CZ303284B6 - Leucite obtained synthetically in hydrothermal environment and intended for preparing ceramo-metallic or all-ceramic dental prostheses - Google Patents

Abstract

The present invention relates to leucite for preparing ceramo-metallic or all-ceramic dental prostheses, obtained synthetically in hydrothermal environment and having the chemical formula Ki2O.Ali2Oi3.4SiOi2, or KAlSii2Oi6. Leucit is made in powder form, see Figure No. I. The content of leucite in spherical crystal paricles is in the range of 95 to 99.9 percent.

Description

Leucite for the production of metal-ceramic or all-ceramic dental restorations, synthetically obtained under hydrothermal conditions

Technical field

The technical solution concerns leucite for producing metal-ceramic or all-ceramic dental restorations synthetically obtained under hydrothermal conditions, the chemical formula ₂ or ICO.AI2O3.4SiO Kalsi? O _sixth Leucite is formed in the form of a homogeneous powder mixture.

BACKGROUND OF THE INVENTION

The first findings of primitive "dental implants" come from ancient Egypt. In Europe, dentistry originated as an independent field in the 18th century. At the beginning of the 18th century the first dental prostheses made of ivory and metal, such as gold and silver, began to be used, and later also porcelain and plastic prostheses appeared.

Advantages of dental ceramics are easy-to-reach color and color fastness, hardness and corrosion resistance in acidic and alkaline environments and above all biocompatibility. E.g. feldspar porcelain used in dental prosthetics therefore has a number of required properties, both chemical and aesthetic, a major drawback is its fragility.

Recent research in the field of dental materials is focused on the search for a suitable technology for genuine materials that can be soldered with metals, and which also exhibits a high value of the fracture toughness of ceramics. This problem is solved by joining dental porcelain with metal reinforcement, however, the difference in thermal expansion of the two materials prevents the formation of a strong bond between the metal and the ceramic. Based on the finding that, for example, leucite, crystallized upon cooling of the product, will increase the coefficient of thermal expansion to a value close to metals (13 to 15x10 ⁶ K -1), a leucite porcelain that can be soldered with metals was prepared.

Leucite is a potassium aluminosilicate with the chemical composition of K ₂ OAl ₂ Ov ₄ SiO ₂ , respectively. KAlSi ₂ O ₆ . It belongs to the class of silicates, subclass of tectosilicates and group of feldspatoids - minerals of igneous rocks with low content of SiO ₂ . In nature, it crystallizes in cubic form in volcanic rocks rich in potassium and silicon deficient. It is not stable under normal conditions and changes into a mixture of nepheline and orthoclase, called pseudoleucite. Two polymorphic modifications are typical of leucite. At high temperatures, the cubic form is stable, while cooling to 605 ± 5 ° C, a diffusion-free martensitic phase conversion to the tetragonal form occurs.

Leucite is the major crystalline phase in most feldspar dental ceramics used in dentistry to manufacture metal-ceramic restorations. Its presence in the glass matrix increases the value of the linear coefficient of thermal expansion of the resulting composite material and thus allows it to be soldered to the metal reinforcement. In addition, Leucite ceramics exhibits higher fracture toughness values than conventional feldspar dental porcelain.

Currently, there are several different ways to prepare leucite. One possible way is to crystallize the molten glass frit, where the type of final phases is controlled by the initial composition of the frit and the addition of suitable nucleation agents [1]. However, nucleation and growth of leucite crystals from the melt are extremely slow, and therefore firing requires many tens of hours. Equally reproducible microstructure control is very difficult in this process. In particular, uniformity of crystal size and homogeneity, and their distribution in the glass matrix, have not yet been achieved by this technology [2, 3, 4, 5].

Leucite has a melting point of 1693 ° C, which makes it difficult to synthesize pure leucite at relatively low temperatures. If we manage to prepare it, it is usually contaminated by the presence of other phases that

B0 negatively affects the resulting mechanical and aesthetic properties of dental ceramics. I. L. Dendry et al. confirmed the presence of sanidium in multiple calcined leueite-reinforced dental ceramics [6]. Another possibility to prepare leueite is the sol-gel method. L. M. Erbe and R. S. Sapieszko prepared a leueite using the sol-gel method at 1000 ° C, but was contaminated with kalsilite [7], Liu et al. synthesized leueite at a relatively low temperature of 900 ° C, but with the presence of a large amount of glass phase 181.

US 5,662,551 A (Oct. 29, 1993) discloses synthetically obtained leueite which is useful as a component of dental porcelain. Leueite is prepared from a stable dispersion of potassium precursor, aluminum precursor and silicon precursor. Potassium precursors include: potassium salts, in particular acetates, nitrates, chlorides, carboxyls, sulfates, perchlorides or mixtures thereof. Most preferred is potassium acetate which is stable in the silicon precursor. Aluminum precursors which may be mentioned are: aluminum salts, preferably in aqueous solution, namely basic carboxylates, basic nitrates, in particular hydrolyzed alkoxides, namely aluminum formacetate. Silicon precursors include: fired residual

SiO ₂ , aqueous silicon sol, alkoxylan solutions or siloxanes of polymers and oligomers. The silica sol should have a pH of not more than 4.

Various additives are added to the dispersion to facilitate processing of the dispersion or formation of the end product, such as transition metal cations, drying control agents, surfactants, plasticizers, monomers, polymers, or organic solvents such as acetone, methyl ethyl ketone, methanol or ethanol. A solution or sol is added as a compatible compatibilizer to prevent solidification, flocculation, precipitation or slurrying for at least one hour from the time the additive is added to the dispersion. Nucleating agents such as crystalline leucite particles are also used.

The potassium, aluminum and silicon precursor in a given ratio are mixed to form a stable aqueous dispersion. The dispersion is dried and then fired at a temperature of about 960 ° C, not more than 1170 ° C. The product obtained contains a crystalline and amorphous phase, wherein the crystalline phase comprises tetragonal leueite. The compound obtained is said to contain at least 40% or 75% to 95% of the theoretical amount of crystalline leucite. Fine granules of leucite are formed, dispersed in uniform in an amorphous matrix of identical chemical composition.

The disadvantage of this process is the relatively high process complexity, the amount of additives and the high firing temperature.

LT 4357 B (July 28, 1997) discloses a process for preparing zeolites, particularly sodium aluminosilicates, which can be used as laundry detergents, water softening agents, sorbents, and catalyst carriers in the oil and chemical industries. Industrial feedstocks such as SKXnFLO contaminated with fluoride admixture are used as feed reactants. The process for preparing these zeolites is based on the reaction of sodium alkali with an amorphous silica gel in an aqueous medium. The product obtained is filtered, the mixture is washed with impurities of unreacted fluorides and dried. The reaction is carried out at atmospheric pressure or in an autoclave at 90 to 200 ° C for 0.5 to 2 hours. Thus, sodium zeolites are synthetically obtained, namely amalcim and hydrosodalite.

The patent describes the production of sodium aluminosilicates by the hydrothermal method from waste silica gel in the presence of fluoride ions. The resulting product contains NaF, which does not matter in the mentioned application, but this product is unsuitable for use in dental prosthetics. The purity of the two compounds obtained and the magnitude of the changes are not given, since they are not important for said industrial purposes.

US 2008 138 768 A1 (19.1.2006), corresponding to DE 10 2005 003 755 B4, discloses a coated inorganic dental powder which is coated with at least one layer containing inorganic and / or organic components or mixtures thereof, and also discloses a process for its preparation . Inorganic dental powder containing glass or glass ceramics or aluminosilicate, aluminophosphosilicate or

Aluminoborosilicate having at least one layer of an inorganic or organic substance or a mixture of both. The layer may have a thickness of 0.5 nm to 1 µm, preferably 0.5 to 200 µm. The average particle size of the powder may be 50 nm to 100 µm, preferably 5 to 50 µm. The dental powder may comprise one or more crystalline phases. The crystalline phase may be leucite or fluorapatite or a mixture thereof. The process for producing an inorganic dental powder consists of two steps 1 and II. Step 1 consists in introducing the organic component into distilled water and adding the dental powder. Thereafter, homogenization is carried out, followed by separation of the liquid form from the powder, which may be accomplished by filtration. Step II is treatment of the aqueous liquid with the inorganic component, addition of the powder coated with the organic substance of step I, homogenization and drying at temperatures of 80 to 200 ° C. The inorganic dental powder coating may contain leucite as the crystalline phase, but is mostly referred to with fluorapatite.

In the examples, only leucito-apatite glass ceramics is mentioned as inorganic dental powder, for the coating of the various components pure leucite is not mentioned. The attached figures show clusters of irregularly spaced particles of very different shapes and sizes. Also, the method of preparation is quite complicated and is obviously for the special claimed use.

WO 00/10509 (Aug. 17, 1998), corresponding to US 6,527,846 B1, discloses a glass ceramic material for dental fillers and a process for its manufacture. The glass ceramic material comprises crystalline needles in the form of needles or cylinders having a thickness of 0.3 to 1.5 µm and a length of 7.5 to 20 µm. The glass ceramic material contains SiO ₂ , Al ₂ O ₃ , Na ₂ O, K ₂ O, CaO, BaO, and also CeO ₂ , TiO ₂ , and Br ₂ O ₃ . The starting mixture of silicates, carbonates or oxides melts at high temperatures of about 1500 ° C. It is a type of leucite ceramic containing a large number of components.

The spherical shape of the leucite crystals and the method for their production are disclosed in JP2001 134 82 20 A (1.6. 2000). The invention solves the formation of spherical particles of crystalline leucite and homogeneous distribution of the prescribed amount in the matrix. The spherical leucite crystals are produced by a process of mixing K ₂ SO ₄ , Al ₂ (SO ₄ ) ₃ and SiO ₂ in a defined ratio and heating the resulting mixture to 900 to 1200 ° C.

WO 2009/038 800 (2U9.2007) discloses controlling the microstructure of a ceramic, more particularly controlling the size of leucite crystals, of the ellipsoidal type, which are obtained from a glass frit by grinding and screening to a particular particle size and subsequent firing. The disadvantage is the sorting of crystals into different types of sizes, which is a relatively lengthy matter and it is necessary to burn the dispersion to a high temperature.

The essence of the technical solution

These disadvantages are eliminated or substantially reduced for leucitin according to the present invention, where leucite is synthetically obtained under hydrothermal conditions, of the chemical formula K ₂ O.A1 ₂ O ₃ .4SiO ₂ and KAlSi ₂ O ₆ , with high purity and free of chemical additions impurities and other minerals formed in the form of a homogeneous powder mixture according to the present invention. The essence of this technical solution consists in that the homogeneous powder mixture of leucite consists only of fully crystalline spherical leucite particles having a content of 95 to 99.9% by weight. leuci45 tin in the final product, with high chemical and mineralogical purity, without detectable amorphous leucite content. The spherical shape of the crystalline leucite particles has a uniform particle size in the range of 0.1 µm to 100 µm, and has a ratio of the longest and shortest axes in the range of 1: 1 to 1: 1.5; wherein the size distribution of the crystalline leucite particles is in the range of 5 ± 4 µm. The starting precursor of the crystalline moieties of leucite is the crystalline particles of analcime for subsequent hydrothermal synthesis of sodium Na-potassium ion exchange. Analcim with the chemical composition of NaAlSi ₂ O ₃ .H ₂ O is the sodium analogue of potassium leucite. The crystalline particles of both leucite and analcime have substantially identical and / or close particle size, shape and dispersion, so that the crystalline particles of the analcum precursor correspond to the final size, shape and size dispersion of the crystalline leucite particles.

-3 CZ 303284 B6

The main advantage of this invention is the low-temperature synthesis of crystalline tetragonal leueite with uniform spherical particle size within a defined particle size and scattering range. The advantage is the high homogeneity of the particles, their final chemical and mineralogical purity, which, while adhering to the technological process, reaches up to 99 wt. Also, the hydrothermal conditions of the synthesis reduce the energy requirements for the production of Icucia. In the hydrothermal synthesis of leueite, the first step is the low-temperature production of analcime under hydrothermal conditions, followed by the second important step, the sodium-potassium ion exchange. A great advantage is the same or similar crystalline particle size of the analcime and the leueite end product, which facilitates particle size control of the final powder product.

Under these conditions, leueite particles are obtained which are fully crystalline, and at room temperature in tetragonal modification, without undesirable amorphous fraction.

It is preferred that the spherical shape of the leueite crystals exhibit a ratio of the longest and shortest axis of both the leueite crystalline particles and the analcime in the range of 1: 1 to 1: 1.1, representing the optimal shape closest to the ideal spherical shape.

The spherical shape of the crystalline particles of leueite and analcim having a size of 1 to 10 µm is suitable for the production of dental leucite raw materials with a homogeneous dispersion of leucite particles. From such prepared leucite raw materials, leucite dental composites with very favorable mechanical properties for dental restorations can be obtained.

In view of the exceptionally good properties of dental composites in terms of mechanical parameters and the possibility of solderability to various construction materials, it is preferable that the dispersion size of both leueite and analcime crystalline particles is in the range of 2 ± 1 µm. This very narrow dispersion is achieved by controlling the hydrothermal synthesis conditions.

In order to synthetically obtain analcime, it is preferred that for the crystalline particles of analcime the feedstock is a silicon containing Si, aluminum Al and sodium Na in an aqueous dispersion. The aqueous dispersion allows relatively undemanding preparation conditions free of the use of organic solvents and complicated admixtures.

Preferably, for the crystalline particles of analcime, the feedstock is a Si-containing source selected from the group consisting of at least one component comprising amorphous SiO ₂ powder, white SiO ₂ , metakaolinite Al ₂ O ₃ .SiO ₂ and baked kaolin at temperature 700 ° C ± 20 ° C. These are commonly available raw materials.

Also preferably, for the crystalline particles of analcim, the feedstock is an aluminum-containing source selected from at least one of amorphous powdered aluminum Al, aluminum oxide At ₂ O ₃ , metakaolinite Al ₂ O ₃ .SiO ₂ or baked kaolin at temperature 700 ° C ± 20 ° C. They are also available raw materials.

It is also preferred that for the crystalline particles of analcime the feedstock is a sodium Na-containing source in a basic solution, such as aqueous sodium hydroxide solution NaOH, preferably a basic aqueous sodium hydroxide solution having a molarity in the range of 1M - 5M. It is also a common raw material, economically undemanding, with optimal molarity for hydrothermal syntheses.

In order to obtain a chemically pure finely crystalline analcim, it is preferable that the feedstock sources of Si and Al, and / or their oxides (SiO ₂ , Al ₂ O ₃ ) or salts thereof, at an optimal Si to Al or SiO ₂ to Si ratio Al ₂ O ₃ in the range of 2.5 to 7 to 1.

For crystalline particles of analcime, a suitable feedstock is silicon dioxide SiO ₂ in an aqueous dispersion where the ratio of water H ₂ O to SiO _{2 is} in the range of 6 to 28, ensuring the hydrothermal synthesis with the end product of analcime at high yield.

-4GB 303284 B6

Preferably, for the analcime, which is the precursor of the ion exchange leucite under hydrothermal conditions, the feedstock is a potassium K-containing source in an aqueous solution such as potassium hydroxide KOH, potassium chloride KCl, potassium nitrate KNO ₃ , potassium carbonate

K2CO3, potassium bicarbonate KHCO3. The use of these raw materials leads to a high degree of ion exchange. This ion exchange takes place at relatively low temperatures of 100 to 250 ° C, which are not common for synthesis of ceramic raw materials for secondary purposes. It brings energy, time and consequently cost savings.

Ion exchange is relatively successful using an aqueous solution of potassium chloride with a molarity of 1 to 5M, it is a common chemical with optimally selected molarity.

BRIEF DESCRIPTION OF THE DRAWINGS

The technical solution is described in detail below in the exemplary embodiments and is illustrated in more detail in the accompanying drawings, in which FIG. 1 is a schematic representation of leucine production, FIG. 2 diffraction spectrum prepared by analcime, FIG. 3 diffraction spectrum prepared leucite; A-2, A-3 prepared by analcime, and FIG. 5 shows images of B1, B-2, B-3 prepared by leucite.

Examples of technical solution

Non-limiting examples of embodiments of the invention are described below.

Example 1 (Fig. 1)

The attached Fig. 1 shows schematically the preparation of leucite by an ion exchange ion exchange in individual technological steps.

Leucite by the chemical formula K ₂ O.Al ₂ O3.4SiO ₂ respectively Kalsi ₂ O ₆ is prepared synthetically in a homogeneous powder mixture under hydrothermal conditions at 200 ° C. This low-temperature leucite production process, in contrast to high temperature technology, allows better control of the microstructure of the resulting product, particularly with regard to its homogeneity and particle size. The manufacturing process comprises two steps (Figure 1). Initially, an analcime is prepared by hydrothermal synthesis, and then, in a second step, the leucite is obtained by means of sodium ion exchange of Na ⁺ in the analcime for potassium ion K from the dispersion.

Both of these technological steps, i.e. obtaining analcime in the first step and leucite ion exchange in the second step, are carried out under hydrothermal conditions in an aqueous environment at low temperatures of 100 to 250 ° C.

In the first step obtained by the analcime is a sodium analogue of leucite. Analcime has the chemical formula NaAlSi ₂ O ₆ .H ₂ O, respectively Na2O.Al7O3.4SiO2.2H2O. A very important point of the described technology is the preparation of feed mixture, which has a decisive influence on the microstructure of

-5 GB 303284 R6 product. A series of experiments were carried out in which the influence of reaction variables (composition of the initial suspension, reaction temperature and time) on the resulting nature of the synthesis product was investigated in order to prepare homogeneous analcimic powders of uniform particle size and shape. Thus, the range of reaction conditions and composition of the feed mixture has been delineated, resulting in the preparation of homogeneous analcim powders. The feed mixture is formed by mixing and thoroughly homogenizing the aluminate and silicate dispersions obtained by separately dissolving the Si-containing raw materials and the Si-containing raw materials. aluminum Al, in a solution such as sodium hydroxide with vigorous stirring. For the crystalline particles of analcime, the feedstock is a source comprising silicon Si, aluminum Al and sodium Na, and / or oxides and / or salts thereof; where the ratio of Si to Al, or oxides of SiO? to AbO 1 is in the range of 2.5 to 7 to 1; and a ratio of water 114) to SiO ₂ in the range of 6 to 28. The Si source is selected from the group consisting of at least one component including amorphous SiO ₂ powder, white SiO ₂ carbon black, AbCb ₂ SiO ₂ metakaolinite and baked kaolin. The aluminum source Al is selected from the group of at least one component, including amorphous aluminum powder Al, aluminum oxide AbCl ₂ , metakaolinite AbO ₃ , SiO ₂ or baked kaolin. Sodium Source Na in an alkaline solution is, for example, an aqueous solution of sodium hydroxide NaOH, with a molarity in the range of 1M to 5M. In order to obtain analcime, both the silicon source Si and the aluminum source Al are dissolved separately in a basic solution of NaOH, preferably with a molarity of 1 to 5M. Upon completion of the separate dissolution, both the Si silicon sources and the Al aluminum sc sources, on the one hand, mix the two dissolved sources and homogenize them thoroughly into the silicate aluminate dispersion for 1 to 60 minutes, with vigorous stirring of the dispersion. The obtained homogeneous feed dispersion of the silicon Si and aluminum Al sources is placed in a sealed reaction vessel where it is heated at 100 to 250 ° C for 2 to 42 hours. The reaction product obtained is cooled to room temperature. It is then removed from the sealed container, then filtered and washed with distilled water to remove unreacted feedstock. The obtained powder is preferably dried at temperatures around 100 ° C. After cooling to room temperature, the leucite precursor, analcim, is obtained in the form of crystalline analcim particles.

In a second step, the crystalline particles of analcim are subjected to an ion exchange of sodium Na for potassium K under hydrothermal conditions, in which the crystalline particles of analcim and the aqueous solution of the potassium compound are first mixed. The resulting mixture is heated to 100 to 250 ° C under hydrothermal conditions in a sealed vessel for 1 to 10 hours. The advantage of obtaining leucite by the Na ⁺ ion exchange in an analcim for K ⁺ from solution is low temperature, short preparation time and preservation of the microstructure under hydrothermal conditions.

It has been found that the percentage of leucite prepared increases significantly with increasing moles of KCl solution arithmetic as well as with increasing reaction temperature. Furthermore, it has been verified that under optimal conditions, e.g. three hours of hydrothermal heating at 200 ° C in 4M KCl solution, they are sufficient to quantitatively convert analcim to leucite.

The homogeneous powder mixture of leucite thus obtained consists only of fully crystalline spherical leucite particles having a content of 95 to 99.9% by weight. leucite in the final product, with high chemical and mineralogical purity.

It has also been found that there is no significant change in particle size or shape of the analcim and leucite particles during ion exchange. The spherical shape of the crystalline leucite and analcime particles has a uniform particle size in the range of 0.1 µm to 100 µm, preferably 1 µm to 10 µm. The spherical shape of the crystalline particles of both leucite and analcime exhibits a ratio of the longest and shortest axes in the range of 1: 1 to 1: 1.5; preferably in the range of 1: 1 to 1: 1.1. The size distribution of both leucite and analcum crystalline particles is in the range of 5 ± 4 µm, preferably 2 ± 1 µm. Crystalline leucite particles have a tetragonal modification that is stable at room temperature.

-6GB 303284 B6

Example 2 (Fig. 2, Fig. 3. Fig. 4, Fig. 5)

Preparation of the input reaction mixture:

The preparation of the feedstock reaction mixture has a fundamental influence on the quality, in particular the homogeneity and particle size of the final product, therefore it has to be given special attention and is separately presented in this example. The input mixture is obtained by mixing the aluminate and křemičitaio new dispersion ratio SiO ₂ / Al ₂ Oi = 4.8 H ₂ O / SiO ₂ = 16.4 NaOH.

Fine ground SiO ₂ (PPH Glivice, PL) and powdered Al (Lachema, CZ) were used as raw materials. The aluminate dispersion of Al ² O ² "is obtained by gradually adding powdered aluminum to a stirred 4M NaOH solution. The resulting dispersion is intensively agitated throughout the preparation with the aid of a magnetic stirrer at a speed of 1000 to 2500 rpm. The SiO3 ² silicate dispersion is prepared by dissolving amorphous SiO ₂ in 4M NaOH solution. After mixing the aluminate and silicate dispersions and thoroughly homogenizing them in a Teflon crucible, a gel is formed which is used as a feed mixture for subsequent hydrothermal synthesis.

Synthesis of analcim:

The resulting reaction mixture was placed in an autoclave and placed in an oven heated to 200 ° C. After two hours, the autoclave is removed from the oven and cooled in a stream of cold water. After filtering and washing with hot distilled water, the synthesis product is dried at 100 ° C. Thus, a fine white powder with a diffraction spectrum as shown in Figure 2 is obtained which corresponds to the desired analcime.

The morphology of the produced powdered analcim is documented by scanning electron microscope images in Fig. 4. In the pictures A1 through A3, a homogeneous mixture of 3 to 4 µm spherical particles of analcim is shown.

A - 1 magnification of analcum 10,000x particles,

A - 2 magnification of analcim particles 5000 x

A-3 magnification of analcime 200x.

It has been shown experimentally that analcim is a stable phase in this temperature range of 100 to 200 ° C and the shortest time to crystallize is 1 hour at 200 ° C.

Leucite preparation:

For the preparation of leucite, an analimum powder prepared by the synthesis described above is used. The Ig powder sample of analcime is mixed with 20 ml of 4M KCl solution and placed in an autoclave in an oven heated to 200 ° C. After three hours, the autoclave was quenched in a stream of cold water, filtered and dried at 100 ° C. Figure 3 shows the diffraction spectrum of the prepared synthetic leucite.

Fig. 5 shows a homogeneous mixture of 3-4 µm spherical leucite particles in Figs.

A - 1 magnification of analcum 10,000x particles,

A - 2 magnification of analcim particles 5000 x

A - 3 magnification of analcim particles 2000x.

-7EN 303284 B6

Comparison of Figures 4 and 5 shows that there are no changes in particle size and shape during ion exchange. It was found that at least 99 wt. leucite, an almost ideal spherical shape, with a particle size of 3 to 4 µm,

This very narrow particle size distribution of the leucite was achieved by strict adherence to the technological process. The small size and narrow size distribution of the leucite particles will improve the mechanical properties of the resulting leucite composite and this is a good precondition for its use in the dental protector field.

ID

Industrial applicability

Lucuc in the form of homogeneous powders can be used as a raw material for the preparation of dental leucite ceramics for metal-ceramic or all-ceramic dentures or fillers.

References:

[1] Cattel M. J. Chadwick, T. C., Knowles, J. C., Clarke R.L .; Dental Materials 21, 811-822 (2005).

[21 T. Ota, M. Takahashi, J. Ymai, H. Suzuki, J. Am. Ceram. Soc. 76, 2379 (1993) [J. J. Mackert, Jour. Dent. Mater., 2, 32-36 (1986). [4] Denry R., J. Meckert, J. Dent. Res., 77, 1928 (1996) [5] B. Burk, A. P. Bumett, US Patent 4, 101.330 (1978) [6] Denry I. L., Holloway J. A., Colijn H. O .: J. Biomed. Mater. Res. 54, 351-359 (2001).

[7] Erbe Ε, M., Sapieszko R. S .: US Patent 5622551 (1997).

[8] Liu Ch., Komameni R .: J. Am. Ceram. Soc. 77, 3105 (1994).

Claims (5)

PATENT CLAIMS 1. Leucite for the manufacture of metal-ceramic or all-ceramic dentures, synthetically obtained 35 in hydrothermal conditions, of the chemical formula K 2O.AI2O3.4SÍO2 respectively Kalsi Of ₂ 'formed in the form of a homogeneous powder obtained in two steps under hydrothermal conditions, wherein in the first step to obtain crystalline particles analcime chemical composition NaAlSi ₃ O ₆ .H ₂ O, respectively Na2O.Al2O3. 4SiO2.2H2O, which is a sodium analogue of potassium leucite, and in a second step, synthetic leucite is obtained from the analysis by ion exchange of sodium Na with potassium K, 40, characterized in that (a) the homogeneous powder form of synthetically obtained leucite from synthetically obtained ion exchange analysis under hydrothermal conditions consists of only fully crystalline spherical leucite particles of high chemical and mineralogical purity with a content of 95 to 99,9% wt. leucitine in the final product (B) the spherical shape of the crystalline leucite particles has a uniform particle size in the range of 0.1 µm to 0.1 µm 100 µm, and (c) exhibits a ratio of longest and shortest axes in the range of 1: 1 to 1: 1.5; wherein (d) the dispersion size of the crystalline leucite particles is in the range of 5 ± 4 µm. 50. The lucit of claim 1, wherein the crystalline leucite particles have a tetragonal modification. -8EN 303284 B6 Leucite according to claim 1, characterized in that the spherical shape of the leucite crystals has a ratio of the longest and shortest axis of the leucite crystals in the range of 1: 1 to 1: 1.1. Leucite according to claim 1, characterized in that the spherical shape of the crystalline leucite particles has a size of 1 μιτι to 10 μηι. Leucite according to claim 1, characterized in that the size distribution of the crystalline leucite particles is in the range of 2 ± 1 µηι.