Dental workpiece

Abstract

The present disclosure provides a dental workpiece from which a sintered body having excellent translucency is obtained even when the holding time at the maximum sintering temperature is 2 minutes. The present disclosure relates to a dental workpiece containing zirconia. The dental workpiece, when observed with a transmission electron microscope after heat treatment under the following condition (i), is found to contain Y4Zr3O12. Condition (i): the dental workpiece is heated from room temperature to 1100°C at a heating rate of 350°C / min, the holding time at 1100°C is set to 0 minutes, the dental workpiece is cooled to 800°C at a cooling rate of 200°C / min, and is then allowed to cool to room temperature.

Description

Dental workpiece

[0001] This disclosure relates to dental workpieces. More specifically, this disclosure relates to dental workpieces in which the sintered body obtained is highly translucent even when the holding time at the maximum sintering temperature is 2 minutes.

[0002] Zirconia sintered bodies are widely used industrially, and in recent years, they have been particularly used in dental materials such as dental prostheses. These dental prostheses are often manufactured by forming zirconia molded bodies into desired shapes such as discs or prismatics by press molding zirconia particles or by molding using a composition containing zirconia particles, then calcining these bodies to form calcined bodies (mill blanks), cutting (milling) them into the shape of the intended dental prosthesis, and finally firing them again.

[0003] Zirconia is a compound in which phase transitions occur between multiple crystal systems. Therefore, partially-stabilized zirconia (PSZ) and fully-stabilized zirconia (FSZ), which suppress phase transitions by solid-solving stabilizers such as yttria (yttrium oxide; Y2O3) into zirconia, are used in various fields.

[0004] In the dental field, zirconia has been used as a frame material due to its high strength but low translucency. However, in recent years, with improvements in the translucency of zirconia, it has become increasingly common to fabricate dental prostheses using only zirconia.

[0005] Traditionally, the fabrication of dental prostheses using only zirconia was often done in dental laboratories. As a result, patients could not receive treatment using dental prostheses on the same day as their initial consultation at the dental clinic, and had to make another visit on a different day to receive treatment with dental prostheses.

[0006] In response to this, a treatment method called "one-visit treatment" has been proposed, which allows patients to receive treatment using dental prostheses in a single visit by having the prostheses fabricated easily at the dental clinic. In this case, it is necessary to fire the zirconia in a short time, and patent documents such as Patent Document 1 have been proposed.

[0007] International Publication No. 2018 / 056330

[0008] The method described in Patent Document 1 demonstrates that a sintered body produced by firing a calcined body at a maximum sintering temperature of 1550°C for 15 minutes can achieve the same transparency as a body fired at the same temperature for 120 minutes. This demonstrates that the firing time can be shortened.

[0009] However, according to the present inventors, in the invention described in Patent Document 1, if the holding time at the maximum sintering temperature of 1550°C is further shortened (for example, to 7 minutes or less), the light transmittance decreases. Therefore, it was found that there is room for improvement in the invention described in Patent Document 1 to further shorten the holding time.

[0010] This disclosure aims to provide a dental workpiece that exhibits excellent light transmittance even when the holding time at the maximum sintering temperature is 2 minutes.

[0011] The present inventors have conducted extensive research to solve the above problems and have found that in a dental workpiece containing zirconia (zirconium(IV) oxide; ZrO2), observation by transmission electron microscope (TEM) after heat treatment under the following conditions: heating from room temperature to 1100°C at a heating rate of 350°C / min, holding time at 1100°C is 0 minutes, cooling to 800°C at a cooling rate of 200°C / min, and then allowing to cool at room temperature, Y4Zr3O 12 We discovered that the above problems can be solved by using a dental workpiece containing [the specified material], and based on this finding, we furthered our research and completed this disclosure.

[0012] This disclosure encompasses the following inventions: [1] A dental workpiece comprising zirconia, wherein, in observation by transmission electron microscope after heat treatment under the following conditions (i), Y4Zr3O 12A dental workpiece comprising. (i) Heating from room temperature to 1100°C at a temperature increase rate of 350°C / min, holding the temperature at 1100°C for 0 minute, cooling to 800°C at a temperature decrease rate of 200°C / min, and then allowing to cool naturally to room temperature. [2] In X-ray diffraction (XRD) measurement after heat treatment under the above condition (i), Y4Zr3O 12 abundance f d1 (%) is more than 13%, the dental workpiece according to [1]. f d1 (%) = I d1 / (I m1 + I t1 + I c1 + I y1 + I d1 ) × 100 (1-1) (wherein f d1 represents the abundance (%) of Y4Zr3O 12 , in XRD measurement, I m1 represents the peak area intensity around 2θ = 28.2° where the peak top of the main peak of monoclinic system appears, I t1 represents the peak area intensity around 2θ = 30.3° where the peak top of the main peak of tetragonal system appears, I c1 represents the peak area intensity around 2θ = 30.0° where the peak top of the main peak of cubic system appears, I d1 represents the peak area intensity around 2θ = 29.6° where the peak top of the main peak of Y4Zr3O 12 appears, I y1 represents the peak area intensity around 2θ = 29.2° where the peak top of the main peak of yttria not dissolved in zirconia appears. Note that since the positions of the main peaks of Y4Zr3O 12 , tetragonal system, and cubic system are close to each other, the area intensity of each main peak is calculated by peak separation.) [3] In X-ray diffraction (XRD) measurement before heat treatment under the above condition (i), Y4Zr3O 12 abundance f d2 (%) is less than 2.5%, the dental workpiece according to [1] or [2]. f d2 (%) = I d2 / (I m2 + I t2 + Ic2 +I y2 +I d2 )×100 (1-2) (where f d2 is Y4Zr3O 12 This represents the prevalence rate (%) of [I] in XRD measurements. m2 This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t2 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c2 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d2 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y2 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 For tetragonal and cubic crystal systems, the positions of the main peaks are approximate, so the area intensity of each main peak is calculated by peak separation.) [4] Y4Zr3O calculated by the above formula (1-2) 12 The probability of existence f d2 A dental workpiece according to [3], wherein (%) is greater than 0%. [5] A dental workpiece according to any one of [1] to [4], which is a calcined zirconia body. [6] A dental workpiece containing zirconia, wherein in X-ray diffraction (XRD) measurement after heat treatment under the following condition (i), the amount of Y4Zr3O calculated by the following formula (1-1) is 12 The probability of existence f d1 A dental workpiece in which (%) is greater than 0%. (i) Heat from room temperature to 1100°C at a heating rate of 350°C / min, hold at 1100°C for 0 minutes, cool to 800°C at a cooling rate of 200°C / min, and then allow to cool at room temperature. f d1 (%) = I d1 / (I m1 +I t1 +I c1 +I y1 +I d1 )×100 (1-1) (where f d1is Y4Zr3O 12 This represents the prevalence rate (%) of [I] in XRD measurements. m1 This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t1 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c1 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d1 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y1 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 , For tetragonal and cubic crystal systems, the positions of the main peaks are approximate, so the area intensity of each main peak is calculated by peak separation.) [7] In the X-ray diffraction (XRD) measurement after heat treatment under condition (i) above, Y4Zr3O calculated by formula (1-1) above 12 The probability of existence f d1 The dental workpiece according to [6], wherein the (%) is greater than 13%. [8] In the X-ray diffraction (XRD) measurement before heat treatment under the above condition (i), Y4Zr3O is calculated by the following formula (1-2). 12 The probability of existence f d2 A dental workpiece according to [6] or [7], wherein the percentage (%) is less than 2.5%. d2 (%) = I d2 / (I m2 +I t2 +I c2 +I y2 +I d2 )×100 (1-2) (where f d2 is Y4Zr3O 12 This represents the prevalence rate (%) of [I] in XRD measurements. m2 This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t2 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and Ic2 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d2 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y2 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 For tetragonal and cubic crystal systems, the positions of the main peaks are approximate, so the area intensity of each main peak is calculated by peak separation.) [9] Y4Zr3O calculated by the above formula (1-2) 12 The probability of existence f d2 A dental workpiece as described in [8], wherein the (%) is greater than 0%.

[10] A dental workpiece as described in any of [6] to [9], which is a zirconia calcined body.

[0013] This disclosure provides a dental workpiece that exhibits excellent light transmittance even when the holding time at the maximum sintering temperature is 2 minutes. Furthermore, by using the dental workpiece of this disclosure, a zirconia sintered body can be obtained that maintains the same level of high light transmittance as that obtained with long-term sintering (holding time of 2 hours) after sintering in a short time, such as 7 minutes or less at 1550°C. This contributes to further improvements in productivity, such as shortening treatment time in dental clinics, and is advantageous in realizing one-visit treatments in dental clinics.

[0014] This is an electron diffraction pattern used to explain the method for calculating the distance and angle of the diffraction spot.

[0015] In this specification, "Y4Zr3O 12 " is a metastable crystalline system of zirconia. Y4Zr3O 12 It is known that it exists up to around 1375°C in the phase diagram. In this specification, "Y4Zr3O 12 The probability of existence f d1 "(%)" refers to the value calculated by formula (1-1) in the X-ray diffraction (XRD) measurement of a dental workpiece after heat treatment under condition (i). In this specification, "Y4Zr3O12 The probability of existence f d2"(%)" refers to the value calculated by formula (1-2) in the X-ray diffraction (XRD) measurement of the dental workpiece before heat treatment under condition (i). In this specification, "zirconia composition" refers to a composition containing zirconia powder and powder of a stabilizer (preferably yttria (Y2O3)) capable of suppressing the phase transition of zirconia. In this specification, "molded body" refers to a body that has not reached either a semi-sintered state (calcined state) or a sintered state. That is, a molded body is distinguished from calcined bodies and sintered bodies in that it is not calcined after being molded. In this specification, "calcined body" refers to a semi-sintered state in which the inorganic particles constituting the calcined body are necked (bonded) to each other and the inorganic particles constituting the calcined body are not completely sintered. In this specification, "sintered body" refers to a sintered state in which the constituent inorganic particles are completely sintered. In this specification, "dental workpiece" includes both molded bodies and calcined bodies. In this specification, "calcined zirconia" means a semi-sintered state in which zirconia particles are necked (bonded) to each other and the zirconia particles are not completely sintered. In this specification, "sintered zirconia" means a sintered state in which the zirconia particles are completely sintered. In a sintered zirconia, the zirconia particles solidify together through sintering, and the relative density increases and densification progresses with sintering, resulting in a completely sintered state with a relative density of 95% or more. In this specification, "zirconia" means zirconium(IV) oxide (ZrO2), and ZrO2 particles may contain trace amounts of HfO2 (0.5% to 3% by mass) relative to the amount of ZrO2. Since HfO2 is difficult to separate, terms such as "zirconia," "zirconia particles," and "zirconia powder" mean those containing both ZrO2 and HfO2. Furthermore, particles and powders in which yttria is solid-dissolved in zirconia are also included in "zirconia particles" and "zirconia powder," respectively. In this specification, "maximum calcination temperature" means the highest heating temperature that is ultimately reached during the calcination process (the firing process to obtain a calcined body) and maintained for a predetermined time.As used herein, the "maximum sintering temperature" refers to the maximum heating temperature that is finally reached and maintained for a predetermined time during the main firing step (the firing step for obtaining a sintered body). As used herein, the content (mol%) of a stabilizer refers to the content calculated by converting zirconia and the stabilizer into oxides. As used herein, "short-time sintering" refers to sintering in which the holding time at the maximum sintering temperature (e.g., 1550°C) is 7 minutes or less. As used herein, "normal pressure" refers to standard atmospheric pressure (1 atm). In the present specification, the upper and lower limits of numerical ranges (temperature ranges, contents of each component, abundance of crystal systems, values calculated from components, etc., and various physical properties, etc.) can be combined as appropriate.

[0016] [Dental Workpiece] The dental workpiece of the present disclosure is a dental workpiece containing zirconia, wherein in observation with a transmission electron microscope after heat treatment under the following condition (i) (hereinafter, also simply referred to as "specific heat treatment"), Y₄Zr₃O 12 , which is a dental workpiece. (i) Heating from room temperature to 1100°C at a temperature increase rate of 350°C / min, setting the holding time at 1100°C to 0 minute, cooling to 800°C at a temperature decrease rate of 200°C / min, and then allowing to cool to room temperature. That is, the present disclosure provides a dental workpiece containing Y₄Zr₃O 12 in an evaluation method of observation with a transmission electron microscope (TEM) after a specific heat treatment.

[0017] In the dental workpiece of the present disclosure, Y₄Zr₃O 12 is produced in a predetermined amount as a crystal system in the initial stage (up to about 1100°C) of the main firing step (the firing step for obtaining a sintered body). Therefore, when TEM observation is performed after the specific heat treatment, Y₄Zr₃O 12 is contained as a crystal system in the state after the heat treatment. The conditions for TEM observation are as described in the Examples below. In the dental workpiece of the present disclosure, Y₄Zr₃O 12 is produced in a predetermined amount as a crystal system in the initial stage (up to about 1100°C) of the main firing step (particularly preferably, the abundance f d1(% is a predetermined ratio), the reason why the zirconia sintered body obtained has excellent light transmittance even when the holding time at the maximum sintering temperature is 2 minutes, and the holding time at 1550° C. is 7 minutes or less. The reason why the same high light transmittance as that obtained by long-time sintering (the holding time is 2 hours) can be maintained after sintering in a short time is not clear, but it is presumed as follows. When firing a dental workpiece, in the initial stage (up to about 1100° C.) of the main firing step (the firing step for obtaining a sintered body), Y₄Zr₃O 12 abundance f d1 is at least a certain amount. In other words, when observed with a transmission electron microscope after the specific heat treatment, Y₄Zr₃O 12 reduces the degree of uneven distribution of yttrium atoms in the dental workpiece during firing, and brings the existence state of yttrium atoms closer to the final state in the sintered body. Therefore, the migration distance of yttrium atoms moving to the zirconia side during main firing is shortened, and as a result, the thermal energy required during firing is reduced. Even when firing is performed in a shorter time compared with the conventional technology, it is considered that a sintered body having the same level of light transmittance as the sintered body obtained by long-time sintering can be obtained. In observation with a transmission electron microscope, Y₄Zr₃O 12 inclusion can be confirmed, for example, by the method described in the examples.

[0018] As one embodiment, a dental workpiece in which the abundance f 12 of Y₄Zr₃O d1 (%) calculated by the following formula (1-1) in X-ray diffraction (XRD) measurement after specific heat treatment under the condition (i) is more than 0% is mentioned. f d1 (%) = I d1 / (I m1 + I t1 + I c1 + I y1 + I d1 ) × 100 (1-1) (In the formula, f d1 represents the abundance (%) of Y₄Zr₃O 12 , in XRD measurement, I m1 represents the area intensity of the peak near 2θ = 28.2° where the peak top of the main peak of the monoclinic system appears, It1 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c1 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d1 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y1 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 Since the positions of the main peaks are similar for tetragonal and cubic crystal systems, the area intensity of each main peak is calculated by peak separation.) In one embodiment, in the X-ray diffraction (XRD) measurement after heat treatment under condition (i) above, Y4Zr3O calculated by formula (1-1) above 12 The probability of existence f d1 Examples include dental workpieces with a percentage (%) of over 13%.

[0019] In this specification, with respect to the position of the peak shown in equations (1-1), (1-2), and (1-3) in X-ray diffraction measurements, "near" is not particularly limited, but means ±0.05°. For example, near 2θ = 29.6° means 29.55° to 29.65°.

[0020] Y4Zr3O in the dental workpiece according to the above embodiment 12 The probability of existence f d1 The percentage (%) is preferably 5.0% or more, and is more preferably over 13%, even more preferably 14% or more, particularly preferably 15% or more, and most preferably 16% or more, in order to maintain high transparency after sintering for a short time, such as when the holding time at the maximum sintering temperature is 7 minutes or less, the zirconia sintered body obtained has excellent light transmittance, or it is easier to maintain high light transmittance after sintering for a short time, such as when the holding time at 1550°C is 7 minutes or less, similar to that of long-term sintering. By controlling the distribution state of the yttrium element as described later, the Y4Zr3O after heat treatment 12 The probability of existence f d1By using a dental workpiece in which the content exceeds 13%, the diffusion of yttrium into the zirconia crystal lattice is promoted from the initial stage of the firing process, even during short firing times. 12 The probability of existence f d1 (%) is Y4Zr3O 12 Considering that the phase transition from to other crystal systems becomes the rate-limiting step, making it difficult for the sintering of dental workpieces to proceed, it is preferable that the amount be 55% or less, more preferably 50% or less, even more preferably 45% or less, particularly preferably 42% or less, and most preferably 40% or less. In other words, the Y4Zr3O 12 The probability of existence f d1 The percentage (%) is preferably 5.0% to 55%, preferably more than 13% and 50%, more preferably 14% to 45%, particularly preferably 15% to 42%, and most preferably 16% to 40%. Y4Zr3O 12 The probability of existence f d1 Regarding the percentage (%), the method for calculating the value in X-ray diffraction measurement after a specific heat treatment can be calculated using the above formula (1-1). Y4Zr3O 12 The probability of existence f d1 Regarding the percentage (%), the measurement method for X-ray diffraction measurement after a specific heat treatment is as described in the examples below.

[0021] In one embodiment, in the X-ray diffraction (XRD) measurement before heat treatment under condition (i), Y4Zr3O calculated by formula (1-2) 12 The probability of existence f d2 Examples of dental workpieces include those in which the percentage is less than 2.5%. When dental workpieces are fired, in the initial stage of the main firing process (up to about 1100°C), Y4Zr3O 12 From the standpoint that it can generate Y4Zr3O in XRD measurements without the aforementioned specific heat treatment, 12 The probability of existence f d2 The percentage (%) is preferably less than 2.5%, more preferably 2.3% or less, and even more preferably 2.0% or less. 12 The probability of existence f d2The (%) is preferably greater than 0%, more preferably 0.01% or more, and even more preferably 0.1% or more. Also, Y4Zr3O 12 By using dental workpieces before sintering with a Y4Zr3O content of less than 2.5%, the thermal energy in the initial stages of firing is reduced. 12 It is preferentially used in the formation of grains, and grain growth in the initial stages of firing can be delayed. This reduces grain growth that incorporates voids before all voids have been removed, and it is thought that a sintered body with fewer voids and excellent light transmission can be obtained even in a short sintering time. In other words, Y4Zr3O in XRD measurements without specific heat treatment 12 The probability of existence f d2 The (%) is preferably greater than 0% and less than 2.5%, more preferably 0.01% or more and 2.3%, and even more preferably 0.1% or more and 2.0%. In this disclosure, Y4Zr3O before and after the heat treatment 12 The material behavior, which manifests as a change in the state of existence, is one of the factors that affect the translucency during short-time firing. This material behavior is caused by the distribution of yttrium elements in the dental workpiece. For example, by adjusting the mixing and grinding conditions in the manufacturing process to control the distribution of yttrium elements, the Y4Zr3O before heat treatment can be controlled. 12 The probability of existence f d2 While keeping the temperature low, heat treatment is performed to remove the heat-treated Y4Zr3O 12 The probability of existence f d1 This enables a change in phase ratio of over 13%. Such a remarkable phase change behavior before and after heat treatment is a property unique to the dental workpiece according to this disclosure that cannot be obtained with conventional dental workpieces, and it is believed that this maintains high translucency even during short firing times. In another embodiment, in XRD measurement without performing a specific heat treatment, the Y4Zr3O calculated by formula (1-2) 12 The probability of existence f d2 Examples include dental workpieces in which (%) is 0%. Y4Zr3O 12 The probability of existence f d2The method for measuring (%) is the same as the measurement method for XRD measurement after the specific heat treatment, except that the specific heat treatment is not performed.

[0022] The shape of the dental workpiece described herein is not particularly limited, but examples include disc-shaped and prismatic (e.g., rectangular parallelepiped).

[0023] One embodiment is a dental workpiece that is a zirconia calcined body. The following description will use the case where the dental workpiece is a zirconia calcined body as a preferred example, but the dental workpiece is not limited to zirconia calcined body. Unless otherwise specified, "zirconia calcined body" can be read as "dental workpiece."

[0024] The zirconia calcined body preferably contains a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer"). Furthermore, the zirconia calcined body preferably contains yttria as the stabilizer, since the resulting sintered body exhibits excellent light transmission even when the holding time at the maximum sintering temperature is 2 minutes. In this specification, the yttria included as a component of the zirconia calcined body does not necessarily have to exist as Y2O3 alone, but can also exist in a state containing the element yttrium (for example, Y4Zr3O 12 Yttria may exist in other forms (such as Y2O3 crystals), and it does not necessarily need to be detected as Y2O3 crystals.

[0025] The zirconia calcined body preferably contains a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer"). Furthermore, the zirconia calcined body preferably contains yttria (Y2O3) as the stabilizer, since the resulting sintered body exhibits excellent light transmission even when the holding time at the maximum sintering temperature is 2 minutes. In this specification, the yttria included as a component of the zirconia calcined body does not necessarily have to exist as Y2O3 alone, but can also exist in a state containing the element yttrium (for example, Y4Zr3O3). 12 Yttria may exist in other forms (such as Y2O3 crystals), and it does not necessarily need to be detected as Y2O3 crystals.

[0026] The zirconia calcined material of this disclosure may contain only yttria as a stabilizer capable of suppressing the phase transition of zirconia, or it may further contain a stabilizer other than yttria capable of suppressing the phase transition of zirconia. Examples of stabilizers other than yttria capable of suppressing the phase transition of zirconia include calcium oxide (CaO), magnesium oxide (MgO), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr2O3, Pr6O3). 11 Examples of oxides include samarium oxide (Sm2O3), europium oxide (Eu2O3), thulium oxide (Tm2O3), gallium oxide (Ga2O3), indium oxide (In2O3), and ytterbium oxide (Yb2O3). The stabilizer may be used alone or in combination of two or more types.

[0027] The yttria content in the calcined zirconia is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, relative to the total mol of zirconia and yttria. When the yttria content is 2.5 mol% or more, it is preferable in that the cubic crystal system is more abundant in the sintered body, improving light transmittance. Furthermore, the yttria content is preferably 10 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.5 mol% or less, and particularly preferably 8.0 mol% or less. When the yttria content is 10 mol% or less, it is preferable in that it prevents a decrease in mechanical strength. In other words, the yttria content in the zirconia calcined body is preferably 2.5 mol% to 10 mol%, more preferably 3.0 mol% to 9.0 mol%, even more preferably 3.5 mol% to 8.5 mol%, and particularly preferably 4.0 mol% to 8.0 mol% based on the total mol of zirconia and yttria. The content of the stabilizer in the zirconia calcined body of this disclosure can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, etc.

[0028] Furthermore, the zirconia calcined body of this disclosure contains Y4Zr3O, which is present in the state before it becomes a sintered body. 12 It is preferable that the zirconia includes monoclinic zirconia, as this contributes to excellent light transmission even during shorter holding times (e.g., 2 minutes) at the maximum sintering temperature. Furthermore, the zirconia calcined body of this disclosure has a monoclinic fraction f of monoclinic zirconia calculated by the following formula (1-3) in the zirconia. m (%) is preferably less than 55%. m (%) = I m / (I m +I t +I c +I y +I d )×100 (1-3) (where f mThis represents the monoclinic fraction (%), and in XRD measurements, I m This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of undissolved yttria appears. Note that Y4Zr3O 12 Since the positions of the main peaks are similar for tetragonal and cubic crystal systems, the area intensity of each main peak is calculated by peak separation. The monoclinic fraction f of monoclinic zirconia is calculated using equation (1-3). m (%) represents the measurement value for zirconia before heat treatment.

[0029] Monoclinic constant f m (%) represents the Y4Zr3O content observed in XRD measurements of zirconia calcined materials after specific heat treatments. 12 In conjunction with the above, the zirconia sintered body obtained even when the holding time at the maximum sintering temperature is 2 minutes exhibits excellent light transmittance, therefore, a monoclinic ratio of 48% or less is more preferable, 46% or less is even more preferable, and 45% or less is particularly preferable. m The (%) is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more. In other words, the monoclinic fraction f in the calcined zirconia body. m The percentage (%) is preferably 5% or more and less than 55%, more preferably 10% or more and 48%, even more preferably 15% or more and 46%, and particularly preferably 20% or more and 45%.

[0030] The zirconia calcined body of this disclosure may contain additives other than zirconia and stabilizers, insofar as they achieve the effects relating to this disclosure. Examples of such additives include colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium dioxide (TiO2), silica (SiO2), and the like. One of these additives may be used alone, or two or more may be used in combination.

[0031] Examples of the aforementioned pigments include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, Cr2O3, etc.) (excluding Y2O3 and CeO2), with a preference for oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, and a preference for oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb. Furthermore, the zirconia calcined body of this disclosure may not contain erbium oxide (Er2O3). Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4.

[0032] The zirconia calcined body of this disclosure may contain a fluorescent agent. The inclusion of a fluorescent agent in the zirconia calcined body gives the zirconia sintered body fluorescence. There are no particular restrictions on the type of fluorescent agent; one or more types that can emit fluorescence at any wavelength of light can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, and Bi and Eu are more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. Furthermore, the fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, BaMgAl 10 O 17 EU, etc., would also be acceptable.

[0033] The content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted as appropriate depending on the type of fluorescent agent or the intended use of the zirconia sintered body. However, from the viewpoint of suitability for use as a dental prosthesis, it is preferable that the content of the fluorescent agent, in terms of oxides of the metal elements contained in it, be 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, based on 100% by mass of zirconia contained in the zirconia calcined body. Furthermore, the content of the fluorescent agent is not particularly limited as long as suitable fluorescence is achieved, but it can be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, based on oxides of the metal elements contained in the fluorescent agent. By having a content above the lower limit, the fluorescence is not inferior to that of natural human teeth, and by having a content below the upper limit, a decrease in light transmittance and mechanical strength can be suppressed. In other words, the fluorescent agent content in the calcined zirconia body is preferably 0.001% by mass or more and 1% by mass or less, more preferably 0.005% by mass or more and 0.5% by mass or less, and even more preferably 0.01% by mass or more and 0.1% by mass or less.

[0034] The zirconia calcined body of this disclosure exhibits excellent light transmittance even when the holding time at 1550°C is 7 minutes or less (for example, 2 minutes). A sintered body prepared by sintering the zirconia calcined body at a heating rate of 350°C / min for a holding time of 7 minutes at 1550°C is defined as a first sintered body. A sintered body prepared by sintering a zirconia calcined body of the same size as the zirconia calcined body used to produce the first sintered body at a heating rate of 10°C / min for a holding time of 120 minutes at 1550°C is defined as a second sintered body. One embodiment of the present disclosure is a zirconia calcined body comprising zirconia and yttria, wherein when comparing the first translucency of a first sintered body produced by sintering the zirconia calcined body at a heating rate of 350°C / min at 1550°C for a holding time of 7 minutes with the second translucency of a second sintered body produced by sintering the zirconia calcined body at a heating rate of 10°C / min at 1550°C for a holding time of 120 minutes, the translucency of the first sintered body is 85% or more of the translucency of the second sintered body.

[0035] When the light transmittance of the first sintered body and the second sintered body are compared, with the holding time at 1550°C being 7 minutes during the production of the first sintered body, it is preferable that the light transmittance of the first sintered body is 85% or more of the light transmittance of the second sintered body, more preferably 86% or more, even more preferably 88% or more, particularly preferably 90% or more, and most preferably 95% or more. As described above, the zirconia calcined body of this disclosure has the advantages of short-time sintering of 7 minutes or less as described above. Details of the method for measuring the light transmittance will be described later in the examples. Another embodiment of the zirconia calcined body of this disclosure is a zirconia calcined body comprising zirconia, yttria, and Y4Zr3O 12 Examples include those in which the light transmittance of the first sintered body is within the aforementioned preferred range (for example, 85% or more) relative to the light transmittance of the second sintered body.

[0036] Furthermore, the bending strength of the zirconia calcined body of this disclosure is preferably 15 MPa or more in order to ensure mechanical strength that enables mechanical processing in the calcined state. Moreover, the bending strength of the zirconia calcined body is preferably 70 MPa or less, and more preferably 60 MPa or less, in order to facilitate mechanical processing in the calcined state. In other words, the bending strength of the zirconia calcined body is preferably 15 MPa or more and 70 MPa or less, and more preferably 15 MPa or more and 60 MPa or less.

[0037] The bending strength can be measured in accordance with ISO 6872:2015 (Dentistry - Ceramic materials), but the measurement is performed using a test specimen measuring 5 mm × 10 mm × 50 mm, with only the size of the test specimen being changed. The surface and chamfer (the surface where the corner of the test specimen is chamfered at a 45° angle) of the test specimen are finished in the longitudinal direction with 600-grit sandpaper. The test specimen is positioned so that its widest surface faces the vertical direction (direction of load). In the three-point bending test measurement, the distance between supports (span) is 30 mm and the crosshead speed is 0.5 mm / min.

[0038] Furthermore, the density of the zirconia calcined material disclosed herein is 2.7 g / cm³. 3 Preferably, it should be 3.0 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 3.2 g / cm³. 3 It is even more preferable that the above conditions are met. Furthermore, the density of the zirconia calcined material is 4.0 g / cm³. 3 Preferably, it is 3.8 g / cm³. 3 It is more preferable that the following conditions be met: 3.6 g / cm³ 3 It is even more preferable that the density is within the above range, which facilitates molding. In other words, the density of the calcined zirconia is 2.7 g / cm³. 3 4.0g / cm or more 3 Preferably, it is 2.7 g / cm³. 3 3.8g / cm or more 3 It is more preferable that the following is the case: 3.2 g / cm³ 3 3.6g / cm or more 3The following is even more preferable:

[0039] The density of a zirconia calcined material can be calculated using the formula: (mass of zirconia calcined material) / (volume of zirconia calcined material). For example, the density of a zirconia calcined material can be calculated by cutting out 10 mm square test specimens at arbitrary locations (n=3) while changing the cutting position of the zirconia calcined material, measuring the mass and volume of the obtained test specimens, calculating the arithmetic mean of the measured values, and then using the above formula with the arithmetic mean.

[0040] [Method for Manufacturing Dental Workpieces] Next, a method for manufacturing dental workpieces will be described. In the following description, the case in which the dental workpiece is a calcined zirconia body will be given as a preferred example, but the method for manufacturing dental workpieces is not limited to the method for manufacturing calcined zirconia bodies. Unless otherwise specified, "calcined zirconia body" can be read as "dental workpiece". Furthermore, in the following description, the case in which the stabilizer capable of suppressing the phase transition of zirconia is yttria will be given as a preferred example, but the stabilizer is not limited to yttria as long as it achieves the effects relating to this disclosure.

[0041] One preferred method for manufacturing a calcined zirconia body involves grinding a zirconia composition, molding the zirconia composition after grinding to form a molded body, and calcining (calcining) the zirconia particles to the extent that they do not sinter together, wherein the grinding process involves applying an excess of energy compared to the conventional technique through a predetermined grinding process. The method for manufacturing a calcined zirconia body includes a step of manufacturing a zirconia composition containing zirconia and yttria, a grinding step of grinding the zirconia composition, a molding step of molding the zirconia composition after grinding to obtain a molded body, and a calcining step of calcining the molded body, wherein the grinding step includes a predetermined grinding process described later. In the manufacturing method according to this disclosure, by going through the manufacturing step and grinding step of the zirconia composition, the Y4Zr3O before heat treatment is obtained. 12 The probability of existence f d2 While keeping it low, Y4Zr3O after heat treatment 12 The probability of existence f d1 A material state in which this increases can be formed.

[0042] The zirconia composition contained herein includes zirconia and yttria (yttria not solid-dissolved in zirconia; hereinafter also simply referred to as "yttria" or "unsolid-dissolved yttria"), and the form of the zirconia composition containing these is not particularly limited, and examples include powder, granules, slurry, paste, etc. In the following, unless otherwise specified, the components such as zirconia and yttria will be described using the powder form as an example. The zirconia composition is obtained by mixing zirconia powder and yttria powder, which are the raw material powders. The mixing method is not particularly limited, and known methods and apparatus can be used.

[0043] Methods for preparing zirconia particles constituting zirconia powder and yttria particles constituting yttria powder include, for example, a breakdown process in which coarse particles are crushed or broken down into fine powder; and a building-up process in which they are synthesized from atoms or ions through nucleation and growth processes.

[0044] The zirconia comprising the zirconia powder preferably includes monoclinic zirconia, as this allows for the production of a sintered body with excellent light transmission even in a short time sintering process after processing in a predetermined step. The content of solid-solution yttria in the monoclinic zirconia is preferably 2.7 mol% or less, more preferably 2.65 mol% or less, even more preferably 2.6 mol% or less, and particularly preferably 2.5 mol% or less, relative to the total mol of zirconia and yttria, in order to provide excellent light transmission for the zirconia sintered body obtained in a short time sintering and excellent machinability for the calcined zirconia body, when combined with the unsolid-solution yttria. In one embodiment, the monoclinic zirconia is a monoclinic zirconia with an yttria content of 0 to 2.7 mol% relative to the total mol of zirconia and yttria. In addition to monoclinic zirconia, tetragonal zirconia and / or cubic zirconia can also be used. The zirconia may be used individually or in combination of two or more types.

[0045] As the zirconia powder, commercially available zirconia particles may be used, or commercially available powder may be used after being ground in a known grinding and mixing device (such as a ball mill). As the yttria powder, commercially available yttria particles may be used, or commercially available powder may be used after being ground in a known grinding and mixing device (such as a ball mill).

[0046] Examples of commercially available zirconia powders include: Zpex® (product name) (Y2O3 content: 3 mol%), Zpex® 4 (Y2O3 content: 4 mol%), and Zpex® Smile (registered trademark) (Y2O3 content: 5.5 mol%), TZ-3Y (Y2O3 content: 3 mol%), TZ-3YS (Y2O3 content: 3 mol%), TZ-4YS (Y2O3 content: 4 mol%), TZ-6Y (Y2O3 content: 6 mol%), TZ-6YS (Y2O3 content: 6 mol%), TZ-8YS (Y2O3 content: 8 mol%), TZ-10YS (Y2O3 content: 10 mol%), TZ-3Y-E (Y2O3 content: 3 mol%), TZ- Examples include "3YS-E" (Y2O3 content: 3 mol%), "TZ-3YB-E" (Y2O3 content: 3 mol%), "TZ-3YSB-E" (Y2O3 content: 3 mol%), "TZ-3YB" (Y2O3 content: 3 mol%), "TZ-3YSB" (Y2O3 content: 3 mol%), "TZ-3Y20AB" (Y2O3 content: 3 mol%), "TZ-8YSB" (Y2O3 content: 8 mol%), and "TZ-0" (Y2O3 content: 0 mol%; monoclinic zirconia); all manufactured by Tosoh Corporation).

[0047] Next, the zirconia composition is further pulverized. By using a zirconia composition obtained by applying an excess of energy compared to the conventional technique in a predetermined pulverization process, the resulting calcined zirconia body is evaluated by TEM observation after the specific heat treatment described above, and Y4Zr3O 12 It can be confirmed that it contains Y4Zr3O. That is, when the manufactured zirconia calcined body is fired, in the initial stage of the main firing process (up to about 1100°C), Y4Zr3O 12This allows for the generation of Y4Zr3O. 12 It is presumed that by generating a predetermined amount of this material, excellent light transmission can be achieved even when the holding time at the highest sintering temperature is 2 minutes. In this disclosure, the abundance f before heat treatment d2 While keeping it low, when a specific heat treatment is applied, Y4Zr3O 12 The probability of existence f d1 The unique material behavior in which the ratio changes to over 13% can be achieved by precisely adjusting various conditions in the mixing or grinding process through specific grinding treatments described later, thereby controlling the distribution state of yttrium elements. Such specific control makes it possible to achieve the aforementioned numerical range that could not be reached with conventional manufacturing methods. In one embodiment, Y4Zr3O 12 As a result of the increased abundance of Y4Zr3O before heat treatment 12 The probability of existence f d2 However, Y4Zr3O after heat treatment 12 The probability of existence f d1 A relationship smaller than (f d2 <f d1 ) may be observed as such.

[0048] In the specified grinding process, it is preferable to use the following methods: (i) using grinding media with a diameter of less than 1 mm, or (ii) using grinding media with a diameter of 1 mm or more, and the grinding time is more than 40 hours.

[0049] When using grinding media with a diameter of less than 1 mm, the diameter of the grinding media should be such that when using grinding media with a fine diameter, Y4Zr3O 12Because it is easier to generate, a diameter of 0.1 to 0.5 mm is preferred. Commercially available grinding media with a diameter of less than 1 mm may be used. Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0050] When using pulverized media with a diameter of less than 1 mm, the pulverization time is not particularly limited, but when the calcined body is manufactured, Y4Zr3O 12 From the standpoint of ease of generation, the grinding time is preferably 10 minutes or more, more preferably 15 minutes or more, and even more preferably 20 minutes or more. Furthermore, the grinding time is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and particularly preferably 2 hours or less. In other words, the grinding time is preferably 10 minutes or more and 20 hours or less, more preferably 15 minutes or more and 10 hours or less, and even more preferably 20 minutes or more and 5 hours or less. Note that when using a grinding device that grinds while circulating the slurry (for example, a circulating bead mill), the grinding time refers to the residence time during which the slurry remains in the vessel (grinding chamber).

[0051] When using grinding media with a diameter of 1 mm or more, the diameter of the grinding media is preferably 1.5 mm or more, and more preferably 2.0 mm or more, because it is easier to increase the amount of energy used in the grinding process by combining it with a long grinding time. Commercially available grinding media with a diameter of 1 mm or more may be used. Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0052] When using grinding media with a diameter of 1 mm or more, the grinding time (grinding processing time) is not particularly limited, but it is preferably more than 40 hours, and more preferably 55 hours or more, as this makes it easier to grind the yttria particles to a very small size, and the maximum calcination temperature during calcination is lowered to produce a zirconia calcined body, and when the obtained zirconia calcined body is fired, in the initial stage of the main firing process (up to about 1100°C), Y4Zr3O 12 The probability of existence fd1 From the standpoint of easily increasing the performance, it is even more preferable to have a duration of 80 hours or more, and particularly preferable to have a duration of 100 hours or more. Furthermore, the duration of the grinding process is preferably 1000 hours or less, more preferably 800 hours or less, even more preferably 500 hours or less, and particularly preferable to have a duration of 300 hours or less. In other words, the duration of the grinding process is preferably more than 40 hours and 1000 hours or less, more preferably 55 hours or more and 800 hours or less, even more preferably 80 hours or more and 500 hours or less, and particularly preferable to have a duration of 100 hours or more and 300 hours or less.

[0053] In the method for producing a calcined zirconia body according to the present disclosure, a desired zirconia composition can be obtained by supplying a pulverization energy, which is increased by adjusting the combination of pulverization time and pulverization media diameter, to the zirconia composition.

[0054] By using a zirconia composition to which the pulverization energy obtained as described above has been added in excess, the zirconia calcined body of this disclosure, in the initial stage of the main calcination process (up to about 1100°C), Y4Zr3O 12 It is presumed that this contains and makes it easier to adjust to a predetermined ratio that is more effective.

[0055] As described above, the zirconia composition may be in the form of powder, granules, slurry, paste, etc. If the zirconia composition is a slurry, the slurry can be produced by mixing the mixed powder obtained by grinding with a solvent (preferably water).

[0056] The average particle size of the particles in the zirconia composition after grinding is preferably 0.2 μm or less, in order to ensure that the sintered body has excellent light transmission even when the holding time at the maximum sintering temperature is 2 minutes.

[0057] The average particle size of zirconia and yttria particles in a zirconia composition after grinding can be measured by a dynamic light scattering particle size distribution analyzer. For example, using a dynamic light scattering particle size distribution analyzer (product name "SZ-100V2", manufactured by Horiba, Ltd.), a slurry diluted with water to approximately 0.1% by mass is irradiated with ultrasound for 30 minutes, and then measured by volume while applying ultrasound.

[0058] Furthermore, the zirconia composition may contain additives such as binders, plasticizers, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, and light transmittance adjusters. Additives may be used individually or in combination of two or more. Examples of binders include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethylcellulose.

[0059] The binder content in the zirconia composition of this disclosure is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, based on 100% by mass of zirconia, in order to improve light transmittance.

[0060] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutylphthalic acid.

[0061] Examples of dispersants include ammonium polycarboxylate (such as triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic ester copolymer, polyacrylic acid, bentonite, carboxymethylcellulose, anionic surfactants (such as polyoxyethylene alkyl ether phosphates like polyoxyethylene lauryl ether phosphate), nonionic surfactants, oleic glycerides, amine salt type surfactants, oligosaccharide alcohols, and stearic acid.

[0062] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.

[0063] Examples of defoaming agents include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0064] Examples of pH adjusting agents include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0065] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0066] Examples of light-transmitting agents include aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0067] The BET specific surface area of ​​the particles constituting the zirconia composition was 7.0 m² when measured in accordance with JIS Z 8830:2013. 2 It is preferable that the amount be 7.5 m or more. 2 It is more preferable that the amount is 8.0 m or more per gram. 2 It is even more preferable that it be 7.0 m or more. 2 When the amount is greater than or equal to 1g, the clouding of the sintered body during sintering can be suppressed. Furthermore, the specific surface area of ​​the BET is 50m². 2 Preferably, it is less than / g, and 45m 2 It is more preferable that it be less than or equal to 40m 2 It is even more preferable that it be less than or equal to / g. 50m 2 If the value is less than or equal to / g, it becomes less susceptible to temperature variations within the firing furnace. In other words, the BET specific surface area of ​​the particles constituting the zirconia composition is 7.0 m². 2 / g or more 50m 2 It is preferable that the amount be less than or equal to 7.5 m 2 / g or more 45m 2 It is more preferable that it be less than or equal to 8.0 m 2 / g or more 40m 2It is even more preferable that the amount is less than or equal to / g. The BET specific surface area can be measured using commercially available products such as a fully automatic specific surface area measuring device (product name "Macsorb® HM model-1200", BET flow method (single-point method / multi-point method), manufactured by Mountec Co., Ltd.). For example, it can be measured using the BET flow method (single-point method) with the aforementioned fully automatic specific surface area measuring device. Furthermore, if the BET specific surface area is within the above range, the light transmittance of the sintered body is less likely to decrease even if the firing time for sintering is shortened. The "BET specific surface area" referred to here is the specific surface area measured without distinguishing between primary and secondary particles.

[0068] Next, a molded body is produced by a molding process in which the zirconia composition after the pulverization treatment is shaped. The molded body is obtained by shaping the zirconia composition by applying external force in a known manner.

[0069] The molding method is not particularly limited, and for example, the following methods can be used: (a) a method comprising the step of slip casting a slurry containing the zirconia composition after grinding; (b) a method comprising the step of gel casting a slurry containing the zirconia composition after grinding; (c) a method comprising the step of press molding the zirconia composition after grinding; (d) a method comprising the step of molding a zirconia composition containing zirconia particles, yttria particles, and resin; (e) a method comprising the step of polymerizing a zirconia composition containing zirconia particles, yttria particles, and polymerizable monomers or oligomers; (f) a method comprising the step of additively manufacturing granules containing zirconia particles and yttria particles.

[0070] (a) When a zirconia molded article is manufactured by a method having a step of slip casting a slurry containing a zirconia composition after slip casting grinding treatment, there are no particular restrictions on the specific slip casting method, and for example, a method of pouring the slurry into a mold and then drying it can be adopted. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, in order to facilitate pouring the slurry into the mold, prevent the drying from taking a great deal of time, and increase the number of times the mold can be used. The slurry may be poured into the mold under normal pressure, but it is preferable to do so under pressurized conditions from the viewpoint of production efficiency.

[0071] (b) When a zirconia molded article is produced by a method having a step of gel casting a slurry containing a zirconia composition after gel casting grinding, there are no particular restrictions on the specific method of gel casting. For example, a method can be employed in which a wet body is formed by gelling the slurry in a mold and then drying it. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, in order to prevent the drying from taking a long time and to suppress the occurrence of cracks during drying. Gelation may be performed, for example, by adding a gelling agent, or by adding a polymerizable monomer and then polymerizing it.

[0072] There are no restrictions on the type of gelling agent; for example, a water-soluble gelling agent can be used, and specifically, agarose, gelatin, etc., are preferably used. One type of gelling agent may be used alone, or two or more types may be used in combination. The amount of gelling agent used is not particularly limited as long as no problems such as cracks occur during sintering, but it can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the gelling agent has been added.

[0073] Furthermore, there are no particular restrictions on the type of polymerizable monomer. Examples include (meth)acrylate polymerizable monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; and (meth)acrylamide polymerizable monomers such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl) (meth)acrylamide. A single polymerizable monomer may be used, or two or more may be used in combination. The amount of polymerizable monomer used is not particularly limited as long as no problems such as cracks occur during sintering, but it can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the polymerizable monomer has been added.

[0074] When gelation is performed by polymerization of polymerizable monomers, it is preferable to use a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but photopolymerization initiators are particularly preferred. As a photopolymerization initiator, one can be appropriately selected from those used in general industry, and among these, photopolymerization initiators used in dental applications are preferred.

[0075] Specific examples of photopolymerization initiators include (bis)acylphosphine oxides (including salts), thioxanthones (including salts of quaternary ammonium salts, etc.), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and α-aminoketone compounds. One photopolymerization initiator may be used alone, or two or more may be used in combination. Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides and α-diketones. This allows polymerization (gelation) to be carried out in both the ultraviolet region (including the near-ultraviolet region) and the visible light region, and in particular, polymerization (gelation) can be carried out sufficiently regardless of the light source used, such as lasers such as Ar lasers and He-Cd lasers; or lighting such as halogen lamps, xenon lamps, metal halide lamps, light-emitting diodes (LEDs), mercury lamps, and fluorescent lamps.

[0076] There are no particular restrictions on the drying method used to dry the formed wet material. Examples include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. One of these methods may be used, or two or more may be used. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred because they can suppress the occurrence of cracks during drying.

[0077] There are no particular restrictions on the type of mold used in slip casting and gel casting. For example, porous molds made of gypsum, resin, ceramics, etc., and non-porous molds made of metal, resin, etc., can be used.

[0078] (c) Press forming: In the step of press forming the zirconia composition after the crushing treatment, there are no particular restrictions on the specific method of press forming, and it can be carried out using a known press forming machine. Specific methods of press forming include, for example, a uniaxial press.

[0079] Furthermore, the molding process may be multi-stage. For example, after press molding the zirconia composition, a CIP (Cold Isostatic Pressing) treatment may be performed.

[0080] The shape of the molded body is not particularly limited and may be disc-shaped, rectangular parallelepiped-shaped, or in the shape of a dental product (e.g., a tooth crown). The molded body may be, for example, a columnar zirconia molded body obtained by filling a mold with a zirconia composition (e.g., granules) and pressing it with a uniaxial pressure press. The higher the surface pressure during press molding, the higher the density of the molded body. On the other hand, if the density of the zirconia molded body is too high, the zirconia calcined body becomes hard. Therefore, the surface pressure during press molding when producing a zirconia molded body is preferably 30 to 200 MPa. When the surface pressure of the press is 30 MPa or higher, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or lower, the density of the zirconia molded body does not increase too much, making it easier to prevent it from becoming hard.

[0081] The aforementioned molded articles also include molded articles that have been densified by high-temperature and high-pressure treatments such as CIP (Cold Isostatic Pressing). From the same viewpoint as above, the pressure for CIP is preferably 30 to 200 MPa.

[0082] (d) Molding of zirconia composition containing resin When a zirconia molded article is manufactured by a method having a step of molding zirconia particles, yttria particles, and a zirconia composition containing resin, there are no particular restrictions on the specific method for molding the zirconia composition, and for example, injection molding, casting, extrusion molding, etc. may be used. Alternatively, a method of fabricating the composition by fused deposition modeling (FDM), an inkjet method, a powder / binder deposition modeling method, or other additive manufacturing methods (3D printing, etc.) may be used. Among these molding methods, injection molding and casting are preferred, and injection molding is more preferred. There are no particular restrictions on the type of resin, but it is preferable to use the binder described above.

[0083] (e) Polymerization of a zirconia composition containing zirconia particles, yttria particles, and polymerizable monomers or oligomers By polymerizing a zirconia composition containing zirconia particles, yttria particles, and polymerizable monomers or oligomers, the polymerizable monomers or oligomers in the composition polymerize and the composition can be cured. When a zirconia molded body is manufactured by a method having the step of polymerization, there are no particular restrictions on the specific method, and for example, a method of polymerizing the zirconia composition in a mold; a stereolithography (SLA) method using the zirconia composition can be employed. Among these, stereolithography (SLA) is preferred. With stereolithography, a shape corresponding to the desired shape of the zirconia sintered body that is finally obtained can be imparted to the zirconia molded body at the time of manufacture. For this reason, stereolithography may be particularly suitable when the zirconia sintered body is used as a dental material such as a dental prosthesis. There are no particular restrictions on the type of polymerizable monomer; it may be any monofunctional polymerizable monomer such as monofunctional (meth)acrylate or monofunctional (meth)acrylamide, or any polyfunctional polymerizable monomer such as a bifunctional aromatic compound, a bifunctional aliphatic compound, or a trifunctional or more functional compound. One polymerizable monomer may be used alone, or two or more may be used. Among these, it is particularly preferable to use a polyfunctional polymerizable monomer when employing photopolymerization. The oligomer is not particularly limited as long as it is a compound that is polymerizable by bonding two or more of the polymerizable monomers.

[0084] Examples of monofunctional (meth)acrylates include hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate Examples include alkyl (meth)acrylates such as acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having functional groups such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane. Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide, N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide, N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.Among these monofunctional polymerizable monomers, (meth)acrylamide is preferred due to its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0085] Examples of bifunctional aromatic compounds include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2, Examples of (meth)acrylates include 2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred due to their excellent polymerizability and the mechanical strength of the resulting zirconia molded articles. Among 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E") are preferred.

[0086] Examples of bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of (meth)acrylates include ethyl dimethacrylate, 1,6-hexanediol dimethacrylate, 2-ethyl-1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, 1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl) dimethacrylate (commonly known as "UDMA"). Among these, triethylene glycol dimethacrylate (commonly known as "TEGDMA") and UDMA are preferred in terms of their excellent polymerizability and the mechanical strength of the resulting zirconia molded articles.

[0087] Examples of compounds with three or more functionalities include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane. Among these, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryoyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred in terms of their excellent polymerizability and the mechanical strength of the resulting zirconia molded articles.

[0088] In any of the methods described above, polymerization of the composition is preferably carried out using a polymerization initiator, and the composition is preferably further comprising a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but photopolymerization initiators are particularly preferred. As the photopolymerization initiator, it can be appropriately selected from photopolymerization initiators used in general industry, and among these, photopolymerization initiators used in dental applications are preferred. Specific examples of photopolymerization initiators are the same as those described above in the explanation of gel casting.

[0089] When manufacturing zirconia molded articles using a stereolithography method with a zirconia composition, there are no particular restrictions on the specific method of stereolithography, and known methods can be appropriately employed for stereolithography. For example, a method can be employed in which a target zirconia molded article is obtained by sequentially forming each layer having the desired shape by photopolymerizing a liquid composition with ultraviolet light, a laser, etc., using a stereolithography apparatus.

[0090] To further improve the density of the cured zirconia molded body, the zirconia molded body may be subjected to humidification treatment before CIP treatment. When press molding is performed, the powder containing zirconia particles may be subjected to humidification treatment before press molding. The method of humidification treatment can be any known method without any limitations, and may be performed by spraying water with a spray bottle or by using a constant humidity chamber or a constant temperature and humidity chamber. The amount of moisture increase due to humidification treatment depends on the average particle size of the zirconia particles and the average particle size of the stabilizer particles, but is preferably more than 2% by mass, more preferably more than 3% by mass, even more preferably more than 4% by mass, particularly preferably more than 5% by mass, and also preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. The increase in moisture content due to the humidification process can be calculated as a percentage by subtracting the mass of the powder and molded body before humidification from the mass of the wet powder (powder after humidification) and molded body, and then dividing this result by the mass of the powder and molded body before humidification. The pressure for the CIP process is the same as described above in the explanation of press molding.

[0091] (f) Steps for additive manufacturing of granules containing zirconia particles and yttria particles There are no particular restrictions on the specific methods used to manufacture granules containing zirconia particles and yttria particles. For example, a method can be employed in which the material is slurryed and then dried in a spray dryer to form granules, and the resulting granules can be used for powder bed additive manufacturing. There are no particular restrictions on the powder bed additive manufacturing method, but examples include the powder bed method, SLS method (selective laser sintering method), SLM method (selective laser melting method), electron beam method, arc discharge method, and binder jet method. For methods in which it is preferable not to include organic matter during additive manufacturing, it is preferable not to include organic matter in the granule manufacturing stage either.

[0092] Next, a calcination step is performed to calcin the molded body, thereby obtaining the zirconia calcined body of this disclosure. The calcination step will be explained using the method for producing a zirconia calcined body as an example to illustrate the method for producing a dental workpiece. However, since dental workpieces are not limited to calcined bodies, the following calcination step is unnecessary if the molded body does not undergo calcination. The calcination temperature (maximum calcination temperature) in the calcination step can be 600°C or higher and 1200°C or lower. When combined with the grinding step, when the obtained calcined body is fired, in the initial stage of the main firing step (up to about 1100°C), Y4Zr3O 12 In order to increase the amount of Y4Zr3O produced and to ensure processability, the maximum calcination temperature is preferably less than 900°C, more preferably 870°C or lower, and even more preferably 850°C or lower. Furthermore, as the maximum calcination temperature, when the above-mentioned specific zirconia composition is used in combination with the grinding step, when the resulting zirconia calcined body is fired, in the initial stage of the main firing process (up to about 1100°C), Y4Zr3O 12 From the standpoint of being able to generate and ensuring a semi-sintered state, the temperature is preferably 600°C or higher, more preferably 620°C or higher, and even more preferably 650°C or higher. In other words, the maximum calcination temperature is preferably 600°C or higher and less than 900°C, more preferably 620°C or higher and 870°C or lower, and even more preferably 650°C or higher and 850°C or lower. Furthermore, by setting the maximum calcination temperature within the above range, Y4Zr3O in dental workpieces can be generated. 12 It becomes easier to adjust the abundance of Y4Zr3O in dental workpieces to a certain amount or less (less than 2.5%). 12 By keeping the abundance of Y4Zr3O below a certain level (less than 2.5%), the thermal energy in the initial stages of firing is reduced. 12 This is preferentially used in the formation of grains, and can delay grain growth in the initial stages of firing. As a result, it is possible to reduce grain growth that incorporates voids before they have completely disappeared, and a sintered body with fewer voids and excellent light transmission can be obtained even in a short sintering time.

[0093] The holding time at the aforementioned maximum calcination temperature allows for a semi-sintered state, and when combined with the grinding process, when the obtained calcined zirconia body is fired, Y4Zr3O is produced in the initial stage of the main firing process (up to about 1100°C). 12 While not particularly limited as long as a zirconia calcined body capable of generating is obtained, 30 minutes to 6 hours is preferred. Furthermore, the heating rate to the maximum calcination temperature and the cooling rate from the maximum calcination temperature are preferably 300°C / min or less. In one embodiment, there are no particular restrictions on the heating rate to the maximum calcination temperature when calcining the zirconia molded body of this disclosure, but it is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, even more preferably 0.5°C / min or more, and also preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. In other words, it is preferably 0.1°C / min or more and 50°C / min or less, more preferably 0.2°C / min or more and 30°C / min or less, and even more preferably 0.5°C / min or more and 20°C / min or less. Productivity is improved when the heating rate is above the above lower limit. Furthermore, by keeping the heating rate below the above upper limit, the volume difference between the inside and outside of the zirconia molded body or calcined zirconia body can be suppressed, and if the zirconia molded body contains organic matter, the rapid decomposition of such organic matter can be suppressed, thereby preventing cracks and fractures.

[0094] Furthermore, in the case where the dental workpiece is a molded body, a suitable method for manufacturing the dental workpiece is described below. When the dental workpiece is a molded body obtained using the zirconia composition obtained by the predetermined grinding treatment described above, Y4Zr3O in the dental workpiece 12 The abundance of Y4Zr3O becomes easier to adjust to a certain amount (2.5%) or less, and when the dental workpiece (molded body) is fired, in the initial stage of the main firing process (up to about 1100°C), 12 It is possible to generate Y4Zr3O in dental workpieces. 12 By keeping the abundance of Y4Zr3O below a certain level (2.5%), the thermal energy at the initial stage of firing is reduced. 12It is preferentially used in the formation of grains and can delay grain growth in the initial stages of firing. This reduces grain growth that incorporates voids before they have completely disappeared, resulting in a sintered body with fewer voids and excellent translucency even in short-time sintering. Furthermore, in the following description, the case in which yttria is the stabilizer capable of suppressing the phase transition of zirconia is given as a preferred example, but the stabilizer is not limited to yttria as long as it achieves the effects of this disclosure. A manufacturing method for a dental workpiece includes a step of manufacturing a zirconia composition containing zirconia and yttria, and a molding step of molding the zirconia composition to obtain a molded body, wherein the binder content in the molded body is 3% or more.

[0095] In the method for manufacturing the dental workpiece, the steps other than the binder content in the molded body are as described in the method for manufacturing the zirconia calcined body described above. The binder content in the molded body is preferably 3% or more, more preferably 5% or more, and even more preferably 8% or more. Furthermore, the binder content in the molded body is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. In other words, the binder content in the molded body is preferably 3% to 30%, more preferably 5% to 20%, and even more preferably 8% to 15%.

[0096] [Zirconia Sintered Body] Next, we will explain the zirconia sintered body. In the following explanation, we will use the case where the dental workpiece is a zirconia calcined body as a preferred example, but we are not limited to zirconia calcined bodies. Unless otherwise specified, "zirconia calcined body" can be read as "dental workpiece". The zirconia sintered body is obtained by firing the dental workpiece (preferably a zirconia calcined body) obtained as described above.

[0097] The content of stabilizers (yttria and non-yttria stabilizers) in the zirconia sintered body of this disclosure is the same as the content of stabilizers in the calcined zirconia body.

[0098] When comparing the first translucency of a zirconia sintered body produced by sintering at a heating rate of 350°C / min at 1550°C for a holding time of 7 minutes with the second translucency of a zirconia sintered body produced by sintering at a heating rate of 10°C / min at 1550°C for a holding time of 120 minutes, it is preferable that the first translucency is 85% or more of the second translucency, more preferably 86% or more, even more preferably 88% or more, particularly preferably 90% or more, and most preferably 95% or more. Therefore, the zirconia sintered body of this disclosure can maintain a high level of translucency comparable to that of long-term sintering after sintering for a short time, such as 7 minutes or less at 1550°C.

[0099] The zirconia sintered body of this disclosure may contain a fluorescent agent. The fluorescent agent is the same as the fluorescent agent in the calcined zirconia body. In this specification, the phrase "for 100% by mass of zirconia contained in the calcined zirconia body" can be read as "for 100% by mass of zirconia contained in the zirconia sintered body."

[0100] The zirconia sintered body of this disclosure may contain a coloring agent. Examples of coloring agents include those used in calcined zirconia bodies. There are no particular restrictions on the coloring agent content in the zirconia sintered body, and it can be appropriately adjusted depending on the type of coloring agent and the intended use of the zirconia sintered body. However, from the viewpoint of suitability for use as a dental prosthesis, the coloring agent content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, based on 100% by mass of zirconia contained in the zirconia sintered body, in terms of oxides of the metal elements contained in the coloring agent. Furthermore, the coloring agent content is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, 0.1% by mass or less, and even more preferably 0.05% by mass or less, based on oxides of the metal elements contained in the coloring agent. In other words, the coloring agent content is preferably 0.001% by mass or more and 5% by mass or less, more preferably 0.005% by mass or more and 1% by mass or less, and even more preferably 0.01% by mass or more and 0.5% by mass or less, based on 100% by mass of zirconia contained in the zirconia sintered body.

[0101] To adjust the translucency of the zirconia sintered body of this disclosure, the zirconia sintered body of this disclosure may contain a translucency modifier. Examples of translucency modifiers include those similar to those used in calcined zirconia bodies. There are no particular restrictions on the content of the translucency modifier in the zirconia sintered body, and it can be appropriately adjusted depending on the type of translucency modifier and the intended use of the zirconia sintered body. However, from the viewpoint of being suitable for use as a dental prosthesis, it is preferable that the content is 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0102] The relative density of the zirconia sintered body is preferably 99.0% or higher, more preferably 99.2% or higher, and even more preferably 99.5% or higher. The relative density can be calculated as the ratio of the measured density, measured by the Archimedes method, to the theoretical density.

[0103] The density of a zirconia sintered body is such that higher density results in fewer internal voids and less light scattering, thus improving light transmission. Therefore, 5.80 g / cm³ is considered ideal. 3 Preferably, it is 5.82 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 5.87 g / cm³. 3 It is even more preferable that the above conditions are met. It is particularly preferable that the zirconia sintered body contains substantially no voids.

[0104] The mechanical strength of the zirconia sintered body is preferable to be as high as possible. For example, a biaxial bending strength of 800 MPa or higher is preferable, 820 MPa or higher is more preferable, and 840 MPa or higher is even preferable. The biaxial bending strength can be measured in accordance with ISO 6872:2015.

[0105] [Method for Manufacturing Zirconia Sintered Bodies] The following description will use the case where the dental workpiece is a zirconia calcined body as a preferred example, but the method for manufacturing zirconia sintered bodies is not limited to the method for manufacturing zirconia calcined bodies. Unless otherwise specified, "zirconia calcined body" can be read as "dental workpiece". The method for manufacturing zirconia sintered bodies according to this disclosure is a method for manufacturing zirconia sintered bodies in which the zirconia calcined body described above is fired. The zirconia calcined body is Y4Zr3O calculated by the above formula (1-2). 12 The probability of existence f d2 (%) is preferably less than 2.5%. Y4Zr3O in zirconia calcined body 12 The probability of existence f d2 The percentages (%) are as described for the zirconia calcined body. A manufacturing method is preferred that includes a step of firing the aforementioned zirconia calcined body at atmospheric pressure at a temperature between 1200°C and 1700°C (hereinafter also referred to as the "firing step"). With such a manufacturing method, a zirconia sintered body of the present disclosure with excellent light transmittance can be easily produced after sintering in a short time, with a holding time of 2 minutes at the maximum sintering temperature. Furthermore, with the manufacturing method of the present disclosure, a zirconia sintered body of the present disclosure that maintains high light transmittance comparable to that of long-term sintering can be easily produced after sintering in a short time, with a holding time of 7 minutes or less at 1550°C.

[0106] When manufacturing a sintered body by firing the zirconia calcined body of this disclosure, the maximum sintering temperature is preferably such that the light transmittance of the zirconia sintered body is maximized. The maximum sintering temperature is preferably greater than 1200°C, more preferably 1250°C or higher, and even more preferably 1300°C or higher, from the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure. Furthermore, the maximum sintering temperature is preferably 1700°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. In other words, the maximum sintering temperature is preferably greater than 1200°C and 1700°C or lower, more preferably 1250°C or higher and 1650°C or lower, and even more preferably 1300°C or higher and 1600°C or lower. By having the maximum sintering temperature above the lower limit and the maximum sintering temperature below the upper limit, sintering can be sufficiently advanced, and a dense sintered body can be easily obtained. Furthermore, by having the maximum sintering temperature below the upper limit, the deactivation of the fluorescent agent can be suppressed. The maximum sintering temperature is not particularly limited as long as it is within the above-mentioned range and higher than the calcination temperature (maximum calcination temperature) in the calcination process. For example, it may be set to any temperature that is 50°C or more higher than the maximum calcination temperature, 100°C or more higher than the maximum calcination temperature, 200°C or more higher than the maximum calcination temperature, or 300°C or more higher than the maximum calcination temperature.

[0107] When manufacturing a sintered body, there are no particular restrictions on the sintering time as long as the holding time at the maximum sintering temperature is 7 minutes or less. However, in order to obtain the desired zirconia sintered body with good productivity, the holding time at the maximum sintering temperature is preferably 5 minutes or less, more preferably 4 minutes or less, even more preferably 3 minutes or less, and particularly preferably 2 minutes or less. The holding time is preferably 30 seconds or more, more preferably 45 seconds or more, and even more preferably 1 minute or more.

[0108] When using the zirconia calcined body of this disclosure to manufacture a zirconia sintered body, the firing time for manufacturing the sintered body can be shortened without reducing the light transmittance of the manufactured zirconia sintered body. In particular, the holding time at the maximum sintering temperature for manufacturing the sintered body can be shortened to 7 minutes or less (for example, 2 minutes). This can increase production efficiency, and when the zirconia calcined body of this disclosure is applied to dental products, the time from determining the dimensions of the dental product to be used for treatment, machining it, and making the dental product usable for treatment can be shortened, thereby reducing the time burden on the patient. Furthermore, energy costs can be reduced. Moreover, because the holding time at the maximum sintering temperature is below the above upper limit, the deactivation of the fluorescent agent can be suppressed.

[0109] In the firing process, the heating rate and cooling rate should preferably be set to minimize the time required for the firing process. For example, the heating rate can be set to reach the maximum sintering temperature in the shortest possible time, depending on the performance of the firing furnace. The heating rate to the maximum sintering temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, 200°C / min or more, 250°C / min or more, 300°C / min or more, or 350°C / min or more. The cooling rate should preferably be set to a rate that prevents defects such as cracks from occurring in the sintered body. For example, after heating is complete, the sintered body can be allowed to cool at room temperature.

[0110] Calcination and firing in this disclosure can be carried out using a firing furnace. There are no particular restrictions on the type of firing furnace; for example, electric furnaces and degreasing furnaces used in general industry can be used. Commercially available dental firing furnaces (for example, trade name "Sintra CS" (manufactured by Shenpaz)) may also be used.

[0111] The zirconia sintered body of this disclosure can be manufactured without HIP treatment, but as an optional step, further improvements in light transmittance and mechanical strength can be achieved by performing HIP treatment after sintering under atmospheric pressure. In the following, the sintered body obtained by sintering at the above-mentioned maximum sintering temperature (sintered body before HIP treatment) will be referred to as the "primary sintered body," and the sintered body after HIP treatment will be referred to as the "HIP-treated sintered body." HIP treatment can be performed using a known hot isohydrostatic press (HIP) apparatus.

[0112] When performing HIP treatment on a primary sintered body, the pressure during HIP treatment is not particularly limited, but a dense sintered body with high mechanical strength can be obtained. Therefore, the pressure during HIP treatment is preferably 100 MPa or higher, more preferably 125 MPa or higher, and even more preferably 130 MPa or higher. Furthermore, there is no particular upper limit to the pressure during HIP treatment, but it can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less. In other words, the pressure during HIP treatment is preferably 100 MPa or more and 400 MPa or less, more preferably 125 MPa or more and 300 MPa or less, and even more preferably 130 MPa or more and 200 MPa or less.

[0113] When the primary sintered body is subjected to HIP treatment, the heating rate is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. Furthermore, the heating rate during HIP treatment is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. Productivity is improved when the heating rate is above the above lower limit. In other words, the heating rate during HIP treatment is preferably 0.1°C / min or more and 50°C / min or less, more preferably 0.2°C / min or more and 30°C / min or less, and even more preferably 0.5°C / min or more and 20°C / min or less.

[0114] When the primary sintered body is subjected to HIP treatment, the HIP treatment time (the time during which the maximum pressure and temperature are maintained) is not particularly limited. However, since a dense zirconia sintered body with high mechanical strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Furthermore, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less. In other words, the HIP treatment time is preferably 5 minutes or more and 10 hours or less, more preferably 10 minutes or more and 6 hours or less, and even more preferably 30 minutes or more and 3 hours or less.

[0115] In the method for manufacturing a zirconia sintered body according to the present disclosure, when the primary sintered body is subjected to HIP treatment, the pressure medium is not particularly limited, and from the viewpoint of minimizing the impact on zirconia, at least one can be selected from the group consisting of oxygen, oxygen mixed gas, air, and inert gas (e.g., nitrogen gas, argon gas, etc.). When the primary sintered body is subjected to HIP treatment under an oxygen mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, greater than 0% and less than or equal to 20%. When using an oxygen mixed gas, at least one inert gas (e.g., nitrogen gas, argon gas, etc.) can be selected as the gas other than oxygen.

[0116] If the HIP treatment is performed in a reducing atmosphere, such as by using an inert gas, blackening may occur due to oxygen vacancies. In that case, in order to remove the blackening, it is preferable to include a step of heat treatment at 1650°C or lower in air or an oxygen-rich atmosphere (hereinafter also referred to as "tempering treatment") after the HIP treatment step, and it is more preferable to perform the heat treatment in an oxygen-rich atmosphere from the viewpoint of efficient heat treatment. An oxygen-rich atmosphere means that the oxygen concentration is higher than the oxygen concentration in the air. The oxygen-rich atmosphere is not particularly limited as long as the oxygen concentration is between 21% and 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0117] The zirconia sintered body of this disclosure is not particularly limited as long as it achieves the effects of this disclosure, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0118] Depending on the aesthetics of the zirconia sintered body (e.g., the shade of the dental prosthesis), the temperature of the heat treatment in air or an oxygen-rich atmosphere can be appropriately changed. In one embodiment, from the viewpoint of aesthetics of the zirconia sintered body, the temperature of the heat treatment in air or an oxygen-rich atmosphere is preferably 1650°C or lower, more preferably 1600°C or lower, and even more preferably 1550°C or lower. In another embodiment, from the viewpoint of aesthetics of the zirconia sintered body, the temperature of the heat treatment in air or an oxygen-rich atmosphere is preferably 1400°C or lower, more preferably 1300°C or lower, and even more preferably 1200°C or lower. Furthermore, in all embodiments, the temperature of the heat treatment is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher. In other words, the temperature of the heat treatment in air or an oxygen-rich atmosphere is preferably 500°C to 1650°C, more preferably 600°C to 1600°C, and even more preferably 700°C to 1550°C.

[0119] For the tempering process, a general-purpose furnace for dental zirconia can be used. Commercially available furnaces for dental zirconia may also be used. Examples of commercially available furnaces include Noritake Katana (registered trademark) F-1, F-1N, F-2, and F-2N (all manufactured by SK Medical Electronics Co., Ltd.).

[0120] The zirconia sintered body obtained by firing the zirconia calcined body of this disclosure can be suitably used in dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, and laminate veneers. By using the zirconia calcined body of this disclosure for components such as implant screws and implant fixtures, discoloration of the gingiva, which occurs when using metal materials, can be suppressed, resulting in superior aesthetics. Furthermore, while an appropriate manufacturing method can be selected depending on the application, for example, dental products can be obtained by machining the zirconia calcined body of this disclosure and then firing it. It is preferable to use a CAD / CAM system in the machining process. The CAD / CAM system is not particularly limited, and known devices can be used. Examples of known devices include CAD / CAM systems (such as the "Katana® CAD / CAM System," manufactured by Kuraray Noritake Dental Co., Ltd.).

[0121] This disclosure includes, to the extent that it achieves the effects relating to this disclosure, embodiments that combine all or part of the above-described configurations in various ways, within the scope of the technical idea of ​​this disclosure. References to “one embodiment / aspect” or “embodiment / aspect” in this specification mean that certain features, structures, or characteristics described in relation to that embodiment / aspect are included in at least one embodiment / aspect of this disclosure. The use of the phrases “one embodiment / aspect” or “another embodiment / aspect” in various parts of this specification does not necessarily refer to the same embodiment / aspect, nor are separate or alternative embodiments / aspects mutually exclusive with other embodiments / aspects. Furthermore, various features are described that are shown in some embodiments / aspects but not in others. Similarly, various requirements are described that are required in some embodiments / aspects but not in others. Embodiments and aspects are, in some cases, interchangeable.

[0122] Next, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited in any way by these examples, and many modifications are possible by those who are ordinary skill in the art within the scope of the technical idea of ​​the present disclosure.

[0123] [Example 1] Commercially available zirconia powder (Y2O3: 0 mol%; monoclinic zirconia) and commercially available yttria powder were added to water. These were placed in a ball mill container along with zirconia grinding media (diameter: 2 mm), and the grinding process was carried out in the ball mill for 168 hours to obtain a slurry (average particle size: 0.2 μm or less).

[0124] Next, an organic binder was added to the obtained slurry and mixed and stirred. The stirred slurry was dried and granulated using a spray dryer to obtain a powder. This powder was poured into a columnar mold and molded by uniaxial pressure pressing at a pressure of 200 MPa to obtain a molded body. The obtained molded body was placed in an electric furnace, heated from room temperature at a rate of 10°C / min and held at 500°C for 2 hours to degrease the organic components, then heated at a rate of 10°C / min and held at 850°C (maximum calcination temperature) for 2 hours, and slowly cooled at -10°C / min to obtain a calcined zirconia body.

[0125] [Example 2 and Comparative Examples 1-4] Zirconia calcined bodies were manufactured in the same manner as in Example 1, except that the conditions listed in Table 1 were changed. In Example 2 and Comparative Examples 1-4, the same yttria raw material as in Example 1 was used. In Example 2, instead of grinding in a ball mill, grinding was performed in a bead mill using zirconia grinding media with a diameter of 0.1 mm, and the grinding time was changed to that listed in Table 1.

[0126] <Yttria content (mol%) in zirconia calcined material> The yttria content (mol%) in zirconia calcined material was measured as the yttria content relative to the total moles of zirconia and yttria, using an X-ray fluorescence analyzer (XRF) (product name "RX3000", manufactured by Matsusada Precision Co., Ltd.).

[0127] <Transmission electron microscopy observations of Y4Zr3O after and before specific heat treatments> 12Evaluation of the presence or absence of Y4Zr3O > The zirconia calcined bodies obtained in each example and comparative example were subjected to a specific heat treatment (condition (i)) in a dental firing furnace (product name "Sintra CS" (manufactured by Shenpaz)) and the state before becoming a sintered body was evaluated. 12 The presence or absence of Y4Zr3O was evaluated using TEM. In addition, the presence or absence of Y4Zr3O in the zirconia calcined bodies (without specific heat treatment) obtained in each example and comparative example was evaluated. 12 The presence or absence of [the substance] was evaluated using TEM. Specifically, after subjecting the calcined body to a specific heat treatment, it was polished to a thickness of 30 μm, and the surface of the calcined body was processed using a precision ion polishing system (product name "Model 691 PIPS", manufactured by Gatan, Inc. (US)). Using the prepared sample, measurements were performed with an atomic resolution analytical electron microscope (product name "JEM-ARM200F ACCELARM", manufactured by JEOL Ltd.) at an acceleration voltage of 200 kV and a magnification of 50,000x (observation range 1 μm × 1 μm). In the obtained TEM observation images, 20 observation points (observation range 5 × 5 nm) were arbitrarily extracted using scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) where the yttrium atoms constituted 50 mol% to 65 mol% of the total molars of zirconium and yttrium atoms. If there were fewer than 20 observation points in one TEM observation image, an additional TEM observation image was created to extract 20 observation points. Subsequently, electron diffraction images were acquired for each observation point with a camera length of 1.0 cm and an acceleration voltage of 200 kV, and Y4Zr3O was obtained using the following method. 12 The presence of Y4Zr3O was confirmed. Of the 20 observation points extracted, Y4Zr3O 12 If there is even one observation point where the presence of Y4Zr3O is confirmed, 12 It was determined that it contained Y4Zr3O. First, from the obtained diffraction pattern, the distances d1 and d2 of the diffraction spots (corresponding to the interplanar spacing) and their angles (corresponding to the interplanar angle φ) were measured, as shown in Figure 1. Next, Y4Zr3O 12Using formulas (1-4) and (1-5) for calculating the interplanar spacing and interplanar angles of a hexagonal crystal by substituting the lattice constants (a=9.738 Å, c=9.115 Å), we checked whether there were any combinations of plane indices (h1, k1, l1) and (h2, k2, l2) corresponding to the measured interplanar spacing (d1, d2) and interplanar angle (φ). Note that Y4Zr3O 12 Regarding the lattice constant, "MAGNETIC SUSCEPTIBILITY OF M4Zr3O 12 AND M4Hf3O 12 (M - RARE-EARTH ELEMENT)” Inorg. Mater., 1991, 27, pp.1495-1497, Red'ko VP, Lopato LM” was referenced. 1 / d 2 = 4 / 3((h 2 +hk+k 2 ) / a 2 ) + l 2 / c 2 (1-4) cosφ = (h1h2+k1k2+1 / 2(h1k2+h2k1)+(3a 2 / 4c 2 ) l1 l2) / (( h1 2 +k1 2 +h1k1+(3a 2 / 4c 2 ) l1 2 ) (h2 2 +k2 2 +h2k2+(3a 2 / 4c 2 ) l2 2 )) 1 / 2 (1-5) When evaluated according to the above method, Y4Zr3O was found to be present after the specific heat treatment in Examples 1 and 2. 12 It was confirmed that it exists. On the other hand, in Comparative Examples 1 to 4, after specific heat treatments, Y4Zr3O 12 The presence of Y4Zr3O could not be confirmed. In addition, the zirconia calcined bodies of Examples 1 and 2 contained Y4Zr3O 12 It was confirmed that Y4Zr3O was present in the calcined zirconia bodies of Comparative Examples 1 to 4. 12 Its presence could not be confirmed.

[0128] <Evaluation of the abundance of crystal systems in X-ray diffraction measurements before and after specific heat treatment> The zirconia calcined bodies obtained in each example and comparative example were subjected to specific heat treatment (condition (i)) in a dental firing furnace (product name "Sintra CS" (manufactured by Shenpaz)), and the Y4Zr3O in the state before becoming a sintered body was evaluated. 12 The probability of existence f d1 , tetragonal crystallinity f t1 , cubic crystal fraction f c1 , and monoclinic constant f m1 This was determined by analyzing the crystal system in the zirconia calcined material. In addition, the Y4Zr3O in the zirconia calcined material obtained in each example and comparative example (without specific heat treatment) was also determined. 12 The probability of existence f d2 , tetragonal crystallinity f t2 , cubic crystal fraction f c2 , and monoclinic constant f m2 This was determined by analyzing the crystal system in the calcined zirconia. Specifically, for X-ray diffraction, measurements were performed using a fully automated horizontal multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and integrated X-ray analysis software (SmartLab Studio II, manufactured by Rigaku Corporation) under the following conditions, and the area intensity of each peak (peak area intensity I) was determined. X-ray source: Cu Kα (λ = 1.54186 Å) Goniometer length: 300 mm Optical system: Focused method Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250) Monochromatization: Kβ filter Tube voltage: 40 kV Tube current: 30 mA Scan axis: 2θ / θ Measurement range (2θ): 5 to 90° Scan speed: 0.2° / min Sampling step: 0.01°

[0129] Using the area intensity of each peak, and applying the above equations (1-1) and (1-2), Y4Zr3O 12 The probability of existence f d1 (%) and abundance f d2 The percentage (%) was calculated. The results are shown in Table 1. Note that Y4Zr3O 12 The probability of existence f d1 (%) and abundance f d2 In calculating the percentage, Y4Zr3O 12Since the main peak positions of the tetragonal and cubic crystal systems are similar, peak separation was performed when the coexistence of these crystal systems was confirmed. Specifically, the presence or absence of each crystal system was first confirmed. Y4Zr3O 12 The presence or absence of the above was confirmed by the TEM evaluation. For the tetragonal system, the presence or absence was confirmed by the subpeaks around 34.6° and 35.4°. For the cubic system, the presence or absence was confirmed by the subpeak around 35.0°. Next, peak separation was performed based on the confirmed crystal systems. For example, if all three crystal systems were confirmed, the peak where the three crystal systems overlap, which is seen around 30°, was identified as Y4Zr3O with a peak top at 29.6°. 12 The peaks of the three crystal systems—a tetragonal crystal with a peak top at 30.3° and a cubic crystal with a peak top at 30.0°—are separated by adjusting the full width at half maximum and peak intensity at the aforementioned peak top positions so that each peak approximates a Gaussian function. d1 , I t1 , I c1 , I d2 , I t2 , I c2 The following was calculated. If two crystal systems were confirmed to exist, the peaks were separated into those of the two crystal systems, and the area intensity of each was calculated.

[0130] <Evaluation of Transparency of Zirconia Sintered Bodies (Measurement of ΔL*(W-B) 1)> Zirconia sintered bodies were prepared by sintering the calcined bodies obtained in the Examples and Comparative Examples in a dental firing furnace (product name "Sintra CS" (manufactured by Shenpaz)) with a heating rate of 350°C / min and a maximum sintering temperature of 1580°C, holding time at the maximum sintering temperature for 2 minutes (2-minute sintering), and cooling rate set to 200°C / min. The obtained zirconia sintered bodies were polished into 1.0 mm thick flat plate samples and used as samples for measuring transparency. The transparency of these samples was measured using a spectrophotometer (product name "Crystal Eye") manufactured by Olympus Corporation, with the measurement mode set to 7-band LED light source. Specifically, to measure the light transmittance of a flat zirconia sintered body sample, the lightness (LW*) was measured when the chromaticity was measured against a white background, and the lightness (LB*) was measured when the chromaticity was measured against a black background using the same sample, measuring device, measurement mode, and light source. The difference between the two (ΔL* = (LW*) - (LB*)) was defined as the light transmittance (ΔL*(W-B)) (arithmetic mean for n=3). The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The light transmittance ΔL*(W-B) for the zirconia sintered body was determined (n=3). The arithmetic mean of the measured values ​​is shown in Table 1. A light transmittance ΔL*(W-B) of 13 or higher was considered acceptable.

[0131] <Evaluation of Transparency of Zirconia Sintered Bodies (Measurement of ΔL*(W-B) 2)> The calcined bodies obtained in the Examples and Comparative Examples were fired in a dental firing furnace (product name "Sintra CS" (manufactured by Shenpaz)) with a heating rate of 350°C / min and a maximum sintering temperature of 1550°C, holding time at the maximum sintering temperature for 7 minutes (7-minute sintering) to produce zirconia sintered bodies (first sintered bodies). Next, the calcined bodies produced by the same method were fired with a heating rate of 10°C / min and a maximum sintering temperature of 1550°C, holding time at the maximum sintering temperature for 120 minutes (120-minute sintering) to produce zirconia sintered bodies (second sintered bodies). The cooling rate was set to 200°C / min for 7-minute sintering and to 10°C / min for 120-minute sintering. The two types of zirconia sintered bodies obtained were polished into 1.0 mm thick flat plate samples to be used as samples for light transmission measurement. The light transmission of these samples was measured using a spectrophotometer manufactured by Olympus Corporation (product name "Crystal Eye"), with the measurement mode set to a 7-band LED light source. Specifically, the light transmission of the flat plate zirconia sintered body was measured by determining the lightness (LW*) when the chromaticity was measured against a white background, and the lightness (LB*) when the chromaticity was measured against a black background using the same sample, the same measuring device, measurement mode, and light source. The difference between the two (ΔL* = (LW*) - (LB*)) was defined as the light transmission (ΔL*(W-B)) (arithmetic mean for n=3). The L* value is the L* value of chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The first translucency ΔL1*(W-B) for the first sintered body, which was prepared by sintering at 1550°C for 7 minutes, and the second translucency ΔL2*(W-B) for the second sintered body, which was prepared by sintering at 1550°C for 120 minutes, were determined. The ratio of ΔL1*(W-B) to ΔL2*(W-B) (ΔL1*(W-B) / ΔL2*(W-B)) was calculated as the rate of change in translucency. The results are shown in Table 1. A rate of change in translucency of 0.85 or higher (85% or higher) was considered acceptable.

[0132] In the table, the yttria content refers to the ratio (mol%) of moles of yttria to the total number of moles of zirconia and yttria. Furthermore, in the table, the commercially available products for Comparative Examples 1 to 4 were manufactured by Tosoh Corporation.

[0133] From the above results, it was confirmed that the dental workpiece of this disclosure exhibits excellent light transmittance even when the holding time at the maximum sintering temperature is 2 minutes. Furthermore, from the above results, it was possible to obtain a zirconia sintered body that maintains the same level of high light transmittance as that obtained with long-term sintering (holding time of 2 hours) after sintering at a short time of 7 minutes or less at 1550°C with this disclosure.

[0134] The dental workpieces disclosed herein are useful in dental treatment because the resulting sintered body exhibits excellent light transmission even when the holding time at the maximum sintering temperature is 2 minutes. The dental workpieces disclosed herein are particularly useful in realizing one-visit treatments in dental clinics.

Claims

1. A dental workpiece containing zirconia, observed by transmission electron microscopy after heat treatment under the following conditions (i): Y4Zr3O 12 Dental workpieces including (i) Heat from room temperature to 1100°C at a heating rate of 350°C / min, hold at 1100°C for 0 minutes, cool to 800°C at a cooling rate of 200°C / min, and then allow to cool at room temperature.

2. In X-ray diffraction (XRD) measurement after the heat treatment under the condition (i), Y4Zr3O 12 abundance f d1 (%) is more than 13%, the dental workpiece according to claim 1. f d1 (%) = I d1 / (I m1 +I t1 +I c1 +I y1 +I d1 )×100 (1-1) (In the formula, f d1 represents the abundance (%) of Y4Zr3O 12 , in XRD measurement, I m1 represents the peak area intensity near 2θ = 28.2° where the main peak of monoclinic system appears, I t1 represents the peak area intensity near 2θ = 30.3° where the main peak of tetragonal system appears, I c1 represents the peak area intensity near 2θ = 30.0° where the main peak of cubic system appears, I d1 represents the peak area intensity near 2θ = 29.6° where the main peak of Y4Zr3O 12 appears, I y1 represents the peak area intensity near 2θ = 29.2° where the main peak of yttria that does not form a solid solution in zirconia appears. Note: Since the positions of the main peaks of Y4Zr3O 12 , tetragonal system, and cubic system are close to each other, the area intensity of each main peak is calculated by peak separation.) 3. In the X-ray diffraction (XRD) measurement before heat treatment under condition (i) above, Y4Zr3O is calculated using the following formula (1-2). 12 The probability of existence f d2 The dental workpiece according to claim 1 or 2, wherein the percentage (%) is less than 2.5%. d2 (%) = I d2 / (I m2 +I t2 +I c2 +I y2 +I d2 )×100 (1-2) (where f d2 is Y4Zr3O 12 This represents the prevalence rate (%) of [I] in XRD measurements. m2 This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t2 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c2 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d2 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y2 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 Since the positions of the main peaks are similar for tetragonal and cubic crystal systems, the area intensity of each main peak is calculated using peak separation.

4. Y4Zr3O calculated using the above formula (1-2) 12 The probability of existence f d2 The dental workpiece according to claim 3, wherein (%) is greater than 0%.

5. The dental workpiece according to claim 1 or 2, wherein the workpiece is a calcined zirconia body.

6. A dental workpiece containing zirconia, in which X-ray diffraction (XRD) measurement after heat treatment under the following conditions (i) is performed, the Y4Zr3O calculated by the following formula (1-1) is obtained. 12 The probability of existence f d1 A dental workpiece in which (%) is greater than 0%. (i) Heat from room temperature to 1100°C at a heating rate of 350°C / min, hold at 1100°C for 0 minutes, cool to 800°C at a cooling rate of 200°C / min, and then allow to cool at room temperature. f d1 (%) = I d1 / (I m1 +I t1 +I c1 +I y1 +I d1 )×100 (1-1) (where f d1 is Y4Zr3O 12 This represents the prevalence rate (%) of [I] in XRD measurements. m1 This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t1 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c1 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d1 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y1 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 Since the positions of the main peaks are similar for tetragonal and cubic crystal systems, the area intensity of each main peak is calculated using peak separation.

7. In the X-ray diffraction (XRD) measurement after heat treatment under condition (i) above, Y4Zr3O calculated by formula (1-1) above 12 The probability of existence f d1 The dental workpiece according to claim 6, wherein the percentage is greater than 13%.

8. In the X-ray diffraction (XRD) measurement before heat treatment under condition (i) above, Y4Zr3O is calculated using the following formula (1-2). 12 The probability of existence f d2 The dental workpiece according to claim 6 or 7, wherein the percentage (%) is less than 2.5%. d2 (%) = I d2 / (I m2 +I t2 +I c2 +I y2 +I d2 )×100 (1-2) (where f d2 is Y4Zr3O 12 This represents the prevalence rate (%) of [I] in XRD measurements. m2 This represents the area intensity of the peak around 2θ = 28.2° where the peak top of the main monoclinic peak appears, and I t2 This represents the area intensity of the peak around 2θ = 30.3° where the peak top of the main peak of the tetragonal crystal system appears, and I c2 This represents the area intensity of the peak around 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d2 is Y4Zr3O 12 This represents the area intensity of the peak around 2θ = 29.6° where the peak top of the main peak appears, and I y2 This represents the area intensity of the peak around 2θ = 29.2° where the peak top of the main peak of yttria, which is not solid-dissolved in zirconia, appears. Note that Y4Zr3O 12 Since the positions of the main peaks are similar for tetragonal and cubic crystal systems, the area intensity of each main peak is calculated using peak separation.

9. Y4Zr3O calculated using the above formula (1-2) 12 The probability of existence f d2 The dental workpiece according to claim 8, wherein (%) is greater than 0%.

10. The dental workpiece according to claim 6 or 7, which is a calcined zirconia body.

Images