Method for producing a blank and dental restoration

Abstract

The invention relates to a method for the preparation of a blank from a ceramic material, wherein at least two layers of ceramic material of different compositions are filled into a die layer-by-layer and after filling of the layers they are then pressed and sintered, wherein after filling of a first layer this is structured on its surface in such a way that the first layer, viewed across its surface, differs in its height from region to region, and then a layer with a composition that differs from the first layer is filled as a second layer into the mold.

Claims

1. A method for producing a blank from a ceramic material, comprising the steps of: filling a die with at least two layers of ceramic materials of different compositions in pourable condition layer-by-layer; pressing the at least two layers of ceramic materials of different composition; and sintering the pressed at least two layers of ceramic materials of different compositions, wherein after filling of a first layer of a first ceramic material in pourable condition, a surface of the first layer is structured in such a way that the first layer when viewed across the surface, the surface differs from region to region in height in such a way that elevations and depressions or valleys are formed, and wherein a layer of a second ceramic material in pourable condition with a composition that is different from that of the first layer is filled into the die to form a second layer, wherein filing the die with the second ceramic material, a portion of the second ceramic material is disposed within the depressions or valleys formed between the elevations the first ceramic material along the structured surface of the first layer to form an intermediate layer having both the first ceramic material and the second ceramic material, the intermediate layer being located between the first layer having the first ceramic material and the second layer having the second ceramic material; and wherein the height of the intermediate layer is 1/10 to 1/5 of the total height of the at least two layers to be filled into the die.

2. The method according to claim 1, wherein the surface of the first layer is structured in such a way that result in the elevations, with the depressions or valleys that are demarcated from the elevations.

3. The method according to claim 1, wherein a ring structure is formed in the surface when viewed from above, which shows concentrical elevations and depressions.

4. The method according to claim 1, wherein the structure is produced by an element that moves in relative to the first layer and which structures the first layer in its surface region by means of a section which has a wave-like, comb-like or saw-tooth-like shape.

5. The method according to claim 1, wherein the structure is generated by a pressure element that acts in the direction of the surface of the first layer.

6. The method according to claim 1, wherein the pressure element used is such that elevations extending concentrically or parallel are pressed into the surface of the first layer with depressions extending between them.

7. The method according to claim 1, wherein the structure is formed such that the volume of the elevations is equal to, or approximately equal to, the volume of the depressions.

8. The method according to claim 1, wherein the materials used as ceramic materials include zirconium dioxide doped with yttrium oxide (Y.sub.2O.sub.3), calcium oxide (CaO), magnesium oxide (MgO) and/or cerium oxide (CeO.sub.2), wherein the material of the first layer differs from the material of the second layer in terms of color and/or the proportions of stabilized crystal forms present at room temperature.

9. The method according to claim 1, wherein the first layer in an unstructured state has a height that is half, or approximately half the total height H of the first and second layers.

10. The method according to claim 1, wherein the material used as the first and/or second ceramic material is one in which the percentage of yttrium oxide in the first layer is 4.5 wt % to 7.0 wt % and/or the percentage in the second layer is 7.0 wt % to 9.5 wt %, wherein the percentage of yttrium oxide in the first layer is lower than in the second layer.

11. The method according to claim 1, wherein prior to the step of sintering, the method further comprises the step of pre-sintering the pressed at least two layers of ceramic materials of different compositions such that the ceramic material used for the first layer and the second layer is one in which the ratio of tetragonal crystal phase to cubic crystal phase of the zirconium dioxide both in the first layer and in the second layer after pre-sintering is 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Figures

(1) FIG. 1a) to d) shows a schematic of an assembly and the process steps that can be carried out with it,

(2) FIG. 2 shows the assembly shown in FIG. 1b) in greater detail,

(3) FIG. 3a) to d) shows schematics to illustrate blank characteristics,

(4) FIG. 4 shows a schematic of the bridge to be prepared from a blank according to FIG. 3, and

(5) FIG. 5a) to d) shows a schematic of an alternative method.

DETAILED DESCRIPTION OF THE INVENTION

(6) The teaching according to the invention is made clear by reference to the figures, in which identical elements are provided with the same reference symbols. On the basis of the teaching, in particular, dental restorations are produced from a ceramic material that have a monolithic structure such that an immediately usable monolithic tooth replacement is obtained after complete sintering. For this purpose, in accordance with the invention, a blank is produced which consists of several layers of ceramic material with differing compositions, by means of which, according to the dental restoration to be produced, in particular desired optical and mechanical properties can be obtained which lead to a direct usable dental replacement without, for example, the need for material to be applied by hand and fired after complete sintering. In addition, desired strength values are achievable in the regions in which high loads occur, as in connector basal side of bridges.

(7) With reference to FIGS. 1 and 2, the production of a blank from which a corresponding dental restoration can be produced is described. Thus, as shown in FIG. 1a) a first material 14 is filled into the die 10 of a press 12, said material, in particular, being zirconium dioxide stabilized with yttrium oxide, may have the following composition in percentage by weight:

(8) TABLE-US-00003 HfO.sub.2 <3.0 Al.sub.2O.sub.3 <0.3 Technically caused, unavoidable components ≤0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O) Y.sub.2O.sub.3 4.5 to 7.0 Coloring oxides: 0-1.5 ZrO.sub.2 = 100 − (Y.sub.2O.sub.3 + Al.sub.2O.sub.3 + HfO.sub.2 + unavoidable components + color-imparting oxides)

(9) Subsequently, a second layer 24 is filled into the die 10 (FIG. 1c), wherein the total height of the layers 14 and 24 is equal to twice the height of the layer 14 in the unstructured state without restriction of the teaching according to the invention. The second layer may have the following composition in percentage by weight:

(10) TABLE-US-00004 HfO.sub.2 <3.0 Al.sub.2O.sub.3 <0.3 Technically caused, unavoidable components ≤0.2 (such as SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O) Y.sub.2O.sub.3 7.0 to 9.5 Color-imparting oxides: 0-1.5 ZrO.sub.2 = 100 − (Y.sub.2O.sub.3 + Al.sub.2O.sub.3 + HfO.sub.2 + unavoidable components + color-imparting oxides)

(11) The color-imparting oxides are in particular members of the group Pr, Er, Fe, Co, Ni, Ti, V Cr, Cu, Mn, Tb, preferably Fe.sub.2O.sub.3, Er.sub.2O.sub.3 or CO.sub.3O.sub.4.

(12) If the first layer 14 preferably has a height which corresponds to half the total height H of the first and second layer 14, 24, then the height of the first layer 14 can also be ½ H to ⅔ H and thus that of the second layer 24 ⅓ H to ½ H.

(13) The smoothed surface is then structured according to step b). For this purpose, for example, a disc-shaped or plate-shaped or web-shaped element 16 is used, which in the example embodiment has a toothed geometry on the layer side, so that a corresponding negative structure is formed in the surface 18 of the layer 14 by displacing material. This structure is represented by concentrically extending elevations and surrounding valleys. The distance between the elevation (peak) and the valley (depression), i.e., the clear distance between the projection 20 and the valley bottom 22 according to FIG. 2, should be approximately ⅕ of the height of all layers.

(14) In particular, it is provided that the structure is formed such that the volume of the elevations is equal to or approximately equal to the volume of the depressions or valleys.

(15) Since the material of the second layer 24 penetrates to the base of the valleys 26 in the surface 18 of the layer 14, there is a continuous transition between the properties of the layer 14 and the layer 24, after the layers 24, 14 have been pressed according to FIG. 1d). The transition or intermediate layer is denoted by the reference numeral 28 in FIG. 1d).

(16) The layer 24 consists of a material which differs from that of the layer 14. The difference lies, in particular, in the color additives and in the proportion of yttrium oxide. The latter is selected in such a way that the proportion of the cubic crystal phase in the layer 24 after pre-sintering is considerably greater than that in the layer 14. In layer 14, the tetragonal crystal phase fraction is more than 90%, while the cubic crystal phase fraction in layer 24 is between 30% and 49%. The remainder is essentially the tetragonal crystal phase.

(17) These different crystal phase fractions result from the fact that the yttrium oxide content in the layer 14 is between 4.5% and 7% by weight and in the layer 24 between 7% and 9.5% by weight, wherein the proportion in the first layer 14 is less than in the second layer 24.

(18) The color oxide fraction in the layer 24 is reduced compared to layer 14, being in the range from 0.0 to 1.5% by weight, preferably from 0.005 to 0.5% by weight. As a result of this measure, there is a continuous color transition between the layers 14 and 24. Due to the higher yttrium oxide content, the bending strength is reduced and there is also a higher translucency in the layer 24 compared to the layer 14.

(19) The highest strength is seen in the layer 14, in which the regions of the dental replacement which are subject to heavy loads, in particular the connector undersides of bridges, extend as shown in FIG. 4.

(20) The layers 14, 24 are pressed by means of a stamp 30, with a pressure between 1000 bar and 2000 bar.

(21) The pourable material, i.e., in the state in which it is filled into the die 10, has a bulk density between 1 g/cm.sup.3 and 1.4 g/cm.sup.3. After pressing, the density is approximately 3 g/cm.sup.3.

(22) As a result of the structuring, a density of up to 2 g/cm.sup.3 is obtained in the transition region between the unmixed regions of the first and second layers 14, 24 before the layers 14 and 24 are compacted. The transition region can also be referred to as middle layer 28.

(23) After pressing, the produced blank 33 is ejected from the mold 10 and pre-sintered in the customary manner at a temperature of between 800° C. and 1000° C. for a period of time between 100 minutes and 150 minutes. A corresponding blank is also shown in FIG. 4. The blank 33 comprises the compressed layer 14, the compressed layer 24 and the compressed middle layer 28, i.e., the transitional region.

(24) If a dental replacement is milled from the blank 33—in the example embodiment a bridge 34—then the milling program is designed in such a way that the lower region of the bridge 34, in particular, in the region of the connector's basal side 36, extends into the layer 14 that has the highest bending strength. The incisal region 40 of the bridge, by contrast, extends into the layer 24.

(25) In the transition region, i.e., in the middle layer 28, in which the quasi-continuous or continuous transition takes place between the layers 14 and 24, there is the transition between the dentin and the incisor region. The dentin extends in the region 14.

(26) Essential features of the teaching according to the invention are once again illustrated with reference to FIG. 3. Thus, FIG. 3 shows once again the blank 33 with the layers 14 and 24, as well as the transition region 28.

(27) FIG. 3b is intended to illustrate that the stabilizing agent in the form of yttrium oxide is approximately 5% by weight in the first layer 14 and approximately 9% by weight in the second layer 24, and that on the basis of the arrangement of the intermediate layer 28 according to the invention the percentage of yttrium oxide increases continuously. The values 0.425H and 0.575H illustrate that the element 16 shown in FIGS. 1 and 2 is placed in the first layer 14 in such a way that valleys are formed which extend with respect to the total height H of the layers 14, 24 in a region from 0.075H beneath the surface 18 and the elevations or peaks extend in a region from 0.075H above the surface 18, wherein as mentioned the distance between the peaks 20 and valleys 22 of the saw-tooth-shaped structure of the element 16 is 0.15H.

(28) Measurements of fully sintered layers 14 and 24 in accordance with DIN ISO 6872 have shown that the bending strength GB in layer 14, in which more than 80% of the tetragonal crystal phase of the zirconium dioxide is present, is approximately 1000 MPa. By contrast, the flexural strength in layer 24, in which 30 to 49% cubic crystal phase is present, is approximately 660 MPa.

(29) FIG. 3d shows the change in the translucency across the height of the layers 14, 24.

(30) With reference to FIG. 5 an alternative method, which follows the teaching according to the invention, wherein a blank or a dental restoration is to be prepared which provides a largely continuous transition between a first layer and a second layer or in the case of a restoration between the dentin region and incisal region in terms of translucency and strength.

(31) Thus, according to FIG. 5a, a first ceramic material, which corresponds to the layer 14 according to FIG. 1, is first filled into a die 10. The corresponding layer in FIG. 5a is indicated by the numeral 114. The height of this layer may be half the height of the total layers which are filled into the die 10. A layer 127 with a thickness which in the example embodiment is 1/10 of the total height of the layers is then applied to the layer 114. The material of the layer 127 can correspond to that of the second layer 24 according to FIG. 1. The layer 127 is then mixed with a surface region of the layer 114 over a depth corresponding to the thickness of the layer 127. This forms an intermediate layer 128 having a thickness of 2/10 of the total height of the layers. A further layer 124, which corresponds to the second layer 24 according to FIG. 1, is then applied to the intermediate layer 128. The height of the layer 124 in the example embodiment is thus 4/10 of the total height H. The layers 124, 128, 114 are then pressed together in accordance with the example embodiment of FIG. 1 to enable performance of the process steps pre-sintering, working and complete sintering as described. Working can naturally be carried out after complete sintering.