Patent Publication Number: US-9839585-B2

Title: Free radically curable dental compositions

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent Application No. 102014116389.3, filed Nov. 11, 2014, which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE DISCLOSURE 
     The present invention relates to novel free-radically curable dental compositions, comprising chain-like and/or cyclic and/or cage-type polysiloxanes substituted by free-radically polymerizable groups and having at least 3 silicon atoms and/or mixed forms thereof, disiloxanes substituted by free-radically polymerizable groups, optionally one, two, three or more free-radically curable dental monomers having no silicon atom, fillers, initiators and/or catalysts for free-radical polymerization, and also further customary additives, to the cured dental products formed from the dental compositions of the invention, and to the respective use thereof as dental material, especially as flowable filling composites (called “flow materials”), core buildup materials and luting cements. The invention further relates to a process for producing the dental compositions and to a method for producing a respective dental product. Additionally claimed are inventive kits containing the novel free-radically curable dental compositions. 
     Further aspects of the present invention and preferred configurations thereof will become apparent from the description which follows, the working examples and the claims. 
     Polysiloxane compounds having at least 3 silicon atoms for the purposes of the present text have at least one chain or a plurality of chains having alternating and mutually connected silicon atoms and oxygen atoms, wherein the chains are also linked to form rings of different size, or to form even more extensive structures such as cages, and wherein organic groups (organic side chains) are bonded to the silicon atoms. These organic groups may be of chemically very different composition and hence lead to a multitude of polysiloxane compounds having different properties. Frequently, these organic groups have one or more organically polymerizable groups (i.e. reactive groups) which can react with, for example, one or more organically polymerizable groups in another polysiloxane compound and hence form crosslinked polymerized polysiloxane compounds. Chain, ring and cage structures may also occur in the form of mixed structures. They are likewise part of the dental compositions of the invention. 
     Polysiloxane compounds have long been known and are obtainable, for example, by hydrolysis and condensation of silanes having hydrolyzable groups (see, for example, DE 27 58 414 A1) or by hydrosilylation of allyl or vinyl compounds with SiH-containing compounds. Polysiloxane compounds can be processed further to give a multitude of products, for example overlayers, coatings, membranes or bulk materials. This further processing is frequently based on a crosslinking reaction of organically polymerizable groups in the polysiloxane compounds (e.g. (meth)acrylate groups) and the resulting formation of crosslinked polysiloxane compounds. 
     “(Meth)acryl . . . ” is understood in the context of the present text to mean both “acryl . . . ” and “methacryl . . . ”. 
     A specific group of polysiloxane compounds contains, in the organic groups (side chains), besides an organically polymerizable group, additional free polar functional groups, for example hydroxyl or carboxyl groups. 
     For instance, DE 44 16 857 C1 relates to hydrolyzable and polymerizable silanes, to processes for preparation thereof and to the use thereof for production of silica (hetero)polycondensates and (hetero)polymers. Hydrolyzable, organically modified silanes find wide use in the production of scratch-resistant coatings for a wide variety of different substrates, for the production of fillers, of adhesives and sealing compounds or of shaped bodies. 
     DE 44 16 857 C1 discloses the use of silica (hetero)-polycondensates (polysiloxane compounds) in curable dental materials. The polysiloxane compounds described here comprise free polar functional groups (e.g. carboxyl or hydroxyl groups) capable of complexing suitable metal ions/transition metal ions (e.g. ions of titanium, zirconium or tin). In curable dental compositions, this can have a positive effect on x-ray opacity, on contact toxicity and on the refractive index of a corresponding curable or cured dental material. 
     DE 198 60 364 C2 relates to polymerizable dental compositions based on siloxane compounds that are capable of curing, and to the use and production thereof. This publication describes the preparation of cyclic polysiloxanes and the use thereof as a basis for polymerizable dental compositions. In spite of high density of groups capable of polymerization, they are said to have a low viscosity which enables high filler loading, which leads to compositions having low polymerization shrinkage. Here too, free polar functions are present as well as the polymerizable units in the organic side chains of the polysiloxanes described. 
     The free polar functional groups, for example in the aforementioned polysiloxane compounds, however, regularly lead to unwanted properties too. For instance, it has been found that the hydrophilicity of the polysiloxane compounds caused by the (free) polar functional groups leads to increased water absorption in the presence of moisture, which reduces the wet strength of the curable dental material in a disadvantageous manner. Probably due to the formation of internal hydrogen bonds, there is an increase in viscosity. This then has an adverse effect on handling in the production of the curable dental compositions. 
     There is a considerable need on the part of dental practitioners and the dental industry to adapt polysiloxane compounds further to the demands on a modern (curable or cured) dental material and to minimize the aforementioned disadvantages. Polysiloxane compounds adapted in such a way should have improved physical properties for dental purposes (i.e. lead to dentally improved physical properties of the corresponding curable/cured dental materials), for example lower polymerization shrinkage on polymerization/crosslinking of the polysiloxane compounds (i.e. on curing), increased strength and/or restricted water absorption with simultaneously comfortable consistency of the curable dental material. 
     The first successes in the improvement of the polysiloxanes were achieved through addition or substitution of different substrates onto the free polar functionalities of the above-described specific polysiloxanes. 
     EP 1 874 847 B1 relates to a process for preparing silanes having two, three or even more structural units linked together by a urethane-, acid amide- and/or carboxylic ester-containing bridge, each of which contains at least one organically polymerizable radical and at least one silyl radical. These silanes should especially be suitable for modification of the properties of silicic acid (hetero)polycondensates and silyl-containing organic polymers. The process disclosed should also be suitable for bridging of already precondensed silicic acid (hetero)polycondensates. 
     The silicic acid (hetero)polycondensates (polysiloxane compounds) disclosed in EP 1 874 847 B1 have a free hydroxyl group (i.e. a free polar functional group). These free hydroxyl groups can react with a dicarboxylic acid derivative or diisocyanate such that hydroxyl groups form a link (bridge) with a dicarboxylic acid derivative or diisocyanate. Such linked polysiloxane compounds have a much higher molecular weight without any significant reduction in the double bond density (as a result of the organically polymerizable (meth)acrylate groups). Double bond density is understood here to mean the quotient of the number of polymerizable double bonds in a compound and the molecular weight of this compound. The higher molecular weight has a positive effect on biocompatibility and polymerization shrinkage on crosslinking of the linked polysiloxane compounds. At the same time, the hydrophobicity of the polysiloxane compounds was increased. However, it has been found that the higher molecular weight has an adverse effect on the viscosity of the linked polysiloxane compounds (and hence on processibility in manufacturing the curable dental material). The viscosity rises markedly with the degree of crosslinking, i.e. with the molecular weight, such that there is no longer satisfactorily tolerable processibility in manufacturing a corresponding curable dental material comprising such linked polysiloxane compounds, even at quite a low degree of linkage. 
     EP 1 685 182 B1 relates to silanes and silicic acid polycondensates and partial condensates formed therefrom, in which an organic radical bonded to a silicon is present, which is branched and bears an independently organically polymerizable group at each of the two branches, or bears such a group at one of the two branches and has a radical having a further silicon atom at the other. 
     The polysiloxane compounds disclosed in EP 1 685 182 B1 also comprise free polar functional groups in the form of hydroxyl groups. By reaction of carboxylic acid or isocyanate derivatives which themselves likewise comprise polymerizable double bonds (e.g. (meth)acrylate groups), it is thus possible to link organically polymerizable groups onto free polar functional groups. These reaction products regularly have elevated strength with simultaneously increased hydrophobicity and improved biocompatibility due to the elevated molecular weight. 
     However, in these cases too, it has been shown that the introduction of additional polymerizable double bonds leads to increased polymerization shrinkage on crosslinking of the polysiloxane compounds, since the double bond density is markedly increased, but the increase in the molecular weight is only comparatively small. 
     WO 2013/041723 A1 discloses hydrolyzable and polymerizable silanes (including silicic acid polycondensates, i.e. siloxanes) having adjustable spatial distribution of the functional groups, and the use thereof. The teaching disclosed in WO 2013/041723 A1 relates to a method for chain extension of radicals bonded to silicon via carbon in silanes or siloxanes. 
     WO 2013/053693 A1 discloses silicic acid polycondensates (siloxanes) having cyclic olefin-containing structures and methods for preparation thereof, and the use thereof. WO 2013/053693 A1 discloses that polymer materials having moduli of elasticity adjustable within wide limits combined with high elastic strain (i.e. without brittleness) and hence high fracture toughness can be produced from silicic acid (hetero)polycondensates having cyclic olefin-containing structures. 
     The as yet unpublished DE 10 2014 210 432 describes polysiloxane compounds which have the aforementioned disadvantages from the prior art in a curable or cured dental composition at least only in attenuated form, if at all. The conceptual approach to these systems is based on the idea of converting the free functional group in the silane such that no additionally polymerizable double bonds are introduced into the system. Instead, hydrocarbyl radicals of high molecular weight having at least 11 carbon atoms are incorporated into the system. Surprising findings in the case of these curable dental compositions were
         a good viscosity of the polysiloxane compounds (the viscosity should be 50 Pa*s or less at a temperature of 25° C.) and an associated excellent processibility in the production of a curable dental material containing the polysiloxane compounds,   good hydrophobicity,   good strength, especially good flexural strength,   very low polymerization shrinkage on crosslinking of the polysiloxane compounds, i.e. on curing of the curable dental material,   good biocompatibility,   a refractive index almost identical to the refractive index of standard dental glasses.       

     The measures taken in DE 10 2014 210 432 thus solved several problems at once:
         Elimination of polar functional groups prevented the formation of intermolecular interactions. It was thus possible to keep the viscosity of the system at a comparatively low level in spite of a remarkable increase in molecular weight.   Incorporation of hydrocarbyl radicals of relatively high molecular weight resulted in widening of intramolecular spacing in the polysiloxane structure, and so it was possible to increase the accessibility of the free-radically polymerizable groups during the curing and hence to optimize the conversion rate. How else could one explain the fact that in these systems, with a comparatively reduced double bond density, the strength of the materials, for example the flexural strength of the cured dental compositions, remains at a very good level and in many cases is actually increased compared to the polysiloxanes without further conversion.   The increase in molecular weight with the same functionality, i.e. in the case of an effective lowering of the double bond density, made it possible to adjust especially what is perhaps the clinically most important technical parameter for a curable dental composition, namely the value of the volume shrinkage during the curing, to an extremely low value. In clinical practice, therapeutic success is also dependent primarily on whether the dental material, for example, seals a cavity prepared by the dentist with high marginal integrity. As a result of shrinkage of the material in the course of polymerization, marginal gaps can form, through which bacteria penetrate into the tooth and then cause the treatment to fail.   Incorporation of hydrocarbyl residues of relatively high molecular weight also made the polysiloxane structure comparatively hydrophobic, such that the unwanted absorption of water now adopts extremely low values.       

     The free-radically curable compositions described in DE 10 2014 210 432 are especially suitable for use in a therapeutic method for temporary or permanent filling of a dental cavity. The systems are additionally suitable for use in a therapeutic method as base material, as adhesive (bonding), as a flowable composite material (flow material), as a fissure sealant, as a crown and bridge material, as an inlay/onlay and/or as core buildup material. 
     SUMMARY OF THE DISCLOSURE 
     In in-house studies, it has now been found that further tremendous improvements in free-radically curable dental compositions containing polysiloxanes, specifically both the novel polysiloxanes from DE 10 2014 210 432 and the above-described systems from the prior art, are possible when free-radically polymerizable disiloxanes are added thereto. These improvements are manifested particularly when the free-radically curable dental compositions have a “moderate” filler loading as envisaged, for example, for applications as flowable composite materials (flow materials), as core buildup materials or as luting cements, or have a “low” filler loading, as appropriate, for example, for “adhesives”, for fissure sealants or for dental lacquers. 
     The term “moderate” filler loading corresponds to a percentage of filler of about 50%-85% by weight, based on the overall composition, wherein the filler comprises all the different fractions of nano- and microscale filler. 
     The term “low” filler loading corresponds to a percentage of filler of about 0%-50% by weight, based on the overall composition, wherein the filler here too comprises all the different fractions of nano- and microscale filler. 
     The abovementioned filler ranges are stated here as guide values and should be regarded as such, since there are also very specific free-radically curable dental compositions which use, for example, greater amounts of nanoscale fillers, such that they are used with a filler content of 70% by weight, based on the overall composition, as fissure sealants. These sealing materials could also be used as flowable composite materials (flow materials). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph showing the moduli of elasticity of Examples 1-4. 
         FIG. 2  shows the curves for the viscosity as a function of shear rate for the inventive flowable material 5-A and for the two comparative materials 5-B and 5-F. 
         FIG. 3  shows the curves for the viscosity as a function of shear rate for the inventive flowable material 5-A and for the three comparative materials 5-B, 5-D, and 5-E. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The improvements achieved are directed primarily to the consistency of the free-radically curable dental compositions of the invention. 
     The consistency of the free-radically curable dental compositions is of exceptional importance in the case of application of the dental material to an extremely narrow application tip, for example by means of a two-chamber mixing cartridge, a compule or a dental syringe, since the (hydrophobic) free-radically curable dental composition must have a good adaptation to the (hydrophilic) tooth substance, in order to ensure successful tooth treatment. The above-described important properties of the polymer, low shrinkage, low water absorption or good mechanical strength, will not be realized in tooth treatment unless the dental composition can be applied optimally to the tooth. 
     On the one hand, the dental material thus must have exceptional flowability, both on application through a narrow application cannula or a static mixer and on adaptation to the tooth substance. Low-resistance flow characteristics through the application cannula or the static mixer are required to keep the push-out forces within acceptable limits. Excessively high push-out forces prevent, inter alia, precise application and thus put successful treatment at risk. Optimal adaptation of the dental material to the tooth substance prevents the formation of marginal gaps, and hence prevents the formation of secondary caries and hence makes a crucial contribution to the success of the treatment. 
     On the other hand, the dental material is also to have a certain stability. While still in the syringe, compule or cartridge, a sufficiently high stability prevents separation of the material and hence increases its storage stability. In addition, the dental material, as soon as it has been applied to the tooth substance or into the cavity and has adapted in an optimal manner, is again to have a sufficiently high stability in order not to “run” from the tooth or out of the cavity. 
     This profile of requirements is achieved by intrinsically opposing properties, for example through the use of rheology-modifying substances such as aerosils. Typically, about one to three percent aerosil is used in order to achieve the desired shear gradient. When the polysiloxanes are used, these amounts of aerosil, however, are insufficient to be able to establish a sufficient shear gradient. In order to achieve a sufficient shear gradient, amounts of aerosil of in some cases ten percent or more are necessary here. However, these large amounts of aerosil then cause a distinct drop in the total filler content and hence in the good properties as well, for example the high flexural strength and low shrinkage. Due to the inventive combination of the polysiloxanes with disiloxanes, a monomer system in which the customary amounts of aerosil of one to three percent are already sufficient to bring about a sufficient shear gradient, has surprisingly been found. The effect found appears to be based on the interaction of polysiloxane and disiloxane and not on mere dilution of the polysiloxane. The mere dilution of the polysiloxane or the drop in the filler content leads to increased flowability over the entire range. This means that the material either has inadequate flow characteristics combined with sufficient stability, or that the material has inadequate stability combined with sufficient flow characteristics. In the extreme case, the material even has neither adequate stability nor adequate flowability. 
     The inventive combinations of polysiloxanes with disiloxanes are thus of particularly good suitability for production of flowable curable dental materials which are applied through an application cannula or a static mixer, such as flowable composites, core buildup materials or luting composites. As well as good flow properties in the cannula or mixer and optimal adaptation to the tooth substance, these materials have sufficiently high stability, and the good physical properties introduced by the polysiloxanes can be fully effective. 
     Furthermore, the combination of polysiloxanes with disiloxanes surprisingly also increases the modulus of elasticity of the cured dental material. The cured material can thus offer greater resistance to deformation and thus better withstand the constant chewing stresses. 
     The use of disiloxanes in free-radically curable dental compositions, having a chemical structure based on the conventional crosslinking “dental monomers” such as bis-GMA (2,2-bis[p-(2′-hydroxy-3′-methacryloyloxy-propoxy)phenyl]propane), UDMA (1,6-bis(methacryloyloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane), TEGDMA (triethylene glycol dimethacrylate), HEDMA (hexanediol dimethacrylate), etc., is known from the prior art. 
     In a publication entitled “Synthesis and properties of a polyfluorinated prepolymer multifunctional urethane acrylate” (J. M. Antonucci, J. W. Stansbury, S. Venz, “Polymeric Materials Science and Engineering”, 59, 388-396 (1988)), in which what are called “low surface energy resins” are examined, bis(methacryloyloxypropyl)tetramethyldisiloxane (BIS-MPTMS) is used together with triethylene glycol dimethacrylate (TEGDMA) and hexamethylene 1,6-dimethacrylate (HEDMA) as organic resin matrix in a dental composite composition in the form of a powder/liquid system. On page 390, in the paragraph “Formulation of composites”, it is stated that BIS-MPTMS is an excellent agent for reducing viscosity and has a voluminous flexible structure. It is said to be miscible with many dental resins over a wide concentration range. 
     In an abstract entitled “Evaluation of siloxane containing dental composites” (J. S. Kuo, J. M. Antonucci, W. Wu, “Journal of Dental Research Abstracts”, 6A, and Abstract No. 30 (1985)), BIS-MPTMS is used together with bis-GMA and UDMA as organic resin matrix. Here too, it is stated that BIS-MPTMS is miscible with dental base monomers over a wide range (10%-50% by weight). The conclusion of this study reads: “Mechanical properties of the siloxane-containing composites were almost comparable to the controls, but, significantly, had reduced WS (water sorption) and enhanced OER (oral environmental resistance).” 
     In a more recent publication entitled “Synthesis of none bisphenol A structure dimethacrylate monomer and characterization for dental composite applications” (X. Liang, F. Liu, J. He, “Dental Materials”, 30, 917-925 (2014)), the reaction product (SiMA) of the ring-opening addition reaction between 1,3-bis[2-(3,4-epoxy-cyclohex-1-yl)ethyl]tetramethyldisiloxane and methacrylic acid as a bis-GMA alternative was examined together with TEGDMA as organic matrix in dental composites. The authors conclude that the “study of SiMA based resin and composite material showed that SiMA had potential to be used in clinic, but mechanical properties of SiMA based resin and composite needed to be improved . . . ” (page 923, point 5, “conclusion”). 
     None of the prior art documents regarding free-radically curable dental compositions which relate to polysiloxanes or disiloxanes as alternative monomer units to the conventional dental monomers have—aside from the question of the mechanical properties of the cured dental composition, the viscosity during the preparation of the siloxane and of the corresponding dental composite, the shrinkage characteristics during the polymerization, the water absorption of the polymer, the biocompatibility or the refractive indices of the individual constituents of the curable dental material—concentrated on the fundamental problem of the push-out characteristics and the adaptation to hard tooth substance in the curable dental composition. 
     According to the invention, the stated object is achieved by a free-radically curable dental compositions comprising
         a.) chain-like and/or cyclic and/or cage-type polysiloxanes substituted by free-radically polymerizable groups and having at least 3 silicon atoms and/or mixed forms thereof,   b.) disiloxanes substituted by free-radically polymerizable groups and having the following structure:
 
R 1   a R 2   (3-a) Si—O—SiR 2   (3-b) R 1   b  with
           R 2 : alkyl, alkenyl, aryl, alkylaryl, arylalkyl, wherein different R 2  may be the same or different,   R 1 : YZ,   Z: free-radically polymerizable group selected from the structural elements —O—(C═O)—CH═CH 2 , —O—(C═O)—C(CH 3 )═CH 2 , —(C═O)—CH═CH 2 , —(C═O)—C(CH 3 )═CH 2 , —CH═CH 2 , —(CH 3 )═CH 2 , —NH—(C═O)—CH═CH 2  and —NH—(C═O)—C(CH 3 )═CH 2 ,   wherein different Z may be the same or different,   a: 1 or 2,   b: 1 or 2,   Y: a connecting element which links the silicon atom to the free-radically polymerizable group and consists of an alkylene group,   wherein the alkylene group is an unsubstituted, linear, straight-chain or branched hydrocarbyl chain or   wherein the alkylene group is an unsubstituted hydrocarbyl group interrupted by a urethane group, urea group, ester group, thiourethane group or amide group or   wherein the alkylene group is a hydrocarbyl group substituted by a hydroxyl group and/or this hydroxyl group has been esterified or etherified or wherein the alkylene group is a hydrocarbyl group interrupted by an oxygen atom and/or nitrogen atom and/or sulfur atom and/or ester groups and/or thioester groups and substituted by a hydroxyl group and/or this hydroxyl group has been esterified or etherified and   wherein different Y may be the same or different and   wherein Y contains 20 or fewer carbon atoms and   wherein YZ is chosen such that Z always has a maximum number of atoms,   
           c.) optionally one, two, three or more free-radically curable monomers having no silicon atom,   d.) 85 percent by weight or less of fillers based on the total weight of the free-radically curable dental composition,   e.) initiators and/or catalysts for the free-radical polymerization and   f.) further customary additives.       

     A preferred composition of the invention is a dental composition free-radically curable in a chemical and/or light-induced manner. 
     A very particularly preferred composition of the invention is a free-radically curable dental composition, wherein the polysiloxanes (a.) are obtained by hydrolysis or partial hydrolysis and subsequent condensation or co-condensation of one, two, three or more compounds R 1   a R 2   b SiX c  with
         X: halogen or alkoxy,   R 2 : alkyl, alkenyl, aryl, alkylaryl, arylalkyl, wherein different R 2  may be the same or different,   R 1 : YZ,   Z: free-radically polymerizable group selected from the structural elements —O—(C═O)—CH═CH 2 , —O—(C═O)—C(CH 3 )═CH 2 , —(C═O)—CH═CH 2 , —(C═O)—C(CH 3 )═CH 2 , —CH═CH 2 , —C(CH 3 )═CH 2 , —NH—(C═O)—CH═CH 2  and —NH—(C═O)—C(CH 3 )═CH 2 ,   wherein different Z may be the same or different,   a: 1 or 2,   b: 0 or 1,   c: 2 or 3,
 
 a+b+c= 4,
   Y: a connecting element which links the silicon atom to the free-radically polymerizable group and consists of an alkylene group,   wherein the alkylene group is an unsubstituted, linear, straight-chain or branched hydrocarbyl chain or   wherein the alkylene group is an unsubstituted hydrocarbyl group interrupted by a urethane group, urea group, ester group, thiourethane group or amide group or   wherein the alkylene group is a hydrocarbyl group substituted by a hydroxyl group or this hydroxyl group has been esterified or etherified or   wherein the alkylene group is a hydrocarbyl group interrupted by an oxygen atom and/or nitrogen atom and/or sulfur atom and/or ester groups and/or thioester groups and substituted by a hydroxyl group or this hydroxyl group has been esterified or etherified and   wherein different Y may be the same or different and   wherein Y contains 20 or fewer carbon atoms and   where YZ is chosen such that Z always has a maximum number of atoms.       

     Constituent a—chain-like and/or cyclic and/or cage-type polysiloxanes substituted by free-radically polymerizable groups and having at least 3 silicon atoms and/or mixed forms thereof. 
     Chain-like and/or cyclic and/or cage-type polysiloxanes substituted by free-radically polymerizable groups and having at least 3 silicon atoms and/or mixed forms thereof can be synthesized via the sol-gel process by controlled hydrolysis and condensation of appropriately functionalized derivatives of alkoxides of silicon or of halosilanes. These production methods have been described many times in the literature. In general, such a synthesis proceeds from a standard silane, for example isocyanatopropyldiethoxysilane, which is reacted in a first step, likewise in a standard reaction, for example in an isocyanate-alcohol polyaddition, for example with glycerol 1,3-dimethacrylate, to give the corresponding urethane. The compound obtained here consists on the one hand of the silicon atom which is furnished with hydrolyzable and condensable groups and is linked via a spacer consisting of an alkyl group (here a propyl group) and a urethane group as structural connecting element to a further functional structural segment, in this case to two free-radically polymerizable methacrylate groups. Such a simple synthesis method can be modified in various ways, since the possible reactions between appropriately functionalized silanes and suitable reactants seem unlimited. There is a correspondingly large number of synthesis suggestions in the literature. The starting compound thus comprises an inorganically condensable structural element, a variable connecting element and a free-radically crosslinkable organic base structure. In a catalytically controlled hydrolysis and condensation, the polysiloxane is obtained as an inorganic condensate substituted by free-radically polymerizable groups. Whether the polycondensate is in the form of chains, rings or three-dimensional cage forms, or in the corresponding mixed forms, depends on the exact conditions of the condensation. These include not only the reaction conditions (pH, amount of solvent and water, type and amount of catalyst, reaction temperature, manner of processing, etc.) but also the structural forms of the starting silane, important factors being the number of alkoxy groups, the number of free-radically polymerizable groups, the chemical nature of the connecting element and the chain length of the spacer. Details of this can be found both in the scientific literature and in the patent literature. 
     The polysiloxanes, being a link between inorganic and organic chemistry, have exceptional material properties. Since they are additionally physiologically inert, i.e. have no significant toxicity, they are especially important for applications in medicine. The reason why polysiloxanes are virtually nontoxic is the low biological attackability of the silicon-carbon bonds and the restricted ability of the highly hydrophobic polymer chains to diffuse through cell membranes, which is why they should be particularly suitable for implantation (in teeth). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Constituent b—disiloxanes substituted by free-radically polymerizable groups and having the following structure: 
     R 1   a R 2   (3-a)  Si—O—SiR 2   (3-b) R 1   b  with 
     R 2 : alkyl, alkenyl, aryl, alkylaryl, arylalkyl, wherein different R 2  may be the same or different, 
     R 1 : YZ, 
     Z: free-radically polymerizable group selected from the structural elements —O—(C═O)—CH═CH 2 , —O—(C═O)—C(CH 3 )═CH 2 , —(C═O)—CH═CH 2 , —(C═O)—C(CH 3 )═CH 2 , —CH═CH 2 , —C(CH 3 )═CH 2 , —NH—(C═O)—CH═CH 2  and —NH—(C═O)—C(CH 3 )═CH 2 , 
     wherein different Z may be the same or different, 
     a: 1 or 2, 
     b: 1 or 2, 
     Y: a connecting element which links the silicon atom to the free-radically polymerizable group and consists of an alkylene group, 
     wherein the alkylene group is an unsubstituted, linear, straight-chain or branched hydrocarbyl chain or 
     wherein the alkylene group is an unsubstituted hydrocarbyl group interrupted by a urethane group, urea group, ester group, thiourethane group or amide group or 
     wherein the alkylene group is a hydrocarbyl group substituted by a hydroxyl group and/or this hydroxyl group has been esterified or etherified or 
     wherein the alkylene group is a hydrocarbyl group interrupted by an oxygen atom and/or nitrogen atom and/or sulfur atom and/or ester groups and/or thioester groups and substituted by a hydroxyl group and/or this hydroxyl group has been esterified or etherified and
 
wherein different Y may be the same or different and
 
wherein Y contains 20 or fewer carbon atoms and wherein YZ is chosen such that Z always has a maximum number of atoms.
 
     Disiloxanes are characterized by exceptional chain mobility, since the compounds have free rotation about the silicon-oxygen bonds, one reason for which is the difference in size between the oxygen atom and the silicon atom. This leads to compounds having a remarkable low viscosity because of the flexibility of the structure thereof. In addition, the shielding of the oxygen atoms by the hydrocarbyl groups on the silicon leads to marked hydrophobicity and to greatly restricted interaction of the chains with one another, such that spreading on surfaces, for example on hard tooth substance, should be favored and should result in extremely good adaptation of the polysiloxanes, for example to prepared cavity walls. 
     As well as some commercially available inventive disiloxanes (e.g. 1,3-bis(3-methacryloyloxypropyl)-tetramethyldisiloxane, 1,3-bis(3-methacryloyloxy-2-hydroxypropoxypropyl)tetramethyldisiloxane, 1,3-bis-[(acryloyloxymethyl)phenethyl]tetramethyldisiloxane), there are numerous synthesis strategies for preparation of the inventive disiloxanes. 
     
       
         
         
             
             
         
       
     
     1,3-Bis(3-methacryloyloxy-2-hydroxypropoxypropyl)disiloxane 6 can be prepared by reaction of the corresponding 1,3-bis(3-glycidoxypropyl)disiloxane 5 with methacrylic acid. 
     
       
         
         
             
             
         
       
     
     The disiloxane 8 can be synthesized from 1,3-bis(3-glycidoxypropyl)disiloxane 5 by reaction with ethanol and then methacrylic anhydride. 
     
       
         
         
             
             
         
       
     
     It is possible to prepare the corresponding disiloxanes 9, 10, 11, 12 and 13 from 1,3-bis(3-methacryloyloxy-2-hydroxypropoxypropyl)disiloxane 6 by further reaction with different acid chlorides or anhydrides. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     It is also possible to synthesize the corresponding disiloxane 14 from 1,3-bis(3-glycidoxypropyl)disiloxane 5 by reaction with mono(2-methacryloyloxyethyl) succinate. 
     
       
         
         
             
             
         
       
     
     The corresponding urea derivative 16 is obtained from commercially available 1,3-bis(3-aminopropyl)disiloxane 15 by reaction with 2-isocyanatoethyl methacrylate. 
     
       
         
         
             
             
         
       
     
     It is possible to prepare the corresponding disiloxanes 17 and 18 from 1,3-bis(3-aminopropyl)disiloxane 15 by reaction with, respectively, 2 and 4 equivalents of glycidyl methacrylate. 
                         
1,3-Bis(3-methacrylamidopropyl)disiloxane 19 is likewise obtainable from 1,3-bis(3-aminopropyl)-disiloxane 15 by reaction with methacryloyl chloride.
 
     
       
         
         
             
             
         
       
     
     The corresponding urethane derivative 21 is obtained from commercially available 1,3-bis(3-hydroxypropyl)-disiloxane 20 by reaction with 2-isocyanatoethyl methacrylate. 
     
       
         
         
             
             
         
       
     
     The corresponding 1,3-bis(3-methacryloyloxy-2-hydroxy-propoxypropyl)disiloxane 6 is also obtainable in turn from 1,3-bis(3-hydroxypropyl)disiloxane 20 by reaction with glycidyl methacrylate. 
     
       
         
         
             
             
         
       
     
     The corresponding 1,3-bis(3-methacryloyloxypropyl)-disiloxane 22 is likewise obtained from 1,3-bis(3-hydroxypropyl)disiloxane 20 by reaction with methacryloyl chloride. 
     
       
         
         
             
             
         
       
     
     The corresponding thiourethane derivative 24 is obtained from commercially available 1,3-bis(3-mercaptopropyl)disiloxane 23 by reaction with 2-isocyanatoethyl methacrylate. 
     
       
         
         
             
             
         
       
     
     The corresponding disiloxane 25 is obtainable from 1,3-bis(3-mercaptopropyl)disiloxane 23 by reaction with glycidyl methacrylate. 
     
       
         
         
             
             
         
       
     
     The corresponding amide derivative 27 is obtained from commercially available 1,3-bis(3-carboxypropyl)-disiloxane 26 by reaction with 2-isocyanatoethyl methacrylate. 
     
       
         
         
             
             
         
       
     
     The corresponding disiloxane 28 is also obtainable from 1,3-bis(3-carboxypropyl)disiloxane 26 by reaction with glycidyl methacrylate. 
     
       
         
         
             
             
         
       
     
     Of course, a multitude of (meth)acryloyl-substituted disiloxanes proceeding from the dichlorodisiloxanes are also obtainable via typical silane chemistry. Mention is made here by way of example of the reaction with lithium aluminum hydride to give the dihydrodisiloxane and subsequent platinum-catalyzed reaction with allyl methacrylate to give the corresponding 1,3-bis(3-methacryloyloxypropyl)disiloxane 22. 
     
       
         
         
             
             
         
       
     
     Of course, the inventive disiloxanes are not just obtainable by functionalization of disiloxanes, but can also be prepared proceeding from monoalkoxysilanes by hydrolysis and condensation. For example, the unsymmetric disiloxanes 32 are also obtainable by reaction of different monoalkoxysilanes 31a/b. For the functionalization of the monoalkoxysilanes, conceivable functionalization reactions include those already described for the disiloxanes. 
     Constituent c—optionally one, two, three or more free-radically curable monomers having no silicon atom 
     The free-radically curable monomers having no Si atom are monomers which are substances having preferably one, two or more ethylenic groups, for example but not restricted to the (meth)acrylate monomers customarily used in dental chemistry. 
     The (meth)acrylate monomers may be monofunctional or else polyfunctional. 
     Monofunctional (meth)acrylate monomers used with preference are the esters of (meth)acrylic acid with alkyl groups of 1 to 12 carbon atoms and esters of (meth)acrylic acid containing aromatic groups having 6 to 12 carbon atoms, wherein the alkyl groups and aromatic groups that form the esters may contain substituents such as hydroxyl groups and ether bonds. 
     The patent literature mentions a multitude of further compounds (for example in DE 39 41 629 A1, which is incorporated in the present application by way of reference), all of which are esters of acrylic or methacrylic acid and are suitable for use in a curable mixture. 
     The free-radically polymerizable monomers may also be hydroxyl compounds having at least one ethylenic double bond. In this case, it is possible with preference to use the hydroxyl compounds of (meth)acrylates customarily used in dental chemistry. 
     Examples of polyfunctional (meth)acrylate monomers also include di(meth)acrylates of alkylene glycol having 2 to 20 carbon atoms, di(meth)acrylates of oligomers of alkylene glycol, polyalkylene glycol di(meth)acrylate, di(meth)acrylates of bisphenol A or of the diglycidyl ether of bisphenol A. 
     Particular preference is further given to free-radically curable compounds based on a central polyalicyclic structural element, for example 3(4),8(9)-bis((meth)acryloyloxymethyl)tricyclo[5.2.1.0 2,6 ]decane, alkoxylated 3(4),8(9)-bis((meth)acryloyl-oxymethyl)tricyclo[5.2.1.0 2,6 ]decane, 2,3-bis((meth)-acryloyloxymethyl)bicyclo[2.2.1]heptane, alkoxylated 2,3-bis((meth)acryloyloxymethyl)bicyclo[2.2.1]heptane, 1,3,5-tri(meth)acryloyloxytricyclo[3.3.1.1 3,7 ]decane, alkoxylated tri(meth)acryloyloxytricyclo[3.3.1.1 3,7 ]-decane, and (meth)acrylates of tricyclo[5.2.1.0 2,6 ]-decane-3(4),8(9)-dimethanol, alkoxylated tricyclo-[5.2.1.0 2,6 ]decane-3(4),8(9)-dimethanol, bicyclo[2.2.1]-heptane-2,3-dimethanol, alkoxylated bicyclo[2.2.1]-heptane-2,3-dimethanol, 1,3,5-adamantanetriol, alkoxylated 1,3,5-adamantanetriol, with urethane, urea, amide, allophanate, acylurea or biuret groups arranged between the polyalicyclic structural element and the (meth)acrylates. 
     Details of the preparation of these substituted (meth)acrylates can be found in patent applications EP 11 183 333, EP 11 183 328, EP 11 183 345, EP 11 183 338, EP 11 183 342 and EP 11 188 086, and in the publications cited in these documents. These citations are likewise incorporated into the present application by way of reference. 
     Preference is likewise given to urethane (meth)acrylates, reaction products formed from 2 mol of a (meth)acrylate with a hydroxyl group and one mole of a diisocyanate. 
     In a preferred curable mixture of the invention, constituent (c) contains one or more (meth)acrylate monomers chosen from the group consisting of 3(4),8(9)-bis((meth)acryloyloxymethyl)tricyclo[5.2.1.0 2,6 ]decane, alkoxylated 3(4),8(9)-bis((meth)acryloyloxy-methyl)tricyclo[5.2.1.0 2,6 ]decane, 2,3-bis((meth)acryl-oyloxymethyl)bicyclo[2.2.1]heptane, alkoxylated 2,3-bis((meth)acryloyloxymethyl)bicyclo[2.2.1]heptane, 1,3,5-tri(meth)acryloyloxytricyclo[3.3.1.1 3,7 ]decane, alkoxylated tri(meth)acryloyloxytricyclo[3.3.1.1 3,7 ]-decane, (meth)acrylates of tricyclo[5.2.1.0 2,6 ]decane-3(4),8(9)-dimethanol, alkoxylated tricyclo[5.2.1.0 2,6 ]-decane-3(4),8(9)-dimethanol, bicyclo[2.2.1]heptane-2,3-dimethanol, alkoxylated bicyclo[2.2.1]heptane-2,3-dimethanol, 1,3,5-adamantanetriol, alkoxylated 1,3,5-adamantanetriol, with urethane, urea, amide, allophanate, acylurea or biuret groups arranged between the polyalicyclic structural element and the (meth)acrylates, ethylene glycol di(meth)acrylate, hexane-1,6-diol di(meth)acrylate (HEDMA), triethylene glycol di(meth)acrylate (TEGDMA), dodecane-1,12-diol di(meth)acrylate, bisphenol A di(meth)acrylate, alkoxylated bisphenol A di(meth)acrylate, bisphenol B di(meth)acrylate, alkoxylated bisphenol B di(meth)acrylate, bisphenol C di(meth)acrylate, alkoxylated bisphenol C di(meth)acrylate, bisphenol F di(meth)acrylate, alkoxylated bisphenol F di(meth)acrylate, polyethylene glycol di(meth)acrylate, 7,7,9-trimethyl-4,13-dioxo-5,12-diazahexadecane1,16-dioxydi(meth)acrylate (UDMA), butanediol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 2-hydroxypropyl 1,3-di(meth)acrylate, 3-hydroxypropyl 1,2-di(meth)acrylate, pentaerythritol di(meth)acrylate, di(meth)acrylates of dihydroxymethyltricyclo[5.2.1.0 2,6 ]decane, 2-hydroxy-ethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 1,2-dihydroxypropyl (meth)acrylate, 1,3-dihydroxypropyl (meth)acrylate, 2,2-bis[4-(3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl]propane (bis-GMA), trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dimethylolpropane tetra(meth)acrylate, pentaerythritol hexa(meth)acrylate, butylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, nonanediol di(meth)acrylate, decanediol di(meth)acrylate, glycerol mono(meth)acrylate, glycerol di(meth)acrylate, trimethylolpropane mono(meth)acrylate, trimethylol-propane di(meth)acrylate, sorbitol mono-, di-, tri-, tetra- or penta(meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, tetrahydro-furfuryl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, allyl (meth)acrylate, glycidyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxy polyethylene glycol (meth)acrylate, isobornyl (meth)acrylate, 2-(N,N-dimethylamino)ethyl (meth)acrylate, N-methylol(meth)acrylamide, diacetone-(meth)acrylamide, 2,2-bis[4-(meth)acryloyloxyphenyl]-propane, 2,2-bis[4-(meth)acryloyloxyethoxyphenyl]-propane, 2,2-bis[4-(meth)acryloyloxydiethoxyphenyl]-propane, 2,2-bis[4-(meth)acryloyloxytriethoxyphenyl]-propane, 2,2-bis[4-(meth)acryloyloxytetraethoxyphenyl]-propane, 2,2-bis[4-(meth)acryloyloxypentaethoxyphenyl]-propane, 2,2-bis[4-(meth)acryloyloxydipropoxyphenyl]-propane, 2-[4-(meth)acryloyloxyethoxyphenyl]-2-[4-(meth)acryloyloxy-diethoxyphenyl]propane, 2-[4-(meth)-acryloyloxydiethoxyphenyl]-2-[4-(meth)acryloyloxytriethoxyp henyl]propane, 2-[4-(meth)acryloyloxydipropoxyphenyl]-2-[4-(meth)acryloyloxytriethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxyisopropoxyphenyl]propane, neopentyl glycol hydroxypivalate di(meth)acrylate, aceto-acetatoxyethyl (meth)acrylate, polypropylene glycol di(meth)acrylate, glycerol alkoxylate dimethacrylate, neopentyl glycol (meth)acrylate, N,N-(1,2-dihydroxyethylene)bisacrylamide, 2,2-bis[4-(meth)acryloyloxypentaethoxyphenyl]propane, 2,2-bis[4-(meth)acryloyloxypolyethoxyphenyl]propane, diethylene glycol di(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)-acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)-propane-1,3-diol]tetra(meth)acrylate, the condensation product of 3-(4)(meth)acryloyloxymethyl-8(9)-hydroxymethyltricyclo[5.2.1.0 2,6 ]decane with dicarboxylic acids, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, methoxy diethylene glycol (meth)acrylate, dicyclopentenyl (meth)acrylate, phenyl (meth)acrylate, pentaerythritol mono(meth)acrylate, dipentaerythritol mono(meth)-acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate. 
     Constituent d—Fillers 
     A free-radically curable dental composition of the invention contains a proportion of filler particles of 85% by weight or less, preferably of 78% by weight or less, based on the total mass of the dental composition of the invention. 
     As constituent (d), it is possible to use organic and/or inorganic fillers. 
     Organic filler particles comprise or consist of, for example, one or more compounds selected from the group consisting of polyvinyl acetate and copolymers of polyvinyl acetate with one or more polymerizable compounds, polystyrene, polyethylene, polypropylene, waxes such as polyethylene wax, polybutylene, polybutadiene, copolymers of butadiene and styrene, polyacrylonitrile, resins such as rosin or hydrocarbon resins, poly(meth)acrylate esters, i.e. reaction products of poly(meth)acrylic acid with linear or branched aliphatic, aromatic or cycloaliphatic alcohols such as methanol, ethanol, propanol, isopropanol, the isomeric butanols and higher homologs of the alcohols mentioned having up to 22 carbon atoms, cyclohexanol, benzyl alcohol and the like, polydialkyl maleates such as dibutyl maleate and copolymers thereof, and polymers containing silyl groups, such as polyvinylsilanes or copolymers of vinylsilane with one or more of the monomers mentioned. The organic fillers can be used alone or as mixtures. 
     The inorganic fillers can likewise be used alone or as mixtures. To optimize the product properties, the inorganic fillers can be introduced into the formulations in different particle sizes. The fillers may have a unimodal or polymodal distribution, for example a bimodal distribution. 
     As inorganic fillers, it is possible to use compact glasses and different silicas in various sizes and states (monodisperse, polydisperse). 
     Suitable inorganic constituents are, for example, amorphous materials based on mixed oxides composed of SiO 2 , ZrO 2  and/or TiO 2 , and also fillers such as quartz glass ceramic or glass powders, barium silicate glasses, barium fluorosilicate glasses, strontium silicate glasses, strontium borosilicate, Li/Al silicate glasses, barium glasses, calcium silicates, sodium aluminosilicates, fluoroaluminosilicate glasses, oxides of aluminum or silicon, zeolites, apatite, zirconium silicates, sparingly soluble metal salts such as barium sulfate or calcium chloride, and x-ray-opaque fillers such as ytterbium fluoride. 
     For better incorporation into the polymer matrix, the fillers may be organically surface-modified. One example is the surface treatment of the fillers with a silane. A particularly suitable adhesion promoter is methacryloyloxypropyltrimethoxysilane. 
     To adjust the rheology, the free-radically curable dental compositions may contain different silicas, preferably fumed silicas. 
     Preferably, the curable compositions of the invention contain nanoscale solid particles. The nanoscale solid particles are particles having an average particle size of not more than 200 nm, preferably not more than 100 nm and especially not more than 70 nm. The nanoscale inorganic solid particles are preferably those of oxides, sulfides, selenides and tellurides of metals, semimetals and mixtures thereof. Particular preference is given to nanoscale particles of SiO 2 , TiO 2 , ZrO 2 , ZnO, SnO 2  and Al 2 O 2 , and mixtures thereof. The nanoscale solid particles are produced in a known manner, for example by flame pyrolysis, plasma methods, gas phase condensation, colloid techniques, precipitation methods, sol-gel methods, etc. 
     In a preferred configuration, the nanoscale particles are in nonagglomerated and/or nonaggregated form, for example dispersed in a medium, preferably in monodisperse form. 
     In order to enable good binding of the nanoparticles into the polymer matrix of a free-radically curable dental composition of the invention, the surfaces of the nanoparticles have likewise been organically surface-modified, meaning that their surfaces have organic structural elements. Examples include the surface treatment of the fillers with a silane. A particularly suitable adhesion promoter here too is methacryloyloxypropyltrimethoxysilane. 
     In a further preferred configuration, the nanoscale particles are thus nonagglomerated and/or nonaggregated, organically surface-modified nanoparticles having an average particle size of less than 200 nm, preferably less than 100 nm, more preferably less than 70 nm, which have in turn preferably been silanized. 
     Commercially available nanoscale, nonagglomerated and nonaggregated silica sols which can be used in accordance with the invention are traded, for example, under the “NALCO COLLOIDAL SILICAS” (Nalco Chemical Co.), “Ludox colloidal silica” (Grace) or “Highlink OG” (Clariant) names. 
     In a preferred configuration, the filler fraction of a free-radically curable dental composition of the invention comprises a mixture of a first filler (d1) in the form of nonagglomerated, nonaggregated organically surface-modified nanoparticles having an average particle size of less than 200 nm and a second filler (d2) in the form of microparticles having an average particle size in the range from 0.4 μm to 10 μm. The combination of (d1) nanoparticles and (d2) microparticles in a free-radically curable dental composition of the invention achieves complete and homogeneous filling of volume of the composite material. This reduces both the shrinkage of the free-radically curable composition in the course of curing of the polymer matrix and the sensitivity of the composition of the invention to abrasion. 
     The proportion of organically surface-modified nanoparticles in a preferred free-radically curable dental composition of the invention having an average particle size of less than 200 nm is greater than 1% by weight, preferably greater than 2% by weight and more preferably greater than 3% by weight. In in-house studies, it has been found that, in the case of a content of 1% by weight or less of nonagglomerated and/or nonaggregated organically surface-modified nanoparticles having an average particle size of less than 200 nm, the free-radically curable dental composition no longer has a sufficient abrasion resistance in each individual case. One reason for this is probably that, in the case of a content of 1% by weight or less of said nanoparticles, the regions between the microparticles having an average particle size of 0.4 μm to 10 μm are no longer filled adequately. On the other hand, it has been shown that, in the case of a content of more than 20% by weight of nonagglomerated and/or -aggregated, organically surface-modified nanoparticles having an average particle size of less than 200 nm, processibility of the composition is no longer adequate. Because of the high solids content, its viscosity then becomes too high. 
     The materials for the nanoparticles for use in accordance with the invention are preferably oxides or mixed oxides and are preferably selected from the group consisting of oxides and mixed oxides of the elements silicon, titanium, yttrium, strontium, barium, zirconium, hafnium, niobium, tantalum, tungsten, bismuth, molybdenum, tin, zinc, ytterbium, lanthanum, cerium, aluminum and mixtures thereof. The preferred oxidic nanoparticles are, as explained, nonagglomerated and/or nonaggregated, and have been organically surface-treated. 
     Within a free-radically curable dental composition of the invention, the microparticles bring about substantially homogeneous filling of volume, with the remaining cavities between the microparticles at least partly filled by the above-described nanoparticles (component (d1)). In connection with the present invention, microparticles are understood to mean particles having an average particle size of 400 nm to 10 μm. Preferably, the average particle size is less than 5 μm. It has been found that the completeness and homogeneity of the filling of volume of the free-radically curable dental composition which is already achievable with the microparticles increases with decreasing microparticle size. 
     The microparticles of component (d2) may have a monomodal or polymodal particle size distribution, for example a bimodal particle size distribution. Microparticles having a bimodal or multimodal particle size distribution are preferable in accordance with the invention, since more complete filling of volume is achievable therewith than in the case of general use of microparticles having monomodal particle size distribution. In the presence of a bi- or multimodal particle size distribution, the particles of the fractions having the larger particle size bring about coarse filling of volume, while the particles of the fraction having the smaller particle size, as far as possible, fill the regions between the particles of the fractions having the larger particle size. The cavities still remaining are filled by nanoparticles as described above. 
     Most preferably, therefore, in a free-radically curable dental composition of the invention, a component (d2) containing two or more fractions of microparticles, with different average particle sizes of the fractions, is used. 
     Preferably, component (d2) contains at least two microparticle fractions wherein the average particle sizes differ from one another by at least 0.5 μm, preferably by at least 0.7 μm. In some configurations, the difference between the average particle sizes of the microparticle fractions is at least 1.0 μm. 
     The microparticles of different fractions may consist of the same material or of different materials; it is also possible for there to be two or more fractions of microparticles having average particle sizes that are approximately the same or within a particular range, in which case the materials of the particles differ between the fractions. 
     More preferably, a free-radically curable dental composition of the invention comprises a component (d2) having one or more first microparticle fractions each having an average particle size in the range from 1 μm to 10 μm, preferably 1 μm to 5 μm, and one or more second microparticle fractions each having an average particle size in the range from &gt;0.4 μm to &lt;1 μm (i.e. larger than 0.4 μm but smaller than 1 μm), preferably 0.5 μm to 0.8 μm. 
     Preferably, the ratio of the total mass of the first microparticle fractions to the total mass of the second microparticle fractions is in the range from 1:1 to 12:1, preferably in the range from 1.5:1 to 8:1. 
     Preferably, the ratio of the average particle size of the or a first microparticle fraction to the average particle size of the or a second microparticle fraction of component (d2) is in the range from 1.5:1 to 10:1, preferably in the range from 2:1 to 5:1. 
     In a particularly preferred free-radically curable dental composition of the invention, component (d2) comprises one or more first microparticle fractions each having an average particle size in the range from 1 μm to 10 μm, preferably 1 μm to 5 μm, and one or more second microparticle fractions each having an average particle size in the range from &gt;0.4 μm to &lt;1 μm, preferably 0.5 μm to 0.8 μm; wherein the ratio of the total mass of the first microparticle fractions to the total mass of the second microparticle fractions is in the range from 1:1 to 12:1, preferably 1.5:1 to 8:1 and/or the ratio of the average particle size of the or a first microparticle fraction to the average particle size of the or a second microparticle fraction of component (d2) is in the range from 1.5:1 to 10:1, preferably 2:1 to 5:1. 
     In a particularly preferred free-radically curable dental composition of the invention, at least a portion of the microparticles of component (d2) is formed by organically surface-modified particles, preferably silanized particles, and/or at least a portion of the microparticles of component (d2) is formed by dental glass particles; preferably, at least a portion of the microparticles of component (d2) is formed by organically surface-modified dental glass particles, preferably silanized dental glass particles. 
     In these cases, component (d2) preferably features a bi- or multimodal particle size distribution, especially a bi- or multimodal particle size distribution having the preferred features described above. 
     As well as components (d1) and (d2), the free-radically curable dental composition may comprise further fillers as component (d3) in addition to the mixture of filler particles. 
     For example, it is possible to use reinforcing filler materials such as glass fibers, polyamide fibers or carbon fibers. A free-radically curable dental composition of the invention may also contain fine splinter or bead polymers, wherein the bead polymers may be homo- or copolymers of organically curable monomers. 
     In a particularly preferred embodiment, a free-radically curable dental composition of the invention contains an x-ray-opaque filler. Most preferably, the composition of the invention contains nanoscale YbF 3  and/or BaSO 4 . 
     Qualitative and quantitative characterization of the filler particles: 
     The steps described hereinafter in the qualitative and quantitative characterization of the filler particles (especially of nanoscale filler particles) are well known to those skilled in the art and are described comprehensively in the literature. 
     Resin/Filler Separation: 
     In a first step, 1 g of a free-radically curable dental composition of the invention (also called composite material hereinafter) is resuspended in 10 mL of acetone and the resultant suspension is then centrifuged with a centrifuge at 5000 rpm for 10 min. The supernatant (called resin phase hereinafter) is decanted off into a collection bottle and the residue is slurried in 5 mL of acetone. The mixture is centrifuged again at 5000 rpm for 10 min and decanted, and the residue is slurried again in 5 mL of acetone. The steps of centrifuge, decanting and slurrying are repeated twice more under identical conditions. The total amount of residues separated from the resin phases is dried, and the total amount of resin phases is freed of acetone on a rotary evaporator. 
     After conducting the first step, the dried total amount of residues regularly includes those filler particles having a particle size of about 400 nm or greater than 400 nm (called macroscopic filler particles hereinafter). The total amount of resin phases freed of acetone (called resin fraction hereinafter) regularly also includes, as well as polymerizable monomers, filler particles having a particle size of about 400 nm or especially less than 400 nm (called nanoscale particles hereinafter). This method therefore ensures that the dental composite material, by centrifugation, is separated completely into (i) a fraction of macroscopic filler particles, especially with regard to the dental glasses having a size in the order of magnitude of greater than 400 nm up to the high micrometer range, and (ii) a resin fraction including nanoscale particles. 
     The median particle size d 50  of the macroscopic filler particles for use in accordance with the invention in the filler component (d2) of a composition of the invention is determined by means of light scattering (laser diffraction), preferably with a Beckman Coulter LS 13320 particle size analyzer. 
     The nanoscale particles present in the resin fraction may, for example, be both nonaggregated and/or nonagglomerated particles, for example including x-ray-opaque particles, for example YbF 3  or BaSO 4 , having particle sizes within a range from about 3 nm to 200 nm, preferably from 5 nm to 200 nm, more preferably from 7 nm to 100 nm and most preferably from 7 nm to 70 nm, and non-x-ray-opaque silicas which take the form, for example, of fumed silicas in the form of aggregates and/or agglomerates having a particle size within a range from about 150 nm to about 300 nm, or else silicas which are synthesized by the sol-gel process (or else from waterglass) and which are likewise in nonaggregated and/or nonagglomerated form and have particle sizes within a range from about 3 nm to 200 nm, preferably from 5 nm to 200 nm, more preferably from 7 nm to 100 mm and most preferably from 7 nm to 70 nm. 
     The total proportion by mass of inorganic particles in the resin fraction is determined gravimetrically by difference weighing after asking of an appropriate resin fraction. 
     TEM in Combination with EELS: 
     In a second step, the filler particles in the resin fraction are subjected to a qualitative and quantitative characterization. For this purpose, TEM (transmission electron microscopy) is used in conjunction with EELS (electron energy loss spectroscopy). 
     By means of TEM, the particle sizes of the individual particles and the number thereof are determined; elemental determination of individual particles is effected by means of EELS. 
     To conduct the combined TEM/EELS characterization, in a first step, the concentration of the nanoscale particles in the resin fraction is first reduced by dilution with curable resin. This very substantially rules out observation of “overlapping” of nanoscale particles in the later images. Such “overlapping” would distort the particle characterization. In-house studies have shown that the optimal particle concentration (i.e. the proportion by volume of the filler particles) for such studies is 1% by volume, based on the total mass of the diluted sample. 
     In a second step, bar specimens are produced by curing the diluted resin fractions obtained by dilution with curable resin. These bar specimens are then used to produce several ultrathin sections of thickness 300 nm with an ultra-diamond knife (for example ULTRACUT UCT, LEICA, Wetzlar). The ultrathin sections are transferred to copper TEM grids for stabilization. This results in thin section preparations. These thin section preparations are then analyzed with acceleration voltage 120 kV in a TEM with bright field images. 
     A TEM analysis of the above-described thin section preparations allows distinction of nonaggregated and nonagglomerated nanoscale particles from aggregated and/or agglomerated particles (e.g. silicas, for example Aerosils) (for identification of the chemical composition see the details which follow). 
     If high-resolution images are to be examined, ultrathin sections having layer thicknesses of less than 100 nm can be produced and examined. 
     In a third step, the filler particles in the ultrathin sections or thin section preparations are chemically characterized by means of EELS point analyses, such that the chemical composition of individual particles becomes known (for determination of the surface modification of particles see the points below). 
     The volume- or weight-based proportions of particle fractions (including a plurality thereof if appropriate) are determined in a fourth step from a TEM image as follows: the image section from a TEM image viewed under a microscope is an area having edge lengths a and b which can be determined by means of the legend. Multiplying by the thickness c of the ultrathin section gives a total volume V total  for the area under consideration in the TEM. This total volume V total  is the sum total of the resin volume V resin  and the volume of all the particles V particles  within this volume (the volume of all the particles may include several groups of particles, for example sorted by various criteria, for example size). The following equation holds:
 
 V   total   =a*b*c=V   resin   +V   particles .
 
     The volume of individual particles (and hence the volume of all the particles in the volume under consideration) can be obtained by calculation via the sphere volume of the individual particles. For this purpose, in the TEM image, the diameter or radius of an appropriate particle is determined. The sphere volume calculated therefrom, multiplied by the density of the corresponding material of which the particle consists (material identifiable by means of EELS), gives the mass of the particle. The resin volume, obtainable from the total volume minus the particle volume, multiplied by the resin density, gives the resin mass. The resin density is obtained very substantially from the density of the resin used for dilution and, if appropriate, the density of the diluted resin fraction (the latter can possibly be neglected in the calculation of the resin density if the proportion of the diluted resin is negligible). The proportion of the particles (or a group of particles) in percent by weight is calculated from m p *100/(m particles +m resin ) where m p  is the mass of the particle fraction under consideration in the volume under consideration, m particles  is the mass of all the particles in the volume in question and m resin  is the mass of the resin in the volume under consideration. In the final calculation of the proportion by weight of the particle fraction under consideration, the dilution factor is taken into account appropriately. 
     Determination of Organic Surface Modifications: 
     Preliminary Assessment: 
     Many known x-ray-opaque filler materials (for example ytterbium fluoride or barium sulfate) have the disadvantage that they can be incorporated only with difficulty into the matrix (resin matrix) composed of polymerizable monomers (called the organic resin phase) because they do not enter into sufficient chemical bonds (binding options) with the hydrophobic groups of the medium. Vitreous fillers can be incorporated in an excellent manner into the resin matrix of dental composite materials, for example, with the aid of silanization via Si—OH groups. In the case of ytterbium fluoride and barium sulfate, no such groups are present on the surfaces; they are therefore not silanizable and lead to inadequate physical and chemical resistance in a cured dental material (see WO 2005/011621 A1, bottom of page 2). 
     The x-ray-opaque nanoscale particles used in a curable dental material of the invention therefore will not have any silanes on their surfaces. Instead, the linking is effected via nitrogen, oxygen, sulfur and/or phosphorus atoms (again see WO 2005/011621 A1 and our remarks further up in the text). 
     Removal of Polymerizable Monomers from Nanoscale Particles: 
     “Cross-Flow” Method: 
     The removal of polymerizable monomers from nanoscale particles is effected, for example, in a “cross-flow” method known to those skilled in the art by means of ultrafiltration membranes. 
     In this method, a resin fraction comprising nanoscale particles, polymerizable monomers and optionally a suitable diluent is pumped from a vessel by means of a pump into a circuit composed of particular membranes, and the polymerizable monomers pass through the pores of the membranes and are separated as filtrate, while the nanoscale particles remain within the circuit (and hence within the vessel). 
     An example of a suitable system for this separating step is the “Vivaflow 50” system from “Sartorius Stedim Biotech GmbH, Göttingen”. The pump drive (7554-95) and pump head come from the “Masterflex L/S” series from “Cole-Parmer Instrument Co.”, Illinois, USA. The operation of the pump is set to 2.5 bar during the filtration. Two separation membranes of the “50,000 MWCO (PES)” type are connected in series. The MWCO (molecular weight cutoff) defines the separation limit here, i.e. the size of the molecules which can still pass efficiently through the membrane. This value is reported in daltons. The fractions obtained are subsequently analyzed as described below. 
     Sedimentation Field-Flow Fractionation (SF3): 
     Even better than the “cross-flow” method is the conduction of a sedimentation field-flow fractionation (SF3). This can especially separate different particle fractions from one another and additionally from the resin fraction. It is a prerequisite here that the different particle fractions differ sufficiently from one another in terms of size and/or density. 
     Corresponding equipment containing a separation column necessary for the purpose is obtainable from Postnova Analytics GmbH, Landsberg. The module containing the separation column is identified as CF2000 Centrifugal FFF and is supplemented by the further modules PN7140 (Eluent Organizer), PN1130 (Isocratic Pump), PN5300 (Autosampler), PN3621 MALS (21-Multi-Angle Light Scattering Detector) and PN8050 (Fraction Collector). In this combination, the Centrifugal FFF system allows not just the analytical but also the preparative separation of particle fractions. The fractions obtained are subsequently analyzed as described below. 
     Characterization of the Surface Modification: 
     A sample which has been produced as above and then freed of solvents, containing nanoscale particles in the form of a powder, is subsequently examined by means of spectroscopic methods (for example by means of 1H NMR, 13C NMR, 15N NMR, 29Si NMR and 31P NMR, and also IR). 
     Signals which cannot be attributed to a silane, for example the gamma-methacryloyloxypropylsilyl radical, are attributed to organic surface modifications not based on silanes, for example surface modifications by means of organic compounds on surfaces of ytterbium fluoride or barium sulfate particles. 
     The proportions of organically surface-modified particles and/or non-organically surface-modified particles can also be determined regularly by evaluation of the intensities of corresponding vibration bands in the IR spectrum. For this purpose, reference vibration bands (reference curves) of organically surface-modified or non-organically surface-modified particles with the corresponding chemical compositions are employed. 
     Characterization by Means of Image Analysis and Raman Spectroscopy: 
     The person skilled in the art is aware of additional methods and coupled methods which allow qualitative and quantitative characterization of the filler particles. In this respect, reference is made, for example, to the article “Chemische Identität einzelner Partikel” [Chemical Identity of Individual Particles] by Deborah Huck-Jones and Renate Hessemann in “Nachrichten aus der Chemie”, Volume 62, September 2014, pages 886 and 887. The combination of image analysis and Raman spectroscopy disclosed therein is regularly also suitable for characterization of the filler particles in the context of the present invention. This is especially true of samples which are obtained by the resin/filler separation described above. An example of a suitable image analysis is again the TEM analysis described in the text above. 
     Constituent e—Initiators and/or Catalysts for the Free-Radical Polymerization 
     A free-radically curable dental composition of the invention is preferably light-curable and/or chemically curable. Preference is given to a free-radically curable dental composition of the invention, wherein constituent (e) comprises or consists of one or more light-curing initiators and/or one or more initiators for chemical curing. 
     Preferred free-radically curable dental compositions of the invention are light-curable (photocurable) and comprise light-curing initiators. Examples of a light-curing initiator include substances having only photosensitizing action and combinations of sensitizer and accelerator. 
     Examples of photosensitizers are alpha-diketones, benzoin alkyl ethers, thioxanthones, benzophenones, acylphosphine oxides, acylgermanium compounds, acetophenones, ketals, titanocenes, sensitizing dyes, etc. The sensitizers can be employed alone or in combination. Specific substance examples from different classes can be found, for example, in DE 10 2006 019 092 A1, or in DE 39 41 629 C2, which are incorporated into the present application by way of reference. 
     Examples of accelerators which are used together with the sensitizers are tertiary amines, secondary amines, barbiturate acids, tin compounds, aldehydes and sulfur compounds. Specific substance examples from different classes can be found, for example, in DE 10 2006 019 092 A1 or in DE 39 41 629 C2, which are incorporated into the present application by way of reference. 
     Further suitable initiators and initiator combinations are described in DE 601 16 142, which is incorporated into the present application by way of reference. 
     The photoinitiators usable in the context of the present invention are characterized in that they can bring about the curing of a free-radically curable dental composition of the invention through absorption of light in the wavelength range from 300 nm to 700 nm, preferably from 350 nm to 600 nm and more preferably from 380 nm to 500 nm, optionally in combination with one or more coinitiators. 
     The absorption maximum of camphorquinone (CQ) is about 470 nm and is therefore within the blue light range. Camphorquinone (CQ) is one of the PI 2  initiators and is regularly used together with a coinitiator. 
     Preferably, a composite material of the invention contains the combination of an alpha-diketone and an aromatic tertiary amine, preference being given to the combination of camphorquinone (CQ) and ethyl p-N,N-dimethylaminobenzoate (DABE). 
     Likewise preferable is the further combination of the “alpha-diketone/aromatic tertiary amine” system with a phosphine oxide, especially with phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and/or 2,4,6-trimethylbenzoyldiphenylphosphine oxide. With regard to the structures of suitable phosphine oxides for use in a free-radically curable dental composition of the invention, reference is made to publications DE 38 01 511 C2, DE 10 2006 050 153 A1, EP 0 184 095 B1, DE 42 31 579 C2, EP 0 366 977 B1, U.S. Pat. No. 7,081,485 B2, DE 32 36 026 A1, US 2007/0027229 A1, EP 0 262 629 B1, EP 0 073 413, U.S. Pat. No. 7,148,382 B2, U.S. Pat. No. 5,761,169, DE 197 08 294 A1, EP 0 057 474, EP 0 047 902 A, EP 0 007 508, DE 600 29 481 T2, EP 0 980 682 B1, EP 0 948 955 B1, EP 1 236 459 B1 and EP 0 173 567 A2, which are incorporated into the present application by way of reference. 
     The phosphine oxides specified in these publications are suitable especially alone or in combination with the “alpha-diketone/amine” system as photo-polymerization initiator system in a free-radically curable dental composition of the invention. 
     EP 1 905 415 describes polymerizable dental compositions comprising acylgermanium compounds as initiators. 
     Alternatively, it is also possible to use borate salts, as described, for example, in U.S. Pat. No. 4,772,530, U.S. Pat. No. 4,954,414, U.S. Pat. No. 4,874,450, U.S. Pat. No. 5,055,372 and U.S. Pat. No. 5,057,393, as photoinitiators, which are incorporated into the present application by way of reference. 
     Further suitable photoinitiators are described in J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring, Hanser Publishers, Munich, Vienna, N.Y. 1995, and in J. F. Rabek (ed.), Radiation Curing in Polymer Science and Technology, Vol. II, Elsevier Applied Science, London, N.Y. 1993, which are incorporated into the present application by way of reference. 
     The person skilled in the art is aware of various initiators for chemical curing. In this regard, reference is made by way of example to EP 1 720 506. Initiators for chemical curing are also described in the publications DE 10 2006 019 092 already mentioned above and in DE 39 41 629. 
     Preferred initiators for chemical curing are benzoyl peroxide, lauroyl peroxide, especially dibenzoyl peroxide, in combination with amines such as N,N-dimethyl-p-toluidine, N,N-dihydroxyethyl-p-toluidine, and structurally related amines. 
     The peroxides and the amines are divided between two different components of the dental material. When the amine-containing component (called the base paste) is mixed with the peroxide-containing component (called the initiator or catalyst paste), the reaction of amine and peroxide (redox reaction) initiates the free-radical reaction. 
     Dual-curing systems comprise a combination of photoinitiators and initiators for chemical curing. 
     For example, the base paste may additionally comprise a photoinitiator, such that the base paste can be used either solely as a light-curing dental composition or, together with the initiator paste, as a light- and self-curing dental composition. 
     As well as the oxidatively active organic peroxide compounds, the redox systems used may also be barbituric acids or barbituric acid derivatives and malonylsulfamides. 
     Among the barbituric acid systems, the “Bredereck systems” are of high importance. Examples of suitable “Bredereck systems” and references to the corresponding patent literature can be found in EP 1 839 640 and in DE 1 495 520, WO 02/092021 or in WO 02/092023, which form part of the present application by way of reference. 
     Rather than the barbituric acids, it is also possible to use salts thereof. Examples of these can be found in the following documents: EP 1 872 767, EP 2 070 506, EP 1 881 010, DE 10 2007 050 763, U.S. Pat. No. 6,288,138, DE 11 2006 001 049, U.S. Pat. No. 7,214,726 and EP 2 070 935. 
     Suitable malonylsulfamides are described in EP 0 059 451, which forms part of the present application by way of reference. Preferred compounds in this context are 2,6-dimethyl-4-isobutylmalonylsulfamide, 2,6-diisobutyl-4-propylmalonylsulfamide, 2,6-dibutyl-4-propylmalonylsulfamide, 2,6-dimethyl-4-ethylmalonylsulfamide and 2,6-dioctyl-4-isobutylmalonylsulfamide. 
     In addition, it is possible to use sulfur compounds in the +2 or +4 oxidation state, such as sodium benzenesulfinate or sodium para-toluenesulfinate. 
     To accelerate the curing, the polymerization can be performed in the presence of heavy metal compounds such as Ce, Fe, Cu, Mn, Co, Sn or Zn, particular preference being given to copper compounds. The heavy metal compounds are preferably used in the form of soluble organic compounds. Preferred copper compounds here are copper benzoate, copper acetate, copper ethylhexanoate, copper di(methacrylate), copper acetylacetonate and copper naphthenate. 
     Constituent f—Further Customary Additives 
     A free-radically curable dental composition of the invention comprises one or more further additive(s) in some cases. 
     These additives may have various functions. Customary additives for use in dental materials are known to those skilled in the art; he or she will select the suitable additive(s) according to the desired function. Typical additives and their functions are described by way of example hereinafter. 
     Free-radically light-curable dental compositions as preferred in accordance with the invention preferably contain one or more inhibitor(s), also called stabilizer(s). These are typically added in order to prevent spontaneous polymerization. They react with free radicals formed prematurely, which are scavenged, prevent premature polymerization and increase the storage stability of the light-curable dental composition. Standard inhibitors are phenol derivatives such as hydroquinone monomethyl ether (HQME) or 2,6-di-tert-butyl-4-methylphenol (BHT). Further inhibitors such as tert-butylhydroxyanisole (BHA), 2,2-diphenyl-1-picrylhydrazyl radicals, galvinoxyl radicals, triphenylmethyl radicals, 2,3,6,6-tetramethylpiperidinyl-1-oxyl radicals (TEMPO), and derivatives of TEMPO or phenothiazine and derivatives of this compound are described in EP 0 783 880 B1, which is incorporated into the present application by way of reference. Alternative inhibitors are specified in DE 101 19 831 A1 or in EP 1 563 821 A1, which are incorporated into the present application by way of reference. 
     A free-radically curable dental composition preferred in accordance with the invention thus comprises, as additive, one or more polymerization inhibitors for increasing the storage stability of the composition, preferably selected from the group consisting of hydroquinone monomethyl ether (HQME), phenols, preferably 2,6-di-tert-butyl-4-methylphenol (BHT) and tert-butylhydroxyanisole (BHA), 2,2-diphenyl-1-picrylhydrazyl radicals, galvinoxyl radicals, triphenylmethyl radicals, 2,3,6,6-tetramethylpiperidinyl-1-oxyl radical (TEMPO) and derivatives thereof, and phenothiazine and derivatives thereof. 
     A free-radically curable composition of the invention may comprise, as additive, one or more fluoride-releasing substances, preferably sodium fluoride and/or amine fluorides. 
     UV absorbers which are capable of absorbing UV radiation, for example, by their conjugated double bond systems and aromatic rings are in some cases part of a free-radically curable dental composition of the invention. Examples of UV absorbers are 2-hydroxy-4-methoxy-benzophenone, phenyl salicylate, 3-(2′-hydroxy-5′-methylphenyl)benzotriazole or diethyl 2,5-dihydroxy-terephthalate. 
     Since the teeth should be restored as naturally as possible, it is necessary to provide dental compositions of the invention in a wide variety of different shades. For this purpose, generally inorganic dyes and organic pigments are utilized in very small amounts, which are thus used as an additive in preferred configurations. 
     Further optional additives are aromas, dental medicaments, organic polymers and oligomers, preferably plasticizers, microbicides, preferably bactericides, interface-active substances, preferably surfactants, preservatives or molecular weight regulators. 
     A preferred inventive composition comprises the components in the following contents:
         a. 10%-35% by weight, preferably 15%-25% by weight,   b. 2%-25% by weight, preferably 5%-15% by weight,   c. 0%-20% by weight, preferably 0%-10% by weight,   d. 50%-85% by weight, preferably 60%-78% by weight,   e. 0.001%-5% by weight, preferably 0.1%-2% by weight and   f. 0.001%-20% by weight, preferably 0.001%-10% by weight,
 
wherein the respective percentages by weight are based on the total mass of the composition.
       

     In particularly preferred cases, a free-radically curable dental composition of the invention does not contain any constituent c. 
     In particularly preferred cases, a free-radically curable dental composition of the invention comprises 1,3-bis(3-methacryloyloxypropyl)tetramethyldisiloxane as constituent b. 
     In a very particularly preferred case, a free-radically curable dental composition of the invention does not contain any constituent c and contains 1,3-bis(3-methacryloyloxypropyl)tetramethyldisiloxane as constituent b. 
     The present invention also relates to the free-radically cured dental composition obtainable from the free-radically curable dental composition of the invention by means of free-radical polymerization of the polysiloxane compound(s) and the disiloxane compound(s) present in the composition, and optionally of further polymerizable constituents present in the dental material. The polymerization or crosslinking is effected by means of the organically polymerizable double bonds present in the (meth)acrylate groups. 
     The statements made above with regard to preferred embodiments of free-radically curable dental compositions of the invention apply correspondingly to the free-radically cured dental compositions of the invention. 
     The present invention likewise relates to a free-radically curable dental composition of the invention or to a dental composition free-radically cured in accordance with the invention for use in a therapeutic method as flowable composite material (flow material), as luting cement and/or as core buildup material. 
     In-house studies have shown that the free-radically curable dental compositions of the invention and the free-radically cured compositions of the invention lead to excellent results in the aforementioned specific applications. 
     The present invention also relates to a method for producing a free-radically curable dental composition, comprising the following steps:
         providing constituents a, b, c, d, e, f and   mixing the constituents.       

     The present invention additionally also relates to a method for producing a free-radically cured dental composition, comprising the following steps:
         providing constituents a, b, c, d, e, f,   mixing the constituents and   curing the mixture.       

     In methods of the invention for producing a free-radically curable dental composition polymerizable by means of radiative curing, preference is given to the production of a one-component system. In this case, the curable composition contains all the constituents required for light curing in a single component, and curing is initiated by irradiation with light of a defined wavelength. 
     Preferably, the one-component system is used as part of a kit of the invention. The present invention thus also relates to a kit comprising
         one, two or more than two light-curing one-component dental materials of the invention in a flow syringe and/or compule,   optionally one, two or more than two adhesives,   optionally one, two or more than two etching gels,   optionally one or more than one shade guide,   optionally one or more than one brush.       

     In methods of the invention for production of a free-radically curable dental composition curable (a) by means of light curing and by means of chemical curing (dual-curing) or (b) only by means of chemical curing, preference is given to the production of a multicomponent system. Curable dental compositions curable by means of chemical curing are generally formulated as two-component systems, such that the substances that trigger polymerization and the polymerizable compounds are present in separate components and curing is not effected until the separated components are mixed. Since dual-curing systems are always also chemically curing, these compositions are likewise formulated and produced in two-component form. 
     Preferably, the two-component system is used as part of a kit of the invention. The present invention thus also relates to a kit to form a core buildup material, comprising
         core buildup material of the invention in a 2-component syringe   static mixer (for mixing of the two components)   a plunger or dispenser (for application of the core buildup material through the static mixer)   optionally a compatible adhesive   optionally one or more root posts   optionally molding aids and/or templates   optionally further accessories (brush, drill, etc.).       

     The present invention therefore also relates to a kit to form a luting material, comprising
         luting material of the invention in a 2-component syringe   static mixer (for mixing of the two components)   a plunger or dispenser (for application of the luting material through the static mixer)   optionally a compatible adhesive   optionally further adhesion promoters (for example for ceramic or metal, etc.)   optionally try-in pastes   optionally further accessories (brush, etc.).       

     EXAMPLES 
     Substances Used 
     
         
         Polysiloxane I: Methacryl-POSS (MA0735, Hybrid Plastics Inc.) 
         Polysiloxane II: condensation product of 3-methacryloyloxypropyldimethoxymethylsilane 
         Polysiloxane III: condensation product of 3-methacryloyloxypropyltrimethoxysilane 
         Polysiloxane IV: condensation product of 3-[(2-hydroxy-3-methacryloyloxy)-propoxy]propyldimethoxymethylsilane 
         Disiloxane I: 1,3-bis(3-methacryloyloxy-propyl)tetramethyldisiloxane 
         Disiloxane II: 1,3-bis[3-[(2-hydroxy-3-meth-acryloyloxy)propoxy]propyl]tetramethyldisiloxane 
         Bis-GMA: 2,2-bis[4-(2-hydroxy-3-meth-acryloyloxypropoxy)phenyl]propane 
         TEGDMA: triethylene glycol dimethacrylate 
         MDP: 10-methacryloyloxydecyl phosphate 
         CQ: DL-camphorquinone 
         DABE: ethyl 4-dimethylaminobenzoate 
         BHT: 2,6-di(tert-butyl)hydroxytoluene 
         DEPT: N,N-bis(2-hydroxyethyl)-p-toluidine 
         NTPB: sodium tetraphenylborate 
         BPO: dibenzoyl peroxide 
       
    
     Synthesis of the Polysiloxanes 
     Synthesis of Polysiloxane II 
     100 g (0.42 mol) of 3-methacryloyloxypropyldimethoxymethylsilane are dissolved in 400 mL of ethyl acetate. 10 mL of 1N HCl solution are added dropwise and the mixture is stirred at 30° C. for 72 h. The mixture is extracted by shaking with 2N NaOH solution, and the organic phase is washed with water and dried over magnesium sulfate. After addition of BHT, the mixture is first concentrated by rotary evaporation at 40° C. and then solvent residues (e.g. water and alcohol residues) are drawn off under reduced pressure by means of an oil pump, in order to remove the alcohol and water residues. This results in a fluid resin having a viscosity of 3 Pa*s at 25° C. 
     n D   20 =1.466 
     Synthesis of Polysiloxane III 
     100 g (0.40 mol) of 3-methacryloyloxypropyltrimethoxy-methylsilane are dissolved in 400 mL of ethyl acetate. 15 mL of 1N HCl solution are added dropwise and the mixture is stirred at 30° C. for 72 h. The mixture is extracted by shaking with 2N NaOH solution, and the organic phase is washed with water and dried over magnesium sulfate. After addition of BHT, the mixture is first concentrated by rotary evaporation at 40° C. and then solvent residues (e.g. water and alcohol residues) are drawn off under reduced pressure by means of an oil pump, in order to remove the alcohol and water residues. This results in a fluid resin having a viscosity of 20 Pa*s at 25° C. 
     n D   20 =1.479 
     Synthesis of Polysiloxane IV 
     a) Synthesis of a monomeric silane unit (cf. EP 1 685 182 B1, ex. 3): 
     Added dropwise to an initial charge of 100 g (0.402 mol) of 3-glycidyloxypropyldiethoxymethylsilane under a dry atmosphere are an addition catalyst, BHT as stabilizer and then 38.05 g (0.442 mol) of methacrylic acid, and the mixture is stirred at about 80° C. (about 24 h). The conversion is monitored via the decrease in the carboxylic acid concentration by means of acid titration, and the epoxide conversion by means of Raman spectroscopy/epoxide titration. The band characteristic of the epoxide group is detected in the Raman spectrum at 1256 cm −1 . The epoxide and carboxylic acid conversions are 99% and 88% respectively (consequence of the carboxylic acid excess). 
     b) Hydrolysis or condensation of the monomeric silane unit to give a polysiloxane compound (cf. EP 1 685 182 B1, ex. 6): 
     After addition of ethyl acetate (1000 mL/mol of monomeric silane unit) and water for hydrolysis with HCl as catalyst to the monomeric silane unit synthesized, the mixture is stirred at 30° C. The progress of the hydrolysis is monitored by water titration. After stirring at 30° C. for several days, the workup is effected by repeatedly extractive shaking with aqueous NaOH, followed by extractive shaking with water and filtration through a hydrophobized filter. After addition of BHT, the mixture is first concentrated by rotary evaporation at 40° C. and then solvent residues (e.g. water and alcohol residues) are drawn off under reduced pressure by means of an oil pump, in order to remove the alcohol and water residues. This results in a fluid resin having a viscosity of 4.5 Pa*s at 25° C. 
     n D   20 =1.483 
     Synthesis of the Disiloxanes 
     Synthesis of Disiloxane II 
     Added dropwise to an initial charge of 100 g (0.28 mol) of 1,3-bis(glycidoxypropyl)disiloxane under a dry atmosphere are an addition catalyst, BHT as stabilizer and then 26.10 g (0.30 mol) of methacrylic acid, and the mixture is stirred at about 80° C. (about 24 h). The conversion is monitored via the decrease in the carboxylic acid concentration by means of acid titration, and the epoxide conversion by means of Raman spectroscopy/epoxide titration. The band characteristic of the epoxide group is detected in the Raman spectrum at 1256 cm −1 . The epoxide and carboxylic acid conversions are 99% and 88% respectively (consequence of the carboxylic acid excess). 300 mL of ethyl acetate are added. This is followed by extractive shaking with 2N NaOH solution, washing with water and drying of the organic phase over magnesium sulfate. After addition of BHT, the solvent is removed under reduced pressure. This results in a mobile resin having a viscosity of 0.3 Pa*s at 25° C. 
     n D   20 =1.466 
     Light-Curing Polysiloxane/Disiloxane Resins (Examples 1-4) 
     CQ and DABE were dissolved in the respective monomers (polysiloxane and disiloxane). The solutions were freed of air at vacuum −0.9 bar. The flexural strength (FS) of the individual resins was determined, and these measurements were used to calculate the modulus of elasticity (MOE). 
     Surprisingly, a higher modulus of elasticity is found for the mixtures of polysiloxane and disiloxane than for the two respective individual components ( FIG. 1 ). The maximum for the modulus of elasticity was found at a ratio of polysiloxane to disiloxane of about 2:1. 
     Example 1 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Composition and properties of poly-/disiloxane resins 1 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 1-A 
                 1-B 
                 1-C 
                 1-D 
                 1-E 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Polysiloxane 
                 99.25 
                 82.71 
                 66.17 
                 49.625 
                 0.00 
               
               
                 I 
               
               
                 Disiloxane I 
                 0.00 
                 16.54 
                 33.08 
                 49.625 
                 99.25 
               
               
                 CQ 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                 DABE 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
               
               
                 FS 
                  9.9 MPa 
                 20.8 MPa  
                  25.2 MPa 
                  28.2 MPa 
                 36.3 MPa  
               
               
                 MOE 
                 560 MPa 
                 960 MPa 
                 1040 MPa 
                 1020 MPa 
                 880 MPa 
               
               
                   
               
            
           
         
       
     
     Example 2 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Composition and properties of poly-/disiloxane resins 2 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 2-A 
                 2-B 
                 2-C 
                 2-D 
                 2-E 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Polysiloxane 
                 99.25 
                 82.71 
                 66.17 
                 49.625 
                 0.00 
               
               
                 II 
               
               
                 Disiloxane I 
                 0.00 
                 16.54 
                 33.08 
                 49.625 
                 99.25 
               
               
                 CQ 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                 DABE 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
               
               
                 FS 
                 13.0 MPa  
                  22.3 MPa 
                  23.0 MPa 
                  27.8 MPa 
                 36.3 MPa  
               
               
                 MOE 
                 920 MPa 
                 1140 MPa 
                 1200 MPa 
                 1130 MPa 
                 880 MPa 
               
               
                   
               
            
           
         
       
     
     Example 3 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Composition and properties of poly-/disiloxane resins 3 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 3-A 
                 3-B 
                 3-C 
                 3-D 
                 3-E 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Polysiloxane 
                 99.25 
                 82.71 
                 66.17 
                 49.625 
                 0.00 
               
               
                 III 
               
               
                 Disiloxane I 
                 0.00 
                 16.54 
                 33.08 
                 49.625 
                 99.25 
               
               
                 CQ 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                 DABE 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
               
               
                 FS 
                  19.6 MPa 
                  31.3 MPa 
                  32.0 MPa 
                  31.7 MPa 
                 36.3 MPa  
               
               
                 MOE 
                 1050 MPa 
                 1360 MPa 
                 1380 MPa 
                 1250 MPa 
                 880 MPa 
               
               
                   
               
            
           
         
       
     
     Example 4 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Composition and properties of poly-/disiloxane resins 4 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 4-A 
                 4-B 
                 4-C 
                 4-D 
                 4-E 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Polysiloxane 
                 99.25 
                 82.71 
                 66.17 
                 49.625 
                 0.00 
               
               
                 IV 
               
               
                 Disiloxane II 
                 0.00 
                 16.54 
                 33.08 
                 49.625 
                 99.25 
               
               
                 CQ 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                 DABE 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
                 0.45 
               
               
                 FS 
                  25.7 MPa 
                  36.3 MPa 
                  38.1 MPa 
                  34.5 MPa 
                  28.4 MPa 
               
               
                 MOE 
                 1260 MPa 
                 1530 MPa 
                 1550 MPa 
                 1470 MPa 
                 1090 MPa 
               
               
                   
               
            
           
         
       
     
     Production and Properties of Flowable Composite Materials (Example 5) 
     For the production of flowable composite pastes, the constituents were each weighed out, homogenized in a SpeedMixer™ DAC 600.1 VAC-P (Hauschild &amp; Co. KG, Hamm, Germany), rolled in a three-roll mill (Exakt, Norderstedt, Germany) and then freed of air in the SpeedMixer™ DAC 600.1 VAC-P at vacuum −0.9 bar. The viscosity and spreadability of the individual pastes were measured. 
     The pastes were dispensed into 1 mL syringes (black, 3-part, Luer lock, with silicone O-ring) from Transcodent GmbH &amp; Co. KG. For the determination of Push-out characteristics and push-out force, cannulas (41 type, VOCO GmbH) were used. 
     
       
         
           
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Compositions of the flowable composites 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 5-B 
                 5-C 
                 5-D 
                 5-E 
               
               
                   
                 5-A 
                 (comp.) 
                 (comp.) 
                 (comp.) 
                 (comp.) 
               
               
                   
               
               
                 Polysiloxane IV 
                 20.00 
                 35.00 
                 0.00 
                 40.00 
                 45.00 
               
               
                 Disiloxane I 
                 10.00 
                 0.00 
                 20.00 
                 0.00 
                 0.00 
               
               
                 Barium silicate 
                 57.40 
                 53.40 
                 62.40 
                 47.90 
                 42.40 
               
               
                 glass (1.5 μm) 
               
               
                 silanized 
               
               
                 Barium silicate 
                 9.00 
                 8.00 
                 14.00 
                 6.00 
                 4.00 
               
               
                 glass (0.7 μm) 
               
               
                 silanized 
               
               
                 Aerosil R8200 
                 2.50 
                 2.50 
                 2.50 
                 5.00 
                 7.50 
               
               
                 CQ 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
               
               
                 DABE 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
               
               
                 BHT 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 5-F 
                   
                 5-H 
                 5-I 
                   
               
               
                   
                 (comp.) 
                 5-G 
                 (comp.) 
                 (comp.) 
                 5-J 
               
               
                   
               
               
                 Polysiloxane IV 
                 32.00 
                 15.00 
                 6.00 
                 0.00 
                 30.00 
               
               
                 Disiloxane I 
                 0.00 
                 7.50 
                 3.00 
                 10.00 
                 15.00 
               
               
                 Bis-GMA 
                 0.00 
                 5.00 
                 16.00 
                 10.00 
                 0.00 
               
               
                 TEGDMA 
                 0.00 
                 2.50 
                 8.00 
                 10.00 
                 0.00 
               
               
                 Barium silicate 
                 56.40 
                 57.40 
                 54.40 
                 57.40 
                 31.40 
               
               
                 glass (1.5 μm) 
               
               
                 silanized 
               
               
                 Barium silicate 
                 8.00 
                 9.00 
                 9.00 
                 9.00 
                 20.00 
               
               
                 glass (0.7 μm) 
               
               
                 silanized 
               
               
                 Aerosil R8200 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
               
               
                 CQ 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
               
               
                 DABE 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
               
               
                 BHT 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 5-K 
                 5-L 
                 5-M 
                 5-N 
                 5-O 
               
               
                   
                   
               
               
                   
                 Polysiloxane IV 
                 20.00 
                 18.00 
                 16.00 
                 16.00 
                 15.00 
               
               
                   
                 Disiloxane I 
                 10.00 
                 9.00 
                 8.00 
                 0.00 
                 7.50 
               
               
                   
                 Disiloxane II 
                 0.00 
                 0.00 
                 0.00 
                 8.00 
                 0.00 
               
               
                   
                 Bis-GMA 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 5.00 
               
               
                   
                 TEGDMA 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 2.50 
               
               
                   
                 Barium silicate 
                 51.40 
                 53.40 
                 49.40 
                 49.40 
                 51.40 
               
               
                   
                 glass (1.5 μm) 
               
               
                   
                 silanized 
               
               
                   
                 Barium silicate 
                 7.00 
                 8.00 
                 7.00 
                 7.00 
                 7.00 
               
               
                   
                 glass (0.7 μm) 
               
               
                   
                 silanized 
               
               
                   
                 Nanoscale SiO 2   
                 8.00 
                 8.00 
                 16.00 
                 16.00 
                 8.00 
               
               
                   
                 (40 nm) silanized 
               
               
                   
                 Aerosil R8200 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
               
               
                   
                 CQ 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
               
               
                   
                 DABE 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
               
               
                   
                 BHT 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
                 0.10 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Properties of the flowable composites 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 5-A 
                 5-B 
                 5-C 
                 5-D 
                 5-E 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 FS 
                 110 
                 MPa 
                 94 
                 MPa 
                 75 
                 MPa 
                 82 
                 MPa 
                 71 
                 MPa 
               
               
                 MOE 
                 6.0 
                 GPa 
                 5.5 
                 GPa 
                 5.0 
                 GPa 
                 5.0 
                 GPa 
                 4.5 
                 GPa 
               
            
           
           
               
               
               
               
               
               
            
               
                 Shrinkage 
                 2.5% 
                 1.8% 
                 3.5% 
                 2.4% 
                 3.1% 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Viscosity 
                 10.0 
                 kPa*s 
                 0.8 
                 kPa*s 
                 6.5 
                 kPa*s 
                 2.6 
                 kPa*s 
                 7.2 
                 kPa*s 
               
               
                 (0.01/s) 
               
               
                 Viscosity 
                 49 
                 Pa*s 
                 53 
                 Pa*s 
                 48 
                 Pa*s 
                 61 
                 Pa*s 
                 68 
                 Pa*s 
               
               
                 (10/s) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Push-out 
                 good 
                 difficult 
                 good 
                 difficult 
                 acceptable 
               
               
                 characteristics 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Push-out force 
                 33 
                 N 
                 112 
                 N 
                 40 
                 N 
                 101 
                 N 
                 79 
                 N 
               
               
                 Spreadability 
                 61 
                 mm 
                 35 
                 mm 
                 31 
                 mm 
                 38 
                 mm 
                 40 
                 mm 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 5-F 
                 5-G 
                 5-H 
                 5-I 
                 5-J 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 FS 
                 118 
                 MPa 
                 115 
                 MPa 
                 118 
                 MPa 
                 110 
                 MPa 
                 91 
                 MPa 
               
               
                 MOE 
                 7.6 
                 GPa 
                 7.0 
                 GPa 
                 7.2 
                 GPa 
                 6.5 
                 GPa 
                 5.1 
                 GPa 
               
            
           
           
               
               
               
               
               
               
            
               
                 Shrinkage 
                 1.6% 
                 3.1% 
                 4.0% 
                 3.6% 
                 3.4% 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Viscosity 
                 11.6 
                 kPa*s 
                 11.4 
                 kPa*s 
                 9.5 
                 kPa*s 
                 7.8 
                 kPa*s 
                 6.8 
                 kPa*s 
               
               
                 (0.01/s) 
               
               
                 Viscosity 
                 370 
                 Pa*s 
                 58 
                 Pa*s 
                 55 
                 Pa*s 
                 51 
                 Pa*s 
                 43 
                 Pa*s 
               
               
                 (10/s) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Push-out 
                 very 
                 good 
                 good 
                 good 
                 very 
               
               
                 characteristics 
                 difficult 
                   
                   
                   
                 good 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Push-out force 
                 189 
                 N 
                 45 
                 N 
                 42 
                 N 
                 30 
                 N 
                 25 
                 N 
               
               
                 Spreadability 
                 24 
                 mm 
                 51 
                 mm 
                 57 
                 mm 
                 55 
                 mm 
                 67 
                 mm 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 5-K 
                 5-L 
                 5-M 
                 5-N 
                 5-O 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 FS 
                 113 
                 MPa 
                 116 
                 MPa 
                 121 
                 MPa 
                 125 
                 MPa 
                 118 
                 MPa 
               
               
                 MOE 
                 6.5 
                 GPa 
                 6.9 
                 GPa 
                 7.3 
                 GPa 
                 7.5 
                 GPa 
                 7.2 
                 GPa 
               
            
           
           
               
               
               
               
               
               
            
               
                 Shrinkage 
                 2.4% 
                 2.2% 
                 2.1% 
                 2.0% 
                 3.1% 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Viscosity 
                 10.8 
                 kPa*s 
                 11.4 
                 kPa*s 
                 11.9 
                 kPa*s 
                 11.8 
                 kPa*s 
                 12.1 
                 kPa*s 
               
               
                 (0.01/s) 
               
               
                 Viscosity 
                 51 
                 Pa*s 
                 59 
                 Pa*s 
                 63 
                 Pa*s 
                 62 
                 Pa*s 
                 61 
                 Pa*s 
               
               
                 (10/s) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Push-out 
                 good 
                 good 
                 acceptable 
                 acceptable 
                 good 
               
               
                 characteristics 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Push-out force 
                 41 
                 N 
                 55 
                 N 
                 81 
                 N 
                 79 
                 N 
                 55 
                 N 
               
               
                 Spreadability 
                 55 
                 mm 
                 51 
                 mm 
                 48 
                 mm 
                 47 
                 mm 
                 49 
                 mm 
               
               
                   
               
            
           
         
       
     
     The results show clearly that combination of polysiloxanes and disiloxanes distinctly improves the properties of the flow material. As already found on consideration of the poly-/disiloxane resin mixtures, synergistic effects also occur in the composite. If the different pastes are adjusted to a comparable processible viscosity (at 10 s −1 ) (5-A to C), it is found that, as well as the expected pure dilution effect on combination of the specific low-viscosity disiloxane with the high-viscosity polysiloxane, unexpectedly better results are achieved with regard to strength and elasticity properties compared to the pastes comprising either only polysiloxane (5-B) or only disiloxane (5-C). 
     The better strength properties cannot be explained by a higher filler content, since paste 5-C based on the disiloxane, in spite of the increased solids content, has a lower strength. The crosslinking properties of the disiloxane cannot be cited as a reason either, since, as shown by the studies on the resins, they actually have a higher crosslinking potential. 
       FIG. 2  shows the curves for the viscosity as a function of shear rate for the inventive flowable material 5-A and of the two comparative materials 5-B and 5-F. Flowable material 5-A has the viscosity curve typical of a flowable composite. In the case of a high shear rate, the viscosity is low and the flowable material can flow readily through the cannula. In the case of a low shear rate, the viscosity is high and the material is stable. 
     In the case of 5-B, the viscosity is set so as to correspond approximately to example 5-A at a shear rate of 10 s −1 . On the other hand, the viscosity at 0.01 s −1  is much lower and the material is correspondingly less stable. In the case of 5-F, the viscosity is set so as to correspond approximately to example 5-A at a shear rate of 0.01 s −1 . On the other hand, the viscosity at 10 s −1  is much higher and the material can be pushed-out only with very great difficulty. 
     If, proceeding from the pure polysiloxane material 5-B, the aerosil content is increased (5-D and E), the shear gradient increases as expected, the viscosity gradually approaches 5-A and the push-out characteristics improve ( FIG. 3 ). At the same time, however, the achievable filler content decreases and hence flexural strength and shrinkage deteriorate. 
     Production and Properties of Core Buildup Materials (Example 6) 
     For the production of the base and catalyst pastes of the core buildup materials, the constituents were each weighed out, homogenized in a SpeedMixer™ DAC 600.1 VAC-P (Hauschild &amp; Co. KG, Hamm, Germany), rolled in a three-roll mill (Exakt, Norderstedt, Germany) and then freed of air in the SpeedMixer™ DAC 600.1 VAC-P at vacuum −0.9 bar. The viscosity and spreadability of the individual pastes were measured. 
     The core buildup materials were dispensed into double-chamber syringes (5 mL, 1:1, SDL X05-01-52, PED X05-01-SI) from Sulzer Mixpac AG (Haag, Switzerland). For mixing, the appropriate static mixers ML 2.5-08-D and IOT 212-20 from Sulzer Mixpac AG were attached to the syringes and the two components were pushed-out and mixed homogeneously with a plunger (PLH X05-01-46). 
     
       
         
           
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 Compositions of the core buildup materials 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 6-B 
                 6-C 
                 6-D 
                 6-E 
               
               
                   
                 6-A 
                 (comp.) 
                 (comp.) 
                 (comp.) 
                 (comp.) 
               
               
                   
               
               
                 Base paste 
               
               
                 Polysiloxane IV 
                 20.00 
                 30.00 
                 40.00 
                 0.00 
                 0.00 
               
               
                 Disiloxane I 
                 10.00 
                 0.00 
                 0.00 
                 30.00 
                 20.00 
               
               
                 Bis-GMA 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 TEGDMA 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Barium silicate glass 
                 55.95 
                 55.95 
                 47.95 
                 55.95 
                 63.95 
               
               
                 (3.5 μm) silanized 
               
               
                 Barium silicate glass 
                 10.00 
                 10.00 
                 8.00 
                 10.00 
                 12.00 
               
               
                 (0.7 μm) silanized 
               
               
                 Nanoscale SiO 2  (40 Nm) 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 silanized 
               
               
                 Aerosil R8200 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                 DEPT 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
               
               
                 CQ 
                 0.18 
                 0.18 
                 0.18 
                 0.18 
                 0.18 
               
               
                 DABE 
                 0.27 
                 0.27 
                 0.27 
                 0.27 
                 0.27 
               
               
                 Catalyst paste 
               
               
                 Polysiloxane IV 
                 20.00 
                 30.00 
                 40.00 
                 0.00 
                 0.00 
               
               
                 Disiloxane I 
                 10.00 
                 0.00 
                 0.00 
                 30.00 
                 20.00 
               
               
                 Bis-GMA 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 TEGDMA 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Barium silicate glass 
                 55.95 
                 55.95 
                 47.95 
                 55.95 
                 63.95 
               
               
                 (3.5 μm) silanized 
               
               
                 Barium silicate glass 
                 10.00 
                 10.00 
                 8.00 
                 10.00 
                 12.00 
               
               
                 (0.7 μm) silanized 
               
               
                 Nanoscale SiO 2  (40 Nm) 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 silanized 
               
               
                 Aerosil R8200 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                 BPO 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                 BHT 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 6-F 
                 6-G 
                 6-H 
                 6-I 
               
               
                   
                   
               
               
                   
                 Base paste 
               
               
                   
                 Polysiloxane IV 
                 16.00 
                 10.00 
                 18.00 
                 16.00 
               
               
                   
                 Disiloxane I 
                 8.00 
                 5.00 
                 9.00 
                 8.00 
               
               
                   
                 Bis-GMA 
                 4.00 
                 10.00 
                 0.00 
                 0.00 
               
               
                   
                 TEGDMA 
                 2.00 
                 5.00 
                 0.00 
                 0.00 
               
               
                   
                 Barium silicate glass 
                 55.95 
                 55.95 
                 51.95 
                 47.95 
               
               
                   
                 (3.5 μm) silanized 
               
               
                   
                 Barium silicate glass 
                 10.00 
                 10.00 
                 8.00 
                 6.00 
               
               
                   
                 (0.7 μm) silanized 
               
               
                   
                 Nanoscale SiO 2  (40 Nm) 
                 0.00 
                 0.00 
                 9.00 
                 18.00 
               
               
                   
                 silanized 
               
               
                   
                 Aerosil R8200 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                   
                 DEPT 
                 0.60 
                 0.60 
                 0.60 
                 0.60 
               
               
                   
                 CQ 
                 0.18 
                 0.18 
                 0.18 
                 0.18 
               
               
                   
                 DABE 
                 0.27 
                 0.27 
                 0.27 
                 0.27 
               
               
                   
                 Catalyst paste 
               
               
                   
                 Polysiloxane IV 
                 16.00 
                 10.00 
                 18.00 
                 16.00 
               
               
                   
                 Disiloxane I 
                 8.00 
                 5.00 
                 9.00 
                 8.00 
               
               
                   
                 Bis-GMA 
                 4.00 
                 10.00 
                 0.00 
                 0.00 
               
               
                   
                 TEGDMA 
                 2.00 
                 5.00 
                 0.00 
                 0.00 
               
               
                   
                 Barium silicate glass 
                 55.95 
                 55.95 
                 51.95 
                 47.95 
               
               
                   
                 (3.5 μm) silanized 
               
               
                   
                 Barium silicate glass 
                 10.00 
                 10.00 
                 8.00 
                 6.00 
               
               
                   
                 (0.7 μm) silanized 
               
               
                   
                 Nanoscale SiO 2  (40 Nm) 
                 0.00 
                 0.00 
                 9.00 
                 18.00 
               
               
                   
                 silanized 
               
               
                   
                 Aerosil R8200 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                   
                 BPO 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 BHT 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
               
                   
               
               
                 Properties of the core buildup materials 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 6-B 
                 6-C 
                 6-D 
                 6-E 
               
               
                   
                 6-A 
                 (comp.) 
                 (comp.) 
                 (comp.) 
                 (comp.) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 FS 
                 108 
                 MPa 
                 115 
                 MPa 
                 97 
                 MPa 
                 75 
                 MPa 
                 85 
                 MPa 
               
               
                 MOE 
                 7.0 
                 GPa 
                 7.2 
                 GPa 
                 6.2 
                 GPa 
                 5.2 
                 GPa 
                 5.8 
                 GPa 
               
            
           
           
               
               
               
               
               
               
            
               
                 Shrinkage 
                 2.6% 
                 1.8% 
                 3.1% 
                 4.2% 
                 3.6% 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Viscosity 
                 8.9 
                 kPa*s 
                 15.1 
                 kPa*s 
                 1.5 
                 kPa*s 
                 5.8 
                 kPa*s 
                 6.7 
                 kPa*s 
               
               
                 (0.01/s, base) 
               
               
                 Viscosity 
                 60 
                 Pa*s 
                 105 
                 Pa*s 
                 58 
                 Pa*s 
                 25 
                 Pa*s 
                 68 
                 Pa*s 
               
               
                 (10/s, base) 
               
               
                 Viscosity 
                 9.1 
                 kPa*s 
                 15.8 
                 kPa*s 
                 1.6 
                 kPa*s 
                 6.1 
                 kPa*s 
                 6.9 
                 kPa*s 
               
               
                 (0.01/s, cat.) 
               
               
                 Viscosity 
                 61 
                 Pa*s 
                 108 
                 Pa*s 
                 60 
                 Pa*s 
                 26 
                 Pa*s 
                 70 
                 Pa*s 
               
               
                 (10/s, cat.) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Push-out 
                 good 
                 very 
                 difficult 
                 very 
                 good 
               
               
                 characteristics 
                   
                 difficult 
                   
                 good 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Push-out force 
                 62 
                 N 
                 225 
                 N 
                 121 
                 N 
                 49 
                 N 
                 77 
                 N 
               
               
                 Spreadability 
                 60 
                 mm 
                 37 
                 mm 
                 41 
                 mm 
                 70 
                 mm 
                 49 
                 mm 
               
               
                 (base) 
               
               
                 Spreadability 
                 58 
                 mm 
                 36 
                 mm 
                 40 
                 mm 
                 68 
                 mm 
                 48 
                 mm 
               
               
                 (cat.) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 6-F 
                 6-G 
                 6-H 
                 6-I 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 FS 
                 111 
                 MPa 
                 112 
                 MPa 
                 115 
                 MPa 
                 120 
                 MPa 
               
               
                 MOE 
                 7.1 
                 GPa 
                 7.0 
                 GPa 
                 7.3 
                 GPa 
                 7.5 
                 GPa 
               
            
           
           
               
               
               
               
               
            
               
                 Shrinkage 
                 2.7% 
                 2.8% 
                 2.4% 
                 2.2% 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Viscosity 
                 9.5 
                 kPa*s 
                 9.9 
                 kPa*s 
                 9.8 
                 kPa*s 
                 10.5 
                 kPa*s 
               
               
                 (0.01/s, base) 
               
               
                 Viscosity 
                 61 
                 Pa*s 
                 61 
                 Pa*s 
                 65 
                 Pa*s 
                 68 
                 Pa*s 
               
               
                 (10/s, base) 
               
               
                 Viscosity 
                 9.9 
                 kPa*s 
                 10.2 
                 kPa*s 
                 10.1 
                 kPa*s 
                 10.8 
                 kPa*s 
               
               
                 (0.01/s, cat.) 
               
               
                 Viscosity 
                 62 
                 Pa*s 
                 63 
                 Pa*s 
                 67 
                 Pa*s 
                 69 
                 Pa*s 
               
               
                 (10/s, cat.) 
               
            
           
           
               
               
               
               
               
            
               
                 Push-out 
                 good 
                 good 
                 good 
                 acceptable 
               
               
                 characteristics 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Push-out force 
                 71 
                 N 
                 76 
                 N 
                 76 
                 N 
                 85 
                 N 
               
               
                 Spreadability 
                 55 
                 mm 
                 51 
                 mm 
                 54 
                 mm 
                 49 
                 mm 
               
               
                 (base) 
               
               
                 Spreadability 
                 53 
                 mm 
                 49 
                 mm 
                 53 
                 mm 
                 48 
                 mm 
               
               
                 (cat.) 
               
               
                   
               
            
           
         
       
     
     Proceeding from 6-A, in the case of exclusive use of polysiloxane (6-B), flexural strength rises slightly, but the material can still be pushed-out and mixed by means of a static mixer only with very high force expenditure. If the filler content is lowered (6-C), the material is still very difficult to push-out and flexural strength decreases. 
     In the case of exclusive use of disiloxane (6-D), the material has very good push-out characteristics, but flexural strength is poor. If the filler content is increased (6-E), flexural strength is still much poorer, with comparable push-out characteristics. 
     Production and Properties of Luting Composites (Example 7) 
     For the production of the base and catalyst pastes of the luting composites, the constituents were each weighed out, homogenized in a SpeedMixer™ DAC 600.1 VAC-P (Hauschild &amp; Co. KG, Hamm, Germany), rolled in a three-roll mill (Exakt, Norderstedt, Germany) and then freed of air in the SpeedMixer™ DAC 600.1 VAC-P at vacuum −0.9 bar. The viscosity and spreadability of the individual pastes were measured. 
     The luting composites were dispensed into double-chamber syringes (5 mL, 1:1, SDL X05-01-52, PED X05-01-SI) from Sulzer Mixpac AG (Haag, Switzerland). For mixing, the appropriate static mixers ML 2.5-08-D and IOT 212-20 from Sulzer Mixpac AG were attached to the syringes and the two components were pushed-out and mixed homogeneously with a plunger (PLH X05-01-46). 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Compositions of the luting composites 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 7-A 
                 7-B 
                 7-C 
                 7-D 
                 7-E 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Base paste 
                   
                   
                   
                   
                   
               
               
                 Polysiloxane IV 
                 22.00 
                 22.00 
                 22.00 
                 25.00 
                 18.00 
               
               
                 Disiloxane I 
                 11.00 
                 0.00 
                 11.00 
                 12.50 
                 9.00 
               
               
                 Disiloxane II 
                 0.00 
                 11.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Barium silicate glass 
                 43.95 
                 43.95 
                 43.75 
                 36.45 
                 47.95 
               
               
                 (1.5 μm) silanized 
               
               
                 Barium silicate glass 
                 20.00 
                 20.00 
                 20.00 
                 22.50 
                 6.00 
               
               
                 (0.7 μm) silanized 
               
               
                 Nanoscale SiO 2  (40 Nm) 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 16.00 
               
               
                 silanized 
               
               
                 Aerosil R8200 
                 2.00 
                 2.00 
                 2.00 
                 2.50 
                 2.00 
               
               
                 DEPT 
                 0.60 
                 0.60 
                 0.40 
                 0.60 
                 0.60 
               
               
                 NTPB 
                 0.00 
                 0.00 
                 0.40 
                 0.00 
                 0.00 
               
               
                 CQ 
                 0.18 
                 0.18 
                 0.18 
                 0.18 
                 0.18 
               
               
                 DABE 
                 0.27 
                 0.27 
                 0.27 
                 0.27 
                 0.27 
               
               
                 Catalyst paste 
               
               
                 Polysiloxane IV 
                 22.00 
                 22.00 
                 18.00 
                 25.00 
                 18.00 
               
               
                 Disiloxane I 
                 11.00 
                 0.00 
                 9.00 
                 12.50 
                 9.00 
               
               
                 Disiloxane II 
                 0.00 
                 11.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 MDP 
                 0.00 
                 0.00 
                 9.00 
                 0.00 
                 0.00 
               
               
                 Barium silicate glass 
                 43.95 
                 43.95 
                 40.95 
                 36.45 
                 47.95 
               
               
                 (1.5 μm) silanized 
               
               
                 Barium silicate glass 
                 20.00 
                 20.00 
                 20.00 
                 22.50 
                 6.00 
               
               
                 (0.7 μm) silanized 
               
               
                 Nanoscale SiO 2  (40 Nm) 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 16.00 
               
               
                 silanized 
               
               
                 Aerosil R8200 
                 2.00 
                 2.00 
                 2.00 
                 2.50 
                 2.00 
               
               
                 BPO 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                 BHT 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
               
               
                   
               
            
           
         
       
     
                     TABLE 10                  Properties of the luting composites                                         7-A   7-B   7-C   7-D   7-E                                                                     FS   104   MPa   113   MPa   102   MPa   91   MPa   119   MPa       MOE   6.8   GPa   7.1   GPa   6.5   GPa   6.1   GPa   7.6   GPa                                     Shrinkage   2.7%   2.4%   2.7%   3.5%   2.2%                                                         Viscosity   8.4   kPa*s   9.6   kPa*s   8.8   kPa*s   7.9   kPa*s   10.3   kPa*s       (0.1/s, base)       Viscosity   55   Pa*s   60   Pa*s   56   Pa*s   49   Pa*s   64   Pa*s       (10/s, base)       Viscosity   8.5   kPa*s   9.9   kPa*s   8.9   kPa*s   8.0   kPa*s   10.5   kPa*s       (0.1/s, cat.)       Viscosity   56   Pa*s   63   Pa*s   60   Pa*s   50   Pa*s   65   Pa*s       (10/s, cat.)                                     Push-out   good   good   good   very   acceptable       characteristics               good                                                         Push-out force   59   N   68   N   69   N   43   N   83   N       Spreadability   61   mm   53   mm   59   mm   69   mm   51   mm       (base)       Spreadability   59   mm   51   mm   50   mm   67   mm   50   mm       (cat.)                    
Determination of the Properties:
 
     Flexural strength (FS): The flexural strength is determined in accordance with ISO 4049. The flowable composites (examples 5) are applied to the mold from 1 mL syringes (black, 3-part, Luer lock, with silicone O-ring) from Transcodent GmbH &amp; Co. KG through cannulas (41 type, VOCO GmbH). The core buildup and luting composites (examples 6 and 7) are applied to the molds from 5 mL double-chamber syringes (SDL X05-01-52, PED X05-01-SI) from Sulzer Mixpac AG (Haag, Switzerland) through a static mixer (ML 2.5-08-D and IOT 212-20). All the materials are light-cured with a Celalux 2 lamp (VOCO GmbH) section by section for 40 seconds. The flexural strength was determined at an advance rate of 0.75 mm/min on a Zwick universal tester (Zwick GmbH &amp; Co. KG, Ulm). 
     Modulus of elasticity (MOE): The modulus of elasticity is determined from the slope in the elastic range of the force-distance curves from the flexural strength measurements. 
     Shrinkage: Shrinkage was determined by the bonded-disk method of Watts et al. (Watts D C, Cash A J, Determination of polymerization kinetics in visible-light cured materials: Methods development,  Dent Mater  1991; 7: 281-287). A difference was that exposure was effected with a Celalux 2 lamp (VOCO GmbH) for 40 seconds per measurement. 
     Viscosity: The viscosity was determined by means of a rheometer (Physica MCR 301) from Anton Paar (Graz, Austria). The measurement is effected at 23° C. in a rotation experiment with plate/plate arrangement (diameter 25 mm, gap 1 mm) in a shear rate range from 10 −2  to 10 s −1 . For each measurement, 16 measured values are recorded within an interval of 30 seconds per shear rate. The tables each state the viscosities for the shear rates of 0.01 and 10 s −1 . A low shear rate approximately corresponds to the viscosity of the material at rest, while high shear rates are observed on application of the material through a narrow cannula or a static mixer. 
     Push-out characteristics: The flowable composites (examples 5) were dispensed into 1 mL syringes (black, 3-part, Luer lock, with silicone O-ring) from Transcodent GmbH &amp; Co. KG and pushed-out through cannulas (41 type, VOCO GmbH). The core buildup and luting composites (examples 6 and 7) were dispensed into 5 mL double-chamber syringes (SDL X05-01-52, PED X05-01-SI) from Sulzer Mixpac AG (Haag, Switzerland) and pushed-out through a static mixer (ML 2.5-08-D and IOT 212-20). Push-out characteristics were rated in five levels: very good, good, acceptable, difficult, very difficult. 
     Push-out force: The flowable composites (examples 5) were dispensed into 1 mL syringes (black, 3-part, Luer lock, with silicone O-ring) from Transcodent GmbH &amp; Co. KG and pushed-out through cannulas (41 type, VOCO GmbH) in a universal tester (Zwick GmbH &amp; Co. KG, Ulm) with an advance rate of 10 mm/min over a distance of 20 mm. The core buildup and luting composites (examples 6 and 7) were dispensed into 5 mL double-chamber syringes (SDL X05-01-52, PED X05-01-SI) from Sulzer Mixpac AG (Haag, Switzerland) and pushed-out through a static mixer (ML 2.5-08-D and IOT 212-20) in a universal tester (Zwick GmbH &amp; Co. KG, Ulm) with an advance rate of 23 mm/min over a distance of 30 mm. The respective maximum force was evaluated as the push-out force. 
     Spreadability: The determination of spreadability is effected in a climate-controlled room at a temperature of 23° C. and a relative humidity of 50% by means of a glass plate arrangement. The dimensions of the plates are 60 mm×60 mm×3 mm, with a plate weight of 25 g. In the determination, 0.5 mL of the respective composite paste is applied to the middle of the first plate. Subsequently, the second plate is placed on cautiously, parallel to the first plate, and a 100 g weight is applied to the middle. After 10 minutes of weight application, the weight is removed and the greatest and smallest diameters of the compressed disk of the composite paste are measured. The average of the two diameters is reported as the spreadability.