CA1290888C

CA1290888C - Reactive organic filler and the use thereof

Info

Publication number: CA1290888C
Application number: CA000547553A
Authority: CA
Inventors: Thomas Buchel; Volker M. Rheinberger
Original assignee: Ivoclar AG
Current assignee: Ivoclar AG
Priority date: 1986-09-23
Filing date: 1987-09-22
Publication date: 1991-10-15
Anticipated expiration: 2008-10-15
Also published as: EP0262488A1; ATE53393T1; DE3632215A1; EP0262488B1; DE3763080D1

Abstract

ABSTRACT
An organic filler is in the form of a solid powder prepared by non-radical polymerisation.
The filler comprises reactive double bonds which are not extractable with solvents in an amount (as determined by the DSC method) of at least 0.5 nmoles/g of the organic filler material. The polymer comprises the reaction product of active hydroxy group-containing (meth)acrylates with isocyanates in an OH-group to NCO-group ratio of approximately 1:1, at least one of the monomers being at least trifunctional. In one embodiment the isocyanate is triisocyanate.

Description

~ 2913~3~38 The present invention relates to organic fillers in the form of solid powders for polymerizable compositions containing compounds with ethylenically unsatu-rated groups which can undergo a radical polymerisation. Such ~ 5 compositions are used in various different technical fields ; and in particular as dental materials. Dental materials are understood to mean e.g. tooth filling materials for pre-servative tooth treatment and materials for producing dentures or parts of teeth, such as crowns or inlays.
The incorporation of different types of fillers into a matrix oE polymerizable monomers is already known in the art. The incorporation of fillers is intended to achieve a thickening effect, which leads to a composition consistency permitting the handling thereof prior to polymerization.
Additionally, the incorporation of fillers is intended to improve the properties of the polymerized end product ma-terial, such as increasing hardness and compression strength, as well as reducing its shrinkage tendency.
Inorganic fillers of different chemical composition are widely used. In general, however, inorganic fillers bond rather poorly with organic matrices, and the mechanical characteristics of the resulting polymers are not satisfac-~ ~ tory. To improve its bond with organic matrices, inorganic ; ~ fillers may be surface-treated with a silane. Nevertheless, even such silanized inorganic fillers do no~ satisfy all of ~;~ the set requirements.
The use of organic bead polymers as fillers is also known. Organic bead polymers may contain irorganic fillers.
Such bead polymers are preferably produced from the same monomers as are used as binders in order to achieve an optimum level of compatibility in all respects. For example, bead polymers of polymethylmethacrylate or other radically poly-merized acrylates are known, cf. German Offenlegungsschrift 28 , ~ ~
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91a and European Offenlegungsschrift 23 321. It is difficult, however, to control the radical polymerization and unreacted monomers are always present after polymerization.
Additionally, such fillers suffer from being inadequately anchored in the matrix. Furthermore, dental materials in-corporating fillers with an average diameter of more than 1jum exhibit the disadvantageous characteristics that they cannot be adequately polished after curing, and in the case of prolonged chewing action, filler particles may break off and accelerate wear to the matrix polymer. These problems are o observed both in silanized, coarse-particle, inorganic fillers and in bead polymers, which are filled with silanized ` inorganic fillers.
Thus, the problem is that in the use of known organic and inorganic fillers, the bond integrity between filler and matrix i9 too weak. It has not hitherto proved possible to modify a filler in such a way that bonding with the completely polymerized ma-trix is satisfactory in all ~ respects. All major modifications to the composition or ;~ production of the filler simultaneously led to significant changes in the physical characteristics such that use as a ; solid filler was not possible.
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An object of the present invention is to provide a filled polymeric material having improved cracking resistance, higher impact strength and greater abrasion resistance and a method of making such polymer.
Another object of the present invention is to provide an organic filler which provides a firm bond between the filler and matrix.
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, ~ ~g~ 38 Still another ob]ect of the present invention is to ` provide improved dental materials, which as a result of incorporation of a filler with a high content of reactive groups co-polymerizable with the matrix monomers exhibit strong bond integrity between filler and matrix and therefore, following complete polymerization, exhibit considerably improved cracking resistance, impact strength and abrasion resistance.
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The present invention therefore relates to a re-active organic filler in the form of a solid powder, which is characterized in that it is prepared by a non-radical polymeri-zation reaction, and comprises at least 0.5 mmole of reactive double bonds per gram of filler (determined by means of the lS DSC method) which are not extractable with solvents.
When using the present filler in polymerizable compo-sitions containing compounds with ethylenically unsaturated groups which can undergo a radical polymerisation, the rela-tively high content of reactive double bonds in the filler leads to a firm bond between filler and matrix. In wear tests, they are able to withstand many more cycles than conventional - materials, which reveal cracking at the latest after 10 cycles. Examination of crack patterns using electron micros-copes (REM) reveals that in conventional materials the cracks i 25 occur along the interface lines between matrix and filler particles. In materials made according to the present invention, the bond integrity between the filler and the matrix is so strong that the cracks run linearly along the impact point, i.e. through the matrix and filler particles.
; 30 The content of double bonds in the filler is preferably 0.5 to 5.0, particularly 1.0 to 3.0 and in a particularly preferred embodiment 1.4 to 2.6 mmole/g of the organic filler. This high reactive double bond content is achieved by a non-radical initiation of the polymerization of :

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the filler, preferably employing an addition reaction. The result is that 75% to 90~ of -the ethylenic double bonds contained in the starting monomer material are still present in the solid powder. In the case of conventional preparation of bead polymers by means of radical polymerization, most double bonds are used up by the polmyerization reaction. In -the present invention, since the monomers are reacted together in a stoichiometric ratio, the filler contains substantially no unreacted monomers, as is revealed by the fac-t that the double bond content cannot be reduced by solvent extraction.
The present fillers, being substantially free of unreacted monomers, are harder than those fillers which contain un-reacted monomers.
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The reactive double bonds contained in the organic filler of the present invention can be quantitatively de-termined by means of the DSC method (Differential Scanning Calorimetry). For this purpose a precisely weighed sample of the filler is mixed with a given quantity of a standardized peroxide solution whereafter the solvent is carefully evaporated. A precisely weighed quantity of the peroxide-coated filler is heated in a Perkin Elmer type DSC-2 apparatus and the heat quantity liberated during the exothermic reaction which takes place is determined from the thermogram. By ~-` 25 comparison with the values for the polymerization heat of the ` monomers used, it is possible to precisely determine the degree of polymerization. The presently used expression "amount of reactive double bonds in the filler" is intended in this sense and is stated in mmoles/g of polymer or organic - 30 filler.
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,, J88~3 ., The filler aceording to the present invention is made by non-radical polymerisation of organic monomers at least one of which has pendant unsaturation such as acrylic, vinyl, vinylidene and conjugated diene groups. Examples of the organie polymer materials include polyurethanes, epoxides, polyesters, polyimides and polyureas.
; Preferably the filler is prepared by reacting :: hydroxy group-containing acrylates or methacrylates (herein-after for short "(meth)acrylates") with isocyanates in an ~ l0 OH-group to NCO-group ratio of 1:1. At least one of the - starting eompounds is trifunctional or higher, in order to achieve the degree of cross-linking adequate for obtaining a solid powder. According to a particularly favourable em-bodiment, use is made of a triisoeyanate or polyisocyanate, it then also being possible to use a stoiehiometrie defieiency of hydroxy(meth)acrylate and to achieve the necessary cross-link-ing with water and/or a polyol, e.g. an aliphatic triol, which reacts with the unreacted isocyanate groups, accompanied by urea or urethane group formation. It is also possible to react a (meth)acrylate having three or more hydroxy groups with a diisocyanate.
Examples of a suitable hydroxy functional (meth)acryl-ates are hydroxyethylmethacrylate (HEMA), polyethyleneglycol-methaerylate, 2-hydroxypropylmethacrylate, 2,3-dihydroxypropyl-methaerylate, pentaerythritol-triacrylate, as well as reaction products of glycidyl(meth)acrylate with polyols, e.g. tri-methylolpropane, or polycarboxylic acids, e.g. succinic acid.
Particular preference is given to bis-GMA (bisphenol A-glycidylmethacrylate).
Preferred isoeyanates are aliphatie eompounds, such as 3-isoeyanatomethyl-3,5,5-trimethyleyelohexylisocyanate, tri-~; ~ methylhexamethylene diisocyanate and triisocyanate tris-(6-isocyanatohexyl)-biure-t ~Desmodur* N 100 oE Bayer AG).

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~29~ 8 .~ , The reaction hetween the hydroxy(meth)acrylates ancl isocyanates can be per~ormed under Ini]d con(l-itions. 'I`ile maximum reaction temperature is approx. 150C and preferably approx. 10C to 60C. A catalyst can be added ~or acceleration purposes, and inter alia, tertiary amines and metallo-organic salts are suitable.
The reaction of the hydroxy functional (meth)acryl-ates is known per se. For example, it is used for the preparation of prepolymers, which can be used as binders in dental materials, c.f. German Offenlegungsschrift 21 26 419.

The filler according to the present invention can also be prepared by copolymerization of hydroxy(meth)acrylates with an epoxy resin and/or trioxan in a stoichiometric ratio.
For example, bisphenol A-diglycidylether (Epikote*828) can be reacted with glycidyl(meth)acrylate and/or HEMA using BF3 as the catalyst. Similar results are obtained through reacting glycidyl(meth)acrylate with trioxan and epoxides with epoxy (meth)acrylates. Further examles are the reaction of hydroxy ~l compounds with carboxylic acid derivatives in which at least -~ ~ one of the starting compounds contains (meth)acrylate groups to give polyesters, and the reaction of allylidenes, e.g.
diallylidenepentaerythritol with alcohols or carboxylic acids.
The ethylenically unsaturated vinyl groups remain unchanged during these reactions and are available as reactive groups for the subsequent reaction with the matrix binder. The filler of the present invention, after production is brought to the necessary particle size by grinding. Preferably, the average diameter oF -the particles after grinding the filler is in the range between 0.5 /um to 100 /um, and part;cular preEerence is given to an average diameter of approximately l0 /um to 50 .
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~ 29~ 38 According to an advantageous embodiment of the invention, an inorganic a~/or an organic filler containi~ no reactive double bo~s is incorporated into the organic filler by addition to the starting compounds prior to the polymerisation reaction.
Thus, the physical characteristics of the filler can be varied within wide limits. The content of inert fillers in -the reactive filler, based on the total weight of the filler, can be between 0% to 80% by weight. Contents of 20~ to 75%, especially approximately 40% to 70% by weight are particularly favourable.
A large number of inorganic compounds is suitable as fillers. Examples are glass powder, alumina, silicon dioxide such as quartz, sand or silica, diatomaceous earth, calcium carbonate, clay, talc, pumice, ground slag, mica, asbestos, lS aluminum sulphate, calcium sulphate or lithopone. Molybdenum ~- sulfide, graphite, carbon black, flyash, potassium titanate and fibres, e.g., glass or carbon fibres are also suitable.
When using the filler in dental materials, glass or quartz ; powders as well as very finely divided silicas, particularly microfine fumed silica, but also precipitated silicas and - .
silica gels, are especially suitable. Another preferred group is constituted by the inorganic fillers, which make the finished dental material radiopaque, such as barium sulphate or fluorides of rare earth elements.
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;~ 25 or many uses, the inorganic filler preferably undergoes surface silanization in order to facilitate its incorporation~ into the organic materials and when using silanes with polymerizable double bonds one achieves a certain binding between the organic matrix and the inorganic filler. A
particularly preferred silane is y-methacryloxypropyltrimeth-;~ oxysilane. Other suitable silanes have hydroxy, amino and ~ epoxy groups.
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When producing the inventive fillers, it is im-portant to take account oE -the fact that the optionally added inorganic Eiller may contain surface groups which participate in the reaction. For example, silicas have silanol groups Si-OH on the surface, which are able to react with isocyanate groups. The content in the inorganic filler of such OH-groups must therefore be taken into account when calculating the OH:NCO ratio of the starting compounds.
Suitable inert organic fillers are, in particular, acrylic and ~ethacrylic polymers, e.g. polymethylmethacrylate and polyurethanes. These polymers are brought to the desired particle size by grinding.
; The presen-t invention also relates to the use of the above-described organic fillers in polymerizable compositions containing binder compounds with radically poly-merizable, ethylenically unsaturated groups. Sultable vinyl monomers for such compositions are, inter alia, 4-methacryl-oxyethyltrimellitic acid and its anhydride; epoxy acrylates of the bisphenol type and their oligomers; urethane dimethacry-late; methacrylate; methyl, ethyl and butyl methacrylate;polyethylene glycol dimethacrylate; 2,2-bis-(p-2'-hydroxy-3'-methacryloxypropoxyphenyl)-propane; 2,2-bis-(4-methacryloxypoly-ethoxyphenyl)-propane; acrylonitrile; vinyl acetate; 2-cyano-acrylic acid; styrene; divinylbenzene and mixtures of the aforementioned monomers. The binders can also be vinyl group containing prepolymers or polymers.
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The illers are particularly suitable for use in radically polymerizable, in particular light curable, dental materials, which also contain vinyl compounds as binders.
~ Particularly suited are monofunctional or palyfunctional - ~ methacrylates, which can be used alone or in mixed form.
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9~)8~8 _ 9 _ Examples of these eompounds are methyl, isobut~l. and eyelo-~ hexyl. methacrylate; triethylene glycol dimetllacrylate; di-; : ethyleneglycol dimethacrylate; ethylene glycol dimethacrylate;
polyethylene glycol dime-thacrylate; butane-diol dimethacryl-' 5 ate; hexanedi.ol dimethacrylate; decane-diol dimethacrylate;
`. dodeeanediol dimethacrylate; bisphenol-A-dimethacrylate; tri-: . me-thylol propane trimethacryl.ate; as well as bis-GMA and the . : reaction products of isocyanates, particularly of diisocyanates ,~ and/or triisocyanates and OH-group containing methacrylates.
Examples of these are the reaction products of 1 mole of , hexamethylenediisoeyanate wi.th 2 moles of 2-hydroxyethyl ., methaerylate; 1 mol.e of tris-(6-isoeyanatohexyl)-biuret and 3 ~' moles of hydroxyethyl methacrylate; as well as 1 mol,e of trimethyl hexamethylenediisocyanate and 2 moles of hydroxy-. . 15 ethylmethacrylate whieh ean be ealled urethane dime-thacrylate . for short. The proportion oE these mainly long-chain compounds ~, in the dental material is between 10 and 50~ by weight.
~ The following examples are intended to serve onl.y as :,~ further illustrations of the present invention and are not intended to restriet the scope of the invention.

, EXAMPLE 1 A sol.ution of 19 g oE hydroxye-thylme-thacrylate, 2.7 : g of water and 0.01 g. of dibutyl tin diacetate is placed in a :~ 25 mortar and mixed with 20 g silanized fumed silica with an : : :
~"~ average primary particle diameter of 40 nm (AER~SIL ~X-50 of Degussa AG). To this mixture are then adcled 86 g of tris-(6-isocyanatohexyl)-biuret, and a further 88 g of the siliea filler is mixed in homogeneously. The material is 30 eompletely homogenized on a three-roll mill.
Curing takes pl.ace in a heating oven at 50C 'cor 100 hours~ The hard plastic is broken, mil.led in a ceramie bal,l ., ~
mill and the larger partieles are removed from it using a sereen with a mesh width oF 90 /um.
~, 35 '~ The sol.ubility is cleterminecd in a Soxlllot apparatus for 24 hours with acetone as 0.9~. Accordillg to the DSC
method, there is a double bond content of 1.6 mmol.e/g oc organic substance.
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41 g of trimethylol propane monoglycidyl methacrylate adduct and 40 g of the Si02 (AEROSIL OX-50) used in Example 1 are mixed in a mixer. After adding 60 g of tris-~6-isocyanatohexyl)-5 biuret, a further 70 g of Si02 is admixed, and the resultingpaste is homogenized on the three-roll mill. After storing for lg0 hours at ambient temperature, the resulting plastic is broken, milled in a ceramic ball mill and passed through a 90 ~m screen.
The solubility is 2.0%. DSC reveals 1.4 mmole of double bonds per g of organic substance.
; EXAMPLE 3 Wor~ing takes place as in Example 2. In place of trimethylol propane monoglycidyl methacrylate, use is made of 50 : 15 g of trimethylol propane diglycidyl methacrylate, to which are added 70 g of tris-(6-isocyanatohexyl)-biuret and 118 g of Si02 : - according to Example 1 (AEROSIL OX--50) silanized with 10 g of ~-methacryloxypropyltrimethoxy-silane.
` The solubility is 1.1%, and the double bond content is 20 1.7 mmole/g of organic substance.

~; As a modification of Example 2, 31 g of 2,3-di-hydroxypropyl methacrylate, 69 g of tris-(6-isocyanatohexyl)-biuret and 100 g of silanized filler according to Example 1 (AEROSIL OX-50) are 25 homogenized on the three-roll mill.
The solubility is 0.8%, and the double bond content is .. .
1.9 mmole/g of organic substance.
. ~ EXAMPLE 5 ; ~ As a modification of Example 2, 75 g of succinic acid 30 diglycidyl methacrylate, 69 g of tris-(6-isocyanatohexyl)-biuret and 144 g of silanized silica (AEROSIL OX-50) are homogenized on the three-roll mill.
The solubility is 2.0,% and the double bond content is ' 1 ~ 2.0 mmole/g of organic substance.
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:., , All three components, namely 89 g of tris-(6-isocyanatohexyl)-biuret, 121 g of silanized silica (AEROSIL* OX-50) and a mixture of 19 g of hydroxyethyl methacrylate and 14 ~ of trimethylol propane are heated to 50C
and subsequently kneaded to a paste. Complete homogenization ' then takes place on the three-roll mill together with a solution of 1 g of hydroxyethyl methacrylate and 0.12 g of dibutyl tin diacetate.
-~ 10 The solubility is 1.7%, and the double bond content is : 1.7 mmole/g of organic substance.

91 g of bisphenol A-glycidyl methacrylate and 29 g of tris-(6-isocyanatohexyl)-biuret are added to the laboratory universal kneader LUK* 025 of Werner & Pfeidler (Fed. Republic of Germany) and 130 g of silanized silica (AEROSIL*OX-50) is kneaded in. The resulting paste is allowed to harden for 80 hours at 60C, the plastic is broken and milled in a ceramic ball mill for 30 hours. After screening through a 90 ~m screen, a powder with ~; 20 an average particle diameter of 31 ~m is obtained.
The solubility in acetone is 1.8%, and the double bond content (by means of DSC) is 2.6 mmole/g of organic substance.
EXAMP~E 8 As a modification of Example 7 only 40% instead of 65% of silica is used. The bisphenol A-glycidyl methacrylate to tris-(6-isocyanatohexyl)-biuret ratio remains the same.
~;~ - The solubility in acetone is 2.3%, and the double bond content is 2-2 mmole/g of organic substance.
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59 g of bisphenol A glycidyl methacrylate and 41 g of tris-~6-isocyanatohexyl)-biuret are homogeneously mixed by stirring in ~; a vessel. After hardening time of 70 hours at 50C, the filler is ground and passed through a 90~m screen.
Particle diameter size is on average 42.5 ~m. The 35 solubility is 2.0g6, and the double bond content is 1.7 mmole/g.
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,9~ 38 i - 12 -EXAMæLE 10 As a modification to Example 7, 37 g of silanized silica j with an average primary particle diameter size of 16 nm I and a BET surface of 110 ~/- 20 m2/g (AEROSIL* R972 of Nippon ' 5 Aerosil Co. Ltd.) are used. The double bond content is 2.1 ~ mmole/g of organic substance.
; ~ EXAMPLE 11 100 g of trimethylol propane triglycidyl methacrylate, 172 g ; of 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate and lO 181 g of silanized silica are homogeneously mixed in a vessel, as in Example 1. After adding 0.1% of dibutyl tin ; diacetate, the filler hardens completely within 70 hours, after which it is ground and screened. The double bond content is 1.5 mmole/g~of organic substance.
; 15 EXAMPLE 12 (Comparison Example - Radically Polymerized Eiller~
-` An equal weight quantity of silanized silica according to Example 1 in a kneader is incorporated into a solution of 79% by weight of 2,2,4-trimethylhexamethylene-bis-(2-20 carbamoyloxyethyl)-dimethacrylate, 20% by weight of decanediol-1,10-dimethacrylate and 2% by weight of benzoyl peroxide. The material is polymerized at 120C for 24 hours. The polymer is subsequently crushed and ground in a ball mill for 60 hours. The ;~ average particle diameter size of the filler obtained after 25 screening is between 30 ~m and 40 ~m. The double bond content ~; is < 0.5 mmole/g of organic substance, and the solubility is 3.1%
by weight.
ExAMoeLE 13 52.6 g of a monomer mixture of the following composition are placed in the laboratory kneader:
84.21% 2,2,4-trimethyl hexamethylene-bis-(2-carbamoyloxyethyl)-dimethacrylate (~-3) ~; lS.00% decane dioldimethacrylate (D
0.28% DL-camphor quinone 0.49% cyanoethyl methylaniline (CFI~) ; ;~ 0.03% 2,6-di-tert.-butyl-p-cresol (BHT) ':
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;l - 13 -122.)3 g of the filler according to Example 7 and 24.4 g oE silanized silica (AE~OSIL OX-5()) are kneaded therewith, so that a paste useful as dental filling com-position is obtained.
The paste is filled into a metal mould (dimensions:
height 4 mm, width 4 mm and length 20 mm) and it is exposed for 90 seconds with a light polymeri7iation apparatus. When removed from the mold, the test pieces are ground with No.
1000 abrasive paper, polished with alumina and stored for one week in water at ambient temperature.
The test pieces were subjected to a fatigue/wear test. The testing apparatus used was a Wolpert/Amsler material testing machine type 2TZM 771 20 KN.
During the test a steel bal] with a diameter of 2 mm lS is pressed on to the surface which is plane-parallel to the bearing surface and is then relieved again. The force range for such a cycle is between 300 N when loading and 50 N when ~j~ the load is removed. The speed is 100 mm/min. The number oE
;; cycles is determined after which the material remains un-harmed, i.e. no cracks appear around the impression edge, which are visible in the case of 100 x magnification with an optical microscope.
Using the aforementioned material, cracks only occur after 5000 cycles. The crack pattern exhibits a linear crack configuration, which reveals high bond integrity between the filler grains and the matrix owing to the fact that breakage occurs through and not along the grains. This homogeneous breakage behavior confirms that the filler produced according to the invention contains sufEicient double bonds in order to form a firm bond of high integrity with the matrix.
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and not 84.21% of RM-3, the remainder being replaced by bisphenol A-glycidyl methacrylate (bis-GMA). The paste has the following composition:
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24.36% monomer mixture ` 33.30~ filler according to Example 7 42.34% silanized silica (AEROSIL OX-50).
The test pieces ~ithstood 2000 cycles in the wear/atigue test, and the crack pattern is comparable with that 10 Of Example 13.
` ExAMoeLE 15 A further paste is prepared in accordance with Example 13 and having the following composition:
27.5% monomer mixture according to Example 14 27.5% silanized silicon dioxide (AEROSI~ OX-50) ~` 45.0% filler according to ~xample 3.
~ The first cracks occur after 100 cycles, exhibiting a ; linear crack configuration through the filler grains.
EXAMoeLE 16 (Comparison Example) - 20 The paste is produced in the same way as in Example 14.
; However, in place of the filler of Example 7, the filler of comparison Example 12 is used.
In the fatigue test, cracks occur after only 10 cycles. The cracks mainly run along the phase boundary between the filler and 25 the matrix, so that jagged crack lines occur. This crack pattern clearly shows the inadequate, poor bond integrity between the filler and matrix.
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EX~MPLE 17 The following pastes are prepared:
Activator PasteBase Paste bis-GMA 23.96% 29.09%
triethyleneglycol dimethacrylate 10.0% 10.0%
benzoyl peroxide ~BPO 50% paste) 0.8% _.__ N,N-diethanol-p-toluidine -.-- 0-7%
2,6-di-tert.-butyl-p-cresol 0.04% 0.01%
conventiona~ W-stabilizers and optical brighteners 0.2% 0.2%
silicon dioxide ~AEROSIL OX-50) 19.9% 19.9%
filler from Example 2 40.0% 40.0%
coloring pigments and titanium dioxide __ _ 0.1P6 _ 0.1%
100.00% 100.00%
The solid substances ~BPO, di-tert.-butyl-p-cresol, N,N-diethanol-p-toluidinene, W-stabilizers and optical brighteners) are completely dissolved in the particular monomer mixture. The -~ ~ pastes are prepared in a kneader, the fillers ~silanized silicon 20 dioxide, filler from Example 2) and the coloring pigments are homogeneously incorporated into the corresponding monomer solution.
The thus prepared pastes have a pleasant consistency and can ~; be easily mixed. The processing time as from the start of mixing 25 is 2 to 3 minutes.
The material is polymerized for 1 hour at 37C and otherwise the test is carried out as in Example 14.
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Cracks occur after 1000 loading cycles and run linearly around the impression point, which shows a high 30 bond integrity between filler and matrix.

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2,2,4-trimethylhexamethylene-bis-(2-carbamoyloxyethyl)- dimethacrylate 27.95%
. 5 butanediol-1,4-dimethacrylate 5.00%
dibenzoyl peroxide 2.00%
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filler from Example 154.80~
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. , The paste is prepared as described in Example 17. A solid, ~: readily processable material is obtained, which is suitable for the production of dentures, as an inlay material, or as a veneering plastic for crown and bridge work.
The polymerization of the test pieces for the fatigue/wear :: test is carried out in a pressure polymerization apparatus ~ (Ivoma~) at 120C, 6 bar and 10 min. Testing takes plac~ as in ~Example 13. The first linear cracks occur after 100 ..
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. An organic filler in the form of a solid powder having been prepared by non-radical polymerisation and comprising reactive double bonds which are not extractable with solvents in an amount (as determined by the DSC method) of at least 0.5 mmoles/g of the organic filler material.
2. The filler according to claim 1, wherein the polymer comprises the reaction product of active hydroxy group-contain-ing (meth)acrylates with isocyanates in an OH-group to NCO-group ratio of approximately 1:1, at least one of the monomers being at least tri-functional.
3. The filler according to claim 2, wherein said isocyanate is a triisocyanate.
4. The filler according to claim 2, wherein said (meth)-acrylates comprise (meth)acrylates of a triol or polyol, and said isocyanate is a diisocyanate.
5. The filler according to claim 2, wherein said polymer is made using a stoichiometric deficiency of active hydroxy group-containing (meth)acrylates and is cross-linked by means comprising water and aliphatic polyols and mixtures thereof.
6. The filler according to claim 2, wherein said isocyanate is an aliphatic isocyanate.
7. The filler according to claim 1, wherein said polymer comprises the reaction product of active hydroxy groups containing (meth)acrylates with a reactant selected from the group consisting of trioxans and epoxy resins in a substantially stoichiometric ratio.
8. The filler according to claim 1, wherein said polymer contains inert fillers comprising inorganic fillers and organic fillers containing no reactive double bonds.
9. The filler according to claim 8, wherein said fillers are incorporated into the monomer mixture prior to polymeri-sation thereof, said fillers constitute from 0% to about 80% of the total weight of said filler, said stoichiometric ratio is determined to take into account the proportion of reactive surface groups present on said fillers, and said organic condensation polymer is covalently bonded to the surface of said filler.
10. The filler according to claim 1, wherein the average size of the diameter of said filler is from about 0.5 /um to about 100 /um.
11. A solid particulate reinforcing filler for polymerizable compositions comprising as binder monomers having ethylenically unsaturated groups which are susceptible to radical polymerisation, said filler comprising:
A. a solid particulate copolymer reaction product, said reaction product having pendant unsaturated groups, B. said organic reaction product being selected from the group consisting of polyurethanes, epoxides, polyesters, polyimides and polyureas;
C. said pendant unsaturated groups comprising acrylic, vinyl, vinylidene and conjugated diene groups;
D. said reaction product containing at least 0.5 mmoles of available free reactive pendant double bonds per gram of said reaction product (as determined by the DSC method);
E. said double bonds being not extractable with a solvent;
F. said available double bonds being reactive in a radical polymerization reaction with said binder.
12. The filler according to claim 11, wherein the reaction product is the product of active hydroxy group-containing (meth)acrylates with isocyanates in an OH-group to NCO-group ratio of approximately 1:1.
13. The filler according to claim 11, wherein said particulate solid organic polymer comprises the reaction product of active hydroxy group-containing (meth)acrylates with a reactant selected from the group consisting of tri-oxans and epoxy resins in a substantially stoichiometric ratio.
14. The filler according to claim 11, wherein said organic reaction product contains fillers comprising inorganic fillers and non-reactive organic fillers.
15. The filler according to claim 14, wherein said fillers are incorporated into said condensation polymer product prior to polymerization thereof, said fillers constitute from 0% to about 80% of the total weight of said filler, and said stoichiometric ratio is determined taking into account the proportion of surface groups present on said fillers.
16. The filler according to claim 11, wherein the average size of the diameter of said filler is from about 0.5 /um to about 100 /um.
17. A method of preparing filled polymeric dental materials comprising:
A. preparing a solid particulate reinforcing filler by non-radical polymerisation from monomers at least one of which comprises ethylenically unsaturated groups, said filler thereby comprising reactive double bonds which are not extractable with solvents in an amount (as determined by the DSC method) of at least 0.5 mmoles/g of the organic filler material;
B. adding said filler to polymerizable compositions containing binder monomers with radically polymerizable, ethylenically unsaturated groups; and C. polymerizing the resulting composition.
18. The method according to claim 17, wherein said organic polymer contains inert fillers comprising inorganic fillers and organic fillers.
19. The method according to claim 18, wherein said inert fillers are incorporated into said organic polymer prior to polymerization thereof, said inert fillers constitute from o%
to about 80% of the total weight of said filler, and the stoichiometric ratio of the monomers is determined taking into account the proportion of surface groups present on said inert fillers.
20. The method according to claim 17 wherein the average size of the diameter of said filler is from about 0.5 /um to about 100 /um.