Bivalve dental appliance and material constructions

Abstract

A reversibly deformable dental device formed from a 3-layer polymer film material consisting of two rigid outer layers A and C and an inner elastomeric layer B, wherein the elastomeric middle layer and the outer layers can move reversibly relative to each other and have a lateral restoring force of less than 100 N per cm 2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 when shifted by 0.05 mm to 0.1 mm relative to each other.

Description

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US Provisional Application No. 62 / 512,786, filed on May 31, 2017, and US Provisional Application No. 62 / 590,627, filed on November 26, 2017, both of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0002] Compositions in the form of polymer films are disclosed. The polymer films are usable, for example, in a dental device and are constructed from layers that impart flexibility, strength, and stain resistance to devices made from the films. BACKGROUND

[0003] There is a need for improved orthodontic and dental appliances with the ability to facilitate orthodontic tooth movement, stabilize tooth positions, or protect teeth from potentially damaging external forces. Existing materials and products are constructed of single-layer, double-layer, or triple-layer materials, which have limited functionality and may suffer from performance deficiencies. Splints are plastic shells that fit over teeth and are designed to exert translational or rotational forces on teeth. Their ability to accurately move teeth is limited by their effective modulus, elasticity, and ability to resist creep and stress relaxation. Furthermore, they should generally be resistant to discoloration and cracking due to environmental stress.

[0004] Dental protection devices, such as sports mouthguards, and mouth guards have conflicting requirements. On the one hand, they should be able to dissipate impact forces, and on the other, they should be thin and not interfere with the natural occlusion of a person's teeth or their speech. SUMMARY

[0005] In one aspect, a composition formed from at least two outer layers A and C and a middle layer B is provided. The A and C layers each comprise a thermoplastic polymer having a modulus of about 1,000 MPa to 2,500 MPa and a glass transition temperature and / or a melting point of about 80°C to 180°C, while the middle B layer is formed from at least one elastomer having a modulus of about 50 MPa to about 500 MPa and one or more of a glass transition temperature and / or a melting point of about 90°C to about 220°C.

[0006] In one embodiment, the A and C layers are formed from one or more of a copolyester, a polycarbonate, a polyester-polycarbonate blend, a polyurethane, a polyamide, and a polyolefin.

[0007] In another embodiment, the middle B layer is formed from one or more of a polyurethane elastomer, a polyolefin elastomer, a polyester elastomer, a styrene elastomer, a polyamide elastomer, a cyclic olefin elastomer, an acrylic elastomer, an aromatic or aliphatic polyether, and a polyester polyurethane.

[0008] In yet another embodiment, the material of the middle B layer has a compression set of less than 35%, 30%, 25%, 20% or 10% after 22 hours at 25°C.

[0009] In yet another embodiment, the A and C layers have a lateral restoring force of less than 100 N (Newton) per cm2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 when shifted relative to each other by 0.05 mm to 0.1 mm.

[0010] In another embodiment, the interlayer peel strength between the A and C layers and the B layer is higher than 50 N per 2.5 cm.

[0011] In one embodiment, the combined thickness of the A, B, and C layers is from about 250 micrometers to about 2,000 micrometers, and the combined thickness of the A and C layers is from 25 micrometers to 750 micrometers, from 50 micrometers to 1,000 micrometers, from 100 micrometers to 700 micrometers, from 150 micrometers to 650 micrometers, or from 200 micrometers to 600 micrometers.

[0012] In still further embodiments, one or more of the A and C layers comprise a microcrystalline polyamide formed from from 50 to 100 mol% of C6 to C14 aliphatic diacid units and about 50 to 100 mol% of 4,4'-methylenebis(cyclohexylamine) (CAS [1761-71-3]), having a glass transition of between about 100°C and 180°C, a heat of fusion of less than 20 J / g, and a light transmittance of greater than 80%.

[0013] In a further embodiment, one or more of the A and C layers comprise a copolyester formed from: (a) a dicarboxylic acid component comprising 70 mol% to 100 mol% of terephthalic acid residues and (b) a diol component comprising i) 0 to 95% ethylene glycol, ii) 5 mol% to 50 mol% of 2,2,4,4-tetramethyl-1,3-cyclobutanediol residues, iii) 50 mol% to 95 mol% of 1,4-cyclohexanedimethanol residues and / or iv) 0 to 1% of a polyol having three or more hydroxy groups, wherein the sum of the mol% of diol residues i) and / or ii) and / or iii) and / or iv) is 100 mol% and the copolyester has a glass transition temperature Tg of 80°C to 150 °C.

[0014] In another embodiment, the middle B layer comprises an aromatic polyether polyurethane having a Shore hardness of about A90 to D55 and a compression set of less than 35%, wherein the interlayer peel strength between the A and C layers and the B layer is higher than 50 N per 2.5 cm.

[0015] In one embodiment, one or more of the A and C layers comprise a polyurethane formed from (a) a diisocyanate comprising 80 mol% to 100 mol% methylenediphenyl diisocyanate residues and / or hydrogenated methylenediphenyl diisocyanate, and (b) a diol component comprising i) 0 to 100 mol% hexamethylenediol and ii) 0 to 50 mol% 1,4-cyclohexanedimethanol, wherein the sum of i) and ii) is more than 90 mol% and the polyurethane has a glass transition temperature Tg of about 85°C to about 150°C.

[0016] In another aspect, a dental device conforming to one or more teeth made from a composition or polymer film as described herein.

[0017] In one embodiment of the dental device, the combined thickness of the A, B, and C layers is from about 250 micrometers to about 2,000 micrometers, and the combined thickness of the A and C layers is from 25 micrometers to 750 micrometers, from 50 micrometers to 1,000 micrometers, from 100 micrometers to 700 micrometers, from 150 micrometers to 650 micrometers, or from 200 micrometers to about 600 micrometers.

[0018] In a further aspect, there is provided a reversibly deformable dental device formed from a composition or polymeric film material as described herein, wherein the elastomeric middle layer and the outer layers are capable of reversible movement relative to one another and exhibit a lateral restoring force of less than 100 N per cm 2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 when shifted by 0.05 mm to 0.1 mm relative to each other.

[0019] In one embodiment, the elastomeric middle layer comprises a polyurethane having a hardness of about A 80 to D 75, A 85 to D 65, or A 90 to D 55.

[0020] In another aspect, there is provided an environmental stress resistant composition, polymer film, or dental device formed from at least two outer layers and an elastomeric inner layer, wherein one or more of the outer layers is a polyester or co-polyester having a modulus of about 1,000 MPa to 2,500 MPa and the inner layer comprises an elastomer having a modulus of about 50 MPa to about 500 MPa, wherein the interlayer peel strength between at least one outer layer and the elastomer is greater than 50 N / inch.

[0021] In another aspect, a reversibly deformable dental device is provided, wherein the thickness of the outer A layer is from about 175 to about 250 micrometers, the thickness of the outer C layer is from about 175 to about 250 micrometers, and the thickness of the middle B layer is from 300 to 500 micrometers, wherein the combined thickness of the A, B, and C layers is from 850 to 1,000 micrometers. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1A is a schematic representation of a sectional view of a three-layer film of the invention with a simple ABC construction. Layer A and layer C can be the same or different materials, and each layer can be formed from one or more materials, blends, or alloys. Layer B can be a single material, a blend of materials, or alloys. Fig.Figure 1B is a schematic representation of a sectional view of a multilayer film. Each layer A, B, and C may be formed from a single layer or multiple layers, and each layer may be formed from one or more materials or a mixture of materials. Layer A may be formed from more than one layer, for example, layers a and a', layer B may be formed from more than one layer, for example, layers b and b', and layer C may be formed from more than one layer, for example, layers c and c', as in Fig. 1B is shown as an example. Fig. 2A and Fig. 2B are schematic representations of exemplary test specimens for determining displacement ( Fig. 2A) and restoring force (translational movement; Fig.2B) a simple 3-layer film formed from two rigid outer layers and an inner elastomeric layer, where A, B, and C are individual layers of the film. In this example, layers A and C are reversibly displaced relative to each other, and layer B provides a restoring force. In a more specific example, layers A, B, and C may each be about 250 micrometers thick, and layers A, B, and C may be formed from one or more materials and may each comprise one or more layers. Fig. Figure 3A is a graphical representation of displacement / force curves for elastomers with different durometers. The graph shows the restoring force (N / cm 2), created by translational movement of layer A relative to layer C with a middle B layer containing TPU elastomers of varying hardness. The hardness of the elastomer affects displacement and restoring force. A harder thermoplastic urethane (TPU) will generate a greater restoring force but may limit the extent of movement. Fig. Figure 3B is a graphical representation of the restoring force (N / cm 2 ) as a function of time (0 to 48 hours) for a given displacement between an A layer and a C layer with a middle B layer containing TPU elastomers of varying hardness in the B layer. TPU 75A exhibits a low compression set and shows the lowest initial force, but the force decreases very little over time. TPU 75D exhibits a high compression set, and while it shows a much higher initial recovery force, the force decreases rapidly over time. Fig.Figure 4 is a graphical representation of the retained force at 5% strain for different designs when exposed to 37 °C and water for 48 hours.

[0022] It should be noted that the Fig.1-4 are specific examples and are not intended to limit the scope of constructions and tests that may be used. In alternative embodiments, other materials, constructions, and sequences of steps may also be practiced. For example, alternative embodiments may include additional layers, including tie layers, pigments, optical additives, or reinforcing agents, and may be fabricated by any process known in the art, such as cast film extrusion, blown film coextrusion, calendering, lamination, and adhesive bonding. The structures (or polymer films) and devices may, in some embodiments, be fabricated by 3D printing or dip coating. Numerous variations, modifications, and alternative constructions will be apparent to those skilled in the art.

[0023] The description and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense. It is understood that various modifications and changes may be made therein without departing from the broader spirit and scope of the disclosure as set forth in the claims.

[0024] Other variations are within the spirit of the present disclosure. Thus, the disclosed embodiments are susceptible to various modifications and alternative constructions, and certain illustrated embodiments thereof are shown in the drawings and described herein. It should be understood, however, that the disclosure is not intended to be limited to the specific form(s) disclosed; on the contrary, the invention is intended to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the disclosure as defined by the appended claims. DETAILED DESCRIPTION

[0025] Current orthodontic splints have a very limited elastic range (typically 4% to 7%) and exhibit a rapid loss of resilience upon deformation. As a result, appliances may need to be changed frequently, increasing manufacturing costs, preventing teeth from moving as desired, and causing patient discomfort from excessively high initial forces. Attempts to improve the elastic range by providing a thin outer layer of elastomer (typically a polyurethane, as described, for example, in US 9,655,693 B2) can result in a tooth contact surface that is easily deformed, thereby reducing the accuracy of tooth movement and increasing the susceptibility to unsightly staining from common foods, drinks, or cigarettes. US Patent No.No. 6,524,101 describes dental appliances with regions of different elastic moduli and appliances with attached stiffening elements. Non-staining polyurethanes used to manufacture dental appliances, such as Zendura® A, available from Bay Materials, LLC (Fremont, CA), exhibit excellent properties, but are hygroscopic, require thorough drying before thermoforming, can be initially uncomfortable, are difficult to clean, and may not be ideal for some applications.

[0026] Many other polyurethanes must also be dried before thermoforming, which increases the time and cost of the manufacturing process. Aromatic polyesters or co-polyesters can be used to make splints, but they exhibit poor chemical resistance and low impact and tear strength. Splints made from rigid materials, such as polyesters or rigid polyurethanes, have a high modulus, for example, higher than approximately 1,000 or 1,500 MPa, and can exert excessive forces on teeth when deformed, causing discomfort and potential damage to tooth roots. Highly elastomeric polymers, such as thermoplastic polyurethane elastomers (TPU) and styrenic elastomers (such as SBS, SEBS, SIS), have a low modulus (typically less than 100 or 200 MPa), which may be insufficient to move teeth and are easily discolored, thus limiting their suitability for splint manufacturing.

[0027] The present disclosure is based on the discovery that many of the deficiencies of prior art materials and dental devices constructed therefrom can be reduced or eliminated with a film or device having outer layers formed from a material having a modulus of greater than about 1,000 MPa up to 2,500 MPa and an inner elastomeric layer or core formed from elastomeric material or materials having a modulus of about 50 MPa to 500 MPa, which can be stain-free, has a lower cost than rigid polyurethanes, exhibits improved elastic properties, and surprisingly has higher environmental stress crack resistance.

[0028] A polymer film or device may be formed from more than two rigid layers; for example, a third rigid layer may be sandwiched between two or more elastomeric layers. The multi-layer construction provides a bivalve dental appliance that may be configured to move teeth, retain teeth in existing positions, or protect teeth from impact. As disclosed herein, the outer shell material that contacts the teeth may be substantially rigid to closely fit the teeth to provide precise forces while maintaining the ability to exert a nearly constant force over extended distances.

[0029] By selecting appropriate modulus and thickness of the outer and inner materials, two or more substantially rigid shells can be reversibly translated relative to each other to a greater extent than a rigid material of comparable thickness and shape to provide a dental appliance capable of exerting desired forces on teeth with a greater range of motion while not generating excessive forces or exhibiting excessive stress relaxation upon deformation. Without limiting the disclosure to specific constructions, a sheet or dental appliance may be referred to herein as a "bivalve" sheet or appliance. A "bivalve" sheet or appliance may comprise two or more shells or layers. The shells or layers may have the same or different thicknesses.A series of dental appliances formed with this "bipartisan" construction can be used to move teeth in incremental stages, where two or more appliances may be formed from the same or different materials. Dental appliances may be fabricated by thermoforming a bipartisan material over a model of one or more teeth, or may be fabricated by sequentially thermoforming rigid and elastomeric precursor sheets, or by sequentially dip-coating a model with polymer solutions or polymer-forming monomers or oligomers, which may optionally be cured or otherwise post-processed. The inventors have discovered that this particular construction can substantially reduce the amount of stress cracking exhibited by a shell or materials, thereby expanding the range of materials that can be used in the sheets or appliance. THE DEFINITION

[0030] The use of the terms "a" and "an" and "the" and similar pronouns in the context of describing the disclosed embodiments (particularly in the context of the claims below) are to be interpreted to cover both the singular and the plural, unless otherwise stated herein or clearly dictated by the context. The terms "comprise," "comprise," "include," and "contain" are to be interpreted as open-ended terms (i.e., having the meaning of "including, but not limited to") unless otherwise noted. The term "connected" is to be interpreted as partially or wholly contained within, bound to, or connected together, even if something in between exists. The term "based on" is to be interpreted as open-ended and in no way limiting, and is intended, where appropriate, to be interpreted or read differently than "at least in part based on."The reciting of ranges of values is provided herein merely as a shorthand method of individually identifying each value falling within the range, unless otherwise noted herein, with each value being incorporated into the description as if individually recited herein. All of the methods described herein may be performed in any suitable order unless otherwise noted herein or clearly dictated by the context. The use of any and all examples or exemplary language (e.g., "such as") given herein is intended merely to better illustrate embodiments of the disclosure and does not impose any limitation on the scope of the disclosure unless otherwise noted. No language in the description should be construed to identify any unclaimed element as necessary to practice the disclosure.

[0031] The term "dental appliance" is used herein to refer to any appliance placed in or on a subject's teeth. Dental appliances include, but are not limited to, orthodontic, prosthetic, restraint, snoring / airway, cosmetic, therapeutic, protective (e.g., mouth guards), and habit-modifying appliances.

[0032] The term “ASTM D638” is used herein to refer to the tensile strength testing of plastics.

[0033] The term “ASTM D1364” is used herein to refer to the testing of interlayer peel strength.

[0034] The term “compression set” is used herein to refer to the permanent deformation of a material when a force is applied and removed.

[0035] The term "flexural modulus" is used herein to refer to a material's stiffness and / or resistance to bending deformation. The higher the material's flexural modulus, the more resistant it is to bending. For an isotropic material, the measured elastic modulus is the same in every direction.

[0036] The term "hardness" is used herein in reference to a Shore hardness scale. Shore hardness and modulus are generally correlated and can be converted by approximation if only one value is known.

[0037] The term "modulus" or "tensile modulus" is used herein to refer to the stiffness of a material and / or the material's resistance to stretching. The higher the material's modulus, the stiffer it is. The flexural modulus and tensile modulus of a material can be the same or different. For isotropic materials, such as A, B, and C, the flexural modulus and modulus (which may also be referred to as tensile modulus) are essentially the same, and depending on the circumstances, one or the other may be measured.

[0038] The term “polymer film” is used interchangeably with the term “plastic film” herein.

[0039] The term "lateral restoring force" in connection with the A and C layers of a polymer film refers to the force that can be exerted by a layer that has been displaced relative to another layer that is fixed in position. If the A and C layers are caused to move independently of each other, they will subsequently return to their original positions unless restrained.

[0040] The term "shear force" as used herein means the translational force applied to two surfaces connected by an elastic material.

[0041] The term “tray” is used herein to refer to polymer trays that fit over the teeth and can be removably placed over the teeth.

[0042] The term “discoloration-resistant” is used herein to refer to a material designed to be resistant to discoloration.

[0043] The term "thermoplastic polymer" is used herein to refer to a polymer that becomes pliable or malleable above a specific temperature and solidifies upon cooling, provided that the heat and pressure do not chemically degrade the polymer.

[0044] The terms “tooth” and “teeth” include natural teeth, including natural teeth that have been modified with fillings or crowns, implanted teeth, artificial teeth that are part of a bridge or other structural component attached to one or more natural or implanted teeth, and artificial teeth that are part of a removable structural component.

[0045] In the following description, various embodiments are described. For purposes of explanation, specific configurations and details are described in order to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that the embodiments may be practiced without the specific details. Furthermore, well-known elements may be omitted or simplified in order not to obscure the described embodiment. EMBODIMENTS

[0046] In some embodiments (referred to herein as Embodiment #1), a thermoformable polymer film is formed from at least two outer layers A and C and a middle layer B, wherein the A and C layers are each formed from a thermoplastic polymer having a modulus of greater than about 1,000 MPa, for example, 1,000 MPa to 1,500 MPa; 1,100 MPa to 1,600 MPa; 1,200 MPa to 1,700 MPa; 1,300 MPa to 1,800 MPa; 1,400 MPa to 1,900 MPa; 1,500 MPa to 2,000 MPa; 1,100 MPa; 1,200 MPa; 1,300 MPa; 1,400 MPa; 1,500 MPa; 1,600 MPa; 1,700 MPa; 1,800 MPa, 1,900 MPa; 2,000 MPa; or up to 2,500 MPa; and a glass transition temperature (Tg) and / or a melting point of about 80°C to 180°C; 90°C to 170°C; 100°C to 160°C; 110°C to 150°C; 120°C to 150°C; 130°C to 170°C; 140°C to 180°C; 80°C; 90°C; 100°C; 110°C; 120°C; 130°C; 140°C; 150°C; 160°C; 170°C; or 180°C.

[0047] In such embodiments, the middle B-layer is made of at least one elastomer having a modulus of about 50 MPa to about 500 MPa; 60 MPa to 470 MPa; 70 MPa to 440 MPa; 80 MPa to 400 MPa; 100 MPa to 350 MPa; 150 MPa to 300 MPa; 200 MPa to 400 MPa; 60 MPa, 70 MPa; 80 MPa, 90 MPa; 100 MPa; 110 MPa; 120 MPa; 130 MPa; 140 MPa; 150 MPa, 160 MPa; 170 MPa; 180 MPa; 190 MPa; 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, or up to 500 MPa and one or more of (a) a glass transition temperature or (b) a melting point of from about 90°C to about 220°C; from 100°C to about 200°C; from 120°C to about 180°C; from 140°C to 220°C; or from 160°C to about 220°C. In some embodiments, the middle B layer is an elastomeric layer or shell, which may include one or more materials and one or more layers.

[0048] In embodiment #1, layers A and C may comprise a polyester or co-polyester, a polyurethane, a polyamide, a polyolefin, a (meth)acrylic polymer, a polycarbonate, a vinyl polymer such as polyvinyl chloride, or a fluoropolymer.

[0049] In embodiment #1, layer B may comprise a polyurethane elastomer, a polyester elastomer, a styrene elastomer, a polyamide elastomer, a siloxane elastomer, a polyether elastomer, a polyolefin elastomer, an olefin copolymer, an acrylic elastomer, or a fluoroelastomer.

[0050] In embodiment #1, the B-layer material has a compression set after 22 hours at 25°C of less than about 35%, 30%, 25%, 20%, 10%, less than 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, or 10%. In contrast to the results of US 9,655,693 B2, which uses an elastomer as an outer layer, we have found that a lower compression set, rather than a higher compression set, is more effective.

[0051] In certain aspects of Embodiment #1, the film has a total thickness of about 250 micrometers to about 2,000 micrometers.

[0052] In certain aspects of Embodiment #1, the combined thickness of the A and C layers is from about 25 micrometers to about 1000 micrometers, 50 micrometers to 750 micrometers, 100 to 750 micrometers, 250 micrometers to 750 micrometers, or 250 micrometers to about 600 micrometers.

[0053] In certain aspects of Embodiment #1, the thermoformable film has a flexural modulus of from about 100 MPa to about 2,000 MPa, from about 250 MPa to about 2,000 MPa, from about 500 MPa to 1,500 MPa, from about 750 MPa to about 2,000 MPa, or from about 750 micrometers to about 1,500 MPa.

[0054] In certain aspects of Embodiment #1, the A and C layers have a Tg of between about 80 and 150°C and the B layer has a Tg or melting point of between about 180°C and 220°C and a heat of fusion of about 5 joules / g to about 20 joules / g or 5 joules / g to 15 joules / g.

[0055] In certain aspects of Embodiment #1, the interlayer peel strength of an A layer is greater than about 50 N / inch, greater than about 60 N / inch, greater than about 70 N / inch.

[0056] In certain aspects of Embodiment #1, the A and C layers each have a thickness of 25 micrometers to about 1000 micrometers, 50 micrometers to 750 micrometers, 100 to 750 micrometers, 125 to 300 micrometers, 250 micrometers to 750 micrometers, or 250 micrometers to about 600 micrometers, and may have a combined thickness of about 250 micrometers to about 600 micrometers, being formed of a rigid co-polyester or polyurethane having a modulus of 1000 MPa to 2.500 MPa with a Tg of between 95°C and 150°C, wherein the elastomeric B layer has a thickness of about 200 micrometers to about 1000 micrometers or 200 to 500 micrometers, formed from a polyether or polyester polyurethane having a hardness of about D 35 to about D 65 and a compression set after 22 hours at 25°C of less than about 35%, 30%, 25%, 20%, 10%, less than 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, or 10%, and an A-layer has an interlayer peel strength of greater than about 50 N / inch, greater than about 60 N / inch, or greater than about 70 N / inch, wherein the polymer film has a flexural modulus of from about 750 MPa to about 1,500 MPa; from about 100 MPa to about 2,000 MPa; from about 250 MPa to about 2,000 MPa; from about 500 MPa to 1,500 MPa; or from about 750 MPa to about 2,000 MPa.

[0057] In some aspects of Embodiment #1, thin layers of additional polymers (tie layers) may be present to improve the adhesion of polymer layers that are not naturally adhesive to each other, for example, a layer of maleic anhydride-grafted polypropylene may be used to increase the adhesion between a polypropylene A layer and a polyester or polyamide B layer.

[0058] In some embodiments (referred to herein as Embodiment #2), the A and C layers of the film or device can be pressed together with a force of less than 100 N per cm 2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 move reversibly by a distance of approximately 0.05 mm to 0.1 mm relative to each other (e.g. by translation).

[0059] In some aspects of Embodiment #2, the A and C layers of the film or device have a total thickness of about 500 micrometers to 1,000 micrometers and can be pressed together with a force of less than 100 N per cm 2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 move reversibly by a distance of 0.05 mm to 0.1 mm relative to each other.

[0060] In some aspects of Embodiment #2, the B-layer material has a compression set after 22 hours at 25°C of less than about 35%, 30%, 25%, 20%, 10%, less than 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, or 10%.

[0061] In some embodiments (referred to herein as Embodiment #3), one or more of the A and C layers comprise a microcrystalline polyamide formed from from 50 to 100, 50 to 90, 50 to 80, 50 to 70, 60 to 90, 60 to 80 or 70 to 90 mol% of C6 to C14 aliphatic diacid units and about 50 to 100, 50 to 90, 50 to 80, 50 to 70, 60 to 90, 60 to 80 or 70 to 90 mol% of 4,4'-methylenebis(cyclohexylamine) (CAS [1761-71-3]), having a glass transition temperature of between about 100°C and 180°C, a heat of fusion of less than 20 J / g, e.g. 5 joules / g to about 20 joules / g or 5 joules / g to 15 joules / g. See, for example, DE application No. 43 10 970 (Embodiment 3). In some aspects of Embodiment 3, the combined thickness of the A and C layers is less than about 500 micrometers, less than about 400 micrometers, or less than about 300 micrometers.

[0062] In some embodiments (referred to herein as Embodiment #4), a dental appliance conformable to one or more teeth comprises at least two outer layers A and C and a middle layer B, wherein the A and C layers are each made of a thermoplastic polymer having a modulus greater than about 1,000 MPa, for example, 1,000 MPa to 1,500 MPa; 1,100 MPa to 1,600 MPa; 1,200 MPa to 1,700 MPa; 1,300 MPa to 1,800 MPa; 1,400 MPa to 1,900 MPa; 1,500 MPa to 2,000 MPa; 1,100 MPa; 1,200 MPa; 1,300 MPa; 1,400 MPa; 1,500 MPa; 1,600 MPa; 1,700 MPa; 1,800 MPa, 1,900 MPa; 2,000 MPa; up to 2,500 MPa, in certain manifestations higher than 1.500 MPa, and a glass transition temperature and / or a melting point of approximately 80°C to 180°C; 90°C to 170°C; 100°C to 160°C; 110°C to 150°C; 120°C to 150°C; 130°C to 170°C; 140°C to 180°C; 80°C; 90°C; 100°C; 110°C; 120°C; 130°C; 140°C; 150°C; 160°C; 170°C; or 180°C, in certain forms 80 to 150°C or 95 to 150°C. In such embodiments, the middle B layer is formed from at least one elastomer having a modulus of about 50 MPa to 500 MPa; 70 MPa to 450 MPa; 80 MPa to 400 MPa; 100 MPa to 350 MPa; 150 MPa to 300 MPa; 200 MPa to 400 MPa; 60 MPa, 70 MPa; 80 MPa, 90 MPa; 100 MPa; 110 MPa; 120 MPa; 130 MPa; 140 MPa; 150 MPa, 160 MPa; 170 MPa; 180 MPa; 190 MPa; 200 MPa, up to 250 MPa, and one or more of a glass transition temperature or melting point of about 90°C to about 220°C.

[0063] In some aspects of Embodiment #4, the A and C layers have a combined thickness of about, in certain aspects, 25 micrometers to about 600 micrometers, e.g., 250 micrometers, 300 micrometers, 350 micrometers, 400 micrometers, 450 micrometers, 500 micrometers, 550 micrometers, or 600 micrometers, formed from a rigid co-polyester or polyurethane having a modulus higher than 1,000 MPa, e.g., 1,000 MPa to 1,500 MPa; 1,100 MPa to 1,600 MPa; 1,200 MPa to 1,700 MPa; 1,300 MPa to 1,800 MPa; 1,400 MPa to 1,900 MPa; 1,500 MPa to 2,000 MPa; 1,100 MPa; 1,200 MPa; 1,300 MPa; 1,400 MPa; 1,500 MPa; 1,600 MPa; 1,700 MPa; 1,800 MPa, 1,900 MPa; 2,000 MPa; or up to 2,500 MPa, with a Tg of 80 °C to 180 °C; 90 °C to 170 °C; 100 °C to 160 °C; 110 °C to 150 °C; 120 °C to 150 °C; 130 °C to 170 °C; 140 °C to 180 °C; 80 °C; 90 °C; 100 °C; 110 °C; 120 °C; 130 °C; 140 °C; 150 °C; 160 °C; 170 °C; or 180 °C, e.g.80 to 150 °C or 95 to 150 °C.

[0064] In some aspects of Embodiment #4, the elastomeric B layer has a thickness of about 200 micrometers to about 1,000 micrometers, e.g., 100 micrometers, 200 micrometers, 250 micrometers, 300 micrometers, 350 micrometers, 375 micrometers, 400 micrometers, 500 micrometers, 750 micrometers, or 1,000 micrometers, formed from a polyether or polyester polyurethane having a hardness of about D 35 to about D 65 and a compression set after 22 hours at 25°C of less than about 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11% or 10%, and an A-layer has an interlayer peel strength of higher than about 50 N / inch, higher than about 55 N / inch, higher than about 60 N, higher than about 70 N, wherein the polymer film has a flexural modulus of from about 100 MPa to about 2,000 MPa, from about 250 MPa to about 2,000 MPa, from about 500 MPa to 1,500 MPa, from about 750 MPa to about 2,000 MPa, e.g.from about 750 micrometers to about 1,500 MPa.

[0065] In some aspects of embodiment #4, the A and C layers have a lateral recovery force of 0.05 mm to 0.1 mm with a force of less than 100 N per cm 2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 on.

[0066] In some embodiments (referred to herein as Embodiment #5), a dental device is formed by thermoforming a multilayer film over a model of teeth, wherein thermoforming is performed at a temperature that is at least higher than the glass transition temperature and / or melting point of the outer layers and lower than the upper glass transition temperature and / or melting point of at least one inner layer elastomeric material.

[0067] In one embodiment of Embodiment #5, a dental device is manufactured by thermoforming a multilayer film having at least an A and C layer having a Tg of about 80°C to 180°C; 90°C to 170°C; 100°C to 160°C; 110°C to 150°C; 120°C to 150°C; 130°C to 170°C; 140°C to 180°C; 80°C; 90°C; 100°C; 110°C; 120°C; 130°C; 140°C; 150°C; 160°C; 170°C; or 180 °C, wherein the B-layer has a glass transition temperature and / or a melting point of about 90 °C and 220 °C, e.g. 180 °C to 220 °C, and a heat of fusion of about 5 J / g to about 20 J / g, e.g. about 5 J / g to about 20 joules / g or 5 joules / g to 15 joules / g.

[0068] In one aspect of Embodiment #5, the A and C layers comprise a copolyester or a polyurethane having a Tg of about 90°C to about 120°C, the B layer is formed from a polyurethane having a modulus of about 50 MPa to 500 MPa and a glass transition temperature and / or melting point of about 170°C to about 220°C, and is thermoformed at a temperature between about 150°C and 200°C.

[0069] It should be noted that elements of two or more embodiments can be combined.

[0070] In some embodiments, the thermoformable polymer film is formed from at least two outer layers A and C and a middle layer B, wherein one or more of the A and C layers comprise a microcrystalline polyamide formed from from 50 to 100 mol% of C6 to C14 aliphatic diacid units and about 50 to 100 mol% of 4,4'-methylenebis(cyclohexylamine) (CAS [1761-71-3]), having a glass transition of between about 100°C and 180°C, a heat of fusion of less than 20 J / g, and a light transmittance of greater than 80%.

[0071] In some embodiments, the thermoformable polymer film is formed from at least two outer layers A and C and a middle layer B, wherein one or more of the A and C layers comprise a copolyester formed from a dicarboxylic acid component comprising 70 mol% to 100 mol% terephthalic acid residues and a diol component comprising (i) 0 to 95% ethylene glycol, (ii) 5 mol% to 50 mol% 2,2,4,4-tetramethyl-1,3-cyclobutanediol residues, (iii) 50 mol% to 95 mol% 1,4-cyclohexanedimethanol residues and / or (iv) 0 to 1% of a polyol having three or more hydroxy groups, wherein the sum of the mol% of diol residues (i), (ii), (iii) and / or (iv) is 100 mol% and the copolyester has a Glass transition temperature Tg of 80 °C to 150 °C.In some aspects of this embodiment, the thermoformable polymer film includes a middle B layer comprising an aromatic polyether polyurethane having a Shore hardness of about A90 to D55 and a compression set of less than 35%, wherein the interlayer peel strength between the A and C layers and the B layer is greater than 50 N per 2.5 cm.

[0072] In some embodiments, a dental appliance conforming to one or more teeth is made from the microcrystalline polyamide or co-polyester described above. Manufacturing process

[0073] Multilayer films can be manufactured by various means, including, without limitation, hot or cold lamination, adhesive lamination, melt lamination, coextrusion multilayer extrusion, and other known processes. Films can be fully fabricated prior to molding into an orthodontic appliance, or an appliance can be manufactured using a sequence of individual thermoforming steps to create multiple layers.

[0074] Thermoforming of films for the production of test specimens or dental devices can be performed using a "Biostar" compression molding press, available from Great Lakes Orthodontic, using processes commonly used in the industry. Alternatively, thermoforming can be performed using a roll-feed thermoformer, a vacuum thermoformer, or other known thermoforming methods. Thermoforming can be performed using different conditions, molds, and patterns to vary the draw ratio and part thickness. Multilayer devices can be manufactured using one or more 3D printing processes or by sequential dip coating, spray coating, powder coating, or similar processes known for the production of films, sheets, and 3D structures.

[0075] The film temperature during thermoforming can be measured using an infrared thermometer or a surface thermocouple. Usability

[0076] The films and materials described herein have utility as thermoformable materials with excellent dimensional stability, shock absorption, and recovery forces. These films can be converted into various types of oral appliances, such as those used to move teeth, for use as a sports mouthguard with improved impact resistance, and for use as an orthodontic retainer. Improved properties of the materials and devices described herein compared to currently available materials and devices include, but are not limited to, greater flexibility, resulting in improved comfort for end users, improved tooth movement results, higher resistance to staining and stress cracking, and excellent cosmesis, all of which promote more consistent wear by subjects. Test procedures

[0077] Tensile properties were measured using an Instron Universal Materials Tester. ASTM D638 procedures were used unless otherwise noted. Color and transparency were measured using a BYK Gardner spin colorimeter.

[0078] Impact strength was measured using a Gardner impact tester. Tear strength was measured using a materials testing machine at a speed of 250 mm per minute.

[0079] Stress relaxation of samples at 37 °C in water was measured by the method described in US Patent No. 8,716,425 B2.

[0080] Stain resistance was measured by exposing test items to a coloring medium, such as mustard or coffee, for 24 hours at 37°C and measuring color on a white color patch before and after exposure.

[0081] Translational restoring force was determined by producing a Fig. 1 and Fig. 2 shown three-layer structure (or polymer film). Samples were displaced from 0 to 0.5 mm and the force was measured in N / cm 2 specified.

[0082] Interlayer peel strength is measured at a rate of 50 mm / min and can be expressed in Newtons (N) per inch or per 2.54 cm (N). Details can be found in test method ASTM D3164.

[0083] Thermal testing to determine glass transition temperatures, melting and freezing points was measured using a differential scanning calorimeter with a heating and cooling rate of 10 °C per minute, unless otherwise noted.

[0084] Resistance to environmental stress cracking can be determined by clamping a film sample around a cylindrical mandrel to induce a specified strain on the outer surface, for example, 3% or 5%, and exposing the sample to a specified environment for a specified time, such as a saliva-mimicking solution, mouthwash, or other solution of interest. The response can be measured semi-quantitatively by visual observation of the type and number of cracks, or quantitatively by subsequent measurement of a mechanical property, such as tear strength. Materials and processes

[0085] Materials of manufacture. Numerous commercially available materials can be used to manufacture the films and devices described herein. Table 1 lists exemplary materials for use in the A or C component. Table 2 lists exemplary materials for use in the B component. Similar or related materials may be obtained from other suppliers or prepared by known methods. Table 1. Example materials that can be used as primary components of A or C materials Trade name Provider Chemical composition Tg or Tm Modulus range (MPa) Hardness range Tritan MX 710, MX 810, MP 100 MP 200 Eastman Chemical Co-polyester of terephthalic acid, cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol Tg 100 to 120 °C 1,000 to 1,500 MPa R 100 to 115 Eastar 6763 Eastman Chemical Co-polyester of terephthalic acid, ethylene glycol and diethylene glycol Tg 80 °C 2,000 to 2,100 MPa R106 Isoplast 2530 Lubrizol Aromatic polyurethane based on MDI and hexanediol Tg 85-95 °C 1,900 MPa R 121 Isoplast 2531 Lubrizol Aromatic polyurethane with aliphatic diols Tg 95-110 °C 2,100 MPa R 121 Polypropylene copolymer Generic Copolymer of propylene, ethylene and C4 to C8 alpha-olefin Tm 135 to 160 °C 1,000 to 1,500 MPa D 55-65 Trogamide CX7323 Evonik Cycloaliphatic polyamide Tg 140 °C Tm 250 °C 1,400 MPa D 81 Table 2. Exemplary materials that can be used as primary components of B-materials Trade name Provider Chemical composition Tg or Tm °C Compression set 23 °C @ 22 h Modulus * MPa Hardness range Elastollan 1195A BASF Aromatic polyether polyurethane Tm 180 - 200 30 % 10 @ 100 % E 95 A Texin RxT 50D Covestro Aromatic polyether polyurethane Tm 180 - 200 20 % 151 50 D Elastollan 1185 A BASF Aromatic polyether polyurethane Tm 180 - 200 14 % 57 85 A Texin 985 Covestro Aromatic polyether polyurethane Tm 180 - 200 17 % 60 85 A Pebax Clear 300 Arkema Polyetherpolyamide TM160 < 20 % 183 53 D Kraton FG 1901 Kraton Polymers Maleated SEBS Days 90 - 100 15 % 25 71 A Noito Mitsui Chemical Microcrystalline propylene-ethylene elastomer Tm Est 120 C 20 % 30 MPa 75 A Vestamide E or ME Evonik Polytetramethylene ether polyamide block polymer Tm Est. 170 to 220 C 25 to 40% 50 to 500 MPa D40 to D70 * Modulus from dealer literature or estimated based on Shore hardness

[0086] Other suitable materials for the A, B and C layers may include compatible or incompatible blends, for example blends of two or more co-polyesters, blends of polypropylene and polyethylene and ethylene-propylene elastomers, fluoropolymers such as polyvinylidene fluoride or its copolymers, styrene-acrylonitrile resins, acrylonitrile-styrene-butadiene resins (ABS), polyurethanes with soft polycarbonate blocks, soft siloxane blocks, silicone elastomers such as Geniomer™, a siloxane-urea copolymer, and cyclic olefin copolymers and cyclic olefin elastomers. EXAMPLES

[0087] The disclosure is further illustrated by the following examples. The examples are provided for illustrative purposes only. They should not be construed as limiting the scope or content of the invention in any way. EXAMPLE 1

[0088] A series of single-layer and multi-layer films with a nominal total thickness of 0.76 mm were prepared as shown in Table 3. Test samples 1-4 were prepared by compression molding and heat lamination of individual films or by extrusion lamination. Examples of prior art materials, P1, P2, and P3, were prepared by compression molding films and, where appropriate, heat lamination.

[0089] Press lamination was performed at 200 to 220 °C, extrusion lamination was performed using a polyurethane melt temperature of 210 to 240 °C, and coextrusion was performed using a polyester melt temperature of 240 °C to 260 °C and a polyurethane melt temperature of 210 to 240 °C. Conditions of time, temperature, and pressure were varied to maximize structural quality (polymer film), thickness, and adhesion.

[0090] Mechanical properties, optical properties, stress relaxation and shape recovery were measured to compare the suitability of obtained structures (polymer films). Table 3. Single-layer and multi-layer films Material properties P1 P2 P3 1 2 3 4 Construction Single layer Single layer ABA ABC ABC ABC ABC P1 layer / micrometer Isoplast 2530 Polyester A 250 Texin 950 75 Polyester B 250 Polyester B 250 Isoplast 2531 Polyester B 175 P2 layer / micrometer Isoplast 2530 Polyester A 250 Polyester A 600 Elastollan 1185A Texin RxT 50D Texin RxT 65D Texin 950 LW P3 layer / micrometer Isoplast 2530 Polyester A 250 Texin 950 75 Polyester B 250 Polyester B 250 Isoplast 2531 Polyester B 175 Flexural modulus 1910 MPa 1750 MPa 675 MPa 824 MPa 968 MPa 729 MPa 575 MPa Elongation at break (%) 100 - 130 100 - 130 100 - 130 100 - 130 100 - 130 100 - 130 100 - 130 Impact strength J / mm 15,2 6,9 - - 9,2 14 - Leg tear strength (N) 18 48 51 156 165 187 170 Load holding capacity g (1) 0 days 4244 3956 2664 2638 2739 2567 1598 1 day 707 853 875 1329 1469 1534 1232 2 days 498 601 823 1257 1389 1398 1247 Color change dB(2) 0,97 2,1 44 2,6 2,3 1,1 2,2 * Polyester A is a copolyester sold by Eastman Chemical (Eastar 6763). Polyester B is a cycloaliphatic copolyester sold by Eastman Chemical under the trade name Tritan. 1 - 5% elongation / 37 °C / water 2 - Mustard / 24 h / 22 °C

[0091] Prior art material P1 is a commercially available thermoformable splint material offered by Bay Materials, LLC, Fremont, CA. Prior art material P2 is a polyester with a glass transition temperature of approximately 90°C, manufactured by Eastman Chemical, sold under the trade name Eastar 6763. Prior art material P3 is described in US Pat. No. 9,655,693 B2. Test specimens 1-4 are multilayer laminates (as described herein) that exhibit improved stress relaxation properties, increased tensile strength, and excellent stain resistance.

[0092] Compared to the prior art materials, test samples 1-4 exhibited several unexpected properties. Comparing test samples 1-4 with prior art materials P1 and P2, it can be seen that test samples 1-4 exhibit significantly lower initial forces in the stress relaxation test (presumably resulting in better user comfort), but surprisingly retain the forces for a longer time. This is in contrast to the teachings of US 9,655,693 B2, which teaches that an outer elastomer layer is required to protect the inner hard layer. The ability of multilayer films to maintain suitable force levels under demanding conditions for long periods of time is well established in Fig. 4. Samples A and B in Fig. 4 are single-layer films, while samples 1 and 2 are multilayer films as described in Table 3.

[0093] Tear strength is an important property of dental devices. Materials with low tear strength have low durability and can fracture at stress concentrations. A comparison of the tear strength of prior art materials P1, P2, and P3 with test samples 1-4 shows that such multilayer structures (or polymer films) with an elastomeric B-layer exhibit significantly higher tear strength than comparable single-layer or multilayer structures from the prior art.

[0094] To further investigate the effect of construction on tear strength, another laminate (#5) was prepared with 0.25 mm A and C layers formed from Eastar 6763, a copolyester available from Eastman Chemical with a Tg of 86 °C, and a 0.2 mm B layer of Shore 50 D urethane elastomer to yield a total thickness of 0.7 mm. The tear strength of this sample was compared with the prior art materials P1, P2, and P3. Sample #5 exhibited a tear strength of 120 N, more than 200% of the value of the prior art material P3, despite having similar ratios of polyurethane to polyester. EXAMPLE 2 (Measurement of translational force)

[0095] A three-layer film was prepared as described in Example 1 for Test Material 2. A 2.54 cm x 1 cm strip of film was bonded between two 2.54 cm wide strips of rigid polyester to create a 0.5 cm overlap ("multi-layer sample A2"). A control test sample of polyester A (state of the art) of the same size and thickness was prepared between two strips of rigid polyester. The displacement / force response was measured at a rate of 0.04 MPa / min, and the results are shown in Table 4. The multi-layer construction allows the two outer layers (or two shells) of a device to accommodate greater elastic movement than the state of the art designs with appropriate forces. Table 4. Controlled elastic movement of multilayer material Force N / cm 2 Displacement (mm) Polyester A 95 A 50D 0 0 0 0 0,1 43 8 12 0,25 106 20 31 0,5 249 50 71

[0096] Orthodontic appliances were fabricated using the materials and methods described herein and compared to appliances made from Zendura A and Essix Plus of the same shape and thickness. The disclosed appliances were significantly more resilient and comfortable to wear. Because the inner and outer shells can deform independently of each other, they can accommodate a greater offset between the actual teeth and the appliance without causing undue discomfort to the patient, and they can exert a nearly constant force over long periods of time to precisely move teeth. EXAMPLE 3

[0097] A 0.25 mm thick clarified polypropylene film, designated BFI 257, supplied by Blue Ridge Films (Petersburg, Virginia), was laminated in a hot press at 180°F to both sides of a 0.25 mm thick film made of Kraton GF (maleated SEBS, available from Kraton Polymers), cooled, and cut into a 125 mm circle. The modulus of the polypropylene is reported to be 1,100 MPa. The SEBS elastomer has a reported hardness of 71 A and a modulus of 25 MPa. The multilayer film exhibited low discoloration and was heat-formable over a tooth pattern to yield a fixture with excellent elastic recovery properties. EXAMPLE 4

[0098] The durability of film materials in the presence of mouthwash was investigated because dental appliances are known to be easily damaged by alcohols and / or surfactants. Test films were prepared 0.75 mm thick, 2.54 cm wide x 12 cm long. Prior art materials P1, P2, and P3 and multilayer film #2 (test material) were wrapped around a mandrel with a diameter sufficient to produce a 5% elongation. The samples were immersed in mouthwash and maintained at 37°C. This environment is known to promote ambient stress cracking and induce hardening, resulting in the materials being in a hoop shape rather than flat. After 24 hours, the samples were rinsed with deionized water, and the amount of recovery was measured immediately and again after 24 and 48 hours at ambient temperature.The samples were then examined under a microscope to determine the extent of stress cracking on the stretched side. A sample that returned to complete flatness was classified as 100% recovery. Stress cracking was rated from 1 to 5, with 5 indicating no visible cracking and 1 indicating severe cracking. The shape recovery of the samples is shown in Table 5. The multilayer film (#2) recovered faster and more completely than the prior art materials P1, P2, and P3. Table 5 Shape recovery of samples % Recovery minutes P1 P2 P3 #2 0,01 53 34 51,6 66 60 54 49 53,8 69 1440 61 65 59,4 77 EXAMPLE 5

[0099] Three laminates were prepared as in Example 1, Sample 2, and designated Samples #6, #7, and #8. Sample #6 was extrusion laminated using untreated polyester film at a roll temperature of 40°C, Sample #7 was extrusion laminated using corona-treated polyester film at a roll temperature of 60°C, and Sample #8 was extrusion laminated using corona-treated polyester film at a roll temperature of 80°C. Corona treatment is commonly used to activate film surfaces to increase their polarity. A control sample of Polyester A was designated Sample #9. The mechanical properties and ambient stress crack resistance of the three samples are shown in Table 6. Table 6. Effect of interlayer peel strength on ESC resistance of A-layer Characteristic #6 #7 #8 #9 Modulus (MPa) 1.490 1.572 1.589 2.700 Yield strength (%) 6,1 5,8 6,1 6,2 Elongation at break (%) 124 131 129 131 Interlayer peel strength (N / inch) 35 53 137 N / A Tear resistance 55 117 179 48 ESCR / Mouthwash / 37 °C 1 2,5 4 1

[0100] The dramatic improvement in environmental resistance observed for Samples #7 and #8 compared to Samples #6 and #9 is unforeseen and unexpected. In each case, the material exposed to the environment is chemically identical and is subjected to the same degree of stress. Without wishing to be bound by theory, we speculate that some concentrated strain-induced stress present in the outer polyester layer may be transferred into the elastomer material, and force transfer is more effective in materials with higher interlayer bond strength. We are unaware of any precedent for this result.

[0101] It is well known that thermoplastic non-crystalline copolyesters (PETGs and PCTGs) exhibit poor environmental stress crack resistance and are prone to rapid deterioration when used as dental appliances. U.S. Patent 9,655,691 teaches that covering both sides of such a copolyester with a thermoplastic polyurethane elastomer having a durometer of about 60A to about 85D surprisingly increased the durability of dental splints made from such materials (described as a "hard polymer layer sandwiched between two soft polymer layers"). Presumably, the outer material provides a physical and / or chemical protective layer. A disadvantage of such materials is that the polyurethane elastomers and other elastomers exhibit poor stain resistance, and the disclosed multilayer structure exhibits poor tear resistance.

[0102] The inventors have unexpectedly discovered that the stress cracking resistance of amorphous polyester films, sheets, or thermoformed parts made therefrom can be dramatically improved by bonding an elastomeric material, such as a polyurethane, between two layers of the polyester. The resulting structure, which has a soft polymer layer sandwiched between two hard polymer layers, exhibits excellent chemical resistance, high transparency, and excellent discoloration resistance. Furthermore, the tear strength of the multilayer structure is higher than that of the polyester or the elastomer alone. Furthermore, the inventors have found that the improved properties require high bond strength between the layers, and that a material with poorly bonded layers exhibits poorer crack resistance and tear strength.

[0103] It is well known in the art that rigid polyurethane films exhibit very good environmental stress cracking resistance. Unexpectedly, we observed that a three-layer ABA structure featuring rigid (outer) polyurethane A layers and an (inner) elastomeric B layer with excellent adhesion exhibited poorer environmental stress cracking resistance than the rigid polyurethane alone, the opposite effect to that observed with a polyester outer layer. EXAMPLE 6

[0104] A test was conducted to investigate the influence of heat treatment and thermoforming conditions on the performance of devices made from the films. Three films (2A, 2B, and 2C) of Test Material 2 (three-layer, polyester, polyurethane, polyester) were dried for 12 hours at 60°C under reduced pressure. The samples were placed in moisture-barrier bags and subjected to the heat treatment and thermoforming conditions shown in Table 7. Sample 2A was held at 22°C, and Samples 2B and 2C were heat-treated at 100°C for 24 hours. The samples were then thermoformed using different thermoforming temperatures to produce a flat film. Samples 2A and 2B were thermoformed at a temperature below the high end of the polyurethane's melting range, while Sample 2C was thermoformed at a temperature above the polyurethane's melting range. Table 7. Effect of heat treatment / hot forming conditions on retained stress Sample treatment and performance Sample / Treatment #2A #2B #2C temperature 22 °C 100 °C 100 °C Time 24 h 24 h 24 h Tm (°C) 160 - 190 170 - 195 170 - 195 J / g 6,8 12,4 12,6 Hot forming temperature 180 180 200 Tm 160 - 190 C 160 - 210 160 - 200 J / g 6,3 8,3 6,4 Maintained tension, 24 h 51 % 72 % 47 %

[0105] Test specimens were cut from thermoformed samples, analyzed by DSC, and subjected to stress relaxation testing at 37 °C in water. DSC showed that the melting point and latent heat of the samples were increased by heat treatment at 100 °C, and that thermoforming decreased the amount of latent heat and the melting range. However, the sample thermoformed below the upper melting range of the polyurethane retained more crystallinity and performed better in the stress relaxation test. The conditions for Sample 2B in Table 7 were used for the fabrication of a dental appliance. EXAMPLE 7

[0106] Further compositions can be prepared by selecting suitable layer materials with differences in modulus and elasticity as shown in Table 8. Table 8. Example multilayer film materials Sample #6 Sample #7 Sample #8 Layers material thickness material thickness material thickness A Trogamide CX 7323 0.125 mm Trogamide CX 7323 / Polyamide 614, blend 90:10 0.2 mm Altuglas Luctor CR 13 0.125 mm A' Altuglas SG10 0.125 mm BB' Pebax Clear 300 0.5 mm Pellethane 2373 55D 0.3 mm Kurarity LA4285 0.25 mm C' Trogamide CX 7323 0.125 mm Trogamide CX 7323 / Polyamide 614 mixture 90: 10 0.2 mm Altuglas SG10 0.125 mm C Altuglas Luctor CR 13 0.125 mm Altuglas SG10 is a transparent impact-modified polymethyl methacrylate, distributed by Arkema Altuglas Luctor CR13 is a transparent impact-modified polymethyl methacrylate, distributed by Arkema Kurarity LA4285 is an acrylic ABA block copolymer of methyl methacrylate and butyl methacrylate EXAMPLE 8

[0107] A 2 mm thick sheet was manufactured by laminating two outer films of 0.250 mm thick polypropylene homopolymer (Blue Ridge Films BFI 3270, modulus 1,200 MPa) and an inner layer of 1.50 mm thick microcrystalline ethylene-propylene elastomer (Noito PN 2070, Mitsui Chemical), modulus 150 MPa. The sheet was cut into a 125 mm diameter disc and thermoformed and trimmed over a model of an individual's maxillary teeth to produce a high-impact sports mouthguard. Surprisingly, the mouthguard provides better impact protection and comfort than a standard device made of 4 mm thick ethylene-vinyl acetate copolymer, marketed by Dreve under the trade name Drufosoft. EXAMPLE 9

[0108] A splint was fabricated by thermoforming a three-layer film over a tooth model. Two outer layers were formed of a rigid polyurethane with a Tg of approximately 120 °C, and an inner B-layer was formed of an aromatic polyether polyurethane with Shore A 85, a hard block melting point of 160 to 195 °C, and a heat of fusion of 8 J / gram. The device was heat-treated for 24 hours at 100 °C, which is lower than the Tg of the outer layer. No deformation was observed. Testing showed that this device was more elastic and exhibited less creep under load than before heat treatment at 100 °C. The improvement is believed to be due to improvements in the microstructure of the polyurethane elastomer.

[0109] In a second test, a comparison was conducted between a multilayer device and a single-layer device, using Zendura A materials as the A / C material and the A / B / C material, respectively. The devices were heat-treated at 90°C for 24 hours. It was observed that the single-layer device deformed significantly, while the multilayer device retained its shape. It is believed that in the multilayer device, the elastomer maintains a stabilizing force on the stiffer material during heat treatment to prevent unwanted shape changes. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 62 / 512,786

[0001] US 62 / 590,627

[0001] US 9,655,693 B2 [0025, 0050, 0091, 0092] DE 43 10 970

[0061] US 8,716,425 B2

[0079] US 9,655,691

[0101]

Claims

[1] A reversibly deformable dental device formed from a 3-layer polymer film material consisting of two rigid outer layers A and C and an inner elastomeric layer B, wherein the elastomeric middle layer and the outer layers can move reversibly relative to each other and have a lateral restoring force of less than 100 N per cm 2 , 50 N per cm 2 , 25 N per cm 2 or 10 N per cm 2 when shifted by 0.05 mm to 0.1 mm relative to each other. [2] A dental device according to claim 1, wherein the outer layers A and C are formed from one or more of a co-polyester, a polyurethane, a polyamide and a polyolefin. [3] The dental device of claim 1, wherein the outer layers A and C comprise a co-polyester. [4] The dental device according to claim 1, wherein the elastomeric middle layer B is formed from one or more of a polyurethane elastomer, a polyolefin elastomer, a polyester elastomer, a styrene elastomer, a polyamide elastomer, a cyclic olefin elastomer, an acrylic elastomer, an aromatic or aliphatic polyether, and a polyester polyurethane. [5] The dental device of claim 1, wherein the elastomeric middle layer B comprises an aromatic polyether polyurethane. [6] The dental device of claim 1, wherein the elastomeric middle layer B comprises a polyurethane having a Shore hardness of about A80 to D75. [7] The dental device of claim 1, wherein the combined thickness of the A, B and C layers is from about 250 micrometers to about 2,000 micrometers. [8] The dental device of claim 1, wherein the combined thickness of the A and C layers is from 200 micrometers to 600 micrometers. [9] The dental device of claim 1, wherein the A, B, C layers are each about 250 micrometers thick. [10] The dental device of claim 1, wherein said dental device has a flexural modulus of from about 250 MPa to about 2,000 MPa, from about 750 MPa to about 2,000 MPa, or from about 750 micrometers to about 1,500 MPa. [11] A dental device according to claim 1, wherein it is designed to move teeth or to retain teeth in an existing position. [12] A dental appliance according to claim 1, wherein the two outer layers that contact the teeth are substantially rigid to fit snugly with the teeth to provide precise forces while maintaining the ability to exert a nearly constant force over extended distances. [13] A dental appliance according to claim 1, which is an orthodontic, prosthetic, restraining, therapeutic or habit-modifying appliance.

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