Patent Description:
The invention also relates to the use of a blank for the production of a dental restoration.

<CIT> discloses a method for the production of a dental product of lithium disilicate, wherein a lithium silicate glass melt is poured into a steel mold and is cooled, so that temperature treatment is then used to transform the glass into a glass ceramic. The glass ceramic is then comminuted to a powder and compressed, and the blank so produced is pre-sintered. The blank is then heated and pressed into a mold to yield a dental restoration.

<CIT> discloses the use of a lithium silicate blank which contains lithium metasilicate as a main crystal phase and is intended for the production of a dental restoration. To produce the blank, the glass melt is poured into a mold to obtain a block which is then subjected to heat treatment to provide a lithium metasilicate glass ceramic blank, so that a dental restoration can be derived from this, for example through milling or grinding,.

<CIT> discloses a lithium disilicate glass ceramic product. A dental product can thereby be derived from a blank, which has been produced by casting a melt into mold, through hot pressing or computer-controlled milling. The dental restoration derived through mechanical working then has to undergo further heat treatment to achieve the desired strength.

<CIT> refers to a lithium silicate glass ceramic and glass with ZrO<NUM> content. Lithium silicate glass is melted in order to then produce a glass frit. Granulate is pressed and sintered. Cylindrical glass blanks are produced which are then subjected to a heat treatment. From the blanks are then produced dental restorations by means of hot-pressing or a CAD/CAM method.

<CIT> refers to a method for making pressable lithium disilicate glass ceramics. A glass ceramic powder is pressed, whereby blanks may be machined to a dental restoration of desired geometry.

<CIT> refers to a lithium silicate glass ceramic and a lithium silicate glass comprising a trivalent metal oxide. A powder pellet is produced, in order to subsequently perform a controlled crystallization. From the pellet dental restorations are produced by means of a CAD/CAM method.

<CIT> refers to green body zirconia dental blanks with chemical compositions of increasing amounts of yttria through a thickness thereof to form the dental prosthesis with an optical characteristic of decreasing chroma through a thickness of the dental prosthesis after sintering.

The aim of the present invention is to further develop a method using a blank of the above-described type in such a way that dental restorations of the desired dimensions are made available without difficulty, wherein with simple measures a desired coloration and/or translucency can be obtained where necessary. In particular, it is intended that after production of the dental restoration from a blank there is no need for further heat treatment steps.

To achieve this aim the invention relates to a method for the production of a restoration from a blank according to claim <NUM>, and the use of a blank to manufacture a dental restoration according to claim <NUM>. Preferred embodiments are described by the dependent claims. The invention in the main provides for at least two layers of powders, which have been derived from starting lithium silicate glasses of different compositions, to be filled into a mold layer-by-layer, wherein after introduction of a first layer the surface of this layer is structured such that the first layer viewed across its surface varies in its height from one region to another, and then as the second layer a layer with a composition that differs from that of the first layer is filled into the mold, or that after introduction of the first layer a further layer of a powder is filled into the mold that differs in its composition from the first layer, that the material of the first layer is mixed with the material of the further layer to form an intermediate layer, and that the second layer is then filled into the mold , and that then after introduction of the layers they are pressed and then sintered to yield a blank, and that the dental restoration is produced from the blank through mechanical working.

A blank derived from pressed powder, which is machine-worked, for example through grinding or milling, is used to derive a desired dental restoration. No poured blocks are used.

Since pressed powder is used for the blank, an individual coloration or translucency can be achieved without difficulty, in that powders of different color and/or translucency properties are mixed together to the desired degree and then pressed. It is thereby possible to introduce powders of different compositions layer-by-layer into a mold and to thereby derive a blank that has regions of different translucency properties and/or color properties. It is in particular provided for the blank to have a transition region between layers of different translucency and/or coloration that virtually joins the layers continuously.

The invention in particular provides for the structuring of the surface of the first layer after it has been formed such that the first layer when viewed along its surface has regions that differ in their height, i.e., do not have a uniform fill height, and then for the second layer that differs from the first layer in its composition to be filled into the mold.

As an alternative, it is possible after introduction of the first layer for the intermediate layer of a powder that is similarly produced from a starting lithium silicate glass to be filled into the mold, wherein the powder differs from that of the first layer, that the material of the first layer is mixed with the material of the intermediate layer and that the second layer is then filled into the mold. It is in particular provided here for the material of the intermediate layer to be mixed with that of the first layer starting from the free surface of the intermediate layer over a height that is twice or approximately twice the height of the intermediate layer. The material of the intermediate layer is the same as that of the second layer.

In accordance with the invention, with the first alternative a first layer of pourable material is filled into a mold. After filling of the powder, which has a grain size of between <NUM> and <NUM>, preferably between <NUM> and <NUM>, the surface is smoothed to yield a structure which has elevations and valleys that in particular extend parallel to one another and in particular however extend concentrically or parallel to one another. It is provided in particular for this purpose for the structure to be formed through an element that moves relative to the first layer, in particular rotates, which is structured in its surface region in particular with a wave-like, comb-like or saw-tooth-like section. There is virtually a "roughening" or "scratching" of the surface to form the structure, i.e., the alternating elevations and depressions.

It is in particular provided for the structure to be formed such that the volume of the elevations is equal to, or approximately equal to, the volume of the depressions / valleys.

The saw-tooth-shaped element should preferably have V-shaped teeth that are symmetrically formed with flanks which include an angle between <NUM>° and <NUM>°. The distance between neighboring teeth, i.e., from one peak to the next, should be between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

The pourable second ceramic material is then filled into the mold, said material increasing in quantity from the depressions of the structure formed by the valleys, so that as a consequence thereof there is a virtually continuous increase in the proportion of the second layer across the height of the elevations. After smoothing of the surface the layers are pressed. There is then a pre-sintering or sintering to a full density at a temperature between <NUM> and <NUM> or between <NUM> and <NUM> for a time period, for example, between <NUM> and <NUM> minutes. Prior to this, or at the same time as pre-sintering or sintering to full density, at least one crystallization step can be carried out to form lithium metasilicate crystals or lithium disilicate crystals therefrom. Naturally, there is no departure from the invention if the crystallization step is carried out with the glass frit from which the powder is produced. The teaching according to the invention also includes the possibility of performing a further crystallization step after mechanical working.

The blank produced from the pressed body, i.e., after pre-sintering or sintering to full density, is then worked, for example through milling and/or grinding, to yield a desired dental restoration.

Sintering to full density is carried out, for example, over a period of time between <NUM> and <NUM> minutes at a temperature in the range <NUM> to <NUM>.

The penetration of the layers brings the advantage that at least different optical characteristics can be achieved over the height of the blank. Thus, once the first layer has been colored to a desired degree, after sintering to full density a tooth-colored boundary region is obtained, in which via the transition region caused by the penetrating first and second layer materials, the intensity of the tooth color continuously reduces and at the same time the translucency increases in the desired manner. The dental restoration is then derived from the blank in particular through milling, taking the course of the layers into consideration, wherein the dental restoration is "laid" in the blank so that the incisal part of the tooth extends in the region of the second layer.

Independently thereof, on the basis of the teaching according to the invention, there is a continuous transition between the layers so that the color/translucency continuously decreases/increases. There is no abrupt transition but as already mentioned a continuous, i.e., virtually constant transition across the height of the dental restoration to be produced.

In a preferred manner the invention provides for the possibility of mixing of the layer materials, whereby an element is rotated about an axis extending along the longitudinal axis of the mold, to achieve the structure, also referred to as being wave-like or saw-tooth-like, through displacement of material of the surface of the first layer. There is also the possibility of forming the structure through a pressure element also referred to as stamp that acts in the direction of the surface on the first layer, that in particular has elevations extending in its surface with depressions extending between them, so that the negative shape of the element is impressed into the surface of the first layer. Then - as already described - the ceramic material of the second layer is filled in, then smoothed to exclusively press the layers together and to then pre-sinter the pressed object.

The invention is also characterized in that the first and second layers in their connecting region are penetrated across a height H which is between <NUM>/<NUM> and one quarter, in particular between <NUM>/<NUM> and <NUM>/<NUM> of the total height of the first and second layers.

The first layer in an unstructured state should have a height that is approximately <NUM>/<NUM> to <NUM> of the sum of the first and second layers.

The invention is characterized in that a starting glass is used that has a composition that contains, or consists of, the following in percentage by weight:.

The composition preferably contains or consists of the following in percentage by weight:.

The sum of the components for the starting glass amounts to <NUM>% by weight.

To achieve a mean grain size between <NUM> and <NUM>, in particular between <NUM> and <NUM> of the powder to be pressed, the invention provides for a powder that is derived from frit and to be sieved with a sieve with a mesh between <NUM> and <NUM>. Where required, further milling can be carried out, for example through a jet mill or an attrition mill (Attritor).

To influence fluorescence/color, the corresponding metal oxides (for example rare earth oxides) are added to the starting material. So, for example, Tb<NUM>O<NUM> and/or Er<NUM>O<NUM> can be used to influence the fluorescence and, for example, MnQ, Fe<NUM>O<NUM>, Y<NUM>O<NUM>, V<NUM>O<NUM>, CeO<NUM> or other rare earth oxides can be used to influence the coloration.

The invention is also characterized through the use of a blank to produce a dental restoration through mechanical/machine working of the blank according to claim <NUM>.

A use that is in particular intended is one in which the body and/or the blank is subject to at least one crystallization step.

A preferred use is one in which the lithium silicate glass percentage of the blank is in the range <NUM> to <NUM>% by volume.

The lithium metasilicate phase can be between <NUM> and <NUM>% by volume of the crystal phase. The disilicate phase can lie between <NUM>% and <NUM>% by volume of the crystal phases. Lithium phosphate may also be contained as a crystal phase.

Further details, advantages and characteristics of the invention result not only from the claims, but also from the following description of the preferred example embodiments and from the drawings.

The teaching according to the invention is described with reference to <FIG>, in which the same elements are given the same reference numbers, on the basis of which the dental restorations are produced from lithium silicate glass ceramic, and have a monolithic structure such that after full sintering a monolithic tooth prosthesis is available that can be used directly. For this purpose it is provided according to the invention for a blank to be produced that consists of a number of layers of powders that are derived from a starting lithium silicate glass, with compositions that differ from one another, through which in particular desired optical characteristics can be achieved which correspond to the dental restoration to be produced, leading to a direct use of the tooth prosthesis without it being necessary, for example, for an incisal layer to be manually applied and burned after full sintering.

A first ceramic material <NUM> is initially produced that is made from a lithium silicate glass ceramic. For this a starting glass powder with a composition in percentage by weight given below is melted:.

The minimum of one additive is at least one additive from the group color pigments and/or fluorescence agents. It is in particular provided for the additive to be at least one oxide from the group of rare earth metals or for it to contain one such oxide.

The corresponding mixture of starting materials is then melted in a suitable crucible of fire-resistant material or noble metal alloy at a temperature between <NUM> and <NUM> for a time period between <NUM> hour and <NUM> hours, in particular for a time period between <NUM> hours and <NUM> hours at a temperature of <NUM>. Homogenization is carried out either at the same time or thereafter, for example through stirring. The liquid glass so derived is then quenched in a suitable medium such as water or high-temperature wool. The quenched glass frit so produced is then dried. It is then milled, for example in a ball mill. It is then sieved, for which a sieve with a mesh size between <NUM> and <NUM> can be used. If necessary it can be milled further, for example using a jet mill or an attrition mill (Attritor).

From the glass powder or glass particle powder so produced, those particles with a grain size between <NUM> and <NUM> are removed by sieving.

To allow the blank to be worked without difficulty, without the molded part produced from the blank being unstable upon full sintering, a crystallization step is performed either for the frit obtained after melting or for the powder after pre-milling or final milling. Thereby in a first heat treatment step the frit/the powder is subjected to a temperature T<NUM> between <NUM> and <NUM> for a time t<NUM> between <NUM> minutes and <NUM> minutes. The first heat treatment step can also be carried out in two stages, i.e., initially at <NUM> and preferably <NUM> for <NUM> minutes and then at <NUM> for <NUM> minutes.

In a preferred manner this is followed by a further heat treatment in the form of tempering, whereby the chosen temperature T<NUM> should lie between <NUM> and <NUM>. The temperature step is carried out over a time t<NUM> in particular for between <NUM> and <NUM> minutes.

There is naturally no departure from the invention if a binding agent is added to the starting powder. It is, however, preferred if no binding agent is used.

The production of a blank, from which a dental restoration can be produced, is now described with reference to <FIG> and <FIG>. Thus a first powder <NUM> is initially filled into a mold <NUM> of a press <NUM> in accordance with <FIG>.

A second layer <NUM> of a second powder is then produced as described before, but with a composition that differs from that of the first powder, and is filled into the mold <NUM> (<FIG>)), wherein the total height of the layers <NUM> and <NUM> is twice the height of the layer <NUM> in an unstructured state, without any resultant limitation of the teaching according to the invention.

If the first layer <NUM> preferably has a height that corresponds to half the total height H of the first and second layers <NUM>, <NUM>, then the height of the first layer <NUM> can also be <NUM>/<NUM> to <NUM> and thus that of the second layer <NUM> can be <NUM>/<NUM> to <NUM>.

The smoothed surface is then structured in accordance with step b). For this purpose an element <NUM> that is disc-shaped, plate-shaped or web-shaped is used, which in the example embodiment on the layer side has a serrated geometry, so that a corresponding negative structure is formed in the surface <NUM> of the layer <NUM> through the displacement of material. This structure takes the form of concentrically extending elevations and surrounding valleys. The distance between an elevation (peak) and valley (depression), i.e., the clearance between projection <NUM> and valley base <NUM> according to <FIG> is approximately <NUM>/<NUM> of the height of all layers.

The invention in particular provides for the structure to be formed in such a way that the volume of the elevations is equal to, or approximately equal to, the volume of the depressions/valleys.

Because the material of the second layer <NUM> penetrates into the base of the valleys <NUM> in the surface <NUM> of the layer <NUM>, there is a continuous transition between the properties of the layer <NUM> and the layer <NUM>, after the layers <NUM>, <NUM> have been pressed according to <FIG>. The transition layer or intermediate layer is indicated by the reference number <NUM> in <FIG>.

The layer <NUM> is made of a material that differs from that of the layer <NUM>. The difference is due in particular to the color additives.

The percentage of color oxides in the layer <NUM> is reduced compared to layer <NUM>. As a result of this measure there is a continuous color transition between the layers <NUM> and <NUM>.

The layers <NUM>, <NUM> are pressed by means of a stamp, with pressing carried out at a pressure between <NUM> MPa and <NUM> MPa.

The blank <NUM> produced is forced out of the mold <NUM> after pressing and is then pre-sintered or fully sintered in the usual manner.

If a dental prosthesis is milled from the blank <NUM> - in the example embodiment a bridge <NUM> - then the milling program is designed such that the lower region of the bridge <NUM> extends in the layer <NUM> and the cutting region <NUM> of the bridge extends in the layer <NUM>.

In the transition region, i.e., in the central layer <NUM>, in which there is a virtually constant/continuous transition between the layers <NUM> and <NUM>, there is the transition between dentine and incisal region. The dentine extends in the region <NUM>.

An alternative method is described with reference to <FIG> which follows the teaching according to the invention, to enable production of a blank or dental restoration that offers a substantially continuous transition between a first layer and a second layer or in the case of a restoration between the dentine and incisal regions in terms of translucency and strength.

Claim 1:
A method for the production of a restoration (<NUM>) from a blank (<NUM>) consisting of, or containing, a lithium silicate glass ceramic, wherein at least one starting lithium silicate glass is melted, the glass melt is cooled rapidly and is comminuted to a powder,
wherein at least two layers (<NUM>, <NUM>) of powders, which are produced from starting lithium silicate glasses of different compositions, are filled into a mold layer-by-layer, wherein after filling of a first layer (<NUM>) its surface is smoothed and then structured in such a way that the first layer (<NUM>) viewed across its surface (<NUM>) varies in its height from one region to another in such a way, that elevations separated by depressions are formed and then as the second layer (<NUM>) a layer with a composition that differs from that of the first layer is filled into the mold,
or after introduction of the first layer (<NUM>) a further layer (<NUM>) of a powder is filled into the mold (<NUM>), the material of the further layer is the same as that of the second layer, that the material of the first layer is mixed with the material of the further layer to form an intermediate layer (<NUM>) and that the second layer (<NUM>) is then filled into the mold (<NUM>),
and after introduction of the layers they are pressed and then sintered to form a blank, and
the dental restoration is produced from the blank by mechanical working: and wherein the starting glass used has a composition which contains, or consists of, in percentage by weight:

<TAB>

At least one additive <NUM> - <NUM>.