Low-melting glass ceramic

Abstract

Glass ceramic for veneering a dental framework structure, characterized in that the glass ceramic contains SiO2 in an amount of 60 to 75 wt.%, preferably 65 to 70 wt.%, and B2O3 in an amount of 6 to 12 wt.%, preferably 7 to 10 wt.%, each based on the total weight of the glass ceramic.

Description

[0001] The present invention relates to a glass ceramic for veneering a dental framework structure, wherein the glass ceramic is characterized by a high content of B2O3, a method for its production and its use in the production of dental restorations.

[0002] Glass ceramics are materials produced from molten glass through controlled crystallization. In this process, the glass is transformed through specific temperature treatments into a partially polycrystalline and partially glassy ceramic state, resulting in a glass-like product whose properties differ from those of ordinary glasses.

[0003] Glass ceramics are used in a wide variety of technical fields, one of the best known being cooktops and cookware in the household sector. Besides other applications, such as high-performance reflectors for digital projectors, glass ceramics are also used as materials in the production of dental restorations.

[0004] For example, DE 197 50 794 describes lithium disilicate glass-ceramic products that can be processed into shaped dental products with high strength by plastic deformation under pressure and heat or by machining.

[0005] Besides being used to fabricate the base of a dental restoration, glass ceramics can also be used as veneering materials to recreate the natural tooth on a framework structure. In this application, a strong bond between the veneer and the framework is crucial to ensure a stable and long-lasting dental restoration. A strong bond is usually achieved by matching the properties of the veneering material, particularly its thermal expansion, to those of the framework material.

[0006] WO 2018 / 071408 describes a dental restoration with a framework structure based on a lithium disilicate glass ceramic or a ZrO2-based ceramic, which contains at least one veneering coating, wherein the veneering coating is thermally compatible with the framework structure.

[0007] EP 2 405 883 discloses a composition for use in bonding a dental veneer to a tooth support structure, wherein the composition contains 10 to 55 wt.% water and 40 to 85 wt.% a glass-ceramic material comprising 55 to 75 wt.% silicon dioxide and 8 to 22 wt.% aluminum oxide. The veneer structure is proportionally enlarged with a magnification factor of 1.12 to 1.9 relative to a sintered veneer and has a coefficient of thermal expansion of 8*10 -6 K -1 up to 15.8*10 -6 K -1 on.

[0008] EP 1 000 588 relates to a ceramic dental restoration consisting of a base ceramic based on a leucite-containing glass ceramic, which is veneered with a dental ceramic, wherein the base ceramic contains as components 40 to 95 wt.% SiO2 and 5 to 25 wt.% Al2O3 It contains [the following]. Dental ceramics have a linear coefficient of thermal expansion. □(20-500°C) of 13.5*10 -6K -1 up to 17.0*10 -6 K -1 and the base ceramic has a linear coefficient of thermal expansion □(20-500°C) of 12.5*10 -6 K -1 up to 15.5*10 -6 K -1 , where the coefficient of thermal expansion of the base ceramic is increased by 1.5*10 -6 K -1 under which lies the veneering ceramic.

[0009] EP 0 544 145 relates to a dental ceramic material for the manufacture and repair of metal-ceramic and all-ceramic dental prostheses with a processing temperature below 700 °C and a coefficient of thermal expansion □ from 13-14*10 -6 K -1 between 20 and 500 °C, characterized by the following composition: 60 to 65 wt.% SiO2; 8.5 to 11 wt.% Al2O3; 8 to 12 wt.% K2O; 10.5 to 12 wt.% Na2O; 0.7 to 2 wt.% CaO; 0.6 to 2 wt.% BaO; 0.5 to 2.5 wt.% B2O3; 0.1 to 0.6 wt% Sb2O3; 0 to 0.5 wt% CeO2; 1.2 to 3.8 wt% TiO2; 0.8 to 1.4 wt% Li2O and 1.2 to 3.8 wt% F2.

[0010] In the fabrication of dental restorations, the veneering structure is used to conceal the framework structure and give the restoration the most natural appearance possible, so that it blends seamlessly into the existing dentition. For this purpose, the veneering structure is applied to the framework structure and subjected to heat treatment together. This treatment serves two purposes: firstly, to ensure a strong bond between the framework and the veneering structure, and secondly, to adjust the optical properties of the dental restoration. Although the glass ceramics described in the prior art are adapted to the thermal behavior of common framework materials, in practice, the differing thermal expansion behavior of the materials used frequently leads to complications.

[0011] Cracks and fissures form in the veneer structure, rendering the dental restoration unusable.

[0012] Another disadvantage of glass ceramics known in the prior art is their high softening point, which complicates processing and necessitates correspondingly high temperatures during the manufacturing process, thus significantly extending the time required to complete the dental restoration. A further disadvantage of the aforementioned high-fusing veneering materials is that their firing temperature exceeds the softening point of the glass ceramics used to form the framework structure, particularly in cases where the framework structure consists of lithium silicate glass ceramics. The softening point of such glass ceramics typically lies between 780 and 840 °C, depending on the composition. Veneering frameworks made of this material group, which is now widespread in the dental market, is therefore not possible, as the framework would deform during the firing of the veneering material.Problems also arise with high-melting-point veneering materials when used with zirconia (ZrO2) framework materials. While the softening point of ZrO2 is significantly higher than that of all known veneering materials, the dental industry frequently uses porous, pre-sintered ZrO2 frameworks that are tinted with dyes to best match the patient's tooth color. However, if these tinted ZrO2 frameworks are reheated to temperatures above 850 °C after dense sintering, some of the tinting components are oxidized, and depending on the composition of the dye used, this can lead to inaccuracies in color fidelity.

[0013] It is therefore an object of the present invention to provide a glass ceramic for veneering a framework structure which, firstly, exhibits good workability and forms a stable bond with the framework structure. Furthermore, the glass ceramic should be characterized by good optical properties that make it possible to reproduce the natural color gradient of a tooth.

[0014] It was surprisingly discovered that this task can be solved by a glass ceramic with a high content of B2O3 exhibits.

[0015] A first object of the present invention is therefore a glass ceramic for veneering a dental framework structure, which contains SiO2 in an amount of 60 to 75 wt.%, preferably 65 to 70 wt.%, and B2O3 in an amount of 6 to 12 wt.%, preferably 7 to 10 wt.%, based on the total weight of the glass ceramic.

[0016] The glass ceramic according to the invention is characterized in particular by a comparatively low softening point, which enables gentle processing, especially with regard to the temperature sensitivity of the materials used for the framework structures. It was surprisingly found that, thanks to the low processing temperature associated with the low softening temperature of the glass ceramic, the deformation of the framework structure that otherwise typically occurs can be reduced and the bond between the veneering ceramic and the framework structure can be improved. Within the scope of the present invention, it has proven particularly advantageous if the softening point of the glass ceramic is not above 800 °C.Therefore, an embodiment of the glass ceramic according to the invention is preferred in which the glass ceramic has a softening point of less than 790 °C, preferably less than 780 °C, and particularly preferably 730 to 770 °C. The softening point can be determined by means of heating microscopy, as described, for example, in DIN 51730.

[0017] The properties of the glass ceramic according to the invention are specifically tailored to the properties of the materials used to produce the framework structure in order to ensure a stable bond between the framework structure and the veneering ceramic. The glass ceramic may contain further components to adjust its thermal properties in particular.

[0018] In a preferred embodiment, the glass ceramic according to the invention further comprises K2O in an amount of 6 to 12 wt.%, preferably 7 to 9 wt.%, in each case based on the total weight of the glass ceramic.

[0019] In a further preferred embodiment, the glass ceramic Al2O3 in a concentration of 3 to 11 wt.%, preferably 5 to 9 wt.%.

[0020] The presence of Na2O has also proven advantageous. Therefore, an embodiment is preferred in which the glass ceramic according to the invention contains Na2O in an amount of 4 to 11 wt.%, preferably 5 to 7 wt.%, in each case based on the total weight of the glass ceramic.

[0021] In contrast to other alkali oxides, the presence of Li₂O in the glass ceramic has proven to be less than advantageous, particularly with regard to bond strength with the framework structure. Therefore, an embodiment of the glass ceramic according to the invention is preferred in which the proportion of Li₂O in the glass ceramic is less than 3 wt.%, preferably less than 2 wt.%, and particularly preferably 0.1 to 1.5 wt.%, in each case based on the total weight of the glass ceramic.

[0022] In a particularly preferred embodiment, the glass ceramic according to the invention comprises the following components: • 60 to 75 wt.%, preferably 65 to 70 wt.% SiO2; • 6 to 12 wt.%, preferably 7 to 10 wt.% B2O3; • 6 to 12 wt.%, preferably 7 to 9 wt.% K2O; • 3 to 11 wt.%, preferably 5 to 9 wt.% Al2O3; • 4 to 11 wt.%, preferably 5 to 7 wt.% Na2O; • 0 to 3 wt.%, preferably 0.1 to 1.5 wt.% Li2O, where the values ​​in wt.% refer to the total weight of the glass ceramic.

[0023] In a further preferred embodiment, the glass ceramic according to the invention contains less than 0.5 wt.% ZnO, preferably less than 0.1 wt.% ZnO, in each case based on the total weight of the glass ceramic.

[0024] A further preferred embodiment is one in which the glass ceramic according to the invention contains less than 0.5 wt.% ZrO2, preferably less than 0.1 wt.% ZrO2, in each case based on the total weight of the glass ceramic.

[0025] Those skilled in the art of glass ceramics are aware that specifying the components of a glass ceramic in the form of their oxides is a common method for describing a glass ceramic. Nevertheless, it should be clarified here that the glass ceramic according to the invention is preferably obtained from a starting mixture containing the components of the glass ceramic in the form of their oxides.

[0026] The glass ceramic according to the invention is characterized by its ability to form a stable bond with the framework structure, thus preventing chipping or damage under stress, for example during chewing, even with thin veneering thicknesses. This advantageous bond is achieved in particular by matching the coefficient of thermal expansion (CTE) of the glass ceramic to the material of the framework structure. The CTE of the glass ceramic according to the invention must never exceed the CTE of the framework. It has proven particularly advantageous if the CTE of the glass ceramic according to the invention is between 0.1 and 2.5 × 10⁻⁶. -6 K -1 below the coefficient of thermal expansion (CTE) of the framework structure. Therefore, an embodiment is preferred in which the glass ceramic has a coefficient of thermal expansion (CTE) of less than 9.5 x 10⁻⁵. -6 K -1 , preferably 8.3*10 -6 K -1 up to 9.3*10 -6 K -1exhibits, determined using a dilatometer.

[0027] The glass ceramic according to the invention is further characterized by high chemical resistance, which makes it particularly suitable for use in dentistry. It was surprisingly found that the glass ceramic according to the invention, despite its high content of B2O3 exhibits low solubility, particularly in acidic environments. Therefore, an embodiment is preferred in which the glass ceramic according to the invention has a solubility of less than 20 µg / cm³. 2 , preferably less than 10 µm / cm 2 , particularly preferably 1 to 5 µg / cm² 2 exhibits [something]. The solubility can be determined, for example, according to DIN ISO 6872.

[0028] The glass-ceramic is preferably provided in powder form, which is processed into a paste using a liquid medium and then applied to the framework structure. It has surprisingly been found that the bond strength between the glass-ceramic and the framework structure can be increased when the glass-ceramic is used in powder form with a selected particle size distribution. Therefore, a preferred embodiment is one in which the glass-ceramic is in powder form with a particle size distribution D50 of 15 to 35 µm, preferably 20 to 25 µm, determined by a laser granulometer. Furthermore, the glass-ceramic according to the invention preferably has a particle size distribution D90 of 50 to 80 µm, preferably 60 to 75 µm, determined by a laser granulometer.In a preferred embodiment, the glass ceramic according to the invention, in the form of a powder, has a particle size distribution D10 of 2 to 10 µm, preferably 3 to 5 µm, determined by means of a laser granulometer.

[0029] In particular, adjusting the particle size distribution of the glass ceramic according to the invention has proven to be an important factor in forming a stable bond between the framework structure and the glass ceramic. The particle size distribution can be achieved, for example, by subjecting the glass ceramic to several milling and melting processes during its production. Therefore, a further object of the present invention is a method for producing the glass ceramic according to the invention, comprising the following steps: a) Producing a base glass by melting the basic components and quenching the melt in water, b) Grinding the glass from step a) to obtain a powder; c) Compressing the powder from step b) to obtain a blank; d) Heat treatment of the blank while maintaining a glass-ceramic finish; and e) Grinding the blank from step e) to obtain a powder.

[0030] Preferably, the glass is produced in step a) of the process according to the invention starting from a starting mixture which contains the components of the glass ceramic in the form of their oxides.

[0031] The heat treatment for forming the glass ceramic in step d) of the process according to the invention is preferably carried out at a temperature of 800 to 900 °C, preferably 820 to 880 °C, particularly preferably 830 to 850 °C.

[0032] The glass ceramic according to the invention is particularly suitable for the production of veneering structures that are applied to framework structures to obtain a dental restoration. Therefore, a further object of the present invention is the use of the glass ceramic according to the invention for veneering a framework structure, preferably a ceramic framework structure based on lithium disilicate or ZrO2.

[0033] To achieve a stable bond between the veneer structure and the framework structure, it has proven advantageous for the veneer structure and the framework structure to have similar coefficients of thermal expansion. Therefore, an embodiment is preferred in which the difference between the coefficient of thermal expansion of the veneer structure and the framework structure is determined by the specific coefficient of thermal expansion of the veneer structure. WAKVK and the coefficient of thermal expansion of the scaffold structure WAK G no more than 2.5*10-6K -1 , preferably less than 1.5*10 -6 K -1, especially preferably less than 1.0*10 -6 K -1 , wherein the framework structure has a higher CTE than the facing structure and the coefficient of thermal expansion can be determined in each case using a dilatometer.

[0034] Another object of the present invention is a dental restoration comprising a framework structure and a veneering structure, wherein the veneering structure is a glass ceramic according to the present invention. The framework structure is preferably a ceramic framework structure based on lithium disilicate or ZrO2. The framework structure can be designed to replicate the natural color gradient of a tooth. In this way, the need for complex staining of the veneering structure is avoided. Staining of the framework structure can be achieved, for example, by introducing staining oxides or by means of staining solutions. It has surprisingly been found that the optical properties of the framework are not affected by the firing of the veneering structure. Therefore, an embodiment in which the framework structure has a color gradient is preferred.Alternatively, an embodiment in which the framework structure is colored is preferred.

[0035] It was surprisingly found that, with the aid of the glass ceramic according to the invention, a stable bond between the veneering structure and the framework structure can be achieved even with small thicknesses of the veneering structure. Therefore, an embodiment is preferred in which the thickness of the veneering structure is 0.2 to 3 mm, preferably 0.5 to 1.5 mm.

[0036] To achieve these small thicknesses, it has proven advantageous to apply the veneering structure to the framework structure in the form of a paste. Therefore, a further object of the present invention is a paste comprising a liquid medium and the glass ceramic according to the invention. Preferably, the liquid medium is water, which may optionally contain further components.

[0037] Another object of the present invention is a method for producing a dental restoration in which a glass ceramic or a paste according to the present invention is applied to a framework structure. In a preferred embodiment, the framework structure is a ceramic framework structure, in particular based on lithium disilicate or ZrO2.

[0038] The present invention is explained in more detail by means of the following examples, which are in no way to be understood as a limitation of the inventive concept. Examples:

[0039] The glass ceramic according to the invention was applied as a veneering material to various framework structures, and its thermal shock resistance was tested in accordance with DIN EN ISO 9693-2:2016-07. For this purpose, the veneered framework structures were alternately heated in an oven and then quenched in ice water, with the oven temperature being increased by 15 °C after each quenching. The holding time in the oven was 30 minutes in each case, and the specimens were examined for cracking and spalling after each quenching. The results are summarized in the following tables.

[0040] The glass ceramics according to the invention exhibited a proportion of B2O3 of 8 wt.%. For comparison, conventional glass ceramics with a proportion of B2O3 of 1 wt.% (see 1) or 5 wt.% (see 2). Table 1: Thermal shock resistance (DIN EN ISO 9693-2:2016-07) on lithium disilicate as a framework material Glass ceramic according to the invention See 1 See 2 Jumps at 105 °C no no no Jumps at 120 °C no no no Jumps at 135 °C no no Yes Jumps at 150 °C no no Yes Jumps at 165 °C no Yes Yes undamaged sample bodies 7 / 7 5 / 7 0 / 7 Table 2: Temperature cycling resistance of ZrO2 frameworks Glass ceramic according to the invention See 1 See 2 Jumps at 105 °C no no no Jumps at 120 °C no no no Jumps at 135 °C no Yes Yes Jumps at 150 °C no no Yes Jumps at 165 °C Yes Yes - undamaged sample bodies 5 / 7 1 / 7 0 / 7

[0041] Furthermore, the bond strength of the veneering materials to ZrO2-based framework materials was determined using the peel / crack initiation test (DIN EN ISO 9693-2:2016-07). The results are summarized in Table 3. Table 3: Average [MPa] Standard deviation [MPa] Glass ceramic according to the invention 45,5 5,9 See 1 32,4 6,3 See 2 36,8 4,8

[0042] As can be seen from the table, the glass ceramic according to the invention exhibits excellent bond strength. The softening point of the glass ceramic according to the invention was determined to be 762 °C by means of heating microscopy. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 197 50 794

[0004] WO 2018 / 071408

[0006] EP 2 405 883

[0007] EP 1 000 588

[0008] EP 0 544 145

[0009] Cited non-patent literature

[0000] DIN EN ISO 9693-2:2016-07 [0039, 0041]

Claims

[1] Glass ceramic for veneering a dental framework structure, characterized by that the glass ceramic contains SiO2 in an amount of 60 to 75 wt.%, preferably 65 to 70 wt.%, and B2O3 in an amount of 6 to 12 wt.%, preferably 7 to 10 wt.%, each based on the total weight of the glass ceramic. [2] Glass ceramic according to claim 1, characterized by that the glass ceramic has a softening point below 790 °C, preferably below 780 °C, particularly preferably between 730 and 770 °C, determined by heating microscope. [3] Glass ceramic according to one or both of claims 1 and 2, characterized by that the glass ceramic further contains K20 in an amount of 6 to 12 wt.%, preferably 7 to 9 wt.%, based on the total weight of the glass ceramic. [4] Glass ceramic according to at least one of the preceding claims, characterized bythat the glass ceramic further contains Al2O3 in an amount of 3 to 11 wt.%, preferably 5 to 9 wt.%, based on the total weight of the glass ceramic. [5] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic further contains Na2O in an amount of 4 to 11 wt.%, preferably 5 to 7 wt.%, based on the total weight of the glass ceramic. [6] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic further contains Li2O in an amount of less than 3 wt.%, preferably less than 2 wt.%, particularly preferably 0.1 to 1.5 wt.%, based on the total weight of the glass ceramic. [7] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic has a coefficient of thermal expansion (CTE) of less than 9.5*10 -6 K -1 , preferably 8.3 * 10 -6 K -1 up to 9.3 *10 -6 K-1 exhibits, determined using a dilatometer. [8] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic has a solubility of less than 20 µg / cm³ 2 , preferably less than 10 µm / cm 2 , particularly preferably 1 to 5 µg / cm² 2 exhibits, determined according to DIN ISO 6872. [9] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic • 60 to 75 wt.%, preferably 65 to 70 wt.% SiO2; • 6 to 12 wt.%, preferably 7 to 10 wt.% B2O3; • 6 to 12 wt.%, preferably 7 to 9 wt.% K2O; • 3 to 11 wt.%, preferably 5 to 9 wt.% Al2O3; • 4 to 11 wt.%, preferably 5 to 7 wt.% Na2O; • 0 to 3 wt.%, preferably 0.1 to 1.5 wt.% Li2O, wherein the values ​​in wt.% refer to the total weight of the glass ceramic. [10] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic contains less than 0.5 wt% ZnO. [11] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic contains Li2O in an amount of less than 3 wt.%. [12] Glass ceramic according to at least one of the preceding claims, characterized by that the glass ceramic contains less than 0.5 wt% ZrO2. [13] Use of a glass ceramic according to at least one of claims 1 to 12 for veneering a dental framework structure, preferably a ceramic framework structure based on lithium disilicate or ZrO2. [14] Use according to claim 13, characterized by , that the difference between the coefficient of thermal expansion of the veneer structure WAKVK and the coefficient of thermal expansion of the scaffold structure WAK G no more than 2.5*10 -6 K -1, preferably less than 1.5*10 -6 K -1 , especially preferably less than 1*10 -6 K -1 , where the coefficient of thermal expansion can be determined according to dilatometry. [15] Dental restoration comprising a framework structure and a veneering structure, characterized by that the veneering structure is a glass ceramic according to at least one of claims 1 to 12. [16] Dental restoration according to claim 15, characterized by that the thickness of the veneering structure is 0.2 to 3 mm, preferably 0.5 to 1.5 mm. [17] Paste comprising a liquid medium and a glass ceramic powder according to at least one of claims 1 to 12 in the form of a powder for veneering a dental framework structure.