Multicolored Zirconium Oxide Blanks for Dental Prostheses

Abstract

The invention relates to a blank for a dental prosthesis having a first layer based on zirconium oxide ceramic and a second layer based on zirconium oxide ceramic, the first and second layers being different in color and forming a boundary surface which is formed in the direction of progression of the dental arch in an undulating shape with alternating wave troughs and crests, the crest lines of the crests extending radially in the mesio-distal direction when viewed in a plan view of the boundary surface. The second layer has a continuous or discontinuous color gradient.

Description

[Technical field]

[0001] The present invention relates to a blank for dental purposes, in particular for the production of dental restorations such as dental prostheses, by means of which the optical properties of natural tooth material and of the natural oral mucosa can be imitated very well, which due to its properties is particularly suitable for the simple production of aesthetically refined dental prostheses, such as maxillary and / or mandibular complete dentures, and is accompanied by very good mechanical properties. [Background technology]

[0002] In dentistry, composite and somewhat wide implant-supported restorations are increasingly being fabricated these days for the treatment of patients in the mandible and maxilla. In addition to the dental esthetics, the color match of the transition to the oral mucosa (gingiva) and the optimal color imitation of the real oral mucosa play an essential role for the overall esthetic result. However, a high degree of manual effort is required to restore the gingival area in a lifelike manner.

[0003] In the past, complete dentures were usually fabricated by making a silicone impression of the patient's edentulous jaw, processing a plaster model on this basis, setting the artificial dentition on the plaster model with the aid of a wax plate, performing a try-in on the patient and, if necessary, post-corrections, embedding the artificial teeth, the wax model and parts of the plaster model in plaster, melting the wax, filling the resulting cavity with a PMMA-based denture material, removing the plaster embedment and performing final cleaning and surface polishing. This procedure usually produces very good results, but is very time-consuming and labor-intensive.

[0004] Multicolored blocks simulating a gradient of color and translucency from dentin to enamel, as well as their use in dental technology, are known from the prior art. Zirconium oxide ceramic-based blanks and their use for the manufacture of dental prostheses in CAD / CAM processes with computer-controlled milling machines are also already known from the prior art. However, even when using such blanks, a high degree of manual effort is required to restore the gingival area in a lifelike manner. This is mainly due to the fact that, according to the first alternative, for example, gingival-colored pressed ingots are used to produce ZrO 2 This is due to the fact that the gingival area needs to be subsequently applied by layering or compressing the gingival area over the restoration and recreating it faithful to nature using all-ceramic techniques. It is also possible to layer the gingival area with composite material after completion of the restoration. However, there is a risk of color instability and plaque or malodor formation.

[0005] According to a second alternative, zirconium oxide blanks with preformed gingival areas are used, however, this still requires post-processing to achieve optimal color imitation of the gingiva. When using tooth-colored and pre-shaded zirconium oxide disks with preformed gingival areas, the tooth-colored areas are covered in several steps with glass-ceramic layering, veneering, coloring, and characterization materials. When using uncolored or lightly colored zirconium oxide disks with preformed gingival areas, the problem is currently solved by the fact that ErCl 3 , ErCl 3 6H 2 O, or Er(NO 3 ) 3 5H 2 Water-soluble Er such as O 3+ The solution is to infiltrate the material with a highly concentrated salt-based solution.

[0006] Er 3+The base highly concentrated infiltration solutions have a strongly acidic pH value, often in the range of 1 to 3. For safety reasons, therefore, if used improperly, i.e. without a suitable fume cupboard or proper room ventilation, when opening the container, the user may be burned or may be exposed to HCl or HNO 3 There is a very high risk of inhaling harmful gases / vapors such as fumes. Moreover, such solutions are usually not stable over long periods of time and therefore change their properties over time. Uncontrolled evaporation of the solvent can also lead to changes in concentration over time. Since these solutions usually contain certain organic compounds, uncontrolled complex formation can also occur. In the worst case, this leads to precipitation of certain compounds.

[0007] Infiltration with the staining solution may further result in the staining solution not being homogeneously distributed in the porous zirconium oxide. This may depend on the user as well as on the surface quality of the restoration, such as the degree of dust-freeness and moisture content. Inhomogeneity may have a significant impact on the final result.

[0008] Infiltration in the gingival area also causes changes in the degree of stabilization and phase composition of zirconium oxide after final sintering. During final sintering, Er 3+ The ions are introduced into the zirconium oxide via the Y 3+ In addition to ions, they can be incorporated into the crystalline framework. This in turn leads to overstabilization and associated changes in the phase composition in the infiltrated areas. This results in a deterioration of the mechanical properties, especially the fracture toughness and biaxial strength. Especially in the gingival area, very large masticatory loads are absorbed by the implant-supported restoration, therefore weakening of this area must be avoided.

[0009] Furthermore, higher concentrations of Er 2 O 3 Doping with Er changes the sintering behavior of zirconium oxide. 2 O 3Er acts as a sintering activator and changes the theoretical density of the stabilized zirconium oxide. The total shrinkage of the infiltrated area increases and therefore the expansion factor taken into account when milling the ingot is no longer correct and the accuracy of the fit of the dense sintered restoration is adversely affected. 2 O 3 If it is used only locally to stain the gingival area, the local shrinkage occurs earlier during sintering, i.e. the gingival area is already shrinking, while the restoration in the tooth area shrinks later. This leads to stresses during the sintering process that remain in the overall structure and permanently weaken it. Sudden fractures often occur in the workshop or when the restoration is placed.

[0010] WO 2010 / 057584 A1 proposes a milling block with a pink-colored component and a tooth-colored component, both of which are essentially made of PMMA or (meth)acrylate-based plastics, to simplify the processing of dentures. Furthermore, the use of such a milling block for the processing of maxillary or mandibular complete dentures is described using a CAD / CAM process by using a numerically controlled milling unit.

[0011] WO 2013 / 068124 also describes a milling block with two areas for the production of dental prostheses. The first area has a denture base that is machined to correspond to the shape of the jaw and can be adapted to the individual mucosa of the patient by milling. The second area has non-individualized, pre-machined artificial teeth that are set in a predetermined arrangement and do not require any further finishing. Among other materials, zirconium oxide ceramics are mentioned as material for the first and second areas. However, when using such a milling block, adaptation to the individual patient's situation in the opposing jaw is not possible.

[0012] US 2021 / 0128283 A1 describes a two-color blank for the fabrication of a prosthesis using CAD / CAM, the blank having a lower pink-colored layer for simulating the gingiva and an upper tooth-colored layer for simulating the teeth. In particular, zirconium oxide ceramic is mentioned as the material for the upper and lower layers. The boundary surface between the two layers has a number of convex and concave portions, and thus the upper surface of the gingival layer has an undulating shape. It is thus explained that the natural transition to the gingiva can be particularly easily imitated, and that it is possible to reduce the number of shading correction steps.

[0013] EP 3 064 170 A1 and EP 3 597 143 A1 each disclose a denture blank consisting of a pale orange resin material and a tooth-coloured resin material, in which the interface surface between the materials is undulating when viewed in the direction of the dental arch.

[0014] It is therefore a great challenge to provide blanks that meet the diverse requirements for use in the field of dental technology, in particular for the production of dental prostheses. Such blanks should not only be easy to manufacture, but they should also be easy to form into the desired geometric shape, while still producing a restoration with high strength. Finally, the blanks should result in an appearance close to that of natural tooth material and natural oral mucosa, so that the costly subsequent creation of the desired optical properties of the dental prosthesis can be omitted. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Publication No. 2010 / 057584 [Patent Document 2] International Publication No. 2013 / 068124 [Patent Document 3] U.S. Patent Application Publication No. 2021 / 0128283 Summary of the Invention [Means for solving the problem]

[0016] According to the invention, the problems mentioned above are avoided. The invention is therefore based in particular on the problem of providing a blank which is easy to manufacture and on which the shape of the desired dental restoration can be given by machining in a simple manner and which, after molding, can be converted into a precise and strong dental prosthesis, which blank is able to very well imitate the optical appearance of natural tooth material and of the natural oral mucosa.

[0017] This problem is solved by the blanks according to claims 1 to 18. It is also an object of the present invention to provide a process for preparing the blanks according to claims 19 to 21, a use of the blanks according to claim 22 and a process for preparing dental prostheses according to claims 23 to 25.

[0018] The present invention relates to a dental prosthesis blank, i.e. a dental prosthesis blank, comprising a first layer on a zirconium oxide ceramic base and a second layer on a zirconium oxide ceramic base, the first and second layers being different in color and forming a boundary surface, which is formed in the direction of progression of the dental arch in an undulating shape with alternating wave troughs and crests, characterized in that when viewed in a plan view of the boundary surface, the crest lines of the crests extend radially in a mesial-distal direction.

[0019] The term "based on" refers to the first and second layers of the blank being composed primarily of zirconium oxide, i.e., ZrO, based on the combined weight of all components of the layers. 2 It means that it contains ZrO 2 and a small amount of impurity HfO 2In addition, the first and / or second layer may comprise components for adjusting the color, such as, for example, Fe, Tb, Ce, Pr, Mn, Cr, Ni, Co, Nd, Dy, Eu, Er, V, and / or Ti, and / or components for adjusting the sintering kinetics, such as Mg, Al, Y, Ce, La, Yb, Gd, Ga, and / or In. Furthermore, the first and / or second layer may contain mixtures of zirconium oxide with other ceramics or spinels in the form of composites and / or mixtures of zirconium oxide with pigments.

[0020] Differences in color, in a narrower sense, refer to differences in color shade and / or differences in translucency, opalescence, or fluorescence. The term "translucency" describes the transmittance of light. The color can be characterized, inter alia, by its Lab value or by a shade guide commonly used in the dental industry. Furthermore, the differences in color of the first and second layers in the blank need not be visible to the human eye. Rather, the differences in shade and / or translucency may only become visible after a sintering step or heat treatment. Similarly, the term "color gradient" includes gradients of translucency, opalescence, or fluorescence in addition to gradients of hue.

[0021] The interface surface between the first layer and the second layer is formed in an undulating shape in the direction of progression of the dental arch of the dental prosthesis to be processed. This means that in a side view of a circular arc shape, in particular a parabolic or semicircular cutting surface through the blank, the interface surface between the first layer and the second layer is wave-shaped. For example, if the blank has the shape of a disk, the cutting surface extends from the upper floor surface of the disk to the lower floor surface and is approximately parallel to the outer surface of the disk. The wave shape has alternating wave troughs and wave crests. The wave troughs can also be referred to as grooves or depressions, and the wave crests can also be referred to as ridges or elevations. The peaks of the wave crests and the peaks of the downwardly facing wave troughs also form apex lines, respectively. In other words, the apex of the wave crest or wave trough each forms a line, in particular a straight line. The crests and preferably also the troughs extend from medial to lateral, i.e., from mesial to distal, when viewed from above the boundary surface or floor surface of the blank. The term "undulating" is not used in this context to describe only corrugations that are purely sinusoidal, but generally includes all corrugations with alternating raised and depressed areas.

[0022] Furthermore, the geometry of the interface surface between the first and second layers of the blank is designed in such a way that the interface surface is radially shaped in the mesial-distal direction, i.e. in the top view of the interface surface of the blank, the crest lines of the wave crests extend radially, i.e. outwardly, from the central region of the blank in the form of rays, preferably in the form of straight lines. The three-dimensional undulating radial geometry is preferably based on data from a large number of real patient cases.

[0023] The blank according to the invention is therefore particularly characterized by the fact that the desired color gradient is created with two different color layers and an integrated undulating radial geometry of the layers, so that the color of the teeth and gingiva as well as the progression of the transition from the tooth material to the gingiva can be particularly well imitated in the finished dental prosthesis. The undulating shape of the first layer allows the gingival margin to be reproduced particularly well. Due to the radially extending wave structure, the gingival margin can be created quasi-automatically at all times, regardless of the size of the required dental arch. This represents a particular advantage over the grid-like distribution of convex and concave surfaces known from US 2021 / 0128283 A1.

[0024] Furthermore, the blank according to the invention is characterized by the fact that by using a zirconium oxide ceramic-based layer, high-strength dental restorations can be produced which fully meet the requirements for the mechanical properties of long-term dental restorations, such as prostheses. 2 The use of leads to further advantages: for example, in the case of zirconium oxide ceramics, the blank can be made flatter overall compared to a plastic material-based blank, so that the overall height of the blank can be reduced and machining of the blank in a conventional CAM milling unit can be simplified, for example due to fewer undercuts in the design.

[0025] When using the blank according to the invention, the optical appearance of the natural oral mucosa as well as the natural tooth material can be very well imitated. Moreover, the blank according to the invention can be given the shape of the desired dental prosthesis in a particularly simple manner. Surprisingly, this is achieved by a combination of a special design of the interface surface between the first and second layers and the use of zirconium oxide as the material of the first and second layers. The blank according to the invention enables efficient monolithic processing in the field of digital fixed and conditionally removable prostheses, so that partial or complete prostheses can be processed in one milling process and only a few manual steps. Also, when using the blank according to the invention, subsequent infiltration with a coloring solution in the gingival area, for example after shaping by CAM milling, is not required, which in the past led to frequent cases of failure of the restoration in vivo. This ensures a stress-free monolithic processing and thus a long-term stable restoration.

[0026] In a preferred embodiment of the blank according to the invention, the geometry of the interface surface between the first and second layers of the blank is designed in such a way that the interface surface, when viewed in a top view of the interface surface, is fan-shaped in the mesio-distal direction in the area of ​​the anterior teeth of the prosthesis to be produced. That is to say, in the top view of the interface surface of the blank, the crest lines of the wave crests extend in a fan-shaped manner in a radial direction, i.e. outwardly, from the center point of the partial cross-section of the dental arch to be produced. This means that in the area of ​​the anterior teeth to be produced, the wave crests and preferably also the wave troughs, when viewed in the buccal-vestibular direction, are fan-shaped, i.e. starting from the ray center and extending radially.

[0027] Furthermore, the interface surface between the first layer and the second layer in the area of ​​the molar to be created preferably has radial apex lines of the wave troughs, in particular also the apex lines of the wave troughs and preferably the wave crests, which are approximately parallel to each other when viewed in a top view of the interface surface in the buccal-buccal direction. The expression "approximately parallel" means that the apex lines of the wave troughs and preferably also the wave crests run parallel or deviate from parallelism by up to 10 degrees, in particular by up to 5 degrees. The design of parallel apex lines of the wave troughs in the area of ​​the molar to be created offers the advantage of better esthetics, in particular in the posterior region.

[0028] Overall, the two above-mentioned embodiments of the fan-shaped design of the crest apex line in the anterior region and the parallel design of the trough apex line in the posterior region make it possible to improve both the function and the esthetics of the final dental prosthesis. In particular, it is possible to provide a tooth set suitable for both small and large dental arches. For the large dental arch, the dental arch is milled slightly more radially outward, i.e. displaced in the vestibular direction, and for the small dental arch, it is milled more inward, i.e. displaced in the oral direction. Due to the parallelization of the crests and troughs of the boundary surfaces with respect to the area of ​​the molars according to the invention, a relatively large occlusal surface is also available for the small dental arch according to the invention.

[0029] Thus, in a preferred embodiment, the blank according to the invention can have a fan-shaped wave trough and wave crest with a true ray center in the area of ​​the central incisor to be created. However, this is no longer properly matched by the apex line of the wave crest for the canine to be created. Instead, this apex line is less fan-shaped and more parallel to the adjacent apex line of the lateral incisor. This also applies to the apex line of the first premolar, which again has an even closer parallel direction of progression. The following apex lines, i.e., the apex lines for the second premolar, first molar and second molar, are completely parallel to each other.

[0030] Furthermore, the apex line preferably runs upwards from distal to mesial. The boundary surfaces are therefore preferably arranged obliquely in the ingot. This allows a particularly good imitation of the color and translucency of natural teeth, in particular the anterior teeth.

[0031] In a further preferred embodiment, the second layer of the blank according to the invention has a continuous, i.e. linear, or discontinuous, i.e. non-linear color gradient, which also allows the color and translucency gradients of natural teeth, in particular the anterior teeth, to be particularly well imitated.

[0032] Particularly preferably, the zirconium oxide ceramic of the second layer contains yttrium and the color gradient, in particular the translucency gradient, is preferably formed by a gradient in the amount of yttrium, i.e. by gradually changing the amount of yttrium. The blank thus preferably exhibits a continuous, i.e. linear, or discontinuous, i.e. non-linear gradient in the amount of yttrium. In particular, the yttrium content increases from the interface surface between the first layer and the second layer towards the outer surface of the second layer opposite the interface surface. This increase in the yttrium content can be continuous or gradual.

[0033] In one embodiment, the second layer of the blank according to the invention has at least two discrete layers which differ in their yttrium content.

[0034] Preferably, the second layer comprises an inner layer and an outer layer, the inner layer being adjacent to the interface between the first layer and the second layer, and the outer layer being adjacent to the outer surface of the second layer opposite the interface. The inner layer in particular serves as a so-called dentin layer, i.e. mimics the dentin area of ​​a natural tooth. The outer layer in particular serves as an incisor layer, i.e. mimics the enamel layer of a natural tooth.

[0035] In this embodiment, (a) the inner layer has a yttrium content of 2.0 to 6.0 mol %, in particular 3.0 to 5.0 mol %, (c) it is particularly preferred that the outer layer has a yttrium content of 3.5 to 8.0 mol %, in particular 4.0 to 7.5 mol %, The yttrium content is Y 2 O 3 , ZrO 2 , and HfO 2 For the total amount of substance of Y 2 O 3 It is defined as the ratio of the amounts of substances in a

[0036] Optionally, there is a so-called intermediate layer between the inner layer and the outer layer. If an intermediate layer is present, (a) the inner layer has a yttrium content of 2.0 to 6.0 mol %, in particular 3.0 to 5.0 mol %, (b) the intermediate layer has a yttrium content of 3.0 to 7.0 mol %, in particular 3.5 to 4.5 mol %, (c) it is particularly preferred that the outer layer has a yttrium content of 3.5 to 8.0 mol %, in particular 4.0 to 7.5 mol %, The yttrium content is Y 2 O 3 , ZrO 2 , and HfO 2 For the total amount of substance of Y 2 O 3 It is defined as the ratio of the amounts of substances in a

[0037] Further, the inner layer, the outer layer, and optionally the middle layer are 2 O 3 In addition to these, it is preferred to contain oxides for adjusting the color, in particular the oxides of Fe, Cr, Mn, Tb, Pr, Ce, Ni, Co, Nd, Dy, Eu, Er, V, and / or Ti, and oxides for adjusting the sintering kinetics, in particular the oxides of Mg, La, Al, Ce, Yb, Gd, Ga, and / or In.

[0038] Preferably, the inner layer, the outer layer, and optionally the middle layer further comprise Y 2 O 3In addition to the above, the inner layer, the outer layer, and optionally the intermediate layer further contain an oxide of Y, preferably at least one of the oxides of Fe, Cr, Mn, Tb, and Pr, in order to adjust the color. 2 O 3 In addition, in order to adjust the sintering kinetics, it contains at least one oxide of Mg, La, Y and Al, particularly preferably all oxides of these elements.

[0039] The second layer may preferably comprise at least one, and in particular all, of the following components in the amounts indicated. [Table 1]

[0040] Additionally, the inner layer may comprise at least one, and in particular all, of the following components, preferably in the amounts indicated: [Table 2]

[0041] Additionally, the outer layer may preferably include at least one, and in particular all, of the following components in the amounts indicated: [Table 3]

[0042] Furthermore, the intermediate layer may preferably comprise at least one, and in particular all, of the following components in the amounts indicated: [Table 4]

[0043] The zirconium oxide ceramic of the first layer preferably comprises zirconium oxide stabilized with erbium and / or yttrium. Preferably, the zirconium oxide ceramic of the first layer has an erbium content of 0.0 to 4.5 mol %, in particular 0.5 to 4.25 mol %, particularly preferably 1.5 to 3.5 mol %; the erbium content is preferably Er 2 O 3 , ZrO 2 , and HfO 2 Er for the total amount of substance 2 O 3 Furthermore, the zirconium oxide ceramic of the first layer preferably has an yttrium content of 0.0 to 4.5 mol %, in particular 0.5 to 4.25 mol %, particularly preferably 0.75 to 2.0 mol %. The yttrium content is defined as the ratio of the amounts of substances Y 2 O 3 , ZrO 2 , and HfO 2 Based on the total amount of substance, Y 2 O 3 It is defined as the ratio of the amounts of substance of erbium and yttrium. Furthermore, it is preferred that the sum of the contents of erbium and yttrium is 1.5-6.0 mol%, in particular 2.0-4.5 mol%, more preferably 2.5-4.0 mol%. Since the first layer of the blank serves to form the gingival area of ​​the dental restoration to be machined, the formation of a color gradient or material gradient of yttrium in the first layer is not advantageous. Therefore, the yttrium content in the first layer is preferably approximately constant. Alternatively, the first layer may have a gradient to represent the fixed and mobile gingival.

[0044] The zirconium oxide ceramic of the first layer preferably contains at least one, in particular all, of the following components in the amounts indicated: [Table 5] The first colored oxide is Fe 2 O 3 And, Tb 2 O 3 And,Pr 2O 3 And, V 2 O 5 and the second coloring oxide is selected from the group consisting of Mn 2 O 3 and Cr 2 O 3 and CoO, which are particularly capable of producing an additive grey colouring of the zirconium oxide ceramic.

[0045] In one embodiment, the first layer of the blank preferably comprises a zirconium oxide ceramic or a mixture of zirconium oxide ceramic and one or more materials selected from the group consisting of alumina toughened zirconium oxide (ATZ), zirconium oxide toughened alumina (ZTA), spinel, pigment, or mixtures thereof.

[0046] Alumina-toughened zirconium oxide (ATZ) is made up of 5 to 40% by weight, and more specifically, approximately 20% by weight of Al. 2 O 3 and 60 to 95 wt. %, in particular about 80 wt. % ZrO 2 Includes: Al 2 O 3 The ZrO portion may be doped with MgO, such as 50 ppm to 3% by weight. 2 The portion is 1 to 3 mol % Y 2 O 3 It may be doped with

[0047] Zirconium oxide-toughened alumina (ZTA) is a material containing 60-95% by weight, and more particularly, about 80-90% by weight of Al. 2 O 3 and 5 to 40 wt. %, in particular about 10 to 20 wt. % ZrO 2 Includes: Al 2 O 3 The ZrO portion may be doped with MgO, such as 50 ppm to 3% by weight. 2 The portion is 1 to 3 mol % Y 2 O 3 It may be doped with

[0048] In the mixtures of zirconium oxide ceramics with ATZ and ZTA, discrete Al 2 O 3 and ZrO 2 Crystallites can be detected in the final structure by SEM. In contrast, in current zirconium oxide ceramics for dental applications, Al 2 O 3 Microcrystals cannot usually be detected in the microstructure by SEM. This is probably due to the Al 2 O 2 Due to the smaller amount of ZrO, typically about 0.05-0.1 wt.%, and its homogeneous distribution, the ATZ and ZTA composites can positively affect the mechanical properties of the blanks, in particular increasing both the biaxial strength and the fracture toughness. The increase in fracture toughness is especially due to the ZrO content of the ATZ or ZTA. 2 The content is 1.5 to 2.5 mol%. Y 2 O 3 This is achieved when the material is stabilized by

[0049] LaMg spinel, etc., MgAl 2 O 4 and SrAl 2 O 4 A spinel selected from the group consisting of La spinel, Y spinel and mixtures thereof is particularly suitable as spinel. The spinel can positively influence the mechanical properties of the blank, in particular increasing both the biaxial strength and the fracture toughness. The increase in fracture toughness is especially due to the ZrO of the zirconium oxide ceramic. 2 The portion is 1.5 to 2.5 mol% Y 2 O 3 In composites of zirconium oxide ceramic and spinel, the spinel usually grows in the form of rods, especially at high sintering temperatures, which has a positive effect on the fracture toughness of the composite.

[0050] The second layer of the blank according to the invention is preferably tooth-colored and retains a tooth-color shade even after heat treatment of the blank, while the first layer can be white or pinkish and retain such a shade even after heat treatment. In the case of a first layer with a white-colored shade, it is common to subsequently coat the gingival area after molding and heat treatment in order to mimic as closely as possible the aesthetics of the gingival area in the finished dental restoration. Such a step can be omitted in the case of a first layer with a pre-colored first layer, and thus in this embodiment, for example, easier production of dental prostheses is possible.

[0051] Particularly advantageous are blanks according to the invention, in which the zirconium oxide ceramic of the first layer and the zirconium oxide ceramic of the second layer are pre-sintered. This improves the throughput and precision during subsequent machining for the fabrication of dental restorations. In particular, due to the lower strength of zirconium oxide in the pre-sintered state, a simple, time-saving and easy-to-handle shaping of the blanks with milling tools is made possible. Preferably, the zirconium oxide ceramic of the first layer and the zirconium oxide ceramic of the second layer have a density of 1.8 to 4.4 g / cm. 3 , especially 2.5 to 4.0 g / cm 3 has a density of

[0052] In the case of such pre-sintered blanks, for the processing of dental restorations, it is necessary to expose the blank to a sintering step, i.e. a heat treatment, so that the desired mechanical properties, in particular high strength and hardness, are achieved. During such heat treatment, sintering shrinkage of the zirconium oxide ceramic occurs. Therefore, when using pre-sintered blanks, it is necessary that the undulating radial geometry of the blank according to the invention is enlarged in comparison with blanks based on materials without sintering shrinkage, for example plastic materials. Preferably, in the blank according to the invention in the pre-sintered state, the dimensions of the geometry are increased by a factor of 1.200 to 1.250, in particular by a factor of 1.22 to 1.25. In the case of blanks according to the invention in the green state, the dimensions of the geometry are increased by a factor of 1.250 to 1.350, in particular by a factor of about 1.275.

[0053] The blanks according to the invention preferably have a biaxial crushing strength of 10 to 150 MPa, in particular of 20 to 120 MPa, more preferably of 25 to 80 MPa. The biaxial crushing strength was determined according to ISO 8672 (2008) (piston on three balls test).

[0054] Furthermore, the blank according to the present invention preferably has a Vickers hardness Hv of 50 to 1,000 MPa, particularly 300 to 850 MPa, and more preferably 300 to 700 MPa. 2.5 The Vickers hardness was measured according to ISO 14705:2016 at a load of 2.5 kg.

[0055] Furthermore, the first and second layers of the blank according to the invention are preferably connected to each other by one-piece manufacturing, which allows efficient monolithic production, i.e. the entire patient-specific prosthesis can be produced from one blank in one milling process.

[0056] The shape of the blank according to the invention is preferably at least partially arc-shaped, in particular the blank has the shape of a disk, particularly preferably the shape of a circular disk.

[0057] Furthermore, the arc-shaped blank preferably has a protrusion on the outer circumference, in particular a clamping edge protruding outwardly. This clamping edge serves as a holder in grinding and milling devices, such as common CAD / CAM devices. The protrusion can be made of the same material as the blank. In this case, the blank may first be provided with a larger circumference and the protrusion may be obtainable, for example, by machining on a milling machine. Alternatively, the protrusion can be formed of a different material, for example by a plastic ring that is subsequently applied to the blank.

[0058] Furthermore, the blank according to the invention preferably has at least two markings, grooves and / or flats on the outer circumference, which are arranged asymmetrically and non-rotationally symmetrically with respect to one another, i.e. diametrically opposite to one another, and serve as rotational or anti-rotational protection. The position of the undulating geometric shape in relation to the disk must be known and fixed in all spatial directions, so that the restoration can be placed in relation to the wave shape in a subsequent step for machining.

[0059] The zirconium oxide ceramic-based blank according to the invention is used in particular for fixed prostheses. This means that the blank according to the invention is suitable for the processing of fixed dental prostheses, which are attached to remaining tooth parts, such as implants or tooth stumps, in particular by screwing or bonding. As a result, in the case of the blank according to the invention for the production of maxillary prostheses, a folding palatal plate, which is required for the bonding of the prosthesis to the palate of the patient, can be omitted. This in turn means that the height of the first layer of the blank, which serves to mimic the gingival area, can be reduced. Furthermore, by eliminating the need for a palatal plate, it is not necessary to make the entire first layer pink or to color it in another way. Rather, the inner area, when viewed from above the arc-shaped plate of the blank, can be omitted or left uncolored.

[0060] As a result, in the case of the blank according to the invention, its height can be reduced and thus remains well below 30 mm, which is the critical limit for machining the blank in a commercial dental milling machine. In a preferred embodiment, the height of the blank, i.e. the distance between the arc-shaped top of the blank and the arc-shaped bottom of the opposite side of the blank, does not exceed 30 mm, preferably 20-30 mm, more preferably 25-29 mm. Furthermore, the height of the first layer is preferably 5.0-9.0 mm, in particular 6.0-7.5 mm, particularly preferably about 7.0 mm, and / or the height of the second layer is preferably 15.0-25.0 mm, in particular 18.0-22.0 mm, particularly preferably about 20 mm. The height of the first layer is preferably defined as the minimum distance between the outer surface of the first layer opposite the boundary surface and the deepest wave trough of the first layer in a side view of the outer surface of the disk-shaped blank. The height of the second layer is preferably defined as the minimum distance between the outer surface of the second layer opposite the boundary surface and the highest crest of the second layer in a side view of the outer surface of the disk-shaped blank, as illustrated below as distance 31 in FIG.

[0061] The ratio of the height of the first layer to the height of the second layer is preferably from 1:1 to 1:5, in particular from 1:2.5 to 1:3.5.

[0062] By combining the special wave geometry of the blank according to the invention with the zirconium oxide material to be used, further advantages can be achieved in addition to the reduction in the overall height of the blank. For example, it has surprisingly been found that, compared to denture blanks known in the prior art, it is possible to reduce (i) the angle between the interface surface between the first and second layers and the surface of the blank, and / or (ii) the angle between the crest line of the wave crest of the interface surface and the surface of the blank.

[0063] In a preferred embodiment, which is particularly suitable for the preparation of prostheses in the maxilla, the blank is characterized in that the angle between an imaginary straight line connecting the lowest point of the wave trough for the second molar to be machined with the lowest point of the wave trough for the central incisor to be machined and the projection of this imaginary straight line above the arc-shaped base surface of the blank is 2.0°-4.5°, preferably 2.0°-4.0°, particularly preferably 2.5°-3.5°, most preferably about 3.0°. By using such a small angle, the advantages of the color gradient can be better utilized, especially in the case of blanks with a color gradient in the second layer, and the color and translucency gradient of the anterior and posterior teeth of the prosthesis to be machined can be improved.

[0064] In a further preferred embodiment, the blank is characterized in that the angle between the arc-shaped floor surface of the blank and the crest line of the undulating boundary surface is between 7° and 13°, preferably between 9° and 11°, particularly preferably about 10°.

[0065] In particular, in combination with the reduction in the overall height of the blank, in these embodiments, less undercutting is required, thus reducing the angle of the boundary surface relative to the surface of the blank and / or reducing the angle of the crest line relative to the surface of the blank, leading to easier machinability of the blank in a milling machine.

[0066] The present invention also relates to a process for preparing the blanks according to the invention.

[0067] The process for preparing the blanks according to the invention comprises: (i) first and second substrates are provided, the first substrate being provided to form a first layer of a blank and the second substrate being provided to form a second layer of the blank, a first side of the first substrate having a first layer wave geometry defined by wave troughs and wave crests and a first side of the second substrate having a corresponding inverse wave geometry; (ii) the first and second substrates are placed on top of each other such that the first side of the first substrate and the first side of the second substrate are in close contact with each other over their entire surfaces; (iii) the first and second bodies are compressed together; (iv) at least one heat treatment is performed to convert the zirconium oxide into pre-sintered zirconium oxide.

[0068] Particularly preferably, the first and second green bodies are provided separately in step (i) by filling the zirconium oxide ceramic starting materials for the first and second layers, respectively, into moulds and subsequently compressing the masses, respectively, uniaxially and / or isostatically, the pressure during which is preferably less than 100 MPa.

[0069] Subsequently, the desired shaping of the surfaces of the first and second bodies may be achieved, preferably by milling.

[0070] Furthermore, it is preferred that the first and second bodies are both isobarically compressed in step (iii), in particular at a pressure above 100 MPa, preferably at a pressure of 150 to 1,000 MPa, preferably at a pressure of 150 to 500 MPa.

[0071] Furthermore, in step (iv), the heat treatment is preferably carried out at a temperature of 700 to 1,200° C., preferably at a temperature of 800 to 1,100° C. The duration of the heat treatment in step (iv) may be within a temperature range of 700 to 1,200° C., preferably 800 to 1,100° C., and preferably 5 to 600 minutes, in particular 10 to 300 minutes.

[0072] Due to the described special properties of the blanks according to the invention, they are particularly suitable for the production of dental restorations, in particular dental prostheses. The invention therefore also relates to the use of the blanks according to the invention for the preparation of dental restorations, in particular dental prostheses, which are preferably selected from the group consisting of maxillary complete dentures, mandibular complete dentures, maxillary partial dentures and mandibular partial dentures. In particular, the dental prosthesis may advantageously be an implant restoration. In this case, the interface surface of the dental prosthesis to the implant can be produced directly, so that the dental prosthesis can be connected directly to the implant, for example by a screw connection. Alternatively, the dental prosthesis can be connected, for example by gluing, to a base, for example a base made of titanium, which is then connected to the implant by a screw connection.

[0073] In a further aspect, the present invention also provides a process for preparing a dental restoration comprising the steps of: (i-1) providing a blank according to the invention with the shape of a dental restoration by machining; (i-2) performing at least one heat treatment to convert the zirconium oxide of the first and second layers into dense sintered zirconium oxide; (i-3) optionally finishing the surface of the dental restoration to be obtained; The present invention relates to a process including the steps of:

[0074] Desirably shaped dental restorations, in particular dental prostheses, can be easily machined from the blanks according to the invention.

[0075] The machining in step (i-1) is usually performed by a material removal process, in particular by milling and / or grinding. Preferably, the machining is performed using a computer-controlled milling and / or grinding device. Particularly preferably, the machining is performed as part of a CAD / CAM process.

[0076] In step (i-2), the blank is subjected to a heat treatment, which leads to the formation of a dense sintered zirconium oxide ceramic. The heat treatment is in particular carried out at a temperature of 1,050 to 1,700° C., preferably 1,100 to 1,600° C. The heat treatment is in particular carried out for a duration of 0 to 240 minutes, preferably 5 to 180 minutes, particularly preferably 30 to 120 minutes, the term “duration” referring to the holding time at the maximum temperature.

[0077] The dental restorations produced according to the invention are in particular dental prostheses, particularly preferably selected from the group consisting of maxillary complete dentures, mandibular complete dentures, maxillary partial dentures and mandibular partial dentures.

[0078] In addition to excellent optical properties, the dental prostheses produced according to the invention are characterized in particular by high strength.Preferably, the dental prostheses have a biaxial crushing strength in the gingival area, i.e. in the first layer, according to ISO 6872 (2208) (piston on three ball test) of more than 800 MPa, in particular more than 900 MPa, particularly preferably more than 1,000 MPa.

[0079] Furthermore, in the dentin area, i.e. in the inner layer of the second layer, the dental prosthesis preferably has a biaxial crushing strength according to ISO 6872 (2208) (piston on three ball test) of more than 600 MPa, in particular more than 600 MPa, particularly preferably more than 800 MPa.

[0080] In addition, the dental prosthesis in the incision area, i.e. in the outer layer of the second layer, preferably has a biaxial crush strength according to ISO 6872 (2208) (piston on three ball test) of more than 300 MPa, in particular more than 400 MPa, particularly preferably more than 500 MPa.

[0081] In the optional step (i-3), the surface of the dental restoration can still be finished. In particular, in order to particularly well mimic the shade of the natural oral mucosa, it is possible to cover the gingival area of ​​the dental prosthesis with a white-tinged gingival area, i.e., when using a blank with a white-tinged first layer, with a layering, veneering, staining or characterizing material. Alternatively or additionally, surface polishing of the tooth-like restoration can be performed in step (i-3).

[0082] Further features and advantages will be apparent from the following description of embodiments of the invention, which proceeds with reference to the drawings. [Brief description of the drawings]

[0083] [Figure 1] FIG. 1 is a schematic perspective view of a blank according to the present invention.

[0084] [Diagram 2] FIG. 2 is a schematic top view of the first layer of the blank shown in FIG.

[0085] [Diagram 3] FIG. 3 is a schematic side view of a blank according to the present invention.

[0086] [Figure 4] FIG. 4 is another schematic side view of a blank according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0087] FIG. 1 shows a blank 1 according to the invention for a dental prosthesis for the upper jaw. The basic structure of the blank 1 is disk-shaped. It has a first layer 3 based on zirconium oxide ceramics and a second layer 5 based on zirconium oxide ceramics. The first layer 3 and the second layer 5 are different in color and form a boundary surface 7. In the illustration according to FIG. 1, the upper side of the first layer 3 and the lower side of the second layer 5 represent the boundary surface 7 of the blank. An exemplary schematic progression direction of the dental arch, i.e. the progression direction of the teeth of the denture to be made, is shown as a line 9 in FIG. 1. In the progression direction of the dental arch 9, the boundary surface 7 is formed in an undulating shape with alternating wave troughs 11 and wave crests 13. In the area 15 of the anterior teeth to be made, the wave crests 13 extend in a fan-shaped manner in the oral-vestibular direction. This means that the apex lines of the wave crests 13 extend in a radial shape from the central point 17 of the dental arch 9 in a radial direction, ie outwardly, towards the vestibular side.

[0088] Figure 2 shows a top view of the upper side of the first layer 3 of the blank 1 shown in Figure 1. In the top view, the fan-shaped progression of the wave crests 13, starting from the ray centre 17, can be seen in the anterior tooth region 15.

[0089] 2 also shows that the apex lines of the wave troughs 11 and wave crests 13 in the molar area 19 to be created run approximately parallel in the buccal-buccal direction. As explained above, this parallelization of the wave crests and troughs in the molar area ensures that a relatively large occlusal surface is available in the finished dental prosthesis, even with a small dental arch.

[0090] The blank according to Fig. 2 also has, on its periphery, i.e. on the outer surface 21, three flats 23, which are not arranged rotationally symmetrically with respect to one another. The flats 23 serve as markings in order to define the position of the undulating and radial geometry in the disc in relation to the disc itself, so that the disc can be correctly positioned during the manufacture of the dental prosthesis. The flats 23 therefore serve as rotational or anti-rotational protection during the subsequent milling process.

[0091] The inner area 25 of the first layer 3 represents the area of ​​the prosthesis to be made that will be in contact with the patient's palate, i.e. in the so-called palatal plate, after insertion of the prosthesis. In the case of implant or tooth-root supported dentures, the area 25 can be omitted or left unstained.

[0092] FIG. 3 shows a side view of the blank 1 shown in FIG. 1. The blank has an overall height 27, which in the specific embodiment of the blank shown in the figure is 26.80 mm. The height 29 of the first layer is 6.80 mm and the height 31 of the second layer is 20.00 mm. Compared to plastic material-based blanks known from EP 3 064 170 A1 and EP 3 597 143 A1, in which the heights of the gingival layer and the tooth layer are usually about 19.00 mm, respectively, the overall height of the blank 1 has been significantly reduced and is below the critical limit of 30 mm, which allows easy machining in commercially available dental milling machines. In addition, the tooth layer to gingival layer ratio can be significantly increased, which allows better color and translucency gradients to be achieved.

[0093] Furthermore, the blank 1 according to Fig. 3 is characterized in that the angle 33 between an imaginary straight line 35 connecting the deepest point of the wave trough 11a for the second molar to be produced with the deepest point of the wave trough 11b for the central incisor to be produced and the projection of this imaginary straight line 35 onto the base surface of the blank, in the present case the upper surface 37 of the blank, is 3° and therefore smaller than the corresponding angle in the case of blanks based on plastic material known from EP 3 064 170 A1 and EP 3 597 143 A1, which is usually 5° there. By reducing the angle 33, the color and translucency of the anterior and posterior teeth of the prosthesis to be processed can be further improved.

[0094] Figure 4 shows a further side view of the blank 1 shown in figure 1. The angle 39 between the surface 37 and the apex line of the crest 13a is 10° in the embodiment shown and is therefore significantly smaller than the corresponding angle in plastic material based blanks known from EP 3 064 170 A1 and EP 3 597 143 A1, which is usually 15°. The reduction of the angle 39, like the reduction of the angle 33, leads to easier machining of the blank in a milling machine, since less undercuts are required in these embodiments.

Claims

1. 1. A blank for a dental prosthesis, the blank having a first layer based on zirconium oxide ceramic and a second layer based on zirconium oxide ceramic, the first layer and the second layer being different in color and forming a boundary surface, the boundary surface being formed in an undulating shape with alternating wave troughs and wave crests in the direction of progression of the dental arch, the crest lines of the wave crests extending radially in a mesial-distal direction when viewed in a plan view of the boundary surface.

2. The blank of claim 1 , wherein the second layer has a continuous or discontinuous color gradient.

3. 3. The blank of claim 2, wherein the zirconium oxide ceramic of the second layer includes yttrium, and the color gradient is formed by a gradient of yttrium content.

4. 4. The blank of claim 3, wherein the yttrium content in the second layer increases from the interface surface to an outer surface of the second layer opposite the interface surface.

5. 3. The blank of claim 2, wherein the second layer comprises an inner layer and an outer layer, the inner layer adjacent the interface surface between the first layer and the second layer, and the outer layer adjacent an outer surface of the second layer opposite the interface surface.

6. (a) the inner layer has a yttrium content of 2.0 to 6.0 mol %, preferably 3.0 to 5.0 mol %; (c) the outer layer has a yttrium content of 3.5 to 8.0 mol %, preferably 4.0 to 7.5 mol %; The yttrium content is Y ２ O ３ , ZrO ２ , and HfO ２ Y ２ O ３ 6. The blank of claim 5, wherein the ratio of the amount of material is defined as:

7. 10. The blank of claim 1, wherein the first layer is made from a zirconium oxide ceramic or a mixture of zirconium oxide ceramic with one or more materials selected from the group consisting of alumina-reinforced zirconium oxide, zirconium oxide-reinforced alumina, spinel, pigment, or a mixture thereof.

8. The zirconium oxide ceramic of the first layer contains erbium and / or yttrium, the first layer preferably having an erbium content of 0.0 to 4.5 mol %, in particular 0.5 to 4.25 mol %, particularly preferably 1.5 to 3.5 mol % (the erbium content is Er ２ O ３ , ZrO ２ , and HfO ２ Er ２ O ３ % of Y ) and / or a yttrium content of 0.0 to 4.5 mol %, in particular 0.5 to 4.25 mol %, particularly preferably 0.75 to 2.0 mol %. ２ O ３ , ZrO ２ , and HfO ２ Y ２ O ３ %. The blank according to claim 1, wherein the sum of the erbium and yttrium contents is further particularly preferably 1.5 to 6.0 mol %, in particular 2.0 to 4.5 mol %, particularly preferably 2.5 to 4.0 mol %.

9. A blank as described in claim 1, wherein the first layer is white or pink in color and the second layer is tooth-colored.

10. The zirconium oxide ceramic of the first layer and the zirconium oxide ceramic of the second layer are pre-sintered, and the zirconium oxide ceramic of the first layer and the zirconium oxide ceramic of the second layer, independently of each other, preferably have a density of 1.8 to 4.4 g / cm ３ , particularly 2.5 to 4.0 g / cm ３ The blank of claim 1 having a density of

11. The blank of claim 1 , wherein the first layer and the second layer are connected to one another by integral manufacturing.

12. 2. The blank according to claim 1, which is at least partially arcuate in shape, preferably having the shape of a disk, in particular the shape of a circular disk.

13. 13. The blank of claim 12, wherein protrusions, preferably outwardly projecting pinching edges, are formed on the outer periphery of the blank.

14. 2. The blank of claim 1, wherein the boundary surface has a wave-like apex line in the shape of a fan in the oral-vestibular direction in the region of the anterior teeth to be produced when viewed in a plan view of the boundary surface.

15. 2. The blank of claim 1, wherein the boundary surface has radial apex lines of the wave troughs or apex lines of the wave troughs that are generally parallel to each other in the oral-buccal direction in the region of the molars to be produced when viewed in a plan view of the boundary surface.

16. 13. A blank according to claim 12, wherein the angle between an imaginary straight line connecting the lowest point of the wave valley for the second molar to be produced with the lowest point of the wave valley for the central incisor to be produced and the protrusion of this imaginary straight line above the floor surface of the arc-shaped blank is 2.0° to 4.5°, preferably 2.0° to 4.0°, particularly preferably 2.5° to 3.5°, and most preferably approximately 3.0°.

17. 13. The blank according to claim 12, wherein the height of the blank does not exceed 30 mm, preferably between 20 and 30 mm, more preferably between 25 and 29 mm, and preferably (i) the height of the first layer is between 5.0 and 9.0 mm, in particular between 6.0 and 7.5 mm, more preferably about 7.0 mm, and / or (ii) the height of the second layer is between 15.0 and 25.0 mm, in particular between 18.0 and 22.0 mm, more preferably about 20 mm.

18. 13. The blank according to claim 12, wherein the angle between the floor surface of the arc-shaped blank and the apex line of the wave crest of the undulating boundary surface is between 7° and 13°, preferably between 9° and 11°, and more preferably about 10°.

19. A process for preparing a blank according to any one of claims 1 to 18, comprising the steps of: (i) providing first and second substrates, the first substrate being provided to form the first layer of the blank, the second substrate being provided to form the second layer of the blank, a first side of the first substrate having a wave geometry of the first layer formed by wave troughs and wave crests, and a first side of the second substrate having a corresponding inverse wave geometry; (ii) placing the first and second substrates on top of each other such that the first side of the first substrate and the first side of the second substrate are in close contact with each other over their entire surfaces; (iii) compressing the first and second bodies together; (iv) performing at least one heat treatment to convert said zirconium oxide into pre-sintered zirconium oxide; The process includes:

20. 20. The process of claim 19, wherein in step (iii) the first and second green bodies are isostatically pressed together at a pressure greater than 100 MPa, preferably at a pressure of 150 to 1,000 MPa, preferably 150 to 500 MPa.

21. 20. The process of claim 19, wherein in step (iv), the heat treatment is carried out at a temperature of 700 to 1,200°C, preferably at a temperature of 800 to 1,100°C.

22. 19. Use of the blank according to any one of claims 1 to 18 for preparing a dental restoration, in particular a dental prosthesis, preferably selected from the group consisting of maxillary complete dentures, mandibular complete dentures, maxillary partial dentures and mandibular partial dentures.

23. 1. A process for preparing a dental restoration, comprising: (i-1) providing the shape of the dental restoration to a blank according to any one of claims 1 to 18 by machining; (i-2) performing at least one heat treatment to convert the zirconium oxide of the first and second layers into high-density sintered zirconium oxide; (i-3) optionally finishing the surface of the dental restoration obtained; The process includes:

24. 24. The process of claim 23, wherein the machining is performed using a computer-controlled milling and / or grinding device.

25. 24. The process of claim 23, wherein the dental restoration is selected from the group consisting of a maxillary complete denture, a mandibular complete denture, a maxillary partial denture, and a mandibular partial denture.

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