EP1648392A1

EP1648392A1 - X-ray opaque dental material comprising surface-modified nanoparticles

Info

Publication number: EP1648392A1
Application number: EP04741315A
Authority: EP
Inventors: Fernando Ibarra
Original assignee: Centrum fuer Angewandte Nanotechnologie CAN GmbH; Nanosolutions GmbH
Current assignee: Centrum fuer Angewandte Nanotechnologie CAN GmbH; Ivoclar Vivadent AG
Priority date: 2003-08-01
Filing date: 2004-07-29
Publication date: 2006-04-26
Also published as: EP1502570A1; WO2005011621A1

Abstract

The invention relates to a dental material, which contains surface-modified nanoparticles with an average particle size of less than 25 nm in the form of a filler, said nanoparticles being selected from the salts of barium, strontium, rare-earth metals, scandium or yttrium, or from wolframates. The surface of said nanoparticles is modified by an organic compound that bonds with the nanoparticles by means of a functional group containing N, P, S and/or O. Said dental material exhibits an excellent X-ray opacity, in addition to important processing characteristics such as transparency or dispersion stability.

Description

X-ray opaque dental material with surface-modified nanoparticles

The present invention relates to an X-ray-opaque dental material, in particular an X-ray-opaque dental material which contains surface-modified salts of rare earth metals, scandium, yttrium, barium or strontium or an olframate, and its use in dental technology.

Technical background

Edges of fillings in dental fillings are often difficult to check clinically, especially in the posterior region, so that the radiological check is an essential support in the diagnosis and differential diagnosis of carious lesions in the marginal area of the filling, marginal gaps and excess or deficit. In addition, X-ray localization of foreign bodies can also be important in the event of accidental swallowing or aspiration.

For this reason, attempts have been made for a long time to modify dental materials in such a way that they contrast in the X-ray image. X-rays are absorbed more by elements of a higher atomic number in the periodic table of elements than by elements of a lower atomic number. To achieve a contrast in the X-ray image (X-ray opacity), elements with high atomic masses must therefore be added to the dental material. In principle, this can be done via the monomer or packing system.

Thus, DE 35 02 594 describes an AI radiopaque dental material based on poly ersierbaren organic binders containing, as fillers at least one fluoride of the rare earth metals, ^• preferably ytterbium trifluoride. An average primary particle size of 5-700 nm is given for these particles, although at the time of this application, no syntheses for rare earth metals with a primary particle size of 5-3 nm were available and even at this time known grinding techniques were unable to produce such small particles.

The introduction to DE 35 02 594 AI refers to other radiopaque fillers. For example, from DE-OS 24 58 380 tooth filling compounds are known, which u.a. May contain oxides and / or carbonates of lanthanum.

Barium sulfate is mentioned as a radiopaque material in DE-OS 24 20 531 and in EP-A-0 011 735. The EP document also discloses x-ray contrast media containing lanthanum. DE-OS 29 35 810 proposes the oxides of the rare earths (elements 57 to 71) as X-ray contrast media, although problems due to undesired discoloration appear to arise.

X-ray-opaque dental materials are also known from EP 0 894.488 A2, which contain mixed crystals as filler, in which the two metal atoms of the mixed crystal are selected from rare earth metals, yttrium, scandium, zirconium or strontium and the counterions are chalcogenides and / or halides. Nothing is said in this document about the particle size of the particles.

However, many known radiopaque filler materials have the disadvantage that they are difficult to disperse in the matrix and / or have no connection options. Glass-like fillers can be better incorporated into the polymer matrix of dental materials, for example by means of silanization via hydroxyl or oxy groups of the glass particles. However, fluoride compounds cannot be silanized and cause inadequate physical and chemical resistance in the hardened filler material. In addition, the highest possible level of transparency is desired for some dental materials, which cannot be achieved with the particle sizes known to be produced.

Another disadvantage of the known radiopaque fillers was that their dispersion behavior could not be flexibly adapted to the type of matrix (hydrophobic or hydrophilic).

It was therefore an object of the present invention to provide a dental material with excellent X-ray opacity in which the X-ray opaque filler can be readily dispersed in the matrix and which exhibits excellent processing properties, such as stability and hardenability.

Another object of the invention includes improvements in the transparency of the dental material.

Finally, the invention aims to provide a dental material whose radiopaque filler can be flexibly adapted to the type of matrix.

Brief description of the invention

These objects are achieved by a dental material that contains surface-modified nanoparticles with an average particle size of less than 25 nm as X-ray opaque filler, which are selected from salts of barium, strontium, rare earth metals, scandium or yttrium or from tungstates, and their surface with an organic compound is modified which binds to the nanoparticles with a functional group containing N, P, S and / or 0. The present invention also relates to various dental uses, as defined in the claims.

Detailed description of the invention

The dental material according to the invention contains at least one nanoparticulate material as X-ray-opaque filler, which is selected from salts of rare earth metals, scandium, yttrium, barium and strontium, or from tungstates.

The radiopaque filler is preferably poorly soluble. The term "poorly soluble" refers to the solubility of the X-ray-opaque filler in human saliva. A suitable and known selection must therefore ensure that the X-ray-opaque filler does not dissolve to an extent that human health and / or stability The sulfates, phosphates or fluorides are particularly suitable as sparingly soluble salts.

Trifluorides are preferred among the salts of rare earth metals (element 57-71), scandium or yttrium.

The preferred rare earth metals include lanthanum, cerium, samarium, gadolinium, dysprosium, erbium or ytterbium. Among their salts, the fluorides are preferred, especially ytterbium trifluoride (YbF3).

Preferred barium and strontium salts are fluorides, phosphates and sulfates, especially the sulfates.

The term "tungstate" includes metal compounds of Ortho tungstates (W04 ²⁾ and polytungstates, the former being preferred. The metal tungstate is preferably a tungstate compound of a polyvalent metal, especially a di- or trivalent metal. Suitable divalent Metals include alkaline earth metals such as magnesium, calcium, strontium or barium, especially calcium, strontium or barium. Strontium and barium tungstates are characterized by a particularly high X-ray opacity, since these compounds combine two good contrast agents. Preferred trivalent metals include scandium, yttrium or rare earth metals such as lanthanum, cerium, samarium, gadolinium, dysprosium, erbium or ytterbium. Here too, a particularly high X-ray opacity results from the fact that a good contrast agent (tungstate) is combined with a strongly contrast-forming metal.

In addition, it is possible to dope the tungstates used according to the invention (or also the other nanoparticulate salts) with metal atoms. For this purpose, the host lattice metal is preferably replaced by the dopant in an amount of up to 50 mol%, more preferably 0.1 to 40 mol%, even more preferably 0.5 to 30 mol%, in particular 1 to 25 mol%. The chosen dopant can contribute to the X-ray opacity. For analytical reasons, however, it may also be of interest to choose one or more doping metals which impart luminescent properties, in particular photoluminescence. Suitable dopants for this purpose are known in the art and are often selected from a lanthanide other than the host lattice metal. Examples include the combined doping with Eu and Bi, or the doping of Ce in combination with Nd, Dy or Tb, or Er in combination with Yb. Likewise, a tungstate can be doped as a host lattice with a suitable lanthanide ion or another metal ion, for example Bi-3 + or Ag ⁺ .

The shape of the radiopaque filler is not subject to any particular restrictions. This can be acicular, ellipsoidal (egg-shaped) or substantially spherical, the latter two options being preferred. The x-ray-opaque filler used according to the invention has an average particle size (diameter), measured along the longest axis, of less than 25 nm. Average particle sizes of 0.5-22 nm, 1-20 nm, 1-10 nm and 1 to less than 5 nm (eg 4.5 nm) are even more preferred. In any case, the standard deviation is preferably less than 30%, in particular less than 10%.

The particle size and distribution can be determined by methods as will be given in the literature for nanoparticles, e.g. with K. Riwotzki et al. , J. Phys. Chem. B 2000, 104, 2824-2828, "Liquid phase synthesis of doped nanoparticles: colloides of luminescing LaPθ4: Eu and CePθ4: Tb particles with a narrow particle size distribution", ie with a transmission electron microscopic (TEM) examination. Gel permeation chromatography and Ultracentrifugation also enables sizing, with TEM measurements being preferred in terms of accuracy.

The surface of these X-ray-opaque nanoparticles is modified with an organic compound that binds to the nanoparticles with a functional group containing N, P, S and / or 0.

This organic compound preferably has 2-60 carbon atoms. The functional group which binds to the surface of the nanoparticles can be, for example, primary or secondary amines (for example mono- or dialkylamines), phosphinic esters, diesters of phosphonic acid, phosphoric acid esters (for example trialkylphosphates), phosphines (for example trialkylphosphines), phosphine oxides (for example trialkylphosphine oxides), sulfoxide (for example DMSO) ), Hydroxy (eg organic polyols), carboxylic acids or carboxylic acid esters. Depending on the type of dental material into which the radiopaque filler is to be incorporated, ie in particular depending on the degree of hydrophilicity / hydrophobicity to choose an appropriate number and type of functional groups and the size of the organic residue.

Would like to. if the X-ray opaque material is incorporated into a hydrophilic matrix (dental material), surface-modifying compounds with a lower carbon number (from 2-10) are preferably used, which furthermore preferably have at least two polar functional groups, e.g. Polyols. One of these functional groups binds to the surface of the filler, while the other conveys hydrophilicity. Fillers modified with a sulfoxide such as DMSO are also suitable for incorporation into hydrophilic matrices.

If one wishes to incorporate the radiopaque filler into a hydrophobic matrix, one preferably works with surface-modifying compounds that have a carbon number of 10-60, in particular 12-40. The functional groups mentioned above are particularly suitable as functional groups.

However, it is also possible to provide the surface-modifying organic compound with a polymerizable double bond in order to ensure optimal integration into a polymerizable dental material or its starting materials. For this purpose, one can use, for example, compounds with the functional groups already mentioned (for example primary or secondary amines, phosphinic acid esters, phosphonic acid diesters, phosphoric acid triesters, phosphines, phosphine oxides, sulfoxides or alcohols, carboxylic acids and carboxylic acid esters, as will be explained in more detail later), in which at least e. an alkyl group was replaced by an alkenyl group, preferably one with a terminal double bond. Surface modification with carboxylic acids and carboxylic acid esters with a carbon number of 3 to 40, more preferably 3 to 30, in particular 3 to 20, which have a polymerizable vinyl bond, is particularly preferred. Especially preference is given to the use of compounds having a (meth) acrylate group, for example acrylic acid, methacrylic acid, methyl acrylate or methyl methacrylate and their derivatives.

These polymerizable compounds are preferably allowed to reign with their surface only after the synthesis of the nanoparticles. ^'To this end, the synthesis product is heated in an excess of the polymerizable compound, for example, to 80 to 160 ° C, in particular 100 to 140 ° C. If the synthesis product already has an organic compound on the surface (eg the crystal growth-controlling solvent from the synthesis mixture), this can be exchanged for the polymerizable surface-modifying compound.

Bifunctional surface-modifying compounds, for example polyols, can also be reacted with a compound having a “reactive” group and a polymerizable double bond. "Reactive" here means the ability to bind to the free (not binding to the nanoparticle surface) functional group. Polyols can be, for example, with carboxylic acids having ^'a polymerizable double bond, such as (meth) acrylic acid and implement their derivatives to form a Esterfunktion. The reaction of polyols with silanes with at least one reactive alkoxy group and a polymerizable double bond such as α-

Methacryloxypropyltrimethoxysilane leads to the formation of C-O-Si bonds.

According to the invention, it is preferred to produce the radiopaque filler in a synthesis mixture which already contains the surface-modifying compound. However, as already described, it is also possible, after the nanoparticles have already been synthesized, to treat the surface by reaction with the surface-modifying agent, for example by exchanging the existing ones Solvent shell with the desired surface modifying compound. This "solvent exchange" is preferably carried out at elevated temperature, typically at temperatures of 50-200 ° C.

The synthesis of X-ray-opaque fillers suitable according to the invention is explained below. Salts, especially fluorides, phosphates and sulfates of rare earth metals, scandium, yttrium, barium or strontium can be synthesized as described in WO 02/20696. There are e.g. concrete examples for the synthesis of doped rare earth metal fluorides which are transferable in their synthesis technique to the present invention, apart from the fact that no doping is required.

The corresponding synthesis (A) comprises the following process steps:

a) the reaction in an organic reaction medium which comprises at least one surface-modifying compound having an N- or P-containing functional group and optionally at least one further solvent, a metal source which is soluble or dispersible in the reaction medium and a fluoride which is soluble or dispersible in the reaction medium Source of phosphate or sulfate,

b) optionally removing the reaction medium from the nanoparticulate metal fluoride, phosphate or sulfate formed, and

c) optionally the isolation of the nanoparticulate salt.

The boiling point of the organic reaction medium is preferably above the reaction temperatures given below. The boiling point is preferably 150-400 ° C, especially in the range of 180-300 ° C (each at normal pressure, 1013 mbar). Depending on the oxidation sensitivity of the metal source, it is preferred to carry out the reaction under an inert gas such as nitrogen or argon.

The reaction is preferably carried out at a temperature of 50-350 ° C., for example 120-320 ° C., in particular 180-290 ° C. A suitable temperature can be on the control of particle formation readily determine, for example, by precipitating the particles from samples of the reaction medium, which can be effected by cooling or addition of a ^{'precipitating} solvent (eg methanol), and then the particle growth examined.

Suitable reaction times can be determined in the same way and are preferably in the range from 10min -48h, in particular 30min-20h.

After the reaction is complete, the reaction mixture is typically allowed to cool to room temperature. If the nanoparticles are not yet completely precipitated, maximum yields can be achieved by adding methanol.

The surface-modifying organic compound used according to the invention not only has a positive effect on the subsequent dispersion in a dental material. It also shows an effect that limits crystal growth and leads to the previously specified small particle sizes of less than 25 nm in a narrow particle size distribution.

The surface-modifying compound is preferably an organophosphorus compound or a mono- or di-substituted amine. Preferred embodiments of the amine are mono- or dialkylamines in which the alkyl radical preferably has from 4-20, in particular from 6-14, carbon atoms, for example dodekylamine or

Bis (ethylhexylamine). The organophosphorus compounds are preferably selected from the following substances: a) Phosphinic acid ester

R ¹ O

R ^ P = O

R ^;

b) phosphonic diesters

R ¹ \ R ² OP = O

R ³ O

C) phosphoric acid triesters, in particular trialkyl phosphates, such as tributyl phosphate or tris (ethylhexyl) phosphate

R ¹ O \ R ² OP = O

R ³ O

d) trialkylphosphines, such as trioctylphosphine (TOP) or

R ¹

R ² P

R ³

e) trialkylphosphine oxides, such as trioctylphosphine oxide (TOPO) R ¹

R ^ P = O

R ^J

wherein R _] _, R2 and R3 are independently a branched or linear aliphatic residue (preferably alkyl), an aliphatic-aromatic or aromatic-aliphatic residue, or an aromatic residue, each from 4-20, more preferably from 4-14 , in particular of 4-10 carbon atoms. An example of an aromatic residue is phenyl, examples of aliphatic-aromatic residues are tolyl or xylyl, and benzyl is an example of an aromatic-aliphatic residue. Among these organophosphorus compounds, (a) to (c) and (e) are, in particular (a) to (c) preferred.

The surface modifying organic compound, i.e. in the synthesis described here, the nitrogen or organophosphorus compound can be the only solvent in the reaction medium. It is then preferably used in an amount of at least 10 mol, based on the molar amount of the metal atoms used as the metal source. A preferred upper limit is around 1000 mol.

Depending on the type of surface-modifying agent and in particular the length of the hydrophobic portion of the molecule, the use of larger amounts of the nitrogenous or organophosphorus compound may be undesirable in view of complete precipitation of the nanoparticles.

It is therefore preferred to additionally use at least one further solvent. In this embodiment, the surface-modifying organic compound (“first solvent”) is preferably in a molar amount of less than 10 mol, in particular in an amount of 0.9-6 mol, based on imol of the metal ions (metal source) used. The amount of the further solvent (s) is preferably from 5-100 mol, based on 1 mol of metal atoms (metal source).

The other solvent (s) should be miscible with the surface-modifying nitrogen or organophosphorus compound. They preferably have a boiling point above 150 ° C, especially above 180 ° C. The preferred upper limit is 350-400 ° C.

The further solvent can be a hydrocarbon or an organic compound with at least one polar group. The latter are preferred if water of crystallization is present in the metal salt used as the starting material. The other solvent or solvents are preferably selected from the following compounds:

• Solvent with at least one ether function, in particular dialkyl ether with 5-10 carbon atoms per alkyl group, such as dipentyl ether, dihexyl ether, diheptyl ether, dioctyl ether or diisoamyl ether; Diaryl ethers or diaralkyl ethers with a total of 12-18 carbon atoms, such as diphenyl ether or dibenzyl ether; or mono- or polyethylene glycol (PEG) dialkyl ether (in which each alkyl group preferably has 1-4 carbon atoms and the average number of PEG units is preferably up to 10), such as diethylene glycol dibutyl ether, triethylene glycol dibutyl ether and / or tetraethylene glycol dimethyl ether;

Branched or unbranched alkanes, which preferably have 10-18 carbon atoms, in particular 12-16 carbon atoms, such as dodecane or hexadecane; and or • An organic high-boiling base, preferably an N-containing aliphatic base, most preferably a tertiary substituted amine, in particular trialkylamine compounds having 5-10 carbon atoms per alkyl group, such as trioctylamine or tris (2-ethylhexyl) amine or an N-containing aromatic base preferably 3-20 carbon atoms, such as imidazole.

These solvents can also be used in combination.

If an acid such as phosphoric acid, hydrofluoric acid (HF) or sulfuric acid is used as the anion source, it is preferred to use the organic high-boiling base in an approximately equimolar amount (e.g. 0.6-1.4 mol) with respect to the hydrogen atoms of the acid.

The cation source is any sufficiently reactive metal salt and preferably a metal chloride, metal alkoxide (wherein the alkoxide preferably has from 1-6 carbon atoms, especially from 1-4 carbon atoms), a metal nitrate or metal acetate. The use of metal chlorides is particularly preferred. If hydrated metal salts are used, it is preferred to remove the water of crystallization before the reaction.

The anion source for phosphates, fluorides or sulfates is preferably selected from the following compounds:

a) sulfuric acid, phosphoric acid or HF,

b) phosphate, sulfate or fluoride salts which are soluble or at least dispersible in the synthesis mixture, in particular salts with an organic cation or alkali metal salts, or

C) esters that release sulfate, phosphate or fluoride anions at higher temperatures, such as alkyl sulfuric acid. The cation mentioned under option (b) is preferably selected from basic N-containing aliphatic, aromatic, aliphatic-aromatic or aromatic-aliphatic substances, which preferably have 4-30, in particular 4-20, carbon atoms. Suitable cations include, for example, quaternary ammonium and phosphonium salts or protonated aromatic bases, such as pyridine or collidine. For the production of phosphate nanoparticles, for example, tetrabutylammonium dihydrogenphosphate, tetramethylammonium dihydrogenphosphate or triethylammonium dihydrogenphosphate can be used as the anion source. Accordingly, sulfate nanoparticles can be made, for example, from tetrabutylammonium hydrogen sulfate, tetramethylammonium hydrogen sulfate, bis-

Prepare tetrabutylammonium sulfate or triethylammonium hydrogen sulfate. In the production of fluoride nanoparticles, for example, triethylamine trishydrofluoride, tetrabutylammonium fluoride,

Use tetrabutylammonium hydrogen difluoride, dodecylamine hydrofluoride or pyridine hydrofluoride or collidine hydrofluoride.

If the cation source dissolves too slowly in the organic synthesis medium, it is preferred to first dissolve it in a lower alcohol, such as methanol, before adding the surface-modifying organic compound and, if appropriate, further reaction solvents. Lower alcohol and water of crystallization are then removed by distillation and the residue is dried before adding further reactants.

The sulfates, phosphates or fluorides obtained according to this synthesis technique are very well dispersible in conventional dental materials, in particular hydrophobic dental materials. No further surface-modifying process steps are required for this, not even silanization. If one would like to disperse the nanoparticles thus produced in hydrophilic dental materials, the dispersibility can optionally be promoted by replacing the surface-modifying organic compound still originating from the reaction mixture with another surface-modifying organic compound with an N-, P-, S- and / or 0-containing functional group and another polar group. This additional polar group then conveys the required hydrophilicity. Alternatively, the synthesis of the nanoparticles can already be carried out in a surface-modifying organic compound which has this additional polar group, for example a carboxy group, amino group or hydroxyl group. For this purpose, preference is given to using N- or P-containing organic compounds, as described above, whose organic radicals (for example R] _, R2 R3) have a further polar group, for example carboxyl, amino and / or hydroxy. This polar group is preferably located at the end of the molecule opposite the particle surface.

This double functionalization of the nanoparticles can also be of interest if further surface-modifying steps, e.g. would like to carry out a silanization in order to optimally disperse the nanoparticles in special dental materials.

Next, the synthesis of nanoparticulate barium and strontium sulfates with a polyol or sulfoxide as solvent and surface-modifying compound will be described (Synthesis B).

The polyols suitable for this preferably have 2-3 hydroxyl groups. Examples include glycerol, ethylene glycol or polyethylene glycol with a preferred average number of ethylene glycol units of up to 4. Dimethyl sulfoxide (DMSO) can be used as the sulfoxide. Preferred sources of metal atoms are barium chloride, strontium chloride and their hydrates. The starting material for the sulfate anion is preferably used

Alkali metal sulfates, ammonium sulfate or sulfates with an organic cation. The corresponding hydrogensulf te are equally suitable.

The organic cation is preferably selected from basic N-containing aliphatic, aromatic, aliphatic-aromatic, and aromatic-aliphatic compounds which preferably have from 4-30, in particular 4-20, carbon atoms. Suitable cations include, for example, quaternary ammonium or phosphonium, with 4 substituents, which can be selected independently of one another from alkyl having preferably 1-10 carbon atoms (preferably 1-5) or benzyl, or protonated bases, such as hydrazine, amantadine, pyridine or collidine.

Accordingly, one can barium or

Strontium sulfate nanoparticles from raw materials, such as ..... Tetrabutylammoniumhydrogensulfat, Tetramethylammoniumsulf t, Bistetrabutylammoniumsulfat or

Prepare triethylammonium hydrogen sulfate. Other suitable starting materials are ammonium hydrogen sulfate, ammonium sulfate, alkali metal hydrogen sulfates, amantadine sulfate, ethylene diammonium sulfate and hydrazinium sulfate.

When using hydrogen sulfates, organic bases, such as imidazole, are preferably added to the reaction medium as acid scavengers.

The reaction is preferably carried out at temperatures of 50-240 ° C, the temperature range of 50-100 ° C for glycerol and higher temperatures in the range of 160-240 ° C, in particular 160-180 ° C for polyols of higher molecular weight or sulfoxide solvents are preferred. Examples of the synthesis of tungstates in an aqueous medium can be found in WO 02/20696 and can be transferred to other tungstates. The nanoparticles thus produced are modified with the organic compound explained above, which binds to the nanoparticles with an N-, P-, S- and / or O-containing functional group after the synthesis, if appropriate after known steps for size selection, for example ultracentrifugation to promote the dispersibility in hydrophobic or hydrophilic dental materials, depending on the choice of the modifier. The corresponding aftertreatment involves heating the tungstate particles in these modifying agents and, if appropriate, isolating them by means known in the art, such as ultracentrifugation, precipitation by adding a non-dispersing solvent, etc.

The barium or strontium sulfate nanoparticles obtained according to synthesis (B) are particularly dispersible in hydrophilic dental materials. If you want to incorporate them into hydrophobic dental materials, it may be necessary to subject the barium or strontium sulfate nanoparticles to a post-treatment to change the surface. For example, the polyol or sulfoxide can be exchanged for a more hydrophobic coordinating solvent, for example the nitrogen or organophosphorus compounds described above. The corresponding aftertreatment involves heating the barium or strontium sulfate nanoparticles in this more hydrophobic solvent. The barium or strontium sulfates produced in a polyol or the tungstenate particles modified with a polyol can also be silanized in order to increase the hydrophobicity on the surface. For silanization, for example, a silane compound with at least one reactive alkoxy group and a polymerizable double bond, such as α-methacryloxypropyltrimethoxysilane, can be used. Such particles can be used to produce prepolymers with at least one vinyl compound, from which a matrix is formed particularly good integration of the radiopaque fillers.

The fluorides, barium or strontium salts or tungstates produced in this way are distinguished by various advantages over conventional radiopaque fillers. They can be dispersed very well in dental materials without further process steps for surface modification. If the particle size is less than 25 nm, there is no interaction with visible light, so that transparent dental materials can be produced according to the invention. Surprisingly, the dental materials according to the invention also have a higher X-ray opacity than known fillers of the same chemical composition, but which have a larger particle size. A decisive advantage of the particles according to the invention is also that they allow flexible adaptation to the chemical nature of the matrix.

The dental material according to the invention preferably comprises a hardenable or already hardened matrix. Metals and metal alloys, as they are also often used in dental technology, are not considered to be hardenable or already hardened systems.

The dental material is preferably a composite, compomer, a cement or an organic polymer (synthetic resin) or the corresponding not yet hardened monomer or oligomer mixture.

The cements can be selected from cements known in the art, for example phosphate cements, silicate cements, silicophosphate cements, zinc oxide eugenol cements, carboxylate cements, glass ionomer cements,

Calcium hydroxide cements as described in Ullmann's Encyclopedia of Industrial Chemistry, Vol. 8, 1987, page 274ff. As a dental material based on polymer, the also use known (see Ullmann, page 277ff) thermosetting, cold-curing or light-curing polymer systems.

Glass ionomer cements were introduced by Wilson & Kent in the 1960s (Wilson, AD; J. Dent. Res. 75 (10), 1723 (1996). The dental material group of the compomers is described, for example, in patent EP 0 219 058. Carboxylate cements are described in DC Smith; British Dental J 125, 381 (1968).

It is particularly preferred that the dental material according to the invention contains at least one polymerizable vinyl compound (or an oligomer or polymer derived therefrom). Monofunctional or polyfunctional methacrylates, which can be used alone or in mixtures, are particularly suitable for this purpose. Examples of these compounds are methyl methacrylate, isobutyl ethacrylate, cyclohexyl methacrylate,

Triethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate (EGDMA),

Polyethylene glycol dimethacrylate, butanediol dimethacrylate, hexanediol dimethacrylate, decanediol dimethacrylate, dodecanediol dimethacrylate, bisphenol-A-dimethacrylate, trimethylolpropane trimethacrylate, but also bis-GMA and the reaction products from isocyanates, especially di- and / or triisocyanate-containing methacrylates and methacrylates. Examples include the reaction products of 1 mole of hexamethyl diisocyanate with 2 moles of 2-hydroxyethylene methacrylate, of 1 mole of tri (6-isocyanatohexyl) biuret with 3 moles of hydroxyethyl methacrylate and of 1 mole of triethylhexamethylene diisocyanate with 2 moles of hydroxyethyl methacrylate, hereinafter referred to as urethane dimethacrylate (UDMA) become. The proportion of these mostly long-chain compounds in the dental material is between 10 and 50% by weight. In principle, all binders that can be used for a dental material are suitable. Preferred mixtures of acrylate monomers known in the art are, for example, mixtures of urethane dimethacrylates and polymethylene dimethacrylates, or mixtures of urethane dimethacrylates and (poly) ethylene glycol dimethacrylates.

Composite materials which have been known as tooth restoration materials since 1962 (Bowen, RL; US 3,066,112) are particularly preferred, in particular the use of the so-called Bowen monomer bis-GMA, which is produced from bisphenol A-di (2,3-epoxypropyl) ether and acrylic acid is used in combination with at least one other acrylate monomer.

For example, polymerizable mixtures of bis-GMA and (poly) ethylene glycol dimethacrylates can be used.

The latter can also be used as a two-component dental filling material. For this purpose, the so-called "peroxide paste" and "amine paste" are mixed with the monomers, the radiopaque filler, optionally another filler, such as amorphous SiO 2, and to adjust the viscosity, if necessary, a prepolymer of these four components and optionally color pigments and stabilizers, the Peroxide paste e.g. Benzyl peroxide and the amine paste contains an amine such as N, N-diethanol-p-toluidine or N, N-dimethyl-p-toluidine.

The dental material according to the invention preferably contains 1-50% by weight of the x-ray-opaque nanoparticles, based on the total weight of the dental material. These can be incorporated into the dental material in the same way as described for larger particles in the prior art.

The dental material may also contain further fillers, if necessary. A suitable filler is pyrogenic silica with a BET surface area of approximately 20-400 m ² / g and an average primary particle size of approximately 5-50 nm. In addition, quartz, glass ceramic, glass powder or mixtures thereof can be used as a further filler, for example glass powder, in particular barium and / or strontium glass powder, which additionally increases the X-ray opacity. The average particle size of these powders is preferably in the range from 0.4 to 1.5 μm and in particular in the range from 0.7 to 1.0 μm.

To increase the X-ray opacity, it is also possible to use precipitated mixed oxides, such as ZrO 2 / SiO 2, as fillers. Mixed oxides with a particle size of 200 to 300 nm and in particular about 200 nm, with a refractive index of 1.52 to 1.55 are preferred. The mixed oxides are preferably spherical and have a uniform size.

The fillers for an organic matrix are preferably silanisie.rt to improve the adhesion between filler and matrix.

Based on the total weight, the additional filler, e.g. contain the silica, the quartz, glass ceramic, glass powder or the mixed oxide in an amount of about 5-84 wt .-%. The total weight of the inorganic fillers in the dental material according to the invention, including the X-ray opaque filler according to the invention with a particle size smaller than 25 nm, is preferably 6-85% by weight, in particular 45-75% by weight.

Depending on the type of catalyst used, the dental material can be hot, cold or curable by photopolymerization.

The known peroxides, such as dibenzoyl peroxide, dilauroyl peroxide, can be used as catalysts for the hot polymerization. -Butyl peroctoate or tert. -Butyl perbenzoate used are, but also α, α'-azo-bis- (isobutyroethyl ester), benzpinacol and 2,2'-dimethylbenzpinacol are suitable.

As catalysts for photopolymerization e.g. Benzophenone and its derivatives as well as benzoin and its derivatives are used. Examples of preferred photosensitizers are the α-diketones such as 9,10-phenathrenequinone, diacetyl, furil, anisil, 4,4'-dichlorobenzil and 4,4'-dialkoxybenzil. Camphorquinone is used with particular preference. The use of the photosensitizers together with a reducing agent is preferred. Examples of reducing agents are amines such as cyanoethylmethylaniline, dimethylaminoethyl methacrylate, n-butylamine, triethylamine, triethanolamine, N, N-dimethylaniline, N-methyldiphenylamine and N, N-dimethyl-sym. -xylidin.

Radical delivery systems, e.g. Benzoyl or. Lauroyl peroxide together with amines such as N, N-dimethyl-sym. -xylidine or N, N-dimethyl-p-toluidine used.

The amount of these catalysts in the dental material is usually between 0.1 and 5% by weight.

Finely divided splinter or pearl polymers, which can be homo- or copolymers of the vinyl compounds already described, can also be incorporated into the dental material. This homo or. Copolymers can in turn be filled with the inorganic fillers described here, including the radiopaque ones. For this purpose, reference is made to EP-PS 11 190 and DE-PS 24 03 211. The dental material can also contain the usual pigmentation agents and stabilizers.

Examples of polymer-based dental materials according to the invention comprise or consist of (a) 10 to 80% by weight, for example 10 to 30% by weight, organic binder on a polymer basis, (b) optionally 0.01 to 5% by weight of additives such as stabilizers, polymerization initiators, dyes, pigments, etc. and (c) 6-85% by weight, in particular 45-75% by weight of fillers, inclusive of the X-ray opaque filler according to the invention with a particle size of less than 25 nm.

The dental material according to the invention preferably serves as tooth filling material. When doing X-ray images, the dentist should be able to determine whether secondary caries has formed or not based on the X-ray opacity of the filling. A light-curing, X-ray-opaque filling material contains, for example, a urethane dimethacrylate or bis-GMA, tri-ethylene glycol dimethacrylate as a diluting monomer, X-ray-opaque fluoride, for example ytterbium trifluoride or barium / strontium salt, a further filler, for example ^' quartz, glass or pyrogenic glass, ceramics, glass ceramics, glass ceramics, glass ceramics with an average size of the primary particles of 40 nm and a BET surface area of 50 m ² / g, camphorquinone and N, N-dimethyl-sym. - xylidine as a catalyst and stabilizers and color pigments.

In order to increase the degree of filling of such filling materials, it is common, e.g. from Bis-GMA,

Triethylene glycol dimethacrylate, radiopaque fluoride, e.g. Ytterbium trifluoride or barium / strontium salt, and the pyrogenic silica to produce a copolymer, to grind it as a splinter polymer and then to incorporate it into the filling material. The polymerization after placing the filling is done with a commercially available halogen lamp.

Tooth filling materials are also manufactured as two-component materials that harden cold after mixing. The composition is similar to that of the light-curing materials, but instead of the photocatalysts, a peroxide, eg benzoyl peroxide, is added to one paste and an amine, eg N, N-, to the other paste. Dimethyl-p-toluidine mixed. By mixing approximately the same parts of the two pastes, a tooth filling material is obtained which hardens in a few minutes.

If one omits the last-mentioned amine materials and only uses benzoyl peroxide as a catalyst, for example, a thermosetting dental material is obtained which can be used for the production of an inlay or artificial teeth. For the production of an inlay, an impression is taken from the mouth of the avity and a plaster model is made. The paste is placed in the cavity of the Giops model and the whole is polymerized in a pressure pot under heat. The inlay is removed, worked ^'and then cemented in the patient's mouth into the cavity.

The invention relates not only to the x-ray opaque dental material, but also to finished parts made therefrom, e.g. artificial teeth, shells, inlays etc. It is explained using the following examples.

Reference Example 1: Synthesis of BaSO4

55 g BaCla are weighed into a round bottom flask and dissolved in 300 ml glycerol. 30 g of imidazole dissolved in glycerol are then added to the Ba-containing solution and the reaction mixture is then dried for 24 hours with gentle heating. In parallel, 73g

Tetrabutylammonium hydrogen sulfate dissolved in glycerin and dried overnight. Both solutions are then combined at 70 ° C and stirred for one hour. After adding 0.5 equivalents of water, based on glycerol, the barium sulfate particles thus synthesized are washed with isopropanol, washed with ethanol and then dried. Approx. 60 g barium sulfate nanoparticles with a homogeneous size distribution result (Standard deviation 22%) with an average particle size of 19 nm.

Reference Example 2: Synthesis of Y F3

17.48 g (45 mmol) of YbCls x 6 H2O are dissolved in 17.5 ml of MeOH and 125 ml of TEHP (tris (2-ethylhexyl) phosphate) are added. In a second vessel, 41.17 g (130.5 mmol) of tetrabutylammonium fluoride x 3 H2O are dissolved in 20 ml of MeOH and taken up in 175 ml of TEHP. Both reaction solutions are freed from the methanol at room temperature in vacuo and combined. The reaction mixture is heated to 200 ° C. under reflux for 2 h, the precipitate formed after cooling is centrifuged, washed twice with methanol and dried (yield 10.08 g, 100.7% of theory).

X-ray diffractometry (XRD) measurements of the particles obtained in this way indicated an average particle size of less than 10 nm.

example 1

If, in a known curable acrylic-based dental material, the non-surface-treated ytterbium fluoride of larger particle size (e.g. 300 mm) is replaced by the ytterbium fluoride produced according to the invention in reference example 2, the surface of which has been modified with TEHP and which shows a particle size of less than 10 nm, it is not only one excellent X-ray opacity, but surprisingly also improvements regarding the dispersibility in the matrix, the stability of the polymer matrix and its transparency. Examples of such conventional X-ray-opaque dental materials with ytterbium fluoride as X-ray-opaque filler are Examples 1, 2 and 3 of DE 35 025 94 AI. The X-ray opacity is measured for aluminum in accordance with European or international standards (EN 24049: 1993 or ISO 9917).

In addition, it was found that the dental materials according to the invention also show good properties with regard to other important material properties, such as abrasion behavior and polishability to a high gloss.

Example 2: Incorporation into a monomer mixture

(Monomer mixture: 43% Nupol, 37% RM3, 20% SR205; Nupol: bisphenol A. diglycidyl ether dimethacrylate; RM 3: 7,7,9-trimethyeth-4, 13-dioxo-3, 14-dioxa-5, 12- diazohexadecan-l, 16-dimethacrylate, SR 205: triethylene glycol dimethacrylate)

1 g of YbF ₃ , which was prepared as in Example 2, is ground in about 20 ml of methyl methacrylate in a mortar, the mixture is transferred to a round bottom flask and heated to 120 ° C. (30 min). After cooling to room temperature, the mixture is evacuated to dryness. The powder obtained is mixed with 10 g of the monomer mixture in a mortar and treated in an ultrasonic bath for several hours. A liquid, homogeneous monomer mixture is obtained which can now be processed into a dental material in a conventional manner, for example by adding known non-X-ray-opaque fillers, further additives, etc.

Claims

claims

1. Dental material which contains at least one filler which is selected from salts of barium, strontium, rare earth metals, scandium or yttrium or from tungstates, characterized in that the filler is in the form of surface-modified nanoparticles with an average particle size of less than 25 nm is present, the surface of which is modified with an organic compound which binds to the nanoparticles with a functional group containing N, P, S and / or O.

2. Dental material according to claim 1, wherein the nanoparticles are selected from fluorides of rare earth metals, scandium or yttrium, barium sulfate and strontium sulfate.

3. Dental material according to claim 1, wherein the nanoparticles are selected from tungstates of alkaline earth metals, rare earth metals, scandium and yttrium.

4. Dental material according to one of the preceding claims, wherein the surface-modifying organic substance is selected from polyols, sulfoxides, phosphinic esters, phosphoric acid diesters, phosphoric acid triesters, trialkylphosphines, trialkylphophine oxides, mono- and dialkylamines, carboxylic acids and carboxylic acid esters.

5. Dental material according to one of the preceding claims, wherein the surface-modifying organic compound has a polymerizable double bond.

6. Dental material according to one of the preceding claims, wherein the nanoparticles in an amount of 1 to 50% by weight, based on the total weight of the dental material.

7. Dental material according to one of the preceding claims, wherein the dental material comprises at least one polymerizable vinyl compound and optionally a further inorganic filler.

8. Dental material according to one of the preceding claims, wherein the total amount of inorganic fillers is 6 to 85 wt.%.

9. Use of a dental material according to one of claims 1 to 8 as a 1- or 2-component dental filling material or dental cement.

10. Use of a dental material according to one of claims 1 to 8 as a crown and bridge material or denture material.

11. Use of a dental material according to one of claims 1 to 8 for the production of artificial teeth, inlays, implants and finished dental parts.