A dental sheet, an apparatus and a method for producing the same

Abstract

The present invention discloses a dental sheet and an apparatus for producing the same. The dental sheet for orthodontist treatment may include at least two outer layers and at least one inner layer. The at least one inner layer is interposed between the at least two outer layers to produce the dental sheet for fabricating aligners for providing comfort to a patient for orthodontist treatment. The at least two outer layers consist of polyester material having hardness from about 65D to 85D, flexural modulus from about 1500 Mpa to 2500 MPa, and glass transition temperature from about 75 °C to 105 °C. The at least one inner layer consists of a thermoplastic urethane elastomer having hardness in range of 50A to 75D, flexural modulus from about 500 Mpa to 1600 MPa, and glass transition temperature from about -40 °C to 45 °C.

Description

A Dental Sheet, An Apparatus And A Method For Producing The SameField of the Invention

[0001] The present invention generally relates to a dental sheet, an apparatus and a method for producing the same. More particularly to the dental sheet, the apparatus and the method for producing the same for orthodontic and dental applicationsBackground of the Invention

[0002] Aligners are widely used in orthodontics to gradually move teeth into their proper positions. Conventional aligners are typically made from polymer sheets such as PC, PETG, TPU, and PET, which often exhibit limitations in their mechanical properties. These materials can be either too rigid, causing discomfort and excessive force on the teeth, or too soft, leading to insufficient force for effective movement. Over time, the aligners may also suffer from stress relaxation, reducing their effectiveness in continuing tooth movement. Additionally, many aligners struggle with poor interlayer bonding, which can result in permanent distortion and peeling of layers, compromising the performance of the device and patient safety. There is, therefore, a significant need for aligners that offer improved interlayer adhesion, consistent force application, better patient comfort, and enhanced durability.Summary of the Invention

[0003] In one aspect of the present invention, a dental sheet may be disclosed. The dental sheet for orthodontist treatment may include at least two outer layers and at least one inner layer. The at least one inner layer is interposed between the at least two outer layers to produce the dental sheet for fabricating aligners for providing comfort to a patient for orthodontist treatment. The at least two outer layers consist of polyester material having hardness from about 65D to 85D, flexural modulus from about 1500 MPa to 2500 MPa, and glass transition temperature from about 75 °C to 105 °C. The at least one inner layer consists of thermoplastic urethane elastomers having hardness in range of 50A to 75D, flexural modulus from about 500 MPa to 1600 MPa, and glass transition temperature from about -40 °C to 45 °C.

[0004] In an exemplary embodiment of the present invention, matte finish is optionally applied to one side.

[0005] In an exemplary embodiment of the present invention, number of layers in the dental sheet is in between 3 to 6.

[0006] In an exemplary embodiment of the present invention, thickness of the dental sheet is in range of 0.45 mm to 1.5mm.

[0007] In an exemplary embodiment of the present invention, the dental sheet possesses light transmission capacity in the range of 90% to 95 % or >90 %.

[0008] In an exemplary embodiment of the present invention, tensile modulus of the dental sheet is in range of 1000 to 2200 MPa.

[0009] In an exemplary embodiment of the present invention, tensile strength at yield of the dental sheet is in range of 20 to 80 MPa.

[0010] In an exemplary embodiment of the present invention, stress relaxation of the aligner sheer is in range between 5% and 30% at room temperature for 2 hours.

[0011] In an exemplary embodiment of the present invention, flexural strength of the dental sheet is in range of 25 to 75 MPa.

[0012] In an exemplary embodiment of the present invention, flexural modulus of the dental sheet is in range of 1000 to 1800 MPa.

[0013] In an exemplary embodiment of the present invention, elongation of the dental sheet is in range of 60% to 200 %.

[0014] In an exemplary embodiment of the present invention, water absorption rate of the dental sheet is in the range between 0.40% to 0.80% at 24 hours, 73°F, and 50% RH.

[0015] In an exemplary embodiment of the present invention, the dental sheet may be coated with an antibacterial agent on both sides.

[0016] In an exemplary embodiment of the present invention, the dental sheet is coated with teeth-cleaning agents on both sides.

[0017] In an exemplary embodiment of the present invention, the at least two outer layers consisting of polyester material are hard and / or rigid in nature.

[0018] In an exemplary embodiment of the present invention, the polyester material is selected from a group consisting of polyester, co-polyester, PETG (Polyethylene Terephthalate Glycol), and PCTG (Poly Cyclohexylenedimethylene Terephthalate Glycol-modified), and the mixtures thereof.

[0019] In an exemplary embodiment of the present invention, polymeric backbone structure of the polyester material includes a diester or diacid component, which is selected from the group consisting of Terephthalic acid (TP A), Isophthalic acid (IP A), Dimethyl terephthalate (DMT), 4,4’-biphenyldicarboxylic acid, and Trans-4, 4’ -stilbenedicarboxylic acid.

[0020] In an exemplary embodiment of the present invention, the polymeric backbone structure of the polyester material further includes a diol component.

[0021] In an exemplary embodiment of the present invention, the diol component consists of Ethylene glycol (EG) from about 35 to 85 mol% and TMCD (cis / trans-2,2,4,4-Tetramethyl-l,3-cyclobutanediol) from about 15 to 65 mol%.

[0022] In an exemplary embodiment of the present invention, the diol component consists of Ethylene glycol (EG) from about 35 to 85 mol% and CHDM (cis / trans-l,4-Cyclohexanedimethanol) from about 15 to 65 mol%.

[0023] In an exemplary embodiment of the present invention, the diol component consists of Ethylene glycol (EG) from about 35 to 85 mol% and a combination of TMCD (cis / trans-2, 2,4,4-Tetramethyl-l,3-cyclobutanediol) and CHDM (cis / trans-l,4-Cyclohexanedimethanol) from about 15 to 65 mol%.

[0024] In an exemplary embodiment of the present invention, the cis / trans ratio of CHDM is in range of 40:60 to 60:40 for providing controlled crystallinity of the polyester material.

[0025] In an exemplary embodiment of the present invention, the at least one inner layer consisting of a thermoplastic urethane elastomer is soft in nature.

[0026] In an exemplary embodiment of the present invention, the thermoplastic urethane elastomer is selected from a group consisting of thermoplastic elastomer (TPE), thermoplastic vulcanizates (TPV), elastomeric co-poly (ether or ester-ester), elastomeric co-poly (ether or esteramide), co-polymers of ethylene-methyl (EMA) or ethyl ene-butyl acrylate (EBA), and the mixtures thereof.

[0027] In an exemplary embodiment of the present invention, the thermoplastic urethane elastomer may include a polymeric backbone structure of the thermoplastic urethane elastomer, which includes a hard segment (diisocyanate), a soft segment (long chain diol), and a chain extender.

[0028] In an exemplary embodiment of the present invention, the hard segment of the polymeric backbone structure of the thermoplastic urethane elastomer containing one or more components selected from the group consisting of 2,4-diisocyanato-l -methylbenzene (TDI), l-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene (MDI), 1,6-diisocyanatohexane (HDI), l,T-methanediylbis(4-isocyanatocyclohexane) (HMDI), 5-isocyanato-l-(isocyanatomethyl)-l,3,3-trimethylcyclohexane (IPDI), l,l’-methylenebis(4-isocyanatocyclohexane), and the mixtures thereof.

[0029] In an exemplary embodiment of the present invention, the soft segment of the polymeric backbone structure of the thermoplastic urethane elastomer containing one or more components selected from the group consisting of ether-based polyols- polytetramethylene ether (PTMEG), polycarbonate polyol- 2, 2'-[sulfanediylbis(benzene-l,4-diyloxy)]di ethanol, polycarbonate polyolpoly hexamethylene carbonate diol, and the mixtures thereof.

[0030] In an exemplary embodiment of the present invention, the chain extender of the polymeric backbone structure of the thermoplastic urethane elastomer containing one or more components selected from the group consisting of Propane-1, 3-diol, Butane-l,4-diol, 1,6-Hexanediol, and the mixtures thereof.

[0031] In an exemplary embodiment of the present invention, molar ratio of the hard segment (diisocyanate) to polyols (NCO OH) is in the range of 1 :2 to 1 :4 for controlling mechanical and thermal properties of the thermoplastic urethane elastomer.

[0032] In an exemplary embodiment of the present invention, the ratio of hard segment to soft segment in the thermoplastic urethane elastomer is in between 35% to 55% and 45% to 65%, respectively.

[0033] In an exemplary embodiment of the present invention, the average molecular weight (Mw) of the polymeric backbone structure of the thermoplastic urethane elastomer is in the range of 100,000 to 300,000 g / mol.

[0034] In another aspect of the present invention, an apparatus for producing a dental sheet is disclosed. The apparatus includes an extrusion unit configured to extrude molten plastic through one or more extruders, a conveying unit for receiving the extruded molten plastic to produce a dental sheet, a thickness monitoring unit configured to measure the thickness of the dental sheet produced by the conveying unit, a corona treatment unit configured to treat designated surfaces of the dental sheet using a high-voltage discharge to enhance surface energy and adhesion properties, an unwinder roll configured to collect the dental sheet after corona treatment for shaping, and a lamination unit for laminating at least three layers of the dental sheet for transparency.

[0035] In an exemplary embodiment of the present invention, the extruded molten plastic maintains a processing temperature in the range of 220°C to 340°C to achieve melt homogeneity.

[0036] In an exemplary embodiment of the present invention, the apparatus optionally includes a drying unit to maintain a drying temperature in the range of 65°C to 95°C for 8 to 12 hours.

[0037] In an exemplary embodiment of the present invention, the L / D ratio of the one or more extruders is 20 to 45.

[0038] In an exemplary embodiment of the present invention, the conveying unit further includes a set of rollers with temperature-controlled quenching to create a microcrystalline structure by maintaining 25±10°C for the first roller, 55±10°C for the second roller, and 100±10°C for the third roller.

[0039] In an exemplary embodiment of the present invention, the set of rollers is configured to impart a desired thickness to the extruded molten plastic, stabilize the extruded molten plastic duringcooling to enhance structural integrity, and cool the extruded molten plastic to a stabilized temperature to prevent deformation and produce the dental sheet.

[0040] In an exemplary embodiment of the present invention, the set of rollers is equipped with a static eliminator to reduce static charge buildup.

[0041] In an exemplary embodiment of the present invention, the conveying unit includes an idler roller to provide alignment to each layer of the dental sheet

[0042] In an exemplary embodiment of the present invention, the conveying unit includes a plurality of rubber conveyor rollers to transport each layer of the dental sheet for further processing.

[0043] In an exemplary embodiment of the present invention, the apparatus includes a trimmer configured to remove excess material or uneven edges from the dental sheet after thickness measurement.

[0044] In an exemplary embodiment of the present invention, the treating of designated surfaces of a layer of the dental sheet in the corona treatment unit involves placing the dental sheet formed by the set of rollers in proximity to a high-voltage discharge unit, creating an air gap between the material and electrodes. A high-voltage potential is then applied across the air gap, ionizing the surrounding air and forming a corona discharge, which appears as a blue flame discharge. This corona discharge is directed towards the designated surface of the dental sheet, where the high-energy corona interacts with the surface, breaking molecular bonds present on it. As a result, free radicals are generated, which react with oxygen molecules in the air, leading to the formation of polar functional groups on the surface of the dental sheet. These polar functional groups increase the surface energy of the dental sheet, making it suitable for coatings, inks, adhesives, or lamination. The corona treatment is applied selectively to the designated surface facing the electrode, ensuring that the opposite surface remains unaffected, ultimately resulting in a controlled increase in surface energy on the treated side.

[0045] In an exemplary embodiment of the present invention, at least one inner layer optionally undergoes corona treatment on both sides.

[0046] In another aspect of the present invention, the corona treatment raises the surface energy of the dental sheet to a range of 46 to 56 Dynes / cm, making the surface suitable for efficient bonding and lamination.

[0047] In an exemplary embodiment of the present invention, the set of rollers further includes a temperature control unit for the set of rollers to optimize the temperature profile for stable cooling of the molten dental sheet to prevent bending and stability issues.

[0048] In an exemplary embodiment of the present invention, the apparatus includes a monitoring unit to ensure that temperature profiles, processing conditions, and thickness parameters remain within specified ranges.

[0049] In yet another aspect of the present invention, a method for producing a dental sheet is disclosed. The method begins with extruding molten plastic through one or more extruders of the extrusion unit, ensuring proper melt flow and material consistency. The extruded plastic is then received by a conveying unit, which stabilizes and transports the dental sheet for further processing. Next, a thickness monitoring unit measures the thickness of the dental sheet, ensuring dimensional accuracy and uniformity The designated surfaces of the dental sheet are then treated by a corona treatment unit, where a high-voltage discharge enhances surface energy and adhesion properties, preparing the dental sheet for coatings, inks, adhesives, or lamination. After surface treatment, the unwinder unit collects the dental sheet, ensuring proper tension control and alignment before further processing. Finally, the lamination unit bonds at least three layers of the dental sheet, ensuring optical transparency, structural integrity, and durability for orthodontic and dental applications. In one of the exemplary embodiments of the present invention, the surface treated dental sheet may be mounted on the set of rollers and may be pre-heated with the heater within the temperature range between 85 °C to 120 °C and post the treatment the surface treated dental sheet may be fed into the heated rollers for the lamination. The lamination temperature ranges between 85 °C to 155 °C.

[0050] In an exemplary embodiment of the present invention, the extruded molten plastic maintains a processing temperature in the range of 220°C to 340°C to achieve melt homogeneity.

[0051] In an exemplary embodiment of the present invention, the apparatus optionally includes a drying unit to maintain a drying temperature in the range of 65°C to 95°C for 8 to 12 hours.

[0052] In an exemplary embodiment of the present invention, the L / D ratio of the one or more extruders is 20 to 45.

[0053] In an exemplary embodiment of the present invention, the conveying unit further includes a set of rollers with temperature-controlled quenching to create a microcrystalline structure by maintaining 25±10°C for the first roller, 55±10°C for the second roller, and 100±10°C for the third roller.

[0054] In an exemplary embodiment of the present invention, the set of rollers is configured to impart a desired thickness to the extruded molten plastic, stabilize the extruded molten plastic during cooling to enhance structural integrity, and cool the extruded molten plastic to a stabilized temperature to prevent deformation and produce the dental sheet.

[0055] In an exemplary embodiment of the present invention, the set of rollers is equipped with a static eliminator to reduce static charge buildup.

[0056] In an exemplary embodiment of the present invention, the conveying unit includes an idler roller to provide alignment to each layer of the dental sheet.

[0057] In an exemplary embodiment of the present invention, the conveying unit includes a plurality of rubber conveyor rollers to transport each layer of the dental sheet for further processing.

[0058] In an exemplary embodiment of the present invention, the apparatus includes a trimmer configured to remove excess material or uneven edges from the dental sheet after thickness measurement.

[0059] In an exemplary embodiment of the present invention, the treating of designated surfaces of a layer of the dental sheet in the corona treatment unit involves placing the dental sheet formed by the set of rollers in proximity to a high-voltage discharge unit, creating an air gap between the material and electrodes. A high-voltage potential is then applied across the air gap, ionizing the surrounding air and forming a corona discharge, which appears as a blue flame discharge. This corona discharge is directed towards the designated surface of the dental sheet, where the high-energy corona interacts with the surface, breaking molecular bonds present on it. As a result, free radicals are generated, which react with oxygen molecules in the air, leading to the formation of polar functional groups on the surface of the dental sheet. These polar functional groups increase the surface energy of the dental sheet, making it suitable for coatings, inks, adhesives, or lamination. The corona treatment is applied selectively to the designated surface facing the electrode, ensuring that the opposite surface remains unaffected, ultimately resulting in a controlled increase in surface energy on the treated side.

[0060] In an exemplary embodiment of the present invention, at least one inner layer optionally undergoes corona treatment on both sides.

[0061] In another aspect of the present invention, the corona treatment raises the surface energy of the dental sheet to a range of 46 to 56 Dynes / cm, making the surface suitable for efficient bonding and lamination.

[0062] In an exemplary embodiment of the present invention, the set of rollers further includes a temperature control unit for the set of rollers to optimize the temperature profile for stable cooling of the molten dental sheet to prevent bending and stability issues.

[0063] In an exemplary embodiment of the present invention, the apparatus includes a monitoring unit to ensure that temperature profiles, processing conditions, and thickness parameters remain within specified ranges.Brief description of the accompanying Drawings

[0064] The novel features and characteristics of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments arenow described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

[0065] Fig. 1 illustrates a dental sheet, in accordance with an exemplary embodiment of the present invention.

[0066] Fig. 2 illustrates an apparatus for producing the dental sheet, in accordance with an exemplary embodiment of the present invention.

[0067] Fig. 3 illustrates a flowchart of a method for treating the dental sheet, in accordance with an exemplary embodiment of the present invention.

[0068] Fig. 4 illustrates an apparatus for producing a multi-layered dental sheet, in accordance with an exemplary embodiment of the present invention.

[0069] Fig. 5 illustrates a flowchart of a method for producing the dental sheet, in accordance with an exemplary embodiment of the present invention.

[0070] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.Detailed Description of the Invention

[0071] Detailed embodiments and implementations of the claimed subject matter are disclosed herein in detail with the technical matters, structural features, achieved objects, and effects with reference to the accompanying drawings as follows. It shall be understood that the disclosed embodiments and implementations are merely illustrative of the claimed subject matter, which may be embodied in various forms. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments and implementations set forth herein. Rather, these exemplary embodiments and implementations are provided so that the description of the present disclosure is thorough and complete and will fully convey the scope of the present disclosure to those skilled in the art. Specifically, the terminologies in the embodiments of the present disclosure are merely for describing the purpose of the certain embodiment but not to limit the disclosure. In the description below, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments and implementations.

[0072] The particular configurations discussed in the following description are nonlimiting examples that can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof

[0073] The present invention discloses a dental sheet and an apparatus for producing the same. The aligner thus formed may be used for orthodontist treatment.

[0074] The terms such as aligner, retainer, dental aligner, dental retainer, clear aligner, invisible aligner, clear retainer, invisible retainer, orthodontic aligner, orthodontal aligner, orthodontic retainer, orthodontal retainer, and / or similar terms may be used interchangeably for the aligner that may be used for proper alignment of teeth.

[0075] The terms such as conveyor roller, rubber conveyor roller, rubber conveying roller, and / or similar terms may be used interchangeably for the conveying roller.

[0076] The terms such as sheet, retainer sheet, dental aligner sheet, dental retainer sheet, clear aligner sheet, invisible aligner sheet, clear retainer sheet, invisible retainer sheet, orthodontic aligner sheet, orthodontal aligner sheet, orthodontic retainer sheet, orthodontal retainer sheet, and / or similar terms may be used interchangeably for the dental sheet that may be used for orthodontic applications.

[0077] Various non-limiting benefits of the present invention include the production of high-transparency and crack-resistant dental sheets, ensuring durability and long-term usability. The dental sheets may maintain consistent mechanical properties, allowing aligners and other dental appliances to sustain controlled force application over time, promoting effective tooth movement. The dental sheets may be produced to be stain-resistant, maintaining their aesthetic appearance throughout extended use. The dental sheet produced may enhance comfort and incorporate optimized hardness and flexibility to reduce patient discomfort. The high optical clarity of the dental sheet may provide clear visibility through the aligner, minimizing visual distortion for a more natural look. The dental sheets may be formulated for efficient thermoforming, ensuring they can be easily molded and released from thermoforming tools without deformation. The dental sheet produced may maintain structural integrity under various conditions, ensuring long-term effectiveness. The dental sheet may exhibit strong interfacial adhesion, preventing delamination or peeling, thereby improving device performance and reliability. The dental sheet may demonstrate excellent stress retention behavior, with its rubbery elastomer composition effectively retaining stress to facilitate efficient tooth movement. The dental sheet may also be coated with antibacterial agents on both sides, enhancing oral hygiene and reducing the risk of bacterial buildup. Additionally, the dental sheet may be coated with teeth-cleaning agents, aiding in the maintenance of oral health during wear. The material possesses low polymer creep, ensuring the dental sheet retains shape and does not deform under prolonged use. The aligners or dental appliances fabricated from the dental sheet may be biocompatible, meeting medical-grade safetystandards with low toxicity and minimal potential for adverse reactions, making them safe and comfortable for long-term intraoral use. Furthermore, the dental sheet may possess low water absorption, preventing moisture-related degradation, thereby enhancing the durability and longevity of the dental sheet.

[0078] The present invention discloses a dental sheet for orthodontist treatment. Fig. 1 of the present invention illustrates the dental sheet (100) in accordance with various embodiments of the present invention. The dental sheet (100) may be used for fabricating aligners. The dental sheet (100) may include at least two outer layers (102) and at least one inner layer (104). The dental sheet (100) may be molded according to the structure of the dental arch of the patient.

[0079] The at least two outer layers (102) of the dental sheet (100) may include polyester material. The co-polyester material as the outer layer in the dental sheet (100) may offer several significant benefits. Firstly, polyester is known for the exceptional transparency, which is significant for maintaining the aesthetic appeal of clear aligners. Polyester material may ensure that the aligners remain virtually invisible when worn, enhancing patient confidence and compliance. Additionally, polyester material may exhibit exceptional resistance to cracking and deformation, contributing to the durability and longevity of the aligner. This resistance to physical stress may ensure that the aligners maintain their shape and functionality over the course of the treatment. Moreover, the resistance of the polyester material to staining helps maintain a clean and clear appearance, even with prolonged use. The high dimensional stability of the polyester materials may ensure that the aligners fit precisely and consistently, providing effective and continuous force application for tooth movement. Moisture of the Polyester material resistance also plays a vital role in preserving the structural integrity of the aligner and performance, even in the moist environment of the mouth. Furthermore, polyester materials facilitate the thermoforming process, allowing for efficient and precise manufacturing of the aligners. This combination of aesthetic, mechanical, and functional properties makes polyester an ideal choice for the outer layer of orthodontic aligners.

[0080] In one of the exemplary embodiments of the present invention, the polyester material may possess hardness from about 65D to 875D. In general, hardness in this context is measured using the Shore D scale, which quantifies the resistance of the material to indentation. The Shore D hardness scale is typically used for harder materials, such as plastics and polymers. In one of the exemplary embodiments of the present invention, the hardness of 65 D signifies the lower end of this range, which means that the material is relatively hard but still offers some degree of flexibility. This level of hardness is sufficient for applications requiring a balance between rigidity and impact resistance. In another exemplary embodiment of the present invention, the hardness of 875 D signifies the upper end, which means that the material is quite rigid, providing significant resistance to deformation under force.This higher hardness makes the material more suitable for applications needing strong structural integrity and minimal deformation.

[0081] In one of the exemplary embodiments of the present invention, the hardness range from 65D to 875D may indicate that the polyester material is versatile and capable of offering various levels of rigidity based on the specific needs of the dental sheet (100). For aligners, this hardness ensures that the material maintains its shape and provides consistent force application while still being comfortable to wear.

[0082] In one of the exemplary embodiments of the present invention, the polyester material may possess flexural modulus from about 1500 Mpa to 2500 MPa. In general, the flexural modulus measures the stiffness of the material when subjected to bending. It indicates how much the material will bend under a given load, with a higher flexural modulus signifying greater stiffness. In one of the exemplary embodiments of the present invention, the flexural modulus of 1500 MPa signifies the lower end of the range, which means that the material has moderate stiffness, allowing it to bend under stress but still maintain its form. This level is suitable for applications requiring some flexibility while ensuring structural stability. In one of the exemplary embodiments of the present invention, the flexural modulus of 1500 MPa signifies a higher end, which means that the material exhibits high stiffness and resistance to bending, making it more rigid and less likely to deform under load. This higher flexural modulus is ideal for applications where maintaining precise shapes and alignment is crucial. A flexural modulus range from 1500 MPa to 2500 MPa means the polyester material can be tailored for different levels of stiffness in the dental sheet (100). This ensures that the aligner can effectively apply corrective forces to teeth while maintaining comfort and durability.

[0083] In one of the exemplary embodiments of the present invention, the polyester material may possess a glass transition temperature from about 75 °C to 105 °C. In general, the glass transition temperature is the temperature range over which a polymer transitions from a hard, glassy state to a softer, rubbery state. Below the Tg, the material is rigid and brittle; above the Tg, it becomes more flexible and less rigid. In one of the exemplary embodiments of the present invention, the glass transition temperature of 75°C Tg signifies the lower end, which means that the material transitions to a rubbery state at a relatively lower temperature. This allows it to remain somewhat flexible and less brittle at temperatures typical for room temperature and slightly elevated conditions. In one of the exemplary embodiments of the present invention, the glass transition temperature of 105°C Tg signifies the higher end, which means that the material remains in a glassy state up to a higher temperature before becoming rubbery. This ensures the material retains its rigidity and structural integrity under more elevated conditions, providing durability and stability in warmer environments. The Tg range of 75°C to 105°C indicates that the polyester material can perform well under a range of temperatures,making it suitable for environments where temperature fluctuations occur. For dental sheet (100), this ensures that the material maintains its desired properties throughout various conditions, including those encountered during daily wear and exposure to different temperatures.

[0084] The polyester material used for the at least two outer layers (102) of the dental sheet (100) may be hard and / or rigid in nature. Such construction may ensure the aligner produced from the dental sheet (100) maintains structural integrity and may provide consistent force for effective tooth movement.

[0085] In one of the exemplary embodiments of the present invention, the polyester material used in the outer layers of the dental sheet (100) may be selected from a group consisting of polyester, copolyester, PETG (Polyethylene Terephthalate Glycol), and PCTG (Poly Cyclohexylenedimethylene Terephthalate Glycol-modified). In another exemplary embodiment of the present invention, the polyester material used in the outer layers of the dental sheet (100) may be a mixture of any two or more components of polyester, co-polyester, PETG (Polyethylene Terephthalate Glycol), and PCTG (Poly Cyclohexylenedimethylene Terephthalate Glycol-modified). Such materials are known for their excellent mechanical properties, including high strength and durability, making them ideal for orthodontic applications where maintaining precise shape and force is critical.

[0086] The polyester material used in the outer layers of the dental sheet (100) may further include a polymeric backbone structure. In one of the exemplary embodiments of the present invention, the polymeric backbone structure of the polyester material may include a diester or a diacid component. The diester or the diacid component may be selected from the group consisting of Terephthalic acid (TP A), Isophthalic acid (IPA), Dimethyl terephthalate (DMT), 4,4’-biphenyldicarboxylic acid, and Trans-4,4’-stilbenedicarboxylic acid. Such diester or diacid components contribute to the rigidity and mechanical stability of the polyester material, ensuring that the aligner can withstand the stresses and strains of daily use without deforming or cracking.

[0087] In addition to the diacid component, the polymeric backbone structure of the polyester material further includes a diol component. The inclusion of the diol component enhances the flexibility and impact resistance of the polyester material, balancing the rigidity provided by the diacid component to create a material that is both strong and resilient.

[0088] In one of the exemplary embodiments of the present invention, the diol component of the polymeric backbone structure may include Ethylene glycol (EG) from about 35 to 85 mol% and TMCD (cis / trans-2,2,4,4-Tetramethyl-l,3-cyclobutanediol) from about 15 to 65 mol%. This specific combination of diols is designed to optimize the balance between rigidity and flexibility in the polyester material, ensuring the aligner remains comfortable for the patient while providing effective orthodontic force.

[0089] In another exemplary embodiment of the present invention, the diol component of the polymeric backbone structure may include Ethylene glycol (EG) from about 35 to 85 mol% and CHDM (cis / trans-l,4-Cyclohexanedimethanol) from about 15 to 65 mol%. CHDM is known for its ability to improve the impact resistance and durability of polyesters, further enhancing the performance of the dental sheet (100).

[0090] In another exemplary embodiment of the present invention, the diol component of the polymeric backbone structure may include a combination of Ethylene glycol (EG) from about 35 to 85 mol% and a mixture of TMCD and CHDM from about 15 to 65 mol%. This combination leverages the benefits of both TMCD and CHDM, providing a polyester material with superior mechanical properties and comfort characteristics for orthodontic aligners.

[0091] In one of the exemplary embodiments of the present invention, the ratio of cis / trans isomers of CHDM in the diol component may be adjusted and may vary in the range of 40:60 to 60:40 to control the crystallinity of the polyester material. Controlled crystallinity is crucial for optimizing the mechanical properties of the material, ensuring that the aligner maintains its desired shape and force application throughout the treatment period.

[0092] The dental sheet (100) fabricated from this multi-layered polyester material offers numerous advantages, such as the aligner thus produced from said dental sheet (100) may be transparent, crack-resistant, and may maintain consistent force application overtime, ensuring effective tooth movement. The resistance of the material to staining preserves the aesthetic appearance of the aligners, and the combination of hard and soft layers enhances patient comfort.

[0093] The dental sheet (100) provides clear visibility and minimizes visual distortion, which is essential for aesthetic orthodontic treatments. The strong interfacial adhesion of the polyester material may be greater than 150 grams / inch between adjacent layers, ensuring structural integrity and longterm performance of the aligner. Also, the dental sheet (100) may be coated with antibacterial agents on both sides to enhance oral hygiene and with teeth cleaning agents to aid in maintaining dental health. Further, the dental sheet (100) may possess reduced polymer creep such that 4 to 10 % at room temperature in 24 hours, biocompatibility, and low water absorption in the range of 0.40% to 0.80% at (24 hr, 73°F, 50% RH) for the overall system which enhances the durability and safety of the aligner, thereby making the aligner suitable for extended use in the human body and meeting medical-grade standards. In a preferred embodiment of the present invention, the low water absorption rate is 0.50% at 24 hr, 73°F, 50% RH for the overall system.

[0094] The at least one inner layer (104) of the dental sheet (100) may include thermoplastic urethane elastomer. Thermoplastic urethane elastomer (TPU) may serve as an exceptional material for the inner layer of orthodontic dental sheet (100)s due to its unique combination of flexibility, strength,and biocompatibility. The Thermoplastic urethane elastomer (TPU) may possess softness, which may enhance patient comfort by allowing the aligner to conform closely to the contours of the teeth, reducing the discomfort often associated with rigid orthodontic devices. Such adaptability is significant for maintaining consistent and gentle pressure on the teeth, which may be essential for effective and gradual tooth movement. The inherent elasticity of the thermoplastic urethane elastomer (TPU) may ensure that the aligner may withstand repetitive stress and deformation without losing shape, providing durable performance throughout the treatment period. Moreover, thermoplastic urethane elastomer (TPU) may possess excellent stress retention capabilities, which may enable the Thermoplastic urethane elastomer (TPU) to maintain the necessary corrective forces over extended periods, reducing the frequency of aligner replacements. In one of the exemplary embodiments of the present invention, the stress relaxation (reduced polymer creep) is in the range between 5% to 30% at room temperature for 2 hours. The biocompatibility of the thermoplastic urethane elastomer (TPU) may make the Thermoplastic urethane elastomer (TPU) safe for prolonged contact with sensitive tissues of the mouth, thereby minimizing the risk of adverse reactions and ensuring patient safety. Additionally, the resistance of the thermoplastic urethane elastomer (TPU) to abrasion and wear may ensure that the aligner remains effective and aesthetically pleasing throughout use. The ability of the thermoplastic urethane elastomer (TPU) to form strong bonds with other materials such as polyester materials in the multi-layered structure of the dental sheet (100) may enhance the overall durability and integrity of the device, preventing delamination and ensuring long-term reliability. Overall, the use of Thermoplastic urethane elastomer (TPU) as the at least one inner layer (104) in orthodontic aligners may provide a blend of comfort, performance, and safety that significantly benefits both patients and practitioners.

[0095] In one of the exemplary embodiments of the present invention, the thermoplastic urethane elastomer may possess hardness from about 50A to 75D. In general, hardness for thermoplastic urethane elastomers is measured on the Shore A scale, which is used for softer materials compared to the Shore D scale. It indicates how resistant the material is to indentation and deformation. In one of the exemplary embodiments of the present invention, the hardness of 50 A signifies the lower end of this range, which means that the thermoplastic urethane elastomers are relatively soft and flexible. This level of hardness allows for considerable deformation under applied force, which can enhance comfort and conformability in applications like aligners. It provides a cushioned feel and adaptability to the teeth of the wearer or user. In another exemplary embodiment of the present invention, the hardness of 90 A signifies the upper end, which means that the thermoplastic urethane elastomers become more rigid but still maintain some degree of flexibility. This hardness level offers a balance between structural support and comfort, ensuring that the aligner can apply effective corrective forces without being overly rigid. In one of the exemplary embodiments of the present invention, the hardness rangefrom 50A to 75D allows for customization of the thermoplastic urethane elastomers layer to suit different needs in aligner applications. Softer materials are more comfortable, while harder ones provide greater support and resistance to deformation.

[0096] In one of the exemplary embodiments of the present invention, the thermoplastic urethane elastomer may possess flexural modulus from about 500 MPa to 1600 MPa. In general, the flexural modulus measures the stiffness of the material in response to bending forces. A higher flexural modulus indicates greater stiffness and resistance to bending. In one of the exemplary embodiments of the present invention, the flexural modulus of 500 MPa signifies the lower end of the range, which means the thermoplastic urethane elastomer exhibits moderate stiffness, allowing it to bend more easily under stress. This provides a degree of flexibility and compliance, which can be beneficial for creating a comfortable fit around the teeth while still supporting corrective movements. In one of the exemplary embodiments of the present invention, the flexural modulus of 1600 MPa signifies a higher end, which means that the thermoplastic urethane elastomer is much stiffer, offering significant resistance to bending. This higher modulus ensures that the material maintains its shape and structural integrity, providing a more rigid support for effective force application. The range from 500 MPa to 1600 MPa in the flexural modulus allows for the thermoplastic urethane elastomer layer to be tailored based on the required balance between flexibility and stiffness. For dental sheet (100)s, this ensures the material can conform to the teeth while maintaining the necessary support for orthodontic treatment.

[0097] In one of the exemplary embodiments of the present invention, the thermoplastic urethane elastomer may possess a glass transition temperature from about -40°C to 45°C. In general, the glass transition temperature is the temperature range over which a polymer transitions from a rigid, glassy state to a softer, rubbery state. Below Tg, the material is hard and brittle, while above Tg, it becomes more flexible and rubber-like. In one of the exemplary embodiments of the present invention, the glass transition temperature of -40°C Tg signifies the lower end, which means that the thermoplastic urethane elastomer remains flexible even at very low temperatures. This characteristic ensures that the dental sheet (100) will not become brittle or lose its flexibility under cold conditions, maintaining comfort and performance even in cooler environments. In one of the exemplary embodiments of the present invention, the glass transition temperature of 45°C Tg signifies the higher end, which means that thermoplastic urethane elastomer starts to transition to a more rubbery state at temperatures above 45°C. This ensures that the material remains functional and does not become excessively soft or deform under typical body temperatures and slightly elevated conditions. The Tg range of -40°C to 45°C ensures that the TPU inner layer maintains its desired properties across a broad temperature range. For dental sheet (100)s, this means the material will stay flexible and comfortable in various environmental conditions, providing reliable performance during use.

[0098] The thermoplastic urethane elastomer (TPU) used for the at least one inner layer (104) of the dental sheet (100) may be soft. Such construction may ensure that the aligner produced from the dental sheet (100) is flexible and comfortable for the patient while still providing the necessary force to move the teeth effectively.

[0099] The thermoplastic urethane elastomer used in the at least one inner layer ( 104) of the dental sheet (100) may be selected from a diverse group of materials, including thermoplastic elastomer (TPE), thermoplastic vulcanizates (TPV), elastomeric co-poly (ether or ester-ester), elastomeric co-poly (ether or ester-amide), co-polymers of ethylene-methyl (EMA) or ethyl ene-butyl acrylate (EBA), and mixtures thereof. These materials are chosen for their excellent flexibility, durability, and biocompatibility, making them ideal for prolonged use in orthodontic applications.

[0100] The thermoplastic urethane elastomer used in the at least one inner layer ( 104) of the dental sheet (100) may include a polymeric backbone structure. The polymeric backbone structure of the thermoplastic urethane elastomer that may be used in the at least one inner layer (104) of the dental sheet (100) may include a hard segment (diisocyanate), a soft segment (long chain diol), and a chain extender. Such unique composition allows the material to exhibit both rigidity and flexibility, which may be crucial for maintaining the shape of the aligner and function over time while providing comfort to the patient.

[0101] In one of the exemplary embodiments of the present invention, the hard segment of the polymeric backbone structure of the thermoplastic urethane elastomer may include at least one component from the group of components such as 2,4-diisocyanato-l-methylbenzene (TDI), 1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene (MDI), 1,6-diisocyanatohexane (HDI), 1,1'-methanediylbis(4-isocyanatocyclohexane) (HMDI), 5-isocyanato-l-(isocyanatomethyl)-l,3,3-trimethylcyclohexane (IPDI), l,l’-methylenebis(4-isocyanatocyclohexane). In another exemplary embodiment of the present invention, the hard segment of the polymeric backbone structure of the thermoplastic urethane elastomer may include a mixture of any two or more components that may be selected from the from the group of components such as 2,4-diisocyanato-l-methylbenzene (TDI), 1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene (MDI), 1,6-diisocyanatohexane (HDI), 1,1'-methanediylbis(4-isocyanatocyclohexane) (HMDI), 5-isocyanato-l-(isocyanatomethyl)-l,3,3-trimethylcyclohexane (IPDI), l,l’-methylenebis(4-isocyanatocyclohexane). These hard segments or diisocyanates are selected for their ability to form strong and durable polymer chains that contribute to the overall strength and stability of the aligner.

[0102] In one of the exemplary embodiments of the present invention, the soft segment or long chain diol of the polymeric backbone structure may include components such as ether-based polyols like polytetramethylene ether (PTMEG) and polycarbonate polyols like 2,2'-[sulfanediylbis(benzene-l,4-diyloxy)]di ethanol and poly hexamethylene carbonatediol. In another exemplary embodiment of the present invention, the soft segment or long chain diol of the polymeric backbone structure of the thermoplastic urethane elastomer may include a mixture of any two or more components that may be selected from the group of components such as ether-based polyols like polytetramethylene ether (PTMEG) and polycarbonate polyols like 2,2'-[sulfanediylbis(benzene-l,4-diyloxy)]diethanol and poly hexamethylene carbonatediol. These components impart flexibility and elasticity to the material, ensuring the aligner can conform comfortably to the teeth of the patient while applying the necessary corrective forces.

[0103] In one of the exemplary embodiments of the present invention, the chain extender in the polymeric backbone structure of the thermoplastic urethane elastomer may include components such as Propane- 1,3 -diol, Butane- 1 ,4-diol, 1,6-Hexanediol, and their mixtures. Chain extenders are crucial in modifying the mechanical properties of the polymer, enhancing its strength, and facilitating the formation of a robust, interconnected polymer network.

[0104] In one of the exemplary embodiments of the present invention, molar ratio of the hard segment (diisocyanate) to polyols (NCO:OH) in the thermoplastic urethane elastomer may be adjusted in the range of 1 :2 to 1 :4. This ratio is critical for controlling the mechanical and thermal properties of the elastomer, allowing the aligner to maintain its structural integrity and performance under various conditions. Also, the ratio of the hard segment (diisocyanate) to the soft segment (long chain diol) in the thermoplastic urethane elastomer may be typically between 35% to 55% and 45% to 65%, respectively. This balance ensures that the material possesses the right combination of rigidity and flexibility, providing a stable yet comfortable fit for the patient throughout the treatment period.

[0105] In one of the exemplary embodiments of the present invention, the average molecular weight (Mw) of the polymeric backbone structure of the thermoplastic urethane elastomer is in the range of 100,000 to 300,000 g / mol. A higher molecular weight contributes to the strength of the material, durability, and overall performance, ensuring the aligner can withstand the mechanical stresses of daily use.

[0106] The multi-layered construction of the dental sheet (100), including hard polyester outer layers and a soft thermoplastic urethane elastomer inner layer in which the at least one inner layer (104) is interposed between the at least two outer layers (102) to produce the dental sheet (100) for fabricating the aligners to provide comfort to the patient for orthodontist treatment, provides several benefits. The hard outer layers protect against wear and deformation, while the soft inner layer enhances comfort and ensures the aligner can effectively move teeth without causing excessive discomfort. Also, the ability of the thermoplastic urethane elastomer to be tailored in terms of hardness and flexibility makes it highly versatile for orthodontic applications. By adjusting the composition and ratios of the hard andsoft segments, the mechanical properties of the aligner can be fine-tuned to meet specific treatment requirements and patient needs.

[0107] Additionally, the structure of the dental sheet (100) may ensure strong interlayer adhesion, preventing delamination and enhancing the overall durability of the aligner. This strong interlayer bonding is crucial for maintaining the integrity and effectiveness of the aligner over the course of the treatment. In one of the exemplary embodiments of the present invention, the manufacturing process for the dental sheet (100) involves precise control of the material composition and processing conditions to achieve the desired properties.

[0108] In one of the exemplary embodiments of the present invention, the present invention discloses an apparatus (200) for producing the dental sheet. Fig. 2 of the present invention illustrates an apparatus (200) for producing the dental sheet in accordance with various embodiments of the present invention. In one of the exemplary embodiments of the present invention, the apparatus (200) for producing the dental sheet may produce one or more layers of the dental sheet. In another exemplary embodiment of the present invention, the apparatus (200) for producing the dental sheet may produce a multi-layered dental sheet. The apparatus (200) for producing the dental sheet may include an extrusion unit, a conveying unit, a thickness monitoring unit (210), a corona treatment unit (214), an unwinder roll (218), a lamination unit, a drying unit, a trimmer (212), , and a monitoring unit.

[0109] The apparatus (200) includes the extrusion unit. The extrusion unit in the apparatus (200) for producing a dental sheet may be responsible for processing and forming the molten plastic (202) into a continuous sheet. In one of the exemplary embodiments of the present invention, the extrusion unit includes one or more extruders that may melt and push the plastic material through a die to achieve the desired thickness and consistency. The extruder may maintain a controlled processing temperature in the range of 220°C to 340°C to ensure melt homogeneity, preventing defects in the dental sheet. The molten plastic (202) may then be guided towards a conveying unit, where the dental sheet may undergo further processing, including thickness measurement, corona treatment, and lamination.

[0110] In one of the exemplary embodiments of the present invention, the one or more extruders of the extrusion unit may include an L / D ratio (length-to-diameter) of 20 to 45, which ensures sufficient shear mixing and uniform melting of the polymer material. This ratio may help in controlling the molecular orientation of the plastic, improving mechanical properties such as flexibility, transparency, and strength of the dental sheet. In another exemplary embodiment of the present invention, the extrusion unit may incorporate multiple heating zones along the barrel to regulate temperature distribution, preventing thermal degradation and ensuring consistent viscosity of the molten plastic (202). This precise thermal control may allow the production of the dental sheet with minimal thickness variation and improved surface quality. In another exemplary embodiment of the present invention, theextrusion unit may include an automated pressure regulation system that may monitor and adjust the extrusion pressure in real time. This may help in maintaining a stable flow rate, preventing defects such as die swell, uneven thickness, or void formation in the dental sheet.[OHl] Further, the apparatus (200) for producing the dental sheet includes a conveying unit. The conveying unit may be an essential component of the apparatus (200) for producing a dental sheet, facilitating the controlled movement of the extruded molten plastic (202) through subsequent processing stages. The conveying unit includes a set of rollers (204), an idler roller (206), and a plurality of conveyor rollers (208), each playing a distinct role in stabilizing, aligning, and processing the dental sheet. The set of rollers (204), the idler roller (206) and the plurality of conveyor rollers (208) may work in conjunction to ensure uniform thickness, structural integrity, and controlled cooling before the dental sheet undergoes thickness measurement, corona treatment, and lamination.

[0112] The conveying unit includes a set of rollers (204). In one of the exemplary embodiments of the present invention, the set of rollers (204) in the conveying unit may include a first roller, second roller, and third roller, each of which may be configured to regulate the cooling profile and impart mechanical stability to the molten plastic (202). The set of rollers (204) may be configured to maintain specific temperature profiles, allowing controlled quenching and preventing deformation. In one of the exemplary embodiments of the present invention, the extrusion unit may operate in conjunction with the set of rollers (204) of the conveying unit, which may be the temperature-controlled rollers, which may stabilize the extruded molten plastic (202) and create a microcrystalline structure. This is achieved by quenching the molten plastic (202) using a three-roller setup where the first roller may be maintained at 10-45°C, the second roller may be maintained at 15-55°C, and the third roller may be maintained at 50-120°C. This controlled cooling process may prevent warping, residual stresses, and thickness inconsistencies.

[0113] In one of the exemplary embodiments of the present invention, the set of rollers (204) of the conveying unit may fabricate the dental sheet upon receiving the extruded molten plastic (202) from the one or more extruders of the extrusion unit. The dental sheet thus produced may be the dental sheet with the microcrystalline structure through a controlled quenching process. In general, quenching is a heat treatment process that may be used to rapidly cool a material from a high temperature to a lower temperature, typically to achieve specific material properties. In the context of polymer processing, quenching refers to the rapid cooling of molten polymer to set its structure and enhance its final properties. The set of rollers (204) may be configured to perform a quenching process that may improve the crystalline structure, transparency, and mechanical properties of the dental sheet. By controlling the cooling rates and temperatures, the apparatus (200) may optimize the microstructure of the polymer, resulting in a final product with enhanced clarity, reduced optical haze, and improvedmechanical performance. In one of the exemplary embodiments of the present invention, the set of rollers (204) receives the extrudate in the molten state to produce one or more layers of the dental sheet using the process of quenching.

[0114] Quenching in polymer processing involves rapidly cooling molten polymer to achieve desired material properties and structure. In one of the exemplary embodiments of the present invention, the polymer may be heated to a high temperature, rendering the polymer molten. This molten polymer may then be extruded through a die to form sheets or films. Upon exiting the die, the polymer may undergo rapid cooling through a quenching system, which may include various methods such as rollers, airblasts, or water baths. The purpose of this rapid cooling is to set the structure of the polymer quickly and uniformly. This process may be crucial for controlling the crystalline structure of the polymer, which may impact the transparency of the dental sheet, mechanical properties, and overall performance. By controlling the quenching process, manufacturers may enhance the clarity of the polymer, optimize the balance between hardness and flexibility, and reduce internal stresses. This precise control over the cooling rate may help to ensure that the final polymer product meets specific quality and performance standards required for the intended application of the dental sheet.

[0115] In one of the exemplary embodiments of the present invention, the set of rollers (204) may be configured to perform multiple critical functions during the production of dental sheets. The set of rollers (204) may be configured to impart a precise and uniform thickness to the dental sheet by exerting controlled pressure across the surface of the extruded molten plastic (202). The configuration may ensure that the dental sheet achieves the desired dimensional accuracy, which may be crucial for orthodontic aligners requiring precise fitting. The set of rollers (204) may also stabilize the dental sheet during the cooling process, minimizing any distortions or irregularities caused by uneven cooling or mechanical stresses. This stabilization may be achieved through careful control of the temperature gradient and rotational speed of the set of rollers (204). Additionally, the set of rollers (204) may cool the dental sheet to a stabilized temperature, ensuring that the material may be solidified uniformly without deformation. By maintaining a consistent cooling rate, the apparatus (200) may enhance the structural integrity and optical properties of the dental sheet, resulting in a high-quality end product.

[0116] The set of rollers (204) is further configured for temperature-controlled quenching to create the microcrystalline structure. The first roller may initiate controlled cooling, the second roller may gradually condition the dental sheet, and the third roller may complete the cooling process, stabilizing the final microstructure while preventing warping and thickness inconsistencies.

[0117] In one of the exemplary embodiments of the present invention, the set of rollers (204) may include a temperature control unit, which may allow real-time adjustments of the cooling profile based on material properties and processing speed to maintain dimensional stability without defects such asbending or thickness variations, supporting the claims directed towards process optimization and uniformity in sheet properties.

[0118] In one exemplary embodiment of the present invention, the set of rollers (204) may include a static eliminator to prevent electrostatic buildup, which may attract contaminants, cause handling difficulties, or interfere with subsequent processing steps such as corona treatment and lamination. The static eliminator may ensure that the dental sheet remains clean and free from unwanted charges, thereby improving processing efficiency and maintaining product quality. In another exemplary embodiment of the present invention, the static eliminator may utilize ionized airflow technology, such as ionizing bars, to neutralize surface charges as the dental sheet passes through the rollers, effectively preventing adhesion-related defects. Electrostatic buildup during production may lead to sheet deformation, dust particle adherence, and operational inefficiencies. To address these issues, the static eliminator may continuously discharge accumulated static electricity, ensuring smooth sheet transport and handling. By integrating a static eliminator within the roller system, the apparatus (200) may enhance operational reliability, prevent mechanical distortions caused by static charge, and ensure that the final product remains free from contamination, thereby meeting stringent quality standards.

[0119] In one of the exemplary embodiments of the present invention, the set of rollers (204) may include a temperature control unit that may optimize the temperature profile for stable cooling of the molten dental sheet to prevent bending and stability issues. The temperature control unit may be configured to optimize the temperature profile of the set of rollers (204), ensuring that the cooling process may be uniform and controlled. Additionally, the set of rollers (204) may be equipped with an adjustment mechanism that may maintain uniform thickness across at least two or more outer layers and at least one inner layer (104) of the dental sheet, ensuring that the dental sheet may meet the required specifications.

[0120] The set of rollers (204) that may be integrated with the temperature control unit, static eliminator, and precise quenching mechanisms may ensure that the dental sheet maintains optimal structural, optical, and mechanical properties. By stabilizing the cooling process and eliminating static charges, the apparatus (200) may guarantee that the dental sheet remains contamination-free and meets stringent quality standards.

[0121] Further, the conveying unit includes the idler roller (206). The idler roller (206) in the conveying unit may serve as a guide and alignment mechanism, which may ensure smooth sheet transport from the extrusion unit to subsequent rollers. The idler roller (206) may help in maintaining proper tension and prevent wrinkling or misalignment of the dental sheet during processing. In one of the exemplary embodiments of the present invention, the idler roller (206) may be configured withlow-friction bearings to reduce drag while ensuring consistent sheet movement. The idler roller (206) may prevent material stress or distortion, ensuring high-quality output.

[0122] Further, the conveying unit may include a plurality of conveyor rollers (208) In one of the exemplary embodiments of the present invention, the plurality of conveying rollers may be the rubber conveying rollers. The plurality of conveying rollers in the conveying unit may transport the dental sheet between various processing stages, maintaining even tension and consistent speed. The plurality of conveying rollers may prevent slack or uneven feeding, ensuring smooth passage through thickness measurement, corona treatment, and lamination. In one of the exemplary embodiments of the present invention, the plurality of conveying rollers may be coated with anti-stick materials to minimize surface defects and prevent material adhesion during transport. This ensures continuous and uniform sheet movement, improving overall processing efficiency and product quality.

[0123] The conveying unit, with the combination of the set of rollers (204) including the first roller, the second roller, the third roller with the static eliminator and temperature controlled units, the idler roller (206), and the plurality of rubber conveyor rollers, may ensure that the dental sheet maintains precise thickness, dimensional stability, and surface cleanliness throughout processing.

[0124] The apparatus (200) may include the thickness monitoring unit (210). The thickness monitoring unit (210) may be configured to measure the thickness of the dental sheet produced by the conveying unit. The thickness monitoring unit (210) may be a critical component in the production of the dental sheet, ensuring dimensional accuracy and consistency. The thickness monitoring unit (210) may continuously measure the thickness of the dental sheet as the dental sheet moves through the conveying unit, detecting variations that may arise due to fluctuations in extrusion conditions, cooling rates, or mechanical stress. By integrating real-time monitoring with feedback control mechanisms, the thickness monitoring unit (210) may play a crucial role in maintaining quality standards and optimizing material usage.

[0125] In one of the exemplary embodiments of the present invention, the thickness monitoring unit (210) may include non-contact sensors, such as laser micrometers, capacitive sensors, or infrared sensors, which may provide continuous real-time measurements of the thickness of the dental sheet. If any deviations from the predefined thickness range are detected, the system may send a feedback signal to the extrusion unit, allowing adjustments to extrusion speed, die gap, or material feed rate. In an example, if the dental sheet may be thicker than required, the system may signal the extrusion unit to slightly reduce material flow, while if the dental sheet is too thin, it may increase the flow rate, ensuring uniformity across the entire sheet.

[0126] In another exemplary embodiment of the present invention, the thickness monitoring unit (210) may work in conjunction with a set of rollers (204), ensuring that the dental sheet may be evenlycompressed and stabilized. The first roller may initiate cooling and stabilization, the second roller conditions the dental sheet, and the third roller completes the cooling process, which may help achieve the desired thickness. In an example, if the monitoring unit detects thickness inconsistencies, the roller pressure or gap may be dynamically adjusted to bring the dental sheet within the required thickness range. For instance, if the dental sheet is too thick, the apparatus (200) increases roller compression, whereas if the dental sheet is too thin, the rollers apply less pressure, allowing slight material expansion.

[0127] In another exemplary embodiment of the present invention, the thickness monitoring unit (210) may incorporate optical interferometry or ultrasonic sensors to detect and log thickness variations along the length of the dental sheet. This method may ensure that any inconsistencies caused by extrusion fluctuations, roller misalignment, or uneven cooling may be identified and corrected before further processing. In an example, ultrasonic sensors may be placed at multiple points across the dental sheet width to measure thickness distribution, ensuring that the dental sheet is uniform from edge to edge. If variations are detected, automatic adjustments may be made to ensure consistent product quality.

[0128] Example 1 : High-Precision Dental Sheet for Orthodontic Aligners

[0129] For orthodontic aligners, precision thickness control is critical to ensuring proper fit and functionality. The thickness monitoring unit (210), integrated with real-time adjustments, ensures that each sheet meets a tolerance range of ±0.02 mm, preventing defects and ensuring uniform strength and flexibility.

[0130] Example 2: Multi-Layered Dental Sheets

[0131] In the production of multi-layered dental sheets, the thickness monitoring unit (210) ensures that each layer maintains the specified thickness. If variations occur in any layer, the monitoring system can adjust lamination pressure, heat settings, or roller speed, ensuring seamless bonding without compromising structural integrity.

[0132] The thickness monitoring unit (210) may ensure that the dental sheet meets the required dimensional precision, structural integrity, and consistency. By integrating real-time measurement, automated feedback, and advanced detection technologies, the thickness monitoring unit (210) may play a key role in preventing material waste, optimizing production efficiency, and maintaining high product quality for dental and medical applications.

[0133] The apparatus (200) includes the trimmer (212). The trimmer (212) may be another essential component of the dental sheet production apparatus (200), configured to remove excess material or uneven edges after the thickness measurement process. The trimmer (212) may ensure that the dental sheet maintains uniform width, smooth edges, and precise dimensions, which may be critical for orthodontic applications, lamination, and further processing. The trimmer (212) may be operatedin conjunction with other processing units, such as the thickness monitoring unit (210), conveying unit, and set of rollers (204), ensuring a defect-free, high-precision dental sheet.

[0134] In one of the exemplary embodiments of the present invention, the trimmer (212) may include rotary blades that may continuously trim excess material from the edges of the dental sheet as the dental sheet moves through the conveying unit. These high-speed rotating blades may ensure that the dental sheet has uniform edges, preventing irregularities that may interfere with lamination or bonding. In an example, in automated sheet processing, the rotary blade system may ensure that even at high production speeds, the dental sheet may be trimmed precisely without causing stress or deformation. The trimmer (212) may be adjusted for different sheet widths, allowing customizable edge trimming based on specific application requirements.

[0135] In another exemplary embodiment of the present invention, the trimmer (212) may be a shear-cutting mechanism, where two sharp blades may move in a scissor-like motion to remove irregular edges from the dental sheet. This method may be particularly useful for thicker dental sheets, where precision cutting may be necessary to avoid rough or jagged edges. In an example, in multilayered dental sheet production, where multiple polymer layers may be laminated together, the shear cutter may ensure that all layers maintain uniformity, preventing misalignment during further processing.

[0136] In another exemplary embodiment of the present invention, the trimmer (212) may use a laser cutting system to remove excess material and smoothen the edges. This method may be particularly useful for high-precision dental sheets, where microscopic edge irregularities may impact adhesion or forming properties. In an example, in transparent dental sheet production, the laser trimming process may ensure that the edges remain crack-free and smooth, preventing stress concentration points that may weaken the aligner fabricated using the dental sheet.

[0137] In another exemplary embodiment of the present invention, the trimmer (212) may include adjustable cutting blades that may be set to different positions based on sheet width requirements. This may ensure that a single production line may accommodate various sheet sizes without requiring frequent equipment changes. In an example, a dental sheet manufacturer producing different sizes of sheets for multiple applications may use an adjustable trimmer (212) to switch between standard and custom sheet widths, improving production efficiency and reducing material waste.

[0138] The trimmer (212) may be an essential part of the dental sheet production process, ensuring edge uniformity, precise width control, and defect-free final products. Whether using rotary blades, shear cutters, laser trimming, or adjustable mechanisms, the trimmer (212) may help maintain high-quality standards, making the dental sheet suitable for orthodontic, prosthetic, and medical applications.

[0139] The apparatus may include the corona treatment unit (214). The corona treatment unit (214) may be configured to treat designated surfaces of the dental sheet as described in Fig. 3, which illustrates a flow chart (300) of a method for treating the dental sheet (100). The corona treatment unit (214) may utilize a high-voltage discharge (302) to treat designated surfaces of the dental sheet, which may enhance the surface energy and adhesion properties of the dental sheet. The corona treatment unit (214) may be a crucial component in the production of dental sheets, which may be configured to modify the surface energy of the dental sheet produced by the conveying unit, ensuring improved adhesion properties for subsequent processes such as coatings, lamination, and bonding. By applying (304) a high-voltage discharge, the corona treatment unit (214) may effectively break molecular bonds on the surface of the dental sheet, introducing (310) polar functional groups that may increase surface energy, making the dental sheet more receptive to adhesives, inks, and coatings. The corona treatment process involves placing the dental sheet near one or more electrodes, which may create an air gap where the high-voltage potential may ionize the surrounding air, which may result in a corona discharge. The corona discharge may modify the surface properties without affecting the mechanical strength or structural integrity of the dental sheet.

[0140] In one of the exemplary embodiments of the present invention, the corona treatment unit (214) may be configured to treat only one side of the dental sheet, ensuring that the treated surface may attain the required surface energy level (46-56 Dynes / cm) for lamination or bonding, while the opposite side remains untreated to maintain the original properties. In an example, in laminated dental sheets, the treated side may ensure strong bonding with an adhesive or overlay material, while the untreated side may retain the original finish and mechanical characteristics.

[0141] In another exemplary embodiment of the present invention, the corona treatment unit (214) may be configured to treat both sides of the dental sheet, which may be beneficial in applications where multi-layer bonding may be required. The dual-side treatment may ensure that each layer in a laminated structure forms a strong bond, improving overall durability and mechanical stability. In an example, in the production of multi-layered orthodontic aligners from the dental sheet, where different polymer layers must adhere seamlessly, the dual-side corona treatment enhances layer-to-layer adhesion, preventing delamination or weak bonding points.

[0142] In another exemplary embodiment of the present invention, the corona treatment unit (214) may be configured for selective treatment, where only specific inner layers of the dental sheet undergo corona discharge (306) while outer layers remain untreated. This may ensure that only critical bonding surfaces are modified, preventing any unwanted changes in the external texture of the dental sheet. In an example, in three-layer dental sheets, where the core layer may need enhanced bonding properties,the inner surfaces of the core layer may be subjected to corona discharge, while the outer protective layers remain unaffected (312), maintaining their natural smoothness and clarity.

[0143] In another exemplary embodiment of the present invention, the corona treatment unit (214) may operate at high-frequency discharge levels, ensuring even and controlled modification across the entire surface of the dental sheet. This may help in preventing inconsistent treatment, which may lead to patchy adhesion areas. In an example, in transparent orthodontic sheets, maintaining optical clarity while ensuring proper adhesion is crucial. A high-frequency corona discharge unit may ensure that the surface energy of the dental sheet is evenly increased without affecting the transparency or flexibility of the dental sheet.

[0144] Example 1: Corona Treatment for Transparent Orthodontic Aligners

[0145] For orthodontic aligners, where optical clarity and precise bonding are critical, the corona treatment unit (214) ensures that the inner bonding layer receives optimal surface energy enhancement, allowing adhesives to form strong, bubble-free bonds while the outer layers remain unaffected to maintain transparency.

[0146] Example 2: Corona Treatment for Multi-Layered Laminated Sheets

[0147] In laminated multi-layer dental sheets, the corona treatment process ensures that each layer properly adheres, preventing delamination during use. This is particularly important in custom dental prosthetics, where multiple material layers must bond seamlessly for long-term durability.

[0148] Example 3 : Corona Treatment for Coating Applications

[0149] For coated dental sheets, such as those requiring antibacterial or UV-resistant coatings, the corona treatment unit (214) increases surface energy, ensuring that coatings adhere evenly and permanently without peeling or flaking.

[0150] The corona treatment unit (214) may play a vital role in enhancing surface adhesion properties, ensuring that the dental sheet may be optimized for lamination, bonding, and coating applications. By incorporating single-side, dual-side, and selective treatment options, along with high-frequency uniform discharge, the corona treatment unit (214) may ensure reliable, high-quality production of dental sheets for orthodontic and medical applications.

[0151] The apparatus includes the unwinder roll. The unwinder roll may be configured to collect the processed sheet after corona treatment and prepare the dental sheet for shaping, lamination, or further processing. As the final collection stage, the unwinder roll may ensure that the dental sheet remains tension-controlled, aligned, and free from defects before being shaped into the desired end product. The unwinder roll may work in synchronization with the conveying unit, maintaining consistent speed and tension to prevent wrinkles, misalignment, or material stretching. Properunwinding may be crucial for ensuring sheet integrity, particularly in applications requiring thermoforming, cutting, or multi-layer lamination.

[0152] In one of the exemplary embodiments of the present invention, the unwinder roll may be equipped with a tension control system, ensuring that the dental sheet may be collected at a uniform tension level to prevent wrinkling or deformation. This is particularly important when handling thin or flexible dental sheets, where excessive tension may cause elongation or uneven winding. The tension control system may consist of load sensors and motor-driven adjustments, which may automatically regulate the unwinding speed based on the thickness and flexibility of the dental sheet. In an example, in thin transparent aligner sheets, the tension-controlled unwinder roll may prevent distortion, ensuring the material remains flat and ready for thermoforming without introducing stress points that could lead to defects.

[0153] In another exemplary embodiment of the present invention, the unwinder roll may be integrated with a programmable control unit, allowing the unwinder roll to adjust winding speed, direction, and roll diameter detection for multi-stage processing. This setup may particularly be useful in multi-layered dental sheet production, where precise unwinding may be required before shaping, lamination, or secondary surface treatments. The programmable system may ensure that each layer may be collected with precise alignment, reducing waste and improving processing efficiency. For example, in dental sheet manufacturing requiring post-corona lamination, the automated unwinder roll may ensure that each sheet may be fed into the lamination unit in perfect synchronization, eliminating misalignment errors and ensuring seamless layer bonding.

[0154] The apparatus for producing the dental sheet includes the lamination unit. The lamination unit may be configured to bond at least three layers of the dental sheet, ensuring structural integrity, transparency, and enhanced mechanical properties. The lamination process may involve heat and pressure, allowing multiple layers to fuse seamlessly without affecting optical clarity or flexibility. This is particularly important in orthodontic and dental applications, where the dental sheet may have to maintain high transparency while providing durability and strength for long-term use. During lamination, the layers may undergo precise temperature control and roller compression, preventing air entrapment, delamination, or surface defects. The process may ensure that the dental sheet remains uniform, bubble-free, and optically clear, making the dental sheet ideal for applications such as clear aligners, retainers, and dental splints.

[0155] In one of the exemplary embodiments of the present invention, the apparatus may include a drying unit. The drying unit may be configured to remove residual moisture from the dental sheet by maintaining a controlled drying temperature between 65°C and 95°C for 8 to 12 hours. This process may be essential for ensuring dimensional stability, preventing defects like bubbles or delamination,and improving adhesion in subsequent lamination or coating processes. The drying unit is particularly useful when processing hygroscopic materials, where moisture retention can impact mechanical properties and final product quality.

[0156] In one of the exemplary embodiments of the present invention, the apparatus may include a monitoring unit. The monitoring unit may be responsible for real-time tracking and control of critical temperature profiles, processing conditions, and thickness parameters throughout the manufacturing process. The monitoring unit may ensure that all operational parameters remain within specified ranges, preventing inconsistencies that could affect sheet uniformity, adhesion, or structural integrity. The monitoring unit may include sensors, automated feedback loops, and data logging systems, allowing for process optimization, defect reduction, and enhanced quality assurance in the production of dental sheets used for medical applications.

[0157] Fig. 4 illustrates a multi-layer sheet lamination process (400), depicting the sequential arrangement of components involved in the dental sheet unwinding, heating, and pressing to form a laminated dental sheet. The process begins with the winder roll (402) of the conveying unit, which may feed multiple layers of the dental sheet into the apparatus. The set of rollers may ensure a continuous and stable supply of material while preventing misalignment or tension variations that may affect the final laminated product.

[0158] As the dental sheets advance, the dental sheet may pass through the plurality of rubber conveyor rollers (404), which may provide stability and uniform movement towards the heating units (406). The heating units (406) may apply controlled heat to the dental sheets, softening the dental sheets to facilitate proper adhesion during lamination. This step may be critical in ensuring that the layers bond effectively without creating delamination issues, air pockets, or structural weaknesses.

[0159] At the final stage, the dental sheets may reach the temperature-controlled pressure rollers, where heat and compression are applied simultaneously. The temperature-controlled pressure rollers (408) may ensure that the layers are firmly bonded, maintaining uniform thickness and mechanical integrity. By carefully controlling the pressure and temperature, this process may enhance the durability, transparency, and adhesion properties of the laminated dental sheet. The resulting product may be ideal for orthodontic and dental applications, such as aligners, retainers, and other medicalgrade dental appliances.

[0160] In one of the exemplary embodiments of the present invention, the present invention discloses a method for producing the dental sheet. Fig. 5 illustrates a flow chart illustrating a method for producing the dental sheet in accordance with various embodiments of the present invention. The method for producing the dental sheet involves a series of controlled steps, ensuring high precision, structural integrity, and surface optimization for orthodontic and medical applications. The methodincludes extrusion, conveying, thickness measurement, corona treatment, unwinding, and lamination, each contributing to the quality and functionality of the dental sheet.

[0161] At step 502, the method begins with extruding molten plastic through an extrusion unit equipped with one or more extruders. Thermoplastic material is melted at a controlled temperature range, ensuring homogeneous mixing and flow consistency. In one of the exemplary embodiments of the present invention, the molten plastic is then forced through a die, shaping it into a continuous sheet. The extrusion unit ensures that the material properties are maintained throughout the process, preventing inconsistencies in thickness and mechanical strength. This extruded sheet is still in a semimolten state, requiring further processing for stabilization and cooling.

[0162] Further, at step 504, the method involves another step. Once extruded, the molten plastic sheet is received by the conveying unit, which plays a crucial role in transporting and stabilizing the dental sheet as it progresses through the production line. The dental sheet passes through a set of rollers, including temperature-controlled quenching rollers, which gradually cool the material while ensuring it attains the desired thickness, crystallinity, and mechanical stability. These rollers regulate the cooling rate, preventing warping, residual stresses, or deformation in the dental sheet. Proper conveying also ensures that the dental sheet moves smoothly without slack, misalignment, or surface defects, preparing it for further refinement.

[0163] Further, at step 506, the method involves another step. As the dental sheet moves forward, the dental sheet enters the thickness monitoring unit, which measures the thickness in real time. In one of the exemplary embodiments of the present invention, this unit is equipped with non-contact sensors, such as laser micrometers or capacitive sensors, ensuring that the dental sheet maintains the specified thickness tolerance. If the thickness monitoring unit detects thickness variations, the thickness monitoring unit sends automated feedback to adjust parameters in the extrusion unit or roller pressure, thereby correcting deviations in real time. This step is critical for ensuring that the dental sheet meets precise dimensional accuracy, which is essential for orthodontic applications, thermoforming, and lamination processes.

[0164] Further, at step 508, the method involves another step. Following thickness measurement, the corona treatment unit applies a high-voltage discharge to designated surfaces of the dental sheet. This process involves placing the dental sheet in proximity to an electrode system, creating an air gap where the high-voltage corona discharge ionizes the surrounding air. As a result, the high-energy corona interacts with the surface of the dental sheet, breaking molecular bonds and generating free radicals, which react with oxygen molecules to introduce polar functional groups. This modification increases surface energy, enhancing adhesion properties for subsequent coating, lamination, or bonding applications. The process can be selectively applied to one side or both sides of the dental sheet,depending on the final application requirements. This step is crucial for ensuring strong bonding in multi-layer laminations and preventing adhesion failures in medical-grade dental sheets.

[0165] Further, at step 510, the method involves another step. After corona treatment, the dental sheet is collected by the unwinder unit, ensuring that the dental sheet remains tension-controlled and properly aligned for the next stage. The unwinder unit is responsible for rolling the dental sheet onto a spool or directing it into further processing, maintaining even winding tension to prevent misalignment, wrinkles, or material stretching. In some embodiments, the unwinder unit is integrated with a programmable system, allowing for variable speed control, roll diameter detection, and tension adjustments based on the properties and thickness of the dental sheet. This ensures that the collected sheet is ready for shaping, lamination, or storage without affecting surface quality or mechanical properties.

[0166] Further, at step 12, the method involves the final step. The final stage involves laminating at least three layers of the dental sheet to achieve optimal transparency, durability, and flexibility. The lamination unit applies controlled heat and pressure, ensuring that the layers bond seamlessly without visible defects. In one of the exemplary embodiments of the present invention, during lamination, the dental sheet is preheated and passed through a series of heated rollers, where pressure is carefully adjusted to eliminate air gaps, bubbles, or delamination risks. The final laminated sheet exhibits enhanced optical clarity, mechanical strength, and surface smoothness, making it ideal for high-quality orthodontic aligners, retainers, and dental splints.

[0167] The method for producing a dental sheet follows a structured sequence of extrusion, conveying, thickness control, corona treatment, unwinding, and lamination, ensuring that the final product meets strict dimensional accuracy, surface adhesion properties, and optical clarity standards. Each stage is precisely controlled and monitored, resulting in a high-quality, multi-layered dental sheet suitable for advanced dental and medical applications.Testing Methods

[0168] The hardness and / or elongation at break are measured according to ASTM D2240. ASTM D2240 is the standard test method for testing hardness using a durometer to measure the indentation hardness of materials like rubber and plastics, often for quality control or specifying material hardness.

[0169] The tensile modulus and tensile strength at yield are measured according to ASTM D638. ASTM D638 is the standard test method for tensile properties of plastics. The test method uses dumbbell-shaped specimens, with specific dimensions depending on the material type and thickness.

[0170] The flexural strength and flexural modulus are measured according to “ASTM D790”. ASTM D790 is the standard test method for flexural properties of unreinforced and reinforced plasticsand electrical insulating materials such that ASTM D790 may help in determining the stiffness, resistance to bending of the material, and how much stress the material can withstand before failure.

[0171] The thermal stability is measured according to ASTM E2550. ASTM E2550 is the standard test method for thermal stability by thermogravimetry. ASTM E2550 assess the thermal stability of materials by determining the temperature at which they begin to decompose or react and the extent of mass change using thermogravimetry.

[0172] The glass transition temperature is measured according to “ASTM D3418”. ASTM D3418 is the standard test method for transition temperatures and enthalpies of fusion and crystallization of polymers by differential scanning calorimetry. ASTM D3418 measures the temperatures and heat flows associated with thermal transitions in polymers, such as glass transition, melting, and crystallization.

[0173] The light transmission capacity (transparency) and water absorption rate are measured according to “ASTM D570”. ASTM D570 is the standard test method for water absorption of plastics. ASTM D570 helps determine the water absorption of plastics, which is the increase in weight of a material after exposure to water.

[0174] The stress relaxation is measured in according to “ASTM D2290”. ASTM D2290 Standard Test Method for Apparent Hoop Tensile Strength of Plastic or Reinforced Plastic Pipe. ASTM D2290 measures the tensile strength of plastic or reinforced plastic pipes, specifically the strength along the hoop direction (circumferential direction).Examples of the Invention

[0175] In some exemplary embodiments of the present invention, a dental sheet may be produced under specific processing conditions as tabulated in below Table 1 [Examples 1 - 5] which possesses the optimum desired properties of the dental aligner as the dental sheet possesses better melt homogeneity as compared to the others (barrel processing temperature is high and balanced line speed put and positive effect on this).condition condition condition condition condition PROCESSex.l ex.l ex.3 ex.4 ex.5 CONDITION(layer- (layer- (layer- (layer- (layer- for Layer-AAl / Cl) A2 / C2) A3 / C3) A4 / C4) A5 / C5) Barrel zone230 to 280 210 to 250 230 to 280 210 to 250 200 to 240 temperature (°C)Extruder line speed2.6 to 2.8 2 to 2.3 3.4 to 3.6 2 to 2.3 1.3 to 1.5 (MPM)Die zone 280 to 290 260 to 270 285 to 295 260 to 270 245 to 255 Roller Temperature20 to 85 22 to 65 55 to 85 55 to 85 35 to 75 (°C)PROCESS condition condition condition condition condition CONDITION ex.l ex.2 ex.3 ex.4 ex.5 for Layer-B (layer-Bl) (layer-B2) (layer-B3) (layer-B4) (layer-B5) Barrel zone170 to 210 165 to 190 170 to 210 165 to 190 165 to 195 temperature (°C)Extruder line speed2.6 to 2.8 2 to 2.3 3.4 to 3.6 2 to 2.3 1.3 to 1.5 (MPM)Die zone 230 to 240 205 to 215 230 to 240 205 to 215 200 to 210 Roller Temperature20 to 85 22 to 65 55 to 85 55 to 85 35 to 75 (°C)Testing propertieslaminating layer A1 / B1 / A1 A2 / B2 / A2 A3 / B3 / A3 A4 / B4 / A4 A5 / B5 / A5 stress relaxation %14 to 16 23.8 to 25.8 26.3 to 28.3 30.6 to 32.6 33 to 36 (2 HOURS)Ultimate Tensile57.83 60.21 49.68 50.8 40.22 Strength (N / mm2)% Elongation at128.97 147.75 101.75 186.12 38.46 Break (Hardness)Tensile Modulus1602.57 1589.82 1492.7 1502.51 1821.34 (N / mm2)flexural strength 60.8 62.9 58.6 63.8 64.9 FLEXURAL1380 1350 1360 1380 1420 modulusNot stable THERMAL Thermally Thermally Thermally Thermallyand more STABILTY stable stable stable stablerigid %>92 >88 >92 >85 >82 TRANSPARENCY(Light TransmissionCapacity)water absorption(%)0.54 0.58 0.65 0.73 0.9(24 H @73°F,50% RH)

[0176] In some exemplary embodiments of the present invention, a dental sheet may be produced under specific processing conditions as tabulated in below Table 2 [examples 6 - 8] which shows the aligner property with respect to the individual layer thickness (as the variation in the middle soft layer thermal and mechanical properties of the aligner product changes).Thickness variationindividual layer thickness Ex.6 Ex.7 Ex.8A 33.3 25 20B 33.3 50 60C 33.3 25 20 Testing propertiesUltimate Tensile Strength (N / mm2) 57.83 36.89 34% Elongation at Break 128.97 158.71 167.43 Tensile Modulus (N / mm2) 1602.57 1398.91 1095.78 stress relaxation % (24 HOURS) 22 to 24 42 to 44 52 to 54% TRANSPARENCY >92 >90 >85 flexural strength 60.8 53.6 48.6 FLEXURAL modulus 1380 1240 1060Not stable Thermally stableand more THERMAL STABILTY DURING Thermally but lessflexible THERMOFORMING stable stable middlemiddle soft layersoft layer water absorption0.54 0.6 0.8(%) (24 H @73°F, 50% RH)

Claims

AMENDED CLAIMSreceived by the International Bureau on 07 April 2026 (07.04.2026)1. A dental sheet comprising:at least two outer layers consisting of polyester material having hardness from about 65D to 85D, flexural modulus from about 1500 Mpa to 2500 MPa, and glass transition temperature from about 75 °C to 105 °C; andat least one inner layer consisting of a thermoplastic urethane elastomer having hardness in range of 50A to 75D, flexural modulus from about 500 Mpa to 1600 MPa, and glass transition temperature from about -40 °C to 45 °C,wherein the at least one inner layer is interposed between the at least two outer layers to produce the dental sheet for fabricating aligners.

2. The dental sheet as claimed in claim 1, wherein a matte finish is applied to one side or both sides.

3. The dental sheet as claimed in claim 1, wherein number of layers in the dental sheet is in between 3 to 6.

4. The dental sheet as claimed in claim 1, wherein thickness of the dental sheet is in range of 0.45 mm to 1.5mm.

5. The dental sheet as claimed in claim 1, wherein the dental sheet possesses light transmission capacity in the range of 90% to 95 % or >90 %.

6. The dental sheet as claimed in claim 1, wherein tensile modulus of the dental sheet is in range of 1000 to 2200 MPa.

7. The dental sheet as claimed in claim 1, wherein tensile strength at yield of the dental sheet is in range of 20 to 80 MPa.

8. The dental sheet as claimed in claim 1, wherein stress relaxation of the dental sheet is in range between 5% and 30% at room temperature in 2 hours.

9. The dental sheet as claimed in claim 1, wherein flexural strength of the dental sheet is in range of 25 to 75 MPa.

10. The dental sheet as claimed in claim 1, wherein flexural modulus of the dental sheet is in range of 1000 to 1800 MPa.

11. The dental sheet as claimed in claim 1, wherein elongation of the dental sheet is in range of 60 to 200 %.

12. The dental sheet as claimed in claim 1, wherein water absorption rate of the dental sheet is in the range between 0.40% to 0.80% at 24 hours, 73°F, and 50% RH.

13. The dental sheet as claimed in claim 1, wherein the dental sheet is coated with an antibacterial agent on both sides.

14. The dental sheet as claimed in claim 1, wherein the dental sheet is coated with teeth-cleaning agents on both sides.

15. The dental sheet as claimed in claim 1, wherein the at least two outer layers consisting of polyester material are hard and / or rigid in nature.

16. The dental sheet as claimed in claims 1 and 15, wherein the polyester material is selected from a group consisting of polyester, co-polyester, PETG (Polyethylene Terephthalate Glycol), and PCTG (Poly Cyclohexylenedimethylene Terephthalate Glycol-modified), and the mixtures thereof.

17. The dental sheet as claimed in claims 1 and 16, wherein polymeric backbone structure of the polyester material includes a diester or diacid component which is selected from the group consisting of Terephthalic acid (TP A), Isophthalic acid (IP A), Dimethyl terephthalate (DMT), 4,4’-biphenyldicarboxylic acid, and Trans-4, 4’ -stilbenedicarboxylic acid.

18. The dental sheet as claimed in claims 1 and 16, wherein the polymeric backbone structure of the polyester material further includes a diol component.

19. The dental sheet as claimed in claim 18, wherein the diol component consists of Ethylene glycol (EG) from about 35 to 85 mol% and TMCD (cis / trans-2,2,4,4-Tetramethyl-l,3-cyclobutanediol) from about 15 to 65 mol%.

20. The dental sheet as claimed in claim 18, wherein the diol component consists of Ethylene glycol (EG) from about 35 to 85 mol% and CHDM (cis / trans-l,4-Cyclohexanedimethanol) from about 15 to 65 mol%.

21. The dental sheet as claimed in claim 18, wherein the diol component consists of Ethylene glycol (EG) from about 35 to 85 mol% and a combination of TMCD (cis / trans-2,2,4,4-Tetramethyl-l,3-cyclobutanediol) and CHDM (cis / trans-l,4-Cyclohexanedimethanol) from about 15 to 65 mol%.

22. The dental sheet as claimed in claims 19-21, wherein cis / trans ratio of CHDM is in range of 40:60 to 60:40 for providing controlled crystallinity of the polyester material.

23. The dental sheet as claimed in claim 1, wherein the at least one inner layer consisting of a thermoplastic urethane elastomer is soft in nature.

24. The dental sheet as claimed in claims 1 and 23, wherein the thermoplastic urethane elastomer is selected from a group consisting of thermoplastic elastomer (TPE), thermoplastic vulcanizates (TPV), elastomeric co-poly (ether or ester-ester), elastomeric co-poly (ether or ester-amide), co-polymers of ethylene-methyl (EMA) or ethylene-butyl acrylate (EBA), and the mixtures thereof.

25. The dental sheet as claimed in claims 1 and 24, wherein the thermoplastic urethane elastomer may include a polymeric backbone structure of the thermoplastic urethane elastomer, includes a hard segment (diisocyanate), a soft segment (long chain diol), and a chain extender.

26. The dental sheet as claimed in claims 1 and 25, wherein the hard segment of the polymeric backbone structure of the thermoplastic urethane elastomer containing one or more components selected from the group consisting of 2,4-diisocyanato-l -methylbenzene (TDI), l-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene (MDI), 1,6-diisocyanatohexane (HDI), l,l'-methanediylbis(4-isocyanatocyclohexane) (HMDI), 5-isocyanato-l-(isocyanatomethyl)-l,3,3-trimethylcyclohexane (IPDI), l,T-methylenebis(4-isocyanatocyclohexane), and the mixtures thereof27. The dental sheet as claimed in claims 1 and 25, wherein the soft segment of the polymeric backbone structure of the thermoplastic urethane elastomer containing one or more components selected from the group consisting of ether-based polyols- polytetramethylene ether (PTMEG), polycarbonate polyol- 2, 2'-[sulfanediylbis(benzene-l,4-diyloxy)]di ethanol, polycarbonate polyolpoly hexamethylene carbonatediol, and the mixtures thereof.

28. The dental sheet as claimed in claims 1 and 25, wherein the chain extender of the polymeric backbone structure of the thermoplastic urethane elastomer containing one or more components selected from the group consisting of Propane-1, 3-diol, Butane-l,4-diol, 1,6-Hexanediol, and the mixtures thereof.

29. The dental sheet as claimed in claims 25 and 26, wherein molar ratio of the hard segment (diisocyanate) to polyols (NCO:OH) is in the range of 1 :2 to 1 :4 for controlling mechanical and thermal properties of the thermoplastic urethane elastomer.

30. The dental sheet as claimed in claim 1, wherein ratio of hard segment to soft segment in the thermoplastic urethane elastomer is in between 35% to 55% and 45% to 65%, respectively.

31. The dental sheet, as claimed in claim 25, wherein average molecular weight (Mw) of the polymeric backbone structure of the thermoplastic urethane elastomer is in the range of 100,000 to 300,000 g / mol.

32. An apparatus for producing a dental sheet, comprising:producing one or more layers of the dental sheet by means of:an extrusion unit configured to extrude molten plastic through one or more extruders; a conveying unit for receiving the extruded molten plastic to produce a dental sheet; a thickness monitoring unit configured to measure the thickness of the dental sheet produced by the conveying unit;a corona treatment unit configured to treat designated surfaces of the dental sheet using a high-voltage discharge to enhance surface energy and adhesion properties; andan unwinder roll configured to collect the dental sheet after corona treatment for shaping, a lamination unit for laminating at least three layers of the dental sheet for transparency.

33. The apparatus as claimed in claim 32, wherein the extruded molten plastic maintains a processing temperature in the range of 220°C to 340°C to achieve melt homogeneity.

34. The apparatus as claimed in claim 32, wherein the apparatus optionally includes a drying unit to maintain a drying temperature in the range of 65°C to 95°C for 8 to 12 hours.

35. The apparatus as claimed in claim 32, wherein the L / D ratio of the one or more extruders is 20 to 45.

36. The apparatus as claimed in claim 32, wherein the conveying unit further includes a set of rollers with temperature-controlled quenching to create a microcrystalline structure by maintaining:25±10°C for the first roller,55±10°C for the second roller, and100±10°C for the third roller.

37. The apparatus as claimed in claim 36, wherein the set of rollers is configured to:imparting a desired thickness to the extruded molten plastic;stabilizing the extruded molten plastic during cooling to enhance structural integrity; and cooling the extruded molten plastic to a stabilized temperature to prevent deformation and produce the dental sheet.

38. The apparatus as claimed in claims 36 and 37, wherein the set of rollers is equipped with a static eliminator to reduce static charge buildup.

39. The apparatus as claimed in claim 32, wherein the conveying unit includes an idler roller to provide alignment to each layer of the dental sheet.

40. The apparatus as claimed in claim 32, wherein the conveying unit includes a plurality of rubber conveyor rollers to transport each layer of the dental sheet for further processing.

41. The apparatus as claimed in claim 32, wherein the apparatus includes a trimmer configured to remove excess material or uneven edges from the dental sheet after thickness measurement.

42. The apparatus as claimed in claim 32, wherein treating the designated surfaces of a layer of the dental sheet in the corona treatment unit comprises:placing the dental sheet formed by the set of rollers in proximity to a high-voltage discharge unit to create an air gap between the material and electrodes in the corona treatment unit;applying a high-voltage potential across the air gap to ionize the surrounding air, resulting in the formation of a corona discharge, which appears as a blue flame discharge;directing the corona discharge towards the designated surface of the dental sheet, such that the high-energy corona interacts with the designated surface of the dental sheet and breaks molecular bonds present on said designated surface;generating free radicals on the designated surface of the dental sheet, which react with oxygen molecules in the surrounding air, leading to the formation of polar functional groups on the surface of the dental sheet;introducing the polar functional groups that increase the surface energy of the dental sheet, making the designated surface of the dental sheet suitable for subsequent processes such as coatings, inks, adhesives, or lamination; andapplying the corona treatment selectively to the designated surface of the dental sheet that faces the electrode, leaving the opposite surface unaffected and resulting in an increase in surface energy on the treated side.

43. The apparatus as claimed in claim 42, wherein at least one inner layer optionally undergoes corona treatment on both sides.

44. The apparatus as claimed in claim 32, wherein the corona treatment raises the surface energy of the dental sheet to a range of 46 to 56 Dynes / cm, making the surface suitable for efficient bonding and lamination.

45. The apparatus as claimed in claim 32, wherein the set of rollers further includes a temperature control unit for the set of rollers to optimize the temperature profile for stable cooling of the molten dental sheet to prevent bending and stability issues.

46. The apparatus as claimed in claim 32, wherein the apparatus includes a monitoring unit to ensure that temperature profiles, processing conditions, and thickness parameters remain within specified ranges.

47. A method for producing a dental sheet, the method comprising:producing one or more layers of the dental sheet by:extruding, by an extrusion unit, molten plastic through one or more extruders of the extrusion unit;receiving, by a conveying unit, the extruded molten plastic to produce a dental sheet; measuring, by a thickness monitoring unit, the thickness of the dental sheet produced by the conveying unit;treating, by a corona treatment unit, designated surfaces of the dental sheet using a high-voltage discharge to enhance surface energy and adhesion properties;collecting, by an unwinder unit, the dental sheet after corona treatment for shaping; and laminating, by a lamination unit, at least three layers of the dental sheet for transparency.

48. The method as claimed in claim 47, wherein the extruded molten plastic maintains a processing temperature in the range of 220°C to 340°C to achieve melt homogeneity.

49. The method as claimed in claim 47, wherein the method optionally includes drying, by a drying unit, to maintain a drying temperature in the range of 65°C to 95°C for 8 to 12 hours.

50. The method as claimed in claim 47, wherein the L / D ratio of the one or more extruders is 20 to 45.

51. The method as claimed in claim 47, wherein the conveying unit further includes a set of rollers with temperature-controlled quenching to create a microcrystalline structure by maintaining:25±10°C for the first roller,55±10°C for the second roller, and100±10°C for the third roller.

52. The method as claimed in claim 47, wherein the set of rollers is configured to:imparting a desired thickness to the extruded molten plastic;stabilizing the extruded molten plastic during cooling to enhance structural integrity; and cooling the extruded molten plastic to a stabilized temperature to prevent deformation and produce the dental sheet.

53. The method as claimed in claims 51 and 52, wherein the set of rollers is equipped with a static eliminator to reduce static charge buildup.

54. The method as claimed in claim 47, wherein the conveying unit includes an idler roller to provide alignment to each layer of the dental sheet.

55. The method as claimed in claim 47, wherein the conveying unit includes a plurality of rubber conveyor rollers to transport each layer of the dental sheet for further processing.

56. The method as claimed in claim 47, wherein the method includes a step of configuring a trimmer, to remove excess material or uneven edges from the dental sheet after thickness measurement.

57. The method as claimed in claim 47, wherein treating the designated surfaces of a layer of the dental sheet in the corona treatment unit comprises:placing the dental sheet formed by the set of rollers in proximity to a high-voltage discharge unit to create an air gap between the material and electrodes in the corona treatment unit;applying a high-voltage potential across the air gap to ionize the surrounding air, resulting in the formation of a corona discharge, which appears as a blue flame discharge;directing the corona discharge towards the designated surface of the dental sheet, such that the high-energy corona interacts with the designated surface of the dental sheet and breaks molecular bonds present on said designated surface;generating free radicals on the designated surface of the dental sheet, which react with oxygen molecules in the surrounding air, leading to the formation of polar functional groups on the surface of the dental sheet;introducing the polar functional groups that increase the surface energy of the dental sheet, making the designated surface of the dental sheet suitable for subsequent processes such as coatings, inks, adhesives, or lamination; andapplying the corona treatment selectively to the designated surface of the dental sheet that faces the electrode, leaving the opposite surface unaffected and resulting in an increase in surface energy on the treated side.

58. The method as claimed in claim 57, wherein at least one inner layer optionally undergoes corona treatment on both sides.

59. The method as claimed in claim 47, wherein the corona treatment raises the surface energy of the dental sheet to a range of 46 to 56 Dynes / cm, making the surface suitable for efficient bonding and lamination.

60. The method as claimed in claim 47, wherein the set of rollers further includes a temperature control unit for the set of rollers to optimize the temperature profile for stable cooling of the molten dental sheet to prevent bending and stability issues.

61. The method as claimed in claim 47, wherein the method includes a step of configuring a monitoring unit to ensure that temperature profiles, processing conditions, and thickness parameters remain within specified ranges.

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