Dental zirconia 3d-printed article having color and translucency gradients and manufacturing method therefor

Abstract

The present invention relates to a dental zirconia 3D-printed article having color and translucency gradients and a manufacturing method therefor and, specifically, to a dental zirconia 3D-printed article and a manufacturing method therefor, the dental zirconia 3D-printed article comprising at least two types of yttria-stabilized zirconia (YSZ) doped with different contents of yttria (Y2O3), wherein the at least two types of yttria-stabilized zirconia are selectively doped with a colorant to have gradients in color and translucency.

Description

Dental zirconia 3D printed structure having color and translucency gradient and method for manufacturing the same

[0001] The present invention relates to a dental zirconia 3D printed object having a color and translucency gradient and a method for manufacturing the same.

[0002]

[0003] Zirconia (ZrO2) is highly valued in dentistry due to its high mechanical properties, excellent corrosion and high temperature resistance, superior biocompatibility, and non-toxicity to the human body. Because of these advantages, zirconia (ZrO2) is considered a viable alternative to conventional metal-ceramics for dental restorations such as crowns, inlays, onlays, veneers, and laminates. Among them, the widely used 3 mol% yttria-stabilized tetragonal zirconia (3YSZ) has a white and opaque appearance, which offers many advantages over other conventional ceramic and metal materials used for dental restoration; however, achieving an appearance close to that of natural teeth remains one of the most challenging tasks to this day.

[0004] Since matching the color and contour of adjacent teeth is important for patient satisfaction, color and translucency are considered important aesthetic requirements for dental crowns, in addition to meeting mechanical and biological standards.

[0005] Natural teeth exhibit a gradual appearance in both color and translucency. While individual variations exist, the color is generally a very opaque reddish-yellow at the bottom (neck) and becomes translucent white towards the top (incisors). Therefore, to satisfy the patient's aesthetic requirements, it is desirable for an ideal zirconia (ZrO2) crown to possess characteristics of gradual color and translucency.

[0006] In the past, various studies were conducted to achieve optimal color or translucency in zirconia (ZrO2) crowns.

[0007] Specifically, regarding the color of zirconia (ZrO2), various shading techniques have been disclosed, and among these techniques, a method of doping zirconia (ZrO2) with metal oxides such as Fe2O3, Bi2O3, CeO2, and Er2O3 to color it is known.

[0008] In addition, regarding the translucency of zirconia (ZrO2), methods are known, such as (a) reducing residual porosity by adding a glassy phase or some sintering additives, (b) refining the microstructure so that grain boundaries do not obstruct light, (c) reducing grain boundaries, and (d) introducing a significant amount of cubic crystals that are optically isotropic and do not induce birefringence.

[0009] Regarding the crystal structure and translucency properties of zirconia (ZrO2), pure zirconia (ZrO2) is a polymorphic material capable of having three crystal structures: monoclinic (m-ZrO2), orthorhombic (t-ZrO2), and cubic (c-ZrO2). In the case of monoclinic (m-ZrO2), it is formed from room temperature up to 1170°C, while orthorhombic (t-ZrO2) is formed between 1170°C and 2370°C, and cubic (c-ZrO2) is formed up to a melting point of 2370°C to 2680°C. However, cubic crystals can be stabilized at room temperature by doping yttria into zirconia (ZrO2) powder. The advantage of the cubic crystal is that it possesses a symmetric microstructure with the same refractive index n in all directions, which efficiently transmits light and enhances the translucency of the material; consequently, cubic zirconia (ZrO2) exhibits more translucent properties than orthorhombic zirconia.

[0010] Meanwhile, although there are technologies for manufacturing zirconia (ZrO2) crowns such as dry pressing, cold isostatic pressing, hot isostatic forming, and CAD / CAM, it is difficult to manufacture zirconia (ZrO2) crowns with color and translucent gradients. Therefore, ceramic additive manufacturing (AM) is rapidly developing as a promising method for manufacturing dental crowns (Non-patent Literature 1), and among them, digital light processing (DLP)-based 3D printing technology is receiving significant attention due to smoother surface finish, improved precision, and increased printing speed.

[0011] Conventional DLP technology uses a light source of a specific wavelength (generally in the ultraviolet range) to selectively cure the surface of a ceramic suspension, mainly containing a photopolymerizable monomer photoinitiator and ceramic, to obtain a printed layer and stack it to form a three-dimensional structure.

[0012] Meanwhile, ceramic particles contained in ceramic suspensions absorb and scatter some of the light. This scattering phenomenon not only causes radical formation and propagation within the intended exposure area but also extends to undesirable areas of the suspension, resulting in excessive curing in these unintended areas and causing problems that degrade the fidelity and structural accuracy of the printed parts. Accordingly, numerous techniques have been studied to solve the problem of overcuring caused by scattering in photopolymerizable slurries. However, most studies target non-ceramic slurries and focus only on mitigating scattering effects during the photopolymerization process, while research on methods to prevent overcuring during 3D printing using ceramic suspensions remains insufficient.

[0013] While researching to manufacture a dental zirconia mold having physical properties and an appearance similar to natural teeth using a 3D printing method, the inventors manufactured a dental zirconia mold with improved structural precision by preventing over-curing during 3D printing and by controlling the content of yttria and coloring agents doped into yttria-stabilized zirconia (YSZ), thereby producing a dental zirconia mold that has a gradient in color and translucency similar to the appearance of natural teeth.

[0014]

[0015] One objective is to provide a dental zirconia 3D printed model having a color and translucency gradient and a method for manufacturing the same.

[0016]

[0017] In order to achieve the above objective,

[0018] In one aspect,

[0019] As a dental zirconia 3D printed object formed by a 3D printing method,

[0020] A dental zirconia 3D printed model is provided, comprising at least two types of yttria-stabilized zirconia (YSZ) doped with yttria (Y2O3) in different amounts, wherein the two or more types of yttria-stabilized zirconia are selectively doped with a coloring agent to have gradients in color and translucency.

[0021]

[0022] In other aspects of work,

[0023] A method for manufacturing a dental zirconia 3D printed object having a gradient in color and translucency,

[0024] A method for manufacturing a dental zirconia 3D printed structure is provided, comprising the step of forming a 3D printed structure using a plurality of photocurable slurries, wherein the yttria-stabilized zirconia (YSZ) powder is doped with a photocurable resin and yttria (Y2O3) and optionally doped with a coloring agent, and wherein at least one of the yttria and the coloring agent is included in different amounts.

[0025]

[0026] The dental zirconia 3D printed model of the present invention has a color and transparency gradient, thereby providing an appearance more similar to natural teeth and high mechanical strength, thus having the advantage of excellent aesthetic quality and functionality as a dental model.

[0027]

[0028] In addition, the dental zirconia 3D-printed structure of the present invention can have a precise structure by being manufactured by 3D printing, and also has the advantage of excellent structural accuracy and shape fidelity by suppressing over-curing during the photocuring stage.

[0029]

[0030] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below.

[0031]

[0032] Figure 1 is a schematic diagram showing the manufacturing process of a photocurable composition (slurry).

[0033] Figure 2a is a graph of the particle size distribution of 3YSZ, 4YSZ, and 5YSZ powders, and Figure 2b is the result of X-ray diffraction analysis for 3YSZ, 4YSZ, and 5YSZ powders.

[0034] FIGS. 3a to 3d are results of evaluating the rheological characteristics of slurries containing different weights of dispersants, FIG. 3a is the result of evaluating viscosity against shear rate of a slurry containing 3YSZ that does not contain iron oxide as a raw powder, FIG. 3b is the result of evaluating viscosity against shear rate of a slurry containing 4YSZ that does not contain iron oxide as a raw powder, FIG. 3d is a figure evaluating viscosity against shear rate when the raw powder is contained at 43 volume% at the optimal dispersant content.

[0035] Figures 4a and 4b are evaluations of hardening depth according to iron oxide content, Figure 4a is a drawing of an evaluation for a slurry containing 3YSZ doped with iron oxide as a raw powder and 4YSZ doped with iron oxide as a raw powder.

[0036] Figure 5 is a diagram evaluating the printability according to the iron oxide content.

[0037] Figure 6 is a drawing showing the color of the sintered structure.

[0038] Figures 7a to 7d are results of measuring CIELAB color parameters L*, a*, and b* and color difference (ΔE*) values ​​on a black background.

[0039] FIGS. 8a to 8c are drawings showing the horizontal and vertical sintering shrinkage rates of 3YSZ, 4YSZ, and 5YSZ sintered bodies sintered at 1500°C according to an example.

[0040] Figure 9 is an SEM image of the surface of disks made of 3YSZ, 4YSZ, and 5YSZ that are not doped with iron oxide or doped with 0.10 wt% iron oxide (Fe2O3), after surface polishing and thermal etching were performed after sintering at 1500°C.

[0041] FIGS. 10a to 10c are drawings showing the bending strength of disks made of 3YSZ, 4YSZ, and 5YSZ that are not or doped with iron oxide, after sintering at 1450°C, 1500°C, and 1550°C.

[0042] FIG. 11 is a schematic diagram showing a continuous film type DLP printer and a three-dimensional (3D) model used in one embodiment.

[0043] FIG. 12 is a diagram evaluating the degree of overcuring under flashing or continuous lighting for a zirconia slurry prepared according to one embodiment.

[0044] FIG. 13 is a drawing evaluating the degree of overcuring under flashing or continuous lighting for a titania slurry prepared according to one embodiment.

[0045] FIG. 14 is a diagram evaluating the curing depth according to the ignition time for a zirconia slurry manufactured according to one embodiment.

[0046] FIG. 15 is a diagram evaluating the curing depth according to the ignition time for a titania slurry manufactured according to one embodiment.

[0047] FIG. 16 is a diagram evaluating the degree of overcuring according to the extinguishing time for zirconia and titania slurries prepared according to one embodiment.

[0048] FIG. 17a is a diagram evaluating the curing depth according to the extinguishing time for a zirconia slurry prepared according to one embodiment, and FIG. 17b is a diagram evaluating the curing depth according to the extinguishing time for a titania slurry prepared according to one embodiment.

[0049] FIG. 18a is a drawing showing a 3D printed structure (green body), a degreased structure (brown body), and a sintered structure (sintered body) made with a zirconia and titania slurry under continuous lighting conditions, and FIG. 18b is a drawing showing a 3D printed structure (green body), a degreased structure (brown body), and a sintered structure (sintered body) made with a zirconia and titania slurry under flashing lighting conditions.

[0050] FIG. 19 is a schematic diagram showing the design configuration of a crown to be manufactured in one embodiment.

[0051] FIG. 20 is a diagram evaluating the degree of overcuring under flashing or continuous lighting for a photocurable composition (slurry) for manufacturing a dental zirconia 3D printed object manufactured according to one embodiment.

[0052] FIG. 21a is a photograph of a dental zirconia 3D printed structure (green body) (left) and a sintered structure (sintered body) (right) manufactured using continuous lighting according to a comparative example, and FIG. 21b is a photograph of a dental zirconia 3D printed structure (green body) (left) and a sintered structure (sintered body) (right) manufactured using flashing lighting according to a comparative example.

[0053] FIG. 22a is a photograph evaluating the translucency of a sintered structure manufactured according to one embodiment, and FIG. 22b is a translucency graph.

[0054]

[0055] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, embodiments of the present invention may be modified in various different forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, the following embodiments are provided to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation. Also, throughout the specification, the term "comprising" a component means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0056]

[0057] In one aspect,

[0058] As a dental zirconia 3D printed object formed by a 3D printing method,

[0059] A dental zirconia 3D printed model is provided, comprising at least two types of yttria-stabilized zirconia (YSZ) doped with yttria (Y2O3) in different amounts, wherein the two or more types of yttria-stabilized zirconia are selectively doped with a coloring agent to have gradients in color and translucency.

[0060]

[0061] Hereinafter, a dental zirconia 3D printed structure according to one embodiment will be described in detail.

[0062] Since the dental zirconia 3D printed structure according to one embodiment is based on zirconia, it has excellent mechanical properties and excellent biocompatibility, thus having excellent advantages as a dental structure.

[0063]

[0064] A dental zirconia 3D printed model according to one embodiment is a dental zirconia 3D printed model formed by a 3D printing method, characterized by having both color and translucency gradients.

[0065]

[0066] A dental zirconia 3D printed structure according to one embodiment comprises two or more types of yttria-stabilized zirconia (YSZ), wherein the two or more types of yttria-stabilized zirconia (YSZ) are doped with yttria (Y2O3) in different amounts and selectively doped with a coloring agent.

[0067] More specifically, according to one embodiment, the dental zirconia 3D printed structure may have a gradient in the content of yttria and coloring agent doped into the zirconia, thereby allowing both the color and translucency to be gradient, and the gradient may preferably be formed in a direction from one end of the structure to the other, for example, if the structure is a dental crown, it may be formed in a direction from the bottom (neck) to the top (incisor) of the crown.

[0068]

[0069] Accordingly, a dental zirconia 3D printed structure according to one embodiment may include multiple regions with different contents of at least one of yttria and a coloring agent, thereby allowing both color and translucency to have gradients.

[0070]

[0071] At this time, the yttria may have a content gradient in the range of 1 to 10 mol% of the total content of zirconia and yttria in the overall structure of the molded object, preferably in the range of 2 to 7 mol%, and more preferably in the range of 3 to 5 mol%.

[0072]

[0073] The above-mentioned mold may include at least two regions with different yttria contents, and the yttria content in the at least two regions may gradually increase or decrease.

[0074] The above mold may include three regions with different yttria contents, for example, a first-1 region containing 3 mol% yttria; a first-2 region containing 4 mol% yttria; and a first-3 region containing 5 mol% yttria, and the ratios of the first-1 region, the first-2 region, and the first-3 region may vary.

[0075]

[0076] In addition, the yttria may have a content gradient of 0 to 0.1 weight percent relative to the weight of the yttria-stabilized zirconia in the overall structure of the molded object.

[0077] A dental zirconia 3D printed structure according to one embodiment may include at least two regions, at least three regions, or at least four regions with different coloring agent contents, and, for example, may include six regions. In this case, the coloring agent content in the at least two regions may gradually increase or decrease.

[0078]

[0079] The above-mentioned mold may include six regions with different amounts of coloring agent, for example, a 2-1 region containing 0.0 wt% of coloring agent, a 2-2 region containing 0.02 wt% of coloring agent, a 2-3 region containing 0.04 wt% of coloring agent, a 2-4 region containing 0.05 wt% of coloring agent, a 2-5 region containing 0.08 wt% of coloring agent, and a 2-6 region containing 0.10 wt% of coloring agent.

[0080]

[0081] A dental zirconia 3D printed structure according to one embodiment has a slope in which the content of yttria (Y2O3) increases from one end to the other and the content of the coloring agent decreases. This is because as the content of yttria decreases and the content of the coloring agent increases, translucency decreases and a dark color may be formed.

[0082] In the case where the above-mentioned mold is a dental crown, the lower part (neck) of the crown has a relatively low yttria content and a high colorant content, and as it moves toward the top, the yttria content increases and the colorant content decreases.

[0083]

[0084] The above coloring agent may include one or more of Fe2O3, Bi2O3, CeO2, and Er2O3, and preferably may be iron oxide (Fe2O3).

[0085]

[0086] A dental zirconia 3D printed model according to one embodiment may have a color gradient in any one of the ranges in which L* is 50 to 95, a* is -4 to 10, b* is 0 to 20, and ΔE* is 0 to 25 in the CIELAB color parameters, and preferably may have a color gradient in a range satisfying all of these.

[0087]

[0088] In addition, a dental zirconia 3D printed structure according to one embodiment may have a translucency gradient in the range of a translucency parameter (TP) value of 10 to 25.

[0089]

[0090] A dental zirconia 3D printed structure according to one embodiment may be a dental crown.

[0091] A dental zirconia 3D printed model according to one embodiment has a color gradient and a translucency gradient within the above range, thereby having the advantage of excellent aesthetics as a dental material, preferably as a dental crown.

[0092] In addition, a dental zirconia 3D printed structure according to one embodiment may have a high density with a relative density of 98% or more, preferably 99% or more, and may have a high strength with a bending strength of 500 to 800 MPa.

[0093] Accordingly, the dental zirconia 3D printed structure according to one embodiment has the advantage of having excellent mechanical properties as a dental material.

[0094]

[0095] A dental zirconia 3D printed body according to one embodiment is formed by sintering a 3D printed body formed by stacking a plurality of printed layers, wherein each of the plurality of printed layers may contain a predetermined amount of yttria (Y2O3) and a coloring agent so that the body may have a gradient in the content of yttria (Y2O3) and a coloring agent, and may have a gradient in color and translucency in the direction of stacking through the stacking of the printed layers.

[0096]

[0097] In other aspects of work,

[0098] A method for manufacturing a dental zirconia 3D printed object having a gradient in color and translucency,

[0099] A method for manufacturing a dental zirconia 3D printed structure is provided, comprising the step of forming a 3D printed structure using a plurality of photocurable slurries, wherein the yttria-stabilized zirconia (YSZ) powder is doped with a photocurable resin and yttria (Y2O3) and optionally doped with a coloring agent, and wherein at least one of the yttria and the coloring agent is included in different amounts.

[0100]

[0101] Hereinafter, a method for manufacturing a dental zirconia 3D printed structure according to one embodiment will be described in detail.

[0102]

[0103] A method for manufacturing a dental zirconia 3D printed product according to one embodiment is a method for manufacturing a dental zirconia 3D printed product having a gradient in color and translucency.

[0104] To this end, the above manufacturing method forms a 3D printed structure using a plurality of photocurable slurries comprising a photocurable resin and yttria-stabilized zirconia (YSZ) powder doped with yttria (Y2O3) and optionally doped with a coloring agent, wherein at least one of yttria and the coloring agent is included in different amounts.

[0105]

[0106] Herein, the plurality of photocurable slurries comprises a first photocurable slurry comprising a photocurable resin and a first yttria-stabilized zirconia (YSZ) powder doped with yttria (Y2O3) and not doped with a coloring agent; and

[0107] It may include a first photocurable slurry comprising a photocurable resin and a second yttria-stabilized zirconia (YSZ) powder doped with yttria (Y2O3) and doped with a coloring agent in the range of 0.01 to 0.1 weight%.

[0108] In addition, any one or more of the first photocurable slurry and the second photocurable slurry may include a plurality of photocurable slurries with different yttria contents.

[0109]

[0110] That is, the first photocurable slurry containing yttria but not containing a coloring agent may be one, but there may be multiple slurries with different yttria contents.

[0111] In addition, the second photocurable slurry containing both yttria and a coloring agent may be a plurality of slurries with different contents of one or more of the yttria and coloring agent.

[0112] When the above plurality of second photocurable slurries contain a relatively large amount of yttria, the coloring agent may contain a relatively small amount. Conversely, when yttria is contained in a relatively small amount, the coloring agent may contain a relatively large amount.

[0113] This is intended to have a slope where the bottom (neck) has relatively low translucency and a dark color, while becoming more translucent and brighter towards the top.

[0114] The above plurality of second photocurable slurries can form a bright color with high translucency by including a relatively large amount of yttria and a relatively small amount of coloring agent, and can form a dark color with low translucency by including a relatively small amount of yttria and a relatively large amount of coloring agent.

[0115]

[0116] The above yttria-stabilized zirconia (YSZ) powder may be doped with yttria in an amount of 1 to 10 mol%, 1 to 7 mol%, 2 to 6 mol%, or 3 to 5 mol%.

[0117] In addition, the yttria-stabilized zirconia (YSZ) powder may contain a coloring agent in an amount of 0 to 0.1% by weight relative to the weight of the yttria-stabilized zirconia (YSZ).

[0118]

[0119] For example, the first photocurable slurry may include 5YSZ doped with 5 mol% yttria and a first zirconia powder not doped with iron oxide.

[0120] Additionally, the second photocurable slurry may include photocurable slurries 2-1 to 2-5, in which one or more of yttria and a coloring agent are included in different amounts.

[0121] For example, a 2-1 photocurable slurry comprising 2-1 zirconia powder doped with 0.02 wt% iron oxide in 4YSZ doped with 4 mol% yttria, a 2-2 photocurable slurry comprising 2-2 zirconia powder doped with 0.04 wt% iron oxide in 4YSZ doped with 4 mol% yttria, a 2-3 photocurable slurry comprising 2-3 zirconia powder doped with 0.06 wt% iron oxide in 4YSZ doped with 4 mol% yttria, a 2-4 photocurable slurry comprising 2-4 zirconia powder doped with 0.08 wt% iron oxide in 3YSZ doped with 3 mol% yttria, and 0.10 wt% iron oxide in 3YSZ doped with 3 mol% yttria It may include a 2-5 photocurable slurry containing doped 2-5 zirconia powder.

[0122]

[0123] A method for manufacturing a dental zirconia 3D printed object according to one embodiment can produce first to sixth regions in which at least one of color and translucency differs in the object by using the first photocurable slurry and the second-1 to second-5 photocurable slurries.

[0124] Here, the number of photocurable slurries and the content of yttria and coloring agents included in the photocurable slurries may vary, and by adjusting the number of photocurable slurries and the content of yttria and coloring agents included in the photocurable slurries, the molded product may form a gradient of color and / or translucency.

[0125]

[0126] A method for manufacturing a dental zirconia 3D printed product according to one embodiment can manufacture a dental zirconia 3D printed product using the plurality of photocurable slurries, which can have a color gradient in the range of CIELAB color parameters where L* is 50 to 95, a* is -4 to 10, b* is 0 to 20, and ΔE* is 0 to 25, and a translucency gradient in the range of translucency parameter (TP) value is 10 to 25.

[0127]

[0128] Meanwhile, each of the above plurality of photocurable slurries includes a photocurable resin that causes the slurry to be cured by light such as UV.

[0129] At this time, the photocurable resin may include an acrylate-based monomer or oligomer having two or more functional groups, and, for example, may be one or more selected from the group consisting of 1,6-hexanediol diacrylate (HDDA), triethylene glycol dimethacrylate (TMPTA), trimethylolpropane triacrylate (TMPTA), urethane dimethacrylate (UDMA), and polypropylene glycol diacrylate (PPGDA), but is not limited thereto.

[0130]

[0131] In addition, each of the plurality of photocurable slurries may contain 20 to 90 volume%, 30 to 80 volume%, 40 to 60 volume%, or 40 to 50 volume% of the yttria-stabilized zirconia (YSZ) powder relative to the total volume of the slurry.

[0132] This may be intended to have a viscosity value for an appropriate shear rate so that when the photocurable slurry is applied in the form of a film, it forms a normal film shape. If the photocurable slurry is not applied in the form of a normal film, a single printed layer (1 layer) for 3D printing may not be formed properly.

[0133]

[0134] Each of the above plurality of photocurable slurries may further include a photoinitiator.

[0135] The above photoinitiator may be a conventional photocurable initiator used in 3D printing. For example, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) (BASF, Germany) may be used.

[0136] Each of the above plurality of photocurable slurries may contain 0.02% to 1% by weight of the photoinitiator based on the total weight of the slurry, but the content of the photoinitiator may vary depending on the wavelength or intensity of light.

[0137] In addition, each of the above plurality of photocurable slurries may further include a dispersant.

[0138] The above dispersant may be used to control the viscosity with respect to the shear rate of the slurry and to increase the dispersion of the powder.

[0139] The above dispersant may be one or more selected from the group consisting of CC-9, KD-4, BYK-111, BYK-163, BYK-180, BYK-2001, BYK-2013 and Anti-Terra-U.

[0140] The above dispersant may be included in an amount of 0.5% to 10% by weight based on the total weight of the slurry, and may be included in an amount of 3% to 5% by weight.

[0141]

[0142] Meanwhile, the step of forming the above-mentioned 3D-printed structure is,

[0143] A slurry supply step of supplying any one of the plurality of photocurable slurries above onto a 3D printing device plate;

[0144] A printing layer forming step of forming a printing layer by irradiating light onto a slurry supplied on the plate; and

[0145] The method may include a step of forming a 3D printed body having a gradient in color and translucency by stacking a plurality of printed layers by repeating the above slurry supply step and the printed layer formation step.

[0146]

[0147] At this time, the above 3D device may preferably be a DLP (Digital Light Processing) device.

[0148]

[0149] Meanwhile, the above-mentioned printing layer formation step can irradiate light using a flashing method that repeatedly turns on and off.

[0150] Here, the light may be ultraviolet (UV) light of 300 nm to 465 nm.

[0151]

[0152] The above printing layer formation step is characterized by forming the printing layer using a flashing photocuring method in which light is irradiated by a flashing method that repeatedly turns on and off to photopolymerize the photocurable resin in the slurry.

[0153] In contrast to the above flashing photocuring, the conventional method of continuously irradiating light to photopolymerize a photocurable resin in a slurry is referred to as continuous photocuring.

[0154]

[0155] In the above step of forming the printing layer, the total curing time for forming the printing layer may be 1 second or more, 1.5 seconds or more, or 2 seconds or more, and 60 seconds or less, 50 seconds or less, 40 seconds or less, 30 seconds or less, 20 seconds or less, or 10 seconds or less, 9 seconds or less, 8 seconds or less, 7 seconds or less, 6 seconds or less, 5 seconds or less, 4 seconds or less, 3 seconds or less, or 2 seconds or less.

[0156]

[0157] In the flashing photocuring method, the total curing time is defined by Equation 1 below:

[0158] <Equation 1>

[0159] Total curing time (total lighting time) = (time per lighting cycle × number of lighting cycles)

[0160]

[0161] Here, the flash time refers to the time when light shines on the slurry, and the off time refers to the time when light is not irradiated.

[0162]

[0163] As the total curing time increases, the curing depth increases; therefore, the above total curing time may vary depending on the required curing depth.

[0164] Here, the curing depth is for forming a single printed layer, and it is preferable to form a curing depth of about 2 to 3 times the thickness of the single printed layer to be formed. Considering the level of currently available devices, it is preferable that the curing depth be 10 μm or more.

[0165]

[0166] The above printing layer forming step can irradiate light using a flashing method that repeats a lighting time of 0.1 to 1 second and a extinguishing time of 0.5 seconds or more.

[0167]

[0168] The degree of overcuring can be controlled by adjusting the flash time in the above printing layer formation step, and specifically, the more the flash time is reduced within the range of 0.1 to 1 second, the more the effect of suppressing the degree of overcuring can be improved.

[0169] Here, the flash time may preferably be 0.1 seconds or more and 0.7 seconds or less, 0.5 seconds or less, 0.3 seconds or less, 0.2 seconds or less, and 0.1 to 0.5 seconds.

[0170] The curing depth decreases as the flash time becomes shorter. If the flash time is less than 0.1 seconds, problems may arise such as the total curing time required to reach the required curing depth being too long, or the problem of not being able to reach the required curing depth.

[0171] In addition, if the flash time is greater than 1 second, the effect of reducing the degree of overcuring (or overgrowth rate) due to the use of the flashing method may be insufficient.

[0172]

[0173] In addition, the degree of overcuring can be controlled by adjusting the off time during the printing layer formation step. Specifically, the degree of overcuring can be suppressed by having an off time of 0.5 seconds or more, and the effect of suppressing the degree of overcuring can be further improved by increasing the off time.

[0174] Here, the off time may be 0.5 seconds or more, 1 second or more, 2 seconds or more, 3 seconds or more, 4 seconds or more, 5 seconds or more, and 10 seconds or less, preferably less than 10 seconds.

[0175] If the above off time is less than 0.5 seconds, the effect of reducing the degree of overcuring (or overgrowth rate) due to the use of the flashing method may be insufficient.

[0176] In addition, the curing depth decreases as the off time increases, so if the off time is increased to 10 seconds or more, problems may arise such as the total curing time required to reach the required curing depth being too long or the problem of not being able to reach the required curing depth.

[0177]

[0178] A method for manufacturing a dental zirconia 3D printed structure according to one embodiment can significantly reduce overcuring caused by scattering of inorganic particles by controlling the flash time and off time together as described above, thereby significantly improving the structural accuracy and shape fidelity of the 3D printed structure ultimately manufactured.

[0179]

[0180] A method for manufacturing a dental zirconia 3D printed structure according to one embodiment is

[0181] A step of degreasing the above 3D printed structure; and

[0182] It may further include a step of sintering the degreased structure.

[0183] At this time, the degreasing step is a step of removing organic components, such as photocurable resin and dispersant, contained in the 3D printed structure, and can be performed at an appropriate temperature range where such organic components can be removed. Preferably, the degreasing can be performed at room temperature in a nitrogen atmosphere or at a temperature range of 25°C to 700°C.

[0184] In addition, the above sintering is a step of densifying to form a final ceramic structure, and can be performed in an atmospheric atmosphere and at a temperature of 1100°C to 1700°C, and preferably at 1500°C to 1700°C.

[0185]

[0186] The present invention will be explained in detail below through embodiments and experimental examples.

[0187] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited by the following examples.

[0188]

[0189] Experimental Example 1: Preparation of 3D Printing Slurry with Color and Translucent Gradient and Evaluation of Printability

[0190] ingredient

[0191] Three yttria-stabilized zirconia powders (3YSZ, 4YSZ, and 5YSZ) doped with yttria at 3 mol%, 4 mol%, and 5 mol% (Tosoh, Japan) were used as zirconia powders. Iron oxide (Fe2O3) (iron(III) oxide - nanopowder, Sigma-Aldrich, USA) was used as a coloring agent.

[0192] A mixture of two monomers, trimethylolpropane triacrylate (TMPTA) and 1,6-hexanediol diacrylate (HDDA), and a non-reactive diluent, polypropylene glycol (PPG P400) (Sigma-Aldrich, USA), was used as the photocurable resin. Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) (BASF, Germany) was used as the photoinitiator (PI). DISPERBYK-111 (BYK111; Altana AG, Germany) was used as a dispersant to disperse and stabilize the ceramic powder in the slurry.

[0193]

[0194] <Manufacturing Example 1-1> Preparation of Photocurable Composition (Slurry)

[0195] Figure 1 is a schematic diagram showing the process of manufacturing a photocurable composition (slurry). As shown in Figure 1, a photocurable composition (slurry) was manufactured using the following method.

[0196] Yttria-stabilized zirconia powder (3YSZ, 4YSZ, and 5YSZ), BYK111 dispersant, and iron oxide (Fe2O3) in the content shown in Table 1 below were ball-milled at 300 rpm for 5 hours using 2 mm ZrO2 balls in anhydrous alcohol (99.9%, Samjeon Pure Chemical, Korea). The milled suspension was vacuum-dried at 30°C and sieved through a 56 μm mesh to prepare a mixed powder containing the raw powder and the dispersant.

[0197] Fe2O3(wt%)S1S2S3S4S5S6S73YSZ00.020.040.060.080.100.124YSZ00.020.040.060.080.100.125YSZ0------

[0198]

[0199] (wt% in Table 1: weight% relative to the weight of yttria-stabilized zirconia powder)

[0200]

[0201] A photocurable resin was prepared by mixing HDDA and TMPTA monomers in a weight ratio of 3:17, adding a PPG diluent in an amount of 20% by weight of the total weight of the resin, adding PI (irgacure 819) in an amount of 0.8% by weight of the total weight of the resin, and adding the mixed powder of Preparation Example 1-1 in an amount of 40% or 43% by volume of the total volume of the slurry, and uniformly mixing for 10 minutes at 2000 revolutions per minute in a planetary mixer (ARE-310, THINKY, USA) to prepare a photocurable composition (slurry).

[0202]

[0203] <Manufacturing Example 1-2> Manufacturing of Printed Structure

[0204] For the slurry prepared in Preparation Example 1-1, wavelength 405 nm, intensity 30 mW cm -2 A molded body was manufactured using the following method with a self-made film-type DLP system operating in continuous mode.

[0205] First, the slurry prepared in Preparation Example 1-1 was spread onto a silicone coating film, exposed to UV in continuous mode for a given curing time, washed with HDDA, and the curing depth was calculated using a micrometer (High-Accuracy Digimatic® Digital Micrometer; Mitutoyo, Kawasaki, Japan).

[0206] A disc sample with a thickness of 2 mm was printed with a layer thickness adjusted according to the curing depth value of each slurry composition.

[0207]

[0208] <Experimental Example 1-1> Evaluation of Characteristics of Zirconia Powder

[0209] Characterization of 3YSZ, 4YSZ, and 5YSZ powders is shown in Figures 2a and 2b.

[0210] Figure 2a is a graph of the particle size distribution of 3YSZ, 4YSZ, and 5YSZ powders. As shown in Figure 2a, the dominant particle size of all powders was nano-sized, and d of 3YSZ, 4YSZ, and 5YSZ 50 The sizes were 0.75μm, 0.82μm, and 0.98μm, respectively, and it was confirmed that all ZrO2 powders had similar powder distribution and particle sizes overall.

[0211] Figure 2b shows the results of X-ray diffraction analysis for 3YSZ, 4YSZ, and 5YSZ powders. As shown in Figure 2b, it can be confirmed that the 3YSZ, 4YSZ, and 5YSZ powders are all composed of a mixture of orthorhombic (t-ZrO2) and cubic (c-ZrO2) phases, and while 3YSZ is mostly composed of t-ZrO2 stabilized at room temperature, the cubic phase is clearly observed by increasing the yttria content.

[0212]

[0213] <Experimental Example 1-2> Evaluation of Rheological Properties of Slurry

[0214] To determine the optimal dispersant content, the slurry was prepared by including 3YSZ, 4YSZ, or 5YSZ powder that does not contain iron oxide as a raw material powder (S1 in Table 1) in the slurry of Example 1-1, and including the raw material powder at 40% by volume of the total slurry volume and varying the amount of dispersant at 1% to 6% by weight of the total slurry weight. The results of the viscosity evaluation for shear rate are shown in FIGS. 3a to 3c.

[0215] Figure 3a shows the viscosity evaluation results for a slurry containing 3YSZ that does not contain iron oxide as a raw powder, Figure 3b shows 4YSZ that does not contain iron oxide as a raw powder, and Figure 3c shows 5YSZ that does not contain iron oxide as a raw powder.

[0216] As shown in FIGS. 3a to 3c, the optimal BYK111 content having minimum viscosity was found to be different in 3YSZ, 4YSZ, and 5YSZ powder slurries, at 3 wt%, 4 wt%, and 5 wt%, respectively.

[0217] Figure 3d shows the viscosity evaluation results for shear rate when the raw powder is contained at 43 volume% at the optimal dispersant content. As shown in Figure 3d, when the dispersant was included at optimal content (3 wt%, 4 wt%, and 5 wt%, respectively) for 3YSZ, 4YSZ, and 5YSZ powders, it was possible to have a viscosity of less than 10 Pa·s along with shear dilution behavior even when the raw powder was increased to 43 volume%. Since the DLP system used in the experiment operates based on a film feed type supply system, where a viscosity value of less than 10 Pa·s is an ideal uniform flow of slurry through the doctor blade, in the following experiments, the dispersant was included at 3 wt%, 4 wt%, and 5 wt% in the 3YSZ, 4YSZ, and 5YSZ powder slurries, respectively, and the raw powder was set to 43 volume%.

[0218]

[0219] <Experimental Example 1-3> Evaluation of Curing Depth According to Iron Oxide (Fe2O3) Content

[0220] To evaluate the curing depth due to the inclusion of iron oxide (Fe2O3), the curing depth was measured when printing was done using the method of Manufacturing Example 1-2 and curing time under UV (continuous illumination) was 1 second to 14 seconds (2-second intervals after 2 seconds), and the results are shown in FIG. 4a and FIG. 4b.

[0221] At this time, the slurry used was the slurry of Preparation Example 1-1, but the slurry used contained 3YSZ or 4YSZ powder doped with the iron oxide (Fe2O3) content of Table 1 as the raw material powder.

[0222] As shown in Figures 4a and 4b, both 3YSZ and 4YSZ exhibited similar curing depth trends. Specifically, when not doped with iron oxide (Fe2O3), both 3YSZ and 4YSZ showed a significantly high curing depth of more than 50 μm at a curing time of 1 second, but as the doping amount of iron oxide (Fe2O3) increased, the curing depth decreased significantly. For example, the curing depth in 3YSZ and 4YSZ slurries not doped with iron oxide (Fe2O3) was about 90 μm, but when doped with 0.04 wt% iron oxide (Fe2O3), it decreased to less than about 30 μm, and when doped with 0.06 wt% iron oxide (Fe2O3), it decreased even further.

[0223] Since 5YSZ slurry is used only on the top part (incisor) of dental crowns, iron oxide (Fe2O3) doping is not required. The hardening depth of the 5YSZ slurry not doped with iron oxide (Fe2O3) was found to be similar to that of the 3YSZ and 4YSZ slurries not doped with iron oxide (Fe2O3).

[0224] In the case of slurries containing 0.06 wt% iron oxide (Fe2O3) doped zirconia powder, most were unstable due to poor curability, and in particular, slurries containing 0.08 wt% and 0.10 wt% iron oxide (Fe2O3) doped zirconia powder showed a curing depth of less than 40 μm at a maximum curing time of 14 seconds for both 3YSZ and 4YSZ.

[0225] The color of the slurry changed to a deep red as the iron oxide (Fe2O3) content increased.

[0226] Meanwhile, in a DLP system, the curability of a material depends on the optical properties of the material and the total energy dose supplied through the UV source. To obtain a printable curing depth of the ceramic slurry, an appropriate energy dose must be supplied. The required amount of energy is determined by the light exposure time and the light intensity of the UV source. The device used in the example has a capacity of 30 mW / cm². 2 Since it operates at an intensity of 405 nm wavelength, the amount of energy is controlled only through the curing time at a constant intensity. Undoped 3YSZ, 4YSZ, and 5YSZ did not differ significantly in optical properties, so they all had similar curing depths for a given curing time. However, depending on the doping amount of iron oxide (Fe2O3), the color of the slurry turned a deep red, and the curing depth decreased sharply due to UV absorption caused by the color. Iron oxide (Fe2O3) significantly absorbed the 405 nm wavelength, which is the operating wavelength of DLP, ultimately reducing the dose available for radical formation and monomer crosslinking; consequently, UV penetration was low, resulting in a lower curing depth and requiring a longer curing time to ensure a printable curing depth.

[0227]

[0228] <Experimental Example 1-4> Evaluation of Printability According to Iron Oxide (Fe2O3) Content

[0229] To evaluate the printability according to the iron oxide (Fe2O3) content, a 2 mm thick disc sample was prepared using the method of Manufacturing Example 1-2, and the results are shown in Fig. 5.

[0230] Here, the slurry used was the slurry of Preparation Example 1-2, but the raw powder used was a raw powder containing 3YSZ, 4YSZ, and 5YSZ powders doped with various iron oxide (Fe2O3) contents, excluding 0.12 wt% in Table 1. The slurry containing 3YSZ and 4YSZ raw powders doped with 0.12 wt% iron oxide (Fe2O3) did not cure well, making it difficult to produce a disc.

[0231] In addition, since material printability and layer adhesion are determined by the curing depth at a given curing time, the layer thickness during printing was appropriately adjusted according to each slurry composition. Specifically, for slurries containing zirconia powder doped with up to 0.04 wt% iron oxide (Fe2O3) (i.e., 0 wt%, 0.02 wt%, and 0.04 wt% Fe2O3), a layer thickness of 20 μm was printed and cured for curing times of 1 second, 2 seconds, and 4 seconds, respectively, and a 5YSZ disc not doped with iron oxide (Fe2O3) was also printed with a layer thickness of 20 μm at a curing time of 1 second.

[0232] However, in the case of slurries containing zirconia powder doped with 0.06 wt%, 0.08 wt%, and 0.10 wt% iron oxide (Fe2O3), the curability was poor, so the layer thickness was reduced to 15 μm and cured for curing times of 6 seconds, 8 seconds, and 12 seconds, respectively.

[0233] During the printing of the green body, the value was set to at least half the curing depth at a given curing time to adjust the layer thickness within the printable range and ensure strong interlayer adhesion; however, due to the low curability and weak bonding between layers of the slurry doped with more than 0.06 wt% iron oxide (Fe2O3), layer separation occurred while some of the printed layer remained on the film instead of accumulating on the build plate surface. To compensate for this, several conditions were maintained during the printing process: First, the pre-delay time, which is the time the build plate contacts the slurry / film (until UV is turned on), was set to 5 seconds to ensure the slurry is uniformly dispersed beneath the build plate and to empty any trapped air bubbles during this time. Additionally, a post-delay time, which is the time until the build plate begins to be rinsed after UV curing (8 seconds), was used to facilitate photocrosslinking and reaction termination. Finally, the lift speed (the speed at which the build plate moves upward after each layer is printed) was adjusted to a minimum of 1 mm / s to ensure gradual separation between the build plate and the film.

[0234]

[0235] Synthesizing the results, it was found that 3YSZ, 4YSZ, and 5YSZ slurry rheology was optimized and printability based on iron oxide (Fe2O3) doping was analyzed, and that all 3YSZ, 4YSZ, and 5YSZ slurries can have a possible viscosity, and that by including the optimal content of BYK111 dispersant (3 wt%, 4 wt%, and 5 wt% for 3YSZ, 4YSZ, and 5YSZ, respectively), the solid loading amount (i.e., ceramic powder content) can be increased.

[0236] In addition, while the curability of 3YSZ, 4YSZ, and 5YSZ slurries that are not doped with iron oxide (Fe2O3) is excellent, the curing depth decreases as the amount of iron oxide (Fe2O3) doping increases, and the smallest curing depth is found in 3YSZ and 4YSZ slurries doped with 0.10 wt% iron oxide (Fe2O3). Therefore, when iron oxide (Fe2O3) is included, a curing time is required to achieve a sufficient curing depth, and consequently, over-curing may occur, so it can be seen that measures to prevent over-curing are necessary.

[0237]

[0238] Experimental Example 2: Evaluation of Sintered Structure Properties

[0239] <Manufacturing Example 2> Degreasing and Sintering

[0240] To remove organic material contained in the slurry for forming a molded body using a DLP printing system, the disc prepared according to Preparation Example 1-2 was degreased in a nitrogen (N2) atmosphere. The degreased conditions were selected based on the thermal behavior of the material determined by thermogravimetric analysis / differential scanning calorimetry (TG / DSC; SDT Q600, TA instrument, USA). Specifically, the disc was heat-treated up to 600°C at temperatures of 110°C, 210°C, 300°C, 375°C, 410°C, and 600°C, respectively, with a slow heating rate of 0.5°C / min and a residence time of 4 hours. Subsequently, the degreased structure was sintered in air for 2 hours at a heating rate of 5°C / min up to 300°C, 1°C / min from 300°C to 530°C, 5°C / min from 530°C to 900°C, and 1°C / min from 900°C to 1500°C.

[0241]

[0242] <Experiment Example 2-1> Color Evaluation of Sintered Structures

[0243] The color of the sintered structure prepared in Example 2 was evaluated using the following method, and the results are shown in FIG. 6 and FIG. 7a to 7d.

[0244] Color evaluation method

[0245] Color measurements of sintered bodies containing or not containing iron oxide (Fe2O3) were performed using a smart color measuring instrument (ColorMeter Pro, Hangzhou Color Spectrum Technology Co., LTD), and CIELAB coordinates (L*, a*, and b*) were recorded. L* represents the degree of brightness (0 = black, 100 = white), a* (green-red) and b* (blue-yellow) can have positive or negative values, and the color difference (ΔE*) was calculated using Equation 1 below.

[0246] <Equation 1>

[0247]

[0248] Figure 6 shows the color measurement results. As shown in Figure 6, the sintered body without iron oxide (Fe2O3) has a completely white appearance, and it can be seen that the color gradually changes as the iron oxide (Fe2O3) content increases in the 3YSZ and 4YSZ samples.

[0249] Figures 7a to 7d show the CIELAB color parameters (L*, a*, and b*) and color difference (ΔE*) values ​​measured against a black background. Referring to Figures 7a to 7d, regarding the L* value, which indicates the degree of brightness, the L* value of the sintered body containing 3YSZ without iron oxide (Fe2O3) doping was approximately 92, which is slightly higher than the L* values ​​of 4YSZ and 5YSZ (L*: 87 and 82). For the sintered bodies containing 3YSZ and 4YSZ, it can be confirmed that the L* value decreased significantly as the doping amount of iron oxide (Fe2O3) was increased, causing the color to shift toward a darker tone. For example, the L* value of the 3YSZ and 4YSZ disks doped with 0.10 wt% iron oxide (Fe2O3) was less than 67.

[0250] In addition, the a* and b* values ​​were nearly similar across all sintered bodies that did not contain iron oxide (Fe2O3), but when iron oxide (Fe2O3) was included, 3YSZ showed higher values ​​compared to 4YSZ, even when containing the same amount of iron oxide (Fe2O3). Sintered bodies containing 4YSZ doped with 0.02 wt% and 0.04 wt% iron oxide (Fe2O3) exhibited a slightly green color, as described by the negative a* value. As the iron oxide (Fe2O3) content increased, the color of the sintered bodies changed to the red and yellow regions. The EΔ value also increased to a maximum of 20 or more at 0.10 wt% iron oxide (Fe2O3) compared to 0.02 wt% iron oxide (Fe2O3) (ΔE* < 5) in both 3YSZ and 4YSZ. The color of the sintered body containing iron oxide (Fe2O3) appeared uniform across the entire area, indicating that the doped iron oxide (Fe2O3) was uniformly distributed within 3YSZ and 4YSZ. The coloring mechanism of 3YSZ and 4YSZ is metal ions (Fe 3+It is related to the coloring of ), which strongly absorbs ultraviolet light and produces a yellow color. CIELAB color space values ​​(L*, a*, and b*) represent the color change of the sintered discs and were pronounced in 3YSZ and 4YSZ when the doping amount of iron oxide (Fe2O3) was high. Since the color was measured against a black background, the lower L* values ​​of 4YSZ and 5YSZ compared to 3YSZ indicate that slightly more light was transmitted through the sintered body, resulting in reduced brightness (L* values). Similarly, the a* and b* values ​​were important for improving the red-yellow appearance of the samples, as these two colors are critically important for the natural tooth shape. In particular, since the yellow shade of natural teeth is dominant over other colors and varies from person to person, the type of tooth color can be easily controlled through the b* value. ΔE* increased significantly with increasing iron oxide (Fe2O3) doping in 3YSZ and 4YSZ, and can be very easily detected with the naked eye because the human eye has difficulty detecting color differences at ΔE* < 1.7. In the example, the content of the coloring agent, iron oxide (Fe2O3), was used in the range of 0 to 0.10 wt%, but the content of the coloring agent can be easily adjusted according to the type of dental crown and can be applied equally to mimic the characteristics of all age groups and all colors required by patients.

[0251]

[0252] <Experimental Example 2-2> Evaluation of Characteristics of Sintered Structures

[0253] The properties of the sintered structure prepared in Example 2 were evaluated using the following method, and the results are shown in Table 2 and Figures 8a to 8c and 9 below.

[0254] Characteristic evaluation method

[0255] In order to define the optimal sintering temperature and analyze the effect of iron oxide (Fe2O3) doping, discs printed by the method of Preparation Example 1-3 using zirconia powder that was not doped with iron oxide (Fe2O3) or doped with 0.1 wt% were sintered by the method of Preparation Example 1-4, with maximum sintering temperatures of 1450℃, 1500℃, and 1550℃.

[0256] For the sintered body prepared in this way, the sintering density was calculated using the Archimedes method (ASTM C373-88) (XPE205, Mettler Toledo, Switzerland), and the three-point bending strength was measured using a universal testing machine (RB-305 MICROLOAD, R&B, Korea).

[0257] Fe2O3(wt.%)3YSZ (%)4YSZ (%)5YSZ (%)(1450°C)(1500°C)(1550°C)(1450°C)(1500°C)(1550°C)(1450°C)(1500°C)(1550°C)0 .097.1099.0599.0696.3198.8398.7995.7898.1098.120.0297.0299.098.9596.2298.7598 .78---0.0496.8298.9698.9096.0198.6698.59---0.0696.5598.9098.8995.6798.5598.54---0.0895.7698.8198.8095.0298.4398.45---0.1095.0998.7298.7194.1998.3698.29---

[0258]

[0259] Table 2 shows the densities of zirconia sintered bodies sintered at three different temperatures (1450°C, 1500°C, and 1550°C). High densities were achieved at 1500°C or higher in all sintered bodies. 3YSZ, 4YSZ, and 5YSZ sintered bodies without iron oxide (Fe2O3) exhibited maximum densities of 99.05%, 98.83%, and 98.10%, respectively, and as the iron oxide (Fe2O3) content increased, the density decreased slightly, so that 3YSZ and 4YSZ sintered bodies doped with 0.10 wt% iron oxide (Fe2O3) were densified to maximum 98.72% and 98.36%, respectively, at a sintering temperature of 1500°C.

[0260] Figures 8a to 8c all show the horizontal and vertical sintering shrinkage rates of 3YSZ, 4YSZ, and 5YSZ sintered bodies sintered at 1500℃.

[0261] Slightly more shrinkage occurred in 3YSZ than in 4YSZ and 5YSZ sintered bodies in both horizontal and vertical planes. In 3YSZ, 4YSZ, and 5YSZ sintered bodies not doped with iron oxide (Fe2O3), the shrinkage rate in the vertical plane (Z direction) was slightly higher than in the horizontal plane (X direction), but was approximately 24%, 23%, and 22% in both the vertical and horizontal planes, respectively.

[0262] In addition, in 3YSZ and 4YSZ sintered bodies, a tendency for sintering shrinkage to decrease slightly was observed when the iron oxide (Fe2O3) content increased. For 3YSZ and 4YSZ sintered bodies, compared to those not doped with iron oxide (Fe2O3), the sintering shrinkage rates of the sintered bodies doped with 0.10 wt% iron oxide (Fe2O3) were X / Z shrinkage rates of 23.12% / 23.45% and 22.30% / 22.59%, respectively.

[0263] Figure 9 shows SEM images of the surfaces of disks prepared from 3YSZ, 4YSZ, and 5YSZ that were either undoped with iron oxide (Fe2O3) or doped with 0.10 wt% iron oxide (Fe2O3), after surface polishing and thermal etching were performed following sintering at 1500°C. The microstructures of the 3YSZ, 4YSZ, and 5YSZ samples were generally homogeneous, but some residual pores were observed in the 3YSZ and 4YSZ samples, which had a high iron oxide (Fe2O3) doping amount of 0.10 wt%. Meanwhile, a high amount of yttria promoted particle growth, so the average particle size was highest in the order of 5YSZ > 4YSZ > 3YSZ, and a similar trend was observed when iron oxide (Fe2O3) was doped into 3YSZ and 4YSZ.

[0264] The density of ceramic materials produced through 3D printing depends on the solid loading during the green body printing step in addition to degreasing and sintering conditions. However, in this experimental example, the solid loading was maintained at 43 vol% for slurry stability and fluidity in a film-feed type DLP system. Consequently, the maximum density achieved was approximately 99.0%, which was observed when 3YSZ was used without iron oxide (Fe2O3) doping and with the smallest amount of yttria doping, and it can be confirmed that the density decreased slightly as the doping amounts of yttria and iron oxide (Fe2O3) increased.

[0265] In both dopants, the main reason for the decrease in density as the doping amount increases can be attributed to particle growth. Referring to Figure 8, it can be seen that the size of cubic particles clearly increases, particularly in 4YSZ and 5YSZ without iron oxide (Fe2O3) doping, and a similar pattern is observed in specimens containing 0.10 wt% iron oxide (Fe2O3). In the case of 3YSZ, the orthorhombic phase is dominant, but iron oxide (Fe2O3) doping promotes the growth of cubic particles. As particle size increases, density decreases and sintering shrinkage is limited, whereas small and fine particles, unlike larger particles, increase density and overall sintering shrinkage.

[0266] The prominent reason for particle growth due to iron oxide (Fe2O3) doping is related to the generation of oxygen vacancies, which can be explained by Equation 2 below.

[0267] <Equation 2>

[0268]

[0269]

[0270] Here, Fe' Zr is an Fe atom occupying a Zr lattice position, and V O is a vacancy at an oxygen lattice position, and 0 O x represents an oxygen atom occupying a normal lattice position. An increase in oxygen vacancies is Fe 3+ Increasing the ion concentration increases the densification and grain growth rate, thereby increasing the average size of the formed particles. Iron oxide (Fe2O3) typically melts at approximately 900°C, which is much lower than the sintering temperature of zirconia. This is distributed at the grain boundaries and promotes grain growth along with residual pores within the structure, which appears to be the main cause of strength loss. Although it is known that the addition of iron oxide (Fe2O3) can increase shrinkage due to the initial melting temperature, additional shrinkage appears to be limited by pore formation.

[0271] FIGS. 10a to 10c are drawings showing the bending strength of disks made of 3YSZ, 4YSZ, and 5YSZ that are not or doped with iron oxide, after sintering at 1450°C, 1500°C, and 1550°C.

[0272] Maximum bending strength was achieved at 1500°C for all 3YSZ, 4YSZ, and 5YSZ. For undoped samples, 3YSZ exhibited the highest strength of 745.64 MPa at 1500°C, while 4YSZ and 5YSZ showed strengths of approximately 708 MPa and 550 MPa, respectively, at the same sintering temperature. Additionally, increasing the doping amount of iron oxide (Fe2O3) resulted in a slight decrease in strength values ​​for both 3YSZ and 4YSZ; specifically, the strengths of 3YSZ and 4YSZ decreased to 678.26 MPa and 645.54 MPa, respectively, when doped with 0.10 wt% iron oxide (Fe2O3). Although a larger amount of yttria was desirable to maintain the cubic structure of ZrO2 (4YSZ and 5YSZ), it appears that the bending strength was reduced due to grain growth. Meanwhile, the decrease in bending strength due to iron oxide (Fe2O3) doping can be attributed to residual pores in addition to grain growth.

[0273] As a result, both yttria and iron oxide promoted grain growth, and in the case of 3YSZ and 4YSZ materials doped with 0.1 wt% iron oxide (Fe2O3), the sintering shrinkage rate and bending strength tended to decrease slightly due to the doping of yttria and iron oxide (Fe2O3) accompanied by residual pores.

[0274]

[0275] Synthesizing the results, regarding the characteristics of zirconia structures containing different amounts of iron oxide (Fe2O3), it can be seen that increasing the iron oxide (Fe2O3) content results in a decrease in the L* value of each CIELAB color space parameter (L*, a*, and b*), changing from white to dark, while increasing the a* and b* values ​​results in a more red and yellow color, indicating that zirconia structures with color gradients can be manufactured by controlling the doping amount of iron oxide (Fe2O3) in the zirconia structures.

[0276] In addition, it can be seen that as the doping content of yttria and iron oxide (Fe2O3) increases, it causes particle growth and / or residual pores in the sample, which partially reduces bending strength, sintering shrinkage rate, and density, but the overall composition exhibits excellent bending strength, sintering shrinkage rate, and density.

[0277]

[0278] Experiment Example 3: Evaluation of Shape Precision According to Application of Flashing Light Irradiation

[0279] <Manufacturing Example 3-1> Preparation of photocurable composition (slurry) (2)

[0280] ingredient

[0281] Commercially available 3 mol% yttria-stabilized zirconia (ZrO2) (CY3Z, Zirpro Saint Gobain, France), titania (TiO2) (KRONOS 1002, KRONOS® USA), and alumina (Al2O3) (AKP-20, Kojundo Chemical Laboratory, Japan) were used as ceramic powder materials to prepare various ceramic slurries. As photocurable resins, two monomers of trimethylolpropane triacrylate (TMPTA) and 1,6-hexanediol diacrylate (HDDA) and a non-reactive diluent polypropylene glycol (PPG P400) (Sigma-Aldrich, USA) were included. Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) (BASF, Germany) was used as a photoinitiator (PI). DISPERBYK-111 (BYK111; Altana AG, Germany) was added as a dispersant to disperse and stabilize the ceramic powder in the slurry.

[0282]

[0283] Slurry manufacturing

[0284] The resin was prepared by adding TMPTA and HDDA in a weight ratio of 3:17. PPG diluent and PI (Irgacure 819) were added at 25% and 0.4% of the total resin, respectively, and uniformly mixed in a planetary centrifugal mixer (ARE-310, THINKY, USA) at a speed of 2,000 revolutions per minute for 5 minutes. Subsequently, the ceramic powder and dispersant BYK-111 were added, and the slurry was mixed for an additional 10 minutes. To uniformly distribute and disperse the ceramic powder within the resin, the BYK-111 content was optimized from 1% to a maximum of 6% by weight of the powder. Slurry rheology was measured using a TS rheometer (Discovery HR-1, TA Instruments, USA) under isothermal conditions (40°C) at shear rates ranging from 1 to 100 s⁻¹. -1It was measured at. To study the flashing effect according to solid loading, ceramic slurries of zirconia and titania were prepared with four different powder contents (40 vol%, 43 vol%, 45 vol%, 47 vol%).

[0285]

[0286] <Manufacturing Example 3-2> Manufacture of printed structure, degreasing structure and sintered structure (2)

[0287] A zirconia and titania slurry containing 45 volume% of ceramic powder from Manufacturing Example 3-1 was used, and a lattice structure of the 3D model of Fig. 11 was printed using continuous or flashing light.

[0288] The zirconia printed structure (green body) took a total curing time of 2 seconds to print with a layer thickness of 30 μm, and the titania printed structure (green body) took a total curing time of 4 seconds to print with a layer thickness of 15 μm.

[0289] Each printed structure (green body) was degreased in nitrogen (N2) at a maximum temperature of 600°C to safely remove the resin components without causing structural defects. Afterward, the degreased brown bodies of zirconia and titania were sintered in air at 1500°C and 1200°C, respectively.

[0290] Evaluation Method

[0291] Slurry Curability and Overcuring Evaluation Method

[0292] A three-dimensional (3D) model of a window structure having three different square pores of 3 × 3 (mm), 2 × 2 (mm), and 1 × 1 (mm) was sliced ​​and subjected to a UV wavelength of 405 nm and 30 mWc m-2 It was used in a continuous film-type DLP printer (in-house manufactured) operating at an intensity (see Fig. 11).

[0293] A ceramic slurry printed layer was exposed to a UV projector and cured for curing times of 1 second, 2 seconds, 4 seconds, and 6 seconds using continuous or flashing. Here, the curing time for flashing lighting is defined as 'time per flash × number of flashes'. For example, if the total curing time is 1 second, the total curing time is 1 second when 0.2-second flashes are repeated 5 times.

[0294]

[0295] A single printed layer of each group was washed with HDDA, and the curing depth was measured using a 54-micrometer (High-Accuracy Digimatic® Digital Micrometer; Mitutoyo, Kawasaki, Japan). Images of the printed layer were collected using a mobile camera (iPhone 13 Pro Max, ultra-wide camera - 13mm, f1.8, 3 MP), and the degree of overcuring was quantified using ImageJ

[0100] software. Based on this, geometric overgrowth was calculated by Equation 3 below.

[0296] <Equation 3>

[0297]

[0298]

[0299] When evaluating based on flash time, the off time between consecutive flashes was set to a constant 0.5 seconds, and when evaluating based on off time, the flash time was set to a constant 0.2 seconds for zirconia and 0.5 seconds for titania.

[0300]

[0301] Measurement of bending strength and sintering density

[0302] The bending strength of the printed structure (green body) and the sintered structure was measured using a general-purpose testing machine (RB-305 MICROLOAD, R&B, Korea), and the sintered density was measured using the Archimedes method (XPE205, Mettler Toledo, Switzerland).

[0303]

[0304] <Experimental Example 3-1> Effect of Flashing Lighting on Preventing Over-curing in Zirconia Slurry

[0305] To verify the flashing light effect on overcuring in the zirconia slurry, a single layer was printed using zirconia slurries prepared in Preparation Example 3-1 containing 40, 43, 45, and 47 volume% of zirconia powder, and evaluated using the aforementioned 'method for evaluating slurry curability and degree of overcuring,' and the results are shown in FIG. 12.

[0306] As shown in Figure 12, overcuring increased as the total curing time increased from 1 second to 6 seconds, and showed a tendency to increase as the ceramic powder content increased.

[0307] In the case of continuous lighting without flashing (No Flash), the overcuring rate was relatively high due to UV scattering even with short curing times; in contrast, when flashing lighting with flashing times of 0.2 seconds, 0.5 seconds, and 1 second was used, it was confirmed that overcuring was significantly reduced. Specifically, it was found that excessive growth was most effectively controlled at the lowest flashing time of 0.2 seconds.

[0308]

[0309] For all four slurries, during a total curing time of 1 second, a very accurate structure was printed when flash irradiation (0.5 seconds and 0.2 seconds) was used, and in particular, the low flashing time of 0.2 seconds was found to be very effective in maintaining shape fidelity and significantly reducing overcuring, whereas when continuous irradiation (no flash) was used, significant overcuring occurred, and at curing times of 2 seconds or more, the porous structure was completely overcured due to extensive scattering, and no square pores were visible regardless of the ceramic content of the slurry.

[0310] When examining the graphs comparing the quantitative geometric overgrowth observed in all structures cured using flashing illumination versus those cured using continuous illumination without flashing, a trend of reduced overgrowth was observed in all four slurries when flashing illumination was used. Specifically, for the 40 vol% slurry, overgrowth of more than 16% was observed at a curing time of 1 second when continuous illumination was used, whereas it decreased to less than 8% when flashing illumination was applied for 0.2 seconds. Structural overgrowth was intensified at longer light exposure times and higher solid loads. For example, the 47 vol% slurry showed overgrowth of more than 45% under continuous irradiation (total curing time) of 2 seconds, while it decreased significantly to approximately 15% under flashing illumination. Shorter illumination times imply that the reduced UV dose can be used for scattering at the minimum scattering distance, as most of the reduced UV dose is used for radical formation within the exposed area of ​​the pattern and minimal radical diffusion occurs in the unexposed area. Therefore, the pattern was found to have the highest accuracy with the least geometric overgrowth during a short lighting period.

[0311]

[0312] <Experimental Example 3-2> Effect of Flashing Illumination on Preventing Over-curing in Titania Slurry

[0313] To verify the flashing light effect on overcuring in the titania slurry, a single layer was printed using titania slurries prepared in Preparation Example 3-1 containing 40, 43, 45, and 47 volume% of titania powder, and the slurry was evaluated using the aforementioned 'method for evaluating curability and degree of overcuring,' and the results are shown in FIG. 13.

[0314] Similar to zirconia, titania also showed a tendency for overcuring to increase as the total curing time increased from 1 second to 6 seconds, and as the ceramic powder content increased. Furthermore, when continuous illumination (no flash) was used, the overcuring rate was relatively high due to UV scattering even at short curing times; in contrast, when flash illumination with flash times of 0.2, 0.5, and 1 second was used, overcuring was significantly reduced, and excessive growth was found to be most effectively controlled at the lowest flash time of 0.2 seconds. Specifically, for a slurry with a content of 40 volume%, overgrowth dropped to less than 10% after a total curing time of 6 seconds using flash irradiation, whereas significant overgrowth of over 70% occurred with continuous irradiation. For all ceramic powder contents, when a total curing time of 2 seconds and a flash time of 0.2 seconds were used, overgrowth remained within a very small range of 12%.

[0315] In addition, it can be confirmed that overgrowth is effectively controlled even when using an ignition time of 0.5 seconds. For example, for slurries with 40 and 43 volume% content and a total curing time of 2 seconds, overgrowth was less than 11% when flashing irradiation was used, but when continuous irradiation was used, the overgrowth growth rates were 20% and 25%.

[0316] Titania exhibited better precision control via flash irradiation compared to zirconia due to the material's high UV absorption characteristics. Since titania powder absorbs a significant amount of UV light in the DLP operating wavelength range (405 nm) compared to alumina and zirconia powders, the amount of UV energy available for photopolymerization reactions at similar curing times is much lower, resulting in scattering unlike in the case of ZrO2. Furthermore, due to the high refractive index of TiO2, curing is difficult at short curing times, and longer curing intervals are required to achieve printable curing depth values. However, longer curing times to achieve a printable curing depth lead to over-curing beyond the exposed area due to scattering. Therefore, for titania with these characteristics, flash irradiation can be a highly effective method as it reduces over-curing even with longer curing times.

[0317]

[0318] <Experiment Example 3-3> Evaluation of Curing Depth According to Flashing Lighting

[0319] For printing using zirconia and titania slurries, the curing depth according to flash time was evaluated and is shown in Figures 14 and 15.

[0320] As shown in Figures 14 and 15, under continuous lighting, the curing depth increased with increasing curing time and decreased with increasing solid loading. A similar trend was observed in the case of flashing lighting, but the curing depth was slightly lower compared to the case using continuous lighting.

[0321] Referring to Figure 14, in the case of zirconia, when using continuous lighting, the curing depth was highest when containing the lowest amount of ceramic powder (40 vol%). For the 40 vol% slurry, at a total curing time of 1 second, the curing depth was 52 μm under continuous lighting, whereas it decreased to approximately 43 μm when using flashing irradiation with a lighting time of 0.2 seconds. Additionally, when a higher ceramic content was loaded into the slurry, the curing depth decreased further; the curing depth of the 47 vol% slurry decreased to 48 μm under continuous lighting conditions at a total curing time of 1 second, and decreased to 39 μm under flashing irradiation with a lighting time of 0.2 seconds.

[0322] Referring to Fig. 15, in the case of titania, the slurry curability was not as good as that of zirconia, and the curing depth did not reach 50 μm (no flash) even at the lowest solid slurry content (40 vol%). As the ceramic content increased, the curing depth showed a decreasing trend, and the lowest curing depth value was observed for the 47 vol% slurry (<44 μm) at a total curing time of 6 seconds (no flash).

[0323]

[0324] <Experimental Example 3-4> Evaluation of Over-curing and Curing Depth According to Off-Time

[0325] In order to evaluate the degree of overcuring and the curing depth according to the off time, a single layer was printed using zirconia (45 volume%) and titania (45 volume%) slurries, respectively, and evaluated using the aforementioned 'method for evaluating slurry curability and degree of overcuring', and the results are shown in FIG. 16 and FIG. 17a and 17b.

[0326] Referring to Fig. 16, for both materials, structural accuracy increased as the off-time increased, regardless of the total curing time; in particular, when the off-time was greater than 5 seconds, printing was achieved with high shape fidelity, and high accuracy was maintained even when cured for a high total curing time of 6 seconds. However, over-curing did not decrease significantly when the off-time was 10 seconds or more. Looking at the geometric overgrowth graph, it can be seen that at an off-time of 10 seconds, overgrowth decreased significantly to less than 4% at all values. For example, when the off-time was 0.5 seconds, overgrowth was nearly 40% for zirconia and over 55% for titania, whereas when the off-time increased to 10 seconds, these values ​​decreased significantly to less than 4%. However, even when the off-time was increased to 20 seconds, overgrowth did not decrease significantly further.

[0327] In addition, referring to Figures 17a and 17b, the curing depth of the two slurries decreased slightly as the off time increased.

[0328] Specifically, for the zirconia slurry, when cured with a 0.5-second off-time between a 0.2-second flash time, the curing depth was approximately 60 μm over a total curing time of 2 seconds; however, as the off-time increased to 5 seconds, the curing depth gradually decreased to less than 50 μm. Additionally, for the titania slurry, when cured with a 5-second off-time between a 0.5-second flash time, the curing depth dropped to less than 25 μm during a total curing time of 2 seconds. The lowest curing depth was recorded at an off-time of 10 seconds, and the curing depth remained unchanged regardless of the total curing time exceeding 2 seconds. Furthermore, the curing depth was identical at off-times of 10 and 20 seconds.

[0329]

[0330] <Experimental Example 3-5> Evaluation of Shape Precision of a 3D Structure

[0331] 3D printed structures (green body), degreased structures (brown body), and sintered structures (sintered body) of zirconia and titania slurries (45 volume% each) prepared according to Manufacturing Example 3-2 under continuous lighting and flashing lighting, respectively, are shown in FIG. 18a and 18b.

[0332] For the zirconia slurry, a grid structure with a pore size of 2 × 2 mm was printed with a layer thickness of 30 μm, and the total curing time was set to 2 seconds for both structures fabricated under continuous lighting and flashing lighting, respectively. As shown in Fig. 18a, when continuous lighting was used, excessive overcuring occurred due to UV scattering, resulting in low structural accuracy after printing. Specifically, the top surface of the grid (Green body-top view) was completely overcured (100% overgrowth), the square pores were completely invisible, and the surface appeared completely flat. On the other hand, as shown in Fig. 18b, when flashing lighting (on for 0.2 seconds, off for 5 seconds) was used, overcuring was significantly reduced to less than 5%, and the structure showed high accuracy, being very close to the original 3D model.

[0333] In the case of titania, the total curing time was set to 4 seconds to print the same grid structure with a layer thickness of 15 μm using both printing types, and printing was performed with 0.5 seconds on and 5 seconds off due to low curability. As shown in a comparison of Figures 18a and 18b, it can be seen that in the titania slurry, excessive overcuring occurred when continuous lighting was used, whereas overcuring was significantly reduced to less than 10% when flashing lighting was used.

[0334]

[0335] <Experimental Example 3-5> Evaluation of 3D Structural Properties

[0336] The relative density and bending strength of the sintered structures of Figures 18a and 18b were measured and are shown in Table 3 below.

[0337] Sintering Density (%) Bending Strength (MPa) Molded Body Sintered Body Type ZrO2 TiO2 ZrO2 TiO2 ZrO2 TiO2 Continuous Irradiation 99.05% 98.75% 21.3 ± 2.8 17.9 ± 3.9 15.6 ± 30.2 58.3 ± 8.3 Flash Irradiation 98.98% 98.72% 19.2 ± 3.4 15.2 ± 2.7 701.7 ± 40.8 54.1 ± 6.7

[0338]

[0339] The relative density was approximately 99% for zirconia (sintered at 1500℃) and approximately 98% for titania (sintered at 1200℃), which was similar regardless of the printing method, and the bending strength was also similar, with 700 MPa or more for zirconia and 50 MPa or more for titania.

[0340]

[0341] In summary, the results of comparing continuous and flashing lighting methods for DLP-based AM systems to overcome the problem of scattering-induced overcuring during ceramic printing show that when flashing lighting is used, scattering-induced overcuring is better controlled, particularly when using short lighting times and relatively long off times, thereby improving printing accuracy.

[0342]

[0343] Experimental Example 4: Fabrication of a dental crown with color and translucency gradient

[0344] <Manufacturing Example 4-1> Preparation of a Photocurable Composition (Slurry) for Manufacturing Dental Zirconia 3D-Printed Objects

[0345] Six slurries were prepared by the method of Manufacturing Example 1-1 to print zirconia dental crowns of color and translucency grades, including 3YSZ doped with 0.10 wt% iron oxide (Fe2O3), 4YSZ doped with 0.08, 0.06, 0.04, or 0.02 wt% iron oxide (Fe2O3), or 5YSZ (not doped with iron oxide (Fe2O3)) as raw powder.

[0346]

[0347] <Manufacturing Example 4-2> Manufacturing of Crown Structure

[0348] A crown with gradients in color and translucency was printed according to the design configuration shown in FIG. 19. Here, the color gradient was achieved through doping with iron oxide (0.0 wt% to 0.10 wt%), and the translucency gradient was achieved through three types of yttria-stabilized zirconia (3,4 and 5 mol% YSZ). More specifically, the lower portion (neck portion) of the crown (30% of the total crown composition) was composed of ceramic powder 3YSZ, 20% of the 30% of 3YSZ used was 3YSZ doped with 0.10 wt% iron oxide (Fe2O3), and 10% was 3YSZ doped with 0.08 wt% iron oxide (Fe2O3). The middle portion of the crown (30% of the total crown composition) was composed of 4YSZ ceramic powder, and each 10% was divided into 4YSZ doped with 0.06 wt%, 0.04 wt%, and 0.02 wt% iron oxide (Fe2O3). Finally, the top portion of the crown (incisor portion) (40% of the total crown composition) was composed solely of 5YSZ without iron oxide doping.

[0349]

[0350] In addition, the crown was printed with a layer thickness of 15 μm using continuous or flashing illumination. The printer intensity was 30 mW / cm². 2 The curing time was appropriately adjusted according to each slurry composition. The delay time was maintained at 10 seconds, and the lift speed was set to 1 mm / second. To ensure stability and smooth flow, the optimal slurry was supplied in a controlled manner through the doctor blade of the slurry tank, and all slurries were used only once to avoid the possibility of contamination from recycling.

[0351]

[0352] The printed crown (green body) was held for 4 hours at 110°C, 210°C, 300°C, 375°C, 410°C, and 600°C, respectively, at a slow heating rate of 0.5°C / min according to TGA results, and degreased in a nitrogen atmosphere up to 600°C. The degreased structure of the crown (brown body) was air sintered at 1500°C for 2 hours.

[0353]

[0354] Evaluation Method

[0355] Evaluation of slurry curability and overcuring

[0356] To measure the curing depth and geometric overgrowth (to determine structural accuracy) of all slurries, three-dimensional (3D) models of window structures with three different square pores of 3 × 3 (mm), 2 × 2 (mm), and 1 × 1 (mm) were sliced ​​and subjected to UV wavelengths of 405 nm and 30 mWc m-2 It was used in a continuous film-type DLP printer (in-house manufactured) operating at an intensity (see Fig. 11).

[0357] A ceramic slurry printed layer was exposed to a UV projector and cured using continuous or flashing. When flashing, it was cured using a flashing method that repeated 0.2 seconds of on and 1 second of off, and the curing depth and geometric overgrowth were measured.

[0358]

[0359] Color evaluation

[0360] The transparency parameter (TP) of the three-dimensional structure was calculated according to Equation 4 below, and ideally calculated using the color difference for a black and white background to evaluate the translucency grade.

[0361] <Equation 4>

[0362]

[0363] Here, L B * , a B* , b B * is a color parameter with a black background, and L W * , a W * , b W * is a color space value with a white background.

[0364]

[0365] <Experimental Example 4-1> Flashing Lighting Effect for Gradient-Functional Crown Structure

[0366] For the slurry prepared in Manufacturing Example 4-1, a single layer was printed using continuous lighting and flashing lighting and evaluated using the aforementioned 'evaluation of slurry curability and over-curing degree,' and the results are shown in FIG. 20 and Table 4 below.

[0367] (Material) Iron Oxide Content (3YSZ) 0.10 wt.% (3YSZ) 0.08 wt.% (4YSZ) 0.06 wt.% (4YSZ) 0.04 wt.% (4YSZ) 0.02 wt.% (5YSZ) 0.0 wt.% Curing Depth (μm) Continuous Irradiation 37.1 ± 2.2 4 3.4 ± 2.5 4 6.6 ± 2.7 5 0.0 ± 2.8 5 2.4 ± 1.9 5 2.1 ± 1.8 Flash Irradiation 33.4 ± 1.9 3 9.5 ± 2.3 4 2.7 ± 1.6 4 5.8 ± 2.3 4 8.6 ± 2.5 4 9.3 ± 3.3 Geometric Overgrowth (%) Continuous Irradiation 88.6 ± 5.7 8 3.5 ± 6.1 7 9.2 ± 8.17 4.7 ± 6.25 9.9 ± 6.8 45.6 ± 5.4 Flashing Irradiation 8.9 ± 2.0 13.8 ± 1.8 12.9 ± 1.9 12.5 ± 1.5 11.7 ± 2.4 8.6 ± 1.7 Total Curing Time 12 sec 7 sec 5 sec 3 sec 2 sec 1 sec

[0368]

[0369] As shown in Table 4 above, the layer cured using continuous lighting exhibited significant overcuring due to scattering, particularly when the iron oxide (Fe2O3) content was high and cured for a longer curing time. Additionally, as shown in Figure 20, most pores became clogged due to overcuring. On the other hand, it was confirmed that when flashing lighting was used, the least amount of overcuring occurred for all compositions, thus preserving their structural characteristics.

[0370] In terms of curing depth, there was little difference between continuous and flashing lighting; for example, the curing depth of undoped 5YSZ was approximately 52μm and 49μm when cured for 1 second (total curing time) under continuous and flashing lighting, respectively, and similar results were observed for other compositions.

[0371] Meanwhile, regarding geometric overgrowth, it was significantly reduced to less than 10% in all composition slurries when flashing lights were used. In addition, when continuous lights were used, for 3YSZ and 4YSZ slurries doped with more than 0.06 wt% iron oxide (Fe2O3), it was close to or greater than 80%, but it was significantly reduced when cured for the same total curing time under flashing conditions of a flash time of 0.2 seconds and an off time of 1 second.

[0372] In the case of iron oxide (Fe2O3) doped slurries, as the amount of doping increases, the UV absorption rate increases, and as this increases, the curing depth decreases. Therefore, a longer curing time is required to print a stable layer during printing. However, as the curing time increases, there is a problem of overgrowth caused by UV scattering, which can be confirmed by the fact that excessive overcuring occurs when continuous lighting is used. On the other hand, it can be confirmed that printing accuracy can be significantly improved by preventing overcuring when flashing lighting is used.

[0373]

[0374] <Experimental Example 4-2> Evaluation of Shape Precision of Functional Gradient Crown 3D-Printed Structure and Sintered Structure

[0375] A 3D printed structure (green body) (left) and a sintered structure (sintered body) (right) manufactured according to Manufacturing Example 4-2 are shown in FIG. 21a and FIG. 21b.

[0376] Referring to Fig. 21a, the crown printed using continuous illumination technology was found to exhibit significant overcuring, primarily due to scattering. Due to scattering-induced overgrowth, the internal hollow regions of the crown 3D-printed structure (green body) were completely filled with cured and uncured slurries of various compositions. Additionally, as seen in the bottom section, it can be observed that the base of the crown, which should have been hollow, was formed as a densely filled structure. Furthermore, it can be confirmed that large cracks and delamination occurred in the sintered structure of the crown printed with continuous illumination. Moreover, the crown was truncated at the bottom interface, and trapped powder was clearly visible in the hollow regions.

[0377] In contrast, referring to FIG. 21b, it can be seen that the crown printed with flashing light is formed with high structural accuracy with significantly controlled overcuring, and the bottom is not filled and a hollow is well formed.

[0378]

[0379] <Experiment Example 4-3> Color Evaluation of Gradient Functional Crown 3D-Printed Structure

[0380] A photograph of a sintered body prepared with the slurry composition of Manufacturing Example 4-1 is shown in FIG. 22a, and the result of measuring translucency is shown in FIG. 22b.

[0381] As shown in Figure 22, translucency was found to increase significantly as the amount of yttria doping increased, whereas it decreased somewhat as iron oxide (Fe2O3) was doped.

[0382] The translucency of 5YSZ was the highest, and the 3YSZ sample doped with 0.10 wt% iron oxide (Fe2O3) appeared relatively opaque compared to the 4YSZ and 5YSZ disks. In addition, for the same 4YSZ material, the amount of iron oxide (Fe2O3) doping resulted in a slight decrease in light transmittance.

[0383] Furthermore, the translucency parameter (TP) values ​​reflected a similar trend. The TP value of 3YSZ (0.10 wt% Fe2O3 doping) was less than 12, whereas the 4YSZ samples had a TP value of approximately 15 for all four configurations, although there were slight differences depending on the amount of iron oxide (Fe2O3) doping. 5YSZ exhibited the highest translucency with a TP of 20 or higher.

[0384] The primary factor determining the translucency of zirconia materials is isotropy, that is, controlling the cubic phase while ensuring the same refractive index in all directions. Cubic zirconia can effectively transmit incident light without scattering that can occur at grain boundaries. Increasing the yttria content doped into zirconia powder allows for the stabilization of a more translucent cubic phase at room temperature compared to the tetragonal phase, thereby enhancing transparency.

[0385] Through the above results, it can be confirmed that the translucency of the zirconia structure can be controlled by adjusting the doping amount of yttria, and that it can also be partially controlled through the doping amount of iron oxide (Fe2O3).

[0386]

[0387] Synthesizing the results, when 3D printing zirconia dental crowns with simultaneous changes in color and translucency using continuous or flashing lighting, it was found that using continuous lighting significantly reduced printing accuracy, resulting in uncured slurry being trapped inside the hollow region of the crown and consequently causing delamination during sintering due to differences in shrinkage, whereas using flashing lighting prevented overgrowth caused by scattering, thereby maintaining the structural characteristics of the crown. From these results, it can be confirmed that zirconia crowns can be formed with high accuracy when using flashing lighting.

[0388] In addition, from the results showing that the translucency parameter (TP) value varied depending on the doping amounts of yttria and iron oxide, it can be confirmed that the translucency of zirconia crowns can be controlled by adjusting the doping amounts of yttria and iron oxide.

[0389]

[0390] Based on these results, the method for manufacturing a dental zirconia 3D printed model according to one embodiment can produce a zirconia dental crown having a gradient in color and translucency, and it can be confirmed that the manufactured zirconia dental crown has excellent structural accuracy and excellent characteristics in terms of bending strength, density, and sintering shrinkage rate.

Claims

1. A dental zirconia 3D printed object formed by a 3D printing method, A dental zirconia 3D printed structure comprising at least two types of yttria-stabilized zirconia (YSZ) doped with yttria (Y2O3) in different amounts, wherein the two or more types of yttria-stabilized zirconia are selectively doped with a coloring agent to have gradients in color and translucency.

2. In Paragraph 1, The above-mentioned mold is a dental zirconia 3D printed mold having a gradient in the content of yttria (Y2O3) and coloring agent.

3. In Paragraph 1, The above-described mold is a dental zirconia 3D printed mold having a slope in which the content of yttria (Y2O3) increases from one end to the other and the content of the coloring agent decreases.

4. In Paragraph 1, The above yttria-stabilized zirconia is a dental zirconia 3D-printed structure in which yttria is doped in the range of 1 to 10 mol% and the coloring agent is doped in the range of 0 to 0.1 weight% of the weight of the yttria-stabilized zirconia.

5. In Paragraph 1, A dental zirconia 3D printed object in which the coloring agent is iron oxide (Fe2O3).

6. In Paragraph 1, A dental zirconia 3D printed structure having a color gradient in the range where L* is 50 to 95, a* is -4 to 10, b* is 0 to 20, and ΔE* is 0 to 25 in the CIELAB color parameters, and a translucency gradient in the range where the translucency parameter (TP) value is 10 to 25.

7. In Paragraph 1, The above dental zirconia 3D printed figure is a dental zirconia 3D printed figure having a relative density of 98% or higher.

8. In Paragraph 1, The above dental zirconia 3D printed structure is a dental zirconia 3D printed structure having a strength of 500 to 800 MPa.

9. In Paragraph 1, The above dental zirconia 3D printed model is a dental zirconia 3D printed model that is a dental crown.

10. A method for manufacturing a dental zirconia 3D printed object having a gradient in color and translucency, A method for manufacturing a dental zirconia 3D printed structure, comprising the step of forming a 3D printed structure using a plurality of photocurable slurries, wherein the slurries include a photocurable resin and yttria-stabilized zirconia (YSZ) powder doped with yttria (Y2O3) and optionally doped with a coloring agent, wherein at least one of the yttria and the coloring agent is included in different amounts.

11. In Paragraph 10, The above plurality of photocurable slurries A first photocurable slurry comprising a photocurable resin and a first yttria-stabilized zirconia (YSZ) powder doped with yttria (Y2O3) and not doped with a coloring agent; and A method for manufacturing a dental zirconia 3D printed article, comprising: a first photocurable slurry comprising a photocurable resin and a second yttria-stabilized zirconia (YSZ) powder doped with yttria (Y2O3) and doped with a coloring agent in the range of 0.01 to 0.1 weight%.

12. In Paragraph 11, A method for manufacturing a dental zirconia 3D printed product, wherein at least one of the first photocurable slurry and the second photocurable slurry comprises a plurality of photocurable slurries having different yttria contents.

13. In Paragraph 11, A method for manufacturing a dental zirconia 3D printed product, wherein the above two photocurable slurries comprise a plurality of photocurable slurries having different contents of one or more of yttria and a coloring agent.

14. In Paragraph 10, A method for manufacturing a dental zirconia 3D printed product, wherein the above yttria-stabilized zirconia (YSZ) powder is doped with yttria at a concentration of 1 to 10 mol%.

15. In Paragraph 10, A method for manufacturing a dental zirconia 3D printed object, wherein the coloring agent is iron oxide (Fe2O3).

16. In Paragraph 10, A method for manufacturing a dental zirconia 3D printed product, wherein the above-mentioned photocurable slurry contains 40 to 50 volume% of the above-mentioned yttria-stabilized zirconia (YSZ) powder relative to the total volume of the slurry.

17. In Paragraph 10, A method for manufacturing a dental zirconia 3D printed model, comprising manufacturing a dental zirconia 3D printed model having a color gradient in a range where L* is 50 to 95, a* is -4 to 10, b* is 0 to 20, and ΔE* is 0 to 25 in the CIELAB color parameter, and a translucency gradient in a range where the translucency parameter (TP) value is 10 to 25.

18. In Paragraph 10, The step of forming the above 3D printed structure is, A slurry supply step of supplying any one of the plurality of photocurable slurries above onto a 3D printing device plate; A printing layer forming step of forming a printing layer by irradiating light onto a slurry supplied on the plate; and A method for manufacturing a dental zirconia 3D printed body, comprising the step of forming a 3D printed body having a gradient in color and translucency by stacking a plurality of printed layers by repeating the above-mentioned slurry supply step and printed layer formation step.

19. In Paragraph 18, A method for manufacturing a dental zirconia 3D printed structure, wherein the above-mentioned printing layer formation step involves irradiating light using a flashing method that repeatedly turns on and off.

20. In Paragraph 19, A method for manufacturing a dental zirconia 3D printed structure, wherein the printing layer forming step involves irradiating light using a flashing method that repeats a lighting time of 0.1 to 1 second and a lighting time of 0.5 seconds or more.

21. In Paragraph 19, A method for manufacturing a dental zirconia 3D printed object, wherein the above-mentioned extinguishing is performed for a period of 1 to 10 seconds.

22. In Paragraph 10, A step of degreasing the above 3D printed structure; and A method for manufacturing a dental zirconia 3D printed structure, further comprising the step of sintering a degreased structure.

Images