and sold as with many of the other force modules known in the 
art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An orthodontic force module for correcting Class II malocclusions that is 
constructed in accordance with one embodiment of the invention is 
illustrated in FIGS. 1-4 and is broadly designated by numeral 20. The 
force module 20 is shown for exemplary purposes in FIGS. 1 and 2 as it 
appears in use when installed on the right side of the patient's oral 
cavity. FIG. 3 shows the force module alone before installation, and FIG. 
4 shows a part of the force module as it appears during an intermediate 
step of manufacture. 
Turning now to FIG. 4, the force module 20 includes a resilient body 22 
having a longitudinal axis. In this embodiment, the body 22 has a 
relatively constant cross-sectional configuration when viewed in reference 
planes perpendicular to the longitudinal axis at different locations along 
the longitudinal axis. The body includes a first end section 24, a second 
end section 26 and a middle section 28 that is located between the first 
end section 24 and the second end section 26. 
A first coupling 30 is connected to the first end section 24 for connecting 
the first end section 24 to a selected orthodontic appliance located on 
the patient's upper jaw. The first coupling 30 includes a circular opening 
32. 
A second coupling 34 is connected to the second end section 26 for 
connecting the second end section 26 to a selected orthodontic appliance 
located on the patient's lower jaw. The second coupling 34 includes a 
circular opening 36. The openings 32, 36 may have a diameter, for example, 
of about 0.05 to 0.06 inch (1.3 to 1.5 mm). 
Preferably, and as shown in FIG. 4, the first coupling 30 and the second 
coupling 34 are integrally connected to the first end section 24 and the 
second end section 26 respectively. As such, the body 22 and the couplings 
30, 34 may be stamped from a section of resilient material such as a 
metallic material. Particularly preferred materials include shape-memory 
alloys such a near stoichiometric nickel-titanium alloy. 
As shown in FIGS. 1 and 3, the second coupling 34 in this embodiment 
extends along a reference plane that is oriented at an obtuse angle 
relative to the longitudinal axis of the body 22. A presently preferred 
angle is about 115 degrees. If the body 22 and the second coupling 34 are 
integrally connected to each other and made of a metallic material, the 
angle of the second coupling 34 is formed during the manufacturing process 
by bending the second coupling 34 relative to the body 22 past the yield 
point of the material along a forming axis that is located at an acute 
angle relative to the longitudinal axis of the body 22. FIG. 4 illustrates 
the body 22 before bending, and FIG. 3 shows the force module 20 as it 
appears after the body 22 is bent. 
The opening 32 of the first coupling 30 extends in a reference plane that 
is substantially parallel to the longitudinal axis of the body 22. 
Preferably, and as shown in the drawings, the first coupling 30 extends 
along a reference axis that is collinear with the longitudinal axis of the 
body 22, and the opening 32 extends in a reference plane that includes the 
longitudinal axis of the body 22. 
Preferably, the body 22 and a portion of the couplings 30, 34 are covered 
by a plastic sheath 38 that is illustrated in FIGS. 1-3. Preferably, the 
sheath 38 is made of a resilient plastic material that is resistant to 
staining by food and beverages. Optionally, the sheath 38 may be made of a 
plastic material that shrinks upon heating so that during manufacture the 
body 22 may be readily inserted in the sheath 38, and the sheath 38 can 
then be fixed to the body 22 by use of a heat gun, heat lamp, oven or the 
like. As another alternative, the sheath 38 may be made by dip-coating the 
body 22 in a curable, liquid polymer. 
The force module 20 also includes a pin 40 that is depicted in FIGS. 1-3 
and stop 42 that is depicted only in FIG. 3. The pin 40 preferably has a 
configuration as illustrated in FIG. 3 before installation of the force 
module 20 in the patient's oral cavity. As shown, the pin 40 includes a 
first elongated leg 44 and a second elongated leg 46 that extends at an 
angle of approximately 90 degrees relative to the direction of extension 
of the first leg 44. The pin initially has an overall, generally 
"L"-shaped configuration. 
The first leg 44 of the pin 40 extends through the first opening 32. The 
pin also includes an enlarged head 48 that is secured to the outer end of 
the first leg 44. Preferably, the head 48 is integrally connected to the 
first leg 44 and has a generally spherical shape, although other 
constructions are also possible. 
The stop 42 has an internal passageway, and the first leg 44 of the pin 40 
extends through the passageway. Preferably, the stop 42 has an overall, 
generally spherical shape. However, other shapes are also possible, 
including ovoids or football shapes and cylindrical sleeves. 
Preferably, an outer end portion of the second leg 46 has a yield stress 
that is less than the yield stress of remaining portions of the pin 40. 
Such construction enables the outer end portion to be permanently deformed 
by the practitioner with less effort than would otherwise be required, and 
may be provided by annealing or partially annealing the outer end portion 
of the second leg 46. Further details for annealing or partially annealing 
the outer portion of the second leg 46 and alternative constructions are 
described in pending U.S. patent application Ser. No. 09/197,309 filed 
Nov. 20, 1998 and entitled "ORTHODONTIC COUPLING PIN", the disclosure of 
which is expressly incorporated by reference herein. 
FIG. 1 illustrates the force module 20 as an example of how it might appear 
once installed in the oral cavity of a patient undergoing orthodontic 
treatment. In FIG. 1, a number of slotted orthodontic brackets 50 are 
fixed to teeth of a patient's upper jaw 52, and an archwire 54 is received 
in the slot of each bracket 50. A ligature 56 extends around each bracket 
50 in order to urge the archwire 54 toward an orientation seated in the 
slot of each bracket 50. 
In the example shown in the drawings, an orthodontic buccal tube 58 is 
fixed to a metallic orthodontic band that is placed around a first molar 
tooth 60. The buccal tube 58 includes a passage that receives an end of 
the archwire 54. The buccal tube 58 is shown in more detail in FIG. 2. 
The buccal tube 58 also includes an auxiliary passage that receives the 
second leg 46 of the pin 40. Once the second leg 46 has been inserted into 
the auxiliary passage, the outer end portion of the second leg 46 is bent 
in an arc as shown in FIGS. 1 and 2 in order to releasably secure the 
first coupling 30 of the force module 20 to the buccal tube 58. 
The stop 42 enables the pin 40 to be cinched to the buccal tube 58 in a 
relatively tight manner without creating binding or otherwise unduly 
hindering movement of the body 22 relative to the pin 40. Preferably, the 
stop 42 is rotatable relative to the pin 40. Alternatively, the stop 42 is 
fixed to the pin 40 once the first leg 44 has been inserted through the 
first opening 32. 
A number of slotted orthodontic brackets 62 are fixed to teeth of the 
patient's lower jaw 64 as shown in FIG. 1. A lower archwire 66 is placed 
in the slot of each bracket, and a ligature 68 extends around each bracket 
62 in order to urge the archwire 66 toward a seated orientation in the 
slot of each bracket 62. The end of the archwire 66 is received in a 
passage of a buccal tube 70 that is mounted on a band that encircles a 
patient's lower first molar tooth 72. 
The second coupling 34 is connected to a selected orthodontic appliance 
located on the patient's lower jaw 64, such as one of the brackets 62 or 
the archwire 66. Preferably, the second coupling 34 is coupled to a 
motion-enhancing appliance such as an attachment device 74 that includes a 
wire segment that crosses over a labial side of the lower archwire 66 as 
the patient's jaws 52, 64 are opened. The attachment device 74 increases 
the range of free sliding motion of the force module 20 and reduces the 
amount of stress that might be otherwise imposed on the force module 20, 
on the brackets 50, 62 and/or on the archwires 54, 66 as the patient's 
jaws 52, 64 are opened. 
The attachment device 74 as presently preferred is described in more detail 
in pending U.S. patent application Ser. No. 09/275,490 filed Mar. 24, 1999 
and entitled "ORTHODONTIC ATTACHMENT DEVICE FOR INTERARCH APPLIANCES", the 
disclosure of which is expressly incorporated by reference herein. In 
brief, the attachment device 74 includes a mesial closed loop that extends 
about the lower archwire 66, and a distal end section that extends through 
a passage of the buccal tube 70. The attachment device 74 includes an 
intermediate segment that passes through the second opening 36. Further 
aspects of the attachment device 74, as well as alternative constructions, 
are described in the aforementioned pending U.S. patent application Ser. 
No. 09/275,490. 
The body 22 has a length selected such that the middle section 28 is bent 
in a curve when the patient's jaws 52, 64 are closed and the force module 
20 is used to correct a Class II malocclusion. Suitable lengths include, 
for example, about 28 mm to about 38 mm as measured from the 
center-to-center distance of the openings 32, 36. 
The construction of the force module 20 has been found to present 
significant advantages over known force modules. In cycle testing, it has 
been found that alignment of the first coupling 30 in straight, collinear 
orientation with the longitudinal axis of the body 22 reduces the 
likelihood of fracture in areas adjacent the opening 32 after extended 
periods of time. While some of the devices known in the art have proven to 
operate in satisfactory manner in the majority of treatments, it is a 
significant benefit to further increase the reliability of the force 
modules so that the likelihood of fracture can be reduced as much as 
possible. Additionally, the coplanar, straight alignment of the first 
coupling 30 with the body 22 simplifies manufacture when the body 22 and 
the couplings 30, 34 are made of a unitary section of metallic material, 
in that the first coupling 30 need not be bent in an arc as known in the 
past. 
The parallel, collinear alignment of the first coupling 30 with the 
longitudinal axis of the body 22 also provides greater freedom of movement 
of the force module 20 when the patient's jaws are opened and closed. By 
aligning the reference plane of the opening 32 in a direction 
perpendicular to a reference axis that extends through the patient's upper 
molar tooth 60 in a buccal-lingual direction (i.e., in a direction 
extending from the patient's cheek to the patient's tongue), the body 22 
can freely swivel with a simple hinging motion as the patient's jaws 52, 
64 are opened and closed with little, if any, restriction of movement. 
Moreover, the second leg 46 of the pin 40 can pivot along its longitudinal 
axis in the passage of the buccal tube 58, to further enhance free 
swinging movement of the force module 20 as the patient's jaws 52, 64 are 
opened or closed. 
A force module 20a for correcting Class II malocclusions according to 
another embodiment of the invention is illustrated in FIG. 5. The force 
module 20a is essentially the same as the force module 20, except for the 
differences as noted below. 
The force module 20a includes a body 22a. The body 22a includes a first end 
section 24a, a second end section 26a and a middle section 28a located 
between the first end section 24a and the second end section 26a. A first 
coupling 30a is connected to the first end section 24a, and a second 
coupling 34a is connected to the second end section 26a. 
The middle section 28a has a cross-sectional area in reference planes 
perpendicular to the longitudinal axis of the body 22a that decreases as 
the first end section 24a and the second end section 26a are approached. 
If, for example, the body 22a and the couplings 30a, 34a are stamped from 
a unitary, flat section of metallic material, the sections 24a, 26a, 28a 
will have cross-sectional shapes of generally rectangular configurations 
with uniform thickness. However, the width of the rectangular 
cross-sectional shape of the middle section 28a will be wider than the 
rectangular cross-sectional shape of the end sections 24a, 26a, and will 
decrease in width as the end sections 24a, 26a are approached. 
In FIG. 5, the force module 20a is shown as it appears before the second 
coupling 34a is bent in an arc relative to the longitudinal axis of the 
body 22a, similar to the view shown in FIG. 4. Additionally, and although 
not shown in the drawings, the force module 20a is preferably provided 
with a pin and stop somewhat similar or identical to the pin 40 and stop 
42 described above. The force module 20a may also include a plastic sheath 
somewhat similar to the sheath 38 described above. 
A force module 20b constructed in accordance with another embodiment of the 
invention is illustrated in FIGS. 6 and 7. The force module 20b includes a 
body 22b that is identical to the body 22a. Additionally, the force module 
20b includes a first coupling 30b that is identical to the first coupling 
30a. 
The force module 20b includes a second coupling 34b that, in this 
embodiment, is somewhat different than the second couplings 34, 34a. The 
second coupling 34b is initially separate from the body 22b and includes a 
sleeve portion 35b and an arm portion 37b. The sleeve portion 35b receives 
a coupling extension of a second end section 26b of the body 22b. The 
coupling extension of the second end section 26b is shown in FIG. 7 and 
includes a series of notches 39b. 
The second coupling 34b may be made from a variety of materials (including 
plastics or metals) and may be made using any suitable technique. For 
example, the coupling 34b may be made of stainless steel that is cast or 
metal-injection molded, and the swaged, staked or pinned in place in 
non-removable fashion to the body 22b. Alternatively, the coupling 22b may 
be made of a plastic material that is molded in place around the coupling 
extension of the second end section 26b or molded separately from the body 
22b and then bonded in place with an adhesive. The notches 39b facilitate 
a fixed, secure connection between the body 22b and the coupling 34b. 
The arm portion 37b extends along a reference axis that is oriented at an 
obtuse angle relative to the longitudinal axis of the body 22b as well as 
to the direction of extension of the sleeve portion 35b. Preferably, that 
obtuse angle is about 115 degrees. The arm portion 37b also includes a 
circular opening 36b that is used in a manner similar to use of the 
openings 36, 36a. 
An orthodontic force module 20c according to another embodiment of the 
invention is illustrated in part in FIG. 8. The force module 20c is 
essentially the same as the force module 20 with the exception of the 
differences described below. The force module 20c includes a body 22c 
having a first end section 24c, a second end section 26c and a middle 
section 28c located between the first end section 24c and the second end 
section 26c. The middle section 28c may have a cross-sectional area in 
reference planes perpendicular to the longitudinal axis of the body 22c 
that is either constant or decreases as the end sections 24c, 26c are 
approached. 
The force module 20c has a first coupling 30c and a second coupling 34c 
that are essentially identical to the couplings 30, 34 respectively 
described above. The second coupling 34c is bent about a forming axis that 
extends at an acute angle relative to the longitudinal axis of the body 
22c. However, the view in FIG. 8 is taken along the forming axis (instead 
of along an axis perpendicular to the longitudinal axis as shown in FIG. 
3) and as such the flat face of the second coupling 34c is not visible in 
FIG. 8. 
The middle section 28c includes a recurve portion 29c that is preferably 
centered along the middle of the length of the body 22c. As shown, the 
recurve portion 29c extends along an arc that is oppositely oriented 
relative to the curved arc that extends between the body 22c and the 
second coupling 34c. The recurve portion 29c is visible whenever the body 
22c is in its normal, relaxed orientation. 
Although not shown in FIG. 8, the force module 20c also preferably includes 
a pin and stop similar to the pin 40 and stop 42. Additionally, a sheath 
may be provided over the body 22c, somewhat similar to the sheath 38 
described above. 
An orthodontic force module 20d according to another embodiment of the 
invention is illustrated in FIG. 9. The force module 20d includes an 
elongated body 22d that is made of an elastomeric material. Preferably, 
the elastic material exhibits resistance to staining by food and 
beverages, and is similar to the elastomeric material described in the 
aforementioned U.S. Pat. No. 5,897,313. 
The force module 20d includes a first coupling 30d and a second coupling 
34d. Each of the couplings 30d, 34d has a sleeve portion 31d, 35d 
respectively that is somewhat similar in shape to a hollow, truncated 
cone. The body 22d includes a first end section 24d that extends through 
the sleeve portion 31d, and a second end section 26d that extends through 
the sleeve portion 35d. 
Each of the end sections 24d, 26d terminates in an outer, enlarged head 
having an outer diameter that is larger than the passageway of the 
adjacent sleeve portion 31d, 35d. The heads present a shoulder that 
retains the couplings 30d, 34d in secure connection with the adjacent end 
sections 24d, 26d. 
The first coupling 30d includes an arm portion 33d that is integrally 
connected to the sleeve portion 31d, and the arm portion 33d presents an 
opening 32d. The opening 32d is circular. The arm portion 33d and the 
opening 32d both lie in a reference plane that is parallel to a 
longitudinal axis 41d of the body 22d when the latter is in its normal, 
relaxed, straight orientation. 
The second coupling 34d includes an arm portion 37d that is integrally 
connected to the sleeve portion 35d. The arm portion 37d extends at an 
obtuse angle relative to the longitudinal axis 41d of the body 22d. 
Preferably, that obtuse angle is about 135 degrees, although other angles 
are also possible. Preferably, both of the couplings 30d, 34d are 
pivotally movable relative to the body 22d in an arc about the axis 41d. 
Optionally, the force module 20d may be used on either the right side of 
the oral cavity or the left side of the oral cavity without alteration. 
However, the practitioner may elect to first slightly pivot the coupling 
30d relative to the coupling 34d in an arc about the axis 41d to optimize 
fitting and use. 
An orthodontic force module 20e constructed in accordance with another 
embodiment of the invention is illustrated in FIGS. 10 and 11. The force 
module 20e includes an elongated, normally straight body 22e that includes 
an inner coil spring 23e (FIG. 11) that is preferably made of a metallic 
material such as stainless steel or a shape-memory alloy such as a near 
stochiometric nickel-titanium alloy. The spring 23e is preferably covered 
by a sheath 38e. Optionally, the sheath 38e is injection-molded around the 
spring 23e by an insert molding process. 
The force module 20e also includes a first coupling 30e and a second 
coupling 34e. The first coupling 30e extends in a reference plane that 
contains the longitudinal axis of the body 22e when the latter is in its 
normal, relaxed configuration. The first coupling 30e includes a circular 
opening 32e that lies in a reference plane that is parallel or that 
contains the longitudinal axis of the body 22e when the latter is in its 
normal, relaxed orientation. 
The force module 20e also includes a second coupling 34e with an arm 
portion 37e. As shown, the arm portion 37e extends at an obtuse angle 
relative to the longitudinal axis of the body 22e when the latter is in 
its relaxed orientation. The arm portion 37e includes a circular opening 
36e. 
Preferably, the force module 20e includes a pin and stop similar or 
identical to the pin 40 and stop 42 described above. Preferably, one or 
both of the couplings 30e, 34e is pivotally movable relative to the body 
22e in an arc about the longitudinal axis of the body 22e. 
As with the force module 20d, the force module 20e may be used on either 
the right side or the left side of the patient's oral cavity without 
alteration. However, the practitioner may opt to first slightly pivot the 
coupling 34e relative to the coupling 30e in an arc about the longitudinal 
axis of the force module 20e to optimize fitting and use. 
Those individuals skilled in the art may recognize that a variety of 
modifications and additions to the presently preferred embodiments are 
possible without departing from the spirit of the invention. For example, 
the force modules 20-20e may be constructed so that both of the couplings 
extend in reference planes parallel to or containing the longitudinal axis 
of the body. In that instance, it may be desirable to provide the body 
with a slight curvature when relaxed or to provide other structure that 
ensures that the body will preferentially bend in a certain direction when 
the patient's jaws are closed. 
Other variations are also possible. For example, the force modules 20, 20a, 
20b, 20c, 20d may have other aspects such as described in U.S. Pat. Nos. 
5,897,313 and 5,651,672. Similarly, the force module 20e may have other 
aspects or features, such as the aspects or features described in U.S. 
Pat. Nos. 4,708,646 and 5,352,116, both of which are incorporated by 
reference herein. Accordingly, the invention should not be deemed limited 
by the embodiments described in detail above, but only by a fair reading 
of the claims that follow along with their equivalents.