Polymerizable dental composition.

The invention relates to dental compositions with an alkalizing effect, such as, for example, cements, cavity liners and root filling materials, in particular a polymerizable dental composition based on at least one polymerizable monomer or prepolymer, a curing catalyst and inorganic fillers suitable as an underfilling material.

In the treatment of tooth cavities, underfill materials are used to cut the pulp before the actual filling is placed. It is known that calcium hydroxide is responsible for the formation of secondary dentin above the pulp and that the thicker and firmer this layer, the better protection is achieved. However, the cements containing calcium hydroxide which are commonly used and which harden on a chelate basis do not provide satisfactory strength.

EP-A-189 903 describes an underfill material containing calcium hydroxide or a calcium hydroxide-forming agent such as calcium oxide, which is photopolymerizable. This underfill material contains ethylenically unsaturated compounds, in particular vinyl compounds, and a photocatalyst, for example camphorquinone in combination with an amine. A fundamental problem is, however, that calcium hydroxide or Calcium oxide are very opaque, so that only small depths of hardening can be achieved, as tests with a commercial product according to EP-A-189 903 Prisma VLC Dycal® from Dentsply International, Inc.) show.

The invention is also intended to provide an underfill material which is hydrolysis and acid resistant, has low water solubility, shows good compressive strength and is non-toxic. In addition, a controlled release of calcium hydroxide is to be achieved in order to achieve an alkalizing effect against the pulp and to protect it against acids and bacterial attacks. In particular, the material should have a greater depth of curing and less shrinkage after the polymerization.

It has surprisingly been found that this object can be achieved by incorporating a glass powder with a high calcium oxide content as filler into the dental material. Ca²⁺ and OH⁻ ions are released by water absorption. The glass powders used according to the invention are not opaque and therefore do not hinder the light curing of the dental material.

The glass powder used according to the invention contains, in addition to 40 to 75% by weight of calcium oxide, 5 to 30% by weight of boron oxide and 5 to 35% by weight of silicon dioxide. A preferred composition consists of 45 to 60% by weight. Calcium oxide, 15 to 28% by weight. Boron oxide and 10 to 30% by weight of silicon dioxide. The average particle size (weight average) of the glass powder is preferably between about 10 and 30 μm, but powders with a particle size of 1 to 100 μm are suitable.

As already stated above, the dental compositions according to the invention are particularly suitable as underfill materials due to the controlled release of calcium ions from the glass powder. It is preferably light-curing one-component compositions. In addition to the glass powder, these may contain further inorganic fillers and at least one polymerizable monomer or prepolymer and suitable catalysts.

If necessary, the glass can also contain oxides, for example kaolin or oxides of Sr, Ba, La, Zr or rare earths. Ca tungsten, Ba tungstate and fluorine and / or phosphorus-containing compounds such as NaF, KF, BaF₂, SrF₂, rare earth fluorides, Ca or Al phosphate and cryolite are further suitable additives.

The fluorides of rare earth metals (SE) with atomic numbers 59 to 71 have proven to be particularly suitable inorganic fillers, preferred compounds being those of elements 66 to 71.

Ytterbium fluoride is preferably used. The fluorides of the rare earth metals are generally incorporated into the dental material as a powder. The average grain size of the primary particles can fluctuate. In the case of a micro-filled dental filling material, it is in the range from 5 to 700, in particular 20 to 500, preferably 50 to 300 nm. If appropriate, the average primary particle size can also be in the range from 700 nm to 15 μm.

The content of RE fluorides, based on the total weight, is between 1 and 50%, in particular 5 to 40%; it is preferably between 10 and 30%. It depends in particular on the desired x-ray opacity or transparency. Mixtures of the SE fluorides can also be used.

In addition, other fillers such as Ba, Sr, Ca, Li-Al silicate glasses as well as BaSO₄, CaWO₄, Bi-Subnitrat and Bi-Carbonat can be used.

Other, non-radiopaque, inorganic constituents are usually present in the dental material. Suitable fillers are, for example, amorphous silicas, in particular pyrogenic or precipitated silicas with a BET surface area of ​​approximately 20 to 400 m² / g. In particular, fumed silicas with a BET surface area of ​​30 to 300 m 2 / g and an average grain size of the primary particles of about 5 to 50 nm are used, with particularly preferred materials in the range between 1 and 50 nm. However, silicas with an average primary particle size of 50 to 1000, preferably 100 to 300 nm can also be used. Li-Al silicate glasses are also suitable, as mentioned above.

The amount of non-X-ray-opaque fillers in the dental material depends on the amount of SE fluorides used and is generally in the range from 5 to 84%, in particular 10 to 70%, preferably 20 to 50%. The total content of fillers (glass powder, RE fluorides and other inorganic compounds) is 6 to 85, preferably 15 to 85 and in particular 30 to 85% by weight.

The inorganic constituents of the dental material can be silanized in the usual way in order to improve the bond between the organic matrix and the inorganic filler. 3-methacryloxypropyltrimethoxysilane is suitable as an adhesion promoter. The amount of adhesion promoter used depends on the type and specific surface of the filler and the desired viscosity of the dental material.

The dental material must also contain a polymerizable vinyl compound. Monofunctional or polyfunctional (meth) acrylates, which can be used alone or in mixtures, are particularly suitable for this purpose. As examples of these compounds are methyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, triethylene glycol dimethacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, butanediol dimethacrylate, hexanediol dimethacrylate, decanediol dimethacrylate, dodecanediol dimethacrylate, bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, ethoxylated bisphenol-A-dimethacrylate, but also bis-GMA (2,2-bis-4- (3-methacryloxy-2-hydroxypropyl) phenylpropane) and the reaction products of isocyanates, in particular di- and / or triisocyanates and OH group-containing methacrylates. Examples of these are the reaction products of 1 mol of hexamethylene diisocyanate with 2 mol of 2-hydroxyethyl methacrylate, of 1 mol of tri (6-isocyanatohexyl) biuret with 3 mol of hydroxyethyl methacrylate and of 1 mol of trimethylhexamethylene diisocyanate with 2 mol of hydroxyethyl methacrylate, which are referred to below as urethane dimethacrylate. The proportion of these mostly long-chain compounds in the dental material is between 10 and 50% by weight. In principle, all binders that can be used for a dental material are suitable.

Depending on the type of catalyst used, the dental material can be hot, cold or hardenable by photopolymerization. Combinations of these are also possible (dual hardening).

The known peroxides such as dibenzoyl peroxide, dilauroyl peroxide, tert-butyl peroctoate or tert-butyl perbenzoate can be used as catalysts for the hot polymerization, but also α, α'-azo-bis (isobutyroethyl ester), benzpinacol and 2,2'-dimethylbenzpinacol suitable.

As catalysts for photopolymerization, for example, benzophenone and its derivatives, acylphosphine oxides and benzoin and its derivatives can be used. Examples of preferred photoinitiators are the α-diketones such as 9,10-phenanthrenequinone, diacetyl, furil, anisil, 4,4'-dichlorobenzil and 4,4'-dialkoxybenzil. Camphorquinone is used with particular preference. The use of the photoinitiators together with a reducing agent is preferred. Examples of reducing agents are amines such as cyanoethylmethylaniline, dimethylaminoethyl methacrylate, triethylamine, triethanolamine, N, N-dimethylaniline, N-methyldiphenylamine and N, N-dimethyl-sym.-xylidine, N, N-dimethyl-p-toluidine and p-dimethylaminobenzoic acid ethyl ester. The photoinitiators and reducing agents can be used as catalyst mixtures together with catalysts for hot polymerization (preferably with peroxides).

Systems which provide free radicals, for example benzoyl or lauroyl peroxide, together with amines such as N, N, -dimethyl-sym.-xylidine, N, N-di-2-hydroxyethyl-p-toluidine or N, N-, are used as catalysts for the cold polymerization. Dimethyl-p-toluidine used.

The amount of these catalysts in the dental material is usually between 0.1 to 5% by weight.

Finely divided splinter or pearl polymers can also be incorporated into the dental material, which can be homopolymers or copolymers of the vinyl compounds already described. These homopolymers or copolymers can in turn be filled with the inorganic fillers described, including the radiopaque ones. For this purpose, reference is made to EP-PS 11 190 and DE-PS 24 03 211. The dental material may also contain the usual pigmentation agents and stabilizers.

In order to increase the degree of filling of such filling materials, it is customary, for example, to prepare a copolymer from bis-GMA, triethylene glycol dimethacrylate, the glass powder and, if appropriate, further inorganic fillers such as ytterbium fluoride and pyrogenic silica, to grind this as a fragment polymer and then to incorporate it into the filling material.

In the case of light-curing materials, the polymerization is carried out after placing the underfill with a commercially available halogen lamp.

Filling materials are also produced as two-component materials, which harden cold after mixing. The composition is similar to that of the light-curing materials, except that instead of the photocatalysts, one paste, for example benzoyl peroxide, and the other paste, for example N, N-dimethyl-p-toluidine, are mixed into the paste. By mixing approximately the same parts of the two pastes, a tooth filling material is obtained which hardens in a few minutes.

The following examples serve to explain the invention.

<b>Examples</b>

To produce the glasses used as filler according to the invention, the raw materials were mixed with one another in a ball mill, and the mixtures were then sintered in an aluminum oxide crucible at 1000 ° C. for one hour. The presintered mixtures were homogenized again. The mixtures were then melted in a platinum crucible (30 minutes at 1500 ° C.). The melts were quenched in water, the mass was dried and finally dry milled in a ball mill. Calcium carbonate, quartz and boron oxide are suitable raw materials. If necessary, small amounts of up to 5% by weight of a flux such as cryolite, NaF, KF etc. are added. The calcium carbonate content is so high that the ratio of CaO: SiO₂ in the glass is normally over 1.5.

The glasses were mixed homogeneously with a polymerizable vinyl compound (monomer). Some mixtures were mixed with other inorganic substances. The monomer for experiments A to F and H to K was a mixture of 2,2-bis [p- (β-hydroxyethoxy) phenyl] propane dimethacrylate (SR 348) and a urethane dimethacrylate (RM3) (reaction product of trimethylhexamethylene diisocyanate and hydroxyethyl methacrylate ). The monomer of Experiment G was a mixture of 56.6 g of 2,7,7,9,15-pentamethyl-4,13-dioxo-3, 14-dioxa-5, 12-diaza-hexadecane-1,16-diyl -dimethacrylate and 5 g 3,6-dioxaoctamethylene dimethacrylate. The comparative test G was carried out with the sales product Prisma VLC Dycal® from De Trey Dentsply. Test A is also a comparative test according to the prior art.

Camphorquinone (CQ) and cyanoethylmethylaniline (CEMA) served as photocatalysts. The binder for experiments A to F and H to K had the following composition:<tables id="tabl0001" num="0001"><img file="EP0449399A2_D0001.tif" /></tables>

Test specimens were produced for measuring the depth of cure, transparency, compressive strength, water solubility, water absorption and Ca (OH) ₂ release. The production of the test specimens and their dimensions:

Curing depth - steel mold diameter 4 mm, height 6 mm. The mold is filled and exposed for 40 seconds with a commercially available light curing device (Heliomat® from Vivadent).

Transparency - the test specimen is manufactured in a steel mold with the dimensions 15 x 9 x 1 mm and cured for 3 minutes in a light curing device under 6 bar pressure. The transparency was measured using a device as described in EP-A-189 540, Example 1.

Compressive strength - test specimens are manufactured in a Delrin mold with a diameter of 4 mm and a height of 6 mm. The material is cured with the light curing device for 3 minutes.

Water solubility and water absorption - The test specimen is produced in a steel mold with a diameter of 15 mm and a height of 0.5 mm. The curing takes place as described above.

The test results are shown in Tables I and II.

Discussion of the test results:

The experiments show for the underfilling materials according to the invention in terms of depth of cure, transparency and compressive strength approximately the same values ​​as are obtained with Ca (OH) ₂ as filler (experiment A). The underfill materials according to the invention are superior in most properties to the sales product Prisma VLC Dycal® (test G).

The products according to the invention are significantly better in their water insolubility or water absorption and in particular in the release of calcium hydroxide.<tables id="tabl0002" num="0002"><img file="EP0449399A2_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0449399A2_D0003.tif" /></tables>