JP7822005B2 - Dental prosthesis and manufacturing method thereof, dental prosthesis manufacturing kit, and ceramic article manufacturing method - Google Patents

Description

The present invention relates to dental prostheses and their manufacturing methods, dental prosthesis manufacturing kits, and ceramic article manufacturing methods.

In particular, in recent years, advances in ICT have led to the widespread adoption of computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies in the dental field. For example, in the production of dental crown prostheses, CAD/CAM systems are increasingly being used. These systems use intraoral images to machine dental blanks made of non-metallic materials. Here, a dental blank refers to a workpiece (also known as a mill blank) that can be attached to a cutting machine in a CAD/CAM system. It typically includes a workpiece to be machined and a holder that allows it to be attached to the cutting machine. Commonly known workpieces include solid blocks shaped like rectangular parallelepipeds or cylinders, or solid disks shaped like plates or plates.

Zirconia-based ceramic materials are often used as non-metallic materials because they offer excellent strength and toughness, allowing for the creation of aesthetically pleasing dental prostheses. Because fully sintered zirconia-based ceramic materials are difficult to machine due to their strength, when using a CAD/CAM system to create dental prostheses (hereinafter also referred to as "zirconia prostheses") made from zirconia-based ceramics, a zirconia-based ceramic pre-sintered body pre-sintered at a relatively low sintering temperature is generally used as the cutting portion of the dental zirconia mill blank (also simply referred to as "zirconia mill blank"). Then, based on CAD that takes into account shrinkage that occurs during high-temperature sintering, the material is machined to a shape corresponding to the final shape of the prosthesis obtained by CAM, and then sintered to create a densified, high-strength zirconia prosthesis.

Regarding zirconia-based ceramics, pure zirconia (zirconium oxide) undergoes a phase transition accompanied by a volume change depending on the temperature. Therefore, stress due to the volume change during the cooling process after sintering can cause cracks and lead to a decrease in strength. To prevent this phase transition, stabilizers such as yttrium oxide, calcium oxide, and magnesium oxide have been added to stabilize zirconia or partially stabilized zirconia, which can exist as a tetragonal or mixed crystal system of tetragonal and cubic crystals stable at high temperatures without transitioning to a monoclinic crystal stable at low temperatures even upon cooling. Such stabilized zirconia or partially stabilized zirconia is also used as the zirconia raw material powder used in zirconia mill blanks, and alumina (an additive) is commonly added to further increase strength. For example, Patent Document 1 describes a raw material powder that can be sintered under atmospheric pressure to give a zirconia sintered body that combines translucency and strength, particularly suitable for use as a front tooth denture, as follows: "A zirconia powder characterized by containing more than 4.0 mol % and not more than 6.5 mol % of yttria and less than 0.1 wt % of alumina, and having a BET specific surface area of 8 to 15 m ² /g."

Zirconia prostheses, including those made from stabilized zirconia or partially stabilized zirconia, are typically treated with a pretreatment agent containing a silane coupling agent and then bonded using a dental adhesive, such as dental resin cement, that contains components that react with the silane coupling agent (e.g., silica components or polymerizable monomers) or components with high affinity (organic components). However, because the amount of Zr-O-Si bonds formed by the silane coupling agent, which contribute to improving adhesive strength, is low, sandblasting (to increase the number of surface Zr-OH groups) is required to achieve practical adhesive strength (see Non-Patent Document 1).

In addition, a method has been proposed in which, instead of using a pretreatment agent containing a silane coupling agent, the dental surface is treated with a dental adhesive composition containing a phosphonic acid group-containing (meth)acrylate monomer, such as an acetone solution of 6-methacryloxyhexyl-phosphonoacetate (see Patent Document 2).

JP 2015-143178 A Japanese Patent Application Laid-Open No. 2006-045179 Japanese Patent Application Publication No. 02-21858

Kimura et al., "Development of a new primer and a new surface treatment method for zirconia dental adhesion," Journal of the Adhesion Society of Japan, 2019, Vol. 55, No. 3, pp. 10-17

The combination of a pretreatment agent containing a silane coupling agent and a dental adhesive, such as dental resin cement, which contains components that react with the silane coupling agent (e.g., silica components or polymerizable monomers) or components with high affinity (organic components) is an adhesive system commonly used in the dental field, but there is currently no known technology for easily applying this system to effectively bond zirconia prostheses.

As described in Non-Patent Document 1, applying the above system to zirconia prostheses requires prior sandblasting, and not only is it affected by this, but it has also been reported that while the tensile bond strength of the hardened hybrid resin composition in the sandblasted system shown in Non-Patent Document 1 after immersion in 37°C water for 24 hours was 18.8 MPa, leaving sandblasted zirconia in the air for several hours significantly reduces the bond strength, meaning that it cannot be said to have sufficient adhesive properties.

Furthermore, the method of using a dental adhesive composition described in Patent Document 2 may be effective for certain adherends such as zirconia ceramics, but is not only inconvenient because it cannot be used with other adherend systems, but also requires that a specific light-curing composition be applied to the margin with the resin cement and then light-cured when used.

The present invention aims to provide a technology that can be easily applied to an adhesive system consisting of a combination of a pretreatment agent containing a silane coupling agent and a dental adhesive such as a dental resin cement, without the need for sandblasting, to effectively bond zirconia prostheses and, in turn, articles made of ceramics made from inorganic oxides that are substantially free of silicon dioxide components.

The present invention solves the above-mentioned problems, and a first aspect of the present invention is a dental prosthesis having a main body comprising a " stabilized zirconia sintered body or partially stabilized zirconia sintered body" which contains zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, cerium oxide, and erbium oxide , and is substantially free of silicon dioxide; and a "composite" in which the "stabilized zirconia sintered body or partially stabilized zirconia sintered body" is combined with "silicon dioxide" ,
the surface of the body has an adhesive surface to be adhered to an adherend and an exposed surface exposed to the surface;
When the range of a depth from the surface to 5 to 300 μm is defined as the surface layer portion, in the surface layer portion of the adhesive surface, the “ silicon dioxide ” present in the surface layer portion and the “stabilized zirconia sintered body or partially stabilized zirconia sintered body” are combined to form the “composite” ,
The dental prosthesis (hereinafter also referred to as "the dental prosthesis of the present invention") is characterized in that the portion of the main body other than the surface layer portion is made of the "stabilized zirconia sintered body or partially stabilized zirconia sintered body ."

A second aspect of the present invention is a method for producing the dental prosthesis of the present invention, comprising the steps of:
a cutting process step of cutting a zirconia dental mill blank having a cuttable portion made of a microporous calcined body of stabilized zirconia or a microporous calcined body of partially stabilized zirconia, the microporous calcined body containing zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, and substantially no silicon dioxide component, using a CAD/CAM system to obtain a semi-finished product made of the microporous calcined body, the semi-finished product having a shape corresponding to the shape of a desired dental prosthesis;
a treatment step of applying a treatment liquid consisting of an aqueous solution of alkali metal silicate to the surface of the semi-finished product corresponding to the bonding surface and allowing the treatment liquid to penetrate the surface, thereby retaining the alkali metal silicate in the surface layer of the surface; and a sintering step of sintering the semi-finished product that has been subjected to the treatment step at a temperature of 1200 to 1800°C.
a method for producing the dental prosthesis, comprising:

In the manufacturing method of the above embodiment (hereinafter also referred to as the "manufacturing method for a dental prosthesis of the present invention"), it is preferable that the microporous calcined body constituting the cutting portion of the zirconia dental mill blank is a microporous calcined body having a relative density of 45 to 65% and pores open to the outside, the treatment liquid is a sodium silicate aqueous solution having a sodium silicate concentration of 15 to 70 mass%, and in the treatment step, sodium silicate is retained in the surface layer portion of the surface to a depth of 5 to 300 μm.

A third aspect of the present invention is a dental prosthesis manufacturing kit for manufacturing the dental prosthesis of the present invention by the dental prosthesis manufacturing method of the present invention, the dental prosthesis manufacturing kit comprising: a zirconia dental mill blank having a cutting portion made of a microporous calcined body of stabilized zirconia or a microporous calcined body of partially stabilized zirconia, which contains zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, and is substantially free of silicon dioxide; and a treatment liquid made of an aqueous sodium silicate solution having a sodium silicate concentration of 15 to 70 mass % (hereinafter also referred to as the "kit of the present invention").

Although the dental prosthesis of the present invention is a zirconia prosthesis, it maintains the same level of aesthetics, mechanical strength, and other physical properties as conventional zirconia prostheses. By simply applying an adhesive system consisting of a combination of a pretreatment agent containing a silane coupling agent and a dental adhesive such as a dental resin cement, the prosthesis can be bonded to adherends such as teeth, metals, and hybrid resins with an adhesive strength sufficient to withstand use in the oral environment (high temperature, high humidity). Furthermore, sandblasting can be omitted during bonding, and even if sandblasting is performed, the bonding is less affected by the conditions.

Furthermore, according to the method for manufacturing a dental prosthesis of the present invention, it is possible to efficiently manufacture a dental prosthesis of the present invention having the excellent characteristics described above, for example, by using the kit of the present invention.

While the present invention is not bound by any theory, the reason why the dental prosthesis of the present invention achieves the above-mentioned excellent effects is believed to be as follows. Specifically, the adhesive system provides good adhesive strength because the surface layer of the adhesive surface is composited with silicon dioxide, increasing the number of surface silanol groups (Si-OH groups) on the adhesive surface. When the adhesive system is applied, these increase in number with the silane coupling agent, forming chemical bonds with components of dental adhesives such as dental resin cement via Si-O-Si bonds and improving affinity. In this case, the silicon dioxide in the surface layer penetrates into the main body in a complex manner with a predetermined thickness, firmly integrating with the main body through an anchoring effect, ensuring that adhesive strength does not decrease even with long-term use in the oral cavity. Furthermore, because the composite layer is not exposed on the surface after adhesion and is limited to the very surface, it does not adversely affect aesthetics or overall mechanical strength.

This type of composite formation in a limited area, such as the surface layer of a specific surface region, is made possible by employing the dental prosthesis manufacturing method of the present invention. For example, if a typical coating method, such as that described in Patent Document 3, is used, in which a silicon dioxide precursor is applied to the surface of a zirconia (present) sintered body and then heat-treated at a relatively low temperature, the strong integration achieved by the anchor effect and chemical bonding described above does not occur, and there is always a concern about a decrease in adhesive strength due to peeling, etc.

The present invention will be described in detail below. In this specification, unless otherwise specified, the expression "x to y" using numerical values x and y means "greater than or equal to x and less than or equal to y." In such expressions, if a unit is assigned only to the numerical value y, the unit also applies to the numerical value x.

1. Dental Prosthesis of the Present Invention A dental prosthesis is an artificial object used to replace lost or missing teeth, and examples thereof include inlays, onlays, crowns, bridges, implant superstructures, and denture bases. During prosthetic treatment, these are used by adhering them to teeth or adherends such as metals and organic-inorganic composite materials using a dental adhesive such as dental resin cement. Therefore, the main body of the dental prosthesis has an adhesive surface that is adhered to the adherend and an exposed surface that is exposed to the surface.

The main body of the dental prosthesis of the present invention is essentially a zirconia prosthesis made of a stabilized zirconia sintered body or a partially stabilized zirconia sintered body. Here, the stabilized zirconia sintered body or partially stabilized zirconia sintered body is a sintered body of crystalline zirconium oxide powder (raw material powder) containing a stabilizer, and the raw material powder preferably further contains aluminum oxide as an additive. However, silicon dioxide components such as silica are not typically blended, and in the present invention, the stabilized zirconia sintered body or partially stabilized zirconia sintered body that constitutes the adhesive surface of the main body of the dental prosthesis, excluding the surface layer, is substantially free of silicon dioxide components. "Substantially free of silicon dioxide" means that the silicon dioxide component is not contained, or, if it is contained, the silicon dioxide component content is 0.030% by mass or less, preferably 0.025% by mass or less, based on the total mass of the main body.

Explaining the raw material powder in more detail, stabilizers that can be used include those conventionally used as stabilizers for zirconium oxide, such as yttrium oxide, calcium oxide, magnesium oxide, cerium oxide, and erbium oxide, without limitation. However, yttrium oxide is particularly preferred, as it becomes stabilized zirconia or partially stabilized zirconia after sintering. Therefore, the yttrium oxide content is preferably 5 to 14 parts by mass per 100 parts by mass of zirconium oxide (0.027 to 0.076 mol per 1 mol of zirconium oxide).

Aluminum oxide functions as a sintering aid for zirconium oxide, and its content is preferably 0.005 to 0.3 parts by weight per 100 parts by weight of zirconium oxide. If the aluminum oxide content is less than 0.005 parts by weight, it may not be effective as a sintering aid, and if the content is more than 0.3 parts by weight, the difference in refractive index with zirconium oxide will result in a decrease in translucency, making it unsuitable for dental prostheses.

The raw material powder is not particularly limited as long as it is easy to handle as a powder, but it is preferable that the average crystallite size be 0.001 μm to 50 μm, and particularly 0.003 μm to 20 μm, because this makes it difficult for phase transformation of the oxide crystals to occur and prevents excessive grain growth during sintering. Examples of such raw material powders that can be used include Zpex Smile (manufactured by Tosoh Corporation), Zpex4 (manufactured by Tosoh Corporation), and Zpex (manufactured by Tosoh Corporation).

The raw material powder may contain a pigment. There are no particular restrictions on the pigment, and any known pigment can be used in any combination. For example, erbium oxide, cobalt oxide, iron oxide, etc. can be used. Furthermore, even if the pigment is white before sintering, it can also be colored after sintering and used as a pigment.

The stabilized zirconia sintered body or partially stabilized zirconia sintered body that constitutes the main body of the dental prosthesis of the present invention means that pore shrinkage and grain growth occur during the sintering process, resulting in a dense structure in which alumina particles are dispersed within a polycrystalline structure in which tetragonal zirconia particles and cubic zirconia particles, each containing a stabilizer dissolved at different concentrations, are randomly dispersed and adjacent to each other.

The dental prosthesis of the present invention is characterized in that the surface layer of the adhesive surface of the main body, specifically the surface layer extending from the surface to a depth of 5 to 300 μm, preferably 10 to 200 μm, is selectively composited with silicon dioxide. This composite in the surface layer can be confirmed by analysis using X-ray diffraction (hereinafter sometimes abbreviated as XRD) or electron probe microanalyzer (hereinafter sometimes abbreviated as EPMA). These analyses reveal the formation of an amorphous silicon dioxide phase that at least partially covers the surface of the main body, with a portion of this (on the main body side) immobilized within complexly shaped pores, and no alkali metal oxides are detected in the surface layer. This composite structure can also be understood from the method of formation (specifically, the treatment and sintering processes in the dental prosthesis of the present invention). In other words, during the sintering process, alkali metals with melting points lower than the sintering temperature disappear through sublimation or other processes, forming amorphous silicon dioxide within the pores and on the surface. It's possible that some of the silicon dioxide (partially near the interface) may have formed a complex oxide with components of the (partially) stabilized zirconia. Cooling after sintering then forms a silicon dioxide phase that at least partially covers the surface of the body, with some of that silicon dioxide (on the body side) immobilized within the complex-shaped pores. In this way, the silicon dioxide (containing Si-OH groups) exposed on the surface of the body is firmly integrated with the body through an anchoring effect (and, in some cases, chemical bonding through the complex oxide formation). Therefore, the silane coupling treatment effectively acts on the adhesive surface, resulting in the aforementioned effects.

2. Regarding the manufacturing method of the dental prosthesis of the present invention, the manufacturing method of the dental prosthesis of the present invention is a method for manufacturing the dental prosthesis of the present invention, and is characterized by including the cutting process, the treatment process, and the sintering process. Each process will be described below.

2-1. Regarding the Cutting Process In the cutting process, a zirconia dental mill blank has a portion to be cut that is made of a microporous calcined body of stabilized zirconia or a microporous calcined body of partially stabilized zirconia, which contains zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, and is substantially free of silicon dioxide, and the portion to be cut is cut using a CAD/CAM system to obtain a semi-finished product made of the microporous calcined body, which has a shape corresponding to the shape of the intended dental prosthesis.

As described below, the above-mentioned zirconia dental mill blank is also a commonly available zirconia dental mill blank, and therefore the cutting process in the dental prosthesis manufacturing method of the present invention is no different from the process used in the past to manufacture zirconia prostheses using a general zirconia mill blank, in which the zirconia mill blank is cut using a CAD/CAM system to obtain a semi-finished product (machined body) corresponding to the shape of the zirconia prosthesis (before sintering). Therefore, this section will first explain the raw materials and manufacturing methods for commonly available zirconia dental mill blanks, and then explain the cutting process.

(1) Regarding zirconia dental mill blanks: A zirconia dental mill blank refers to a mill blank having a portion to be machined and a holder for attaching the portion to a machine, wherein the portion to be machined is a microporous calcined body of stabilized zirconia or a microporous calcined body of partially stabilized zirconia that contains zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, and is substantially free of silicon dioxide. The portion to be machined is generally a (solid) block formed into a rectangular or cylindrical shape, or a (solid) disk formed into a plate or plate-like shape.

The term "calcined body" (also referred to as "pre-sintered body") refers to the state before the material is sintered during the sintering process. During the sintering process, necks are formed where the constituent particles of the raw material powder partially join together, and as these necks grow, open pores (i.e., pores open to the outside) originating from the voids between the particles are formed. In the present invention, a microporous calcined body refers to a body in which many of these open pores remain and have not disappeared.

The microporous calcined body used in the present invention is preferably a microporous calcined body with a relative density of 45 to 65% and pores that are open to the outside. The cutting portion of commonly available zirconia dental mill blanks consists of a microporous calcined body of stabilized zirconia or partially stabilized zirconia with a relative density of 45 to 65% and pores that are open to the outside. Therefore, in the present invention, general zirconia dental mill blanks that have such a cutting portion can be used without any particular restrictions.

Note that relative density is the ratio of actual density to theoretical density (calculated as relative density = (actual density/theoretical density) x 100 (%)), and can be adjusted by controlling the pre-sintering temperature and pre-sintering time. Furthermore, if pre-sintering is performed to achieve this relative density, the pre-sintered body will typically be microporous, with pores open to the outside. The average pore diameter of these pores is typically in the range of 50 to 200 nm. Here, average particle diameter refers to the median diameter determined from the pore volume distribution in the pore diameter range of 5 nm to 250 μm obtained by mercury intrusion porosimetry, i.e., measurement using a mercury porosimeter.

For example, the theoretical density of zirconium oxide varies depending on the type and content of stabilizer and the content of alumina additive, and tends to decrease slightly from 6.10 g/ ^cm3 , the theoretical density of tetragonal zirconia, as these contents increase. For example, Table 1 of Patent Document 1 shows the theoretical density of zirconia containing yttria and alumina, which is reproduced below for reference. The actual density can be determined by density measurement such as the Archimedes method.

(2) Manufacturing Method of Zirconia Dental Mill Blanks Zirconia dental mill blanks are generally manufactured by molding the raw material powder into a predetermined shape and then calcining it. The raw material powder may optionally contain binders, fine fillers, light-shielding agents, fluorescent agents, etc., and then calcining the resulting microporous calcined body to form the cutting portion. When a binder component is added, for example, an acrylic binder, an olefin binder, or wax may be used.

The raw material composition containing such raw material powders is molded by obtaining a compression-molded body or green body of a predetermined shape using methods such as press molding, extrusion molding, injection molding, and casting. Multi-stage molding may also be used. For example, the raw material powder may be uniaxially pressed and then further subjected to CIP (Cold Isostatic Pressing). Furthermore, multiple types of mixed powders may be stacked and molded during the molding process. The shape of the compression-molded body or green body may be determined appropriately depending on the shape of the desired mill blank, but typically it is disk-shaped (disk type) or rectangular or approximately rectangular parallelepiped-shaped (block type).

The molded body thus obtained can be calcined (preliminary sintered) to produce a microporous calcined body. For calcination (preliminary sintering), the compression molded body or green body is degreased as necessary and then calcined (fired) at a temperature lower than that for main sintering. Here, degreasing refers to a process in which moisture, solvents, binders, etc. contained in the compression molded body or green body are removed by volatilization or decomposition. Calcination refers to a process in which heating causes molecular and atomic diffusion (adhesion and fusion) on the surface of metal oxide powder particles, transforming them into a polycrystalline body and improving the strength of the resulting microporous preliminarily sintered body to a level that makes it easy to handle and process. The preliminarily sintering temperature is typically between 600°C and 1200°C, and preferably between 800°C and 1000°C.

Conventionally known methods can be used for the degreasing and/or calcination treatment without any particular limitations, and the treatment may be carried out continuously or in multiple stages. Furthermore, to efficiently remove organic matter, it is preferable to carry out the treatment in an oxygen-containing air atmosphere. The degreasing and/or calcination treatment can also be carried out continuously by a method using the same equipment as the preceding molding process, such as the SPS (Spark Plasma Sintering) method or the HP (Hot Press) method.

(3) Regarding the Cutting Method In the cutting process, the portion to be cut of the zirconia dental mill blank is cut using a CAD/CAM system to obtain a semi-finished product made of the microporous calcined body having a shape corresponding to the shape of the intended dental prosthesis.

A CAD/CAM system is a system that uses computer-aided design (CAD) to design the desired three-dimensional shape data and then performs computer-aided manufacturing (CAM). As mentioned above, CAD is performed taking into account shrinkage that occurs when sintering at high temperatures. The shape of the semi-finished product is similar to the main body, but is larger by the amount of the shrinkage (rate), so it has a surface that corresponds to the adhesive surface and a surface that corresponds to the exposed surface.

During cutting, the zirconia dental mill blank is machined while still joined via a support rod. After cutting using a CAD/CAM system, the support rod can be removed and the shape can be further modified using a dental laboratory engine or the surface can be polished. If necessary, the color tone can also be adjusted using a penetrating colorant or clarifying liquid.

2-2. Treatment Step In the treatment step, a treatment liquid consisting of an aqueous solution or suspension of an alkali metal silicate is impregnated into the surface of the semi-finished product that corresponds to the adhesive surface, thereby retaining the alkali metal silicate in the surface layer of the surface.

As the alkali metal silicate, alkali metal silicates having a SiO ₂ /M ₂ O (M represents an alkali metal element) molar ratio of 1.0 to 5.0 can be used alone or in combination. Sodium silicate and/or potassium silicate are preferred from the viewpoints of water solubility and availability, and sodium silicate is particularly preferred from the viewpoints of sintering temperature and melting point. The SiO ₂ /M ₂ O molar ratio is preferably 2.0 to 4.0.

The treatment liquid may be a suspension or colloidal dispersion of fine particles of alkali metal silicate in a dispersing medium, preferably water, but from the perspective of penetration into the micropores of the semi-finished product, an aqueous solution is preferred. When the treatment liquid is an aqueous solution, the concentration of the alkali metal silicate is preferably 15 to 70% by mass, particularly 25 to 60% by mass, from the perspective of penetration of the treatment liquid. When the treatment liquid is an aqueous sodium silicate solution, various concentrations of water glass are commercially available, so a solution of the appropriate concentration can be used as is, or a higher concentration can be diluted and used.

When applying the treatment liquid to the adhesive surface of the main body, any common application method, such as application using an application brush or paintbrush, or spraying, can be used without particular limitation. The amount of application is preferably 0.001 to ^0.07 g/ ^cm2 , particularly 0.003 to 0.06 g/ ^cm2 , and most preferably 0.005 to 0.05 g/ ^cm2 , of alkali metal silicate per 1 cm2 of application surface, calculated as silicon dioxide. By applying such an amount, the treatment liquid can penetrate to a depth of 5 to 300 μm, preferably 10 to 200 μm, from the surface.

After the processing step is completed and before proceeding to the sintering step, it is preferable to carry out a drying process to remove the dispersion medium and solvent. The drying process can also be carried out by leaving the material at room temperature under atmospheric pressure, for example.

3-3. Regarding the Sintering Step The sintering process in the method for producing a dental prosthesis of the present invention is not particularly different from the conventional process of sintering a semi-finished product (machined body) when producing a zirconia prosthesis using a general zirconia mill blank, except that the semi-finished product (machined body) to be sintered has undergone the above-mentioned processing step, and the semi-finished product is sintered at a temperature of 1200 to 1800° C. If the sintering temperature is less than 1200° C., the structure may not be sufficiently densified, and if the sintering temperature is more than 1800° C., the silicon dioxide may disappear.
The sintering temperature is preferably 1250 to 1750°C, more preferably 1300 to 1700°C, because this is expected to result in densification of the zirconia structure and efficient compounding of zirconia and silicon dioxide. Sintering is typically carried out in the atmosphere using a furnace such as a dental firing furnace. The sintering time varies depending on the sintering temperature, but is typically about 10 minutes to 6 hours, preferably about 30 minutes to 4 hours. For example, a good sintered body can be obtained by sintering for 2 hours at 1450°C. In this way, the dental prosthesis of the present invention, which has the excellent adhesiveness described above, can be obtained.

4. Regarding the Kit of the Present Invention When manufacturing the dental prosthesis of the present invention by the manufacturing method of the dental prosthesis of the present invention, it is preferable to use a kit including the zirconia dental mill blank and the treatment solution, in order to smoothly carry out the cutting process and the treatment process.

5. Method of Using (Adhering) the Dental Prosthesis of the Present Invention As described above, the dental prosthesis of the present invention is used by adhering it to an adherend, such as a tooth, that has adhesive properties with the dental adhesive, using an adhesive system comprising a combination of a pretreatment agent containing a silane coupling agent and a dental adhesive, such as dental resin cement, that contains a component that reacts with or has high affinity for the silane coupling agent.

The pretreatment agent in the adhesive system preferably contains a silane coupling agent with a polymerizable group, from the perspective of adhesion to dental resin cement, a general-purpose dental adhesive, and ease of handling. Particularly preferred silane coupling agents include gamma-methacryloxypropyltrimethoxysilane, gamma-methacryloxypropyltri(trimethylsiloxy)silane, omega-methacryloxydecyltrimethoxysilane, and gamma-methacryloxypropylpentamethyldisiloxane.

In addition, dental adhesives such as dental resin cements are preferably made from dental adhesive compositions containing 100 parts by mass of a polymerizable monomer such as bisphenol A dimethacrylate or triethylene glycol dimethacrylate, 100 to 400 parts by mass of an inorganic filler such as silica and/or a silicon-based composite oxide, and 0.001 to 10 parts by mass of a polymerization initiator such as a chemical polymerization initiator formed by a combination of benzoyl peroxide and an amine compound and/or a photopolymerization initiator formed by a combination of camphorquinone and an amine compound.

6. Regarding the manufacturing method of a ceramic article (hereinafter also referred to as "the article of the present invention") in which a portion of the surface layer region of a body made of ceramics composed of inorganic oxides substantially free of silicon dioxide is composited with silicon dioxide: The adhesiveness problems of conventional zirconia prostheses are not limited to zirconia prostheses, but are also seen in ceramics made of inorganic oxides substantially free of silicon dioxide. It is believed that the adhesiveness of these ceramics can be improved by composite bonding of the adhesive surface layer, as obtained by the manufacturing method of a dental prosthesis of the present invention. The method for manufacturing an article of the present invention has been conceived based on this idea, and is a method for manufacturing a ceramic article in which a portion of the surface region of a main body made of a ceramic composed of an inorganic oxide substantially free of a silicon dioxide component is composited with silicon dioxide, and is characterized by comprising: a semi-finished product manufacturing step of processing, as necessary, a microporous molded body made of a molded body of a raw material composition containing an inorganic powder that is a raw material for the ceramic that constitutes the main body, or a heat-treated microporous molded body obtained by heat-treating the microporous molded body, to obtain a semi-finished product having a shape corresponding to the main body; a treatment step of infiltrating a surface layer portion of a predetermined region on the surface of the semi-finished product with a treatment liquid consisting of an aqueous solution of an alkali metal silicate; and a sintering step of sintering the semi-finished product that has undergone the treatment step.

Here, the raw material composition containing the inorganic powder used as the ceramic raw material may be an inorganic powder raw material composition consisting solely of inorganic components, or an organic component-containing raw material composition obtained by adding an organic component such as a binder to the inorganic powder raw material composition. Examples of the microporous molded body include a microporous molded body obtained by compression molding the inorganic powder raw material composition. Examples of the heat-treated microporous molded body include a green body obtained by molding the organic component-containing raw material composition and then degreasing it (a microporous degreased body), and a pre-green body that is calcined either directly or after degreasing (a microporous calcined body). The degree of microporosity is not particularly limited as long as it allows a treatment solution applied to the surface to penetrate into the interior and retain the treatment solution to a predetermined depth from the surface, specifically in the range of 5 to 300 μm, preferably in the range of 10 to 200 μm. Typically, the average pore diameter is in the range of 50 to 200 nm.

In the manufacturing method of the article of the present invention, examples of the inorganic oxide constituting the main body include stabilized zirconia, partially stabilized zirconia, alumina, titania, etc. When a microporous pre-sintered body is used in the semi-finished product manufacturing process, the pre-sintering can be performed at a temperature lower than the sintering temperature of the inorganic oxide, as described in Section 2-1, "(2) Manufacturing Method for Zirconia Dental Mill Blanks," depending on the type of inorganic oxide. The processing step can be performed similarly to the processing step in the manufacturing method of the dental prosthesis of the present invention, and the sintering step can be performed at a sintering temperature that produces a dense sintered body, depending on the type of inorganic oxide. For example, when manufacturing a ceramic article composed of alumina, alumina powder (Taimicron TM-DAR, manufactured by Taimei Chemical Industry Co., Ltd.) with an average particle size of 0.12 μm and purity of 99.99% is molded and pre-sintered at 800°C for 1 hour to obtain a pre-sintered body with a relative density of 63%. Next, the same processing steps as in the method for manufacturing a dental prosthesis of the present invention are carried out, and sintering is carried out at 1400°C for 2 hours to produce a ceramic article made of the alumina.

The present invention will be explained in detail below using examples and comparative examples. However, the present invention is not limited to these examples.

Example 1
[Production of zirconia-based ceramic articles]
Using a zirconia mill blank "Katana Zirconia UTML (manufactured by Kuraray Noritake Dental)" with a cutting portion made of a partially stabilized zirconia microporous calcined body, data was created so that a disk-shaped body of a predetermined size of 11 mm in diameter and 4 mm in thickness (specifically, a 1 cm x 1 cm x 3 mm plate-shaped body or a disk-shaped body of 11 mm in diameter and 4 mm in thickness) would be obtained after sintering, and cutting was performed to produce plate-shaped semi-finished products 1 and 2 of different sizes (corresponding to simulated semi-finished products of zirconia prostheses). Next, for each of these plate-shaped semi-finished products 1 and 2, one surface was used as a simulated bonding surface, and a treatment solution consisting of "No. 3 sodium silicate (manufactured by Toso Sangyo, an aqueous solution of 28-30% by mass of silicon dioxide and 9-10% by mass of sodium oxide: _SiO2 / _Na2O =3.05)" was applied to the simulated bonding surface at 0.02 ^g per 1 cm2 using a disposable sponge. The sintered product was then dried at room temperature for 5 minutes and sintered. The sintering was carried out by increasing the temperature from 25°C to 1550°C at a rate of 10°C/min, maintaining the temperature at 1550°C for 2 hours, and then decreasing the temperature from 1550°C to 25°C at a rate of 10°C/min. Using this method, a zirconia-based ceramic article 1 for analysis samples was produced, which consisted of a 1 cm x 1 cm x 3 mm plate (corresponding to a simulated zirconia prosthesis), and a zirconia-based ceramic article 2 for physical property evaluation samples was produced, which consisted of a disk-shaped body having a diameter of 11 mm and a thickness of 4 mm.

[Analysis of Zirconia-Based Ceramic Article 1]
One surface layer of the zirconia-based ceramic article 1 was measured by X-ray diffraction (XRD) to confirm the presence of a silicon dioxide layer. Furthermore, measurement using an electron probe microanalyzer (EPMA) confirmed that the penetration depth of the silicon dioxide was 54 μm, and that no alkali metal oxides derived from alkali metal silicates were detected.

[Adhesion evaluation of zirconia-based ceramic article 2]
The bonding surface of the zirconia-based ceramic article 2 was polished with #800 waterproof abrasive paper. Then, a double-sided tape with a 4 mm diameter hole was attached to the polished surface. The bonding surface exposed through the hole in the double-sided tape was then treated with "Tokuyama Universal Primer (manufactured by Tokuyama Dental)," a pretreatment agent containing a silane coupling agent, according to the manufacturer's instructions. A SUS304 round bar (diameter 8 mm, height 18 mm) that had been previously polished using dental resin cement "Estecem II (manufactured by Tokuyama Dental)" was then bonded to the bonding surface.

After bonding, the dental resin cement was left in a thermostatic bath maintained at 37°C and 100% humidity for approximately one hour to allow chemical polymerization. The test piece was then immersed in 37°C water. After 24 hours, the test piece was removed from the water and used as the initial sample. The test piece was then removed from the water after 24 hours and alternately immersed in a water bath with a water temperature of 5°C and a water bath with a water temperature of 55°C for 30 seconds each. This immersion treatment was repeated 10,000 times, and the test piece was used as the durability sample.

The tensile adhesive strength of these samples was measured using a Shimadzu Autograph (crosshead speed 1 mm/min). For each example and comparative example, the measured values of four samples were averaged to obtain the measurement results. As a result of the measurement, the adhesive strength of the initial sample was 30 MPa, and that of the durable sample was 20 MPa.

Comparative Example 1
A disk-shaped semi-finished product was prepared in the same manner as for zirconia-based ceramic article 2 described in Example 1 using "Katana Zirconia UTML (manufactured by Kuraray Noritake Dental)," and zirconia-based ceramic article 3 was produced in the same manner as for zirconia-based ceramic article 2 described in Example 1, except that the treatment with the treatment solution (coating and drying) was not carried out, and adhesion evaluation was carried out. The measurement results showed that the adhesive strength of the initial sample was 20 MPa, and that of the durability sample was 10 MPa.

Claims (4)

A dental prosthesis having a main body comprising a " stabilized zirconia sintered body or partially stabilized zirconia sintered body" which contains zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, cerium oxide, and erbium oxide, and which is substantially free of silicon dioxide; and a "composite" in which the "stabilized zirconia sintered body or partially stabilized zirconia sintered body" is combined with "silicon dioxide,"
the surface of the body has an adhesive surface to be adhered to an adherend and an exposed surface exposed to the surface;
When the range of a depth from the surface to 5 to 300 μm is defined as the surface layer portion, in the surface layer portion of the adhesive surface, the “ silicon dioxide ” present in the surface layer portion and the “stabilized zirconia sintered body or partially stabilized zirconia sintered body” are combined to form the “composite” ,
The portion of the main body other than the surface layer portion is made of the "stabilized zirconia sintered body or partially stabilized zirconia sintered body",
A dental prosthesis characterized by: A method for producing a dental prosthesis according to claim 1, comprising the steps of:
a cutting process step of cutting a zirconia dental mill blank having a cuttable portion made of a microporous calcined body of stabilized zirconia or a microporous calcined body of partially stabilized zirconia, the microporous calcined body containing zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, and substantially no silicon dioxide component, using a CAD/CAM system to obtain a semi-finished product made of the microporous calcined body, the semi-finished product having a shape corresponding to the shape of a desired dental prosthesis;
a treatment step of applying a treatment liquid consisting of an aqueous solution of alkali metal silicate to the surface of the semi-finished product corresponding to the bonding surface and allowing the treatment liquid to penetrate the surface, thereby retaining the alkali metal silicate in the surface layer of the surface; and a sintering step of sintering the semi-finished product that has been subjected to the treatment step at a temperature of 1200 to 1800°C.
a method for producing the dental prosthesis, comprising: the microporous calcined body constituting the cutting portion of the zirconia dental mill blank is a microporous calcined body having a relative density of 45 to 65% and pores that are open to the outside,
the treatment liquid is a sodium silicate aqueous solution having a sodium silicate concentration of 15 to 70 mass %,
In the treatment step, sodium silicate is retained in a surface layer portion of the surface up to a depth of 5 to 300 μm.
A method for manufacturing a dental prosthesis according to claim 2. A dental prosthesis manufacturing kit for manufacturing the dental prosthesis according to claim 1 by the method according to claim 2, comprising:
a zirconia dental mill blank having a cutting portion made of a microporous calcined body of stabilized zirconia or a microporous calcined body of partially stabilized zirconia, which contains zirconium oxide and at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, and is substantially free of silicon dioxide;
a treatment liquid comprising an aqueous sodium silicate solution having a sodium silicate concentration of 15 to 70 mass %;
A dental prosthesis manufacturing kit comprising: