NO143127B - DENTAL FILLING MATERIALS CONTAINING A MIXTURE OF A BINDING AGENT AND A FILLING MATERIAL - Google Patents

Abstract

Dental filling material containing a mixture of a binder and a filler.

Description

The present invention relates to a dental filling material which contains a mixture of a binder and a filler. The dental filling material is characterized in that the binder is a polymerizable material

a) a polymerizable prepolymer containing at least two ethylenically unsaturated groups, and which is the reaction product of a urethane prepolymer and an acrylate ester of the formula

where R is hydrogen or methyl, and R and R are both hydrogen, or one of R^ and R^ means hydrogen and the other methyl, the urethane prepolymer being the reaction product of a diisocyanate with the 1 2 formula OCN - R - NCO - and a diol with the formula HO - R - OH, where R<1> is a cycloaliphatic, aromatic or aliphatic group, and R 2 is the residue of a condensate of an alkylene oxide with a compound containing two phenolic groups, and b) up to 100% by weight of a vinyl monomer, calculated in relation to the weight of the polymerizable prepolymer,

and that the filler constitutes 60-90% by weight of the dental filling material and is an indifferent, inorganic, particulate filler, of which at least 50% of the particles have a maximum dimension of no more than 500 µm and a Knoop hardness of at least 100.

The tooth filling material has such a consistency that it can easily be shaped at ambient temperature, e.g. simply under manual pressure. The material will preferably have a paste-like consistency.

From Danish patent no. 104 697 it is known that a urethane prepolymer with free isocyanate groups can be used to line the walls of a dental cavity with a view to forming a lining before introducing a dental filling material. With the dental filling material according to the present invention, a new and advantageous product has been provided on the basis of the reaction product of a certain urethane prepolymer which has free isocyanate groups;

with a hydroxyalkyl acrylate, this reaction product in the form of a polymerizable prepolymer (a vinyl urethane) together with a vinyl monomer being an excellent binder for a dental filling material of the binder/filler type.

From British patent no. 1 352 063, a material is known which comprises a binder of the same kind as according to the present invention, as well as fillers such as e.g. may be glass fibres.

In the present invention, a selection of the binders described in the aforementioned British patent is used, with regard to diisocyanate, aromatic residue in the bisphenol, carboxylic acid residue in the alkoxylated bisphenol, acrylate end group and concentration of the comonomer as well as a specific choice of the concentration range, par- the tickle size and the hardness of the filler, as all these parameters are selected to be particularly suitable for filling teeth. This application is not proposed in the British patent, and the fillers described there are not immediately suitable for such an application.

In a preferred embodiment of the present invention, the polymerizable material contains a polymerization catalyst capable of effecting polymerization of the polymerizable material.

In a further preferred embodiment of the invention, the polymerizable material comprises a) a polymerizable prepolymer which is the reaction product of a urethane prepolymer and 2-hydroxyethyl methacrylate, the urethane prepolymer being the reaction product of a diisocyanate selected from 4,4<1->diisocyanate diphenylmethane, hexamethylene diisocyanate, 4,4 '-dicyclohexyl methane diisocyanate, 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, with a diol which is the condensate obtained by reacting 2,2-bis-(p-hydroxyphenyl)propane with propylene oxide in a molar ratio of 1: 2,

b) up to 100% by weight, calculated in relation to the weight of the polymerizable prepolymer, of a vinyl monomer which is ethylene glycol dimethacrylate or triethylene glycol dimethacrylate or an ester with the formula

q o Q Q CH2=C(R )C00R , where R is hydrogen or methyl, and R is an alkyl group with 1-10 carbon atoms, and

c) 0.01-10% by weight, calculated on the polymerizable material, of a photosensitive catalyst comprising a photosensitizer selected

among fluorenone, benzyl, camphorquinone and o-naphthyl, as well as a reducing agent, which is dimethylaminoethyl methacrylate,

and that 60-90% - of the dental filling material - is a translucent, inert, inorganic, particulate filling material, of which substantially all the particles have a maximum dimension of no more than 100 ym and a Knoop hardness of at least 300.

The dental care preparation can be applied to the tooth, e.g. in a hole in the tooth, and the polymerizable components are polymerized so that the material is formed into a hard filling. This polymerization process will hereafter be referred to as hardening of the material.

The material may contain a polymerizable prepolymer which is a solid substance, and as the filler will also be a solid substance, it is necessary to produce a material which is fluid, to add to the material sufficient liquid ethylenically unsaturated monomer which is copolymerizable with the polymerizable prepolymer to to make the material fluid and especially to give the material a paste-like consistency. If desired, the material can contain liquid copolymerizable ethylenically unsaturated monomer even if the polymerizable prepolymer itself is a liquid.

The urethane prepolymer can be formed by reacting at least one polyisocyanate with at least one polyvalent compound containing isocyanate reactive groups, e.g. with a polyol which can for example be a polyether or polyester polyol, or with a polycarboxylic acid. The urethane prepolymer may contain terminal isocyanate groups, in which case the ethylenically unsaturated monomer reactive therewith contains an isocyanate reactive group, e.g. a hydroxyl or carboxyl group. Alternatively, the urethane prepolymer can contain e.g. terminal hydroxyl or carboxyl groups where the prepolymer is formed from a polyhydric compound which is respectively a polyol or a polycarboxylic acid, in which case the ethylenically unsaturated monomer reactive therewith should contain a group reactive with the hydroxyl or carboxyl group, e.g. an isocyanate group. Preferably, the urethane prepolymer contains terminal isocyanate groups.

The urethane prepolymer may conveniently have a straight-chain, non-branched structure, that is, it may be formed by reacting a diisocyanate with a divalent compound, e.g. a diol

or a dicarboxylic acid.

For the sake of convenience and especially for easy preparation, the urethane prepolymer can preferably be straight-chain, contain terminal isocyanate groups and be formed by reacting a diol with a urethane prepolymer having the structural formula

where the diisocyanate has the structural formula OCN-^-NCO and the diol has the structural formula HO-R2-OH, R1 and R2 being divalent hydrocarbyl groups, and n being an integer. In this case, the reaction of the urethane prepolymer with the ethylenically unsaturated monomer will give a polymerizable prepolymer having the structural formula

where X is ec divalent radical and R is hydrogen or a hydrocarbyl group.

In order for the urethane prepolymer to have terminal isocyanate groups, it will be understood that a molar excess of the diisocyanate in relation to the diol must be used during the production of the prepolymer, as the value of n in the prepolymer depends on the molar ratio between the diisocyanate and diol used so that the value of n decreases when this latter ratio increases.

The formation of the prepolymer with terminal isocyanate groups

can be promoted by the use of catalysts known in the field to promote polyurethane formation, e.g. tertiary amines and metal salts, such as stannous octoate and especially dibutyltin laurate.

The reaction of the diol with the diisocyanate can provide

a viscous prepolymer and, especially where n is a large number, the prepolymer can be solid, and under these conditions it is thus desirable that the reaction of the diol with the diisocyanate is carried out in close

be of an inert diluent. Likewise, it is desirable where the urethane prepolymer is very viscous or solid, that the reaction of the latter prepolymer with the ethylenically unsaturated monomer, containing an isocyanate reactive group to form the polymerizable prepolymer, is carried out in the presence of an inert diluent. The diluent should be substantially free of groups reactive with isocyanate groups, at least to such an extent that

the diluent does not interfere with the formation of the prepolymer. The diluent may be the liquid ethylenically unsaturated monomer that is copolymerizable with the prepolymer.

When the polymerizable prepolymer having the structural formula II is prepared in an inert diluent, the prepolymer can be separated from the diluent, e.g. by evaporating the diluent or by adding to the diluent a solvent which does not dissolve the polymerizable prepolymer.

In order for a filling produced by curing the dental filling material to possess a higher strength and stiffness and a higher resistance to shrinkage, it is preferred that the urethane prepolymer is formed from a polyisocyanate and a polyvalent compound, of which at least one and preferably both contain at least one cyclic group, preferably a aromatic group, respectively in the chain between the isocyanate-reactive groups in the polyvalent compound or between the isocyanate groups in the polyisocyanate. Thus, when the urethane prepolymer is formed from a diol and a diisocyanate having the respective structural formulas HO-R2-OH and OCN-R-^-NCO, it is preferred that at least one of the divalent hydrocarbon radicals R^ and R2 has a cyclic group, preferably an aromatic group, inside the chain.

When a dental filling is desired which has a particularly high strength and stiffness as well as shrinkage resistance, it is preferred that the polymerizable prepolymer in the dental filling material has the structural formula II where R^, R2, R^ and X have the previously described meaning, n is an integer from 1 to 20, at least one of the groups R^ and R2 contains at least one cyclic group in the prepolymer's chain and there are no more than 30 atoms, and where higher strength is desired no more than 20 and preferably no more than 12 atoms in the chain between two on consecutive cyclic groups, and when n is 1 and only R2 contains at least one cyclic group in the chain, there are no more than 30, preferably no more than 20 and more advantageously no more than 12 atoms in the chain between the cyclic group in R2 and the nitrogen atom attached to the group X.

For easy production of the urethane prepolymer, and consequently the polymerizable prepolymer, the value of n in the urethane prepolymer is preferably not higher than 10 and more advantageously not higher than 5, that is to say that the molar ratio between the isocyanate groups in the diisocyanate or mixture thereof and the hydroxyl groups in the diol or mixture thereof, from which the prepolymer with terminal isocyanate groups is prepared, is preferably 1.1:1 or higher and more advantageously 1.2:1 or higher.

Most conveniently, the value of n in the urethane prepolymer is not

higher than 3, that is to say that the molar ratio between isocyanate groups in the diisocyanate or mixture thereof and hydroxyl groups in the diol or mixture thereof from which the urethane prepolymer is produced is 1.33:1 or higher.

Particularly preferred diols with a view to desired properties of the produced fillings are diols with the structural formula

that is, oxyalkylated derivatives of phenolic compounds where R^ and R,j are hydrogen atoms or alkyl groups, e.g. methyl, and Ar is a divalent aromatic group where each free valence is on an aromatic carbon atom, and in which a + b together preferably does not total more than 8 and a preferably does not exceed b + 3. In this case, the divalent has group R2 the structural formula Ar can have a nucleus as in phenylene, condensed nuclei as in naphthalene or anthracene, or preferably have the structural formula where Y is a divalent term, e.g. -O-, -SC^-, -CO- or -CH2~/ or substituted derivatives of -CH,,-» e.g. One of the groups R^ and R^ is suitably hydrogen and the other methyl, or both R4 and R^ are hydrogen, that is, the diol can be prepared by reacting propylene oxide or ethylene oxide with a phenolic compound having the structural formula HO-AR-OH, preferably

Advantageously, a plus b is not higher than 4.

Examples of diols that do not have cyclic groups in the chain include, for example, ethylene glycol and propylene glycol, in which to-9H3

trap R^ has the structural formula -Ci^-Ct^- or -CH^- CH-, butylene glycol, diethylene glycol and derivatives thereof where one or more of the carbon atoms are substituted with atoms or groups that are not reactive with hydroxyl and isocyanate groups.

Diisocyanates which contain cyclic groups which can be used for the production of the urethane prepolymer include, for example, diisocyanates in which the chain between the free valences is provided with at least one aromatic group or at least one cycloaliphatic group, or in which the chain between the free valences contains in combination at least one aromatic and at least one cycloaliphatic group.

Cycloaliphatic diisocyanates include, for example, diisocyanates with the structural formula

where -Y- is a divalent term which can for example be -CI^- or substituted derivatives thereof, -O-, -SC^-, -CO-, and the isocyanate groups are connected in the meta or para position to the groups Y. A special example is 4,4'-dicyclohexylmethane diisocyanate.

Aromatic diisocyanates that can be used are, for example, 2,4- or 2,6-tolylene diisocyanates or mixtures thereof, in which case the divalent group R-^ has the structural formula

or a combination of the aforementioned structures. Another suitable aromatic diisocyanate is that which has the structure OCN - (CH2)m

where m is an integer that is

chosen so that there are preferably no more than 30 atoms between cyclic groups in the urethane prepolymer derived from it. A suitable diisocyanate with the latter structure is xylylene diisocyanate.

A particularly suitable aromatic diisocyanate is that which has the structure:

where Y is a divalent term which can have the meanings described above, and where the isocyanate groups are bound in the meta or para position to the group Y. A preferred example is 4,4'-diisocyanate-diphenylmethane.

Diisocyanates which do not contain cyclic groups can be used in the production of the urethane prepolymer. Such suitable diisocyanates include e.g. tetramethylene diisocyanate, pentamethylene diisocyanate and hexamethylene diisocyanate, in which case the divalent group will have the structure -(Cf^^-» ~^CH2^5~ or^ler ~^CH2^6"

Suitable examples of acrylate esters which are reacted with the urethane prepolymer to form the polymerizable prepolymer include hydroxyethyl or hydroxypropyl acrylate or methacrylate produced by reacting acrylic acid or methacrylic acid with ethylene oxide or propylene oxide, in which case the group X in the polymerizable prepolymer II will have the structural formula where respectively both R 1 and R 2 are hydrogen, and one of R 2 and R 2 is hydrogen and the other methyl.

Other suitable isocyanate-reactive ethylenically unsaturated monomers include allyl alcohol, in which case group X in the polymerizable prepolymer has the structural formula -C^-O-CO-, and acrylamide and methacrylamide, in which case group X in the polymerizable prepolymer II has the structural formula - CONH-OCO-.

As previously mentioned, at least 50% of the particles in the filler should have a maximum dimension not greater than 1000 µm. By this is meant that the particle's dimension in any direction should not be greater than 1000 µm. Where the filler is therefore in the form of spheres, at least 50% of the spheres should have a diameter that is not greater than 1000 µm. Where the filler is in the form of fibres, at least 50% should

of the fibers have a length not greater than 1000 µm. Preferably, essentially all particles in the filler should have a maximum dimension that is not greater than 1000 µm.

Mixing the filler with the polymerizable prepolymer is made easier by reducing the particle size in the filler. The preferred maximum size of the particles in the filler is determined by the shape of the filler. Where the filler is thus in the form of fibres, the maximum size of the fibers is not greater than 500 µm and more advantageously not greater than 100 µm. On the other hand, when the filler is in the form of spheres, small plates or has an irregular shape, the maximum dimension of the filler particles is preferably not greater than 300 µm and is more advantageously in the range of 1 to 100 µm.

In order for a hard dental filling to be produced by curing the dental filling material, it is desirable that the filler particles have a Knoop hardness of at least 100. Generally speaking, it can be said that the greater the hardness of the filler particles in the material, the greater the hardness of the manufactured dental filling will be hardening of the material, and for that reason it is preferred that the Knoop hardness of the filler is at least 300 and more advantageously at least 500. In general, the required hardness, and especially the preferred hardness, is provided by means of inorganic fillers.

In order for the tooth filling produced by curing the tooth filling material to have the appearance of a natural tooth, it is preferable to use a filling material that is translucent.

The dental filling material can, for example, contain from 10 to

90% by weight filler on the basis of the material, although in order for the dental filling produced by curing the material to have a particularly desired wear resistance, hardness, small shrinkage during curing and a low coefficient of thermal expansion, the dental filling material should preferably contain from 30 to 80% by weight and more advantageously from 60 to 80

weight % filler of the dental filling material. Mixtures of different fillers can be used.

The filler can, for example, be in the form of balls, small

plates, fibers, "whiskers" or it may have an irregular shape. Suitable fillers include, for example, apatite, soda glass,

quartz, silica gel, borosilicate glass, synthetic sapphire (aluminium

oxide) or metal fibers.

Mixing of the polymerizable prepolymer with filler

for the formation of the dental filling material can be carried out by stirring together

but the prepolymer and the filler. However, when the polymerizable prepolymer, optionally together with a copolymerizable monomer, can become viscous and thus difficult to stir with the filler to achieve a sufficient mixture, the polymerizable prepolymer, optionally together with a copolymerizable monomer, can be conveniently diluted with a suitable diluent to reduce viscosity

the teat and thus enable adequate mixing of the filler.

When the mixing is done, the diluent can be removed, e.g.

by evaporation. The diluent may suitably be a copolymerizable, ethylenically unsaturated monomer, the monomer being, if desired, completely removed after the mixture is obtained, or if the dental filling material is to contain a copolymerizable, ethylenically

unsaturated monomer, the amount of monomer is reduced after mixing to the desired level.

For the production of a dental filling where the filler binds particularly well to the hardened, polymerizable prepolymer in the filling, it is preferred that the filler is treated with a coupling agent that is capable of reacting with both the filler and the polymerizable prepolymer; before mixing the filler with the polymerizable prepolymer is performed. The coupling agent should cause an increase in the bond strength between the filler and the hardened, polymerizable prepolymer in the filling.

Suitable coupling agents for use in connection with glass include silanes, e.g. >!-methacryloxypropyltrimethoxysilane, >-aminopropyltriethoxysilane and ;-glycidoxypropyltrimethoxysilane.

As previously mentioned, the dental filling material can contain a liquid, ethylenically unsaturated monomer which is copolymerizable with the polymerizable prepolymer, and should contain such a monomer when the polymerizable prepolymer is a solid substance in order for the dental filling material to be fluid and especially to have a paste-like consistency.

The amount of ethylenically unsaturated monomer used in this way can, if desired, be just sufficient to achieve the desired fluidity in the dental filling material. Since the use of such a monomer can lead to a reduction in the strength of the dental filling made from the material, it is preferred in the dental filling material not to use more than 100% by weight of ethylenically unsaturated monomer based on the polymerizable prepolymer and more advantageously not more than 50% by weight.

Suitable liquid copolymerizable ethylenically unsaturated monomers, whose polymers should be water soluble, include vinyl monomers, e.g. vinyl esters and acrylic and methacrylic acids. The monomers must not be toxic.

Suitable vinyl esters include, for example, vinyl acetate, esters of acrylic acid having the formula CH2=CH-C00Rg, where R is an alkyl, aryl, alkaryl, aralkyl or cycloalkyl group. For example, Rg can be an alkyl group with from 1 to 20 and preferably 1 to 10 carbon atoms. Special vinyl esters that can be mentioned include, for example, methyl acrylate, ethyl acrylate, n- and iso-propyl acrylate, and n-, iso- and tertiary butyl acrylate.

Other suitable vinyl esters include, for example, esters with the formula CH2=C(R^)C00Rg, where R^ can be an alkyl group, e.g.

a methyl group. In the ester with the formula CH2=C(R^)C00Rg, R^ and R^ may be the same or different. Special vinyl esters that can be mentioned include, for example, methyl methacrylate, ethyl methacrylate, n-

and iso-propyl methacrylate, and n-, iso- and tertiary butyl methacrylate.

Mixtures of acids and esters can be used.

Polyvalent vinyl monomers, i.e. monomers containing two or more vinyl groups, are also suitable. Suitable monomers include, for example, glycol dimethacrylate, diallyl phthalate and triallyl cyanurate.

The dental filling material according to the invention can be formed into a suitable shape and then hardened to form a hard filling by polymerization of the polymerizable prepolymer, possibly together with an ethylenically unsaturated monomer which is copolymerizable

thus.

Hardening of the material for the production of a dental filling

can be promoted with the help of a catalyst. It is desirable that the catalyst is able to harden the material at a relatively low temperature, e.g. at or near the ambient temperature, as the use of higher temperatures may cause discomfort to the patient being treated. Suitable catalysts which are capable of effecting curing at a relatively low temperature include, for example, a mixture of a peroxide and an accelerator, e.g. a peroxide and an amine, e.g. a mixture of benzoyl peroxide and N,N-dimethyl-p-toluide. Other catalysts include a mixture of a peroxide and a cobalt accelerator, e.g. a mixture of methyl ethyl ketone peroxide and cobalt octoate, cobalt naphthenate or cobalt naphthenate and dimethylaniline.

Where the catalyst used is able to effect hardening of the material at a relatively low temperature, it is desirable that the catalyst is mixed with the dental filling material shortly before the material is used, as otherwise an undesirable degree of hardening takes place before the material is formed into the desired shape of the dental filling material .

The amount of catalyst generally used will be in the range of 0.01 to 20% by weight based on the polymerizable material in the dental material, i.e. 0.01 to 20% by weight of catalyst

lysator on the basis of polymerizable prepolymer, or of polymerizable prepolymer plus copolymerizable monomer when such is present. Smaller or larger amounts of catalyst may be used if desired, although 0.1 to 10 wt% catalyst is preferred, and more preferably 0.5 to 5 wt% catalyst.

The catalyst used can be radiation-activatable, and according to a preferred feature of the invention, a dental filling material is provided as described in the following and which contains a light-sensitive catalyst consisting of

(a) at least one photosensitizing compound selected from

.fluorenone, substituted derivatives thereof, and α-diketones having the structural formula

where the groups A, which may be the same or different, are hydrocarbon groups or substituted hydrocarbon groups, and

(b) at least one reducing agent capable of

reduce the photosensitizing compound when it is in an activated state.

Dental filling materials according to the invention, which can contain a light-sensitive catalyst, can be cured by irradiating the material with ultraviolet radiation, i.e. radiation that has a wavelength in the range of 230 ym up to 400 p. The materials can also be irradiated with visible radiation and especially with visible radiation having a wavelength in the range of 400 µm to 500 µm. Alternatively, a mixture of ultraviolet and visible radiation can be used.

In the α-diketone having the above formula, the groups A, when they are hydrocarbon, can for example be aliphatic, e.g. alkyl with 1 - 10 carbon atoms, aromatic, e.g. phenyl, cycloaliphatic, e.g. cyclohexyl, aralkyl, e.g. benzyl, or alkaryl, e.g. tolyl.

Alternatively, the groups A can together form a divalent radical so that in the photosensitizing compound the groups A together with the carbonyl groups will form a cyclic structure. For example, the groups A can form a divalent aliphatic group or they can form an aromatic group and in particular they can form a condensed aromatic ring system.

Suitable α-diketones include diacetyl having the structure

benzyl which has the structure a-naphthyl which has the structure /3-naphthyl which has the structure acenaphthene which has the structure or camphorquinone which has the structure

Where the groups A are substituted hydrocarbyl, the substituent group or groups should not result in a significant inhibition of the polymerization of the polymerizable material. Examples of photosensitizing compounds where the groups A are substituted hydrocarbons include p,p'-dimethoxybenzyl and p,p'-dichlorobenzyl.

A particularly preferred photosensitizing compound is benzyl.

The photosensitizing compounds can be present in the dental filling material in a concentration of e.g. 0.01 to 10% by weight of the polymerizable material in the dental filling material, although concentrations outside this range may be used if desired. Preferably, the light sensitizing compound is present in a concentration in the range of 0.5 to 5% by weight of polymerizable material in the dental filling material.

The reducing agent present in the photosensitizing catalyst should be able to reduce the photosensitizing compound when it is in an activated state. The reducing agent should have little or no inhibitory effect on the polymerization. Whether a reducing agent has an inhibitory effect or not can be determined by simple experiments, for example by carrying out polymerization of the polymerizable material in the dental filling material using a thermal initiator alone and in the presence of a reducing agent in the desired concentration and comparing the polymerization rates in the presence and in the absence of the reducing agent.

Suitable reducing agents include compounds which have

R

the structure R-M-R, where M is an element from group V in the periodic table, and the units R, which may be the same or different, are hydrogen atoms, hydrocarbon groups, substituted hydrocarbon groups or groups where the units R together with the element M form a cyclic ring system, not more than two of the units R are hydrogen atoms and the element M is bonded directly to an aromatic group.

The element M in the reducing agent can be, for example, phosphorus or, more preferably, nitrogen. If desired, M can be arsenic or antimony.

The reducing agent can be primary, secondary or tertiary,

R

which means that in the structure R-M-R two, one or none of the units R can respectively be hydrogen atoms. For example, the reducing agent can be a primary, secondary or tertiary amine or phosphine.

One or more groups R can be a hydrocarbon residue. The hydrocarbon group can be alkyl, cycloalkyl or aralkyl. The group R may suitably be an alkyl group having from 1 to 10 carbon atoms.

Examples of suitable reducing agents where one or more

of the units R is a hydrocarbon residue, includes propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, dimethylaminoethyl methacrylate and long-chain fatty amines, e.g. . C18H37NMe2.

It will be understood that where the present description refers to specific examples of suitable reducing agents where the element M is nitrogen, it will also include corresponding specific examples where the element M is phosphorus, arsenic or antimony.

One or more of the units R can be substituted hydrocarbon groups and in particular the hydrocarbon group can have a substituent

which has the structure

where M is an element from the group Vb

in the periodic table and the unit R^ for example is an alkylene chain and the units R2, which may be the same or different, for example are hydrogen atoms or hydrocarbon groups.

R

Examples of reducing agents that have the structure R-M-R where at least one of the units R is a substituted hydrocarbon group,

includes diamines with the structure

where n is a

whole number of at least 2 and the groups R 2 , which may be the same or different, are hydrogen atoms or hydrocarbon residues, especially alkyl groups. For example, the reducing agent can be ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine or

hexamethylenediamine, or an N-hydrocarbon residue, especially N-alkyl derivatives thereof. Other suitable reducing agents include derivatives

with the structure R2 J^N-(CH2) n~N,^ ' R2where one or more of hydrogen-

R2 R2 r

the atoms in the -CH2~ units have an -N^ -group, especially an -NH,, group. R2

Examples of reducing agents where the element M forms part of a cyclic ring system include piperidine and N-hydrocarbon residues, especially N-alkyl, as well as derivatives of piperidine.

Other reducing agents include triallylamine,

(allyl)

allylthiourea and soluble salts

of aromatic sulfinic acids.

Appropriate concentrations of the reducing agent in relation to the photosensitizing compound can lie in the ranges described above. Preferably, the reducing agent is present in a concentration of 1 to 5% by weight of the polymerizable material in the dental filling material.

The invention will be further illustrated by the following examples where all parts are expressed as parts by weight.

Example 1

352 parts of a condensate obtained by reacting 2,2-bis-(p-hydroxyphenyl)propane with propylene oxide in a molar ratio of 1:2,

was heated to melt the condensate and stirred under redu-

high pressure for degassing the condensate.

500 parts of 4,4'-diisocyanate diphenylmethane were likewise heated, stirred and degassed separately. The condensate and the diisocyanate (molar ratio diisocyanate to condensate equal to 2:1) were then mixed together

but and 556 parts of methyl methacrylate, which had been dried over calcium hydride, was added to the mixture followed by the addition of 0.14 part of dibutyltin laurate. This mixture was cooled by means of an ice bath to control the exothermic reaction of the prepolymer formation so that the temperature did not exceed 55°C. The stirring was continued for 1.5 hours after the end of the exothermic reaction.

260 parts of 2-hydroxyethyl methacrylate, which had previously been distilled and degassed, was then added and the resulting mixture

ding stirred for 1.5 hours to form the ethylenically unsaturated polymerizable prepolymer.

60 parts of the mixture of polymerizable prepolymer and methyl methacrylate prepared above was: mixed with 180 parts of glass beads ("Ballatini 3000 CPOl", Plastichem Ltd.) of which 80% by weight

had a diameter between 4 and 44 pm.

The mixture was then stirred, further methyl methacrylate was added to ameliorate the mixture and there was then added 6 parts catalyst solution formed by dissolving 2 parts benzyl in 4 parts dimethylaminoethyl methacrylate and 4 parts methyl methacrylate. After stir-

ing for 15 minutes, the pressure was reduced and methyl methacrylate which had been added to improve the mixture was removed by evaporation.

The paste-like mixture was then poured into a cylindrical glass mold and exposed to irradiation from a blue lamp for 15 minutes to cure the mixture.

The cured material had the following properties:

Example 2

The procedure in Example 1 was followed with the exception that 30 parts of the mixture of ethylenically unsaturated, polymerizable prepolymer and methyl methacrylate and 3* parts of the catalyst solution were used, and instead of the glass balls, 60 parts of hammer-ground glass fibers having a dimension of 10 pm x 200 pm (Glass Fibers Ltd.). Before mixing with the other components of the dental filling material, the glass fibers were surface-coated with >'-meth-acryloxypropyltrimethoxysilane by adding 100 parts of glass fibers, which had previously been heated to 400°C and then cooled in a desiccator, to a solution of 1 part Vmethacryloxypropyl- trimethoxysilane in 100 parts methanol, stirring for 1 hour, evaporating the methanol, sieving the fibers through a 62 µm mesh sieve and finally heating the fibers to 140°C to cure the silane. The cured material had the following properties: Example 3 The procedure in Example 1 was followed with the exception that 15 parts of the mixture of ethylenically unsaturated, polymerizable prepolymer and methyl methacrylate and 1.5 parts of catalyst were used. Instead of glass beads, 36 parts of quartz powder were used, the surface of which had been coated with ^-methacryloxypropyltrimethoxysilane using the method described in Example 2. ;The hardened material had the following properties: ;;Example 4 ;500 g of freshly distilled 4,4'-diisocyanate diphenylmethane was washed with 300 ml of methylene chloride in a 5 liter flanged flask which had been purged with nitrogen gas. The flask was then fitted with a glass stirrer, nitrogen purge device, water cooler and thermometer. ;352 g of molten condensate, obtained by condensation of 2,2-bis(p-hydroxydiphenol)propane and propylene oxide, and 0.15 g of dibutyltin laurate were weighed into a 1 liter dropping funnel which had been purged with nitrogen gas. 200 ml of methylene chloride was added to the dropping funnel to prevent the condensate from solidifying. ;The dropping funnel was then placed over the flask and its contents were added dropwise to the flask over a period of 45 minutes after which the reaction was allowed to continue for approx. 45 minutes at which time 300 g of hydroxyethyl methacrylate was added together with 0.15 g of dibutyltin laurate over a period of 3 minutes. There was a rise in the temperature of the contents of the flask and when the temperature rise had subsided, the flask was heated on a water bath (under reflux of the methylene chloride) and its contents stirred under a nitrogen purge until the infrared spectrum of the resulting product showed only traces of present isocyanate groups (approx. ; 3 days). The water bath was then removed and methanol added to the stirred contents of the flask to effect separation of the polymerizable polymer in the flask. The contents of the flask were then clarified by settling the bottom and the methanol layer was removed with a sieve and discarded. Washing with methanol as above was repeated several times until a clear methanol layer was obtained. The polymerizable prepolymer in the flask was then dried at room temperature under vacuum until the formation of a dry foam. The foam was then crushed and dried to remove traces of methanol. In the absence of blue light, 13.37 parts of powder of the polymerizable prepolymer was dissolved in 10.94 parts of ethylene glycol dimethacrylate and 0.625 part of dimethylaminoethyl methacrylate was added to the solution followed by 0.0625 part of camphorquinone. 75 parts of borosilicate glass powder of particle size less than 53 µm and coated with 1% by weight of Y-methacryloxypropyltrimethoxysilane was stirred into the mixture and the resulting fluid paste was passed through a roller mill during which passage it was degassed. Cylindrical samples of the paste 3 mm in diameter and 2.5 mm in length in polytetrafluoroethylene molds were irradiated with light using a light source fitted with 18 inch (457.2 mm) wire optics for 2 minutes. The cured samples were removed from the molds and stored under water at 37°C and tested after a period of 1 hour, 24 hours and 1 week respectively. The results are shown in the table below. Example 5 2.585 parts of a polymerizable prepolymer prepared as in example 4 were dissolved in 2.115 parts ethylene glycol dimethacrylate and 0.1 part fluorenone and 0.2 part dimethylaminoethyl methacrylate were added to the solution. 7.5 parts of borosilicate glass powder (as in Example 4, but coated with 2% by weight of the silane) was mixed into the resin under degassing, and then thick samples of the resulting paste were cured as in Example 4 for 100 minutes using a light source consisting of a low-intensity mercury-silver lamp filtered for the transmission of radiation of 437 pm. The depth of curing was 1.5 mm. ;Example 6 ;A paste was prepared and cured as in example 5 with the exception that α-naphthol was used instead of fluorenone. The depth of curing was 2.5 mm. ;Examples 7-12 ;6.7 parts of the polymerizable prepolymer prepared as in example 4 were dissolved in 3.3 parts of methyl methacrylate and 0.2 parts of a solution of fluorenone (0.1 part) in dimethylaminoethyl methacrylate (4 parts) were added to the solution. 15 parts of filler were stirred into the solution, and the resulting paste was poured into glass tubes with a diameter of 6 mm. The samples were then cured by irradiation with light from a fluorescent tube for 30 minutes. The cured samples were cut into 12 mm lengths and their compressive strength was determined. Example 13 5.5 parts of the polymerizable prepolymer in Example 4 were dissolved in 4.5 parts of ethylene glycol dimethacrylate and 0.025 parts of N,N-dimethyl-p-toluidine were added to the solution. ;0.3 part of this mixture was mixed in a few seconds with 0.7 part of a coated filler using a spatula. The coated filler was a coated borosilicate glass powder with a particle size of less than 53 µm and was obtained by successively coating 23.33 g of glass powder with 0.23 part Y-methacryloxypropyltrimethoxysilane and 0.03 part benzoyl peroxide from methylene chloride. The resulting paste was packed into 3 mm x 3 m cylindrical molds which were allowed to stand for several hours after which the stiff samples were removed from the molds and tested. The rigid material had a compressive strength of 160 N mm and a diametric compression of 30 N mm~. Example 14: 33.33 parts of polymerizable prepolymer prepared as in Example 1 were dissolved in 16.66 parts of methyl methacrylate and 170 parts of "Ballotini" glass spheres ("FPOl 3000") of average diameter 4.4 µm were mixed into the solution. 5 parts of a solution of dimethylaminoethyl methacrylate (40%) and benzyl (20%) in methyl methacrylate (40%) were added and the mixture then heated. Excess methyl methacrylate was added and the mixture was then stirred for 15 minutes, after which excess methyl methacrylate was removed under vacuum. The resulting paste was packed into 3 conical cavities drilled in the canine of a hare dog bitch and cured in situ using an 18 inch (457.2 mm) wire optic light source. After 26 months, the fillings were still in the tooth and showed no visible signs of significant mechanical failure or of working loose in the cavities. ;Examples 15-22 ;A polymerizable prepolymer was prepared as described in Example 4. In the absence of blue light, 3.1 g of the prepolymer was dissolved in 2.54 g of monomer (see below) and 0.24 g of dimethylamine ethyl methacrylate was added to the solution followed by 0.12 g of benzyl. 14 g of pulverized borosilicate glass with a particle size of less than 53 µm and coated with 2% by weight of Y-methacryloxypropyltrimethoxysilane was stirred into the mixture (an amount such that the filler constituted 70% by weight of the dental filling material) and the resulting paste was passed through a roller mill under which it was degassed. ;Cylindrical paste samples of diameter 3 mm and length 2.5 mm were cured in polytetrafluoroethylene molds by irradiation for 1 hour at a distance of 304.8 mm from a "Thorn" closed beam lamp. The samples were removed from the molds after 1 hour and tested for compressive strength and hardness. ;Example 23 ;A. The procedure in example 21 was repeated with the exception that after exposure of the sample to radiation for 1 hour, the sample was removed from the mold and allowed to rest for 2 days before testing. B. For comparative purposes, the above procedure was repeated using a different polymerizable prepolymer prepared as follows: Freshly distilled 2,4-toluene diisocyanate was washed in a flask with methylene chloride and a mixture of 2,2-propane-bis-[3-(4-phenoxy ) -1,2-hydroxypropane-1-methacrylate] and dibutyltin laurate were added dropwise to the flask. The reaction was allowed to continue until infrared analysis of the mixture indicated that only traces of isocyanate groups were present. Methanol was added to the flask to separate the resulting prepolymer which was then dried and finally crushed. C. For further comparison purposes, the procedure under A was repeated with the exception that phenyl isocyanate was used instead of 2,4-toluene diisocyanate. D. For further comparison purposes, the procedure under A was repeated using a prepolymer as prepared under B, but using aniside diisocyanate instead of 2,4-toluene diisocyanate. ;E. For yet another comparison purpose, process A was again repeated using a prepolymer prepared as in B, but using 4,4<1->diisocyanate diphenylmethane instead of 2,4-toluene diisocyanate. ;Example 24 ;A. 35.2 g (0.1 mol) of oxypropylated bisphenol A was dissolved in approx. 100 g of methylene chloride, and the resulting solution was added dropwise to a solution of 33.6 g (0.2 mol) of hexamethylene diisocyanate in 100 g of methylene chloride under an atmosphere of nitrogen gas. 4 drops of dibutyltin dilaurate (available under the trade name "Mellite 12") were added as a catalyst. The mixture was stirred under nitrogen for 1 hour after which it was heated under reflux for 9 hours. The mixture was then cooled, and a solution of 26 g (0.2 mol) of 2-hydroxyethyl methacrylate in 100 g of methylene chloride was added, after which the mixture was heated under reflux for 3 hours. The mixture was then cooled and the resulting polymerizable prepolymer was isolated as a viscous gum by treating the mixture with petroleum ether followed by removal of residual solvent in a rotary evaporator. ;A dental filling preparation was prepared from the viscous gum, with the following composition: ;x treated with 1% by weight of the silane (A174) coupling agent "Silan A17" ;(trade name for a ^/-methoxypropyltrimethoxysilane). When preparing the preparation, the ethylene glycol dimethacrylate was weighed into a 250 ml beaker containing the viscous gum. The mixture was stirred until the gum was dissolved, and then the amine and camphorquinone were added with stirring. When the catalyst was completely dissolved, the glass powder filler was stirred into the mixture to produce a paste which was then placed in a vacuum chamber where it was aerated for approx. 2 minutes. Samples of the aerated mixture were placed in a polytetrafluoroethylene mold of length 3 mm and diameter 3 mm, and the samples were exposed for 2 hours to radiation from a standard d* lamp and 457.2 mm long wire optics, after which time they were immersed in water for 24 hours at 37°C and then tested. The following characteristics were measured: _2

Compressive strength - average 323.4Nmm

- maximum 341,ONmm

_2

Tensile strength - average 55.4Nmm

(diameter) , c.. -2

- maximum 59.4Nmm

Curing depth (after 1 minute) 6 mm

a 150w/21v G.E. quartz filament lamp.

B. For the sake of comparison, the above procedure was repeated, but using 4,4'-diisocyanate-diphenylmethane-diisocyanate (0.2 mol) instead of hexamethylene diisocyanate.

C-G For the sake of comparison, samples of 3 mm x 3 mm of conventional dental filling materials were prepared in the normal way and

tested.

C. "Prestige" tooth filling preparation (Lee Pharmaceuticals)

D. "Cosmic" dental filling preparation (De Trey)

E. "HL-72" dental filling preparation (Lee Pharmaceuticals)

F. Conventional amalgam

G. Encapsulated conventional amalgam

The handling characteristics of products A and B were also compared. The polymerizable prepolymer in product A is a viscous rubber, while that in product B is a solid. Therefore, product A containing 75% by weight of the filler is less viscous and easier to handle than product B. Alternatively, it is easier to fill product A than product B up to 80% by weight or even more of the filler, and the increase results in improved wear resistance -

stone and improved hardness in fillings made from the products.

Example 25

52.4 g (0.2 mol) of 4,4<1->dicyclohexylmethane diisocyanate was placed in a flask together with 30 ml of dry methylene chloride, under nitrogen gas. 35.2 g (0.1 mol) of oxypropylated bisphenol-A was

dissolved in 50 ml of dry methylene chloride, and the solution was washed with 20 ml aliquots of dry methylene chloride in a dropping funnel. 10 drops of dibutyltin dilaurate ("Mellite 12") were added to the solution in the dropping funnel. 0

The mixture in the flask was heated to the methylene chloride

was carefully cooled down, and then the solution from the dropping funnel was added drop by drop over a period of approx. 1 hour while stirring. The stirring was continued for approx. 1 1/2 hours, after which 26 g

(0.2 mole) of hydroxyethyl methacrylate and 10 drops of dibutyl tin dilaurate ("Mellite 12") were added through the dropping funnel over time

of 15 minutes. The mixture was stirred for a further 3 hours and then allowed to stand for approx. 70 hours. I.R. spectral analysis of the mixture showed residual isocyanate, and the mixture was allowed to stand for a further 48

hours. The resulting polymerizable prepolymer was isolated as a solid by treating the mixture with petroleum ether followed by removal of residual solvent in a rotary evaporator.

A dental filling preparation was prepared from this solid prepolymer as described, and to the mixture described in example 24. The samples were cured, also as described in example 24.

The prepolymer paste had good flow properties and the cured material was very translucent. The depth of cure achieved in 1 minute was 6.1 mm, and after immersion in water for 24 hours at 37°C (Example 24), the cured material had a compressive strength (average) of 264.2 N/mm 2 and a tensile strength (average) of 41.7 N/mm 2.

Example 26

A dental filling material was prepared, with a composition and cured as described in example 25 with the exception that 34.8 g (0.2 mol) of 2,4-toluene diisocyanate was used instead of the dicyclohexylmethane diisocyanate. The paste had good flow properties and the hardened material was translucent. The curing depth within 1 minute was 5.5 mm. After immersion in water at 37°C for 24 hours, the material had a compressive strength (average) of 290.65 N/mm 2 and a tensile strength (average) of o 47.6 N/mm 2.

Claims (4)

1. Dental filling material containing a mixture of a binder and a filler, characterized in that the binder is a polymerizable material comprising a) a polymerizable prepolymer containing at least two ethylenically unsaturated groups, and which is the reaction product of a urethane prepolymer and an acrylate ester of the formula where R^ is hydrogen or methyl, and R^ and R^ are both hydrogen, or one of R 6 and R 7 means hydrogen and the other methyl, the urethane prepolymer being the reaction product of a diisocyanate with the formula OCN - R - NCO and a diol of the formula HO - R - OH, where R"*" is a cycloaliphatic, aromatic or aliphatic group, and R 2 is the residue of a condensate of an alkylene oxide with a compound containing two phenolic groups, and b) up to 100% by weight of a vinyl monomer, calculated in relation to the weight of the polymerizable prepolymer, and that the filler constitutes 60-90% by weight of the dental filling material and is an indifferent, inorganic, particulate filler, of which at least 50% of the particles have a maximum dimension of no more than -500yum and a Knoop hardness of at least 100. 2. Dental filling material according to claim 1, characterized in that the polymerizable material contains a polymerization catalyst. 3. Dental filling material according to claim 2, characterized in that the catalyst is a photosensitive catalyst comprising a) a photosensitizer chosen from fluorenone, biacetyl, benzyl, α- and β-naphthyl, acenaphthenquinone and camphorquinone, and b) a reducing agent selected from primary, secondary and tertiary amines and phosphines. 4. Dental filling material according to claim 1, characterized in that the polymerizable material comprises a) a polymerizable prepolymer, which is the reaction product of a urethane prepolymer and 2-hydroxyethyl methacrylate, the urethane prepolymer being the reaction product of a diisocyanate selected from among 4,4'-diisocyanate diphenylmethane, hexamethylene diisocyanate, 4 ,4'-dicyclohexylmethane diisocyanate, 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, with a diol which is the condensate obtained by reacting 2,2-bis-(p-hydroxyphenyl)propane with propylene oxide in a molar ratio of 1:2, b) up to 100% by weight calculated in relation to the weight of the polymerizable prepolymer of a vinyl monomer, which is ethylene glycol dimethacrylate or triethylene glycol dimethacrylate or an ester with the Q Q Q Q formula CH2=C(R )COOR , where R is hydrogen or methyl, and R is an alkyl group with 1-10 carbon atoms, and c) from 0.01 to 10% by weight - of the polymerizable material - of a photosensitive catalyst comprising a photosensitizer selected among others ant fluorenone, benzyl, camphorquinone and ct-naphthyl, as well as a reducing agent, which is dimethylaminoethyl methacrylate, and that 60-90% by weight - of the tooth filling material - is a translucent, indifferent, inorganic, particulate filler, of which essentially all the particles have a maximum dimension - of no more than 100 ym and a Knoop hardness of at least 300.