Zirconia workpiece

Abstract

To obtain a zirconia sintered body with excellent light transmittance, the present invention provides a zirconia workpiece for dental cutting that can reduce the number of types of zirconia workpieces for dental cutting held by dental laboratories and the like. [Solution] As one embodiment of the present invention, a zirconia workpiece for dental cutting is provided, which yields a zirconia sintered body with different optical properties depending on the sintering temperature, wherein the different sintering temperatures can be selected from at least the range of 1500°C to 1600°C and the range of 1400°C to 1500°C.

Description

Technical Field

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

Background Art

[0002] In recent years, techniques for fabricating prosthetic devices by cutting using dental CAD / CAM systems have been rapidly spreading. As a result, it has become possible to easily fabricate 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 full sintered body) cannot be machined using a dental CAD / CAM system because of its very high hardness. Therefore, a zirconia workpiece for dental cutting is used, which is 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 full 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 with 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, as they have varying translucency. Thus, dental laboratories and similar facilities need to stock various types of zirconia workpieces for dental cutting that meet the required physical properties.

[0010] The present invention aims to provide a zirconia workpiece for dental cutting that can reduce the number of types of zirconia workpieces for dental cutting that dental laboratories and the like possess, in order to obtain a zirconia sintered body with excellent light transmittance. [Means for solving the problem]

[0011] The inventors investigated a zirconia workpiece for dental cutting that could reduce the number of types of zirconia workpieces held by dental laboratories and the like in order to obtain a zirconia sintered body with excellent light transmittance. As a result, they found that sintered bodies with different optical properties can be obtained by changing the sintering temperature. The details of the present invention are described below.

[0012] As one embodiment, the present invention provides a zirconia workpiece for dental cutting, which allows obtaining zirconia sintered bodies with different optical properties depending on the sintering temperature, wherein the different sintering temperatures can be selected from at least the range of 1500°C to 1600°C and the range of 1400°C to 1500°C.

[0013] As one embodiment, the present invention provides a zirconia workpiece for dental cutting, which yields zirconia sintered bodies with different optical properties depending on the sintering temperature, wherein the different sintering temperatures are in the range of 1400°C to 1600°C and the sintering temperature difference is 50 to 150°C.

[0014] As one embodiment, the present invention provides a zirconia workpiece for dental cutting in which zirconia sintered bodies with different optical properties are obtained by different sintering temperatures, wherein the difference between the total light transmittance of a 1.0 mm thick sintered body produced by sintering at one of the different sintering temperatures for 1 hour and the total light transmittance of a 1.0 mm thick zirconia sintered body produced by sintering at the other of the different sintering temperatures for 1 hour is 0.5%pt or more, and the total light transmittance at 700 nm when sintered at any temperature in the range of 1500°C to 1600°C is 37% or more.

[0015] As one embodiment, the present invention provides a zirconia workpiece for dental cutting, which allows obtaining zirconia sintered bodies with different optical properties depending on the sintering temperature, wherein the grain size of the zirconia sintered body produced by sintering at one of the different sintering temperatures for 1 hour is 2.0 times or more that of the zirconia sintered body produced by sintering at the other of the different sintering temperatures for 1 hour.

[0016] 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.

[0017] In this invention, the stabilizer can be yttria.

[0018] In the present invention, a coloring element may be further included.

[0019] 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. [Effects of the Invention]

[0020] The zirconia workpiece for dental cutting according to the present invention can reduce the number of types of zirconia workpieces for dental cutting that dental laboratories and the like possess, in order to obtain a zirconia sintered body with excellent light transmittance. [Modes for carrying out the invention]

[0021] The zirconia workpiece for dental cutting according to the present invention can be understood as a zirconia workpiece for dental cutting that obtains zirconia sintered bodies with different optical properties by sintering at different sintering temperatures, wherein the different sintering temperatures can be selected from at least the ranges of 1500°C to 1600°C and 1400°C to 1500°C. The zirconia workpiece for dental cutting according to the present invention can be understood, in one view, as a zirconia workpiece for dental cutting that obtains zirconia sintered bodies with different optical properties by sintering at different sintering temperatures, wherein the different sintering temperatures are in the range of 1400°C to 1600°C and the difference in sintering temperatures is 50 to 150°C. The zirconia workpiece for dental cutting according to the present invention can be understood as a zirconia workpiece for dental cutting that, from one perspective, provides zirconia sintered bodies with different optical properties obtained by sintering at different sintering temperatures, wherein the difference between the transmittance of the zirconia sintered body obtained by sintering at a first sintering temperature and the transmittance of the zirconia sintered body obtained by sintering at a second sintering temperature is 0.5%pt or more, and the total light transmittance at 700nm when sintered at any temperature in the range of 1500℃ to 1600℃ is 37% or more. The zirconia workpiece for dental cutting in the present invention, from one perspective, is a zirconia workpiece for dental cutting that obtains zirconia sintered bodies with different optical properties by sintering at different sintering temperatures. The difference between the total light transmittance of a 1.0-mm-thick sintered body produced by sintering for 1 hour at one of the different sintering temperatures and the total light transmittance of a 1.0-mm-thick zirconia sintered body produced by sintering for 1 hour at the other of the different sintering temperatures is 0.5%pt or more, and the total light transmittance at 700 nm when sintered at any temperature in the range of 1500°C to 1600°C is 37% or more. It can be understood as a zirconia workpiece for dental cutting. The zirconia workpiece for dental cutting in the present invention, from one perspective, is a zirconia workpiece for dental cutting that obtains zirconia sintered bodies with different optical properties by different sintering temperatures. The crystal grain size of the zirconia sintered body obtained by sintering at the first sintering temperature is 2.0 times or more the crystal grain size of the zirconia sintered body obtained by sintering at the second sintering temperature. It can be understood as a zirconia workpiece for dental cutting. The zirconia workpiece for dental cutting in the present invention, from one perspective, is a zirconia workpiece for dental cutting that obtains zirconia sintered bodies with different optical properties by different sintering temperatures. The crystal grain size of the zirconia sintered body produced by sintering for 1 hour at one of the different sintering temperatures is 2.0 times or more the crystal grain size of the zirconia sintered body produced by sintering for 1 hour at the other of the different sintering temperatures. It can be understood as a zirconia workpiece for dental cutting. The zirconia workpiece for dental cutting in the present invention, from one perspective, can be understood as a zirconia workpiece for dental cutting that obtains zirconia sintered bodies with different optical properties by sintering at different sintering temperatures.

[0022] The components of the present invention will be specifically described. The zirconia workpiece for dental cutting of the present invention is a zirconia workpiece for dental cutting for producing a prosthetic device by cutting. This zirconia workpiece for dental cutting is a semi-fired zirconia workpiece for dental cutting containing a semi-fired body (green body / pre-sintered body) of ceramic particles, and can be manufactured using a known zirconia raw material powder.

[0023] The zirconia workpiece for dental cutting of the present invention can, for example, contain zirconium oxide and a stabilizer composed of an oxide (hereinafter also simply referred to as "stabilizer" in this specification). In the present invention, the content of the stabilizer can be, for example, 2.0 mol% or more and 7.0 mol% or less in terms of oxide, and can be 5.8 mol% or more and 7.0 mol% or less. In the present invention, the content of the stabilizer refers to the value expressed in mol% of the ratio of (amount of stabilizer) / (total inorganic oxides contained in the semi-fired body of ceramic particles).

[0024] In the present invention, the amount of the stabilizer can be specified by elemental analysis of the sample. There is no particular limitation on the method of elemental analysis, but for example, fluorescent X-ray analysis can be used.

[0025] The zirconia workpiece for dental cutting of the present invention can be substantially free of alumina.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The content of the water-soluble stabilizing element compound can be, for example, 0.1 to 3.5 mol%, or 0.5 to 3.0 mol%. In this invention, the content of the water-soluble stabilizing element compound refers to the value expressed in mol% as the ratio of (amount of water-soluble stabilizing element compound) / (total inorganic oxides contained in the zirconia workpiece for dental cutting).

[0033] If the content of the water-soluble stabilizing element compound is less than 0.1 mol%, it may not be possible to impart sufficient translucency to the zirconia workpiece for dental cutting. On the other hand, if it exceeds 3.5 mol%, although the translucency of the zirconia fully sintered body improves, it may be difficult to impart sufficient strength. In the present invention, the water-soluble stabilizing element compound may include yttria. By including yttria in the water-soluble stabilizing element compound, translucency can be further improved.

[0034] 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.

[0035] The zirconia workpiece for dental cutting in this invention may contain hafnium. The hafnium content can be, for example, 2 wt% or less.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The zirconia workpiece for dental cutting according to the present invention can be made into a zirconia sintered body with different optical properties depending on the sintering temperature.

[0041] The sintering temperature of the zirconia workpiece for dental cutting according to the present invention is not particularly limited, but can be selected from, for example, a temperature range of 1400 to 1650°C, a temperature range of 1400 to 1600°C, or a temperature range of 1450 to 1600°C. That is, the "different sintering temperatures" of the present invention are not particularly limited, but can be two or more temperatures selected from, for example, a temperature range of 1400 to 1650°C, a temperature range of 1400 to 1600°C, or a temperature range of 1450 to 1600°C.

[0042] Specifically, the "different sintering temperatures" of the present invention can be two or more different temperature ranges selected from, for example, the temperature range of 1400-1450°C, the temperature range of 1450-1500°C, the temperature range of 1500-1550°C, the temperature range of 1550-1600°C, and the temperature range of 1600-1650°C.

[0043] In this invention, the temperature ranges in which "different sintering temperatures" are selected can be temperature ranges that do not overlap with each other, except for their endpoints.

[0044] More specifically, when the "different sintering temperatures" of the present invention are two temperatures, for example, they can be selected from the temperature range of 1400-1500°C and the temperature range of 1500-1600°C, or from the temperature range of 1450-1550°C and the temperature range of 1550-1650°C, or from the temperature range of 1400-1500°C and the temperature range of 1550-1650°C. In particular, when the "different sintering temperatures" of the present invention are two temperatures, they can be selected from the temperature range of 1400-1500°C and the temperature range of 1500-1600°C.

[0045] The "different sintering temperatures" of this invention can be two or more different temperatures selected from the same temperature range. In this case, the same temperature range can be, for example, the temperature range of 1400 to 1650°C, or the temperature range of 1450 to 1600°C. Furthermore, the temperature difference between the two or more temperatures can be 50°C or more, or the range of 50 to 150°C, or the range of 50 to 100°C, or the range of 100 to 150°C.

[0046] More specifically, if the "different sintering temperatures" of the present invention are two temperatures, the two temperatures can be selected from, for example, a temperature range of 1400°C to 1600°C, and the difference between the sintering temperatures can be 50 to 150°C.

[0047] In the present invention, there are no limitations on the method by which zirconia sintered bodies obtained by sintering at different sintering temperatures have different optical properties. Specifically, elements that change the optical properties of the zirconia sintered body obtained by sintering at different sintering temperatures can be added. Examples of such elements include gallium, indium, titanium, scandium, barium, niobium, and tantalum. These elements can be added to zirconia workpieces for dental cutting by mixing a solution containing these elements with a zirconium oxychloride solution, which is the zirconia raw material; by mixing zirconia powder with a compound containing these elements and granulating it; or by impregnating the zirconia workpiece for dental cutting with a solution containing these elements.

[0048] The optical properties of a zirconia sintered body are influenced, for example, by the grain size of the resulting zirconia sintered body. In this invention, "grain size" refers to the diameter of a circle with the same area as the grain size (Heywood diameter). There are no limitations on the method for measuring grain size, but for example, the zirconia sintered body can be observed using an SEM, and the obtained image can be measured using commercially available particle image analysis software. In such a measurement method, in order to prevent bias in the measured values, the grain size is measured from 50 or more randomly selected crystal grains, and the median diameter is taken as the grain size of the sample.

[0049] Stabilizing elements such as yttrium can also affect particle size differences. Yttrium is generally added as a solution when producing zirconia powder. Yttrium added in this way is generally distributed uniformly within the zirconia particles. On the other hand, yttrium can also be added by mixing zirconia powder and yttria powder, or by impregnating a calcined zirconia body with a yttrium solution. Yttrium added in this way is located on the outside of the zirconia particles. Differences in this yttrium distribution affect the grain size difference of the sintered body, and the grain size difference tends to be larger when yttrium is added to the outside of the zirconia particles. In other words, yttrium added to the outside of zirconia particles acts not only as a stabilizer but also as a particle size difference modifier.

[0050] 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.

[0051] Specific grain size differences that affect the optical properties of zirconia sintered bodies include, for example, the grain size of one sintered body produced by sintering at different temperatures for one hour being 2.0 times or more than the grain size of the other. More specifically, for example, the grain size of a sintered body produced by sintering at 1550°C for one hour may be 2.0 times or more than the grain size of a sintered body produced by sintering at 1450°C for one hour, or the grain size of a sintered body produced by sintering at 1500°C for one hour may be 2.0 times or more than the grain size of a sintered body produced by sintering at 1600°C for one hour.

[0052] When the grain size of one sintered body, produced by sintering at different temperatures for one hour, is less than 2.0 times that of the other, the changes in translucency, intensity, and color due to the change in sintering temperature are small, making it impossible to adjust translucency by changing the sintering temperature according to the case. However, when the grain size of one sintered body, produced by sintering at different temperatures for one hour, is 2.3 times or more, 2.5 times or more, or 2.7 times or more than that of the other, the changes in translucency, intensity, and color due to the change in sintering temperature become larger, allowing for adjustment of translucency by changing the sintering temperature according to the case.

[0053] The amount of stabilizer, converted to oxides, is preferably 5.8 mol% or more. If it is less than 5.8 mol%, the change in translucency, intensity, and color due to changes in sintering temperature is small, which makes it difficult to adjust translucency, intensity, and color by changing the sintering temperature according to the case. The amount of stabilizer, converted to oxides, is preferably 7.0 mol% or less. If the amount of stabilizer, converted to oxides, exceeds 7.0 mol%, the problem arises that translucency and / or intensity decrease. The amount of stabilizer, converted to oxides, can be 6.2 mol% or more and 7.0 mol% or less. By setting it within this range, the change in translucency, intensity, and color due to changes in sintering temperature becomes larger, making it easier to adjust translucency, intensity, and color by changing the sintering temperature according to the case.

[0054] The grain size of one of the zirconia sintered bodies obtained by sintering at different sintering temperatures 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.

[0055] In this invention, the difference between the total light transmittance at a wavelength of 700 nm of a 1.0 mm thick sintered body made from one of zirconia sintered bodies obtained by sintering at different sintering temperatures and the total light transmittance at a wavelength of 700 nm of a 1.0 mm thick sintered body made from the other can be set to 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 set to 2%pt or more, and even 3%pt or more. By setting such a difference in total light transmittance, the range of adjustment for light transmittance can be increased.

[0056] In this invention, when sintered at any temperature in the range of 1500°C to 1600°C, the total light transmittance at 700 nm can be 37% or more, or even 38% or more. In this case, a zirconia sintered body with excellent light transmittance can be obtained.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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%, and more preferably about 4.0 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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]

[0081] The present invention will be described in more detail and specifically below with reference to examples, but the present invention is not limited thereto.

[0082] (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.

[0083] (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.

[0084] (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.

[0085] (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.

[0086] (Preparation of zirconia calcined body 5) A calcined zirconia body was obtained in the same manner as calcined zirconia body 1, except that zirconia powder containing 3.0 mol% solid-solution yttria was used.

[0087] (Preparation of zirconia calcined body 6) A calcined zirconia body was obtained in the same manner as calcined zirconia body 1, except that zirconia powder containing 4.0 mol% solid-solution yttria was used.

[0088] (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.

[0089] [Table 1]

[0090] (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.

[0091] (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.

[0092] (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.

[0093] (Repeated impregnation) In Examples 6 and 13, the process from impregnation to removal of residual organic matter was repeated multiple times.

[0094] (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.

[0095] (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.

[0096] (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.

[0097] (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: high temperature (1500°C~16000°C), low temperature (1400°C~15000°C), holding time: 1 hour). Subsequently, the thickness (1.0 mm) of each test specimen was adjusted using a surface grinding machine. 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 (high-temperature sintering) ≥ 50%, and total light transmittance at 700nm (low-temperature sintering) > 35% 2: Total light transmittance at 50% > 700 nm (high-temperature sintering) ≥ 44%, and total light transmittance at 700 nm (low-temperature sintering) > 35% 1: Total light transmittance at 700nm (high-temperature sintering) ≥ 37%, and total light transmittance at 700nm (low-temperature sintering) > 35% 0: Total light transmittance at >700nm (high-temperature sintering) or 35% total light transmittance at >700nm (low-temperature sintering) Furthermore, the difference in light transmittance between high-temperature and low-temperature sintered bodies was scored according to the following criteria. 3: Difference in total light transmittance at 700nm ≥ 6pt 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

[0098] (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 (1550°C or 1450°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 (Mac-View, manufactured by MOUNTECH), and the median diameter was used as the crystal grain size of each test specimen at the sintering temperature (1550°C or 1450°C).

[0099] (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: Translucency evaluation score × Translucency difference evaluation score ≥ 6 B:6>Transparency evaluation score × Transparency difference evaluation score ≥ 1 C: Translucency evaluation score × Translucency difference evaluation score = 0 If the overall evaluation is A, both the ability to adjust light transmittance by changing the sintering temperature and the light transmittance itself are excellent, and at least one of them is particularly excellent, making it suitable for use in many applications where different light transmittances are required. If the overall evaluation is B, it has both the ability to adjust light transmittance by changing the sintering temperature and light transmittance, so it can be used for multiple applications where different light transmittances are required. If the overall rating is C, it means that either the ability to adjust light transmittance by changing the sintering temperature or the light transmittance itself is insufficient, and therefore it can only be used for specific applications.

[0100] Tables 2 and 3 show the fabrication conditions and characteristic test results for the zirconia workpieces used in dental cutting processes, which were prepared in the examples and comparative examples.

[0101] [Table 2]

[0102] [Table 3]

[0103] Examples 1-15 demonstrated that they possess both the ability to adjust light transmittance by changing the sintering temperature and inherent light transmittance, thus confirming their applicability to multiple applications requiring different levels of light transmittance.

[0104] Comparative Example 1 showed low total light transmittance in both high-temperature and low-temperature sintered bodies, confirming that it can only be used in applications where light transmission is not required for either high-temperature or low-temperature sintered bodies.

[0105] Comparative Examples 2-5 showed that the difference in total light transmittance between the sintered bodies at high temperatures and those at low temperatures was small, and it was not possible to significantly change the light transmittance. Therefore, it was confirmed that these materials could not be used for multiple applications requiring different light transmittances.

[0106] Comparative Example 6 showed that the sintering temperature in low-temperature sintering was too low, resulting in low light transmittance. This confirmed that the zirconia sintered body, while possessing excellent light transmittance, could not be used for multiple applications requiring different levels of light transmittance. [Industrial applicability]

[0107] According to the present invention, it is possible to provide a zirconia workpiece for dental cutting that can reduce the number of types of zirconia workpieces for dental cutting that dental laboratories and the like possess in order to obtain a zirconia sintered body with excellent light transmittance.

Claims

1. A zirconia workpiece for dental cutting, which yields zirconia sintered bodies with different optical properties depending on the sintering temperature, A zirconia workpiece for dental cutting, in which different sintering temperatures can be selected from at least the range of 1500°C to 1600°C and the range of 1400°C to 1500°C.

2. A zirconia workpiece for dental cutting, which yields zirconia sintered bodies with different optical properties depending on the sintering temperature, A zirconia workpiece for dental cutting, having different sintering temperatures in the range of 1400°C to 1600°C, and with a sintering temperature difference of 50 to 150°C.

3. A zirconia workpiece for dental cutting, which yields zirconia sintered bodies with different optical properties depending on the sintering temperature, The difference between the total light transmittance of a 1.0 mm thick sintered body produced by sintering at one of two different sintering temperatures for one hour and the total light transmittance of a 1.0 mm thick zirconia sintered body produced by sintering at the other of two different sintering temperatures for one hour is 0.5%pt or more. A zirconia workpiece for dental cutting, having a total light transmittance of 37% or more at 700 nm when sintered at any temperature in the range of 1500°C to 1600°C.

4. A zirconia workpiece for dental cutting, which yields zirconia sintered bodies with different optical properties depending on the sintering temperature, A zirconia workpiece for dental cutting, wherein the grain size of a zirconia sintered body produced by sintering at one of two different sintering temperatures for one hour is 2.0 times or more that of a zirconia sintered body produced by sintering at the other of two different sintering temperatures for one hour.

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