Multi-Coloured Blank For Dental Purposes

Abstract

The present invention relates to a blank for dental purposes which has a first and a second layer which, independently of each other, are based on glass, glass-ceramic or ceramic, wherein the first layer and the second layer differ in colour and form a boundary surface, wherein the boundary surface runs obliquely.

Claims

1. Blank for dental purposes which comprises a first and a second layer which, independently of each other, are based on glass, glass-ceramic or ceramic, wherein the first layer and the second layer differ in colour and form a boundary surface, wherein the boundary surface runs obliquely.

2. Blank according to claim 1, in which in a first sectional plane through the blank, which runs parallel to the insertion axis of the blank, the boundary surface has an angle of 10 to 70° to the rotation axis.

3. Blank according to claim 1, in which in a first sectional plane through the blank, which runs parallel to the insertion axis of the blank, the boundary surface does not run perpendicular to the insertion axis.

4. Blank according to claim 3, in which the boundary surface in the first sectional plane runs substantially straight, wherein the boundary surface in the first sectional plane is preferably at an angle of from 20 to 80° to the insertion axis.

5. Blank according to claim 3, in which the boundary surface in the first sectional plane runs arcuately and the line of best fit through the arcuate boundary surface in the first sectional plane is at an angle of from 20 to 80° to the insertion axis.

6. Blank according to any one of claim 2, in which the angle between the insertion axis and the rotation axis of the blank in the first sectional plane is from 70 to 110°.

7. Blank according to any one of claim 2, in which the boundary surface runs arcuately through the blank in a second sectional plane which runs perpendicular to the first sectional plane, wherein the boundary surface runs convexly curved in the second sectional plane.

8. Blank according to claim 7, in which the boundary surface in the second sectional plane has a mamelon structure.

9. (canceled)

10. Blank according to claim 1, in which the first layer has a refractive index which differs from the refractive index of the second layer by not more than 0.1.

11. Blank according to claim 1, which comprises a mark which is recognized by a CAD/CAM device and with which the position of the boundary surface can be determined with an accuracy of 0.1 mm.

12. Blank according to claim 1, in which the glass, the glass-ceramic or the ceramic are selected from lithium silicate glass, lithium silicate glass-ceramic, silicon dioxide glass, silicon dioxide glass-ceramic and/or zirconium oxide.

13. Blank according to claim 12, in which the first and second layer, independently of each other, are based on lithium silicate glass, lithium silicate glass with nuclei or lithium metasilicate glass-ceramic, wherein the lithium silicate glass, the lithium silicate glass with nuclei or the lithium metasilicate glass-ceramic comprise at least one of the following components in the amounts indicated: TABLE-US-00006 Component wt.-% SiO.sub.2 64.0 to 73.0 Li.sub.2O 12.0 to 18.0 K.sub.2O  1.0 to 5.0 Al.sub.2O.sub.3  0.5 to 5.0 P.sub.2O.sub.5  1.0 to 7.0.

14. Blank according to claim 13, in which the amount of oxides of elements with an atomic number of 19 or higher in the first layer differs by not more than 2 wt.-% from the amount of oxides of elements with an atomic number of 19 or higher in the second layer.

15. Blank according to claim 12, in which the first and second layer, independently of each other, are based on silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic, wherein the silicon dioxide glass, the silicon dioxide glass with nuclei or the silicon dioxide glass-ceramic comprise at least one of the following components in the amounts indicated: TABLE-US-00007 Component wt.-% SiO.sub.2 58.0 to 92.0 Li.sub.2O  2.0 to 10.0 Me.sup.I.sub.2O   0 to 13.0 Me.sup.IIO   0 to 11.0 Me.sup.III.sub.2O.sub.3   0 to 10.0 Me.sup.IVO.sub.2   0 to 21.0 P.sub.2O.sub.5   0 to 7.0 Me.sup.V.sub.2O.sub.5   0 to 6.0 Me.sup.VIO.sub.3   0 to 6.0 Fluorine   0 to 5.0, wherein Me.sup.I.sub.2O is selected from Na.sub.2O, K.sub.2O, Rb.sub.2O and/or Cs.sub.2O; Me.sup.IIO is selected from MgO, CaO, SrO and/or ZnO; Me.sup.III.sub.2O.sub.3 is selected from Al.sub.2O.sub.3, B.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3, Ga.sub.2O.sub.3 and/or In.sub.2O.sub.3; Me.sup.IVO.sub.2 is selected from ZrO.sub.2, GeO.sub.2, CeO.sub.2, TiO.sub.2 and/or SnO.sub.2; Me.sup.V.sub.2O.sub.5 is selected in particular from V.sub.2O.sub.5, Ta.sub.2O.sub.5 and/or Nb.sub.2O.sub.5; and Me.sup.VIO.sub.3 is selected in particular from WO.sub.3 and/or MoO.sub.3.

16. (canceled)

17. Blank according to claim 12, in which the first and second layer, independently of each other, comprise unsintered zirconium oxide or presintered zirconium oxide.

18. (canceled)

19. Process for the production of a blank according to claim 1, in which (a) a first layer based on glass, glass-ceramic or ceramic is provided, (b) the surface of the first layer is shaped in order to provide the desired course of the boundary surface of the first and second layer of the blank, and (c) a second layer based on glass, glass-ceramic or ceramic is applied to the surface of the first layer.

20. Process for the production of a blank according to claim 12 with layers of lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass-ceramic, silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic, in which (a1) a first layer of lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass-ceramic, silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic with a viscosity of at least 6.6 Pa.Math.s is provided in a mould, (b1) the surface of the first layer is shaped in order to provide the desired course of the boundary surface of the first and second layer of the blank, and (c1) a second layer of lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass-ceramic, silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic is applied to the surface of the first layer.

21. Process for the production of a blank with layers of zirconium oxide according to claim 17, in which (a2) a first layer of unsintered or dispersed zirconium oxide is provided in a mould, (b2) the surface of the first layer is shaped in order to provide the desired course of the boundary surface of the first and second layer of the blank, and (c2) a second layer of unsintered or dispersed zirconium oxide is applied to the surface of the first layer.

22. Process for the production of a dental restoration, in which (d) a blank according to claim 1 is given the shape of the dental restoration by machining, (e) optionally at least one heat treatment is carried out, and (f) optionally the surface of the dental restoration obtained is finished.

23. (canceled)

24. (canceled)

25. (canceled)

26. Process according to claim 22, in which the dental restoration is selected from the group of crowns, abutments, abutment crowns, inlays, onlays, veneers, facets, bridges and overstructures.

27. (canceled)

Description

[0044] For example, FIG. 1 shows a schematic view of a multi-coloured blank 1 according to the invention, which has a first layer 3 and a second layer 5 which differ in colour and form a boundary surface 7. The boundary surface 7 runs in a first sectional plane, which runs parallel to the insertion axis 8 and in FIG. 1 is represented as side surface 15 of the blank, formed by edges 11 and 13, at an angle 16 to the insertion axis 8. The insertion axis 8 in the first sectional plane 15 runs perpendicular to the rotation axis 9 of the blank. The boundary surface 7 in the first sectional plane 15 runs at an angle 17 to the rotation axis 9. In a second sectional plane, which is represented in FIG. 1 by the side surface 23 formed by edges 19 and 21, the boundary surface 7 runs convexly curved and has a mamelon structure 25 with indentations 27. The blank 1 further has a holder 29 for the fixing in a CAD/CAM device, as well as marks 31a and 31b, which can be recognized by a CAD/CAM device, with the result that the course of the boundary surface 7 can be recognized by the CAD/CAM device.

[0045] FIG. 2 shows a schematic view according to a further embodiment of a multi-coloured blank 1, in which the boundary surface 7 between the first layer 3 and the second layer 5 in the sectional plane 15 does not run completely straight, but at least partially arcuately.

[0046] FIG. 3 shows a cross-section through the multi-coloured blank 1 according to FIG. 1 in the second sectional plane 23. The generally convexly curved course of the boundary surface 7 between the first layer 3 and the second layer 5 can be seen. This arcuate course is superimposed by the mamelon structure 25 with individual indentations 27.

[0047] FIG. 4 shows a schematic view of a further embodiment of the blank 1 according to the invention, in which the insertion axis 8 runs perpendicular to the rotation axis of the holder 29. Moreover, the position of the dental restoration 33 to be produced from the blank 1 is represented in the blank 1, wherein one part of the restoration 33, namely the part which is meant to imitate the incisal edge in an anterior region of the restoration 33, lies above the boundary surface 7, and another part of the restoration 33, namely the part which is primarily meant to imitate the dentine layer, lies below the boundary surface 7.

[0048] In a further embodiment, the boundary surface can be designed with colour effects. A subsequent colouring of the dental restoration to be produced from the blank can thereby be avoided. The colour effect can, for example, imitate an enamel crack, an enamel spot or another characterization. Such colour effects can be realized during the production of the blank, in that they are applied to the first layer before the second layer is applied to the first layer. 3D powder printing processes are also suitable for realizing the colour effects, wherein the effect is printed onto the blank which is then sintered.

[0049] With regard to the material of the blank according to the invention, it is preferred that the glass, the glass-ceramic or the ceramic are selected from lithium silicate glass, lithium silicate glass-ceramic, silicon dioxide glass, silicon dioxide glass-ceramic and/or zirconium oxide.

[0050] According to a first aspect, it is preferred that the layers of the blank according to the invention are based on lithium silicate glass, lithium silicate glass with nuclei or lithium metasilicate glass-ceramic, or consist thereof. Due to its relatively low strength, the shape of the desired dental restoration can be given to such a blank particularly simply by machining. According to an alternative embodiment, the layers of the blank according to the invention are based on lithium disilicate glass-ceramic.

[0051] Particularly preferably, the lithium silicate glass, the lithium silicate glass with nuclei, the lithium metasilicate glass-ceramic or the lithium disilicate glass-ceramic contain at least one and preferably all of the following components in the amounts indicated, wherein the amounts of the components are calculated as oxides, as is usual in the case of glasses and glass-ceramics:

TABLE-US-00001 Component wt.-% SiO.sub.2 64.0 to 73.0 Li.sub.2O 12.0 to 18.0 K.sub.2O  1.0 to 5.0 Al.sub.2O.sub.3  0.5 to 5.0 P.sub.2O.sub.5  1.0 to 7.0.

[0052] Furthermore, the lithium silicate glass, the lithium silicate glass with nuclei, the lithium metasilicate glass-ceramic or the lithium disilicate glass-ceramic preferably contain at least one and in particular all of the following components in the amounts indicated:

TABLE-US-00002 Component wt.-% ZrO.sub.2 0 to 1.0, such as about 0.1 ZnO 0 to 6.0 Na.sub.2O 0 to 2.0 Me.sup.IIO 0 to 5.0,

[0053] wherein Me.sup.IIO is a divalent oxide which is selected in particular from MgO, CaO and/or SrO.

[0054] Further preferred compositions for a lithium silicate glass, a lithium silicate glass with nuclei, a lithium metasilicate glass-ceramic or a lithium disilicate glass-ceramic are described in EP 1 505 041 A1 and EP 1 688 398 A1.

[0055] In particular, such compositions are preferred in which the amount of oxides of elements with an atomic number of 19 or higher in the first layer differs by not more than 2 wt.-%, preferably not more than 1.5 wt.-%, from the amount of oxides of elements with an atomic number of 19 or higher in the second layer.

[0056] It has surprisingly been found that it is possible, through the above-mentioned preferred compositions and in particular through the above-mentioned preferred condition with regard to the amount of oxides with an atomic number of 19 or greater, to provide a first and second layer which, despite their different colour have almost identical refractive indices. In this way it is possible to provide a blank and subsequently also a dental prosthesis in which no disruptive boundary surface between layers is visible.

[0057] The lithium silicate glass is usually produced by melting suitable starting substances. This glass can be converted into the lithium silicate glass with nuclei by heat treatment. The nuclei are those which are suitable for the crystallization of lithium metasilicate and/or lithium disilicate. The lithium silicate glass with nuclei can be converted to the lithium metasilicate glass-ceramic by heat treatment.

[0058] Finally it is possible to convert the lithium metasilicate glass-ceramic into high-strength lithium disilicate glass-ceramic by further heat treatment. The lithium silicate glass, the lithium silicate glass with nuclei and the lithium metasilicate glass-ceramic are therefore precursors of the lithium disilicate glass-ceramic.

[0059] A blank is further preferred in which the lithium metasilicate glass-ceramic contains lithium metasilicate as main crystal phase and in particular contains more than 5 vol.-%, preferably more than 10 vol.-% and particularly preferably more than 20 vol.-% lithium metasilicate crystals. The term “main crystal phase” refers to the crystal phase which has the highest proportion by volume compared with other crystal phases.

[0060] In a further embodiment, a blank based on a glass-ceramic is preferred which, in addition to a lithium silicate crystal phase, in particular a lithium metasilicate or lithium disilicate crystal phase, contains a further crystal phase, preferably an SiO.sub.2 crystal phase, such as low quartz. Particularly preferably, such a blank contains at least one and preferably all of the following components in the amounts indicated:

TABLE-US-00003 Component wt.-% SiO.sub.2 59.0 to 79.0, or 68.0 to 79.0 Li.sub.2O  8.0 to 15.0 P.sub.2O.sub.5   0 to 9.0 Me.sup.I.sub.2O  1.0 to 8.0 Me.sup.IIO  1.0 to 9.0 Me.sup.III.sub.2O.sub.3  1.0 to 8.0,

[0061] wherein Me.sup.I.sub.2O is selected from the group of K.sub.2O, Na.sub.2O, Rb.sub.2O, Cs.sub.2O and mixtures thereof, Me.sup.IIO is selected from the group of CaO, MgO, SrO, ZnO and mixtures thereof and Me.sup.III.sub.2O.sub.3 is selected from the group of Al.sub.2O.sub.3, B.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3, Ga.sub.2O.sub.3, In.sub.2O.sub.3 and mixtures thereof.

[0062] In the case of such glass-ceramics, the molar ratio of SiO.sub.2 to Li.sub.2O is preferably in the range of from 2.2 to 3.8. Furthermore, it is preferred that the lithium disilicate content in the glass-ceramic is more than 20 wt.-%, preferably 25 to 55 wt.-%. It is also preferred that the low quartz content is 0.2 to 28 wt.-%. Further preferred glass-ceramics which contain a low quartz crystal phase in addition to a lithium silicate crystal phase are described in EP 3 315 641.

[0063] In a preferred embodiment, the blank according to the invention has monolithic layers of lithium silicate glass, monolithic layers of lithium silicate glass with nuclei, monolithic layers of lithium metasilicate glass-ceramic or monolithic layers of lithium disilicate glass-ceramic.

[0064] The term “monolithic” refers to layers which are continuous and thus differ from discontinuous layers such as layers of particles, e.g. powder or granular-material layers. The monolithic layers used according to the invention can also be referred to as solid layers of the glasses and glass-ceramics.

[0065] The presence of monolithic layers in the blank according to the first aspect of the invention is also responsible for the fact that its conversion to the desired high-strength dental restoration is possible by heat treatment without substantial shrinkage. By contrast, the discontinuous layers present in the case of conventional blanks, such as pressed layers of powders or granular materials, still have to be densely sintered in order to produce the final dental restoration. However, this dense sintering leads to substantial shrinkage. In order to produce accurately fitting dental restorations, an enlarged form of the restoration must therefore be produced first and this enlarged form is then densely sintered. Such a procedure is, however, complex and prone to failure. It also first requires the precise determination of the enlargement factor to be selected in each case, which depends on the precise sintering conditions and the type of blank used, among other things.

[0066] According to a second aspect, it is preferred that the layers of the blank according to the invention are based on silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic, or consist thereof. In particular a blank in which the layers are based on silicon dioxide glass-ceramic or consist thereof is preferred. The shape of the desired dental restoration can be given to such a blank, even in a completely crystallized form, relatively simply by machining. A heat treatment after the machining is no longer necessary in this case, whereby such a blank is particularly advantageous.

[0067] Particularly preferably, the silicon dioxide glass, the silicon dioxide glass with nuclei or the silicon dioxide glass-ceramic contain at least one and preferably all of the following components in the amounts indicated:

TABLE-US-00004 Component wt.-% SiO.sub.2 58.0 to 92.0 Li.sub.2O  2.0 to 10.0 Me.sup.I.sub.2O   0 to 13.0 Me.sup.IIO   0 to 11.0 Me.sup.III.sub.2O.sub.3   0 to 10.0 Me.sup.IVO.sub.2   0 to 21.0 P.sub.2O.sub.5   0 to 7.0 Me.sup.V.sub.2O.sub.5   0 to 6.0 Me.sup.VIO.sub.3   0 to 6.0 Fluorine   0 to 5.0,

[0068] wherein Me.sup.I.sub.2O is selected in particular from Na.sub.2O, K.sub.2O, Rb.sub.2O and/or Cs.sub.2O; Me.sup.IIO is selected in particular from MgO, CaO, SrO and/or ZnO; Me.sup.III.sub.2O.sub.3 is selected in particular from Al.sub.2O.sub.3, B.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3, Ga.sub.2O.sub.3 and/or In.sub.2O.sub.3; Me.sup.IV.sub.2O is selected in particular from ZrO.sub.2, GeO.sub.2, CeO.sub.2, TiO.sub.2 and/or SnO.sub.2; Me.sup.V.sub.2O.sub.5 is selected in particular from V.sub.2O.sub.5, Ta.sub.2O.sub.5 and/or Nb.sub.2O.sub.5; and Me.sup.VIO.sub.3 is selected in particular from WO.sub.3 and/or MoO.sub.3.

[0069] Particularly preferably, the silicon dioxide glass-ceramic contains SiO.sub.2, in particular low quartz, cristobalite or a mixture thereof, as main crystal phase.

[0070] Further preferred silicon dioxide glasses, silicon dioxide glasses with nuclei or silicon dioxide glass-ceramics are described in WO 2015/173394 A1.

[0071] The blank according to the second aspect preferably has monolithic layers of silicon dioxide glass, monolithic layers of silicon dioxide glass with nuclei or monolithic layers of silicon dioxide glass-ceramic.

[0072] According to a third aspect, it is preferred that the first and second layer of the blank according to the invention contain unsintered zirconium oxide or presintered zirconium oxide.

[0073] Particularly preferably, a blank according to the third aspect contains at least one and preferably all of the following components in the amounts indicated:

TABLE-US-00005 Unit first layer second layer ZrO.sub.2 + HfO.sub.2 wt.-% 86.77-96.50 86.28-93.00 Y.sub.2O.sub.3 wt.-% 3.5-8.0 7.0-10.0 Al.sub.2O.sub.3 wt.-% 0.0-1.0 0.0-0.1 SiO.sub.2 wt.-% ≤0.02 ≤0.02 Na.sub.2O wt.-% ≤0.04 ≤0.04 TiO.sub.2 wt.-% ≤0.10 ≤0.10 CaO wt.-% ≤0.10 ≤0.10 Fe.sub.2O.sub.3 wt.-% 0.001-0.200 0.002-0.100 Mn.sub.2O.sub.3 wt.-% 0.000-0.001 0.000-0.001 Cr.sub.2O.sub.3 wt.-% 0.00-0.01 0.000-0.005 Pr.sub.2O.sub.3 wt.-% 0.000-0.003  0.00-0.002 Tb.sub.2O.sub.3 wt.-% 0.00-0.02 0.000-0.015 Er.sub.2O.sub.3 wt.-% 0.0-1.0 0.0-0.5 CoO wt.-%  0.0-0.04  0.0-0.04 NiO wt.-% ≤0.10 ≤0.10 Yb.sub.2O.sub.3 wt.-% ≤1.0 ≤1.0 La.sub.2O.sub.3 wt.-% ≤1.0 ≤1.0 MgO wt.-% ≤0.10 ≤0.10 further wt.-% ≤0.50 ≤0.50 oxides

[0074] The blanks according to the invention, including the blanks according to the invention of the first, second and third aspect, are preferably present in the form of blocks, cuboids, discs or cylinders, such as circular cylinders or cylinders with an elliptical base. In these forms, they can be further processed into the desired dental restorations particularly simply. Particularly preferably, the blanks according to the invention are present in the form of blocks.

[0075] In a further preferred embodiment, the blanks according to the invention have a holder for fixing in a processing device. The holder allows the fixing of the blanks in a processing device, such as in particular a milling or grinding device. The holder is usually in the form of a peg, and the holder preferably consists of metal or plastic.

[0076] The invention also relates to a process for the production of the blanks according to the invention.

[0077] The process for the production of the blank according to the invention according to the first aspect, i.e. a blank with layers, in particular monolithic layers, of lithium silicate glass, lithium silicate glass with nuclei or lithium metasilicate glass-ceramic, or the second aspect, i.e. a blank with layers, in particular monolithic layers of silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic, is characterized in that [0078] (a1) a first layer of lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass-ceramic, silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic with a viscosity of at least 6.6 Pa.Math.s is provided in a mould, [0079] (b1) the surface of the first layer is shaped in order to provide the desired course of the boundary surface of the first and second layer of the blank, and [0080] (c1) a second layer of lithium silicate glass, lithium silicate glass with nuclei, lithium metasilicate glass-ceramic, silicon dioxide glass, silicon dioxide glass with nuclei or silicon dioxide glass-ceramic is applied to the surface of the first layer.

[0081] Particularly preferably, in step (a1) a first layer of a glass, in particular of lithium silicate glass or silicon dioxide glass, is provided in the mould.

[0082] The shaping of the surface of the first layer carried out in step (b1) can preferably be achieved by pressing with a structured counter die, e.g. a die made of graphite. Due to the relatively low strength of the glass preferably used in step (a1), in step (b1) a slight pressing power of e.g. less than 10 MPa is sufficient to achieve the desired shaping.

[0083] Furthermore, it is preferred that in step (c1) a second layer of a glass, in particular of lithium silicate glass or silicon dioxide glass, is applied to the shaped first layer. This application can be effected for example by means of casting of the glass.

[0084] It is further preferred that, between shaping of the boundary surface and coating with the material of the second layer, the blank is not subjected to any heat treatment for forming crystalline phases. Rather, it is preferred that, following step (c1), the complete blank is subjected to a heat treatment, e.g. for forming crystal phases, such as a lithium metasilicate glass-ceramic or a silicon dioxide glass-ceramic.

[0085] In an alternative process, a blank according to the first or second aspect can be produced by gradually filling starting materials in the form of powder into a pressing die.

[0086] The process for the production of the blank according to the invention according to the third aspect, i.e. a blank with layers of zirconium oxide, is characterized in that [0087] (a2) a first layer of unsintered or dispersed zirconium oxide is provided in a mould, [0088] (b2) the surface of the first layer is shaped in order to provide the desired course of the boundary surface of the first and second layer of the blank, and [0089] (c2) a second layer of unsintered or dispersed zirconium oxide is applied to the surface of the first layer.

[0090] The term “dispersed” refers to zirconium oxide which is homogeneously distributed in a suspension in a liquid medium, such as aqueous or organic solvent. The viscosity of the suspension is preferably so high that, after the shaping in step (b2), the shaped form of the surface is maintained.

[0091] Particularly preferably, following step (c2), the complete blank is subjected to a heat treatment in order to provide a presintered blank and thus to improve the processability and precision in the case of a subsequent machining for the production of dental restorations.

[0092] Due to their properties, the blanks according to the invention are particularly suitable for further processing into dental restorations.

[0093] The invention therefore also relates to a process for the production of dental restorations, in which [0094] (d1) a blank according to the first aspect of the invention is given the shape of the dental restoration by machining, [0095] (e1) at least one heat treatment is carried out in order to convert the lithium silicate glass, the lithium silicate glass with nuclei or the lithium metasilicate glass-ceramic into lithium disilicate glass-ceramic, and [0096] (f1) optionally the surface of the dental restoration obtained is finished

[0097] or in an alternative embodiment [0098] (d2) a blank according to the second aspect of the invention is given the shape of the dental restoration by machining, [0099] (e2) optionally a heat treatment is carried out in order to convert the silicon dioxide glass or the silicon dioxide glass with nuclei into a silicon dioxide glass-ceramic or to increase the crystal content of a silicon dioxide glass-ceramic, and [0100] (f2) optionally the surface of the dental restoration obtained is finished

[0101] or in an alternative embodiment [0102] (d3) a blank according to the third aspect of the invention is given the shape of the dental restoration by machining, [0103] (e3) at least one heat treatment is carried out in order to convert the unsintered or presintered zirconium oxide into densely sintered zirconium oxide, and [0104] (f3) optionally the surface of the dental restoration obtained is finished.

[0105] The dental restorations, shaped as desired, can be simply carved out of the blanks according to the invention by machining. According to the first aspect of the invention, in particular blanks with layers of lithium silicate glass with nuclei or lithium metasilicate glass-ceramic (step (d1)) or, according to the second aspect in particular blanks with layers of silicon dioxide glass-ceramic (step (d2)) or, according to the third aspect of the invention in particular blanks with layers of presintered zirconium oxide (step (d3)) are used for this.

[0106] The machining is usually effected by material-removing processes and in particular by milling and/or grinding. It is preferred that the machining is effected with computer-controlled milling and/or grinding devices. Particularly preferably, the machining is effected during a CAD/CAM process.

[0107] In step (e1) the blank is subjected to a heat treatment in order to bring about the controlled crystallization of lithium disilicate and thus the formation of lithium disilicate glass-ceramic. The heat treatment takes place in particular at a temperature of from 750 to 950° C. and preferably 800 to 900° C. The heat treatment is carried out in particular for a duration of from 1 to 30 min, preferably 2 to 15 min.

[0108] In step (e2) the blank is optionally subjected to a heat treatment. However, in the case of a blank based on silicon dioxide glass-ceramic it is preferred that no heat treatment according to (e2) is carried out. Such a process is particularly simple and cost-effective and therefore particularly preferred.

[0109] In step (e3) the blank is subjected to a heat treatment in order to bring about the formation of densely sintered zirconium oxide ceramic. The heat treatment takes place in particular at a temperature of from 1050 to 1600° C. and preferably 1450 to 1550° C. The heat treatment is carried out in particular for a duration of from 0 to 240 min, preferably 5 to 180 min, particularly preferably 30 to 120 min, wherein the term “duration” relates to the holding time of the maximum temperature.

[0110] After steps (e1) or (e2) or (e3) have been carried out, dental restorations are present with layers of lithium disilicate glass-ceramic, silicon dioxide glass-ceramic or zirconium oxide ceramic which have excellent mechanical properties and a high chemical stability. In addition, due to the multiple layers that differ in colour, they allow an excellent imitation of the optical properties of natural tooth material, e.g. of colour gradients from the dentine to the incisal edge. Finally, with the aid of steps (d1) to (f1) or (d2) to (f2), the restorations can also be produced from the blanks according to the invention without substantial shrinkage. This is due, in particular, to the fact that the blanks according to the invention according to the first and second aspect have monolithic layers and not discontinuous layers such as powder or granular-material layers, whereby a sintering after the shaping and an associated shrinkage can be dispensed with. By using the blanks according to the invention, dental restorations with precisely the desired dimensions can therefore be produced particularly simply. In the case of blanks according to the invention according to the third aspect, the problem of the sintering shrinkage occurring in step (e3) can be solved in that the first and the second layer have a substantially identical total shrinkage during step (e3). Such a setting of the total shrinkage can be effected in that the starting and final densities, before and after the heat treatment, are in each case identical in both layers. In particular, as regards the beginning of sintering, the individual layers can be matched to each other by their composition, in particular by means of addition of sintering activators and/or inhibitors. Due to the oblique course of the boundary surface of the first and the second layer, the fit of the dental restoration to be produced is determined in particular by the fit and thus by the sintering shrinkage of the first layer of the blank according to the invention, which imitates the dentine layer and is less strongly influenced by possible different sintering shrinkage behaviours in the individual layers, than would be the case with conventional blanks with a horizontal layer sequence.

[0111] The dental restorations produced according to the invention are preferably selected from crowns, abutments, abutment crowns, inlays, onlays, veneers, facets and bridges, as well as overstructures for multi-part restoration frameworks which can consist e.g. of oxide ceramic, metals or dental alloys.

[0112] In the optional steps (f1), (f2) and (f3), the surface of the dental restoration can still be finished. It is in particular still possible to carry out a glaze firing at a temperature of from 700 to 850° C. or to polish the restoration. In addition, a layering material made of glasses and/or glass-ceramics can also be applied.

[0113] Due to the particular properties of the blanks according to the invention described, these are in particular suitable for producing dental restorations. The invention therefore also relates to the use of the blanks for the production of dental restorations and in particular of crowns, abutments, abutment crowns, inlays, onlays, veneers, facets and bridges, as well as overstructures. The use of the blanks according to the invention for the production of a dental prosthesis in the anterior tooth region, such as of an anterior tooth crown, is particularly preferred.