JP2015137187A - Dental zirconia sintered body, crown frame, and bridge frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dental zirconia sintered body that has less occurrence of fracture or detachment when used as a frame or when the frame is bonded to porcelain, and in which the low-temperature deterioration is suppressed.SOLUTION: The dental zirconia sintered body contains at least ZrOand YO, and satisfies the following (a) to (f) requirements: (a) it has a two layer structure of a dense layer and a porous layer; (b) the porosity of the dense layer is 1.0% or less; (c) the porosity of the porous layer is 5 to 20%; (d) the average pore diameter of the porous layer is 5 to 40 μm; (e) the YO/ZrOmole ratio of the dense layer and porous layer is 2.0/98.0 to 5.0/95.0; and (f) the average crystal grain size of the dense layer and the porous layer is 0.20 to 0.50 μm.

Description

  The present invention relates to a dental zirconia sintered body used as a crown restoration material, a crown frame and a bridge frame made of the sintered body.

  In recent years, crown restoration materials have been attracting attention to ceramics with excellent aesthetics and biocompatibility similar to natural teeth due to the demand for advanced aesthetics and the problem of metal allergy, and the price of metals has been rising. It is growing. Among them, zirconia is becoming mainstream because it has excellent mechanical properties such as high toughness and high strength compared to other ceramic materials. For example, Patent Document 1 discloses a zirconia sintered body having high sintered body density and strength and excellent translucency. However, when applied as a frame for a crown and a frame for a bridge, it is bonded to porcelain. Since the strength is low, there is a problem that the porcelain is broken or peeled off in the oral cavity, resulting in poor safety. In order to increase the adhesive strength with this porcelain material, a blasting process is applied in which hard fine particles such as alumina are sprayed onto a zirconia frame at a high pressure to give fine irregularities on the surface. However, there is a problem that the strength of the frame is remarkably reduced due to cracks and the like on the surface after blasting.

Therefore, Patent Document 2 discloses a technique for making a zirconia sintered body porous in order to improve adhesion to porcelain. In this document, porcelain penetrates into the pores of the surface and high adhesive strength can be realized. However, porous zirconia has lower strength and toughness than dense zirconia, so all ceramic crowns that require strength are required. It is not applicable to.
In order to prevent such a decrease in the strength of the porous body, Patent Document 3 discloses a technique for impregnating specific glass in the pores of the porous body to prevent a decrease in strength and toughness. However, in the bridge where the extracted crown and the adjacent crowns are integrated, a large stress is concentrated at the lower part of the connecting part of the crown, so a particularly high strength is required. Ceramics do not have sufficient strength to withstand this large stress.
Thus, the conventional dental zirconia sintered body composed of a single compact has a problem that the ceramic is broken or peeled off due to its low adhesive strength with the ceramic. Since strength and toughness are low, there is a problem that it cannot be applied to portions that require high strength.

On the other hand, partially stabilized zirconia using Y ₂ O ₃ as a stabilizer, which accounts for the majority of current dental zirconia, undergoes a phase transition from tetragonal zirconia to monoclinic zirconia when used in a low temperature range of high humidity. However, the problem of low temperature deterioration has been pointed out that a large number of microcracks are generated by the volume change that occurs at that time, leading to a decrease in strength. In order to overcome this low temperature deterioration, a technique for increasing the number of stabilizers or controlling the crystal grain size of the zirconia sintered body in a specific range as disclosed in Patent Document 1 has been proposed. However, even in a low-temperature and humid environment such as the oral cavity, the occlusal force is repeatedly applied over a long period of time, so that moisture such as saliva causes stress corrosion at the zirconia crystal grain boundary and causes low-temperature deterioration. Therefore, it has been pointed out that the conventional dental zirconia sintered body is inferior in reliability, and a dental zirconia sintered body in which deterioration at low temperature is suppressed is desired.

JP 2009-269812 A JP 2007-22889 A JP-A-5-58835

The present invention has less breakage and peeling when used in a frame and when the frame is bonded to porcelain than a dental zirconia sintered body using Y ₂ O ₃ as a stabilizer, An object of the present invention is to provide a dental zirconia sintered body in which low temperature deterioration is suppressed, and a crown frame and a bridge frame made of the sintered body.

As a result of intensive studies, the present inventors have found that it is extremely effective to make a dental zirconia sintered body composed of a conventional dense single body into a two-layer structure of a dense layer and a porous layer. I found out. By controlling the porosity of the dense layer and the porous layer, the average pore diameter of the porous layer, the Y ₂ O ₃ / ZrO ₂ molar ratio of the dense layer and the porous layer, and the average crystal grain size within a specific range The present invention has been completed by finding a dental zirconia sintered body that can suppress the breaking and peeling of porcelain and has few breakage when applied to a crown or the like.
Furthermore, it has also been found that by controlling the SiO ₂ content of the dense layer and the porous layer within a specific range, it is possible to achieve lower temperature degradation than conventional dental zirconia sintered bodies.
That is, the above-mentioned problems are solved by the following inventions 1) to 5).
1) A dental zirconia sintered body containing at least ZrO ₂ and Y ₂ O ₃ and satisfying the following requirements (a) to (f):
(A) It has a two-layer structure of a dense layer and a porous layer.
(B) The porosity of the dense layer is 1.0% or less.
(C) The porosity of the porous layer is 5 to 20%.
(D) The average pore diameter of the porous layer is 5 to 40 μm.
(E) The Y ₂ O ₃ / ZrO ₂ molar ratio of the dense layer and the porous layer is 2.0 / 98.0 to 5.0 / 95.0.
(F) The average crystal grain size of the dense layer and the porous layer is 0.20 to 0.50 μm.
2) (g) The dental zirconia sintered body according to 1), further containing SiO ₂ , wherein the dense layer and the porous layer have an SiO ₂ content of 0.10 to 0.50% by weight.
3) (h) Dental zirconia according to 1) or 2), further comprising Al ₂ O ₃ , wherein the dense layer and the porous layer have an Al ₂ O ₃ content of 0.10 to 0.40% by weight. Sintered material.
4) A crown frame comprising the dental zirconia sintered body according to any one of 1) to 3).
5) A bridge frame comprising the dental zirconia sintered body according to any one of 1) to 3).

According to the present invention, compared to a conventional dental zirconia sintered body using Y ₂ O ₃ as a stabilizer, breakage or peeling when used in a frame and when the frame is bonded to porcelain, etc. There can be provided a dental zirconia sintered body that is low in deterioration and low temperature deterioration, and a crown frame and a bridge frame made of the sintered body.
The dental zirconia sintered body of the present invention has a conventional two-layer structure in which a portion to which porcelain and abutment teeth are bonded is a porous layer and a portion requiring high strength is a dense layer. Adhesiveness to porcelain and abutment teeth is improved compared to those consisting only of dense materials, and the breakage and peeling of the porcelain and the frame are reduced, and the reliability can be improved. In addition, conventional dental zirconia sintered crowns and bridges that are not covered by insurance have to be remanufactured when the porcelain breaks down, which is an economic burden on the patient. If a ligature is used, such a burden can be greatly reduced. Further, by suppressing the low temperature deterioration, the possibility of frame breakage such as zirconia joint head breakage reported in artificial hip joints can be reduced.
As described above, since the dental zirconia sintered body of the present invention has characteristics superior to those of the prior art, it can also be used for dental implant materials.

The figure which shows an example when the dental zirconia sintered compact of the 2 layer structure of this invention is used for the frame | frame for crowns of a molar part. The figure which shows an example when the conventional dental zirconia sintered compact is used for the crown frame of a molar part. The photograph which observed the boundary part of the dense layer and porous layer of the dental zirconia sintered compact of the 2 layer structure of this invention with the scanning electron microscope. The schematic diagram for demonstrating a mode that a shear test is performed by applying a load to the joining interface of the sample which built up the porcelain, and measuring the adhesive strength with a universal testing machine equipped with a shear test jig. The external appearance photograph after the fracture load test of the sample of Example 1 and the sample of Comparative Example 1. (A) Example 1, (B) Comparative Example 1 The schematic diagram of the three-point bending test of the accelerated deterioration test using a universal testing machine.

Hereinafter, each requirement that the dental zirconia sintered body of the present invention should satisfy will be described in detail.
(A) Point that has a two-layer structure consisting of a dense layer and a porous layer The conventional dental zirconia sintered body made of a dense single body has high strength, but has low adhesive strength with porcelain and is adhesive. Since it was inferior, there was a problem that the porcelain was broken or peeled off. On the other hand, although the porous simple substance is excellent in adhesiveness, it cannot be applied to a frame that requires high strength because it has lower strength and toughness than dense. Therefore, in the present invention, in order to solve these problems, a two-layer structure of a dense layer and a porous layer is adopted.
The porous layer in the present invention is provided in order to obtain high adhesive strength with porcelain. When there is a porous layer, the porcelain paste at the time of building up the porcelain penetrates into the pores of the porous layer, the anchor effect is increased, and the adhesiveness is improved. Similarly, when the resin cement for bonding penetrates into the pores of the porous layer, the adhesion to the abutment tooth is also improved. As a result, the zirconia sintered body of the present invention can achieve high adhesion without blasting.
On the other hand, in order to compensate for the strength reduction due to the porous layer, a high-strength dense layer is provided below the porous layer to ensure the strength of the entire zirconia frame and to prevent frame breakage.

FIG. 1 shows an example when such a dental zirconia sintered body having a two-layer structure of the present invention is used for a crown frame of a molar portion. FIG. 2 shows an example when a conventional dental zirconia sintered body made of a compact single body is used. As shown in FIG. 1, in the frame made of the sintered body of the two-layer structure of the present invention, the porous layer is located in the part where the porcelain material is built up and the part where the abutment tooth is bonded, and the lower part of the porous layer. It is a structure in which a dense layer is located.
The thicknesses of the dense layer and the porous layer are not particularly limited and can be appropriately adjusted according to the type and shape of the teeth, but the thickness ratio of the dense layer and the porous layer is preferably 10:90 to 90:10, 20: 80-80: 20 is more preferable.
In addition, about the dental zirconia sintered compact of 2 layers structure of this invention, the photograph which observed the boundary part of a dense layer and a porous layer with the scanning electron microscope is shown in FIG. As can be seen from this figure, since there is no interface between the dense layer and the porous layer, the bond strength between the layers is high, and the risk of the layer peeling off is extremely low.

(B) The porosity of the dense layer is 1.0% or less The porosity of the dense layer is 1.0% or less, preferably 0.8% or less. When the porosity exceeds 1.0%, the strength of the entire zirconia sintered body having a two-layer structure is lowered. The lower limit of the porosity is about 0.3% from the manufacturing limit.
The porosity as used in the field of this invention refers to what was computed by the following formula. The bulk density is measured by the Archimedes method.
Porosity (%) = [100− (sintered body bulk density / theoretical density)] × 100

(C) Point that the porosity of the porous layer is 5 to 20% The porosity of the porous layer is 5 to 20%, preferably 5 to 18%. If the porosity is less than 5%, the number of pores into which the porcelain paste when building up the porcelain and the resin cement for bonding when fixing the abutment tooth will decrease, and the adhesive strength with the porcelain and the abutment tooth will decrease. To do. On the other hand, when the porosity of the porous layer exceeds 20%, the strength of the entire zirconia sintered body is lowered. The method for measuring the porosity is the same as in the case of the dense layer.

(D) The point that the average pore diameter of the porous layer is 5 to 40 μm The average pore diameter of the porous layer is 5 to 40 μm, preferably 5 to 38 μm. When the average pore diameter is less than 5 μm, the porcelain paste and the adhesive resin cement do not penetrate into the pores, and the adhesive strength decreases. On the other hand, when the average pore diameter exceeds 40 μm, the strength of the entire zirconia sintered body decreases.
The average pore diameter is a mirror-finished zirconia sintered body, observed with a scanning electron microscope (measurement magnification: 200 to 500 times), randomly measured on the long diameter side of 100 pore diameters, and the average value D is Obtained and calculated by the following formula.
Average pore diameter (μm) = 1.5 × D (μm)

(E) The dense layer and the porous layer have a Y ₂ O ₃ / ZrO ₂ molar ratio of 2.0 / 98.0 to 5.0 / 95.0. Y _{2 of the} dense layer and the porous layer The molar ratio of O ₃ / ZrO ₂ is 2.0 / 98.0 to 5.0 / 95.0, preferably 2.2 / 97.8 to 4.8 / 95.2. In addition, HfO ₂ which may be contained in a small amount in the zirconia raw material may be mixed, and the total amount of zirconia and HfO ₂ is defined as the amount of ZrO ₂ .
When the molar ratio is less than 2.0 / 98.0, the amount of monoclinic zirconia in the sintered body increases, cracks are generated inside the sintered body, and when a load is applied, the cracks develop and the zirconia material The strength of the entire sintered body is reduced. On the other hand, when the molar ratio exceeds 5.0 / 95.0, cubic zirconia increases and the amount of tetragonal zirconia decreases, so that the amount of transformation from tetragonal zirconia to monoclinic zirconia is small. The effect of strengthening the stress-induced transformation is not obtained and the strength decreases. The monoclinic zirconia content is 5% by volume or less. The content is measured by X-ray diffraction in a scanning range of diffraction angles of 27 ° to 33 ° using a sample having a mirror surface of the sintered body, and obtained from the following formula.

The X-ray diffraction conditions were as follows: X-ray source: CuKα, output: 40 kV / 40 mA, diverging slit: 1/2 °, scattering slit: 1/2 °, light receiving slit: 0.15 mm, scan speed: 0.5 ° / Min, scanning axis: 2θ / θ, monochrome light receiving slit: 0.8 mm, counter: scintillation counter, monochromator: automatic monochromator.
In the present invention, by adjusting the Y ₂ O ₃ / ZrO ₂ molar ratio of the dense layer and the porous layer within the above range, a microstructure having no interface between the porous layer and the dense layer is obtained. be able to.

(F) The average crystal grain size of the dense layer and the porous layer is 0.20 to 0.50 μm. The average crystal grain size of the dense layer and the porous layer is 0.20 to 0.50 μm, preferably It is set to 0.22 to 0.48 μm. When the average crystal grain size is less than 0.20 μm, the interfacial area of crystal grains in the zirconia sintered body is increased, and stress corrosion due to water is likely to proceed, and the effect of suppressing low-temperature deterioration is reduced. In addition, the increase in the crystal grain interface area results in an increase in light scattering at the crystal interface, resulting in a loss of translucency, making it difficult to reproduce aesthetics close to natural teeth. On the other hand, when the average crystal grain size exceeds 0.50 μm, not only the strength of the entire zirconia sintered body is lowered, but also the thermal stability of tetragonal zirconia is lowered and the effect of suppressing low-temperature degradation is lowered. .

The average grain size is obtained by polishing the sintered body surface to a mirror surface, subjecting the obtained mirror surface to thermal etching or chemical etching, and then observing with a scanning electron microscope (measurement magnification: 1000 to 3000 times). The average value measured at 10 points by the method is used. The calculation formula is as follows.
D = 1.5 × L / n
D: Average crystal grain size (μm)
n: Number of crystal grains per length L
L: Measurement length (μm)
The average crystal grain size of the dense layer and the porous layer is preferably approximated in order to achieve stability of each characteristic, and the crystal grain size ratio between the dense layer and the porous layer (the density of the dense layer) The average crystal grain size / average crystal grain size of the porous layer is preferably 0.8 to 1.2, more preferably 0.9 to 1.1.

(G) a SiO ₂ content of dense layer and the porous layer, the present invention points to 0.10 to 0.50 wt%, by containing SiO ₂ traces the dense layer and the porous layer , SiO ₂ segregates at the zirconia grain boundaries, suppresses hydration reaction of Y ₂ O ₃ and / or ZrO ₂ with water near the grain boundaries, suppresses stress corrosion, and suppresses low-temperature deterioration. This is preferable. In the conventional zirconia sintered body, SiO ₂ is an impurity and is a harmful component that does not contribute to the improvement of properties, and its content has to be reduced as much as possible. On the other hand, SiO ₂ in the present invention is a component that controls the zirconia grain boundaries and contributes to the suppression of low-temperature deterioration as described above, and is completely different from the prior art. As described later in the manufacturing method, the present invention uses a fine particle powder composed of extremely fine SiO ₂ particles in the present invention, so that even if a larger amount of SiO ₂ is contained than the amount of impurities, the zirconia grain boundary This is because the zirconia crystal grain boundaries can be controlled.
The SiO ₂ content is preferably 0.10 to 0.50% by weight, and more preferably 0.15 to 0.45% by weight. If the content is less than 0.10% by weight, the effect of adding SiO ₂ cannot be obtained. If the content exceeds 0.50% by weight, it reacts with impurities and there are many glass phases at the triple point of the zirconia crystal grain boundary. As a result, stress corrosion progresses, and the effect of suppressing low temperature deterioration is reduced.

(H) The content of Al ₂ O ₃ in the dense layer and the porous layer is 0.10 to 0.40% by weight In the present invention, a specific amount of Al ₂ O _{3 is} added to the dense layer and the porous layer. It is preferable because Al ₂ O ₃ acts as a zirconia sintering aid and improves the sinterability. Thereby, the distortion which remains on the joint surface which arises by the shrinkage | contraction rate difference of a dense layer and a porous layer can be suppressed. In addition, since it has the effect of suppressing deformation after sintering, it is excellent in compatibility with abutment teeth, and for bridges that are more complicated in shape than a single crown such as a frame and require high accuracy of fitting. Can also be suitably used.
The content of Al ₂ O ₃ is preferably 0.10 to 0.40% by weight, more than 0.20% by weight, more preferably 0.40% by weight or less, more than 0.30% by weight and 0.40% by weight or less. Is more preferable. When the Al ₂ O ₃ content is less than 0.10% by weight, the effect of adding Al ₂ O ₃ cannot be obtained. When the Al ₂ O ₃ content exceeds 0.40% by weight, the amount of Al ₂ O ₃ present as particles in the zirconia sintered body increases, so that light scattering due to the refractive index difference between zirconia and Al ₂ O ₃ is increased. Increases the loss of translucency. Further, the bonding strength between the dense layer and the porous layer is lowered, and deformation after sintering is increased.

Although the dental zirconia sintered body of the present invention can be produced by various methods, an example is shown.
In this invention, the zirconia raw material powder refine | purified by the liquid phase method can be used. An aqueous solution of a zirconium compound (for example, zirconium oxychloride) and an aqueous solution of an yttrium compound (for example, yttrium chloride) are uniformly mixed so that the content of zirconia and Y ₂ O ₃ becomes a predetermined molar ratio, and hydrolyzed to hydrate. If a product is obtained, dehydrated and dried, and then calcined at 500 to 1000 ° C., a yttria-containing zirconia calcined powder with less impurities can be obtained. It is also possible to mix the zirconia material and _Y 2 _{O 3} raw material. The raw material powder of Y ₂ O ₃ can be used in the form of hydroxide, oxide or the like. The purity of each raw material powder used is 99.7% or more, and the average particle size is 1.0 μm or less. If the purity of each raw material powder is less than 99.7%, the amount of impurities contained in the raw material powder increases, and a large amount of glass phase is formed at the crystal grain boundaries of the zirconia sintered body, resulting in a decrease in strength. On the other hand, if the average particle diameter exceeds 1.0 μm, the predetermined pulverization / mixing / dispersion processing time becomes longer, and as a result, a large amount of impurities are mixed due to abrasion of the pulverizer, resulting in a decrease in strength. The lower limit of the average particle diameter is about 0.2 μm. Note that the impurity in the present invention is a component to be mixed from the stock material and manufacturing process described above, is primarily _{MgO, CaO, K 2 O,} TiO 2, Fe 2 O 3 and Na ₂ O or the like. The total amount of these impurities is 0.3% by weight or less, and the lower limit is about 0.05% by weight from the limit in the production process.

When SiO ₂ is added, it is added in the form of an oxide when the zirconia calcined powder is pulverized, mixed, or dispersed, or in the form of an organometallic compound such as ethyl silicate that can be left by thermal decomposition. It may be added. When added in the form of an organometallic compound, SiO ₂ can be uniformly dispersed in the zirconia powder. SiO ₂ uses fine particles having a primary particle diameter of 50 nm or less. When the primary particle diameter of the SiO ₂ fine particles exceeds 50 nm, SiO ₂ reacts with impurities without being segregated at the zirconia grain boundaries, and a lot of glass phases are formed at the triple points of the zirconia grain boundaries, and stress corrosion proceeds. The effect of suppressing low temperature deterioration is reduced. In addition, the lower limit of the primary particle diameter is about 5 nm.
In the case of adding Al ₂ O ₃ , Al ₂ O ₃ raw material powder can be used. The average particle diameter of the Al ₂ O ₃ raw material powder is 1.0 μm or less. When the average particle diameter of the Al ₂ O ₃ raw material powder exceeds 1.0 μm, the amount of Al ₂ O ₃ precipitated as particles in the zirconia crystal grain boundary increases, so the light due to the refractive index difference between zirconia and Al ₂ O ₃ Scattering increases, translucency is lost, and reproduction of aesthetics close to natural teeth becomes difficult. The lower limit of the average particle diameter is about 0.2 μm.

  The above raw material powder is blended so as to have a predetermined ratio, and is pulverized / mixed / dispersed in a wet manner using water or an organic solvent by a pulverization / mixing / dispersing device such as a pot mill, an attrition mill, or a medium stirring mill .

The average particle size of the slurry obtained by pulverization / mixing / dispersion treatment is 0.2 to 0.7 μm. If the average particle diameter is less than 0.2 μm, the moldability is lowered, and many fine internal defects are contained inside the sintered body, resulting in a decrease in strength. On the other hand, when it exceeds 0.7 μm, the sinterability is lowered, the porosity is increased, and the strength is lowered. The average particle size of the powder after pulverization / mixing / dispersion can be controlled by adjusting the slurry concentration and treatment time during pulverization / mixing / dispersion.
The average particle size of the raw material powder and the slurry in the present invention is an average value of the volume average particle size of the secondary particles in which the primary particles are aggregated, and for example, measured by a laser diffraction type particle size distribution measuring device or the like. Can do.

If necessary, a known molding aid (for example, acrylic resin, PVA (polyvinyl alcohol), etc.) is added to the slurry after pulverization, mixing, and dispersion, and dried by a known method such as a spray dryer to form a dense layer. Powder is prepared.
The molding powder for the porous layer can be obtained by adding a pore-forming agent to the slurry after pulverization / mixing / dispersion so as to achieve a desired porosity and then mixing with a known stirrer or the like. If necessary, a known molding aid (for example, acrylic resin, PVA, etc.) is added to the mixed slurry, and dried by a known method such as a spray dryer to produce a molding powder for the porous layer. In addition, a predetermined amount of pore-forming agent may be added to the compacting powder for the dense layer and mixed in a dry manner to produce the compacting powder for the porous layer.

The average particle diameter of the pore forming agent is 6 to 50 μm. When the average particle diameter is less than 6 μm, the average pore diameter of the porous layer is less than 5 μm, and the adhesive strength is lowered. On the other hand, if the average particle diameter exceeds 50 μm, the average pore diameter of the porous layer exceeds 40 μm, and the strength of the entire zirconia sintered body decreases. The material for the pore forming agent is preferably an organic substance that decomposes and scatters during the firing process. For example, polyethylene resin particles, polysaccharide particles, paraffin particles, and the like can be used.
The amount of the pore-forming agent added is 10 to 50% by volume. When the addition amount is less than 10% by volume, the porosity of the porous layer is less than 5%, and the adhesive strength is lowered. On the other hand, if the addition amount exceeds 50% by volume, the porosity of the porous layer exceeds 20%, so that the strength of the entire zirconia sintered body decreases.
When adding a pore-forming agent to the slurry, it should be added to the total amount of the blended ceramic powder, and when mixed dry, it should be added to the molding powder for the dense layer so as to achieve the desired porosity. Adjust as appropriate.

Next, the molding powders for the dense layer and the porous layer are filled in a mold or a rubber mold in order, and a known method such as mechanical press molding, rubber press molding, CIP molding (hydrostatic press molding) or the like is used. Mold. The thicknesses of the dense layer and the porous layer are controlled by the amount of each powder charged.
The molded body obtained as described above is fired at 1350 to 1500 ° C. in the air. When the firing temperature is less than 1350 ° C., the amount of monoclinic zirconia increases, the porosity of the dense layer increases, and the strength decreases. In addition, since the average crystal grain size of zirconia is reduced, the effect of suppressing low temperature deterioration is reduced. On the other hand, when the firing temperature exceeds 1500 ° C., the average crystal grain size of zirconia becomes large, so that the strength is lowered and the effect of suppressing low temperature deterioration is lowered.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples.

[Examples 1 to 12, Comparative Examples 1 to 13]
Examples 1 to 12 and Comparative Examples 1 to 2 and 4 to 13 are zirconia raw material powder having a purity of 99.9% and an average particle size of 0.9 μm, and Y ₂ O having a purity of 99.9% and an average particle size of 0.5 μm. ₃ raw material powders, SiO ₂ fine particle powders having a purity of 99.9% and a primary particle diameter of 30 nm, Al ₂ O ₃ raw material powders having a purity of 99.9% and an average particle diameter of 0.6 μm, Tables 1-1 and 1-2 Each slurry was obtained by blending so as to have the composition shown in each column of the Examples and Comparative Examples, and pulverizing, mixing, and dispersing with a medium stirring mill using water as a solvent. The average particle size of these slurries was 0.6 μm.
Comparative Example 3 is a zirconia raw material powder having a purity of 99.9% and an average particle diameter of 0.9 μm, a Y ₂ O ₃ raw material powder having a purity of 99.9% and an average particle diameter of 0.5 μm, and a primary particle diameter of 99.9% purity. 30 nm SiO ₂ fine particle powder, Al ₂ O ₃ raw material powder having a purity of 99.9% and an average particle diameter of 0.6 μm, so as to have the composition shown in the column of Comparative Example 3 in Table 1-1 and Table 1-2. In a medium stirring mill using water as a solvent, the treatment time was shortened to ½ or less than other examples and comparative examples, and pulverization, mixing, and dispersion treatment were performed to obtain a slurry. The average particle size of this slurry was 0.8 μm.
Next, 3% by weight of PVA as a binder was added to each of the above slurries, and dried with a spray dryer to prepare a molding powder for a dense layer.
The molding powder for the porous layer was prepared by adding a pore forming agent composed of polysaccharide particles (corn starch) to each of the slurries, mixing with a stirrer, and drying with a spray dryer.
Next, molding powders for the dense layer and the porous layer were put in the mold in order, and mechanical press molding was performed at a pressure of 1 tonf / cm ² to prepare each molded body having a two-layer structure. In addition, Comparative Example 1 was produced with only the molding powder for the dense layer, and Comparative Example 2 was produced with only the molding powder for the porous layer.
Next, each molded body was fired at a firing temperature of 1320 to 1550 ° C. in the atmosphere to produce a sintered body. The characteristics of the obtained sintered bodies are shown in Table 1-1 and Table 1-2.

[Test of adhesive strength between porous layer and porcelain]
As a test sample, a two-layer structure in which a dense layer and a porous layer processed to have a length of 12 mm, a width of 10 mm, and a thickness of 2.4 mm were each 1.2 mm was used. Comparative Example 1 was a single-phase structure having a dense layer of 2.4 mm, and Comparative Example 2 having a porous layer of 2.4 mm. A porcelain material (Celabian ZR, manufactured by Kuraray Noritake Dental Co., Ltd.) was built on the porous layer side so as to have a diameter of 5 mm and a height of 3 mm, and baked according to a firing schedule recommended by the porcelain manufacturer. In Comparative Example 1, blasting was performed before building up the porcelain.
Using a universal testing machine equipped with a shear test jig, a load was applied to the joint interface of the sample constructed of porcelain as shown in the schematic diagram of FIG. 4, and a shear test was performed at a crosshead speed of 1.0 mm / min. The adhesive strength was measured. The results are shown in Table 1-1 and Table 1-2. In addition, the adhesive strength in a table | surface is an average value at the time of 10 sample measurement.

[Crown fracture load test]
In order to evaluate the strength of the crown, an all-ceramic crown was produced as follows, and the breaking load when the crown was broken by applying a load from above was measured.
Measurement of the titanium abutment tooth, design of the zirconia frame, and cutting were performed by a dental CAM / CAD (manufactured by Panasonic Dental Co., Ltd.) to prepare a two-layer frame. Porcelain (Celabian ZR, manufactured by Kuraray Noritake Dental Co., Ltd.) was built and fired on this frame to produce an all-ceramic crown. In addition, the sample of the comparative example 1 performed the blasting process before building up porcelain. This crown was bonded to a titanium abutment tooth with an adhesive resin cement (SA routing, manufactured by Kuraray Medical Co., Ltd.). After the adhesive resin cement has hardened, an iron ball with a diameter of 7 mm is interposed in the center of the top surface of the crown, and a load is applied from the vertical direction at a crosshead speed of 0.5 mm / min using a universal testing machine. A compressive fracture test was performed and the fracture load was measured. The results are shown in Table 1-1 and Table 1-2. The breaking load in the table is an average value when 10 samples are measured.

As can be seen from the adhesive strength test results shown in Table 1-1 and Table 1-2, all of the examples have an adhesive strength of 30 MPa or more, and the adhesive strength does not cause breakage or detachment of the porcelain. It was.
On the other hand, since Comparative Examples 1, 4, and 6 had an adhesive strength of less than 30 MPa, they were adhesive strengths at which the porcelain was broken or detached.
In addition, as can be seen from the test results of the fracture load of the crown shown in Table 1-1 and Table 1-2, the fracture load of all the samples of the examples is as high as 2000 N or more, and it is suitable for all ceramic crowns and bridges that require strength. The strength was applicable. On the other hand, the samples of the comparative examples, except for the samples of Comparative Examples 4 and 6, had a breaking load of less than 2000 N, and were not applicable to portions requiring strength.

  About the sample of Example 1 and the sample of Comparative Example 1, the external appearance photograph of the sample after a destructive load test is shown in FIG. (A) is the sample of Example 1, and (B) is the sample of Comparative Example 1. As can be seen from FIG. 5, the sample of Example 1 was broken together with the zirconia frame, whereas the sample of Comparative Example 1 was completely different from the fractured form because the porcelain was peeled off. Since the sample of Comparative Example 1 has a low adhesive strength between the porcelain and the zirconia frame, the stress concentrates on the interface between the porcelain and the frame having a low adhesive strength, the porcelain peels off, and the fracture load is also low at 1850 N It was. On the other hand, since the sample of Example 1 had high adhesive strength, the porcelain did not peel off, and the breaking load showed a high value of 2720N. That is, the zirconia frame of the present invention had a high breaking load, and was less likely to break or peel off the porcelain or the frame than the sample of Comparative Example 1, and had high reliability.

The reason why the characteristics of the samples of Comparative Examples 1 to 13 are inferior to the examples is as follows.
Since the sample of Comparative Example 1 was composed of a dense layer alone, the adhesive strength with the porcelain was low, and the breaking load as a crown was low.
Since the sample of Comparative Example 2 was composed of a single porous layer, the fracture load as a crown was low.
In the sample of Comparative Example 3, since the porosity of the dense layer exceeded the specified range, the fracture load as a crown was low.
The sample of Comparative Example 4 had a low adhesive strength because the porosity of the porous layer was less than the specified range.
In the sample of Comparative Example 5, since the porosity of the porous layer exceeded the specified range, the fracture load as a crown was low.
The sample of Comparative Example 6 had a low adhesive strength because the average pore size of the porous layer was less than the specified range.
In the sample of Comparative Example 7, the average pore size of the porous layer exceeded the specified range, so that the fracture load as a crown was low.
In the sample of Comparative Example 8, since the Y ₂ O ₃ / ZrO ₂ molar ratio is less than the specified range, the amount of monoclinic zirconia increases, cracks are generated inside the sintered body, the strength decreases, and the crown The breaking load was low.
In the sample of Comparative Example 9, since the Y ₂ O ₃ / ZrO ₂ molar ratio exceeds the specified range, the amount of tetragonal zirconia is reduced, the effect of strengthening stress-induced transformation is not obtained, and the fracture load as a crown is low. It was a thing.
Since the sample of Comparative Example 10 had a high firing temperature and the average crystal grain size exceeded the specified range, the fracture load as a crown was low.
In the sample of Comparative Example 11, the firing temperature was low, the porosity of the dense layer was less than the specified range, and the average crystal grain size was less than the specified range, so the fracture load as a crown was low.
In the sample of Comparative Example 12, since the Y ₂ O ₃ / ZrO ₂ molar ratio of the dense layer exceeds the specified range, the amount of tetragonal zirconia is reduced, and the effect of strengthening the stress-induced transformation cannot be obtained. The breaking load was low.
In the sample of Comparative Example 13, since the Y ₂ O ₃ / ZrO ₂ molar ratio of the porous layer is less than the specified range, the amount of monoclinic zirconia increases, cracks are generated inside the sintered body, and the strength decreases. The fracture load as a crown was low.

The samples of Examples 1 to 12 and the samples of the two-layer structure of Comparative Examples 3 to 13 were subjected to the following accelerated deterioration test, and low temperature deterioration was evaluated by strength deterioration. In addition, the amount of deformation after sintering was evaluated.
[Accelerated deterioration test]
As a test sample, a two-layer structure in which the thickness of the dense layer and the porous layer was 0.6 mm each processed to 20 mm long × 5 mm wide × 1.2 mm thick was used.
Distilled water was put into a decomposition container equipped with a Teflon (registered trademark) container, and then each sample was added and sealed. This decomposition container was put into a constant temperature dryer, and an accelerated deterioration test was conducted for 50 hours at 200 ° C. and 2 atm. A three-point bending test according to ISO 6872, which is a dental ceramic standard, was performed on samples before and after the heating test, and the strength deterioration rate was evaluated. In the three-point bending test, a universal testing machine was used, each sample was set as shown in the schematic diagram of FIG. 6, and the crosshead speed was 1.0 mm / min and the distance between fulcrums was 13.5 mm. The results are shown in Table 2. In addition, the strength deterioration in the table is an average value when 10 samples are measured.

[Deformation evaluation test]
As a test sample, a disk-shaped molded body having a diameter of 60 mm × thickness of 2 mm and a dense layer and a porous layer each having a thickness of 1.0 mm was used. The molded body was fired at the firing temperature shown in the column of firing temperature in Table 1-1 and Table 1-2, and the sintered body was placed on a surface plate to measure the gap between the sintered body and the surface plate, This gap was defined as the amount of deformation. The results are shown in Table 2. In addition, the deformation amount in the table is an average value when five samples are measured.
From the results shown in Table 2, the sample satisfying the specified range of claim 2 has a small strength deterioration of 20% or less, and the effect of suppressing the low temperature deterioration is improved. On the other hand, the samples of Examples 9 to 11 and Comparative Examples 3 to 10 that do not satisfy the specified range of claim 2 had a strength deterioration exceeding 30%, and the effect of suppressing the low temperature deterioration was lowered. Further, the sample satisfying the specified range of claim 3 has a small deformation amount of 35 μm or less, and the effect of suppressing deformation was improved. On the other hand, in Examples 11 to 12 and Comparative Examples 8 to 13 that do not satisfy the specified range of claim 3, the deformation amount exceeds 55 μm, and the effect of suppressing the deformation is reduced.

The reason why the effect of suppressing the low-temperature deterioration of each sample is reduced and the reason why the effect of suppressing deformation is reduced are as follows.
Since the sample of Example 9 had a small SiO ₂ content in the dense layer and the porous layer, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Example 10 had a high SiO ₂ content in the dense layer and the porous layer, the strength was greatly deteriorated and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Example 11 had a small SiO ₂ content in the dense layer and the porous layer, the strength deterioration was large, and the effect of suppressing low temperature deterioration was reduced. Moreover, since the Al ₂ O ₃ content of the dense layer and the porous layer is small, the effect of suppressing deformation is reduced.
Since the sample of Example 12 had a high Al ₂ O ₃ content in the dense layer and the porous layer, the effect of suppressing deformation was reduced.
Since the sample of Comparative Example 3 contained a large amount of SiO ₂ in the dense layer and the porous layer, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Comparative Example 4 had a small SiO ₂ content in the dense layer and the porous layer, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Comparative Example 5 had a large SiO ₂ content in the porous layer, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Comparative Example 6 had a small SiO ₂ content in the dense layer, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Comparative Example 7 had a small average crystal grain size, the strength deterioration was large, and the effect of suppressing low temperature deterioration was reduced.
Since the sample of Comparative Example 8 had a large average crystal grain size, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced. Moreover, since the firing temperature was high, the effect of suppressing deformation was reduced.
Since the sample of Comparative Example 9 had a small SiO ₂ content in the dense layer and the porous layer, the strength deterioration was large and the effect of suppressing low temperature deterioration was reduced. Moreover, since the Al ₂ O ₃ content of the dense layer and the porous layer is small, the effect of suppressing deformation is reduced.
Since the sample of Comparative Example 10 had a small SiO ₂ content in the porous layer, the strength was greatly deteriorated, and the effect of suppressing low temperature deterioration was reduced. Also, because many Al ₂ O ₃ content in the dense layer, the effect of suppressing deformation was reduced.
Since the sample of Comparative Example 11 had a small Al ₂ O ₃ content in the dense layer and the porous layer, the effect of suppressing deformation was reduced.
Since the sample of Comparative Example 12 had a small Al ₂ O ₃ content in the dense layer, the effect of suppressing deformation was reduced.
Since the sample of Comparative Example 13 had a high Al ₂ O ₃ content in the porous layer, the effect of suppressing deformation was reduced.

Claims (5)

A dental zirconia sintered body containing at least ZrO ₂ and Y ₂ O ₃ and satisfying the following requirements (a) to (f):
(A) It has a two-layer structure of a dense layer and a porous layer.
(B) The porosity of the dense layer is 1.0% or less.
(C) The porosity of the porous layer is 5 to 20%.
(D) The average pore diameter of the porous layer is 5 to 40 μm.
(E) The Y ₂ O ₃ / ZrO ₂ molar ratio of the dense layer and the porous layer is 2.0 / 98.0 to 5.0 / 95.0.
(F) The average crystal grain size of the dense layer and the porous layer is 0.20 to 0.50 μm. (G) further contains SiO _2, SiO ₂ content of dense layer and the porous layer, dental zirconia sintered body according to claim 1, wherein 0.10 to 0.50 wt%. (H) Further containing Al ₂ O ₃ , and the dense layer and the porous layer have an Al ₂ O ₃ content of 0.10 to 0.40% by weight, The dental zirconia-based firing according to claim 1 or 2 Union.   A crown frame comprising the dental zirconia sintered body according to claim 1.   A bridge frame comprising the dental zirconia sintered body according to claim 1.