Burnable polymer-based material for lost-wax technology

Abstract

Radically polymerizable composition that (a) at least one radically polymerizable monomer, (b) at least one initiator for radical polymerization and (c) contains at least one inert component, characterized in that the inert component (c) is soluble in the polymer formed by polymerization of the monomer(s) (a), wherein the solubility of component (c) decreases with increasing temperature, so that phase separation takes place above a certain temperature, and wherein the composition contains as inert component (c) at least one polypropylene glycol (PPG), PEG-PPG copolymer, propoxylated glycerol, ethylenediaminetetrakispropoxylate or a mixture thereof.

Description

[0001] The present invention relates to materials that are particularly suitable for the production of models for lost-wax casting processes using additive manufacturing techniques, and especially stereolithographic techniques. Lost-wax casting processes are used to produce molded parts that require high accuracy, for example, for the manufacture of jewelry or dental restorations.

[0002] To fabricate dental restorations using the classic lost-wax casting method, a wax model (wax-up) is formed, embedded in an investment material, and heated in a furnace after the investment has set. The wax melts and flows out of the mold. The mold is then heated further, burning off any remaining wax. This process creates a negative of the wax model, into which an alloy or ceramic material is subsequently cast. The resulting cast object is then the positive, exactly matching the wax model.

[0003] The wax model can be created in various ways. In manual modeling, the dental technician builds up a model of the dental restoration layer by layer on a plaster model using a special dental wax. The waxes soften when heated and, after melting, generally flow out of the investment material without causing cracks. This method remains the gold standard for the quality of cast and pressed restorations.

[0004] In newer methods, the wax model is milled from wax discs or blocks using CAD / CAM technology. The waxes used in this process require a compromise between machinability and burnout properties. Most commercially available products today fulfill both requirements adequately. These waxes also soften when heated and, after melting, flow out of the investment material without cracking.

[0005] Wax models are relatively fragile, so alternative materials are increasingly being used for their production. For example, CAD / CAM processes utilize plastic discs and blocks, as well as plastic-wax hybrid discs. In manual modeling, curable resins are used as an alternative to waxes. These resins can be cold-cured by mixing two components, thermally cured, or preferably by light curing. These materials contain relatively large amounts of non-melting thermosets.

[0006] Recently, so-called additive manufacturing processes have been increasingly used to produce models. These are manufacturing processes in which three-dimensional models or components are produced from computer-aided design data (CAD data) (A. Gebhardt, Vision of Rapid Prototyping, Ber. DGK 83 (2006) 7-12). These processes include stereolithography (SL), selective laser sintering (SLS), 3D printing, fused deposition modeling (FDM), inkjet printing (IJP), 3D plotting, multi-jet modeling (MJM), solid freeform fabrication (SFF), laminated object manufacturing (LOM), and laser powder forming (LPF), which allow for the cost-effective production of models, components, or molded parts, even in small batches (A. Gebhardt, Generative Manufacturing Processes, 3rd ed., Carl Hanser Verlag, Munich 2007, pp. 77ff.).In stereolithography, a molded part is built up layer by layer from a liquid and curable monomer resin based on CAD data (A. Beil, Manufacturing of Micro-Components Using Stereolithography, Düsseldorf 2002, VDI-Verlag 3 ff.). Additive manufacturing processes are often grouped under the term "Rapid Prototyping" (RP).

[0007] A disadvantage of materials used as alternatives to waxes is their melting behavior. Pure waxes soften upon heating, then melt and subsequently flow out of the mold. Therefore, they do not exert significant forces on the investment material during thermal expansion. The alternative materials do not exhibit this melting behavior. They expand thermally as the investment material sets / cures and the associated temperature rise occurs, and during subsequent heating. However, they do not flow out of the mold but are primarily removed through thermal decomposition. During expansion, they exert pressure on the investment material, leading to stresses and, particularly in large-volume dental restorations, to cracks in the negative mold. These cracks can result in press and casting flash, and, in the case of larger cracks, mispressing or miscasting.

[0008] It is known to add wax particles to curable materials. These are intended to melt when the investment material sets or during kiln curing, thus creating space for the expanding material. However, the molten wax often cannot escape, or can only escape poorly, because it is trapped by the polymerized material and because the diffusion coefficient of the molten wax molecules through the polymer matrix is ​​very low. In the worst case, the large volume increase of the waxes during melting actually increases the thermal expansion of the model instead of reducing it.

[0009] The invention is based on the objective of providing materials for modeling dental prostheses that do not exhibit the aforementioned disadvantages. They should allow the production of models, particularly by stereolithographic processes, that can be removed without cracking after the investment material has set, thus yielding flawless molds and restorations.

[0010] According to the invention, this problem is solved by radically polymerizable compositions which contain (a) at least one radically polymerizable monomer, (b) at least one initiator for radical polymerization and (c) at least one inert component.

[0011] The compositions according to the invention are characterized in that the inert component (c) is soluble in the polymer formed by polymerization of the monomer (a), wherein the solubility of component (c) decreases with increasing temperature, such that phase separation occurs above a certain temperature. This temperature is referred to here as the critical temperature or lower critical solution temperature (LCST). Component (c) is an organic compound.

[0012] Component (c) is liquid or solid under normal conditions (20°C, 1013 mbar) and has a pour point below the LCST. Preferably, it has a pour point of more than -150°C, more preferably more than -100°C, and most preferably more than -50°C.

[0013] According to DIN 51597, the pour point of a liquid product is the temperature at which it just barely flows upon cooling. The set point, according to DIN 51583, is the temperature at which the previously liquid product solidifies. The pour point is determined according to DIN 51597 / ISO 3016.

[0014] Component (c) preferably has a boiling point above 80°C, more preferably above 120°C, and particularly preferably above 150°C. Components that do not boil without decomposition under normal pressure preferably have a thermal decomposition temperature above 120°C, more preferably above 135°C, and particularly preferably above 150°C. The relatively high boiling or decomposition temperature ensures that component (c) remains solid or liquid even under operating conditions and does not evaporate, for example, during printing or when the investment material sets. Compounds with a boiling point of no more than 350°C and / or a decomposition temperature of no more than 500°C are preferred.

[0015] Component (c) is chemically inert, meaning that it does not react, or reacts only minimally, with the other components of the material under storage and application conditions. In particular, component (c) contains no radically polymerizable groups and therefore does not copolymerize with monomer (a). It is homogeneously miscible with component (a), and mixtures of (a) and (c) are stable at the processing temperature, meaning that no phase separation occurs; in particular, component (c) does not precipitate or crystallize during processing. The processing of the materials according to the invention, i.e., the production of models, for example by stereolithographic printing, is preferably carried out at a temperature of 15 to 35°C, more preferably 15 to 30°C.Preferred materials are those that can be processed and stored at room temperature (20°C), so that the materials do not need to be additionally heated for processing or cooled for storage.

[0016] Component (c) is particularly suitable for use as residue-free combustible compounds. These are defined as substances that preferably form less than 0.1 wt% ash upon combustion. Compounds that burn at a temperature of approximately 850°C when heated in an oxidizing atmosphere are preferred.

[0017] The compositions according to the invention contain as component (a) at least one radically polymerizable monomer and as component (b) at least one initiator for radical polymerization. They preferably exist in the form of a homogeneous mixture of components (a), (b), (c) and any optional components. Depending on the initiator used, they can be cured thermally, via a two-component initiator system, or photochemically. Compositions containing a photoinitiator are preferred.

[0018] According to the invention, materials for the production of models by manual modeling, especially by additive manufacturing processes, and particularly by stereolithography, are preferred. Here, a model is understood to be, in particular, the desired positive mold for the lost-wax casting process. Unlike the classic lost-wax casting process, the model is primarily removed from the mold by burning out after the investment material has set; nevertheless, the process is referred to here as a lost-wax casting process. The material according to the invention is particularly suitable for the production of models for the fabrication of dental restorations.

[0019] After hardening below the critical temperature, component (c) is stably integrated into the material, thus allowing for trouble-free further processing. Above the critical temperature, phase separation occurs, and at least part of component (c) seeps out of the hardened material. This temperature-induced seepage reduces the thermal expansion of the material, so that even with large-volume models, no cracks occur in the investment material, and pressed and cast objects can be obtained without flash or casting flash.

[0020] Fig.Figure 5 shows the thermal expansion behavior of a conventional material. Conventional materials expand thermally when heated, and their volume increases continuously. Above a certain temperature, the materials begin to decompose. This decomposition manifests as a decrease in volume. The decomposition temperature is material-dependent and is above 300°C for most organic materials.

[0021] Materials according to the invention also usually exhibit a slight expansion when heated, but this is significantly less than that of conventional materials ( Fig.1-4). The expansion curves drop off significantly again even before the decomposition temperature is reached. This decrease in volume is caused by the exudation of component (c). The exudation largely compensates for the thermal expansion of the material. Although a slight increase in the curves is observed again at higher temperatures, this is comparatively small. Overall, the materials according to the invention expand significantly less than known materials over the entire temperature range up to decomposition.

[0022] The expansion curves pass through a maximum. This maximum of thermal expansion is referred to here as maximum linear thermal expansion.

[0023] The modeling materials according to the invention are characterized by a relatively low maximum linear thermal expansion. Preferably, this is below 1.5%, particularly preferably below 1%, and most preferably below 0.7%. The linear thermal expansion is measured in the temperature range from 30°C to 800°C, whereby most materials begin to decompose before reaching 800°C. The decomposition manifests itself as a shrinkage of the measuring bodies.

[0024] A particular advantage is that the maximum expansion is achieved at a temperature below 150°C, preferably below 120°C, particularly preferably below 100°C, and most preferably below 90°C. In contrast, commercially available burnable SL resins typically exhibit a maximum thermal expansion of 2% or more, which is only reached at relatively high temperatures.

[0025] The determination of thermal expansion is preferably carried out on cylinders with a diameter of 6 mm and a height of 6 mm in a temperature range of 30°C to 800°C at a heating rate of 5 K / min in an air atmosphere. The measuring probe is applied to the sample with a contact force of 0.1 N. The linear expansion of the cylinders during heating and thermal expansion is measured. The measurement can be performed, for example, with a TA Instruments Q400 thermomechanical analyzer (TMA) equipped with a macro-expansion tool. The length of the cylinder at 30°C is assumed to be the original length, i.e., 0% expansion.

[0026] Generally, it is not necessary to use a specific temperature profile for the outflow of component (c), and no additional process step is required. After the investment material has set, the embedded model can be placed directly into an oven preheated to the temperature required for melting and / or burning out the model. Typically, melting and / or burning out occurs at a temperature of approximately 850°C. Preferably, the temperature cycle suggested by the investment material manufacturer is used. Often, the model is completely burned or out after just one hour. The maximum dwell time in the oven can vary depending on the investment material and manufacturer. In most cases, it is sufficient to leave the mold in the oven at the maximum temperature for 1 to 8 hours.The heating process can take several hours (1-12 h), and this period is sufficient to cause the necessary amount of exudation of component (c).

[0027] The seepage effect is presumably due to the fact that the solubility of component (c) in the polymer matrix decreases with increasing temperature, and a noticeable phase separation occurs above the Lower Critical Solution Temperature (LCST). However, since component (c) still exhibits some solubility in the polymer matrix even at higher temperatures, which is formed by the radical polymerization of component (a), the undissolved portion can diffuse relatively quickly through the matrix and thus escape from deeper layers of the model.

[0028] When the polymer matrix is ​​heated, the molecules of component (c) located between the polymer chains can migrate at least partially out of the matrix before the polymerized portions of the mixture are depolymerized and pyrolyzed. This significantly reduces, and usually completely eliminates, the risk of defects such as cracks or even mold destruction during burnout. The release of component (c) removes a portion of the organic mass during heating at a comparatively low temperature, allowing the subsequent heating process to be carried out quickly until all organic components are completely removed. In this way, the materials according to the invention produce crack-free molds with high accuracy and precision.

[0029] The materials according to the invention preferably contain at least one (meth)acrylate and / or (meth)acrylamide as a radically polymerizable monomer (a), preferably one or more mono- or multifunctional (meth)acrylates or a mixture thereof. Materials containing at least one multifunctional (meth)acrylate or a mixture of mono- and multifunctional (meth)acrylates as a radically polymerizable monomer are particularly preferred. Monofunctional (meth)acrylates are understood to be compounds with one, and polyfunctional (meth)acrylates are understood to be compounds with two or more, preferably 2 to 6, radically polymerizable groups. Methacrylates are preferred over acrylates in all cases.

[0030] Particularly suitable mono- or multifunctional (meth)acrylates are methyl, ethyl, 2-hydroxyethyl, butyl, benzyl, tetrahydrofurfuryl, or isobornyl (meth)acrylate, p-cumyl phenoxyethylene glycol methacrylate (CMP-1E), bisphenol A di(meth)acrylate, Bis-G(M)A (an addition product of (meth)acrylic acid and bisphenol A diglycidyl ether), ethoxylated or propoxylated bisphenol A di(meth)acrylate, such as bisphenol A di(meth)acrylate with 3 (SR-348c = methacrylate; SR-349 = acrylate, Sartomer) or 2 ethoxy groups (SR-348L - methacrylate, Sartomer), 2,2-bis[4-(2-(meth)acryloxypro-poxy)phenyl]propane, UD(M)A (a Addition product of 2-hydroxyethyl(meth)acrylate and 2,2,4- or 2,4,4-trimethylhexamethylene-1,6-diisocyanate), di-, tri-, tetra-, penta-, hexa- or hepta-ethylene glycol di(meth)acrylate, di-, tri-, tetra-, penta-, hexa- or hepta-propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated or propopoxylated trimethylolpropane tri(meth)acrylate, e.g.Triple-propoxylated trimethylolpropane triacrylate (Sartomer SR-492) and tripropylene glycol diacrylate, pentaerythritol tetra(meth) acrylate, as well as glycerin di- and tri(meth) acrylate, 1,4-butanediol di(meth) acrylate, 1,10-decanediol di(meth) acrylate (D3MA), 1,12-dodecanediol di(meth) acrylate or oligomeric polyether, polyester, epoxy, urethane (meth) acrylates and tricyclodecane dimethanol di(meth) acrylate.

[0031] Particularly preferred are mono- and especially di- and trifunctional acrylates and methacrylates with a molecular weight of <1000 g / mol, such as 2-phenoxyethyl(meth)acrylate, aliphatic urethane diacrylates, phthalic acid HEA esters (Photomer 4173), pyromellitic acid di-HEA esters (HEA = 2-hydroxyethyl acrylate), Bis-G(M)A (an addition product of (meth)acrylic acid and bisphenol A diglycidyl ether), 2,2-bis[4-(2-(meth)acryloxypropoxy)phenyl]propane, UD(M)A, triethylene glycol di(meth)acrylate (TEGD(M)A) and 2-phenoxyethyl(meth)-acrylate (acrylate SR339C Fa Sartomer / Arkema). These monomers are characterized by high reactivity, high double bond conversion, good mechanical properties, low polymerization shrinkage, and relatively low viscosity. Materials containing (a) UDMA, TEGDMA, Bis-GMA (addition product of methacrylic acid and bisphenol A diglycidyl ether), or 2-phenoxyethyl acrylate (SR339C, [Company Name]) as component are particularly preferred.Sartomer / Arkema), a mixture of UDMA, TEGDMA and 2-phenoxythyl acrylate or preferably UDMA, TEGDMA and Bis-GMA and in particular a mixture of UDMA and TEGDMA.

[0032] The properties of materials before and after curing can be influenced by a targeted combination of monomers. Mixtures of monofunctional and difunctional monomers are characterized by a relatively low viscosity and reactivity of the resin mixture, with viscosity and reactivity decreasing with increasing monofunctional monomer content. A high content of monofunctional monomers results in lower stiffness of the models obtained by curing the materials. Mixtures of difunctional and trifunctional monomers exhibit higher reactivity, with reactivity increasing with increasing trifunctional monomer content. A high trifunctional monomer content also leads to increased brittleness. The reactivity and viscosity of the resin mixture, as well as the polymerization shrinkage, are also determined by the molar mass of the monomers; with increasing molar mass, polymerization shrinkage decreases while viscosity increases.

[0033] Preferred photoinitiators (b) for initiating radical photopolymerization are benzophenone, benzoin and their derivatives, or α-diketones or their derivatives, such as 9,10-phenanthrenequinone, 1-phenylpropane-1,2-dione, diacetyl, or 4,4'-dichlorobenzil. Camphorquinone (CQ) and 2,2-dimethoxy-2-phenylacetophenone are particularly preferred, and α-diketones in combination with amines as reducing agents, such as 4-(dimethylamino)benzoic acid ester (EDMAB), N,N-dimethylaminoethyl methacrylate, N,N-dimethyl symmetric-xylidine, or triethanolamine, are especially preferred. Diethylthioxanthone (DETX, CAS 82799-44-8) and isopropylthioxanthone (ITX, CAS 75081-21-9) are further preferred, both preferably in combination with ethyl 4-(dimethylamino)benzoate (EMBO, CAS No. 10287-53-3). [1- / 4-Phenylsulfanylbenzoyl)heptylideneamino]benzoate (Irgacure OXE 01) and [1[9-Ethyl-6-(2-methylbenzoyl)carbazol-3-yl]ethylideneamino]acetate (Irgacure OXE 02) are also preferred.

[0034] Particularly preferred photoinitiators are Norrish type I photoinitiators, especially monoacyl or bisacylphosphine oxides, and in particular monoacyltrialkyl or diacyldialkylgermanium compounds, such as benzoyltrimethylgermanium, dibenzoyldiethylgermanium, or bis(4-methoxybenzoyl)diethylgermanium (MBDEGe). Mixtures of the various photoinitiators can also be advantageously used, such as bis(4-methoxybenzoyl)diethylgermanium in combination with camphorquinone and ethyl 4-dimethylaminobenzoate.

[0035] Particularly preferred are camphorquinone (CAS No. 10373-78-1) in combination with ethyl 4-(dimethylamino)benzoate (EMBO, CAS No. 10287-53-3) as well as phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (Irgacure 819, CAS 162881-26-7), diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO, CAS No. 75980-60-8), and 2-benzyl-2-(dimethylamino)-4'-morpho-lino-butyro-phenone (Irgacure 369, CAS No. 119313-12-1). 1-Buta-non-2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morphophenolyl)phenyl (Irgacure 379, CAS No. 119344-86-4) and especially Bis (4-methoxy-benzoyl)diethylgermanium (MBDEGe; Ivocerin).

[0036] According to the invention, component (c) consists of polypropylene glycols (PPG), PEG-PPG copolymers, propoxylated glycerol, ethylenediaminetetrakispropoxylates and mixtures thereof.

[0037] Component (c) can be solid at room temperature as long as it does not precipitate from the monomer or monomer mixture at the processing temperature. Substances that are pasty and, in particular, liquid at room temperature are preferred. The consistency of component (c) can be adjusted, for example, by the proportion of PPG groups, e.g., by mixing propoxylated and ethoxylated compounds or by increasing the proportion of PPG groups within a molecule, e.g., in PEG-PPG copolymers. The proportion of PPG groups is preferably high enough that the component is liquid or pasty, and particularly preferably high enough that the pour point is lower than the processing temperature.

[0038] Component (c) preferably has a molecular weight of 1000 to 10000 g / mol, particularly preferably 1000 to 5000 g / mol. Polypropylene glycols (PPG) preferably have a molecular weight of 1000 to 4000 g / mol, particularly preferably 1500 to 3000 g / mol and especially 2000 g / mol, and PEG-PPG copolymers have a molecular weight of 1000 to 10000 g / mol, preferably 1500 to 5000 g / mol and especially 2000 to 4000 g / mol.

[0039] The ethylenediaminetetrakis propoxylates preferably have a molecular weight of 1000 to 10000 g / mol, in particular of 1000 to 5000 g / mol.

[0040] Unless otherwise stated, the molar mass of polymers referred to here is in all cases the molar mass Mη (viscosity mean) determined by viscometry.

[0041] Particularly preferred as component (c) are polypropylene glycols (PPG), in particular PPG with a molecular weight of 1000 to 4000 g / mol, preferably 1500 to 3000 g / mol, Co-PEG-PPG with a molecular weight of 1000 to 10000 g / mol, preferably 1500 to 5000 g / mol and most particularly polypropylene glycol with a molecular weight of approximately 2000 g / mol.

[0042] Mixtures of the aforementioned substances can also be used to advantage. In addition to the components mentioned, these mixtures can also contain, in a minor amount, compounds with a molecular weight of less than 1000 g / mol.

[0043] Terminal -OH groups of the aforementioned compounds can be esterified or etherified, for example with methyl, ethyl, propyl or iso-propyl groups or formate, acetate, propionate or iso-propionate groups.

[0044] According to the invention, the type and quantities of components (a) and (c) are matched to achieve the desired solubility behavior. The solubility behavior is influenced, among other things, by the molecular weight of component (c). With increasing molecular weight of component (c), its incompatibility with the polymerized matrix increases. High incompatibility promotes the seepage of component (c), i.e., component (c) seeps out more quickly, at lower temperatures, and in larger quantities.

[0045] Simultaneously, exudation is promoted by high mobility of component (c) in the polymerized matrix, i.e., by a high diffusion coefficient. However, the diffusion coefficient of component (c) decreases with increasing molecular weight. Thus, a high molecular weight promotes exudation of component (c) on the one hand by increasing incompatibility, and on the other hand, it worsens exudation by reducing the diffusion coefficient. For a given polymeric matrix, a range of molecular weights can be determined at which the exudation rate is maximal. By varying the molecular weight of component (c), the exudation behavior can therefore be controlled and adjusted.

[0046] The solubility behavior also depends on the polarity of the polymer matrix and component (c). The properties of the polymer matrix are largely determined by component(s) (a). The polarity of the matrix can be increased, for example, by using monomers with polar groups. Exudation is further promoted by high flexibility of the polymer network. The flexibility of the polymer network can be controlled by the degree of crosslinking and the type of monomers.

[0047] A suitable incompatibility for the purposes of the invention can be determined using test specimens. The incompatibility causes an increase in opacity during polymerization. A high degree of incompatibility manifests itself in a large increase in opacity, while a lower degree of incompatibility results in a correspondingly smaller increase in opacity. An advantageous incompatibility exists when polymerization leads to only slight supersaturation, which is evident in the test specimens being slightly opaque to transparent after polymerization. If the test specimens are completely opaque after polymerization, this indicates a high degree of incompatibility.

[0048] The components are matched to achieve the desired thermal expansion behavior, i.e., that the maximum thermal expansion is below 1.5%, preferably below 1%, particularly preferably below 0.7%, wherein, according to a particularly preferred embodiment, the maximum expansion is achieved at a temperature of below 150°C, preferably below 120°C, particularly preferably below 100°C and most preferably below 90°C.

[0049] The LCST is below the temperature of maximum thermal expansion, preferably 20 to 30°C below this temperature. According to the invention, materials with an LCST below 120-130°C are therefore preferred, preferably below 90-100°C, particularly preferably below 70-80°C, and most preferably below 60 to 70°C.

[0050] Furthermore, the LCST is preferably higher than the processing temperature, so that component (c) does not ooze out during the hardening of the composition but only during subsequent heating. Preferably, the LCST is higher than 20°C, more preferably higher than 30°C, and particularly preferably higher than 35°C.

[0051] It was found that the inert component (c) used according to the invention, and in particular the aforementioned preferred components, are homogeneously miscible with radically polymerizable monomers, and especially with acrylates and methacrylates, and do not impair the polymerization of these monomers. This ensures high reactivity and short exposure and processing times during stereolithographic processing of the compositions according to the invention in the liquid state.

[0052] The component (c) used according to the invention is further characterized in that it can be at least partially absorbed by the investment mass during exudation.

[0053] According to the invention, materials in which component (a) contains UDMA, TEGDMA, or a mixture thereof are preferred. Particularly preferred are materials in which component (a) contains, in addition to UDMA and / or TEGDMA, a maximum of 20 wt.%, preferably a maximum of 10 wt.%, particularly preferably a maximum of 5 wt.%, and most preferably less than 3 wt.% or no other monomers, wherein the percentages refer to the total mass of component (a). Particularly preferred are materials in which component (a) contains UDMA or TEGDMA, particularly preferably a mixture of UDMA, TEGDMA, and SR339C or of UDMA, TEGDMA, and Bis-GMA, and especially a mixture of UDMA and TEGDMA. Component (c) in each case is PPG with a molar weight of 1000 to 4000 g / mol, preferably 1500 to 3000 g / mol, and most preferably 2000 g / mol.

[0054] In the case of the monomers preferred according to the invention, PPG with a molecular weight of 2000 g / mol represents a good compromise between low viscosity, sufficient phase incompatibility, and adequately rapid diffusion. By varying the molecular weight of component (c) within the aforementioned ranges, the seepage behavior can be further optimized for the desired application.

[0055] In the case of PEG-PPG-PEG, a molecular weight of approximately 3500 g / mol is advantageous. Using this component shifts the temperature of maximum thermal expansion to higher values.

[0056] In addition to the components mentioned above, the materials according to the invention may advantageously contain further additives. For stereolithographic applications, materials containing at least one colorant and preferably also at least one polymerization inhibitor are preferred.

[0057] Organic dyes and pigments are preferred as colorants, in particular azo dyes, carbonyl dyes, cyanine dyes, azomethines and methines, phthalocyanines, and dioxazines. Dyes that are soluble in the materials, especially azo dyes, are particularly preferred. Inorganic and, in particular, organic pigments that disperse well in the materials are also suitable as colorants. Azo pigments and non-azoparticles are preferred. Colorants that burn off without leaving residue are preferred. For this reason, organic pigments are preferred over inorganic pigments. If inorganic pigments are used, their quantity is preferably determined such that their ash content after burning off is less than 0.1% by weight based on the total weight of the burnable material.

[0058] Preferably, the materials contain at least one colorant that absorbs in the same wavelength range as the polymerization initiator. Colorants exhibiting an absorption maximum corresponding to the wavelength of the light used for curing are particularly preferred. Colorants with an absorption maximum in the range of 350 to 550 nm, preferably 380 to 480 nm, are very advantageous.

[0059] Colorants prevent the light used for curing from penetrating too deeply into the materials, thus improving the precision of the components in the printing process, especially in stereolithographic processes. Colorants can also be added for aesthetic purposes.

[0060] The polymerization inhibitor(s) act as stabilizers to prevent spontaneous polymerization. These inhibitors / stabilizers improve the storage stability of the materials and also prevent uncontrolled polymerization in the stereolithographic tank. The inhibitors are preferably added in such a quantity that the materials remain stable for approximately 2-3 years. Particularly preferably, the inhibitors are used in an amount of 0.001 to 1.0 wt.%, and most preferably 0.001 to 0.20 wt.%, based on the total mass of the material.

[0061] Preferred are so-called aerobic inhibitors, e.g., phenols such as hydroquinone monomethyl ether (MEHQ) or 2,6-di-tert-butyl-4-methylphenol (BHT), which are only effective in the presence of oxygen and are preferably used in a concentration range of 100–2000 ppmw. Suitable anaerobic inhibitors are phenothiazine, 2,2,6,6-tetramethylpiperindine-1-oxyl radical (TEMPO), iodine, and copper(I) iodide. These are effective even at low concentrations of preferably 10–200 ppmw, even in the absence of oxygen. Polymerization only occurs when these additives are consumed. It is advantageous to use a mixture of aerobic and anaerobic inhibitors.

[0062] Aerobic inhibitors are preferably used in an amount of 0.001 to 0.50 wt% and anaerobic inhibitors in an amount of 0.001 to 0.02 wt%, each based on the total mass of the material. Preferred mixtures contain 0.005 to 0.10 wt% of aerobic inhibitors and 0.001 to 0.02 wt% of anaerobic inhibitors, also based on the total mass of the material.

[0063] The modeling materials according to the invention may also contain particulate filler. Generally, organic particles are preferred as fillers, in particular fillers that burn without ash. The filler(s) preferably have a particle size of less than 25 µm, more preferably less than 10 µm, and most preferably less than 5 µm. Unless otherwise specified, all particle sizes mentioned herein are D50 values, i.e., 50 vol% of the particles have a diameter smaller than the specified value. Fillers primarily serve to adjust the viscosity, mechanical, and / or optical properties of the materials.

[0064] The surface of the fillers can be modified, for example, to improve their dispersibility in the organic matrix. Compounds that are chemically bound to the surface of the fillers, i.e., by ionic or covalent bonds, are preferably used for surface modification. Compounds containing either acid groups, preferably carboxylic acid, phosphonic acid, hydrogen phosphate groups, or acidic phosphoric acid ester groups, or silyl groups, preferably alkoxysilyl groups, are preferred. The particle surface can be partially or preferably completely covered with the modifying agent. The modifying agents used according to the invention are monomeric compounds. Linear carboxylic acids, such as formic acid, acetic acid, propionic acid, octanoic acid, isobutyric acid, isovaleric acid, pivalic acid, or phosphonic acids, are particularly suitable as surface modifying agents.such as methylphosphonic, ethylphosphonic, propylphosphonic, butylphosphonic, octylphosphonic, or phenylphosphonic acid. Silanes containing silyl groups, such as propyltrimethoxysilane, phenyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, trimethylchlorosilane, trimethylbromosilane, trimethylmethoxysilane, and hexamethyldisilazane, are preferred. Particularly preferred surface modifying agents are acidic phosphoric acid esters, such as dimethylphosphate, diethylphosphate, dipropylphosphate, dibutylphosphate, dipentylphosphate, dihexylphosphate, dioctylphosphate, or di(2-ethylhexyl)phosphate. The surface modifying agents may also contain radically polymerizable groups, for example, (meth)acrylate groups, which react with component (a) and are thus incorporated into the polymer network.

[0065] Preferred fillers are particulate waxes, in particular carnauba wax, preferably with a particle size of 1 to 10 µm, cross-linked polymethyl methacrylate (PMMA) particles, preferably with a particle size of 500 nm to 10 µm, and polyamide-12 particles, preferably with a particle size of 5 to 10 µm. For stereolithography, fillers are preferably used whose maximum particle size is smaller than the thickness of the stereolithographically produced layers. Particles with a maximum size of 25 µm are preferred, preferably a maximum of 15 µm.

[0066] According to the invention, filler-free materials are preferred.

[0067] The rheological properties of the materials according to the invention are adapted to the desired application. Materials for stereolithographic processing are preferably formulated so that their viscosity is in the range of 50 mPa·s to 100 Pa·s, preferably 100 mPa·s to 10 Pa·s, and particularly preferably 100 mPa·s to 5 Pa·s. The viscosity is determined at the desired processing temperature of the material using a cone-plate viscometer (shear rate 100 / s). The processing temperature is preferably in the range of 10 to 70°C, and particularly preferably 20 to 30°C.

[0068] Materials for manual processing are preferably adjusted to have a paste-like consistency.

[0069] For the production of low-viscosity materials, liquid monomers and low-viscosity components (c) are preferably used, while for the production of materials with high viscosity, e.g. solid monomers and / or viscous or solid components (c) can also be used.

[0070] The materials according to the invention may also preferably contain one or more additional UV absorbers. Preferred UV absorbers are 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethyl-butyl)phenol] (CAS No. 103597-45-1), 2,2',4,4'-tetrahydroxybenzophenone (CAS No. 131-55-5), 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol (CAS No. 3896-11-5), 2,2'-benzene-1,4-diyl-bis(4h-3,1-benzoxa-zin-4-one) (CAS No. 18600-59-4). and 2-(2H-Benzotriazol-2-yl)-6-dodecyl-4-methylphenol (CAS No. 23328-53-2).

[0071] Equally suitable are so-called Hindered Amine Light Stabilizers such as Bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate (CAS No. 41556-26-7) and Methyl-1,2,2,6,6-pentamethyl-4-piperidylsebacate (CAS No. 82919-37-7), Bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl)sebacate (CAS No. 129757-67-1), Bis(1,2, 2,6,6-pentamethyl-4-piperidyl)-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate (CAS No. 63843-89-0).

[0072] In addition to the components mentioned above, the materials according to the invention may contain one or more further additives, which are preferably selected from thickening agents, optical brighteners (e.g. Lumilux LZ Blue, CAS No. 658084-50-5, or 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene, CAS No. 7128-64-5) and, in the case of filler-containing materials, from dispersing agents.

[0073] The materials according to the invention preferably have the following composition: - 20 to 90 wt.%, preferably 42.5 to 82.5 wt.%, particularly preferably 50 to 79.3 wt.% component (a), - 0.1 to 5 wt.%, preferably 0.3 to 2.5 wt.%, particularly preferably 0.5 to 1.5 wt.% (photo-)initiator (b) and - 9.9 to 79.9 wt.%, preferably 15 to 55 wt.%, particularly preferably 20 to 48.5 wt.% inert component (c).

[0074] One particularly preferred composition contains: - 54.7 to 77.7 wt.%, preferably 64 to 74 wt.% component (a), preferably UDMA, TEGDMA, a mixture of UDMA and TEGDMA or a mixture of UDMA, TEGDMA and Bis-GMA, - 0.5 to 1.5 wt.%, preferably 0.6 to 1.2 wt.% (photo-)initiator (b) and - 23.8 to 44.8 wt.%, preferably 24.8 to 35.4 wt.% inert component (c), preferably PPG with a molecular weight of 1000 to 4000 g / mol, particularly preferably 1500 to 3000 g / mol, Co-PEG-PPG with a molecular weight of 1000 to 10000 g / mol, particularly preferably 1500 to 5000 g / mol, most preferably 2000 to 4000 g / mol and in particular polypropylene glycol with a molecular weight of approximately 2000 g / mol.

[0075] The most preferred composition is one that - 64 to 74 wt% UDMA, TEGDMA, a mixture of UDMA and TEGDMA or a mixture of UDMA, TEGDMA and Bis-GMA as component (a), - 0.6 to 1.2 wt.% photoinitiator (b) and - Contains 24.8 to 35.4 wt% polypropylene glycol (PPG) with a molecular weight of 1000 to 4000 g / mol, particularly preferably 1500 to 3000 g / mol and particularly with a molecular weight of approximately 2000 g / mol as an inert component (c).

[0076] Furthermore, the materials according to the invention preferably also contain: - 0.0001 to 1 wt.%, preferably 0.0001 to 0.5 wt.%, particularly preferably 0.0001 to 0.2 wt.% colorant; and / or - 0.0001 to 2 wt.%, preferably 0.0001 to 1 wt.%, particularly preferably 0.0001 to 0.5 wt.% UV absorber; and / or - 0 to 40 wt.%, preferably 0 to 30 wt.%, particularly preferably 1 to 20 wt.% organic filler.

[0077] Furthermore, the materials preferably contain - 0 to 5 wt.%, preferably 0 to 3 wt.%, particularly preferably 0 to 2 wt.% of further additive(s).

[0078] Unless otherwise stated, all specifications refer to the total weight of the material. The individual components are preferably selected from the preferred components mentioned above.

[0079] The materials according to the invention are particularly suitable for the production of models for castings made of metal or glass ceramics, in particular for the production of models for dental restorations, such as inlays, onlays, veneers, crowns, bridges or frameworks as well as removable (partial) dentures.

[0080] The invention further relates to a method for the production of dental restorations in which one (A) forms a model of the tooth or teeth to be restored using a modeling material according to the invention, (B) the model is then embedded in an investment material, (C) after the investment material has set, the embedded model is heated in an oven until the modeling material is completely removed from the mold, (D) an alloy or glass-ceramic material is poured or pressed into the mold thus produced.

[0081] The production of the model in step (A) is preferably carried out using a stereolithographic process. For this purpose, a virtual image of the dental situation is created on the computer by direct or indirect digitization of the tooth(s) to be restored, then a model of the dental restoration is designed on the computer based on this image and then produced by additive stereolithographic manufacturing.

[0082] The model can then be embedded in an investment material in step (B) using conventional methods. The materials according to the invention are suitable for use with conventional dental investment materials. A distinction is made between gypsum-containing and gypsum-free investment materials. Gypsum-containing investment materials contain gypsum and quartz as their main components in a ratio of 1:2 to 1:4. Gypsum serves as a binder. A preferred quartz modification is cristobalite. Gypsum-free investment materials containing phosphates as a binder are preferred. Phosphate-bonded investment materials contain high-temperature-resistant SiO2 modifications and a binder. A mixture of magnesium oxide and ammonium phosphate (NH4H2PO4) is preferably used as the binder. The materials set after mixing with water.

[0083] The removal of the model from the mold in step (C) is achieved by heating, for example in an oven, to a temperature preferably between 600°C and 1000°C. Heating can be performed in one or more stages. It is possible, but not absolutely necessary, to raise the temperature in a controlled manner to the desired final temperature. During heating, component (c) partially or completely exudes, flows out of the mold, and / or is absorbed by the embedding material. The mold is then heated further, causing the remaining model material to thermally decompose.

[0084] In step (D), a metal alloy or a suitable glass-ceramic material is cast into the negative mold of the original model thus produced. Preferably, metal alloys or glass-ceramic materials suitable for dental purposes are used.

[0085] The invention will be explained in more detail below with reference to figures and exemplary embodiments. Fig. Figure 1 shows the thermal expansion curve of the material according to the invention from Example 2, measured on cylinders with a diameter of 6 mm and a height of 6 mm. The measurement was carried out using a Q400 type measuring device from TA Instruments with a Macro-Expansion Tool. Fig. Figure 2 shows the thermal expansion curve of the material according to the invention from Example 4. Fig. Figure 3 shows the thermal expansion curve of the material according to the invention from Example 5. Fig. Figure 4 shows the thermal expansion curve of the material according to the invention from Example 6. The Fig. 5 and Fig. Figure 6 shows the expansion curves of commercially available materials according to the state of the art. The Fig. 7 and Fig.Figure 8 shows the thermal expansion curves of comparison materials that do not contain an inert component (c). The Fig. 9, Fig. 10 to Fig. Figure 11 shows dental bridge frameworks made of glass ceramic, which are produced using the materials according to the invention from Examples 4 ( Fig. 9), 5 ( Fig. 10) and 8 ( Fig. 11) were manufactured directly after the bedding was removed. The bridge scaffolds show no signs of compression. The Fig. 12, Fig. 13 to Fig. Figure 14 shows dental bridge frameworks made of glass ceramics, which were produced using comparison materials without component (c) ( Fig. 12, Material V1; Fig. 13, Material V2; Fig. 14, Material V3). The bridge scaffolds show clearly visible compression marks. The Fig. 15 and Fig.Figure 16 shows dental bridge frameworks made of glass ceramics, manufactured using commercially available materials. The bridge frameworks exhibit clearly visible press marks. Examples of implementation (Examples 1 to 9) Modeling materials

[0086] The components listed in Table 1 were homogeneously mixed together in the specified quantities. The components were weighed out, stirred for 1 hour at approximately 50°C, and then stirred at room temperature for approximately 16 hours (overnight). For compositions containing pigments and fillers, the pigment or filler was stirred into UDMA, the mixture was then homogenized and dispersed three times using a three-roller block with a gap of 10 µm, and subsequently stirred into the remaining, already dissolved organic matrix (at least 1 hour at room temperature). Finally, any additional additives, such as thickeners, were added to the paste and stirred again for at least 1 hour. Table 1: Modeling materials for stereolithography component Composition [wt.%] 1 2 3 4 5 6 7 8 9 Monomer (a) UDMA 1) 42 44 49 48,95 49 36,15 34 49 32 TEGDMA 2) 27 25 10,04 20 20 20,88 17 20 27 Bis-GMA 3) - - - - - - - - 10 Initiator (b) Irgacure 819 4) 0,95 - - 0,95 - - - - TPO 5) - 0,95 0,95 - 0,95 0,92 0,95 0,95 0,95 Inert component (c) PPG 2000 6) 30 30 40 30 30 30 - 20 30 PPG 1500 7) - - - - - - 20 - - PPG 4000 8) - - - - - - 8 - - PPG 400 9) - - - - - - - 10 - dye Sudan IV 10) 0,05 - 0,01 0,05 0,05 0,05 0,05 0,05 0,05 Sudan Black B 11) - 0,05 - - - - - - - White pigment (TiO2) 12) - - - 0,05 - - - - - Other components wax particles 13) - - - - - 10 - - - Thickener 14) - - - - - 2 - - - PMMA-Particles 15) - - - - - - 20 - - 1) Urethandimethacrylate (CAS-Nr. 72869-86-4) 2) Triethylenglycoldimethacrylat (CAS-Nr. 109-16-0) 3) Addition product of methacrylic acid and bisphenol-A diglycidyl ether 4) Phenylbis(2,4,6-trimethylbenzoyl)phosphinoxid (CAS-Nr. 162881-26-7) 5) Diphenyl(2,4,6-trimethylbenzoyl)phosphinoxid (CAS-Nr. 75980-60-8) 6) Poly(propylene glycol) (CAS No. 25322-69-4), MW = 2000 g / mol 7) Poly(propylene glycol) (CAS No. 25322-69-4), MW = 1500 g / mol 8) Poly(propylene glycol) (CAS No. 25322-69-4), MW = 4000 g / mol 9) Poly(propylene glycol) (CAS No. 25322-69-4), MW = 400g / mol 10) CAS No. 85-83-6 11) CAS No. 4197-25-5 12) Titanium dioxide white pigment, particle size D50 <500 nm 13) MC6015, micronisiertes Carnaubawachs, d = 1-10 µm 14) Solution of a high molecular weight, urea-modified, medium-polar polyamide (Byk 430) 15) highly cross-linked PMMA, Chemisnow MX80H3wT (Soken Chemical & Engineering Co., Ltd., Japan), D50 = 800 nm Example 10: Modeling materials - comparison examples

[0087] Analogous to examples 1 to 9, the comparison materials listed in Table 2 were produced. Table 2: Comparison materials for stereolithography component Composition [wt. %] V1* V2* V3* Monomer (a) UDMA 1) - 74 40 TEGDMA 2) - 25 25 SR348C 16) 59 - - SR480 17) 40 - - Initiator (b) TPO 5) 0,95 0,9 0,95 Inert component (c) - - - dye Sudan IV 10) 0,05 0,1 0,05 Other components wax particles 13) - - 34 * Comparison material 1-15) See Table 1 16) Bisphenol-A dimethacrylate with 3 ethoxy groups (Sartomer) 17) Bisphenol-A dimethacrylate; on average 10-fold ethoxylated Example 11: Measurement of thermal expansion

[0088] To determine the thermal expansion of the materials, cylinders with a diameter of 6 mm and a height of 6 mm were stereolithographically produced from the materials described in Tables 1 and 2 using a printer. The cylinders were hardened layer by layer and then post-exposure in a post-curing unit at a wavelength of 400 nm and an intensity of 10 mW / cm². 2The cylinders were post-exposed for 5 minutes. They were then placed in the sample chamber of a thermomechanical analyzer (TA Instruments Q400 type with macro-expansion tool) and heated to 800°C at a rate of 5 K / min. The linear thermal expansion of the cylinders during heating and thermal decomposition was measured in an air atmosphere over a temperature range of 30°C to 800°C. The contact force of the measuring probe was 0.1 N.

[0089] In the Fig. 1, Fig. 2, Fig. 3 to Fig.Figure 4 shows the expansion curves for the materials from Examples 2, 4, 5, and 6. In all cases, the thermal expansion remained well below 0.7% across the entire measurement range. The tests demonstrate that the thermal expansion of the materials is largely compensated by the exudation of component (c). The maximum linear thermal expansion was reached in all cases at a temperature below 90°C. Afterward, the length of the cylinders remained below the maximum value. Above 300°C, the materials thermally decomposed and burned away completely (ignition residue in all cases < 0.1 wt.%). The decomposition manifests itself in a sharp drop in linear thermal expansion.

[0090] Example 6 shows that the wax particles used as filler do not hinder the exudation of component (c) and have practically no effect on the expansion.

[0091] The expansion curves of the other examples are similar. In example 8, the maximum thermal expansion of < 1.5% is reached at 125°C.

[0092] For comparison, the expansion curves of conventional, commercially available stereolithography materials for the lost-wax technique were determined. Fig. Figure 5 shows the expansion curve of the material Bego VarseoWax CAD-Cast. The material expands by more than 4%, and the temperature of maximum expansion is only reached shortly before thermal decomposition, i.e., at more than 300°C.

[0093] In Fig. Figure 6 shows the expansion curve of another commercially available stereolithography resin for the lost-wax technique (3D Systems Visijet FTX-Cast). The material expands by more than 2%, and the temperature of maximum thermal expansion is above 200°C.

[0094] The Fig. 7 and Fig.Figure 8 shows the expansion curves of the comparison materials V1 and V3. Material V1 expanded by more than 6% ( Fig. 7), the material V3 by more than 8% ( Fig. 8) The temperature of maximum expansion was reached in both cases only shortly before thermal decomposition, i.e. at over 300°C and over 200°C respectively.

[0095] The measurements show that the maximum thermal expansion of the comparison materials is in all cases greater than that of the materials according to the invention. The thermal expansion can be effectively reduced by adding component (c). Furthermore, the maximum linear thermal expansion of the comparison materials occurs at significantly higher temperatures, which are determined by the decomposition temperature of the materials. Example 12: Model making

[0096] Models of a three-part bridge were produced using a 3D printer and the materials described in Examples 1 to 9, as well as commercially available materials. The same data set was used to produce the models in all cases.

[0097] The models were waxed up on a muffle base using the appropriate muffle gauge and provided with press channels. The models were then embedded in a commercially available phosphate-based investment material (200 g PressVest Speed; Ivoclar Vivadent AG). Fine embedding of the cavities was achieved with a small brush. The embedded muffle was left to set for 35 minutes without vibration. Afterward, the muffles were placed directly into the preheating oven, which had been preheated to 850°C, and left there for 1.5 hours at 850°C to completely remove the models. The muffles were then removed from the preheating oven, loaded with a ceramic blank (IPS e.max Press blank, Ivoclar Vivadent AG), placed in the hot press oven (Programat EP 5010, Ivoclar Vivadent), and the selected press program was started.

[0098] After the pressing process was complete, the muffles were removed from the furnace and placed on a cooling rack in a draft-free location. Once cooled to room temperature, the muffles were separated using a cutting disc, and the pressed objects were divested. The initial divesting was performed with abrasive blasting media at 4 bar pressure, and the final divesting with abrasive blasting media at 2 bar pressure. The pressing results were evaluated immediately after the final divesting.

[0099] The Fig. 9, Fig. 10 to Fig. Figure 11 shows exemplary bridge scaffolds manufactured using the materials according to the invention from Examples 4, 5, and 8. The images were taken immediately after the bedding process. No compression slabs are visible. The bridges manufactured with the other materials according to the invention were similar; in no case were compression slabs present.

[0100] In contrast, the bridges manufactured using the comparison materials showed clearly visible press marks, which were due to cracks in the casting mold that arose during the expansion of the modeling materials.

[0101] The Fig. 12, Fig. 13 to Fig. Figure 14 shows the bridge scaffolds obtained using the comparative materials V1 to V3. Fig. Figure 15 shows a CAD-Cast using the commercially available material Bego Varseo Wax and Fig. 16. A bridge fabricated using the 3D Systems Visijet FTX-Cast product. In all cases, press marks are present, necessitating more or less extensive post-processing of the restorations. In some cases, the restorations were unusable.

[0102] Even the bridge obtained using the 3D Systems Visijet FTX-Cast product exhibited compression marks, although this material has a relatively low maximum thermal expansion of approximately 2%. In contrast, the bridge obtained with the material according to the invention from Example 8 ( Fig. 11; max. expansion < 1.5%) without defects. The maximum thermal expansion is reached at 125°C in the case of the material according to the invention, and only at over 200°C in the case of the comparison material.

[0103] The comparison material V3 contained wax particles but no component (c). The wax particles melted during the burnout process, but the wax could only flow out of the surface of the component and remained trapped in the center. The model expanded considerably during the burnout process, resulting in poor pressing results.

Claims

[1] Radically polymerizable composition that (a) at least one radically polymerizable monomer, (b) at least one initiator for radical polymerization and (c) contains at least one inert component, characterized by , that the inert component (c) is soluble in the polymer formed by polymerization of the monomer(s) (a), wherein the solubility of component (c) decreases with increasing temperature, such that phase separation takes place above a certain temperature, and wherein the composition contains as inert component (c) at least one polypropylene glycol (PPG), PEG-PPG copolymer, propoxylated glycerol, ethylenediaminetetrakispropoxylate or a mixture thereof. [2] Composition according to claim 1, comprising as component (a) at least one (meth)acrylate and / or (meth)acrylamide, preferably one or more mono- or multifunctional (meth)acrylates or a mixture thereof. [3] Composition according to claim 1 or 2, comprising a photoinitiator as initiator (b). [4] Composition according to claim 3, comprising as photoinitiator benzophenone, benzoin or a derivative thereof, an α-diketone or a derivative thereof, 9,10-phenanthrenequinone, 1-phenylpropane-1,2-dione, diacetyl, 4,4'-dichlorobenzil, camphorquinone (CQ), 2,2-dimethoxy-2-phenylacetophenone, an α-diketone in combination with an amine as a reducing agent, a Norrish type I photoinitiator, a monoacyl or bisacylphosphine oxide, a monoacyltrialkyl or diacyldialkylgermanium compound, benzoyltrimethylgermanium, dibenzoyldiethylgermanium, bis(4-methoxybenzoyl)diethylgermanium (MBDEGe), a mixture of bis(4-methoxybenzoyl)diethylgermanium in combination with camphorquinone and 4-Dimethylaminobenzoic acid ethyl ester, camphorquinone (CAS No. 10373-78-1) in combination with ethyl 4-(dimethylamino)benzoate (EMBO, CAS No. 10287-53-3), 2,4,6-trimethylbenzoyldipenylphosphine oxide (TPO, CAS No. 75980-60-8), Ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L, CAS No.84434-11-7), Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure 819, CAS 162881-26-7), Bis(2,6-difluoro-3-(1-hydropyrrol-1-yl)phenyl)titanocene (Irgacure 784, CAS No. 125051-32-3), 2-Benzyl-2-(dimethyl-amino)-4'-morpholinobutyrophenone (Irgacure 369, CAS No. 119313-12-1), 1-Butanone-2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholinyl)phenyl (Irgacure 379, CAS No. 119344-86-4) and / or Contains bis(4-methoxybenzoyl)di-ethylgermanium (MBDEGe; K69). [5] Composition according to any one of claims 1 to 4, comprising as component (c) PPG having a molecular weight of 1000 to 4000 g / mol, or Co-PEG-PPG having a molecular weight of 1000 to 10000 g / mol. [6] Composition according to claim 5, comprising as component (c) PPG having a molecular weight of 1500 to 3000 g / mol, Co-PEG-PPG having a molecular weight of 1500 to 5000 g / mol and in particular polypropylene glycol having a molecular weight of approximately 2000 g / mol. [7] Composition according to any one of claims 1 to 6, which additionally contains at least one colouring agent and / or one inhibitor. [8] Composition according to any one of claims 1 to 7, which - 20 to 90 wt.%, preferably 42.5 to 82.5 wt.%, particularly preferably 50 to 79.3 wt.% component (a), - 0.1 to 5 wt.%, preferably 0.3 to 2.5 wt.%, particularly preferably 0.5 to 1.5 wt.% (photo-)initiator (b) and - 9.9 to 79.9 wt.%, preferably 15 to 55 wt.%, particularly preferably 20 to 48.5 wt.% inert component (c), in each case based on the total mass of the composition. [9] Composition according to claim 8, which - 54.7 to 77.7 wt.%, preferably 64 to 74 wt.% component (a), preferably UDMA, TEGDMA, a mixture of UDMA and TEGDMA or a mixture of UDMA, TEGDMA and Bis-GMA, - 0.5 to 1.5 wt.%, preferably 0.6 to 1.2 wt.% (photo-)initiator (b) and - 23.8 to 44.8 wt.%, preferably 24.8 to 35.4 wt.% inert component (c), preferably PPG with a molecular weight of 1000 to 4000 g / mol, particularly preferably 1500 to 3000 g / mol, Co-PEG-PPG with a molecular weight of 1000 to 10000 g / mol, particularly preferably 1500 to 5000 g / mol, most preferably 2000 to 4000 g / mol and in particular polypropylene glycol with a molecular weight of approximately 2000 g / mol, in each case based on the total mass of the composition. [10] Composition according to claim 8 or 9, further comprising - 0.0001 to 1 wt.%, preferably 0.0001 to 0.5 wt.%, particularly preferably 0.0001 to 0.2 wt.% colorant; and / or - 0.0001 to 2 wt.%, preferably 0.0001 to 1 wt.%, particularly preferably 0.0001 to 0.5 wt.% UV absorber; and / or - 0 to 40 wt.%, preferably 0 to 30 wt.%, particularly preferably 1 to 20 wt.% organic filler; and / or - 0 to 5 wt.%, preferably 0 to 3 wt.%, particularly preferably 0 to 2 wt.% further additive(s), in each case based on the total mass of the composition. [11] Composition according to any one of claims 1 to 10, which has a maximum linear thermal expansion of less than 1.5%, preferably less than 1% and particularly preferably less than 0.7%. [12] Composition according to claim 11, wherein the maximum thermal expansion is achieved at a temperature below 150°C, preferably below 120°C, particularly preferably below 100°C and most preferably below 90°C. [13] Method for the production of dental restorations in which one (A) forms a model of the tooth or teeth to be restored with a composition according to any one of claims 1 to 12, (B) the model is then embedded in an investment material, (c) after the investment material has set, the embedded model is heated in an oven so that the modeling material is completely removed from the mold, (d) an alloy or a ceramic or glass-ceramic material is poured or pressed into the mold thus produced. [14] Method according to claim 13, wherein the model is produced in step (A) by a stereolithographic process. [15] Use of a material according to any one of claims 1 to 12 for the production of a model of a dental restoration. [16] Use according to claim 15, wherein the dental restoration is an inlay, onlay, veneer, crown, bridge, framework or removable (partial) prosthesis.

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