Method for producing multicolored glass ceramic blanks

Abstract

The invention relates to a method for producing a multicolored glass-ceramic blank for dental use, in which lithium silicate glasses of different compositions are introduced into a mold to form a glass blank, optionally compacted by pressing, the glass blank is subjected to a heat treatment to obtain a glass ceramic blank having lithium silicate as the main crystalline phase, and the glass ceramic blank is compacted by hot pressing.

Description

[0001] This application is a divisional application of the Chinese invention patent application with a priority date of April 4, 2019, an application date of April 1, 2020, an invention name of “Method for Preparing Multicolor Glass-Ceramic Blanks”, and an application number of 202010252700.5. Technical Field

[0002] The invention relates to a method by which multi-colored glass-ceramic blanks can be produced in a simple manner, which can simulate the optical properties of natural tooth material very well and are particularly suitable for the simple production of aesthetically demanding dental restorations with very good optical and mechanical properties. Background Art

[0003] The formation of blanks that meet the various requirements for use in the field of dental technology presents a major challenge. Such blanks should not only be easy to produce, but should also be easy to shape into the desired dental restoration and still produce a high-strength restoration. Finally, the blanks should already have a structure such that the restoration produced from them has optical properties that are very close to those of the natural tooth material, so that subsequent expensive veneering of the restoration can be dispensed with. This is because the color of natural teeth is not uniform, but rather has a complex color, since different areas of the same tooth often differ from one another in their color and their translucency.

[0004] Blanks for use in dental technology are known from the prior art.

[0005] DE10336913A1 describes a blank based on lithium metasilicate glass ceramics, which is made by heat treating a glass blank from a casting starting glass, a so-called solid glass blank or a monolithic glass blank. Therefore, this process is also referred to as "solid glass technology". The blank produced can be machined in a simple manner due to its relatively low strength, and can be converted into a high-strength dental restoration based on lithium metasilicate glass ceramics by further heat treatment. However, the blank produced is only a blank of a single color, and therefore only a dental restoration of a single color is obtained. Therefore, in order to achieve a variety of colors, it is also necessary to carry out expensive subsequent veneer on the prepared dental restoration.

[0006] H. Zhang et al., J. Am. Ceram. Soc. 98; 3659-3662 (2015), describe the preparation of lithium metasilicate glass ceramics by hot pressing a special glass powder at 760° C. for 30 minutes using a pressure of 30 MPa. In this process, surface crystallization apparently occurs mainly, which may be the reason for the low bending strength of the lithium disilicate glass ceramics obtained from this glass ceramic by further heat treatment at 855° C.

[0007] WO2014 / 124879 describes a multi-colored lithium silicate blank having integral layers of different colors. For its preparation, for example, the solid glass layers of different colors are joined to one another by pouring a glass melt of another color onto an existing solid glass layer and then subjecting it to a heat treatment. However, in order to match the optical properties of the natural tooth material to be replaced well, it is necessary to provide a whole series of solid glass layers of different colors, which is very expensive and time-consuming when using the described process. Furthermore, it is not possible to simulate a continuous color gradient in this way. Summary of the invention

[0008] According to the invention, the problems associated with conventional methods are avoided. The object of the invention is in particular to provide a method by which a multi-colored glass-ceramic blank can be produced in a simple manner, by which the optical properties of natural tooth material can be well simulated, which can be given the shape of the final desired dental restoration by mechanical processing in a simple manner and which can be transformed after shaping into a dental restoration having excellent mechanical and optical properties.

[0009] This object is achieved by the method according to claims 1 to 15. The invention also provides a multicolor glass ceramic blank according to claim 16, the use of a glass ceramic blank according to claim 17, and a method for producing a dental restoration according to claims 18 to 21.

[0010] The method according to the invention for producing a multi-color glass-ceramic blank for dental use having lithium silicate as the main crystalline phase is characterized in that:

[0011] (a) introducing (i) lithium silicate glass powders of different colors or (ii) a suspension of lithium silicate glass powders of different colors in a liquid medium into a mold to form a glass blank,

[0012] (b) compacting the glass blank from step (a) optionally by pressing,

[0013] (c) heat treating the glass blank from step (a) or (b) to obtain a glass ceramic blank having lithium silicate as the main crystalline phase, and

[0014] (d) compacting the glass-ceramic green body from step (c) by hot pressing.

[0015] Surprisingly, the method according to the invention enables the production of glass ceramic blanks which can be made multi-colored in a very simple manner and which enable the production of dental restorations which not only simulate the optical properties of natural tooth material and can in particular have a continuous color gradient, but also have excellent mechanical properties.

[0016] The polychromatic nature of the glass-ceramic blank produced according to the invention means that it has regions of different composition which, during the conversion of the blank into the desired dental restoration by heat treatment, produce regions of different colors, making the dental restoration polychromatic. Differences in color also mean differences in translucency, opalescence and / or fluorescence.

[0017] The color can be determined in particular by Lab values ​​or with the aid of color scales customary in dentistry.

[0018] Translucency can be determined according to British Standard BS 5612, inter alia, by the contrast ratio (CR value).

[0019] Opalescence can be determined photometrically, in particular as described in WO 2014 / 209626.

[0020] The fluorescence can be determined in particular by means of a fluorescence spectrometer, for example a fluorescence spectrometer of the type FL1039, using a photomultiplier tube detector of the type PMT 1424M, both from Horiba Jobin Yvon GmbH.

[0021] In step (a) of the method according to the invention, in a first variant (i), lithium silicate glass powders of different colors, or in a second variant (ii), a suspension of lithium silicate glass powders of different colors in a liquid medium, are introduced into a mold to form a glass blank.

[0022] In variants (i) and (ii), powders of different colors are powders of different compositions which, during further processing of the glass ceramic blank produced according to the invention to form a dental restoration, produce areas of different colors in the dental restoration. Such desired polychromatic properties of the dental restoration may in particular be continuously changing colors, such as color gradients and / or translucency gradients. Such color and translucency gradients often occur in natural tooth material, for example between dentin and incisal edge.

[0023] The different colors of the lithium silicate glass powder used in variants (i) and (ii) can be produced by different compositions of the lithium silicate glass or also by mixing additives, such as color components and / or fluorescent components, into the glass. This represents a particular advantage of the method according to the invention, since in this way different colors of the powder can be achieved not only by components of the glass, such as coloring ions, but also by adding pigments, such as coloring pigments and / or fluorescent pigments, to the glass. In contrast, when using so-called solid glass technology, i.e. when using a cast monolithic glass blank, coloring is only possible by ion coloring.

[0024] To prepare lithium silicate glass, a mixture of suitable starting materials, such as a mixture of carbonates, oxides, phosphates and fluorides, is usually first melted at a temperature of, in particular, 1300 to 1600° C. for 1 to 10 hours. The resulting glass melt is then poured into water to produce a glass frit. In order to achieve a particularly high degree of homogeneity, the glass frit can be melted again and the resulting glass melt can be converted into a glass frit again by pouring into water. Finally, the glass frit is crushed into a powder with the desired particle size. Suitable mills for this are, for example, roller mills, ball mills or jet mills. Additives can then also be added to the resulting powder to produce different powders for the first variant (i) and the second variant (ii).

[0025] The powders of the first variant (i) may contain, for example, coloring and / or fluorescent pigments, for example ceramic pigments, pressing agents and, in particular, binders as additives. The binders serve for the cohesion of the powder particles, so that they contribute to obtaining a stable glass blank. Preferred examples of binders are polyvinyl alcohol and cellulose derivatives, for example sodium carboxymethylcellulose. Polyethylene glycol or stearates are preferably used as pressing agents.

[0026] In addition to the lithium silicate glass, the powder of the first variant (i) generally contains up to 10% by weight of additives. As preferred additives, coloring and / or fluorescent pigments are generally used in an amount of 0 to 5% by weight, pressed agents are generally used in an amount of 0 to 3% by weight, preferably 0 to 1% by weight, and binders are generally used in an amount of 0 to 5% by weight, preferably 0.3 to 3% by weight.

[0027] The powder of the suspension used in the second variant (ii) may contain coloring and / or fluorescent pigments as additives, their types and amounts being as previously specified for variant (i).

[0028] To prepare a suspension, these powders are usually suspended in a liquid medium, especially an aqueous medium. The liquid medium preferably contains auxiliaries, such as binders, dispersants, especially in amounts of 0 to 3% by weight, viscosity regulators, especially in amounts of 0 to 3% by weight, and pH regulators, especially in amounts of 0 to 1% by weight, preferably 0.001 to 0.5% by weight.

[0029] Preferred binders are polyvinyl alcohol and cellulose derivatives, such as sodium carboxymethylcellulose. Polymers and lecithin are examples of suitable dispersants. Xanthan gum and starch are examples of suitable viscosity modifiers. Inorganic or organic acids, such as acetic acid and hydrochloric acid are examples of suitable pH modifiers.

[0030] The suspension comprises in particular 30 to 90% by weight and preferably 40 to 70% by weight of powder.

[0031] In step (a) of the process according to the invention, at least two powders of different colors (i) or a suspension (ii) of at least two powders of different colors are used.

[0032] The different powders (i) or the different suspensions (ii) are introduced into the mould in a suitable manner in order to achieve the desired polychromatic properties in the glass ceramic blank and the dental restoration produced therefrom, and in particular to achieve the desired progression of colour, translucency and / or fluorescence. This is generally achieved by introducing the different powders (i) or the different suspensions (ii) into the mould in a controlled manner. For example, by appropriately controlled mixing of the different powders or the different suspensions, a continuous variation of the composition of the mixture introduced into the mould can be achieved, and thus a continuous colour gradient can be produced. For example, two or more different powders can be introduced into the mould, so that initially only the first powder is added and then at least one further powder is gradually added in a steadily increasing proportion.

[0033] In a preferred embodiment of the method according to the invention, the powder (i) or the suspension (ii) is introduced into the mold in such a way that the multi-colored glass ceramic blank produced has a continuously changing color. With such a glass ceramic blank, the color gradient of natural tooth material can be simulated particularly well.

[0034] In a preferred embodiment of the method according to the invention, in step (a), different powders (i) are introduced into a mold and an optional step (b) is carried out. The pressing according to step (b) results in a glass blank having good strength. The pressed glass blank is also referred to as a powder compact, because it consists of pressed powder particles.

[0035] In a further preferred embodiment of the method according to the invention, in step (a), the different suspension (ii) is introduced into the mold and the liquid medium is removed.

[0036] Typically, the glass blank obtained after removal of the liquid medium is further subjected to a drying treatment at 10 to 100° C. A particular advantage of this embodiment is that the glass blank obtained thereafter generally has sufficient strength for further processing even without further compaction by pressing.

[0037] The suspension (ii) is usually introduced into a mold having holes. The introduction is usually carried out by pouring. The holes are openings through which the liquid medium can be at least partially removed from the suspension, with the result that the powder particles can be deposited in the mold and ultimately form a glass blank.

[0038] Typically, substantially all of the liquid medium is removed through the holes. However, it is also possible that residual liquid which has not been removed through the holes is poured or sucked out of the mould. This is usually the case when a sufficiently thick layer of powder particles has been deposited.

[0039] The mold can be, for example, one of the molds commonly used for slip casting or pressure casting processes. These are in particular molds with walls made of plaster, through which liquid media, such as water, can be removed from the suspension due to the capillary action of the plaster pores. However, it is also possible to use molds made of plastic, ceramic or metal, which already have holes or are provided with holes therein, for example by providing them with filter elements, such as membrane filters, paper filters and sintered filters.

[0040] The mold used consists in particular of several parts in order to facilitate the simple removal of the formed blank from the mold. In a particularly preferred embodiment, the mold has a connection by means of which pressure can be exerted on the introduced suspension, for example by means of compressed air, and / or a negative pressure can be applied to the bore. Both measures serve to accelerate the removal of the liquid medium from the mold, thereby shortening the process. With its help, the glass blank can be produced very quickly and therefore economically, which is particularly advantageous in the case of production on an industrial scale.

[0041] Furthermore, the removal of the liquid medium can also be achieved by freeze drying. For this purpose, the glass blank produced by slip casting is cooled in a dense but flexible mold, for example made of silicone, to a temperature at which the liquid components of the suspension freeze. By subsequently sublimating these liquid components under reduced pressure, they are removed and complete drying is thus achieved. A separate heat treatment for drying the blank is then generally no longer necessary.

[0042] In a further preferred embodiment of the method according to the invention, the powder (i) has a particle size of 0.5 to 150 µm, in particular 1 to 100 µm, and the powder of the suspension (ii) has a particle size of 0.5 to 80 µm, in particular 0.5 to 70 µm, measured by laser diffraction according to ISO 13320 (2009). The sample for determining the particle size is prepared in particular according to DIN ISO 14887 (2010), water being used as solvent for dispersing the sample.

[0043] Powders (i) and (ii) as d 50 The average particle size of the values ​​is 5 to 30 μm, preferably 10 to 20 μm, determined based on the volume fraction measured by laser diffraction according to ISO 13320 (2009).

[0044] The glass blank formed in step (a) is usually in the form of a block, cylinder or disk, since blanks of such geometry can easily be given the shape of the desired dental restoration in conventional processing machines. The blank may also already have fixing means, such as fixing pins, formed integrally with the blank, which makes subsequent connection thereof, for example by gluing, unnecessary.

[0045] Therefore, the mold used usually also has a geometry that allows the preparation of such a blank. The mold can be one-piece, or in order to more easily remove the prepared blank, the mold can also be composed of several pieces, in particular three pieces.

[0046] In optional step (b) of the method according to the invention, the glass blank from step (a) is compacted by pressing. This optional step is preferably carried out on the powder of the first variant (i) used in step (a).

[0047] Further preferably, the pressing in step (b) is carried out at a temperature of less than 60° C., preferably 15 to 35° C., and in particular at a pressure of 20 to 120 MPa, preferably 50 to 120 MPa. Pressing is usually carried out at room temperature and is therefore also referred to as cold pressing.

[0048] In step (c) of the method according to the invention, the glass blank from steps (a) and (b) is subjected to a heat treatment to obtain a glass ceramic blank having lithium silicate as the main crystalline phase. The heat treatment is preferably carried out at a temperature of less than 700° C., preferably 550 to 690° C., and for a period of time of, in particular, 2 to 60 minutes, preferably 5 to 30 minutes.

[0049] The glass blank is usually debonded at a temperature of, in particular, 400 to 450° C. before the heat treatment to remove any binder or other organic additives that may be present. The glass blank is then usually heated directly to the heat treatment temperature. Heating to the heat treatment temperature and maintaining this temperature enables the formation of nuclei and the crystallization of lithium silicate, in particular lithium metasilicate, as the main crystalline phase.

[0050] In step (d) of the method according to the invention, the glass ceramic blank from step (c) is compacted by hot pressing. Surprisingly, this compaction succeeds in making the density of the glass ceramic blank essentially indistinguishable from the density of a glass ceramic blank conventionally produced by solid glass technology. Although in the method according to the invention glass powders and therefore so-called "powder technology" are used to produce the glass ceramic blank, in solid glass technology, a glass melt is poured into a mold to form a single glass blank, which after heat treatment produces the desired glass ceramic blank.

[0051] The hot pressing in step (d) is preferably carried out in a mold that does not adhere to the glass. Suitable materials for such molds are carbon-based materials and nitride-based ceramics. Metallic materials are also suitable if a suitable release agent is placed between the mold and the glass-ceramic blank to be compacted.

[0052] The hot pressing is preferably carried out at a temperature of 650 to 780° C., in particular 700 to 750° C., and in particular at a pressure of 5 to 50 MPa, preferably 10 to 30 MPa.

[0053] It is further preferred that the hot pressing is carried out for a period of 0.1 to 10 minutes, preferably 0.3 to 5 minutes. A further advantage of the method according to the invention is that hot pressing for such a short period of time is sufficient to produce a glass ceramic blank from which a dental restoration with excellent optical and mechanical properties can be produced in a fast and easy manner.

[0054] In a further preferred embodiment, the hot pressing is carried out at an atmospheric pressure of less than 0.1 bar, preferably in the range of 0.01 to 0.08 bar.

[0055] The multicolor glass ceramic blank obtained after hot pressing preferably has a density of 2.4 to 2.6, in particular 2.44 to 2.56 g / cm³. The density of the blank is determined in deionized water according to the Archimedean principle. Thus, the glass ceramic blank according to the invention surprisingly has a density similar to that of a corresponding conventional blank produced by solid glass technology.

[0056] In the case of glass blanks and glass ceramic blanks obtained after steps (a), (b) and (c), the mass was determined by weighing and the volume was determined by optical measurement with the aid of the strip projection method (ATOS 3D scanner from GOM GmbH, Germany). The density was then calculated according to the formula ρ = mass / volume.

[0057] The obtained multicolor glass ceramic blank has in particular lithium metasilicate as the main crystalline phase. It is further preferred that the glass ceramic blank has less than 20% by weight, in particular less than 10% by weight, preferably less than 5% by weight and even more preferably less than 3% by weight of lithium disilicate, since a larger amount of lithium disilicate crystals would impair the shaping by mechanical working.

[0058] The term "main crystalline phase" refers to the crystalline phase with the highest mass ratio of all crystalline phases present in the glass ceramic. The mass of the crystalline phase is determined in particular using the Rietveld method. For example, in the doctoral thesis of M. Dittmer "Glaser und Glaskeramiken im System MgO-Al 2 O 3 -SiO 2mit ZrO 2 als Keimbildner" [in the presence of ZrO 2 MgO-Al as nucleating agent 2 O 3 -SiO 2 In Glass and Glass Ceramics in Systems], Jena University, 2011, a suitable method for the quantitative analysis of crystalline phases by means of the Rietveld method is described.

[0059] In a preferred embodiment, the glass ceramic blank contains more than 10% by weight, preferably more than 20% by weight and particularly preferably more than 25% by weight of lithium metasilicate crystals.

[0060] The multicolor glass-ceramic blank contains, in particular, at least one and preferably all of the following components in the amounts indicated:

[0061] Component weight %

[0062] SiO 2 64.0 to 75.0, preferably 64.0 to 72.0

[0063] Li 2 O13.0 to 17.0, preferably 13.5 to 16.0

[0064] K 2 0 to 5.0, preferably 3.0 to 5.0

[0065] Al 2 O 3 0.5 to 5.0, preferably 1.5 to 3.5

[0066] P 2 O 5 2.0 to 5.0, preferably 2.5 to 4.0

[0067] In a further preferred embodiment, the multi-color glass-ceramic blank comprises at least one and preferably all of the following components in the amounts indicated:

[0068] Component weight %

[0069] SiO 2 64.0 to 75.0

[0070] Li 2 O13.0 to 17.0

[0071] K 2 O0 to 5.0

[0072] Al 2 O 3 0.5 to 5.0

[0073] P 2 O 5 2.0 to 5.0

[0074] ZrO 2 0 to 5.0

[0075] MgO 0 to 5.0

[0076] SrO0 to 5.0

[0077] ZnO 0 to 5.0

[0078] F0 to 1.0

[0079] Coloring and / or fluorescent components 0 to 10.0, preferably 0 to 7.0,

[0080] The coloring and / or fluorescent component is particularly selected from the group consisting of oxides of Sn, Ce, V, Mn, Co, Ni, Cu, Fe, Cr, Tb, Eu, Er and Pr.

[0081] The invention also relates to a multi-colored glass ceramic blank obtainable by the method according to the invention. Compared to blanks already obtained by solid glass technology, the blank according to the invention is not only characterized by a much simpler possibility of producing a variety of colors, but it can also be machined in a shorter time and with less tool wear. This is a particularly important advantage in the very fast and cost-effective production of the highly aesthetic dental restorations that are desired today.

[0082] Due to the specific properties of the blank according to the invention described, it is particularly suitable for use in dentistry and in particular as a dental material, and preferably for the production of dental restorations. Therefore, the invention also relates to the use of the blank as a dental material, preferably for the production of dental restorations, in particular for the production of crowns, abutments, abutment crowns, inlays, onlays, veneers, facets, bridges and caps.

[0083] Finally, the present invention also relates to a method for producing a dental restoration, wherein:

[0084] (i) carrying out the method according to the invention to produce a multi-colored glass-ceramic blank,

[0085] (ii) giving the multi-colored glass-ceramic blank a shape of a dental restoration by machining, and

[0086] (iii) at least one heat treatment is carried out at a temperature greater than 750°C, preferably 800 to 900°C.

[0087] The mechanical processing in step (ii) is usually carried out by material removal methods, in particular by milling and / or grinding. Preferably, the mechanical processing is carried out using a computer-controlled milling and / or grinding device. Such devices are known to those skilled in the art and are also customary in the industry.

[0088] In a preferred embodiment of the method, the heat treatment in step (iii) achieves the formation of lithium disilicate as the main crystalline phase. Glass ceramics having lithium disilicate as the main crystalline phase are characterized by excellent mechanical properties, such as are required for materials that replace natural tooth material. In the glass ceramic produced by heat treatment, the crystals, in particular the lithium disilicate crystals, are surprisingly very uniformly distributed, even though the glass ceramic is not produced using the so-called solid glass technology, i.e. not using a cast monolithic glass block.

[0089] After carrying out step (iii), a dental restoration with very good mechanical properties and high chemical stability is obtained. In addition, due to its polychromatic nature, it is able to simulate the optical properties of natural tooth material very well, for example simulating the color gradient from dentin to the incisal edge.

[0090] Preferably, the dental restoration obtained has a biaxial bending strength σ determined according to ISO 6872: 2008 (piston-on-three-ball test) of at least 300 MPa, in particular 360 to 600 MPa. B and / or at least 2.0 MPa m determined according to ISO 6872: 2008 (SEVNB method) 1 / 2 , especially 2.1 to 2.5 MPa m 1 / 2 Fracture toughness K lc .

[0091] Finally, dental restorations can also be produced from the glass ceramic blanks according to the invention without significant shrinkage. This is based in particular on the fact that the blanks according to the invention have a high density of, in particular, 2.4 to 2.6, preferably 2.44 to 2.56 g / cm³, and therefore have only a very low porosity. In this respect, they differ from glass ceramic blanks which are usually produced in the usual way with the aid of powder technology and which usually have a high porosity. Thus, by using the blanks according to the invention, dental restorations can be produced in a particularly simple manner with exactly the desired dimensions.

[0092] The dental restoration produced by the method according to the invention is preferably selected from the group of crowns, abutments, inlays, onlays, veneers, facets, bridges and caps. DETAILED DESCRIPTION

[0093] The present invention is described in more detail below with reference to Examples.

[0094] Example

[0095] The examples illustrate the preparation of multi-colored glass-ceramic blocks having gradients of color and translucency, and their use for the preparation of dental restorations.

[0096] Examples 1 to 9

[0097] A. Preparation of lithium silicate glass

[0098] First, nine different lithium silicate glasses having the compositions shown in Table I were prepared, wherein the glasses were used to simulate dentin or tooth incisal edges. Additives also shown in Table I were added to these glasses.

[0099] To produce these glasses, a mixture of the corresponding raw materials was first melted at 1500° C. for a period of 1.5 hours, where it was possible to melt very easily without the formation of bubbles or streaks. In each case, a glass frit was prepared by pouring the melt obtained into water.

[0100] B. Preparation of Monochrome Glass-Ceramic Blocks for Determination of Properties

[0101] In each case, these glass frits were first crushed to a size of <3 mm in an FM 2 / 2 roller mill (MerzAufbereitungstechnik GmbH, Germany) and then further crushed to 15 µm (d 50 value) to prepare glass powder.

[0102] The obtained glass powder was granulated by spraying an aqueous suspension with 1.0 wt. % of binder and 0.5 wt. % of pressing agent onto the glass powder in a fluidized bed using a GPCG 3.1 spray granulator (Glatt GmbH, Germany).

[0103] In each case, the granulated glass powder was then introduced into a three-piece steel mold consisting of a template and upper and lower punches to produce a single-color glass blank.

[0104] These monochromatic glass blanks were compacted in an isostatic press at room temperature by pressing at the pressures indicated in Table II.

[0105] Under the conditions shown in Table II, the compacted blanks were debonded in an N11 / HR sintering furnace (Nabertherm GmbH, Germany) and crystallized to form glass ceramic blanks with lithium metasilicate as the main crystalline phase. These glass ceramic blanks were then hot pressed in a DSP 515 pressure sintering press (Dr. Fritsch Sondermaschinenbau GmbH, Germany) under the conditions also shown in Table II. The density of the obtained glass ceramic blanks was measured according to the Archimedean principle, and their lithium metasilicate content was also determined by X-ray diffraction examination using Rietveld analysis. The values ​​obtained are listed in Table II.

[0106] Finally, these blanks were further crystallized under the conditions also shown in Table II to produce lithium disilicate as the main crystalline phase. The lithium disilicate blanks produced in this way have the properties also shown in Table II. Biaxial bending strength σ was measured according to ISO 6872:2015 (three-ball piston test) B , and determine the fracture toughness K according to ISO 6872: 2015 (SEVNB method) lc To determine the Lab values ​​and the contrast ratio (CR value), a CM-3700d spectrophotometer from Konica Minolta was used, with the contrast ratio being determined in accordance with British Standard BS 5612. The density was determined in accordance with the Archimedean principle, and the lithium metasilicate content and lithium disilicate content were measured by X-ray diffraction examination using Rietveld analysis.

[0107] Surprisingly, the flexural strength of these lithium disilicate blanks produced by powder technology is very high and comparable to the flexural strength of lithium disilicate glass-ceramics produced in a conventional manner by solid glass technology, typically having a strength of at least 360 MPa.

[0108] Surprisingly, the fracture toughness of the lithium disilicate blanks is also completely comparable to the fracture toughness of lithium disilicate glass ceramics prepared in a conventional manner by solid glass technology and is typically between 2.2 and 2.3 MPa.m 1 / 2 fracture toughness.

[0109] C. Preparation of Multicolor Glass-Ceramic Blocks

[0110] a) Gradient blocks of glass powder according to Examples 1 and 2

[0111] To produce the multi-colored glass ceramic blocks, the granulated glass powder according to Example 1 was used to simulate the dentin and the granulated glass powder according to Example 2 was used to simulate the incisal edge.

[0112] These granulated powders are prepared in the same manner as described above in B. The powders are then introduced into the three-piece steel mold mentioned in B, using a device for stepwise addition and mixing, in such a manner as to produce a glass blank with a gradual color and translucency. The glass blank is then converted into a glass-ceramic mass having lithium metasilicate as the main crystalline phase, in the manner described above in B.

[0113] The obtained multi-colored glass ceramic blocks were machined in a CAD / CAM unit to form the crowns. To this end, the blocks were provided with suitable fixtures and then given the desired shape in an inLab MC XL grinding unit (Sirona Dental GmbH, Germany). For the machining of the blocks, the same grinding parameters as the commercialized e.maxCAD blocks from Ivoclar Vivadent, Liechtenstein, could be used.

[0114] The machinability of the glass ceramic blocks was tested in comparison with commercial glass ceramic blocks of the type e.max CAD LT from Ivoclar Vivadent AG, Liechtenstein, produced by solid glass technology. The tool life was also tested. For this purpose, identical crowns were always ground from the blocks with the same dimensions provided by the fixture on the inLab MC XL grinding unit and the time from start to end of machining was determined. For the tool life, the number of crowns that could be produced until the unit indicated the need for the first tool change was determined.

[0115] It was shown that the glass-ceramic blocks according to the invention are superior to commercial blocks, since they can be machined at least 10% faster and the tool life is at least 35% longer.

[0116] These advantageous properties determine that the glass ceramic block according to the invention can be used to very quickly provide the patient with a dental restoration which meets very high requirements both in terms of its optical properties and its mechanical properties.

[0117] b) Gradient mass of glass powder according to Examples 3 and 4

[0118] A multi-colored glass ceramic block was prepared in the same manner as described above in a), with the only difference being that the glass powder according to Example 3 was used to simulate dentin, while the glass powder according to Example 4 was used to simulate the incisal edge.

[0119] These glass ceramic blocks are also significantly superior to commercial glass blocks because they can be machined faster and tool life is longer.

[0120] Glass-ceramic blocks which were produced analogously to a) and b), but in which at least one of the glass powders used was replaced by another glass powder listed in Table I, also exhibit these advantageous properties.

[0121] D. Heat treatment for the preparation of dental restorations

[0122] The machined blocks obtained in C were subsequently heat treated for a period of 7 minutes at 840° C. The crowns obtained were then slowly cooled to room temperature and X-ray diffraction examinations showed that they had lithium disilicate as the main crystalline phase.

[0123] The crowns obtained have high strength. In addition, they show a continuous color and translucency gradient from dentin to incisal edge, thus, they simulate the optical properties of natural tooth material in an excellent way.

[0124] The flexural strength of 12 examined samples of lithium disilicate blocks prepared from gradient blocks according to a) (powders according to Examples 1 and 2) had an average value of 403.82 MPa with a standard deviation of 55.16 MPa. The fracture toughness of 6 examined samples of these lithium disilicate blocks had an average value of 2.27 MPa.m 1 / 2 , standard deviation is 0.15 MPa.m 1 / 2 .

[0125] The flexural strength of the 12 examined samples of lithium disilicate blocks made from gradient blocks according to b) (powders according to Examples 3 and 4) had an average value of 470.57 MPa with a standard deviation of 100.66 MPa.

[0126]

[0127]

Claims

1. A method for preparing a multi-color glass-ceramic blank for dental use having lithium silicate as the main crystalline phase, wherein: (a) introducing (i) lithium silicate glass powders of different colors or (ii) a suspension of lithium silicate glass powders of different colors in a liquid medium into a mold to form a glass blank, (b) compacting the glass blank from step (a) optionally by pressing, (c) heat treating the glass blank from step (a) or (b) to obtain a glass ceramic blank having lithium silicate as the main crystalline phase, and (d) compacting the glass-ceramic green body from step (c) by hot pressing.

2. The method according to claim 1, wherein in step (a), powder is introduced into the mold and step (b) is performed.

3. The method according to claim 1, wherein in step (a), a suspension is introduced into the mold and the liquid medium is removed. 4 . The method according to claim 1 , wherein in step (a), a powder or a suspension is introduced into the mold in such a way that the multicolored glass-ceramic blank produced has a continuously changing color.

5. The method according to any one of claims 1 to 4, wherein in step (a), the powder (i) has a particle size of 0.5 to 150 µm, preferably 1 to 100 µm, and the powder (ii) of the suspension has a particle size of 0.5 to 80 µm, preferably 0.5 to 70 µm, and / or the powder (i) and the powder (ii) have a particle size of 5 to 30 µm, preferably 10 to 20 µm as d 50 The average granularity of the values.

6. The method according to any one of claims 1 to 5, wherein in step (b), the pressing is carried out at a temperature of less than 60°C, preferably at a temperature of 15 to 35°C, and in particular at a pressure of 20 to 120 MPa, preferably 50 to 120 MPa.

7. The method according to any one of claims 1 to 6, wherein in step (c), the heat treatment is carried out at a temperature of less than 700°C, preferably 550°C to 690°C, and for a period of time of in particular 2 to 60 min, preferably 5 to 30 min.

8. The method according to any one of claims 1 to 7, wherein in step (d), the hot pressing is carried out at a temperature of 650 to 780°C, in particular 700 to 750°C, and at a pressure of in particular 5 to 50 MPa, preferably 10 to 30 MPa.

9. The method according to any one of claims 1 to 8, wherein in step (d), the hot pressing is performed for a period of 0.1 to 10 min, preferably 0.3 to 5 min.

10. The method according to any one of claims 1 to 9, wherein in step (d), the hot pressing is carried out at an atmospheric pressure of less than 0.1 bar, and preferably 0.01 to 0.08 bar. 11 . The method according to claim 1 , wherein the multicolor glass-ceramic blank has lithium metasilicate as the main crystalline phase. 12 . The method according to claim 1 , wherein the multicolor glass ceramic blank contains more than 10% by weight, preferably more than 20% by weight and particularly preferably more than 25% by weight of lithium metasilicate crystals.

13. The method according to any one of claims 1 to 12, wherein the multi-color glass ceramic blank has a carbon content of 2.4 to 2.6, and in particular 2.44 to 2.56 g / cm 3 density.

14. The method according to any one of claims 1 to 13, wherein the multi-color glass-ceramic blank comprises at least one and preferably all of the following components in specified amounts: Component weight % SiO2 64.0 to 75.0 Li2O 13.0 to 17.0 K2O 0 to 5.0 Al2O3 0.5 to 5.0 P2O5 2.0 to 5.

0.

15. The method according to any one of claims 1 to 14, wherein the multi-color glass-ceramic blank comprises at least one and preferably all of the following components in specified amounts: Component weight % SiO2 64.0 to 75.0 Li2O 13.0 to 17.0 K2O0 to 5.0 Al2O3 0.5 to 5.0 P2O5 2.0 to 5.0 ZrO2 0 to 5.0 MgO 0 to 5.0 SrO 0 to 5.0 ZnO 0 to 5.0 F 0 to 1.0 Coloring and / or fluorescent components 0 to 10.0, The coloring and / or fluorescent component is particularly selected from the group consisting of oxides of Sn, Ce, V, Mn, Co, Ni, Cu, Fe, Cr, Tb, Eu, Er and Pr.

16. A multi-coloured glass-ceramic blank obtainable by the method according to any one of claims 1 to 15.

17. Use of the multi-color blank according to claim 16 as dental material, preferably for producing dental restorations.

18. A method for preparing a dental restoration, wherein: (i) carrying out a method according to any one of claims 1 to 15 to produce a multi-colored glass-ceramic blank, (ii) giving the multi-colored glass-ceramic blank a shape of a dental restoration by machining, and (iii) at least one heat treatment at a temperature greater than 750°C, preferably 800 to 900°C.

19. The method of claim 18, wherein in step (iii), the heat treatment effects the formation of lithium disilicate as the main crystalline phase.

20. A method according to claim 18 or 19, wherein in step (ii) the machining is performed using a computer controlled milling and / or grinding device.

21. The method of any one of claims 18 to 20, wherein the dental restoration is selected from the group consisting of a crown, an abutment, an inlay, an onlay, a veneer, a facet, a bridge and a cap.

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