Zirconia workpiece

Abstract

This invention provides a zirconia workpiece for dental cutting and a method for manufacturing the same, which allows for a significant change in the translucency of the sintered body while maintaining high strength by changing the sintering temperature. [Solution] A zirconia workpiece for dental cutting is provided, which contains a stabilizer in an oxide equivalent of 5.8 mol% to 7.0 mol%, substantially free of alumina, and having a portion of the sintered body produced by sintering at 1550°C for 1 hour in which the grain size is 2.0 times or more than that of the sintered body produced by sintering at 1450°C for 1 hour.

Description

Technical Field

[0001] The present invention relates to a zirconia workpiece for dental cutting.

Background Art

[0002] In recent years, techniques for producing prosthetic devices by cutting using dental CAD / CAM systems have been rapidly spreading. As a result, it has become possible to easily produce prosthetic devices by machining workpieces made of ceramic materials such as zirconia, alumina, and lithium disilicate, and resin materials such as acrylic resin and hybrid resin.

[0003] In particular, zirconia has high strength and is clinically applied in various cases. On the other hand, fully sintered zirconia (hereinafter, zirconia fully sintered body) cannot be machined using a dental CAD / CAM system because of its very high hardness. Therefore, zirconia workpieces for dental cutting are used, which are calcined at a low firing temperature without being fully sintered and adjusted to a hardness that can be machined.

[0004] A general zirconia workpiece for dental cutting is manufactured by molding zirconia powder by press molding or the like and then calcining it at 800 to 1200°C.

[0005] The properties of a zirconia workpiece for dental cutting, that is, the properties of a zirconia fully sintered body, are affected by the properties of the zirconia powder used.

[0006] Patent Document 1 discloses that a zirconia sintered body excellent in translucency can be obtained by sintering a zirconia calcined body having a specific stabilizer concentration according to a specific sintering schedule.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] While zirconia sintered bodies with excellent translucency, as described in Patent Document 1, facilitate the reproduction of natural tooth color, color adjustment becomes difficult in cases where the abutment tooth is severely discolored or the adjacent teeth have low translucency.

[0009] Therefore, it is necessary to use different types of zirconia workpieces for dental cutting depending on the case, and dental laboratories need to keep various types of zirconia workpieces for dental cutting in stock.

[0010] The present invention aims to provide a zirconia workpiece for dental cutting and a method for manufacturing the same, which can significantly change the translucency of the sintered body while maintaining high strength by changing the sintering temperature, in order to reduce the number of types of zirconia workpieces for dental cutting held by dental laboratories and the like. [Means for solving the problem]

[0011] The inventors of the present invention investigated a zirconia workpiece for dental cutting in which the translucency of the sintered body can be significantly altered while maintaining high strength by changing the sintering temperature. As a result, they found that having a specific composition and that the grain size of a sintered body produced by sintering at 1550°C for 1 hour and a sintered body produced by sintering at 1450°C for 1 hour satisfy a specific relationship is particularly important for imparting the translucency adjustment function by sintering temperature to a zirconia workpiece for dental cutting. The details of the present invention are described below.

[0012] The present invention relates to a zirconia workpiece for dental cutting, which contains a stabilizer in an oxide equivalent of 5.8 mol% to 7.0 mol%, substantially free of alumina, and has a portion of the sintered body produced by sintering at 1550°C for 1 hour in which the grain size of the sintered body is 2.0 times or more than the grain size of the sintered body produced by sintering at 1450°C for 1 hour.

[0013] In this invention, the grain size of the sintered body produced by sintering at 1550°C for 1 hour can be 3.0 μm or larger.

[0014] In this invention, the stabilizer can be yttria.

[0015] In the present invention, a coloring element may be further included.

[0016] In this invention, the difference between the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1550°C for 1 hour and the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1450°C for 1 hour and the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1450°C for 1 hour can be 0.5%pt or more.

[0017] The present invention provides a method for manufacturing a zirconia workpiece for dental cutting, comprising one or more of the following (1) to (3). (1) A step of mixing a compound containing the elements that make up the stabilizer with zirconia powder and adding it. (2) A step of adding a solution containing a compound that includes elements constituting the stabilizer to a raw material solution of zirconia powder. (3) A step of impregnating a zirconia workpiece for dental cutting with a solution containing a compound that includes elements constituting a stabilizer.

[0018] In this invention, the element constituting the stabilizer can be yttrium.

[0019] The present invention includes step (3), Before penetration of the solution containing the compound containing the elements constituting the stabilizer, the zirconia workpiece for dental cutting can contain a stabilizer of 3.0 mol% or more and less than 6.0 mol% in terms of oxide, and can be substantially free of alumina.

[0020] In the present invention, it includes the step of (1). The zirconia powder can contain a stabilizer of 3.0 mol% or more and less than 6.0 mol% in terms of oxide, and can be substantially free of alumina.

[0021] In another aspect, the present invention can be understood as a zirconia workpiece for dental cutting in which the difference between the total light transmittance of a 1.0-mm-thick sintered body produced by sintering at 1550°C for 1 hour at a wavelength of 700 nm and the total light transmittance of a 1.0-mm-thick sintered body produced by sintering at 1450°C for 1 hour at a wavelength of 700 nm is 0.5%pt or more.

Advantages of the Invention

[0022] The zirconia workpiece for dental cutting of the present invention can significantly change the light transmittance of the sintered body while maintaining high strength by changing the sintering temperature.

Embodiments for Carrying Out the Invention

[0023] The constituent elements of the present invention will be specifically described. The present invention is a zirconia workpiece for dental cutting, which contains a stabilizer of 5.8 mol% or more and 7.0 mol% or less in terms of oxide, does not substantially contain alumina, and has a portion where the crystal grain size of a sintered body produced by sintering at 1550°C for 1 hour is 2.0 times or more the crystal grain size of a sintered body produced by sintering at 1450°C for 1 hour.

[0024] In the present invention, the "crystal grain size" refers to the diameter (Heywood diameter) of a circle having the same area as the area of the crystal grain. There is no limitation on the method for measuring the crystal grain size. For example, a zirconia sintered body can be observed by SEM, and measurement can be performed using commercially available particle image analysis software from the obtained image. In such a measurement method, in order to prevent bias in the measured values, the crystal grain size is measured from 50 or more randomly extracted crystal particles, and the median diameter thereof is taken as the crystal grain size of the sample.

[0025] In the present invention, there is no limitation on the method for controlling and adjusting the particle size difference of zirconia sintered bodies sintered at different sintering temperatures. Specifically, for example, an element that affects the particle size can be added to a zirconia workpiece for dental cutting. Examples of such elements include gallium, indium, titanium, scandium, barium, niobium, tantalum, and the like. In order to add these elements to the zirconia workpiece for dental cutting, they can be added by mixing a solution containing these elements into a zirconium oxychloride solution which is a zirconia raw material, or by mixing zirconia powder and a compound containing these elements and granulating, or by infiltrating a solution containing these elements into the zirconia workpiece for dental cutting.

[0026] Stabilizer elements such as yttrium may also affect the particle size difference. Yttrium is generally added as a solution when producing zirconia powder. Yttrium added in this way is present generally uniformly in the zirconia particles. On the other hand, yttrium can also be added by mixing zirconia powder and yttria powder and adding them, or by infiltrating a yttrium solution into a zirconia green compact. Yttrium added in this way is present outside the zirconia particles. Such a difference in yttrium distribution affects the crystal grain size difference of the sintered body, and the crystal grain size difference tends to be larger when added outside the zirconia particles. That is, yttrium added outside the zirconia particles acts not only as a stabilizer but also as a particle size difference adjuster.

[0027] The reason for the difference in grain size due to the yttrium addition method is unclear, but it is possible that the mobility of grain boundaries due to the uneven distribution of yttrium is influencing the result. Yttrium added to the outside of zirconia particles dissolves into the zirconia during sintering. At this time, yttrium cannot diffuse into the interior of the zirconia particles, so the yttrium concentration near the surface of the zirconia particles is higher than in the interior. On the other hand, when yttrium is uniformly added to the zirconia particles, the difference in yttria concentration between the surface and the interior of the zirconia particles is relatively small. The concentration of impurity ions near the grain boundaries strongly affects the mobility of the grain boundaries, which is thought to cause differences in grain size.

[0028] In this invention, the amount of stabilizer can be determined by elemental analysis of the sample. There are no particular limitations on the method of elemental analysis, but for example, X-ray fluorescence analysis can be used.

[0029] In this invention, "substantially alumina-free" means that the material does not contain an amount of alumina that would affect the properties of the zirconia workpiece for dental cutting or the zirconia sintered body obtained by sintering it. Specifically, this means that the alumina content of the zirconia workpiece for dental cutting is 500 ppm by weight or less. The alumina content can be 300 ppm or less, or 200 ppm or less. Depending on the zirconia raw material, even if alumina is not intentionally added, a trace amount of alumina may inevitably be present, but in such cases, the alumina content is generally 500 ppm or less. The alumina content can be determined by various elemental analyses. There are no particular limitations on the method of elemental analysis, but for example, X-ray fluorescence analysis can be used. In this case, depending on the measurement and analysis conditions, alumina may be detected even in samples that do not actually contain alumina, but in such cases, the alumina content is generally 500 ppm or less.

[0030] If the grain size of a sintered body produced by sintering at 1550°C for 1 hour is less than 2.0 times that of a sintered body produced by sintering at 1450°C for 1 hour, the change in light transmittance due to the change in sintering temperature is small, making it impossible to adjust the light transmittance by changing the sintering temperature according to the case. The grain size of a sintered body produced by sintering at 1550°C for 1 hour can be 2.0 times or more, 2.3 times or more, 2.5 times or more, or 2.7 times or more than that of a sintered body produced by sintering at 1450°C for 1 hour. By setting the grain size of a sintered body produced by sintering at 1550°C for 1 hour and the grain size of a sintered body produced by sintering at 1450°C for 1 hour to this relationship, the change in light transmittance due to the change in sintering temperature becomes large, making it possible to adjust the light transmittance by changing the sintering temperature according to the case.

[0031] In the present invention, the portion of a sintered body prepared by sintering at 1550°C for 1 hour containing a stabilizer in an oxide equivalent of 5.8 mol% to 7.0 mol%, substantially free of alumina, and having a grain size of 2.0 times or more that of a sintered body prepared by sintering at 1450°C for 1 hour, may be a part of or all of the zirconia workpiece for dental cutting. A preferred example of a part of the zirconia workpiece for dental cutting is a workpiece in which the above condition is satisfied in the portion up to 30% of the length from one surface (one end) of the opposing surface surface of the zirconia workpiece for dental cutting in the direction from one surface (one end) to the other surface (the other end) (the portion up to 30% of the distance between surface surfaces from one end). By using such a zirconia workpiece for dental cutting, the translucency of the enamel portion of the prosthesis can be changed by changing the sintering temperature when manufacturing the prosthesis.

[0032] If the amount of stabilizer, converted to oxides, is less than 5.8 mol%, the change in light transmittance due to changes in sintering temperature is small, which makes it difficult to adjust the light transmittance by changing the sintering temperature according to the case. If the amount of stabilizer, converted to oxides, exceeds 7.0 mol%, the problem arises that the light transmittance and / or intensity decreases. The amount of stabilizer, converted to oxides, can be set to between 6.2 mol% and 7.0 mol%. By setting it within this range, the change in light transmittance due to changes in sintering temperature becomes larger, making it easier to adjust the light transmittance by changing the sintering temperature according to the case.

[0033] The grain size of the sintered body produced by sintering at 1550°C can be 2.0 μm or larger, 3.0 μm or larger, or 4.0 μm or larger. In this case, the change in light transmittance when the sintering temperature is changed is significant, and the number of cases that can be treated can be increased by adjusting the sintering temperature.

[0034] In this invention, the difference between the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1550°C for 1 hour and the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1450°C for 1 hour at a wavelength of 700 nm can be 0.5%pt or more. In this case, the light transmittance can be adjusted according to the case by changing the sintering temperature. The difference in total light transmittance can be 2%pt or more, and even 3%pt or more. By making the difference in total light transmittance such that the range of adjustment for light transmittance can be increased.

[0035] There are no particular restrictions on the stabilizer contained in the zirconia workpiece for dental cutting according to the present invention, but yttria can be used because it is readily available and widely used in dental zirconia. Other stabilizers that can be used include ytterbium oxide, erbium oxide (which also has a coloring effect), neodymium oxide, praseodymium oxide, and terbium oxide. In the present invention, the stabilizer can be one or more selected from yttrium oxide, magnesium oxide, calcium oxide, scandium oxide, gallium oxide, indium oxide, and lanthanide oxides.

[0036] The zirconia workpiece for dental cutting in this invention may contain coloring elements. Specifically, examples include iron for imparting yellow coloration and erbium for imparting red coloration. In addition to these coloring elements, there is no problem in using cobalt, manganese, chromium, etc. in combination for color adjustment. By including coloring elements, this invention can be easily colored to match tooth coloration.

[0037] The stabilizing agent contained in the zirconia workpiece for dental cutting in this invention can exist as a solid solution in the zirconia crystal, or it can exist as a stabilizing element compound without being solidly dissolved as a stabilizing agent. Specifically, the stabilizing element compound can be a compound consisting of an oxide, halogen compound, nitrate, sulfate, or organic acid salt. Furthermore, the coloring element contained in the zirconia workpiece for dental cutting in this invention can exist in the zirconia crystal, or it can exist as a coloring element compound separate from the zirconia crystal. Specific examples of the case where the coloring element exists in the zirconia crystal include the presence of the coloring element at the zirconium site in the zirconia crystal, or the presence of the coloring element at the interstitial position in the zirconia crystal. Specifically, the coloring element compound separate from the zirconia crystal can be a compound consisting of an oxide, halogen compound, nitrate, sulfate, or organic acid salt of the coloring element.

[0038] Specific examples of water-soluble stabilizing element compounds include yttrium chloride, yttrium nitrate, yttrium acetate, yttrium carboxylate, yttrium sulfate, yttrium carbonate, ytterbium chloride, ytterbium nitrate, ytterbium acetate, ytterbium carboxylate, ytterbium sulfate, ytterbium carbonate, erbium chloride, erbium nitrate, erbium acetate, erbium carboxylate, erbium sulfate, erbium carbonate, neodymium chloride, neodymium nitrate, neodymium acetate, neodymium carboxylate, neodymium sulfate, neodymium carbonate, praseodymium chloride, praseodymium nitrate, praseodymium acetate, praseodymium carboxylate, praseodymium sulfate, praseodymium carbonate, terbium chloride, terbium nitrate, terbium acetate, terbium carboxylate, terbium sulfate, and terbium carbonate. Specific examples of coloring element compounds include iron chloride, iron nitrate, iron acetate, nickel chloride, nickel nitrate, and nickel acetate.

[0039] Among water-soluble stabilizing element compounds and coloring element compounds, organic acid salts are particularly preferred from the viewpoint of having a low decomposition temperature and minimizing contamination of the firing furnace. Specifically, examples include yttrium acetate and yttrium carbonate. Organic acid salts decompose at lower temperatures compared to inorganic salts such as halogen compounds, nitrates, and sulfates. If the decomposition temperature is high, pores will remain during the sintering process, making it difficult to impart sufficient translucency and strength to the zirconia sintered body.

[0040] The zirconia workpiece for dental cutting in this invention may contain additives other than stabilizers and colorants. Specific examples of additives include compounds such as gallium, lanthanum, niobium, and tantalum. The addition of these additives can control the sintering behavior, reduce translucency, or improve fracture toughness. These additives may or may not be solid-dissolved in the zirconia.

[0041] The zirconia workpiece for dental cutting in this invention may contain hafnium. The hafnium content can be, for example, 2 wt% or less.

[0042] The zirconia powder used in the production of the zirconia workpiece for dental cutting according to the present invention is not limited in any way as long as it is produced from known zirconia powder. Specifically, the zirconia powder used in the production of the zirconia workpiece for dental cutting according to the present invention may be produced by hydrolysis. More specifically, this method involves heating a solution of a mixture of zirconium salt and yttrium compound to perform a hydrolysis reaction, drying and calcining the resulting sol to produce zirconia powder, which is then pulverized and granulated. Furthermore, by mixing an aluminum compound before this pulverization step, zirconia powder containing alumina can be produced.

[0043] The primary particle size of the zirconia powder used in the production of the zirconia workpiece for dental cutting according to the present invention is preferably 10 to 500 nm. If the primary particle size is less than 10 nm, it tends to be difficult to impart sufficient strength to the zirconia sintered body. On the other hand, if the primary particle size is 500 nm or more, it also tends to be difficult to impart sufficient strength to the zirconia sintered body.

[0044] In the present invention, the relative density of the zirconia sintered body, obtained by sintering a zirconia workpiece for dental cutting at 1550°C, is preferably 98% or more of the theoretical density. The relative density is determined by the ratio of the measured density to the theoretical density. If the relative density is less than 98%, the strength and light transmittance tend to decrease.

[0045] In the present invention, the crystalline phase of the zirconia workpiece for dental cutting is preferably tetragonal and / or cubic. If the crystalline phase is monoclinic, it is undesirable because sufficient translucency cannot be imparted after complete sintering of the zirconia.

[0046] The method for manufacturing the zirconia workpiece for dental cutting in this invention is not particularly limited, and any known manufacturing method can be used without any problems. Specifically, it is preferable to mold the zirconia powder by press molding. Furthermore, it is also possible to press-molde zirconia powders with different colors and compositions in multiple stages to create a multi-layered mold.

[0047] In the present invention, the zirconia workpiece for dental cutting is preferably one that has been press-formed and then subjected to isotropic pressure by cold isostatic pressing (CIP treatment).

[0048] In the present invention, the maximum load pressure for the CIP treatment is preferably 50 MPa or higher. If the maximum load pressure is less than 50 MPa, it may not be possible to impart sufficient light transmission and strength to the zirconia sintered body.

[0049] In the present invention, there are no particular limitations on the holding time at the maximum load pressure during CIP processing, but it is usually preferably 0 to 150 seconds, and more preferably 0 to 60 seconds.

[0050] There are no particular restrictions on the time required for the aforementioned series of processes, but it is usually preferably 30 seconds to 10 minutes, and more preferably 3 to 7 minutes. If the time is too short, the molded product may be destroyed, and if it is too long, production efficiency will be poor, which is undesirable.

[0051] In the present invention, the calcination temperature of the zirconia workpiece for dental cutting is preferably 800 to 1200°C. If the calcination temperature is below 800°C, the Vickers hardness and / or flexural strength become too low, making chipping and fracture more likely during cutting. On the other hand, if the calcination temperature is above 1200°C, the Vickers hardness and / or flexural strength become too high, leading to excessive wear of the milling bur of the cutting machine and a tendency for higher running costs.

[0052] The manufacturing process for a zirconia workpiece for dental cutting in this invention may include a step of impregnating it with an impregnation solution containing metal ions. Specifically, at least one type of impregnation solution is impregnated into a calcined zirconia body, and the metal compound is supported in the zirconia pores by steps such as drying and degreasing. This makes it possible to impart desired translucency, color tone, mechanical properties, etc., to desired parts of the zirconia workpiece for dental cutting. It is more preferable to use two or more types of impregnation solutions. In this case, ion diffusion between the impregnation solutions can impart a smooth gradation of translucency and / or color tone and / or mechanical properties to the zirconia workpiece. Furthermore, an impregnation solution that does not contain metal ions may be used for the purpose of ion diffusion.

[0053] At least one of the metal ions contained in the impregnation solution can be a rare earth metal ion. Specifically, the rare earth metal ion is yttrium ion. By including rare earth metal ions, it becomes possible to improve the light transmittance of the zirconia sintered body or to color the zirconia sintered body. Only rare earth metal ions may be used as metal ions.

[0054] At least one of the metal ions contained in the impregnation solution can be a transition metal ion. Specifically, the transition metal ion is iron. The inclusion of a transition metal ion makes it possible to color the zirconia sintered body. Only transition metal ions may be used as metal ions.

[0055] At least one of the metal ions contained in the impregnation liquid can be an aluminum ion, a gallium ion, or an indium ion. Including any of these three ions can improve the sinterability and light transmittance of the zirconia sintered body. The metal ions can be limited to aluminum ions, gallium ions, and / or indium ions. The metal ions can be limited to rare earth metal ions, transition metal ions, aluminum ions, gallium ions, and / or indium ions.

[0056] There are no particular restrictions on the metal ion concentration of the impregnation solution, but for example, in the case of yttrium ions, it is preferably about 2.0 wt% to 10.0 wt%. If it is less than 2.0 wt%, the amount of yttrium supported is small, and sufficient properties may not be obtained. If it is more than 10.0 wt%, the amount of yttrium supported is large, and it may adversely affect the physical properties. The optimal amount of metal supported varies depending on the type of metal and the desired properties, so it is preferable to determine the metal ion concentration of the impregnation solution from the desired amount of metal supported and the solubility of the metal ion source in the solvent.

[0057] There are no particular restrictions on the solvent used in the impregnation solution, but water is preferred because it is easy to obtain and handle.

[0058] Acids, bases, or pH adjusters may be added to the impregnation solution to control the pH. There are no particular restrictions on the acids or bases used, but it is preferable to use organic acids such as acetic acid or citric acid, or aqueous ammonia, in order to avoid leaving any residue on the porous zirconia molded body.

[0059] The impregnation solution may contain a precipitating agent. The precipitating agent precipitates the metal compound by performing an operation such as heat treatment after the impregnation solution has penetrated the material. Specific examples include urea and hexamethylenetetramine. Urea is preferred because it is readily available and easy to handle. This suppresses the segregation of the metal compound.

[0060] The impregnation solution may contain various additives. Examples of additives include glycols and polymers to adjust the viscosity of the impregnation solution, and chelating agents to enhance the stability of metal ions. The former specifically includes ethylene glycol, propylene glycol, polyethylene glycol, etc., while the latter specifically includes citric acid, ammonium ethylenediaminetetraacetate, etc. The impregnation solution may also contain hydroxy acids. Examples of hydroxy acids include citric acid, malic acid, and lactic acid. Including such hydroxy acids can suppress segregation of metal compounds after drying.

[0061] The method for impregnating the calcined zirconia body with the impregnation liquid is not particularly limited, as long as the impregnation liquid can penetrate into the pores of the porous zirconia molded body. A simple and preferred method is to immerse the entire and / or a part of the porous zirconia molded body in the impregnation liquid. In this case, the impregnation liquid can penetrate into the interior by capillary action. The immersion time can be 3 minutes or more, and can range from 10 minutes to 10 hours.

[0062] The impregnation liquid may be permeated into the entire porous zirconia molded body, or into only any part of it. There are no particular restrictions on the method of impregnating only any part of it; examples include controlling the weight or volume of the impregnation liquid or controlling the impregnation time.

[0063] Multiple impregnation solutions may be used for a single calcined zirconia body. A specific example is to impregnate the body with the first type of impregnation solution from one end, and then impregnate it with the second type of impregnation solution from the same end or the other end.

[0064] There are no particular restrictions on the atmosphere used when impregnating with the aforementioned impregnation liquid; air, inert gas, etc., can be used under atmospheric pressure, reduced pressure, or pressurized conditions. Since no special equipment is required, it is preferable to carry out the process in atmospheric pressure. From the viewpoint of shortening the manufacturing time, placing the surrounding environment under a reduced pressure atmosphere or a pressurized atmosphere is a preferred method as it promotes the penetration of the impregnation liquid. Furthermore, repeating the operation of returning to atmospheric pressure after a reduced pressure operation (reduced pressure / atmospheric pressure operation) or returning to atmospheric pressure after a pressurized operation (pressurized / atmospheric pressure operation) multiple times is effective in shortening the time of the impregnation process. The time for immersing the zirconia calcined body in the impregnation liquid is not determined by the size of the zirconia calcined body, the degree of penetration of the impregnation liquid, and the immersion method, etc., and can be adjusted as appropriate. For example, when immersing, it is usually 1 to 120 hours, when immersing under reduced pressure, it is usually 0.5 to 12 hours, and when contacting under pressurized conditions, it is usually 0.2 to 6 hours.

[0065] It is preferable to have a drying step after the penetration step. The drying step is a step of drying the porous zirconia molded body on which the metal compound has been deposited. The drying temperature is preferably 50 to 200°C, and the time is preferably 15 minutes to 20 hours. After drying, it is preferable to allow the solvent to vaporize completely. In some cases, a heat treatment step may be carried out following this drying step. The drying step may also be included in the heat treatment step. It is preferable to have a degreasing step after the penetration step. The degreasing step is a step of removing unwanted components such as organic matter contained in the impregnation liquid. The degreasing temperature can be 200 to 600°C, and the time can be 50 to 200 hours. Unwanted components can be completely removed by degreasing. In some cases, a heat treatment step may be carried out following this degreasing step. The degreasing step may also be included in the heat treatment step.

[0066] The porous zirconia molded body on which the metal compound obtained in this manner is deposited and supported contains residual solvents, unreacted materials, and by-products, so heat treatment is preferable. There are no particular restrictions on the heat treatment method, but heat treatment in atmospheric pressure is preferred because it does not require special equipment. There are no particular restrictions on the heat treatment temperature, but 500°C to 1200°C is preferred. Heat treatment can remove impurities, organic matter, and odors.

[0067] By this manufacturing method, the zirconia workpiece for dental cutting according to the present invention is obtained. The obtained zirconia workpiece for dental cutting is then cut, machined, and surface polished to the desired size as needed.

[0068] There are no particular limitations on the method for completely sintering the zirconia workpiece for dental cutting according to the present invention, but a simple and preferred method is firing at atmospheric pressure. There are no particular limitations on the firing temperature, but 1450 to 1600°C is preferred. There are no particular limitations on the holding time at the firing temperature, but 1 minute to 12 hours is preferred, and 2 to 4 hours is particularly preferred. There are no particular limitations on the heating rate, but 1 to 400°C / min is preferred, and more preferably 3 to 100°C / h is particularly preferred.

[0069] There are no particular restrictions on the type of prosthetic device that can be machined using the zirconia workpiece for dental machining of the present invention; any prosthetic device such as inlays, onlays, veneers, crowns, or bridges can be used without any problems. Therefore, there are no particular restrictions on the shape of the zirconia workpiece for dental machining used to manufacture prosthetic devices by machining; any shape of zirconia workpiece for dental machining can be used, such as a block shape corresponding to inlays, onlays, veneers, or crowns, or a disc shape corresponding to bridges. [Examples]

[0070] The present invention will be described in more detail and specifically below with reference to examples, but the present invention is not limited thereto.

[0071] (Preparation of zirconia calcined body 1) 486 g of zirconia powder without alumina, containing 5.2 mol% solid-solution yttria, was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a molded body. The obtained molded body was subjected to CIP treatment (maximum load pressure: 200 MPa, holding time: 1 minute), and then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined zirconia body with a diameter of 98.5 mm and a thickness of 18 mm.

[0072] (Preparation of Zirconia Calcined Body 2) A calcined zirconia body was obtained in the same manner as calcined zirconia body 1, except that zirconia powder containing 5.2 mol% solid-solution yttria and 0.05 wt% alumina was used.

[0073] (Fabrication of zirconia calcined body 3) A calcined zirconia body was obtained in the same manner as calcined zirconia body 1, except that zirconia powder containing 6.5 mol% solid-solution yttria was used.

[0074] (Preparation of zirconia calcined body 4) A calcined zirconia body was obtained in the same manner as calcined zirconia body 1, except that zirconia powder containing 5.2 mol% solid-solution yttria and yttria powder added to achieve a total yttria concentration of 6.5 mol% were ball-milled and spray-dried to obtain the zirconia powder.

[0075] (Preparation of impregnation solution) Table 1 shows the composition of the impregnation solution. According to the composition in Table 1, metal salts and additives were added to deionized water and stirred for 1 hour to prepare 100 g of impregnation solution.

[0076] [Table 1]

[0077] (Impregnation of calcined zirconia body with impregnation solution) A plastic container was placed on a level workbench, and a calcined zirconia body was placed inside. The impregnation solution was poured in so that the liquid level reached 80% of the thickness of the calcined zirconia body, and it was left to stand for 15 hours.

[0078] (Heat treatment after impregnation) If the impregnation solution contained urea, heat treatment was performed after impregnation. The calcined zirconia body after impregnation was placed in a resin bag and degassed. The degassed porous zirconia molded body in the resin bag was placed in a dryer and heat-treated at 95°C for 15 hours to precipitate the metal compound. After heat treatment, the porous zirconia molded body was removed from the resin bag and dried (120°C, 1 hour) to obtain a porous zirconia molded body supporting the metal compound.

[0079] (Removal of residual organic matter) The calcined zirconia body after impregnation and / or heat treatment was heat-treated in an electric furnace (500°C, 30 minutes) to remove residual organic matter, thereby obtaining a zirconia workpiece for dental cutting in which the metal compound is supported within the pores.

[0080] (Repeated impregnation) In Example 6 and Comparative Example 4, the process from impregnation to removal of residual organic matter was repeated multiple times.

[0081] (Partial impregnation) In Example 11, the zirconia calcined body 1 was placed on a horizontal workbench, and a jig was attached to the top surface of the zirconia calcined body 1 so that the solution could be held there. 30 g of solution 1 was poured onto the top surface of the zirconia calcined body 1, and the body was left to stand until the entire amount was absorbed by the zirconia calcined body, thereby partially impregnating it with solution 1.

[0082] (Preparation of test specimens for measuring stabilization materials and light transmittance) Using a dental milling machine (Roland DWX51D), a test specimen measuring 12 mm in diameter and 2.0 mm in thickness was prepared from the center of a zirconia workpiece for dental milling, in which a metal compound was supported within the pores.

[0083] (Preparation of test specimens for three-point bending tests) Using a dental milling machine (Roland DWX51D), test specimens measuring 22 mm in length, 5.5 mm in width, and 2.2 mm in thickness were prepared from a zirconia workpiece for dental milling in which a metal compound was supported within the pores.

[0084] (Evaluation of stabilizer dosage) Using an X-ray fluorescence analyzer (manufactured by Rigaku Corporation), the mole fraction of the stabilizer in terms of oxide (stabilizer oxide in the case of yttrium: Y2O3) contained in each test specimen was measured. Within the scope of this example and comparative example, the stabilizer concentration was calculated using yttrium and ytterbium as stabilizers. Measurements were performed on the upper and lower surfaces of the test specimen, and the average of these measurements was taken as the measured value for that specimen.

[0085] (Evaluation of light transmittance) After evaluating the stabilizer concentration, each test specimen was completely sintered in a firing furnace (heating rate: 3°C / min, firing temperature: 1550°C or 1450°C, holding time: 1 hour). Subsequently, the thickness (1.0 mm) of each test specimen was adjusted using a surface grinder. Transmittance was evaluated using the total light transmittance at an irradiation wavelength of 700 nm, obtained from the transmission spectrum measured with a UV-Vis spectrophotometer (JASCO Corporation, V-750). Light transmittance was scored according to the following criteria. 3: Total light transmittance at 700nm (sintered at 1550°C) ≥ 50%, and total light transmittance at 700nm (sintered at 1450°C) > 35% 2: Total light transmittance at 50% > 700 nm (sintered at 1550°C) ≥ 44%, and total light transmittance at 700 nm (sintered at 1450°C) > 35% 1: Total light transmittance at 700nm (sintered at 1550°C) ≥ 39%, AND total light transmittance at 700nm (sintered at 1450°C) > 35% 0: Total light transmittance at >700nm (sintered at 1550°C) or 35% Total light transmittance at >700nm (sintered at 1450°C) Furthermore, the difference in light transmittance between the 1550°C sintered body and the 1450°C sintered body was scored according to the following criteria. 3: Total light transmittance difference at 700nm ≥ 6 points 2:6%pt > Total light transmittance difference at 700nm ≥ 3%pt 1:3%pt > Total light transmittance difference at 700nm ≥ 0.5%pt 0:0.5%pt > Total light transmittance difference at 700nm

[0086] (Evaluation of crystal grain size) The microstructure of each test specimen was observed using a scanning electron microscope (manufactured by JEOL Ltd.). The test specimens used were those prepared by mirror-polishing the translucency evaluation specimens, and then, as a thermal etching to facilitate the observation of crystal grains that were difficult to observe due to polishing, firing them at a temperature 50°C lower than the sintering temperature (1500°C or 1400°C) for 10 minutes, followed by gold deposition on the surface. From the obtained microscope images, the particle size distribution (Heywood diameter, volume distribution) of each test specimen was measured using image analysis particle size distribution measurement software (MOUNTECH, Mac-View), and the median diameter was used as the crystal grain size of each test specimen at the sintering temperature (1550°C or 1450°C).

[0087] (Three-point bending strength evaluation) The three-point bending strength was measured in accordance with ISO 6872 (Dentistry - Ceramic materials). The test was performed using an Instron 5967 universal testing machine, with a span distance of 12 mm and a crosshead speed of 1.0 mm / sec. The three-point bending strength σ (MPa) was calculated using equation (1). Here, P is the fracture load (N), L is the span distance (mm), w is the width of the specimen (mm), and b is the thickness of the specimen (mm). The obtained three-point bending strength was scored according to the following criteria.

number

[0088] (comprehensive evaluation) A comprehensive evaluation was conducted using the scores from the light transmittance evaluation, light transmittance difference evaluation, and three-point bending strength evaluation, according to the following criteria. A: Transparency evaluation score × Transparency difference evaluation score × Three-point bending strength evaluation score ≥ 6 B:6>Transparency evaluation score × Transparency difference evaluation score × Three-point bending strength evaluation score ≥ 1 C: Transparency evaluation score × Transparency difference evaluation score × Three-point bending strength evaluation score = 0 If the overall evaluation is A, the material possesses the ability to adjust light transmittance by changing the sintering temperature, light transmittance, and strength, and at least two of these are excellent or particularly excellent, making it suitable for many applications requiring different levels of light transmittance. If the overall evaluation is B, it possesses the ability to adjust light transmission by changing the sintering temperature, light transmission, and strength, and one of these is particularly excellent, or at least one is excellent, so it can be used for multiple applications where different light transmissions are required. If the overall rating is C, it means that at least one of the following is insufficient: the ability to adjust light transmission by changing the sintering temperature, light transmission, or strength, and therefore it can only be used for specific applications.

[0089] Table 2 shows the fabrication conditions and characteristic test results for the zirconia workpieces for dental cutting prepared in the examples and comparative examples.

[0090] [Table 2]

[0091] Examples 1 to 12 contain a stabilizer in an oxide equivalent of 5.8 mol% to 7.0 mol%, substantially free of alumina, and the grain size of the sintered body produced by sintering at 1550°C for 1 hour is 2.0 times or more than that of the sintered body produced by sintering at 1450°C for 1 hour. This confirms that they possess all of the following properties: adjustability of light transmission by changing the sintering temperature, light transmission, and strength, and that at least one of these properties is particularly excellent or excellent, thus allowing them to be used in multiple applications where different light transmission properties are required.

[0092] Comparative Example 1, due to its high alumina content, had low total light transmittance and was found to be unsuitable for applications where light transmission is not required.

[0093] Comparative Examples 2, 3, and 5 were found to have small grain size ratios or low stabilizer concentrations, resulting in small differences in total light transmittance due to sintering temperature. This prevented significant changes in light transmittance, and therefore they could not be used for multiple applications requiring different light transmittance properties.

[0094] Comparative Example 4 had a low three-point bending strength due to an excessively high stabilizer concentration, confirming that it can only be used in applications where high strength is not required. [Industrial applicability]

[0095] According to the present invention, it is possible to provide a zirconia workpiece for dental cutting that can significantly change the light transmittance of the sintered body while maintaining high strength by changing the sintering temperature.

Claims

1. A zirconia workpiece for dental cutting, A zirconia workpiece for dental cutting, containing a stabilizer in an oxide equivalent of 5.8 mol% to 7.0 mol%, substantially free of alumina, and having a portion of the sintered body produced by sintering at 1550°C for 1 hour having a grain size at least 2.0 times that of the sintered body produced by sintering at 1450°C for 1 hour.

2. The zirconia workpiece for dental cutting according to claim 1, wherein the sintered body produced by sintering at 1550°C for 1 hour has a crystal grain size of 3.0 μm or more.

3. The zirconia workpiece for dental cutting according to claim 1, wherein the stabilizer is yttria.

4. The zirconia workpiece for dental cutting according to claim 1, further comprising a coloring element.

5. A zirconia workpiece for dental cutting according to any one of claims 1 to 4, wherein the difference between the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1550°C for 1 hour in light at a wavelength of 700 nm and the total light transmittance of a 1.0 mm thick sintered body produced by sintering at 1450°C for 1 hour in light at a wavelength of 700 nm is 0.5% pt or more.

6. A method for manufacturing a zirconia workpiece for dental cutting, comprising one or more of the following (1) to (3). (1) A step of mixing a compound containing the elements that make up the stabilizer with zirconia powder and adding it. (2) A step of mixing a solution containing a compound that includes elements constituting the stabilizer with the raw material solution of zirconia powder and adding it. (3) A step of impregnating a zirconia workpiece for dental cutting with a solution containing a compound that includes elements constituting a stabilizer.

7. The manufacturing method according to claim 6, wherein the element constituting the stabilizer is yttrium.

8. (3) including step, The manufacturing method according to claim 6, wherein the zirconia workpiece for dental cutting, before penetration with a solution containing a compound comprising elements constituting the stabilizer, contains 3.0 mol% or more and less than 6.0 mol% of the stabilizer in terms of oxide, and is substantially free of alumina.

9. (1) including step, The manufacturing method according to claim 6, wherein the zirconia powder contains a stabilizer in an oxide equivalent of 3.0 mol% or more and less than 6.0 mol%, and is substantially free of alumina.

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