Dental mill blank, method for fabricating the same, and use of the same

Abstract

To provide a dental mill blank suitable for fabricating a dental restoration, a method for fabricating the dental mill blank, and a method for fabricating a dental restoration by using the dental mill blank.SOLUTION: Provided is a dental mill blank comprising a yttria-containing zirconia material. In one embodiment, a dental mill blank comprising a yttria-containing zirconia material is provided, where the yttria-containing zirconia material has at least 6.0 MPa*m1 / 2 of fracture resistance determined by a high-density sintered test piece of the yttria-containing zirconia material, and at least 1200 MPa of biaxial flexural strength determined by a high-density sintered test piece of the yttria-containing zirconia material. Furthermore, provided is a method for fabricating a dental mill blank, a method for fabricating a dental restoration by using a dental mill blank, and such a dental restoration itself.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a dental mill blank and a method for producing a dental mill blank. The present invention also relates to a dental restoration obtained using the dental mill blank and such a dental restoration. The present invention further relates to the use of zirconia powder for producing a dental mill blank.

Background Art

[0002] Ceramic dental restorations are typically made from dental mill blanks. A dental mill blank is usually a porous and not fully sintered block or disk based on a ceramic material such as zirconia. The dental mill blank can be machined in a CAD / CAM process to produce a precursor of the ceramic dental restoration. This dental restoration precursor has the shape of the final ceramic dental restoration but does not yet have the final density and thus does not have the final dimensions. The dental restoration precursor is then subjected to a sintering process to provide the final density and dimensions of the ceramic dental restoration.

[0003] Many commercially available dental mill blanks are based on yttria-stabilized zirconia materials. For example, dental mill blanks based on 3 mol%, 4 mol%, or 5 mol% yttria-stabilized zirconia materials (also referred to as 3Y-, 4Y-, and 5Y-TZP) are available on the market. These materials, particularly 3Y-TZP, can be used to provide dental restorations with relatively high flexural strength. However, the fracture toughness or fracture resistance of the materials is not always satisfactory, especially in more difficult applications in dental restorations, such as multi-unit bridges or minimally invasive restorations. In the art, attempts have been made to increase the fracture toughness / fracture resistance of ceramic dental restorations by using ceria-stabilized zirconia materials containing a large amount of aluminum oxide. However, this material typically provides a dental restoration that is completely opaque and / or yellowish, and thus does not meet the high aesthetic requirements in dentistry with respect to color and translucency (transparency).

[0004] In the art, there is a continuing need for dental mill blanks that have improved mechanical properties and are particularly suitable for making dental restorations having increased fracture toughness or fracture resistance. Furthermore, it is desirable that the dental mill blank be suitable for making dental restorations that provide significant color and translucency. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] One of the problems of the present invention is to provide a dental mill blank suitable for making a dental restoration having improved mechanical properties compared to conventional dental mill blanks. One of the problems of the present invention is to provide a dental mill blank suitable for making a dental restoration having high flexural strength and high fracture toughness or fracture resistance. One of the problems of the present invention is to provide a dental mill blank suitable for making a dental restoration having a good balance between mechanical properties such as flexural strength and fracture toughness or fracture resistance, and optical properties such as color or translucency.

Means for Solving the Problems

[0006] One or more of the above-described problems are solved by a dental mill blank, a method for producing a dental restoration, a dental restoration according to the present invention, and / or the use according to the present invention.

[0007] One aspect of the present invention provides a dental mill blank comprising a yttria-containing zirconia material. One embodiment of the present invention provides a dental mill blank comprising a yttria-containing zirconia material. In this case, the yttria-containing zirconia material - has a fracture resistance of at least 6.0 MPa determined by a high-density sintered specimen of the yttria-containing zirconia material * m 1 / 2 and - has a biaxial flexural strength of at least 1200 MPa determined by a high-density sintered specimen of the yttria-containing zirconia material.

[0008] One embodiment of the present invention provides a dental mill blank comprising a yttria-containing zirconia material. In this case, the yttria-containing zirconia material contains yttria in an amount of up to 4.0% by weight based on the total weight of the yttria-containing zirconia material.

[0009] One of the findings according to the present invention is that the dental mill blank according to the present invention is useful for producing a zirconia ceramic having good mechanical properties, for example, a zirconia ceramic dental restoration. In particular, a dental restoration having high biaxial flexural strength and high fracture resistance can be produced. Further, the inventors have found that a dental mill blank comprising a zirconia material containing up to 4.0% by weight of yttria is particularly suitable for producing a zirconia ceramic having the above-described mechanical properties, for example, a zirconia ceramic dental restoration. Furthermore, the dental mill blank is suitable for producing a zirconia ceramic having a good balance between mechanical properties and optical properties, for example, a zirconia ceramic dental restoration. Therefore, the dental mill blank may be suitable for producing, for example, an aesthetic dental restoration having a thin wall thickness that enables minimally invasive treatment.

[0010] Another aspect of the present invention provides a method for producing a dental mill blank according to an embodiment of the present invention. The method comprises - providing zirconia powder; - optionally, treating the zirconia powder with one or more colorants; - compressing the zirconia powder to provide a green body; - pre-sintering the green body to provide a dental mill blank; - and optionally, pre-coloring the dental mill blank.

[0011] Another aspect of the present invention provides the use of zirconia powder for producing a dental mill blank. In this case, the zirconia powder comprises a total amount of zirconia and hafnia of 95.0 to 98.5% by weight, preferably 95.5 to 98.0% by weight, for example 96.0 to 97.7% by weight, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), and Based on the total weight of the zirconia powder, it contains 0.0 to 0.3% by weight, preferably 0.0 to 0.1% by weight, for example 0.0 to 0.05% by weight of other oxides.

[0012] Another aspect of the present invention provides a method for producing a dental restoration. This method includes - machining a dental mill blank according to an embodiment of the present invention to provide a dental restoration precursor; - optionally, surface-treating the dental restoration precursor; - sintering the dental restoration precursor to provide a dental restoration.

[0013] Another aspect of the present invention provides a dental restoration. According to one embodiment, a dental restoration obtained by the method according to an embodiment of the present invention is provided.

[0014] In the context of the present invention, the following terms have the following meanings.

[0015] "Dental mill blank" means a porous and solid geometrically defined three-dimensional object such as a block or a disk, from which a precursor of a dental restoration can be machined, for example, by cutting, milling, grinding, or drilling. Machining is usually performed using a computer-aided design / computer-aided manufacturing (CAD / CAM) process.

[0016] As used herein, "dental restoration precursor" refers to a workpiece machined from a dental mill blank that already has the shape of a dental restoration but has not yet been sintered to a high density and thus does not have the final dimensions.

[0017] "Dental restoration" refers to an article useful in the dental or orthodontic field for repairing, reforming, supporting, and / or reconstructing a tooth or part of a tooth, or a group of teeth or parts of teeth. Dental restorations can be, but are not limited to, crowns, partial crowns, abutments, abutment crowns, inlays, onlays, veneers, shells, or bridges.

[0018] "Green body" refers to a compacted body of ceramic powder that has not been subjected to a sintering or pre-sintering step and may contain an organic binder, an inorganic binder, or other additives. The compacted body is typically produced by compressing (e.g., pressing) the ceramic powder.

[0019] As used herein, "porous" means that the material has pores and includes open porous materials and closed porous materials. An "open porous" material is a material having pores that are at least partially interconnected and are at least partially accessible from the outside, for example, by a gas or liquid flow. An open porous material as defined herein may also have pores that are inaccessible from the outside, for example, by a gas or liquid flow. A "closed porous" material is a material that is not open porous and has closed pores, i.e., pores that are inaccessible from the outside, for example, by a gas or liquid flow. "Porosity" is the degree of voids, such as pores, in a solid material and is the ratio of the volume of voids to the total volume of the solid material. This can be expressed as a percentage from 0 to 100%.

[0020] As used herein, "sintering" means densifying a porous inorganic material into a higher density and lower porosity inorganic material by heating at a temperature suitable for densification. This temperature is below the melting point of the main component in the inorganic material.

[0021] As used herein, "debinding" means applying heat to the green body to partially or completely remove or decompose an organic binder, an inorganic binder, or a thermally unstable component. Debinding can be performed before the pre-sintering step or as part of the pre-sintering step.

[0022] As used herein, "pre-sintered" or "pre-sintering" means applying heat to the green body to promote at least partial formation of sintering necks at the grain boundaries in the material of the green body and to facilitate the processability or machinability of the material for thermal curing of the material. Pre-sintering can include debinding of the green body. The relative densification from the green body to the pre-sintered material is typically 5% or less relative to the dimensions of the green body. The pre-sintered material usually has an open porous structure that can be further densified by sintering the material to a high density in a subsequent sintering step. The density of the pre-sintered material, such as a pre-sintered zirconia material, can be in the range of 45 to 70% of the theoretical density of the ceramic material. The temperature at which the material is pre-sintered can be determined by one skilled in the art, for example, by measuring thermal expansion using a dilatometer.

[0023] As used herein, "densely sintered" or "densely sintering" means that a ceramic material is sintered to a density of at least 98.5%, such as at least 99.5%, or at least 99.8% of the theoretical density of the ceramic material. The density of the material can be determined by the Archimedes method in accordance with DIN EN 623-2, or by weighing the material and geometrically measuring its volume. The theoretical density of a densely sintered material can be determined, for example, by one skilled in the art based on the chemical composition of the material. Additionally or alternatively, the theoretical density of the ceramic material can be determined by grinding the ceramic material into a powder having a volume-based median particle size in the range of, for example, 10 to 30 μm (e.g., 20 μm), and measuring the density of the powder by pycnometry. The volume-based median particle size can be determined by laser diffraction, for example, in accordance with ISO 13320 (2009).

[0024] As used herein, "yttria-stabilized zirconia" means zirconia (ZrO2) in which an amount of yttria (Y2O3) sufficient to at least partially prevent the tetragonal and cubic phases from each transforming to the monoclinic phase during cooling to room temperature is incorporated into the crystal lattice. At room temperature, pure zirconia exists in the monoclinic phase, which is the most stable crystal phase. When the temperature of zirconia rises to about 1170 °C, the monoclinic phase transforms to the tetragonal phase, and at about 2370 °C, the tetragonal phase transforms to the cubic phase. By incorporating an appropriate amount of yttria into the crystal lattice of zirconia, the tetragonal or cubic phase of zirconia can be at least partially stabilized, i.e., the tetragonal and cubic phases can be at least partially prevented from each transforming to the more stable monoclinic phase of zirconia (at room temperature).

[0025] A "pre-colored" dental mill blank means that a yttria-containing zirconia material contains coloring oxides in an amount and / or combination effective to impart color (e.g., a color matching the natural color of teeth, and / or a color according to the VITA classical A1-D4® shade guide having VITA Bleached Shades of Vita Zahnfabrik, or a similar dental shade guide system) to a dental restoration machined from the dental mill blank and then sintered at high density.

[0026] When the term "comprising" is used in this specification, it does not exclude the presence of further elements not specified. When the term "essentially consisting of" is used in this specification, it does not exclude the presence of further elements that do not substantially affect the essential characteristics of the defined subject matter. For example, when a substance is defined by its chemical composition, the substance may contain a total of 0.1 < wt% of unavoidable trace impurities (e.g., SiO2, CaO, and / or Na2O), even if not explicitly specified. In this specification, the terms "essentially consisting of" and "consisting of" are considered specific examples of the term "comprising of". When the terms "including" or "having" are used, they are synonymous with "comprising" as defined above.

[0027] The term "obtained (obtainable)" does not necessarily indicate that an embodiment is obtained by a series of steps following the term "obtained", although such a limited understanding is always included as a preferred embodiment by the term "obtained".

[0028] The numerical values defined in this specification are rounded to the last digit and are meant to include the range of values rounded according to established rounding rules. For example, the numerical value 3 means it includes values in the range of 2.5 to 3.4, and the numerical value 1.5 means it includes values in the range of 1.46 to 1.54.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0030] The dental mill blank according to the present invention comprises a yttria-containing zirconia material. The yttria-containing zirconia material is further characterized by its mechanical properties and / or chemical properties. 1.1 Mechanical properties and optical properties

[0031] One embodiment of the present invention provides a dental mill blank comprising a yttria-containing zirconia material. In this case, the yttria-containing zirconia material - has a fracture resistance of at least 6.0 MPa determined on a high-density sintered specimen of the yttria-containing zirconia material * m 1 / 2 and - has a biaxial flexural strength of at least 1200 MPa determined on a high-density sintered specimen of the yttria-containing zirconia material.

[0032] The fracture resistance can be determined (measured) by the indentation fracture (IF) method in accordance with ISO 14627, particularly ISO 14627:2012. The determination of the fracture resistance can be carried out by evaluating across the crack in accordance with ISO 14627, particularly ISO 14627:2012 (see "Method A" described in the "Measurement Method" section of this specification). Alternatively, the determination of the fracture resistance can be carried out by evaluating the radial crack using Niihara's equation for the radial crack (see "Method B" described in the "Measurement Method" section of this specification).

[0033] The measurement method is carried out using a high-density sintered specimen of a yttria-containing zirconia material (sintered at a maximum sintering temperature of 1250 - 1350 °C, such as 1250 °C or 1300 °C). The high-density sintered specimen is typically obtained by cutting a portion from a dental mill blank (e.g., by milling), sintering the portion at high density, and lapping (rough polishing) and / or polishing the surface of the high-density sintered portion. Lapping and / or polishing are typically carried out in accordance with DIN EN 843-1, particularly DIN EN 843-1:2008-08. The portion can be sintered at high density at a maximum sintering temperature of 1250 - 1350 °C, such as 1250 °C or 1300 °C. This maximum sintering temperature can be maintained for 2 hours. Further details for determining the fracture resistance of the yttria-containing zirconia material are described in the "Measurement Method" section of this specification.

[0034] The yttria-containing zirconia material has at least 8.0 MPa * m 1 / 2 Preferably, at least 10.0 MPa * m 1 / 2 For example, at least 12.0 MPa * m 1 / 2 At least 13.0 MPa * m 1 / 2 Or at least 14.0 MPa * m 1 / 2can have fracture resistance. The yttria-containing zirconia material can have a fracture resistance of up to 23 MPa * m 1 / 2 up to 22.0 MPa * m 1 / 2 up to 20.0 MPa * m 1 / 2 or up to 19.0 MPa * m 1 / 2 can have fracture resistance. Thus, the yttria-containing zirconia material can have a fracture resistance in the range of 6.0 to 23.0 MPa * m 1 / 2 preferably in the range of 8.0 to 22.0 MPa * m 1 / 2 more preferably in the range of 10.0 to 20.0 MPa * m 1 / 2 for example, in the range of 11.0 to 19.5 MPa * m 1 / 2 12.0 to 19.0 MPa * m 1 / 2 or 14.0 to 19.0 MPa * m 1 / 2 can have fracture resistance in the range.

[0035] The yttria-containing zirconia material has a fracture resistance of at least 11.0 MPa as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and the "Method A" described herein * m 1 / 2 preferably at least 13.0 MPa * m 1 / 2 for example, at least 14.0 MPa * m 1 / 2 at least 15.0 MPa * m 1 / 2 or at least 15.5 MPa * m 1 / 2 can have fracture resistance. The yttria-containing zirconia material has a fracture resistance of up to 23.0 MPa as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and the "Method A" described herein * m 1 / 2 up to 22.0 MPa * m1 / 2 and up to 20.0 MPa * m 1 / 2 and up to 19.0 MPa * m 1 / 2 can have a fracture resistance. Thus, the yttria-containing zirconia material has a fracture resistance in the range of 11.0 to 23.0 MPa, preferably in the range of 13.0 to 22.0 MPa, more preferably in the range of 14.0 to 20.0 MPa, for example, in the range of 15.0 to 19.5 MPa or 15.5 to 19.0 MPa, as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and "Method A" described herein. * m 1 / 2 Preferably in the range of 13.0 to 22.0 MPa * m 1 / 2 More preferably in the range of 14.0 to 20.0 MPa * m 1 / 2 For example, in the range of 15.0 to 19.5 MPa * m 1 / 2 or in the range of 15.5 to 19.0 MPa * m 1 / 2 can have a fracture resistance.

[0036] In one embodiment, the yttria-containing zirconia material has a fracture resistance in the range of 14.5 to 19.5 MPa, for example in the range of 15.0 to 18.5 MPa or 15.5 to 18.0 MPa, as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and "Method A" described herein. Optionally, the yttria-containing zirconia material is a yttria-containing zirconia material according to "Embodiment P1" as described below. In one embodiment, the yttria-containing zirconia material has a fracture resistance in the range of 16.0 to 20.5 MPa, for example in the range of 17.0 to 20.0 MPa or 17.5 to 19.5 MPa * m 1 / 2 For example, in the range of 15.0 to 18.5 MPa * m 1 / 2 For example, in the range of 15.5 to 18.0 MPa * m 1 / 2 and optionally, the yttria-containing zirconia material is a yttria-containing zirconia material according to "Embodiment P1" as described below. In one embodiment, the yttria-containing zirconia material has a fracture resistance in the range of 16.0 to 20.5 MPa, for example in the range of 17.0 to 20.0 MPa or 17.5 to 19.5 MPa * m 1 / 2 For example, in the range of 17.0 to 20.0 MPa * m 1 / 2 For example, in the range of 17.5 to 19.5 MPa * m 1 / 2has fracture resistance in the range of, and optionally, the yttria-containing zirconia material is the yttria-containing zirconia material according to "Embodiment P2" as described below.

[0037] The yttria-containing zirconia material has at least 8.0 MPa, as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and "Method B". * m 1 / 2 , preferably at least 10.0 MPa * m 1 / 2 , for example, at least 12.0 MPa * m 1 / 2 , at least 13.0 MPa * m 1 / 2 , or at least 14.0 MPa * m 1 / 2 The yttria-containing zirconia material can have a fracture resistance of up to 19.0 MPa, as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and "Method B" described herein. * m 1 / 2 , up to 18.0 MPa * m 1 / 2 , up to 17.5 MPa * m 1 / 2 , up to 17.0 MPa * m 1 / 2 Therefore, the yttria-containing zirconia material has a fracture resistance in the range of 6.0 to 19.0 MPa, as determined in accordance with ISO 14627 (in particular ISO 14627:2012) and "Method B". * m 1 / 2 , preferably in the range of 8.0 to 19.0 MPa * m 1 / 2 , more preferably in the range of 10.0 to 18.0 MPa * m 1 / 2 , for example, in the range of 11.0 to 17.5 MPa * m 1 / 2 , 12.0 to 17.0 MPa * m 1 / 2 , or 14.0 to 17.0 MPa * m 1 / 2can have fracture resistance within a certain range.

[0038] In one embodiment, the yttria-containing zirconia material has a fracture resistance in the range of 10.5 to 16.5 MPa, as determined in accordance with ISO 14627 (especially ISO 14627:2012) and "Method B". * m 1 / 2 For example, in the range of 11.0 to 16.0 MPa * m 1 / 2 For example, in the range of 11.5 to 15.5 MPa * m 1 / 2 and optionally, the yttria-containing zirconia material is the yttria-containing zirconia material according to "Embodiment P1" as described below. In one embodiment, the yttria-containing zirconia material has a fracture resistance in the range of 13.5 to 18.5 MPa, as determined in accordance with ISO 14627 (especially ISO 14627:2012) and "Method B". * m 1 / 2 For example, in the range of 14.0 to 18.0 MPa * m 1 / 2 For example, in the range of 14.5 to 17.5 MPa * m 1 / 2 and optionally, the yttria-containing zirconia material is the yttria-containing zirconia material according to "Embodiment P2" as described below.

[0039] The biaxial flexural strength can be determined in accordance with ISO 6872, in particular ISO 6872:2008. The measurement method is carried out using a high-density sintered test piece of yttria-containing zirconia material (such as sintered at a maximum sintering temperature of 1250 - 1350 °C, for example 1250 °C or 1300 °C). The high-density sintered test piece is typically obtained by cutting a portion from a dental mill blank (such as by milling), sintering that portion at high density, and polishing the surface of the high-density sintered portion in accordance with ISO 6872, in particular ISO 6872:2008. The portion can be sintered at high density at a maximum sintering temperature of 1250 - 1350 °C, for example at a maximum sintering temperature of 1250 °C or 1300 °C. This maximum sintering temperature can be maintained for 2 hours. Further details for determining the biaxial flexural strength of the yttria-containing zirconia material are described in the "Measurement Method" section of this specification.

[0040] The yttria-containing zirconia material can have a biaxial flexural strength of at least 1300 MPa, preferably at least 1350 MPa, for example at least 1400 MPa, or at least 1500 MPa. The yttria-containing zirconia material can have a biaxial flexural strength of at most 2200 MPa, at most 2150 MPa, at most 2000 MPa, or at most 1900 MPa. Accordingly, the yttria-containing zirconia material can have a biaxial flexural strength in the range of 1200 - 2200 MPa, preferably in the range of 1300 - 2200 MPa, more preferably in the range of 1350 - 2200 MPa, for example in the range of 1400 - 2150 MPa.

[0041] In one embodiment, the yttria-containing zirconia material has a biaxial flexural strength in the range of 1350 - 1900 MPa, for example in the range of 1400 - 1900 MPa, and optionally, the yttria-containing zirconia material is a yttria-containing zirconia material according to "Embodiment P1" as described below.

[0042] In one embodiment, the yttria-containing zirconia material has a biaxial flexural strength in the range of 1700 to 2200 MPa, for example, in the range of 1750 to 2150 MPa, and optionally, the yttria-containing zirconia material is the yttria-containing zirconia material according to "Embodiment P2" as described below.

[0043] The yttria-containing zirconia material can be further characterized by its hardness in the high-density sintered state. As used herein, when referring to the "Vickers hardness VH" of the yttria-containing zirconia material, this refers to the hardness of the yttria-containing zirconia material determined on a high-density sintered specimen of the yttria-containing zirconia material as described below. The Vickers hardness VH can be determined using a test load of 196.1 N (HV20) in accordance with ISO 14705, in particular ISO 14705:2008. The measurement method is carried out using a high-density sintered specimen of the yttria-containing zirconia material. The high-density sintered specimen is typically obtained by cutting a portion from a dental mill blank (e.g., by milling), sintering the portion at high density, and lapping and / or polishing the surface of the high-density sintered portion. Lapping and / or polishing can typically be carried out in accordance with DIN EN 843-1, in particular DIN EN 843-1:2008-08. The portion can be sintered at high density at a maximum sintering temperature of 1250 to 1350 °C, for example, a maximum sintering temperature of 1250 °C or 1300 °C. This maximum sintering temperature can be held for 2 hours. Further details for determining the Vickers hardness VH of the yttria-containing zirconia material are described in the "Measurement Method" section of this specification.

[0044] The yttria-containing zirconia material can have a Vickers hardness VH of at least 9,000 MPa, preferably at least 10,000 MPa, for example at least 11,000 MPa, or at least 11,250 MPa. The yttria-containing zirconia material can have a Vickers hardness VH of at most 14,500 MPa, at most 13,500 MPa, or at most 12,750 MPa. The yttria-containing zirconia material can have a Vickers hardness VH in the range of 9,000 - 14,500 MPa, preferably in the range of at least 10,000 - 13,500 MPa, for example in the range of 11,000 MPa - 12,750 MPa, or 11,250 - 12,750 MPa. In one embodiment, the yttria-containing zirconia material has a Vickers hardness VH in the range of 11,500 - 12,750 MPa, and optionally, the yttria-containing zirconia material is a yttria-containing zirconia material according to "Embodiment P1" as described hereinafter. In one embodiment, the yttria-containing zirconia material has a Vickers hardness VH in the range of 11,000 - 12,250 MPa, and optionally, the yttria-containing zirconia material is a yttria-containing zirconia material according to "Embodiment P2" as described hereinafter.

[0045] The yttria-containing zirconia material is CIE L * a * b *It can have specific optical properties such as color values, opacity, translucency (light transmittance), etc. Unless otherwise specified, the optical properties of the yttria-containing zirconia materials described in this specification refer to the optical properties determined using a high-density sintered specimen of the yttria-containing zirconia material with a thickness of 1.00 ± 0.05 mm. The high-density sintered specimen is typically obtained by cutting a portion from a dental mill blank (e.g., milling), sintering the portion at high density, and surface polishing the high-density sintered portion. The portion can be sintered at high density at a maximum sintering temperature of 1250 - 1350 °C, for example, a maximum sintering temperature of 1250 °C or 1300 °C. This maximum sintering temperature can be maintained for 2 hours. For more details on determining the optical properties of the yttria-containing zirconia materials, refer to the "Measurement Methods" section of this specification.

[0046] The yttria-containing zirconia material can have a contrast ratio of less than 90%, preferably less than 88%, for example less than 86%. The yttria-containing zirconia material can have a contrast ratio in the range of 70 - 90%, preferably 72 - 88%, for example 74 - 86%. In one embodiment, the yttria-containing zirconia material has a contrast ratio in the range of 82 - 88%, and optionally, the yttria-containing zirconia material is the yttria-containing zirconia material according to "Embodiment P2" as described below. In one embodiment, the yttria-containing zirconia material has a contrast ratio in the range of 72 - 81%, and optionally, the yttria-containing zirconia material is the yttria-containing zirconia material according to "Embodiment P1" as described below.

[0047] The contrast ratio can be determined in accordance with BS 5612, in particular BS 5612:1978. The contrast ratio is related to the ratio of the illuminance (Y) of the material when placed on a black background (Yb) to the illuminance of the same material when placed on a white background (Yw) (CR = Yb / Yw). The contrast ratio can be used to characterize the light transmittance of a material, which is expressed as the ratio of the transmitted light intensity to the incident light intensity, i.e., the transparency of the material. When the contrast ratio is close to 0%, it indicates that a given material is almost completely transparent, while when the contrast ratio is 100%, it indicates that the material is completely opaque.

[0048] CIE L of yttria-containing zirconia materials * a * b * The color values are L * in the range of 76 to 96, a * in the range of (-2) to 6, b * can be in the range of 0 to 25.

[0049] CIE L * a * b * The color values can be measured in accordance with DIN 6174. The measurement can be carried out, for example, with L * = 93.1; a * = (-0.64); b * = 4.22 as the background. CIE L * a * b * The values characterize the color of the material in a three-dimensional color space. The individual color L * is a measure representing luminance and brightness and is represented on the vertical axis of the color space. The coordinates of a * and b * are measures representing chromaticity and are represented on the horizontal axis of the color space. In this case, positive a * is red, positive a * is green, negative b * is green, positive b * is yellow, negative b * represents blue.

[0050] CIE L of yttria-containing zirconia materials* a * b * The value depends on the presence of colored oxides in the material. If the material contains colored oxides, the CIE L * a * b * values are different. The dental mill blank according to the present invention may or may not be pre-colored. This will be described in more detail in other parts of the present disclosure. When the dental mill blank is a pre-colored dental mill blank, the yttria-containing zirconia material is machined from the dental mill blank and then sintered at high density to a dental restoration having a color (e.g., a color matching the natural color of teeth, and / or a color according to the VITA classical A1-D4 (registered trademark) shade guide having VITA Bleached Shades manufactured by Vita Zahnfabrik, or a color according to a similar dental shade guide system) in an effective amount and / or combination of colored oxides. The color can be characterized by the CIE L * a * b * values.

[0051] In one embodiment, the yttria-containing zirconia material L * is in the range of 84 to 96, for example in the range of 86 to 93, a * is in the range of (-2.0) to 1.0, for example in the range of (-1.5) to 0.5, b * is in the range of 0.0 to 4.0, for example in the range of 0.5 to 3.0, of CIE L * a * b * color values.

[0052] The yttria-containing zirconia material is preferably further characterized by the chemical properties described in the following sections. 1.2 Chemical properties

[0053] One embodiment of the present invention provides a dental mill blank comprising a yttria-containing zirconia material, where the yttria-containing zirconia material contains yttria in an amount of up to 4.0 wt% based on the total weight of the yttria-containing zirconia material.

[0054] The yttria-containing zirconia material is typically a yttria-stabilized zirconia material. The yttria-stabilized zirconia material may have a monoclinic phase fraction of less than 20%, less than 15%, or less than 10% based on the entire crystal phase of the material. The monoclinic phase fraction of the crystal phase can be measured using quantitative X-ray diffraction. The measurement method is known to those skilled in the art. The monoclinic fraction can be determined according to DIN EN ISO 13356 (see ASTM C1499). The yttria-containing zirconia material has a theoretical density of about 6.1 g / cm 3 , for example, about 6.11 g / cm 3 and can be.

[0055] The yttria-containing zirconia material contains yttria. The yttria-containing zirconia material preferably contains yttria in an amount of up to 4.0 wt%, more preferably in the range of 1.5 - 4.0 wt%, still more preferably in the range of 2.0 - 3.8 wt%, for example in the range of 2.2 - 3.4 wt% based on the total weight of the yttria-containing zirconia material.

[0056] The yttria-containing zirconia material contains zirconia. The yttria-containing zirconia material preferably contains zirconia in an amount of at least 82.0% by weight, more preferably at least 84.0% by weight, still more preferably at least 86.0% by weight, for example, at least 88.0% by weight, at least 90.0% by weight, at least 92.0% by weight, or at least 94.0% by weight, based on the total weight of the yttria-containing zirconia material. The yttria-containing zirconia material can contain zirconia in an amount in the range of 82.0 to 98.5% by weight, preferably in the range of 84.0 to 98.5% by weight, more preferably in the range of 86.0 to 98.0% by weight, for example, in the range of 88.0 to 98.0% by weight, 90.0 to 98.0% by weight, 92.0 to 97.0% by weight, or 94.0 to 96.0% by weight, based on the total weight of the yttria-containing zirconia material.

[0057] The yttria-containing zirconia material can contain hafnia (HfO2). The yttria-containing zirconia material can contain hafnia in a weight ratio to zirconia in the range of 0:100 to 5:95, 1:99 to 4:96, 2:98 to 3:97, based on the total weight of the total amount of hafnia and zirconia present in the material. The yttria-containing zirconia material can contain hafnia in a range of up to 5.0% by weight, preferably up to 4.0% by weight, for example 0.5 to 4.0% by weight, 1.0 to 3.0% by weight, or 1.5 to 2.5% by weight, based on the total weight of the yttria-containing zirconia material. The total amount of zirconia and hafnia present in the yttria-containing zirconia material can be in the range of 92.5 to 98.5% by weight, 93.2 to 98.0% by weight, or 94.0 to 98.0% by weight, based on the total weight of the yttria-containing zirconia material. The "total amount of zirconia and hafnia" includes the case where the amount of hafnia is 0% by weight, or hafnia is substantially absent from the yttria-containing zirconia material.

[0058] The yttria-containing zirconia material can contain aluminum oxide (Al2O3). The material can contain aluminum oxide in an amount up to 2.0 wt%, preferably in the range of 0.0 - 1.5 wt%, more preferably in the range of 0.0 - 1.0 wt%, still more preferably in the range of 0.0 - 0.7 wt%, for example, in the range of 0.0 - 0.5 wt%, 0.1 - 0.7 wt%, or 0.1 - 0.5 wt%, based on the total weight of the yttria-containing zirconia material. In one embodiment, the yttria-containing zirconia material contains aluminum oxide in an amount of 0.1 - 0.4 wt% based on the total weight of the yttria-containing zirconia material. In one embodiment, the yttria-containing zirconia material contains aluminum oxide in an amount of 0.4 - 0.7 wt% based on the total weight of the yttria-containing zirconia material.

[0059] The yttria-containing zirconia material can contain oxides other than zirconia, yttria, hafnia, and aluminum oxide. These other oxides can include colored metal oxides and / or trace components of metal oxides derived from the manufacturing process and / or raw materials of the yttria-containing zirconia material. The amount of the other oxides can vary depending on whether the dental mill blank is a pre-colored dental mill blank. If the dental mill blank is pre-colored, the amount and type of the colored metal oxide can vary depending on the color intended for the dental restoration made using the dental mill blank (e.g., a color that matches the natural color of teeth, and / or a color according to the VITA classical A1-D4® shade guide having VITA Bleached Shades manufactured by Vita Zahnfabrik, or a similar dental shade guide system). The dental mill blank may or may not be pre-colored.

[0060] The yttria-containing zirconia material can contain zirconia, yttria, hafnia, and oxides other than aluminum oxide in amounts of up to 5.0 wt%, up to 4.0 wt%, up to 3.0 wt%, up to 2.0 wt%, up to 1.0 wt%, up to 0.5 wt%, up to 0.3 wt%, up to 0.3 wt%, up to 0.1 wt%, or up to 0.5 wt% based on the total weight of the porous zirconia ceramic material.

[0061] The yttria-containing zirconia material can contain one or more colored metal oxides. Suitable colored metal oxides include, but are not limited to, oxides of Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu, Bi, and any mixture thereof. The one or more colored metal oxides can include iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof, and optionally can additionally contain one or more colored metal oxides.

[0062] The yttria-containing zirconia material can contain one or more colored metal oxides in amounts of at least 0.02 wt%, at least 0.1 wt%, at least 0.2 wt%, up to 2.0 wt%, up to 1.5 wt%, or up to 1.0 wt%, up to 0.5 wt% based on the total weight of the yttria-containing zirconia material. The yttria-containing zirconia material can contain one or more colored metal oxides in amounts in the range of 0.02 - 2.0 wt%, 0.1 - 1.5 wt%, 0.2 - 1.0 wt%, 0.1 - 1.0 wt%, or 0.2 - 1.0 wt% based on the total weight of the yttria-containing zirconia material. The yttria-containing zirconia material can contain a colored metal oxide in an amount less than 0.02 wt%, which is preferably the case when the dental mill blank is not pre-colored.

[0063] The manufacturing process of the yttria-containing zirconia material and / or the trace components of the metal oxide derived from the raw materials can be, but are not limited to, Fe2O3, TiO2, SiO2, CaO, or Na2O.

[0064] The yttria-containing zirconia material can be characterized by the chemical composition described in the following paragraphs. Unless otherwise specified, the weights of the components described are selected so that the total is 100.0% by weight. The weights of the components of the described yttria-containing zirconia material are based on the total weight of the yttria-containing zirconia material. When the dental mill blank is composed of the yttria-containing zirconia material, the total weight of the yttria-containing material can be regarded as equivalent to the total weight of the dental mill blank.

[0065] The yttria-containing zirconia material has a total amount of zirconia and hafnia of 90.0 to 98.5% by weight, preferably 91.0 to 98.0% by weight, for example 93.0 to 97.7% by weight, yttria of 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight, aluminum oxide of 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), and other oxides of 0.0 to 5.0% by weight, preferably 0.0 to 4.5% by weight, for example 0.0 to 3.0% by weight, optionally one or more colored metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof.

[0066] The yttria-containing zirconia material has zirconia of 85.0 to 98.5% by weight, preferably 87.0 to 97.5% by weight, for example 90.0 to 96.7% by weight, hafnia of 0.0 to 5.0% by weight, preferably 0.5 to 4.0% by weight, for example 1.0 to 3.0% by weight, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), and 0.0 to 5.0% by weight, preferably 0.0 to 4.5% by weight, for example 0.0 to 3.0% by weight of other oxides, optionally one or more coloring metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof.

[0067] The yttria-containing zirconia material 90.0 to 98.5% by weight, preferably 91.0 to 98.0% by weight, for example 93.0 to 97.7% by weight of the total amount of zirconia and hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of one or more coloring metal oxides selected from the group consisting of iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, and any combination thereof, and 0.0 to 3.0% by weight, preferably 0.0 to 2.5% by weight, for example 0.0 to 2.0% by weight of other oxides (which may additionally contain coloring metal oxides not part of the defined group of coloring metal oxides).

[0068] The yttria-containing zirconia material 85.0 to 98.5% by weight, preferably 87.0 to 97.5% by weight, for example 90.0 to 96.7% by weight of zirconia, 0.0 to 5.0% by weight, preferably 0.5 to 4.0% by weight, for example 1.0 to 3.0% by weight of hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of one or more colored metal oxides selected from the group consisting of iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, and any combination thereof, and 0.0 to 3.0% by weight, preferably 0.0 to 2.5% by weight, for example 0.0 to 2.0% by weight of other oxides (which may additionally contain colored metal oxides not part of the defined group of colored metal oxides) can be included.

[0069] According to one embodiment, the yttria-containing zirconia material is 93.0 to 98.5% by weight, preferably 94.0 to 98.0% by weight, for example 95.0 to 97.7% by weight of the total amount of zirconia and hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), and 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of other oxides, optionally one or more colored metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof.

[0070] According to one embodiment, the yttria-containing zirconia material is 88.0 to 98.5% by weight, preferably 90.0 to 97.5% by weight, for example 92.0 to 96.7% by weight of zirconia, 0.0 to 5.0% by weight, preferably 0.5 to 4.0% by weight, for example 1.0 to 3.0% by weight of hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), and 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of other oxides, optionally one or more colored metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof.

[0071] According to one embodiment, the yttria-containing zirconia material is 93.0 to 98.5% by weight, preferably 94.0 to 98.0% by weight, for example 95.0 to 97.7% by weight of the total amount of zirconia and hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of one or more colored metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof, and Optionally, it contains less than 0.2% by weight of other oxides (for example, TiO2, SiO2, CaO, and / or Na2O).

[0072] According to one embodiment, the yttria-containing zirconia material is 88.0 to 98.5% by weight, preferably 90.0 to 97.5% by weight, for example 92.0 to 96.7% by weight of zirconia, 0.0 to 5.0% by weight, preferably 0.5 to 4.0% by weight, for example 1.0 to 3.0% by weight of hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of one or more coloring metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof, and Optionally, contains less than 0.2% by weight of other oxides (for example, TiO2, SiO2, CaO, and / or Na2O).

[0073] According to one embodiment, the yttria-containing zirconia material is 95.0 to 98.5% by weight, preferably 95.5 to 98.0% by weight, for example 96.0 to 97.7% by weight of the total amount of zirconia and hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight of aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight), and Optionally, contains less than 0.2% by weight of other oxides (for example, Fe2O3, TiO2, SiO2, CaO, and / or Na2O).

[0074] According to one embodiment, the yttria-containing zirconia material is 90.0 to 98.5% by weight, preferably 91.5 to 97.5% by weight, for example 93.0 to 96.7% by weight of zirconia, 0.0 to 5.0 wt%, preferably 0.5 to 4.0 wt%, for example 1.0 to 3.0 wt% of hafnia, 1.5 to 4.0 wt%, preferably 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.0 to 1.0 wt%, preferably 0.0 to 0.7 wt%, for example 0.1 to 0.7 wt% of aluminum oxide, and optionally, less than 0.2 wt% of other oxides (e.g., Fe2O3, TiO2, SiO2, CaO, and / or Na2O).

[0075] According to one embodiment (also referred to herein as "Embodiment P1"), the yttria-containing zirconia material is 95.8 to 97.9 wt%, for example 96.3 to 97.6 wt% of the total amount of zirconia and hafnia, preferably 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, preferably 0.1 to 0.4 wt%, for example 0.2 to 0.3 wt% of aluminum oxide, and optionally, less than 0.1 wt% of other oxides (e.g., Fe2O3, TiO2, SiO2, CaO, and / or Na2O).

[0076] According to one embodiment (also referred to herein as "Embodiment P2"), the yttria-containing zirconia material is preferably 91.5 to 97.1 wt%, for example 93.0 to 96.4 wt% of zirconia, 0.5 to 4.0 wt%, for example 1.0 to 3.0 wt% of hafnia, 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.4 to 0.7 wt%, for example 0.4 to 0.6 wt% of aluminum oxide, and optionally, less than 0.2 wt% of other oxides (e.g., TiO2, SiO2, CaO, and / or Na2O). 2. Structure of Dental Milling Blanks

[0077] The dental mill blank is porous. The dental mill blank can typically be open porous or can have an open porous structure. The density of the dental mill blank can be in the range of at least 45%, for example 45 - 70%, 45 - 60%, or 45 - 55% relative to its theoretical density. The theoretical density of the dental mill blank is about 6.1 g / cm 3 , for example about 6.11 g / cm 3 and can be. The density of the dental mill blank is 2.5 - 4.2 g / cm 3 , 2.6 - 3.8 g / cm 3 , or 2.7 - 3.4 g / cm 3 and can be in the range of.

[0078] The dental mill blank can comprise an yttria-containing zirconia material in an amount of at least 98 wt%, at least 99 wt%, or at least 99.8 wt% based on the total weight of the dental mill blank. The dental mill blank can be composed of, substantially composed of, or consist of an yttria-containing zirconia material. In one embodiment of the present invention, the dental mill blank consists of an yttria-containing zirconia material.

[0079] Alternatively, the dental mill blank may comprise an yttria-containing zirconia material in the form of a sub-part of the dental mill blank. In such an embodiment, the sub-part consists of an yttria-containing zirconia material. When the dental mill blank comprises an yttria-containing zirconia material as a sub-part, the specimens described herein are made from that sub-part. The sub-part of the dental mill blank can be useful for making a sub-part of a dental restoration precursor. The remainder of the dental mill blank can be composed of other materials for making other parts of the dental restoration precursor.

[0080] Dental mill blanks can be characterized by their hardness, such as their white hardness. As used herein, "white hardness" refers to the hardness of the porous dental mill blank before sintering. Thus, when white hardness is defined herein, this refers to the porous dental mill blank before sintering according to one embodiment of the present invention. The white hardness of dental mill blanks is related to their machinability and / or milling properties. The white hardness can be determined in accordance with ISO 14705, in particular ISO 14705:2008, using a test load of 24.5 N (HV2.5). The measurement method is carried out using a test piece obtained by cutting (e.g., milling) a portion from the dental mill blank. The test piece is not sintered to high density and is tested in a porous state. Further details for determining the white hardness of dental mill blanks are described in the "Measurement Method" section of this specification.

[0081] Dental mill blanks can have a white hardness of at least 250 MPa, preferably at least 300 MPa, for example at least 350 MPa or at least 400 MPa. Dental mill blanks can have a white hardness of at most 1000 MPa, at most 900 MPa, or at most 850 MPa. Dental mill blanks can have a white hardness in the range of 250 - 1000 MPa, preferably in the range of 300 - 900 MPa, for example in the range of 350 - 850 MPa, or 400 - 850 MPa. In one embodiment, dental mill blanks have a white hardness in the range of 250 - 550 MPa, for example in the range of 300 - 550 MPa, for example in the range of 350 - 500 MPa. In an alternative embodiment, dental mill blanks have a white hardness in the range of 600 - 1000 MPa, for example in the range of 650 - 950 MPa, for example in the range of 700 - 900 MPa.

[0082] The dental mill blank is not particularly limited in its shape and dimensions as long as it is suitable for use in the production of dental restoration precursors (e.g., using a CAD / CAM process). The dental mill blank can have the form of a rectangular block, disk, cylinder, dental preform (e.g., abutment preform or tooth sector), cone, cone segment, pyramid, or pyramid segment, but is not limited thereto. In one embodiment, the dental mill blank has the form of a disk, cylinder, or rectangular block. For example, the dental mill blank may be a disk having a height in the range of 8 to 30 mm (e.g., about 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 25 mm), for example in the range of 10 to 20 mm and a diameter in the range of 40 to 150 mm, but is not limited thereto. For example, the dental mill blank can have a diameter of about 40 mm and a height in the range of 10 to 20 mm. Other dimensions are also possible.

[0083] The dental mill blank is typically a pre-sintered dental mill blank. The dental mill blank can be obtained by pre-sintering a green body of the dental mill blank at a maximum pre-sintering temperature in the range of at least 600 °C, at least 650 °C, or at least 675 °C, for example in the range of 600 - 800 °C, 650 - 750 °C, or 675 - 725 °C. The maximum pre-sintering temperature can be maintained over a range of 1 to 5 hours, for example in the range of 2 to 3 hours. The green body can be a green body obtained using a compression pressure in the range of 200 - 400 MPa, for example in the range of 300 - 400 MPa (e.g., applied by cold isostatic pressing).

[0084] In one embodiment, a dental mill blank can be obtained by the method for producing a dental mill blank according to the present invention. This method is described in more detail in the following section. II. Method for Producing a Dental Mill Blank

[0085] One aspect of the present invention provides a method for producing a dental mill blank according to an embodiment of the present invention. This method includes the following steps (performed in the order described), namely, - providing zirconia powder; - optionally, treating the zirconia powder with one or more colorants; - compressing the zirconia powder to provide a green body; - pre-sintering the green body to provide a dental mill blank; - optionally, pre-coloring the dental mill blank. This method includes the steps of providing zirconia powder. The zirconia powder can be characterized by the chemical composition described below. Unless otherwise specified, the weights of the components described are selected to total 100.0% by weight and are based on the total weight of the zirconia powder.

[0086] The zirconia powder

[0087] contains a total amount of zirconia and hafnia of 95.0 to 98.5% by weight, preferably 95.5 to 98.0% by weight, for example 96.0 to 97.7% by weight; yttria of 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight; aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight) of 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight; and other oxides (for example, Fe2O3, TiO2, SiO2, CaO, and / or Na2O) of 0.0 to 0.3% by weight, preferably 0.0 to 0.1% by weight, for example 0.0 to 0.05% by weight.

[0088] The zirconia powder contains 90.0 to 98.5% by weight, preferably 91.5 to 97.5% by weight, for example 93.0 to 96.7% by weight of zirconia; 0.0 to 5.0 wt%, preferably 0.5 to 4.0 wt%, for example 1.0 to 3.0 wt% of hafnia, 1.5 to 4.0 wt%, preferably 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.0 to 1.0 wt%, preferably 0.0 to 0.7 wt%, for example 0.1 to 0.7 wt% of aluminum oxide (for example 0.1 to 0.4 wt% or 0.4 to 0.7 wt%), and 0.0 to 0.3 wt%, preferably 0.0 to 0.1 wt%, for example 0.0 to 0.05 wt% of other oxides (for example, Fe2O3, TiO2, SiO2, CaO, or Na2O) can be included.

[0089] In one embodiment, the zirconia powder is 95.5 to 98.0 wt%, for example 96.0 to 97.7 wt% of the total amount of zirconia and hafnia, 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.1 to 0.4 wt%, for example 0.2 to 0.3 wt% of aluminum oxide, and 0.0 to 0.1 wt%, for example 0.0 to 0.05 wt% of other oxides (for example, Fe2O3, TiO2, SiO2, CaO, or Na2O) is included.

[0090] In one embodiment, the zirconia powder is 91.5 to 97.5 wt%, for example 93.0 to 96.7 wt% of zirconia, 0.5 to 4.0 wt%, for example 1.0 to 3.0 wt% of hafnia, 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.4 to 0.7 wt%, for example 0.5 to 0.6 wt% of aluminum oxide, and 0.0 to 0.1 wt%, for example 0.0 to 0.05 wt% of other oxides (for example, Fe2O3, TiO2, SiO2, CaO, or Na2O) is included.

[0091] A person skilled in the art knows how the zirconia powder described in this specification is obtained. The zirconia powder can be obtained, for example, as a commercially available product from Tosoh Corporation in Japan. The zirconia powder can be provided in combination with a binder, particularly an organic binder. However, the zirconia powder can also be provided without an organic binder or a binder. The zirconia powder may be provided in the form of an aqueous suspension.

[0092] The method can include the step of treating the zirconia powder with one or more colorants. Treating the zirconia powder with one or more colorants is optional. In one embodiment, the method does not include the step of treating the zirconia powder with one or more colorants and / or one or more sintering additives before the compression step.

[0093] The method can include treating the zirconia powder with one or more colorants. The colorant can be added in the form of a solution such as an aqueous solution. Such a treatment step is known in the art and is described, for example, in Patent Document 1 (European Patent No. 2707342). Suitable colorants can be polyvalent ions of 3d- and / or 4f-elements in different valence states, such as Fe 3+ , Mn 2+ , Pr 3+ , Tb 3+ , Cr 3+ , Er 3+ , and salts of these compounds (such as nitrates), but are not limited thereto. If the method includes treating the zirconia powder with one or more colorants before the compression step, at the end of the method, the coloring of the dental mill blank can be omitted as further described below. However, if necessary, the two steps can also be combined.

[0094] This method further includes the step of compressing the zirconia powder to provide a green body. The optionally treated zirconia powder can be filled into a mold and then compressed. The compression can be a pressure such as uniaxial pressing, cold isostatic pressing, or a combination of both. Therefore, the compression can include two or more pressing steps. In one embodiment, the compression includes uniaxial pressing followed by cold isostatic pressing. When the zirconia powder is provided in the form of an aqueous suspension, the compression can be performed by appropriate wet pressing techniques such as slip casting and / or pressure filtration. Compression such as uniaxial pressing, cold isostatic pressing, or a combination of both can be carried out using a pressure in the range of 200 - 400 MPa, for example, in the range of 300 - 400 MPa. In one embodiment, the compression includes uniaxial pressing using a pressure in the range of 10 - 150 MPa and subsequent cold isostatic pressing using a pressure in the range of 300 - 400 MPa. The green body can have a density in the range of 2.5 - 4.2 g / cm 3 , 2.6 - 3.8 g / cm 3 , or 2.7 - 3.4 g / cm 3 .

[0095] This method further includes pre-sintering the green body to provide a dental mill blank. The pre-sintering can include debinding of the green body. However, it is also possible to perform thermal debinding in an air furnace before pre-sintering. The pre-sintering can be carried out at a maximum pre-sintering temperature in the range of at least 600°C, at least 650°C, or at least 675°C, for example, in the range of 600 - 800°C, 650 - 750°C, or 675 - 725°C. In one embodiment, the pre-sintering is carried out at a maximum pre-sintering temperature in the range of 600 - 800°C, 650 - 750°C, or 675 - 725°C, in which case the maximum pre-sintering temperature is maintained over a range of 1 - 5 hours, for example, in the range of 2 - 3 hours.

[0096] The method can further include pre-coloring the dental mill blank. The pre-coloring can be performed, for example, by treating the dental mill blank with one or more colorants, such as by immersion or painting. The one or more colorants can be provided in the form of a solution, such as an aqueous solution. Suitable colorants can include polyvalent ions of 3d- and / or 4f-elements in different valence states, such as Fe 3+ 、Mn 2+ 、Pr 3+ 、Tb 3+ 、Cr 3+ 、Er 3+ 、and salts of these compounds (such as nitrates), but are not limited thereto. If the method includes pre-coloring the dental mill blank after pre-sintering, it is possible to omit treating the zirconia powder with the colorant in the previous method step. However, both steps can also be combined.

[0097] The method includes one or more additional method steps that are typical in the art and can be performed before, during, or after the steps described herein. The additional steps can include adjusting the particle size distribution of the zirconia powder (such as by sieving), and / or surface treatment of the green body and / or the dental mill blank (such as by grinding, lapping, or polishing), but are not limited thereto. III. Dental restorations and methods for making dental restorations

[0098] The dental mill blank according to the present invention is useful for making dental restorations. One aspect of the present invention relates to the use of the dental mill blank according to the present invention for making dental restorations. One aspect relates to a method for making a dental restoration using the dental mill blank according to the present invention.

[0099] One aspect relates to a method for producing a dental restoration using a dental mill blank according to the present invention. One aspect of the present invention provides a method for producing a dental restoration. This method includes the following steps (performed in the order described), namely, - machining a dental mill blank according to an embodiment of the present invention to provide a dental restoration precursor; - optionally, surface-treating the dental restoration precursor; - sintering the dental restoration precursor to provide a dental restoration; and includes.

[0100] The method includes machining a dental mill blank according to an embodiment of the present invention to provide a dental restoration precursor. Machining of the dental mill blank can be performed by any conventional method for machining a dental mill blank, typically by a CAD / CAM process. Such methods are known in the art. Machining can include, but is not limited to, cutting, drilling, and / or grinding of the dental mill blank. The dental restoration precursor typically has an open porous structure.

[0101] The method optionally includes surface treatment of the dental restoration precursor, for example, by polishing and / or coloring, or any other optional step for modifying the surface of the dental restoration precursor. Surface treatment can include manual surface treatment of the dental restoration precursor (for example, manual surface polishing using a rotating dental polishing tool). Surface treatment can include coloring of the dental restoration precursor, for example, an infiltration method using a coloring solution (for example, a brush infiltration method). Such coloring steps are known in the art and suitable coloring solutions are commercially available.

[0102] The method includes the step of sintering a dental restoration precursor to provide a dental restoration. Sintering can be carried out by a sintering process for sintering dental restoration precursors, in particular zirconia-based dental restoration precursors, as is known in the art. Suitable sintering furnaces are known to those skilled in the art.

[0103] Sintering can be carried out at a maximum sintering temperature in the range of up to 1350 °C, for example 1200 - 1350 °C. It has been found that dental restorations with good mechanical and optical properties can be obtained using a relatively low maximum sintering temperature in the range of up to 1350 °C, for example 1200 - 1350 °C. This is advantageous in terms of energy consumption and may also be able to shorten the overall sintering time.

[0104] The method can further include additional steps after the sintering step. For example, the method can include coloring and / or glazing of the dental restoration, which are known in the art.

[0105] Another aspect of the present invention provides a dental restoration comprising an yttria-containing zirconia ceramic (or consisting essentially of an yttria-containing zirconia ceramic). The dental restoration can have a desired color. The dental restoration can have a color that matches the Vita classical A1-D4® shade guide of Vita Bleached Shades manufactured by Vita Zahnfabrik. The shade can be, but is not limited to, A1, A2, A3, A3.5, A4, B1, B2, B3, B4, C1, C2, C3, C4, D1, D2, D3, D4, BL1 or BL2. The yttria-containing zirconia ceramic can have specific optical properties such as CIE L * a * b * color values, opacity, translucency, etc. The optical properties are determined in accordance with BS 5612 and / or (CIE L * a * b* It can be determined in accordance with DIN 6174 for determining the color value. The yttria-containing zirconia ceramic has the following CIE L * a * b * color values, that is, L * is in the range of 76 to 96, a * is in the range of (-2) to 6, b * can have color values in the range of 0 to 25. The yttria-containing zirconia ceramic can have a contrast ratio in the range of 70 to 90%, preferably in the range of 72 to 88%, for example, in the range of 74 to 86%.

[0106] The yttria-containing zirconia ceramic preferably contains yttria in an amount in the range of up to 4.0% by weight, more preferably in the range of 1.5 to 4.0% by weight, still more preferably in the range of 2.0 to 3.8% by weight, for example in the range of 2.2 to 3.4% by weight, based on the total weight of the yttria-containing zirconia ceramic. The yttria-containing zirconia ceramic preferably contains zirconia in an amount in the range of 82.0 to 98.5% by weight, preferably in the range of 84.0 to 98.5% by weight, more preferably in the range of 86.0 to 98.0% by weight, for example in the range of 88.0 to 98.0% by weight, 90.0 to 98.0% by weight, 92.0 to 97.0% by weight, or 94.0 to 96.0% by weight, based on the total weight of the yttria-containing zirconia ceramic. The yttria-containing zirconia ceramic can contain hafnia in a weight ratio to zirconia in the range of 0:100 to 5:95, 1:99 to 4:96, 2:98 to 3:97, based on the total weight of the combined amount of hafnia and zirconia in the yttria-containing zirconia ceramic. The yttria-containing zirconia ceramic can contain aluminum oxide in an amount in the range of up to 2.0% by weight, preferably in the range of 0.0 to 1.5% by weight, more preferably in the range of 0.0 to 1.0% by weight, still more preferably in the range of 0.0 to 0.7% by weight, for example in the range of 0.0 to 0.5% by weight, 0.1 to 0.7% by weight, or 0.1 to 0.5% by weight, based on the total weight of the yttria-containing zirconia ceramic. In one embodiment, the yttria-containing zirconia ceramic contains aluminum oxide in an amount in the range of 0.1 to 0.4% by weight based on the total weight of the yttria-containing zirconia ceramic. In one embodiment, the yttria-containing zirconia ceramic contains aluminum oxide in an amount in the range of 0.4 to 0.7% by weight based on the total weight of the yttria-containing zirconia ceramic.

[0107] Yttria-containing zirconia ceramics typically contain colored metal oxides. Suitable colored metal oxides include, but are not limited to, oxides of Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu, Bi, and any mixture thereof. One or more colored metal oxides can include iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof, and optionally can additionally include one or more colored metal oxides. Yttria-containing zirconia ceramics can contain one or more colored metal oxides in an amount in the range of 0.02 to 2.0 wt%, 0.1 to 1.5 wt%, 0.2 to 1.0 wt%, 0.1 to 1.0 wt%, or 0.2 to 1.0 wt% based on the total weight of the yttria-containing zirconia ceramic.

[0108] Yttria-containing zirconia ceramics can contain a total amount of zirconia and hafnia of 90.0 to 98.5 wt%, preferably 91.0 to 98.0 wt% (e.g., 93.0 to 97.7 wt%), 1.5 to 4.0 wt% of yttria, preferably 2.0 to 3.8 wt% (e.g., 2.2 to 3.4 wt%), 0.0 to 1.0 wt%, preferably 0.0 to 0.7 wt% (e.g., 0.1 to 0.4 wt% or 0.4 to 0.7 wt%), 0.0 to 5.0 wt%, preferably 0.0 to 4.5 wt% (e.g., 0.0 to 3.0 wt%) of other oxides, and optionally can include one or more colored metal oxides, optionally including iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof.

[0109] The yttria-containing zirconia ceramic contains 85.0 to 98.5% by weight, preferably 87.0 to 97.5% by weight (for example, 90.0 to 96.7% by weight) of zirconia, 0.0 to 5.0% by weight, preferably 0.5 to 4.0% by weight (for example, 1.0 to 3.0% by weight) of hafnia, 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight (for example, 2.2 to 3.4% by weight) of yttria, 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight (for example, 0.1 to 0.4% by weight or 0.4 to 0.7% by weight) of aluminum oxide, and 0.0 to 5.0% by weight, preferably 0.0 to 4.5% by weight (for example, 0.0 to 3.0% by weight) of other oxides, and optionally contains one or more coloring metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof. The weights of the described components are selected to total 100.0% by weight. The weights of the components of the described yttria-containing zirconia ceramic are based on the total weight of the yttria-containing zirconia ceramic.

[0110] In a further embodiment, the yttria-containing zirconia ceramic can be characterized by any one of the chemical compositions described hereinabove for the yttria-containing zirconia material present in the dental mill blank of the present invention.

[0111] The dental restoration can be a crown, partial crown, abutment, abutment crown, inlay, onlay, veneer, shell, or multi-unit framework, or bridge (for example, a 2-, 3-, or 4-unit bridge), implant bridge, etc., but is not limited thereto.

[0112] In one embodiment of the present invention, there is provided a dental restoration obtained by the method for producing a dental restoration according to one embodiment of the present invention. The dental restoration can be further characterized as defined above herein. IV. Use of Zirconia Powder

[0113] Another aspect of the present invention provides the use of zirconia powder for producing dental mill blanks. In this case, the zirconia powder is a total amount of zirconia and hafnia of 95.0 to 98.5% by weight, preferably 95.5 to 98.0% by weight, for example 96.0 to 97.7% by weight, yttria of 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight, aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight) of 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight, and other oxides (for example, Fe2O3, TiO2, SiO2, CaO, or Na2O) of 0.0 to 0.3% by weight, preferably 0.0 to 0.1% by weight, for example 0.0 to 0.05% by weight. The weights of the described components are selected to total 100.0% by weight and are based on the total weight of the zirconia powder.

[0114] The zirconia powder is zirconia of 90.0 to 98.5% by weight, preferably 91.5 to 97.5% by weight, for example 93.0 to 96.7% by weight, hafnia of 0.0 to 5.0% by weight, preferably 0.5 to 4.0% by weight, for example 1.0 to 3.0% by weight, yttria of 1.5 to 4.0% by weight, preferably 2.0 to 3.8% by weight, for example 2.2 to 3.4% by weight, aluminum oxide (for example 0.1 to 0.4% by weight or 0.4 to 0.7% by weight) of 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight, and can contain other oxides (for example, Fe2O3, TiO2, SiO2, CaO, or Na2O) of 0.0 to 0.3% by weight, preferably 0.0 to 0.1% by weight, for example 0.0 to 0.05% by weight.

[0115] In one embodiment, the zirconia powder is a total amount of zirconia and hafnia of 95.5 to 98.0% by weight, for example 96.0 to 97.7% by weight, 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.1 to 0.4 wt%, for example 0.2 to 0.3 wt% of aluminum oxide, and 0.0 to 0.1 wt%, for example 0.0 to 0.05 wt% of other oxides (e.g., Fe2O3, TiO2, SiO2, CaO, or Na2O).

[0116] In one embodiment, the zirconia powder is 91.5 to 97.5 wt%, for example 93.0 to 96.7 wt% of zirconia, 0.5 to 4.0 wt%, for example 1.0 to 3.0 wt% of hafnia, 2.0 to 3.8 wt%, for example 2.2 to 3.4 wt% of yttria, 0.4 to 0.7 wt%, for example 0.5 to 0.6 wt% of aluminum oxide, and 0.0 to 0.1 wt%, for example 0.0 to 0.05 wt% of other oxides (e.g., Fe2O3, TiO2, SiO2, CaO, or Na2O).

[0117] The zirconia powder can be used to produce a dental mill blank according to an embodiment of the present invention.

[0118] Hereinafter, the present invention will be described by specific examples, but these examples do not limit the present invention in any way. V. Exemplary Section 1. Measurement Method 1.1 Biaxial Bending Strength

[0119] The biaxial flexural strength was determined in accordance with ISO 6872:2008. Each specimen was produced by milling a part from a dental mill blank, followed by high-density sintering of the part in a sintering furnace and surface polishing of the sintered part. Sintering was carried out in a commercially available sintering furnace (Programat S1 1600) with a maximum sintering temperature T(max) of 1250 °C or 1300 °C using the sintering program described in Table 1. The sintered part had the following dimensions, namely, 13 mm (d), 1.2 mm (h), and a chamfer of 0.12 mm. Surface polishing was carried out in two steps, namely, (1) polishing with a diamond disk (particle size 35 μm, 20 N) until the grooves of the milling disappeared, and (2) polishing with a cloth using a diamond suspension (particle size 15 μm; 10 N; 3 x 6 min).

[0120]

Table 1

[0121] The fracture resistance was determined by the indentation fracture (IF) method with a test load of 196.1 N (HV20) in accordance with ISO 14627:2012. Each specimen was produced by milling a part from a dental mill blank, followed by high-density sintering of the part in a sintering furnace and surface treatment of the sintered part. Sintering was carried out in a commercially available sintering furnace (Programat S1 1600) with a maximum sintering temperature T(max) of 1250 °C or 1300 °C using the sintering program described in Table 1. The sintered surface was rough ground / polished in accordance with DIN EN 843‐1:2008‐08. The thickness of the specimen was 2.0 mm.

[0122] Two methods were used to calculate the fracture resistance based on different analyses regarding cracks. · Method A: Transverse cracks in accordance with ISO 14627:2012 · Method B: Radial cracks regarding the Niihara's equation (see Equation (I) below)

Equation

[0123] Analysis of the radial cracks according to Niihara's formula (I) is known to those skilled in the art. For example, refer to Non-Patent Document 1 (D. Munz, T. Fett; Ceramics, “Mechanical Properties, Failure Behaviour, Materials Selection“, 1999, ISBN 3-540-65376-7, Springer Verlag Berlin Heidelberg, pages 34-37). 1.3 Vickers hardness

[0124] The hardness (Vickers hardness) of the dental mill blank before sintering was determined according to ISO 14705:2008 with a test load of 24.5 N (HV2.5). Each test piece was produced by milling a part from the dental mill blank. For that part, no subsequent step for high-density sintering was carried out. 1.4 Vickers hardness

[0125] The Vickers hardness was determined according to ISO 14705:2008 with a test load of 196.1 N (HV20). Each test piece was produced by milling a part from the dental mill blank, then sintering that part at high density in a sintering furnace, and finally surface-treating the sintered part. The sintering was carried out in a commercially available sintering furnace (Programat S1 1600) with a maximum sintering temperature T(max) of 1250 °C or 1300 °C using the sintering program described in Table 1. The sintered surface was rough-ground / polished according to DIN EN 843-1:2008-08. The thickness of the test piece was 2.0 mm. 1.5 CIE L * a * b * Color space and contrast ratio

[0126] CIE color coordinates L* a * b * was determined in accordance with DIN 5033 and DIN 6174, and the light transmittance was determined in accordance with BS 5612. The measurements were performed using a spectrophotometer of the CM-3700d (Konica-Minolta) type. Each test specimen was produced by milling a part from a dental mill blank, followed by high-density sintering of the part in a sintering furnace and surface treatment of the sintered part. The surface treatment was performed by continuously grinding / polishing both sides of the sintered part with diamond particles of decreasing particle size (35 μm diamond disk, 20 N, 2 x 6 min; 9 μm diamond suspension, 10 N, 2-4 x 6 min; 3 μm diamond suspension, 5 N, 2-4 x 6 min; 1 μm diamond suspension, 5 N, 2-4 x 6 min). The thickness of the test specimen was 1.00 ± 0.05 mm.

[0127] The light transmittance was calculated from the CR value determined in accordance with BS 5612 by the following formula, i.e., light transmittance [%] = 100% - CR [%]. 2. Example

[0128] Zirconia powders P1 and P2 were used to produce a dental mill blank according to an embodiment of the present invention. Powder P1 was obtained as a commercial product from Tosoh Corporation, Japan. The properties of powder P1 are shown in Table 2. The properties of powder P2 are shown in Table 3.

[0129] [Table 2]

[0130] [Table 3]

[0131] Zirconia powders P1 and P2 were used to produce dental mill blanks according to an embodiment of the present invention. Powders P1 and P2 were used in a binder-free form or in combination with an organic binder. The dental mill blanks according to the present invention were produced as follows. Powder P1 or powder P2 was pre-pressed axially to form a compact, and then cold isostatic pressing (CIP) was applied to obtain a green body. Subsequently, the green body was subjected to a debinding / pre-sintering step to obtain the dental mill blank according to the present invention. When powders P1 and P2 were used with a binder, (based on the total weight of the powder containing the binder), powder P1 was used in an amount of about 4% by weight with the organic binder, and powder P2 was used in an amount of about 3% by weight with the organic binder. When the powder was used without a binder, about 6% by weight of water was added to the powder to modify the pressing characteristics. No colorant or other additives were added. The pressure and debinding / pre-sintering parameters are shown in Table 4.

[0132]

Table 4

[0133] The white hardness (hardness in a porous material before high-density sintering) of the dental mill blanks of the present invention was determined for various types of dental mill blanks according to the method described in the "Measurement Method" section above and according to the method shown in the following table. The results are shown in Table 5 below.

[0134]

Table 5

[0135] As described in the "Measurement Method" section above, high-density sintered specimens were made from parts of the dental mill blanks, and tests were conducted on the mechanical and optical properties of the yttria-containing zirconia materials of the dental mill blanks according to the present invention. The high-density sintered specimens had the properties shown in Tables 6.1 to 6.4.

[0136]

Table 6

[0137]

Table 7

[0138]

Table 8

[0139]

Table 9

[0140] From the results of Tables 5 and 6, it has been shown that the dental mill blank of the present invention comprises a yttria-containing zirconia material that provides high fracture resistance, along with high biaxial flexural strength and desirable color characteristics, when sintered at high density. Therefore, the dental mill blank of the present invention is suitable for producing dental restorations having high biaxial flexural strength, desirable color characteristics, and high fracture resistance.

[0141] When specimens obtained from the dental mill blank of the present invention were sintered at a maximum sintering temperature of 1350 °C (e.g., 1250 °C and 1300 °C), better material properties were obtained compared to the case where the maximum sintering temperature was 1400 °C or higher.

[0142] Known values of the mechanical properties of specimens obtained from prior art dental mill blanks are shown in Table 7 for reference.

[0143]

Table 10

[0144] As can be seen from the reference data shown in Table 7, the dental mill blank of the present invention is suitable for providing dental restorations with improved mechanical properties. Also, the increase in the fracture resistance of the specimens made from the dental mill blank of the present invention can be seen from the shorter crack length after Vickers indentation shown in the exemplary optical microscope images in FIGS. 1A - 1D as compared to the crack length of the specimens made from the prior art dental mill blanks shown in the exemplary optical microscope images in FIGS. 2A - 2D.

[0145] The dental restoration was obtained by milling a dental restoration precursor from the dental mill blank of the present invention using a CAD / CAM process. The dental restoration precursor was sintered at a high density at a maximum sintering temperature of 1250 °C or 1300 °C. Images of the dental restoration precursor and the dental restoration are shown in FIGS. 3 - 5. In some examples, the dental restoration precursor was colored by the brush infiltration method using a commercially available coloring solution (see FIG. 5). [Related Patent Documents]

Prior Art Documents

Patent Documents

[0146]

Patent Document 1

Non - Patent Documents

[0147]

Non - Patent Document 1

Claims

1. 1. A dental mill blank comprising a yttria-containing zirconia material, the yttria-containing zirconia material comprising: at least 6.0 MPa, as determined on a high density sintered specimen of said yttria-containing zirconia material; * m 1 / 2 and the destruction resistance of a biaxial bending strength of at least 1200 MPa, determined on a dense sintered specimen of said yttria-containing zirconia material; 1. A dental mill blank having a

2. 2. A dental mill blank according to claim 1, wherein the yttria-containing zirconia material comprises yttria in an amount of up to 4.0 wt.%, preferably in the range of 1.5 to 4.0 wt.%, more preferably in the range of 2.0 to 3.8 wt.%, for example in the range of 2.2 to 3.4 wt.%, based on the total weight of the yttria-containing zirconia material.

3. 3. A dental mill blank according to claim 1 or 2, wherein the yttria-containing zirconia material comprises an amount of aluminium oxide of up to 2.0% by weight, preferably in the range of 0.0 to 1.5% by weight, more preferably in the range of 0.0 to 1.0% by weight, even more preferably in the range of 0.0 to 0.7% by weight, for example in the range of 0.0 to 0.5% by weight, 0.1 to 0.4% by weight, or 0.4 to 0.7% by weight, based on the total weight of the yttria-containing zirconia material.

4. 4. The dental mill blank according to claim 1, wherein the yttria-containing zirconia material comprises, based on a total weight of the yttria-containing zirconia material: a combined amount of zirconia and hafnia of 92.5 to 98.5 wt.%, preferably 93.2 to 98.0 wt.%, for example 94.0 to 98.0 wt.%, 1.5 to 4.0 wt. %, preferably 2.0 to 3.8 wt. %, for example 2.2 to 3.4 wt. % yttria; 0.0 to 1.5% by weight, preferably 0.0 to 1.0% by weight, for example 0.1 to 0.7% by weight, of aluminum oxide, and 0.0 to 5.0% by weight, preferably 0.0 to 4.5% by weight, for example 0.0 to 3.0% by weight, of other oxides, optionally with colouring metal oxides; 4. A dental mill blank comprising:

5. 5. The dental mill blank of claim 4, wherein the yttria-containing zirconia material comprises: a combined amount of zirconia and hafnia of 93.0 to 98.5 wt.%, preferably 94.0 to 98.0 wt.%, for example 95.0 to 97.7 wt.%, 1.5 to 4.0 wt. %, preferably 2.0 to 3.8 wt. %, for example 2.2 to 3.4 wt. % yttria; 0.0 to 1.0 wt. %, preferably 0.0 to 0.7 wt. %, for example 0.1 to 0.7 wt. % aluminum oxide (for example 0.1 to 0.4 wt. % or 0.4 to 0.7 wt. %), 0.0 to 2.0% by weight, preferably 0.0 to 1.5% by weight, for example 0.0 to 1.0% by weight of one or more coloring metal oxides, optionally iron oxide, erbium oxide, chromium oxide, manganese oxide, terbium oxide, praseodymium oxide, or any combination thereof; and Optionally, less than 0.2 wt. % of other oxides (e.g., TiO 2 , SiO 2 , CaO, and / or Na 2 O), 4. A dental mill blank comprising:

6. 6. The dental mill blank according to claim 1, wherein the yttria-containing zirconia material has a hardness of at least 8.0 MPa as determined on a high density sintered specimen of the yttria-containing zirconia material. * m 1 / 2 , preferably at least 10.0 MPa * m 1 / 2 , e.g. at least 12.0 MPa * m 1 / 2 4. A dental mill blank having a fracture resistance of 0.1 to 0.2 mm.

7. 7. A dental mill blank according to claim 1 , wherein the yttria-containing zirconia material has a biaxial bending strength of at least 1300 MPa, preferably at least 1350 MPa, for example at least 1400 MPa, determined on a dense sintered specimen of the yttria-containing zirconia material.

8. 8. A dental mill blank according to claim 1, wherein the yttria-containing zirconia material is - a contrast ratio of less than 90%; and / or L * is in the range of 76 to 96, a * is in the range of (-2) to 6, b * is in the range 0 to 25, - CIE L * a * b * having a color value, The contrast ratio and / or the CIE L * a * b * A dental mill blank, wherein the color value is determined on a dense sintered specimen of said yttria-containing zirconia material having a thickness of 1.00 mm ± 0.

05.

9. 9. A dental mill blank according to any one of claims 1 to 8, wherein the yttria-containing zirconia material has a Vickers hardness VH of at least 9 000 MPa, preferably at least 10 000 MPa, for example at least 11 000 MPa, determined on a dense sintered specimen of the yttria-containing zirconia material.

10. 10. A dental mill blank according to claim 1, having a white hardness of at least 250 MPa, preferably at least 300 MPa, such as at least 350 MPa or at least 400 MPa, determined according to ISO 14705 using a test load of 24.5 N.

11. A dental mill blank according to any one of claims 1 to 10, which is made of said yttria-containing zirconia material, or A dental mill blank comprising the yttria-containing zirconia material in the form of a subsection of the dental mill blank.

12. A method for producing a dental mill blank according to any one of claims 1 to 11, comprising: - providing a zirconia powder; - optionally treating said zirconia powder with one or more colorants; - compressing said zirconia powder to obtain a green body; - pre-sintering said green body to obtain a dental mill blank; - optionally pre-coloring said dental mill blank; A method comprising:

13. 13. The method of claim 12, wherein the provided zirconia powder comprises: a combined amount of zirconia and hafnia of 95.0 to 98.5 wt.%, preferably 95.5 to 98.0 wt.%, for example 96.0 to 97.7 wt.%, 1.5 to 4.0 wt. %, preferably 2.0 to 3.8 wt. %, for example 2.2 to 3.4 wt. % yttria; 0.0 to 1.0% by weight, preferably 0.0 to 0.7% by weight, for example 0.1 to 0.7% by weight, of aluminum oxide, and 0.0-0.3 wt. %, preferably 0.0-0.1 wt. %, for example 0.0-0.05 wt. %, of other oxides, based on the total weight of the zirconia powder; A method comprising:

14. 1. A method for making a dental restoration, comprising: - machining a dental mill blank according to any one of claims 1 to 11 to provide a dental restoration precursor, - optionally a surface treatment of said dental restoration precursor, - sintering said dental restoration precursor to provide a dental restoration; A method comprising:

15. 15. The method according to claim 14, wherein sintering of the dental restoration precursor is carried out at a maximum sintering temperature of up to 1350°C, for example in the range of 1200-1350°C.

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