Zirconia workpiece for dental cutting and its manufacturing method

Abstract

To provide a zirconia cutting object for dental cutting that is excellent in cutting of a thin workpiece such as inlay, onlay, veneer, and does not require special sintering such as HIP treatment, and allows for giving of high strength and translucency to a fully sintered zirconia body, and a production method thereof.SOLUTION: The present invention provides a zirconia cutting object for dental cutting with its porosity set to 15-30%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a zirconia workpiece for dental cutting and a method for manufacturing the same, and more particularly to a zirconia workpiece for dental cutting that is compatible with high-speed sintering and a method for manufacturing the same. [Background technology]

[0002] In recent years, the technology of fabricating prosthetic devices through cutting using dental CAD / CAM systems has rapidly become widespread. This has made it possible to easily fabricate prosthetic devices by processing workpieces made from ceramic materials such as zirconia, alumina, and lithium disilicate, or resin materials such as acrylic resin and hybrid resin.

[0003] In particular, zirconia has been used clinically in a variety of cases due to its high strength. However, fully sintered zirconia (hereinafter referred to as fully sintered zirconia) is so hard that it cannot be machined using dental CAD / CAM systems. Therefore, zirconia cutting objects for dental machining are not fully sintered, but are pre-fired at a low firing temperature to adjust the hardness to a level that allows for machining.

[0004] A typical zirconia cutting object for dental cutting is produced by molding zirconia powder by press molding or the like, and then calcining it at 800 to 1200°C.

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

[0006] For example, Patent Document 1 discloses a fully sintered zirconia body prepared from a zirconia body for dental cutting using zirconia powder containing 3 mol% yttrium. Because the sintered body has high strength, it has been used clinically in bridge frames with four or more units. However, because the sintered body has low translucency, it has been difficult to reproduce a color similar to that of natural teeth.

[0007] Patent Document 2 discloses a fully sintered zirconia body prepared from a zirconia workpiece for dental cutting using zirconia powder containing 3 mol% yttrium with a reduced alumina content. Because this sintered body maintains high strength while improving translucency, it has been used clinically in long-span bridges with four or more units and full crowns in the molar region. However, because this sintered body still lacks sufficient translucency, it has been difficult to apply it to cases requiring high aesthetics, such as the anterior teeth.

[0008] Patent Document 3 discloses a fully sintered zirconia body prepared from a zirconia workpiece for dental cutting using zirconia powder containing 4 to 6.5 mol% yttrium. Because the sintered body has high translucency, it has been used in cases where high aesthetics are required, such as in the anterior teeth. However, the translucency of the sintered body is still lower than that of lithium disilicate materials, making it insufficient for use in cases such as inlays, onlays, and veneers.

[0009] Patent Document 4 discloses a fully sintered zirconia body using zirconia powder containing 2 to 7 mol% yttrium. This sintered body has high translucency similar to that of porcelain and lithium disilicate materials, and therefore can be applied not only to anterior teeth but also to cases such as inlays, onlays, and veneers. However, this sintered body requires hot isostatic pressing (HIP) treatment, making it difficult to produce in a typical dental laboratory.

[0010] Patent Document 5 discloses a zirconia workpiece for dental cutting that has mesopores. Because the zirconia workpiece has a high specific surface area, it has the advantage of being easily permeable to a coloring liquid containing metal ions. However, because it lacks sufficient strength, it is prone to chipping and fracture when cutting thin-walled workpieces. Furthermore, a fully sintered zirconia body made from the zirconia workpiece is prone to retaining pores, making it difficult to impart sufficient strength and translucency.

[0011] Zirconia prosthetic devices can be obtained by forming a zirconia dental cutting workpiece into a desired shape by cutting or other processes, and then firing it at a temperature equal to or higher than the sintering temperature until it is completely sintered. This firing process requires several hours or more to heat up the temperature and several hours to hold the temperature, which reduces production efficiency and requires patients to visit the hospital multiple times before they can wear the prosthetic device.

[0012] In recent years, sintering furnaces capable of firing in a few minutes to a few hours have become popular. However, when conventional zirconia cutting bodies for dental cutting are sintered in a short time, there is a problem that sufficient translucency and strength cannot be obtained.

[0013] For example, the zirconia cutting body for dental cutting described in Patent Document 6, which is sintered for a short time, has insufficient translucency and strength, making it difficult to apply to cases requiring high aesthetics such as anterior teeth or cases requiring high strength such as molars.

[0014] Patent Document 7 discloses a zirconia cutting object for dental cutting that can obtain sufficient translucency when sintered for a holding time of 15 minutes. However, the strength of this sintered object is insufficient, and it is not suitable for cases requiring high strength, such as full crowns on molars.

[0015] Patent Document 8 discloses a zirconia cutting body for dental cutting that can be sintered within 30 minutes. However, the sintered body has insufficient translucency and is unsuitable for cases where high aesthetics are required, such as in the front teeth.

[0016] Patent Document 9 discloses a method for obtaining a fully sintered zirconia body in 30 to 90 minutes. However, the sintered body has insufficient translucency or strength, making it difficult to apply to cases requiring high aesthetics, such as anterior teeth, or cases requiring high strength, such as molars. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Patent Publication No. 60-235762 [Patent Document 2] Patent No. 5608976 [Patent Document 3] WO2015―199018 [Patent Document 4] Patent 5396691 [Patent Document 5] Patent 6321644 [Patent Document 6] WO2015-098765 [Patent Document 7] WO2018―056330 [Patent Document 8] WO2018―029244 [Patent Document 9] CN107162603 Summary of the Invention [Problem to be solved by the invention]

[0018] An object of the present invention is to provide a zirconia workpiece for dental cutting that has excellent machinability for thin-walled workpieces such as inlays, onlays, and veneers, and that can impart high strength and translucency to a fully sintered zirconia body without requiring special sintering such as HIP treatment, and a method for producing the same.

[0019] Another object of the present invention is to provide a zirconia workpiece for dental cutting that can impart high strength and translucency to a fully sintered zirconia body even after short sintering time, and a method for producing the same. [Means for solving the problem]

[0020] The present inventors have investigated a zirconia workpiece for dental cutting that has excellent machinability for thin-walled workpieces such as inlays, onlays, and veneers, and that can impart high strength and translucency to fully sintered zirconia without requiring special sintering such as HIP treatment. As a result, they have found that the pore structure of the zirconia workpiece for dental cutting is particularly important for achieving excellent machinability for thin-walled workpieces and imparting high strength and translucency to fully sintered zirconia.

[0021] The present inventors also investigated zirconia cutting bodies for dental cutting that can impart high strength and translucency to fully sintered zirconia bodies even with short sintering times, and found that the pore structure of the zirconia cutting body for dental cutting is particularly important for imparting high strength and translucency to fully sintered zirconia bodies even with short sintering times.

[0022] The zirconia object for dental cutting of the present invention is a zirconia object for dental cutting, characterized in that the porosity of the zirconia object for dental cutting is 15 to 30%.

[0023] In the present invention, the zirconia workpiece for dental cutting preferably contains zirconia particles (a1) containing dissolved yttrium.

[0024] In the present invention, the amount of yttrium in the zirconia particles (a1) containing dissolved yttrium is preferably 3.0 to 6.5 mol% in terms of oxide in the zirconia workpiece for dental cutting, which can impart high strength and translucency to the fully sintered zirconia body even after short sintering time.

[0025] In the present invention, the amount of yttrium in the zirconia particles (a1) containing dissolved yttrium is preferably 3.5 to 4.5 mol % in terms of oxide in the zirconia workpiece for dental cutting.

[0026] In the present invention, it is preferable that the zirconia workpiece for dental cutting further contains an yttrium compound (a2) that is not solid-dissolved in zirconia.

[0027] In the present invention, the yttrium compound (a2) that is not dissolved in the zirconia is preferably in a dispersed state on the surface of the zirconia particles (a1) containing dissolved yttrium.

[0028] In the present invention, the amount of yttrium in the yttrium compound (a2) that is not dissolved in the zirconia is preferably 0.1 to 3.0 mol % in terms of oxide in the zirconia workpiece for dental cutting.

[0029] In the present invention, the pore volume of the zirconia workpiece for dental cutting is 0.03 to 0.07 cm 3 / g is preferred.

[0030] In the present invention, the specific surface area of ​​the zirconia workpiece for dental cutting is 1 to 10 m 2 / g is preferred.

[0031] In the present invention, the zirconia object to be cut for dental cutting preferably has a pore size of 50 to 200 nm.

[0032] The method for producing a zirconia workpiece for dental cutting of the present invention comprises the steps of: forming the zirconia powder; and forming by cold isostatic pressing, The method for producing a zirconia workpiece for dental cutting includes, in the molding by the cold isostatic pressing method, a series of steps of applying a load pressure, increasing the load pressure to a maximum load pressure, and releasing the load pressure, repeated at least twice.

[0033] In the present invention, the zirconia powder is preferably molded by press molding.

[0034] In the present invention, it is preferable that the forming by the cold isostatic pressing method further comprises a step of holding the maximum load pressure.

[0035] In the present invention, it is preferable that the difference between the maximum load pressure and the load pressure after release is at least 50 MPa or more.

[0036] In the present invention, it is preferable to further include a step of dispersing an yttrium compound on the zirconia particles containing dissolved yttrium after the step of forming by cold isostatic pressing.

[0037] In the present invention, it is preferable that a series of steps of applying the load pressure, maintaining the maximum load pressure, and releasing the load pressure is repeated at least 10 times.

[0038] In the present invention, short-time sintering preferably means a sintering time of 90 minutes or less.

[0039] In the present invention, the zirconia workpiece for dental cutting is preferably made of zirconia particles containing dissolved yttrium. [Effects of the Invention]

[0040] The zirconia workpiece for dental cutting and the method for producing the same of the present invention are excellent in machinability for thin-walled workpieces such as inlays, onlays, and veneers, and can impart high strength and translucency to a fully sintered zirconia body without requiring special sintering such as HIP treatment. DETAILED DESCRIPTION OF THE INVENTION

[0041] The constituent features of the present invention will now be described in detail. The present invention provides a zirconia object for dental cutting, characterized by having an appropriate pore structure and a porosity of 15 to 30%. The zirconia object for dental cutting of the present invention has excellent machinability for thin-walled workpieces such as inlays, onlays, and veneers, and can impart translucency similar to that of natural tooth enamel to a fully sintered zirconia body, despite being pressureless sintered.

[0042] Preferably, the zirconia workpiece for dental cutting of the present invention is a zirconia workpiece for dental cutting that contains both zirconia particles (a1) containing dissolved yttrium and an yttrium compound (a2) that is not dissolved in zirconia, and the yttrium compound (a2) that is not dissolved in zirconia is in a dispersed state on the surface of the zirconia particles (a1) containing dissolved yttrium.More preferably, the zirconia workpiece for dental cutting of the present invention is a zirconia workpiece for dental cutting that contains zirconia particles (a1) containing dissolved yttrium and an yttrium compound (a2) that is not dissolved in zirconia.

[0043] Preferably, the zirconia object for dental cutting of the present invention is a zirconia object for dental cutting made of zirconia particles containing dissolved yttrium. Despite being sintered for a short time, this zirconia object for dental cutting can impart translucency and strength to a fully sintered zirconia body similar to those of conventional long-sintered bodies.

[0044] The porosity of the zirconia workpiece for dental cutting in the present invention is 15 to 30%, and more preferably 22 to 27%. The porosity of the zirconia workpiece for dental cutting in the present invention is calculated from the following formula (1). Porosity (%) = pore volume / (pore volume + skeleton volume) × 100 (1) If the porosity is more than 30% or less than 15%, the chipping resistance of the zirconia workpiece for dental cutting will decrease and sufficient translucency will not be imparted to the zirconia fully sintered body, which is undesirable.

[0045] The porosity of the zirconia workpiece for dental cutting in the present invention is substantially different from the relative density calculated from the theoretical density. The relative density calculated from the theoretical density is a value calculated from the density including all pores, from micropores to macropores, including closed pores. On the other hand, the porosity in the present invention is determined based on the pore volume measured by mercury porosimetry, and therefore refers to the measurement of interconnected pores, excluding closed pores, having diameters of approximately 5 nm to 250 μm. It has been found that the porosity determined based on the pore volume measured by mercury porosimetry in the present invention is particularly important for the machinability of the zirconia workpiece for dental cutting and for imparting high translucency to a fully sintered zirconia compact sintered by atmospheric sintering. The presence or absence of pores less than 5 nm is virtually irrelevant to imparting translucency to a fully sintered zirconia compact, since they are unlikely to remain as pores during sintering. On the other hand, pores greater than 250 μm are preferably substantially absent, since they reduce chipping resistance during cutting and the translucency of the fully sintered zirconia compact.

[0046] The zirconia particles (a1) containing dissolved yttrium in the present invention can be produced without any limitation as long as they are produced from known zirconia powder. Specifically, the zirconia powder used in the present invention is preferably produced by a hydrolysis method. More specifically, this method involves heating a solution in which a zirconium salt and an yttrium compound are mixed and dissolved, causing a hydrolysis reaction, and then calcining the resulting sol to obtain zirconia powder. The method for producing the zirconia particles (a1) containing dissolved yttrium in the present invention is not particularly limited, but it is preferable to produce them by, for example, calcining the zirconia powder at 800 to 1200°C.

[0047] The amount of yttrium contained in the zirconia particles (a1) containing dissolved yttrium in the present invention is preferably 3.0 to 6.5 mol % and more preferably 3.5 to 4.5 mol % in terms of oxide in the zirconia cutting body for dental cutting. If the amount of yttrium is less than 3.0 mol %, sufficient translucency cannot be imparted after fully sintered zirconia, which is undesirable. On the other hand, if the amount of yttrium exceeds 6.5 mol %, although the translucency of the fully sintered zirconia is improved, it is difficult to impart sufficient strength, which is undesirable.

[0048] The primary particle size of the zirconia powder in the present invention is preferably 1 to 500 nm. If the primary particle size is less than 1 nm, the translucency of the zirconia fully sintered body is improved, but it is difficult to impart sufficient strength, which is not preferred. On the other hand, if the primary particle size is 500 nm or more, it is difficult to impart sufficient strength to the zirconia fully sintered body, which is not preferred.

[0049] The specific surface area of ​​the zirconia powder in the present invention is 1 to 10 m 2 / g. The specific surface area is preferably 1 m 2 If the specific surface area is less than 10 m / g, it is not preferable because sufficient translucency cannot be imparted to the zirconia after complete sintering. 2 If the content is more than 1 / g, the translucency of the completely sintered zirconia is improved, but it is difficult to impart sufficient strength, which is not preferable.

[0050] In the present invention, the yttrium compound (a2) not dissolved in zirconia can be any known yttrium compound without any limitations. Specifically, the yttrium compound used in the present invention is preferably a water-soluble compound consisting of yttrium oxide and / or a halogen compound, nitrate, sulfate, or organic acid salt (including carbonate) of yttrium. Specific examples of water-soluble yttrium compounds include yttrium chloride, yttrium nitrate, yttrium acetate, yttrium carboxylate, yttrium sulfate, and yttrium carbonate.

[0051] Among water-soluble yttrium compounds, yttrium compounds of organic acid salts (including carbonates) are particularly preferred from the viewpoints of low decomposition temperature and minimal contamination of the firing furnace. Specific examples include yttrium acetate and yttrium carbonate. Organic acid salts decompose at lower temperatures than inorganic salts such as halogen compounds, nitrates, and sulfates. If the decomposition temperature is high, pores remain during the sintering process, making it difficult to impart sufficient translucency and strength to the zirconia for complete sintering.

[0052] The amount of yttrium contained in the yttrium compound (a2) not dissolved in zirconia in the present invention is preferably 0.1 to 3.0 mol% in terms of oxide in the zirconia cutting body for dental cutting. If the amount of yttrium is less than 0.1 mol%, it is not preferable because sufficient translucency cannot be imparted after fully sintered zirconia. On the other hand, if the amount of yttrium exceeds 3.0 mol%, although the translucency of the fully sintered zirconia is improved, it is difficult to impart sufficient strength, which is also not preferable.

[0053] In the zirconia cutting body for dental cutting of the present invention, the molar ratio of the zirconia particles (a1) containing dissolved yttrium to the yttrium compound (a2) not dissolved in zirconia is preferably (a1):(a2) = 1:1 to 65:1, more preferably 3:1 to 20:1. If the molar ratio of (a1) to (a2) is greater than 65, the translucency of the fully sintered zirconia will be improved, but it will be difficult to impart sufficient strength, which is not preferred. On the other hand, if the molar ratio of (a1) to (a2) is less than 1, it will be difficult to impart sufficient translucency to the fully sintered zirconia, which is not preferred.

[0054] In the present invention, the yttrium compound (a2) that is not solid-solved in zirconia is preferably in a state of being dispersed on the surface of the zirconia particles (a1) containing solid-solved yttrium.

[0055] In the present invention, the state of being dispersed on the surface refers to a state in which the yttrium compound is supported and / or adsorbed on a part and / or the whole of the zirconia primary particles.

[0056] In the present invention, it has been found that dispersing the yttrium compound (a2) that is not solid-dissolved in zirconia on the surface of the zirconia particles (a1) containing dissolved yttrium is important for imparting high workability to the zirconia workpiece for dental cutting, and further for imparting high translucency and strength to the fully sintered zirconia.

[0057] Although the reasons for these are unclear, it is speculated that the reason why the zirconia workpiece for dental cutting has high workability is that the yttrium compound that is not dissolved in zirconia reinforces the neck portions between the zirconia primary particles. Normally, the zirconia workpiece for dental cutting is in a semi-sintered state, so the strength of the neck portions between the zirconia primary particles is low. Therefore, when cutting a thin-walled workpiece, chipping and fracture occur during processing. On the other hand, the neck portions of the zirconia workpiece for dental cutting of the present invention are reinforced by the yttrium compound, so it is speculated that good workability can be imparted even when cutting a thin-walled workpiece.

[0058] Furthermore, it is believed that the reason why a fully sintered zirconia body can be endowed with high translucency is that by dispersing an yttrium compound, which dissolves in zirconia, on the outermost surface of the zirconia, the dispersed yttrium compound segregates near the grain boundaries during the sintering process, promoting the phase transition of the crystalline phase near the grain boundaries (from tetragonal to cubic). Furthermore, the state in which the yttrium compound is dispersed on the surface of zirconia particles also has the effect of reducing the amount of closed pores remaining during the sintering process, and it is believed that a fully sintered zirconia body can achieve both high translucency and strength.

[0059] The zirconia workpiece for dental cutting in the present invention may contain a coloring agent. Specific examples include iron oxide for imparting a yellow color and erbium for imparting a red color. In addition to these coloring agents, coloring agents containing elements such as cobalt, manganese, and chromium may also be used in combination to adjust the color tone.

[0060] The zirconia workpiece for dental cutting in the present invention may contain a sintering aid. Specifically, it preferably contains 0.01 to 0.3 wt% alumina for the purposes of improving sinterability and suppressing low-temperature deterioration. If the alumina content is less than 0.01 wt%, the zirconia cannot be fully sintered after complete sintering, and sufficient strength and translucency cannot be imparted, which is undesirable. On the other hand, if the alumina content exceeds 0.3 wt%, although the strength of the zirconia fully sintered body is improved, it is difficult to impart sufficient translucency, which is undesirable.

[0061] The crystalline phase of the zirconia workpiece for dental cutting in the present invention is preferably a tetragonal phase and / or a cubic phase. If the crystalline phase is a monoclinic phase, sufficient translucency cannot be imparted after complete sintering of the zirconia, which is not preferred.

[0062] The specific surface area of ​​the zirconia workpiece for dental cutting in the present invention is measured by a nitrogen adsorption method. The specific surface area of ​​the zirconia workpiece for dental cutting in the present invention is 1 to 10 m 2 / g. The specific surface area is preferably 1 m 2 If the specific surface area is less than 10 m / g, it is not preferable because the fully sintered zirconia body cannot be given sufficient translucency. 2 If it exceeds 1 / g, it is not preferable because the fully sintered zirconia body cannot be given sufficient strength.

[0063] The pore volume of the zirconia workpiece for dental cutting in the present invention is measured by mercury intrusion porosimetry. The pore volume measured by mercury intrusion porosimetry is measured for pores having a diameter of about 5 nm to 250 μm. The pore volume of the zirconia workpiece for dental cutting in the present invention is 0.03 to 0.07 cm 3 / g. The pore volume is preferably 0.03 cm 3 If the pore volume is less than 0.07 cm3 / g, it is not possible to impart sufficient translucency to the fully sintered zirconia body, which is not preferable. 3 If it exceeds 1 / g, it is not preferable because the fully sintered zirconia body cannot be given sufficient strength.

[0064] The pore diameter of the zirconia workpiece for dental cutting in the present invention refers to the diameter of the pores at the median pore volume measured by mercury intrusion porosimetry. The pore diameter of the zirconia workpiece for dental cutting in the present invention is preferably 50 to 200 nm. A pore diameter of less than 50 nm is not preferred because it is not possible to impart sufficient translucency to the zirconia fully sintered body. On the other hand, a pore diameter of more than 200 nm is not preferred because it is not possible to impart sufficient translucency and strength to the zirconia fully sintered body.

[0065] The skeletal volume of the zirconia workpiece for dental cutting in the present invention is calculated from the true density measured by the gas phase displacement method. Here, the skeletal volume in the present invention is the skeletal volume (cm 3 / g)=1 / true density(g / cm 3 The skeletal volume calculated by the gas phase displacement method is characterized by having more interconnected pores including finer pores than the value measured by the liquid phase displacement method, since gas is used. The skeletal volume of the zirconia workpiece for dental cutting in the present invention is 0.16 to 0.17 cm 3 / g. The skeleton volume is preferably 0.16 cm 3 On the other hand, when the skeleton volume is less than 0.17 cm3 / g, sufficient translucency cannot be imparted, which is not preferable. 3 If it exceeds 1 / g, it is not preferable because the fully sintered zirconia body cannot be given sufficient strength.

[0066] The Vickers hardness of the zirconia workpiece for dental cutting in the present invention is preferably 30 to 150 Hv0.2. If the Vickers hardness is less than 30 Hv0.2, chipping and fracture are likely to occur during cutting, which is undesirable. On the other hand, if the Vickers hardness exceeds 150 Hv0.2, the milling bur of the cutting machine will wear out rapidly, which is undesirable as it increases running costs.

[0067] The flexural strength of the zirconia workpiece for dental cutting in the present invention is preferably 25 to 150 MPa. If the flexural strength is less than 25 MPa, chipping and fracture are likely to occur during cutting, which is undesirable. On the other hand, if the flexural strength exceeds 150 MPa, the milling bur of the cutting machine will wear out rapidly, which is undesirable because it increases running costs.

[0068] The method for producing the zirconia cutting body for dental cutting in the present invention is not particularly limited, and any known manufacturing method can be used without any problems. Specifically, a zirconia powder molded by press molding is preferred. Furthermore, a multi-layer molded body obtained by press molding zirconia powders with different color tones and compositions in multiple stages is more preferred.

[0069] The zirconia workpiece for dental cutting in the present invention is preferably press-molded and then isostatically pressed by cold isostatic pressing (CIP molding / treatment).

[0070] The maximum load pressure of the CIP molding and treatment in the present invention is preferably 50 MPa or more. If the maximum load pressure is less than 50 MPa, it is not preferable because sufficient translucency and strength cannot be imparted to the fully sintered zirconia body.

[0071] In the present invention, there are no particular limitations on whether or not to hold the maximum load pressure during CIP molding and processing, and the holding time, but it is usually preferable that the holding time be no hold to 150 seconds, and more preferably no hold to 60 seconds. Holding in the present invention means maintaining an arbitrary load pressure.

[0072] In the CIP molding and processing of the present invention, a series of steps of applying a load pressure, maintaining the maximum load pressure, and releasing the load pressure is preferably repeated at least twice, more preferably five times, and most preferably ten times. By repeating this series of steps, it is possible to reduce the pores in the zirconia workpiece for dental cutting to an appropriate size. Alternatively, a method may be used in which the maximum load pressure is increased in multiple stages and then the load pressure is released. If the series of steps is repeated less than once, it is not preferable because sufficient translucency and strength cannot be imparted to the zirconia fully sintered body.

[0073] There is no particular limit to the time required for the series of steps, 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 body may be destroyed, and if it is too long, production efficiency will decrease, which is not preferable.

[0074] In the present invention, the difference between the maximum load pressure and the pressure after release is preferably at least 50 MPa or more, more preferably 100 MPa or more, and even more preferably 200 MPa or more. If the release pressure is less than 50 MPa, it is not preferable because sufficient translucency and strength cannot be imparted to the zirconia fully sintered body.

[0075] The repeated CIP treatment in the present invention may include a degreasing step midway. There are no particular restrictions on the degreasing method, but degreasing by general heat treatment is preferred as it does not require special equipment. There are no particular restrictions on the degreasing temperature, but a temperature of 300 to 800°C is preferred. A degreasing temperature of 300°C or lower may not fully remove the binder, while a temperature of 800°C or higher may cause partial sintering, preventing the full effect of the repeated CIP treatment, which is not preferred.

[0076] The pre-sintering temperature of the zirconia workpiece for dental cutting in the present invention is preferably 800 to 1200°C. If the pre-sintering temperature is less than 800°C, the Vickers hardness and / or bending strength will be too low, making chipping and fracture more likely to occur during cutting, which is undesirable. On the other hand, if the pre-sintering temperature is 1200°C or higher, the Vickers hardness and / or bending strength will be too high, causing excessive wear on the milling bur of the cutting machine and increasing running costs, which is undesirable.

[0077] In the present invention, the yttrium compound (a2) not dissolved in zirconia is preferably dispersed on the surface of the zirconia particles. Here, the dispersed state in the present invention refers to a state in which no coarse particles are present, preferably particles of 100 nm or more, more preferably particles of 50 nm or more. A method for confirming the dispersed state includes TEM-EDS observation. For example, a method for dispersing the yttrium compound on the surface of zirconia is to spray and / or contact an yttrium-containing solution prepared by dissolving a water-soluble yttrium compound in water onto zirconia powder and / or a zirconia workpiece for dental cutting, followed by drying. The yttrium compound coated by this method is supported and / or adsorbed on the surface of the zirconia primary particles at the elemental level, which facilitates solid solution in zirconia during the sintering process, making this a preferred method.

[0078] The content of the yttrium compound in the yttrium-containing liquid used to disperse the yttrium compound on the zirconia surface is preferably 1 to 60 wt%, more preferably 5 to 30 wt%. If the content of the yttrium compound is less than 1 wt%, it is not preferable because a sufficient amount of the yttrium compound cannot be dispersed in the zirconia powder and / or the zirconia workpiece for dental cutting. On the other hand, if the content exceeds 60 wt%, the amount of the yttrium compound becomes excessive, which is also not preferable.

[0079] The method for preparing the yttrium-containing liquid in the present invention is not particularly limited, and any preparation method will suffice as long as a water-soluble yttrium compound is dissolved in water.

[0080] In the present invention, the method for spraying and / or contacting the yttrium-containing solution with the zirconia powder is not particularly limited, and any preparation method will suffice as long as the yttrium-containing solution is dispersed into zirconia primary particles.

[0081] In the present invention, after spraying and / or contacting the yttrium-containing solution with the zirconia powder, it is preferable to include a drying step to remove water. The drying method is not particularly limited, and there is no problem as long as the temperature, time, etc. are sufficient to remove water.

[0082] The method for contacting the zirconia object to be cut for dental cutting in the present invention with the yttrium-containing solution is not particularly limited as long as the yttrium-containing solution can penetrate into the gaps in the zirconia object to be cut, but a simple and preferred method is to immerse the entire zirconia object to be cut and / or part thereof in the yttrium-containing solution. By immersing the entire zirconia object to be cut and / or part thereof, the yttrium-containing solution can penetrate into the interior by capillary action.

[0083] In the present invention, a specific method for immersing a zirconia object for dental cutting in the yttrium-containing solution is to immerse the zirconia object in the yttrium-containing solution in an amount of preferably 1 to 100%, more preferably 10 to 100%, of the total volume of the zirconia object. In addition, by controlling the volume of the yttrium-containing solution immersed in the zirconia object for dental cutting, the yttrium compound can be dispersed only in desired portions of the zirconia object for dental cutting.

[0084] The specific atmosphere in which the zirconia workpiece for dental cutting in the present invention is immersed in the yttrium-containing solution is not particularly limited, and any of atmospheric pressure, reduced pressure, and pressurized atmospheres is acceptable. From the viewpoint of shortening the manufacturing time, placing the surrounding environment in a reduced pressure or pressurized atmosphere is preferred because it promotes the penetration of the yttrium-containing solution. Furthermore, repeating the operation of returning the pressure to atmospheric pressure after the reduced pressure operation (reduced pressure / normal pressure operation) multiple times is effective in shortening the time required for the process of penetrating the yttrium-containing solution into the zirconia workpiece.

[0085] The time for immersing the zirconia object for dental cutting in the yttrium-containing solution is not universally determined, but can be adjusted appropriately depending on the density of the zirconia object, the size of the zirconia object, the penetration level of the yttrium-containing solution, the immersion method, etc. For example, the immersion time is usually 1 to 72 hours, usually 1 minute to 6 hours in the case of immersion under reduced pressure, and usually 1 minute to 6 hours in the case of contact under pressure.

[0086] Next, after the yttrium-containing solution has penetrated into the zirconia workpiece for dental cutting, the zirconia workpiece is removed from the yttrium-containing solution, and the method preferably includes a drying step of the yttrium-containing solution. The drying step is not particularly limited, but a simple and preferred method is drying under atmospheric pressure. The drying temperature is not particularly limited, but is preferably 25 to 1200°C, more preferably 25 to 1100°C. The drying time is also not particularly limited, but is typically 30 minutes to 72 hours.

[0087] In this way, a zirconia object for dental cutting can be obtained by the manufacturing method of the present invention. The obtained zirconia object for dental cutting can be cut to a desired size, cut, and surface polished as needed.

[0088] The method for completely sintering the zirconia cutting body for dental cutting of the present invention is not particularly limited, but a simple and preferred method is firing at normal pressure. The firing temperature is not particularly limited, but is preferably 1450 to 1600°C, more preferably 1500 to 1600°C. The holding time at the maximum firing temperature is not particularly limited, but is preferably 1 minute to 12 hours, more preferably 2 to 4 hours. The temperature rise rate is not particularly limited, but is preferably 1 to 400°C / min, more preferably 3 to 100°C / h.

[0089] Furthermore, when the yttrium content of the zirconia workpiece for dental cutting of the present invention is 3.0 to 6.5 mol% in terms of oxide, short-time sintering can be used as a method for complete sintering. In this case, the sintering temperature is not particularly limited, but is preferably 1450 to 1600°C, more preferably 1500 to 1600°C. The holding time at the maximum sintering temperature is not particularly limited, but is preferably 1 minute to 1 hour, more preferably 2 to 10 minutes. The heating rate is not particularly limited, but is preferably 5 to 400°C / min, more preferably 50 to 300°C / min.

[0090] There are no particular limitations on the type of prosthetic device that can be machined using the zirconia workpiece for dental cutting of the present invention, and any prosthetic device such as an inlay, laminate, crown, bridge, etc. Therefore, there are no particular limitations on the shape of the zirconia blank for dental cutting from which the prosthetic device is cut, and any shape of zirconia blank for dental cutting can be used, such as a block shape corresponding to an inlay, laminate, crown, etc. or a disk shape corresponding to a bridge. [Example]

[0091] The present invention will be explained in more detail and specifically below with reference to examples, but the present invention is not limited to these examples.

[0092] <Examples 1 to 19 and Comparative Examples 1 to 7> [Preparation of yttrium-containing solution] The compositions of the yttrium-containing solutions are shown in Tables 1 and 2. The yttrium-containing solutions were prepared by adding various yttrium compounds to ion-exchanged water and stirring and mixing for 12 hours while heating at 80°C.

[0093] [Table 1]

[0094] [Table 2]

[0095] [Preparation of zirconia cutting body (D1)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) under atmospheric pressure for 24 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (100°C, 30 minutes) to obtain a zirconia cutting body (D1).

[0096] [Preparation of zirconia cutting body (D2)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure not maintained: 10 cycles). The green body was then calcined in an electric furnace (1200°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) for 12 hours under atmospheric pressure. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (25°C, 72 hours) to obtain a zirconia cutting body (D2).

[0097] [Preparation of zirconia cutting body (D3)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure not maintained: 10 cycles). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y2) under atmospheric pressure for 1 hour. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (850°C, 30 minutes) to obtain a zirconia cutting body (D3).

[0098] [Preparation of zirconia cutting body (D4)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 3 minutes, number of repetitions: 10). The green body was then calcined in an electric furnace (900°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) under atmospheric pressure for 72 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (900°C, 30 minutes) to obtain a zirconia cutting body (D4).

[0099] [Preparation of zirconia cutting body (D5)] Zirconia powder (Zpex, manufactured by Tosoh Corporation) containing 3.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y3) under atmospheric pressure for 12 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (120°C, 30 minutes) to obtain a zirconia cutting body (D5).

[0100] [Preparation of zirconia cutting body (D6)] Zirconia powder containing 6.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure not maintained: 10 cycles). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y4) under atmospheric pressure for 72 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (1000°C, 30 minutes) to obtain a zirconia cutting body (D6).

[0101] [Preparation of zirconia cutting body (D7)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 2). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) under atmospheric pressure for 12 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (100°C, 30 minutes) to obtain a zirconia cutting body (D7).

[0102] [Preparation of zirconia cutting body (D8)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 30). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) for 10 minutes under reduced pressure. The calcined body was then removed from the yttrium-containing solution, dehydrated under normal pressure, and dried (1000°C, 30 minutes) to obtain a zirconia cutting body (D8).

[0103] [Preparation of zirconia cutting body (D9)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 50 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 30). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) under a pressurized atmosphere for 1 hour. The calcined body was then removed from the yttrium-containing solution, dehydrated under normal pressure, and dried (100°C, 30 minutes) to obtain a zirconia cutting body (D8).

[0104] [Preparation of zirconia cutting body (D10)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y5) under atmospheric pressure for 36 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (1000°C, 30 minutes) to obtain a zirconia cutting body (D10).

[0105] [Preparation of zirconia cutting body (D11)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y6) under atmospheric pressure for 12 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (1000°C, 30 minutes) to obtain a zirconia cutting body (D11).

[0106] [Preparation of zirconia cutting body (D12)] 100 g of zirconia powder containing 4.0 mol% dissolved yttrium was sprayed with 20 g of yttrium-containing solution (Y1), followed by drying under normal pressure to remove moisture. The dried zirconia powder was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). The green body was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia cutting body (D12).

[0107] [Preparation of zirconia cutting body (D13)] 100 g of zirconia powder containing 4.0 mol% dissolved yttrium was sprayed with 20 g of yttrium-containing solution (Y2), followed by drying under normal pressure to remove moisture. The dried zirconia powder was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure hold time: 1 minute, number of repetitions: 10). The green body was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia cutting body (D13).

[0108] [Preparation of zirconia cutting body (D14)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and pressed (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, post-release load pressure: 0 MPa, hold time: 1 minute, number of cycles: 10). It was then calcined in an electric furnace (1000°C, 30 minutes) to produce a zirconia cutting body (D14).

[0109] [Preparation of zirconia cutting body (D15)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 2.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure not maintained: 10 cycles). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y7) under atmospheric pressure for 12 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (1000°C, 30 minutes) to obtain a zirconia cutting body (D15).

[0110] [Preparation of zirconia cutting body (D16)] 100 g of zirconia powder containing 4.0 mol% dissolved yttrium and 1 g of yttrium oxide were mixed in a ball mill. The mixed zirconia powder was filled into a mold (φ100 mm) and press-molded (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). It was then calcined in an electric furnace (1000°C, 30 minutes) to produce a zirconia cutting body (D16).

[0111] [Preparation of zirconia cutting body (D17)] Zirconia sol (primary particle size: 29 nm, manufactured by CIK Nanotech) containing 4.0 mol% dissolved yttrium was poured into a mold (φ100 mm), and the solvent was dried to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure hold time: 1 minute, number of repetitions: 10). It was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia cutting body (D17).

[0112] [Preparation of zirconia cutting body (D18)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and pressed (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure hold time: 1 minute, number of repetitions: 1). It was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia cutting body (D18).

[0113] [Preparation of zirconia cutting body (D19)] Zirconia powder (Zpex, manufactured by Tosoh Corporation) containing 3.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and pressed (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure hold time: 1 minute, number of repetitions: 1). It was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia cutting body (D19).

[0114] [Preparation of zirconia cutting body (D20)] Zirconia powder containing 6.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and pressed (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 1). It was then calcined in an electric furnace (1000°C, 30 minutes) to produce a zirconia cutting body (D20).

[0115] [Preparation of zirconia workpiece (D21)] Zirconia powder containing 2.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 1). The green body was then calcined in an electric furnace (1000°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y7) under atmospheric pressure for 12 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (100°C, 30 minutes) to obtain a zirconia cutting body (D21).

[0116] [Preparation of zirconia cutting body (D22)] 100 g of zirconia powder containing 4.0 mol% yttrium dissolved therein and 1 g of yttrium oxide were mixed in a ball mill. The mixed zirconia powder was filled into a mold (φ100 mm) and pressed (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 1). It was then calcined in an electric furnace (1000°C, 30 minutes) to produce a zirconia cutting body (D22).

[0117] [Preparation of zirconia cutting body (D23)] Zirconia powder (Zpex SMILE, manufactured by Tosoh Corporation) containing 5.5 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP molding (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 1). The green body was then calcined in an electric furnace (1300°C, 30 minutes) to obtain a calcined body. The calcined body was then immersed in an yttrium-containing solution (Y1) under atmospheric pressure for 12 hours. The calcined body was then removed from the yttrium-containing solution, dehydrated under atmospheric pressure, and dried (120°C, 30 minutes) to obtain a zirconia cutting body (D23).

[0118] The methods for evaluating the properties of the zirconia workpieces D1 to D23 are shown below.

[0119] [Evaluation of the amount of yttrium contained in the test specimen] Test specimens for evaluating the yttrium content were prepared by cutting each zirconia specimen into a round plate (φ14 mm x 1.6 mm). The mole fraction of yttrium (yttrium oxide) contained in each specimen was measured using an X-ray fluorescence analyzer (Rigaku Corporation). The amount of yttrium obtained in this test was the total amount of yttrium dissolved in zirconia and yttrium not dissolved in zirconia.

[0120] [Method for calculating the amount of yttrium in the zirconia particles (a1) containing dissolved yttrium and the yttrium compound (a2) not dissolved in zirconia] The amount of yttrium in the zirconia particles (a1) containing dissolved yttrium and the yttrium compound (a2) not dissolved in zirconia was calculated by the acid extraction method. The yttrium in the zirconia particles containing dissolved yttrium in the present invention is not substantially decomposed or dissolved by acid, so the molar fraction of yttrium oxide relative to zirconia does not change. On the other hand, the yttrium compound in the yttrium compound (a2) not dissolved in zirconia in the present invention is decomposed or dissolved by acid, so the molar fraction of yttrium oxide relative to zirconia changes. Therefore, in the present invention, the yttrium that decomposes or dissolves in acid is calculated as the yttrium that is not dissolved in zirconia.

[0121] [Measurement and calculation of the amount of yttrium in the zirconia particles (a1) containing dissolved yttrium and the yttrium compound (a2) not dissolved in zirconia] Each test specimen (φ14 mm × 1.6 mm) for evaluating the yttrium content was immersed in nitric acid (15 vol%) for 48 hours to dissolve undissolved yttrium. After dissolution, the molar fraction of yttrium (yttrium oxide) in oxide equivalent in each test specimen was measured using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation). In the present invention, the amount of yttrium oxide obtained after dissolution was taken as the amount of yttrium dissolved in zirconia. The amount of yttrium not dissolved in zirconia was calculated by dividing the amount of yttrium dissolved in zirconia by the total amount of yttrium calculated in the evaluation of the yttrium content.

[0122] [Evaluation of specific surface area] Test specimens for specific surface area were prepared by cutting each zirconia workpiece into a rectangular column (5mm x 5mm x 5mm). The specific surface area of ​​each test specimen was measured using an automatic specific surface area / pore size distribution measuring device (Quantachrome). The specific surface area was calculated from the data obtained during desorption using the multipoint method (P / P = 0.10-0.30).

[0123] [Evaluation of skeletal volume] The skeletal volume test specimens were prepared by cutting each zirconia workpiece into a rectangular column (5 mm x 5 mm x 5 mm). The true density of each test specimen was measured using a dry automatic density meter (AccuPyc II 1340, manufactured by Shimadzu Corporation). In the present invention, the skeletal volume was calculated from the obtained true density using the following formula (2). Skeletal volume (cm 3 / g)=1 / true density(g / cm 3 )····(2)

[0124] [Evaluation of pore volume and pore diameter] Pore ​​volume test specimens were prepared by cutting each zirconia workpiece into a rectangular column (5mm x 5mm x 5mm). The pore volume of each test specimen was measured using a fully automatic multi-function mercury porosimeter (POREMASTER, manufactured by Quantachrome). The measurement conditions were mercury surface tension: 480 erg / cm 2 The test was carried out under the conditions of contact angle: 140°, discharge contact angle: 140°, and pressure: 0 to 50,000 psia.

[0125] [Porosity evaluation] The porosity of the present invention was calculated by the following formula (3). Porosity (%) = pore volume / (pore volume + skeleton volume) × 100 (3)

[0126] [Evaluation of three-point bending strength] The three-point bending strength test specimens were prepared by cutting each zirconia workpiece into a plate (width: 4.0 mm, length: 20 mm, thickness: 1.2 mm). The bending test was conducted in accordance with ISO 6872 (span distance: 12 mm, crosshead speed: 1.0 mm / min).

[0127] [Vickers hardness evaluation] Test specimens for Vickers hardness were prepared by cutting each zirconia workpiece into a round plate (φ14 mm × 1.6 mm). Vickers hardness tests were conducted in accordance with JIS Z 2244 (Vickers hardness test - test method).

[0128] [Evaluation of workability] The evaluation of workability was carried out using a molar crown model (minimum thickness: 0.05 mm). Test specimens were prepared by cutting each zirconia workpiece. Workability was evaluated visually, with no chipping observed being rated as excellent (◎), slight chipping observed but not clinically problematic being rated as good (◯), and chipping presenting a possible clinical problem being rated as poor (×).

[0129] The methods for evaluating the properties of the fully sintered zirconia bodies produced from the zirconia cut bodies D1 to D23 are shown below.

[0130] [Evaluation of three-point bending strength] Three-point bending specimens were prepared by cutting each zirconia workpiece into a plate (width: 4.8 mm x length: 20 mm x thickness: 1.6 mm). Each specimen was fully sintered in a firing furnace (sintering temperature: 1450-1600 °C, heating rate: 5 °C / min, holding time: 2 hours). The specimens were then adjusted to their size (width: 4.0 mm x length: 16 mm x thickness: 1.2 mm) using a surface grinder. The bending test was performed in accordance with ISO 6872 (span distance: 12 mm, crosshead speed: 1.0 mm / min).

[0131] [Translucency evaluation] Translucency test specimens were prepared by cutting each zirconia workpiece into a round plate (φ14 mm × 1.6 mm). Each test specimen was fully sintered in a firing furnace (firing temperature: 1450–1600°C, heating rate: 5°C / min, holding time: 2 hours). The thickness of each test specimen (1.0 mm) was then adjusted using a surface grinder. Translucency was evaluated by measuring the contrast ratio. The contrast ratio was measured using a spectrophotometer (Konica Minolta). The Y value when a white board was placed under each test specimen and color measurement was performed was defined as Yw, and the Y value when a black board was placed under the test specimen and color measurement was performed was defined as Yb. The contrast ratio was calculated using the following formula (4): Contrast ratio = Yb / Yw (4) The closer the contrast ratio is to 0, the more transparent the material is; the closer the contrast ratio is to 1, the more opaque the material is.

[0132] Tables 3 to 7 show the results of the property tests on the zirconia workpieces D1 to D23 for dental cutting.

[0133] [Table 3]

[0134] [Table 4]

[0135] [Table 5]

[0136] [Table 6]

[0137] [Table 7]

[0138] Examples 1 to 15 The porosity of the zirconia objects for dental cutting in Examples 1 to 15 was confirmed to be 15 to 30%. Furthermore, it was confirmed that the zirconia objects for dental cutting had yttrium compounds (a2) not dissolved in zirconia dispersed on the surfaces of the zirconia particles (a1) containing dissolved yttrium. It was confirmed that the machinability of the zirconia objects for dental cutting was superior to that of conventional zirconia objects for dental cutting, with no chipping or fracture. Furthermore, the fully sintered zirconia bodies produced from the zirconia objects for dental cutting in Examples 1 to 15 had excellent bending strengths of 500 MPa or more and exhibited extremely high translucency with a contrast ratio of less than 0.70.

[0139] Example 16 The porosity of the zirconia object for dental cutting of Example 16 was confirmed to be 15 to 30%. The machinability of this zirconia object for dental cutting was confirmed to be less chipping and fracture than that of conventional zirconia objects for dental cutting. Furthermore, the fully sintered zirconia body produced from the zirconia object for dental cutting of Example 16 was confirmed to have excellent bending strength and translucency (contrast ratio) of 500 MPa or more.

[0140] Example 17 The porosity of the zirconia object for dental cutting of Example 17 was confirmed to be 15 to 30%. Furthermore, it was confirmed that the zirconia object for dental cutting had yttrium compounds (a2) not dissolved in zirconia dispersed on the surfaces of the zirconia particles (a1) containing dissolved yttrium. It was confirmed that the machinability of the zirconia object for dental cutting was superior to that of conventional zirconia objects for dental cutting, with no chipping or fracture. Furthermore, it was confirmed that the fully sintered zirconia body produced from the zirconia object for dental cutting of Example 17 had excellent bending strength and translucency (contrast ratio) of 500 MPa or more.

[0141] Example 18 The porosity of the zirconia object for dental cutting of Example 18 was confirmed to be 15 to 30%. Furthermore, it was confirmed that the zirconia object for dental cutting contained zirconia particles (a1) containing dissolved yttrium and yttrium compounds (a2) not dissolved in zirconia. Compared to conventional zirconia objects for dental cutting, the machinability of the zirconia object for dental cutting was confirmed to be excellent, with no chipping or fracture. Furthermore, it was confirmed that the fully sintered zirconia body produced from the zirconia object for dental cutting of Example 18 had excellent bending strength and translucency (contrast ratio) of 500 MPa or more.

[0142] Example 19 The porosity of the zirconia object for dental cutting of Example 19 was confirmed to be 15 to 30%. The machinability of this zirconia object for dental cutting was confirmed to be less chipping and fracture than that of conventional zirconia objects for dental cutting. Furthermore, the fully sintered zirconia body produced from the zirconia object for dental cutting of Example 19 was confirmed to have excellent bending strength and translucency (contrast ratio) of 500 MPa or more.

[0143] Comparative Example 1 Comparative Example 1 is a zirconia workpiece for dental cutting containing 5.5 mol% of dissolved yttrium. This zirconia workpiece for dental cutting had a translucency (contrast ratio) of less than 0.80 after complete sintering and was clinically usable without any problems, but had a porosity of more than 30%, resulting in poor chipping resistance during cutting.

[0144] Comparative Example 2 Comparative Example 2 is a zirconia workpiece for dental cutting containing 3.0 mol% of dissolved yttrium. Although the translucency (contrast ratio) of this zirconia workpiece for dental cutting after complete sintering was less than 0.80 and clinically usable, the porosity exceeded 30%, resulting in poor chipping resistance during cutting.

[0145] Comparative Example 3 Comparative Example 3 is a zirconia workpiece for dental cutting containing 6.0 mol% of dissolved yttrium. Although the translucency (contrast ratio) of this zirconia workpiece for dental cutting after complete sintering was less than 0.80 and clinically usable, the porosity exceeded 30%, resulting in poor chipping resistance during cutting.

[0146] Comparative Example 4 Comparative Example 4 is a zirconia workpiece for dental cutting containing 2.0 mol% dissolved yttrium and 3.5 mol% undissolved yttrium. Because the porosity of this zirconia workpiece for dental cutting was less than 15%, it exhibited poor chipping resistance during cutting. Furthermore, the bending strength after complete sintering was insufficient, the contrast ratio was 0.80 or more, and visual inspection revealed insufficient translucency compared to Examples 1 to 15.

[0147] Comparative Example 5 Comparative Example 5 is a zirconia workpiece for dental cutting containing 4.0 mol% dissolved yttrium and 1.0 mol% undissolved yttrium. This zirconia workpiece for dental cutting had poor chipping resistance during cutting because the porosity exceeded 30% and the yttrium compound (a2) not dissolved in zirconia was not dispersed on the surface of the zirconia particles (a1) containing dissolved yttrium. Furthermore, the contrast ratio was 0.80 or more, and visual inspection revealed insufficient translucency compared to Examples 1 to 15.

[0148] Comparative Example 6 Comparative Example 6 is a zirconia workpiece for dental cutting containing 5.5 mol% dissolved yttrium and 0.5 mol% undissolved yttrium. Because the porosity of this zirconia workpiece for dental cutting was less than 15%, the translucency (contrast ratio) after complete sintering was less than 0.80, and although it could be used clinically without any problems, it had poor chipping resistance during cutting.

[0149] <Examples 20 to 30, Comparative Examples 7 to 12, and Reference Examples 1 and 2>

[0150] [Preparation of zirconia cutting body (D24)] Zirconia powder (Zpex4: Tosoh Corporation) containing 4.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and pressed (surface pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure holding time: 1 minute, number of repetitions: 10). It was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia cutting body (D24).

[0151] [Preparation of zirconia cutting body (D25)] A zirconia cut body (D25) was prepared in the same manner as the zirconia cut body (D24), except that the CIP treatment was repeated five times, and was then evaluated.

[0152] [Preparation of zirconia cutting body (D26)] A zirconia cut body (D26) was prepared in the same manner as the zirconia cut body (D24), except that the CIP treatment was repeated 20 times, and was then evaluated.

[0153] [Preparation of zirconia cutting body (D27)] Zirconia powder (Zpex4, manufactured by Tosoh Corporation) containing 4.0 mol% dissolved yttrium was filled into a mold (φ100 mm) and press-molded (contact pressure: 50 MPa) to obtain a green body. The green body was then subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure hold time: 1 minute, number of cycles: 10). It was then degreased in an electric furnace (500 °C, 30 minutes). The degreased green body was further subjected to CIP (maximum load pressure: 200 MPa, load pressure after release: 0 MPa, maximum load pressure hold time: 1 minute, number of cycles: 10). It was then calcined in an electric furnace (1000 °C, 30 minutes) to produce a zirconia machinable body. The rest of the evaluation was performed in the same manner as for the zirconia machinable body (D24).

[0154] [Preparation of zirconia cutting body (D28)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D24), except that zirconia powder containing 5.5 mol% of dissolved yttrium (Zpex SMILE: manufactured by Tosoh Corporation) was used as the raw material powder, and evaluation was carried out.

[0155] [Preparation of zirconia cutting body (D29)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D27), except that zirconia powder containing 5.5 mol% of dissolved yttrium (Zpex SMILE: manufactured by Tosoh Corporation) was used as the raw material powder, and evaluation was carried out.

[0156] [Preparation of zirconia cutting body (D30)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D24), except that the maximum load pressure in the CIP treatment was set to 180 MPa, and an evaluation was carried out.

[0157] [Preparation of zirconia cutting body (D31)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D24), except that the load pressure after release in the repeated CIP treatment was set to 50 MPa, and an evaluation was carried out.

[0158] [Preparation of zirconia cutting body (D32)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D24), except that the load pressure after release in the repeated CIP treatment was set to 100 MPa, and an evaluation was carried out.

[0159] [Preparation of zirconia cutting body (D33)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D24), except that the holding time in the CIP treatment was set to 0 seconds, and an evaluation was carried out.

[0160] [Preparation of zirconia cutting body (D34)] A zirconia cutting body was prepared in the same manner as the zirconia cutting body (D24), except that the holding time in the CIP treatment was changed to 3 minutes, and an evaluation was carried out.

[0161] [Preparation of zirconia cutting body (D35)] A zirconia cuttable body was prepared in the same manner as the zirconia cuttable body (D24), except that the CIP treatment was repeated once, and then evaluated.

[0162] [Preparation of zirconia cutting body (D36)] A zirconia cuttable body was prepared in the same manner as the zirconia cuttable body (D28), except that the CIP treatment was repeated once, and then evaluated.

[0163] [Preparation of zirconia cutting body (D37)] A zirconia machinable body was prepared in the same manner as the zirconia machinable body (D36), except that complete sintering was performed by normal sintering (sintering temperature: 1450°C, heating rate: 5°C / min, holding time: 2 hours), and then evaluated.

[0164] [Preparation of zirconia cutting body (D38)] A zirconia cutting body was prepared in the same manner as the zirconia cutting body (D35), except that the holding time in the CIP treatment was changed to 10 minutes, and an evaluation was carried out.

[0165] [Preparation of zirconia cutting body (D39)] A zirconia cutting body was prepared in the same manner as the zirconia cutting body (D24) except that zirconia powder containing 2.5 mol % of dissolved yttrium was used as the raw material powder, and an evaluation was carried out.

[0166] [Preparation of zirconia cutting body (D40)] A zirconia machinable body was prepared in the same manner as the zirconia machinable body (D39), except that complete sintering was performed by normal sintering (sintering temperature: 1450°C, heating rate: 5°C / min, holding time: 2 hours), and then evaluated.

[0167] [Preparation of zirconia cutting body (D41)] A zirconia cutting body was prepared in the same manner as the zirconia cutting body (D24) except that zirconia powder containing 7.0 mol % of dissolved yttrium was used as the raw material powder, and an evaluation was carried out.

[0168] [Preparation of zirconia cutting body (D42)] A zirconia cutting body was prepared in the same manner as the zirconia cutting body (D41), except that complete sintering was performed by normal sintering (sintering temperature: 1450°C, heating rate: 5°C / min, holding time: 2 hours), and evaluated.

[0169] [Preparation of zirconia cutting body (D43)] A zirconia workpiece was prepared in the same manner as the zirconia workpiece (D35), except that the maximum load pressure in the CIP treatment was set to 40 MPa, and an evaluation was carried out.

[0170] [Preparation of zirconia cutting body (D44)] A zirconia cutting body was prepared in the same manner as the zirconia cutting body (D35), except that the calcination temperature was set to 1300°C, and an evaluation was carried out.

[0171] The specific surface area, skeletal volume, pore volume, porosity, three-point bending strength, and Vickers hardness of the zirconia cut bodies D24 to D44 were evaluated using the same evaluation methods as those for the zirconia cut bodies D1 to D23.

[0172] The methods for evaluating the properties of the fully sintered zirconia bodies produced from the zirconia cut bodies D24 to D44 are shown below.

[0173] [Evaluation of three-point bending strength] Three-point bending specimens were prepared by cutting each zirconia workpiece into a plate (width: 4.8 mm, length: 20 mm, thickness: 1.6 mm). Each specimen was sintered in a sintering furnace for a short time (sintering temperature: 1600 °C, heating rate: 70 °C / min, holding time: 2 min). In addition, zirconia workpieces D38, D41, and D42 were fully sintered in a sintering furnace using standard sintering (sintering temperature: 1450–1600 °C, heating rate: 5 °C / min, holding time: 2 h). Each specimen was then ground to a size (width: 4.0 mm, length: 16 mm, thickness: 1.2 mm) using a surface grinder. Bending tests were performed in accordance with ISO 6872 (span distance: 12 mm, crosshead speed: 1.0 mm / min).

[0174] [Translucency evaluation] Translucency test specimens were prepared by cutting each zirconia cut specimen into a round plate (φ14 mm × 1.6 mm). Each specimen was sintered for a short time in a sintering furnace (sintering temperature: 1600 °C, heating rate: 70 °C / min, holding time: 2 min). Furthermore, zirconia cut specimens D38, D41, and D42 were also fully sintered in a sintering furnace using standard sintering (sintering temperature: 1450–1600 °C, heating rate: 5 °C / min, holding time: 2 h). The thickness of each specimen was then adjusted (1.0 mm) using a surface grinder. Translucency was evaluated by measuring the contrast ratio. The contrast ratio was measured using a spectrophotometer (Konica Minolta). The Y value measured with a white board placed under each specimen was defined as Yw, and the Y value measured with a black board placed under each specimen was defined as Yb. The contrast ratio was calculated using the following formula (5). Contrast ratio = Yb / Yw (5) The closer the contrast ratio is to 0, the more transparent the material is; the closer the contrast ratio is to 1, the more opaque the material is.

[0175] [Table 8]

[0176] [Table 9]

[0177] [Table 10]

[0178] [Table 11]

[0179] Examples 20 to 30 The porosity of the zirconia cutting bodies D24 to D34 for dental cutting in Examples 20 to 30 was confirmed to be 15 to 30%. Furthermore, the fully sintered zirconia bodies produced by short-time sintering from the zirconia cutting bodies for dental cutting in Examples 20 to 30 were confirmed to have excellent bending strength and translucency (contrast ratio) of 600 MPa or more. Furthermore, with regard to translucency, they were confirmed to exhibit very high translucency with a contrast ratio of 0.70 or less.

[0180] Comparative Example 7 In Comparative Example 7, a zirconia workpiece D35 for dental cutting, which contained 4.0 mol% dissolved yttrium and was produced without repeated CIP treatment, was sintered for a short time. After complete sintering with a short sintering time, the translucency (contrast ratio) was less than 0.80, which means that it can be used clinically without any problems. However, the pore volume was large and the porosity exceeded 30%, so chipping resistance during cutting was poor.

[0181] Comparative Example 8 In Comparative Example 8, a zirconia cutting object D36 for dental cutting, which contained 5.5 mol% dissolved yttrium and was produced without repeated CIP treatment, was sintered for a short time. After complete sintering by short sintering, the translucency (contrast ratio) was less than 0.80, which means that it can be used clinically without any problems. However, because the pore volume was large and the porosity exceeded 30%, the chipping resistance during cutting was poor, and the strength after complete sintering by short sintering was insufficient.

[0182] Comparative Example 9 In Comparative Example 9, a zirconia workpiece D37 for dental cutting, which contained 5.5 mol% dissolved yttrium and was produced without repeated CIP treatment, was sintered in the usual way. After complete sintering in a short time, the translucency (contrast ratio) was less than 0.80, which means that it can be used clinically without any problems. However, the pore volume was large and the porosity exceeded 30%, so chipping resistance during cutting was poor.

[0183] Comparative Example 10 In Comparative Example 10, a zirconia workpiece D38 for dental cutting, which contained 4.0 mol% dissolved yttrium and was produced without repeated CIP treatment, was sintered for a short time. The translucency (contrast ratio) after complete sintering by short sintering was less than 0.80, and although it was clinically usable, the pore volume was large and the porosity exceeded 30%, resulting in poor chipping resistance during cutting.

[0184] [Reference example 1] In Reference Example 1, a zirconia workpiece D39 for dental cutting, which contained 2.5 mol% dissolved yttrium and was produced by repeating CIP treatment 10 times, was sintered for a short time. Because the amount of dissolved yttrium was small, the translucency (contrast ratio) was insufficient, and it was visually confirmed that the translucency was inferior to that of the Examples.

[0185] Example 31 Example 31 is a zirconia cutting object D40 for dental cutting, containing 2.5 mol% dissolved yttrium and prepared by repeating CIP treatment 10 times, followed by conventional sintering. Similar to Examples 20 to 30, it was found to have excellent bending strength of 600 MPa or more. Furthermore, with regard to translucency, the contrast ratio was less than 0.080, indicating that it can be used clinically without any problems.

[0186] [Reference example 2] In Reference Example 2, a zirconia workpiece for dental cutting, which contained 7.0 mol% dissolved yttrium and was produced by repeating CIP treatment 10 times, was subjected to short-time sintering. Although sufficient translucency (contrast ratio) was obtained due to the large amount of dissolved yttrium, it was found that the strength was inferior to that of Examples 20 to 30, which were sintered for a short time.

[0187] Example 32 Example 32 is a zirconia cutting body for dental cutting, containing 7.0 mol% dissolved yttrium and prepared by repeating CIP treatment 10 times, followed by conventional sintering. Similar to Examples 20 to 30, it was found to have excellent bending strength of 600 MPa or more. Furthermore, it was found to exhibit very high translucency, with a contrast ratio of 0.70 or less.

[0188] Comparative Example 11 In Comparative Example 11, a zirconia workpiece for dental cutting was prepared by repeating CIP treatment 10 times, containing 4.0 mol% dissolved yttrium, with a maximum load pressure of 40 MPa during repeated CIP treatment. The workpiece was then sintered for a short time. The translucency (contrast ratio) after complete sintering using the short sintering method was less than 0.80, meaning it could be used clinically without any problems. However, the pore volume was large, and the porosity exceeded 30%, meaning that the workpiece had poor chipping resistance during cutting.

[0189] Comparative Example 12 In Comparative Example 12, a zirconia workpiece for dental cutting was sintered for a short time, containing 4.0 mol% dissolved yttrium and prepared at a pre-sintering temperature of 1300° C. The translucency (contrast ratio) after complete sintering by short sintering was less than 0.80, and although it could be used clinically without any problems, the pore volume was small and the porosity was less than 15%, resulting in poor chipping resistance during cutting.

Claims

1. A method for manufacturing a zirconia workpiece for dental cutting, comprising: forming the zirconia powder; and forming by cold isostatic pressing, The method for producing a zirconia workpiece for dental cutting, which comprises a series of steps of applying and releasing a load pressure at least twice in the molding by the cold isostatic pressing method.

2. 2. A method for producing a zirconia workpiece for dental cutting according to claim 1, comprising: A method for producing a zirconia workpiece for dental cutting, characterized in that the zirconia powder is molded by press molding.

3. 3. A method for producing a zirconia workpiece for dental cutting according to claim 1 or 2, comprising: A method for producing a zirconia workpiece for dental cutting, characterized in that the method for forming by cold isostatic pressing further comprises a step of maintaining a maximum load pressure.

4. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 3, comprising: A method for producing a zirconia workpiece for dental cutting, characterized in that the difference between the maximum load pressure and the load pressure after release is at least 50 MPa.

5. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 4, comprising: The method for producing a zirconia workpiece for dental cutting, wherein the zirconia powder is zirconia particles containing dissolved yttrium, and the method further comprises, after the step of molding by cold isostatic pressing, a step of dispersing an yttrium compound on the zirconia particles containing dissolved yttrium.

6. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 5, comprising: A manufacturing method comprising a series of steps of applying a load pressure and releasing the load pressure at least 10 times.

7. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 6, comprising: A manufacturing method characterized in that the load pressure is increased in multiple stages up to a maximum load pressure.

8. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 7, comprising: The manufacturing method is characterized in that the time required for the series of steps is 30 seconds to 10 minutes.

9. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 8, comprising: The manufacturing method is characterized in that the repeated CIP treatment includes a degreasing step in between.

10. 10. The method for producing a zirconia workpiece for dental cutting according to claim 9, The manufacturing method is characterized in that the degreasing temperature in the degreasing step is 300 to 800°C.

11. A method for producing a zirconia workpiece for dental cutting according to any one of claims 1 to 10, comprising: The manufacturing method further comprises a step of calcining at a temperature of 800 to 1200°C.

12. 6. The method for producing a zirconia workpiece for dental cutting according to claim 5, A manufacturing method characterized in that the content of the yttrium compound in the yttrium-containing liquid used when dispersing the yttrium compound on the surface of zirconia is 1 to 60 wt %.

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