AU612986B2 - Reactive organic filler and the use thereof - Google Patents

Description

fit~-;~ 612986 COMMONWEALTH OF AUSTRALIA Patents Act 1952 C O M P L E T E S P E.C I F CA T I O N

(ORIGINAL)

Application Number Lodged Complete Specification Lodged Accepted Published Priority Related Art :23 September 1986 Name of Applicant Address of Applicant :IVOCLAR AG :FL-9494 Schaan/ Liechtenstein, ;2~in. P Ai- nl 'n I e F twmfi- Actual Inventor/s :Dr. Volker M. Rheinberger Thomas Buchel Address for Service F.B. RICE CO., Patent Attorneys, 28A Montague Street, Balmain N.S.W. 2041 S. aComplete Specification for the invention entitled: REACTIVE ORGANIC FILLER AND THE USE THEREOF The following statement is a ful? description of this invention including the bpst method of performing it known to us:- -1 S- la BACKGROUND OF THE INVENTION The invention relates to the subject matter of claims 1 to 10. Such 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 preservative 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 of 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 material, 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 0O rather poorly with organic matrices, and the mechanical characteristics of the resulting polymers are not satisfactory. To improve its bond with organic matrices, inorganic fillers may be surface-treated with a silane. Nevertheless, even such silanized inorganic fillers do not satisfy all of the set requirements.

The use of organic bead polymers as fillers is also known. Organic bead polymers may contain inorganic fillers.

Such bead polymers. are preferably produced from the same monomers as are used as binders in order to achieve an optimum S0 level of compatibility in all respects. For example, bead polymers of polymethylmethacrylate or other radically polymerized acrylates are known, cf. German Offenlegungsschrift 28 yr -2- 918 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 incorporating fillers with an average diameter of more than 1 /um 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 1 0 accelerate wear to the matrix polymer. These problems are 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 0 0 filler and matrix is too weak. It has not hitherto proved o possible to modify a filler in such a way that bonding with the completely polymerized matrix is satisfactory in all respects. All major modifications to the composition or 0 production of the filler simultaneously led to significant changes in the physical characteristics such that use as a solid filler was not possible.

OBJECTS OF THE INVENTION 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 cf the present invention is to provide an organic filler which provides a firm bond between the filler and matrix.

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I 3- Still another object 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.

SUMMARY OF THE INVENTION i C) The present invention therefore relates to a reactive organic filler in the form of a solid powder, which is characterized in that it is prepared by a non-radical polymerization reaction, and comprises at least 0.5 mmole of reactive double bonds per gram of filler (determined by means of the DSC method) which are not extractable with solvents.

When using the present filler in polymerizable compositions containing compounds with ethylenically unsaturated groups which can undergo a radical polymerisation, the relatively high content of reactive double bonds in the filler L.C) 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 cycles. Examination of crack patterns usiiig electron microscopes (REM) reveals that in conventional materials the cracks 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.

0 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 ,1, k Is- I W op -4the 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 fact that the S 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 unreacted monomers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reactive double bonds contained in the organic filler of the present invention can be quantitatively determined by means of the DSC method (Differential Scanning Calorimetry). For this purpose a precisely weighed sample of L0 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 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 1,1 this sense and is stated in mmoles/g of polymer or organic filler.

I I 4a The filler according to the present invention is made by non-radical polymerisation of organic monomers with hydroxy groups containing (meth)acrylates at least one of which has pendant unsaturation such as acrylic, vinyl, vinylidene and conjugated diene groups. Examples of the organic polymer materials include polyurethanes, epoxides, polyesters, polyimides and polyureas.

L- L C-U i LU~~h ~yhorygmups CC=' n- Ck m C% CL- C made by non-radical polymerisationjof organ nomers at least one of which has pendant un ion such as acrylic, vinyl, vinylidene and g ed diene groups. Examples of the organic materials include polyurethanes, epoxides, Preferably the filler is prepared by reacting hydroxy group-containing acrylates or methacrylates (hereinafter for short "(meth)acrylates") with isocyanates in an 1 OH-group to NCO-group ratio of 1:1. At least one of the starting compounds is trifunctional or higher, in order to achieve the degree of cross-linking adequate for obtaininT a solid powder. According to a particularly favourable ambodiment, use is made of a triisocyanate or polyisocyanate, it then also being possible to use a stoichiometric deficiency of hydroxy(meth)acrylate and to achieve the necessary cross-linking 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 z a (meth)acrylate having three or more hydroxy groups with a diisocyanate.

Examples of a suitable hydroxy functional (meth)acrylates are hydroxyethylmethacrylate (HEMA), polyethyleneglycolmethacrylate, 2-hydroxypropylmethacrylate, 2,3-dihydroxypropylmethacrylate, pentaerythritol-triacrylate, as well as reaction products of glycidyl(meth)acrylate with polyols, e.g. trimethylolpropane, or polycarboxylic acids, e.g. succinic acid.

Particular preference is given to bis-GMA (bisphenol A-glycidylmethacrylate).

Preferred isocyanates are aliphatic compounds, such as 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate, trimethylhexamethylene diisocyanate and triisocyanate tris-(6isocyanatohexyl)-biuret (Desmodur N 100 of Bayer AG).

(B P

N-

__LI f- _Li i .i U T -W 6 The reaction between the hydroxy(meth)acrylates and isocyanates can be performed under mild conditions. The maximum reaction temperature is approx. 150 C and preferably approx. 10 C to 60 C. A catalyst can be added for acceleration purposes, and inter alia, tertiary amines and metallo-organic salts are suitable.

The reaction of the hydroxy functional (meth)acrylates is known per se. For example, it is used for the preparation of prepolymers, which can be used as binders in i 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 BF 3 as the catalyst. Similar results are obtained through reacting glycidyl(meth)acrylate with trioxan and epoxides with epoxy c_ (meth)acrylates. Further examles are the reaction of hydroxy 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 ansaturated 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 C diameter of the particles after grinding the filler is in the range between 0.5 /um to 100 /um, and particular preference is given to an average diameter of approximately 10 /um to /um.

L

7 According to an advantageous embodiment of the invention, an inorganic and/or non-reactive organic filler is incorporated into the reactive 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 especially approximately 40% to 70% by weight are particularly 0 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, aluminum sulphate, calcium sulphate or lithopone. Molybdenum sulfide, graphite, carbon black, flyash, potassium titanate and fibres, 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 0 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.

For 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 inorgunic filler. A particularly preferred silane is y-methacryloxypropyltrimethoxysilane. Other suitable silanes have hydroxy, amino and epoxy groups.

LI r Y ii I- 8- When producing the inventive fillers, it is important to take account of the fact that the optionally added inorganic filler 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, i U acrylic and methacrylic polymers, e.g. polymethylmethacrylate and polyurethanes. These polymers are brought to the desired particle size by grinding.

The present invention also relates to the use of the above-described reactive organic fillers in polymerizable compositions containing binder compounds with radically polymerizable, ethylenically unsaturated groups. Suitable vinyl monomers for such compositions are, inter alia, 4-methacryloxyethyltrimellitic acid and its anhydride; epoxy acrylates of the bisphenol type and their oligomers; urethane dimethacrylate; methacrylate; methyl, ethyl and butyl methacrylate; polyethylene glycol dimethacrylate; 2,2-bis-(p-2'-hydroxy- 3 '-methacryloxypropoxyphenyl)-propane; 2,2-bis-(4-methacryloxypolyethoxyphenyl)-propane; acrylonitrile; vinyl acetate; 2-cyanoacrylic acid; styrene; divinylbenzene and mixtures of the aforementioned monomers. The binders can also be vinyl group containing prepolymers or polymers.

*i The fillers 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 polyfunctional methacrylates, which can be used alone or in mixed form.

J

9 9 Examples of these compounds are methyl, isobutyl and cyclohexyl methacrylate; triethylene glycol dimethacrylate; diethyleneglycol dimethacrylate; ethylene glycol dimethacrylate; polyethylene glycol dimethacrylate; butane-diol dimethacrylate; hexanediol dimethacrylate; decane-diol dimethacrylate; dodecanediol dimethacrylate; bisphenol-A-dimethacrylate; trimethylol propane trimethacrylate; as well as bis-GMA and the reaction products of isocyanates, particularly of diisocyanates and/or triisocyanates and OH-group containing methacrylates.

i Examples of these are the reaction products of 1 mole of hexamethylenediisocyanate with 2 moles of 2-hydroxyethyl methacrylate; 1 mole of tris-(6-isocyanatohexyl)-biuret and 3 moles of hydroxyethyl methacrylate; as well as 1 mole of trimethyl hexamethylenediisocyanate and 2 moles of hydroxyethylmethacrylate which can be called urethane dimethacrylate for short. The proportion of these mainly long-chain compounds in the dental material is between 10 and 50% by weight.

The following examples are intended to serve only as further illustrations of the present invention and are not c. intended to restrict the scope of the invention.

EXAMPLE 1 A solution of 19 g of hydroxyethylmethacrylate, 2.7 g of water and 0.01 g. of dibutyl tin diacetate is placed in a mortar and mixed with 20 g silanized fumed silica with an averaqe primary particle diameter of 40 nm (AEROSIL OX-50 of Degussa AG). To this mixture are then added 86 g of tris-(6-isocyanatohexyl)-biuret, and a further 88 g of the silica filler is mixed in homogeneously. The material is completely homogenized on a three-roll mill.

Curing takes place in a heating oven at 500C for 100 hours. The hard plastic is broken, milled in a ceramic ball mill and the larger particles are removed from it using a screen with a mesh width of 90 /um.

The solubility is determined in a Soxhlet apparatus for 24 hours with acetone as According to the DSC method, there is a double bond content of 1.6 mmole/g of organic substance.

-1 10 EXAMPLE 2 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)biuret, a further 70 g of Si02 is admixed, and the resulting paste is homogenized on the three-roll mill. After storing for 140 hours at ambient temperature, the resulting plastic is broken, milled in a ceramic ball mill and passed through a 90 pm screen.

iL The solubility is DSC reveals 1.4 mmole of double bonds per g of organic substance.

EXAMPLE 3 Working takes place as in Example 2. In place of trimethylol propane monoglycidyl methacrylate, use is made of 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 y-methacryloxypropyltrimethoxy-silane.

The solubility is and the double bond content is U 1.7 mmole/g of organic substance.

EXAMPLE 4 As a modification of Example 2, 31 g of 2,3-di-hydrcxypropyl methacrylate, 69 g of tris-(6-isocyanatohexyl)-biuret and 100 g of silanized filler according to Example 1 (AEROSIL OX-50) are homogenized on the three-roll mill.

The solubility is and the double bond content is 1.9 mmole/g of organic substance.

EXAMPLE As a modification of Example 2, 75 g of succinic acid 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 and the double bond content is mmole/g of organic substance.

t .7 11 EXAMPLE 6 All three components, namely 89 g of tris-(6isocyanatohexyl)-biuret, 121 g of silanized silica (AEROSIL OX-50) and a mixture of 19 g of hydroxyethyl methacrylate and 14 g of trimethylol propane are heated to 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.

)5 i The solubility is and the double bond content is 1.7 mmole/g of organic substance.

EXAMPLE 7 41 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 the plastic is broken and milled in a ceramic ball mill for hours. After screening through a 90 p~ screen, a powder with an average particle diameter of 31 im is obtained.

The solubility in acetone is and the double bond content (by means of DSC) is 2.6 nmnole/g of organic substance.

EXAMPLE 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 and the double bond content is 2.2 mmole/g of organic substance.

EXAMPLE 9 59 g of bisphenol A glvcidyl 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 90m screen.

Particle diameter size is on average 42,5 ptm The solubility is and the doub bond content is 1.7 mmole/g.

12 EXAMPLE As a modification to Example 7, 37 g of silanized silica with an average primary particle diameter size of 16 nm and a BET surface of 110 20 m 2 /g (AEROSIL R972 of Nippon 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-trimethylcyclohexylisocyana-e and 0 181 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 mmole/g of organic substance.

EXAMPLE 12 (Comparison Example Radically Polymerized Filler) 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-(2carbamoyloxyethyl)-dimethacrylate, 20% by weight of decanediol- 1,10-dimethacrylate and 2% by weight of benzoyl peroxide. The material is polymerized at 120 0 C 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 screening is between 30 LTm and 40 pm. The double bond content is 0.5 mmole/g of organic substance, and the solubility is 3.1% by weight.

EXAMPLE 13 52.6 g of a mcnomer mixture of the following composition Sare placed in the laboratory kneader: 84.21! 2,2,4-trimethyl hexamethylene-bis-(2carbamoyloxyethyl)-dimethacrylate (RM-3) 15.00% decane dioldimethacrylate (03MA) 0.28% DL-camphor quinone 0.49% cyanoethyl methylaniline (CEMA) 0.03% 2,6-di-tert.-butyl-p-cresol (:HT) I_ u u L~ 13 122.8 g of the filler according to Example 7 and 24.4 g of silanized silica (AEROSIL OX-50) are kneaded therewith, so that a paste useful as dental filling composition 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 polymerization apparatus. When removed from the mold, the test pieces are ground with No.

1000 abrasive paper, polished with alumina and stored for one 0 week in water at ambient temperature.

The test pieces were subjected to a !atigue/wear test. The testing apparatus used was a Wolpert/Amsler material testing machine type 2TZM 771 20 KN.

During the test a steel ball with a diameter of 2 mm 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 the load is removed. The speed is 100 mm/min. The number of cycles is determined after which the material remains un- .O 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 sufficient double bonds in order to form a firm bond of high integrity with the matrix.

1 1 14 EXAMPLE 14 Diverging from Example 13, the monomer mixture contains and not 84.21% of RM-3, the remainder being replaced by bisphenol A-glycidyl methacrylate (bis-GMA). The paste has the following composition: 24.36% monomer mixture 33.30% filler according to Example 7 42.34% silanized silica (AEROSIL The test pieces withstood 2000 cycles in the 0 wear/fatigue test, and the crack pattern is comparable with that of Example 13.

EXAMPLE 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 (AEROSIL 45.0% filler according to Example 3.

The first cracks occur after 100 cycles, exhibiting a linear crack configuration through the filler grains.

0 EXAMPLE 16 (Comparison Example) 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 the matrix, so that jagged crack lines occur. This crack pattern clearly shows the inadequate, poor bond integrity between the filler and matrix.

I -1 -AL. 1W I I 15 EXAMPLE 17 The following pastes are prepared: Activator Paste Base Paste bis-GMA 28.96% 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% 1 conventional UV-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 0.1% 0.1% 100.00% 100.00% The solid substances (BPO, di-tert.-butyl-p-cresol, N,Ndiethanol-p-toluidinene, UV-stabilizers and optical brighteners) are completely dissolved in the particular monomer mixture. The pastes are prepared in a kneader, the fillers (silanized silicon 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 is 2 to 3 minutes.

The material is polymerized for 1 hour at 37 0 C and otherwise.

the test is carried out as in Example 14.

Cracks occur after 1000 loading cycles and run linearly ,C/0 around the impression point, which shows a high bond integrity between filler and matrix.

C1 1~ C- c-Y I i -L.r -16 EXAMPLE 18 The following paste is prepared: 2,2,4-trimethylhexamethylene-bis- (2-carbamoyloxyethyl)- dimethacrylate 27.95% butanediol-1,4-dimethacrylate 5.00% dibenzoyl peroxide 2.00% di-tert.-butyl-p-cresol 0.05% silicon dioxide (AEROSIL R972) 10.00% filler from Example 1 54.80% coloring pigments 0.20% 100.00% 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 (Ivomat) at 120'C, 6 bar and 10 min. Testing takes place as in SExample 13. The first linear cracks occur after 100 c-O cycles.

Claims (15)

1. A reactive organic filler in the form of a solid powder having been prepared by non-radical polymerisation of organic monomers comprising hydroxy groups containing (meth)acrylates with isocyanates or trioxanes and/or epoxy resins, 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 o i group-containing (meth)acrylates with isocyanates in an o 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. 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. S6. 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 trioxanes and epoxy resins in a stoichiometric ratio.

8. The filler according to claim 1, wherein said polymer contains inert fillers comprising inorganic fillers and non-reactive organic fillers. i, i 1~ i r I- -r r i I 18

9. The filler according to claim 8, wherein said fillers are incorporated into the monomer mixture prior to polymerisation thereof, said fillers constitute from 0% to 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. The filler according to claim 1, wherein the average size of the diameter of said filler is from 0.5/um to 100/um.

11. A reactive particulate reinforcing filler for polymerisable compositions comprising binder monomers with ethylenically unsaturated groups which are susceptible to radical polymerisation, said filler comprising:- a) a solid particulate copolymer organic reaction product, wherein the reaction product is the product of non-radical polymerisation of hydroxy groups containing (meth)acrylates with isocyanates or trioxanes and/or epoxides resins, and said reaction product having pendant unsaturated groups, b) said pendant unsaturated groups comprising acrylic, vinyl, vinylidene and conjugated diene groups; c) said reaction product comprising available reactive pendant double bonds which are not extractable with solvents in an amount, as determined by the DSG method, of at least 0.5 millimoles/g of said reaction product; d) 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. 19

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 trioxans and epoxy resins in a stoichiometric ratio.

14. The filler according to claim 11, wherein said organic reaction product contains fillers comprising inorganic fillers and non-reactive organic fillers. 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 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 0.5/um to 100/um.

17. A method of preparing filled polymeric dental product comprising: A. preparing a reactive solid particulate reinforcing filler by non-radical polymerization of hydroxy groups containing (meth)acrylates with isocyanates or trioxanes and/or epoxy resins, 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. _r i~c>;B Ah y -j I 20

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 0% to 80% for 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. The method according to claim 17 wherein the average size of the diameter of said filler is from 0.5/um to 100/um. DATED this 7 day of May 1991 IVOCLAR AG Patent Attorneys for the Applicant: F.B. RICE CO. i