阅读说明：本技术 牙科切削加工用氧化锆被切削体及其制造方法 (Zirconia workpiece for dental cutting and method for producing same ) 是由 野中和理 高桥周平 于 2019-08-22 设计创作，主要内容包括：本申请提供一种牙科切削加工用氧化锆被切削体以及制造方法,该牙科切削加工用氧化锆被切削体在嵌体、高嵌体、贴面等薄壁加工物中的切削加工性优异,且不需要HIP处理等特殊的烧结,能够使氧化锆完全烧结体具有高强度和透光性。作为牙科切削加工用氧化锆被切削体,牙科切削加工用氧化锆被切削体的空孔率为15～30％。(Provided are a zirconia cutting object for dental cutting which has excellent cutting properties in thin-walled workpieces such as inlays, onlays and veneers, does not require special sintering such as HIP treatment, and can give a zirconia sintered compact having high strength and light transmittance, and a method for producing the same. The zirconia cutting body for dental cutting has a porosity of 15 to 30%.)

1. A zirconia workpiece for dental cutting, characterized in that,

the zirconia workpiece for dental cutting has a porosity of 15 to 30%.

2. The zirconia cutting object for dental cutting processing according to claim 1,

the zirconia cutting object for dental cutting comprises: zirconia particles (a1) containing solid-solution yttrium.

3. The zirconia cutting object for dental cutting processing according to claim 2,

the amount of yttrium in the zirconia particles (a1) containing solid-solution yttrium is 3.0 to 6.5 mol% in terms of oxide in the dental zirconia cutting body for cutting.

4. The zirconia cutting object for dental cutting processing according to claim 2,

the amount of yttrium in the zirconia particles (a1) containing solid-solution yttrium is 3.5 to 4.5 mol% in terms of oxide in the dental zirconia cutting body for cutting.

5. The zirconia cutting body for dental cutting according to any one of claims 2 to 4,

the zirconia cutting object for dental cutting processing further includes: an yttrium compound (a2) which is not dissolved in zirconia.

6. The zirconia cutting object for dental cutting processing according to claim 5,

the yttrium compound (a2) which is not dissolved in zirconia is dispersed on the surface of zirconia particles (a1) containing yttrium in solid solution.

7. The zirconia cutting object for dental cutting processing according to claim 5 or 6,

the amount of yttrium in the yttrium compound (a2) that is not dissolved in zirconia is 0.1 to 3.0 mol% in terms of oxide in the dental zirconia cutting body for cutting.

8. The zirconia cutting object for dental cutting according to any one of claims 1 to 7,

the zirconia workpiece for dental cutting has a pore volume of 0.03 to 0.07cm³/g。

9. The zirconia cutting object for dental cutting according to any one of claims 1 to 8,

the zirconia-based material for dental cutting has a specific surface area of 1 to 10m²/g。

10. The zirconia cutting object for dental cutting according to any one of claims 1 to 9,

the zirconia object to be cut for dental cutting has a pore diameter of 50 to 200 nm.

11. A method for manufacturing a zirconia cutting object for dental cutting, comprising:

a step of molding zirconia powder; and

a step of molding by a cold isostatic pressing method,

the molding by the cold isostatic pressing method includes a series of steps of at least two times: applying the load pressure to increase the load pressure to a maximum load pressure and releasing the load pressure.

12. A method for manufacturing a zirconia cutting object for dental cutting according to claim 11,

the zirconia powder is formed by press forming.

13. The method for manufacturing a zirconia cutting object for dental cutting according to claim 11 or 12,

the forming by the cold isostatic pressing method further includes: and maintaining the maximum load pressure.

14. The method for manufacturing a zirconia cutting object for dental cutting according to any one of claims 11 to 13,

the difference between the maximum load pressure and the load pressure after release is at least 50MPa or more.

15. The method for manufacturing a zirconia cutting object for dental cutting according to any one of claims 11 to 14, wherein the zirconia cutting object is a dental cutting object,

after the step of forming by the cold isostatic pressing method, the method further comprises: and dispersing an yttrium compound in zirconia particles containing solid-solution yttrium.

16. The method for manufacturing a zirconia cutting object for dental cutting according to any one of claims 11 to 15, wherein the zirconia cutting object is a dental cutting object,

comprises a series of procedures for at least more than ten times as follows: applying the load pressure, maintaining the maximum load pressure, and releasing the load pressure.

Technical Field

The present invention relates to a zirconia cutting body for dental cutting and a method for manufacturing the same, and more particularly, to a zirconia cutting body for dental cutting and a method for manufacturing the same, which are suitable for high-speed sintering.

Background

In recent years, a technique for manufacturing a prosthetic device by cutting using a dental CAD/CAM system has been rapidly spread. Thus, the prosthetic device can be easily manufactured by processing a body to be cut, which is made of a ceramic material such as zirconia, alumina, or lithium disilicate, or a resin material such as acrylic resin or hybrid resin (hybrid resin).

In particular, zirconia has high strength and is therefore clinically used in a wide variety of conditions. On the other hand, since fully sintered zirconia (hereinafter, referred to as a fully sintered zirconia compact) has very high hardness, cutting cannot be performed using the dental CAD/CAM system. Therefore, as a zirconia cutting object for dental cutting, a cutting object is used which is subjected to pre-firing at a low firing temperature, is not sintered to a full state, and has hardness adjusted to be capable of cutting.

A general dental cutting zirconia workpiece is produced by molding zirconia powder by press molding or the like and then calcining the molded zirconia powder at 800 to 1200 ℃.

The properties of the zirconia material to be cut for dental cutting, that is, the properties of the zirconia sintered compact, are affected by the properties of the zirconia powder used.

For example, patent document 1 discloses a zirconia sintered compact produced by using a zirconia powder containing 3 mol% of yttrium to produce a zirconia cutting body for dental cutting, and using the zirconia cutting body. The sintered body has high strength and is therefore clinically used in bridges (bridge frames) of 4 units or more. However, the sintered body has low light transmittance, and thus it is difficult to reproduce a color tone similar to that of a natural tooth.

Patent document 2 discloses a zirconia sintered compact produced by using a zirconia powder containing 3 mol% of yttrium and having a reduced amount of alumina to produce a zirconia cutting body for dental cutting, and using the zirconia cutting body. Since the sintered body has improved light transmittance while maintaining high strength, it is clinically used for long span bridges (long span bridges) of 4 or more units, full crowns of molar parts, and the like. However, even this sintered body has insufficient light transmittance, and thus it is difficult to apply the sintered body to a disease requiring high aesthetic quality such as an anterior tooth portion.

Patent document 3 discloses a zirconia sintered body produced by using a zirconia powder containing 4 to 6.5 mol% of yttrium to produce a zirconia cutting body for dental cutting, and using the zirconia cutting body. The sintered body has high light transmittance, and therefore, can be used for a disease requiring high aesthetic quality such as an anterior tooth part. However, since the light transmittance of the sintered body is still lower than that of a lithium disilicate material or the like, the sintered body is not sufficiently suitable for use in a disorder such as an inlay (inlay), an onlay, or a facing (veneer).

Patent document 4 discloses a zirconia sintered compact using a zirconia powder containing 2 to 7 mol% of yttrium. The sintered body has high light transmittance similar to that of a ceramic material, a lithium disilicate material, or the like, and thus can be applied to not only an anterior tooth portion but also inlays, onlays, veneers, or the like. However, since the sintered body needs to be subjected to Hot Isostatic Pressing (HIP), it is difficult for a general technician to manufacture the sintered body.

Patent document 5 discloses a zirconia cutting object for dental cutting having a mesopore (mesopore). The zirconia workpiece has an advantage that a coloring liquid containing metal ions easily penetrates because of its high specific surface area, but has a problem that chipping or breakage is easily caused when a thin-walled workpiece is cut because of insufficient strength. Further, the zirconia sintered compact produced from the zirconia workpiece is likely to have pores left in the sintered compact, and thus it is difficult to impart sufficient strength and light permeability.

The zirconia prosthesis is obtained by molding a zirconia workpiece for dental cutting into a desired shape by cutting or the like, firing the molded product at a temperature equal to or higher than a sintering temperature, and completely sintering the molded product. This firing requires a heating time of several hours or more and a holding time of several hours, and therefore, the production efficiency is low, and the patient needs to go to the hospital many times before the patch device can be attached.

In recent years, sintering furnaces capable of achieving sintering for several tens of minutes to several hours have come into widespread use. However, if a conventional zirconia cutting body for dental cutting is sintered in a short time, there is a problem that sufficient light transmittance and strength cannot be obtained.

For example, a sintered body obtained by sintering a zirconia cutting object for dental cutting in a short time as described in patent document 6 has insufficient light transmittance and strength, and thus is difficult to be applied to a condition requiring high aesthetic quality such as an anterior tooth portion and a condition requiring high strength such as a molar portion.

Patent document 7 discloses a zirconia cutting object for dental cutting that can obtain sufficient light transmittance in a sintered body sintered within a holding time of 15 minutes. However, the sintered body is not sufficient in strength, and is not suitable for a disease requiring high strength such as a full crown of a molar portion.

Patent document 8 discloses a zirconia cutting body for dental cutting that can be sintered within 30 minutes. However, the sintered body has insufficient light transmittance and is not suitable for a disease requiring high aesthetic quality such as an anterior tooth portion.

Patent document 9 discloses a method for obtaining a zirconia sintered compact in 30 to 90 minutes. However, the sintered body has insufficient light transmittance and strength, and is difficult to be applied to a disease requiring high aesthetic quality such as an anterior tooth portion and a disease requiring high strength such as a molar portion.

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a zirconia cutting object for dental cutting which has excellent cutting performance in thin-walled workpieces such as inlays, onlays, and veneers, does not require special sintering such as HIP treatment, and can give a zirconia sintered compact having high strength and light transmittance, and a method for producing the same.

Another object of the present invention is to provide a zirconia cutting object for dental cutting, which can provide a zirconia sintered body having high strength and light transmittance even when sintered for a short time, and a method for producing the same.

Means for solving the problems

The present inventors have studied a zirconia cutting object for dental cutting which is excellent in machinability in a thin-walled workpiece such as an inlay, an onlay, or a veneer, does not require special sintering such as HIP treatment, and can give a zirconia sintered compact having high strength and light transmittance. As a result, it was found that: the pore structure of a zirconia workpiece for dental cutting is particularly important for providing a fully sintered zirconia compact with high strength and light transmittance while being excellent in machinability in a thin workpiece.

The present inventors have also studied a zirconia cutting object for dental cutting that can provide a fully sintered zirconia compact with high strength and light transmittance even when sintered for a short period of time. As a result, it was found that: the pore structure of a zirconia workpiece for dental cutting is particularly important for imparting high strength and light permeability to a zirconia sintered compact even after sintering for a short time.

The dental zirconia cutting object of the present invention is characterized in that the porosity of the dental zirconia cutting object is 15 to 30%.

In the present invention, it is preferable that the zirconia cutting object for dental cutting includes: zirconia particles (a1) containing solid-solution yttrium.

In the present invention, it is preferable that the amount of yttrium in the zirconia particles (a1) containing solid-solution yttrium is 3.0 to 6.5 mol% in terms of oxide in the dental zirconia cutting body for cutting. In this case, the zirconia sintered compact can be made to have high strength and light transmittance even in a short-time sintering.

In the present invention, it is preferable that the amount of yttrium in the zirconia particles (a1) containing solid-solution yttrium is 3.5 to 4.5 mol% in terms of oxide in the dental zirconia cutting body for cutting.

In the present invention, it is preferable that the zirconia cutting object for dental cutting further includes: an yttrium compound (a2) which is not dissolved in zirconia.

In the present invention, it is preferable that the yttrium compound (a2) which is not solid-dissolved in zirconia is dispersed on the surface of the zirconia particles (a1) containing solid-dissolved yttrium.

In the present invention, it is preferable that the amount of yttrium in the yttrium compound (a2) that is not dissolved in zirconia is 0.1 to 3.0 mol% in terms of oxide in the dental zirconia cutting body for cutting.

In the present invention, it is preferable that the zirconia cutting object for dental cutting has a pore volume of 0.03 to 0.07cm³/g。

In the present invention, it is preferable that the zirconia cutting object for dental cutting has a specific surface area of 1 to 10m²/g。

In the present invention, it is preferable that the zirconia cutting object for dental cutting has a pore diameter of 50 to 200 nm.

The method for manufacturing a zirconia cutting object for dental cutting according to the present invention includes: a step of molding zirconia powder; and a step of molding by a cold isostatic pressing method, wherein the molding by the cold isostatic pressing method includes a series of steps of: applying load pressure, increasing load pressure to a maximum load pressure, and releasing load pressure.

In the present invention, it is preferable that the zirconia powder is molded by press molding.

In the present invention, it is preferable that the forming by the cold isostatic pressing further includes: and maintaining the maximum load pressure.

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

In the present invention, it is preferable that the method further comprises, after the step of forming by a cold isostatic pressing method: and dispersing an yttrium compound in zirconia particles containing solid-solution yttrium.

In the present invention, it is preferable that the method comprises a series of steps of: applying the loading pressure, maintaining a maximum loading pressure, releasing the loading pressure.

The short-time sintering in the present invention means a sintering time of preferably 90 minutes or less.

In addition, in the present invention, it is preferable that the zirconia cutting object for dental cutting processing includes: zirconia particles containing solid-solution yttrium.

Effects of the invention

The zirconia cutting object for dental cutting and the method for producing the same according to the present invention are excellent in machinability in thin-walled workpieces such as inlays, onlays, and veneers, and can provide a zirconia sintered compact having high strength and light transmittance without requiring special sintering such as HIP treatment.

Detailed Description

The constituent elements of the present invention will be specifically explained.

The present invention is characterized in that a zirconia cutting object for dental cutting has an appropriate pore structure and a porosity of 15 to 30%. The zirconia cutting object for dental cutting of the present invention has excellent cutting workability in thin-walled workpieces such as inlays, onlays, veneers and the like, and can impart a transparency similar to that of natural enamel to a zirconia sintered compact even when sintered at normal pressure.

Preferably, the zirconia cutting object for dental cutting of the present invention comprises: zirconia particles (a1) containing solid-solution yttrium and an yttrium compound (a2) not solid-solution-dissolved in zirconia, wherein the yttrium compound (a2) not solid-solution-dissolved in zirconia is dispersed on the surface of the zirconia particles (a1) containing solid-solution yttrium. More preferably, the zirconia cutting object for dental cutting according to the present invention includes: zirconia particles (a1) containing yttrium in solid solution and an yttrium compound (a2) not in solid solution in zirconia.

Preferably, the zirconia cutting object for dental cutting of the present invention comprises: zirconia particles containing solid-solution yttrium. Such a zirconia cutting object for dental cutting can impart the same light transmittance and strength to a zirconia sintered compact as a conventional long-term sintered compact even when sintered for a short period of time.

The porosity of the zirconia workpiece for dental cutting in the present invention is 15 to 30%, and more preferably 22 to 27%. The porosity of the zirconia workpiece for dental cutting in the present invention is calculated from the following formula (1).

Porosity (%) ═ pore volume/(pore volume + framework volume) × 100 … … (1)

When the porosity is more than 30% or less than 15%, chipping resistance (resistance) of the zirconia material to be cut for dental cutting is lowered, or sufficient light transmittance cannot be imparted to the zirconia sintered body, which is not preferable.

The porosity of the zirconia workpiece for dental cutting in the present invention is substantially different from the relative density calculated from the theoretical density. The relative density calculated from the theoretical density is a value calculated from the densities of all fine pores including from fine pores to large pores in addition to the closed pores. On the other hand, the porosity in the present invention is determined based on the pore volume measured by the mercury intrusion method, and therefore is determined by measuring the interconnected pores not including the closed pores having a diameter of about 5nm to 250 μm. It is found that: the porosity determined based on the pore volume measured by the mercury intrusion method in the present invention is particularly important for imparting machinability to a zirconia workpiece for dental cutting and high light transmittance to a fully sintered zirconia body obtained by sintering under normal pressure. Since pores smaller than 5nm hardly remain as pores during sintering, the presence or absence of pores smaller than 5nm does not substantially affect the transparency of the zirconia sintered compact. On the other hand, pores larger than 250 μm preferably do not substantially contain pores larger than 250 μm because chipping resistance during cutting or light transmittance of the zirconia sintered compact is reduced.

The zirconia particles (a1) containing solid-solution yttrium in the present invention can be used without any limitation as long as they are produced from a known zirconia powder. Specifically, the zirconia powder used in the present invention is preferably produced by a hydrolysis method. More specifically, the following method is used: the zirconia powder is obtained by heating a solution obtained by mixing and dissolving a zirconium salt and an yttrium compound, performing a hydrolysis reaction, and firing the resulting sol. The method for producing the zirconia particles (a1) containing yttrium in solid solution of the present invention is not particularly limited, and for example, the zirconia particles are preferably produced by firing the zirconia powder at 800 to 1200 ℃.

The amount of yttrium contained in the zirconia particles (a1) containing yttrium in solid solution in the dental zirconia cutting body for cutting is preferably 3.0 to 6.5 mol%, more preferably 3.5 to 4.5 mol% in terms of oxide. When the amount of yttrium is less than 3.0 mol%, sufficient light transmittance cannot be imparted to the zirconia after the zirconia is completely sintered, which is not preferable. On the other hand, when the amount of yttrium is more than 6.5 mol%, the light transmittance of the zirconia sintered compact is improved, but it is difficult to provide sufficient strength, which is not preferable.

The primary particle size of the zirconia powder in the present invention is preferably 1 to 500 nm. When the primary particle diameter is less than 1nm, the transparency of the zirconia sintered compact is improved, but it is difficult to provide sufficient strength, which is not preferable. On the other hand, when the primary particle diameter is 500nm or more, it is difficult to impart sufficient strength to the zirconia sintered compact, which is not preferable.

The specific surface area of the zirconia powder in the present invention is preferably 1 to 10m²(ii) in terms of/g. In the specific surface area of less than 1m²In the case of/g, sufficient light transmittance cannot be imparted after the zirconia is completely sintered, which is not preferable. On the other hand, the specific surface area is 10m²When the amount of the binder is not less than g, the transparency of the zirconia sintered compact is improved, but it is difficult to provide sufficient strength, which is not preferable.

The yttrium compound (a2) which is not dissolved in zirconia in the present invention can be used without any limitation as long as it is a known yttrium compound. Specifically, the yttrium compound used in the present invention is preferably yttrium oxide and/or a water-soluble compound containing any one of a halogen compound, a nitrate, a sulfate, and an organic acid salt (including a carbonate) of yttrium. Specific examples of the water-soluble yttrium compound include yttrium chloride, yttrium nitrate, yttrium acetate, yttrium carboxylate, yttrium sulfate, and yttrium carbonate.

Among the water-soluble yttrium compounds, organic acid salts (including carbonates) are particularly preferable from the viewpoint of low decomposition temperature and less pollution of the firing furnace. Specific examples thereof include yttrium acetate and yttrium carbonate. The decomposition temperature of the organic acid salt is lower than that of inorganic salts such as halogen compounds, nitrates, and sulfates. When the decomposition temperature is high, pores remain during sintering, and it is difficult to impart sufficient transparency and strength to the zirconia by complete sintering.

The amount of yttrium contained in the yttrium compound (a2) that is not dissolved in zirconia in the present invention is preferably 0.1 to 3.0 mol% in terms of oxide in the dental zirconia cutting body for cutting. When the amount of yttrium is less than 0.1 mol%, sufficient light transmittance cannot be imparted to the zirconia after the zirconia is completely sintered, which is not preferable. On the other hand, when the amount of yttrium is more than 3.0 mol%, the light transmittance of the zirconia sintered compact is improved, but it is difficult to provide sufficient strength, which is not preferable.

In the dental zirconia cutting target of the present invention, the mixing molar ratio of the zirconia particles (a1) containing yttrium in solid solution to the yttrium compound (a2) not in solid solution to zirconia is preferably (a 1): (a2) 1: 1-65: 1, more preferably 3: 1-20: 1. when the molar ratio is 1 with respect to (a2) and (a1) is more than 65, the transparency of the zirconia sintered compact is improved, but it is difficult to provide sufficient strength, which is not preferable. On the other hand, when the molar ratio is 1 with respect to (a2) and (a1) is less than 1, sufficient light transmittance cannot be imparted after the zirconia is completely sintered, which is not preferable.

The yttrium compound (a2) which is not dissolved in zirconia in the present invention is preferably in a state of being dispersed on the surface of zirconia particles (a1) containing dissolved yttrium.

The state of being dispersed on the surface in the present invention means a state in which the yttrium compound is supported on and/or adsorbed on a part of and/or the whole of the zirconia primary particles.

It is found that: in the present invention, it is important to provide a high workability to a dental cutting zirconia workpiece and further to provide a high light transmittance and strength to a zirconia sintered compact by dispersing an yttrium compound (a2) not dissolved in zirconia on the surface of zirconia particles (a1) containing dissolved yttrium.

Although these reasons are not clear, the reason for imparting high workability to a zirconia workpiece for dental cutting is presumed to be that: the yttrium compound not dissolved in zirconia reinforces the neck (neck) portion of each primary zirconia particle. In general, since the zirconia material to be cut for dental cutting is in a semi-sintered state, the strength of the neck portion between the primary zirconia particles is low. Therefore, when a thin-walled workpiece is machined, chipping and breakage occur during machining. On the other hand, it is presumed that: since the neck portion of the zirconia cutting object for dental cutting according to the present invention is reinforced with an yttrium compound, it is possible to provide good workability even when a thin-walled workpiece is cut.

Further, the reason why the high light transmittance can be imparted to the zirconia sintered compact is presumed to be that: by dispersing the yttrium compound dissolved in zirconia in the outermost surface of zirconia, the dispersed yttrium compound segregates in the vicinity of the grain boundary during sintering, and the phase transition of the crystal phase in the vicinity of the grain boundary (from tetragonal to cubic) is promoted. In addition, it is considered that: the state in which the yttrium compound is dispersed on the surface of the zirconia particles also gives an effect of reducing the residual amount of closed pores during sintering, and can achieve both high light transmittance and strength of the fully sintered zirconia body.

The zirconia cutting object for dental cutting in the present invention may contain a coloring material. Specifically, iron oxide for imparting yellow color, erbium for imparting red color, and the like can be cited. Further, there is no problem in using a coloring material containing an element such as cobalt, manganese or chromium in addition to these coloring materials for color tone adjustment.

The zirconia cutting body for dental cutting use in the present invention may contain a sintering aid. Specifically, 0.01 to 0.3 wt% of alumina is preferably contained for the purpose of improving sinterability and suppressing low-temperature deterioration. When the amount of alumina is less than 0.01 wt%, the zirconia cannot be sufficiently sintered after being completely sintered, and sufficient strength and light transmittance cannot be imparted, which is not preferable. On the other hand, when the amount of alumina is more than 0.3 wt%, the strength of the zirconia sintered compact is improved, but it is difficult to impart sufficient light transmittance, which is not preferable.

The crystal phase of the zirconia cutting object for dental cutting in the present invention is preferably a tetragonal phase and/or a cubic phase. When the crystal phase is a monoclinic phase, sufficient light transmittance cannot be imparted to the zirconia after the zirconia is completely sintered, which is not preferable.

The specific surface area of the zirconia material for dental cutting of the present invention was measured by a nitrogen adsorption method. The specific surface area of the zirconia material to be cut for dental cutting in the present invention is preferably 1 to 10m²(ii) in terms of/g. In the specific surface area of less than 1m²In the case of/g, sufficient light transmittance cannot be imparted to the zirconia sintered compact, which is not preferable. On the other hand, in the case of a specific surface area of more than 10m²In the case of/g, sufficient strength cannot be imparted to the zirconia sintered compact, which is not preferable.

The pore volume of the zirconia workpiece for dental cutting in the present invention is measured by mercury intrusion method. The pore volume measured by mercury intrusion method is obtained by measuring pores having a diameter of about 5nm to 250 μm. The pore volume of the zirconia material to be cut for dental cutting in the present invention is preferably 0.03 to 0.07cm³(ii) in terms of/g. The pore volume is less than 0.03cm³In the case of/g, sufficient light transmittance cannot be imparted to the zirconia sintered compact, which is not preferable. On the other hand, in the case of a pore volume of more than 0.07cm³In the case of/g, zirconia cannot be providedThe completely sintered body is not preferable because it has sufficient strength.

The pore diameter of the zirconia workpiece for dental cutting in the present invention means the diameter of the micropores at the median of the pore volume measured by mercury intrusion method. The pore diameter of the zirconia material to be cut for dental cutting in the present invention is preferably 50 to 200 nm. When the pore diameter is less than 50nm, sufficient light transmittance cannot be imparted to the zirconia sintered compact, which is not preferable. On the other hand, when the pore diameter is larger than 200nm, sufficient light transmittance and strength cannot be imparted to the zirconia sintered compact, which is not preferable.

The skeleton volume of the zirconia workpiece for dental cutting in the present invention is calculated from the true density measured by the gas phase displacement method. The skeleton volume in the present invention means a volume in terms of skeleton volume (cm)³1/true density (g/cm)³) The calculated value. The skeleton volume calculated by the gas phase displacement method is characterized by using a gas, and therefore is a communicating pore including a fine pore as compared with a value measured by the liquid phase displacement method. The volume of the skeleton of the zirconia material to be cut for dental cutting in the present invention is preferably 0.16 to 0.17cm³(ii) in terms of/g. The volume of the skeleton is less than 0.16cm³In the case of/g, sufficient light transmittance cannot be imparted, and therefore, it is not preferable. On the other hand, in a skeletal volume of more than 0.17cm³In the case of/g, sufficient strength cannot be imparted to the zirconia sintered compact, which is not preferable.

The Vickers hardness of the zirconia cutting body for dental cutting in the present invention is preferably 30 to 150 Hv0.2. When the vickers hardness is less than 30hv0.2, chipping and breakage are likely to occur during cutting, which is not preferable. On the other hand, if the vickers hardness is more than 150hv0.2, the milling bar (milling bar) of the cutting machine is consumed seriously, and the running cost becomes high, which is not preferable.

The bending strength of the zirconia cutting object for dental cutting in the present invention is preferably 25 to 150 MPa. When the bending strength is less than 25MPa, chipping and breakage are likely to occur during cutting, which is not preferable. On the other hand, if the bending strength is more than 150MPa, the milling bar of the cutting machine is undesirably worn, which increases the running cost.

The method for producing the dental cutting zirconia workpiece of the present invention is not particularly limited, and any known method can be used without any problem. Specifically, a method of molding the zirconia powder by press molding is preferable. Further, it is more preferable to perform multi-layer molding by press-molding zirconia powders having different color tones and compositions in multiple stages.

The zirconia cutting material for dental cutting use in the present invention is preferably subjected to isotropic pressing by a cold isostatic pressing (CIP forming/treatment) method after press forming.

The maximum load pressure of the CIP forming/processing in the present invention is preferably 50MPa or more. When the maximum load pressure is less than 50MPa, sufficient light transmittance and strength cannot be imparted to the zirconia sintered compact, which is not preferable.

The retention at the maximum load pressure and the retention time in the CIP molding/treatment in the present invention are not particularly limited, and the retention is usually preferably no for 150 seconds, and more preferably no for 60 seconds. The holding in the present invention means maintaining an arbitrary load pressure.

The CIP forming/treating in the present invention is preferably repeated at least two times, more preferably five times or more, and most preferably ten times or more, as a series of steps of: apply load pressure, maintain maximum load pressure, release load pressure. By repeating the above-described series of steps, the pores of the zirconia workpiece for dental cutting can be reduced to an appropriate size. Further, it is also possible to increase the maximum load pressures in multiple stages and release the load pressures. When the above-mentioned series of steps is performed once or less, sufficient light transmittance and strength cannot be imparted to the zirconia sintered compact, which is not preferable.

The time taken for the series of steps is not particularly limited, but is preferably 30 seconds to 10 minutes, and more preferably 3 minutes to 7 minutes. If the time is too short, the molded article may be broken, and if the time is too long, the productivity is deteriorated, which is not preferable.

The difference between the maximum load pressure and the post-release pressure in the present invention is preferably at least 50MPa or more, more preferably 100MPa or more, and still more preferably 200MPa or more. When the releasing pressure is less than 50MPa, sufficient light transmittance and strength cannot be imparted to the zirconia sintered compact, which is not preferable.

The repeated CIP treatment in the present invention may include a degreasing step in the middle. The method of degreasing is not particularly limited, and degreasing by a general heat treatment is preferable because no special equipment is required. The degreasing temperature is not particularly limited, and is preferably 300 to 800 ℃. When the degreasing temperature is 300 ℃ or lower, the binder may not be sufficiently removed, and when the degreasing temperature is 800 ℃ or higher, partial sintering may be performed, and the effect of repeated CIP treatment may not be sufficiently obtained, which is not preferable.

The pre-firing temperature of the zirconia material to be cut for dental cutting in the present invention is preferably 800 to 1200 ℃. When the pre-firing temperature is less than 800 ℃, the vickers hardness and/or the bending strength are too low, and chipping and breakage are likely to occur during cutting, which is not preferable. On the other hand, if the pre-firing temperature is 1200 ℃.

In the present invention, it is preferable that the yttrium compound (a2) which is not dissolved in zirconia is dispersed on the surface of the zirconia particles. In the present invention, the dispersed state is a state in which coarse particles are not present, and preferably, particles of 100nm or more, more preferably 50nm or more are not present. Examples of a method for confirming the dispersed state include TEM-EDS observation. The method of dispersing the yttrium compound on the surface of zirconia is a method of: for example, a solution containing yttrium, which is obtained by dissolving a water-soluble yttrium compound in water, is sprayed in the form of a mist onto a zirconia powder and/or a dental cutting zirconia workpiece, and/or the yttrium-containing solution is brought into contact with the zirconia powder and/or the dental cutting zirconia workpiece, followed by drying. The yttrium compound covered by this method is supported at the elemental level and/or adsorbed on the surface of the zirconia primary particle, and therefore, is easily dissolved in zirconia during sintering, and is therefore a preferred method.

The content of the yttrium compound in the yttrium-containing liquid used for dispersing the yttrium compound on the surface of zirconia is preferably 1 to 60 wt%, more preferably 5 to 30 wt%. When the content of the yttrium compound is less than 1 wt%, it is not preferable because sufficient yttrium compound cannot be dispersed in the zirconia powder and/or the zirconia cutting object for dental cutting. On the other hand, when the content of the yttrium compound is more than 60 wt%, the amount of the yttrium compound is excessive, which is not preferable.

The method for producing the yttrium-containing liquid in the present invention is not particularly limited, and any method can be used as long as the water-soluble yttrium compound is dissolved in water.

The method for spraying the yttrium-containing solution in the present invention in the form of a mist onto the zirconia powder and/or bringing the yttrium-containing solution into contact with the zirconia powder is not particularly limited, and any preparation method is not particularly limited as long as it is dispersed in the zirconia primary particles.

The yttrium-containing solution in the present invention is preferably sprayed in a mist form onto the zirconia powder and/or the yttrium-containing solution is brought into contact with the zirconia powder, and then water is removed. The drying method is not particularly limited, and any problem may be posed as long as the temperature, time, and the like required for removing water are satisfied.

The method of bringing the zirconia cutting object for dental cutting work into contact with the yttrium-containing solution in the present invention is not particularly limited as long as the yttrium-containing solution can penetrate into the gap of the zirconia cutting object, but a simple and preferable method is to immerse the entire or a part of the zirconia cutting object in the yttrium-containing solution. By impregnating the whole and/or a part of the zirconia workpiece, the yttrium-containing solution can be infiltrated into the inside by utilizing the capillary phenomenon.

As a specific method of immersing the zirconia cutting object for dental cutting in the yttrium-containing solution of the present invention, the yttrium-containing solution is preferably immersed in an amount of 1 to 100%, more preferably 10 to 100%, based on the total volume of the zirconia cutting object. Further, by controlling the volume of the zirconia cutting object impregnated with the yttrium-containing solution, the yttrium compound can be dispersed only in any portion of the zirconia cutting object for dental cutting.

The specific atmosphere in which the dental cutting zirconia material of the present invention is immersed in the yttrium-containing solution is not particularly limited, and there is no problem in any of the atmospheric pressure atmosphere, the reduced pressure atmosphere, and the pressurized atmosphere. From the viewpoint of shortening the production time, it is a preferable method because permeation of the yttrium-containing solution is promoted when the ambient atmosphere is placed under a reduced pressure atmosphere or a pressurized atmosphere. Further, repeating the operation of returning to the normal pressure after the operation of reducing the pressure (operation of reducing the pressure/the normal pressure) a plurality of times is effective for shortening the time of the step of infiltrating the yttrium-containing solution into the zirconia workpiece.

The time for immersing the dental cutting zirconia workpiece in the yttrium-containing solution can be appropriately adjusted depending on the density of the zirconia workpiece, the size of the molded body of the zirconia workpiece, the degree of penetration of the yttrium-containing solution, the immersion method, and the like, and cannot be generally said. For example, in the case of immersion, it is usually 1 to 72 hours; in the case of impregnation under reduced pressure, it is usually 1 minute to 6 hours; in the case of contact under pressure, it is usually 1 minute to 6 hours.

Then, it preferably includes: and a step of taking out the zirconia cutting object from the yttrium-containing solution and drying the yttrium-containing solution after the yttrium-containing solution has entered the zirconia cutting object for dental cutting. The drying step is not particularly limited, but a method of drying under a normal pressure atmosphere is a simple and preferable method. The drying temperature is not particularly limited, but is preferably 25 to 1200 ℃ and more preferably 25 to 1100 ℃. The drying time is also not particularly limited, and is usually 30 minutes to 72 hours.

Thus, the zirconia cutting object for dental cutting can be obtained by the production method of the present invention. The obtained zirconia cutting object for dental cutting is cut, and surface-polished as necessary to have a desired size.

The method for completely sintering the zirconia cutting object for dental cutting of the present invention is not particularly limited, but a method of sintering at normal pressure is a simple and preferable method. The firing temperature is not particularly limited, but is preferably 1450 to 1600 ℃, more preferably 1500 to 1600 ℃. The residence time at the maximum firing temperature is not particularly limited, but is preferably 1 minute to 12 hours, more preferably 2 to 4 hours. The rate of temperature rise is not particularly limited, but is preferably 1 to 400 ℃/min, more preferably 3 to 100 ℃/hr.

In addition, when the amount of yttrium in the dental cutting zirconia workpiece of the present invention is 3.0 to 6.5 mol% in terms of oxide, sintering in a short time can be used as a method of complete sintering. In this case, the firing temperature is not particularly limited, but is preferably 1450 to 1600 ℃, more preferably 1500 to 1600 ℃. The residence time at the maximum firing temperature is not particularly limited, but is preferably 1 minute to 1 hour, more preferably 2 to 10 minutes. The rate of temperature rise is not particularly limited, but is preferably 5 to 400 ℃/min, more preferably 50 to 300 ℃/min.

The type of the prosthetic device for cutting using the zirconia cutting object for dental cutting of the present invention is not particularly limited, and any prosthetic device such as an inlay, a patch (laminate), a crown (crown), and a bridge does not have any problem. Therefore, the shape of the dental cutting zirconia blank for producing the prosthetic device by cutting is not particularly limited, and a dental cutting zirconia blank having any shape of a block shape corresponding to an inlay, a patch, a crown, or the like, a disc shape corresponding to a bridge, or the like can be used.