Surface post-processing methods for 3D printed transparent dental trays

Abstract

This invention relates to the field of dental tray printing technology, specifically to a method for post-processing the surface of 3D-printed transparent dental trays, comprising the following steps: Step 1, cleaning the dental tray print using a resin cleaner; Step 2, polishing the cleaned dental tray print to remove surface defects; Step 3, forming a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray print; Step 4, curing the fluid resin layer to obtain the finished dental tray. This application can produce dental trays with high transparency. In this application, a fluid resin layer with a thickness of 8-15 μm is formed on the surface of the dental tray print, and the fluid resin layer is then cured. At this point, the outer surface of the finished dental tray is the outer surface of the fluid resin layer. The fluid resin layer can be used to fill in scratches caused by the polishing process, preventing these surface defects from affecting the transparency of the finished dental tray.

Description

Technical Field

[0001] This invention relates to the field of dental tray printing technology, specifically to a method for post-processing the surface of 3D printed transparent dental trays. Background Technology

[0002] In the field of modern additive manufacturing, photopolymerization additive manufacturing technology occupies an important position due to its unique molding advantages. Resin 3D printing technology, as a typical representative of this field, has gradually developed into one of the core technologies in rapid prototyping and small-batch manufacturing due to its excellent high precision and high surface detail retention characteristics, providing key technical support for product development and production in many industries. This resin 3D printing technology uses photosensitive resin with specific properties as the molding material. Its core working principle is to selectively cure liquid photosensitive resin using ultraviolet light (common implementation methods include SLA laser scanning and DLP projection exposure, etc.), gradually building a three-dimensional solid product layer by layer according to preset three-dimensional model data.

[0003] The current manufacturing process for transparent dental trays is as follows: First, a half-jaw oral model (including teeth and gums) is 3D printed. Then, a transparent thermoplastic film (PETG, polyurethane, etc.) is heated to a softening temperature. Next, a vacuum forming machine or pressure forming machine is used to attach the film to the printed model. After cooling and shaping, the dental tray base is formed. Then, a laser is used to cut along the edge of the dental tray base corresponding to the gum line to obtain the dental tray (dental tray) used to wrap the teeth. Finally, the dental tray is manually polished.

[0004] While the above manufacturing process can produce dental trays with a certain degree of transparency, there are some issues that need improvement, as follows:

[0005] First, the semi-jaw oral model that needs to be printed is relatively large, which requires a long printing time, resulting in a longer production time for the dental tray and a higher printing cost.

[0006] Secondly, the edges of the laser-cut dental trays are quite sharp and can easily cut the gums. This requires repeated grinding and inspection, which also leads to a longer production time and increased labor costs. In addition, there is still a risk of the dental trays cutting the gums.

[0007] Third, laser cutting is expensive and leads to longer production time for dental trays.

[0008] Furthermore, during manual grinding or mechanical polishing, excessive removal of material from certain areas of the dental tray can easily occur, or new scratches can be left on the surface of the tray. This may reduce the smoothness of the tray surface and ultimately result in a "matte" or "frosty" finish. This can lead to a significant gap between the appearance and texture of the finished dental tray and the initial design expectations. It can also affect the transparency (transmittance) of the finished dental tray, failing to meet the stringent requirements for surface quality of high-end products.

[0009] Therefore, how to overcome the shortcomings of the existing technology is the subject of this invention. Summary of the Invention

[0010] The purpose of this invention is to provide a method for post-processing the surface of 3D printed transparent dental trays.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] The post-processing method for the surface of 3D printed transparent dental trays includes the following steps:

[0013] Step 1: Input the dental tray model file containing the support structure design into the 3D printer;

[0014] Step 2: Select resin and have the 3D printer print the dental tray part;

[0015] Step 3: Remove the dental tray printout from the 3D printer;

[0016] Step 4: Remove the support structure from the surface of the dental tray printout;

[0017] Step 5: Clean the dental tray printouts with resin cleaner;

[0018] Step 6: Polish the cleaned dental tray print to remove defects at the connection between the support structure and the dental tray print (or remove defects on the surface of the dental tray print).

[0019] Step 7: Form a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray printout using resin;

[0020] Step 8: Curing the fluid resin layer to obtain the finished dental tray.

[0021] It should be emphasized that steps one through four are for illustrative purposes only. The substantive content of this application is steps five through eight. Steps one through four can be removed, in which case step five becomes the actual step one. The following description uses the processing steps without removing steps one through four.

[0022] Preferably, the thickness of the fluid resin layer is 10-12 μm. The material of the resin in this application is selected according to actual needs.

[0023] In step three, tools such as a scraper can be used to remove the dental tray print from the printing platform.

[0024] The dental tray printouts are obtained through steps one through four. Compared to the semi-jaw oral model, the dental tray model is smaller, requiring less printing time, thus shortening the production time and reducing printing costs. The support structure is existing and will not be described in detail here.

[0025] Since the dental tray is printed directly, there is no need for subsequent laser cutting, which reduces the risk of the tray edges cutting the user's gums and saves the cost of laser cutting. Furthermore, by eliminating the repeated grinding and inspection process, the production time of the dental tray is shortened and labor costs are reduced.

[0026] Considering that there is generally uncured photosensitive resin on the surface of the dental tray print, a resin cleaner is used to clean the dental tray print in step five.

[0027] To ensure successful printing of the dental tray, a support structure is typically added during the printing process. However, at the connection between the support structure and the dental tray, surface defects such as burrs, pits, and residual protrusions often occur due to stress concentration or insufficient curing. Therefore, step six involves hand grinding or mechanical polishing to refine the surface of the dental tray and improve its surface quality.

[0028] It is important to note that during manual sanding or mechanical polishing, excessive removal of material in certain areas of the dental tray printout can occur, or new scratches can be left on the surface of the dental tray printout. This may reduce the smoothness of the surface of the dental tray printout, and may ultimately result in a "matte" or "frosty" effect. This will cause a significant gap between the appearance and texture of the finished dental tray and the original design expectations, and will also affect the transparency (light transmittance) of the finished dental tray, failing to meet the stringent requirements for the surface quality of high-end products.

[0029] To address the issue of potentially unsatisfactory appearance and texture of the finished dental tray, step seven involves forming a fluid resin layer with a thickness of 8-15 μm on the surface of the printed dental tray. Step eight then cures this fluid resin layer. At this point, the outer surface of the finished dental tray is the outer surface of the fluid resin layer, thus resolving the problem of reduced appearance and texture due to surface treatment. The fluid resin layer can also be used to smooth the surface of the printed dental tray through filling methods. For example, it can fill in scratches caused by the polishing process, preventing these surface defects from affecting the transparency of the finished dental tray.

[0030] The fluid resin layer allows for adjustment of the parameters of the dental tray printout, essentially performing a secondary printout to fine-tune the final dental tray. This helps to bridge the parameter gaps (such as thickness differences) between the printout and the final product. By limiting the thickness of the fluid resin layer to 8-15 μm, both defects such as grooves on the printout surface and excessive thickness in the final product can be addressed.

[0031] In a further technical solution, step eight, the curing process includes the following steps:

[0032] The printed dental tray, coated with a layer of fluid resin, is placed in a nitrogen-protected light-curing chamber or an argon-protected light-curing chamber (argon atmosphere light-curing device) and cured for 3-7 minutes. The curing time is 3-7 minutes, but not limited to this range.

[0033] For example, curing can be performed using a nitrogen-protected light-curing oven (such as a nitrogen-protected UV curing oven), with a curing time of 3-7 minutes (preferably 5 minutes, depending on the material). The nitrogen protection isolates oxygen, thus preventing the finished dental tray from easily sticking to the surface. This method generally has a higher structural cost but a shorter curing time. The only difference between a nitrogen-protected light-curing oven and an argon-protected light-curing oven is the type of protective gas introduced into the oven.

[0034] In a further technical solution, step eight, the curing process includes the following steps:

[0035] S1. Place the dental tray printout coated with a fluid resin layer into a container containing a glycerol aqueous solution with a concentration of 70%–85% (preferably this concentration but not limited);

[0036] S2. Place the container in a light curing chamber and continue curing for 3-7 minutes (this time is preferred but not limited).

[0037] S3. Remove the dental tray printout from the container;

[0038] S4. Rinse the dental tray print with water.

[0039] Understandably, the dental tray print was immersed in a glycerin solution.

[0040] First, the printed dental tray is placed in a 70%–85% glycerol aqueous solution. This forms a glycerol layer on the surface of the printed tray to isolate it from oxygen, thus preventing the finished tray from sticking together. This method generally results in lower structural costs but a longer curing time (compared to using a nitrogen-protected light curing chamber).

[0041] The concentration of the glycerol aqueous solution is 70%–85%, as explained below:

[0042] First, at this concentration, glycerin is almost oxygen-impermeable, which can reduce the phenomenon of incomplete curing of dental tray prints due to oxygen inhibition.

[0043] Secondly, low-concentration glycerol has a lower viscosity, which makes it easier to evenly cover the surface of the dental tray printed parts, and it is easy to rinse with water after curing. High-concentration glycerol, although it has better oxygen barrier, has a high viscosity, which makes it difficult to evenly cover the surface of the dental tray printed parts. The 70%–85% glycerol aqueous solution selected in this application can combine the excellent effects of both low-concentration and high-concentration glycerol.

[0044] Third, glycerol has high transparency in the visible and near-ultraviolet bands and will not significantly absorb the ultraviolet light required for curing (such as 365nm and 405nm). The glycerol aqueous solution with a concentration of 70%–85% selected in this application can cover the entire surface of the dental tray, which helps to form a uniform liquid film and avoids uneven light spots caused by local refractive index changes.

[0045] A further technical solution involves selecting isopropanol with a concentration of 90%-99% as the resin cleaning agent.

[0046] Preferably, the concentration of isopropanol is 95%.

[0047] Isopropanol is an organic solvent with strong dissolving power, which can effectively dissolve uncured photosensitive resin. This allows for the effective cleaning of dental tray prints made with photosensitive resin without damaging the chemical structure of the cured resin, especially when the isopropanol concentration is 90%-99%.

[0048] In some embodiments, the resin cleaning agent may be selected from any one of ethanol, tripropylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.

[0049] In a further technical solution, in step seven, a brushing structure is used to uniformly apply resin to the surface of the dental tray print to form a fluid resin layer with a thickness of 8-15μm.

[0050] Alternatively, in step seven, the dental tray print is completely immersed in resin for 30 seconds to 2 minutes (preferably but not limited to this time), and then the dental tray print is placed in a centrifuge for centrifugation to remove excess resin from the surface of the dental tray print, thereby forming a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray print.

[0051] The coating structure can be an existing brush (such as a bristle brush).

[0052] Immersion time is between 30 seconds and 2 minutes, depending on the specific flowability and viscosity of different resins.

[0053] Preferably, in step seven, the fluid resin layer and the dental tray printing part are made of the same material, that is, the same resin is used for both.

[0054] When a brush coating structure is used to form a fluid resin layer, the structural cost is lower, but the formation time of the fluid resin layer is longer, and the thickness uniformity of the fluid resin layer is poor. For example, the overall thickness of the fluid resin layer is 10μm, but the thickness of some local areas of the fluid resin layer is 9.5μm. It is more suitable for scenarios where the manufacturing cost of the finished dental tray is sensitive.

[0055] While the structural cost increases when the fluid resin layer is formed by immersion followed by centrifugation (compared to the coating structure), the formation time of the fluid resin layer is generally shorter than that required by the coating structure. Furthermore, the reduction in manual operation lowers labor costs. In addition, this method can improve the uniformity of the fluid resin layer thickness, making it more suitable for scenarios with higher requirements for the quality of finished dental trays.

[0056] This application clarifies two methods for forming fluid resin layers, which can meet different needs and improve the applicability of the surface post-processing method for 3D printed transparent dental trays.

[0057] A further technical solution involves applying high-frequency vibrations to the resin during the process of coating the surface of the dental tray print, using high-frequency ultrasound, with the ultrasound frequency range being 20-40kHz (preferably within this range but not limited thereto).

[0058] Alternatively, during the process of completely immersing the dental tray print in the resin, high-frequency vibrations are applied to the resin by high-frequency ultrasound, with the ultrasound frequency range being 20-40kHz (preferably within this range but not limited).

[0059] Preferably, the ultrasonic time is the same as the resin application time; for example, if the dental tray print is immersed in the resin for 1 minute, then the ultrasonic time is 1 minute.

[0060] High-frequency vibration is applied to the resin by high-frequency ultrasound. The specific steps are as follows: electrical energy is converted into high-frequency mechanical vibration by an ultrasonic transducer, and then the vibration is transmitted to the resin by an amplitude transformer or vibration probe. A contact method or a non-contact method can be used. In the contact method, the vibration probe is directly inserted into the container that holds the resin.

[0061] Applying high-frequency vibration to the resin via high-frequency ultrasound has several advantages. First, it generates minute pressure waves and shear forces within the resin, causing bubbles to rupture or detach from the resin surface due to alternating stress, thus promoting the rupture or expulsion of bubbles from the fluid resin layer. Second, it suppresses the development of ripples or radial thickness inhomogeneity in the fluid resin layer due to rotation, thereby improving the uniformity of the fluid resin layer's thickness.

[0062] To facilitate understanding, the working principle of the above-mentioned high-frequency ultrasound is supplemented as follows:

[0063] First, when the bubble diameter is related to the wavelength of the sound wave, the bubble will resonate and vibrate, which will periodically weaken its surface tension, making it easier to be "sheared" by the surrounding liquid or to break.

[0064] Second, high-frequency sound waves can induce microflows in liquids, thereby applying shear force to bubbles and causing them to detach from the surface of the object.

[0065] Third, high-frequency vibration reduces the local viscosity of the resin (acoustic rheological effect), making it easier for bubbles to migrate to the outer edge of the fluid resin layer and be thrown out under the action of centrifugal force.

[0066] By setting the ultrasonic frequency range to 20-40kHz, degassing of the fluid resin layer can be achieved, resulting in significant cavitation, and the heat can be controlled to avoid deformation of the dental tray print.

[0067] This application reduces defects (such as pinholes and shrinkage cavities) in the fluid resin layer and improves the optical properties (such as light transmittance) and mechanical properties (such as structural strength) of the fluid resin layer by applying high-frequency vibration to the resin and limiting the ultrasonic frequency range.

[0068] A further technical solution involves applying resin to the surface of the dental tray print or performing a centrifugal process, with the tray opening facing to the side.

[0069] It should be noted that if the open end of the bracket faces upward, it can easily cause the fluid resin to accumulate inside the bracket.

[0070] In a further technical solution, in step eight, a light curing machine is first used to pre-cur the dental tray printout (for a short time), and then a continuous curing process is performed on the dental tray printout to prevent the resin on the surface of the dental tray printout from dripping during the continuous curing process.

[0071] The UV curing machine can be an existing handheld UV curing machine.

[0072] During the continuous curing process, the resin has fluidity. Although its fluidity is poor, the continuous curing process generally takes several minutes (e.g., 5 minutes), and the initial curing (restricting resin flow) generally takes a certain amount of time (e.g., 1 minute). This causes a small amount of resin to drip from the fluid resin layer during the initial curing process, which reduces the uniformity of the thickness of the cured fluid resin layer, affects the appearance of the finished dental tray, and may also affect the transparency of the finished dental tray.

[0073] In this application, before the continuous curing process, the dental tray print is pre-cured using a light curing machine, which quickly restricts the flow of resin in the fluid resin layer, ensures the uniformity of the thickness of the cured fluid resin layer, and thus ensures the quality of the finished dental tray (such as appearance quality).

[0074] It should be noted that compared to nitrogen-protected UV curing chambers (for example), handheld UV curing machines (for example) are more convenient to use and therefore can be pre-cured more quickly.

[0075] In a further technical solution, in step six, after the grinding process, the dental tray print is sandblasted using a sandblasting device. The sandblasting device uses alumina micro powder or glass beads with a particle size of 20–50 μm.

[0076] During the sandblasting process, the blasting pressure is 0.15–0.25 MPa, the blasting angle is 60–80°, the blasting distance is 50–100 mm, and the duration of each blasting session is 1–3 seconds.

[0077] The sandblasting device is an existing device. For example, the sandblasting device can be a desktop micro-sandblaster with a sandblasting gun that can adjust the pressure (0.1–0.4 MPa) and has a nozzle diameter of 0.5–1.0 mm.

[0078] Each continuous spraying time is 1–3 seconds. For example, after the sandblasting device sandblasts part one of the dental tray print for 2 seconds, it switches to sandblasting part two to avoid deformation of the dental tray print due to local overheating and to ensure the quality of the finished dental tray.

[0079] The sandblasting process described above can roughen the surface of the dental tray printout, increasing the adhesion and retention of the fluid resin layer and further ensuring the uniformity of the fluid resin layer's thickness. Specifically, when using the sandblasting process, micro-dimples (approximately 5-20 μm in diameter) can be created on the surface of the dental tray printout. These micro-dimples facilitate the anchoring of the fluid resin layer to the surface of the dental tray printout in subsequent steps.

[0080] In a further technical solution, step seven involves forming a fluid resin layer through centrifugation. The steps for performing the centrifugation process are as follows:

[0081] Secure the printed dental tray to the rotor of the centrifuge;

[0082] Start the centrifuge and set the centrifuge running time to t (preferably ≤2 min).

[0083] During centrifuge operation, the instantaneous coating thickness h(t) is calculated using the following formula:

[0084]

[0085] in:

[0086] h0 is the initial thickness of the fluid resin layer when the dental tray print is fixed to the rotor of the centrifuge;

[0087] η is the viscosity of the fluid resin;

[0088] ρ is the density of the fluid resin;

[0089] r is the shortest distance between the center of gravity of the printed dental tray and the axis of the centrifuge;

[0090] τ is the time constant;

[0091] ω is the angular velocity.

[0092] In a further technical solution, step seven involves forming a fluid resin layer through centrifugation. The steps for performing the centrifugation process are as follows:

[0093] Secure the printed dental tray to the rotor of the centrifuge;

[0094] Start the centrifuge and set the centrifuge running time to t (preferably ≤2 min).

[0095] Using n (preferably ≥2) ultrasonic transducers to apply high-frequency vibration to the fluid resin layer during the operation of the centrifuge can be achieved by uniformly arranging n ultrasonic transducers on the rotor sidewall of the centrifuge.

[0096] During centrifuge operation, the instantaneous coating thickness h(t) is calculated using the following formula:

[0097]

[0098] in:

[0099] C f is the adjustment coefficient for the ultrasonic transducer at a frequency of f;

[0100] n represents the number of ultrasonic transducers;

[0101] h0 is the initial thickness of the fluid resin layer when the dental tray print is fixed to the rotor of the centrifuge;

[0102] η is the viscosity of the fluid resin;

[0103] ρ is the density of the fluid resin;

[0104] r is the shortest distance between the center of gravity of the printed dental tray and the axis of the centrifuge;

[0105] τ is the time constant;

[0106] ω is the angular velocity.

[0107] The terms “include,” “including,” and “have” used in this article are all open-ended, meaning they include but are not limited to.

[0108] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0109] The working principle and advantages of this invention are as follows:

[0110] This application directly prints the dental tray, eliminating the need for subsequent laser cutting. This reduces the risk of the dental tray edges cutting the user's gums and saves the cost of laser cutting. Furthermore, by eliminating the repeated grinding and inspection process, it shortens the production time of the dental tray and reduces labor costs.

[0111] Considering that uncured photosensitive resin generally exists on the surface of dental tray prints, this application uses a resin cleaning agent to clean the dental tray prints.

[0112] To ensure successful printing of dental trays, a support structure is typically added during the printing process. However, at the connection between the support structure and the printed tray, surface defects such as burrs, pits, and residual protrusions often occur due to stress concentration or insufficient curing. Therefore, the surface of the printed trays can be repaired by manual grinding or mechanical polishing to improve their surface quality.

[0113] It is important to note that during manual sanding or mechanical polishing, excessive removal of material in certain areas of the dental tray printout can occur, or new scratches can be left on the surface of the dental tray printout. This may reduce the smoothness of the surface of the dental tray printout, and may ultimately result in a "matte" or "frosty" effect. This will cause a significant gap between the appearance and texture of the finished dental tray and the original design expectations, and will also affect the transparency (light transmittance) of the finished dental tray, failing to meet the stringent requirements for the surface quality of high-end products.

[0114] To address the issue of unsatisfactory appearance and texture of finished dental trays, this application forms a fluid resin layer with a thickness of 8-15 μm on the surface of the printed dental tray and then cures the fluid resin layer. At this point, the outer surface of the finished dental tray is the outer surface of the fluid resin layer, thus resolving the problem of reduced appearance and texture due to surface treatment. The fluid resin layer can fill in scratches caused by the polishing process to ensure a smooth surface on the printed dental tray, preventing these surface defects from affecting the transparency of the finished dental tray.

[0115] The fluid resin layer allows for adjustment of the parameters of the dental tray printout, essentially performing a secondary printout to fine-tune the final dental tray. This helps to bridge the parameter gaps (such as thickness differences) between the printout and the final product. By limiting the thickness of the fluid resin layer to 8-15 μm, both defects such as grooves on the printout surface and excessive thickness in the final product can be addressed.

[0116] Through further scheme design, this application also has the following effects:

[0117] 1. During the curing process, the dental tray print is first placed in a glycerin aqueous solution. A glycerin layer is formed on the surface of the dental tray print to isolate oxygen, thereby preventing the finished dental tray from sticking together.

[0118] 2. During the formation of the fluid resin layer, the dental tray print is completely immersed in the resin, and high-frequency vibration is applied to the resin through high-frequency ultrasound. Then, the dental tray print is placed in a centrifuge for centrifugation to remove excess resin from the surface of the dental tray print. At this time, on the one hand, the high-frequency vibration will generate tiny pressure waves and shear forces in the resin, causing the bubbles to be subjected to alternating stress and rupture or detach from the resin surface, thus promoting the rupture or expulsion of bubbles in the fluid resin layer. On the other hand, the high-frequency micro-vibration will suppress the phenomenon of ripples or radial thickness non-uniformity in the fluid resin layer due to rotation, thereby improving the thickness uniformity of the fluid resin layer.

[0119] Based on the above settings, the technical solution in this application has the following synergistic effects:

[0120] 1) The filling effect of the fluid resin layer is the basis for achieving a smooth surface of the dental tray print. However, during the molding process, the resin in the fluid state is prone to oxidation upon contact with air, and the uncured resin on the surface may stick together due to its stickiness. The setting of the glycerin layer precisely solves this derivative problem. The glycerin layer forms a dense oxygen barrier film, which does not affect the filling effect of the fluid resin layer on the surface depressions and gaps of the dental tray print. It can also prevent the fluid resin layer from yellowing and cracking due to oxidation after filling. At the same time, it prevents the uncured resin from sticking to the external environment (such as storage containers), providing a stable protective environment for the smooth molding of the fluid resin layer.

[0121] 2) After the fluid resin layer is filled, the dental tray print is placed in a centrifuge for centrifugation to remove excess resin from the surface of the dental tray print. At this time, the fluid resin layer is prone to defects such as surface ripples and radial thickness unevenness due to centrifugal force, which weakens the smoothness of the initial filling. The vibration of high-frequency ultrasound specifically suppresses this defect. The uniform kinetic energy generated by the vibration cancels out the influence of centrifugal force caused by rotation, avoids the resin layer from shifting radially, and improves the thickness uniformity of the fluid resin layer. At the same time, the presence of the glycerin layer can reduce the friction between the resin layer and the air during ultrasonic vibration, reduce the probability of ripples, and achieve full-process precision control of "filling and smoothing - isolation and protection - stable molding". Attached Figure Description

[0122] Appendix Figure 1 This is a flowchart of the surface post-processing method for 3D printing transparent dental trays according to an embodiment of the present invention;

[0123] Appendix Figure 2 This is a physical image of the retainer produced using the 3D-printed transparent dental tray surface post-processing method described in this embodiment of the invention.

[0124] Appendix Figure 3 The image shows a physical picture of the finished dental tray produced using the 3D printing transparent dental tray surface post-processing method in this embodiment of the invention.

[0125] Appendix Figure 4 For the appendix Figure 3 A picture of a finished dental tray in its installation state. Detailed Implementation

[0126] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0127] Example: The present invention will be clearly described below with illustrations and detailed description. Any person skilled in the art who understands the examples of the present invention can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0128] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this work. Singular forms such as “a,” “this,” “this,” “the,” and “the” as used herein also include plural forms.

[0129] See appendix Figure 1 The post-processing method for the surface of 3D printed transparent dental trays includes the following steps:

[0130] Step 1: Input the dental tray model file containing the support structure design into the 3D printer;

[0131] Step 2: Select resin and have the 3D printer print the dental tray part;

[0132] Step 3: Remove the dental tray printout from the 3D printer;

[0133] Step 4: Remove the support structure from the surface of the dental tray printout;

[0134] Step 5: Clean the dental tray printouts with resin cleaner;

[0135] Step 6: Polish the cleaned dental tray print to remove defects at the connection between the support structure and the dental tray print (or remove defects on the surface of the dental tray print).

[0136] Step 7: Form a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray printout using resin;

[0137] Step 8: Curing the fluid resin layer to obtain the finished dental tray.

[0138] It should be emphasized that steps one through four are for illustrative purposes only. The substantive content of this embodiment is steps five through eight. Steps one through four can be removed, in which case step five becomes the actual step one. The following description uses the processing steps without removing steps one through four.

[0139] The surface post-processing method for 3D printed transparent dental trays in this embodiment can be used not only to produce transparent dental trays, but also to produce retainers (such as Harley retainers, see Appendix). Figure 2 ).

[0140] Preferably, the thickness of the fluid resin layer is 10-12 μm. In this embodiment, the resin material is selected according to actual needs.

[0141] In step three, tools such as a scraper can be used to remove the dental tray print from the printing platform.

[0142] The dental tray printouts are obtained through steps one through four. Compared to the semi-jaw oral model, the dental tray model is smaller, requiring less printing time, thus shortening the production time and reducing printing costs. The support structure is existing and will not be described in detail here.

[0143] Since the dental tray is printed directly, there is no need for subsequent laser cutting, which reduces the risk of the tray edges cutting the user's gums and saves the cost of laser cutting. Furthermore, by eliminating the repeated grinding and inspection process, the production time of the dental tray is shortened and labor costs are reduced.

[0144] Considering that there is generally uncured photosensitive resin on the surface of the dental tray print, a resin cleaner is used to clean the dental tray print in step five.

[0145] To ensure successful printing of the dental tray, a support structure is typically added during the printing process. However, at the connection between the support structure and the dental tray, surface defects such as burrs, pits, and residual protrusions often occur due to stress concentration or insufficient curing. Therefore, step six involves hand grinding or mechanical polishing to refine the surface of the dental tray and improve its surface quality.

[0146] It is important to note that during manual sanding or mechanical polishing, excessive removal of material in certain areas of the dental tray printout can occur, or new scratches can be left on the surface of the dental tray printout. This may reduce the smoothness of the surface of the dental tray printout, and may ultimately result in a "matte" or "frosty" effect. This will cause a significant gap between the appearance and texture of the finished dental tray and the original design expectations, and will also affect the transparency (light transmittance) of the finished dental tray, failing to meet the stringent requirements for the surface quality of high-end products.

[0147] To address the issue of potentially unsatisfactory appearance and texture of the finished dental tray, step seven involves forming a fluid resin layer with a thickness of 8-15 μm on the surface of the printed dental tray. Step eight then cures this fluid resin layer. At this point, the outer surface of the finished dental tray is the outer surface of the fluid resin layer, thus resolving the problem of reduced appearance and texture due to surface treatment. The fluid resin layer can also be used to smooth the surface of the printed dental tray through filling methods. For example, it can fill in scratches caused by the polishing process, preventing these surface defects from affecting the transparency of the finished dental tray.

[0148] The fluid resin layer allows for adjustment of the parameters of the dental tray printout, essentially performing a secondary printout to fine-tune the final dental tray. This helps to bridge the parameter gaps (such as thickness differences) between the printout and the final product. By limiting the thickness of the fluid resin layer to 8-15 μm, both defects such as grooves on the printout surface and excessive thickness in the final product can be addressed.

[0149] You can perform the sanding step (step six) first, followed by the cleaning step (step five), or you can perform the cleaning step both before and after the sanding step. After sanding, you can clean with water. Sanding can be done with sandpaper and / or an angle grinder.

[0150] In this embodiment, step eight, the curing process includes the following steps:

[0151] Place the printed dental tray with the fluid resin layer into a nitrogen-protected light curing chamber or an argon-protected light curing chamber (argon atmosphere light curing device) and cure for 3-7 minutes.

[0152] By using a nitrogen-protected light-curing oven for curing, with a curing time of 3-7 minutes (preferably 5 minutes, depending on the material), the nitrogen protection isolates oxygen, thus preventing the finished dental tray from easily sticking to the surface. This method generally results in higher structural costs but a shorter curing time.

[0153] In this embodiment, step eight, the curing process includes the following steps:

[0154] S1. Place the dental tray printout coated with a fluid resin layer into a container containing a 70%–85% aqueous glycerol solution.

[0155] S2. Place the container in a light curing chamber and continue curing for 3-7 minutes;

[0156] S3. Remove the dental tray printout from the container;

[0157] S4. Rinse the dental tray print with water.

[0158] Understandably, the dental tray print was immersed in a glycerin solution.

[0159] First, the printed dental tray is placed in a 70%–85% glycerol aqueous solution. This forms a glycerol layer on the surface of the printed tray to isolate it from oxygen, thus preventing the finished tray from sticking together. This method generally results in lower structural costs but a longer curing time (compared to using a nitrogen-protected light curing chamber).

[0160] The concentration of the glycerol aqueous solution is 70%–85%, as explained below:

[0161] First, at this concentration, glycerin is almost oxygen-impermeable, which can reduce the phenomenon of incomplete curing of dental tray prints due to oxygen inhibition.

[0162] Secondly, low-concentration glycerol has a lower viscosity, which makes it easier to evenly cover the surface of the dental tray printed parts, and it is easy to rinse with water after curing. High-concentration glycerol, although it has better oxygen barrier, has a higher viscosity, which makes it difficult to evenly cover the surface of the dental tray printed parts. The 70%–85% glycerol aqueous solution selected in this embodiment can combine the excellent effects of both low-concentration and high-concentration glycerol.

[0163] Third, glycerol has high transparency in the visible and near-ultraviolet bands and will not significantly absorb the ultraviolet light (such as 365nm and 405nm) required for curing. The 70%–85% glycerol aqueous solution selected in this embodiment can cover the entire surface of the dental tray, which helps to form a uniform liquid film and avoids uneven light spots caused by local refractive index changes.

[0164] In this embodiment, the resin cleaning agent is selected as isopropanol with a concentration of 90%-99%.

[0165] Preferably, the concentration of isopropanol is 95%.

[0166] Isopropanol is an organic solvent with strong dissolving power, which can effectively dissolve uncured photosensitive resin. This allows for the effective cleaning of dental tray prints made with photosensitive resin without damaging the chemical structure of the cured resin, especially when the isopropanol concentration is 90%-99%.

[0167] In some embodiments, the resin cleaning agent may be selected as any one of ethanol, tripropylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.

[0168] In this embodiment, in step seven, a brushing structure is used to uniformly apply resin to the surface of the dental tray print to form a fluid resin layer with a thickness of 8-15 μm.

[0169] Alternatively, in step seven, the dental tray print is completely immersed in resin for 30 seconds to 2 minutes, and then placed in a centrifuge for centrifugation to remove excess resin from the surface of the dental tray print, thereby forming a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray print.

[0170] The coating structure can be an existing brush (such as a bristle brush).

[0171] Immersion time is between 30 seconds and 2 minutes, depending on the specific flowability and viscosity of different resins.

[0172] Preferably, in step seven, the fluid resin layer and the dental tray printing part are made of the same material, that is, the same resin is used for both.

[0173] When a brush coating structure is used to form a fluid resin layer, the structural cost is lower, but the formation time of the fluid resin layer is longer, and the thickness uniformity of the fluid resin layer is poor. For example, the overall thickness of the fluid resin layer is 10μm, but the thickness of some local areas of the fluid resin layer is 9.5μm. It is more suitable for scenarios where the manufacturing cost of the finished dental tray is sensitive.

[0174] While the structural cost increases when the fluid resin layer is formed by immersion followed by centrifugation (compared to the coating structure), the formation time of the fluid resin layer is generally shorter than that required by the coating structure. Furthermore, the reduction in manual operation lowers labor costs. In addition, this method can improve the uniformity of the fluid resin layer thickness, making it more suitable for scenarios with higher requirements for the quality of finished dental trays.

[0175] This embodiment clarifies two methods for forming fluid resin layers, which can meet different needs and improve the applicability of the surface post-processing method for 3D printed transparent dental trays.

[0176] In this embodiment, in step seven, a fluid resin layer is formed through centrifugation. The steps for performing the centrifugation are as follows:

[0177] Secure the printed dental tray to the rotor of the centrifuge;

[0178] Start the centrifuge and set the centrifuge running time to t (preferably ≤2 min).

[0179] During centrifuge operation, the instantaneous coating thickness h(t) is calculated using the following formula:

[0180]

[0181] in:

[0182] h0 is the initial thickness of the fluid resin layer when the dental tray print is fixed to the rotor of the centrifuge;

[0183] η is the viscosity of the fluid resin;

[0184] ρ is the density of the fluid resin;

[0185] r is the shortest distance between the center of gravity of the printed dental tray and the axis of the centrifuge;

[0186] τ is the time constant;

[0187] ω is the angular velocity.

[0188] When using a centrifuge to centrifuge the printed dental tray, the fluid resin layer can be approximated as a thin film flow. Therefore, when the centrifugal force drives the resin to move radially along the centrifuge, the thickness change of the fluid resin layer satisfies the following kinetic equation:

[0189]

[0190] To ensure smooth acceleration and deceleration of the centrifuge, thereby stabilizing the centrifugation process and ultimately obtaining a coating (fluid resin layer) of uniform thickness, the centrifuge speed is controlled using the following smoothing function:

[0191]

[0192] Wherein, ω0 represents the initial speed and the final speed. ω0 is estimated based on the motor performance of the centrifuge and the viscosity of the resin. At this speed, the amount of resin detachment is low (negligible) and can be used as a preheating and buffer before the centrifuge stops, thus preventing the formation of centrifugal lamination.

[0193] ω f The target steady-state rotational speed directly determines the final thickness, which is obtained by inverse solving of the instantaneous coating thickness. The formula for the instantaneous coating thickness is:

[0194]

[0195] Therefore, the inverse solution yields the target steady-state rotational speed ω. f The value is approximately:

[0196]

[0197] Where T is the total centrifugation time.

[0198] In the process of centrifugation, the time constant τ represents the ratio of the acceleration process to the total time.

[0199] In practice, τ can be taken as 0.2T-0.4T.

[0200] The following is a test item for illustration:

[0201] Test instructions: Select a 3D printed transparent orthodontic appliance after removing the support and polishing, and seal one half of it with tape;

[0202]

[0203] Wherein, the target steady-state rotational speed ω f ≈251.3 rad / s;

[0204] Taking τ=8s, the speed control function is:

[0205]

[0206] The rotation speed curve obtained from the test shows that the rotation speed curve is stable, and the region reaches a steady state after about 20 seconds. This effectively controls the uniformity of the resin detachment process, and the final film thickness error is ≤ ±8%, which meets the expected process requirements.

[0207] Seen in Figure 3 This is a picture of the finished product after the implementation of this project. As can be seen from the picture, the transparency and smoothness of the parts of the orthodontic appliance after the coating is added are significantly improved. The transparency and smoothness of the parts that are sealed with tape in advance to prevent the formation of fluid resin layer are significantly lower.

[0208] After taking measurements at multiple points on the orthodontic appliance (using an electronic laser thickness gauge to measure at the same location), the coating thickness was found to be 15±1μm.

[0209] Seen in Figure 4 This is a picture of the 3D-printed transparent orthodontic appliance in the installation state from the above test project.

[0210] Based on this, the technical solution provided in this embodiment enables 3D-printed transparent orthodontic appliances to have better transparency and smoothness. This is because a fluid resin layer is added to the surface of the semi-finished orthodontic appliance after initial printing. This fluid resin layer can smooth the surface of the semi-finished appliance through filling; for example, it can fill scratches caused by the sanding process, preventing these surface defects from affecting the transparency of the finished orthodontic appliance. Furthermore, the fluid resin layer allows for adjustment of the parameters of the semi-finished orthodontic appliance, essentially performing a second printing to fine-tune and form the finished appliance. This compensates for the parameter differences (such as thickness differences) between the semi-finished and finished orthodontic appliances. The use of a centrifuge device, based on an instantaneous coating thickness formula, effectively controls the coating thickness, such as effectively controlling it within the range of 8-15 μm. By limiting the thickness of the fluid resin layer to 8-15 μm, both the need to cover surface defects such as grooves on the semi-finished orthodontic appliance and the need to avoid an excessively thick finished appliance can be met. Effective control of the coating thickness is key to accurately achieving the above objectives.

[0211] In another embodiment, in step seven, a fluid resin layer is formed by centrifugation. The steps for performing the centrifugation are as follows:

[0212] Secure the printed dental tray to the rotor of the centrifuge;

[0213] Start the centrifuge and set the centrifuge running time to t (preferably ≤2 min).

[0214] Using n (preferably ≥2) ultrasonic transducers to apply high-frequency vibration to the fluid resin layer during the operation of the centrifuge can be achieved by uniformly arranging n ultrasonic transducers on the rotor sidewall of the centrifuge.

[0215] During centrifuge operation, the instantaneous coating thickness h(t) is calculated using the following formula:

[0216]

[0217] in:

[0218] C f is the adjustment coefficient for the ultrasonic transducer at a frequency of f;

[0219] n represents the number of ultrasonic transducers;

[0220] h0 is the initial thickness of the fluid resin layer when the dental tray print is fixed to the rotor of the centrifuge;

[0221] η is the viscosity of the fluid resin;

[0222] ρ is the density of the fluid resin;

[0223] r is the shortest distance between the center of gravity of the printed dental tray and the axis of the centrifuge;

[0224] τ is the time constant;

[0225] ω is the angular velocity.

[0226] C f The parameters and n are related to the ultrasonic transducer, and the settings of the ultrasonic transducer can accelerate the centrifugation efficiency.

[0227] In this embodiment, during the process of applying resin to the surface of the dental tray print, high-frequency vibration is applied to the resin by high-frequency ultrasound, and the ultrasonic frequency range is 20-40kHz.

[0228] Alternatively, during the process of completely immersing the dental tray print in the resin, high-frequency vibrations are applied to the resin using high-frequency ultrasound, with the ultrasonic frequency range being 20-40kHz.

[0229] Preferably, the ultrasonic time is the same as the resin application time; for example, if the dental tray print is immersed in the resin for 1 minute, then the ultrasonic time is 1 minute.

[0230] High-frequency vibration is applied to the resin by high-frequency ultrasound. The specific steps are as follows: electrical energy is converted into high-frequency mechanical vibration by an ultrasonic transducer, and then the vibration is transmitted to the resin by an amplitude transformer or vibration probe. A contact method or a non-contact method can be used. In the contact method, the vibration probe is directly inserted into the container that holds the resin.

[0231] In some embodiments, the dental tray print is immersed in a tank containing a fluid resin solution, and the sidewall of the tank is provided with at least one ultrasonic transducer.

[0232] Applying high-frequency vibration to the resin via high-frequency ultrasound has several advantages. First, it generates minute pressure waves and shear forces within the resin, causing bubbles to rupture or detach from the resin surface due to alternating stress, thus promoting the rupture or expulsion of bubbles from the fluid resin layer. Second, it suppresses the development of ripples or radial thickness inhomogeneity in the fluid resin layer due to rotation, thereby improving the uniformity of the fluid resin layer's thickness.

[0233] To facilitate understanding, the working principle of the above-mentioned high-frequency ultrasound is supplemented as follows:

[0234] First, when the bubble diameter is related to the wavelength of the sound wave, the bubble will resonate and vibrate, which will periodically weaken its surface tension, making it easier to be "sheared" by the surrounding liquid or to break.

[0235] Second, high-frequency sound waves can induce microflows in liquids, thereby applying shear force to bubbles and causing them to detach from the surface of the object.

[0236] Third, high-frequency vibration reduces the local viscosity of the resin (acoustic rheological effect), making it easier for bubbles to migrate to the outer edge of the fluid resin layer and be thrown out under the action of centrifugal force.

[0237] By setting the ultrasonic frequency range to 20-40kHz, degassing of the fluid resin layer can be achieved, resulting in significant cavitation, and the heat can be controlled to avoid deformation of the dental tray print.

[0238] This embodiment uses high-frequency ultrasound to apply high-frequency vibration to the resin and limits the range of ultrasound frequencies, which can reduce defects (such as pinholes and shrinkage cavities) in the fluid resin layer and improve the optical properties (such as light transmittance) and mechanical properties (such as structural strength) of the fluid resin layer.

[0239] In this embodiment, during the process of applying resin to the surface of the dental tray print or performing centrifugation, the tray opening end of the dental tray print faces to the side.

[0240] It should be noted that if the open end of the bracket faces upward, it can easily cause the fluid resin to accumulate inside the bracket.

[0241] In this embodiment, in step eight, a light curing machine is first used to perform a short-term pre-curing treatment on the dental tray print, and then a continuous curing treatment is performed on the dental tray print to prevent the resin on the surface of the dental tray print from dripping during the continuous curing process.

[0242] The UV curing machine can be an existing handheld UV curing machine.

[0243] During the continuous curing process, the resin has fluidity. Although its fluidity is poor, the continuous curing process generally takes several minutes (e.g., 5 minutes), and the initial curing (restricting resin flow) generally takes a certain amount of time (e.g., 1 minute). This causes a small amount of resin to drip from the fluid resin layer during the initial curing process, which reduces the uniformity of the thickness of the cured fluid resin layer, affects the appearance of the finished dental tray, and may also affect the transparency of the finished dental tray.

[0244] In this embodiment, before the continuous curing process, the dental tray print is pre-cured using a light curing machine. This quickly restricts the flow of resin in the fluid resin layer, ensuring the uniformity of the thickness of the cured fluid resin layer and thus guaranteeing the quality of the finished dental tray (such as appearance quality).

[0245] It should be noted that compared to nitrogen-protected UV curing chambers (for example), handheld UV curing machines (for example) are more convenient to use and therefore can be pre-cured more quickly.

[0246] In this embodiment, in step six, after the grinding process, the dental tray print is sandblasted using a sandblasting device. The sandblasting device uses alumina micro powder or glass beads with a particle size of 20–50 μm.

[0247] During the sandblasting process, the blasting pressure is 0.15–0.25 MPa, the blasting angle is 60–80°, the blasting distance is 50–100 mm, and the duration of each blasting session is 1–3 seconds.

[0248] The sandblasting device is an existing device. For example, the sandblasting device can be a desktop micro-sandblaster with a sandblasting gun that can adjust the pressure (0.1–0.4 MPa) and has a nozzle diameter of 0.5–1.0 mm.

[0249] Each continuous spraying time is 1–3 seconds. For example, after the sandblasting device sandblasts part one of the dental tray print for 2 seconds, it switches to sandblasting part two to avoid deformation of the dental tray print due to local overheating and to ensure the quality of the finished dental tray.

[0250] The sandblasting process described above can roughen the surface of the dental tray printout, increasing the adhesion and retention of the fluid resin layer and further ensuring the uniformity of the fluid resin layer's thickness. Specifically, when using the sandblasting process, micro-dimples (approximately 5-20 μm in diameter) can be created on the surface of the dental tray printout. These micro-dimples facilitate the anchoring of the fluid resin layer to the surface of the dental tray printout in subsequent steps.

[0251] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for post-processing of a 3D printed transparent denture surface, characterized in that: The method comprises the following steps: Step 1: cleaning the dental tray print using a resin cleaner to remove uncured photosensitive resin on the surface of the dental tray print; Step 2: polishing the cleaned dental tray print to remove defect structures on the surface of the dental tray print, thereby improving the surface quality of the dental tray print; Step 3: forming a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray print by filling the fluid resin layer to make the surface of the dental tray print flat; Step 4: curing the fluid resin layer to obtain a finished dental tray. In step 3, the fluid resin layer with a thickness of 8-15 μm is formed on the surface of the dental tray print by uniformly applying resin to the surface of the dental tray print using a brushing structure, and high-frequency vibration is applied to the resin by high-frequency ultrasonic waves during the application of the resin; or, in step 3, the dental tray print is completely immersed in the resin, and then the dental tray print is placed in a centrifuge for centrifugation to remove excess resin on the surface of the dental tray print, thereby forming a fluid resin layer with a thickness of 8-15 μm on the surface of the dental tray print, and high-frequency vibration is applied to the resin by high-frequency ultrasonic waves during the complete immersion of the dental tray print in the resin.

2. The 3D printed transparent denture base surface post-processing method according to claim 1, characterized in that: The steps of centrifugation are as follows: Fix the dental tray print at the rotor of the centrifuge; Start the centrifuge, and the running time of the centrifuge is set to t; During the running of the centrifuge, the instantaneous coating thickness h(t) is calculated using the following formula: ， Wherein: h0 is the initial thickness of the fluid resin layer when the dental tray print is fixed to the rotor of the centrifuge; η is the viscosity of the fluid resin; ρ is the density of the fluid resin; r is the shortest distance between the center of gravity of the dental tray print and the axis of the centrifuge; τ is the time constant; ω is the angular velocity.

3. The 3D printed transparent denture base surface post-processing method according to claim 1, characterized in that: The steps of centrifugation are as follows: Fix the dental tray print at the rotor of the centrifuge; Start the centrifuge, and the running time of the centrifuge is set to t; n ultrasonic transducers are used to apply high-frequency vibration to the fluid resin layer during the running of the centrifuge; During the running of the centrifuge, the instantaneous coating thickness h(t) is calculated using the following formula: ， Wherein: C f is the adjustment factor for the frequency f of the ultrasonic transducer; n is the number of ultrasonic transducers; h0 is the initial thickness of the fluid resin layer when the dental tray print is fixed to the rotor of the centrifuge; η is the viscosity of the fluid resin; ρ is the density of the fluid resin; r is the shortest distance between the center of gravity of the dental tray print and the axis of the centrifuge; τ is the time constant; ω is the angular velocity.

4. The 3D printed transparent denture surface post-processing method according to any one of claims 1-3, characterized in that: In step 4, the curing process comprises the following steps: Put the dental tray print wrapped with the fluid resin layer into a nitrogen protection photocuring box or an argon protection photocuring box for curing.

5. The 3D printed transparent denture surface post-processing method according to any one of claims 1-3, characterized in that: In step 4, the curing process comprises the following steps: S1, put the dental tray print wrapped with the fluid resin layer into a container containing a glycerol aqueous solution; S2, put the container into a photocuring box for continuous curing; S3, take out the dental tray print from the container; S4, rinse the dental tray print with water.

6. The 3D printed transparent denture surface post-processing method according to any one of claims 1-3, characterized in that: In step 4, the dental tray print is first subjected to pre-curing treatment using a photocuring machine, and then subjected to continuous curing treatment, so as to prevent the resin on the surface of the dental tray print from dripping during the continuous curing treatment.

7. The 3D printed transparent denture surface post-processing method according to any one of claims 1-3, characterized in that: In step two, after polishing, the sandblasting device is used to spray the dental tray printing piece, and the sandblasting device uses aluminum oxide powder or glass beads with a particle size of 20-50 μm; During the sandblasting process, the spraying pressure is 0.15-0.25 MPa, the spraying angle is 60-80°, the spraying distance is 50-100 mm, and the continuous spraying time is 1-3 seconds each time.

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