(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`
`
`(43) International Publication Date
`1 November 2001 (01.11.2001)
`
`(10) International Publication Number
`
`PCT
`
`WO 01/80764 A1
`
`(51)
`
`International Patent Classification“:
`
`A61C 3/00
`
`(21)
`
`(22)
`
`(25)
`
`(26)
`
`(30)
`
`International Application Number:
`
`PCT/USOl/13217
`
`International Filing Date:
`
`24 April 2001 (24.04.2001)
`
`Filing Language:
`
`:
`
`L
`
`.
`.
`t
`P bl
`anguage
`tea [on
`u
`Priority Data:
`60/199549
`60/199,650
`09/616,830
`09/616,222
`
`English
`
`.
`E 1 h
`rig is
`
`25 A911,] 2000 (25042000) Us
`25 April 2000 (25.04.2000)
`US
`1—- July 2000 (14.07.2000)
`US
`
`177 July 2000 (14.07.2000)
`US
`
`(63)
`
`Related by continuation (CON) or continuation-in-part
`(CIP) to earlier application:
`US
`Filed on
`
`09/616,830 (CIP)
`14 July 2000 (14.07.2000)
`
`(71)
`
`Applicant (for all designated States except US): ALIGN
`TECHNOLOGY, INC. [US/US]; 851 Martin Avcnuc,
`Santa Clara, CA 95050 (US).
`
`(72)
`(75)
`
`Inventors; and
`Inventors/Applicants (far US only): PHAN, Loc, X.
`[US/US]; 31 Jacklin Circle, Milpitas, CA 95035 (US).
`
`CHISHTI, Muhammad [US/US]; 970 Corte Madera Av—
`enue, # 302, Sunnyvale, CA 94086 (US). MILLER, Ross,
`J. [US/US]; 243 Buena Vista Avenue, #1513, Sunnyvale,
`CA 94086 (US). VAN DEN BERG, H., Robert [NL/US];
`Suite A, 1501 Bollinger Canyon Road, San Ramon, CA
`94583 (US). KUO, Eric [US/US]; 101 Woodland Avcnuc,
`
`San Francisco, CA 94117 (US).
`
`(
`
`74) Agents: HESLIN James M; Townsend and Townsend
`’
`’
`’
`and Crew LLP, Two Embarcadero Center, Eight Floor, San
`Franc1sco, CA 94111 ct al. (US).
`(81) Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ BA BB BG BR BY BZ CA CH CN CO CR CU
`CZlDElDKY DM DZ’ EE ES, FI ,GB GD ,GE ,GHlGM,
`a
`a
`,
`,
`,
`,
`’
`,
`,
`5
`5
`5
`’
`HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, K7., LC, LK,
`LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX,
`MZ, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL,
`TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW.
`
`(84) Designated States (regional): ARIPO patent (GH, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TlVI), European
`patent (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE,
`IT, LU, MC, NL, PT, SE, TR), OAPI patent (BF, BJ, CF,
`CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`Published:
`7 with international search report
`
`[Continued on next page]
`
`(54) Title: SYSTEMS AND METI IODS FOR VARYING ELASTIC MODULUS APPLIANCES
`
`/00\
`
`WO01/80764A1
`
`///
`
`
`
`devices,
`Improved
`(57) Abstract:
`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
`(100)
`configured to receive the teeth (115)
`and incrementally reposition individual
`teeth in a series of successive steps. The
`individual appliances may he formed
`from layers (110, 111) having different
`stiffnesses (elastic moduluses), and the
`stiffnesses of successive appliances may
`be different, or both.
`
`

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`WO 01/80764 A1
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`||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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`For two-letter codes and other abbreviations, refer to the "Guid-
`ance Notes on Codes andAbbreviations ” appearing at the begin-
`ning ofeach regular issue ofthe PCT Gazette
`
`

`

`WO 01/80764
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`PCT/US01/13217
`
`SYSTEMS AND METHODS FOR
`VARYING ELASTIC MODULUS APPLIANCES
`
`BACKGROUND OF THE INVENTION
`
`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.
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`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
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`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 maybe required to wear
`
`supplementary appliances, such as elastic bands or headgear, to supply additional or
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`extraoral forces.
`
`Although conventional braces are effective, they are oflen 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
`
`25
`
`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
`
`30
`
`configurations eventually move 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 US. Patent No. 5,975,893, and in published PCT
`
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`WO 01/80764
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`PCT/US01/13217
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`application W0 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.
`
`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 stiffiiess 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 oflen 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.
`
`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.
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`SUIVIMARY OF THE INVENTION
`
`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 stiffiiess creates limitations in
`
`ease of use, patient compliance, and overall cost in material, manufacturing labor and
`
`treatment time.
`
`To overcome these limitations, the present invention utilizes polymeric or
`
`other material appliances with portions differing in rigidity, hardness, or stiffiiess.
`
`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 stiffiiess appliances which may be used independently for
`
`purposes other than repositioning, such as for retaining teeth in a desired position. Thus,
`
`reference hereinafier 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.
`
`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 stiffiiess 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
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`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 sofi 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.
`
`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
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`
`20
`
`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, TiOz, 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 fi'om 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
`
`25
`
`I from another portion by 25% to 600%, or more.
`
`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
`
`30
`
`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 no.
`
`09/250,962, where the stiffness of a dental appliance shell may change over time by
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`PCT/US01/13217
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`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 no. 09/250,962, the full disclosure of which is incorporated herein by
`
`reference.
`
`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.
`
`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.
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`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 check 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.
`
`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,
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`while the harder inner layer firmly engages the teeth to provide a better grip or anchor
`
`upon the teeth.
`
`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.
`
`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
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`invention may be comprised of appliances having stiffness varying within the appliance
`
`and/or from one appliance to the next in the series.
`
`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.
`
`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.
`
`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
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`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.
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`For example, an appliance may be produced with a tooth arrangement which is
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`substantially misaligned from the initial arrangement. High modulus appliances may not
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`be flexible enough to allow the appliance to fit over the teeth in the initial arrangement.
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`However, a series of appliances of the same shape may be produced with increasing
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`elastic moduluses from relatively low to adequately high. The patient may begin with the
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`lowest’elastic modulus appliance which may be the most flexible to fit over the teeth. As
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`the teeth are repositioned, the patient may successively utilize each appliance in
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`increasing modulus until the teeth have conformed to the successive tooth arrangement.
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`At that time, the patient may begin a new series of appliances with varying moduluses
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`and a shape to reposition the teeth to the arrangement of the next step in the repositioning
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`progression. The ability to reduce the number of different appliance geometries required
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`for a single course of treatment can provide a significant reduction in planning effort and
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`manufacturing costs.
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`In a fourth aspect of the present invention, the elastic modulus of an
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`appliance or portions of an appliance may be modified in a number of different ways. To
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`begin with, the elastic modulus may be determined by the choice of materials. For
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`example, metals will generally have a higher elastic modulus than polymers due to atomic
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`structure. For example, the modulus values for metals may range between 48 and 414
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`GPa , whereas the modulus for polymers may range from 0.5 to 35 GPa. Thus, it will be
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`possible to form appliances having moduluses which differ greatly by forming different
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`portions from metal(s) and polymer(s), or by forming successive appliances from metals
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`and polymers. Usually, however, the appliances will comprise or consist of a polymeric
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`shell fonned from a single polymer, multiple polymers, copolymers, and the like,
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`typically by thermoforming and/or lamination. Stiffness of a polymer may be varied
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`within a range (typically 0.5 GPa to 5 GPa) by changing the molecular structure of the
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`polymer chains. Polymer chains with hindered side—chains are unable to pack as closely
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`as those with smaller side-chains. Thus, such a polymer may have more intermolecular
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`motion and therefore a lower bulk elastic modulus. Stiffness can also be changed by
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`controlling the degree of cross-linking as well as the cross—linking entity within a polymer
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`or copolymer. Further, alternatively, differing elastic moduluses may be created within
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`the same polymer shell by layering or laminating the same or different polymers. Two
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`layers of a polymer material bonded together to form an integral appliance, i.e., an
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`appliance having a monolithic shell structure where the layers are resistant to
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`delamination, may have a higher elastic modulus than a single layer of such material.
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`Thirdly, different elastic moduluses may be created with a single layer of one type of
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`polymer material by production methods, such as coating, treating with various chemical
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`agents, and altering the temperature, to name a few.
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`Further, different elastic moduluses may be produced by forming
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`selectively reinforced and/or composite-type materials. For example, a polymer material
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`may be reinforced with structures such as strips, wires, pieces, mesh, lattices, networks,
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`and the like. These structures may be comprised of any suitable material, particularly
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`metals and alloys but also including polymer filaments, wires, braids, and the like.
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`Likewise, composite materials may be comprised of interpenetrating polymeric networks.
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`An interpenetrating polymeric network is comprised of a base material and an additional
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`material that interpenetrates the base material to alter its mechanical properties. For
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`example, the base material (A) may be a solid polycarbonate. The added material (B)
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`may be a liquid polymer, monomer or crosslinking agent which is allowed to
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`interpenetrate and activate to form a composite network. The composite (A+B) may have
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`a stiffiiess which is greater than the sum of its parts, (A) and (B). Further, another
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`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
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`sum of its parts, (A), (B) and (C). With this method, any number of composites may be
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`formed providing a wide range of mechanical properties, specifically stiffnesses. In
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`addition, a number of these production methods may provide materials with gradual
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`changes in elastic moduluses. For example, purposely irregular coating of a polymer
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`material may provide higher stiffness in areas with thicker coating and lower stiffness in
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`areas with thinner coating. This may be applied to a number of production methods.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`-
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`Fig. l is a perspective illustration of an embodiment of an appliance of the
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`present invention and descriptive axes.
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`Fig. 2 illustrates an embodiment of an appliance with relatively large
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`portions varying in elastic modulus along a mesial—distal axis.
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`Fig. 3 illustrates an embodiment of an appliance with smaller portions
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`varying in elastic modulus in a non-symmetric pattern along a mesial-distal axis.
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`Fig. 4 illustrates an embodiment of an appliance varying in elastic modulus
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`along a mesial—distal axis in which portions covering proximal or interproximal spaces are
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`of differing modulus.
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`Fig. 5 illustrates a variety of appliance portions varying in elastic modulus
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`along a mesial-distal axis.
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`Fig. 6 is a perspective illustration of an embodiment of an appliance
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`varying in elastic modulus along a facial-lingual axis.
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`Fig. 7 illustrates a variety of appliance portions varying in elastic modulus
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`along a facial—lingual axis.
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`Fig. 8 is a perspective illustration of an embodiment of an appliance
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`varying in elastic modulus along a gingival-crown axis.
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`Fig. 9 illustrates a variety of appliance portions varying in elastic modulus
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`along a gingival-crown axis.
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`Fig. 10 illustrates a variety of appliance portions varying in elastic
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`modulus along one or more described axes.
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`Fig. 11 depicts a series of