Note: Descriptions are shown in the official language in which they were submitted.
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ORTHODONTIC APPLIANCE FOR TREATING OVERJET
BACKGROUND OF THE INVENTION
[0001] This invention relates to orthodontic appliances and, in particular, to
orthodontic
appliances for treating overjet in patients.
[0002] A Class II malocclusion with excessive overjet refers to a condition
where a greater
than normal horizontal gap exists between the upper and lower front teeth,
usually due to
proclination or flaring of the upper front teeth, or a deficient lower jaw.
Typical treatments
fall into several categories. The first is retracting or pushing back the
upper teeth. A second
is proclining or pushing forward the lower teeth. A further treatment is
surgical lengthening
of the lower jaw. Another treatment is orthopedic correction whereby forces on
the teeth are
transmitted to the jaws of growing children.
[0003] A known device for correcting a Class II malocclusion is the Forsus
(TM) Fatigue
Resistant Device EZ Module from 3M Unitek, hereafter referred to as the Forsus
Spring. This
comprises a telescoping spring which connects to braces to push the upper
teeth back and the
lower teeth forward. It delivers 200 grams of force when fully compressed and
loses
approximately 20 grams of force for each 1 mm of deactivation. It was designed
to be used
with full braces and to push against the lower braces without breaking off
individual braces
(or orthodontic brackets), that is, without overcoming the bond strength of
the resin cement
that adheres the bracket to the etched enamel ofthe tooth. When used with
braces, the Forsus
Spring is normally never completely compressed. The Forsus Spring, therefore,
never fully
utilizes its full force potential. Periodic reactivation is necessary as the
teeth move and
the compression spring deactivates. This is accomplished by either adding
crimpable split
stainless steel tubing (shims) to the pushrod or replacing the pushrod with a
longer one.
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[0004] A further bite jumping appliance on the market is described in United
States Patent
No. 6,168,430, entitled ORTHODONTIC APPLIANCE FOR TREATING OVERJET, the
disclosure of which is hereby incorporated by reference. Referring to Figure 1
of this
application, the embodiment described in the above patent is a Class II
correction appliance.
This embodiment used Gurin locks 66.a as the stop for its flexible spring
54.a. As the upper
teeth 18.a moved back, the flexible spring 54.a deactivated. This required
periodic
reactivation of the flexible spring 54.a by moving the Gurin locks 66.a
posteriorly.
Accordingly, this previous embodiment required significant maintenance and
monitoring.
Moreover, the Gurin locks 66.a could be a source of sores on the cheek. The
Gurin locks 66.a
are also relatively expensive. The flexible spring 54.a was prone to breakage
and was replaced
by a compression spring, in this case, the Forsus Spring.
[0005] One attempt at addressing the above and other issues was to replace the
Gurin Lock
with an elastic module connected at one end to a hook on the lower molar band
and at the
other end to the lower eyelet ofthe compression spring. The problem with this
approach was
that when the elastic module was exposed to saliva, it lost so much force that
it could not
keep the compression spring activated. This was a problem because in
orthodontics, the goal
is a light, continuous force. Moreover, in view of the relatively small scale
of the required
forces for such devices, such as 200 grams, the effect of this elastic force
decay was
magnified, further magnifying the drawbacks of such an elastic module
approach. The Gurin
lock was in fact still easier to activate, because further crimpable stops
(shims) needed to be
added to the pushrod to keep the spring compressed when the elastic module was
used.
SUMMARY OF THE INVENTION
[0006] To overcome the discomfort and cost issues surrounding the use of Gurin
locks, the
frequent adjustments needed when using the Forsus Spring with braces alone,
and the
problems discovered by the present inventor with respect to the elastic module
approach, the
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Class II correction device of the present application makes use of a device
that now includes
a compression spring together with a supplementary tension spring. More
particularly, the
preferred tension spring has been identified as a nickel titanium tension
spring which has the
most constant force over the range of the spring extension.
[0007] According to one embodiment, there is provided an orthodontic appliance
for
treating overjet in a patient having an upper jaw, a lower jaw, lower teeth in
the lower jaw
and upper teeth in the upper jaw which are abnormally forward of the lower
teeth. The teeth
have lingual sides and labial sides. The appliance includes an upper
attachment device
configured to be secured to at least one of the upper teeth. The appliance
includes a lower
attachment device having a pair of lower connectors. Each lower connector is
configured to
be secured to at least one of the lower teeth of the patient on each side of
the lower jaw. The
appliance includes a rigid, wire-like lingual bow extendable between the lower
connectors
about the lingual sides of the lower teeth. The appliance includes a rigid,
wire-like labial bow
extendable between the lower connectors about the labial sides of the lower
teeth. The bows
are connected to the lower connectors. The appliance includes a force-
delivering module
interconnecting the upper attachment device to a corresponding side ofthe
lower attachment
device. The force-delivering module has a first connector for connecting to
the upper
attachment device. The force-delivering module has a second connector for
connecting to the
lower attachment device. The force-delivering module has a compression spring
operatively
interposed between the first connector and the second connector. The force-
delivering
module has a tension spring operatively connected to the compression member.
The tension
spring is so positioned to actuate the compression spring to bias the lower
attachment device
forwardly with respect to the upper attachment device.
[0008] According to another aspect of the invention, there is provided an
orthodontic
appliance for treating overjet in a patient having an upper jaw, a lowerjaw,
lower teeth in the
lower jaw and upper teeth in the upper jaw which are abnormally forward of the
lower teeth.
The teeth have lingual sides and labial sides. The appliance includes an upper
attachment
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device configured to be secured to at least one of the upper teeth on each
side of the upper
jaw. The appliance includes a lower attachment device having a pair of lower
connectors.
Each lower connector is configured to be secured to at least one of the lower
teeth of the
patient on each side of the lower jaw. The appliance includes a rigid, wire-
like lingual bow
extendable between the lower connectors about the lingual sides of the lower
teeth. The
appliance includes a rigid, wire-like labial bow extendable between the lower
connectors
about the labial sides of the lower teeth. The bows are connected to the lower
connectors.
The appliance includes a force-delivering module interconnecting each side of
the upper
attachment device to a corresponding side of the lower attachment device. Each
force-
delivering module includes a compression spring and a tension spring
operatively connected
to the compression spring. The tension spring is so positioned as to actuate
the compression
spring to bias the lower attachment device forwardly with respect to the upper
attachment
device.
[0009] According to a further aspect ofthe invention, there is provided a
method oftreating
overjet in a patient having an upper jaw, a lower jaw, lower teeth in the
lower jaw and upper
teeth in the upper jaw which aie abnormally forward ofthe lower teeth. The
teeth have lingual
sides and labial sides. The method includes affixing an upper attachment
device to at least
one of the upper teeth on each side of the upper jaw via a pair of upper
connectors. The
method includes affixing a lower attachment device to at least one of the
lower teeth of the
patient via a pair of lower connectors, each lower connector being configured
to be secured
on each side of the lower jaw. The method includes connecting a rigid, wire-
like lingual bow
to the lower connectors and positioning the lingual bow between the lower
connectors about
the lingual sides of the lower teeth. The method includes connecting a rigid,
wire-like labial
bow to the lower connectors and positioning the labial bow between the lower
connectors
about the labial sides of the lower teeth. The method includes interconnecting
a force-
delivering module on each side ofthe upper attachment device to a
corresponding side of the
lower attachment device, each said force-delivering module including a
compression spring
and a tension spring operatively connected to the compression spring. The
method includes
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so positioning the tension spring as to actuate the compression spring to bias
the lower
attachment device forwardly with respect to the upper attachment device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a side view of an orthodontic appliance fitted to the mouth
of a patient
according to the prior art;
[0011] FIG. 2 is a side view of an orthodontic appliance, according to an
embodiment of
the invention, as viewed from the right side of a patient's mouth, with the
patient's jaws closed
and in a Class II position;
[0012] FIG. 3 is an elevational view of the orthodontic appliance of FIG. 2 as
viewed from
the front of the patient's mouth;
[0013] FIG. 4 is a bottom plan view of the upper attachment device thereof, as
viewed on
the top set of the patient's teeth;
[0014] FIG. 5 is a top plan view of the lower attachment device thereof, as
viewed on the
bottom set of the patient's teeth;
[0015] FIG. 6 is a fragmentary, side view of the installation of part of the
force-delivering
module thereof;
[0016] FIG. 7 is a fragmentary, side view ofthe part ofthe force-delivering
module of FIG.
6 illustrated in installed mode;
[0017] FIG. 8 is a side view of the orthodontic appliance of FIG. 2, with the
patient's jaws
closed and in a corrected Class I position;
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[0018] FIG. 9 is a side view of the orthodontic appliance of FIG. 2, with
patient's jaws in
the open position; and
[0019] FIG. 10 is a side view of the orthodontic appliance of FIG. 2, with the
patient's jaws
closed and in an over-corrected Class III position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Referring to the drawings, and first to FIGS. 2 and 3, these illustrate
an orthodontic
appliance 10 in a patient having an upper jaw 12 and a lower jaw 14 which are
in a Class II
starting position. There are lower teeth 16 in the lower jaw 14 and upper
teeth 18 in the upper
jaw 12. The appliance corrects a condition where the upper teeth 18 are
abnormally forward
of the lower teeth 16.
[0021] The appliance includes an upper attachment device 20 configured to be
secured to
at least one of the upper teeth on each side of the upper jaw 12. In this
example, the upper
attachment device is a palatal expansion appliance. The attachment device is
secured either
to permanent teeth or primary teeth which are retained relatively late, or a
combination of
both. The palatal expansion appliance is known and, therefore, is not
described in detail. It
includes bands 19, 21, 22 and 24, as best illustrated in FIG. 4, which extend
about two teeth
on each side of the jaw and an arch 25 extending therebetween. In this
example, the bands
22 and 24 extend about the upper first molars 18e. Also, the upper first
bicuspid teeth 18c
have erupted, so these teeth also have bands 19 and 21 to facilitate the
opening of space for
(cuspid) teeth 18b. If an upper second molar tooth 18f has or is erupting,
there is an occlusal
rest 29 placed over the top of the tooth.
[0022] There is a lower attachment device 30, as best illustrated in FIG. 5,
which includes
a pair of lower connectors in the form ofbands 32 and 34 extending about
molars 36 and 38
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on opposite sides of the patient's lower jaw 14. In this example, the bands 32
and 34 extend
about lower first molars 16e. Hooks 33 and 35 extend posteriorly from the
bands 32 and 34,
respectively. There is a rigid, wire-like lingual bow 40 which extends between
the lower
connectors about the lingual sides of the lower teeth of the patient. In this
example, the
lingual bow 40 is of 0.045" stainless steel wire. The lingual bow 40 is
connected to the lower
connectors, in this case by soldering. Those skilled in the art will
appreciate that it may also
be connected via tubes welded to the bands. The lingual bow 40 in this example
has a pair
of occlusal rests 42 and 44 which extend over the occlusal surfaces of the
first bicuspid teeth
16c. These help prevent the lingual and labial wires from moving down and
impinging on the
gum tissue.
100231 The lower attachment device 30 also includes a rigid, wire-like labial
bow 46 which
extends between the bands 32 and 34 about the labial sides of the lower teeth.
This bow is
made of stainless-steel wire in this example similar to the lingual bow 40.
The labial bow 46
is also connected to the bands 32 and 34, in this example by soldering. The
labial bow 46
bypasses the lower canine (cuspid) 16b and bicuspid teeth 16c and 16d,
respectively. It
contacts the incisor teeth 16a to prevent then from proclining or flaring so
much as to open
spaces between the teeth.
[0024] Referring back to FIGS. 2 and 3, there is a force-delivering module 47.
The force-
delivering module 47 includes a compression spring 54. In this example, the
compression
spring 54 is part of a 3M Unitek Forsus (TM) Fatigue Resistant Device EZ
Module (the
"Forsus Spring") 50, interconnecting the upper attachment device 20 and the
lower
attachment device 30 on one side of the patient's mouth. A similar Forsus
Spring 52 may
interconnect the upper attachment device 20 and the lower attachment device 30
on the
opposite side of the patient's mouth.
[0025] Forsus Springs are known and, accordingly, these are not described in
detail. The
compression spring 54, when compressed, biases the lower attachment device 30
forwardly
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with respect to the upper attachment device 20. This occurs when the patient's
jaws are closed
as seen in FIGS. 2 and 3, and continues as the patient's mouth opens. The
Forsus Spring 50
also includes a pushrod 55 which extends through the compression spring 54.
Each Forsus
Spring has an interengageable upper portion 51 which connects together with a
corresponding
interengageable portion 53 welded to the band 22, as illustrated in FIGS. 6
and 7. Each
Forsus Spring has a bottom eyelet, as illustrated in FIG. 3 by numerals 62 and
64,
respectively. The labial bow 46 extends slidably through each of the eyelets
62 and 64,
respectfully.
[0026] The force-delivering module 47 includes tension springs 70 and 72,
respectively, on
each side of the lower jaw 14. The tension springs 70 and 72 are connected via
first eyelets
71 and 73, respectively, to corresponding anterior curves 81 and 83 of the
pushrods 55 and
57, respectively. Drops of solder 77 and 79 are added along the anterior,
leading edges of the
pushrods 55 and 57 so as to keep the tension springs 70 and 72 from sliding
down and back
along the pushrods 55 and 57 of the Forsus Springs 50 and 52, respectively.
The tension
springs 70 and 72 are so positioned to inhibit tension spring distortion or
breakage by, for
example, biting pressure. The tension springs 70 and 72 are also positioned to
prevent the
pushrod 55 and Forsus Spring 50 from coming apart when the patient's mouth
opens wide.
The tension springs are also connected posteriorly as best illustrated in FIG.
8. The tension
spring 70 is connected via second eyelet 76 to hook 33 of band 32 posteriorly.
[0027] In operation, the tension springs 70 and 72 are so shaped and
positioned as to limit
forward movement of the Forsus Springs 50 and 52, and keep the Forsus Springs
50 and 52
compressed as the upper teeth are moved back. From an open mouth position as
illustrated
in FIG. 9, bottom eyelet 62 slides forwardly along the labial bow 46 when the
patient closes
his or her jaws until the eyelet 62 is stopped or inhibited by tension spring
70, and the same
occurs on the other side of the mouth. Referring to FIGS. 2 and 3, further
closing ofthe jaws
causes compression of the Forsus Springs 50 and 52, which forces the upper
teeth backwards
and the lower teeth forwardly. However, opening of the jaws is not impeded
since the eyelets
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62 and 64 can slide rearwardly along the labial bow 46. The force vector is in
the direction
of pulling the patient's lower jaw forward but the muscles can overcome the
force so the jaw
stays back. The result is that the lower teeth move forward in the jaw bone
and the upper
teeth move back in their jaw bone. This is called orthodontic movement.
[0028] The tension springs 70 and 72 are available in forces ranging from 25
to 300 grams.
In one preferred embodiment, the tension springs 70 and 72 are 250 gram, 9mm
nickel
titanium closed coil tension springs and the compression spring is 200 grams.
Such a light
tension spring keeps the Forsus Spring compressed but allows the lower jaw to
remain in
place in the jaw joint. It has been discovered that a nickel titanium tension
spring has a more
constant force over the range ofthe spring extension compared to stainless
steel. This makes
force delivery to the teeth more constant because Forsus Springs 50 and 52 are
kept relatively
active or compressed even when the patient's mouth is open or when the upper
and lower
teeth are moved relative to each other, namely, the upper teeth moving back
and lower teeth
moving forward. By using lighter or heavier tension springs, one can control
the force level
of each Forsus Spring and keep it at that force level as the teeth move.
[0029] The force-delivering module 47 provides a two-stage activation. At the
beginning
both of the tension springs 70 and 72 and Forsus Springs 50 and 52 are active.
In one
example, the tension springs 70 and 72 are extended to 20 mm and deliver a
force to
compress the Forsus Springs 50 and 52 and move the teeth with a force
ofapproximately 250
grams. The compression spring in this example is 200 grams and is completely
compressed.
The tooth movement force is supplied bythe 250 gramtension springs 70 and 72.
The tension
springs 70 and 72 are so shaped to cause the teeth to move from Class II
approximately 7 mm
to a Class I corrected position, as illustrated in FIG. 8, without need of any
adjustment of the
device 47. This long activation is made possible by the labial bow 46 which
acts as a sliding
rail. This makes the appliance of the present invention a self-activating
Class II correction
appliance. In other words, the first stage of tooth movement (Class II to
Class I) is a result
of the stretched tension springs 70 and 72 which activate the Forsus Springs
50 and 52.
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[0030] The second stage ofmovement (Class Ito over-corrected or Class III) is
a result of
the Forsus Springs 50 and 52 taking over as the tension springs 70 and 72
become passive.
Reference is made to FIG. 10. The tension springs 70 and 72 at this point are
closed but the
Forsus Springs 50 and 52 are still compressed enough to over-correct the teeth
from Class
I another 7 mm to Class III with a decreasing force which is safer so as to
inhibit too much
over-correction. This is somewhat analogous to a two-stage rocket. Here too no
adjustment
of the device 47 is needed.
[0031] In contrast, the earlier appliance used a Gurin lock as the stop for
the compression
spring. As the upper teeth moved back, the compression spring deactivated. The
Forsus
Spring supplied a force of 200 grams when fully compressed and lost 20 grams
of force for
every 1 mm of deactivation. This required periodic reactivation ofthe
compression spring by
moving the Gurin lock posteriorly. Also, in the past, the compression spring
was only
completely active when the patient's mouth was closed. The tension springs 70
and 72 in the
embodiment ofthe present invention keep the Forsus Springs 50 and 52 active as
the patient
opens his or her mouth, keeping the pushrod 55 from disengaging the
compression spring 54.
[0032] One of the reasons why such a long activation is provided by the
tension springs 70
and 72 is because the labial bow 46 acts like a long, sliding rail with
approximately 20 mm of
length per side. 20 mm is also the maximum extension for the 9mm nickel
titanium tension
spring. The Forsus Spring used without a labial bow does not have such a 20 mm
rail. As a
result, the Forsus Spring used merely with braces only allows for an inter-
bracket distance of
approximately 4 mm. The long, sliding rail effect of the labial bow 46
therefore is a major
reasonwhytheForsusSpringworksbetterwiththeembodimentofthepresentinventionthan
with braces alone. Also, in the appliance according to the present invention,
there are no
braces required on the lower teeth and the Forsus Spring may be completely
compressed
without fear of anything breaking.
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[0033] The appliance according to the present invention provides a number of
advantages
generally speaking. It has inhibited or eliminated the need for Class II bite
problems to be
corrected with traditional braces in combination with either headgear, rubber
bands, lowerjaw
advancement surgery, or the extraction ofteeth and upper incisor retraction.
This is especially
true if the teeth are well aligned and the only problem is a Class II bite
problem. These
advantages therefore act to decrease the cost to the patient. The force-
delivering module 47
is also advantageous since it can be used bilaterally or unilaterally. It can
also be used
"upside-down" in Class III or underbite patients. An upper expansion appliance
can be used
at the same time. The appliance according to the present invention can be used
with or
without braces on the upper front teeth. Morever, the appliance according to
the present
invention is automatic and removes patient compliance with headgear or rubber
bands. Lastly,
the appliance according to the present invention opens space for crowded upper
canine (eye
teeth) which is a very common problem.
[0034] It will be understood by someone skilled in the art that many ofthe
details described
above are by way of example only and are not intended to limit the scope of
the invention
which is to be interpreted with reference to the following claims.
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