3D printing appliance step-by-step curing method based on gray level regulation and control

Abstract

The invention discloses a 3D printing appliance step-by-step curing method based on gray level regulation and control. The method comprises the following steps: preparing used photosensitive resin which contains an epoxy acrylate component, and adding a certain amount of thermal initiator into the photosensitive resin; segmenting an area corresponding to the specified tooth from the 3D printing model of the appliance, and modifying the pattern gray scale of the area corresponding to the specified tooth; slicing the 3D printing model of the appliance to obtain a plurality of slice patterns with gray processing; completing gray photocuring treatment on each layer of the appliance based on the plurality of slice patterns; and putting the appliance subjected to gray photocuring treatment into a drying oven, and heating for a specified time at a specified temperature. On the basis of gray level regulation and control, a step-by-step curing scheme of photocuring and thermocuring is adopted in the process of 3D printing of the appliance, the internal monomer amount is reduced while the mechanical performance of the 3D printing appliance is guaranteed, monomer precipitation can be effectively reduced, and biocompatibility is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing, and in particular to a step-by-step curing method and system for a 3D printed appliance based on grayscale control. Background Art

[0002] During the growth and development process, due to the influence of congenital genetics or acquired diseases and bad habits, problems such as uneven teeth, abnormal upper and lower bite relationships, and abnormal jaw size, shape and position are collectively referred to as malocclusion. It affects our oral health and causes periodontal inflammation and other problems. In order to improve malocclusion, the clinical treatment method is to wear braces.

[0003] Bracketless invisible braces are a new type of orthodontic treatment. Compared with traditional metal appliance orthodontics, invisible orthodontic treatment has rapidly developed and grown in my country with its advantages of beauty, comfort and short treatment cycle, and its market share has gradually increased. The current mainstream manufacturing method of invisible braces is to use hot pressing molding technology. This technology uses 3D printing to manufacture the patient's dental mold, and then heats the thermoplastic membrane on the dental mold and presses it into shape. However, compared with the original size of the membrane, the hot pressing process will form an uneven thickness, which will affect its mechanical properties and clinical treatment effects.

[0004] With the continuous development of 3D printing technology and biocompatible materials, direct 3D printed braces are considered to be the next stage in the development of brace manufacturing. Compared with the hot pressing film process, direct 3D printing improves the manufacturing accuracy of braces and reduces resource waste and time costs. However, when dealing with complex orthodontic forces, invisible braces have obvious limitations, such as difficulty in controlling torque and root resorption. For this reason, an effective way is needed to help the braces provide adjustable orthodontic forces to ensure that the teeth move in the correct position and prevent excessive correction force from causing damage to the periodontal tissue around the moving teeth.

[0005] Grayscale photocuring printing is a manufacturing technology that has developed rapidly in recent years. It can achieve different material properties by controlling the local material cross-linking degree. Using grayscale printing to manufacture braces can make up for the shortcomings of the single material performance of 3D printed braces to adapt to more complex correction cases. However, since 3D printing resins are biotoxic before complete polymerization, secondary curing and processing must be used to eliminate the potential toxicity of 3D printed braces, which limits the application of grayscale printing.

[0006] Regarding grayscale photocuring printing, the prior art proposes a method based on two-color photocuring. Although this method can reduce the precipitation of monomers inside the printed body to a certain extent, the amount of monomers inside the printed body is not reduced. The prior art also proposes a method using photodegradable monomers, which will decompose after long-term exposure to light, thereby increasing biological activity, but this method will lead to a decrease in the mechanical properties of the printed body.

[0007] How to ensure the mechanical properties of the printed body while reducing the amount of monomers inside the printed body has become an urgent problem to be solved. Summary of the invention

[0008] In view of the above problems, the present invention is proposed to provide a step-by-step curing method and system for a 3D printed appliance based on grayscale control that overcomes the above problems or at least partially solves the above problems.

[0009] An embodiment of the present invention provides a step-by-step curing method for a 3D printed appliance based on grayscale control, the method comprising:

[0010] Prepare a photosensitive resin, wherein the photosensitive resin contains an epoxy acrylate component and a certain amount of thermal initiator is added to the photosensitive resin;

[0011] Segmenting a region corresponding to a designated tooth from the 3D printed model of the orthodontic appliance, and modifying the pattern grayscale of the region corresponding to the designated tooth;

[0012] Slicing the 3D printed model of the appliance to obtain a plurality of slice patterns with grayscale processing;

[0013] completing grayscale photocuring of each layer of the appliance based on a plurality of slice patterns;

[0014] The grayscale light-cured appliance is placed in an oven and heated at a specified temperature for a specified time to complete the thermal curing operation;

[0015] Wherein, the carbon-carbon double bond functionality of the epoxy acrylate component in the photosensitive resin is greater than the epoxy group functionality.

[0016] Optionally, the preparing of the photosensitive resin comprises:

[0017] The thermal initiator and the photosensitive resin are added into a light-proof container, and then placed into a stirrer for thorough stirring to obtain a stirred mixture, and the stirred mixture is placed into an ultrasonic cleaning machine for ultrasonic dispersion to completely dissolve the thermal initiator into the photosensitive resin to obtain a photosensitive resin for printing.

[0018] Optionally, the epoxy acrylate component is composed of one or more of bisphenol A glycidyl methacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and neopentyl glycol diglycidyl ether diacrylate.

[0019] Optionally, the weight ratio of the thermal initiator to the photosensitive resin is 0.2-2 parts.

[0020] Optionally, the thermal initiator is one or two of dimethyl azobisisobutyrate, diisoheptanenitrile, tert-butyl peroxy-2-ethylhexanoate, 593 curing agent, T31 curing agent, 1-methylimidazole, and diisopropyl peroxydicarbonate.

[0021] Optionally, the modifying the grayscale of the area corresponding to the designated tooth includes:

[0022] Adjusts the grayscale of the area corresponding to the specified tooth higher or lower.

[0023] Optionally, lowering the grayscale of the area corresponding to the designated tooth includes:

[0024] Lower the grayscale of the area corresponding to the designated teeth by 40%-60%.

[0025] Optionally, when the grayscale of the area corresponding to the designated tooth is lowered, the method further includes:

[0026] The surface pixels of the designated tooth are obtained, and the grayscale values ​​of the surface pixels of the designated tooth are restored to original values.

[0027] Optionally, obtaining the surface pixels of the designated tooth includes:

[0028] Acquire the edge of each slice pattern corresponding to the designated tooth, where the edge of each slice pattern corresponding to the designated tooth is the surface pixel of the designated tooth in the horizontal direction;

[0029] The surface pixels of the designated tooth in the vertical direction are obtained according to the difference between the grayscale values ​​of the pixels of the adjacent slice patterns.

[0030] Optionally, the grayscale light curing process of each layer of the appliance based on a plurality of slice patterns includes:

[0031] Grayscale photocuring of each layer of the appliance is performed based on a multi-slice pattern using UV light.

[0032] Optionally, the oven is heated to a designated temperature of 60-120° C. and a designated time of 1-12 h.

[0033] Another embodiment of the present invention provides a 3D printed appliance step-by-step curing system based on grayscale control, which adopts the 3D printed appliance step-by-step curing method based on grayscale control as described above.

[0034] The beneficial effect of the present invention is that by modifying the grayscale of the area corresponding to the specified teeth in the bracketless invisible orthodontic appliance model, the cross-linking degree of the area is controlled by changing the light intensity, so that the Young's modulus of the area changes, thereby creating different soft and hard areas, which means that a customized design can be provided for the correction force of the teeth, thereby achieving the effect of regulating the correction force. The present invention does not modify the thickness of the appliance model, which means a uniform thickness; by regulating the grayscale, a larger correction amount can be achieved during correction without causing discomfort to the patient. Based on grayscale regulation, the present invention adds a thermal initiator to the photosensitive resin used, and adopts a light-curing and heat-curing step-by-step curing scheme in the process of 3D printing the appliance. While ensuring the mechanical properties of the 3D printed appliance, the amount of monomers inside is reduced, which can effectively reduce the precipitation of monomers and improve biocompatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of a process of a step-by-step curing method of a 3D printed appliance based on grayscale control according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the principle of a step-by-step curing method for a 3D printed appliance based on grayscale control according to an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the principle of a step-by-step curing system for a 3D printed appliance based on grayscale control according to an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of obtaining an orthodontic appliance based on a 3D printed model of the orthodontic appliance according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Figure 1 FIG. 1 is a flow chart of a step-by-step curing method of a 3D printed appliance based on grayscale control according to an embodiment of the present invention. Figure 1 As shown, the method of the embodiment of the present invention includes:

[0041] S11: preparing a photosensitive resin, wherein the photosensitive resin comprises an epoxy acrylate component, and a certain amount of thermal initiator is added to the photosensitive resin;

[0042] Wherein, the carbon-carbon double bond functionality of the epoxy acrylate component in the photosensitive resin is greater than the epoxy group functionality.

[0043] S12: segmenting a region corresponding to a designated tooth from the 3D printed model of the orthodontic appliance, and modifying a grayscale of a pattern of the region corresponding to the designated tooth;

[0044] It is understandable that the basic principle of the embodiment of the present invention is to modify the local modulus of the appliance model using grayscale, thereby adjusting the effect on the correction force. In the preprocessing process of the model, if the correction force needs to be adjusted in a local area of ​​the appliance model, the grayscale of the area is modified.

[0045] S13: Slicing the 3D printed model of the appliance to obtain a plurality of slice patterns with grayscale processing;

[0046] In practical applications, the model is sliced ​​using 3D printing software to obtain multiple slice patterns. The grayscale value in the slice pattern is positively correlated with the light intensity of the projected pattern light. The higher the grayscale value, the higher the light intensity. The more energy the resin receives, the higher the degree of curing.

[0047] S14: completing grayscale photocuring of each layer of the appliance based on the multiple slice patterns;

[0048] S15: placing the grayscale light-cured appliance into an oven and heating it at a specified temperature for a specified time to complete the thermal curing operation.

[0049] In the embodiment of the present invention, a thermal initiator is added to the photosensitive resin used. In the first stage, grayscale light curing treatment is performed to adjust the mechanical properties of the orthodontic appliance. In the second stage, the orthodontic appliance is placed in an oven for heat curing treatment.

[0050] It should be noted that the photosensitive resin used in the embodiment of the present invention contains an epoxy acrylate component, which can simultaneously have the fast curing speed of acrylate and the low shrinkage rate and good mechanical properties of epoxy resin. Under the light irradiation in the first stage of photocuring treatment, the photoinitiator in the photosensitive resin is cracked to produce free radicals, and the newly formed free radicals will diffuse into the resin medium and undergo polymerization reaction with the acrylate monomer to form a cross-linked network. After heating in the second stage, the heat triggers the polymerization reaction of the epoxy group, further increasing the cross-linking density. Due to the differences in the two reaction mechanisms, an interpenetrating polymer network will be formed inside the printed structure. The monomers in the resin used have epoxy groups and carbon-carbon double bond groups that can participate in the polymerization reaction. In the photocuring reaction, the carbon-carbon double bond participates in the reaction, while in the thermal curing conditions, the epoxy group participates in the reaction. In the first stage of photocuring treatment, the change of the local light intensity of the projection is achieved by regulating the local grayscale of the projection pattern, thereby regulating the local cross-linking degree of the appliance. (The local cross-linking degree here refers to the cross-linking network formed by the monomer through the carbon-carbon double bond reaction, and the epoxy group does not participate in the reaction under light.) In the second stage of thermal curing, the thermal initiator produces active groups that undergo polymerization reactions with the epoxy groups in the components (the carbon-carbon double bonds do not participate in the reaction, so the two reactions do not affect each other and are orthogonal). As the epoxy groups polymerize, the overall cross-linking density continues to increase. Since the carbon-carbon double bond functionality of the epoxy acrylate component in the photosensitive resin is greater than the epoxy group functionality, compared to thermal curing, since more functional groups can participate in the reaction, light curing can form a denser cross-linking network.

[0051] The following combination Figure 2 The principle of the step-by-step curing method of a 3D printed appliance based on grayscale control according to an embodiment of the present invention is described. Figure 2 In the left figure, the photosensitive resin used is subjected to the first stage of light curing, where the left projection is set to 100% grayscale and the right is set to 50% grayscale. Since thermal curing does not occur, the network formed is completely a light-cured cross-linked network. In addition, the network on the left is denser than the network on the right, and the local residual monomer content is less. Figure 2 In the right figure, the photosensitive resin used is subjected to a second stage of thermal curing. Since there are more unreacted monomers on the side of the 50% grayscale projection, the thermal curing network is mainly formed on the grayscale side. Finally, under the action of grayscale photocuring, a photothermal cross-linked interpenetrating network with different degrees of cross-linking can be formed. Since the thermally cured cross-linked network is softer than the photocured network, the advantage of grayscale printing in regulating mechanical properties can be effectively retained. And since the thermal curing process can further increase the degree of cross-linking, the monomer content inside the printed body can be effectively reduced, thereby reducing the precipitation of monomers and improving the biocompatibility of the printed body.

[0052] The embodiment of the present invention modifies the grayscale of the area corresponding to the specified teeth in the bracketless invisible orthodontic appliance model, and uses the change of light intensity to control the degree of cross-linking in the area, so that the Young's modulus of the area changes, thereby creating areas with different hardness and softness, which means that a customized design can be provided for the correction force of the teeth, thereby achieving the effect of regulating the correction force. The present invention does not modify the thickness of the appliance model, which means uniform thickness; by regulating the grayscale, a larger amount of correction can be achieved during correction without causing discomfort to the patient. Based on grayscale regulation, the embodiment of the present invention adds a thermal initiator to the photosensitive resin used, and adopts a light-curing and heat-curing step-by-step curing scheme in the process of 3D printing the appliance, which reduces the amount of monomers inside while ensuring the mechanical properties of the 3D printed appliance, can effectively reduce the precipitation of monomers, and improve biocompatibility.

[0053] In an optional implementation of the embodiment of the present invention, the step of preparing the photosensitive resin includes:

[0054] The thermal initiator and the photosensitive resin are added into a light-proof container, and then placed into a stirrer for thorough stirring to obtain a stirred mixture, and the stirred mixture is placed into an ultrasonic cleaning machine for ultrasonic dispersion to completely dissolve the thermal initiator into the photosensitive resin to obtain a photosensitive resin for printing.

[0055] In practical applications, the stirring time may be 10 minutes, and the ultrasonic dispersion time may be 15 minutes.

[0056] In practical applications, the epoxy acrylate component is composed of one or more of bisphenol A glycidyl methacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and neopentyl glycol diglycidyl ether diacrylate.

[0057] The weight ratio of the thermal initiator to the photosensitive resin is 0.2-2 parts.

[0058] The thermal initiator is one or two of dimethyl azobisisobutyrate, diisoheptanenitrile, tert-butyl peroxy-2-ethylhexanoate, 593 curing agent, T31 curing agent, 1-methylimidazole, and diisopropyl peroxydicarbonate.

[0059] Another embodiment of the present invention provides a grayscale-controlled 3D printed appliance step-by-step curing system, which uses the grayscale-controlled 3D printed appliance step-by-step curing method described above. In practical applications, the hardware structure of the 3D printed appliance system can utilize existing technologies.

[0060] Figure 3The schematic diagram of the principle of a 3D printed appliance step-by-step curing system based on grayscale control according to an embodiment of the present invention is shown below. Figure 3 Provide explanation.

[0061] like Figure 3 As shown, the 3D printing appliance step-by-step curing system of the embodiment of the present invention includes a stepper motor 1, a guide rail 2, a printing platform 3, a material tank 5 containing a photosensitive resin 4, a reflector 6, a motor driver 7, a display 8, a DLP optical machine 9, and a control main board 10. Among them, the stepper motor 1 is used to control the movement of the printing platform 3; the guide rail 2 is used to limit the moving direction of the printing platform 3, so that the printing platform 3 can move in the vertical direction; the printing platform 3 is connected to the guide rail 2 through a crossbeam, and the print body is formed on the printing platform 3; the reflector 6 is used to reflect the projection light to the bottom of the material tank 5; the motor driver 7 is used to drive the stepper motor 1 to move; the display 8 is used to provide an operation interface; the DLP optical machine 9 is used to project pattern light; and the control main board 10 is responsible for the control of the overall 3D printing process. The operator can set the printing parameters through the display 8. Among them, the printing parameters include the moving speed of the printing platform, the moving distance, the set printing layer thickness, and the exposure time of the DLP optical machine. Among them, the moving speed and moving distance of the printing platform will affect the printing success rate of the printed body, the printing layer thickness affects the printing accuracy of the printed body in the vertical direction, and the exposure time affects the success rate and accuracy of the printing. If the exposure is small, the adhesion between the layers may fail due to insufficient resin curing. Too much exposure may cause over-curing and affect the accuracy of the printed body. The control motherboard 10 transmits the slice pattern to the DLP optical machine 9 and projects it. After waiting for a certain period of exposure, the photosensitive resin corresponding to the pattern inside the material tank 5 is cured, and the DLP optical machine 9 turns off the light. Subsequently, the stepper motor 1 receives the control command and starts to move upward, so that the cured resin is separated from the bottom surface of the material tank 5, completing the printing process of one layer. After that, the DLP optical machine projects the next slice pattern and goes through the same process to finally produce a grayscale appliance.

[0062] Specifically, the modifying the grayscale of the area corresponding to the designated tooth includes:

[0063] Adjusts the grayscale of the area corresponding to the specified tooth higher or lower.

[0064] The grayscale value in the slice pattern is positively correlated with the light intensity value of the projected pattern light. The higher the grayscale value, the higher the light intensity. The more energy the resin receives, the higher the degree of curing. When the grayscale of the area corresponding to the designated tooth is lowered, the light intensity of the area is reduced, so that the degree of curing of the photosensitive resin in the area is reduced, thereby reducing the modulus of the area. Conversely, when the grayscale of the area corresponding to the designated tooth is increased, the light intensity of the area is increased, so that the degree of curing of the photosensitive resin in the area is increased, thereby increasing the modulus of the area.

[0065] The modulus is directly proportional to the correction force. The adjustment of the modulus of the specified tooth area is completed based on grayscale modification, and the regulation of the correction force is also achieved.

[0066] Furthermore, lowering the grayscale of the area corresponding to the designated tooth includes:

[0067] Lower the grayscale of the area corresponding to the designated teeth by 40%-60%.

[0068] Preferably, the gray scale of the area corresponding to the designated teeth is lowered by 50%.

[0069] Furthermore, when the grayscale of the area corresponding to the designated tooth is lowered, the method further includes:

[0070] The surface pixels of the designated tooth are obtained, and the grayscale values ​​of the surface pixels of the designated tooth are restored to original values.

[0071] It is understandable that, considering that photosensitive resin has biological toxicity, and the higher the degree of curing, the lower the toxicity, it is necessary to improve the surface curing degree of the orthodontic appliance. In the grayscale processing of the model, since the grayscale value of the area of ​​the specified tooth is reduced, the degree of curing of the area will be reduced and its biological toxicity will be increased, so the area with modified grayscale value should be processed to enhance the surface curing degree. The idea of ​​this processing operation is to first obtain the surface pixels of the specified tooth, restore the grayscale value of the surface pixels of the specified tooth to the original value, thereby increasing the exposure and enhancing the surface curing degree of the modified area.

[0072] Specifically, obtaining the surface pixels of the designated tooth includes:

[0073] Acquire the edge of each slice pattern corresponding to the designated tooth, where the edge of each slice pattern corresponding to the designated tooth is the surface pixel of the designated tooth in the horizontal direction;

[0074] The surface pixels of the designated tooth in the vertical direction are obtained according to the difference between the grayscale values ​​of the pixels of the adjacent slice patterns.

[0075] It is understandable that the acquisition of surface pixels in the vertical direction requires calculating the difference in grayscale values ​​of each pixel of two adjacent slice patterns. For example, if a pixel A is a model surface pixel, the grayscale value of the corresponding pixel B of the adjacent slice pattern is 0, which means that there is no pattern at the B pixel position, and also indicates that the A pixel position is the model surface. Then by subtracting the two slices of the model, if it is the model surface, the difference of the corresponding pixel is the absolute value of the A pixel. Then, according to the set grayscale value of 50%, the pixels whose difference matches the 50% grayscale are screened out, and these pixels are the surface area of ​​the model in the vertical direction.

[0076] After obtaining the surface pixels of the model, the grayscale value is modified back to 100%. The purpose of this operation is to increase the amount of light transmitted through the surface of the printed appliance and improve the degree of surface solidification.

[0077] In practical applications, the grayscale light curing process of each layer of the appliance based on multiple slice patterns includes:

[0078] Grayscale photocuring of each layer of the appliance is performed based on a multi-slice pattern using UV light.

[0079] Preferably, the oven is heated to a designated temperature of 60-120° C. and a designated time of 1-12 h.

[0080] Figure 4 This is a schematic diagram of obtaining an orthodontic appliance based on a 3D printed model of the orthodontic appliance according to an embodiment of the present invention. Figure 4 As shown, Figure 4 The left side is the 3D printed model of the braces. The middle 6 teeth are designated as teeth with grayscale lowered by 50%, and the grayscale of the remaining teeth is not adjusted. In the first stage of the above method, UV light is used for grayscale photocuring to adjust the mechanical properties of the braces. In the second stage, the braces are placed in an oven for heat curing to obtain the following. Figure 4 The actual printed aligner shown on the right.

[0081] It should be noted that:

[0082] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0083] Similarly, it should be understood that in order to streamline the present invention and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the following intention: that the claimed invention requires more features than the features explicitly recited in each claim. More specifically, as reflected in the claims below, inventive aspects lie in less than all the features of the individual embodiments disclosed above. Therefore, the claims that follow the specific embodiment are hereby expressly incorporated into the specific embodiment, with each claim itself serving as a separate embodiment of the present invention.

[0084] Furthermore, those skilled in the art will appreciate that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is meant to be within the scope of the present invention and to form different embodiments.

[0085] The above is only a specific embodiment of the present invention. Under the above teachings of the present invention, those skilled in the art can make other improvements or modifications on the basis of the above embodiments. Those skilled in the art should understand that the above specific description is only to better explain the purpose of the present invention, and the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A step-by-step curing method for a 3D printed appliance based on grayscale control, characterized in that: include: Prepare a photosensitive resin, wherein the photosensitive resin contains an epoxy acrylate component and a certain amount of thermal initiator is added to the photosensitive resin; Segmenting a region corresponding to a designated tooth from the 3D printed model of the orthodontic appliance, and modifying the pattern grayscale of the region corresponding to the designated tooth; Slicing the 3D printed model of the appliance to obtain a plurality of slice patterns with grayscale processing; completing grayscale photocuring of each layer of the appliance based on a plurality of slice patterns; The grayscale light-cured appliance is placed in an oven and heated at a specified temperature for a specified time to complete the thermal curing operation; Wherein, the carbon-carbon double bond functionality of the epoxy acrylate component in the photosensitive resin is greater than the epoxy group functionality.

2. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The preparation of the photosensitive resin comprises: The thermal initiator and the photosensitive resin are added into a light-proof container, and then placed into a stirrer for thorough stirring to obtain a stirred mixture, and the stirred mixture is placed into an ultrasonic cleaning machine for ultrasonic dispersion to completely dissolve the thermal initiator into the photosensitive resin to obtain a photosensitive resin for printing.

3. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The epoxy acrylate component is composed of one or more of bisphenol A glycidyl methacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and neopentyl glycol diglycidyl ether diacrylate.

4. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The weight ratio of the thermal initiator to the photosensitive resin is 0.2-2 parts.

5. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The thermal initiator is one or two of dimethyl azobisisobutyrate, diisoheptanenitrile, tert-butyl peroxy-2-ethylhexanoate, 593 curing agent, T31 curing agent, 1-methylimidazole, and diisopropyl peroxydicarbonate.

6. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The step of modifying the grayscale of the area corresponding to the designated tooth comprises: Adjusts the grayscale of the area corresponding to the specified tooth higher or lower.

7. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 6, characterized in that: The step of lowering the grayscale of the area corresponding to the designated tooth includes: Lower the grayscale of the area corresponding to the designated teeth by 40%-60%.

8. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 6, characterized in that: In the case of lowering the grayscale of the area corresponding to the designated tooth, it also includes: The surface pixels of the designated tooth are obtained, and the grayscale values ​​of the surface pixels of the designated tooth are restored to original values.

9. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 8, characterized in that: The step of obtaining the surface pixels of the designated tooth comprises: Acquire the edge of each slice pattern corresponding to the designated tooth, where the edge of each slice pattern corresponding to the designated tooth is the surface pixel of the designated tooth in the horizontal direction; The surface pixels of the designated tooth in the vertical direction are obtained according to the difference between the grayscale values ​​of the pixels of the adjacent slice patterns.

10. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The grayscale light curing process of each layer of the appliance based on multiple slice patterns includes: UV light is used to perform grayscale photocuring of various layers of the appliance based on multiple slice patterns.

11. The method for 3D printing an orthodontic appliance based on grayscale control according to claim 1, characterized in that: The specified temperature of the oven heating is 60-120°C and the specified time is 1-12h.

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