U.S. patent application number 16/877136 was filed with the patent office on 2020-09-03 for systems and methods for varying elastic modulus appliances.
The applicant listed for this patent is Align Technology, Inc.. Invention is credited to Muhammad CHISHTI, Eric KUO, Ross J. MILLER, Loc X. PHAN, H. Robert VANDENBERG.
Application Number | 20200276746 16/877136 |
Document ID | / |
Family ID | 1000004838423 |
Filed Date | 2020-09-03 |
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United States Patent
Application |
20200276746 |
Kind Code |
A1 |
PHAN; Loc X. ; et
al. |
September 3, 2020 |
SYSTEMS AND METHODS FOR VARYING ELASTIC MODULUS APPLIANCES
Abstract
The present invention provides improved devices, systems and
methods for repositioning teeth from an initial tooth arrangement
to a final tooth arrangement. Repositioning is accomplished with a
system comprising a series of polymeric shell appliances configured
to receive the teeth and incrementally reposition individual teeth
in a series of successive steps. The individual appliances may be
formed from layers having different stiffnesses (elastic
moduluses), and the stiffnesses of successive appliances may be
different, or both.
Inventors: |
PHAN; Loc X.; (San Jose,
CA) ; CHISHTI; Muhammad; (Washington, DC) ;
MILLER; Ross J.; (Sunnyvale, CA) ; VANDENBERG; H.
Robert; (San Ramon, CA) ; KUO; Eric; (San
Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Align Technology, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
1000004838423 |
Appl. No.: |
16/877136 |
Filed: |
May 18, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15811292 |
Nov 13, 2017 |
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16877136 |
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15139796 |
Apr 27, 2016 |
9855701 |
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15811292 |
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14298030 |
Jun 6, 2014 |
9351809 |
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15139796 |
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13245574 |
Sep 26, 2011 |
8858226 |
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14298030 |
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11227810 |
Sep 14, 2005 |
8235713 |
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13245574 |
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10206873 |
Jul 26, 2002 |
6964564 |
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11227810 |
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09874724 |
Jun 4, 2001 |
6454565 |
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10206873 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29L 2009/00 20130101;
B29C 51/002 20130101; B29K 2105/256 20130101; A61C 7/36 20130101;
A61C 7/002 20130101; A61C 7/08 20130101; B29C 48/154 20190201; B29L
2031/753 20130101; B29K 2995/0082 20130101; A61C 19/00 20130101;
A61C 7/00 20130101 |
International
Class: |
B29C 51/00 20060101
B29C051/00; B29C 48/154 20060101 B29C048/154; A61C 7/00 20060101
A61C007/00; A61C 7/08 20060101 A61C007/08; A61C 7/36 20060101
A61C007/36; A61C 19/00 20060101 A61C019/00 |
Claims
1. A dental appliance comprising: a polymeric shell having cavities
shaped to engage individual teeth, the polymeric shell comprising:
a first layer being a discontinuous inner layer; a discontinuity in
the first layer; and a second layer being a continuous outer layer
and being formed over the first layer; wherein one or more
discontinuities of the first layer comprise a first window formed
through said first layer.
2. The dental appliance of claim 1, wherein the first layer has a
first elastic modulus and the second layer has a second elastic
modulus, the first and second elastic moduli being in the range
from 0.5 to 5 GPa.
3. The dental appliance of claim 2, wherein the first elastic
modulus differs from the second elastic modulus by 25% to 600%.
4. The dental appliance of claim 1, wherein portions of the dental
appliance vary along one or more of a mesial-distal axis,
facial-lingual axis, and gingival-crown axis.
5. The dental appliance of claim 1, wherein the first window is
formed through the first layer on a buccal wall of a cavity.
6. The dental appliance of claim 1, wherein the first window is
formed through the first layer on a lingual wall of a cavity.
7. The dental appliance of claim 1, wherein the first window is
formed through the first layer on an occlusal surface of a
cavity.
8. The dental appliance of claim 1, wherein at least a region of
the polymeric shell comprises a material reinforced with a
structure comprising one or more of strips, wires, mesh, lattices,
and networks.
9. The dental appliance of claim 8, wherein the structure comprises
a polymer.
10. The dental appliance of claim 8, wherein the structure
comprises a metal or alloy.
11. The dental appliance of claim 1, wherein at least a region of
the polymeric shell comprises a metal or alloy.
12. A method for producing a dental appliance, the method
comprising: providing a mold of the patient's dentition; forming a
first material layer over the mold; forming a window though the
first layer; and forming a second material layer over the first
material layer so as to produce the dental appliance.
13. The method of claim 12, wherein an appliance with a uniform
elastic modulus is produced.
14. The method of claim 12, wherein an appliance with one or more
portions of differing elastic moduli are produced.
15. The method of claim 12, wherein removing one or more portions
of the first material layer forms one or more discontinuities.
16. The method of claim 15, wherein the one or more discontinuities
through the first layer comprise windows.
17. An orthodontic system comprising: a plurality of dental
appliances configured to move at least one tooth between a first
position and a second position, each of the plurality of dental
appliances comprising: a polymeric shell having cavities shaped to
engage individual teeth, the polymeric shell comprising: a first
layer being a discontinuous inner layer; a discontinuity in the
first layer; and a second layer being a continuous outer layer and
being formed over the first layer; wherein one or more
discontinuities of the first layer comprise a first window formed
through said first layer.
18. The orthodontic system of claim 17, wherein portions of the
dental appliance vary along one or more of a mesial-distal axis,
facial-lingual axis, and gingival-crown axis.
19. The orthodontic system of claim 17, wherein the first window is
formed through the first layer on a buccal wall of a cavity.
20. The orthodontic system of claim 17, wherein the first window is
formed through the first layer on a lingual wall of a cavity.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/811,292, filed Nov. 13, 2017, which is a
continuation of U.S. patent application Ser. No. 15/139,796, filed
Apr. 27, 2016, now U.S. Pat. No. 9,855,701, issued Jan. 2, 2018,
which is a continuation of U.S. patent application Ser. No.
14/298,030, filed Jun. 6, 2014, now U.S. Pat. No. 9,351,809, issued
May 31, 2016, which is a divisional of U.S. patent application Ser.
No. 13/245,574, filed Sep. 26, 2011, now U.S. Pat. No. 8,858,226,
issued Oct. 14, 2014, which is a continuation of U.S. patent
application Ser. No. 11/227,810, filed Sep. 14, 2005, now U.S. Pat.
No. 8,235,713, issued Aug. 7, 2012, which is a continuation of U.S.
patent application Ser. No. 10/206,873, filed Jul. 26, 2002, now
U.S. Pat. No. 6,964,564, issued Nov. 15, 2005, which is a
continuation of U.S. patent application Ser. No. 09/874,724, filed
Jun. 4, 2001, now U.S. Pat. No. 6,454,565, issued Sep. 24, 2002,
which are incorporated herein by reference in their entirety. U.S.
application Ser. No. 09/616,830, filed Jul. 14, 2000, and U.S.
application Ser. No. 09/616,222, filed Jul. 14, 2000, are
incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] This invention relates in general to a method of
repositioning teeth for use in orthodontic treatment. Particularly,
this invention relates to the use of orthodontic appliances for
producing tooth movements. More particularly, this invention
relates to the use of a plurality of elastic repositioning
appliances for producing such tooth movements.
[0003] Orthodontic treatments involve repositioning misaligned
teeth and improving bite configurations for improved cosmetic
appearance and dental function. Repositioning teeth is accomplished
by applying controlled forces to the teeth over an extended period
of time. This is conventionally accomplished by wearing what are
commonly referred to as "braces." Braces comprise a variety of
appliances such as brackets, bands, archwires, ligatures, and
O-rings. After they are bonded to the teeth, periodic meetings with
the orthodontist are required to adjust the braces. This involves
installing different archwires having different force-inducing
properties or by replacing or tightening existing ligatures.
Between meetings, the patient may be required to wear supplementary
appliances, such as elastic bands or headgear, to supply additional
or extraoral forces.
[0004] Although conventional braces are effective, they are often a
tedious and time consuming process requiring many visits to the
orthodontists office. Moreover, from a patient's perspective, they
are unsightly and uncomfortable. Consequently, alternative
orthodontic treatments have developed. A particularly promising
approach relies on the use of elastic positioning appliances for
realigning teeth. Such appliances comprise a thin shell of elastic
material that generally conforms to a patient's teeth but is
slightly out of alignment with the initial tooth configuration.
Placement of the elastic positioner over the teeth applies
controlled forces in specific locations to gradually move the teeth
into the new configuration. Repetition of this process with
successive appliances comprising new configurations eventually
moves the teeth through a series of intermediate configurations to
a final desired configuration. A full description of an exemplary
elastic polymeric positioning appliance is described in U.S. Pat.
No. 5,975,893, and in published PCT application WO 98/58596 which
designates the United States and which is assigned to the assignee
of the present invention. Both documents are incorporated by
reference for all purposes.
[0005] In addition to their ease of use, polymeric positioning
appliances are generally transparent, providing an improved
cosmetic appearance, and impart substantial force on the teeth, due
to stiffness of the appliance. The stiffness of an elastic
positioning appliance is a result of the modulus of the
thermoformable polymer materials from which it is made. The higher
the modulus of the materials, the higher the stiffness of the
appliance. When a patient positions such an appliance over a
prescribed group of teeth, one or more of the teeth will provide a
base or anchor region for holding the positioning appliance in
place while the stiffness of the polymeric material will impart a
resilient repositioning force against one or a portion of the
remaining teeth. However, the stiffer the appliance, the more
difficult it is to slip the misaligned appliance over the teeth and
fully engage the appropriate surfaces; the appliance often has the
tendency to disengage or "pop off". Likewise, once it is firmly
seated, it is more difficult to remove. Further, a stiff appliance
is less forgiving in cases of lowered patient compliance. If a
patient were to remove the appliance for an unprescribed period of
treatment time, the patient's teeth may move slightly out of the
planned tooth arrangement. When attempting to reapply the
appliance, it may be too rigid to accommodate these slight
differences and a new appliance may need to be created. Similarly,
the tooth positions defined by the cavities in each successive
appliance must not differ beyond a limiting dimension from those
defined by the prior appliance or, again, it may be too rigid to
accommodate the differences. Consequently, only small increments in
tooth repositioning may be made with each appliance.
[0006] Thus, it would be desirable to provide tooth positioners,
systems, and methods which apply adequate force to selected teeth
yet overcome the inherent limitations of stiffness in the polymeric
material. Likewise, it would be desirable to reduce the number of
positioners required for a treatment plan by increasing the size of
the repositioning increments throughout the plan. Further, it would
be desirable to reduce the cost of lowered patient compliance by
reducing the need for new appliances to be created for patient
treatment resumption. At least some of these objectives will be met
by the designs and methods of the present invention described
hereinafter.
SUMMARY OF THE INVENTION
[0007] The present invention provides improved devices, systems and
methods for repositioning teeth from an initial tooth arrangement
to a final tooth arrangement. Repositioning is accomplished with a
system comprising a series of polymeric appliances configured to
receive the teeth in a cavity and incrementally reposition
individual teeth in a series of successive steps. This is
accomplished by applying force to specific surfaces of the teeth to
cause directed movement. In order to apply such force, one or more
of the teeth will provide a base or anchor region for holding the
positioning appliance in place while the stiffness of the polymeric
material will impart a resilient repositioning force against one or
more of the remaining teeth. However, such stiffness creates
limitations in ease of use, patient compliance, and overall cost in
material, manufacturing labor and treatment time.
[0008] To overcome these limitations, the present invention
utilizes polymeric or other material appliances with portions
differing in rigidity, hardness, or stiffness. Portions of the
appliance designed to apply specific forces may have different
elastic moduluses (stiffnesses) and/or hardnesses than other
portions. Alternatively, elastic moduluses and/or hardnesses may
vary from one appliance to the next in a successive series to
accomplish various treatment goals. Thus, the systems and methods
of the present invention provide the design, production and use of
such multiple stiffness positioning appliances in orthodontic
treatment. Similarly, the devices of the present invention provide
variable stiffness appliances which may be used independently for
purposes other than repositioning, such as for retaining teeth in a
desired position. Thus, reference hereinafter to repositioning
appliances with portions having differing or varying stiffnesses or
hardnesses is not intended to limit the scope of the present
invention and is understood to include appliances of the described
design for other purposes.
[0009] In a first aspect of the present invention, an elastic
repositioning appliance may be comprised of portions with differing
elastic moduluses. Elastic modulus may be used to express or
describe the stiffness of a material or a material's resistance to
elastic deformation. Therefore, elastic modulus may be used
hereinafter to refer to stiffness. The different portions of the
appliances will also usually vary in hardness. More usually,
stiffer portions will be harder while the less stiff portions will
be softer. Hardness is usually measured as a "durometer" reading on
either the A or the D scale. In most instances, the present
invention will be more concerned with the elastic modulus of the
material since that will effect the force applied to the teeth for
either moving the teeth or for gripping or anchoring the teeth. In
other instances, however, the hardness of the material may be more
important, e.g., to avoid trauma to soft tissue regions engaged by
the appliance. The remaining description and claims generally refer
to materials having greater and lesser stiffnesses. It will be
appreciated that such terminology will also comprise materials
having greater and lesser hardnesses.
[0010] The elastic modulus of a material is the ratio of the
increment of unit stress to an increment of unit deformation within
the elastic limit. When a material is deformed within the elastic
limit, the bonds between adjacent atoms are stretched but not
broken. The magnitude of the elastic modulus is indicative of the
atomic and molecular bonding forces. When the stress is relieved,
the material returns to its original shape and the deformation is
nonpermanent. Different materials may have different elastic
moduluses based on their molecular structures. Some materials, such
as certain polymers, may be specially produced to have different
elastic moduluses while retaining similar chemical compositions
(and thus assuring compatibility of the different modulus materials
in a single structure). Likewise, the elastic modulus of a polymer
or other material may be enhanced or otherwise modified. This may
be achieved by adding a powder, such as CaCO3, talc, TiO2, glass,
diamond or a polymer powder, to name a few. In addition, this may
be achieved by embedding structural reinforcements, such as metal
pieces, strips, wires, mesh, lattices, networks, polymeric
filaments, or the like. In addition, the elastic modulus may be
altered by post-production methods, such as layering, coating,
interpenetrating, treating with various chemical agents, and
altering the temperature, to name a few. In the resulting
appliance, the elastic moduluses of the varying portions will
usually range from 0.5 to 5 GigaPascal (GPa), although in some
instances portions of the appliance may fall outside of this range.
The elastic modulus of one portion may differ from another portion
by 25% to 600%, or more.
[0011] The differing elastic moduluses of different portions of the
dental appliance shells of the present invention will exist while
the device is present over teeth in a normal oral environment.
Thus, different portions of the appliance shell will impart
different forces to the immediately underlying teeth, where the
level of the force depends both on the device geometry or tooth
positions (relative to the underlying tooth or teeth, which may
vary over time) and on the elastic modulus of that portion of the
device (which will remain constant over time in the normal oral
environment). The present invention should be distinguished from
that described in copending application Ser. No. 09/250,962, where
the stiffness of a dental appliance shell may change over time by
expose to a non-oral environment, such as elevated temperature or
changed osmolality. Of course, the dental appliance shells of the
present invention which have different portions with differing
stiffness may also incorporate regions (including the entire
appliance) where a change in stiffness may be induced according to
the teachings of application Ser. No. 09/250,962, the full
disclosure of which is incorporated herein by reference.
[0012] In a first embodiment, portions of the shell of an elastic
repositioning appliance may be composed of material(s) which differ
in elastic moduluses and/or hardnesses along a mesial-distal axis.
A mesial-distal axis may be defined as an axis following the
gingival line or dental arch. Thus, the elastic repositioning
appliance may be comprised of portions with a lower elastic modulus
covering the molars, for example, and portions with a higher
elastic modulus covering the remainder of the teeth. In this
example, the portions may be relatively large so that a portion may
receive one or more teeth, such as contiguous molars. This may be
utilized when one or more teeth are to provide an anchor or base
region for imparting repositioning force against another tooth or
teeth. The portion of the appliance covering the anchor teeth may
be of a relatively flexible nature with a lower elastic modulus
than the portion covering the teeth to be repositioned. This is
because the portions covering the anchor teeth may not need to
apply repositioning forces to the teeth they cover; they may merely
be designed to hold the appliance in place. Consequently, a high
level of rigidity or stiffness may not be required. However, it may
be appreciated that portions covering anchor teeth may in fact
require a higher stiffness material than other portions, including
portions which are designed to apply repositioning forces. Thus,
any variation of stiffness or elastic modulus along a mesial-distal
axis is included in this embodiment.
[0013] The introduction of such portions or regions with more
flexibility provides utility in ease of use for the patient. The
patient may find ease in positioning the appliance with the more
flexible portions first which may guide the appliance in placement
of the more rigid, slightly misfit portions designed for
repositioning. This sequence may be reversed in removal of the
appliance. Likewise, such flexibility may also allow for any slight
differences in mold versus appliance versus dentition geometry
which may otherwise make placement and removal of the appliance
more difficult. In some cases, a generally misfit appliance may
"pop off" or have a tendency to disengage even when properly
positioned over the teeth. Increased flexibility may reduce these
tendencies.
[0014] In further embodiments, portions of the elastic
repositioning appliance may vary in elastic moduluses along
different and/or additional axes. For example, moduluses may vary
along a facial-lingual axis. Facial may be defined as next to or
toward the lips or cheek, including terms labial and buccal.
Lingual may be defined as next to or toward the tongue. Thus, a
facial-lingual axis may be described as an axis following a radial
or similar line from the tongue toward the lips or cheek and vice
versa. Likewise, moduluses may vary along a gingival-crown axis.
This may be described as a substantially vertical axis following a
line from the top of the crown at the edge of the occlusal surface
of a tooth toward the gingival line or root and vice versa. In a
preferred embodiment, an appliance may have a portion with a lower
elastic modulus covering the occlusal surfaces of the teeth and a
portion with a higher elastic modulus covering the remaining
surfaces of the teeth. Thus, the moduluses may vary along a
facial-lingual axis and/or a gingival-crown axis, depending on the
boundaries of the delineated portions. Such a design may
incorporate added flexibility to the appliance while maintaining
adequate repositioning forces in the most efficient areas.
[0015] In addition to varying in stiffness along the axes described
above, the appliances of the present invention may vary in
stiffness or hardness over the "thickness" of the appliance.
Usually, such variations and stiffness over the thickness will be
accomplished by layering the device, i.e., with layers of differing
stiffnesses or hardnesses being placed successively over the mold
used to form the appliances, as described in more detail below.
Thus, the appliances may comprise shells having first and second
portions, as generally described above, where each of those
portions comprise layers in a laminar structure. Usually, at least
one of the first and second portions will comprise a continuous
layer along the mesial-distal axis. The second and optionally
additional layers may also be continuous along the mesial-distal
axis, but will often be discontinuous, i.e., broken into two or
more segments. Such layered devices can provide a variety of
benefits. For example, layers formed from stiffer or harder
materials can be used to more firmly engage teeth, while the less
stiff or softer layers can be used to provide compliance and
greater elasticity. In a particular preferred embodiment, the
appliance comprises a discontinuous inner layer and a continuous
outer layer. At least a portion of the inner layer is configured to
engage individual teeth or groups of teeth and will be stiffer or
harder than the outer layer. The outer layer, which is less stiff
and therefore more compliant, provides the elasticity to move the
teeth relative to one another, while the harder inner layer firmly
engages the teeth to provide a better grip or anchor upon the
teeth.
[0016] It may be appreciated that the elastic modulus of the
appliance shells may vary over any number of delineated portions.
Such portions may be of any size, shape, thickness, or dimension.
Thus, such portions may receive entire teeth or they may be of the
size to cover only a portion of a tooth or dental surface. When
portions are relatively large, an appliance may be divided into,
for example, two to five portions. Portions adjacent to one another
differ in elastic moduluses, however not all portions of an
appliance may differ from each other, such as in the case of an
appliance with portions alternating between two moduluses. When
portions are relatively small, an appliance may contain an
unlimited number of portions, varying along any axis or combination
of axes.
[0017] In a second aspect of the present invention, such appliances
comprised of portions having differing stiffness may be used
independently or in a series with similar or differing devices.
When used independently, the appliance may be worn to achieve a
specific goal with a single device. For example, the appliance may
be used as a "retainer" to hold the teeth in a desired position.
Or, the appliance may be used for a specific one-time repositioning
movement, such as "finishing" or correcting a slight misalignment.
When used in a series, the appliances may comprise a system for
repositioning teeth from an initial tooth arrangement to a final
tooth arrangement. In this case, a plurality of incremental elastic
position adjustment appliances comprising polymeric or other
material shells are successively worn by a patient to move teeth
from one arrangement to a successive arrangement. Individual
appliances may be configured so that their tooth-receiving cavity
has a shape or geometry corresponding to an intermediate or end
tooth arrangement intended for that appliance. Thus, successive
individual appliances may have a shape or geometry differing from
that of the immediately prior appliance. According to the present
invention, some or all of the individual appliances may also be
comprised of a material stiffness differing from the stiffness of
the immediately prior appliance. In addition, each individual
appliance be comprised of portions with varying stiffnesses. In
some cases, of course, individual appliances in the system may not
vary in stiffness from prior or successive appliances, but only in
geometry. In other cases, individual appliances may vary only in
stiffness (and not in geometry) when compared to immediately prior
or subsequent appliances. Thus, systems according to the present
invention may be comprised of appliances having stiffness varying
within the appliance and/or from one appliance to the next in the
series.
[0018] In a specific embodiment, a system of elastic repositioning
appliances may comprise individual appliances having uniform
elastic moduluses over their entire tooth contact area where the
moduluses will differ among successive appliances used in a course
of treatment. The elastic modulus of a given appliance may be
chosen to be most suitable for a specific type of tooth movement,
such as translating, tipping, root uprighting, rotation, extrusion,
intrusion or a combination of these. For example, translation may
require 70-120 gm of force, whereas rotation may only require 35-60
gm of force. Therefore, an elastic positioning appliance designed
for translating teeth may need to have a higher elastic modulus
than one designed for purely rotating teeth. This is again due to
the fact that stiffness of the appliance is a critical factor in
imparting repositioning force. Consequently, a series of appliances
may be produced for a treatment plan in which successive appliances
designed for a specific tooth movement may all have substantially
similar elastic moduluses. At the point in the treatment plan in
which a different type of tooth movement is desired, further
appliances designed for the new tooth movement may have
substantially similar elastic moduluses to each other but different
from the previous appliances. Such a sequence may be repeated at
any time or may continue with new moduluses and tooth
movements.
[0019] In an additional specific embodiment, one or more appliances
may be produced with a suitably flexible elastic modulus to receive
and resiliently reposition teeth from an unprescribed arrangement
to a prescribed arrangement. This might be necessary in cases of
lowered patient compliance. If a patient were to remove an
appliance for an unintended and/or extended period of a prescribed
treatment time, the patient's teeth may move slightly out of the
planned tooth progression. When attempting to reapply the
appliance, an appliance which is too rigid may not be able to
accommodate these slight differences. Thus, a more flexible
appliance (but having an identical geometry) may be produced for
this purpose and may be incorporated into the treatment plan at any
given point in the series of successive appliances. The ability to
return to the same geometry is an advantage because it minimizes
the need to replan the treatment protocol.
[0020] In a third aspect of the present invention, systems for
repositioning teeth from an initial tooth arrangement to a
successive tooth arrangement comprise a plurality of incremental
elastic position adjustment appliances in which at least one
appliance has the same shape yet different elastic modulus as an
immediately prior appliance. In a specific embodiment, a series of
incremental appliances may be produced with differing elastic
moduluses to reposition teeth from an initial tooth arrangement to
the next successive tooth arrangement in a progression of
arrangements to the final arrangement. Each of the appliances in
the series from the first to the next successive tooth arrangement
may have the same shape or geometry since the tooth movement
represents one step in tooth movement. However, the variance in
elastic moduluses may allow for a larger step or increment in tooth
movement than may be obtainable with consistent, rigid appliances.
For example, an appliance may be produced with a tooth arrangement
which is substantially misaligned from the initial arrangement.
High modulus appliances may not be flexible enough to allow the
appliance to fit over the teeth in the initial arrangement.
However, a series of appliances of the same shape may be produced
with increasing elastic moduluses from relatively low to adequately
high. The patient may begin with the lowest elastic modulus
appliance which may be the most flexible to fit over the teeth. As
the teeth are repositioned, the patient may successively utilize
each appliance in increasing modulus until the teeth have conformed
to the successive tooth arrangement. At that time, the patient may
begin a new series of appliances with varying moduluses and a shape
to reposition the teeth to the arrangement of the next step in the
repositioning progression. The ability to reduce the number of
different appliance geometries required for a single course of
treatment can provide a significant reduction in planning effort
and manufacturing costs.
[0021] In a fourth aspect of the present invention, the elastic
modulus of an appliance or portions of an appliance may be modified
in a number of different ways. To begin with, the elastic modulus
may be determined by the choice of materials. For example, metals
will generally have a higher elastic modulus than polymers due to
atomic structure. For example, the modulus values for metals may
range between 48 and 414 GPa, whereas the modulus for polymers may
range from 0.5 to 35 GPa. Thus, it will be possible to form
appliances having moduluses which differ greatly by forming
different portions from metal(s) and polymer(s), or by forming
successive appliances from metals and polymers. Usually, however,
the appliances will comprise or consist of a polymeric shell formed
from a single polymer, multiple polymers, copolymers, and the like,
typically by thermoforming and/or lamination. Stiffness of a
polymer may be varied within a range (typically 0.5 GPa to 5 GPa)
by changing the molecular structure of the polymer chains. Polymer
chains with hindered side-chains are unable to pack as closely as
those with smaller side-chains. Thus, such a polymer may have more
intermolecular motion and therefore a lower bulk elastic modulus.
Stiffness can also be changed by controlling the degree of
cross-linking as well as the cross-linking entity within a polymer
or copolymer. Further, alternatively, differing elastic moduluses
may be created within the same polymer shell by layering or
laminating the same or different polymers. Two layers of a polymer
material bonded together to form an integral appliance, i.e., an
appliance having a monolithic shell structure where the layers are
resistant to delamination, may have a higher elastic modulus than a
single layer of such material. Thirdly, different elastic moduluses
may be created with a single layer of one type of polymer material
by production methods, such as coating, treating with various
chemical agents, and altering the temperature, to name a few.
[0022] Further, different elastic moduluses may be produced by
forming selectively reinforced and/or composite-type materials. For
example, a polymer material may be reinforced with structures such
as strips, wires, pieces, mesh, lattices, networks, and the like.
These structures may be comprised of any suitable material,
particularly metals and alloys but also including polymer
filaments, wires, braids, and the like. Likewise, composite
materials may be comprised of interpenetrating polymeric networks.
An interpenetrating polymeric network is comprised of a base
material and an additional material that interpenetrates the base
material to alter its mechanical properties. For example, the base
material (A) may be a solid polycarbonate. The added material (B)
may be a liquid polymer, monomer or crosslinking agent which is
allowed to interpenetrate and activate to form a composite network.
The composite (A+B) may have a stiffness which is greater than the
sum of its parts, (A) and (B). Further, another material (C) may
also be allowed to interpenetrate and activate to form a new
composite network. The composite (A+B+C) may also have a stiffness
which is greater than the sum of its parts, (A), (B) and (C). With
this method, any number of composites may be formed providing a
wide range of mechanical properties, specifically stiffnesses. In
addition, a number of these production methods may provide
materials with gradual changes in elastic moduluses. For example,
purposely irregular coating of a polymer material may provide
higher stiffness in areas with thicker coating and lower stiffness
in areas with thinner coating. This may be applied to a number of
production methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a perspective illustration of an embodiment of an
appliance of the present invention and descriptive axes.
[0024] FIG. 2 illustrates an embodiment of an appliance with
relatively large portions varying in elastic modulus along a
mesial-distal axis.
[0025] FIG. 3 illustrates an embodiment of an appliance with
smaller portions varying in elastic modulus in a non-symmetric
pattern along a mesial-distal axis.
[0026] FIG. 4 illustrates an embodiment of an appliance varying in
elastic modulus along a mesial-distal axis in which portions
covering proximal or interproximal spaces are of differing
modulus.
[0027] FIG. 5 illustrates a variety of appliance portions varying
in elastic modulus along a mesial-distal axis.
[0028] FIG. 6 is a perspective illustration of an embodiment of an
appliance varying in elastic modulus along a facial-lingual
axis.
[0029] FIG. 7 illustrates a variety of appliance portions varying
in elastic modulus along a facial-lingual axis.
[0030] FIG. 8 is a perspective illustration of an embodiment of an
appliance varying in elastic modulus along a gingival-crown
axis.
[0031] FIG. 9 illustrates a variety of appliance portions varying
in elastic modulus along a gingival-crown axis.
[0032] FIG. 10 illustrates a variety of appliance portions varying
in elastic modulus along one or more described axes.
[0033] FIG. 11 depicts a series of appliances differing in elastic
modulus at specific intervals throughout a treatment plan.
[0034] FIG. 12 illustrates the use of an "off track" appliance in a
prescribed treatment plan.
[0035] FIG. 13 illustrates the use of a series of appliances with
gradually increasing elastic moduluses and similar or identical
geometry in a series of intervals throughout a treatment plan.
[0036] FIG. 14 illustrates a method of fabricating a multi-modulus
appliance.
[0037] FIG. 15 illustrates a method of layering to fabricate a
multi-modulus appliance.
[0038] FIG. 16 illustrates an additional method of layering to
fabricate a multi-modulus appliance.
[0039] FIG. 17 illustrates an exemplary layered appliance according
to the present invention with portions broken away.
[0040] FIG. 18 is a cross-sectional view taken along line 18-18 of
FIG. 17.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0041] The present invention provides improved devices, systems and
methods for incrementally repositioning teeth using a plurality of
discrete polymeric appliances of variable flexibility, where each
appliance successively repositions one or more of the patient's
teeth by relatively small amounts. Flexibility may be defined by
elastic modulus of the polymeric material and may vary within a
given appliance or may vary throughout a series of appliances
according to a prescribed orthodontic treatment plan.
[0042] Referring to FIG. 1, portions of an elastic repositioning
appliance 100 may vary in elastic modulus along a mesial-distal
axis 101, facial-lingual axis 102, gingival-crown axis 103, or any
axis in-between these representative axes. As previously described,
a mesial-distal axis may be described as an axis following the
gingival line or dental arch, a facial-lingual axis may be
described as an axis following a radial or similar line from the
tongue area toward the lip or cheek area, and a gingival-crown axis
may be described as an axis following a substantially vertical line
from the crown of a tooth toward the gingival line or root. Such
axes are defined for descriptive purposes and are not intended to
limit the scope of the present invention.
[0043] As shown in FIG. 2, portions of an elastic repositioning
appliance 100 may vary in elastic modulus mesial-distally. For
illustrative purposes, portions with a lower elastic modulus 110
are shaded to easily distinguish differences in elastic modulus
throughout a device. In this example, the appliance 100 may be
described as having three portions. Two portions cover contiguous
sets of molars and are comprised of an elastomeric material of a
lower elastic modulus 110 and are thus shaded. The portion
in-between these portions is of a higher elastic modulus 111 and is
thus not shaded. All portions in this embodiment are relatively
large so that the portions may receive one or more teeth, such as
molars, premolars, incisors, and the like. Likewise, nonadjacent
portions may have the same elastic modulus, such as the two lower
elastic modulus 110 portions, or they may be different from each
other while maintaining a difference from the higher elastic
modulus 111 portion. In other words, an appliance 100 with three
distinct portions may be comprised of two or three elastic
moduluses.
[0044] As illustrated in FIG. 3, such portions may not be
symmetrical and they may not cover more than one tooth. Portions
with a lower elastic modulus 110 may alternate in an uneven fashion
along a mesial-distal axis as shown. In addition, adjacent portions
may be of a size to cover only a portion of a tooth or dental
surface. Referring to FIG. 4, portions of lower elastic modulus 110
may be present covering the facial or lingual surfaces of the
teeth, while portions of higher elastic modulus 111 may be present
covering the proximal or interproximal spaces. This may be
advantageous to provide repositioning forces, such as translation
forces, at the most efficient locations for this type of movement.
At the same time, flexibility is provided in portions that may be
less involved in the application of force, allowing more freedom
and comfort for the patient.
[0045] Referring to FIG. 5, the elastic modulus of an appliance 100
may vary over any number of delineated portions and may be of any
size, shape, thickness or dimension, to name a few. Such portions
may be sized to receive an entire tooth 115 or they may be of the
size to cover only a portion of a tooth. For example, a portion
with a lower elastic modulus 110 may be sized to cover a proximal
or interproximal space 116, including portions covering the
gingival line. This may be desirable to provide comfort to the gums
when wearing the appliance, and also to increase the contact of the
appliance with the interproximal regions. In this case, softer,
more flexible material may be able to form more closely to the
interproximal regions, enabling a higher level of repositioning
force to be applied.
[0046] Portions may also be sized and arranged to cover part of a
facial surface 117, or two or more of such portions may cover part
of a facial surface 118, allowing the elastic modulus to vary
mesial-distally within a single tooth. Further, the portion may be
sized to cover an isolated region of a facial surface 119. Such
embodiments are a limited presentation of the possible sizes,
configurations, and combinations of varying elastic modulus
portions in an appliance 100 of the present invention. Such
possibilities may be unlimited.
[0047] As shown in FIG. 6, portions of an elastic repositioning
appliance 100 may vary in elastic modulus facial-lingually. In this
embodiment, the appliance 100 is shown to have a portion with a
lower elastic modulus 110 covering a portion of the occlusal
surfaces of the teeth and a portion with a higher elastic modulus
111 covering the remaining surfaces of the teeth. Thus, the elastic
modulus varies along a facial-lingual axis. Such a design may be
beneficial to provide repositioning forces, such as translation
forces, along the proximal and/or interproximal spaces which are
the most efficient locations for this type of movement. At the same
time, flexibility is provided in portions that may be less involved
in the application of force, the occlusal surfaces. This may allow
increased freedom and comfort for the patient while maintaining
adequate repositioning forces.
[0048] Referring to FIG. 7, the elastic modulus of an appliance 100
may again vary over any number of delineated portions and may be of
any size, shape, thickness or dimension, to name a few. A portion
of lower elastic modulus 110 may be sized to cover only a portion
of a tooth. For example, it may cover the center of the occlusal
surface 125, alternating cusps or cusp tips 126, or isolated
portions of any given cusp or cusp tip 127. Likewise, a portion of
lower elastic modulus 110 may be of a larger size to cover, for
example, the outside margin or buccal cusps of a tooth 128 or the
inside margin or lingual cusps of a contiguous grouping of teeth
129. As before, such embodiments are a limited presentation of the
possible sizes, configurations, and combinations of varying elastic
modulus portions in an appliance 100 of the present invention. Such
possibilities may be unlimited.
[0049] As shown in FIG. 8, portions of an elastic repositioning
appliance 100 may vary in elastic modulus crown-gingivally. In this
embodiment, the appliance 100 is shown to have a portion with a
lower elastic modulus 110 covering the occlusal surfaces of the
teeth and a portion with a higher elastic modulus 111 covering the
remaining surfaces of the teeth. This is a modified representation
of the embodiment depicted in FIG. 6 in which the portion of lower
elastic modulus 110 partially covered a portion of the occlusal
surfaces. In this embodiment, the occlusal surface is substantially
covered with the lower elastic modulus 110 material, therefore it
may be considered to be uniform, non-variable, along a
facial-lingual axis. It may be more properly described as varying
along a gingival-crown axis, as the lower elastic modulus 110
portion may extend over the cusps of the tooth crowns. Thus, the
lower elastic modulus 110 material may be seen as being located at
the tip of the crown region and vary to a higher elastic modulus
111 material toward the gingival line or margin. In addition, a
higher elastic modulus 111 material along the gingival line or
margin may improve retention of the device on the teeth. This may
also reduce the need for attachment devices to aid in retention. A
full description of exemplary attachment devices and methods for a
dental appliance is described in co-pending application Ser. No.
09/454,278, incorporated by reference for all purposes and assigned
to the assignee of the present inventor. However, such modulus
differences are presented only for descriptive purposes and such
portions may vary over one or many axes simultaneously or in
isolated regions of an appliance 100.
[0050] It may be appreciated that the advantages offered by a lower
elastic modulus along the occlusional surfaces, as depicted in FIG.
6 and FIG. 8, may be further increased by removing the material
from the shell in these areas. Removal of material may form a
window such that when the shell is positioned over the patient's
teeth, portions of the teeth beneath the window may be exposed. In
a preferred embodiment, a polymeric shell may have a plurality of
windows over portions of the occlusal surfaces of the teeth. In
this case, segments of the shell may still be present along the
facial and lingual surfaces of the teeth and across the interdental
regions or spaces between the teeth. Exposure of the occlusal
surfaces in appropriate size and location may allow interdigitation
of the upper and lower teeth. This may also be achieved with the
presence of one or a few larger windows over portions of the
occlusal surfaces of the teeth. In these cases, segments of the
shell may not be present across the interdental regions or spaces
between the teeth. In either case, interdigitation of at least
portions of the upper and lower teeth may benefit tooth and jaw
orientations, leading to improved treatment, appearance, comfort
and consequently patient compliance. Thus, such windows may provide
the benefits offered by a lower elastic modulus, such that the
lowest stiffness may be provided by the absence of the material,
while providing additional benefits described above. A full
description is provided in U.S. patent application Ser. No.
09/616,222, assigned to the assignee of the present invention.
[0051] Referring to FIG. 9, the elastic modulus of an appliance 100
may again vary over any number of delineated portions and may be of
any size, shape, thickness or dimension, to name a few. A portion
of lower elastic modulus 110 may be sized to cover only a portion
of a tooth along this axis. For example, it may cover the upper
portion of the lingual surfaces near the cusps of the crown 135, or
a midway "stripe" through the lingual surface of a tooth 136.
Likewise, it may be sized so that more than one "stripe" may cover
the surface of a tooth 137, as in the case of a portion at the
gingival margin and a portion near the cusps of the crown.
Similarly, a portion of lower modulus may be sized so that it
covers a contiguous grouping of teeth, such as the buccal surfaces
along the gingival margin 138. As before, such embodiments are a
limited presentation of the possible sizes, configurations, and
combinations of varying elastic modulus portions in an appliance
100 of the present invention. Such possibilities may be
unlimited.
[0052] As illustrated in FIG. 10, variance in elastic modulus in
relation to size, shape, location, orientation, and axis, as
described above, may be combined in a single appliance 100 to
provide an unlimited variety of appliance 100 designs and
constructions. In this example, portions of the appliance 100 vary
mesial-distally, such as by comparing the lower elastic modulus 110
portion covering a group of incisors with the higher elastic
modulus 111 portion covering the canine tooth. Portions may also
vary facial-lingually, as depicted by the partial covering of the
occlusal surfaces of the molars 150 or the isolated portion of a
given cusp or cusp tip 127. Likewise, portions may vary
crown-gingivally, such as the portions covering the buccal surfaces
along the gingival margin 138. These portions also vary
mesial-distally creating a compound variance, as portions adjacent
to these areas are not identical, as in comparison of portions
covering the buccal surfaces along the gingival margin 138 with the
adjacent tooth 151 having partial covering of the occlusal surface
of the molar 150. Portions may also vary along the three major axes
simultaneously. This can be seen in the portion covering the center
of an occlusal surface 125, which varies facial-lingually, the
lingual face of a molar along the gingival margin 152, which varies
crown-gingivally, and the adjacent uniformly covered molar 153,
which varies mesial-distally in relation to the previous
portions.
[0053] According to the present invention, systems for
repositioning teeth from an initial tooth arrangement to a final
tooth arrangement may be comprised of a plurality of incremental
elastic position adjustment appliances with varying elastic
moduluses. Thus, in addition to combined variances in a given
appliance 100, as described above, a plurality of such appliances
100 with differing patterns of elastic modulus variance may be used
in a system for repositioning teeth throughout a sequence of tooth
arrangements. This may be illustrated by FIGS. 2-10 with differing
tooth geometries, viewed as a series of appliances 100 for a single
treatment plan.
[0054] Alternatively, as shown in FIG. 11, the polymeric shells of
the appliances 100 may have uniform elastic moduluses over their
entire tooth contact area. In this depiction, each appliance 100
differs in shape or tooth geometry and represents a stage in the
overall treatment plan. Thus, five stages are depicted, as there
are five appliances 100 shown. The first three appliances 200, 201,
and 202, respectively, may have a uniform elastic modulus chosen
for a specific type of tooth movement. For example, appliances 200,
201 and 202 may be designed for pure translation, requiring a
relatively high elastic modulus 111. Thus, the appliances are not
shaded in the illustration. At stage 4, a different type of tooth
movement, such as tipping, may be desired requiring a lower elastic
modulus 110. Therefore, appliances 203 and 204 may continue the
series of differing shape or tooth geometries to create such
movements, but the elastic modulus may differ from the prior
appliances, 200, 201, and 202. Thus, these appliances are shaded in
the illustration. The remainder of the treatment plan may feature a
similar series of appliances, including appliances with uniform
elastic moduluses which differ from the appliances immediately
prior and/or any appliances previously presented in the series.
Likewise, such a series may also include appliances with combined
variances, as described above.
[0055] Similarly, as shown in FIG. 12, a treatment plan may be
prescribed with a series of appliances 100 differing in shape or
tooth geometry, of which four stages are depicted, 210, 211, 212
and 213. Such appliances may have any given elastic modulus that is
suitable for the prescribed function. Likewise, such appliances may
have internal variance in elastic modulus, described previously, or
may vary wholly from appliance to appliance throughout the
prescribed treatment plan. However, if a patient were to
discontinue usage of an appliance for an unprescribed period of
treatment time, such as between stages two (appliance 211) and
three (appliance 212) depicted in FIG. 12, the patient's teeth may
move slightly out of the planned tooth arrangement. Such a patient
may be considered "off track" in which their current tooth
arrangement has diverted from the series of projected tooth
arrangements, creating an unprescribed tooth arrangement. When
attempting to apply the next successive appliance 212, it may be
too rigid to accommodate these slight differences. Therefore, a new
more flexible appliance 214 may be produced for this purpose and
may be incorporated into the treatment plan. Such an appliance 214
may have the same shape or tooth geometry as the next successive
appliance 212, but it may have a lower elastic modulus 110,
depicted by shading. The increased flexibility may allow the
appliance 214 to conform to the unprescribed arrangement and
reposition the teeth toward an arrangement that the next successive
appliance 212 may therefore fit. Such an appliance 214 may be used
at any point in the series of successive appliances.
[0056] As shown in FIG. 13, a series of incremental appliances,
300, 301, 302, 303, 304 and 305, may be produced with differing
elastic moduluses, illustrated by variation in shading, to
reposition teeth from an initial tooth arrangement to the next
successive tooth arrangement in a progression of arrangements to
the final arrangement. FIG. 13 illustrates two steps in such a
progression. A step or stage represents a change in shape or
geometry of an appliance 100 to reposition the teeth into the next
prescribed arrangement in a series. Therefore, appliances 300, 301,
and 302 represent the first stage and have one shape and 303, 304,
and 305 represent the second stage and have a differing shape. The
appliances 300, 301, and 302 representing the first stage may vary
in elastic moduluses from more flexible (appliance 300) to more
rigid (appliance 302). The patient may begin the treatment sequence
with the more flexible appliance 300 of the first stage. Such
flexibility may allow an appliance with a substantially misaligned
geometry to fit over the patient's teeth and apply repositioning
forces. As the teeth gradually move toward the desired arrangement,
the patient may progress to the next appliance 301 in the first
stage. This appliance 301 may be more rigid than the prior
appliance 300. The patient may continue through any number of
appliances throughout a stage. Upon completion of the stage, the
patient may repeat the process in stage two, beginning with the
more flexible appliance 303 and culminating with the more rigid
appliance 305. The patient may then continue through any number of
stages to the endpoint of treatment.
[0057] Such a system may provide a number of benefits. First, the
variance in elastic modulus throughout each step may allow for a
larger step or increment in tooth movement between each step than
may be obtainable with consistent, rigid appliances. Such
flexibility may allow the appliance to fit over a tooth arrangement
that is more misaligned while the increase in rigidity throughout
each stage may provide sufficient repositioning forces which may
not be obtainable with highly flexible appliances. These larger
steps require fewer appliances in a series to have a change in
shape or geometry. Consequently, fewer molds may be required to
form such appliances, which lowers cost and treatment time for the
patient. In addition, if the patient were to become "off track" by
suspending treatment, it may be possible for the patient to resume
the prescribed treatment plan by reentering treatment at the start
of the step or stage in which the patient previously aborted. This
appliance may be flexible enough to fit over the teeth in the
unprescribed arrangement and gradually reposition the teeth
throughout the stage as originally prescribed. This may also reduce
cost and treatment time since the production and fitting of a
flexible "off track" appliance, as illustrated in FIG. 12, may be
avoided.
[0058] The elastic modulus of an appliance or portions of an
appliance of the present invention may be determined by a number of
design features, methods, materials and similar means. In a
preferred embodiment, the appliance may be comprised of a polymeric
shell which is heat formed over a mold of a patient's dentition.
This is typically accomplished by heating a thermoformable polymer
material and applying vacuum or pressure to form the polymer to the
mold. Alternatively, reaction casting may be used to produce such
an appliance. Hereinafter, description will pertain to
thermoforming, however such concepts and techniques may be equally
applied to reaction casting or similar methods and are not to limit
the scope of the invention.
[0059] To produce an appliance with uniform elastic modulus, a
polymer sheet with a specific elastic modulus and thickness may be
thermoformed over a mold and trimmed for patient use. Appliances
with differing uniform elastic moduluses may be produced by
altering one or more of three variables: 1) polymer type, 2)
elastic modulus, 3) thickness. To produce an appliance with
portions of differing elastic moduluses, a number of techniques may
be utilized. Referring to FIG. 14, portions of polymer sheeting 400
may be positioned over a mold 401 in designated areas and
thermoformed together into a final polymeric appliance. Each
portion of sheeting 400 may be chosen based on the three above
mentioned variables to provide a desired elastic modulus. Each
portion of sheeting 400 may then be positioned in the desired
location for elastic modulus changes throughout the finished
appliance. In FIG. 14, three portions are presented, a first sheet
402 placed over the right side molars, a second sheet 403 placed
over the left side molars and a third sheet 404 placed over the
remainder of the teeth. Sheets 402 and 403 are depicted as having
differing elastic moduluses to each other and to sheet 404, as
shown by shading gradations, however such sheets 402, 403, may be
identical. After thermoforming, a finished appliance may appear as
that illustrated in FIG. 2.
[0060] In addition, portions with differing elastic moduluses may
be created with the same polymer or different polymers material by
layering. Two layers of a polymer material bonded together may have
a higher or elastic modulus than a single layer of such material.
As illustrated in FIG. 15, a first sheet 405 may be placed over the
incisors, canines and premolars of the mold 401 and a second sheet
406 may be placed over the entire dentition. Each sheet may be the
same or may differ in terms of any or all of the above mentioned
variables. After thermoforming, a finished appliance may also
appear as that illustrated in FIG. 2. In this case, the shell
covering the molars is comprised of one layer and the remainder of
the appliance is comprised of two layers formed into an integral
appliance structure. Therefore, the portions covering the molars
may have a lower elastic modulus, depending on the combination of
materials, than the remaining portion. However, it is possible that
a multi-layered structure may have a lower elastic modulus than a
single layered structure depending on the above mentioned
variables. Thus, it may be appreciated that the described layering
technique may provide a variety of moduluses and those stated
examples are not intended to limit the scope of the invention.
[0061] Similarly, portions with different elastic moduluses may be
created by a multi-step process of layering. Referring to FIG. 16,
a first sheet may be thermoformed over the entire dentition of a
mold 401 to form a base appliance 410. Portions desired to be of a
differing elastic modulus 411, demarcated by a dashed line, may be
cut and removed from the formed base appliance 410. A second sheet
412 may then be thermoformed over the entire dentition. This may
result in a single layer of material in the portion of differing
elastic modulus 411 and a double layer of material in the remaining
areas.
[0062] It may be appreciated that appliances with differing and
gradually changing elastic moduluses may be created by any number
of production methods. For example, a base appliance 410 may be
coated in a specific area with one or more polymer solutions to
"build up" a portion of the appliance for localized rigidity. Such
a build-up may also be gradual for a more gradual increase in
rigidity. Likewise, a base appliance 410 may be treated in specific
areas with various chemical agents to either increase or reduce
localized rigidity. This may also include treatments involving
temperature changes and other phase altering methods. Similarly,
such methods may be combined, including any or all of the above
described methods. Likewise, such methods may be utilized for
appliances of uniform elastic modulus.
[0063] The fabrication process illustrated in FIG. 16 may be used
to prepare a preferred laminated appliance structure 500, as
illustrated in FIGS. 17 and 18. An inner layer 502 is formed from a
relatively stiff polymeric material and molded over a positive
tooth model which represents the desired appliance geometry. After
the layer 502 is formed, it can be segmented into two or more
sections which conform to individual teeth or groups of teeth when
the appliance is placed over the patient's jaw. As shown in FIG.
17, gaps 504 may be formed between individual sections 506, each of
which conform to and receive an individual tooth or group of teeth.
An outer layer 508 is continuous in the mesial-distal axis and
covers all the segments 506 of the inner layer 502. By providing an
inner layer 502 having a higher stiffness, firm gripping or
anchoring of the underlying teeth can be achieved. Moreover, by
providing an outer layer 508 which is less stiff or more compliant,
ease of removing and replacing the appliance can be significantly
improved. Moreover, the stiffness or anchoring force can be
enhanced without having to concurrently modify the overall or
effective elasticity of the appliance which can be selected based
on the clinical requirements of moving teeth. That is, the
elasticity of the outer layer can be selected to provide an
appropriate tooth movement force while that of the inner layer can
be chosen to enhance seating characteristics over the teeth. In a
specific embodiment, the compliance of the outer layer 508 could be
varied along the mesial-distal axis in order to provide for
differing forces on the teeth, as discussed generally above.
[0064] Although the foregoing invention has been described in some
detail by way of illustration and example, for purposes of clarity
of understanding, it will be obvious that various alternatives,
modifications and equivalents may be used and the above description
should not be taken as limiting in scope of the invention which is
defined by the appended claims.
* * * * *