Light-polymerizable dental compositions comprise a polymerizable monomer, a light- sensitive polymerization initiator, and optionally further components such as an organic or inorganic filler or an organic or inorganic pigment. It is known to use a stabilizer for preventing a composition containing polymerizable acrylates and/or methacrylates from spontaneous polymerization. 2,6-Di-tert-butyl-4-cresol (BHT), hydroquinone or hydroquinonemonomethylether (HQME) are known as free radical savengers for dental compositions.

Light curing polymerisable dental compositions are usually applied in the presence of substantial irradiation of the environment particularily radiation generated by operating lamps. In order to insure suffciently long working times, international standards require that a dental dental composite remains stable under an illumination of 10.000 lux for 60 seconds (ISO 4049). Dental pit and fissure sealants are required to remain stable under an illumination of 8000 lux for 25 seconds (ISO 6874) and light activated water- based cements are required to remain stable under an illumination of 8000 lux for 30 seconds (ISO 99917-2).

From SU 3,34845 it is known that 2,2,6,6-tetramethylpiperidinyl-1-oxide (TEMPO) may be used to inhibit the polymerisation of acrylate. Moreover, it is known to use galvinoxyl radicals, hydroxy-TEMPO and 2,2-diphenyl-1-picrylhydrazyl radicals as anaerobic polymerization inhibitors (US 5,468,789).

The effect of TEMPO as polymerization inhibitor in polymerizable dental compositions and its influence on the depth of curing is known for light curing restorative materials from W. D. Cook, P. M. Standish, Austr. Dent. J., 28 (1983) 307. Moreover, US 5,847,025 discloses the use of TEMPO and other stable radiclas such as 2,2-Diphenyl- 1-picrylhydrazyl radicals, galvinoxyl radicals and triphenylmethyl radicals for reducing the light sensitivity of a dental light-curing composite material.

Although many attempts have been made to lengthen the working times under the conditions of a dental practice by choosing a combination of an initiator and an inhibitor, only minor reductions of light sensitivity are obtained without increasing the working times.

Therefore, it is the problem of the present invention to provide a dental composition, which has a sufficiently long working time while still providing an acceptable light sensitivity of the composition and whereby the mechanical properties and the color shading of the dental material are not deteriorated.

This problem is solved according to claim 1 with a light-polymerizable dental composition comprising (i) a polymerizable monomer component, (ii) a light-sensitive polymerization initiator, (iii) an inhibitor, (iv) optionally a filler and/or pigment, and (v) optionally a solvent whereby the inhibitor is a substituted fullerene compound present in an amount suitable for improving light stability of the dental composition.

It was found that when a substituted fullerene such as 1,2- (dimethoxymethano)- fullerene is added to a dental composition, surprisingly the stability of the composition under an irradiation with 10,000 lux is about 90 seconds. This is more than twice as much as the stability observed with a comparable composition that only comprises BHT as stabilizer which shows a stability under an irradiation with 10,000 lux of only 40 seconds. At the same time, the mechanical properties and the storage stability of the dental composition remain excellent in the presence of the inhibitor of the present invention.

The dental composition of the present invention comprises an inhibitor which is a substituted fullerene compound. The inhibitor may contain one or more substituted fullerene compounds. The substituted fullerene compoundd is preferably soluble in the composition, in particular in the polymerisable monomer. Preferably, the inhibitor is selected from the group of substituted C60, C70, C72, C76, C78, or C84 fullerenes. A substituted fullerene compound according to the invention is derived from an unsubstituted fullerene compound by addition or insertion of substituents to the fullerene cage. The substituents added or inserted to the fulleren cage may be further modified in order to provide the desired substituted fullerene compound used in the dental compositions of the invention. The substituents are preferably able to render the fullerene compound soluble in the composition, in particular in the polymerisable monomer. Moreover, the substituents preferably contribute to the electronic properties of the inhibitor as a radical scavenger. Finally, the substituents preferably are able to modify the fullerene cage such that any chromophores absorbing in the range of visible light are destroyed.

One or more substituents may be present on the fullerene cage whereby it is preferred that at least two substituents are present. In case at least two substituents are present on the fullerene cage, the substituents may be the same or different. The substituents of the substituted fullerenes are preferably selected from the group of substituted or unsubstituted C, _2o-alkyl groups, C1 20-alkoxy groups, C, 20-alkyl-C, 20-alkoxy groups, Ci.

20-alkyl thio groups, C, _2o-alkylthio-C, _2o-alkyl groups, C, 20alkylamino groups, C _po alkoxy-poly-C, 6-alkyleneoxy groups or C1 20-aryl groups. In case the substituents of the fullerene cage are substituted, such substituents may be selected form the group of substituents given as substituents for the fullerene cage. Moreover, such substituents may be selected from the group consisting of hydroxyl groups, amino groups, thiol groups. In a specific embodiment, one or more substituents of the fullerene cage are substitued with a polymerizable group. The polymerizable group may be selected from acryloyl, C1 20-alkylacryloyl, or C, 20-alkenyl groups.

The substituted fullerenes are added to the dental composition in an amount ranging from 0.001 to 3.0% by weight, preferably in an amount of from 0.01 to 1.0% by weight and most preferably in an amount of from 0.01 to 0.2% by weight.

The dental composition of the present invention comprises a light-polymerizable monomer component. The light-polymerizable monomer component contains one or more monomer compounds. In case the monomer component contains two or more monomer compounds, the monomer compounds may differ with regard to the molecular weight and/or the number of polymerizable moieties. In a preferred embodiment, a macromonomer and a reactive diluent are used in the polymerizable monomer component.

The monomer compound to be used in the monomer component of the dental composition of the present invention preferably has at least one polymerizable group and is a mono-or polyfunctional (meth) acrylate or a macromonomer. Preferable monomers are 2,2-Bis- [p- (2-hydroxy-3-methacryloyloxypropoxy)-phenyl]-propane, 7, 7,9-trimethyl-4, 13-dioxo-3, 14-dioxa-5, 12-diazahexadecan-1, 16-diol methacrylate, dipentaerthrytrolpentamethacrylate monophosphate, a, co-methacryloyl terminated epoxide-amine macromonomers, a, (o-methacryloyl terminated epoxidecarboxylic acid macromonomers, a,-methacryloyl terminated epoxide-phenol macromonomers. Specifically, reference is made to the macromonomers disclosed in U. S. Patent application serial number 08/359,217 filed December 19,1994.

Reactive diluents are mono (meth) acrylates and polyfunctional (meth) acrylates, such as polyalkylenoxide di- (meth) acrylates or poly (meth) acrylates, urethane di (meth) acrylates or poly (meth) acrylates, vinyl-, vinylen-or vinyliden-, acrylate-or methacrylate substituted spiroorthoesters, spiroorthocarbonates or bicycloorthoesters. Preferred reactive diluents are diethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, 3, (4), 8, (9) dimethacryloyloxymethyltricyclodecane, dioxolan bismethacrylate, glycerol trimethacrylate, and furfuryl methacrylate.

The polymerizable monomer component may be present in the dental composition of the present invention in an amount of from 1 to 99 percent by weight, preferably in an amount of from 10 to 60 percent by weight.

The dental composition of the present invention comprises a light-sensitive polymerization initiator. Suitable initiators are benzophenone, benzoin or derivatives therof. Preferred initiators are a-diketones such as 9,10-phenanthrene quinone, diacetyl, furyl, anisyl, 4,4'-dichlorobenzil and 4,4'-dialkoxybenzil. Particularily preferred is camphorquinone. The initiators may be used in combination with an amine as activator. Examples for such activators are N, N-dimethyl-p-toluidine, N, N- dihydroxyethyl-p-toluidine, and N- (2-cyanoethyl)-N-methylaniline.

The initiator may be present in the dental composition of the present invention in an amount of 0.001 to 2 percent by weight, preferably in an amount of from 0.5 to 1 percent by weight.

The dental composition of the present invention optionally comprises a filler. The filler may be an inorganic fillers such as La203, Zur02, BiP04, CaW04, BaWO4, SrF2, Bi203, glasses. The filler may also be or an organic fillers, such as a polymer granulate.

Moreover, the filler may be a combination of organic and inorganic fillers. The filler may be present in the dental composition of the present invention in an amount of 20 to 85 percent by weight. Preferably in case of a composite the filler is present in an amount of from 50 to 85 percent by weight, and in case of a sealer the filler is preferably present in an amount of from 20 to 50 percent by weight.

The dental composition of the present invention optionally comprises a pigment.

Examples of pigments which may be incorporated into a composition of the present invention are titanium oxides and iron oxides.

The dental composition of the present invention optionally comprises a solvent.

Suitable solvents for use in a dental composition according to the invention are acetone, methylethyl ketone, and ethanol.

A preferred dental composition according to the invention is a composite comprising from 15 to 50 percent by weight of a polymerizable monomer component, 0.1 to 3.0 percent by weight of a light-sensitive polymerization initiator, 0. 01 to 1 percent by weight of an inhibitor, and 50 to 85 percent by weight of a filler and/or pigment.

A preferred dental composition according to the invention is a sealer comprising from 50 to 80 percent by weight of a polymerizable monomer component, 0.1 to 3.0 percent by weight of a light-sensitive polymerization initiator, 0.01 to 1.0 percent by weight of an inhibitor, optionally 20 to 50 percent by weight of a filler and/or pigment, and optionally 0 to 10 percent by weight of a solvent.

The dental composition according to the present invention may be prepared by mixing the components of the composition.

The invention will now be further illustrated by the following example and comparative example.

Example 1 19,814 g Urethane dimethacrylate, 1.239 g trimethylolpropane trimethacrylate, 3.715 g diethyleneglycol dimethacrylate, 0.075 g camphorquinone, 0.087 g dimethylaminoethylbenzoicacid ethylester, 0.025 g (0.113 mmol) BHT and 0.025 g (0.031 mmol) 1,2- (dimethoxymethano)-fullerene (Fluka) were homogeneously mixed.

To this resin mixture, 75.020 g of a strontium alumofluorosilicate glass was added and homogeneously mixed to provide a dental composition. The properties of the dental composition were measured and the properties are summarized in Table 1. The light sensitivity to ambient light was also measured. The results are shown in Figure 1.

Example 2 19.854 g Urethane dimethacrylate, 1. 241 g trimethylolpropane trimethacrylate, 3.723 g diethyleneglycol dimethacrylate, 0.075 g camphorquinone, 0.087 g dimethylaminoethylbenzoicacid ethylester and 0.020 g (0.025 mmol) 1,2- (Dimethoxymethano)-fullerene (Fluka) were mixed homogeneously. To this resin mixture 75.000 g of a strontiumalumofluoro silicate glass was added and mixed homogeneously. The sensitivity to ambient light of this composite is 110 seconds.

Comparative Example 1 19.056 g Urethane dimethacrylate, 1.191 g trimethylolpropane trimethacrylate, 3.573 g diethyleneglycol dimethacrlyate, 0,072 g camphorquinone, 0.084 g dimethylaminoethylbenzoicacid ethylester and 0.024 g BHT were homegeneously mixed. To the resin mixture, 76.000 g of a strontium alumofluorosilicate glass were added and homogeneously mixed. The properties of the dental composition were measured and the properties are summarized in Table 1. The light sensitivity to ambient light was also measured. The results are shown in Figure 1.

Comparative Example 2 19.711 g Urethane dimethacrylate, 1.232 g trimethylolpropane trimethacrylate, 3.696 g diethyleneglycol dimethacrylate, 0.074 g camphorquinone, 0.087 g dimethylaminoethyl benzoic acid ethylester, 0,025 g (0.113 mmol) BHT and 0.025 g (0.035 mmol) buckminsterfullerene C, 30 (Fluka) were homogeneously mixed. To this resin mixture 75.150 g of a strontium alumofluorosilicate glass was added and homogeneously mixed.. It was found that the stability of the composition was about the same as the stability of the composition of comparative example 1.

Table 1 Properties of dental composites of example 1 and of comparative example 1 Example Comp. 1 Example 1 Sensitivity to ambient light, ISO 4049 sec 40 90 (10000 lux) Compressive strength MPa 276.0 ~ 6. 2 267.1 i 7. 0 Flexural strength, ISO 4049 MPa 82.5 ~ 7. 4 81.0 ~ 5. 6 E-modulus MPa 7562 ~ 169 7150 ~ 336 Figure 1 Sensitivity to ambient light of composites comprising BHT or 1,2- (Dimethoxymethano)-fullerene and BHT vs. storage time at 23°C (w=weeks)