Multilayer dental appliance with customized transition temperature and thickness

Abstract

Improved dental appliances and polymeric sheet compositions are disclosed. The polymeric sheet compositions can be used to manufacture dental appliances whose outer layer is composed of a material having an elevated glass transition temperature (Tg) above 110°C. In multi-layer appliances, the outer layer can have an elevated Tg in combination with a thickness that is greater than an elastomeric inner layer.

Description

Cross-references to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 549,687, filed February 5, 2024, entitled “MULTI-LAYER DENTAL APPLIANCE WITH CUSTOMIZED TRANSITION TEMPERATURES AND THICKNESSES”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] Compositions in the form of polymer sheets are disclosed. These polymer sheets can be used, for example, in dental appliances and are constructed of layers that impart flexibility, strength, and stain resistance to devices made from the sheets. Background Technology

[0003] There is a need for improved orthodontic and dental appliances that can facilitate orthodontic tooth movement, stabilize tooth position, or protect teeth from potentially destructive external forces. Existing materials and products are constructed from single-layer, double-layer, or triple-layer materials, which have limited functionality and may suffer from performance defects. Orthodontic appliances are plastic shells that fit onto the teeth and are designed to apply translational or rotational forces to the teeth. Their ability to precisely move teeth is limited by their effective modulus of elasticity, elasticity, stiffness, and resistance to creep and stress relaxation. Furthermore, they should generally be resistant to staining and environmental stress cracking.

[0004] Appliances used to protect teeth, such as sports mouthguards and dental splints, have conflicting requirements. On the one hand, they should be able to dissipate impact forces, while on the other hand, they should be thin and not interfere with the natural occlusion of the teeth or impede speech. Summary of the Invention

[0005] In one aspect, this disclosure relates to polymer sheet compositions comprising an elastomeric inner layer disposed between two outer layers. The two outer layers are polyesters or copolyesters having a glass transition temperature of about 110°C to about 130°C. The elastomeric inner layer is a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, the specific logarithmic viscosity being determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane. Polyesters or copolyesters with higher specific logarithmic viscosities generally provide better co-extrusion capability and a more robust sheet construction, such as better impact resistance. Such polymer sheet compositions have been found to provide an optimal combination of strength, flexibility, and durability, ensuring effective performance in orthodontic and dental applications by maintaining consistent force application, resisting deformation over time, and withstanding environmental stresses and contamination. In some embodiments, the polymer sheet composition has a stiffness D value of about 0.4 to about 0.5. In some embodiments, the thickness of each of the outer layers is greater than the thickness of the inner elastomeric layer. In some embodiments, the polymer sheet composition is a three-layer composition having a thickness ratio of 11:8:11, 12:6:12, 13:4:13, or 14:2:14. Such multilayer constructions significantly improve performance compared to conventional materials. The specified thickness ratio optimizes key properties such as modulus, elasticity, and stiffness, which are important for effective tooth movement and long-term durability. The stiffer outer layers resist staining and environmental stress cracking, maintaining both functionality and aesthetics.

[0006] In some embodiments, the two outer layer materials are different, wherein each outer polyester or copolyester material has a glass transition temperature of about 110°C to about 130°C. The Tg of each different outer layer may be the same, similar, or different.

[0007] In some embodiments, the polymer sheet composition is a three-layer composition having an asymmetric thickness ratio of the three layers, such as 12:8:10, 13:6:11, 14:4:12, or 15:2:13, which advantageously provides enhanced directional / controlled bending behavior.

[0008] In some embodiments, at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C, resulting in a blend material having a Tg of about 110°C to about 130°C or higher. In some embodiments, the blend of the two materials reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves its resistance to cyclic deformation during repeated stretch-release events. This results in enhanced longevity and consistent performance of the appliance comprising the sheet composition, as it retains its shape and force application capability over an extended period of use.

[0009] In some embodiments, the combined thickness of all layers is from about 250 micrometers to about 2,000 micrometers; this provides a balance between flexibility and durability, ensuring the device is both comfortable for the wearer and strong enough to apply the forces required for effective orthodontic treatment. In some embodiments, the two outer layers have a stiffness value D of about 0.45 to about 0.50. In some embodiments, the polymer sheet composition further includes two intermediate layers, each disposed between the inner elastomer and one of the two outer layers, which helps to minimize / prevent cracking at the interface between the outermost layer and the inner layer.

[0010] In some embodiments, the glass transition temperatures of the two intermediate layers are each lower than those of their adjacent outer layers, which advantageously results in improved fatigue properties and durability or sustainability. In some embodiments, the two intermediate layers each have a smaller thickness compared to the thickness of their adjacent outer layers and advantageously act as interface modifiers.

[0011] In some embodiments, dental appliances conforming to one or more teeth, such as dental retainers, are made of multilayer sheet compositions described herein.

[0012] In another aspect, this disclosure relates to a dental appliance for repositioning one or more teeth of a patient, formed of a polymer sheet composition comprising an elastomeric inner layer disposed between two outer layers. The two outer layers are polyesters or copolyesters having a glass transition temperature of about 110°C to about 130°C, and the elastomeric inner layer is a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, the specific logarithmic viscosity being determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane. In some embodiments, the polymer sheet composition has a stiffness D value of about 0.4 to about 0.5. In some embodiments, the thickness of each of the two outer layers is greater than the thickness of the elastomeric inner layer. In some embodiments, the polymer sheet composition is a three-layer composition having a thickness ratio of 11:8:11, 12:6:12, 13:4:13, or 14:2:14. In some embodiments, at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C. In some embodiments, the blend reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves its resistance to cyclic deformation during repeated tensile-release events. In some embodiments, the combined thickness of all layers is about 250 micrometers to about 2,000 micrometers. In some embodiments, the two outer layers have a stiffness value D of about 0.45 to about 0.50. In some embodiments, the dental appliance further includes two intermediate layers disposed between the elastomeric inner layer and one of the two outer layers. In some embodiments, the glass transition temperature of each of the two intermediate layers is lower than the glass transition temperature of their adjacent outer layers. In some implementations, the thickness of each of the two intermediate layers is less than the thickness of their adjacent outer layers.

[0013] In another aspect, this disclosure relates to a method of forming a dental appliance for repositioning one or more teeth of a patient, comprising: co-extruding a polymer sheet composition, and thermoforming the polymer sheet composition on a model of the patient's dentition to form the dental appliance. The co-extruded layer of the polymer sheet composition includes an elastomeric inner layer disposed between two outer layers. The two outer layers are polyesters or copolyesters having a glass transition temperature of about 110°C to about 130°C, and the elastomeric inner layer is a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, the specific logarithmic viscosity being determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane. In some embodiments, the thickness of each of the two outer layers is greater than the thickness of the elastomeric inner layer. In some embodiments, the polymer sheet composition is a three-layer composition having a thickness ratio of 11:8:11, 12:6:12, 13:4:13, or 14:2:14. In some embodiments, at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C. In some embodiments, the blend reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves its resistance to cyclic deformation during repeated tensile-release events.

[0014] In another aspect, this disclosure relates to a method of forming a dental orthodontic appliance for repositioning one or more teeth of a patient, comprising co-extruding a polymer sheet composition having five layers. The five layers include a first outer layer; a second outer layer; a first intermediate layer adjacent to the first outer layer; a second intermediate layer adjacent to the second outer layer; and an inner layer located between the first intermediate layer and the second intermediate layer. The first and second outer layers are polyesters or copolyesters having a glass transition temperature of about 110°C to about 130°C. The inner layer is an elastic layer comprising a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, the specific logarithmic viscosity being determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane. The glass transition temperatures of the first and second intermediate layers are each lower than the glass transition temperatures of their adjacent outer layers.

[0015] Other features and advantages of the invention will be apparent from the remainder of the specification, including the accompanying drawings and claims. These other features and advantages, as well as the structure and operation of various embodiments of the invention, are described in detail below in conjunction with the accompanying drawings. In the drawings, the same reference numerals denote the same elements or elements with similar functions. Attached Figure Description

[0016] Specific embodiments are described with reference to the accompanying drawings. The use of the same reference numerals in different instances in the specification and drawings may indicate similar or identical items.

[0017] Figure 1 This is a schematic cross-sectional view of a three-layer sheet according to one embodiment of the present disclosure, the three-layer sheet having an outer layer that is thicker than the inner layer.

[0018] Figure 2 This is another schematic cross-sectional view of a three-layer sheet according to one embodiment of the present disclosure, the three-layer sheet having an outer layer that is thicker than the inner layer.

[0019] Figure 3 This is a schematic cross-sectional view of a five-layer sheet according to one embodiment of the present disclosure, the five-layer sheet having a rigid outer layer that is thicker than the inner layer, and an intermediate layer.

[0020] Figure 4 This is a graph depicting stress relaxation data of a three-layer material with different outer glass transition temperatures (Tg) according to one embodiment of the present disclosure.

[0021] Figure 5 It is a diagram depicting the force retention over time of a three-layer material with different outer glass transition temperatures according to one embodiment of the present disclosure.

[0022] Figure 6 It is a graph depicting the correlation between stiffness and initial force according to one embodiment of the present disclosure.

[0023] Figures 7 to 9 The diagram shows a graph of tensile stress versus tensile strain in several three-layer materials according to one embodiment of the present disclosure.

[0024] Figure 10 It is a graph depicting the tensile hysteresis (%) of three materials relative to the number of cycles according to one embodiment of the present disclosure.

[0025] It should be understood that Figures 1 to 10The structures and properties illustrated are specific examples and are not intended to limit the scope of usable structures and tests. Other materials, structures, and sequence of steps may also be performed according to alternative embodiments. For example, alternative embodiments may include additional layers, including tie layers, pigments, optical additives, or reinforcing agents, and may be constructed in any manner known in the art, such as flat sheet extrusion, multilayer sheet co-extrusion, co-extrusion blown film, calendering, lamination, and adhesive bonding. The structures (or polymer sheets) and devices may be fabricated by 3D printing or dip coating in some embodiments. Those skilled in the art will recognize and understand the numerous variations, modifications, and alternatives to the described structures.

[0026] Therefore, the specification and drawings should be considered illustrative rather than restrictive. However, it will be apparent that various modifications and changes may be made thereto without departing from the broader spirit and scope of this disclosure as set forth in the claims.

[0027] Other variations are within the spirit of this disclosure. Therefore, while the disclosed embodiments are readily adaptable to various modifications and alternative constructions, specific exemplary embodiments are shown in the accompanying drawings and described herein. However, it should be understood that this disclosure is not intended to be limited to the specific one or more forms disclosed, but rather is intended to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of this disclosure as defined in the appended claims. Detailed Implementation

[0028] This disclosure relates to dental appliances, which may include, for example, clear dental aligners. During orthodontic treatment planning, dental aligners are typically worn for a period of time (e.g., seven to fourteen days) and then replaced with a new set. Examples of multilayer materials and dental appliance manufacturing techniques can be found in U.S. Patent Nos. 11,541,643; 11,325,358; 10,987,907; 10,870,263; 10,549,511; and International Application Serial No. PCT / US2018 / 035384, each of which is incorporated herein by reference in its entirety.

[0029] During each period or phase of the treatment plan, typically lasting seven to fourteen days, the appliance continuously deforms and loses at least slightly its force. However, such force is necessary to propel the teeth into their intended positions. One way to achieve better force retention in dental appliances, including multi-layered systems, is often to use higher modulus materials. These higher modulus materials translate into more rigid appliances, which can cause additional pain for the patient. The stiffness of the material typically translates into increased pain for the patient during the first few hours or days of wearing a new appliance. However, lower stiffness materials do not necessarily result in lower appliance effectiveness, as appliance effectiveness is more related to force retention over time than to stiffness.

[0030] According to one embodiment of this disclosure, a multilayer orthodontic material may include a flexible intermediate layer and one or more rigid outer layers (hard-soft-hard arrangement), wherein the rigider outer layer has a higher glass transition temperature (Tg) compared to previously used outer layer materials. Furthermore, in some embodiments, the rigid outer layer may have a greater thickness compared to the softer intermediate layer.

[0031] As an example, Bay Materials products sold under the Zendura FLX™ brand are constructed from equal-thickness (mil) layers (in a 10:10:10 ratio) and use an outer layer material with a Tg of approximately 110°C. According to one embodiment of this disclosure, the three layers are constructed, for example, with a thickness ratio of 11:8:11 and an outer layer with a Tg greater than 110°C (e.g., Tg ≥ 120°C). The combination of the thicker outer rigid layer and the outer layer with a higher Tg unexpectedly produces significantly higher force retention values ​​over time.

[0032] Furthermore, in some embodiments, the multilayer material can be prepared via multilayer co-extrusion, eliminating entrained bubbles and defects observed in extruded laminated products. Multilayer co-extrusion also eliminates processing steps, thus reducing processing costs and providing a more efficient and simplified manufacturing method. Additionally, in some embodiments, the multilayer material can be made from all copolyester materials in all layers, enabling full recycling capability in future products.

[0033] According to some embodiments, it has been found that multilayer polymeric materials having an outer layer made of a polymer with a high glass transition temperature can be used to prepare orthodontic appliances, such as dental braces, that are endowed with greater force retention during wear. One such exemplary polymer includes, for example, Tritan MP200™ copolyester having a Tg of about 120°C. In other embodiments, material constructions comprising polymeric materials having a Tg > 110°C can provide the increased force retention properties described herein. In some embodiments, suitable polymeric materials for the outer layer of a multilayer polymeric structure may include polymers or polymer blends having a Tg of about 110°C to 200°C, 115°C to 200°C, 115°C to 190°C, 115°C to 180°C, 115°C to 170°C, 115°C to 160°C, 115°C to 150°C, 115°C to 140°C, 115°C to 130°C, 120°C to 200°C, 120°C to 190°C, 120°C to 180°C, 120°C to 170°C, 120°C to 160°C, 120°C to 150°C, 120°C to 140°C, 120°C to 130°C, and 120°C to 125°C.

[0034] Polymer materials with a glass transition temperature above 110°C, when used as the outer layer of multilayer dental appliances, can provide increased force retention when worn by a patient, partly because they have a higher Tg relative to the internal temperature of the patient's oral cavity compared to materials with a lower Tg. Surprisingly, such benefits in force retention can be observed even when materials with higher Tg have lower stiffness. Therefore, additional benefits of this disclosure may include dental appliances with superior force retention properties and lower stiffness (which translates to lower initial pain for the patient).

[0035] In one specific exemplary embodiment, an orthodontic appliance is fabricated using a three-layer polymer sheet comprising an outer layer of Tritan MP200 copolyester having a Tg of approximately 120°C, and an inner layer of a copolyester elastomer (e.g., Ecdel 9967™). In this exemplary embodiment, the three-layer polymer sheet has a total thickness of approximately 750 micrometers. The resulting orthodontic appliance exhibits greater force retention during wear compared to other appliances.

[0036] In another exemplary embodiment, an orthodontic appliance is fabricated using a three-layer polymer sheet comprising an outer layer of Tritan MP200 copolyester having a Tg of approximately 120°C, and an inner layer of a copolyester elastomer (e.g., Ecdel 9967). In this exemplary embodiment, the three-layer polymer sheet has a total thickness of approximately 750 micrometers, wherein layer thickness ratios include 11:8:11, 12:6:12, and 13:4:13 (i.e., the outer layer is thicker than the inner layer by its respective indicated ratio). It has been found that using an outer layer material with a combination of a higher Tg and increased thickness (relative to the inner layer) produces orthodontic appliances with greater force retention during wear.

[0037] In some implementations, the choice of outer and inner layer materials and construction—where the dimensionless value of the composite stiffness (which integrates the modulus and thickness of the various layers) falls within the medium stiffness range (e.g., between about 0.4 and about 0.6)—translates into an effective orthodontic appliance without causing additional discomfort or pain to the patient during application and removal. In contrast, appliances based on other common materials (e.g., PETG, PCTG, and rigid thermoplastic polyurethane) have stiffness values ​​in the range of about 0.6 to about 0.8, resulting in increased pain and discomfort for the patient.

[0038] Figure 1 This is a schematic cross-sectional view of a three-layer sheet according to one embodiment of the present disclosure, the three-layer sheet having an outer layer 101 that is thicker than the inner layer 103. In some embodiments, the outer layers 101 may comprise the same or different materials, and each layer may consist of one or more materials, blends, or alloys. Similarly, in some embodiments, the inner layer 103 may be a single material or a blend or alloy of materials. In some embodiments, each of layers 101 and 103 may consist of a single layer or multiple layers.

[0039] exist Figure 1 In the exemplary embodiment shown, the outer layer 101 is thicker than the inner layer 103 and may have a thickness ratio in the range of about 10:10:10 to about 4:1:4. For example, the illustrated embodiment corresponds to a thickness ratio of 11:8:11. The outer layer 101 may comprise a polymeric material (e.g., a copolyester) having a Tg higher than 110°C, and the inner layer 103 may comprise an elastomeric material (also a copolyester, such as Ecdel 9967). It has been found that using an outer layer material with a Tg higher than 110°C combined with an increased thickness compared to the inner layer produces orthodontic appliances with greater force retention during wear.

[0040] Figure 2This is a schematic cross-sectional view of a three-layer sheet according to one embodiment of the present disclosure, the three-layer sheet having an outer layer 201 that is thicker than the inner layer 203. In some embodiments, the outer layers 201 may comprise the same or different materials, and each layer may consist of one or more materials, blends, or alloys. Similarly, in some embodiments, the inner layer 203 may be a single material or a blend or alloy of materials. In some embodiments, each of layers 201 and 203 may consist of a single layer or multiple layers.

[0041] exist Figure 2 In the exemplary embodiment shown, the outer layer 201 is thicker than the inner layer 203 and may correspond to a thickness ratio of 12:6:12 (2:1:2). The outer layer 201 may comprise a polymeric material (e.g., a copolyester) having a Tg higher than 110°C, and the inner layer 203 may comprise an elastomeric material (also a copolyester, such as Ecdel9967). It has been found that using an outer layer material with a Tg higher than 110°C combined with an increased thickness compared to the inner layer produces orthodontic appliances with greater force retention during wear.

[0042] Figure 3 This is a schematic cross-sectional view of a five-layer sheet according to one embodiment of the present disclosure, the five-layer sheet having a rigid outer layer 301 that is thicker than the inner layer 303, and an intermediate layer 304. In this exemplary embodiment, a five-layer polymer sheet is disclosed, comprising an outer layer 301 and an intermediate layer 304 made of materials with different glass transition temperatures, which results in improved fatigue properties and high force retention. In one exemplary embodiment, the outer layer 301 comprises a rigider copolyester material having a glass transition temperature greater than 110°C, the inner layer 303 comprises an elastomer (which may be a copolyester) material, and the intermediate layer 304 comprises a rigid copolyester material having a lower glass transition temperature (e.g., Tg between about 80°C and about 110°C) than the glass transition temperature of the outer layer 301. Figure 3 As shown, the different layers can include different thickness ratios. For example, in some embodiments, the five layers can have a thickness ratio of, for example, 9:2:8:2:9, and a total thickness of approximately 750 micrometers. In this example, the thickness ratio between the outermost layer and the intermediate layer can be, for example, 10:1, 9:2, 8:3, 7:4, or 6:5, where the intermediate layer is constant at 8 in this example. The use of a thinner intermediate layer with a slightly lower Tg compared to the thicker outermost layer can provide an interface layer between the rigid and high-Tg outer layer and the elastomer inner layer. In some embodiments, the five-layer material structure can have an asymmetric thickness ratio.

[0043] According to some implementation plans, Figure 3 The five-layer polymer material of the design shown can be manufactured using any copolyester material. In such exemplary embodiments, the outer layer 301 can be made of Tritan MP200 material (Tg of approximately 120°C), the middle layer 304 can be made of Tritan MP100™ material (Tg of approximately 110°C), and the inner layer 303 can be made of Ecdel 9967 (copolyester elastomer). As mentioned above, each of the five layers can have a different thickness ratio. In some embodiments, the thickness of the outermost rigid layer 301 can be greater than or equal to half the combined thickness of layer 301 + layer 304. The use of a thinner middle layer 304 compared to the outer layer 301 provides an interface modifier between the outer layer 301 and the inner elastomer layer 303.

[0044] Table 1

[0045] Examples of materials that can be used for the outer layer 301 (polymer 1) and the intermediate layer 304 (polymer 2) are shown in Table 1 above. Preferably, the outermost layer Tg1 is about 180°C to about 110°C, and the intermediate layer Tg2 is about 110°C to about 80°C, wherein the difference (Tg1 – Tg2) is about 10°C to about 100°C. Furthermore, in some embodiments, the intermediate layer 304 has a greater elongation at break (%) compared to the outermost layer 301, wherein the difference in elongation at break (EB2% - EB1%) is about 5% to about 170%.

[0046] In some embodiments, polymer 2 may have a lower yield elongation compared to polymer 1. Even with a higher elongation at break, polymer 2 will still serve as a beneficial intermediate layer. The benefits of this intermediate outer layer can be achieved either in a layered design (depending on co-extrusion capability, up to 5 layers or more) or in a blend.

[0047] DA001 in Table 1 represents an example of available Tritan™ grade polymer materials.

[0048] Figure 4 This is a graph depicting stress relaxation data of a three-layer material with different glass transition temperatures (Tg) of the outer layer material according to one embodiment of the present disclosure.

[0049] Figure 4 The stress relaxation behavior of a three-layer laminate with an Ecdel 9967 (copolyester elastomer) inner layer and an outer layer with elevated Tg of 110°C, 120°C, 150°C and 190°C is shown. Figure 4The four materials tested were each constructed with all three layers of essentially equal thickness (i.e., a 10:10:10 thickness ratio). For example... Figure 4 As shown, the laminate including an outer layer with an elevated Tg provides greater force retention over time.

[0050] Table 2 below shows the resulting properties of a series of three-layer laminates using an outer layer with an elevated Tg value and an inner layer of Ecdel 9967 copolyester. Each layer is 10 mils thick, providing a laminate with a thickness ratio (10:10:10) and a total thickness of approximately 750 micrometers. The five materials used for the outer layer include Medstar™, Tritan MP100™, Tritan MP200™, polycarbonate (PC), and polyethersulfone (PESU).

[0051] Table 2

[0052] The outer layer materials described in Table 2 have a 10:10:10 structure within a Tg range of 85°C to 190°C. As the outer layer Tg increases from 110°C to 190°C, the tear properties decrease from 186 N / mm to 110 N / mm, then to 61 N / mm, and finally to 17 N / mm. The tear resistance target for the three-layer sheet is greater than 60 N / mm, preferably greater than 100 N / mm.

[0053] Initial stress relaxation (SR) force (g) is generally related to the material's stiffness or modulus and its resistance to flexural bending. However, force retention over time is more important than initial stiffness. As shown in Table 1, Medstar material has a Tg of approximately 85°C and is a more rigid and higher modulus material compared to its copolyester counterparts (Tritan MP100 and MP200), but exhibits decreasing force retention over time. The retained forceratio (24 h / 1 h) increases from 41% to 70%, 76%, 88%, and 89%, showing a clear trend with the Tg of the outer layer material.

[0054] Table 3 shows data comparing various 750-micron laminates with different structures. Materials 3 and 6-8 are all 30-mil three-layer laminates, with Tritan MP200 (Tg = 120℃) as the outer layer and Ecdel9967 copolyester elastomer as the inner layer. Material 3 has a thickness ratio of 10:10:10; Material 6 has a thickness ratio of 11:8:11; Material 7 has a thickness ratio of 12:6:12; and Material 8 has a thickness ratio of 13:4:13. Material 9 is a single layer of Tritan MP200 with a thickness of approximately 750 microns (approximately 30 mils).

[0055] Table 3

[0056] As shown in Table 3, surprisingly, the tearing properties increased from 110 to 230 N / mm between the 10:10:10 (material 3) and 11:8:11 (material 6) configurations. Although the following material groups 7 and 8 showed lower tearing values ​​of 93 and 106 N / mm respectively, these are still acceptable tearing values ​​compared to the 19.5 N / mm of a single layer of material 9 (a single layer of 30 mil MP200).

[0057] In stress relaxation tests on pressed samples, the 11:8:11 configuration (material 6) exhibited higher 24-hour and 48-hour retention forces (1321g vs. 1251g, and 1250g vs. 1182g) compared to the 10:10:10 configuration (material 3). The subsequent 12:6:12 and 13:4:13 groups showed slightly greater forces compared to the 10:10:10 configuration. In thermoformed-immersion samples, the 11:8:11 configuration also showed favorable 24-hour and 48-hour force retention when tested at a constant deflection of 2.54 mm. Table 3 also shows that force retention was improved with the use of an outer layer having a higher Tg for all configurations.

[0058] Table 4 shows data related to force retention (g) one week after a stress relaxation test in deionized water at 37°C with an equal bending deflection of 2.54 mm.

[0059] Table 4

[0060] The test samples in Table 4 consisted of thermoformed sheets of four materials (Materials 10, 11, 12, and 6). Material 10 was a 30-mil thick (before thermoforming) rigid polyurethane monolayer; Material 11 was a 30-mil three-layer (10:10:10) material with a polyurethane elastomer (50D) inner layer sandwiched between Tritan MP100 outer layers; Material 12 was a 35-mil three-layer (10:15:10) material with a polyurethane elastomer (50D) inner layer sandwiched between Tritan MP100 outer layers; and Material 6 was a 30-mil three-layer (11:8:11) material with an Ecdel 9967 inner layer and a Tritan MP200 outer layer. Each sheet was thermoformed on a rectangular polycarbonate block in a Biostar™ VII apparatus at a maximum temperature of 428°F. The top flat surface of the formed part was cut out for testing. The molded test components were pre-conditioned by immersing them in deionized water at 37°C for 48 hours.

[0061] After immersion for 48 hours prior to stress relaxation testing (at a constant deflection of 2.54 mm), material 6, with its 11:8:11 configuration, exhibited superior 7-day force retention. Material 12 showed the highest initial force in this group, due to its greater overall thickness (35 mils vs. 30 mils). After the initial 24 hours and through 7 days of testing, the force of material 12 decreased to below that of material 6. Material 6 exhibited significantly greater force retention relative to material 11. Material 10 showed the lowest 7-day force retention. These results are summarized in Table 4 and... Figure 5 As shown in the image.

[0062] Figure 5 This is a graph depicting the force retention over time of a three-layer material with different outer glass transition temperatures according to one embodiment of the present disclosure. Figure 5 It is also evident that material 6 exhibits the greatest force retention over seven days, while also possessing a lower initial force compared to materials 10 and 12. This reduced initial force translates into lower initial pain for the patient, while still providing better force retention over time.

[0063] The stiffness D of a shell consisting of three layers (two surface layers and one core layer) can be calculated according to the following linear sandwich theory equation, shown as equation (1). Equation (1) integrates the modulus, thickness, and position of the layers (inner or outer layer). For a sandwich beam with the same sheet material and unit width, the value D is calculated according to equation (1), where E f = Outer layer modulus, E c = core modulus, f = surface layer thickness, and 2h = core thickness.

[0064] Equation (1): Table 5 below shows the stiffness values ​​D calculated according to equation (1) for different three-layer structures and single-layer products. The initial load (g) values ​​were obtained from stress relaxation tests conducted on an Instron machine equipped with a 37°C water bath. The tests were performed on 30 mil (approximately 750 micrometers) specimens.

[0065] Table 5

[0066] Table 5 lists the calculated stiffnesses in ascending order, with corresponding initial forces (loads, g) for various 30 mil (approximately 750 micrometers) single-layer products and three-layer sheets. Based on all copolyester three-layer products (also with a total thickness of approximately 750 micrometers) using MP100 or MP200 as the outer layer, including materials 2 and 5, stiffness values ​​are shown in a tight range from approximately 0.46 to approximately 0.50, with corresponding moderate initial force values ​​between approximately 3,000 and approximately 3,300 gf (excluding single-layer MP100 and MP200).

[0067] The first row of Table 5 shows a three-layer product with a 3:25:3 construction, based on an outer layer comprising a polyurethane elastomer (hardness approximately 65D) and an inner layer of MP100 (approximately 25 mils, or 635 microns), referred to in Table 5 as PUE-MP100-PUE. This first construction, corresponding to a soft-hard-soft construction, results in a minimum stiffness of approximately 0.3325. Changing the construction to 1:28:1 in these soft-hard-soft materials increases the stiffness to approximately 0.39.

[0068] Referring further to Table 5, the PCTG and PETG copolyester types exhibit high stiffness values ​​(0.5875 and 0.6303, respectively), due to their inherently higher modulus properties than MP100 and MP200. Consequently, these materials generate large initial forces, which typically translates to greater pain for patients wearing orthotics made from these materials. Material 12, with its 10:15:10 construction, corresponds to a high stiffness value of approximately 0.7025 due to its relatively high total thickness of 35 mils (approximately 889 micrometers); however, it generates relatively lower initial forces compared to other stiff products.

[0069] Figure 6 This is a graph depicting the correlation between the stiffness (D) and initial force (g) of single-layer and three-layer sheets according to one embodiment of this disclosure. The initial force (g) was calculated during a stress relaxation test at 5% strain in water at 37°C. Figure 6As shown, the material with the highest initial load (g) corresponds to the material with the highest stiffness. Therefore, a reduction in the initial load (which can lead to a reduction in stiffness) may be desirable for the patient to reduce initial pain when wearing the orthodontic appliance.

[0070] Figure 6 The figure illustrates the general dependence of initial product force on stiffness. It also shows a unique medium stiffness-load window (highlighted) where products of material 2 and material 5 are operating. The composition and construction of material 5 were designed to have a small increase in stiffness (compared to 10:10:10) while producing significantly enhanced force retention properties.

[0071] Table 6 shows the mechanical properties, tensile hysteresis, and stress relaxation properties of materials 6 and 13. Material 6 comprises a three-layer material with an 11:8:11 structure, having MP200 as the outer layer and Ecdel9967 as the inner layer of the elastomer.

[0072] Material 13 corresponds to a three-layer material with an 11:8:11 configuration, wherein the outer layer comprises a blend of MP200 and MP100, and the inner layer is Ecdel 9967. In this particular embodiment, the outer layer comprises a 75%-25% blend of MP200 and MP100. In some embodiments, one or more of the outer layer materials may be blended prior to extrusion.

[0073] In some embodiments, the outer layer material can be blended at different blending ratios of MP200:MP100 (99:1 to 1:99), for example 95%:5%, 90%:10%, 85%:15%, 80%:20%, 75%:25%, 70%:30%, 65%:35%, 60%:40%, 55%:45%, 50%:50%, with the material having a higher Tg occupying a larger percentage of the blend, aiming for higher force retention properties. As will be apparent to those skilled in the art, blending can include mixing two resin materials (e.g., not yet melted) together at the same or different rates to produce a blend, followed by extrusion of the blended resin.

[0074] In some embodiments, at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C, resulting in a desired blend material with a desired Tg (e.g., >110°C). Examples of blends of Tritan MP200 (75%) and MP100 (25%) are described herein; however, it will be apparent to those skilled in the art that other polyester or copolyester materials can be blended in the various exemplary blending ratios described above to achieve the desired Tg properties in the blend material. For example, different Tritan-grade materials can be blended with other Tritan-grade materials or other materials. Similarly, other non-Tritan-grade polyesters or copolyesters can be blended together. Examples of other materials may include Skygreen™ (a copolyester developed by SK Chemicals) or Ecozen T120 and Ecozen T110 copolyesters prepared by SK Chemicals. Examples of other available polyester or copolyester materials will be apparent to those skilled in the art.

[0075] The improvement in tensile fatigue properties of material 13 compared to material 6 is noteworthy, and this was achieved without any significant loss in stress relaxation performance.

[0076] Table 6

[0077] Stretch hysteresis Additional experiments were conducted to explore alternative methods and constructions for achieving higher force retention and improved tensile fatigue (tensile hysteresis) properties. As described herein, tensile hysteresis tests were performed at 0–3% strain and at a rate of 2 inches per minute for 10,000 cycles as a means of measuring tensile fatigue properties in three-layer sheets.

[0078] Therefore, tensile fatigue properties were determined and compared in three different materials: material 3, material 6, and material 13, and... Figure 7-9 As shown in the image.

[0079] Figure 7 The graph shows the tensile stress (psi) versus tensile strain in Material 3, cyclicated between 0 and 3% strain at room temperature for 10,000 cycles at 2 inches per minute. Material 3 corresponds to a three-layer material with a 10:10:10 configuration, using MP200 as the outer layer and Ecdel 9967 as the inner layer.

[0080] Figure 8The graph shows tensile stress (psi) versus tensile strain in Material 6, cyclicated between 0 and 3% strain at room temperature for 10,000 cycles at 2 inches per minute. Material 6 corresponds to a three-layer material with an 11:8:11 configuration, consisting of MP200 as the outer layer and Ecdel 9967 as the inner layer.

[0081] Figure 9 The graph shows tensile stress (psi) versus tensile strain in material 13, cyclicated between 0 and 3% strain at room temperature for 10,000 cycles at 2 inches per minute. Material 13 corresponds to a three-layer material with an 11:8:11 configuration, wherein the outer layer comprises a blend of MP200 and MP100, and the inner layer is Ecdel 9967. In this particular embodiment, the outer layer comprises a 75% / 25% blend of MP200 and MP100. In other embodiments, different percentages of these materials may be blended together to obtain an outer layer material with a customized Tg value (and customized stiffness and modulus values).

[0082] The above test methods were used to evaluate the tensile hysteresis (%) in material 3 (see Table 3), such as Figure 7 As shown in the figure. The material withstood 10,000 cycles and showed 54% tensile hysteresis (TH%) at the end of the test.

[0083] In similar tests, Material 6 reached 100% TH after only 1210 cycles and failed due to sample fracture. This TH behavior of Material 6... Figure 8 As shown in the figure, this difference in TH performance between the 10:10:10 configuration and the 11:8:11 configuration in the MP200-Ecdel-MP200 system indicates that some loss of elasticity occurs as the thickness of the Ecdel elastomer inner layer decreases from 10 mils to 8 mils and / or the thickness of the MP200 outer layer increases.

[0084] Surprisingly, it was found that by using blends of materials with different Tg ℃ (Tg1 and Tg2) in the outer layer (keeping the inner layer of Ecdel 9967 unchanged), where Tg1>Tg2 and Tg1 accounts for ≥50% of the blend composition, the TH behavior in the 11:8:11 three-layer system could be restored to withstand 10,000 cycles.

[0085] For example, a blend of Tritan MP200 (Tg 120C) and Tritan MP100 (Tg 110C) (75% / 25%) was used as the outer layer, and Ecdel 9967 was used as the inner layer in Material 13 of Table 6. The TH results for Material 13 are shown in... Figure 9 As shown in the figure, it clearly demonstrates a substantial improvement in tensile fatigue properties.

[0086] Figure 10 It is a graph depicting the tensile hysteresis (%) of three materials relative to the number of cycles according to one embodiment of the present disclosure. Figure 10 The three materials compared are materials 3, 6, and 13. The test was conducted at room temperature with a strain between 0 and 3%, running for 10,000 cycles at 2 inches per minute.

[0087] As described above, material 3 corresponds to a three-layer material with a 10:10:10 structure, comprising MP200 as the outer layer and Ecdel 9967 as the inner layer. Material 6 corresponds to a three-layer material with an 11:8:11 structure, comprising MP200 as the outer layer and Ecdel 9967 as the inner layer. Material 13 corresponds to a three-layer material with an 11:8:11 structure, wherein the outer layer comprises a 75% / 25% blend of MP200 and MP100, and the inner layer is Ecdel 9967.

[0088] The techniques and materials disclosed herein provide increased force retention and reduced stress relaxation over time. These benefits can be associated with a variety of properties of the disclosed novel materials, including increased outer layer Tg and a thicker outer layer compared to the inner layer of the elastomer (e.g., thickness ratios of 11:8:11, 12:6:12, 13:4:13, etc.).

[0089] A specific benefit in force retention is found when the Tg of the outer layer of a multilayer material increases. In addition, a thicker outer layer also improves performance. In some embodiments, the combination of an increased Tg of the outer layer and increased thickness can provide improved performance. In some embodiments, the use of a thin intermediate layer between a thicker outer layer and an inner layer, or the use of a blended outer layer, can also improve performance.

[0090] High-modulus materials are rigid and therefore often more painful for patients. Therefore, PETG materials are typically rigid and painful. PETG has a Tg of 80, but its modulus is higher than copolyester materials such as MP100 and MP200. However, MP200 has a sufficiently high Tg to be stronger than PETG. This is because the intraoral temperature of 37°C is close enough to the 80°C Tg of PETG that it can weaken. When the Tg is high, the modulus is less affected by oral temperature.

[0091] limited In the context of describing the disclosed embodiments (particularly in the context of the following claims), unless otherwise indicated herein or the context clearly contradicts, the use of the terms “a,” “an,” and “the,” and similar pronouns, shall be construed as encompassing both the singular and plural. Unless otherwise stated, the terms “comprising,” “having,” “including,” and “containing” shall be construed as open-ended terms (i.e., meaning “including but not limited to”). The term “connected” shall be construed as being partially or wholly contained in, attached to, or joined together, even with certain intervening elements. The word “based on” shall be understood as open-ended and not limited in any way, and is intended, where appropriate, to be construed or otherwise interpreted as “at least partially based on.” Unless otherwise indicated herein, the description of ranges of numerical values ​​herein is intended only as a shorthand method of individually referring to each individual numerical value falling within that range, and each individual numerical value is incorporated into the specification as if individually described herein. Unless otherwise indicated herein or the context clearly contradicts, all methods described herein may be performed in any suitable order. Unless otherwise asserted, the use of any and all instances or exemplary language (e.g., “for example”) provided herein is intended only to better illustrate embodiments of this disclosure and does not constitute a limitation on the scope of this disclosure. No language in the specification should be construed as indicating that any non-limiting element is necessary for the practice of this disclosure.

[0092] The term "dental appliance" is used herein to refer to any device placed in or on the teeth of a subject. Dental appliances include, but are not limited to, orthodontic appliances, prosthetic appliances, retention devices, anti-snoring / airway devices, cosmetic appliances, therapeutic appliances, protective devices (such as mouth guards), and habit correction devices.

[0093] The term "flexural modulus" is used in this document to refer to the stiffness of a material and / or its resistance to deformation during bending. The higher the flexural modulus of a material, the stronger its resistance to bending. For isotropic materials, the elastic modulus is the same in all directions.

[0094] The term "hardness" is used herein to refer to the Shore hardness scale and, unless otherwise stated, is measured according to ASTM D2240. A hardness tester measures the penetration depth of a metal foot or needle into the surface of a material. Different hardness tester scales exist, but Shore A and Shore D are commonly used. A material with a higher hardness tester value is harder than a material with a lower hardness tester value. Shore hardness is generally related to modulus and, if only one value is known, can be approximated using methods described in this art.

[0095] The terms “modulus,” “Young’s modulus,” and “elastic modulus” are used herein to refer to the stiffness of a material and / or its resistance to tension. A higher modulus indicates greater stiffness. The flexural modulus and elastic modulus of a material may be the same or different. For polymers, mechanical properties, including the elastic modulus and other properties, can be measured using the methods specified in ASTM D638. The flexural modulus can be measured using the tests listed in ASTM D790, using units of force per area. Unless otherwise specified, “modulus” refers to the elastic modulus.

[0096] The term "lateral restoring force" for the outer layers of a polymer sheet refers to the force that a layer can exert when it has been translated relative to another layer that is fixed in position. If this causes the outer layers to move independently of each other, they will subsequently return to their original positions when unrestrained.

[0097] "Translational force" refers to the amount of force required to displace the outer layers a given distance from their neutral position, and is measured in Newtons per centimeter (N / cm²) at the given displacement, where the area (cm²) is calculated based on the overlapping area of ​​the outer layers. This measurement can be performed by preparing a test sample with known overlap and displacing the outer layers relative to each other by a given distance, for example, by applying a force of 0.04 MPa / min using a mechanical force testing instrument (e.g., an Instron material tester). The forces measured at different displacements are recorded. For elastic materials, the lateral translational force will be the same as the lateral restoring force.

[0098] As used in this article, the term "shear force" refers to a translational force applied to two surfaces joined by an elastic material.

[0099] The term “shell” is used herein to refer to a polymer shell that is fitted onto and removably placed on the tooth.

[0100] The term “stain-resistant” is used in this article to refer to materials designed to resist staining.

[0101] The term “thermoplastic polymer” is used herein to refer to polymers that become flexible or moldable above a certain temperature and solidify upon cooling, provided that heat and pressure do not cause the polymer to chemically decompose.

[0102] The terms “teeth” and “tooth” include natural teeth, including natural teeth modified by fillings or crowns, implanted teeth, artificial teeth as part of a bridge or other attachment to one or more natural or implanted teeth, and artificial teeth as part of a removable attachment.

[0103] Various embodiments are described in the following description. Specific configurations and details are described for illustrative purposes to provide a thorough understanding of the embodiments. However, it will also be apparent to those skilled in the art that the embodiments can be practiced without specific details. Furthermore, well-known features may be omitted or simplified so as not to obscure the described embodiments.

[0104] Implementation Plan In some embodiments, the outer layer may comprise polyester or copolyester, polyurethane, polyamide, polyolefin, (meth)acrylic polymer, polycarbonate, polyethersulfone, vinyl polymer (e.g., polyvinyl chloride) or fluoropolymer.

[0105] In some embodiments, the inner layer may comprise a copolyester elastomer, 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 fluorinated elastomer.

[0106] In some embodiments, the inner layer material exhibits a compression set 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% after 22 hours at 25 °C. Contrary to the findings of US 9,655,693 B2 (where an elastomer is used as the outer layer), the inventors have found that lower compression set, rather than higher compression set, is more effective.

[0107] In some embodiments, the total thickness of the sheet is about 250 micrometers to about 2,000 micrometers, about 300 micrometers to about 1,900 micrometers, about 400 micrometers to about 1,750 micrometers, or about 500 micrometers to about 1,500 micrometers.

[0108] In some embodiments, the combined thickness of the outer layer is 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.

[0109] In some embodiments, the outer layer has a Tg of about 110°C to 180°C, and the inner layer has a Tg or melting point of about -30°C to 206°C, and a heat of fusion of about 5 joules / g to about 20 joules / g, or 5 joules / g to 15 joules / g.

[0110] It should be understood that elements of two or more implementation schemes can be combined.

[0111] In some embodiments, the thermoformable polymer sheet comprises at least two outer layers and an intermediate layer, wherein one or more of the outer layers comprises a copolyester, or a blend of two different copolyesters, consisting of a dicarboxylic acid component and a diol component, the dicarboxylic acid component comprising 70 mol% to 100 mol% of terephthalic acid residues, the 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, and (ii) 50 mol% to 95 mol% of 1,4-cyclohexanediethanol residues, and (iii) 0 to 1% of a polyol having three or more hydroxyl groups, wherein the sum of the mol% of diol residues (i), (ii), and (iii) is 100 mol%, and the copolyester exhibits a glass transition temperature Tg of 80 °C to 150 °C. In some aspects of this embodiment, the thermoformable polymer sheet includes an intermediate 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 outer layer and the inner layer is greater than 50 N per 2.5 cm.

[0112] In some implementations, dental appliances conforming to one or more teeth are made of microcrystalline polyamide or the aforementioned copolyester.

[0113] Material Constructor Multilayer sheets can be prepared in a variety of ways, including but not limited to hot lamination or cold lamination, adhesive lamination, melt lamination, co-extrusion or multilayer extrusion, or other known methods.

[0114] In some embodiments, the dental appliance may be made of a multilayer sheet prepared by co-extrusion as described and illustrated in the following five co-extrusion examples.

[0115] Examples 1-4.

[0116] Three layers of ABA material (Material 6, Table 6: MP200-Ecdel 9967-MP200) were extruded in a pilot-scale co-extrusion preparation line equipped with a feed block and a die, with a thickness (mil) ratio of 11:8:11. The MP200 resin constituting the outer layer was fed into extruder A. The Ecdel 9967 resin constituting the inner layer was fed into extruder B. The extrusion temperatures (°C) of the outer layer (MP200) and inner layer (Ecdel 9967) of Examples 1-5 are summarized in Table 7. The three-layer extruded sheets of Examples 1-4 were quenched on a three-roll assembly (upper roll, middle roll, and lower roll) at four different temperatures. The three-roll quenching temperatures for Example 1 were 20°C / 20°C / 16°C; for Example 2, they were 37°C / 37°C / 30°C; for Example 3, they were 50°C / 50°C / 40°C; and for Example 4, they were 60°C / 60°C / 50°C. The total sheet thickness in Examples 1-4 was controlled at 30 mils (0.76 mm).

[0117] Table 7

[0118] Example 5.

[0119] A three-layer ABA material, consisting of an outer layer (A) of MP200 / MP100 (75 / 25 wt%) resin blend (also referred to as Material 13 in Table 6) and an inner layer of Ecdel 9967, was extruded in a pilot-scale co-extrusion production line equipped with a feed block and sheet die at a thickness (mil) ratio of 11:8:11. The MP200 / MP100 (75 / 25) resin blend constituting the outer layer was fed into extruder A. The Ecdel 9967 constituting the inner layer was fed into extruder B. The extrusion temperatures for MP200 / MP100 (outer blend) and Ecdel 9967 (inner layer) are summarized in Table 7. The three-layer extruded sheet was quenched on a three-roll assembly at 37°C / 37°C / 30°C. The total sheet thickness was controlled at 30 mils (0.76 mm).

[0120] The properties of the co-extruded materials of Examples 1-5 are summarized in Table 8. As summarized in Table 8, all three-layer co-extruded materials consisting of an MP200 outer layer and Ecdel 9967 exhibit excellent layer thicknesses at the thickness targets of 279 µm and 203 µm for the outer and inner layers, respectively. As expected, increasing the cold roll temperature (quenching temperature) resulted in some increase in sheet haze and a small change in dB color (yellow). Surprisingly, the materials of Examples 1-5 exhibited similar flexural modulus (MPa) values, indicating that this volumetric property is unaffected by variations in cold roll temperature (20°C - 60°C). At the end of a 24-hour tube winding test in deionized water at 37°C, all arched materials of Examples 1-5 were intact and exhibited good elastic recovery (>70%). The sample quenched at 20°C, Example 1, showed the highest recovery rate of 84%. However, it also showed more crazing compared to the corresponding portions at higher temperatures (37°C - 60°C cold roll temperatures). All samples from Examples 1-5 also exhibited similar force retention at the end of the 48-hour stress relaxation test at 5% strain.

[0121] Perhaps the main notable difference between the material of Example 5 (the blended outer layer) and that of Example 2 (with a similar quenching temperature of 37°C) is the lower glass transition temperature (116.2°C cf 118.8°C).

[0122] Table 8

[0123] Table 9 summarizes four properties of the thermoformed co-extruded materials of Examples 1-5: three were tested in thermoformed flat sheets, and one was tested in a thermoformed aligner. All five examples were readily thermoformed on dental models, producing very good clear aligners that were easy to remove from the models.

[0124] The thermoformed sheets exhibited thicknesses ranging from 0.68 mm to 0.69 mm and haze between 2.4% and 13.4%. The stress relaxation properties of the thermoformed-immersion samples were characterized by good low initial forces of 2559 gf to 2949 gf and excellent force retention at the end of 24 or 48 hours.

[0125] The properties of the thermoformed co-extruded materials of Examples 1-5 are summarized in Table 9.

[0126] Table 9

[0127] The sheet can be fully prepared before being molded into an orthodontic appliance, or the appliance can be prepared using a series of separate thermoforming steps to form multiple layers.

[0128] Thermoforming sheets to prepare test specimens or dental appliances can be performed using the Biostar pressure forming machine, available from Great Lakes Orthodontics, employing procedures commonly used in industry. Alternatively, thermoforming can be performed using roll-fed thermoforming machines, vacuum forming machines, or other known thermoforming techniques. Thermoforming can be performed under different conditions, in different forms, or using different models to vary the draw ratio and part thickness. Multilayer appliances can be manufactured using one or more 3D printing methods, or through sequential dip coating, spraying, powder coating, or similar methods known for preparing films, sheets, and 3D structures.

[0129] Material Exemplary materials that can be used for the outer layer include: Tritan MP200: A copolyester made from three monomers: dimethyl terephthalate (DMT), cyclohexanediol (CHDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), from Eastman Chemicals, Kingsport, Tennessee.

[0130] Tritan MP100: A copolyester made from three monomers: dimethyl terephthalate (DMT), cyclohexanediol (CHDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), from Eastman Chemicals, Kingsport, Tennessee. Eastar 6763 (PETG): CHDM-modified PET copolyester from Eastman Chemicals; Medstar (PCTG): Diol-modified PCT copolyester from Eastman Chemicals.

[0131] Lexan 3412 (PC): Polycarbonate, from Sabic (formerly GE Plastics).

[0132] Udel 1708HC(PESU): Polyethersulfone, high clarity grade, from Solvay.

[0133] Exemplary materials that can be used in the inner layer include Ecdel 9966: Copolyester elastomer, from Eastman Chemicals.

[0134] Ecdel 9965: Copolyester elastomer, from Eastman Chemicals.

[0135] Texin RxT50D (PUE 50D): Polyurethane elastomer with a hardness of 50D, sourced from Covestro.

[0136] The properties of exemplary polymers used for the outer layer are shown in Table 10.

[0137] Table 10

[0138] Rockwell hardness, 109 The properties of exemplary copolyester elastomers used for the inner layer are shown in Table 11.

[0139] Table 11

[0140] Preparation of three-layer laminates (materials 1-12) A 30-mil thick three-layer laminate is prepared through two processing steps: First, sheets of varying thicknesses, intended for use as outer or inner layers, were prepared by hot-pressing pre-dried resin within a 6”x6” metal frame of matched thickness, surrounded by two Teflon release films and two metal plates, in a heated Carver Press. All resins were pre-dried in a vacuum oven at the drying temperature specified below for five hours. The resin weights (g) and pressing conditions used to prepare the sheets of different thicknesses are summarized in Tables 12 and 13.

[0141] Table 12

[0142] Table 13

[0143] In the second step, the 30-mil three-layer laminate of materials 1-12 is prepared by sandwiching a 10-mil inner layer material sheet between two 10-mil outer layer materials, and hot-pressing it in a heated Carver Press at the specified temperature, pressure and time as described in Tables 14 and 15 below, within a 30-mil metal frame surrounded by two Teflon release films and two metal plates.

[0144] Table 14

[0145] Table 15

[0146] Material 9 is a 30-mil monolayer sheet of Tritan MP200, prepared by hot pressing 22g of dry MP200 resin in a 6” x 6” x 0.030” frame at 520F and a maximum pressure of 10 tons.

[0147] Material 10 is a 30-mil monolayer sheet of rigid polyurethane, prepared by hot pressing 22g of dry Isoplast 2530 resin (from Lubrizol) in a 6” x 6” x 0.030” frame at 430F and a maximum pressure of 10 tons.

[0148] Materials 11 and 12 are three-layer sheets prepared by lamination in a hot press at a maximum pressure of 430°F and 5 tons, as summarized in Table 15.

[0149] Material 13 uses a Tritan MP200 / MP100 (75 / 25 wt%) blend as the outer layer with a thickness ratio of 11:8:11, sandwiching an Ecdel 9967 inner layer.

[0150] Material 13 was prepared in the following three steps: First, a copolyester blend (MP200 / MP100) was prepared by blending 37.5 g of dry Tritan MP200 resin and 12.5 g of Tritan MP100 resin, and then mixing the blend in a 60 cc Brabender mixer at 260°C and 60 rpm for five minutes. 7.72 g of the blend was then hot-pressed in a 6” x 6” frame to prepare an 11-mil sheet for use as the outer layer. A second 11-mil sheet of the blend was pressed in a similar manner to serve as the second outer layer.

[0151] In the second step, 5.6 g of Ecdel 9967 resin was pressed in a 6 x 6 x 0.008 inch frame at 464F, as described in Table 3, to prepare an 8-mil sheet for use as an inner layer.

[0152] In the third step, two sheets of 11-mil MP200 / MP100 (75 / 25) blend were assembled on top of and below an 8-mil Ecdel 9967 sheet, placed in a 6” x 6” x 0.030” frame, and the stack was pressed at a temperature of 464°F and a maximum pressure of 5 tons for one minute to prepare a three-layer laminate, Material 13, Table 15.

[0153] Thermoforming All 30 mil laminate materials #1-13 (except #10: single-layer MP200 and #11: single-layer RPU) were punched into 125 mm circular parts and thermoformed in a Biostar VII compression molding machine (available from Great Lakes Orthodontics). Thermoforming was performed on square blocks measuring 63.5 mm x 63.5 mm x 10 mm in height, and the flat top surface of the formed parts was used for testing. Thermoforming of different material types was performed at the temperatures, heating times, pressures, and cooling times summarized in Table 16.

[0154] Table 16

[0155] These conditions are also used for thermoforming on teeth or other models to manufacture orthodontic appliances, retainers or other devices.

[0156] Test Summary Strength and elongation Tensile properties were tested according to ASTM D638-14. Test specimens were die-cut using a type IV die. Testing was conducted on an Instron machine equipped with Blue Hill Universal software. The specimens were clamped between jaws and stretched at a crosshead speed of two inches per minute until fracture. The tensile modulus (MPa) was determined by the slope of the linear portion of the stress-strain curve. Tensile yield elongation (%), elongation at break (%), yield stress (MPa), and tensile strength (MPa) were all determined from the stress-strain curve.

[0157] Flexural modulus Three-point bending properties were tested according to ASTM D790-17. A 0.76 mm thick rectangular test specimen measuring 25.4 mm x 50.8 mm was die-cut and tested on a flexual fixture with a span of 16 mm. The bending test was performed at a strain rate of 6.04 mm / min until 10% of the total strain was reached. The bending modulus (MPa) was determined by the slope of the stress-strain curve in the linear portion of the stress-strain curve. The maximum bending stress (MPa) was recorded as the bending strength (MPa).

[0158] ripped pants The trouser tear properties were tested according to ASTM D1938-02. 1-inch x 3-inch test specimens were die-cut with a 2-inch slit in the middle. The trouser tear test was performed in an Instron machine at a tensile rate of 250 mm / min for a total of 50 mm. The maximum tear force (N) was measured, and the tear strength (N / mm) was determined.

[0159] hardness The material hardness was tested according to ASTM D2240 using a Shore D hardness tester. A 6.35mm thick molded part measuring 76mm x 76mm was used as the test sample. The test sample was conditioned at ambient room temperature for 24 hours before testing. The test was run manually at room temperature, and the initial maximum hardness observed was recorded as the Shore D hardness value.

[0160] Haze, transparency, and clarity Haze%, transparency%, and clarity were measured according to ASTM D1003-13 test method. A 0.76mm test sample measuring 50.8 x 50.8mm was tested at room temperature in a Byk haze-gardi apparatus.

[0161] Layer thickness The thickness (µm) of individual layers in the multilayer component was measured using a Leica DMS300 digital microscope system equipped with Application Suite X software (LAS X). The thickness (µm) of outer layers 1 and 2 (upper and lower layers) and the inner layer was measured at approximately 280X magnification.

[0162] DSC thermal properties According to ASTM D3418 test method, the thermal properties of a differential scanning calorimeter (DSC) were measured, including the glass transition temperature Tg °C, melting temperature Tm °C, and enthalpy of fusion (J / g) and enthalpy of crystallization (J / g). The DSC test was run in a TA instrument model Q2000 for three cycles: heating / cooling / heating at a heating rate of 10 °C per minute and a cooling rate of 10 °C per minute. The Tg °C value was taken from the second heating cycle.

[0163] Color LAB LAB color properties were tested according to ASTM D2244. A Byk-Gardner colorimeter: Spectro-guide spherical gloss meter was used to measure the color differences between materials, dL, dA, and dB. A glossy white board was used as a standard reference. A 0.76mm transparent test sample with a smooth surface (measured as 25.4mm x 50.8mm) was tested on the glossy white board, and color was measured by reflectance. In the CIE LAB system, L is the lightness of the object; A is the green-red hue component; and B is the blue-yellow hue component.

[0164] Elastic recovery This is an internal test, also known as the "pipe winding test," developed to measure the elastic recovery properties of a material after being wound around a PVC pipe segment and immersed in deionized (DI) water at 37°C for 24 hours. In this test, a 0.76 mm rectangular strip sample, measuring 1.0 inch x 4.0 inches, is wound half a turn around a PVC pipe with an outer diameter of 48.5 mm and clamped at both ends with C-clamps. The clamped sample is then immersed in deionized water at 37°C for 24 hours. At the end of the immersion time, the sample is removed to room temperature and allowed to recover for 24 hours. Elastic recovery is determined as a percentage of the distance recovered between the bent ends of the strip, with 100% recovery being the distance between the ends of a flat strip. Minor silver streaks are also examined on the recovered strip.

[0165] Stretch hysteresis Tensile fatigue properties of the three-layer sheet were tested on an Instron machine according to ASTM D638-17 test method by measuring tensile hysteresis (loss) after multiple cycles of deformation. For the test specimens, 4.5-inch Type IV tensile bars were die-cut using Pioneer Die-tecs dies. The tensile hysteresis test was performed as described below, running 10,000 cycles at a rate of 2 inches per minute at 0–3% strain. In the pre-cycle category, 10,000 cycles were selected. The parts were tested at a rate of 2 inches per minute at minimum 0% and maximum 3% strain. Cyclic data are acquired at a rate of 10 readings per second. Acquired data includes time (msec), minimum and maximum tensile strain (%), and tensile stress (psi); force (lbs) is optional. Cyclic stress (psi) data are plotted continuously between 0 and 3% strain for 10,000 cycles or until component failure (fracture).

[0166] Stretch hysteresis (%) is calculated using the following equation: TH (%) = 100 ((σi i) - (σn n)) / (σi i) Where σi = initial (first cycle) maximum stress (psi); i = initial maximum strain (3.00 / 100); σn = maximum stress at the (n)th cycle, psi; n = the maximum strain during the (n)th cycle, i.e. (3.00 - loss strain / 100).

[0167] Stress relaxation Stress relaxation tests were conducted in an Instron machine equipped with a temperature-controlled water bath and a three-point bending fixture (with a support span of 16 mm and a loading head of 2 mm radius). A 0.76 mm test sample measuring 25.4 mm x 50.8 mm was tested after being exposed to ambient room temperature for 24 hours. The stress relaxation test was performed for 48 hours in deionized water at 37°C with a strain of 5%. The test sample was placed on the fixture support and immersed in deionized water at 37°C. The sample was loaded at a rate of 36.3 kg / min to reach a strain of 5% within approximately 5 seconds. The test sample was held at a constant strain of 5% for 48 hours or longer. The maximum force (g) at 5% strain was recorded as the initial force (g). Force decay was monitored and recorded every 2 seconds for 48 hours or until the end of the test. The stress relaxation results of different materials in deionized water at 37°C with a strain of 5% for 48 hours were compared. Tables were created for the initial force (g), 60-minute force (g), 24-hour force, and 48-hour force. Force retention was determined and compared as a force ratio (24hr gf) / (1hr gf).

[0168] Stress relaxation test in thermoformed shapes The flat top surface of the aforementioned thermoformed square shape was cut out, and rectangular test specimens measuring 25.4 mm x 50.8 mm were die-cut. Typical thicknesses of the test specimens ranged from 0.68 mm to 0.70 mm. The thermoformed test specimens were immersed in deionized water for 48 hours prior to stress relaxation property testing. Stress relaxation tests on the thermoformed-immersed specimens were conducted in a similar test setup to those on the unmodified 0.76 mm specimen. However, for the thermoformed-immersed parts, the load was applied at a decreasing rate of 31.8 kg per minute, and the test was conducted for 48 hours at a constant deflection of 2.54 mm.

[0169] The sheets and materials described herein can be used as thermoformable materials with excellent dimensional stability, shock absorption, and resilience. The sheets can be transformed into a variety of types of dental appliances, such as for tooth movement, as sports mouthguards with improved impact resistance, and as orthodontic retainers. Compared to currently available materials and appliances, the improved properties of the materials and appliances described herein include, but are not limited to, greater flexibility (leading to improved end-user comfort), improved tooth movement outcomes, greater resistance to staining and stress cracking, and superior cosmetic properties, all of which contribute to more consistent wear by the subjects.

[0170] Terms: Clause 1: A polymer sheet composition comprising: An elastic inner layer, wherein the elastic inner layer is disposed between two outer layers. The two outer layers are polyester or copolyester with a glass transition temperature of about 110°C to about 130°C. The elastomer inner layer is composed of a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, which is determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane.

[0171] Clause 2: The polymer sheet composition according to Clause 1, wherein the polymer sheet composition has a stiffness D value of about 0.4 to about 0.5.

[0172] Clause 3: The polymer sheet composition according to any one of the preceding clauses, wherein the thickness of each of the two outer layers is greater than the thickness of the elastomer inner layer.

[0173] Clause 4: The polymer sheet composition according to any one of the preceding clauses, wherein the polymer sheet composition is a three-layer composition and the thickness ratio of the three layers is 11:8:11, 12:6:12, 13:4:13 or 14:2:14.

[0174] Clause 5: The polymer sheet composition according to any one of the preceding clauses, wherein at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C.

[0175] Clause 6: The polymer sheet composition according to any of the preceding clauses, wherein the blend reduces the tensile hysteresis loss (tensile fatigue) property of the polymer sheet composition and improves its resistance to cyclic deformation during repeated stretch-release events.

[0176] Clause 7: The polymer sheet composition according to any one of the preceding clauses comprises a combined thickness of all layers from about 250 micrometers to about 2,000 micrometers.

[0177] Clause 8: The polymer sheet composition according to any one of the preceding clauses, wherein the two outer layers have a stiffness value D of about 0.45 to about 0.5.

[0178] Clause 9: The polymer sheet composition according to any of the preceding clauses further comprises two intermediate layers, wherein each intermediate layer is disposed between the inner layer of the elastomer and one of the two outer layers.

[0179] Clause 10: The polymer sheet composition according to any of the preceding clauses, wherein the glass transition temperature of each of the two intermediate layers is lower than the glass transition temperature of their adjacent outer layers.

[0180] Clause 11: The polymer sheet composition according to any of the preceding clauses, wherein the thickness of each of the two intermediate layers is less than the thickness of their adjacent outer layers.

[0181] Clause 12: A dental appliance for repositioning one or more teeth of a patient, formed of a polymer sheet composition comprising: An elastic inner layer, wherein the elastic inner layer is disposed between two outer layers. The two outer layers are polyester or copolyester with a glass transition temperature of about 110°C to about 130°C. The elastomer inner layer is composed of a polyester or copolyester having a specific logarithmic viscosity of 1.0 to 1.3 DL / g, which is determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane.

[0182] Clause 13: The dental orthodontic appliance according to Clause 12, wherein the polymer sheet composition has a stiffness D value of about 0.4 to about 0.5.

[0183] Clause 14: A dental appliance according to any one of Clauses 12 to 13, wherein the thickness of each of the two outer layers is greater than the thickness of the inner layer of the elastomeric body.

[0184] Clause 15: A dental appliance according to any one of Clauses 12 to 14, wherein the polymer sheet composition is a three-layer composition having a thickness ratio of 11:8:11, 12:6:12, 13:4:13 or 14:2:14.

[0185] Clause 16: A dental appliance according to any one of Clauses 12 to 15, wherein at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C.

[0186] Clause 17: The dental appliance according to any one of Clauses 12 to 16, wherein the blend reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves resistance to cyclic deformation during repeated stretch-release events.

[0187] Clause 18: The dental appliance described in any one of Clauses 12 to 17 comprises a combined thickness of all layers from about 250 micrometers to about 2,000 micrometers.

[0188] Clause 19: The dental appliance according to any one of Clauses 12 to 18, wherein the two outer layers have a stiffness value D of about 0.45 to about 0.5.

[0189] Clause 20: The dental appliance according to any one of Clauses 12 to 19 further comprises two intermediate layers, wherein each intermediate layer is disposed between the inner layer of the elastomeric body and one of the two outer layers.

[0190] Clause 21: A dental appliance according to any one of Clauses 12 to 20, wherein the glass transition temperature of each of the two intermediate layers is lower than the glass transition temperature of their adjacent outer layers.

[0191] Clause 22: A dental appliance according to any one of Clauses 12 to 21, wherein the thickness of each of the two intermediate layers is less than the thickness of their adjacent outer layers.

[0192] Clause 23: Methods for forming dental appliances for repositioning one or more teeth of a patient, comprising: A co-extruded polymer sheet composition, the polymer sheet composition comprising: An elastic inner layer, wherein the elastic inner layer is disposed between two outer layers. The two outer layers are polyester or copolyester with a glass transition temperature of about 110°C to about 130°C. The elastomer inner layer is composed of a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, the specific logarithmic viscosity being determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane; and The polymer sheet composition is thermoformed on a model of the patient's dentition to form the dental appliance.

[0193] Clause 24: The method of claim 23, wherein the thickness of each of the two outer layers is greater than the thickness of the inner layer of the elastomeric body.

[0194] Clause 25: The method according to any one of Clauses 23 to 24, wherein the polymer sheet composition is a three-layer composition having a thickness ratio of the three layers of 11:8:11, 12:6:12, 13:4:13 or 14:2:14.

[0195] Clause 26: The method according to any one of Clauses 23 to 25, wherein at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C.

[0196] Clause 27: The method according to any one of Clauses 23 to 26, wherein the blend reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves its resistance to cyclic deformation during repeated stretch-release events.

[0197] Clause 28: Methods for forming dental appliances for repositioning one or more teeth of a patient, comprising: Co-extruded polymer sheet composition having five layers, the five layers comprising: First outer layer; Second outer layer; The first intermediate layer adjacent to the first outer layer; The second intermediate layer adjacent to the second outer layer; and The inner layer located between the first intermediate layer and the second intermediate layer. The first and second outer layers are polyesters or copolyesters having a glass transition temperature of about 110°C to about 130°C. The inner layer is an elastic layer composed of polyesters or copolyesters having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, which is determined at 25°C at a concentration of 0.5 g / 100 ml in 60 / 40 (wt / wt) phenol / tetrachloroethane. The glass transition temperatures of the first and second intermediate layers are each lower than the glass transition temperatures of their adjacent outer layers.

[0198] All references cited in this article, including publications, patent applications and patents, are incorporated herein by reference to the same extent that each reference is individually and explicitly indicated to be incorporated by reference and fully elaborated in this article.

[0199] In the context of describing the disclosed subject matter (particularly in the context of the following claims), unless otherwise indicated herein or the context clearly contradicts it, the use of the terms “a,” “an,” “the,” “at least one,” and similar pronouns shall be construed as encompassing both the singular and plural. Unless otherwise indicated herein or the context clearly contradicts it, the term “at least one” followed by a list of one or more items (e.g., “at least one of A and B”) shall be construed as referring to one item selected from the list (A or B) or any combination of two or more of the list (A and B). Unless otherwise stated, the terms “comprising,” “having,” “including,” and “containing” shall be construed as open-ended terms (i.e., meaning “including but not limited to”). Unless otherwise indicated herein, the descriptions of numerical ranges herein are intended only as a way of abbreviating each individual value falling within the range, and each individual value is incorporated into the specification as if separately described herein. Unless otherwise indicated herein or the context clearly contradicts it, all methods described herein may be performed in any suitable order. Unless otherwise specified, the use of any and all instances or exemplary language (e.g., “for example”) provided herein is intended only to better illustrate the disclosed subject matter and does not constitute a limitation on the scope of the invention. No language in the specification should be construed as indicating that any non-limiting element is necessary for the practice of the invention.

[0200] Specific embodiments are described herein. Variations of those embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors anticipate that those skilled in the art will appropriately employ such variations, and the inventors intend that the embodiments be practiced in ways different from those specifically described herein. Therefore, this disclosure includes all modifications and equivalents to the subject matter described in the appended claims as permitted by applicable law. Furthermore, unless otherwise indicated herein or where the context clearly contradicts it, any combination of the foregoing elements in all possible variations is covered by this disclosure.

Claims

1. A polymer sheet composition comprising: An elastic inner layer, wherein the elastic inner layer is disposed between two outer layers. The two outer layers are polyester or copolyester with a glass transition temperature of about 110°C to about 130°C. The inner layer of the elastomer is composed of a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g.

2. The polymer sheet composition according to claim 1, wherein the polymer sheet composition has a stiffness D value of about 0.4 to about 0.

5.

3. The polymer sheet composition according to claim 1, wherein the thickness of each of the two outer layers is greater than the thickness of the elastomer inner layer.

4. The polymer sheet composition according to claim 3, wherein the polymer sheet composition is a three-layer composition, and the thickness ratio of the three layers is 11:8:11, 12:6:12, 13:4:13 or 14:2:

14.

5. The polymer sheet composition according to claim 1, wherein at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C.

6. The polymer sheet composition of claim 5, wherein the blend reduces the tensile hysteresis loss (tensile fatigue) property of the polymer sheet composition and improves its resistance to cyclic deformation during repeated stretch-release events.

7. The polymer sheet composition of claim 1, wherein the polymer sheet composition comprises a combined thickness of all layers from about 250 micrometers to about 2,000 micrometers.

8. The polymer sheet composition according to claim 1, wherein the two outer layers have a stiffness value D of about 0.45 to about 0.

50.

9. The polymer sheet composition of claim 1, further comprising two intermediate layers, wherein each intermediate layer is disposed between the inner layer of the elastomer and one of the two outer layers.

10. The polymer sheet composition of claim 9, wherein the glass transition temperature of each of the two intermediate layers is lower than the glass transition temperature of the adjacent outer layer.

11. The polymer sheet composition of claim 9, wherein the thickness of each of the two intermediate layers is less than the thickness of the adjacent outer layer.

12. A dental appliance for repositioning one or more teeth of a patient, formed of a polymer sheet composition comprising: An elastic inner layer, wherein the elastic inner layer is disposed between two outer layers. The two outer layers are polyester or copolyester with a glass transition temperature of about 110°C to about 130°C. The inner layer of the elastomer is composed of a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g.

13. The dental appliance of claim 12, wherein the polymer sheet composition has a stiffness D value of about 0.4 to about 0.

5.

14. The dental appliance of claim 12, wherein the thickness of each of the two outer layers is greater than the thickness of the inner layer of the elastomeric body.

15. The dental appliance of claim 14, wherein the polymer sheet composition is a three-layer composition having a thickness ratio of 11:8:11, 12:6:12, 13:4:13 or 14:2:

14.

16. The dental appliance of claim 12, wherein at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C.

17. The dental appliance of claim 16, wherein the blend reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves resistance to cyclic deformation during repeated stretch-release events.

18. The dental appliance of claim 12, wherein the dental appliance comprises a combined thickness of all layers from about 250 micrometers to about 2,000 micrometers.

19. The dental appliance of claim 12, wherein the two outer layers have a stiffness value D of about 0.45 to about 0.

50.

20. The dental appliance of claim 12, further comprising two intermediate layers, wherein each intermediate layer is disposed between the inner layer of the elastomeric body and one of the two outer layers.

21. The dental appliance of claim 20, wherein the glass transition temperature of each of the two intermediate layers is lower than the glass transition temperature of the adjacent outer layer.

22. The dental appliance of claim 20, wherein the thickness of each of the two intermediate layers is less than the thickness of the adjacent outer layer.

23. A method for creating a dental appliance that repositions one or more teeth of a patient, comprising: A co-extruded polymer sheet composition, the polymer sheet composition comprising: An elastic inner layer, wherein the elastic inner layer is disposed between two outer layers. The two outer layers are polyester or copolyester with a glass transition temperature of about 110°C to about 130°C. The elastomer inner layer is composed of a polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g; and The polymer sheet composition is thermoformed on a model of the patient's dentition to form the dental appliance.

24. The method of claim 23, wherein the thickness of each of the two outer layers is greater than the thickness of the inner layer of the elastomeric body.

25. The method of claim 24, wherein the polymer sheet composition is a three-layer composition having a thickness ratio of 11:8:11, 12:6:12, 13:4:13, or 14:2:

14.

26. The method of claim 23, wherein at least one of the two outer layers is a blend of two materials having a glass transition temperature (Tg) of about 80°C to about 190°C.

27. The method of claim 26, wherein the blend reduces the tensile hysteresis loss (tensile fatigue) properties of the polymer sheet composition and improves its resistance to cyclic deformation during repeated stretch-release events.

28. A method for forming a dental appliance for repositioning one or more teeth of a patient, comprising: Co-extruded polymer sheet composition having five layers, the five layers comprising: First outer layer; Second outer layer; The first intermediate layer adjacent to the first outer layer; The second intermediate layer adjacent to the second outer layer; and The inner layer between the first intermediate layer and the second intermediate layer, The first outer layer and the second outer layer are polyester or copolyester having a glass transition temperature of about 110°C to about 130°C, the inner layer is an elastic layer composed of polyester or copolyester having a specific logarithmic viscosity of about 1.0 to 1.3 DL / g, and the glass transition temperature of the first intermediate layer and the second intermediate layer is lower than that of the adjacent outer layer.

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