U.S. patent application number 09/757385 was filed with the patent office on 2002-05-02 for system and method for releasing tooth positioning appliances.
This patent application is currently assigned to ALIGN TECHNOLOGY, INC.. Invention is credited to Chishti, Muhammad, Phan, Loc X..
Application Number | 20020051951 09/757385 |
Document ID | / |
Family ID | 26807785 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020051951 |
Kind Code |
A1 |
Chishti, Muhammad ; et
al. |
May 2, 2002 |
System and method for releasing tooth positioning appliances
Abstract
An improved dental appliance system, and methods for using and
fabricating the improved appliance, including a polymeric overlay
or shell having a teeth-receiving cavity formed therein. The dental
appliance having the necessary stiffness or strength to firmly
secure the appliance on the teeth and provide controlled forces
required for repositioning the teeth, until such time as removal of
the appliance is desired. The appliance may be configured for use
with a removal mechanism. The removal mechanism provides for
selective release of the appliance from the teeth as the removal
mechanism undergoes a state change stimulated by an environmental
stimulus or environmental switch.
Inventors: |
Chishti, Muhammad;
(Sunnyvale, CA) ; Phan, Loc X.; (San Francisco,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
ALIGN TECHNOLOGY, INC.
|
Family ID: |
26807785 |
Appl. No.: |
09/757385 |
Filed: |
January 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09757385 |
Jan 8, 2001 |
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09250962 |
Feb 16, 1999 |
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6183248 |
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60110189 |
Nov 30, 1998 |
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Current U.S.
Class: |
433/6 |
Current CPC
Class: |
A61C 7/002 20130101;
A61C 2201/007 20130101; A61C 7/00 20130101; A61C 7/08 20130101 |
Class at
Publication: |
433/6 |
International
Class: |
A61C 003/00 |
Claims
8. An appliance as in claim 7, wherein the removal mechanism
comprises at least one polymeric layer laminated to at least a
portion of the polymeric shell.
9. An appliance as in claim 8, wherein the polymeric layer
comprises a material selected from the group consisting of memory
polymers, methacrylate containing polymers, acrylate containing
polymers, thermoplastic polymers, cross-linked thermoplastic
polymers, thermoplastic polymer blends, cross-linked thermoplastic
polymer blends, thermoplastic elastomer polymers, and thermoset
polymers.
10. An appliance as in claim 7, wherein the removal mechanism
comprises a plurality of polymeric layers laminated to the shell,
wherein at least one of the plurality of layers undergoes the state
switch.
11. An appliance as in claim 7, wherein the removal mechanism
comprises a plurality of polymeric layers laminated to the shell,
wherein each layer undergoes the state switch independent of the
other layers
12. An appliance as in claim 7, wherein the removal mechanism
comprises an adhesive within at least a portion of the cavities,
the adhesive having a first peel strength when in the first state
and a second peel strength when in the second state.
13. An appliance as in claim 7, wherein the removal mechanism is
formed at least in part from a material having a first state with a
first modulus and a second state with a second modulus, the first
modulus being different from the second modulus.
14. An appliance as in claim 7, wherein the removal mechanism is a
structure, the structure having a first state with a first
deformation and a second state with a second deformation, the first
deformation being different from the second deformation.
15. An appliance as in claim 7, wherein the removal mechanism
switches from the first state to the second state in response to an
environmental stimulus.
16. An appliance as in claim 15, wherein the environmental stimulus
is selected from the group consisting of temperature, ionic
strength, pH ratio, and liquid absorption.
17. An appliance as in claim 7, wherein the removal mechanism
switches from the first state to the second state in response to an
external stimulus.
18. An appliance as in claim 17, wherein the external stimulus is
selected from the group consisting of light, magnetism,
electricity, and radio waves.
19. An appliance as in claim 1, wherein at least a portion of the
shell has a stiffness in the range from 0.1 GPa to 4 GPa in the
first state and wherein the stiffness is reduced by at least 10% in
the second state.
20. An appliance as in claim 19, wherein at least a portion of the
shell has a stiffness in the range from 0.1 GPa to 4 GPa in the
first state and wherein the stiffness is reduced by at least 90% in
the second state.
21. A dental positioning adjustment appliance comprising: a
polymeric shell having a cavity shaped to receive and resiliently
reposition teeth from one arrangement to a successive arrangement;
and an attachment device which couples to the shell, the attachment
device having a first state where the shell is held onto the teeth
and a second state where the shell may be removed from the
teeth.
22. An appliance as in claim 21, wherein the attachment device is
positionable between an outer surface of the teeth and an inner
surface of the cavity.
23. An appliance as in claim 21, wherein the attachment device is
an anchor device.
24. An appliance as in claim 23, wherein the anchor comprises a
geometric shape, the geometric shape allowing installation of the
shell on to the teeth and restricting removal of the shell when the
anchor device is in the first state.
25. An appliance as in claim 21 wherein the attachment device
comprises at least one polymeric layer laminated to at least a
portion of the attachment device.
26. An appliance as in claim 25, wherein the polymeric layer
comprises a material selected from the group consisting of memory
polymers, methacrylate containing polymers, acrylate containing
polymers, thermoplastic polymers, cross-linked thermoplastic
polymers, thermoplastic polymer blends, cross-linked thermoplastic
polymer blends, thermoplastic elastomer polymers, and thermoset
polymers.
27. An appliance as in claim 21, wherein the attachment device
comprises a plurality of polymeric layers laminated to the
attachment device, wherein at least one of the plurality of layers
undergoes the state switch.
28. An appliance as in claim 21, wherein the attachment device
comprises a plurality of polymeric layers laminated to the
attachment device, wherein each layer undergoes the state switch
independent of the other layers
29. An appliance as in claim 21, wherein the attachment device
switches from the first state to the second state in response to an
environmental stimulus.
30. An appliance as in claim 29, wherein the environmental stimulus
is selected from the group consisting of temperature, ionic
strength, pH ratio, and liquid absorption.
31. An appliance as in claim 21, wherein the attachment device
switches from the first state to the second state in response to an
external stimulus.
32. An appliance as in claim 31, wherein the external stimulus is
selected from the group consisting of light, magnetism,
electricity, and radio waves.
33. An appliance as in claim 21, wherein the attachment device is
embedded within the shell.
34. An appliance as in claim 33, wherein the attachment device is a
structure selected from the group consisting of wires, filaments,
meshes, rings, and braids.
35. An appliance as in claim 33, wherein at least a portion of the
attachment device comprises a shape memory alloy, the alloy being
reconfigured when subjected to an external stimulus.
36. A dental positioning adjustment appliance comprising: a shell
including at least one layer of a polymeric material and having a
cavity which fits closely over a contiguous group of teeth; and an
attachment device coupled to the shell and positionable between an
outer surface of the teeth and an inner surface of the cavity, the
at least one layer of polymeric material and the attachment device
each having a first state where the shell is held onto the teeth
and a second state where the shell may be removed from the
teeth.
37. An improved method for removing a dental appliance from teeth,
the appliance including a polymeric shell having cavities shaped to
receive and resiliently reposition teeth, wherein the improvement
comprises reversibly transforming a component of the appliance from
a first state, where the appliance is held onto the teeth, to a
second state where the appliance may be removed from the teeth with
less force than would be required in the first state.
38. An improved method as in claim 37, wherein the transforming
comprises applying a stimulus.
39. An improved method as in claim 37, wherein the component
comprises a polymeric layer which undergoes the reversible
transformation.
40. An improved method as in claim 39, wherein the polymeric layer
comprises a material selected from the group consisting of memory
polymers, methacrylate containing polymers, acrylate containing
polymers, thermoplastic polymers, cross-linked thermoplastic
polymers, thermoplastic polymer blends, cross-linked thermoplastic
polymer blends, thermoplastic elastomer polymers, and thermoset
polymers.
41. An improved method as in claim 37, wherein the component
comprises a plurality of polymeric layers each of which undergo the
reversible transformation.
42. An improved method as in claim 41, wherein each layer comprises
a material selected from the group consisting of memory polymers,
methacrylate containing polymers, acrylate containing polymers,
thermoplastic polymers, cross-linked thermoplastic polymers,
thermoplastic polymer blends, cross-linked thermoplastic polymer
blends, thermoplastic elastomer polymers, and thermoset
polymers.
43. An improved method as in claim 37, wherein the component is
formed at least in part from a material having a first state with a
first modulus and a second state with a second modulus, the first
modulus being different from the second modulus.
44. An improved method as in claim 37, wherein the component
switches from the first state to the second state in response to an
environmental stimulus.
45. An improved method as in claim 44, wherein the environmental
stimulus is selected from the group consisting of temperature,
ionic strength, pH ratio, and liquid absorption.
46. An improved method as in claim 37, wherein the component is
embedded within the shell.
47. An improved method for removing a dental appliance from the
teeth comprising a polymeric shell having cavities shaped to
receive and resiliently reposition teeth to produce a final tooth
arrangement, wherein the improvement comprises transforming an
interface between the shell and the teeth from a first state, where
the interface holds the shell on the teeth, to a second state where
the shell may be removed from the teeth.
48. An improved method as in claim 47, wherein the interface
comprises a polymeric layer which undergoes the transformation.
49. An improved method as in claim 48, wherein the polymeric layer
comprises a material selected from the group consisting of memory
polymers, methacrylate containing polymers, acrylate containing
polymers, thermoplastic polymers, cross-linked thermoplastic
polymers, thermoplastic polymer blends, cross-linked thermoplastic
polymer blends, thermoplastic elastomer polymers, and thermoset
polymers.
50. An improved method as in claim 47, wherein the interface
comprises a plurality of polymeric layers each of which undergo the
transformation.
51. An improved method as in claim 50, wherein each layer comprises
a material selected from the group consisting of memory polymers,
methacrylate containing polymers, acrylate containing polymers,
thermoplastic polymers, cross-linked thermoplastic polymers,
thermoplastic polymer blends, cross-linked thermoplastic polymer
blends, thermoplastic elastomer polymers, and thermoset
polymers.
52. An improved method as in claim 47, wherein the interface
comprises an adhesive within at least a portion of the cavities,
the adhesive having a first peel strength when in the first state
and a second peel strength when in the second state.
53. An improved method as in claim 47, wherein the interface is
formed at least in part from a material having a first state with a
first modulus and a second state with a second modulus, the first
modulus being different from the second modulus.
54. An improved method as in claim 47, wherein the interface is a
structure, the structure having a first state with a first
deformation and a second state with a second deformation, the first
deformation being different from the second deformation.
55. An improved method as in claim 47, wherein the transforming
comprises applying an environmental stimulus.
56. An improved method as in claim 55, wherein the environmental
stimulus is selected from the group consisting of temperature,
ionic strength, pH ratio, and liquid absorption.
57. An improved method as in claim 47, wherein the interface is
positionable between an outer surface of the teeth and an inner
surface of the cavities.
58. An improved method as in claim 47, wherein the interface is an
anchor device comprising a geometric shape, the geometric shape
allowing installation of the shell on to the teeth and restricting
removal of the shell when the anchor device is in the first
state.
59. A method for fabricating a removable incremental tooth position
adjustment appliance, said method comprising: forming a shell of at
least one layer of a polymeric material with a teeth mold, the
shell having cavities shaped to receive and resiliently reposition
teeth from one arrangement to a successive arrangement; wherein the
shell transforms from a first state where the appliance is held
onto the teeth to a second state where the appliance may be
released from the teeth.
60. A system for repositioning teeth from an initial tooth
arrangement to a final tooth arrangement, said system comprising: a
plurality of dental position adjustment appliances including a
polymeric shell with cavities shaped to receive and resiliently
reposition teeth; and a removal mechanism coupled to the polymeric
shell, the removal mechanism being switchable from a first state
where the shell is held onto the teeth to a second state where the
shell may be removed from the teeth, the appliances including: a
first appliance having a geometry selected to reposition the teeth
from the initial tooth arrangement to a first intermediate
arrangement; one or more intermediate appliances having geometries
selected to progressively reposition the teeth from the first
intermediate arrangement to successive intermediate arrangements; a
final appliance having a geometry selected to progressively
reposition the teeth from the last intermediate arrangement to the
final tooth arrangement; and wherein each position adjustment
appliance is formed of at least one layer of a polymeric material,
the polymeric material transformable from a first state, where the
appliance is held onto the teeth to a second state, where the
appliance can be removed from the teeth, the transformation
activated by an environmental stimulus.
Description
[0001] The present application is a continuation of Application No.
09/250,962, filed Feb. 16, 1999, which claims the benefit and
priority of U.S. Provisional Patent Application No. 60/110,189,
filed Nov. 30, 1998. The full disclosures of which are hereby
incorporated by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is related generally to the field of
orthodontics. More particularly, the present invention is related
to improved dental appliances and systems, and methods for using
and making the same.
[0004] Elastic positioners optionally in combination with
attachments to the patient's teeth are employed in orthodontic
treatments for controlled tooth movement to a pre-determined
position. In providing such appliances and treatments, it is
important to move teeth to an ideal pre-determined position with
gentle controlled forces. Typically, the appliance is fabricated to
provide accuracy of placement in compliance with the exact shape of
the teeth or the exact shape and placement of the attachment
device.
[0005] The use of elastic positioners for repositioning teeth is
known. Such elastic positioners 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. By
properly choosing the configuration, placement of the elastic
positioner over the teeth will move individual teeth to desired
intermediate or final positions over time. Of particular interest
to the present invention, a system comprising multiple elastic
tooth positioning appliances for performing orthodontic procedures
is described in published PCT application WO98/58596 which
corresponds to co-pending application serial number 08/947,080,
assigned to the assignee of the present application.
[0006] The resilient repositioning forces required to move a tooth
from one position to another position in a reasonable amount of
time may be formidable. The design of appliances capable of
imparting such forces with acceptable comfort and appearance has
been a challenge. To achieve such forces, the appliance must be
relatively stiff (i.e. possess a high strength or high modulus) to
provide a sufficient grip on the teeth. The stiffness both ensures
that the dental appliance remains firmly in position on the
patient's teeth and provides the repositioning force necessary to
move the teeth. The stiffness also permits the dental appliance to
"grab hold" of an anchor device or other surface feature which may
be present on the tooth to apply a directed force to execute
orthodontic tooth movements.
[0007] While appliance stiffness is desirable for providing
repositioning forces and for maintaining appliance position on the
teeth, the removal of stiff appliances can be difficult. Tooth
positioners which are stiff and tightly conform to the teeth can
require the use of orthodontic tools for removal, making removal by
the patient very difficult. Periodic removal is desirable for a
number of purposes including cleaning, dental hygiene, removal
before meals, removal for cosmetic purposes, and removal and
replacement in the course of treatment. In most or all of these
cases, however, it will be inconvenient for the patient to visit
the practitioner. Moreover, the use of tools can damage the
appliance, making its reuse difficult or impossible.
[0008] For these reasons, it would be desirable to provide
alternative methods, appliance designs, and systems for removing a
dental appliance from the teeth. Such methods and apparatus,
systems should be economical and, in particular, should reduce the
difficulty experienced and the amount of time required by the
practitioner and/or patient in removing and subsequently
re-applying the appliance. At least some of these objectives will
be met by the methods and systems of the present invention
described hereinafter.
[0009] 2. Description of the Background Art
[0010] WO98/5896 and co-pending application Ser. No. 08/947,080 are
referenced above. Tooth positioners for finishing orthodontic
treatment are described by Kesling in the Am. J. Orthod. Oral.
Surg. 31:297-304 (1945) and 32:285-293 (1946). The use of silicone
positioners for the comprehensive orthodontic realignment of a
patient's teeth is described in Warunek et al. (1989) J. Clin.
Orthod. 23:694-700. Clear plastic retainers for finishing and
maintaining tooth positions are commercially available from
Raintree Essix, Inc., New Orleans, La. 70125, and Tru-Tain
Plastics, Rochester, Minn. 55902. The manufacture of orthodontic
positioners is described in U.S. Pat. Nos. 5,186,623; 5,059,118;
5,055,039; 5,035,613; 4,856,991; 4,798,534; and 4,755,139.
[0011] Other publications describing the fabrication and use of
dental positioners include Kleemann and Janssen (1996) J. Clin.
Orthodon. 30:673-680; Cureton (1996) J. Clin. Orthodon. 30:390-395;
Chiappone (1980) J. Clin. Orthodon. 14:121-133; Shilliday (1971)
Am. J. Orthodontics 59:596-599; Wells (1970) Am. J. Orthodontics
58:351-366; and Cottingham (1969) Am. J. Orthodontics 55:23-31.
SUMMARY OF THE INVENTION
[0012] The present invention provides improved dental appliances
and methods for using and fabricating such appliances. Individual
appliances comprise a polymeric shell having a teeth-receiving
cavity formed therein. The shell will have the necessary stiffness
to firmly secure the appliance on the teeth and provide controlled
forces required for repositioning the teeth. As discussed in detail
below, one or more removal features or mechanisms will be provided
to facilitate removal of the appliances from the teeth. The removal
mechanism may be an integral property or characteristic of the
shell and/or may be a separate component or components in addition
to the shell. Exemplary shell properties include changes in
stiffness or shape induced by exposure of the shell to different
environmental conditions, e.g. a change in temperature, a change in
pH, a change in ionic strength, or the like. Exemplary additional
components include adhesives, interface layers (between the shell
and the tooth), tooth anchors, reinforcement components (layers,
filaments, braids, etc.), where such components can change
stiffness, dimensions, orientations, or the like to selectively
hold or release the shell onto the teeth. Usually, the changes in
the additional components will be induced by the same types of
environmental changes used for inducing property changes in the
shell. Alternatively, removal mechanisms comprising separate
components could be stimulated by exposure to an external energy
source, e.g. being mechanically, electrically, optically,
magnetically or otherwise triggered to induce a change which causes
or permits release of the shell from the teeth.
[0013] Use of such removal mechanisms is advantageous in a number
of respects. Environmental changes can be easily implanted by a
practitioner or patient. For example, the practitioner or patient
can wash the mouth with an appropriately heated, pH-modified, ionic
strength controlled, or other solution which can induce the desired
change in the removal mechanism. While the use of mechanically,
electrically, or optically triggered removal mechanisms may require
additional equipment, such mechanisms can also be very simple and
suitable for use by the patient as well as the practitioner. In all
cases, the removal mechanisms can usually be made reversible, i.e.
the appliance can be "switchable" between attached configurations
where the appliance will remain in place on the teeth and a release
configuration where the appliance can be removed form the teeth.
This is a particular advantage since is allows the appliance to be
temporarily "reconfigured" and removed for any purpose and then
repositioned over the teeth to continue the treatment.
[0014] In a first aspect of the invention, a state change reduces
the stiffness or shape (or both) of the shell material such that
the engagement forces between the shell and the teeth or other
interfaces are reduced or eliminated. The state change can be a
change in any material property which affects stiffness or shape,
such as hardness/softness (as measured by durometer), elasticity,
phase (as with shape memory polymers and materials), or the like.
Preferably, the state change will be reversible so that the shell
can recapture the stiffness lost or recover the shape which was
lost while undergoing the initial state change. The reduction of
stiffness will usually comprise a softening and/or increasing
elasticity of the shell material, permitting the shell to become
more easily pulled from over the teeth. A change in shape will
reduce or eliminate engagement forces between the appliance and the
teeth or other interfaces due to an expansion, contraction, partial
opening, reduction of interference, or other reconfiguration of the
appliance. The desired state change will preferably be induced by
an environmental change which can easily be effected in the
patient's mouth. Preferred environmental changes are these which
can be implemented by a simple mouth wash with a solution having a
particular composition, pH, temperature, ionic strength or other
property. The selected property should be one that the patient will
not normally encounter in daily life, at least during periods when
release of the appliance is not intended. For example, temperature
would not be a good choice unless it is intended that the appliance
be removed when eating or drinking hot foods and drinks. The
property should also be one that is physiologically acceptable,
e.g. very high or very low pH might not be desirable.
[0015] It is not necessary, however, that the "released"
configuration be long term or sustainable. In many instances, the
removal mechanism will permit mounting of the appliance onto the
teeth when the removal mechanism is in its "attached"
configuration. To remove the appliance, the released configuration
need be sustained only long enough to complete the removal. The
removal mechanism can then revert to the attached configuration, as
the result of for example, cooling, pH change, and ionic strength
change, and still be replaced over the teeth without the need to
restore the released configuration.
[0016] In one embodiment, the removal mechanism may be an integral
property of the appliance, usually being an inherent property of
the shell or a part of the shell. An orthodontic appliance is
provided which has a shell formed of at least one layer of a
polymeric material. The shell has a cavity which fits closely over
a contiguous group of teeth. A contiguous group of teeth includes
at least 3 teeth, but usually 4 or more. The at least one layer of
polymeric material has a first state where the appliance is held
onto the teeth and a second state where the appliance may be
removed from the teeth. The first state will exist when the shell
is in place in the patient's mouth in the absence of any "non-oral"
conditions or externally applied energy or other stimuli. The
second state can then be selectively induced by creating a
"non-oral" environment in the patient's mouth, as discussed above.
The non-oral environment may consist of a non-physiological
temperature (above 37.degree. C., preferably 40-55.degree. C.; or
below 37.degree. C., preferably below 30.degree. C.), a
non-physiologic pH (above 8, preferably above 9, more preferably
above 8.5 or below 7, preferably below 6, more preferably below
6.5), a non-physiologic ionic strength, such as 3% sodium chloride,
or the like.
[0017] In another embodiment, the removal mechanism is formed as
one or more additional component(s) or mechanism(s). Such systems
will include at least one polymeric shell which can be removably
placed over a patient's teeth. The separate removal component or
mechanism is switchable from a first state to a second state.
[0018] In yet another embodiment, a dental appliance system will
include a dental appliance, which has a shell with a cavity. The
system will further include an attachment device which is formed or
exists separately from the shell. The attachment device is usually
configured to be positioned between the outer surface of the teeth
and an inner surface of the cavity. The device is switchable
between a first state, where the appliance is held onto the teeth,
and a second state, where the appliance may be removed from the
teeth. The switch is stimulated or made to occur as a response to
an environmental change.
[0019] In another aspect of the invention, an improved method is
provided for removing an appliance from the teeth. Preferably, the
appliance is a polymeric shell, which has cavities shaped to
receive and resiliently reposition teeth to produce a final tooth
arrangement. In a first aspect, the improvement comprises
transforming the shell from a first state, where the appliance is
held onto the teeth, to a second state where the appliance may be
removed from the teeth. The transformation is performed in situ in
the patient's mouth, usually the exposure to an environmental
change or external stimulus as described above. The transformation
is repeatable so that the appliance can be reinserted.
[0020] In another aspect a method for fabricating a removable
incremental tooth position adjustment appliance is provided
including forming a shell of at least one layer of a polymeric
material with a teeth mold. The shell is formed with cavities
shaped to receive and resiliently reposition teeth from one
arrangement to a successive arrangement. The shell transforms from
a first state, where the appliance is held onto the teeth, to a
second state, where the appliance may be released from the
teeth.
[0021] In another aspect, an appliance system comprises a plurality
of individual appliances that can be used for repositioning teeth
from an initial tooth arrangement to a final tooth arrangement
using a plurality of dental incremental position adjustment
appliances. In this embodiment, the plurality of position
adjustment appliances will include a first appliance having a
geometry selected to reposition the teeth from the initial tooth
arrangement to a first intermediate arrangement. The plurality of
position adjustment appliances will also have one or more
intermediate appliances having geometries selected to progressively
reposition the teeth from the first intermediate arrangement to
successive intermediate arrangements. The position adjustment
appliances will still further have a final appliance having a
geometry selected to progressively reposition the teeth from the
last intermediate arrangement to the final tooth arrangement. The
system will also include a removal mechanism formed into each
adjustment appliance described above. The removal mechanism
transforms from a first state to a second state to release each
appliance from the teeth. In a preferred embodiment, the
transformation is activated by a stimulus, preferably an
environmental stimulus or condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 illustrates the jaw of a patient together with a
dental appliance which has been configured according to the present
invention.
[0023] FIGS. 2, 2A, and 2B are cross-sectional views of embodiment
for securing the appliance of FIG. 1 on to the teeth.
[0024] FIGS. 3, 3A, and 3B are cross-sectional views of an
attachment device for securing the appliance of FIG. 1 on to the
teeth.
[0025] FIGS. 4A-4D are schematic illustrations of the layering
geometry used in accordance with the present invention.
[0026] FIGS. 5A-5B are cross-sectional views of a process for
forming an appliance in accordance with the present invention.
[0027] FIG. 6 is an illustration of a cross-sectional view of an
embodiment of the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0028] Referring to FIG. 1, the apparatus, systems, and methods
according to the present invention will include at least one
appliance 100 removably replaceable over the teeth. Usually,
appliance 100 is one of a plurality of incremental position
adjustment appliances. The appliances are intended to effect
incremental repositioning of individual teeth in the jaw. The
appliance 100 may be used in place of any of the known positioners,
retainers, or other removable appliances which are known for
finishing and maintaining teeth positions in connection with
orthodontic treatment. The appliances of the present invention, in
contrast with prior apparatus and systems, are particularly
suitable for use by a patient successively in order to achieve
gradual tooth repositioning. A full description of an exemplary
repositioning appliance is described in co-pending U.S. application
Ser. No. 08/947,080 (Attorney Docket No. 18563-000110), filed Oct.
10, 1997, which is herein incorporated by reference for all
purposes. A description of this exemplary dental appliance for use
with the removal mechanism of the present invention is described
below.
[0029] The exemplary appliance 100 includes a polymeric shell 102
having an inner cavity 120, a proximal edge 116, and a distal edge
118. Cavity 120 is shaped to receive and resiliently reposition
teeth from one tooth arrangement to a successive tooth arrangement.
The polymeric shell will preferably, but not necessarily, fit over
all teeth present in the upper or lower jaw 114. Often, only
certain one(s) of the teeth will be repositioned while others of
the teeth will provide a base or anchor region for holding the
repositioning appliance in place as it applies the resilient
repositioning force against the tooth or teeth to be repositioned.
The gums and/or the palette can also serve as an anchor region,
thus allowing all or nearly all of the teeth to be repositioned
simultaneously. Additionally, anchors and adhesives, which are
described in more detail below, are available which may also serve
as attachment points for appliance 100. What follows is a
description of various embodiments for securing appliance 100 to
the teeth.
[0030] As can be best understood with reference to FIGS. 2, 2A, and
2B, shell 102 is forced down over teeth T, typically by the patient
biting down on the shell or by other forms of manual pressure being
applied to the shell. Edges 116 and 118 are made to engage what is
known as the undercut U of the teeth. Typically, this type of
engagement is helpful in that it allows for specific tooth
movements, such as extrusions (i.e. upward movement of the
tooth).
[0031] Shell 102 is made of a material that has a predetermined
modulus, also referred to as the stiffness, of the material.
Generally, the modulus is a measurement of the inherent stiffness
of a material determined by conducting stress and strain tests on a
material specimen and plotting the results. The value of the slope
of the line generated by the results is the modulus. The modulus
can be predetermined to match the compliance required to reposition
the teeth based on requirements set by an individual patient's
repositioning needs. In one example, the shell may have a modulus
in the range of between about 0.1 GPa to 4 GPa, usually 0.5 GPa to
3 GPa, preferably about 0.8 GPa to 1.5 GPa.
[0032] Often, the shell is formed from a material that has uniform
properties, particularly stiffness, over the entire area. In some
cases, however, it will be desirable to vary the stiffness,
thickness, or other material properties of the shell at different
points or segments. Also, other layers, reinforcement elements,
holes, or components may be added to the shell to vary its
stiffness and/or other mechanical properties.
[0033] The stiffness of the shell keeps edges 116 and 118 engaged
with undercut U, which is designed to hold the appliance in place
and effect tooth repositioning. The stiffness, however, prevents
the shell from being easily removed from the undercut. Therefore,
to reduce the effort of removing the shell from the teeth, the
shell stiffness can be modified. For instance, in the example
above, to reduce the 1 to 4 GPa stiffness between shell 102 and
interfaces with the teeth, the stiffness of the shell may need to
be temporarily reduced by at least 10%, usually at least 50%,
typically by approximately 10% to 90%, more typically about 50% to
90%.
[0034] Once shell 102 is in position e.g. engaged with the undercut
U of the tooth, the shell provides the desired repositioning forces
to the teeth. At such time as desired, shell 102 may then be
removed from the teeth. In one embodiment directed at removing the
shell, shell 102 may be made of a polymeric material which can
undergo a change from a first state to a second state. The state
may include, for example a change in material property or a change
in shape. The changes can be made to occur throughout the shell,
but at least in the region of engagement with the undercut. The
changes in material property or shape remove or reduce, as
appropriate, the stiffness of the shell, which makes removal of the
appliance substantially easier. The shell may include a single
layer of material or else a plurality of polymeric materials. Each
layer may undergo the property change independent of one another or
simultaneously. The layer or layers may also be made of a
cross-linked polymer capable of undergoing a change in shape. In
this embodiment, shell 102 may be deformed, such that edges 116 and
118 of shell 102 can be made to disengage undercut U, which then
allows for easy removal of appliance 100.
[0035] In an alternative embodiment, in addition to the engagement
with the undercut, or in some cases instead of the engagement with
the undercut, an adhesive 122 (FIG. 2B) may be used to add holding
strength between appliance 100 and the teeth. The adhesive may have
a peel strength that may be reduced or eliminated in order to
remove the shell. For example, in its initial state the adhesive
should have a peel strength of no less than about 250 g/cm,
however, to remove the shell, the peel strength is reduced to a
value below the 250 g/cm threshold. Adhesives, with compositions
that are side chain crystalizable based polymer such as
polyethylacrylate-hexadecylacrylate copolymer with XAMA 2,
polypentadecylacrylate with cross linker, polyoctadecylacrylate
with XAMA 2, and the like, may be used for such purposes. The
ability to reduce the peel strength of the adhesive, facilitates
removal of the appliance. In a manner described below, the adhesive
can be subjected to an environmental change (e.g. temperature) or
other appropriate stimulus to reduce the peel strength. Since the
peel strength can be recovered after the environmental change or
stimulus is changed or removed, only one application of the
adhesive to the shell may be necessary, regardless of the number of
times the shell is removed from the teeth.
[0036] In another alternative embodiment, shell 102 may also be
held or anchored to the teeth through an engagement between shell
102 and an attachment device such as anchor 124 (FIGS. 3, 3A and
3B). Attachment device 124 may be anchored to a distal surface
(between tooth and cheek) and/or a proximal surface (between tooth
and tongue) of the teeth using an adhesive or similar bonding
substance. Various attachment device designs are described in more
detail below. Tooth anchors used with convention wire braces are
well known and described in the patent and dental literature. For
use in the present invention, the anchors may have any of a variety
of material properties with the objective being to point a
force-transmitting interface between the appliance and the tooth
when the appliance is in place. The anchors may be formed from most
solid, physiologically acceptable materials, particularly metals,
ceramics, and polymers. The materials may be rigid, resilient, or
programmable, e.g. shape memory polymers or metal alloys. In some
instances, it is also possible that the anchors would be
mechanically complex, e.g. articulated, rotatable, or otherwise
repositionable to facilitate mounting or removal of the appliance
from the teeth.
[0037] Attachment device 124 has an engagement surface 130 that
corresponds to an indentation feature 128 formed on the inner
surface of cavity 120. As shell 102 is forced onto the teeth T, as
described above, inner surface 126 of shell cavity 120 slidingly
contacts engagement surface 130 until indentation feature 128
matches up to engagement surface 130. At that time, the indentation
128 conforms around the shape of anchor 124 with a snug fit to hold
shell 102 in position. As can be appreciated from the geometric
shape of anchor 124 shown in FIGS. 3, 3A, and 3B, the engagement
between anchor 124 and shell 102 is a "one-way" engagement, which
means shell 102 is substantially locked in position.
[0038] In this alternative embodiment, anchor 124 may be made of a
polymeric material that can be made to undergo a change in material
property. In particular, the combination of the strength of anchor
124, in an initial state, and the strength of shell 102, may be
enough to hold shell 102 to the teeth, such that shell 102 may not
be easily removed. However, as the material property of the anchor
changes, the combination of strengths is reduced. When the strength
is reduced below the force being applied to remove shell 102, the
shell lifts-off from the teeth. Alternatively, anchor 124 may be
made of a cross-linked polymer. In this alternative embodiment,
anchor 124 can undergo a change in shape, which changes the
geometry of the anchor such that the engagement between the anchor
and the shell is weakened or else removed. Although, the entire
shape of the anchor may be changed, the shape change may occur at
least in the region of engagement between the anchor and the shell.
The anchor may be made of a single layer or a plurality of layers
each made of a polymer or cross-linked polymer as described in more
detail below.
[0039] Shell 102 may also be configured with a reinforcement
structure, such as a wire, a filament, a mesh, a ring, and/or a
braid. The reinforcement structure may also be capable of
undergoing a change in material property or else a change in shape,
such that the change facilitates the removal of the appliance from
the teeth. For example, appliance 100 may be fabricated with a
polymeric external layer and a metal inner wire embedded in at
least a portion of the appliance proximate to either the engagement
with the undercut or the engagement with the anchor. The metal
inner wire can be made of a memory shape metal, such as
Nitinol.RTM., Bimetal.RTM., Memotal.RTM. or similar alloy. The wire
undergoes a change in material property (and/or shape) as it is
subjected to a thermal stimulus or other external stimulus. In this
example, the wire changes geometry. Since the wire is embedded
within the appliance, the appliance also changes shape, which
reduces the shells hold on the teeth.
[0040] In a preferred embodiment, the changes described above may
be provided through use of various polymers which undergo a glass
transition at a preselected temperature, preferably a temperature
above the average body temperature. What follow is a description of
the various material property and shape changes undertaken by a
change in glass transition temperature.
[0041] The glass transition may occur by using a plastic, such as a
polymer, that has a molecular transition incorporated in the same.
The polymeric material is biocompatible and is formulated so that
the achieved transition can be activated upon subjecting the
appliance to thermal stimuli as hereinafter explained. The
molecular transitions, which are incorporated in the appliance, are
typically in the form of thermotransitions, as for example, a
crystalline melting point, above about 37.degree. C., preferably
between 40.degree. C. and 55.degree. C., of the polymer side chain,
the polymer main chain, or a liquid-crystal (mesophase) transition
of the polymer chain. The thermotransitions may also be accessed
via a glass transition phenomenon or a local mode molecular
transition. Examples 1-12 provide exemplary lists of such
materials.
[0042] In one embodiment, a glass transition removal mechanism may
comprise a single layer or a plurality of material layers 131
configured in shell 102, as shown in FIGS. 4A, 4B and 4C. The shell
may include a variable number of layers 132, which may each have
variable thickness and/or variable glass transition temperatures.
The layers may be formed in various orientations and configurations
to suit the modulus and application requirements. The shell layers
will be formed by a process, such as thermoforming or similar
process, and will have formed on them the desired shell cavities
and indentations necessary for proper application of the
repositioning forces to the teeth.
1 GLASS TRANSITION POLYMERS Layer Material Thickness Temp. Phase
Example 1. 1 Polycarbonate 5 mils Hi Temp. 2 Polyvinyl chloride
(PVC) 10 mils Low Temp. 3 PVC 10 mils Low Temp. 4 PVC 10 mils Low
Temp. 5 PVC 10 mils Low Temp. 6 Polycarbonate 5 mils Hi Temp
Example 2. 1 Polycarbonate 10 mils Hi Temp. 2 PVC 10 mils Low Temp.
3 PVC 10 mils Low Temp. 4 Polycarbonate 10 mils Hi Temp. Example 3.
1 PMMA 5 mils Hi Temp. 2 Polyethelyne (PE) 10 mils Low Temp. 3 PE
10 mils Low Temp. 4 PE 10 mils Low Temp. 5 PE 10 mils Low Temp. 6
PMMA 5 mils Hi Temp. Example 4. 1 PMMA 10 mils Hi Temp. 2 PE 10
mils Low Temp. 3 PE 10 mils Low Temp. 4 PMMA 10 mils Hi Temp.
Example 5. 1 Polycarbonate 5 mils Hi Temp. 2 PE 10 mils Low Temp. 3
PE 10 mils Low Temp. 4 PE 10 mils Low Temp. 5 PE 10 mils Low Temp.
6 Polycarbonate 5 mils Hi Temp. Example 6. 1 Polycarbonate 10 mils
Hi Temp. 2 PE 10 mils Low Temp. 3 PE 10 mils Low Temp. 4
Polycarbonate 10 mils Hi Temp. Example 7. 1 PMMA 5 mils Hi Temp. 2
PE 10 mils Low Temp. 3 PE 10 mils Low Temp. 4 PE 10 mils Low Temp.
5 PE 10 mils Low Temp. 6 PMMA 5 mils Hi Temp. Example 8. 1 PMMA 10
mils Hi Temp. 2 PE 10 mils Low Temp. 3 PE 10 mils Low Temp. 4 PMMA
10 mils Hi Temp. Example 9. 1 Polycarbonate 20 mils Hi Temp. 2 PE
20 mils Low Temp. Example 10. 1 PMMA 20 mils Hi Temp. 2 PVC 20 mils
Low Temp. Example 11. 1 Polycarbonate 20 mils Hi Temp. 2 PVC 20
mils Low Temp. Example 12. 1 Polysulfone 20 mils Hi Temp. 2 PE 20
mils Low Temp.
[0043] In an exemplary embodiment, using the materials as in
Example 1 above for illustration purposes, shell 102 may include
first, second, and third internal layers 132, each including 10
mils of polyvinyl chloride (PVC) material, having a glass
transition temperature of about 50.degree. C. Internal layers 132
are sandwiched between external layers 134, each of 5 mils of
Polycarbonate material, which have a glass transition temperature
of about 150.degree. C. The Polycarbonate external layers 134 and
the PVC inner layers 132, while under the glass transition
temperature of both materials should have the combined modulus of
all of the layers to provide the shell with the requisite modulus
or strength to grab hold of and reposition the teeth.
Alternatively, the inner layers may be configured with a higher
transition temperature than that of the external layers. By
reversing the threshold glass transition temperatures between the
layers, the external layers can be made to lose stiffness while the
inner layers maintain their stiffness.
[0044] In a preferred operation, a thermal stimulus is applied to
shell 102. The temperature being above the glass transition
temperature of inner layers 132, but below the glass transition
temperature of outer layers 134. Once inner layers 132 reach their
glass transition temperature, they lose stiffness, thus removing
their contribution to the stiffness of shell 102. Since, shell 102
is less stiff, the appliance can be manipulated and removed from
the teeth.
[0045] External layers 134 provide a structural member or
superstructure that is kept from reaching its glass transition
temperature so that it maintains its original shape. Thus, once
appliance 100 is removed from the teeth, the above process can be
reversed. To reverse the process, inner layers 132 may be brought
below their glass transition temperature, which will cause inner
layers 132 to return to their original high stiffness state.
Appliance 100 can then be re-applied to the teeth in the manner
described above and will have substantially the same stiffness, and
therefore the same effectiveness, as before the initiation of the
removal mechanism.
[0046] The glass transition removal mechanism may also comprise at
least one layer of various different homopolymers, cross-linked
homopolymers, and/or copolymer blends of thermoplastics, which have
a "built-in" memory capability. The materials, a representative
list shown in Examples 13-21 below, are individually selected or
blended together to have a preselected glass transition
temperature. As shown in FIG. 4D for illustrative purposes, the
layer geometry may include a single material layer 132, which may
range from about 1.0 mil to 60 mils, preferably 10-40 mils.
2 GLASS TRANSITION POLYMERS - CROSS-LINKED Temp. Layer Material
Thickness Phase Example 13. 1 Polycapralactone 40 mils
40-55.degree. C. Example 14. 1 Vestenamer 40 mils 40-55.degree. C.
Example 15. 1 PMMA/Polyethylene Blend 40 mils 40-55.degree. C.
Example 16. 1 Polycarbonate/Polyethylene Blend 40 mils
40-55.degree. C. Example 17. 1 Polysulfone/Polyethylene Blend 40
mils 40-55.degree. C. Example 18. 1 Polyester 40 mils 40-55.degree.
C. Example 19. 1 Polyester/Polycarbonate Blend 40 mils
40-55.degree. C. Example 20. 1 Polyurathane 40 mils 40-55.degree.
C. Example 21. 1 Polyurathane/Polycarbonate Blend 40 mils
40-55.degree. C.
[0047] In FIGS. 5A and 5B, the memory removal mechanism,
incorporated into shell 102 is shown in various stages of
production. To form the memory removal mechanism, materials, such
as those provided in Examples 13-21, may be extruded in sheets and
then formed into any shape that is different, and yet approximates
the general shape of the appliance.
[0048] Specifically, the cross-linked polymers may be formed into a
rectangular cross-sectional form 140 or alternatively, the form may
be any shape, such as a dome or a flat sheet. This form is
considered the initial or first state. Form 140 may be fabricated
into an appliance 142 by thermoforming or similar process, with the
desired surface features necessary for proper application of
repositioning forces to the teeth. Appliance 142 is then allowed to
cool below its glass transition temperature, while being restrained
in the desired appliance shape. Appliance 142 will maintain this
shape as long as the appliance is not exposed to temperatures above
the pre-set glass transition temperature.
[0049] After being secured to the teeth and upon such time when
removal is desired, the single-layered shell will be subjected to a
thermal stimulus which causes the material to surpass its glass
transition temperature. The change in temperature causes appliance
142 to return to its original state (e.g. form 140). Since the
original state of form 140 has a different shape than appliance
142, the engagement forces are reduced.
[0050] The memory removal mechanism can be made reversible. In an
exemplary embodiment, form 140 may be made of a plurality of inner
layers 150 sandwiched between an outer layer 152 as shown on
appliance 148, illustrated in FIG. 6. The layers may have variable
thickness and variable glass transition temperatures depending on
the modulus requirements. The internal layers 150 may be made from
a homopolymer, cross-linked homopolymer, copolymer, and /or
cross-linked copolymer like those described in Examples 13-21.
External layer 152 may be made of a Polycarbonate or similar
material, which has a higher (or lower) glass transition
temperature then the inner layers. The layers will be formed with
the desired surface features and indentations necessary for proper
application of the repositioning forces to the teeth.
[0051] In an exemplary operation of this embodiment, after the
appliance has been applied to the teeth and upon such time as
removal of the appliance is desired, a thermal stimulus is applied
to shell 102. The temperature of the initiator is above the glass
transition temperature of inner layers 150 but below the glass
transition temperature of outer layer 152. Once inner layers 150
reach their glass transition temperature, they attempt to
reconfigure to their original form, while outer layers 152 continue
to maintain their original shape. The internal forces generated by
the attempted reconfiguration of the inner layers, push outer
layers 152 outward in the direction of arrows 154 until edges 116
and 118 reach positions 156. In moving the edges to positions 156,
a reduction in the engagement forces between appliance 148 and the
teeth is provided to allow for removal of the appliance.
[0052] The process may be reversed by cooling the shell below the
glass transition temperature of the inner layers 150. Outer layers
152 maintain their useful shape and will continue to apply a
biasing inward force in the direction of arrows 158 until the
appliance returns to its original state.
[0053] In yet another embodiment of the glass transition removal
mechanism, shown in FIGS. 3A and 3B, at least one anchor 124 may be
used to secure the appliance to the teeth. In the same manner as
the appliance, anchor 124 may be made of the same polymers
described above, to undergo the same types of state changes. For
example, anchor 124 may comprise a plurality of layers, but at
least one layer, that include the formulations of materials in the
above Examples. When subjected to a thermal stimulus, anchor 124
may undergo a glass transition. Accordingly, anchor 124 may either
be configured to lose strength, change shape, or both, which will
facilitate removal of the shell from the anchor.
[0054] All of the embodiments described above may be used either in
combination or independently, subject to the discretion of the
practitioner.
[0055] In each of the above described embodiments, the glass
transition temperature is described as the threshold temperature
for activating the state change process of the appliance. However,
alternatively, the melting point temperature may be used as the
threshold temperature. An advantage to using the melting point
temperature is that the change in properties from one state to
another is greater, Also, the change in property occurs over a
smaller temperature range.
[0056] A variety of thermal stimuli have been identified which can
be used to initiate the state changes in any of the embodiments
described above. For example, the heat may be supplied to the
appliance by introducing a source of heat energy, preferably a
liquid because of its greater heat transfer capabilities. The
heated liquid causes heat to rapidly transfer to the shell 102 to
raise the temperature of the shell until the temperature reaches
the transition temperature of the shell, causing the shell to
transition to a second state.
[0057] Similarly magnetism, electricity, and radio waves can be
used as secondary sources of heat to cause the desired state
changes. Such external heat can also be applied by using an
infrared, microwave, or radio frequency sources as well as
resistive heating.
3 FORMULATIONS FOR ULTRA VIOLET AND/OR THERMALLY INITIATED
POLYMERIZATION Material Percent by Weight Example 22. Methyl
Methacrylate 50% Butyl Methacrylate 15% Hexyl Methacrylate 30% 1,4
Butanediol Dimethacrylate 4.6% USP 245 .4% Example 23. Isobutyl
Methacrylate 30% Hexyl Methacrylate 20% Octadecyl Methacrylate 22%
Polyethylene Glycol Dimethacrylate 10% Perkadox 16N 0.3% Methyl
Methacylate 18%
[0058] Examples 22 and 23 are glass transition materials which may
be polymerized either thermally using a conventional heat source or
by using Ultra Violet (UV) light. If polymerization by UV is
desired then a UV initiator such as Duracure 1173 or benzoin
methylether may be added in place of USP 245 or Perkadox 16N in
Examples 22 and 23 above. The materials of Examples 22 and 23 may
be used in the shell or in the anchor, as described above.
[0059] The removal mechanism of the present invention may also
include polymers used together to provide a formulation which
changes from a first state to a second state when subjected to an
aqueous buffer solution having a predetermined pH ratio. Typical,
material formulations as shown, for example, as Examples 24-27.
[0060] Typically, when the pH sensitive appliance is applied to the
teeth, shell 102 will hydrate minimally, for example up to about
10%, when exposed to the pH level of the human mouth (normal
physiological pH level). When the appliance is to be removed, the
appliance may be subjected to a solution which will cause a change
in the pH ratio of the mouth. Depending on the material formulation
used, the change in pH causes the appliance to hydrate, for
example, up to about 90% more than when at the normal pH level.
When the appliance undergoes the change in hydrating states, the
appliance changes dimension. For example, the linear dimension may
change from about 2% to 300% when going from a lower hydration
state to a higher hydration state. The swelling of the appliance
removes its ability to properly engage the teeth.
4 FORMULATIONS FOR CHANGES BY ABSORPTION OF A LIQUID Material
Percent by Weight Example 24. N-Vinyl Pyrrolidone 25% Butyl
Acrylate 40% Isobornyl Methacrylate 30% 1,6-Hexane
Dioldimethacrylate 5% Azobis Isobutyl Nitrile 0.5% Example 25.
2-Hydroxy Ethylmethacrylate 45% Methyl Methacrylate 35% Butyl
Methacrylate 15% Polyethylene Glycoldimethacrylate 5% Benzoyl
Peroxide 0.5% Example 26. Methacrylic Acid 20% Methyl Methacrylate
40% Octadecyl Methacrylate 35% Ethylene Glycoldimethacrylate 5%
Azobis Isobutyl Nitrile 0.5% Example 27. Acrylic Acid 20% Methyl
Methacrylate 40% Octadecyl Methacrylate 35% Ethylene
Glycoldimethacrylate 5% Azobis Isobutyl Nitrile 0.5%
[0061] Alternatively, the anchor attachment may be made from the
materials, such as those listed in Examples 24-27 and may be made
to undergo a hydration state change when subjected to a different
pH ratio. In one embodiment, while at the normal pH level, the
attachment device may swell to a size that facilitates the
engagement between the appliance and the teeth. For example, the
hydration of the anchor may be up to about 90%. When the attachment
device is exposed to a different pH level, the attachment device
will dehydrate and shrink to disengage from the appliance. The
range of dimensional change depends on the attachment device
material composition, but will nonetheless be sufficient to allow
for removal of the appliance. As before, the change in the
appliance properties and in the attachment device may take place
together or independently.
[0062] The removal mechanism may also respond to a state change
caused by ionic strength changes, which causes water absorption in
polymers subjected to different concentration of salts, including
NaCl or sugar.
[0063] Typically, when the appliance is applied to the teeth, the
shell will hydrate minimally, for example up to about 10%, based on
the average concentration of salts in the human mouth (normal ionic
strength). When the appliance is to be removed, the appliance may
be subjected to a solution which will cause a change in the
concentration of the salts. Depending on the material formulation
used, the change in salt concentration causes the appliance to
hydrate, for example, up to about 90% more than when in the normal
concentration ranges. Exemplary material formulations are described
in Examples 28 and 29. When the appliance undergoes the change in
hydrating states, the appliance changes dimension. For example, the
linear dimension may change from about 2% to 300% when going from a
lower hydration state to a higher hydration state.
5 FORMULATION FOR CHANGES BY ABSORPTION OF A LIQUID IN DIFFERENT
IONIC STRENGTH CONDITIONS Material Percent by Weight Example 28.
N-Vinyl Pyrrolidone 25% Butyl Acrylate 40% Isobornyl Methacrylate
30% 1,6-Hexane Dioldimethacrylate 5% Azobis Isobutyl Nitrile 0.5%
Example 29. 2-Hydroxy Ethylmethacrylate 45% Methyl Methacrylate 35%
Butyl Methacrylate 15% Polyethylene Glycoldimethacrylate 5% Benzoyl
Peroxide 0.5%
[0064] Alternatively, the anchor attachment may also be made from
materials in Examples 28 and 29 and may undergo a hydration state
change when subjected to a different concentration of salts. While
in its initial state, the attachment device may swell to a size
that facilitates the engagement between the appliance and the
teeth. For example, the hydration of the anchor may be up to about
90%. When the attachment device is exposed to a different
concentration of salts, the attachment device will dehydrate and
shrink to disengage from the appliance. The range of dimensional
change depends on the attachment device material composition. As
before, the change in the appliance properties and in the
attachment device may take place together or independently.
[0065] While the above is a complete description of the preferred
embodiments of the invention, various alternatives, modifications,
and equivalents may be used. In one example, appliance 100 may be
removed from the teeth when a pressure is directed down on the top
surface of the teeth, either through biting down or through a
direct manual application of the pressure. The pressure may force
edges 116 and 118 in an outward direction, thus removing engagement
between the appliance and interfaces on the teeth.
[0066] Therefore, the above description should not be taken as
limiting the scope of the invention which is defined by the
appended claims.
[0067] a removal mechanism coupled to the polymeric shell, the
removal mechanism being switchable from a first state where the
shell is held onto the teeth to a second state where the shell may
be removed from the teeth.
* * * * *