Multi-layer structure

Abstract

The present invention relates to a molded body with a color profile for use in the production of dental restorations obtainable by sintering a press-molded body comprising two or more color-different ceramic powder layers, wherein each powder layer comprises at least 80 wt.% of ZrO2 and is essentially free of iron oxide, characterized in that at least one powder layer comprises terbium oxide (Tb4O7).

Description

[0001] Multi-layer structure

[0002] The present invention relates to a sintered molded body with a color gradient for use in the production of dental restorations, obtainable by sintering a molded body comprising two or more ceramic powder layers of different colors, as well as a method for its production and the use of the molded body for the production of dental restorations.

[0003] Zirconium dioxide ceramics have found their way into dental technology for the fabrication of dental restorations due to their strength and good workability, as well as their controllable translucency properties. ZrO2 ceramics are typically colored by adding coloring oxides, which are sintered together with the zirconium dioxide. To achieve a color gradient that matches the natural tooth color, it is advisable to vary the concentration of the coloring oxides layer by layer and adjust them so that the color gradient is as close as possible to the natural tooth color. A problem with this, however, is that the coloring metal oxides can influence the sintering behavior of zirconium dioxide ceramics. This has been observed particularly with the use of iron oxides. A layered buildup of a zirconium dioxide ceramic in which the iron oxide concentration is varied layer by layer can lead to sintering distortion of the ceramic.This distortion may subsequently require complex adjustment or correction. Furthermore, varying sintering behavior from layer to layer also leads to different hardnesses of the individual layers, which further complicates processing with subtractive materials for the fabrication of dental restorations. Another problem is the sensitivity of ZrO2 ceramics coated with coloring inorganic oxides to sintering times. Rapid sintering at high temperatures often leads to irregularities in color stability and sintering distortion, despite a balanced and adapted sintering material.

[0004] The present invention is therefore based on the object of providing a sintered molded body that solves the aforementioned problems, in particular, can be sintered without distortion over a wide temperature range and, moreover, can be sintered within a short period of time, which significantly reduces production times in dental laboratories and dental practices. Furthermore, an object of the present invention is to provide a ceramic sintered molded body with a color gradient that can be sintered under rapid sintering conditions without adversely affecting the mechanical and optical properties.

[0005] The above-mentioned objects are achieved by a sintered shaped body according to claim 1 of the present invention.

[0006] The present invention, in a first embodiment, relates to a sintered molded body with a color gradient for use in the production of dental restorations, obtainable by sintering a molded body comprising two or more, preferably color-different, ceramic powder layers, wherein each powder layer comprises a) at least 85 wt.% ZrO2 and / or HfO2, b) Y2O3, c) terbium oxide d) TiO2 and e) optionally Er2O3, wherein the weight is based on each powder layer.

[0007] The individual inorganic oxides in the powder layers are typically matched to create a color gradient. It has been shown that certain coloring oxides can negatively influence the sintering behavior, particularly with regard to sintering distortion and color stability during rapid sintering.

[0008] In one embodiment of the present invention, the sintered shaped body according to the invention is substantially free of iron oxide.

[0009] Essentially free of iron oxide in the sense of the present invention means that 0.15 wt.% or less, preferably 0.1 wt.% or less, more preferably less than 0.5 wt.% or less than 0.4 wt.%, particularly preferably less than 0.3 wt.% or less than 0.2 wt.%, particularly preferably less than 0.1 wt.% or less than 0.05 wt.%, especially preferably less than 0.01 wt.% or less than 0.005 wt.%, for example less than 0.001 wt.% or less than 0.0001 wt.%, in each case based on the total weight of the powder layer, is present. In a preferred embodiment, the sintered shaped body is free of iron oxide.

[0010] In a further preferred embodiment of the present invention, the sintered shaped body is substantially free of other, in particular coloring, inorganic oxides.

[0011] Other inorganic oxides within the meaning of the present invention are all inorganic oxides with the exception of zirconium oxide, hafnium oxide, yttrium oxide, aluminum oxide, silicon oxide, terbium oxide, erbium oxide, cobalt oxide, and titanium oxide. Essentially free of other inorganic oxides within the meaning of the present invention means that less than 0.01 wt.%, preferably less than 0.001 wt.%, or less than 0.0001 wt.%, are present, in each case based on the total weight of the powder layer. In a preferred embodiment, the sintered molded body is free of other inorganic oxides.

[0012] It has surprisingly been shown that the use of the combination of terbium oxide and titanium oxide for zirconium dioxide ceramics in the dental field brings considerable advantages, in particular because it opens up the possibility of sintering dental ceramics quickly and without distortion, while at the same time the mechanical and optical properties are not impaired.

[0013] Terbium oxide within the meaning of the present invention generally encompasses all terbium oxides. The terbium oxide is preferably selected from the group consisting of Tb2O5, Tb4O7, Tb8O12, TbnO2, TbO2, and mixtures thereof.

[0014] Particularly preferred terbium oxide is selected from the group consisting of Tb4Ü7, Tb7Üi2, Tbn02o and any mixtures thereof.

[0015] The terbium oxide is especially preferably present as Tb4Ü7 or as a mixture of Tb4Ü7 with Tb70i2 and / or Tbn02o.

[0016] Terbium oxides present in mixed valence are also preferred. The molded body used according to the invention preferably comprises terbium oxide in at least two powder layers, or at least three powder layers, or at least four powder layers, especially five powder layers, or each powder layer in an amount of 0.001 to 0.25 wt. %, preferably 0.002 to 0.19 wt. %, in particular 0.003 to 0.17 wt. %, especially 0.01 to 0.15 wt. %, with the weight data being based in each case on the total weight of the powder layer.

[0017] In a preferred embodiment, the shaped body has a layer-by-layer increase in the amount of terbium oxide, in particular a layer-by-layer increase in the concentration of terbium oxide.

[0018] Surprisingly, it has been shown that the addition of titanium dioxide to the powder layers enables rapid sintering with improved mechanical and optical properties.

[0019] The molded body used according to the invention preferably has titanium dioxide in at least 2 powder layers or at least 3 powder layers or at least 4 powder layers, especially 5 powder layers or each powder layer in an amount of 0.001 to 0.09 wt.%, preferably 0.002 to 0.08 wt.%, or 0.002 to 0.06 wt.%, in particular 0.005 to 0.05 wt.%, wherein the weight data are in each case based on the total weight of the powder layer.

[0020] The interaction of terbium oxide and titanium dioxide in the powder layers contributes advantageously to rapid sintering. The amounts of terbium oxide and titanium dioxide are preferably matched to achieve optimal rapid sintering conditions.

[0021] The molded body used according to the invention therefore preferably has a weight ratio of terbium oxide to titanium oxide of 0.05 to 90, preferably 0.1 to 85, in particular 0.5 to 75 and especially 1 to 60 in at least 2 powder layers or at least 3 powder layers or at least 4 powder layers, especially 5 powder layers or each powder layer.

[0022] It has surprisingly been found that each of the sintered powder layers experiences a substantially equal volume change over a temperature range of 25 to 1650 °C, in particular over a temperature range of 50 to 1600 °C or 900 to 1580 °C and especially over a temperature range of 900 to 1550 °C.

[0023] This is particularly surprising since the constant volume change results in essentially no sintering distortion even under rapid sintering conditions.

[0024] In the sense of the present invention, a substantially equal volume change means that the difference in the volume change at a predetermined temperature in the range from 25 to 1650 °C of 2 layers of the sintered blank according to the invention is a maximum of 1%, preferably a maximum of 0.5%, in particular a maximum of 0.05%.

[0025] This leads to a low sintering distortion for the sintered molded bodies according to the invention.

[0026] In a preferred embodiment of the present invention, at least one powder layer, preferably two or more powder layers, in particular each powder layer, comprises cobalt oxide. Cobalt oxide has proven to be a suitable coloring metal oxide for dental dyes, but without adversely affecting the rapid sintering properties of the articles of the present invention.

[0027] In a further preferred embodiment of the present invention, each powder layer of the molded body has a different concentration of erbium oxide and / or cobalt oxide.

[0028] In a further preferred embodiment of the present invention, the weight ratio of terbium oxide to cobalt oxide in at least one powder layer, preferably in at least 2 or 3 powder layers, in particular in each powder layer is in the range of 80: 1 to 5: 1, preferably 75: 1 to 10: 1 and especially 60: 1 to 15: 1. In particular, good coloring and sintering properties could be achieved with the aforementioned adjusted weight ratios, especially when using Tb4O?.

[0029] In a preferred embodiment, each powder layer comprises exclusively terbium oxide, erbium oxide, and cobalt oxide as coloring metal oxides. Titanium dioxide is not a coloring metal oxide within the meaning of the present invention. In a further embodiment, each powder layer comprises terbium oxide, erbium oxide, and cobalt oxide, but is essentially free of other coloring metal oxides.

[0030] Essentially free of other coloring metal oxides within the meaning of the present invention means that less than 0.01 wt.%, preferably less than 0.001 wt.% or less than 0.0001 wt.%, are present, in each case based on the total weight of the powder layer. In a preferred embodiment, the sintered molded body is free of other coloring metal oxides.

[0031] Preferably, at least one powder layer, particularly preferably 2 or more powder layers, in particular each powder layer, comprises erbium oxide (ErzCh) in an amount of 0 to less than 1 wt.%, in particular from 0.1 to less than 0.9 wt.% or from 0.2 wt.% to 0.8 wt.%, in particular from 0.25 to 0.7 wt.%, especially from 0.3 to 0.6 wt.%, in each case based on the total weight of the constituents of the powder layer.

[0032] Surprisingly, it has been shown that erbium oxide can be used as a coloring metal oxide in these quantities without negatively affecting the sintering properties. At the same time, the presence of erbium oxide positively supports the rapid sintering properties, especially in combination with titanium dioxide and terbium oxide.

[0033] In a further preferred embodiment of the present invention, the weight ratio of erbium oxide to terbium oxide in at least one powder layer, preferably in at least 2 or 3 powder layers, in particular in each powder layer, is in the range from 2.5: 1 to 900: 1, preferably 5: 1 to 750: 1 and especially 8: 1 to 500: 1 or 10: 1 to 250: 1. In particular, good coloring and sintering properties could be achieved with the aforementioned set weight ratios.

[0034] In a further preferred embodiment of the present invention, the weight ratio of erbium oxide to titanium dioxide in at least one powder layer, preferably in at least 2 or 3 powder layers, in particular in each powder layer, is in the range from 1:1 to 900:1, preferably 2:1 to 750:1 and especially 5:1 to 500:1 or 10:1 to 250:1. In particular, good coloring and sintering properties could be achieved with the aforementioned adjusted weight ratios.

[0035] Each powder layer can preferably be produced by mixing base powders. In a preferred embodiment, each powder layer is produced by mixing two or more, preferably three or more, in particular four or more, base powders. Using a limited amount of base powders in different quantities to produce each powder layer has advantages with regard to the compatibility of the individual layers arranged one above the other and their color gradient in the sintered molded body. Suitable base powders can be obtained, for example, from Tosoh.

[0036] The sintered molded bodies of the present invention preferably exhibit a gradual color gradient. In one embodiment of the invention, the blank comprises layers of different colors, and the sintering process creates a gradual color gradient.

[0037] In a preferred embodiment of the present invention, at least 2 or at least 3 or 4, preferably all powder layers have a substantially identical yttrium oxide content or a substantially different yttrium oxide content.

[0038] Substantially identical yttrium oxide content in two or more layers in the sense of the present invention means that the difference within the layers is not more than 0.1 mol%, preferably not more than 0.05 mol%, in particular less than 0.01 mol%.

[0039] In an alternative embodiment of the present invention, the sintered molded body exhibits a translucency gradient. Preferably, the molded body according to the invention exhibits a layer-by-layer increase in the amount of yttrium oxide. This has proven particularly advantageous, as it allows the translucency and, advantageously, also the hardness to be controlled. In a particularly preferred embodiment of the present invention, the difference in the yttrium oxide content between two adjacent layers is at least 0.01 wt. %, particularly preferably at least 0.1 wt. %, especially at least 0.2 or at least 0.3 wt. %, in each case based on the total weight of the powder layer with the higher yttrium oxide content.

[0040] The powder layers used according to the invention preferably each contain less than 0.1 wt.% AI2O3, preferably AI2O3 in an amount of less than 0.06 wt.%, in particular AI2O3 in an amount of 0 to 0.05 wt.%.

[0041] The preferred amount of AI2O3 in the individual powder layers leads to improved stability and strength behavior of the molded bodies according to the invention.

[0042] In a further aspect of the present invention, at least one, preferably at least 2 or at least 3 of the powder layers, in particular all powder layers, comprise Y2O3 and / or Er2O3, preferably in an amount of at least 3 wt.%, in particular of at least 5 wt.% or at least 6 wt.% and in particular of 4.5 to 12 wt.%, especially of 6 to 10 wt.% or 6 to 8.9 wt.%, based on the total weight of the constituents of the powder layer.

[0043] The Y2O3 has a stabilizing function for the zirconium dioxide crystal phases and is not a coloring metal oxide in the sense of the present invention.

[0044] The erbium oxide (Er2O3) has a stabilizing function for the ZrO2 crystal phases and is a coloring metal oxide in the sense of the present invention.

[0045] The powder layers preferably comprise zirconium dioxide and / or HfO2 in an amount of at least 89 wt.%, preferably in an amount of 89 to 98 wt.%, in particular 90 to 96 wt.%, each based on the total weight of the constituents of the powder layer. In a preferred embodiment, the powder layers comprise zirconium dioxide and hafnium dioxide; particularly preferably, the amount of hafnium dioxide is 0.1 to 5 wt.%, especially 0.5 to 2.5 wt.%, based on the total weight of zirconium dioxide and hafnium dioxide.

[0046] In a preferred embodiment of the present invention, the mold body consists of 3 or 4 or in particular 5 different ceramic powder layers.

[0047] In a further preferred embodiment of the present invention, the pressed molded body consists of 5 ceramic powder layers, wherein the first powder layer comprises 5 to 40%, preferably 10 to 35%, particularly preferably 12 to 30% or 14 to 28%, especially 15 to 25%, for example 22 to 28%, the second powder layer 8 to 25%, preferably 10 to 20%, particularly preferably 12 to 18%, the third powder layer 8 to 30%, preferably 10 to 25%, further preferably 12 to 22%, particularly preferably 15 to 20%, the fourth powder layer 5 to 40%, preferably 10 to 35%, particularly preferably 12 to 30% or 14 to 28%, especially 15 to 25%, for example 22 to 28% and the fifth powder layer 15 to 40%, preferably 20 to 35%, especially 22 to 32% of the Total thickness of the powder layers arranged one above the other and with the proviso that the total thickness adds up to 100%.

[0048] The layer sequence from the first to the fifth layer corresponds to the color gradient from the cutting edge (first layer) to the neck (fifth layer).

[0049] In a preferred embodiment, the thickness of the layer for the neck region (e.g. fifth layer) is greater than or equal to the first layer (e.g. first layer).

[0050] In one embodiment of the invention, the sintered molded body is first pre-sintered and processed using subtractive processes, and preferably subsequently finally sintered in a further step. The sintered molded bodies of the present invention are used in particular as dental restorations or for the production of dental restorations.

[0051] In a preferred embodiment, the molded body has organic binders in at least two powder layers, preferably in each powder layer, which are present in particular in an amount of 0.5 to 10 wt.%, especially 1 to 6 wt.%, particularly 2 to 5 wt.%, wherein the weight data are in each case based on the powder layer.

[0052] In a further embodiment of the present invention, at least one powder layer, preferably all powder layers, additionally contain organic components, preferably in an amount of 3-6 wt.%, in particular in an amount of 4-5 wt. Suitable organic components include, in particular, binders and pressing aids, which can be easily removed thermally during the debinding step. Suitable binders for zirconium dioxide sinter powder are known to those skilled in the art. These include, for example, polyvinyl alcohol (PVA).

[0053] In a particularly preferred embodiment of the present invention, the molded body has 2 or more, preferably 3 or more, particularly preferably 4 or more, especially 5 ceramic powder layers, each powder layer comprising a) at least 85 wt.% ZrO2 and / or HfO2, b) 6 to 8.9 wt.% Y2O3, c) 0.003 to 0.17 wt.% terbium oxide d) 0.002 to 0.06 wt.% TiO2 and e) optionally 0 to 0.7 wt.% Er2O3, and f) optionally cobalt oxide, the weight specifications being based in each case on the powder layer.

[0054] The powders preferably have a bulk density below 1.2 g / cm 3 on.

[0055] It has proven advantageous to use powders with an average granule size D50 of 35 pm - 85 pm, preferably 40 pm - 80 pm, and especially 50 pm - 70 pm or 40 pm - 60 pm. The granule powders are measured dry by laser diffraction using a Cilas Granulometer.

[0056] Typically, the inorganic components of the base powder, i.e., after removal of the organic components such as binders, etc., have a particle size D50 of 0.1 to 1 pm, preferably 0.2 pm - 0.8 pm, and especially 0.2 pm - 0.7 pm, as measured by laser diffraction. It has been found that the particle sizes contribute positively to sintering and, in particular, to the color transitions between the individual powder layers.

[0057] The compact to be sintered according to the invention can be obtained by layering two or three, or in particular four or five or more, ceramic powder layers one above the other. The layers can be arranged, for example, in a cylindrical container to form discs or disks. Typically, the powder layers can be uniaxially compressed after each layer application. This can be done, for example, using a press die, although this only results in pre-consolidation. The uniaxial compression of the layers perpendicular to the layer surface is preferably carried out at a pressure of 10-20 MPa, in particular 12-15 MPa.

[0058] In a further preferred embodiment, the pressing of the ceramic powder layers arranged one above the other to form a molded body is carried out by pressing initially uniaxially and perpendicular to the layer surface, preferably forming a pre-compacted molded body with a density below 2.8 g / cm 3 , preferably with a density in the range of 2.5 - 2.7 g / cm 3 , e.g. 2.65 g / cm 3 Uniaxial pre-compaction can lead to better and more intimate mixing and thus a smooth transition between the layers.

[0059] In a further preferred embodiment, the pressing to produce the molded body is carried out isostatically, wherein the isostatic pressing preferably takes place after a uniaxial pre-compaction, forming a molded body with a density below 3.4 g / cm 3 , in particular a density of 2.80 - 3.3 g / cm3 , specifically with a density of 2.85

[0060] - 3.25 g / cm 3 Isostatic pressing is preferably performed after all layers of the molded body have been arranged. Suitable pressures for isostatic pressing are usually in the range of 500–10,000 bar, preferably in the range of 800–8,000 bar, for example, 1,000–7,000 bar, or 1,000–3,000 bar.

[0061] The thicknesses of the individual powder layers of the molded body can vary. In a preferred embodiment, at least two of the ceramic powder layers differ in thickness. Preferably, at least two of the ceramic powder layers of the molded body have a thickness difference of at least 5%. Typically, the molded bodies can be in the form of cylindrical, circular discs with diameters in the range of 50 to 200 mm, for example 75 to 150 mm. The total thickness of the cylindrical discs can, for example, be in the range of 8 to 40 mm, preferably 10 to 30 mm, especially 13 to 25 mm. The dimensions refer to the molded body in the unsintered state.

[0062] With regard to color design and subsequent processing, it has proven advantageous that at least one of the outer ceramic powder layers, preferably both outer ceramic powder layers of the molded body, has / have a greater thickness than a ceramic powder layer located between the outer ceramic powder layers. Particularly when using the ceramic molded bodies produced according to the invention for the production of dental restorations, the previously described layer structure with at least one thicker outer layer has proven advantageous, as this represents a suitable structure for processing in CAD / CAM systems or other subtractive processing methods.

[0063] In a particularly preferred embodiment of the present invention, the molded body comprises five ceramic powder layers, wherein the first powder layer comprises 10 - 30%, preferably 22 - 28%, the second powder layer comprises 10 - 20%, preferably 12 - 18%, the third powder layer comprises 10 - 30%, preferably 17

[0064] - 23%, the fourth powder layer 10 - 20%, preferably 12 - 18% and the fifth powder layer 20 - 40%, preferably 22 - 28% of the total thickness of the superimposed powder layers and with the proviso that the total thickness adds up to 100%.

[0065] In a further embodiment of the present invention, sintering takes place at a temperature in the range of 950–1100°C, preferably 980–1050°C, to form a pre-sintered ceramic molded body (white body). Typically, sintering takes place over a period of time sufficient to remove the existing binders and impart sufficient strength to the molded body for processing by subtractive processes. The pre-sintered and debindered molded bodies are referred to as white bodies.

[0066] In one embodiment, the sintering to produce the white body takes place over a period of time above 30 minutes, preferably above 1 hour, in particular above 20 hours or above 50 hours, for example 60 to 200 hours or 70 to 150 hours.

[0067] Especially for the production of ceramic dental restorations, it is advisable to process the pre-sintered ceramic molding using subtractive processes and then, preferably, to undergo final sintering in a further step. When using subtractive processes, sintering shrinkage is usually taken into account.

[0068] The final sintering usually takes place at temperatures above 1350 °C, preferably above 1400 °C, especially in the range of 1420 °C to 1600 °C or 1450 °C to 1590 °C or 1480 to 1580 °C.

[0069] The sintering time for the final sintering usually takes place over a period of more than 4 minutes, preferably more than 5 minutes, in particular in the range of 5 to 120 minutes.

[0070] The shaped bodies according to the invention can be used particularly in the dental field. Here, they are characterized by high edge strength in dental restorations, an excellent microstructure, and high 3-point flexural strength. The ceramic shaped bodies of the present invention are therefore preferably used for dental restorations, such as inlays, onlays, crowns, bridges, or veneers.

[0071] A further object of the present invention is the use of the ceramic molded body according to the invention for dental restorations or for the production of dental restorations.

[0072] A further object of the present invention is the use of a base powder comprising zirconium dioxide and terbium oxide, in particular Tb4Ü7, and yttrium oxide and preferably titanium dioxide for the production of sintering distortion-free ceramic dental restorations, preferably with color gradient.

[0073] The base powder preferably comprises yttrium oxide in an amount of 5 to 10 wt.%, preferably 6 to 9 wt.%, terbium oxide in an amount of 0.1 to 0.4 wt.%, preferably 0.1 to 0.3 wt.% and zirconium dioxide in an amount above 80 wt.%, preferably from 82 wt.% to 94 wt.%, especially 84 wt.% to 90 wt.%, in each case based on the total weight of the base powder.

[0074] The present invention further provides a process for producing the sintered molded body according to the invention with a color gradient, comprising the following steps: a) providing 2 or 3 or 4 or 5 or more, preferably color-different, ceramic powder layers which are arranged one above the other in layers, b) pressing the ceramic powder layers arranged one above the other in layers to form a pressed molded body and c) sintering the molded body obtained in step b) to form a ceramic molded body, wherein the ceramic powder layers each have a different composition from one another and wherein each powder layer comprises a) at least 85% by weight of ZrO2 and / or HfO2, b) Y2O3, c) terbium oxide, d) TiO2 and e) optionally Er2O3, wherein the weight specifications are in each case based on the powder layer.

[0075] Preferred embodiments of the method according to the invention have already been explained above.

[0076] In a preferred embodiment, the pressing is carried out uniaxially and isostatically.

[0077] It is further preferred that step c) comprises a debinding step to form a white body.

[0078] The white body can be processed by subtractive processes and finally sintered in a subsequent step d).

[0079] The process may further comprise a final sintering step d) which is carried out at a temperature of 1500 to 1650°C, preferably 1550 to 1600°C and preferably for a period of less than 30 minutes, preferably less than 20 minutes and especially between 5 and 15 minutes.

[0080] The present invention further provides a sintered molded body with a layered structure and color gradient for use in the production of dental restorations, wherein the molded body comprises at least three different ceramic powder layers, each layer consisting of at least three or four different base powders, each base powder comprising at least 80% by weight of ceramic oxides, the weights being based on the total weight of the base powder. The ceramic powder layers preferably comprise ceramic oxides as defined above. The base powders to be used correspond to the base powders defined above.

[0081] The invention further relates to the use of titanium oxide and terbium oxide for dental ceramics comprising zirconium oxide. Preferred amounts and configurations have been described above.

[0082] Examples:

[0083] Table 1 shows five base powders A to E, which are used for the compositions of the ceramic powder layers. The granule size Dso of the base powders is in the range of 40-80 pm. The inorganic components of the base powders have a particle size Dso of 0.2 to 0.7 pm.

[0084] The weight information refers to the total weight of the powder composition.

[0085] Table 1

[0086] Table 1 (continued)

[0087] The layer arrangements listed in Table 2 below show the composition of each individual ceramic powder layer in the mold. The molds are intended for use in the production of dental restorations, so the layer compositions are designed according to their position in the tooth. The compositions of the powder layers are formed from the base powders by varying the proportions to achieve an ideal color gradient. The composition of each powder layer is achieved by homogeneously mixing the base powders in the specified quantities. The powders are then added layer by layer to a cylindrical mold with a diameter of 100 mm and a layer thickness of 18 mm is set. The powder layers are pre-pressed uniaxially at a pressure of 13 MPa perpendicular to the layer surface and then isostatically pressed at a pressure of 2000 bar.

[0088] Subsequently, debinding takes place at approximately 1000 °C for approximately 100 hours. The resulting white samples are milled into dental restorations using CAD / CAM systems.

[0089] These pre-sintered and processed white pieces are then finally sintered at 1450 °C for a period of 120 minutes.

[0090] Table 2

[0091] In the present example, the ceramic powder layers are arranged such that layer 1 (cutting edge) makes up 25%, layer 2 (dentin / cutting edge) 15%, layer 3 (dentin) 20%, layer 4 (dentin / neck) 15% and layer 5 (neck) 25% of the total thickness of the mold body.

[0092] It has surprisingly been found that, in comparison to iron oxide-containing formulations, which lead to the same color, no sintering distortion could be observed even at higher temperatures. In comparison, sintering distortion was observed in iron oxide-containing formulations known from the prior art. Sintering increases with increasing iron oxide content, so that the Vickers hardness in the white part also increases from light layers (lower iron oxide content) to darker layers (higher iron oxide content). In contrast, the embodiments according to the invention, which are colored with terbium oxide, are distortion-free across all layers and thus the degree of sintering is homogeneous across all layers, which in turn leads to a homogeneous distribution of the Vickers hardness and thus also to consistent machining properties during CAM processing.

[0093] The layer and shade transitions are seamless. The restorations exhibit excellent edge strength and stability. Reworking or readjusting the tooth shade is unnecessary.

[0094] The optimal structure and composition of the layers results in largely homogeneous shrinkage throughout the sintering process. This is particularly advantageous for the precise fabrication of dental restorations, as time-consuming reworking can be largely avoided. Table 3 below shows examples of different VITA classical Al-D4® tooth shades that can be created using the base powders.

[0095] Table 3:

[0096] Regarding the components, the weight quantities listed are determined by the

[0097] Binder and zirconium dioxide are filled to 100 wt.%. The weight percentage of titanium dioxide introduced via base powder D is not listed.

[0098] Table 4: Different tooth colors that can be obtained by mixing base powders. They can serve, for example, as powder coating material for the sintered moldings according to the invention.

[0099] Table 5: Examples of single-layer compositions. The powder layer compositions are obtained by mixing the base powders.

[0100] The powder compositions for the individual powder layers of the sintered molded body according to the invention are obtained by mixing the base powders.

[0101] To produce the multilayer sintered molded body, the layered powder compositions listed in Tables 4 and 5 are pressed in a P / O Weber press (Program No. 22; 100 MPa = 80 kN). The total weight per block is 40 g. The different layers are distributed as shown in Tables 6 and 7:

[0102] Table 6:

[0103] Table 7:

[0104] The density of the pressed blanks is 3.08 g / cm 3 .

[0105] The blanks produced in Tables 6 and 7 are then debound. Debounding takes place in a Thermo-STAR furnace. Debounding or sintering of the blocks is carried out using the following debounding program (approximately 20 h). Tmax = 1040°C.

[0106] The white density of the debound green compacts is 3.17 g / cm 3 .

[0107] The Vickers hardness of the white specimens was determined using a Zwick hardness testing machine. The hardness on the top and bottom surfaces was determined by six measurements and averaging (test load 19.61 N; load level HV 2; waiting time at the load point: 20 s): Vickers hardness HV 2 (top surface): 55.3 Vickers hardness HV 2 (bottom surface): 55.0

[0108] Two anterior crowns are milled from the white block and then finally sintered. The crowns are first heated to 1450 °C and held there for 2 hours and then continuously cooled to room temperature.

[0109] The Vickers hardness of the sintered bodies according to the invention is particularly surprising. While the Vickers hardness of the pre-sintered blank (white body) with non-inventive sintered bodies increases with increasing FeZCh content, the Vickers hardness of the sintered bodies according to the invention remains unchanged at approximately 55 HV 2 across the entire block. Furthermore, the sintered bodies according to the invention demonstrated rapid sintering. Aesthetically, the variant with the higher yttrium content (Table 5) in the cutting edge (base powder E) offers slightly higher translucency along the cutting edge.

[0110] Rapid sintering test and flexural strength

[0111] A) Comparison example

[0112] Three-point flexural strength of a white material with different Y2O3 contents, adjusted by mixing the pure, white base powders A and E (see Table 1). The blocks were produced on a pilot plant (P / O-Weber PW40E+Pressys). Pre-sintering took place at 1040°C. All samples were flash sintered in an induction furnace (14:48 minutes total time, Tmax: 1580°C, holding time at Tmax: 270 s).

[0113] Table 8:

[0114] B) Comparison example

[0115] 3-point flexural strength of a white material with different Y2O3 contents, adjusted by mixing the pure, white base powders A and E (see Table 1). The blocks were produced on a pilot plant (Osterwalder CA-NC 250). Pre-sintering took place at 1065°C. All samples were flash sintered in an induction furnace (total time: 14:48 minutes, Tmax: 1580°C, holding time at Tmax: 270 s).

[0116] Table 9:

[0117] C) Example according to the invention

[0118] 3-point flexural strength of a tooth-colored material with different Y2O3 contents, adjusted by mixing the base powders A to E (Table 1). The mixtures are shown in Tables 10 and 11 below. The blocks were produced on a pilot plant (Osterwalder CA-NC 250). Pre-sintering took place at 1045°C. All samples were flash sintered in an induction furnace (total duration: 14:48 minutes, Tmax: 1580°C, holding time at Tmax: 270 s). Samples A were prepared from the outermost incisal layer, and samples B from the outermost neck layer. The flexural strength data are shown in Table 12.

[0119] Table 10:

[0120] Table 11:

[0121] Table 12:

[0122] Surprisingly, the compositions according to the invention exhibit no sintering distortion even with faster sintering, and the strength values ​​are within an excellent range. D) Translucency measurements

[0123] The transmittances were measured on molded articles according to the invention with different YzCh contents, which were adjusted by mixing the base powders A to E. The platelets were produced on a pilot plant (Maassen MP250M). Pre-sintering took place at 1040°C. The samples were densely sintered in several furnaces using different programs:

[0124] Program 1 : Tmax: 1450°C, holding time at Tmax: 120 minutes, total duration: 7 hours

[0125] Program 2: Tmax: 1530°C, holding time at Tmax: 120 minutes, total duration: 5 hours

[0126] Program 3: Tmax: 1510°C, holding time at Tmax: 30 minutes, total time: 1 hour

[0127] Program 4: Tmax: 1580°C, holding time at Tmax: 450s, total time: 23:52 minutes

[0128] Program 5: Tmax: 1580°C, holding time at Tmax: 270s, total time: 18:48 minutes

[0129] Program 6: Tmax: 1580°C, holding time at Tmax: 270s, total time: 14:48 minutes

[0130] All programs, including the very short 14-minute program, exhibit translucency gradients. This is even most pronounced in program 6.

Claims

Claims 1. Sintered molded body with color gradient for use in the production of dental restorations obtainable by sintering a molded body comprising 2 or more, preferably color-different, ceramic powder layers, wherein each powder layer comprises a) at least 85 wt.% ZrO2 and / or HfO2, b) Y2O3, c) terbium oxide, d) TiO2 and e) optionally Er2O3, wherein the weight is based on each powder layer.

2. Sintered shaped body according to claim 1, characterized in that at least one powder layer, preferably each powder layer, is substantially free of iron oxide.

3. Sintered shaped body according to one of the preceding claims, characterized in that each powder layer has a different concentration of erbium oxide and / or cobalt oxide.

4. Sintered shaped body according to one or more of the preceding claims, characterized in that the blank has layers of different colors and a gradual color gradient is created by the sintering process.

5. Sintered shaped body according to one or more of the preceding claims, characterized in that the shaped body has a translucency gradient, preferably a layer-by-layer increase in the amount of yttrium oxide.

6. Sintered shaped body according to one or more of the preceding claims, characterized in that it has at least one, preferably at least 2 or at least 3 of the powder layers, in particular all powder layers ErzCh, preferably in an amount of 0 to less than 1 wt.%, in particular from 0.1 to less than 0.9 wt.% or from 0.2 wt.% to 0.8, in particular from 0.25 to 0.7 wt.%, especially from 0.3 to 0.6 wt.% based on the total weight of the constituents of the powder layer.

7. Sintered molded body according to one or more of the preceding claims, characterized in that the molded body consists of 4 or more powder layers, preferably 5 ceramic powder layers.

8. Sintered shaped body according to one or more of the preceding claims, characterized in that a pre-sintered ceramic shaped body is processed by subtractive processes and is preferably subsequently finally sintered in a further step.

9. Sintered molded body according to one or more of the preceding claims, characterized in that the molded body has terbium oxide in at least 2 powder layers, preferably in each powder layer in an amount of 0.001 to 0.25 wt.%, preferably from 0.002 to 0.19 wt.%, in particular from 0.003 to 0.17 wt.%, especially 0.01 to 0.15 wt.%, wherein the weight specifications (wt.%) are in each case based on the total weight of the powder layer.

10. Sintered molded body according to one or more of the preceding claims, characterized in that the molded body has titanium dioxide in at least 2 powder layers, preferably in each powder layer in an amount of 0.001 to 0.09 wt.%, preferably from 0.002 to 0.08 wt.%, or 0.002 to 0.06 wt.%, in particular from 0.005 to 0.05 wt.%, wherein the weight specifications (wt.%) are in each case based on the total weight of the powder layer.

11. Sintered molded body according to one or more of the preceding claims, characterized in that the molded body has a weight ratio of terbium oxide to titanium oxide of 0.05 to 90, preferably 0.1 to 85, in particular 0.5 to 75 and especially 1 to 60 in at least 2 powder layers, preferably in each powder layer.

12. Sintered shaped body according to one or more of the preceding claims, characterized in that the molded body has 2 or more, preferably 3 or more, particularly preferably 4 or more, especially 5 ceramic powder layers, each powder layer comprising a) at least 85 wt.% ZrO2 and / or HfO2, b) 6 to 8.9 wt.% Y2O3, c) 0.003 to 0.17 wt.% terbium oxide d) 0.002 to 0.06 wt.% TiO2 and e) optionally 0 to 0.7 wt.% Er2O3, and f) optionally cobalt oxide, the weight specifications being in each case based on the powder layer.

13. Use of the shaped body according to one of the preceding claims for dental restorations or for the production of dental restorations.

14. A method for producing a sintered shaped body with a color gradient according to one of claims 1 to 12, comprising the following steps: a) providing 2 or 3 or 4 or 5 or more, preferably color-different, ceramic powder layers arranged one above the other in layers, b) pressing the ceramic powder layers arranged one above the other in layers to form a pressed shaped body, and c) sintering the shaped body obtained in step b) to form a ceramic shaped body, wherein the ceramic powder layers each have a different composition from one another and wherein each powder layer i) at least 85 wt.% ZrO2 and / or HfO2, ii) Y2O3, Hi) terbium oxide, iv) TiO2 and v) optionally Er2O3, the weights being based on the powder layer.

15. A process according to claim 14 comprising a final sintering step d) which is carried out at a temperature of 1500 to 1650°C, preferably 1550 to 1600°C and preferably over a period of less than 30 minutes, preferably less than 20 minutes and especially between 5 and 15 minutes.

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