Lithium silicate glass ceramic with easy machinability

Abstract

To provide lithium silicate glass ceramic with easy machinability.SOLUTION: A lithium silicate glass ceramic has lithium metasilicate as a main crystal phase, and contains 30 wt.% or less of lithium metasilicate crystals.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to lithium silicate glass ceramics, particularly suitable for use in dentistry, and especially suitable for the preparation of dental restorations, and the present invention relates to a precursor for the preparation of this glass ceramic. [Background technology]

[0002] Lithium silicate glass ceramics are generally characterized by their excellent mechanical properties, and for some time now, they have been used in the dental field, primarily for the fabrication of dental crowns and small dental bridges.

[0003] International Publication No. 95 / 32678 describes lithium disilicate glass ceramics that can be processed into dental restorations by compression in a viscous state. However, the use of a deformable crucible is essential, which makes the processing very complicated.

[0004] European Patent Application Publication No. 0827941 and European Patent Application Publication No. 0916625 disclose lithium glass ceramic disilicate that can be given the shape of a desired dental restoration by compression or machining. European Patent Application Publication No. 1505041 and European Patent Application Publication No. 1688398 describe a method for producing lithium disilicate glass ceramic dental restorations. In this method, a glass ceramic containing lithium metasilicate as the main crystalline phase is first produced as a precursor, which can be mechanically processed, for example, using a CAD / CAM process. Next, this precursor is subjected to further heat treatment to form the desired high-strength lithium disilicate glass ceramic. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 95 / 32678

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Means for Solving the Problems

[0006] The machining of conventional lithium disilicate glass ceramics is difficult due to their high strength, and thus the tools used are regularly worn out significantly. The machining of lithium metasilicate glass ceramics is basically easier and is expected to have less tool wear. However, known lithium metasilicate glass ceramics can only be machined relatively slowly, for example, only by the grinding tools of a general CAD / CAM machine. This is particularly problematic when it is frequently desired to provide dental restorations to patients in a single treatment session (so-called treatment beside the examination table).

[0007] Therefore, there is a need for a lithium silicate glass ceramic that can be machined more rapidly than known lithium metasilicate glass ceramics and can then be converted into a high-strength dental product that still exhibits high chemical resistance and excellent optical properties.

[0008] This problem is solved by the lithium silicate glass ceramics according to claims 1 to 10 and 12. The subject matter of the present invention is also the starting glass according to claims 11 and 12, the method according to claims 13 and 14, the use according to claims 15 to 17, and the method according to claim 18. The present invention provides, for example, the following aspects. (1) A lithium silicate glass ceramic containing lithium metasilicate as the main crystalline phase, and containing 30 wt% or less of lithium metasilicate crystals. (2) A glass ceramic according to any of the above embodiments, comprising lithium metasilicate crystals in an amount of 28 wt% or less, preferably 26 wt% or less, particularly preferably 22 wt% or less, particularly 10 to 30 wt%, preferably 12 to 28 wt%, particularly preferably 15 to 26 wt%, and most preferably 18 to 22 wt%. (3) A glass ceramic according to any of the above embodiments, wherein the average size of the lithium metasilicate crystals is in the range of 5 to 80 nm, particularly in the range of 10 to 50 nm, preferably in the range of 15 to 45 nm, and most preferably in the range of 25 to 35 nm. (4) A glass ceramic according to any of the above embodiments, containing 71.0 to 82.0, preferably 73.1 to 80.0, and particularly preferably 74.0 to 78.0 wt% of SiO2. (5) A glass ceramic according to any of the above embodiments, containing 6.0 to 14.0, preferably 7.0 to 12.9, and particularly preferably 8.0 to 12.0 wt% Li2O. (6) A further amount of monovalent element oxides Me in 4.0 to 13.0, preferably 5.1 to 10.0, and particularly preferably 5.5 to 7.0 wt% I Including 2O, Me I A glass ceramic according to any of the above embodiments, wherein 2O is selected from Na2O, K2O, Rb2O, Cs2O and mixtures thereof, preferably K2O. (7) A glass ceramic according to any of the above embodiments, comprising 2.0 to 10.0, preferably 4.0 to 7.0, and particularly preferably 5.1 to 6.5 wt% Al2O3. (8) A glass ceramic according to any of the above embodiments, containing 0.5 to 7.0, preferably 1.0 to 4.0, particularly preferably 1.2 to 2.6, and even more preferably 1.5 to 2.5 wt% of P2O5. (9) The following ingredients are included in the amounts shown in the table below, preferably all of the following ingredients: [Table 3] Me I2O is selected from Na2O, K2O, Rb2O, Cs2O and mixtures thereof. Me II O is selected from MgO, CaO, SrO, ZnO, and mixtures thereof. Me III 2O3 is selected from B2O3, Y2O3, La2O3, Ga2O3, In2O3, and mixtures thereof. Me IV O2 is selected from TiO2, ZrO2, GeO2, SnO2, CeO2, and mixtures thereof. Me V 2O5 is selected from V2O5, Nb2O5, Ta2O5, and mixtures thereof. Me VI O3 is selected from MoO3, WO3, and mixtures thereof. A glass ceramic in any of the above embodiments. (10) A glass ceramic according to any of the above embodiments, wherein the molar ratio of SiO2 to Li2O is in the range of 2.5 to 5.0, preferably in the range of 2.9 to 4.6, and more preferably in the range of 3.3 to 4.4. (11) A starting glass comprising the components of any of the above embodiments of a glass ceramic, and in particular comprising a nucleus for the formation of lithium metasilicate crystals. (12) A glass ceramic or a starting glass of any of the above embodiments, wherein the glass ceramic and the starting glass are in the form of powder, granules, blanks or dental restorations. (13) A method for preparing a glass ceramic according to any of the above embodiments, comprising subjecting a starting glass according to any of the above embodiments to at least one heat treatment in the range of 450 to 750°C. (14)(a) The starting glass is subjected to heat treatment at a temperature of 450 to 600°C to form a starting glass containing a nucleus. (b) A method according to any of the above embodiments, wherein the starting glass containing the nucleus is subjected to heat treatment at a temperature of 550 to 750°C to form the glass ceramic. (15) Use of any of the glass ceramics or any of the starting glasss as dental materials, preferably for coating dental restorations, and particularly preferably for preparing dental restorations. (16) Any use of the above embodiments for the preparation of dental restorations, in which the glass ceramic is given the shape of a desired dental restoration, in particular a bridge, inlay, onlay, veneer, abutment, partial crown, crown or facet, by compression or machining. (17) Any of the above embodiments, wherein the glass ceramic is subjected to heat treatment at a temperature of 750 to 950°C, preferably 820 to 890°C, and particularly preferably 840 to 870°C for a period of particularly 1 to 60 minutes, preferably 5 to 30 minutes, more preferably 5 to 15 minutes, and even more preferably 5 to 10 minutes. (18) A method for preparing dental restorations, in particular bridges, inlays, onlays, veneers, abutments, partial crowns, crowns or facets, comprising, in particular in a CAD / CAM process, a method for giving a glass ceramic or starting glass of any of the embodiments the shape of a desired dental restoration by compression or machining. [Modes for carrying out the invention]

[0009] The present invention relates to lithium silicate glass ceramics, and has lithium metasilicate as the main crystalline phase, and contains 30 wt% or less of lithium metasilicate crystals.

[0010] The lithium silicate glass ceramic according to the present invention is characterized by having lithium metasilicate as the main crystalline phase and containing 30 wt% or less of lithium metasilicate crystals.

[0011] Remarkably, the glass ceramic according to the present invention has been shown to incorporate a highly desirable combination of mechanical and optical properties, particularly as needed for dental restorative materials. This glass ceramic has low strength and toughness, and therefore can be easily and quickly machined into the shapes of complex dental restoratives. After such machining, it can be converted into a glass ceramic product with excellent mechanical properties, excellent optical properties, and very good chemical stability by heat treatment.

[0012] The term "main crystalline phase" is used to describe the crystalline phase that has the highest proportion of mass among all crystalline phases present in glass ceramics. The mass of the crystalline phase is determined, in particular, using the Rietveld method. A suitable procedure for quantitative analysis of crystalline phases using the Rietveld method is described, for example, in the paper by M. Dittmer, "Glaser und Glaskeramiken im System MgO-Al2O3-SiO2mit ZrO2als Keimbildner," University of Jena 2011.

[0013] Preferably, the glass ceramic according to the present invention contains 28 wt% or less, preferably 26 wt% or less, and particularly preferably 22 wt% or less of lithium metasilicate crystals. Particularly preferably, the glass ceramic contains 10 to 30 wt%, preferably 12 to 28 wt%, more preferably 15 to 26 wt%, and most preferably 18 to 22 wt% of lithium metasilicate crystals.

[0014] In the glass ceramic according to the present invention, the average size of the lithium metasilicate crystals is preferably in the range of 5 to 80 nm, particularly in the range of 10 to 50 nm, preferably in the range of 15 to 45 nm, and even more preferably in the range of 25 to 35 nm.

[0015] The average size of lithium metasilicate crystals can, in particular, be determined by X-ray diffraction using CuKα radiation for the glass-ceramic powder. For this purpose, the obtained X-ray diffraction pattern can be evaluated according to the Rietveld method, and the average size of the lithium metasilicate crystals can be calculated from the half-value width of the peak of lithium metasilicate according to Scherrer's equation. This evaluation can preferably be carried out using software support, for example, using TOPAS 5.0 software manufactured by Bruker.

[0016] The lithium silicate glass-ceramic according to the invention contains in particular SiO2 of 71.0 to 82.0, preferably 73.1 to 80.0, particularly preferably 74.0 to 78.0 wt%.

[0017] It is further preferred that the glass-ceramic contains Li2O of 6.0 to 14.0, preferably 7.0 to 12.9, particularly preferably 8.0 to 12.0 wt%. Li2O is considered to reduce the viscosity of the glass matrix and thus promote the crystallization of the desired phase.

[0018] In another preferred embodiment, the glass-ceramic contains a further oxide Me2O of a monovalent element of 4.0 to 15.0, preferably 5.1 to 10.0, particularly preferably 5.5 to 7.0 wt%. I 2O, Me I 2O is selected from Na2O, K2O, Rb2O, Cs2O and mixtures thereof, preferably K2O.

[0019] Particularly preferably, the glass-ceramic contains at least one, particularly all, of the following further oxides Me2O of a monovalent element in the indicated amounts. I 2O.

Table 4

[0020] In a particularly preferred embodiment, the glass ceramic according to the present invention contains 2.0 to 10.0, preferably 5.1 to 9.0, and especially preferably 5.5 to 7.0 wt% of K2O.

[0021] Furthermore, the glass ceramic preferably contains 2.0 to 10.0, preferably 4.0 to 7.0, and particularly preferably 5.1 to 6.5 wt% Al2O3.

[0022] In another preferred embodiment, the glass ceramic contains 0.5 to 7.0, preferably 1.0 to 4.0, particularly preferably 1.2 to 2.6, and most preferably 1.5 to 2.5 wt% of P2O5. The P2O5 is thought to act as a nucleating agent.

[0023] The glass ceramic contains 1.0 to 9.0, preferably 2.0 to 8.0, and particularly preferably 3.0 to 7.0 wt%, of divalent element oxides Me selected from the group consisting of MgO, CaO, SrO, ZnO, and mixtures thereof. II It is even more preferable to include O.

[0024] In another preferred embodiment, the glass ceramic contains less than 2.0 wt% BaO. In particular, the glass ceramic is substantially BaO-free. Preferably, the glass ceramic contains the following divalent element oxides Me in the indicated amounts. II At least one of O, especially all of them. [Table 5]

[0025] In a particularly preferred embodiment, the glass ceramic contains 0.1 to 4.0, preferably 0.5 to 3.0, and especially preferably 1.0 to 2.0 wt% MgO.

[0026] In another particularly preferred embodiment, the glass ceramic contains 0.1 to 7.0, preferably 1.0 to 6.0, especially preferably 2.0 to 5.0, and most preferably 3.0 to 4.0 wt% of SrO.

[0027] Furthermore, 0 to 8.0, preferably 1.0 to 7.0, and particularly preferably 2.0 to 6.0 wt%, of a further trivalent element oxide Me selected from the group consisting of B2O3, Y2O3, La2O3, Ga2O3, In2O3 and mixtures thereof. III Glass ceramics containing 2O3 are preferred.

[0028] Particularly preferred is the glass ceramic containing the following further trivalent element oxides Me III At least one of 2O3, especially all of them. [Table 6]

[0029] Furthermore, 0 to 10.0, preferably 1.0 to 8.0, and particularly preferably 2.0 to 6.0 wt%, of a tetravalent element oxide Me selected from the group consisting of TiO2, ZrO2, GeO2, SnO2, CeO2, and mixtures thereof. IV Glass ceramics containing O2 are preferred.

[0030] Particularly preferred is the glass ceramic containing the following tetravalent element oxides Me IV Contains at least one, and especially all, O2 atoms. [Table 7]

[0031] In another embodiment, the glass ceramic contains 0 to 8.0, preferably 1.0 to 7.0, and particularly preferably 2.0 to 6.0 wt%, of a further pentavalent element oxide Me selected from the group consisting of V2O5, Nb2O5, Ta2O5, and mixtures thereof. V Contains 2O5.

[0032] Particularly preferred is the glass ceramic containing the following further pentavalent element oxides Me V At least one of 2O5, especially all of them. [Table 8]

[0033] In another embodiment, the glass ceramic contains 0 to 5.0, preferably 1.0 to 4.0, and particularly preferably 2.0 to 3.0 wt% of a hexavalent element oxide Me selected from the group consisting of MoO3, WO3, and mixtures thereof. VI Contains O3.

[0034] Particularly preferred is the glass ceramic containing the following amount of oxide Me VI At least one of O3, especially all of them. [Table 9]

[0035] In further embodiments, the glass ceramic according to the present invention contains 0 to 1.0, particularly 0 to 0.5 wt%, of fluorine.

[0036] Particularly preferred is the inclusion of at least one, preferably all, of the following components in the indicated amounts: [Table 10] Me I 20, Me II O, Me III 203, Me IV O2, Me V 2O5 and Me VI O3 has the above meaning. It is glass ceramic.

[0037] In another particularly preferred embodiment, the glass ceramic comprises at least one, preferably all, of the following components in the amounts shown. [Table 11]

[0038] Some of the aforementioned components can act as colorants and / or fluorescent agents. The glass ceramic according to the present invention may further contain additional colorants and / or fluorescent agents. These can be selected from, for example, Bi2O3 or Bi2O5, in particular from further inorganic pigments and / or oxides of elements d and f, such as oxides of Mn, Fe, Co, Pr, Nd, Tb, Er, Dy, Eu, and Yb. By using these colorants and fluorescent agents, it becomes possible to easily color the glass ceramic, particularly to mimic the desired optical activity of natural dental materials.

[0039] In preferred embodiments of the glass ceramic, the molar ratio of SiO2 to Li2O is in the range of 2.5 to 5.0, preferably 2.9 to 4.6, and particularly preferably 3.3 to 4.4. Despite these high molar excesses of SiO2 relative to Li2O, it is remarkable that the glass ceramic of the present invention can be formed using lithium metasilicate as the main crystalline phase.

[0040] The glass ceramic according to the present invention may contain further crystalline phases in addition to lithium metasilicate, such as quartz, particularly low-temperature quartz, apatite, cesium aluminosilicate, and particularly lithium phosphate. However, the amount of cristobalite should be as low as possible, especially less than 1.0 wt%. It is particularly preferable that the glass ceramic according to the present invention is substantially free of cristobalite.

[0041] The type, and especially the amount, of the crystalline phase formed can be controlled by the composition of the starting glass and the heat treatment applied to produce glass ceramics from the starting glass. Examples of this are shown by varying the composition of the starting glass and the heat treatment applied.

[0042] The glass ceramic preferably has a biaxial fracture strength of at least 80 MPa, and particularly preferably 100 to 200 MPa. The biaxial fracture strength was determined according to ISO 6872 (2008) (piston-on-three-balls test).

[0043] The glass ceramic according to the present invention is preferably 9.5 to 14.0·10 -6 K -1 It has a coefficient of thermal expansion CTE (measured in the range of 100 to 500°C). The CTE is determined according to ISO 6872 (2008). The coefficient of thermal expansion is adjusted to a desired value, in particular, depending on the type and amount of crystalline phase present in the glass ceramic, as well as the chemical composition of the glass ceramic.

[0044] The translucency of the glass ceramic was determined in relation to the contrast value (CR value) according to the British standard BS5612, and this contrast value was preferably between 40 and 92.

[0045] The present invention also relates to various precursors of corresponding compositions that can be used to produce lithium silicate glass ceramics according to the present invention by heat treatment. These precursors are starting glasses comprising a correspondingly composed starting glass and a correspondingly composed nucleus. The term "corresponding composition" means that these precursors contain the same components as the glass ceramics in the same amounts, and these components are calculated as fluorine-free oxides, as is common in glass and glass ceramics.

[0046] Therefore, the present invention also relates to a starting glass comprising the components of a lithium silicate glass ceramic according to the present invention.

[0047] Therefore, the starting glass according to the present invention contains appropriate amounts of SiO2 and Li2O, which are necessary to form the glass ceramic according to the present invention, particularly with lithium metasilicate as the main crystalline phase. Furthermore, the starting glass may also contain other components, as previously shown for the lithium silicate glass ceramic according to the present invention. All such embodiments are shown as preferred for the components of the starting glass, and these components are also shown as preferred for the components of the lithium silicate glass ceramic according to the present invention.

[0048] The present invention also relates to such a starting glass, which includes a nucleus for forming lithium metasilicate crystals.

[0049] The lithium silicate ceramics and starting glass according to the present invention exist, in particular, in the form of powders, granules, or blanks of any shape and size, such as monolithic blanks, such as platelets, rectangular parallelepipeds, or cylindrical objects, or powder compacts, and exist in unsintered, partially sintered, or densely sintered forms. In these forms, the lithium silicate ceramics and starting glass according to the present invention can be easily further processed. However, the lithium silicate ceramics and starting glass according to the present invention may also be in the form of dental restorations, such as inlays, onlays, crowns, veneers, facets, or abutments.

[0050] The procedure for preparing the starting glass involves, in particular, melting a suitable starting material, such as a mixture of carbonates, oxides, phosphates, and fluorides, at a temperature of 1300-1600°C for 2-10 hours. To achieve particularly high homogeneity, the resulting glass molten material is poured into water to form glass granules, which are then melted again.

[0051] Next, the molten material can be poured into a mold to produce a blank of starting glass, also known as a solid glass blank or monolithic blank.

[0052] It is also possible to reintroduce the molten material into water to produce granules. After grinding and, if necessary, adding further components such as colorants and fluorescent agents, these granules can be compressed into a blank, or so-called compact.

[0053] Finally, the starting glass can also be processed into powder after granulation.

[0054] Subsequently, the starting glass, for example in the form of a solid glass blank, compacted powder, or powder, is subjected to at least one heat treatment. Preferably, the first heat treatment is performed to produce the starting glass according to the present invention containing nuclei for forming lithium metasilicate crystals. Next, the starting glass containing the nuclei is subjected to at least one further heat treatment, typically at a higher temperature, to crystallize the lithium metasilicate and prepare the lithium silicate glass ceramic according to the present invention.

[0055] Accordingly, the present invention also relates to a method for preparing lithium silicate glass ceramics according to the present invention, comprising subjecting a starting glass or a starting glass containing a nucleus to at least one heat treatment at a temperature of 450 to 750°C for a period of particularly 1 to 120 minutes, preferably 5 to 120 minutes, and most preferably 10 to 60 minutes.

[0056] At least one heat treatment performed in the method according to the present invention may also be performed during the heating, compression, or sintering of the starting glass or the starting glass containing the nucleus according to the present invention.

[0057] To produce a starting glass containing nuclei for the crystallization of lithium metasilicate, the starting glass is preferably subjected to heat treatment at a temperature of 450-600°C, preferably 480-580°C, and particularly preferably 480-520°C, for a period of 1-120 minutes, preferably 10-60 minutes.

[0058] To produce lithium silicate glass ceramics, the starting glass containing the nucleus is more preferably subjected to heat treatment at a temperature of 550-750°C, preferably 580-700°C, and particularly preferably 590-630°C, for a period of 1-120 minutes, preferably 5-60 minutes, and most preferably 10-30 minutes.

[0059] Therefore, in a preferred embodiment, the method for preparing lithium silicate glass ceramic according to the present invention is (a) The starting glass is subjected to a heat treatment at a temperature of 450 to 600°C, preferably 480 to 580°C, particularly preferably 480 to 520°C, for a period of 1 to 120 minutes, preferably 10 to 60 minutes, to form a starting glass containing a nucleus, and (b) The starting glass containing the nucleus is subjected to a heat treatment at a temperature of 550 to 750°C, preferably 580 to 700°C, and most preferably 590 to 630°C, for a period of particularly 1 to 120 minutes, preferably 5 to 60 minutes, and most preferably 10 to 30 minutes, to form a glass ceramic. Includes.

[0060] The glass ceramics and glass according to the present invention are particularly suitable for use in dentistry due to their aforementioned properties. Therefore, an object of the present invention is also the use of the glass ceramics or glass according to the present invention as dental materials, particularly for the preparation of dental restorations, or as coating materials for dental restorations.

[0061] In particular, the glass ceramic and glass according to the present invention can be used to prepare dental restorations, such as bridges, inlays, onlays, veneers, abutments, partial crowns, crowns, or facets. Therefore, the present invention also relates to the use of the glass ceramic or glass according to the present invention for the preparation of dental restorations. In this situation, it is preferable to give the glass ceramic or glass the shape of the desired dental restoration by compression or machining.

[0062] The present invention also relates to a method for preparing dental restorations, wherein a glass ceramic or glass according to the present invention is given the shape of a desired dental restoration by compression or machining.

[0063] Compression is typically carried out at increased pressure and elevated temperature. Compression is preferably carried out at a temperature of 700–1200°C. Compression is even more preferably carried out at a pressure of 2–10 bar. During compression, the desired shape change is achieved by the viscous flow of the material used. The starting glass according to the present invention, particularly the starting glass containing a nucleus according to the present invention, and the lithium silicate glass ceramic according to the present invention can be used for compression. The glass and glass ceramic according to the present invention can be used in particular in the form of blanks of any shape and size, such as solid blanks or compacts, and can be used, for example, in unsintered, partially sintered, or densely sintered forms.

[0064] Machining is typically carried out by material polishing processes, particularly by milling and / or grinding. Machining is especially preferably carried out as part of a CAD / CAM process. The starting glass according to the present invention, the starting glass containing the nucleus according to the present invention, and the lithium silicate glass ceramic according to the present invention can be used for machining. The glass and glass ceramic according to the present invention can be used in particular in the form of blanks, such as solid blanks or compacts, and can be used in, for example, unsintered, partially sintered or densely sintered forms. Preferably, the lithium silicate glass ceramic according to the present invention is used for machining.

[0065] Surprisingly, it has been shown that the lithium silicate glass ceramic according to the present invention can be machined more rapidly than known lithium silicate glass ceramics when the same force is applied. To illustrate this property, in particular, the removal rate of the glass ceramic relative to the sample body can be determined. For this purpose, a plate-like material is cut from the sample body and weighed. Next, the plate-like material is bonded to a holder and ground under water cooling using an automatic grinding machine, for example, one available from Struers, with a diamond grinding wheel having a particle size of, for example, 20 μm. The grinding machine pressure is selected so that the same force, for example, 15 N, is applied to each plate-like material. After grinding the plate-like material for 1 minute, the plate-like material is dried and weighed again. Next, the removal rate is calculated according to the following formula. Polishing rate [wt%·min] -1 ] = 100 × (1 - (m 研削 :m 非研削 ))

[0066] It was further demonstrated that easily machinable lithium silicate glass ceramics containing lithium metasilicate as the main crystalline phase can be converted to glass ceramics containing lithium disilicate as the main crystalline phase through further heat treatment. This glass ceramic exhibits not only excellent mechanical properties, such as high strength, but also other properties necessary for dental restorative materials.

[0067] Therefore, after the glass ceramic has obtained the shape of the desired dental restoration, it can be subjected to further heat treatment to convert the lithium metasilicate crystals to lithium disilicate crystals. Preferably, the glass ceramic is subjected to heat treatment at a temperature of 750 to 950°C, preferably 820 to 890°C, and particularly preferably 840 to 870°C, for a period of 1 to 60 minutes, preferably 5 to 30 minutes, more preferably 5 to 15 minutes, and even more preferably 5 to 10 minutes. Suitable conditions for a given glass ceramic can be determined, for example, by performing X-ray diffraction analysis at different temperatures.

[0068] The conversion to lithium disilicate glass ceramics is associated with only a very small linear shrinkage of about 0.2–0.3%, which has been shown to be almost negligible compared to the linear shrinkage of up to 30% when ceramics are sintered.

[0069] However, the glass ceramics and glass according to the present invention are also suitable as coating materials for ceramics and glass ceramics, for example. Therefore, the present invention also relates to the use of the glass or glass ceramic according to the present invention for coating ceramics, glass ceramics, and especially dental restorations.

[0070] The present invention also relates to a method for coating ceramics, metals, metal alloys and glass ceramics, comprising applying a glass ceramic or glass according to the present invention to a ceramic, metal, metal alloy or glass ceramic and subjecting it to an elevated temperature.

[0071] This can be carried out particularly by compression, by sintering or by bonding overlays produced by using CAD-CAM with a suitable glass solder or adhesive. In the case of sintering, the glass ceramic or glass is applied in the usual manner, for example as a powder, to the material to be coated, e.g., ceramic or glass ceramic, and then sintered at an elevated temperature. In the preferred compression process, the glass ceramic or glass according to the present invention, for example in the form of a compact or monolithic blank, is compressed by applying pressure, e.g., 2 to 10 bar, at an elevated temperature, e.g., 700 to 1200°C. In particular, the method described in European Patent Application Publication No. 0231773 and the compression furnace disclosed in that document can be used for this purpose. A suitable furnace is, for example, the Programat EP 5000 made by Ivoclar Vivadent AG, Liechtenstein.

[0072] After the coating process is complete, glass ceramics containing lithium silicate, particularly lithium disilicate, as the main crystalline phase are preferable because they exhibit particularly good properties.

[0073] The present invention will be described in more detail below with reference to non-limiting examples. [Examples]

[0074] A total of 28 comparative examples having the glass according to the present invention and the compositions listed in Table I were prepared. The glass was crystallized into glass ceramics according to Table II. The following meanings apply. T g Glass transition temperature determined using DSC T S and t S Temperature and time applied for melting T Kb and t Kb Temperature and time applied for nucleation T C1 and t C1 Temperature and time applied for the first crystallization T C2 and t C2 Temperature and time applied for the second crystallization

[0075] In the example, first, a starting glass having the composition described in Table I is heated to a temperature T S During the period t S When melting common raw materials in 100-200g increments over a period of time, it was possible to melt them very well without the formation of bubbles or streaks. Glass frit was prepared by pouring the starting glass into water, and then melting it a second time at 1500°C or 1400°C for 1 hour for homogenization. The resulting molten starting glass was then poured into a graphite mold to produce a solid glass block.

[0076] The temperature of the obtained glass monolith, T Kb Period t in KbThe initial heat treatment over a certain period formed nucleated glass. These nucleated glasses, at temperature T C1 Period t in C1 Further heat treatment over several periods crystallized the material, forming a glass ceramic containing lithium metasilicate as the main crystalline phase, as determined by X-ray diffraction analysis at room temperature.

[0077] The amount and average size of the crystalline phase of lithium metasilicate crystals were determined by X-ray diffraction. For this purpose, each glass-ceramic powder was prepared by grinding and sieving (<45 μm) and mixed with Al2O3 (Alfa Aesar, product number 42571) as an internal standard in a ratio of 80 wt% glass-ceramic to 20 wt% Al2O3. This mixture was slurryed with acetone to achieve the best possible mixture. The mixture was then dried at approximately 80°C. Next, diffractograms were recorded using a Bruker D8 Advance diffractometer in the range of 10–100°²θ, using CuKα radiation and a step size of 0.014°²θ. These diffractograms were then analyzed according to the Rietveld method using Bruker TOPAS 5.0 software. The phase fractions were determined by comparing the peak intensities of lithium metasilicate and Al2O3, respectively. The average size of lithium metasilicate crystals was determined from the full width at half maximum (FMAX) of the lithium metasilicate peak, according to Scherrer's formula.

[0078] To determine the machinability of the glass ceramic blocks obtained in this way, each was measured at 170 mm. 2 ±10mm 2Two plate-like pieces with an area of ​​approximately 12.5 mm × 13.8 mm and a thickness of 4.0 ± 0.5 mm were cut out and weighed on a precision balance. Next, the plate-like pieces were glued onto a holder and ground using an automatic grinding machine (LaboForche-100, Struers) with a diamond grinding wheel having a particle size of 20 μm, under water cooling. The grinding machine pressure was selected so that a force of 15 N was applied to each plate. The turntable with the diamond grinding wheel and the grinding machine head with the holder holding the specimens had the same direction of rotation. The turntable speed was 300 revolutions per minute. The plate-like pieces were ground for 1 minute, then dried and weighed again. The polishing rate was calculated according to the following formula. Polishing rate [wt%·min] -1 ] = 100 × (1 - (m 研削 :m 非研削 ))

[0079] As can be seen from Table II, the polishing rates of Examples 1 to 28 according to the present invention were consistently higher than those of the comparative examples. This indicates that the lithium silicate glass ceramic according to the present invention can be machined more rapidly than known lithium silicate glass ceramics when the same force is applied.

[0080] The remaining glass ceramic block, at temperature T C2 During the period t C2 Further heat treatment was performed over a certain period. This resulted in the formation of a glass ceramic containing lithium disilicate as the main phase. Lithium phosphate and, in the case of Example 27, lithium strontium phosphate were found as minority phases. Table I [Table 1-1] [Table 1-2] [Table 1-3] Table II Table 2-1 Table 2-2 Table 2-3

Claims

1. A lithium silicate glass-ceramic comprising lithium metasilicate as the predominant crystalline phase and containing up to 30 wt % lithium metasilicate crystals.

2. 2. The glass-ceramic according to claim 1, comprising at most 28 wt. %, preferably at most 26 wt. %, particularly preferably at most 22 wt. %, in particular 10 to 30 wt. %, preferably 12 to 28 wt. %, particularly preferably 15 to 26 wt. %, and most preferably 18 to 22 wt. % of lithium metasilicate crystals.

3. 2. The glass-ceramic according to claim 1, wherein the lithium metasilicate crystallites have an average size in the range of 5 to 80 nm, in particular in the range of 10 to 50 nm, preferably in the range of 15 to 45 nm, particularly preferably in the range of 25 to 35 nm.

4. 71.0 to 82.0, preferably 73.1 to 80.0, particularly preferably 74.0 to 78.0 wt% SiO ２ 2. The glass-ceramic of claim 1, comprising:

5. 6.0 to 14.0, preferably 7.0 to 12.9, particularly preferably 8.0 to 12.0 wt% Li ２ 2. The glass-ceramic of claim 1 , comprising O.

6. 4.0 to 13.0, preferably 5.1 to 10.0, particularly preferably 5.5 to 7.0 wt. % of further oxides of monovalent elements Me Ｉ ２ Contains O, Me Ｉ ２ O is Na ２ O.K. ２ O, Rb ２ O, Cs ２ O and mixtures thereof, preferably K ２ 2. The glass-ceramic of claim 1 , wherein

7. 2.0 to 10.0, preferably 4.0 to 7.0, particularly preferably 5.1 to 6.5 wt. % Al ２ O ３ 10. The glass-ceramic of claim 1, comprising:

8. 0.5 to 7.0, preferably 1.0 to 4.0, particularly preferably 1.2 to 2.6, and even more preferably 1.5 to 2.5 wt % P ２ O ５ 10. The glass-ceramic of claim 1, comprising:

9. It comprises at least one, and preferably all, of the following ingredients in the amounts indicated: 【Table 12】 Me Ｉ ２ O is Na ２ O.K. ２ O, Rb ２ O, Cs ２ O and mixtures thereof; Me ＩＩ O is selected from MgO, CaO, SrO, ZnO and mixtures thereof; Me ＩＩＩ ２ O ３ But B ２ O ３ , Y ２ O ３ , La ２ O ３ , Ga ２ O ３ , In ２ O ３ and mixtures thereof; Me ＩＶ O ２ However, TiO ２ , ZrO ２ , GeO ２ , SnO ２ , CeO ２ and mixtures thereof; Me Ｖ ２ O ５ But, V ２ O ５ , Nb ２ O ５ , Ta ２ O ５ and mixtures thereof; Me ＶＩ O ３ But, MoO ３ , W.O. ３ and mixtures thereof; The glass-ceramic of claim 1 .

10. SiO ２ Li ２ 2. The glass-ceramic according to claim 1, wherein the molar ratio of H to O is in the range of 2.5 to 5.0, preferably in the range of 2.9 to 4.6, more preferably in the range of 3.3 to 4.

4.

11. A starting glass comprising components of a glass-ceramic according to any one of claims 1 to 10, in particular comprising nuclei for the formation of lithium metasilicate crystals.

12. A glass ceramic according to any one of claims 1 to 10 or a starting glass comprising components of a glass ceramic according to any one of claims 1 to 10, wherein the glass ceramic and the starting glass are in the form of a powder, granules, a blank or a dental restoration.

13. 11. A method for the preparation of a glass ceramic according to any one of claims 1 to 10, comprising subjecting a starting glass comprising the components of the glass ceramic according to any one of claims 1 to 10 to at least one heat treatment in the range of 450 to 750°C.

14. (a) subjecting the starting glass to a heat treatment at a temperature of 450 to 600°C to form a starting glass containing nuclei; (b) subjecting the starting glass containing nuclei to a heat treatment at a temperature of 550-750°C to form the glass-ceramic; The method of claim 13.

15. 11. Use of a glass ceramic according to any one of claims 1 to 10 or a starting glass comprising components of a glass ceramic according to any one of claims 1 to 10 as a dental material, preferably for coating dental restorations, particularly preferably for preparing dental restorations.

16. 16. Use according to claim 15 for the preparation of a dental restoration, in which the glass ceramic is given 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 compaction or machining.

17. 16. Use according to claim 15, wherein the glass ceramic is subjected to a heat treatment at a temperature of 750 to 950°C, preferably 820 to 890°C, particularly preferably 840 to 870°C, in particular for a period of 1 to 60 minutes, preferably 5 to 30 minutes, more preferably 5 to 15 minutes, even more preferably 5 to 10 minutes.

18. 11. A method for the preparation of a dental restoration, in particular a bridge, inlay, onlay, veneer, abutment, partial crown, crown or facet, in which a glass ceramic according to any one of claims 1 to 10 or a starting glass comprising components of a glass ceramic according to any one of claims 1 to 10 is given the shape of the desired dental restoration by compaction or machining, in particular in a CAD / CAM process.

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