METHOD TO MANUFACTURE A COLORED BLANK, AND BLANK

Abstract

The invention relates to a method for manufacturing a colored blank, which contains zirconium dioxide and is intended for the manufacture of a dental restoration, whereby raw materials in powder form, at least some of which contain one coloring substance each, are mixed with, zirconium dioxide as the main ingredient, the resulting mixture is pressed and subsequently subjected to at least one thermal treatment. To generate the desired fluorescence, it is intended that in the raw materials in powder form one uses as coloring substances at least terbium, erbium, cobalt, as well as one substance that generates a fluorescence effect in the dental restoration, however not iron, aside from naturally occurring impurities.

Claims

1. A method for manufacturing a colored blank comprising zirconium dioxide that is intended for the production of a dental restoration, whereby raw materials in powder from, at least several of which contain one coloring element each, are mixed with zirconium dioxide as the main constituent, the resulting mixture is pressed, and subsequently subjected to at least one thermal treatment, wherein as the coloring elements in the raw materials in powder form one uses at least terbium, erbium, cobalt, as well as one element that generates a fluorescent effect in the dental restoration, while iron, apart from natural impurities, is not present.

2. The method of claim 1, wherein bismuth is used as the element that generates the fluorescent effect.

3. The method of claim 1, wherein disregarding naturally occurring impurities, a first raw material in powder form contains bismuth as the element that generates the fluorescent effect and/or a second raw material in powder from contains exclusively terbium or terbium and praseodymium and/or a third, raw material in powder form contains exclusively erbium and/or a fourth raw material in powder form contains exclusively cobalt or cobalt and manganese and/or cerium.

4. The method of claim 1, wherein one of the raw materials in powder form is free of coloring elements, apart from natural impurities.

5. The method of claim 1, wherein raw materials in powder form contains yttrium-stabilized zirconium dioxide of the following composition:
HfO.sub.2<3.0
Al.sub.2O.sub.3<0.3 Unavoidable impurities due to technical limitations ≦0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O)
Y.sub.2O.sub.3 4.5 to 9.5
ZrO.sub.2=100%−(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable impurities) in particular
HfO.sub.2<3.0
Al.sub.2O.sub.3<0.3 Unavoidable impurities due to technical limitations ≦0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O)
Y.sub.2O.sub.3 4.5 to 9.5
ZrO.sub.2=100%−(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable impurities)
or
HfO.sub.2<3.0
Al.sub.2O.sub.3<0.3 Unavoidable impurities due to technical limitations ≦0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O)
Y.sub.2O.sub.3 4.5 to 9.5
ZrO.sub.2=100%−(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable impurities)

6. The method for manufacturing a blank (28, 48) of claim 1, wherein introduced into a mold (10) is a layer of a first ceramic material (14), which consists of a first mixture, in that a first open cavity (18) is formed in the layer, in that at least into the first open cavity is introduced a second ceramic material (20), which consists a second mixture with a composition that is different from that of the first mixture, and in that the materials are together subjected to<pressing and a subsequent thermal treatment.

7. The method of claim 1, wherein after introduction of the second ceramic material (18), a second open cavity (26, 36) is created in it.

8. The method of claim 1, wherein into the second open cavity (36) is filled a third ceramic material (38), which possesses a composition that is different from those of the first and/or second ceramic material (20).

9. The method of claim 1, wherein in the layer formed of the first ceramic material (14) are formed several first open cavities (18) and into these is filled a ceramic material (18) in particular the second ceramic material.

10. The method of claim 1, wherein at least some of the several open first cavities (18) possess differing inside geometries.

11. The method of claim 1, wherein as the second ceramic material (20) one uses a material that after the sintering, to full density possesses a thermal expansion coefficient that is 0.2 to 0.8 μm/m*K greater than that of the first ceramic material (14).

12. The method of claim 1, wherein the interior geometry of the first open cavity (18) is geometrically matched'to the shape of a dental jaw region that is to be provided with a restoration, such as a tooth stump, or to that of an abutment originating from a jaw region.

13. The method of claim 1, wherein when working the dental restoration out of the blank (28, 48), the dentine region of the dental restoration is at least partially composed of the second ceramic material (20) and the incisal region of the first ceramic material (14),

14. The method of claim 1, wherein as the first and/or second ceramic material (14, 20) one choses the materials so that the yttrium oxide content in the first material is 7.0% by weight to 9.5% by weight and/or the content in the second and/or third material is 4.5% by weight to 7.0% by weight, whereby the yttrium oxide content in the first ceramic material is higher than that of the second or third material.

15. The method of claim 1, wherein in the chosen ceramic materials the quotient of the tetragonal crystal phase and the cubic crystal phase of the zirconium dioxide in the materials (14, 20) after pre-sintering is 1.

16. A method for the manufacture of a blank (133) of a ceramic material, whereby at least two layers (114, 124) are introduced by filling into a mold (110) ceramic material, which includes mixtures that were created in accordance with claim 1 and possess different compositions, and that after introduction of the layers, these are pressed and subsequently sintered, after introduction of a first layer (114) comprising of a first mixture, the surface of this layer is structured in such a way that the surface (118) of the first layer, viewed along the surface, possesses regions of different heights, and subsequently a second layer (124) comprising of a mixture with a composition different from that of the first mixture is filled into the mold, or in that after introduction of the first layer (214), a further layer (227) is filled on top of it into the mold (110), which consists of a mixture that is different from that of the first layer, in that the material of the first layer is intermixed with the material of the further layers to form an intermediate layer (228), and that subsequently the second layer (224) is filled into the mold (110).

17. The method of claim 16, wherein the surface (118) of the first layer (114) is being structured in a way so that depressions and elevations are created whereby the latter confine the former.

18. The method of claim 16, wherein in a top view of the surface (118) the created structure has an annular pattern, which comprises the depressions and the elevations bordering them.

19. The method of claim 1, wherein the structure is created by an element (116), which moves, in particular rotates, relative to the first layer (114), and which in particular structures the surface region of the first layer (114) with a segment that is embodied with a wave-like, comb-like or serrated shape.

20. The method of claim 1, wherein the structure is created by a pressure element that acts along a direction perpendicular to the surface (118) of the first layer (114).

21. The method of claim 1, wherein the employed pressure element imprints into the surface (118) of the first layer (114) elevations that extend concentrically or in parallel, and depressions extending in between the elevations.

22. The method of claim 16, wherein the structure is formed in such a way that the volume of the elevations is equal or approximately equal to the volume of the depressions.

23. The method of claim 16, wherein the material of the mixture of the additional layer (227) is intermixed with the material of the mixture of the first layer (214) downward from the free surface of the additional layer along a height that corresponds to twice or approximately twice the height of the additional layer.

24. The method of claim 23, wherein the mixture used for the additional layer (227) is identical to that of the second layer (124, 224).

25. The method of claim 1, wherein that the contacting regions of the first layer (114) and the second layer (124) are mixed over a height that corresponds to ⅕ H to ¼ H, in particular 1/10 H to ⅕ H, where H is the total height H of the first and second layer.

26. The method of claim 1, wherein that the first layer (114) in its unstructured state possesses a height that corresponds to half or approximately half the height of the total height H of the first and second layer (114, 124),

27. The method of claim 1, wherein the mixtures used for the first layer (114) and the second layer (124) are such that the quotient of the tetragonal crystal phase to the cubic crystal phase of the zirconium dioxide in both the first layer and the second layer will be a ≧1 after pre-sintering.

28. A pre-sintered or fully sintered blank (28, 48, 133) that is manufactured in accordance with claim 1.

29. A pre-sintered or fully sintered blank (28, 48) to be used in the manufacture of a dental restoration (42), such as a dental framework, crown, partial crown, bridge, coping, veneer, abutment, post and core, in particular a crown or partial crown, comprising of a ceramic material that in particular contains zirconium dioxide, and possesses regions of different compositions, whereby a first region (28) includes of a first ceramic material (14) and at least a second region (34) includes of a second ceramic material (20) of a different composition, and the regions adjoin each other, whereby in particular the first ceramic material and/or the second ceramic material include of a mixture according to claim 1, wherein the second region (34, 52, 54, 56) extends within the first region (32) and possesses an outside geometry that narrows as the distance from a base region (35) or base surface increases.

30. The blank of claim 28, wherein the base region (35) or rather the base surface of the second region (34) extends in the area of an outer surface (33) of the first region (32), and preferably merges flushly with this surface.

31. The blank of claim 28, wherein that the second region (34) has a cavity (26) that originates from its base region (35), or rather base surface.

32. The blank of claim 28, wherein the second region (34) possesses a cone-like exterior geometry.

33. The blank of claim 28, wherein within the second region (34) extends a third region (38), which includes of a third ceramic material with a composition that is different from that of the first and/or second ceramic material (14, 20).

34. The blank of claim 28, wherein a first region (32, 50) encompasses several second regions (52, 54, 56).

35. The blank of claim 28, wherein at least a few of the several second regions (52, 54, 56) have differing exterior geometries.

36. The blank of claim 28, wherein the blank (28, 48) contains zirconium dioxide doped with yttrium oxide.

37. The blank of claim 28, wherein the yttrium oxide content in the second or third ceramic material (20) is between 4.5% by weight and 7.0% by weight, while it is between 7.0% by weight and 9.5% by weight in the first ceramic material (14), whereby the yttrium oxide content in the first ceramic material is greater than in the second ceramic material.

38. The blank of claim 28, wherein the second ceramic material (20) is colored differently from the first ceramic material (14).

39. The blank of claim 28, wherein the content of the element generating the;fluorescent effect in the first ceramic material (14) is different from that in the second ceramic material (20).

40. The blank of claim 28, wherein after sintering to full density, the restoration (42) produced from the blank (28) possesses a higher strength on the dentine side than on the incisal side and/or a higher translucency on the incisal side than on the dentine side and/or in the dentine region a higher content of the element generating the fluorescence effect than in the incisal region.

41. The blank of claim 28, wherein the thermal expansion coefficient of the first region (32, 50) is 0.2 μm/m*K to 0.8 μm/m*K lower than the thermal expansion coefficient of the second and/or third region (34, 38).

42. The blank (133) of claim 28, wherein the blank (133) comprises at least three layers, one of which is a middle layer (128), which extends over at least 1/10 H to ⅕ H of the total height H of the blank, and which includes of a material of the first layer (114) and the second layer (124).

43. The blank of claim 42, wherein in the middle layer (128) the fraction of the material of the first layer (114) decreases along the direction from the first layer towards the_second layer (124) in a continuous or largely continuous manner.

44. The blank of claim 42, wherein the yttrium oxide content in the middle layer (128) increases from the first layer (114) towards the second layer (124) preferably in a continuous or largely continuous manner.

45. The blank of claim 42, wherein the first layer (114) is colored differently than the second layer (124) and/or contains different, amounts of the element generating the fluorescent effect.

46. The blank of claim 42, wherein after the sintering to completeness of the blank (133), the restoration (134) produced from the former exhibits, viewed along the tooth axis, a higher rigidity on the root side than on the incisal side and/or exhibits a higher translucency on the incisal side than on the root side.

47. A dental restoration (42), in particular a crown or partial crown, manufactured in accordance with claim 1, wherein the restoration (42) is embodied monolithically and includes at least of a first layer (32), which includes of a first ceramic material (14) and extends on the incisal side, and a second layer (34), which includes of a second ceramic material (20) and extends on the dentine side, whereby the first layer possesses a higher translucency and/or lower rigidity and/or a lower degree of fluorescence than the second layer.

48. The dental restoration of claim 47, wherein the thermal expansion coefficient of the first layer (32) is 0.2 μm/m*K to 0.8 μm/m*K lower than the thermal expansion coefficient of the second layer (34).

49. A dental restoration (134), in particular a crown, partial crown, or bridge, produced from a blank of claim 28, wherein the restoration (134), viewed along the axial direction of the tooth, includes of at least a first layer (140) extending on the root side, a second layer (124) extending on the incisal side, and, extending in between these, a middle layer (128) or intermediate layer (228), in which the strength decreases from the first layer towards the second layer in a continuous or largely continuous manner and/or in which the translucency increases continuously or largely continuously and/or in which the fluorescence characteristic decreases.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The figures show:

[0068] FIG. 1 shows a schematic diagram of a device for manufacturing a blank,

[0069] FIG. 2a) shows a schematic diagram of a device and a processing step performed with it,

[0070] FIG. 2b) shows another schematic diagram of the device shown if FIG. 2a) and a processing step performed with it,

[0071] FIG. 2c) shows another schematic diagram of the device shown in FIG. 2b) and a processing, step performed with it,

[0072] FIG. 3 shows an enlarged view of FIG. 2b),

[0073] FIG. 4 shows a blank with regions of different material properties,

[0074] FIG. 5 shows a further blank, with regions of differing material properties,

[0075] FIG. 6 shows a schematic diagram of a blank with the tooth to be produced from it, and

[0076] FIG. 7 shows a top view onto a blank with several regions of different material characteristics.

[0077] FIG. 8a) shows a schematic diagram of a device and a processing step it performs,

[0078] FIG. 8b) shows a schematic diagram of the device shown in FIG. 8a) and another processing step it performs,

[0079] FIG. 8c) shows a schematic diagram of the device shown in FIG. 8b) and another processing step it performs,

[0080] FIG. 8d) shows a schematic diagram of the device shown in FIG. 8c) and another processing step it performs,

[0081] FIG. 9 shows an enlarged view of FIG. 8b),

[0082] FIG. 10a) shows a schematic diagram to illustrate a characteristic of the blank,

[0083] FIG. 10b) shows another schematic diagram to illustrate another characteristic of the blank,

[0084] FIG. 10c) shows another schematic diagram to illustrate another characteristic of the blank,

[0085] FIG. 10d) shows another schematic diagram to illustrate another characteristic of the blank,

[0086] FIG. 11 shows a schematic diagram of a bridge to be produced from a blank of FIGS. 8a)-d), and

[0087] FIG. 12a) shows a schematic diagram of an alternative method and a processing step performed with it,

[0088] FIG. 12b) shows a schematic diagram of an alternative method and a processing step performed with it,

[0089] FIG. 12c) shows a schematic diagram of an alternative method and a processing step performed with it, and

[0090] FIG. 12d) shows a schematic diagram of an alternative method and a processing step performed with it.

DETAILED DESCRIPTION OF THE INVENTION

[0091] In the production of a dental restoration, one at first produces several starting raw material mixtures in powder form, which have the following composition:

[0092] Raw material 1 zirconium dioxide base (unpigmented zirconium dioxide powder) in percent by weight

HfO.sub.2<3.0

Al.sub.2O.sub.3<0.3

[0093] Unavoidable impurities due to technical limitations ≦0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O)

Y.sub.2O.sub.3 4.5 to 9.5

ZrO.sub.2=100%−(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable impurities)

[0094] Raw material 1 zirconium dioxide variant I (unpigmented zirconium dioxide powder) in % by weight:

HfO.sub.2<3.0

Al.sub.2O.sub.3<0.3

[0095] Unavoidable impurities due to technical limitations ≦0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O)

Y.sub.2O.sub.3 4.5 to 9.5

ZrO.sub.2=100%−(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable impurities)

[0096] Raw material 1 zirconium dioxide variant II (unpigmented zirconium dioxide powder) in percent by weight:

HfO.sub.2<3.0

Al.sub.2O.sub.3<0.3

[0097] Unavoidable impurities due to technical limitations ≦0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O)

Y.sub.2O.sub.3 4.5 to 9.5

ZrO.sub.2=100%−(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable impurities)

[0098] Raw material 2: zirconium dioxide variant II without Y.sub.2O.sub.3 and with erbium oxide (Er.sub.2O.sub.3) content of 9.2% by weight

[0099] Raw material 3; zirconium dioxide base, variant I or variant II with cobalt oxide (Co.sub.3O.sub.4) content of 0.04% by weight

[0100] Raw material 4; zirconium dioxide base, variant I or variant II with terbium oxide (Tb.sub.2O.sub.3) content of 2.0% by weight

[0101] Raw material 5; zirconium dioxide base, variant I or variant II with bismuth oxide (Bi.sub.2O.sub.3) content of 0.3% by weight

[0102] The above-specified number of raw materials in powder form should not be understood to be a limiting factor to the scope of protection of the invention.

[0103] To produce an artificial tooth of the VITA color A2, one mixes the following portions of the raw materials in powder form into, a mixture;

[0104] 91.40% by weight of raw material 1 zirconium dioxide variant II

[0105] 3.80% by weight of raw material 2

[0106] 1.25% by weight of raw material 3 (with zirconium dioxide variant II)

[0107] 3.50% by weight of raw material 4 (with zirconium dioxide variant II)

[0108] 0.05% by weight of raw material 5 (with zirconium dioxide variant II)

[0109] Additionally a binding agent may be added, which however is not taken into consideration in the above-listed percentages by weight.

[0110] The mixture 1 created in this manner then is filled into a mold 2 and pressed.

[0111] After the compacted piece has been removed from the mold, it is subjected to pre-sintering at a temperature between 800° C. and 1000° C. for a duration between 100 min and 150 min. In this, a de-binding takes place prior to the pre-sintering. After the pre-sintering, the density of the blank produced in this manner is approximately 3 g/m.sup.3. The breaking strength of the pre-sintered blank is in the region between 10 MPa and 60 MPa.

[0112] Subsequently the blank is provided with a holder or is accommodated by such, so that subsequently it can be machined in a milling or grinding machine, in order to work out an artificial tooth from the blank, for example for a dental restoration. This is followed by a sintering to final density at a temperature between 1450° C. and 1550° C., in particular at 1500° C. for a duration of 1-5 hours, in particular for 2 hours. The tooth produced in this manner possesses the tooth color VITA color A2 and possesses a fluorescence that corresponds to that of a natural tooth.

[0113] To produce the VITA color A4, one uses the following raw materials:

[0114] 79.16% by weight of raw material 1 zirconium dioxide variant II

[0115] 5.54% by weight raw material 2

[0116] 7.50% by weight raw material 3 (with zirconium dioxide variant II)

[0117] 7.50% by weight of raw material 4 (with zirconium dioxide variant II)

[0118] 0.30% by weight of raw material 5 (with zirconium dioxide variant II)

[0119] This is followed by thermal treatments and thermal treatment and processing steps, which were explained above. The completed natural tooth possessed the desired VITA color A4 with a fluorescence that corresponds to that of a natural tooth.

[0120] In a further experiment to produce a dental prosthesis in the VITA color A4 with a greater strength than the dental prosthesis described above, the following raw materials were mixed:

[0121] 80.46% by weight of raw material 1 zirconium dioxide variant I

[0122] 5.54% by weight of raw material 2

[0123] 6.25% by weight of raw material 3 (with zirconium dioxide variant I)

[0124] 7.50% by weight of raw material 4 (with zirconium dioxide variant I)

[0125] 025% by weight of raw material 5 (with zirconium dioxide variant I)

[0126] Even after the thermal treatment and the machining—as described above—it was found that the tooth possessed the VITA color A4 with a fluorescence.

[0127] FIGS. 2 to 7, in which identical elements always carry the same reference labels, will be used to illustrate an aspect that characterizes the present invention, which specifies the manufacture of a dental restoration with a monolithic structure from a ceramic material.

[0128] For this purpose the invention specifies the production of a blank that comprises regions of ceramic material that possess differing compositions and consequently possess properties that make it possible to achieve the desired optical and mechanical characteristics suitable for the particular restoration to be manufactured, and as mentioned above create the possibility to use the monolithically created dental prostheses immediately after sintering to final density, without the need, for example, to manually apply and burn an incisal.

[0129] It is also possible—in a targeted and selective manner—to achieve the desired strength values in those regions that are subject to high loads. Also achievable are the desired optical, such, as the color, translucency, and fluorescence characteristics.

[0130] FIGS. 2 to 4 are used to describe the manufacture of a blank, from which a dental restoration can be produced, in particular a tooth in the embodiment example.

[0131] At first one fills powder of the first raw material variant II into a mold 10 since this material is meant to be used as incisal material. The corresponding powder may contain a binding agent.

[0132] The relatively high yttrium oxide content ensures that in the completed molded part, i.e. the dental restoration, the tetragonal crystal phase content is as low as 50 to 60%, whereby the rest is present in, the cubic and monoclinic crystal phases.

[0133] Subsequently an open cavity 18 is formed by means of a press stamper 16 in the material 14 or rather in the layer formed by this material. The material 14 is displaced or slightly compacted by means of the press stamper. After the cavity 18 has been formed (FIG. 2b), the press stamper 16 is removed and a second ceramic material 20, which may possess the following composition is filled into the cavity 18, to manufacture a dental prosthesis with the color VITA color A2:

[0134] 91.66% by weight raw material 1 zirconium dioxide variant I

[0135] 3.26% by weight raw material 2

[0136] 2.0% by weight raw material 3 (with zirconium dioxide variant I)

[0137] 3.0% by weight raw material 4 (with zirconium dioxide variant I)

[0138] 0.08% by weight raw material 5 (with zirconium dioxide variant I)

[0139] Additionally, a binding agent may be present, but is not taken into consideration in the above-listed by-weight percentages.

[0140] In this, coloring oxides and bismuth oxide are present in such a quantity that one obtains the desired tooth color and fluorescence, since the second ceramic material 20 is used to form the dentine of the tooth to be manufactured.

[0141] Furthermore, the comparatively low proportion of Y.sub.2O.sub.3 ensures that the fully sintered dental prosthesis possesses a high tetragonal phase content of at least 85%, preferably at least 90%, which results in high stability.

[0142] After filling the second ceramic material 20 into the cavity 18 (FIG. 2c), the materials 14, 20, or rather the layers or regions formed from these materials, are then pressed in the mold 10 of the press 12—in particular by means of a lower or upper stamper 22, 24—, which is used for the compressing. After pressing, the density of the blank 28 is approximately 3 g/cm.sup.3 auf. Pressing preferably takes place at a pressure between 1000 bar and 2000 bar.

[0143] With respect to the materials 14, 20 it should be noted that their bulk density should be between 1 g/cm.sup.2 and 1.4 g/cm.sup.3.

[0144] After pressing, the density is approximately 3 g/cm.sup.3.

[0145] FIG. 3 reproduces in more detail the illustration of FIG. 2b). It is evident that a cavity 18 has been formed by the press stamper 16 in the first ceramic material 14 or rather in the layer consisting of this material. On the bottom side, the mold 10 is bordered by the press stamper 22.

[0146] As is illustrated in FIG. 4, a second cavity 26 can be created in the second material 20 after its compression by means of the press stamper 22, 24 or possibly after the pre-sintering, e.g. by means of milling.

[0147] However, one also has the option to form a second cavity 26 in the material 20 of FIG. 2c), which completely fills the cavity 18 that is open on its bottom side, by means of a not illustrated press stamper.

[0148] Irrespective of whether the second cavity 26 is present or not, the blank 28 is pre-sintered after pressing, at a temperature in particular in the range between 800° C. and 1000° C. for a duration of between 100 min and 150 min. In this, a de-binding is followed by the pre-sintering. The density of the blank 28 after pre-sintering is approximately 3 g/cm.sup.3. The breaking strength of the pre-sintered blank 28 should be between 10 MPa and 60 MPa.

[0149] The blank 28 is then, equipped with a holder 30, so that subsequently the blank 28 can be machined, e.g. in a milling or grinding machine, to produce a dental restoration such as a tooth out of the blank 28, as will be explained with the help of FIG. 6. In this, the tooth to be produced is at least virtually placed inside the blank 28 in such a manner that the incisal region extends within the region 32 consisting of the first ceramic material 14 and the dentine region in parts extends in the second region 34 consisting of the second ceramic material 20. The subsequent machining of the blank 28 takes these data into consideration.

[0150] FIG. 5 illustrates that after completing the first cavity 18 in the first ceramic material 14 and filling the second ceramic material 20 into the cavity 18, a second cavity 36 may possibly be created in accordance with the procedure according to FIG. 2b), in order to subsequently introduce into the cavity 36 formed in this manner a third ceramic, material 38, which differs in its composition from the second ceramic material in a way that in particular allows achieving a higher strength. As was explained in connection with FIG. 4 it is also possible to form a cavity 40 in the third ceramic material 38.

[0151] FIG. 6 illustrates how a dental restoration, a tooth 42 in the present embodiment example, is created out of the blank 28. For this purpose, knowing the extent of the first region 32 consisting of the first ceramic material 14 and the second region 34 consisting of the second ceramic material 20, the tooth 42 to be manufactured is virtually positioned inside the blank 28 into the regions 32, 34 in such a way that the incisal extends within the first region 32 and the dentine 46 extends within the second region 34.

[0152] After working the virtually positioned tooth 42 out of the blank 28, one has available a dental prosthesis that in principle can be deployed immediately, and in particular does not require any veneering. A monolithic tooth 42 is manufactured on the basis of the invention's teaching. In this, working the result out of the blank 28 is facilitated by the fact that the second region 34 already possesses an open cavity 26, as was explained in connection with FIG. 4 and is evident in FIG. 6.

[0153] The invention's teaching provides the possibility to create a blank 48 with a multitude of regions 52, 54, 56, that consist of the second and possibly of the third ceramic material and may possess different geometries (FIG. 7), to be able to produce teeth of different geometries. The so-called second regions 50, 52, 54, which are formed of the second ceramic material 20, are embedded in the first ceramic material 48, i.e. are surrounded by the latter, as is evident in the figures. The second regions 50, 52, 54 are not covered on the bottom side.

[0154] As is particularly well illustrated in FIGS. 3-5, the second regions exhibit exterior geometries that narrow with increasing distance from the bottom region, i.e, the base region 35. This can be referred to as a cone-like geometry, whereby the external contour is a freeform surface.

[0155] The base region 35, or rather the base surface bordering this region at the lower side, merges evenly into the lower side or bottom surface 33 of the first region 32.

[0156] To produce the sections 52, 54, 56 of the blank, which are also referred to as nests, one requires—as is explained in connection with FIG. 2—corresponding open cavities in the layer that is produced from the first material 14 and referred to as first region 50, in order to subsequently fill the cavities with the second ceramic material 20 in bulk form and to subsequently press, i e compact, the materials 14, 20 together.

[0157] It should be noted with respect to the physical characteristics of the materials 14, 20, that in addition to a different fluorescence, translucency, and rigidity characteristics, the two materials should also possess different thermal expansion coefficients. It is in particular intended by the invention that the first ceramic material 14 possesses after the sintering to full density a thermal expansion coefficient that is 0.2 μm/m*k to 0.8 μm/m*K lower than that of the second region 38, 52, 54, 56 that is formed by the second ceramic material 20. This generates a compressive stress in the first, region 50, i.e. in the incisal material, which results in an increase of the strength.

[0158] With respect to the blanks 28, 48 it should be noted that they may for example possess a cuboid shape with for example the dimensions 18×15×25 mm or a disk shape, e.g. with a diameter of 100 mm, without this placing any restrictions on the invention's teaching. This in particular offers the advantage—as is illustrated in connection with FIG. 7—that for example in a disk-shaped blank several second regions 52, 54. 56—so-called dentine cores—can be introduced to produce restorations of different geometries, but with a layer layout that is favorable with respect to translucency and rigidity.

[0159] Since the positions of one or several second regions 52, 56, i.e. of the nests, which possibly possess differing geometries, are known, they can be saved as records in a data set. Subsequently, the restorations to be manufactured are positioned relative to and within the sections of the blank, in order to create the dental prosthesis from the blank by milling and/or grinding.

[0160] In this, the artificial tooth to be manufactured is worked out of the blank 28, 48 in a way that takes into account the fluorescence characteristics generated during the sintering to full density, so that after the dense-sintering one, has available a tooth that is immediately useable.

[0161] Of course it is still within the scope of the invention's teaching if the artificial tooth is machined out of the blank only after the blank's sintering to full density.

[0162] A further embodiment of the invention's teaching is illustrated in FIGS. 8 to 12, where again identical elements carry the same reference labels. These figures also illustrate that the dental restorations can, be manufactured from a ceramic material and possess a monolithic structure of a nature so that after the sintering to final density a dental prosthesis is available for immediate use. For this it is intended according to the invention that a blank is manufactured that contains, several layers, which consist, of ceramic material but have differing compositions, which make it possible to achieve the particular optical and mechanical properties that are desired for a particular dental restoration to be manufactured, and that result in an immediate possible use of the dental prosthesis, without the need, for example, to manually apply and fire an incisal after the sintering to full density. It is also possible to obtain specific desired strength values in the regions that are subject to high loads, such as the lower sides of bridge connectors.

[0163] FIGS. 8 and 9 illustrate the manufacture of a blank, from which a corresponding dental restoration can be produced. In accordance with FIG. 8a), into the mold 110 of a press 112 is at first filled a first material 114, which is a mixture, of raw materials in powder form of the above-described type with the following proportions:

[0164] 97.19% by weight raw material 1 zirconium dioxide variant I

[0165] 0.54% by weight raw material 2

[0166] 1.25% by weight raw material 3 (with zirconium dioxide variant I)

[0167] 1.00% by weight raw material 4 (with zirconium dioxide variant I)

[0168] 0.01% by weight raw material 5 (with zirconium dioxide variant I)

[0169] Now the smoothed surface of the first layer 114 is provided with a pattern in accordance with step b). For this, one uses for example an element 116 with a disk- or plate- or bar-shaped geometry, which in the present embodiment example on the layer side possesses a serrated geometry, so that in the surface 118 of the layer 114 a corresponding negative pattern is formed by displacement of material. This structure is present as concentric elevations and valleys in between them. In this, the spacing between elevation (peak) and valley (depression), i.e. the clear distance between the projection 120 and the valley bottom 122 of FIG. 9 should be approximately ⅕ of the height of all layers.

[0170] In particular it is intended that the structure is applied in such a way that the volume of the elevations is equal or approximately equal to the volume of the depressions or valleys.

[0171] Subsequently the second layer 124 is filled into the mold 110 (FIG. 8c). The second layer 124 consists of a mixture of the raw materials in powder form with the following composition:

[0172] 80.46% by weight; raw material 1 zirconium dioxide variant II

[0173] 5.54% by weight: raw material 2

[0174] 6.25% by weight raw material 3 (with zirconium dioxide variant II)

[0175] 7.50% by weight raw material 4 (with zirconium dioxide variant II)

[0176] 0.25% by weight raw material 5 (with zirconium dioxide variant II)

[0177] The overall height of the layers 114 and 124 is equal to twice the height of the layer 114 in its unstructured state, without this having any limiting effect on the scope of the invention's teaching.

[0178] While the first layer 114 preferably has a height that corresponds to half the overall surface H of the first and the second layers 114, 124, the height of the first layer 114 may also range between ½ H and ⅔ H and consequently that of the second layer 124 between ⅓ H and ½ H.

[0179] The fact that the material of the second layer 124 penetrates to the bottom of the valleys 126 in the surface 118 of the layer 114 results in a continuous transition between the properties of the layer 114 and the layer 124, after the layers 124, 114 have been pressed in accordance with FIG. 8d). The transition or intermediate layer is, identified with the reference label 128 in FIG. 8d).

[0180] The layer 124 consists of a material that is different from that of the layer 114. Differences exist in particular in the coloring agents, the element generating fluorescence, and the yttrium oxide content. The latter is chosen so that the proportion of the cubic crystalline phase in the layer 124 after pre-sintering is significantly higher than the one in the layer 114. In the layer 114, the fraction of the tetragonal crystal phase is greater than 90%, whereas the cubic crystal phase content in the layer 124 is between 30% and 49%. The rest essentially is present in the, tetragonal crystal phase.

[0181] These differences in the crystalline phase fractions are the result of an yttrium oxide content of between 4.5% and 7% by weight in the layer 114 and of 7% to 9.5% by weight in the layer 124, whereby the content in the first layer 114 is lower than the one in the second layer 124.

[0182] Irrespective of the different proportions of the raw materials in the layers 114, 124, a continuous color transition is realized between the layers 114 and 124. The higher yttrium oxide content reduces the flexural strength. One also obtains a higher translucency in the layer 124 in comparison to the layer 114.

[0183] Because of the higher bismuth oxide content in the layer 114 in comparison to the layer 124 one obtains desired fluorescence characteristics in the completed, dental reconstruction.

[0184] The highest strength is found in the layer 114, which in the dental prosthesis to be created from the blank contains the regions that are subject to the highest loads, e.g. in particular the lower sides of the connectors of bridges, as is illustrated in FIG. 11.

[0185] The layers 114, 124 are pressed by means of a stamper 128, whereby the pressing takes place at a pressure of between 1000 bar and 2000 bar.

[0186] The material in bulk form, i.e. in the state in which it is introduced into the mold 110, has a bulk density between 1 g/cm.sup.3 and 1.4 g/cm.sup.3. The density after the pressing is approximately 3 g/cm.sup.3.

[0187] As a result of the structuring, one finds in the transition region between the unmixed regions of the first and the second, layers 114 and 124, before the layers 114 and 124 have been compacted, a density that can be as high as 2 g/cm.sup.3. The transition region may also be referred to as middle layer 128.

[0188] After pressing, the produced blank 133 is discharged from the mold 110 and is pre-sintered in the customary manner, in particular at a temperature between 800® C. and 1.000° C. for a duration between 100 min and 150 min. A corresponding blank is illustrated in FIG. 11. The blank 133 comprises the compacted layer 114, the compacted layer 124 and the compacted middle layer 128, i.e. the transition region.

[0189] If a dental prosthesis—in the embodiment example a bridge 134—is milled from the blank 133, the milling program should be designed so that the lower region of the bridge 134, in particular the area of the lower sides of the connectors 136, should be the location of the layer 114 with the greatest flexural strength. On the other hand, the incisal area 140 of the bridge is positioned within the layer 124.

[0190] In the transition area, i.e. in the middle layer 128, location of the quasi-continuous or continuous transition between the layers 114 and 124, is also the location of the transition between dentine and incisal. The dentine extends within the region 114.

[0191] Substantial features of the invention's teaching will be illustrated again with the help of FIG. 10. FIG. 10 shows the blank 133 with the layers 114 and 124 as well as the transition region 128.

[0192] FIG. 10b illustrates that the content proportion of the stabilizing agent in the form of yttrium oxide in the first layer 114 is approximately 5% by weight and is approximately 9% by weight in the second layer 124, and that because of the invention's embodiment of the intermediate layer 128, the yttrium oxide content increases continuously. The numbers 0.425 H and 0.575 H emphasize that the element 116 that is shown in FIGS. 8 and 9 dips into the first layer 114 in a way so that valleys are formed, which are situated—relative to the total height H of the layers 114, 124—in a region of 0.075 H below the surface 118 and the elevations or mountains are situated in a region of 0.075 above the surface 118, whereby—as mentioned above—the distance between the peaks 120 and troughs 122 of the serrated structure of the element 116 is 0.15 H.

[0193] Measurements pursuant to DIN-ISO 6872 that were carried out onr the fully sintered layers 114 and 124 have shown that the flexural strength σ.sub.B in the layer 114, in which more than 80% of the zirconium dioxide is present in the tetragonal crystalline phase, is approximately 1000 MPa. In contrast, the flexural strength of the layer 124, in which 30-49% are present in the cubic crystalline phase, is approximately 660 MPa.

[0194] FIG. 10d illustrates the change in translucency across the height of the layers 114, 124.

[0195] FIG. 12 will be used to explain an alternative method, which follows the invention's teachings to manufacture a blank or a dental restoration that offers a mostly continuous transition with respect to translucency and strength between a first layer and a second layer, or in the case of a restoration, between the dentine region and the incisal region.

[0196] In accordance with FIG. 12a, one at first introduces a first ceramic material, which should correspond to that of the layer 114 of FIG. 8 into a mold 110. The corresponding layer in FIG. 12a is identified with the label 214. The height of this layer may be half of the height of all the layers that are introduced into the mold 110. Onto the layer 214, one subsequently fills a layer 227 with a height that in the embodiment example is 1/10 of the total height of the layers. The material of the layer 227 can correspond to that of the second layer 124 of FIG. 8. This is followed by a mixing of the layer 227 with a surface region of the layer 214 throughout a depth that corresponds to the thickness of the layer 227. This creates an intermediate layer 228, which possesses a thickness of 2/10 of the overall height of the layers. Onto the intermediate layer 228, one subsequently applies a further layer 224, which corresponds to the second layer 124 of FIG. 8. The height of the layer 224 in the embodiment example consequently will be 4/10 of the total height H. Subsequently, in accordance with the embodiment example of FIG. 8, the layers 224, 228, 214 are pressed as a whole, which is followed by the process steps pre-sintering, machining, and sintering to final density, as was explained above. Of course it is also possible to carry out the machining after the sintering to final density.