Elastically modifiable orthodontic appliances

Abstract

Orthodontic appliances have a temporary flexural modulus that decreases when subjected to environmental conditions such as heat. As the flexural modulus decreases, the appliance becomes more flexible and therefore less initially uncomfortable. As the appliance is worn, it cools, gradually increasing the flexural modulus and applying greater orthodontic forces to the teeth.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 62 / 863,770, filed June 19, 2019, which is incorporated herein by reference. This application is related to U.S. Patent No. 16,775,202, filed January 28, 2020, which is incorporated herein by reference. [Background technology]

[0002] The subject matter of this disclosure relates generally to the field of orthodontic appliances. More particularly, this disclosure relates to user-removable orthodontic appliances.

[0003] The goal of orthodontics is to move a patient's teeth to positions that optimize function and / or esthetics. Traditionally, appliances such as braces are applied to a patient's teeth by the treating physician, with the set of braces exerting a continuous force on the teeth, gradually urging them toward their intended positions. Over time, with a series of clinical visits and reactive adjustments to the braces by the practitioner, the braces move the teeth toward their final destination.

[0004] More recently, alternatives to traditional orthodontic treatment using traditional fixed appliances (e.g., braces) have become available. For example, a system comprising a series of molded plastic aligners is commercially available from Align Technology, Inc. of San Jose, California, under the trade name Invisalign® System. The Invisalign® System is described in numerous patents and patent applications assigned to Align Technology, Inc., including, for example, U.S. Pat. No. 6,450,807 and U.S. Pat. No. 5,975,893.

[0005] The Invisalign® system typically involves designing and fabricating multiple aligners to be worn by the patient before they are administered and used to reposition the teeth (e.g., at the beginning of treatment). Often, designing and planning customized treatment for a patient utilizes computer-based three-dimensional planning / design tools. Aligner design relies on computer modeling of the patient's teeth in a series of planned sequential tooth positions, with individual aligners designed to be worn over the teeth such that each aligner exerts a force on the teeth, elastically repositioning the teeth into each of the planned tooth positions.

[0006] Perhaps these aligners are less noticeable than traditional braces because they are typically constructed of transparent materials, though many believe the sheen of the transparent material makes them easily noticeable. Like traditional braces, aligners must be worn nearly constantly (20–22 hours per day), with breaks allowed for eating and cleaning. Based on the aligner's physical and material properties, aligners are not flexible enough to accommodate tooth drift out of alignment, so only small breaks are permitted. Increasing the working tolerance to accommodate greater drift requires increasing the aligner's working elasticity—that is, the amount the aligner can stretch to fit the teeth without causing permanent deformation. However, high-elasticity aligners typically do not provide sufficient force to move the teeth required for orthodontic treatment. These issues can lead to patients being unable to wear the aligners according to prescribed requirements, resulting in failed results or the need to restart treatment. Summary of the Invention

[0007] Embodiments of the present invention relate to orthodontic appliances, systems, and methods of use, as summarized in the following paragraphs. Some embodiments relate to orthodontic appliances that can be modified by exposure to one or more environmental conditions.

[0008] Some embodiments relate to an orthodontic appliance. The orthodontic appliance can have a working flexural modulus configured to therapeutically move teeth. The orthodontic appliance can include a material configured to have a temporary flexural modulus that is reduced from the working flexural modulus when the orthodontic appliance is exposed to environmental conditions.

[0009] Some embodiments relate to orthodontic appliances that can have shells shaped to receive teeth. The shells can be stackable and can include at least one of a fixed shell and a variable shell. The variable shell can be configured to have a significant decrease in modulus of elasticity upon exposure to environmental conditions. The fixed shell can be configured to not have a significant decrease in modulus of elasticity upon exposure to environmental conditions.

[0010] Some embodiments relate to an orthodontic appliance that can have shells shaped to receive teeth. The shells can be stackable and can include at least one of a fixed shell and a variable shell. The variable shell can be configured to plastically soften when the shell is heated, and the anchor shell is configured to reshape the variable shell to a pre-softened state after heating of the shell ceases.

[0011] Some embodiments relate to orthodontic appliances that can have shells shaped to receive teeth. The shells can be stackable and can include at least one of a fixed shell and a variable shell. The variable shell can be configured to significantly increase flexibility from exposure to environmental conditions. The fixed shell can be configured to provide structural form to the variable shell after cessation of effect.

[0012] Some embodiments relate to an orthodontic appliance having an anchor shell that can be formed from a first polymeric material having a first glass transition temperature. The orthodontic appliance can include a deformable shell molded to stack with the anchor shell. The second shell can be formed from a second polymeric material having a second glass transition temperature. The second polymeric material can transition to a substantially liquid state at a temperature at which the first polymeric material remains substantially solid.

[0013] In some embodiments, the first polymeric material comprises a polycarbonate material and the second polymeric material comprises a polyurethane material.

[0014] Some embodiments relate to methods in which any one of the above orthodontic appliances is obtained and exposed to environmental conditions to reduce the flexural modulus of the orthodontic appliance.

[0015] In some embodiments, the environmental conditions warm the orthodontic appliance. In some embodiments, the appliance is heated to between 60 and 100°C.

[0016] In some embodiments, the surface of the orthodontic appliance can be heated to below 45° C. and then cooled to prevent burns.

[0017] For a better understanding of at least some embodiments, reference is made to the following detailed description, which should be read in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view of a jaw and an orthodontic appliance, according to some embodiments. [Figure 2] FIG. 1 is an exploded view of an orthodontic appliance, according to some embodiments. [Figure 3] 1 is a connection schematic diagram for orthodontic appliances, according to some embodiments. [Figure 4A]1 is a graph illustrating physical properties of various orthodontic appliance materials, according to some embodiments. [Figure 4B] 1 is a graph illustrating physical properties of various orthodontic appliance materials, according to some embodiments. [Figure 4C] 1 is a graph illustrating physical properties of various orthodontic appliance materials, according to some embodiments. [Figure 5] 1A-1C are perspective views of a process for shaping orthodontic appliances, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0019] The drawings depict various embodiments of the present invention for purposes of illustration only, and the drawings use like reference numerals to identify like elements. Those skilled in the art will readily recognize from the following discussion that alternative examples of the structures and methods shown in the drawings may be used without departing from the principles of the present invention described herein.

[0020] Disclosed herein are embodiments of orthodontic appliances constructed from multiple shells for the purpose of maximizing working elasticity, defined as the appliance's ability to elastically deform to accommodate initial tooth positions. This flexibility may allow the appliance to achieve a wider range of initial tooth alignment (i.e., flexion) positions that differ from the appliance's target tooth alignment (i.e., rest) position. Potential advantages include longer rest periods (e.g., 8-12 hours) between required wear periods and greater tolerance for patient non-compliance with the required wear time, thus increasing effectiveness. This flexibility may be temporarily increased by exposing the orthodontic appliance to one or more environmental conditions (e.g., heat).

[0021] Before describing the present invention in more detail, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. Moreover, the scope of the present invention will be limited only by the appended claims, and the terminology used herein has the purpose of describing particular embodiments only, and is not intended to be limiting.

[0022] Where a range of values ​​is provided, unless the context clearly dictates otherwise, it is understood that each intervening value, such as one-tenth of the unit of the lower limit, between the upper and lower limits of the range, and any other stated or intervening value within the stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0023] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative exemplary methods and materials are described herein.

[0024] It should be noted that when used in this application or the accompanying patent specification, the singular forms "a," "an," and "the" include plural referents unless the context dictates otherwise. It should be further noted that the claims are drafted to exclude any optional elements. Accordingly, this statement is intended to serve as a prerequisite for using exclusive terminology such as "solely," "only," and the like, or for using a "negative" limitation in connection with the recitation of claim elements.

[0025] As will be apparent to those skilled in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has individual components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the invention. Any recited method may be carried out in the order of events recited or in any other order which is logically possible.

[0026] FIG. 1 provides a suitable starting point for a detailed description of various embodiments of the present invention relating to a tooth repositioning appliance designed to apply a repositioning force to teeth. An orthodontic appliance 10 can be worn by a patient to achieve incremental repositioning of individual teeth within a jaw 12. The orthodontic appliance 10 can include a shell having tooth-receiving cavities that receive and resiliently reposition the teeth. In some embodiments, a polymeric appliance can be formed from a sheet of appropriate layers of polymeric material. The appliance can fit all or fewer than all of the teeth present in the upper or lower jaw.

[0027] In some embodiments, only certain teeth received by the appliance are repositioned by the appliance, while other teeth can provide base or anchor areas to hold the appliance in place as it applies force against the tooth or teeth targeted for repositioning. In some cases, many, most, or even all teeth will be repositioned at some point during treatment. The teeth being moved can also serve as bases or anchors to hold the appliance when it is worn by the patient. Typically, no wires or other means are provided to hold the appliance in place on the teeth. However, in some cases, it may be desirable or necessary to provide individual anchors on the teeth with receptacles or openings corresponding to the appliances so that the appliances can apply selected forces to the teeth. The basic method for determining an orthodontic treatment plan using a series of incremental appliances and instructions for shaping orthodontic appliances is described in U.S. Pat. No. 6,450,807 and U.S. Pat. No. 5,975,893, which are incorporated herein by reference, but only to the extent that these patents do not contradict the more recent teachings disclosed herein.

[0028] An appliance can be designed and / or provided as part of a set of multiple appliances. In such embodiments, each appliance may be configured so that the tooth-receiving cavities have a geometry corresponding to the intermediate or final tooth arrangement intended for the appliance. The patient's teeth can be progressively repositioned from an initial tooth arrangement to a target tooth arrangement by placing a series of incremental positioning appliances on the patient's teeth. The target tooth arrangement can be a planned final tooth arrangement selected for the patient's teeth at the end of all planned orthodontic treatment. Alternatively, the target arrangement can be one of many intermediate arrangements for the patient's teeth during the course of orthodontic treatment. It is therefore understood that the target tooth arrangement can be any planned resulting arrangement for the patient's teeth, following one or more incremental repositioning steps. Similarly, the initial tooth arrangement can be any initial arrangement for the patient's teeth, followed by one or more incremental repositioning steps.

[0029] Orthodontic appliances can all be produced at the same stage, or in sets or batches, e.g., at the beginning of a stage of treatment, with the patient wearing each appliance until pressure from each appliance on the teeth is no longer felt or until the maximum amount of expressive tooth movement has occurred for that given stage. A number of different appliances (e.g., a set) can even be designed and manufactured before the patient wears any of the appliances. After wearing an appliance for an appropriate period of time, the patient replaces the current appliance with the next appliance in the series until no appliances remain. Orthodontic appliances are generally not fixed to the teeth, and the patient can place and replace appliances (e.g., patient-removable appliances) at any time during treatment.

[0030] Such overcorrection may be desirable to offset potential relapse after the repositioning method is completed, i.e., to allow individual teeth to move back toward their pre-corrected positions. Such overcorrection may have a geometry selected to overcorrect the tooth arrangement, i.e., to have a geometry that (if fully achieved) will move the individual teeth beyond the tooth arrangement selected as "final." Overcorrection may also be beneficial for accelerating the rate of correction; i.e., by having appliances with a geometry that is positioned beyond the desired intermediate or final position, the individual teeth are shifted toward position at a faster rate. In such cases, the use of the appliances may be terminated before the teeth reach the positions defined by the appliances.

[0031] FIG. 2 shows an exploded view of one example of an orthodontic appliance 10. The orthodontic appliance 10 may include a first shell 14 having a tooth-engaging surface and an opposing upper surface. The orthodontic appliance 10 may also include a second shell 16 having a lower shell-engaging surface and an opposing upper surface that is exposed to the mouth. Optionally, one or more additional shells 18 may be positioned between the first shell 14 and the second shell 16. In some embodiments, the more shells used, the greater the working resilience of the orthodontic appliance 10.

[0032] Although the orthodontic appliance 10 is shown in an exploded view for better understanding, in some embodiments the shells are layers of laminate material, i.e., the shells are bonded together during the formation (e.g., extrusion) of the laminate material.

[0033] In some embodiments, it is intended that the shells of the orthodontic appliance 10 be stacked and mechanically engaged with one another. "Mechanically engaged" is defined herein as a substantially unsecured or variably secured engagement between one or more shells to approximate the strength of a single-shell appliance of approximately the same thickness as the stacked shells. The mechanical engagement can be achieved by stacking the shells, with the lower shell-engaging surface of the second shell largely conforming to the upper surface of the first shell. In some embodiments, prior to being substantially unsecured or variably secured, the shells can be stacked loosely, i.e., without a compression or interference fit between the shells, or such that the elevated stacked shells self-dissolve. The shells are substantially unsecured (or variably secured) because a significant amount of the surface area between the shells is not bonded or otherwise rendered inseparable by some process, and the remaining surfaces are secured. In some embodiments, the substantially unsecured or variably secured shell has less than 1-2%, 1-5%, 1-10%, 1-20%, 1-40%, 1-60%, or 1-80% of the bond contact surface of the secured shell. The unsecured area can be limited depending on the needs of the device, thus in some embodiments the majority of the surface area of ​​the device is secured, with the remaining portion being unsecured since only the latter requires high working resilience.

[0034] In some embodiments, the lack of substantial fixation between the shells allows the outer shell to flex in multiple directions away from the tooth-engaging shell, while the tooth-engaging shell, being thinner, allows it to flex more, providing greater working resilience to the orthodontic appliance 10. In some embodiments, this can result in partial mechanical disengagement between some of the engaging surfaces of the shells, but this disengagement is not sufficient to significantly impair the flexural modulus of the device needed to align the teeth in the target positions.

[0035] Figure 3 shows a schematic diagram for attaching the shells of the orthodontic appliance 10 to separate locations. Each circled "X" represents a possible anchoring point between the shells. Alternatively, as indicated by the dashed lines, the edges of each shell can serve as continuous or discontinuous anchoring areas. Generally, the more anchoring provided, the less working elasticity the orthodontic appliance 10 will have. The anchoring points can be determined based on the amount of working elasticity required, which teeth are being moved, and which teeth are acting as anchors. Alternatively, the shells can be uniformly and weakly bonded with a highly elastic material that has low cohesive strength, allowing for a large amount of stretch and / or shear. Such an embodiment can be substantially unbonded or variably bonded, since the working flexibility of such an orthodontic appliance is maintained due to the weak bond characteristics.

[0036] In some embodiments, the shell can have a thickness ranging from 0.001 to 0.015 inches and can be constructed from polyester, copolyester, polycarbonate, polyurethane (PU), thermoplastic polyurethane (TPU), polypropylene, polyethylene, polypropylene and polyethylene copolymers, acrylic, cyclic block copolymers, polyetheretherketone, polyamide, polyethylene terephthalate, polybutylene terephthalate, polyetherimide, polyethersulfone, polytrimethylene terephthalate, or combinations thereof. In some embodiments, the shell is coated with a lubricious material or has a surface treatment to reduce friction between the shells. In some embodiments, the interior of the shell is treated with a hydrophobic coating to prevent liquid from entering the shell. In some embodiments, a relatively flexible shell can be used in combination with a more rigid shell. The flexible shell can be constructed from hydrogel, styrenic block copolymer (SBC), silicone rubber, elastomeric alloy, thermoplastic elastomer (TPE), thermoplastic vulcanizate (TPV) elastomer, polyurethane elastomer, block copolymer elastomer, polyolefin blend elastomer, thermoplastic copolyester elastomer, thermoplastic polyamide elastomer, or combinations thereof. Flexible shells can also offer the benefit of a gasket to prevent liquid intrusion between the shells.

[0037] In some embodiments, the shell of an orthodontic appliance can be formed from a material that provides a reduced modulus of elasticity in one or more aspects of the appliance, which can reduce the overall flexural modulus of the appliance. When the orthodontic appliance is used in a patient's mouth, it has a working flexural modulus sufficient to function as an aligner, i.e., to therapeutically move teeth. However, when the orthodontic appliance is exposed to certain environmental conditions, such as physical, chemical, or biological stimuli or a combination of environmental conditions, one or more portions of the appliance can respond with a temporary or permanent physical change (e.g., increased elasticity), resulting in the orthodontic appliance having a temporary flexural modulus. Some of these environmental conditions can include increased / decreased energy exposure (e.g., due to temperature changes, electromagnetic exposure (e.g., UV, infrared), magnetization, applied current and / or voltage), chemical exposure (e.g., due to increased / decreased pH, reduction-oxidation reactions, solvent exposure), and / or reaction with biological agents (e.g., exposure to glucose, exposure to enzymes).

[0038] The temporary flexural modulus can be reduced from the working flexural modulus, for example, by 2-15% of the flexural modulus, and in some embodiments, by 2-5%, 4-8%, 7-12%, or 11-15%. Cessation of the particular environmental condition, i.e., removal and / or reversal of the stimulus, can cause the orthodontic appliance to resume its previous therapeutic tooth alignment configuration with a working flexural modulus.

[0039] To provide a memory effect after the cessation of environmental conditions, the orthodontic appliance may include one or more anchor shells in addition to one or more variable shells. The variable shells can be configured to respond to environmental conditions, and the anchor shells can be configured to not respond (or to only a very small extent) to environmental conditions. In this way, the anchor shells can provide a memory mold for the variable shells, for example, when the variable shells lose their shape memory when the anchor shells are heated to their glass transition temperature or exposed to reactive solvents or biological agents. In other words, the anchor shells provide a mold for reshaping the variable shells when they return to their elastic state.

[0040] In some embodiments, the anchor shell is constructed entirely or predominantly of a material that is substantially unresponsive to triggering environmental conditions. For example, the anchor shell can be formed from polycarbonate, which is resistant to many solvents and biological agents, has a glass transition temperature of approximately 150° C., and can begin to soften at approximately 90° C. In comparison, a mutable shell can be formed from a polymer with different reactive qualities.

[0041] For example, the deformable shell can be formed from a polymeric material, one or both of which have a significantly low glass transition temperature and onset softening temperature below 90° C. Thus, when the deformable shell is exposed to temperatures below 90° C. and at least its onset softening temperature, the flexural modulus of the orthodontic appliance decreases due to softening of the deformable shell.

[0042] In some embodiments, a user (e.g., a patient or caregiver) can apply heat to an appliance having at least one convertible shell and at least one fixed shell, using, for example, hot (e.g., 60-100°C) water, a hair dryer, a microwave, or other common household heating appliances, to induce a change in state that softens the convertible shell. In some embodiments, the user can briefly cool the exterior surface of the appliance (e.g., using running water or an ice-water plunge) to prevent burns (e.g., so that the surface is below 45°C) while retaining sufficient heat within the convertible shell to provide the desired effect. The user can then apply the appliance to the teeth while the convertible shell is in its rubbery state. At this point, most or all of the force applied to the teeth is provided by the anchor shell, and such force may not be sufficient to induce the desired orthodontic treatment. After a period of time in the oral cavity, the convertible shell gradually cools to a harder state, simultaneously increasing the force applied to the teeth along with the fixed shell to induce the level of force required for orthodontic treatment. The gradual application of force may reduce pain from the brace, at least until the patient begins to experience it, and therefore may improve compliance with the brace.

[0043] In some embodiments, the transformable shell is formed from a thermoplastic polyurethane (TPU), such as ISOPLAST 2530, which has a glass transition temperature of about 77° C. and can begin to soften at about 40° C. In one example, an orthodontic appliance is formed from a TPU transformable shell and a polycarbonate retaining shell. In another example, an orthodontic appliance is formed from a TPU transformable shell and a polyurethane retaining shell.

[0044] In some embodiments, the orthodontic appliance includes a modifiable shell and an anchor shell, with the modifiable shell positioned between two or more anchor shells. This configuration can be advantageous in heating methods that require some cooling (e.g., using cold tap water or ice water) to bring the appliance to the appropriate transition temperature to affect the modifiable shell before placing the appliance in the oral cavity, but to avoid burns. Thus, in such a configuration, the fixed shell provides insulation to retain heat within the modifiable shell, allowing it to cool to a safe temperature.

[0045] Figure 4A shows a graph of dynamic mechanical analysis data (modulus vs. temperature) for both TPU and polycarbonate. The graph visually illustrates the different behavior of the two materials with respect to melt temperature, where the TPU melts well before the polycarbonate softens significantly. Figure 4B shows a graph of dynamic mechanical analysis data (modulus vs. temperature) for a TPU and polycarbonate laminate structure. Each material has a different effect on the physical properties of the laminate. At temperatures above 70°C, the modulus decreases by approximately 25%.

[0046] Generally, the grade of polymer selected for the shell controls the rate of change in flexural modulus. Conventional materials for variable shells, for example, soften / melt according to a second-order transition, i.e., over a wide temperature range typical of polymers. However, it is possible to use chain-crystallizable polymers with a sharp melting transition, such as first-order transition materials like pentadecyl acrylate. In some embodiments, such a primary polymer can be added to the secondary polymer at 10-20 wt%. Thus, if the melting temperature of the primary polymer is reached, it can disrupt the combined structure and cause a significant drop in flexural modulus. In such instances, using a single shell may be feasible for orthodontic appliances. Additive blends of different secondary polymers can also be used, such as a blend of polyurethane and nylon. Figure 4C shows modulus vs. temperature graphs for nylon (top curve) and polyurethane (bottom curve). The blend of materials is represented by the middle curve, which shows how the addition of polyurethane can initiate softening of the blended material at a much lower temperature than nylon alone.

[0047] In some embodiments, polymers can be doped with specific materials to aid in inducing environmental conditions. For example, if a relatively high melting temperature (e.g., 100°C) is desired to induce a mutable shell, the polymer can be placed in boiling water, but this heating method can be dangerous to the patient, and waiting for the polymer to cool to a safe temperature before inserting the appliance into the patient's mouth can circumvent the desired flexural modulus. However, doping the polymer with microwave-absorbing or -reflecting materials (e.g., nanoparticles or microparticles composed of metals, hydrogels, or ceramics) can be useful for directly heating the mutable shell without heating the entire appliance. Exposing the appliance to microwaves can induce a localized heating effect directly in the mutable portion due to microwave-absorbing particles (or electron-emitting, in the case of metal particles), which can then be covered by one or more anchor shells (which can be formed from non-microwave-absorbing polymers) to insulate the patient from the heated mutable shell. In this way, the use of polymeric materials with relatively high melting temperatures (i.e., unsafe for direct handling) can be achieved without requiring the use of unsafe heating conditions.

[0048] As mentioned above, the mutable shell is not limited to materials where the specific environmental condition that triggers the modulus change is heat. For example, the collisional properties of sodium chloride in water and the upper critical solution concentration of an ionic polymer, such as dimethylaminoethyl acrylate (DMAEA), can be used. That is, at a specific osmolality or sodium chloride concentration, the DMAEA polymer completely reverses its polarity from hydrophobic to hydrophilic, or vice versa. Another example is a polymer material with a photo-triggerable liquid crystal-liquid crystal transition.

[0049] The benefits of orthodontic appliances with environmentally induced temporary flexural modulus include the general benefits of highly flexible orthodontic appliances, but to an even greater extent. For example, by immersing the orthodontic appliance in warm water before insertion or swishing warm water in the patient's mouth before removal, the patient can be exposed to specific environmental effects that induce the temporary flexural modulus, resulting in less pain and discomfort for the patient. This provides easier insertion and removal, and reduces discomfort during initial insertion. In this way, orthodontic appliances can be designed to provide a higher level of attachment by taking the temporary flexural modulus into account during removal. Refinement of addressing cases (through stress relaxation) can also occur in the same manner, for example, by placing the orthodontic appliance in very hot water to restore its initial formation. In cases of mild relapse, orthodontic appliances can be used with four-week aligners with multiple stages of exercise programmed into a single appliance. This can be achieved by instructing the patient to place the aligners in warm water for the first two weeks of treatment before use.

[0050] FIG. 5 illustrates an example of a basic process 30 for forming an orthodontic appliance. As shown, material 32 can be formed into an orthodontic appliance 36. The material 32 can be one layer to form a single shell, or multiple, non-adherent layers of material to form multiple shells at once. In this exemplary process, a tooth positioning appliance 36 can be fabricated using a physical tooth model or mold 34. The tooth positioning appliance 36 can be fabricated by heating a thermoformable material 32 and then vacuum or pressure forming the material over the teeth of the physical tooth model 34. The tooth positioning appliance 36 is a direct representation of the physical tooth model.

[0051] Once formed, the shells can be secured together according to the desired working elasticity required for the patient. Securement methods include chemical bonding, localized melting, fasteners, and / or localized physical deformation to lock the shells together. Before or after securement, excess material from the sheet can be trimmed to form the final tooth positioning appliance that can be used in the patient's orthodontic treatment. The edges of the shells can be sealed with a flexible material, such as silicone, to prevent liquid ingress.

[0052] One or a series of physical tooth models, such as those described above, can be used to create elastic repositioning appliances for orthodontic treatment. Similar to the process described above, each appliance can be created by thermoforming a multilayer polymeric material onto a mold of the desired tooth configuration to form the dental appliance. The tooth positioning appliance for the desired tooth configuration generally matches the patient's teeth but is slightly offset from the initial tooth configuration. When elastic positioners are placed on the teeth, they apply controlled forces at specific locations, gradually moving the teeth to the desired shape. Repeating this process with successive appliances containing new configurations ultimately moves the teeth through a series of intermediate configurations to the final desired configuration.

[0053] Throughout the foregoing description, and for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the described techniques. However, it will be apparent to those skilled in the art that these techniques may be practiced without some of these specific details. While various embodiments incorporating these teachings have been shown and described in detail, those skilled in the art can readily devise many other different embodiments or mechanisms to incorporate these techniques. Also, embodiments may include different, fewer, or more operations or sequences of operations as described above. The scope and spirit of the present invention should therefore be determined in terms of the following claims and their legal equivalents.

Claims

1. 1. An orthodontic appliance comprising a shell stack shaped to receive teeth, the shell stack being a stack of a plurality of shells, the plurality of shells including an anchor shell and a displaceable shell, the shells having some free surfaces between them, the deformable shell is configured to plastically soften and have a significantly reduced modulus of elasticity upon exposure to environmental conditions, and the anchor shell is configured to have a modulus of elasticity that does not significantly decrease upon exposure to the environmental conditions; the exposure to environmental conditions is heating the shell laminate outside the oral cavity; the anchor shell comprises a first polymeric material having a first glass transition temperature; the changeable shell comprises a second polymeric material having a second glass transition temperature; when the shell laminate is exposed to the environmental conditions, the second polymeric material transitions to a liquid state at a temperature at which the first polymeric material is in a solid state; the first polymeric material is a polycarbonate material and the second polymeric material is a thermoplastic polyurethane material; The second glass transition temperature of the thermoplastic polyurethane material is less than 90° C., and the softening onset temperature of the thermoplastic polyurethane material is 40° C. or higher and less than 90° C. Orthodontic appliances.

2. the anchor shell is configured to provide a structural form to the deformable shell to reshape the deformable shell to its pre-softened condition after exposure of the deformable shell to the environmental conditions ceases.

10. The orthodontic appliance of claim 1.

3. the shell laminate has a working flexural modulus configured to therapeutically move teeth; The second polymeric material of the deformable shell is adapted to allow the orthodontic appliance to adapt to the environmental conditions. configured to have a temporary flexural modulus lower than the working flexural modulus when exposed to 10. The orthodontic appliance of claim 1.

4. obtaining an orthodontic appliance comprising a shell stack shaped to receive teeth, the shell stack being a stack of a plurality of shells, the plurality of shells including an anchor shell and a deformable shell, the deformable shell configured to plastically soften and have a significant decrease in elastic modulus upon exposure to environmental conditions, the anchor shell configured not to have a significant decrease in elastic modulus upon exposure to the environmental conditions, and a portion of the surfaces between the shells being unfixed; exposing the orthodontic appliance to the environmental conditions extra-orally prior to placement in the oral cavity to reduce the flexural modulus of the orthodontic appliance; the anchor shell comprises a first polymeric material having a first glass transition temperature; the changeable shell comprises a second polymeric material having a second glass transition temperature; when the shell laminate is exposed to the environmental conditions, the second polymeric material transitions to a liquid state at a temperature at which the first polymeric material is in a solid state; the first polymeric material is a polycarbonate material and the second polymeric material is a thermoplastic polyurethane material; The second glass transition temperature of the thermoplastic polyurethane material is less than 90° C., and the softening onset temperature of the thermoplastic polyurethane material is 40° C. or higher and less than 90° C. method.

5. 5. The method of claim 4, wherein exposing the orthodontic appliance to environmental conditions comprises warming the orthodontic appliance to a temperature between 60-100 degrees Celsius.

6. 6. The method of claim 5, further comprising cooling a surface of the orthodontic appliance to less than 45°C after warming the appliance and prior to placing the appliance in the oral cavity.

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