Lithium silicate low-temperature quartz glass ceramic

Abstract

To provide lithium silicate-low quartz glass ceramics.SOLUTION: Lithium silicate-low quartz glass ceramics are described which are characterized by a combination of very good mechanical and optical properties and can therefore be used in particular as restoration material in dentistry. The lithium silicate-low quartz glass ceramic according to the invention comprises lithium silicate as a main crystal phase and low quartz as a further crystal phase. It has surprisingly been shown that the glass ceramic according to the invention has a combination of very desirable mechanical and optical properties, such as are necessary precisely for a restorative dental material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lithium silicate-low temperature quartz-glass ceramic, which is preferably suitable for the preparation of tooth restorations, in particular for use in dentistry, and also to a precursor for the preparation of this glass ceramic. [Background technology]

[0002] Lithium silicate glass ceramics are generally characterized by very good mechanical properties, for which reason they have been used for some time in the dental field, and there mainly for the preparation of dental crowns and small dental bridges.

[0003] U.S. Patent Nos. 5,507,981 and 5,702,514 describe lithium disilicate glass ceramics that are processed by pressing in a viscous state to form dental restorations, but the use of a deformable crucible is necessary, making the processing very expensive.

[0004] EP 827941 and EP 916625 disclose lithium disilicate glass ceramics that can be pressed or machined into the shape of a desired dental restoration.

[0005] EP 1505041 and EP 1688398 describe methods for preparing dental restorations from lithium disilicate glass ceramics. First, an intermediate product is produced, a glass ceramic having lithium metasilicate as the main crystalline phase, which can be machined very easily, for example, by CAD / CAM processes. This intermediate product is then subjected to a further heat treatment to form the desired high-strength lithium disilicate glass ceramic. The heat treatment used during the process should be selected to prevent the formation of undesired crystalline phases, such as cristobalite.

[0006] WO 2013 / 053864 discloses lithium silicate glass ceramics that contain divalent metal oxides and can be processed by hot pressing and then machining to form dental restorations.

[0007] Glass ceramics having lithium disilicate as the main crystalline phase and apatite as a further crystalline phase are known from WO 2013 / 164256. These glass ceramics are characterized by high chemical stability and can be shaped to form the desired dental restorations by machining or hot pressing.

[0008] US Patent Application Publication No. 2015 / 0104655 describes glass-ceramics that can contain lithium disilicate, lithium metasilicate, lithium phosphate, cristobalite, tridymite, quartz, or spodumene as crystalline phases, depending on the composition and temperature treatment selected for crystallization. These glass-ceramics are intended in particular for overlaying zirconium oxide ceramics.

[0009] However, due to their high strength, machining of conventional lithium disilicate glass ceramics is only possible with difficulty, and as a result, it is generally accompanied by high wear of the tools used. Machining of the corresponding lithium metasilicate glass ceramics as precursors is similarly possible but much easier. However, this still requires a further heat treatment after machining to produce a high-strength lithium disilicate glass ceramic restoration.

[0010] Therefore, there is a need for lithium silicate glass ceramics that can be easily machined and that, after this machining, do not require further heat treatment to impart the desired mechanical properties to the resulting dental restoration. These lithium silicate glass ceramics should not only have very good mechanical properties, but also very good optical properties so that they also meet the high aesthetic demands made on restorative dental materials. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 5,507,981 [Patent Document 2] U.S. Patent No. 5,702,514 [Patent Document 3] European Patent No. 827941 [Patent Document 4] European Patent No. 916625 [Patent Document 5] European Patent No. 1505041 [Patent Document 6] European Patent No. 1688398 [Patent Document 7] International Publication No. 2013 / 053864 [Patent Document 8] International Publication No. 2013 / 164256 [Patent Document 9] US Patent Application Publication No. 2015 / 0104655 Summary of the Invention [Means for solving the problem]

[0012] This object is achieved by a lithium silicate low-temperature quartz glass-ceramic according to claims 1 to 14 and 17. The subject of the invention is also the starting glasses according to claims 15, 16 and 17, the methods according to claims 18, 19 and 22, and also the uses according to claims 20 and 21. DETAILED DESCRIPTION OF THE INVENTION

[0013] The lithium silicate-low temperature quartz glass ceramic according to the invention is characterized in that it comprises lithium silicate as the main crystalline phase and low temperature quartz as a further crystalline phase.

[0014] Surprisingly, it has been shown that the glass ceramic according to the present invention possesses a combination of highly desirable mechanical and optical properties, precisely what is required for restorative dental materials. Despite its high strength, the glass ceramic can be easily machined into the shape of a dental restoration. Subsequent heat treatment is not required to achieve satisfactory strength. Furthermore, it was unexpected that by providing low-temperature quartz as an additional crystalline phase in addition to lithium silicate as the main crystalline phase, such good optical properties could still be achieved. This is because many additional crystalline phases adversely affect the optical properties of lithium silicate glass ceramics. For example, they can reduce translucency and further impair the stainability of the glass ceramic, making it significantly more difficult to mimic the color of the natural tooth material being replaced.

[0015] The lithium silicate low-temperature quartz glass ceramic according to the invention in particular comprises 59.0 to 79.0, preferably 64.0 to 78.0, particularly preferably 64.0 to 76.0 wt.-% SiO2.

[0016] In another embodiment, the lithium silicate low-temperature quartz glass ceramic according to the invention comprises in particular 68.0 to 79.0, preferably 69.0 to 78.0, particularly preferably 70.0 to 76.0 wt.-% SiO2.

[0017] It is further preferred that the lithium silicate low-temperature quartz glass-ceramic according to the invention comprises 8.0 to 15.0, particularly preferably 9.0 to 14.0, and very particularly preferably 10.0 to 13.5 wt.% LiO, which is presumed to reduce the viscosity of the glass matrix and thus promote the crystallization of the desired phases.

[0018] In a further preferred embodiment, the glass ceramic comprises 0 to 9.0, preferably 2.0 to 6.0, particularly preferably 3.0 to 5.0 wt. % P2O5, which is presumed to act as a nucleating agent.

[0019] The glass ceramic comprises 1.0 to 8.0, in particular 2.0 to 7.0 wt. % of oxides of monovalent elements Me selected from the group consisting of K2O, Na2O, Rb2O, Cs2O, and mixtures thereof. I It is also preferred to include 2O.

[0020] Particularly preferably, the glass ceramic contains, in the specified amounts, oxides of the following monovalent elements: Me I 2. Including at least one, especially all, of O. [ka]

[0021] In a particularly preferred embodiment, the glass ceramic according to the invention comprises 0 to 5.0, preferably 1.0 to 4.0, particularly preferably 2.0 to 3.5 wt. % K2O.

[0022] Furthermore, the glass ceramic contains from 1.0 to 9.0, preferably from 2.0 to 8.0, particularly preferably from 3.0 to 7.0 wt. % of oxides of divalent elements selected from the group consisting of CaO, MgO, SrO, ZnO and mixtures thereof. II It is preferred that it contains O.

[0023] In a further preferred embodiment, the glass ceramic comprises less than 2.0 wt. % BaO. In particular, the glass ceramic is substantially free of BaO.

[0024] Preferably, the glass ceramic contains, in the specified amounts, oxides of the following divalent elements: Me II O, including at least one, especially all. [ka]

[0025] In a particularly preferred embodiment, the glass ceramic according to the invention comprises 1.0 to 6.0, in particular 1.5 to 6.0, preferably 2.0 to 5.5, particularly preferably 3.1 to 5.5, very particularly preferably 3.4 to 5.0 wt.-% MgO.

[0026] 0 to 8.0, preferably 1.0 to 7.0, particularly preferably 2.0 to 6.5 wt. % of oxides of trivalent elements Me selected from the group consisting of Al2O3, B2O3, Y2O3, La2O3, Ga2O3, In2O3 and mixtures thereof III Glass ceramics containing 2O3 are even more preferred.

[0027] The glass ceramic particularly preferably contains the oxides of the following trivalent elements in the specified amounts: Me III 2O3, including at least one, especially all. [ka]

[0028] In a particularly preferred embodiment, the glass ceramic according to the invention comprises 1.0 to 6.0, preferably 2.0 to 5.0 wt. % Al2O3.

[0029] Furthermore, from 0 to 10.0, particularly preferably from 0 to 8.0 wt. % of oxides of tetravalent elements selected from the group consisting of ZrO2, TiO2, SnO2, CeO2, GeO2 and mixtures thereof, Me IV Glass ceramics containing O2 are preferred.

[0030] The glass ceramic particularly preferably contains, in the specified amounts, oxides of the following tetravalent elements: Me IV Contains at least one, especially all, of O2. [ka]

[0031] In a further embodiment, the glass ceramic comprises 0 to 8.0, preferably 0 to 6.0 wt. % of an oxide of a pentavalent element selected from the group of V2O5, Ta2O5, Nb2O5 and mixtures thereof, Me V Includes 2O5.

[0032] The glass ceramic particularly preferably contains the following oxides of pentavalent elements in the amounts specified: Me V Includes at least one, especially all, of the 2O5. [ka]

[0033] In a further embodiment, the glass ceramic comprises 0 to 5.0, preferably 0 to 4.0 wt. % of an oxide of a hexavalent element selected from the group of WO3, MoO3 and mixtures thereof, MeO3. VI Includes O3.

[0034] The glass ceramic particularly preferably contains the following oxides Me in the amounts specified: VI Includes at least one, especially all, of the O3s. [ka]

[0035] In a further embodiment, the glass ceramic according to the invention comprises 0 to 1.0, in particular 0 to 0.5 wt. % fluorine.

[0036] Particularly preferred are glass-ceramics which contain at least one, preferably all, of the following components in the amounts specified: [ka] Here, Me I 2O, Me II O, Me III 2O3, Me IV O2, Me V 2O5, and Me VI O3 has the meaning specified above.

[0037] In further particularly preferred embodiments, the glass ceramic comprises at least one, preferably all, of the following components in the amounts specified: [ka]

[0038] Some of the components listed above can act as colorants and / or fluorescent agents. The glass ceramic according to the present invention can also contain additional colorants and / or fluorescent agents. For example, these can be selected from Bi2O3 or Bi2O5, in particular from additional inorganic pigments and / or oxides of d-block and f-block elements, such as the oxides of Mn, Fe, Co, Pr, Nd, Tb, Er, Dy, Eu, and Yb. With the aid of these colorants and fluorescent agents, simple coloring of the glass ceramic is possible, particularly to mimic the desired optical properties of natural tooth materials. Surprisingly, this is possible without any problems, despite the presence of low-temperature quartz as an additional crystalline phase.

[0039] In a preferred embodiment of the glass-ceramic, the molar ratio of SiO to LiO is in the range of 2.2 to 4.1, preferably 2.2 to 3.8, particularly preferably 2.2 to 3.5. It is surprising that the preparation of glass-ceramics according to the invention having lithium silicate as the main crystalline phase and low-temperature quartz as a further crystalline phase can be achieved within these wide ranges.

[0040] The term "main crystalline phase" refers to the crystalline phase that has the largest mass fraction among all crystalline phases present in the glass-ceramic. The mass of the crystalline phase is determined in particular using the Rietveld method. Suitable methods for quantitative analysis of crystalline phases by the Rietveld method are described, for example, in M. Dittmer's in his doctoral dissertation, "Glasses and glass ceramics in the MgO-Al2O3-SiO2 system with ZrO2 as a nucleating agent,” University of Jena, 2011 do.

[0041] The glass ceramic according to the invention preferably comprises lithium disilicate or lithium metasilicate as the predominant crystalline phase. In a particularly preferred embodiment, the glass ceramic according to the invention comprises lithium disilicate as the predominant crystalline phase, since this glass ceramic has a particularly advantageous combination of desirable properties.

[0042] In the case of glass ceramics according to the invention having lithium metasilicate as the main crystalline phase, it is preferred that the glass ceramic also comprises, in addition to low-temperature quartz, lithium disilicate as a further crystalline phase.

[0043] The glass ceramic according to the invention preferably comprises at least 20 wt. %, preferably 25 to 55 wt. %, particularly preferably 30 to 55 wt. % of lithium disilicate crystals.

[0044] It is further preferred that the glass ceramic according to the invention comprises 0.2 to 28 wt. %, particularly preferably 0.5 to 25 wt. %, of low-temperature quartz crystals.

[0045] In addition to lithium silicate and low-temperature quartz, the glass ceramic according to the invention can contain further crystalline phases, such as apatite, cesium aluminosilicate, and especially lithium phosphate. However, the amount of cristobalite should be as small as possible, in particular less than 1.0 wt%. It is particularly preferred that the glass ceramic according to the invention is substantially free of cristobalite.

[0046] The type and especially the amount of crystalline phases formed can be controlled by the composition of the starting glass and also by the heat treatment used to prepare the glass-ceramic from the starting glass. The examples illustrate this with respect to variations in the composition of the starting glass and the heat treatment used.

[0047] The glass ceramic preferably has a high biaxial fracture strength of at least 200 MPa, particularly preferably 250 to 460 MPa. The biaxial fracture strength is determined in accordance with ISO 6872 (2008) ) (piston-on-ball test).

[0048] It is particularly surprising that, despite this high fracture strength, the glass ceramic according to the invention can be easily and quickly machined by computer-aided milling and grinding equipment to give the glass ceramic the shape of, for example, a dental restoration.

[0049] The glass ceramic according to the invention preferably has a viscosity of 9.5 to 14.0·10 -6 K -1 The coefficient of thermal expansion (CTE) is determined in accordance with ISO 6872 (2008). The coefficient of thermal expansion is particularly important for glass-ceramics. The desired value can be adjusted by the type and amount of crystalline phases present in the glass ceramic as well as the chemical composition of the glass ceramic.

[0050] The translucency of glass ceramics is measured by the contrast value ( The contrast value was determined in the form of a CR value, and the contrast value was preferably 40 to 92.

[0051] The particular combination of properties present in the case of the glass ceramic according to the invention even allows it to be used as a dental material, in particular as a material for the preparation of dental restorations.

[0052] The present invention further relates to various precursors with corresponding compositions from which the lithium silicate low-temperature quartz glass ceramic according to the invention can be prepared by heat treatment. These precursors are starting glasses with corresponding compositions and starting glasses with corresponding compositions and nuclei. The term "corresponding composition" means that these precursors contain the same components and amounts as the glass ceramic, where, as is customary for glasses and glass ceramics, the components, with the exception of fluorine, are calculated as oxides.

[0053] The present invention therefore also relates to a starting glass comprising the components of the lithium disilicate-low temperature quartz glass ceramic according to the invention.

[0054] The starting glass according to the invention therefore particularly comprises the appropriate amounts of SiO and LiO necessary to form a glass ceramic according to the invention having lithium silicate as the main crystalline phase and low-temperature quartz as a further crystalline phase. Furthermore, the starting glass can also comprise further components, as specified above for the lithium silicate-low-temperature quartz glass ceramic according to the invention. All of these embodiments specified as preferred components of the lithium silicate-low-temperature quartz glass ceramic according to the invention are also preferred as components of the starting glass.

[0055] The present invention also relates to a starting glass comprising nuclei for the crystallization of lithium metasilicate, lithium disilicate and / or low-temperature quartz.

[0056] The further precursor starting glass having nuclei can first be produced by heat treatment of the starting glass. The lithium silicate low-temperature quartz glass ceramic according to the invention can then be produced by heat treatment of this further precursor. It is preferred to form the lithium silicate low-temperature quartz glass ceramic according to the invention by heat treatment of the starting glass having nuclei.

[0057] To produce a starting glass containing nuclei for the crystallization of lithium metasilicate, lithium disilicate and / or low-temperature quartz, the starting glass is preferably subjected to a heat treatment at a temperature of 400 to 600°C, in particular 450 to 550°C, for a period of preferably 5 to 120 minutes, in particular 10 to 60 minutes.

[0058] To prepare a lithium silicate-low temperature quartz glass ceramic, it is further preferred that the starting glass with nuclei is heat-treated at a temperature of 700 to 900° C., in particular for 1 to 120 minutes, preferably 5 to 120 minutes, particularly preferably 10 to 60 minutes. To prepare a lithium silicate-low temperature quartz glass ceramic, the starting glass with nuclei is particularly preferably heat-treated at a temperature of 700 to 880° C., in particular 750 to 850° C., preferably for 5 to 120 minutes, particularly preferably 10 to 60 minutes.

[0059] The present invention also relates to a method for the preparation of a lithium silicate low-temperature quartz glass ceramic according to the invention, in which the starting glass, or the starting glass with nuclei, is subjected to at least one heat treatment at a temperature of 700 to 900°C, in particular for a period of 1 to 120 minutes, preferably 5 to 120 minutes, particularly preferably 10 to 60 minutes.

[0060] The starting glasses, and starting glasses with nuclei, can be subjected to at least one heat treatment, for example, in the form of a solid glass blank, a powder compact or a powder.

[0061] The at least one heat treatment carried out in the method according to the invention may also be carried out during hot pressing or sintering of the starting glass according to the invention or of the starting glass comprising the nuclei according to the invention. It can also be done in.

[0062] In a preferred embodiment, the method according to the present invention comprises: (a) heat treatment of the starting glass at a temperature of 400 to 600°C to form a starting glass having nuclei; and (b) Heat treatment of the starting glass with the nuclei at a temperature of 700 to 900°C to form a lithium silicate-low temperature quartz glass ceramic. Includes.

[0063] The duration of the heat treatment carried out in (a) and (b) is in particular from 5 to 120 minutes, preferably from 10 to 60 minutes.

[0064] To prepare the starting glass, the procedure is to melt a mixture of suitable starting materials, in particular carbonates, oxides, phosphates and fluorides, for 2 to 10 hours at temperatures of 1300 to 1600° C. To achieve a particularly high degree of homogeneity, the resulting glass melt is poured into water to form a granular glass material, and the resulting granules are then melted again.

[0065] The melt can then be poured into a mold to produce a blank of the starting glass, a so-called solid glass blank or monolith blank.

[0066] It is also possible to reintroduce the melt into water to prepare granules, which, after grinding and optionally adding further ingredients (such as colorants and fluorescent agents), can be pressed to form blanks, so-called powder compacts.

[0067] Finally, the starting glass may also be processed to form a powder after granulation.

[0068] The starting glass, for example in the form of a solid glass blank, a powder compact, or a powder, is then subjected to at least one heat treatment. Preferably, a first heat treatment is first carried out to prepare the starting glass according to the present invention having nuclei suitable for forming crystals of lithium metasilicate, lithium disilicate, and / or low-temperature quartz. The glass having nuclei is then usually subjected to at least one further heat treatment at a higher temperature to bring about the crystallization of lithium silicate, especially lithium disilicate, and low-temperature quartz.

[0069] The glass ceramics according to the invention and the glasses according to the invention are present in unsintered, partially sintered or densely sintered form, in particular in the form of powders, granules or blanks of any shape and size, for example monolithic blanks such as plates, cubes or cylinders, or powder compacts. In these forms, they can be easily further processed. However, they can also be present in the form of dental restorations, such as inlays, onlays, crowns, veneers, facets or abutments.

[0070] Dental restorations, such as bridges, inlays, onlays, crowns, veneers, facets, or abutments, can be prepared from the glass ceramics according to the invention and the glasses according to the invention. The invention therefore also relates to their use for the preparation of dental restorations. The glass ceramic or glass is preferably pressed or machined into the shape of the desired dental restoration.

[0071] Pressing is usually carried out under elevated pressure and at elevated temperature. Pressing is preferably carried out at a temperature of 700 to 1200°C. It is even more preferred to press at a pressure of 2 to 10 bar. During pressing, the desired change in shape is achieved by the viscous flow of the materials used. This is achieved by the following. The starting glasses according to the invention, in particular the starting glasses with nuclei according to the invention, and the lithium silicate low-temperature quartz glass ceramics according to the invention can be used for pressing. The glasses and glass ceramics according to the invention can be used in the form of blanks of any shape and size, for example solid blanks, or powder compacts, for example in unsintered, partially sintered, or densely sintered form.

[0072] Machining is usually carried out by a material-removing process, in particular by milling and / or grinding. It is particularly preferred that machining is carried out during a CAD / CAM process. The starting glasses according to the invention, the starting glasses with nuclei according to the invention, and the lithium silicate low-temperature quartz glass ceramics according to the invention can be used for machining. The glasses and glass ceramics according to the invention can be used, for example, in unsintered, partially sintered, or densely sintered form, in particular in the form of blanks, for example solid blanks, or powder compacts. The lithium silicate low-temperature quartz glass ceramics according to the invention are preferably used for machining.

[0073] After preparation of the desired shaped dental restoration, for example by pressing or machining, it may be further heat treated to reduce the porosity of, for example, the porous powder compact used.

[0074] However, the glass ceramics according to the invention and the glasses according to the invention are also suitable as coating materials, for example for ceramics and glass ceramics.The invention therefore also relates to the use of the glasses according to the invention or the glass ceramics according to the invention, in particular for coating ceramics and glass ceramics.

[0075] The invention also relates to a method for coating ceramics, metals, metal alloys and glass ceramics, in which the glass ceramic according to the invention or the glass according to the invention is applied to the ceramic or glass ceramic and exposed to elevated temperatures.

[0076] This can be done in particular by sinter-application or by joining a CAD / CAM-prepared superstructure with a suitable glass solder or adhesive, preferably by press-application. In the case of sinter-application, the glass ceramic or glass is applied to the material to be coated, for example to the ceramic or glass ceramic, for example as a powder, in the usual way and then sintered at elevated temperature. In the preferred press-application, the glass ceramic according to the invention or the glass according to the invention is press-application in the form of a powder compact or monolith blank at elevated temperatures, for example from 700 to 1200°C, for example, and under pressures of from 2 to 10 bar. For this purpose, in particular, the method described in EP-A-231773 and the pressing furnaces disclosed therein can be used. Suitable furnaces are, for example, those manufactured by Ivoclar Vivadent. AG (Liechtenstein) Programat EP 5000.

[0077] After the coating process is over, it is preferred that a glass ceramic according to the invention is present which has lithium silicate, in particular lithium disilicate, as the main crystalline phase and low-temperature quartz as a further crystalline phase, since such glass ceramics have particularly good properties.

[0078] Due to the above-mentioned properties of the glass ceramics according to the invention and the glasses according to the invention, they are particularly suitable for use in dentistry. The subject of the present invention is therefore also the use of the glass ceramics according to the invention as dental materials, in particular for the preparation of dental restorations, for example crowns, The use of the glass ceramic according to the invention or the glass according to the invention as coating material for bridges and abutments is also provided.

[0079] The invention is explained in more detail below with reference to non-limiting examples. [Example]

[0080] Examples 1 to 34 - Composition and Crystalline Phases A total of 34 glasses and glass-ceramics according to the invention, having the compositions specified in Table I, were prepared by melting the corresponding starting glasses and subsequent heat treatment for controlled nucleation and crystallization.

[0081] The heat treatments used for controlled nucleation and controlled crystallization are also specified in Table I. The following meanings apply: T g Glass transition temperature, determined by DSC T S and t S The temperature and time used to melt the starting glass T Kb and t Kb The temperature and time used for nucleation of the starting glass T C and t C The temperature and time used for crystallization T press and t press The temperature and time used for hot-press crystallization CR Value Contrast value of glass ceramic according to British Standard BS 5612 and Equipment: CM-3700d spectrometer (Konica-Minolta) Measurement parameters: Measurement area: 7mm x 5mm Measurement method: reflectance / reflection Measurement range: 400nm to 700nm Sample size: Diameter: 15~20mm Thickness: 2mm±0.025mm Surface parallelism: ±0.05mm Surface roughness: approx. 18 μm Determined using. Coefficient of thermal expansion of glass ceramics according to CTE ISO 6872 (2008), 100 Measured in the range of 500°C σBiax Biaxial breaking strength, measured according to ISO 6872 (2008)

[0082] The amount of crystalline phases was determined by the Rietveld method. For this purpose, powders of the individual glass ceramics mixed in a ratio of 50 wt% glass ceramic to 50 wt% Al2O3 were used, with Al2O3 (product name: Taimicron TM-DAR, manufactured by Taimei Chemical Industry Co., Ltd., Japan) as an internal standard. This mixture was slurried with acetone to achieve as good a complete mixing as possible. The mixture was then dried at about 80 °C. The Cu phase was then analyzed by a Bruker D8 Advance diffractometer. Kα Diffractograms were obtained in the range of 10 to 100°2θ using a line and a step size of 0.014°2θ. The diffractograms were then evaluated with TOPAS software by Bruker to determine the phase fractions. A lower limit of approximately 30 nm for the LiPO crystallite size was used for all diffractograms.

[0083] To produce the glasses and glass ceramics according to the invention, starting glasses in the range of 100 to 200 g were first melted from the usual raw materials at 1500° C. or 1400° C. for 1 to 3 hours, whereby melting was very easy without the formation of bubbles or streaks. Glass frit was prepared by pouring the starting glass into water, and then the frit was remelted at 1500°C or 1400°C for 1 hour for homogenization.

[0084] A first heat treatment of the starting glass at a temperature of 460 to 550°C resulted in the formation of a glass containing nuclei. As a result of a further heat treatment at 760 to 880°C, the glass containing these nuclei crystallized to form a glass-ceramic having lithium silicate as the main crystalline phase and low-temperature quartz as a further crystalline phase, as confirmed by X-ray diffraction studies. A lithium silicate-low-temperature quartz glass-ceramic according to the invention was thus obtained.

[0085] A) Solid glass block

[0086] In Examples 1 to 26, 28 and 31 to 34, the glass ceramics were prepared from solid glass blocks. S At a temperature of t S The resulting starting glass melt was then poured into a graphite mold to produce a solid glass block. These glass monoliths were then melted again for a period of time. Kb At a temperature of t Kb The starting glass containing the nuclei was then subjected to stress relaxation for a period of T C At a temperature of t C This resulted in the formation of a glass ceramic according to the invention having lithium disilicate as the main crystalline phase and low-temperature quartz as a further phase, as could be confirmed by X-ray diffraction studies at room temperature.

[0087] It is speculated that the transformation in this manner involved volume crystallization of lithium disilicate and low-temperature quartz.

[0088] B) Powder Compact

[0089] In Example 27, a glass ceramic was prepared from a powder compact. For this purpose, the obtained glass granules were ground in a zirconium oxide mill to a particle size of <90 μm. Approximately 4 g of this powder was then pressed to form a cylindrical blank and sintered in a sintering furnace (Programat®, Ivoclar Vivadent AG) at T C temperature, t C The mixture was sintered at a holding time of 100°C to form a high-density glass-ceramic body. As confirmed by X-ray diffraction studies at room temperature, a glass-ceramic body according to the invention was formed by sintering, having lithium metasilicate as the main crystalline phase and lithium disilicate and low-temperature quartz as further phases.

[0090] C) Preparation of dental restoration from block according to A)

[0091] The glass ceramic blocks produced according to Examples 1-26, 28, and 31-34 were machined in a CAD / CAM system to form the desired dental restorations, such as crowns. For this purpose, the crystallized blocks were mounted in suitable supports and then ground to the desired shape using an inLab MC XL grinding machine from Sirona Dental GmbH (Germany). For machining the blanks according to the invention, it was possible to use the same grinding parameters as for the commercially available e.max CAD blocks (Ivoclar Vivadent, Liechtenstein).

[0092] D) Hot pressing of glass ceramics

[0093] T press and t press In Example 19, where a glass ceramic is designated, the glass ceramic was prepared from a solid glass block by hot pressing.

[0094] For this purpose, the obtained glass granules are S At a temperature of t S It was melted again for The resulting melt of the starting glass was then poured into a preheated steel mold to produce rods. These monolithic glass rods were then molded into a T Kb At a temperature of t Kb The rod was then sawed to form small cylinders having a mass of about 4 to 6 g. These small cylinders were then cut into pieces by a process called T C At a temperature of t C The nucleated and crystallized cylinders were then crystallized for a period of time T press At a temperature of t press The mixture was pressed in a hot-press furnace for a holding time of 100 seconds to form a shaped body. After hot-pressing, a glass ceramic according to the invention was formed having lithium disilicate as the main crystalline phase and low-temperature quartz as a further crystalline phase, as could be confirmed by X-ray diffraction examination of the formed body at room temperature.

[0095] E) Sintering of nucleated glass

[0096] In Example 29, the starting glass was melted at 1500°C for 2 hours and then quenched in water. The resulting glass granules were then Kb At a temperature of t Kb The nucleated starting glass was pulverized to form a powder having an average particle size of 20 μm. Test specimens were prepared from this nucleated glass powder for determining the thermal expansion and optical properties. C At a temperature of t C After sintering to high density, a glass ceramic according to the invention was formed having lithium disilicate as the main crystalline phase and low-temperature quartz as a further additional phase, as could be confirmed by X-ray diffraction examination of the formed bodies at room temperature. [Table 1-1] [Table 1-2] [Table 1-3] [Table 1-4] [Table 1-5] [Table 1-6] [Table 1-7] For example, the present invention provides the following items. (Item 1) A lithium silicate-low temperature quartz glass ceramic comprising lithium silicate as the main crystalline phase and low temperature quartz as a further crystalline phase. (Item 2) 2. The glass-ceramic according to item 1, comprising 59.0 to 79.0, preferably 64.0 to 78.0, particularly preferably 64.0 to 76.0 wt.-% SiO2 or 68.0 to 79.0, preferably 69.0 to 78.0, particularly preferably 70.0 to 76.0 wt.-% SiO2. (Item 3) 3. The glass-ceramic according to claim 1 or 2, comprising 8.0 to 15.0, preferably 9.0 to 14.0, particularly preferably 10.0 to 13.5 wt.-% LiO. (Item 4) 4. The glass-ceramic according to any one of items 1 to 3, comprising 0 to 9.0, preferably 2.0 to 6.0, particularly preferably 3.0 to 5.0 wt.% P2O5. (Item 5) 1.0 to 8.0, preferably 2.0 to 7.0 wt % of oxides of monovalent elements Me selected from the group consisting of K2O, Na2O, Rb2O, Cs2O, and mixtures thereof I 5. The glass ceramic according to any one of items 1 to 4, comprising 2O. (Item 6) 6. The glass-ceramic according to any one of the preceding claims, comprising 0 to 5.0, preferably 1.0 to 4.0, particularly preferably 2.0 to 3.5 wt.% of K2O. (Item 7) 1.0 to 9.0, preferably 2.0 to 8.0, particularly preferably 3.0 to 7.0 wt. % of oxides of divalent elements Me selected from the group consisting of CaO, MgO, SrO, ZnO and mixtures thereof II 7. The glass ceramic according to any one of the preceding claims, comprising O. (Item 8) 8. The glass ceramic according to any one of the preceding claims, comprising 1.0 to 6.0, in particular 1.5 to 6.0, preferably 2.0 to 5.5, particularly preferably 3.1 to 5.5, very particularly preferably 3.4 to 5.0 wt.-% MgO. (Item 9) 0 to 8.0, preferably 1.0 to 7.0, particularly preferably 2.0 to 6.5 wt. % of oxides of trivalent elements Me selected from the group consisting of Al2O3, B2O3, Y2O3, La2O3, Ga2O3, In2O3 and mixtures thereof III 9. The glass-ceramic according to any one of the preceding claims, comprising 2O3. (Item 10) 10. The glass-ceramic according to any one of the preceding items, comprising 1.0 to 6.0, preferably 2.0 to 5.0 wt.% Al2O3. (Item 11) 11. The glass-ceramic according to any one of items 1 to 10, comprising SiO and LiO in a molar ratio ranging from 2.2 to 4.1, preferably from 2.2 to 3.8, particularly preferably from 2.2 to 3.5. (Item 12) 12. The glass-ceramic according to any one of the preceding items, comprising lithium disilicate or lithium metasilicate as the predominant crystalline phase, preferably lithium disilicate as the predominant crystalline phase. (Item 13) 13. The glass ceramic according to any one of the preceding claims, comprising at least 20 wt. %, preferably 25 to 55 wt. %, particularly preferably 30 to 55 wt. % lithium disilicate crystals. (Item 14) 14. The glass-ceramic according to any one of the preceding claims, comprising 0.2 to 28 wt. %, preferably 0.2 to 25 wt. %, of low-temperature quartz crystals. (Item 15) 12. A starting glass comprising the components of the glass-ceramic according to any one of items 1 to 11. (Item 16) 15. The starting glass according to item 14, comprising nuclei for the crystallization of lithium metasilicate, lithium disilicate and / or low-temperature quartz. (Item 17) 17. The glass ceramic according to any one of items 1 to 14, or the starting glass according to item 15 or 16, wherein the glass ceramic and starting materials are present in the form of a powder, granules, a blank or a dental restoration. (Item 18) 15. A method for the preparation of a glass ceramic according to any one of claims 1 to 14, wherein the starting glass according to claim 15 or 16 is subjected to at least one heat treatment in the range of 700° to 900°C. (Item 19) (a) the starting glass is subjected to a heat treatment at a temperature of 400 to 600°C to form the starting glass having nuclei; (b) the starting glass with nuclei is subjected to a heat treatment at a temperature of 700 to 900°C to form the lithium silicate-low temperature quartz glass ceramic; Item 19. The method according to item 18. (Item 20) 18. Use of a glass ceramic according to any one of items 1 to 14 or 17, or of a starting glass according to items 15, 16 or 17, as a dental material, preferably for coating dental restorations, particularly preferably for the preparation of dental restorations. (Item 21) 21. The use for preparing a dental restoration according to item 20, wherein the glass ceramic is brought into the shape of the desired dental restoration, in particular a bridge, an inlay, an onlay, a veneer, an abutment, a partial crown, a crown or a facet, by pressing or machining. (Item 22) 15. A method for the preparation of a dental restoration, in particular a bridge, inlay, onlay, veneer, abutment, partial crown, crown or facet, in which the glass ceramic according to any one of items 1 to 14 is brought into the shape of the desired dental restoration by pressing or machining, in particular during a CAD / CAM process.

Claims

1. Use of a lithium silicate-low temperature quartz glass ceramic as a dental material, the lithium silicate-low temperature quartz glass ceramic containing 1.0 to 3.5 wt % K. ２ 0 and 5.0 to 9.0 wt % P 2 O 5, and comprising lithium silicate as the main crystalline phase and low-temperature quartz as a further crystalline phase, wherein said glass-ceramic has at least 20 wt % lithium disilicate crystals and / or 0.2 to 28 wt % low-temperature quartz crystals.

2. The glass ceramic has a SiO content of 59.0 to 79.0, preferably 64.0 to 78.0, particularly preferably 64.0 to 76.0 wt. %. ２ or 68.0 to 79.0, preferably 69.0 to 78.0, particularly preferably 70.0 to 76.0 wt. % SiO ２ The use according to claim 1, comprising:

3. The glass ceramic contains 8.0 to 15.0, preferably 9.0 to 14.0, particularly preferably 10.0 to 13.5 wt. % Li ２ 3. The use according to claim 1 or 2, comprising O.

4. The glass ceramic has 1.0 to 8.0, preferably 2.0 to 7.0 wt % K ２ O, Na ２ O, Rb ２ O, Cs ２ Oxides of monovalent elements selected from the group consisting of O, and mixtures thereof. Ｉ ２ The use according to any one of claims 1 to 3, comprising O.

5. The glass ceramic contains 2.0 to 3.5 wt % K. ２ The use according to any one of claims 1 to 4, comprising O.

6. The glass ceramic contains 1.0 to 9.0, preferably 2.0 to 8.0, particularly preferably 3.0 to 7.0 wt. % of an oxide of a divalent element selected from the group consisting of CaO, MgO, SrO, ZnO and mixtures thereof. ＩＩ The use according to any one of claims 1 to 5, comprising O.

7. 7. Use according to any one of claims 1 to 6, wherein the glass ceramic comprises 1.0 to 6.0, in particular 1.5 to 6.0, preferably 2.0 to 5.5, particularly preferably 3.1 to 5.5, very particularly preferably 3.4 to 5.0 wt.-% MgO.

8. The glass ceramic contains 0 to 8.0, preferably 1.0 to 7.0, particularly preferably 2.0 to 6.5 wt. % Al ２ O ３ , B ２ O ３ , Y ２ O ３ , La ２ O ３ , Ga ２ O ３ , In ２ O ３ and mixtures thereof, ＩＩＩ ２ O ３ 8. The use according to any one of claims 1 to 7, comprising:

9. The glass ceramic contains 1.0 to 6.0, preferably 2.0 to 5.0 wt % Al ２ O ３ 9. The use according to any one of claims 1 to 8, comprising:

10. The glass ceramic is SiO ２ and Li ２ 10. Use according to any one of claims 1 to 9, wherein O is present in a molar ratio ranging from 2.2 to 4.1, preferably from 2.2 to 3.8, particularly preferably from 2.2 to 3.

5.

11. 11. Use according to any one of claims 1 to 10, wherein the glass ceramic comprises lithium disilicate or lithium metasilicate as the predominant crystalline phase, preferably lithium disilicate as the predominant crystalline phase.

12. 12. Use according to any one of claims 1 to 11, wherein the glass ceramic comprises at least 20 wt. %, preferably 25 to 55 wt. %, particularly preferably 30 to 55 wt. % of lithium disilicate crystals.

13. 13. Use according to any one of the preceding claims, wherein the glass ceramic comprises 0.2 to 28 wt%, preferably 0.2 to 25 wt%, of low-temperature quartz crystals.

14. 14. The use according to any one of claims 1 to 13, wherein the glass ceramic is present in the form of a powder, granules, a blank or a dental restoration.

15. 15. Use of a glass ceramic according to any one of claims 1 to 14 for coating a dental restoration or for the preparation of a dental restoration.

16. 16. The use for preparing a dental restoration according to claim 15, wherein the glass ceramic is pressed or machined into the desired shape of the dental restoration, in particular a bridge, an inlay, an onlay, a veneer, an abutment, a partial crown, a crown or a facet.

17. 14. A method for the preparation of a dental restoration, in particular a bridge, inlay, onlay, veneer, abutment, partial crown, crown or facet, wherein a glass ceramic according to any one of claims 1 to 13 is brought into the shape of the desired dental restoration by pressing or machining, in particular during a CAD / CAM process.

18. (a) 1.0 to 3.5 wt % K to form a starting glass with a nucleus ２ A starting glass containing O and 5.0 to 9.0 wt % P 2 O 5 is subjected to a heat treatment at a temperature of 400 to 600° C., (b) the starting glass with nuclei is subjected to a heat treatment at a temperature of 700 to 900°C to form the lithium silicate-low temperature quartz glass ceramic; A method for the preparation of a glass-ceramic according to any one of claims 1 to 13.

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