Process for preparing a tooth filling

The present invention relates to a dental composition and in particular a dental filling composition comprising a polymerizable material.

The subject of the invention is a dental composition which is a fluid composition comprising a prepolymer which contains at least two polymerizable ethylenically unsaturated radicals, hereinafter called polymerizable prepolymer, which polymerizable prepolymer is the reaction product of a prepolymer urethane and t

of a polymerizable ethylenically unsaturated monomer reactive with respect to the prepolymer urethane, in addition to a particulate filler, preferably inorganic, the particles of which have at least $ 50 ung maximum dimension not exceeding 1,000 microns .

By fluid composition is meant a composition which has sufficient mobility so that it can be easily molded at room temperature, for example simply by molding under the pressure of the hand. Advantageously, the composition has a pasty consistency.

According to another embodiment, the invention relates to a dental composition of the type described above, which contains a catalyst capable of causing the polymerization of the polymerizable prepolymer.

The dental composition can be applied to the tooth, for example in a cavity of the tooth, and the polymerizable prepolymer can be polymerized so that the composition converts into a hard filling. This polymerization is hereinafter called curing of the composition.

The composition may contain a polymerizable prepolymer which is a solid and, since the filler is also solid, it is necessary, in order to have a fluid composition, to add to the composition a liquid to non-liquid monomer. saturation · ”“ ethylenic dopplymerisable with the polymerizable prepolymer in sufficient quantity to make the composition fluid and in particular to give it a pasty consistency. If desired, the composition may include a liquid monomer

35with copolymerizable ethylenic unsaturation, even when the polymerizable prepolymer is itself liquid.

The prepolymer urethane can be formed by reacting at least one polyisocyanate with at least one polyfunctional compound containing radicals reactive with respect to isocyanates,

1 + 0 for example with a polyol which can be for example a polyCD./MK. ÂdC.ll

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etherpolyol or polyesterpolyol or · with a polycarboxylic acid. The prepolymer urethane may comprise terminal isocyanate radicals, in which case the ethylenically unsaturated monomer capable of reacting with the urethane must include a radical reactive with regard to isocyanates, such as a hydroxyl or carboxyl radical. Alternatively, the prepolymer urethane can carry, for example, terminal hydroxyl or carboxyl radicals when it is formed from a polyfunctional compound which is a

I polyol or a polycarboxylic acid respectively, in which case the ethylenically unsaturated monomer reactive with respect to the urethane prepolymer must bear a reactive radical with respect to. * iradical hydroxyl or carboxyl, such as an isocyanate radical. Preferably, the prepolymer urethane carries terminal isocyanate radicals.

The prepolymer urethane may advantageously have a linear, unbranched structure, that is to say may result from the reaction of a diisocyanate and a difunctional compound, such as a diol or a dicarboxylic acid.

Preferably, for reasons of convenience and in particular for reasons of ease of preparation, the prepolymer urethane is linear, ports, terminal isocyanate radicals and is formed by reaction of a diol with a diisocyanate giving a prepolymer urethane. formula :

OCN ^ -NH-CO-OR ^ O-OC-NH) AcO I the diisocyanate having the motule OCN-R ^ -NCO and the diol having the formula 2 12 HO-R -OH, where R and R represent divalent hydrocarbyl radicals, and n representing an integer.

In this case, the reaction of the prepolymer urethane with the ethylenically unsaturated monomer capable of reacting with this prepolymer gives a polymerizable prepolymer of formula:

R

R³

CH₂= CX-NH (R¹-NH-C0-0-R²-0-0C-NH> NR¹-NH-Xi = CH2 II where. X represents a divalent radical and R³ represents a hydrogen atom or a hydrocarbyl radical.

In order for the prepolymer urethane to carry terminal isocyanate radicals, it is obvious that the diisocyanate must be taken in molar excess on the diol for the preparation of the prepolymer, the value of n in the prepolymer depending on the

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diisocyanate to diol molar ratio and decreasing as this molar ratio rises.

The formation of the prepolymer with terminal isocyanate radicals can be promoted by the use of known catalysts to facilitate the formation of polyurethanes, for example tertiary amines and metal salts, such as tannous octoate and in particular dibutyltin dilaurate.

The reaction of the diol and the diisocyanate can give a viscous prepolymer urethane and, especially when n represents a high number, the prepolymer can be solid, so that it is. desirable in this case that the reaction of the diol and the diisocyanate is carried out in the presence of an inert diluent. Likewise,_{? T} when the prepolymer urethane is highly viscous or solid, its reaction with the ethylenically unsaturated monomer containing a radical capable of reacting with isocyanates to give the polymerizable prepolymer can be carried out with advantage in the presence of an inert diluent. This diluent must be substantially free from radicals capable of reacting with isocyanate radicals at least to a degree such that the diluent does not interfere with the formation of the prepolymer. The diluent can be the liquid ethylenically unsaturated monomer copolymerizable with the prepolymer.

When the polymerizable prepolymer of formula II is prepared in an inert diluent, it can be separated from this diluent, for example by evaporation of the diluent or by adding to this diluent a non-solvent for the polymerizable prepolymer.

In order that a filling produced by hardening the dental filling composition has a high mechanical strength and modulus as well as a high creep resistance, it is preferable that the prepolymer urethane is formed from a polyoleyanate and of a polyfunctional compound of which at least * one and preferably both carry at least one cyclic, preferably aromatic, radical in the main chain between the ra- _treactive with respect to isocyanates in the polyfunctional compound or between isocyanate radicals in the polyisocyanate respectively. Thus, when the prepolymer urethane is formed from a diol and a diisocyanate of respective formula H0-R²-0H and OCli-R ^ -RCO, it is preferable that at least

2 one of the divalent hydrocarbyl radicals R and R comprises, during the chain, a cyclic radical which is preferably an aromatic radical.

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When it is desirable to have a dental filling having particularly high mechanical strength and modulus and resistance to creep, it is preferable that the polymerizable prepolymer of the dental filling composition be of formula II where r \ R ^, and X have the meanings assigned to them above and n represents an integer from 1 to 20, at least one of the radicals R and R² containing at least one cyclic radical in the chain of the prepolymer and the number of atoms not exceeding 30 and, if higher mechanical strength is desired, not exceeding 20 and preferably not .12 "d^years the chain between adjacent cyclic radicals,_>or if n represents 1 and only R contains at least one cyclic radical in the chain, there is not more than 3 °, preferably 'not more than 20 and more advantageously not more than 12 ato15 mes in the chain between the cyclic radical of the radical R and the nitrogen atom united with the radical X.

For reasons of ease of preparation of the prepolymer urethane and therefore of the polymerizable prepolymer, the value of n in the prepolymer urethane is preferably not more than 10 and more advantageously not more than 5, that is to say that the molar ratio of the isocyanate radicals in the diisocyanate or the mixture thereof to the hydroxyl radicals in the diol or the mixture thereof, by means of which the prepolymer with terminal isocyanate radicals is formed, is preferably 1.1: 1 or more and more preferably 1.2: 1 or more.

Most advantageously, the value of n in the urethane prepolymer is not greater than 3, that is to say that the molar ratio of isocyanate radicals in the diisocyanate or a mixture. the hydroxyl radicals in the diol or a mixture, from which the prepolymer urethane is formed, is advantageously 1.33: 1 or more.

Examples of diols containing cyclic radicals which are suitable for preparing the prepolymer urethane are, for example, cycloalkanediols, such as 1,3-cyclohexanediol and 1,4-cyclohexanediol, as well as the diols of formula:

<img file="LU69906A1_D0001.tif" />

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in which case the radical R ^ in the prepolymer urethane is of formula:

-o ~ respectively. Other suitable diols are, for example, cycloalpanedialcanols, such as cyclohexanedimethanol or cyclohexanediethanol; polycycloalcanediols; polycycloalkane10 dialcanols, aryldialcanols and condensation products of oxides.'dalkylene with aromatic compounds carrying two phenolic radicals.

^! Particularly preferred diols because of the interesting properties of fillings which can be produced

1? are the structure diols:

H0 {CH - CH - 0 K Ar f 0 - CH - CH OH ii aiic

R i.e. the oxyalkylated derivatives of phenolic compounds, where L Ç,

20R and R⁷ represent hydrogen atoms or alkyl radicals, for example methyl, and Ar represents a divalent aromatic radical in which each free valence is carried by an aromatic carbon atom while the sum a + b preferably does not exceed 8 and that a is preferably not greater than b + 3.

o

In this case, the divalent radical R has the formula;

-6 CH - CH - 0 4 Ar &lt;0 - CH 118 I

R 'where Ar can represent a mononuclear radical, for example phe30nylene, or tin / condensed polynuclear radical, for example of naphthalene or, of anthracene, but is preferably of formula;

'/ w where Y represents a divalent bridge, for example -0-, -S0₂~, -CO- or -CH ^ —or a substituted derivative of the CH radical₂, as

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CH.

-u ⁵ KJP \

Advantageously, one of the symbols R ⁺ and R · '' represents a hydrogen atom and the other, a methyl radical or else all k, * two represent hydrogen atoms, that is to say that the diol can be obtained by reaction propylene oxide or ethylene oxide with a phenolic compound of the formula:

HO - Ar '-' OH and preferably&gt;

<img file="LU69906A1_D0002.tif" />

• Preferably, the sum of a and b does not exceed 4.

Examples of diols which do not include cyclic radicals in the chain are ethylene glycol and propy * 2 lene glycol, in which case R represents the radical -CHg-CH ^ or

-CH ^ -C * - CHj * butylene glycol, diethylene glycol and derivatives in which one or more of the carbon atoms bear as substituents atoms or radicals inert with respect to hydroxyl and isocyanate radicals.

Diisocyanates containing cyclic radicals which are suitable for the preparation of the prepolymer urethane are, for example, diisocyanates whose chain between the free valences- comprises at least one aromatic radical or at least one cycloaliphatic radical or whose chain between the valences

20.libres comprises in combination at least one aromatic radical and at least one cycloaliphatic radical.

Cycloaliphatic diisocyanates are, for example, diisocyanates of the formula:

OCN

NCO where -ï- represents a divalent bridge which can be, for example,

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a radical -Ci ^ - ^{or one his} substituted derivatives or a -0-, -SO2 * · or -CO- bridge, while the isocyanate radicals occupy the meta or para positions with respect to the Y bridge. A particular example is 4,4'-diisocyanatodicyclohexylmethane.

Due to the advantageous properties of fillings which can be produced, aromatic diisocyanates are preferred, as is 2,4-diisocyanatotoluene or 2,6-diisocyanatotoluene as well as their mixtures, in which case the divalent radical R ^ is of formula:

<img file="LU69906A1_D0003.tif" />

possibly in combination. Another suitable aromatic diisocyanate is that of the formula:

<img file="LU69906A1_D0004.tif" />

where m represents an integer such that there is preferably no more than 3θ atoms between the cyclic radicals in the urethane prepolymer derived therefrom. A suitable diisocyanate of the latter kind is diisoeyanatoxylylene.

A particularly suitable diisocyanate is that of formula:

OCN NCO

3O where Y represents a divalent bridge which can be one of those indicated above and whose isocyanate radicals occupy the meta or para position with respect to the bridge Y. A preferred example of such a compound is -4.4 'diisocyanatodiphenylmethane.

Diisocyanates which do not contain ring radicals can be used for the preparation of the urethane prepolymer. Suitable diisocyanates of this kind are, for example, 1,4-diisocyanatobutane, 1,5-diisocyanatopentane and "

1® 1,6-dilsocyanatohexane, in which case the divalent radical R ^ is

CD./MK. AdC.ll

Q / PH 26060 / 'of formula - (CH₂)_{l (}-, - (0¾) ^ or - (CH₂)₆-..

The ethylenically unsaturated monomer which is reacted with the prepolymer urethane for the formation of the polymerizable prepolymer can comprise, for example, an · isocya5 nate radical or a radical reacting with isocyanates depending on the fact that the prepolymer urethane isocyanate radicals or radicals reacting with isocyanates respectively ",

The ethylenically unsaturated monomer which reacts with the urethane prepolymer to give the polymerizable prepolymer can be, for example, acrylic acid or one of its derivatives of formula: ·&gt; R³

I · '· * · CH₂ = C COOH where R³ represents a hydrogen atom or a hydrocarbyl radical, for example alkyl, such as methyl. In this case, the radical -X of the polymerizable prepolymer of formula XI has the formula:

- c II °

after removal of carbon dioxide from the reaction product initially formed.

Other suitable ethylenically unsaturated monomers are, for example, the hydroxylated monomers of formula 25:

R³

I

CH₂ = C -_oC00 - (CH₂)_p - OH • where R³ represents a hydrogen atom or a hydrocarbyl radical, for example; alkyl, such as methyl, and p represents an integer of at least 2_zbut preferably 2, as are the derivatives of these monomers in which one or more of the hydrogen atoms of the radical ~ (θΗ ^ ρ “ ^{are rem}PX^acas P^{ar 1111} hydrocarbyl radical, for example alkyl, such as methyl. In this case, the radical

3j&gt; -X- of the polymerizable prepolymer of formula IX has the formula: -C00- (CH₂)_p-0-C0.

Examples of suitable compounds are hydroxyethyl or hydroxypropyl acrylate and hydroxyethyl or hydroxypropyl methacrylate obtained by reaction of acrylic or methacrylic acid with ethylene oxide or oxide of

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propylene, in which case the radical X-of the polymerizable prepolymer of formula II has the formula:

<img file="LU69906A1_D0005.tif" />

h - C00 (Cil - CH) - 0 - CO 6 7, where, respectively, the two symbols R and R 'represent hydrogen atoms or one of the symbols R and H' represents a hydrogen atom and the other represents a methyl radical.

Other suitable ethylenically unsaturated monomers which can react with isocyanates are alcohol, allyl, to which ca. The radical X of the polymerizable prepolymer has the formula -Ç ^ -O-CO-, as well as 1 acrylamide or methacrylamide, to which not the radical X of the polymerizable prepolymer II has the formula -CONH-OCO.

As previously indicated, the particles of the filler must have for at least $ 50 a maximum dimension not exceeding 1,000 microns. This means that the maximum particle size in any direction cannot exceed 1,000 microns. Thus, when the load is in the form of spheres, these must have for at least 5θ $ a diameter not exceeding 1,000 microns. When the filler is in the form of fibers, these must be at least $ 50 · a length not exceeding 1,000 microns. Preferably, substantially all of the particles of the filler have a maximum dimension not exceeding 1,000 microns.

Mixing the filler with the polymerizable prepolymer generally becomes easier as the grain size of the filler becomes finer. The preferred maximum size for the filler particles is determined by the shape of these particles. Thus, when the filler is in the form of fibers, the maximum dimension of the fibers is preferably not more than 500 microns and more advantageously not more than 100 microns. On the other hand, when the charge is in the form of irregular spheres, platelets or corpuscles, the maximum particle size is preferably not more than 300 microns and more advantageously falls within the range of 1 to 100 microns.

In order for a hard dental filling to be formed by hardening the composition, it is desirable that the particles of the filler have a Knoop hardness of at least 100.

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i ίο general rule, as the hardness of the filler particles in the composition increases, the hardness of the dental filling resulting from the hardening of the composition increases and, for this reason, it is preferable that the Knoop hardness of the filler is at least 3θθ and more advantageously still at least 5θθ · As a general rule, the required hardness and in particular the preferred hardness is manifested by the inorganic fillers.

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

_t « |.

The dental filling composition may contain, for example, $ 10 to $ 90 filler, based on the weight of the composition, although, in order for the dental filling resulting from curing of the composition to have resistance to particularly desirable abrasion and hardness, low shrinkage upon hardening and a low coefficient of thermal expansion, the dental filling compositions preferably contain 3θ to 80 $ and more advantageously 60 to 80 $ of charge, based on the weight of the dental filling composition. It is possible to use mixtures of different charges.

The filler can be, for example, in the form of spheres, platelets, fibers or crystalline whiskers or can be of irregular shape. Suitable fillers are, for example, apatite, soda glass, quartz, silica gel, borosilicate glass, synthetic sapphire (alumina) or a fiber metal.

Mixing of the polymerizable prepolymer with the filler for the formation of the dental filling composition can be carried out by stirring the prepolymer with the filler. However, due to the failure of the polymerizable prepolymer, possibly in combination with a copolymerizable monomer, may be viscous and therefore difficult to agitate with the filler to mix it properly, the polymerizable prepolymer, possibly in combination with the copolymerizable monomer, may advantageously be diluted with a suitable diluent which lowers the viscosity and thus makes it easier to mix the filler properly.

When the mixing has been carried out, the diluent can be removed, for example by evaporation. Advantageously, the diluent can be a copolymerizable ethylenically unsaturated monomer, this

CD-CH .AdC.ll

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monomer being, if desired, removed completely when the mixture is formed, but alternatively, when the dental filling composition is to contain copolymerizable ethylenically unsaturated monomer, the monomer content can then be lowered to the required value.

In order for it to be possible to form a dental filling, the filler of which adheres particularly well to the hardened polymerizable prepolymer of the filling, it is far preferable for the filler to be treated using an association agent which is capable of reacting with both the filler and the polymerizable prepolymer before this filler and this polymerizable prepolymer are mixed together. The combination agent should have the effect of increasing the toughness of the bond between the filler and the cured polymerizable prepolymer in the closure.

Appropriate combination agents for glass are in particular silanes, for example Y-methacryloxypropyltrime- '· · thoxysilane, Y-aminopropyltrlethoxysilane and Y-glycidoxypropyltrimethoxysilane.

As already indicated, the dental filling composition may contain a liquid ethylenically unsaturated monomer copolymerizable with the polymerizable prepolymer and must contain such a monomer when the polymerizable prepolymer is solid so that the composition is fluid and in particular has a pasty consistency. .

The amount of this ethylenically unsaturated monomer used may desirably be just sufficient to impart the desired fluidity to the dental filling composition.

As the incorporation of such a monomer can lead to a reduction in the mechanical strength of a filling made of the composition, it is preferable to use the ethylenically unsaturated monomer in the filling composition in one quantity not exceeding $ 100 and preferably not exceeding $ 50 of the weight of the polymerizable prepolymer. \

Suitable copolymerizable liquid ethylenically unsaturated monomers whose polymers must be insoluble in water are in particular vinyl monomers, such as vinyl esters, acrylic acid and methacrylic acid. These monomers cannot be toxic.

Suitable vinyl esters are, for example, vinyl acetate and acrylic acid esters of the formula

CD-CH »AdC.ll

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CH₂= CH ~ COOR⁶, where R⁶ represents an allcyl, aryl, allcaryl, aralkyl or cycloalkyl radical. For example, R ^ may represent an alkyl radical of 1 to 20 and preferably of 1 to 10 carbon atoms. Particular vinyl esters which should be mentioned are, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate , isobutyl acrylate and t-butyl acrylate.

Other suitable vinyl esters are, for example, the esters of formula CH₂-C (R⁷) CQ0R⁶, whereR⁷ may represent an alkyl radical, for example methyl. · In the above formula CH_O = C (R? ') CÛ0r6 of the ester, R⁶ and R? can be the same or

Ä '*! · Different. Particular vinyl esters which may be mentioned include, for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-15 sopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and t-butyl methacrylate.

Mixtures of acids and esters can also be used.

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

The dental filling composition according to the invention can be molded to the required shape of the dental filling and can then be hardened into a hard filling by polymerization of the polymerizable prepolymer, optionally in combination with an ethylenically unsaturated monomer. copolymerizable • with · prepolymer.

The hardening of the composition giving the dental filling can be promoted by a catalyst. It is desirable that the catalyst be able to cure the composition at a relatively low temperature, i.e., at or near room temperature, because maintenance of a high temperature may be unpleasant for the patient undergoing treatment. Suitable catalysts suitable for curing at a relatively low temperature are, for example, a mixture of a peroxide and an accelerator, such as a mixture of a peroxide and an amine such as a mixture of peroxide

1.0 of benzoyl and N, N-dimethyl-p-toluidine. Other catalysts are formed by a mixture of a peroxide and a cobalt accelerator, such as a mixture of methyl ethyl ketone peroxide with cobalt octoate, cobalt naphthenate or cobalt naphthenate and dimethylaniline. .

When the catalyst which is used is capable of causing the composition to cure at a relatively low temperature, it is desirable that the catalyst be mixed with the dental composition shortly before use thereof because otherwise hardening of the composition may become exaggerated before the composition has been molded to the required shape of the dental filling.

The generally chosen proportions are from 0.01 to 20 $ of catalyst, based on the weight of the polymerizable material of the dental composition, that is to say from 0.01 to 20 $ of catalyst, on based on the weight of the polymerizable prepolymer or on the basis of the weight of the polymerizable prepolymer increased by the polymerizable monomer possibly present. If desired, it is possible to take higher or lower amounts of catalyst, but an amount of 0.1 to 10 $ by weight of catalyst is preferable. It is more preferable to take $ 0.5 to $ 5ⁱⁿ weight of catalyst.

The catalyst used can be activatable by radiation and, according to a preferred embodiment, the subject of the invention is a dental composition of the type described above containing a photosensitive catalyst which comprises (a) at least one photosensitizer chosen from fluorenone , its substituted derivatives and the α-diketones of formula:

A - C - C - A Il II 0 0

3θ where the radicals A, which are identical or different, are substituted hydrocarbyl or hydrocarbyl radicals, and (b) at least one, reducing agent capable of reducing the photosensitizer when the latter is in an excited state.

The dental compositions of the invention which contain a photosensitive catalyst can be cured by irradiation using ultraviolet radiation, i.e., from a wavelength of about 230 millimicrons to 400 millimicrons. The compositions can also be cured by irradiation by means of visible radiation and especially visible radiation with a wavelength from 400 millimicrons to 500 millimicrons. Alternatively, it is possible to take a mixture of ultraviolet and visible radiation.

In the α-dketone of the above formula, when the radicals A are hydrocarbyl radicals, they can be, for example, aliphatic radicals such as alkyl radicals of 1 to 10 carbon atoms, aromatic radicals such as radicals phenyl, cycloaliphatic radicals such as cyclohexyl radicals, aralkyl radicals such as benzyl radicals or alkaryl radicals such as tolyl radicals. As a variant, the radicals A can form a divalent radical together so that, in the photosensitizer, these radicals A, in association with the carbonyl radicals, constitute a cyclic structure. For example, radicals A can form an aliphatic radical

J divalent or else can formal '' an aromatic radical and in particular a condensed aromatic friendly.

Suitable α-diketones are in particular the biacetyl of formula j

CH, - C - C - CH ü 'the benzile of formula:

It has the formula naphthile:

0 ß-naphthile ^ of formula:

the formula acenaphthenedione

CD-CH / AdC.ll.

Q / PH 26060 / ...

<img file="LU69906A1_D0006.tif" />

When the radicals A are substituted hydrocarbyl radicals, the substituent radical (s) cannot cause appreciable inhibition of the polymerization of the polymerizable material. Examples of photosensitizers of which the radicals A are substituted hydrocarbyl radicals are no · &lt;

especially the, ρ, ρ'-dimethoxybenzile and the ρ, ρ'-dichlorobenzile.

The particularly preferred photosensitizer is benzile.

The photosensitizer can be present in the dental composition in a concentration ranging, for example, from 0.01 to 10 $ by weight of the polymerizable material of the composition, although concentrations falling outside this range can be chosen, if the thing is desired. Preferably, the photosensitizer is present in a concentration of 0.5 to 5% of the weight of the polymerizable material of the composition.

The reducer present in the photosensitive catalyst • must be capable of reducing the photosensitizer when it is in an excited state. The tendency of the reducing agent to inhibit polymerization should be little or no. The fact that a reducing agent exerts an inhibition or not can be appreciated by means of a simple experiment, for example by conducting the polymerization of the polymerizable material which the composition contains using only a thermal initiator and also in the presence of a reducing agent at the required concentration and then by comparison of the polymerization rates in the presence and in the absence of the reducing agent.

^ Appropriate reducing agents are in particular the compounds of formula r?&gt; MR, where M represents an element of the group VB of taCD-CE AdC.ll

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periodic beau and the symbols R, identical or different, represent hydrogen atoms or hydrocarbyl radicals, substituted hydrocarbyl radicals or radicals in which two R radicals, in association with the element M, form a ring system, at maximum two of the symbols R representing hydrogen atoms and the element M not being directly linked to an aromatic radical ”

The periodic table mentioned above is that published in "Advanced Inorganic Chemistry", second edition, by FA Cotton and G. Wilkinson (Interscience 1966).

The element M of the reducing agent can be, for example, phosphorus and more advantageously nitrogen. If the thing is desired,&gt;

element M can also be arsenic or antimony.

· The reducer can be primary, secondary or tertiary, that is to say that, in the formula _R2 ^ MR, the number of hydrogen atoms represented by the symbols R can be 2, 1 or 0.

For example, the reducing agent can be a primary, secondary or tertiary amine or phosphine.

»

One or more of the radicals R may be hydrocarbyl radicals. These hydrocarbyl radicals can be alkyl, cycloalkyl or aralkyl radicals. Advantageously, the radical R can be an alkyl radical of 1 to 10 carbon atoms.

Examples of suitable reducing agents comprising one or more hydrocaiyl radicals represented by R are propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, trimethylamine, triethylamine , tripropylamine, tributylamine, tripentylamine, dimethylaminoethyl methacrylate and long chain fatty amines, such as those of formula ^ 13 ^ 37 ^ (^ 3 ^ 2 *

It should be noted that the specific examples of reducing agents whose element M is nitrogen are also illustrative of reducing agents whose element M is phosphorus, arsenic or antimony.

The radicals R numbering 1 or more may be substituted hydrocarbyl radicals and in particular these hydrocarbyl radicals may carry a substituent of formula -R ^ -MCR ^ where M represents an element from group Vb of the periodic table while R¹ represents, for example, an alkylene radical and that the symbols R, identical or different, represent for example-.

CD-CH AdC.ll

Q / PH 26060 / ..

ίο pie hydrogen atoms or hydrocarbyl radicals.

Examples of reducing agents of formula of which at least one of the symbols R represents a substituted hydrocarbyl radical are the diamines of formula (R²) 2N (CH2) nN (R²) 2 where n represents an integer equal to at least two and the symbols R², identical or different, represent hydrogen atoms or hydrocarbyl and especially alkyl radicals. For example, the reducing agent can be ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine or hexamethylene diamine or one of their N-hydrocarbylated and especially N-allcylated derivatives. . Other suitable reducing agents are in particular the compounds of formula (R²) 2N (CH2) nN (R²) 2 in which one or more of the hydrogen atoms of the radicals -CH₂-are a radical -N (R²)₂and especially a radical -NHg. ·

Examples of reducing agents, the element M of which is part of a ring system are piperidine and its N-hydrocarbyl derivatives and. especially N-alkylated.

Other reducers are triallylamine, p-xylylenediallylamine, allylthiourea and the soluble salts of sulfur aromatic acids.

Advantageously, the concentration of reducing agent can fall within the ranges indicated above with respect to the photosensitizer. Preferably, the reducing agent is present in a concentration of 1 to the weight of the polymerizable material of the dental composition.

The invention is illustrated by the following examples in which the parts are by weight.

EXAMPLE 1 352 parts of a condensation product resulting from the reaction of 2,2-bis (p-hydroxyphenyl) propane and propylene oxide in a molar ratio of 1 are heated to fusion. 2 and stirred under reduced pressure to degas.

By operating dp even separately, heating, stirring and degassing 5θθ parts of 4,4'-diisocyanatodiphenylmethane. The condensation product and the diisocyanate are then mixed in a diisocyanate: condensation product molar supply of 2: 1 and 556 parts of methyl methacrylate are added to the mixture, which has been dried over calcium hydride, then 0.14 part of dibutyltin dilaurate. The mixture is cooled in an ice bath to moderate the evolution of heat resulting from the formation of uCD-CH .AdC.ll

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4ο rethanes prepolymer so that the temperature does not exceed 55 ° O ·

Stirring is continued for 90 minutes after the end of the exothermic reaction.

260 parts of methacrylate are then added. 2-hydroxyethyl which was first distilled and degassed and the resulting mixture was stirred for 90 minutes to form the polymerizable prepolymer with ethylenic unsaturation.

. 60 parts of the mixture of polymerizable prepolymer and methyl methacrylate obtained as above are mixed with 180 parts of glass beads (Ballo.tini 3000 CP01 from the company Plastichem.Ltd.) Which have a diameter of $ 80 by weight. 4 to 44 microns. '^&gt; The mixture is then stirred and an additional methyl methacrylate is added thereto to promote incorporation, after which 6 parts of a catalytic solution obtained by dissolving 2 parts of benzyl in 4 parts of dimethylaminoethyl methacrylate are added and 4 parts of methyl methacrylate. After 15 minutes of stirring, the pressure is lowered and the methyl methacrylate which has been added is evaporated off to promote stirring.

The pasty mixture is then poured into a cylindrical glass mold and exposed to the radiation of a blue lamp for 15 minutes in order to harden it.

The cured product has the following properties.

Compressive strength

Compression module

Rockwell hardness

Flexural module

Water absorption (after • 65 days of immersion

Λ. in water at 37 ° C)

178 N. mm '

3.690 N. mm

171 scale H 14.500 N. mm ”²

$ 0.75 weight

EXAMPLE 2 The operations of Example 1 are repeated, but using 30 parts of the mixture “of polymerizable prepolymer with ethylenic unsaturation and methyl methacrylate and 3 parts of the catalytic solution and replacing the glass beads with 60 parts of glass fibers passed through a hammer mill with a size of 10 microns x 200 microns (from Glass Fibers Ltd.). Before mixing with the other constituents of the composition, the glass fibers are coated with Y-methacryloxypropyltrimethoxysilane by adding 100 parts of

CD-CH .AdC.ll

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glass previously heated to 400 ° C and then allowed to cool in a desiccator with a solution of 1 part of Y ~ methacryloxy ~ propyltrimethoxysilane in 100 parts of methanol, stirring the mixture for 3. hour, evaporating the methanol, collecting the fibers on a 62 micron mesh screen and finally by heating the fibers to 140 ° C to crosslink the silane.

The cured product has the following properties.

201 N. mm

3.640 N.mm scale B

168 scale H -2

0.05 mg.tam

Compressive strength t

Compression module 10 Rockwell hardness, Rockwell hardness. 'ii ·'_&gt; Abrasion resistance EXAMPLE, 3. The operations of Example 1 are repeated, but taking 15 parts of the mixture of polymerizable prepolymer with ethylenic non-saturation and of: methyl methacrylate and 1.5 parts of the catalyst - and replacing the glass beads with 36 parts quartz powder with which the surface of Y-methacryloxypropyltrimethoxysilane has been coated as described in Example 2.

The cured product has the following properties.

Compressive strength Compression module Rockwell hardness Rockwell hardness Abrasion resistance

157.6 N mm '3.050 N mm 81 scale B

I70 H scale 0.007 mg mm^-2

EXAMPLE 4 Linear thermal expansion coefficient

33.7 ppm at 40 ° C

Transfer by washing with 300 ml of methylene chloride · 500 g of 4,4'-diisocyanatodiphenylmethane freshly

(3) distilled darfs; a 5 liter capacity balloon purged with azo • ·. i- * te. The flask is fitted with an anchor-shaped glass stirrer, a nitrogen purge tube, a water condenser and a thermometer. '

By weighing, 352 g of a molten condensing product resulting from the reaction of 2,2-bis (p-hydroxydiphenol) propane with propylene oxide and 0.15 g of dibutyltin dilaurate are introduced into a vial. bromine with a capacity of 1 liter, which has been purged with nitrogen. 200 ml of methylene chloride are further introduced into the ampoule to prevent the condensation product from solidifying. .

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The bromial bulb is then placed above the flask and its contents are added dropwise to the contents of the flask over 45 minutes, after which the reaction is allowed to progress for approximately 45 minutes at the end of which 3θθ g of metha5 crylate are added of hydroxyethyl as well as 0.15 S of dibutyltin dllaurate in 3 minutes. The contents of the flask heat up and, when this heating ceases, the flask is heated in a water bath (until the reflux of methylene chloride) while the contents are stirred under a stream of nitrogen until time when the infrared spectrum of the resulting product indicates the presence of a trace

-only.isocyanate radicals (duration of about 3 days).

» * !·

Remove the water bath and add methanol to the con&gt; ...

held agj.té of the flask to separate the polymerisable prepolymer. · The contents of the flask are allowed to settle, then the methanolic layer which is discarded is siphoned off. The methanol wash is repeated several times as above, until the methanolic layer is clear. The polymerizable prepolymer is then dried in the flask at room temperature under vacuum until a dry foam is formed. This foam is crushed and dried to remove the last traces of methanol.

In the absence of blue light, 13.37 parts of the polymerizable prepolymer powder are dissolved in 10.94 parts of ethylene glycol dimsfeacrylate and 0.625 parts of dimethylaminoethyl methacrylate are added to the solution, then 0.0625 parts of camphorquinone. 75 parts of a powdered borosilicate glass with a particle size of less than 53 · microns, which have been coated with $ 1 by weight of Y-methacryloxypropyl trimethoxysilane, are incorporated by stirring into this mixture, after which the fluid paste is passed. aunt results in a grille where it is degassed during its passage.

Cylindrical specimens of this paste with a diameter of 3 mm and a length of 2.5 mm are irradiated in polytetrafluoroethylene molds by exposure for 2 minutes to the light of a source provided with a 47 cm fiber optic. The hardened test pieces are removed from the molds and stored in water at 37 ° C for testing after immersion times of 1 hour, 24 hours and 1 week. The results are given in the following table.

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BOARD.

<td>duration immersion</td><td>Average compressive strength (N.mra ~ ^)</td><td>Average tensile strength (N.mm “^).</td><td>Rockwell hardness (H scale)</td>

<td>1 hour</td><td> 259</td><td> 42</td><td> -</td>

<td>24 hours</td><td> 274</td><td> 45</td><td> 115</td>

<td>1 week</td><td>30I</td><td> 46</td><td> -</td>

EXAMPLE 5.I.

2.585 parts of the polymerizable prepolymer prepared as in Example 4 are dissolved in 2.115 parts of ethylene glycol dimethacrylate and 0.1 part of fluorenone and 0.2 part of dimethylaminoethyl methacrylate are added to the solution. While degassing is carried out, this polymer is mixed with ^ parts of borosillate glass powder (the same as in example 15 pie h · but coated with 2% by weight of silane), then thick specimens are hardened the resulting paste as in Example 4 for 100 minutes using a low intensity mercury vapor lamp fitted with a filter transmitting radiation of 437 millimicrons. Curing takes place to a depth of 1.5 mm.

EXAMPLE .. 6. A paste is prepared and hardened as in Example 5, but using a-naphthol instead of fluorenone. Curing takes place to a depth of 2.5 mm.

EXAMPLES 7 TO 12. 6.7 parts of the polymerizable prepolymer prepared as in Example 4 are dissolved in 3.3 parts of methyl methacrylate and 0.2 part of a solution formed of 0.1 l is added to the solution part of fluorenone in to- parts of dimethylaminoethyl methacrylate. By stirring, 15 parts of filler are incorporated, pdis, the resulting paste is poured into glass tubes with a diameter of 6 mm. The specimens are hardened by exposure to light from a fluorescent tube for 3θ minutes. The hardened specimens are cut into 12 mm lengths and their compressive strength is determined.

<td>Example No.</td><td>Charge</td><td>Compressive strength. (Ν.ιμΓ ^)</td>

<td> 7</td><td>Borosilicate glass under 53 microns</td><td>I78</td>

<td> 8</td><td>Glass plates with a diameter of 0.8 mm</td><td> 98</td>

<td> 9</td><td>Glass marbles (Ballotini)</td><td> 158</td>

<td> 10 .</td><td>Quartz less than 53 microns</td><td> 158</td>

<td> 11</td><td>Silica gel spheres less than 53 microns</td><td> 120</td>

<td> 12 . ’ * &gt;</td><td>Soda glass fibers passed through a hammer mill, with a diameter of 10 microns and a length of 200 microns</td><td> 202</td>

EXAMPLE 13.15 5.5 parts of the polymerizable prepolymer obtained as in Example 4 are dissolved in 4.5 parts of ethylene glycol dimethacrylate and 0.025 part of N, N-dimethyl-p-toluidine is added to this solution.

»

Using a spatula, incorporate in a few seconds from 0.3 part of this mixture to 0.7 part of a coated charge. This charge is formed from borosilicate glass powder coated with a particle size of less than 53 microns obtained by coating 23.33 g of glass sprayed successively by means of 0.23 part of Y-methacryloxypropyltrimethoxysilane and 0.03 part of benzoyl peroxide in methylene chloride.

The resulting paste is pressed into cylindrical molds of 3 wm x 3 mm where it is left to stand for a few hours, after which the rigid test pieces are removed and subjected to testing. , The rigid material has a compressive strength of 160 N. mmq- and a diametral compressive strength of 30 N.mm “².

EXAMPLE 14 3 * 3.33 parts of a polymerizable prepolymer obtained as in Example 1 are dissolved in 16.66 parts of methyl methacrylate and 170 parts of glass beads with an average diameter of 4.4 microns (Ballotini FP01 3000).

5 parts of a solution comprising 40% of dimethylaminoethyl methacrylate, 20% of benzile and 40% of methyl methacrylate are added to the mixture which is then heated. The excess methyl methacrylate is removed and the mixture is stirred for

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minutes after removal of the excess methyl methacrylate under vacuum.

The resulting paste is pressed into three conical cavities formed in the canines of Beagle females and the paste is hardened in situ by means of a fiber optic guide with a length of cm. After 26 months, the fillings are still in the teeth and do not give visible signs of serious mechanical failure or loosening in the cavities.

EXAMPLES 15 TO 22 A polymerizable prepolymer is prepared as in Example 4. In the absence of blue light, 3.1 g of the prepolymer 's data are dissolved 2.54 g of monomer (see below) and to this solution is added 0.24 g of dimethylaminoethyl methacrylate, then

I

0.12 g of benzile. By stirring, 14 g of powdered borosilicate glass with a particle size of less than microns coated with $ 2 by weight of Y-methacryloxypropyltrimetho * xysilane are incorporated into this mixture (quantity such that the filler forms $ 70 of the composition), then the resulting paste is passed through a calender where it is degassed during its passage.

Cylindrical test pieces of this paste with a diameter of 3 mm and a length of 2.5 mm are hardened in polytetrafluoroethylene molds by exposure for 1 hour at a distance of 30.5 cm to a sealed Thorn lamp. The test pieces are removed from the molds after 1 hour and the compressive strength and hardness are determined.

<td>Example no.</td><td>monomer</td>

<td> 15</td><td>methyl methacrylate</td>

<td> 16</td><td>methacrylic acid</td>

<td> 17</td><td>hydroxyethyl methacrylate</td>

<td>_Λ 18</td><td>vinyltoluene</td>

<td>. i?</td><td>styrene</td>

<td> . 20 </td><td>triethylene glycol dimethacrylate</td>

<td> 21</td><td>ethylene glycol dimethacrylate</td>

<td> 22</td><td>allyl methacrylate</td>

rm rrrr

<td></td><td>Example No.</td><td>Compressive strength (N. mm “²)</td><td>Rockwell hardness (H scale)</td>

<td></td><td> 15</td><td>I73</td><td> 56</td>

<td></td><td> 16</td><td> 172</td><td> 54</td>

<td> 5</td><td> 17</td><td> 164</td><td> 48</td>

<td></td><td> 18</td><td> 166</td><td> 30</td>

<td></td><td> 19</td><td> 163</td><td> 22</td>

<td></td><td>2Ö</td><td> 179</td><td> 70</td>

<td></td><td> 21</td><td> 184</td><td> 85</td>

<td> 10</td><td> 22</td><td> 155</td><td> 52</td>

EXAMPLE 23 ?! II -I. 1 I! T f

A., The operations of Example 21 are repeated, but after exposure of the specimen for 1 hour to radiation, the specimen is removed from the mold and allowed to stand for 2 days before carrying out the tests. .

B. For comparison, the above operations are repeated using a different polymerizable prepolymer. This prepolymer is obtained as described below.

Freshly distilled 2,4-diisocyanatotoluene is introduced by washing with methylene chloride into a flask and a mixture of 2,2-propane bis / methacrylate is added dropwise to the content of the flask.^-3- (4-phenoxy) -1,2-hydroxypropane1_7 and dibutyltin dilaurate. The reaction is allowed to progress until the infrared analysis of the mixture indicates that the isocyanate radicals only remain in trace amounts.

Methanol is added to the contents of the flask to separate the resulting prepolymer, which is dried and finally crushed.

C. "Again by comparison, the operations indicated in A. are repeated, taking a prepolymer prepared as in B., the difference being that the 2,4-diisocyanatotoluene is replaced by i so cyandtobenzene.

D. As another comparison, the operations indicated in A. are repeated, taking the prepolymer prepared in B. but in

3j&gt; using diisocyanatoanisidine instead of 2,4-diisocyanatotoluene.

E. Also for comparison, the operations indicated in A. are repeated using the prepolymer prepared in B._? but taking 4.4 * -diisocyanatodiphenylmethane instead of 2,4-diisocya40 natotoluene.

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<td></td><td>Compressive strength (K. mm ”²)</td><td>Tensile strength (ïï.mm “²)</td><td>Rockwell 'hardness (H scale)</td><td>Hardening depth in mm after 1,000 seconds</td>

<td>AT</td><td> 197</td><td> 37</td><td> 105</td><td> ^,7</td>

<td>B</td><td> 178</td><td> 32</td><td> 88</td><td> -</td>

<td>VS</td><td> 1½</td><td> 28</td><td>test tube exploded</td><td> -</td>

<td>D *</td><td> -</td><td> -</td><td> -</td><td> -</td>

<td>E</td><td> 201</td><td> 3^lh</td><td> 96</td><td> 3,1</td>

* = The mixture has very poor curing properties "* 1 'qt does not allow obtaining' test specimens.