Dental appliance with regional differentiation physical properties and additive manufacturing method thereof

Abstract

The invention relates to the field of dental medical instruments, and discloses a dental appliance with regional differentiation physical properties and an additive manufacturing method thereof. The appliance comprises a three-dimensional shell structure made of light-cured resin, wherein the resin contains urethane acrylate and a monomer. Different areas of the base body have different mechanical properties by adjusting printing process parameters, so that correction forces with different directions and sizes are applied to different teeth in the same appliance, and the clinical complex requirements are met. According to the material properties of the appliance, the tensile modulus is 420-2650 MPa, the yield strength is 22-78 MPa, the yield strain is larger than 1.8%, the fracture strain is larger than 10%, the glass-transition temperature is larger than 40 DEG C, and the average thickness is smaller than 2.0 mm. The method disclosed by the invention is simple and convenient in process, and can improve the correction precision and biocompatibility and improve the treatment efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dental medical devices, in particular to a dental appliance and a manufacturing method thereof, and more particularly to a dental appliance with different physical properties in different regions by adjusting the parameters of additive manufacturing process and an additive manufacturing method thereof. BACKGROUND

[0002] Dental malocclusion is a common oral disease. Invisible aligners gradually become an important means of orthodontic treatment due to their aesthetics, comfort and ease of cleaning. Compared with traditional metal bracket appliances, invisible aligners have the advantages of being less noticeable and comfortable to wear, and can continuously exert gentle correction force to achieve tooth movement and occlusal improvement, so they are widely used in clinical applications. Existing invisible aligners are usually prepared by hot forming or additive manufacturing methods.

[0003] In the hot forming process, first, the patient's mouth is scanned to obtain the three-dimensional structure of the dental arch, and the orthodontist formulates a treatment plan according to the three-dimensional model. Then, a mold is made using the model, a thermoplastic sheet is heated to a plastic state and covered on the surface of the mold, and after cooling and setting, the aligner is obtained. In the additive manufacturing method, light-cured resin is used as the main material, and the aligner or its mold is directly manufactured by layer-by-layer solidification. Typical additive manufacturing processes include stereolithography (SLA), fused deposition modeling (FDM) and digital light processing (DLP), etc. These methods improve the design freedom and processing accuracy to some extent.

[0004] However, the existing hot forming and three-dimensional printing combined process is relatively complex. For example, the preparation of the mold requires steps such as demolding, cutting and trimming, and the aligner after forming also needs further cutting, trimming and polishing. In some clinical cases, mechanical attachments need to be added to the aligner, especially additional attachments. It is difficult to directly obtain such structures by hot forming, and usually needs to be pre-fabricated by injection molding or other methods, and then fixed to the aligner by adhesion, further increasing the complexity and cost of the manufacturing process. Although direct use of three-dimensional printing methods can simplify the process to some extent and form complex structures, aligners printed by polymer materials usually contain residual monomers, which may gradually separate out in a humid oral environment, causing biocompatibility problems. At the same time, there is a risk of structural performance degradation due to water absorption during use of the aligner.

[0005] In addition, the existing invisible aligner adopts uniform material parameters and processing technology in the whole structure, resulting in that the physical properties of each region are basically consistent. In other words, the existing aligner generally shows the characteristics of single mechanical properties. However, in the actual clinical treatment process, the tooth movement mode is complex and diverse, and the mechanical requirements of different regions are significantly different. For example, when the dental arch is expanded or large-scale translation is performed, a high-stiffness region is needed to provide sufficient orthodontic force; when the space between the teeth is closed or the teeth are moved significantly, a high-elasticity, long-acting force region is needed; when the arrangement is light or fine control is needed, a region with lower modulus and higher strain capacity is needed; for patients with periodontal disease, the mechanical strength in the relevant region needs to be reduced to avoid damage to the periodontal tissue.

[0006] Due to the coexistence of the above-mentioned different requirements in the same aligner, the uniform structure of the existing technology cannot simultaneously meet the complex requirements of different teeth. This not only reduces the treatment efficiency, but also may increase the discomfort and potential risk of patients. In some complex cases, doctors have to make up for this deficiency by increasing accessories, replacing aligners in stages, or prolonging the treatment period, but these means increase the treatment cost and the burden of patients.

[0007] In summary, the existing invisible aligner has deficiencies in preparation process and material performance, and it is difficult to meet the comprehensive needs of efficiency, accuracy and safety in orthodontic clinical treatment. Therefore, how to realize the distribution of regionally differentiated physical properties in the same aligner so that it can provide matching orthodontic force according to different teeth and different movement modes has become a technical problem that needs to be solved in the field. SUMMARY

[0008] The purpose of the present application is to overcome the defects of the existing dental aligner that the physical properties are uniform in the whole, and it is difficult to meet the differentiated clinical needs of different teeth and different movement modes, and to propose a dental aligner with regionally differentiated physical properties and an additive manufacturing method thereof. Through the present application, the physical properties of different regions can be distributed differently in the same aligner, so as to provide matching orthodontic force for different tooth movement types, improve treatment efficiency and accuracy.

[0009] In one possible implementation, the present application provides a dental appliance having regionally differentiated physical properties for moving at least one tooth of a patient from a first position and orientation to a second position and orientation. The dental appliance includes a base having a three-dimensional shell structure configured to receive the teeth of the patient in accordance with a treatment plan, and made of a photocurable resin including polyurethane acrylate (PUA) and monomer. The base includes a first region having a first value of a mechanical property parameter and a second region having a second value of the mechanical property parameter different from the first value, thereby forming a regionally differentiated physical property distribution. The first region includes a first tooth-receiving cavity configured to receive a tooth of the patient and to generate a first tooth-moving force having a first direction against the tooth; and the second region includes a second tooth-receiving cavity configured to receive another tooth of the patient and to generate a second tooth-moving force having a second direction against the tooth, and the first direction is different from the second direction. The base has an average thickness less than 2.0 mm, and the mechanical property parameter of the appliance includes a tensile modulus between 420 MPa and 2650 MPa, a yield strength between 22 MPa and 78 MPa, a yield strain greater than 1.8%, a break strain greater than 10%, and a glass transition temperature (Tg) greater than 40℃.

[0010] In one possible implementation, the first region and the second region correspond to different tooth regions along an arch path, respectively.

[0011] In one possible implementation, the first region and the second region correspond to different layers of a same tooth, respectively, and the layers are arranged along a direction perpendicular to the arch path.

[0012] In one possible implementation, the mechanical property parameter gradually changes between the first region and the second region along the arch path.

[0013] In one possible implementation, the first region and the second region correspond to an edge region and a non-edge region of the base, respectively.

[0014] In one possible implementation, the first region or the second region is a spot-hardened region.

[0015] In one possible implementation, the photocurable resin includes 20% to 50% by weight of polyurethane acrylate (PUA) and 50% to 80% by weight of monomer.

[0016] In one possible implementation, a coating layer is formed on at least part of the inner surface or the outer surface of the base body, and the coating layer is configured to prevent monomer migration.

[0017] In one possible implementation, the application further provides an additive manufacturing method for preparing a dental appliance with regionally differentiated physical properties. The method comprises: forming a base body by an additive manufacturing process using a photocurable resin, the base body having a three-dimensional shell structure configured to receive teeth of a patient according to a treatment plan, the photocurable resin comprising polyurethane acrylate (PUA) and monomers. During the formation of the base body, a first region of the base body is prepared using a first printing process parameter value, and a second region of the base body is prepared using a second printing process parameter value different from the first printing process parameter value, so that the first region and the second region have different mechanical property parameters. The first region is configured to exert a first tooth movement force having a first direction on the teeth of the patient, and the second region is configured to exert a second tooth movement force having a second direction on another part of the teeth of the patient, and the first direction is different from the second direction. The average thickness of the base body is less than 2.0 mm.

[0018] In one possible implementation, the printing process parameters include one or more of light exposure time, light intensity, light source shape, light wavelength, or reaction temperature.

[0019] Compared with the prior art, the application has the following beneficial effects. First, the application forms differentiated mechanical property parameters in different regions of the dental appliance, so that the appliance can exert different directions and different sizes of treatment forces on different teeth in the same appliance, thereby meeting the clinical demand for individual tooth movement. This solution can effectively avoid the problems of insufficient or excessive treatment forces caused by the uniform physical properties of existing appliances, and improves the accuracy of tooth movement and treatment efficiency.

[0020] In addition, the application uses an additive manufacturing process to realize regionally differentiated properties by adjusting the printing process parameters, without the need for additional assembly or complex processes. The selected photocurable resin formulation has good thermal stability and forming precision while ensuring the required mechanical properties, and can ensure the stability and durability of the appliance during use.

[0021] Further, the application can also adjust the ratio of polyurethane acrylate to monomers, or form a barrier coating on the surface of the appliance, to improve the biocompatibility of the material and reduce the risk of monomer migration, thereby improving the safety of use by patients. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings described in the following embodiments are only some of the embodiments of the present application, not all. The present application can also be implemented or applied through other different specific embodiments, and each detail in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0023] Figure 1A is a side view of an appliance base according to an embodiment of the present application.

[0024] Figure 1B is a bottom view of an appliance base according to an embodiment of the present application.

[0025] Figure 1C is a perspective view of an appliance base according to an embodiment of the present application.

[0026] Figure 2 is a cross-sectional view of a transparent appliance according to an embodiment of the present application.

[0027] Figure 3 is a schematic diagram of physical properties of a three-dimensional printing material according to an embodiment of the present application.

[0028] Figure 4A is a schematic diagram of a dental arch according to an embodiment of the present application.

[0029] Figure 4B is another schematic diagram of a dental arch according to an embodiment of the present application.

[0030] In the drawings, appliance base 10; connecting member 11; hook-shaped member 12; base outer surface 13; base inner surface 14; cross-sectional view base 200; coating 201; tooth-receiving cavity 202; labial edge region 203; lingual edge region 204; tooth-receiving cavity entrance 205; dental arch 400; arcuate path 401. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will illustrate the embodiments of the present application through specific, concrete examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. Obviously, the described embodiments are only some of the embodiments of the present application, not all. The present application can also be implemented or applied through other different specific embodiments, and each detail in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] It should be noted that the following description covers various aspects of embodiments within the scope of protection of this invention. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using other structures and / or functionalities besides one or more of the aspects set forth herein.

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention.

[0034] In one embodiment, such as Figure 1A and Figure 1B As shown, the orthodontic appliance base 10 is a shell structure formed by 3D printing. The base 10 has receiving cavities for receiving the patient's teeth and can also integrally form certain solid functional components, such as connecting components 11 and hook-shaped components 12. These functional components are difficult to obtain directly through thermoforming, but can be integrally formed with the shell structure through 3D printing. The base 10 has an outer surface 13 and an inner surface 14, and its main structure is a shell structure. In some embodiments, the orthodontic appliance includes only multiple tooth receiving cavities without any solid functional components; in other embodiments, the orthodontic appliance includes both tooth receiving cavities and one or more solid functional components; in further embodiments, the orthodontic appliance may even contain only one tooth receiving cavity to fit a single tooth. The following description uses an orthodontic appliance containing multiple tooth receiving cavities and without solid functional components as an example, but the same method is applicable to orthodontic appliances with different structural forms.

[0035] In one embodiment, the orthodontic appliance may include a matrix and one or more functional layers covering it. The functional layers may be formed as needed, for example, to improve the performance of the matrix or to add special functions.

[0036] In one embodiment, such as Figure 1CAs shown, the base 10 is shown in perspective view. In some cases, the aligner includes only the base without any functional layer; in other cases, the aligner includes the base and one or more functional layers that are overlaid on the surface of the base. The base with functional layers can be dimensioned differently compared to the base without functional layers, e.g., the base can be appropriately reduced in size to achieve the desired shape when overlaid with the functional layers. Of course, the base can also be dimensioned to be consistent with the base without functional layers.

[0037] In one embodiment, as shown in FIG. 1A, the base 10 is formed using a digital light processing (DLP) process. First, the STL model is sliced into multiple two-dimensional patterns in the Z-axis direction. Then, a light beam containing the two-dimensional pattern is projected by a DLP projector onto the surface of a vat containing liquid photopolymer resin. In some cases, the liquid photopolymer resin can include monomers (e.g., isobornyl acrylate, 2-hydroxyethyl methyl acrylate, and tripropylene glycol diacrylate (TPGDA)), oligomers (e.g., polyurethane acrylate, polyester acrylate, epoxy acrylate), and photoinitiators (e.g., 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO)). Figure 1C As shown, the base 10 is in a state before the functional layer is deposited. The base 10 is a transparent structure that can be prepared using various three-dimensional printing techniques, such as digital light processing (DLP), stereolithography (SLA), liquid crystal display (LCD), continuous liquid interface production (CLIP), material jetting (e.g., inkjet or polyjet), or fused deposition modeling (FDM). An STL model is often used in the preparation process, which is typically generated prior to printing based on the patient’s treatment plan.

[0038] In one embodiment, the base 10 can be formed using a digital light processing (DLP) process. First, the STL model is sliced into multiple two-dimensional patterns in the Z-axis direction. Then, a light beam containing the two-dimensional pattern is projected by a DLP projector onto the surface of a vat containing liquid photopolymer resin. In some cases, the liquid photopolymer resin can include monomers (e.g., isobornyl acrylate, 2-hydroxyethyl methyl acrylate, and tripropylene glycol diacrylate (TPGDA)), oligomers (e.g., polyurethane acrylate, polyester acrylate, epoxy acrylate), and photoinitiators (e.g., 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO)).

[0039] In one specific embodiment, the liquid photopolymer resin can include the following components (in total liquid weight percentage): 25% trifunctional aliphatic polyurethane acrylate oligomer, 45% isobornyl acrylate, 28% tripropylene glycol diacrylate, 1.8% diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 0.1% phenol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, and 0.1% di-tert-butylhydroxytoluene.

[0040] In another embodiment, the liquid photosensitive resin can comprise the following components (in total liquid weight percentage): 30% aliphatic urethane acrylate, 38% isobornyl acrylate, 22% 2-hydroxyethyl acrylate, 8.5% polyethylene glycol diacrylate, 1.3% diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, 0.05% 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBOT), and 0.15% p-methoxyphenol (MEHQ).

[0041] In yet another embodiment, the liquid photosensitive resin can comprise the following components (in total liquid weight percentage): 50% difunctional aliphatic polyether urethane methacrylate, 10% aliphatic urethane dimethacrylate, 10% N,N-dimethylacrylamide, 28% tricyclo[5.2.1.0^2,6]decane dimethanol diacrylate, 1.5% 2-hydroxy-2-methyl-l-phenylpropanone, 0.3% N-nitroso-N-phenylhydroxylamine aluminum salt, and 0.2% 2-(2H-benzotriazol-2-yl)-4,6-bis(l-methyl-l-phenylethyl)phenol.

[0042] In one embodiment, the liquid photosensitive resin is cured by light beam irradiation to form a solid layer. The solid layer is composed of copolymers of the aforementioned monomers and oligomers, such as acrylate, epoxy, and / or urethane polymer fragments. The photopolymerization reaction proceeds in the horizontal direction, and the shape of the solid layer is consistent with the light beam pattern. When the light beam irradiates the liquid photosensitive resin from top to bottom, the process is top-to-bottom shaping; in this process, the printing platform is gradually lowered, and the cured layer gradually sinks into the liquid. When the light beam irradiates from bottom to top, the process is bottom-to-top shaping; in this process, the printing platform is gradually raised, and the cured layer gradually rises out of the tank, while the residual liquid resin in the tank enters the gap between the cured layer and the tank bottom, and then the liquid resin is again subjected to light irradiation and cured, and combined with the previous cured layer. The above process is repeated until the complete matrix 10 is formed. Thus, the matrix 10 is composed of a stack of multiple polymer cured layers.

[0043] In some cases, there can be some unreacted photoinitiator after the photosensitive resin is cured. For example, in some cases, about 10% of the photoinitiator can not have reacted completely; after post-curing treatment, the unreacted photoinitiator content can still be about 1%. The presence of unreacted photoinitiator can be used as an indicator of the photopolymerization reaction by which the matrix 10 is made.

[0044] In one embodiment, the photosensitive resin can also be referred to as a photocurable resin. The photosensitive resin, after curing, forms a thermoset polymer material that is composed of a three-dimensional cross-linked polymer network. The three-dimensional polymer network can include a variety of repeating structural units, such as urethane groups, ester side chains, thioether groups, and / or alkyl structural units.

[0045] In one embodiment, the base 10 can be fabricated using a stereolithography (SLA) process. First, the STL model is sliced along the Z-axis direction to obtain a plurality of two-dimensional patterns. Subsequently, a laser beam traces the two-dimensional patterns point-by-point on the surface of a printing platform, and cures the photosensitive resin at the points where the beam is incident. The irradiated photosensitive resin forms a solid layer that conforms to the shape of the two-dimensional pattern. The diameter of the beam determines the resolution in the X and Y directions. For example, when a UV laser with a wavelength of 405 nm is used, the spot width can be 140 microns in some cases. Similar to the DLP process, the SLA can also form the part layer-by-layer in a top-down or bottom-up manner. The printing platform is moved step-by-step, each time forming a corresponding solid layer, until the complete base 10 is generated. In some embodiments, the photosensitive resin used can include the following components (in total liquid weight percentage): 30% polyurethane diacrylate, 20% bisphenol A epoxy diacrylate, 32% isobornyl acrylate, 10% N-vinylpyrrolidone, 5.5% tripropyleneglycol diacrylate, 2% 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 0.1% 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBOT), 0.3% di-tert-butylhydroxytoluene (BHT), and 0.1% organomodified polysiloxane.

[0046] In another embodiment, the base 10 can be fabricated using a liquid crystal display (LCD) process. The LCD process is similar in principle to the DLP process, with the main difference being that the DLP uses a projector to generate the two-dimensional patterns, while the LCD process uses a liquid crystal display to generate the two-dimensional patterns. Similar to the DLP process, the irradiated photosensitive resin cures to form a solid layer that conforms to the shape of the pattern, and the base 10 is formed layer-by-layer, for example, in a bottom-up manner.

[0047] In yet another embodiment, the base 10 can be fabricated using a continuous liquid interface production (CLIP) process. The CLIP process is also similar to the DLP process, with the main difference being that a layer of oxygen-permeable film is provided in the CLIP process, which forms a “dead zone” between the film and the polymerizing part, i.e., a continuously existing liquid interface. In this way, the photopolymerization process no longer proceeds in a layer-by-layer manner, but can continuously cure as the part is continuously pulled out of the vat. Compared to the DLP process, the CLIP process avoids the repeated lifting and lowering of the printing platform, thereby significantly improving the printing speed.

[0048] In one embodiment, the substrate 10 can be prepared using a material jetting process. In this process, a nozzle (which can be a single nozzle or multiple nozzles) reciprocates on a printing platform, jetting droplets of photosensitive resin to a selected location and immediately curing them with an ultraviolet light source. As a solid layer of the two-dimensional pattern is formed, the printing platform descends one layer thickness at a time, and the jetting and curing process is repeated until the entire substrate 10 is constructed.

[0049] In another embodiment, the substrate 10 can be prepared using a fused deposition modeling (FDM) process. In this process, a printing device melts a thermoplastic material (e.g., bisphenol A (BPA)-free polyethylene terephthalate modified material PETG) in the form of filaments or continuous droplets. The molten filaments or droplets are laid layer by layer on a printing platform and adhere to each other based on their own thermal properties to form the substrate 10. The substrate 10 is formed by progressively stacking multiple layers of heated and adhered filaments or droplets. Because this process does not require photocuring, in some cases, articles formed by the FDM process do not contain photoinitiators.

[0050] In some cases, residual monomers may exist in the substrate 10 prepared by 3D printing. These monomers may gradually leach out in the moist environment of the oral cavity, leading to biocompatibility issues. Therefore, a coating layer that blocks monomer migration can be formed on the surface of the substrate 10. This coating not only prevents monomer leaching but also provides waterproofing and other functions. The following embodiments will focus on describing the coating structure and its function.

[0051] In one embodiment, such as Figure 2 As shown, the clear aligner has a shell structure including a substrate 200, a coating 201, and a tooth-receiving cavity 202. The substrate 200 has edge regions 203 and 204 located at its ends and adjacent to the entrance 205 of the tooth-receiving cavity 202. In some cases, regions other than the edge regions may be referred to as non-edge regions. Both the substrate 200 and the coating 201 are transparent and biocompatible. Here, "transparent" typically means that the transmittance of visible light is not less than 70%.

[0052] In one embodiment, the substrate 200 and the tooth receiving cavity 202 can be personalized according to the patient's orthodontic plan and fabricated using the aforementioned 3D printing process. The substrate 200 may be composed of one or more thermosetting polymer materials. The tooth receiving cavity 202 is used to receive the patient's teeth and apply predetermined orthodontic forces.

[0053] After the substrate 200 is 3D printed, it can be further trimmed, cut, deburred, sanded, cleaned, or polished. For example, the substrate 200 may have supporting structures (such as sharp flanges), which need to be cut off and surface residues removed. The supporting structures can be removed by manual peeling, laser cutting, mechanical cutting, high-pressure fluid cutting, centrifugation, high-frequency vibration, or any combination of the above methods. Residues on the surface of the substrate 200 can be removed by cleaning and polishing, or by high-pressure gas purging, centrifugation, solvent cleaning, or any combination of the above methods.

[0054] In some embodiments, the substrate 200 may also undergo post-curing treatment to further enhance the degree of polymerization or photopolymerization. The post-curing treatment may include UV curing and / or heat curing. Optionally, the post-curing treatment may also be performed in an inert gas environment or a liquid environment. Furthermore, the substrate 200 may also be cured after coating with an oxygen barrier agent.

[0055] In one embodiment, such as Figure 2 As shown, coating layer 201 serves as a barrier layer to prevent monomers from entering the oral cavity or from migrating from substrate 200 to the oral cavity. Coating layer 201 covers and can completely encapsulate substrate 200. The surface of the tooth-receiving cavity 202 of substrate 200 can be referred to as the inner surface, and the opposite side can be referred to as the outer surface. Coating layer 201 can selectively cover all surfaces of substrate 200, i.e., cover 100% of the inner and outer surfaces. Optionally, coating layer 201 may cover only a portion of the surface, for example, at least 50% of the inner and / or outer surfaces of substrate 200.

[0056] In one embodiment, the coating layer 201 serves as a physical barrier and diffusion barrier for the monomer. Its small pore size and porosity result in extremely low monomer permeability, thereby preventing monomer migration and avoiding monomer precipitation into the oral cavity.

[0057] In another embodiment, the molecular weight cutoff value (MWCO) can be used to characterize the filtering or blocking performance of the coating layer 201. In some cases, the MWCO of the coating layer 201 may be less than or equal to 2000 Daltons to prevent monomer migration. In more stringent cases, the MWCO may be less than or equal to 700 Daltons to further enhance the blocking effect on monomers, thereby reducing the release of monomers into the oral cavity.

[0058] In some embodiments, in addition to being a barrier to monomers, the coating layer 201 can also have water repellent properties to insulate or at least reduce the contact of the substrate 200 with water. As used herein, "water repellent" means that the material does not allow water to penetrate to some extent, and / or is able to repel water to some extent. For example, in some cases, water repellency can be defined by a water vapor transmission rate (WVTR) of less than 0.5 g-m"2-h"1; in more stringent cases, the WVTR can be less than 0.4 g-m"2-day"1. When the coating layer 201 is water repellent, the outgassing of monomers from the substrate 200 can be further reduced.

[0059] In one embodiment, the coating layer 201 can be made of a hydrophobic material. Such materials generally have a low surface energy, and thus exhibit strong water repellency and hydrophobicity. In general, good hydrophobicity can be achieved when the surface energy of the material is less than 50 mJ / m2. Materials that can be used to form such a coating include parylene, polyurea, fluoropolymers, polyurethanes, acrylics, certain silicon materials, certain epoxy materials, certain ceramic materials, and the like. In some embodiments, these low surface energy materials can be deposited on the surface of the substrate 200 to form a coating layer 201 that is both water repellent and a barrier to monomers.

[0060] In another embodiment, the surface of the coating layer 201 can be formed with micro- or nano-textures. The microstructures can trap air or form air gaps, such that water droplets cannot come into direct contact with the surface, and thus exhibit hydrophobicity. For example, water droplets can sit on top of the surface without penetrating, and thus enhance water repellency. Optionally, the average roughness Ra of the surface of the coating layer 201 can be in the range of 0.01-10 microns to achieve hydrophobicity.

[0061] In some embodiments, the coating layer 201 can also contain certain additives to reduce surface energy or enhance hydrophobicity. The additives can improve the properties of the coating surface, and enhance its water repellency and hydrophobicity. Exemplary additives include hydrophobic particles or fillers, fluorine-containing additives, surface modifiers, crosslinking agents, anti-wetting agents, and the like. The coating layer 201 can contain one or more additives, and the amount of the additive is generally in the range of 0.1%-5% by weight of the coating layer. This amount is effective to enhance hydrophobicity, and does not adversely affect the adhesion, mechanical durability, uniformity, transparency, and appearance of the coating layer to the substrate.

[0062] In some embodiments, the hydrophobic particles or fillers can include nano-silica particles, microbeads, microspheres, carbon nanotubes, polytetrafluoroethylene (PTFE) particles, and the like. These particles can enhance the hydrophobicity of the coating layer 201, and thus enhance its water repellency.

[0063] In another embodiment, the fluorine-containing additives can include fluorine-containing polymers (e.g., polytetrafluoroethylene dispersions), fluorine-containing surfactants (e.g., perfluoro-octyl acrylate), perfluorinated compounds (e.g., perfluoro-octyl triethoxysilane), and the like. These additives can reduce the surface energy of the coating layer 201 and enhance its hydrophobicity and water repellency.

[0064] In a further embodiment, the surface modification agents can include silane coupling agents and silicon-based surface modification agents. By forming chemical bonds with the surface of the coating layer, the modification agents can build a hydrophobic layer on the surface and thus improve the water drainage property.

[0065] In other embodiments, the cross-linking agents can include multifunctional isocyanates (e.g., toluene diisocyanate), amino resins (e.g., melamine-formaldehyde resin), epoxy-functional cross-linking agents, and the like. Such cross-linking agents can facilitate the cross-linking of polymer chains in the coating layer and thus improve its overall hydrophobic property, water repellency, and long-term durability.

[0066] In yet another embodiment, the anti-wetting agents can include certain polymeric additives (e.g., polyethylene glycol (PEG)) and certain surfactants (e.g., silicon-based surfactants or polysiloxane surfactants). These anti-wetting agents can reduce the surface tension and decrease the wetting effect of water, thus helping the coating layer 201 maintain its hydrophobic characteristics.

[0067] In one embodiment, the coating layer 201 can have a small pore size and limited porosity, so as to simultaneously block the migration of monomers and water, making it difficult for monomers to be precipitated and for water to penetrate in. For example, in some cases, the coating layer 201 can have a pore size of less than 500 nanometers and a porosity of no more than 20%; in more stringent cases, the pore size and porosity can be less than 100 nanometers and 10%, respectively; in further embodiments, the pore size and porosity can even be less than 10 nanometers and 2%, respectively. In certain embodiments, the coating layer 201 can exhibit an average pore size of about 500 nanometers and a surface energy of about 1 mJ / m2.

[0068] In one embodiment, the coating layer 201 can be formed by various deposition processes, including chemical vapor deposition (CVD), physical vapor deposition (PVD), dip coating, air spraying, airless spraying, electro-spraying, or any combination of the above. When dip coating, air spraying, airless spraying, or electro-spraying is used, it generally includes two steps: first, the substrate 200 is coated with a wet film layer by immersing it in a liquid or spraying droplets; second, the wet film layer is cured, for example, by UV irradiation or heating, to harden it into a coating layer.

[0069] In another embodiment, a parylene coating can be deposited on the surface of the substrate 200 by a CVD method to form the coating layer 201 on the inner and outer surfaces of the substrate. The parylene coating can have the following parameters: a thickness of about 15 microns, a surface energy of 20-30 mJ / m2, a surface roughness Ra of 10-100 nm, a pore size of less than 10 nm, and a porosity of less than 10%. The parylene layer can effectively block monomers and has good water resistance. Since the deposition process does not involve photopolymerization, the parylene layer does not contain photoinitiators. In other embodiments, the coating layer 201 can also be a silicon carbide (SiC) layer having a thickness of about 20 microns and deposited on the surface of the substrate 200 by a CVD method. Both parylene and SiC are transparent and biocompatible materials. When deposited by a CVD method, the thickness of the coating layer 201 on the inner and outer surfaces of the substrate, including the recessed or hollow portions, is relatively uniform, and the ratio of the thickest portion to the thinnest portion can be controlled to be within 1.5-2.

[0070] In further embodiments, the coating layer 201 can be a silicone layer formed on the substrate 200 by a dip coating method. The substrate 200 is first immersed in a liquid silicone, taken out after a period of time, and cured under ultraviolet light. The cured silicone layer is the coating layer 201. For example, an alkoxysilicone can be used to prepare the coating layer. The silicone layer can block monomers and is water-resistant, transparent, flexible, and biocompatible.

[0071] In another embodiment, the coating layer 201 can be an epoxy coating formed by an air spray method. In this process, a liquid epoxy material is sprayed on the inner and outer surfaces of the substrate 200 by a spray system, and then cured by ultraviolet light to form an epoxy layer as the coating layer 201. For example, Master Bond UV18Med can be used to prepare the epoxy layer. The epoxy layer can block monomer release and is water-resistant, transparent, and biocompatible.

[0072] In some embodiments, the coating layer 201 can be a polyurea layer formed by an air spray method. In this process, a liquid polyurea material is sprayed on the inner and outer surfaces of the substrate 200 to form a liquid layer, which is then hardened at room temperature to form the coating layer 201. In other cases, the polyurea is generated by the reaction of an isocyanate component with a synthetic resin component containing an amine-terminated compound. The two components can be sprayed separately and simultaneously onto the surface of the substrate and cured at room temperature to form a polyurea layer. The polyurea layer also has the characteristics of blocking monomers, water resistance, transparency, and biocompatibility.

[0073] In one embodiment, the coating layer 201 can comprise a fluoropolymer material, such as polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), etc. Such fluoropolymers have a low surface energy and can repel water, thus enabling the coating layer 201 to serve as a water barrier and a monomer barrier at the same time.

[0074] In other embodiments, the coating layer 201, after being formed by the above-mentioned methods and materials, can have a water vapor transmission rate (WVTR) of less than 0.5 g m⁻² h⁻¹, or even less than 0.4 g m⁻² day⁻¹. Before the coating layer 201 is deposited, the substrate 200 can also be subjected to cleaning, surface roughening, chemical etching, or plasma treatment to enhance the bonding between the coating and the substrate.

[0075] In one embodiment, as mentioned above, the transparent aligner can be directly prepared by three-dimensional printing, and if necessary, one or more functional coating layers can be applied on the surface thereof to block monomers and impart other additional functions. Direct three-dimensional printing of the aligner has several advantages: first, it can simplify the overall production process, and only a printing and relatively simple post-processing step is needed to obtain the final product; second, it helps to improve the geometric accuracy of the aligner, making it more conformable to the patient's dentition; third, it can provide more flexible mechanical design space and allow complex structural features, such as perforations, local reinforcement, or surface microstructures, etc., to be realized on the aligner; and fourth, it can significantly reduce material waste during production.

[0076] However, in existing three-dimensional printing processes, the same material and the same forming parameters are generally used for overall printing, and thus the physical properties (e.g., mechanical properties) of the obtained aligner are often uniform across different regions. Such uniform distribution of properties is difficult to meet the differentiated mechanical requirements for different dental regions in clinical practice.

[0077] In one embodiment, if the aligner has the same physical properties across all regions, it will not be able to meet the diversified needs in clinical practice, which also limits the flexibility of treatment options and strategy selection. In clinical practice, different local regions in the same case often require completely different stiffness and elastic properties. For example, when performing rapid and large-scale tooth movement or gap opening, regions with high elasticity are needed to provide persistent and effective orthodontic forces; when implementing dental arch expansion, regions with high stiffness are needed to generate sufficient forces to expand the spacing between teeth; and when performing fine alignment of teeth, regions with high modulus, low elasticity, and good creep resistance are needed to accommodate small amplitude movements of teeth and provide stable orthodontic effects.

[0078] The different clinical requirements often contradict each other, and a uniform performance appliance cannot meet all the requirements. Moreover, the existing 3D printing light-cured resin is usually difficult to simultaneously have multiple mechanical properties such as toughness, rigidity, and creep resistance, so as to be unable to provide sufficient orthodontic force in different areas, and also difficult to balance the comfort during wearing and the reliability in clinical use.

[0079] In one embodiment, a light-cured resin is provided, which has fixed component composition and fixed component ratio. The fixed components only include one ingredient capable of initiating a light-cured reaction. In the additive manufacturing process, the process parameters of light-cured printing, such as light exposure time, light intensity, light spot shape, light wavelength, and reaction temperature, can be adjusted, so that under the condition of using the same light-cured resin, different areas form differentiated physical properties. For example, different mechanical properties (such as elastic modulus, elongation at break, yield strain, and / or stress relaxation characteristics) and differentiated microstructures (such as molecular level structures) can be obtained.

[0080] In another embodiment, the light-cured resin simultaneously contains free monomers and bound monomers. The free monomers are chemical molecules that have not reacted, exist in the form of independent small molecules, maintain their original small molecule structure, and are not combined with other molecules through chemical bonds. The bound monomers form long-chain molecules, i.e., high molecular polymers, through polymerization reaction, and these polymers are connected through chemical bonds such as covalent bonds to form a three-dimensional network structure. The free monomers and the bound monomers have significant differences in performance. The polymerization process has a feature similar to the “firecracker effect”, i.e., the polymerization of monomers does not strictly follow the traditional stoichiometric ratio, but occurs to a certain extent in a chain reaction according to different initiation conditions, thereby generating a series of polymer products.

[0081] In one embodiment, the proportion of bound and free components in the polymer network can be precisely controlled by adjusting the process parameters of 3D printing (such as light exposure time, light intensity, light source shape, light wavelength, and / or reaction temperature, etc.). This control method can also adjust the length of single chains, the degree of inter-chain cross-linking, the molecular weight of the main chain, and the length ratio of the main chain and the side chain, etc. that constitute the polymer network. In this way, a polymer material with adjustable physical properties (such as mechanical properties) can be prepared. For example, the elastic modulus of the material can vary between 500 MPa and 2200 MPa; the elongation at break can vary between 20% and 160%; the yield strain can vary between 2% and 6%; and the residual stress after 24 hours of stretching can vary between 10% and 80%.

[0082] In another embodiment, dental appliances formed by 3D printing (such as clear aligners) can exhibit differentiated physical properties in different areas. For example, the occlusal surface area, crown surface area, and marginal area of ​​the appliance (such as...) Figure 2 The edge regions 203 and 204 shown may have enhanced or modified physical properties. These regulated regional properties are organically combined within the same orthodontic appliance, thereby better enabling the edge regions of the appliance (e.g., regions with a thickness of approximately 0.5 mm) to exhibit higher toughness and enhanced fracture resistance compared to some non-edge regions in one embodiment. High-toughness polymers typically have high elongation at break, thus effectively preventing the appliance from breaking during wear and use. However, such polymers may have certain limitations in applying corrective forces due to their lower elastic modulus and residual stress.

[0083] In another embodiment, for areas requiring larger staged movement (e.g., greater than 0.3 mm), the elastic properties can be enhanced. Highly elastic polymers typically have large yield strains and high residual stresses, enabling sustained and gentle application of forces to achieve rapid tooth movement. Such highly elastic polymers are suitable for large-scale, rapid movement, but their lower elastic modulus may limit their ability to control the root.

[0084] In another embodiment, for tilt correction in the anterior region, the stiffness of the corresponding area can be enhanced. High-stiffness polymers have a high elastic modulus, making them suitable for complex orthodontic procedures involving the tooth roots, enabling precise adjustment of tooth position. However, excessive stiffness may lead to decreased wearing comfort, such as lower yield strain and elongation at break, thus reducing compliance.

[0085] In photopolymerization, the reaction process of monomers and other compounds does not strictly follow traditional stoichiometric relationships. In typical stoichiometric reactions, if the proportions of raw materials added do not meet the requirements, unreacted components often remain. However, the situation is different in photopolymerization. The reaction and consumption of monomers are not entirely limited by the initial ratio, but depend more on the conditions for photo-initiated chain reactions. Therefore, polymer products with significantly different properties may be generated under different reaction conditions, meeting the diverse needs of clinical treatment.

[0086] In one embodiment, the polymerization reaction can be controlled by the temperature variable. Under certain light conditions, when the reaction temperature is 40°C, the polymerization conversion rate can reach about 99%, and the resulting polymer has a higher ratio of side chain to short chain structure. When the reaction temperature is lowered to 10°C, the polymerization conversion rate is about 95%, and the residual amount of unreacted monomer increases, and the ratio of long chain structure in the polymer increases. Therefore, under the condition of keeping other photopolymerization conditions unchanged, the change of temperature can significantly affect the morphology of the polymer network and the proportion of residual monomer, thereby leading to differences in macroscopic physical properties.

[0087] In another embodiment, the photopolymerization process itself has a certain degree of uncertainty. It is difficult to achieve precise control at the microscale, and it is also difficult to accurately predict the reaction results in some cases. This uncertainty provides space for controlling the microstructure and properties of the polymer, while still maintaining a high conversion rate. The so-called "firecracker effect" embodies this feature, which provides an additional control dimension for the manufacturing process, so that in some cases the performance of the product can be optimized by adjusting the amount of compound added and the light conditions.

[0088] In many cases, the final product obtained by photopolymerization reaction contains both free monomer and bound monomer in the polymer network.

[0089] In yet another embodiment, a photocurable resin containing polyurethane acrylate (PUA) and monomers can be used for photopolymerization. The monomers can be monofunctional monomers or multifunctional monomers. In some cases, the weight percentage of PUA is about 20% to 50% of the total weight of the photocurable resin, and the weight percentage of the monomers is about 50% to 80% of the total weight of the photocurable resin. In addition, the photocurable resin can also contain some additives, such as ultraviolet blockers, photoinitiators, inhibitors, antioxidants, etc., to further improve the forming properties and use stability of the material.

[0090] In one embodiment, the monomers in the photocurable resin can include one or more monofunctional monomers, such as (meth)acrylate monomers, epoxy compounds, and vinyl monomers. For example, methyl methacrylate (MMA), butyl methacrylate (BMA), 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), triethylene glycol divinyl ether (DVE-3), and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexyl carboxylate (ECC) can be used. By adjusting the light time and light intensity, the degree of polymerization of the monomers and the network density can be controlled. When the light time is longer and the light intensity is higher, the degree of polymerization of the monomers increases, forming a more dense network structure, and the resulting material exhibits higher hardness; on the contrary, when the light time is shorter and the light intensity is lower, the resulting polymer network is more loose, and the material has enhanced flexibility.

[0091] In another embodiment, the monomers in the photocurable resin can include one or more multifunctional monomers, such as (meth)acrylate monomers, epoxies, and vinyl monomers. For example, methacryloyloxypropyl glycidyl ether (GMA), acrylated epoxidized soybean oil (AESO), 3-ethylallyl methoxyoxetane, (3-ethyl-3-oxetanyl)propyl acrylate, and the like can be used. In some cases, both a free radical photoinitiator (such as TPO) and a cationic photoinitiator (such as 4-isobutylphenyl-4'-methylphenyl iodonium hexafluorophosphate) can be present in the photoinitiator to initiate free radical polymerization and cationic polymerization under 405 nm and 355 nm light, respectively. By controlling the light conditions (such as light wavelength, light exposure time, light intensity, light spot size, and light spot energy distribution), the reaction kinetics of free radical polymerization and cationic polymerization can be adjusted, thereby changing the microstructure of the polymer. Different light conditions can result in different degrees of crosslinking and molecular chain lengths, which in turn regulate the hardness and elasticity of the material. For example, when the monomer molecule contains both multiple acrylate groups and an epoxy group, 405 nm light is more likely to initiate polymerization of the acrylate groups, generating a hard polymer network with a high degree of crosslinking; while 355 nm light mainly initiates ring-opening polymerization of the epoxy group, resulting in a polymer material that is overall softer with a lower degree of crosslinking.

[0092] In one embodiment, the light exposure time during photopolymerization affects the degree of crosslinking of the polymer network. When the light exposure time is longer, the system obtains more energy, the polymerization reaction is more complete, the crosslinking density increases, and the polymer network structure is more compact, thereby increasing the hardness of the material. However, if the light exposure time is too long, the material can become brittle due to excessive crosslinking, and the stiffness may, in turn, decrease. Within a certain range, the stiffness of the material and the light exposure time show a convex function relationship. For example, when the light exposure time is t1 (such as 4 seconds), the polymerization reaction can only form a preliminary polymer structure, the crosslinking is insufficient, the material is relatively soft and has good toughness; when the light exposure time is extended to t2 (such as 8 seconds), the optimal crosslinking density is reached, and the material has the highest hardness; when the light exposure time is further extended to t3 (such as more than 10 seconds), the material becomes brittle due to excessive crosslinking, and the hardness slightly decreases.

[0093] In another embodiment, light intensity directly determines the strength of light energy and affects the rate and depth of polymerization. Higher light intensity can provide more energy, accelerate the polymerization rate, and generate a denser polymer network, thus improving the material hardness and creep resistance. The product of light intensity and light exposure time reflects the total energy input. When the energy input is too low (e.g., less than 50 mJ / cm²), it is difficult to form; when the energy input is too high (e.g., greater than 300 mJ / cm²), the material performance no longer changes significantly. Overall, the effect of light intensity on physical properties is greater than that of light exposure time. For example, lower light intensity (e.g., 10 mW / cm²) combined with shorter light exposure time (e.g., 4 seconds) can not form a complete structure, resulting in poor performance; while higher light intensity (e.g., 40 mW / cm²) combined with longer time (e.g., 8 seconds) can obtain higher hardness and stronger creep resistance.

[0094] In yet another embodiment, the wavelength of light determines the characteristics of light energy and the polymerization mechanism. Because a specific photoinitiator absorbs more strongly at a specific wavelength, different wavelengths of light will trigger different polymerization pathways. At certain wavelengths, the polymerization reaction is more intense, and a better crosslinked network can be formed, thus improving the toughness and stiffness of the material; while at other wavelengths, the polymerization reaction is relatively mild, and the resulting material performance combination is different. The commonly used light wavelength in three-dimensional printing is in the range of 250-520 nm, among which 355 nm and 405 nm are more commonly used. For example, under 405 nm light, the polymerization reaction is intense, and the resulting polymer has high stiffness and creep resistance, but low toughness and yield strain; under 355 nm light, the polymerization reaction is relatively mild, and the resulting polymer has poor stiffness and creep resistance, but better toughness.

[0095] In one embodiment, reaction temperature has an important influence on polymerization kinetics and the mobility of polymer segments. At low temperatures, the polymerization rate slows down, the system viscosity rises, the gel point comes earlier, and the network structure formed is relatively loose, and the material exhibits soft properties. At high temperatures, the polymerization rate increases, but may be accompanied by an increase in side reactions, an increase in the proportion of short chains and side chains, thus affecting the quality and performance of the polymer. In some cases, the reaction temperature can range from -30°C to 45°C, and it is required to maintain uniform temperature, with a temperature difference controlled within ±2°C. At low temperatures (e.g., 0°C), the reaction rate slows down, and the material formed is softer; at high temperatures (e.g., 40°C), the reaction accelerates, and the resulting material is harder. When the temperature is lower than -30°C, the polymerization reaction can not occur; and when the temperature is higher than 45°C, the monomer components can volatilize, affecting the molding quality.

[0096] In another embodiment, the form of the light source (e.g., point source, line source, or area source) determines the manner in which the light energy is distributed and the locality of the polymerization reaction. Different light source forms can create different crosslinking regions in the structure and affect the temperature field and reaction pathway during the reaction, thereby obtaining a complex structure with differentiated physical properties. In some cases, the spot diameter can be 0.03-0.15 mm, and a commonly used spot diameter is 0.075 mm or 0.1 mm. A smaller diameter spot can form a highly concentrated crosslinking in a local area, which is suitable for areas requiring high hardness; while a larger diameter spot is conducive to achieving uniform crosslinking, thereby obtaining a product with relatively uniform physical properties.

[0097] Illumination time (s) Light intensity (mW / cm2) Spot diameter (mm) Wavelength (nm) Temperature (°C) Elastic modulus (MPa) Elongation at break (%) Yield strain (%) 24h residual stress (%) 4 10 0.075 350 40 1393 78 3.3 19 5 10 0.075 350 40 1433 66 3.7 20 5 15 0.075 350 40 1495 95 3.5 32 5 40 0.075 350 40 1846 33 4.5 53 5 40 0.1 350 40 1693 29 4.5 45 5 40 0.075 405 40 1725 25 4.2 38 5 40 0.075 350 0 1146 37 3.1 25 6 40 0.075 350 0 1178 42 3.0 48 8 9 0.075 405 40 1195 75 4.2 35 8 9 0.075 405 0 830 94 5.3 11 8 10 0.075 350 40 1273 81 3.2 42 8 10 0.1 350 40 1235 68 3.7 25 9 5 0.075 350 40 963 56 2.9 13 10 10 0.075 405 40 1436 72 3.8 31 10 40 0.1 350 40 1704 29 4.6 26 10 40 0.075 350 0 1303 31 4.8 26

[0098] Table 1. Exemplary three-dimensional printing parameters and material physical properties

[0099] As shown in Table 1, the combination of light exposure time and light intensity has a significant impact on the physical properties of the material. For example, when the light exposure time is 5 seconds and the light intensity is 40 mW / cm2, the resulting material has a higher elastic modulus, but the elongation at break is significantly lower than when the light exposure time is 8 seconds and the light intensity is 10 mW / cm2. This indicates that in some cases, the degree of influence of light intensity on physical properties can exceed that of light exposure time.

[0100] Table 1 also reflects the effect of light wavelength and reaction temperature on material properties. For example, when the light exposure time is 8 seconds, the light intensity is 9 mW / cm2, and the light wavelength is 405 nm, the material obtained at 0°C has a lower elastic modulus than that obtained at 40°C, but a higher elongation at break and yield strain. This indicates that reducing the temperature can decrease the stiffness of the material, but increase its toughness and deformation ability.

[0101] In another embodiment, when the temperature is low (e.g., 0°C) and the light exposure time is long (e.g., 6 seconds), even if the light intensity is high (e.g., 40 mW / cm2), the reaction rate can still be limited by the temperature, resulting in a material with lower hardness than expected and a higher yield strain.

[0102] Conversely, when the temperature is high (e.g., 40°C) and the light exposure time is short (e.g., 4 seconds), even if the light intensity is low (e.g., 10 mW / cm2), the high temperature can accelerate the polymerization reaction, resulting in a material with higher hardness. However, at the same time, the stress relaxation rate of this material can be high in some cases.

[0103] In one embodiment, as shown in Figure 3 Figure 1, a schematic diagram of the physical properties of a three-dimensional printing material is shown. In this embodiment, the light wavelength is 405 nm, the reaction temperature is 25°C, the spot diameter is 0.1 mm, and the light exposure time and light intensity are variables. In Figure 3In the present embodiment, the abscissa and ordinate represent the light exposure time and light intensity, respectively, and the size and color of the bubbles (or dots) represent the elastic modulus and elongation at break, respectively. The larger the bubble, the higher the elastic modulus; the darker the color, the greater the elongation at break. As can be seen from FIG. 3, by reasonably combining the light exposure time and light intensity, the high elastic modulus and elongation at break can be taken into account to some extent, and performance balance can be achieved. At the same time, in some cases, different parameter combinations can also enable a single physical property to reach a high level. It can be seen that the local performance of the material at different positions is adjustable and can be optimized according to actual needs. Figure 3

[0104] In another embodiment, when the three-dimensional printing process parameters are fixed, the resulting appliance exhibits uniform physical properties as a whole. However, such appliances are difficult to meet the diverse clinical needs. For example, in some cases, the orthodontic force of the anterior tooth region is insufficient; in some cases, the anchorage capacity of the posterior tooth region is insufficient, but the local stiffness is difficult to improve; and for patients with periodontal disease, a softer orthodontic force is needed to reduce the concentrated stress on the periodontal tissue. However, in clinical practice, a balance between efficiency and risk is often needed: on the one hand, patients with periodontal disease need a material with a lower elastic modulus to exert a gentle force; on the other hand, a material with a higher elastic modulus is needed to maintain the stability of the dental axis and avoid uncontrollable tooth inclination during treatment.

[0105] In the embodiments of the present application, by adjusting the three-dimensional printing process parameters, the different regions of the appliance can have differentiated physical properties using the same light-cured resin. The process parameters include light intensity, light exposure time, light spot size, light wavelength, and reaction temperature, etc. For example, a combination of light intensity of 16 mW / cm², light exposure time of 4 seconds, light spot diameter of 0.075 mm, light wavelength of 405 nm, and reaction temperature of 35°C can be used to prepare the appliance. In some embodiments, some of the parameters can be selectively adjusted to achieve optimization of local performance. The following description takes the combination of light intensity and light exposure time as an example, and the remaining parameters can also be adjusted to achieve the same or similar effect.

[0106] In one embodiment, by reducing the light intensity and extending the light exposure time, the elastic modulus of the anterior tooth region of the appliance can be enhanced. For example, when the light intensity is reduced from 16 mW / cm² to 10 mW / cm² and the light exposure time is extended from 4 seconds to 8 seconds, the elastic modulus of the anterior tooth region can be increased from about 1200 MPa to about 1500 MPa, thereby enhancing the root control ability and optimizing the local material strength and elasticity.

[0107] ​In another embodiment, the toughness of the edge region of the orthodontic appliance can be improved by increasing the light intensity and illumination time. For example, when the edge region thickness is 0.5 mm, extending the illumination time from 4 seconds to 5 seconds and increasing the light intensity from 16 mW / cm² to 40 mW / cm² can increase the elongation at break of this region to approximately 120%, thereby significantly improving the durability and fracture resistance of the edge region.

[0108] In another embodiment, the physical properties of the interdental space of the orthodontic appliance can be optimized by adjusting the light intensity and illumination time. When the interdental space is large, the thickness of the filling material used to fill the space can reach 0.7 mm (measured along the direction passing through the centers of two adjacent teeth). When the light intensity and illumination time are set to 5 mW / cm² and 9 seconds, respectively, the yield strain of the interdental space can be increased from approximately 3.2% to approximately 4.5%. This design improves the resistance to deformation of the interdental space during wearing and removal while maintaining good force transmission characteristics.

[0109] In one embodiment, the orthodontic appliance can create localized, point-like hardening zones by adjusting the light intensity and illumination time. These point-like zones can have a diameter of 0.1 mm to 0.5 mm and are typically located on the labial side of the incisors near the gingiva. In some cases, the elastic modulus of these point-like zones can be increased to 2000 MPa, thereby providing precise point forces locally, particularly suitable for small-range tooth movements and axial control.

[0110] In another embodiment, the jaw alignment structure of the orthodontic appliance can be optimized by varying the light intensity and illumination time. For example, the occlusal plate on the appliance can be designed with a honeycomb structure, where the elastic modulus of the internal honeycomb cells can be controlled between 1000 MPa and 1500 MPa, while the elastic modulus of the outer area of ​​the honeycomb cells can be controlled between 1600 MPa and 2200 MPa. This design differentiates the mechanical properties of different areas, improving the patient's occlusal comfort while maintaining overall stiffness.

[0111] In another embodiment, personalized patterns or text can be formed on the orthodontic appliance by adjusting the light intensity and illumination time. These patterns or texts not only enhance the aesthetics and personalization of the appliance, but also impart specific physical properties to certain areas. For example, they can increase localized orthodontic forces in certain tooth areas, or achieve specific orthodontic functions through special structures.

[0112] In one embodiment, certain physical properties of the orthodontic appliance can be gradually distributed along a specific direction by adjusting the light intensity and illumination time. For example, the elastic modulus of the appliance can gradually change along the direction of the patient's dental arch. Figure 4A and Figure 4BAs shown, the dental arch 400 is a curved structure extending along an arc-shaped path 401. The tangent direction at a point on the arc-shaped path 401 can be considered as the direction of the dental arch at that point. Figure 4B As shown, at a point P on path 401, the direction of its tangent is indicated by the arrow, which represents the direction of the dental arch at that point. When a small segment of the arc-shaped path 401 is sufficiently short (e.g., less than 1 mm), the orientation of that segment can also be approximated as the direction of the dental arch for that segment. The direction of the dental arch changes continuously as path 401 extends. In some cases, the elastic modulus of the appliance in the anterior region is higher than that in the posterior region, and it gradually decreases along the dental arch direction from the anterior to the posterior, continuing to decrease in the posterior region, thereby meeting the needs of different tooth movements.

[0113] In another embodiment, by adjusting the light intensity and illumination time, a multi-layered structure with different physical properties can be formed in a certain part of the orthodontic appliance. These layers can be arranged around a single tooth or multiple teeth, stacked on top of each other to form a multi-layered structure. For example, in a cross-section perpendicular to the dental arch, the inner layer of the orthodontic appliance can be designed as a highly resilient material to improve wearing comfort; the outer layer can be designed as a highly rigid material to provide effective orthodontic force; and the middle layer can be endowed with corresponding physical properties according to treatment needs, thereby achieving a balance between function and comfort.

[0114] In another embodiment, microstructures can be formed within the orthodontic appliance by adjusting light intensity and illumination time. For example, the appliance can be designed with structures containing micropores, microgrids, microsprings, or stretchable material units. These microstructures are not true "cavities," but rather achieve a relative reduction in stiffness in localized areas by adjusting physical properties at the microscale. This type of design improves the adaptability and comfort of the appliance, reduces pressure in the patient's mouth, and enhances the overall flexibility of the material. Unlike traditional open cavity structures formed by hollowing out, these microstructures can be directly sealed during 3D printing, avoiding open oral gaps on the surface, thus preventing bacterial growth and aesthetic impact, while optimizing physical properties and balancing hygiene and appearance.

[0115] In one embodiment, the appliance or its base can be configured to move one or more teeth of the patient from a first position and orientation to a second position and orientation, as described previously. The magnitude of the orthodontic force required depends on the specific treatment goal, the manner of tooth movement, and the individual condition of the patient. Since each patient has different tooth and bone conditions, the required orthodontic force varies. Factors such as the patient's age, oral health, and bone density can affect the setting of the orthodontic force. Generally, the orthodontic force needs to be sufficient to achieve effective tooth movement while ensuring that the tooth and surrounding tissue are not damaged. For example, the required orthodontic force can be 0.2 N to 0.6 N for tooth tipping, 0.7 N to 1.2 N for tooth translation, 0.35 N to 0.6 N for tooth rotation, 0.1 N to 0.4 N for tooth extrusion, and 0.1 N to 0.15 N for tooth intrusion.

[0116] In another embodiment, different portions of the base of the appliance can be designed to have different tooth-receiving cavities. For example, one portion of the base includes tooth-receiving cavities for receiving a portion of the patient's teeth and applying an orthodontic force to the portion of the teeth in a first direction, while another portion of the base includes tooth-receiving cavities for receiving another portion of the patient's teeth and applying an orthodontic force to the portion of the teeth in a second direction. The first direction is different from the second direction, thereby enabling complex clinical treatment requirements to be met.

[0117] In yet another embodiment, the base can have specific physical properties, such as a tensile modulus of 420 MPa to 2650 MPa, a yield strength of 22 MPa to 78 MPa, a yield strain of greater than 1.8%, a breaking strain of greater than 10%, and a glass transition temperature (Tg) of greater than 40 °C. The Tg refers to the temperature at which a polymer material transitions from a glassy state to a high-elastic state. During the 3D printing process, the Tg can increase with increasing light intensity. Maintaining the Tg of the base above 40 °C is important because the average normal body temperature of a human is about 37 °C. Once the temperature of the base exceeds the Tg, the mechanical properties of the material can decrease significantly, thermal deformation can occur, wear resistance and scratch resistance can decrease, and the long-term stability of the appliance can be affected.

[0118] In another embodiment, the average thickness of the base or shell structure is less than 2.0 mm. The thickness refers to the distance between a point on the inner surface of the base and the nearest point on the outer surface of the base. If the base is too thick, excessive heat accumulation can occur during the 3D printing process, leading to excessive internal stress, deformation, and even whitening defects. Therefore, controlling the thickness not only helps to ensure the printing accuracy and structural stability, but also improves the wearing comfort and transparent aesthetic appearance.

[0119] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A dental appliance with regionally differentiated physical properties for moving at least one tooth of a patient from a first position and orientation to a second position and orientation, characterized in that, include: A matrix having a three-dimensional shell structure configured to receive a patient's tooth, the matrix being made of a light-cured resin comprising polyurethane acrylate (PUA) and monomers; The matrix includes a first region and a second region. The mechanical property parameters of the first region have a first value, and the mechanical property parameters of the second region have a second value that is different from the first value, thereby forming a regionally differentiated physical property distribution. The first region includes a first tooth receiving cavity for receiving a patient's tooth, the first tooth receiving cavity being configured to abut against the patient's tooth to generate a first tooth movement force having a first direction; The second region includes a second tooth receiving cavity for receiving another portion of the patient's tooth, the second tooth receiving cavity being configured to abut against the portion of the tooth to generate a second tooth movement force having a second direction, and the first direction being different from the second direction; The average thickness of the substrate is less than 2.0 mm; The material properties of the orthodontic appliance include: a tensile modulus between 420 MPa and 2650 MPa, a yield strength between 22 MPa and 78 MPa, a yield strain greater than 1.8%, a fracture strain greater than 10%, and a glass transition temperature (Tg) greater than 40°C.

2. The dental appliance according to claim 1, wherein, The first region and the second region correspond to different tooth regions on the dental arch path, respectively.

3. The dental appliance according to claim 1, wherein, The first region and the second region correspond to different layers of the same tooth, and the layers are arranged in a direction perpendicular to the dental arch path.

4. The dental appliance according to claim 1, wherein, The mechanical properties of the first and second regions gradually change along the dental arch path.

5. The dental appliance according to claim 1, wherein, The first region and the second region correspond to the edge region and non-edge region of the substrate, respectively.

6. The dental appliance according to claim 1, wherein, The first or second region is a point-like hardened region.

7. The dental appliance according to claim 1, wherein, The weight percentage of polyurethane acrylate (PUA) in the photocurable resin is 20% to 50%, and the weight percentage of monomer in the photocurable resin is 50% to 80%.

8. The dental appliance according to claim 1, wherein, A coating layer is formed on at least a portion of the inner or outer surface of the substrate, the coating layer being used to prevent monomer migration.

9. An additive manufacturing method for preparing dental appliances with regionally differentiated physical properties, characterized in that, include: A matrix is ​​formed using a light-cured resin via an additive manufacturing process. The matrix has a three-dimensional shell structure configured to receive a patient's teeth according to a treatment plan. The light-cured resin includes polyurethane acrylate (PUA) and monomers. During the formation of the substrate, a first region of the substrate is prepared using a first printing process parameter value, and a second region of the substrate is prepared using a second printing process parameter value that is different from the first printing process parameter value, so that the first region and the second region have different physical properties. The first region is configured to apply a first tooth movement force in a first direction to the patient's teeth, and the second region is configured to apply a second tooth movement force in a second direction to another portion of the patient's teeth, wherein the first direction is different from the second direction; The average thickness of the substrate is less than 2.0 mm; The material properties of the orthodontic appliance include: a tensile modulus between 420 MPa and 2650 MPa, a yield strength between 22 MPa and 78 MPa, a yield strain greater than 1.8%, a fracture strain greater than 10%, and a glass transition temperature (Tg) greater than 40°C.

10. The method according to claim 9, wherein, The printing process parameters include one or more of the following: illumination time, light intensity, light source shape, light wavelength, or reaction temperature.

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