GB2064550A - Radio-opaque dental restorative compositions - Google Patents

Abstract

Thorium oxide or tantalum oxide, or combinations thereof are used as the x-ray material for radio-opaque filler compositions having particular applicability in dental restorative compositions. The filler compositions contain from 3% by weight to 10% by weight, based on the total filler composition, of the x-ray absorbing materials and the remainder being conventional particulate glass or silica, quartz or ceramic filler material. The radio-opaque filler compositions are insoluble and non-leachable in alkaline, acidic or neutral aqueous environments, are essentially non- toxic are either essentially colourless or translucent and are compatible with acrylic monomers and other polymerizable binder systems.

Description

SPECIFICATION Radio-opaque dental compositions This invention relates to x-ray opaque filler compositions, and to dental restorative compositions utilizing such x-ray opaque filler compositions.

Particulate reinforced polymer matrix composites are widely used as dental restoratives, particularly for fillings and incisal edge restorations, inlays, and the like. The inorganic filler phase has typically been a siliceous material, such as silica, quartz, refractory salts, glass or ceramic material.

While these reinforced polymer materials often provide satisfactory results with respect to strength, coloration, non-toxicity and thermal expansion coefficient, these materials suffer from the disadvantage of being hard to distinguish by x-ray analysis such as used in dental diagnostics.

Accordingly, there have been many efforts to provide radio-opaque dental composites in which a barium-containing glass has been used to replace a part or all of the siliceous filler, for example, U.S.

Patent No: 3808170 to S. Rogers and U.S. Patent Nos: 3801344, 3826778, 3911581 to E. Dietz, and U.S. Patent No: 4032504 to Lee Pharmaceuticals. However, glass fillers formulated to contain enough barium to achieve sufficient radio-opacity suffer from the disadvantage that the glass is appreciably soluble and barium ion is leached from the glass in an aqueous environment and particularly the oral environment. There is very strong evidence that barium, in this form, presents a toxic hazard.

There have been recent attempts to substitute other radio-opaque filler materials for barium glass.

These attempts have included, for example, the use of highly insoluble barium salts, such as barium carbonate and barium sulphate, in combination with'the siliceous filler. However, these reinforcing ceramic materials have been unsatisfactory with respect to the mechanical strength of the resulting composite.

U.S. Patent No: 3959212 to Rockett et al., teaches using a finely-divided crystalline silicate containing barium and specifically calcium barium silicate in crystalline form for use in a direct filling dental composite which comprises a polymerizable binder, a catalyst system for polymerizing the binder and a finely-divided inorganic filler, at least a portion of which is formed from the radio-opaque crystalline calcium barium silicate. While this composition provides some improvement with respect to the solubility of the barium constituent of the inorganic filler, it still is not entirely satisfactory with respect to the leachability of the barium constituent and the radio-opacity of the composite material.

It has also been proposed, for example, in U.S. Patent No: 3971754 to A. Jurecic, and in U.S.

Patent Nos: 3973972 and 4017454 to G. Muller, to take advantage of the high x-ray absorbing capacity of atoms of high atomic weight. For instance, Jurecic teaches ceramic filler compositions utilizing x-ray absorbing atoms selected from lanthanum, strontium and tantalum and marginally hafnium, in the form of oxides, carbonates or fluorides. According to the Jurecic patent, the compounds of the x-ray absorbing atoms comprise about 5 to 60% and preferably between 25 and 40% of the total fused glass composition which is then incorporated into the restorative matrix.

The Muller patents teach transparent, colourless glass ceramics having a low coefficient of expansion, a high absorptivity for x-rays and which is useful in dental filling compositions in which the glass ceramic composition includes about 10 to about 20% La203 and up to about 7% by weight of Ta20, in addition to the other glass components which are principally SiO2, At203, Li20, P205 and ZrO2.

In this composition La203 is the principal x-ray absorbing compound and tantalum oxide, together with zirconium oxide, acts as a nucleating agent.

In addition, Dietz suggests that other radio-opaque producing oxides, such as strontium oxide or lanthanum oxide and other rare-earth oxides of the lanthanide series, Nos: 57-71, such as samarium oxide, dysprosium oxide, and terbium oxide can be used although the lanthanum oxide generally imparts undesirable colour to the tooth filling and facing compositions as does praseodymium oxide. See Dietz, U.S. Patent No: 3801344 at column 3, line 55 to column 4, line 2.

All of the above approaches, involving various glasses, described above are dissimilar to the composition described hereafter. Manufacture of such glasses is difficult, expensive and presents a problem in terms of matching the index of refraction of the resin.

According to one aspect of the present invention a radio-opaque dental restorative composite composition is formed from a liquid polymerizable organic resin binder and finely-divided, insert, inorganic radio-opaque filler particles, using as substantially the only x-ray absorbing constituent of the radio-opaque filler particles, from about 3 to about 1 0%, by weight, of the total filler of thorium oxide (ThO2) or tantalum oxide (Ta205) or a blend of thorium oxide (the2) and tantalum oxide (Ta205).

According to a further aspect of the present invention a finely-divided, particulate filler composition, which is substantially insoluble and non-leachable in an aqueous environment, which is essentially colourless or translucent and which will impart x-ray opacity to a dental restorative composite composition filled with said filler composition, consists essentially of a uniform blend of from about 90 to about 97% by weight, of siliceous, glass or ceramic filler particles and about 3 to about 10%, by weight, of thorium oxide (ThO2) or tantalum oxide (Ta205) or a mixture of thorium oxide (ThO2 and tantalum oxide (Ta205), said oxide or oxides being substantially the only x-ray absorbing materials present in said composition.

It has now been found that the amount of high atomic weight x-ray absorbing rare-earth element in dental restorative compositions can be substantially lowered by utilizing either thorium oxide (ThO2) or (Ta205), or a mixture thereof, as substantially the only x-ray absorbing components. While it has been known to make use of the ability of thorium to absorb x-rays, in x-ray contrast media liquids, it is believed by applicants that thorium oxide or thallium oxide or mixtures thereof alone has never been proposed or used as the x-ray absorbing constituent in a dental filler composition.

Thus the present invention seeks to provide filler compositions suitable for use in dental restorative composites which include at least one component in minor proportions having high x-ray absorbing capability, which is essentially colourless or translucent, is available in finely-divided form, and is substantially completely insoluble in water or an oral environment. The present invention also seeks to provide dental restorative composite materials from a conventional polymerizable resin binder, a catalyst therefore, and finely-divided inorganic filler capable of being coupled to the binder such that the composite material exhibits high absorption of short wavelength x-ray radiation such as utilized in dental diagnostics, has a relatively low coefficient of thermal expansion, has low toxicity, high mechanical strength and optical translucency matching tooth enamel.

According to a still further aspect of the present invention a radio-opaque composite material useful as a dental restorative comprises a polymerizable resin binder, a catalyst for the binder, and a finely-divided inorganic filler containing a minor amount of thorium oxide, tantalum oxide or a mixture of thorium oxide and tantalum oxide, the filler material being substantially free from radio-opaque soluble or leachable constituents, such as barium.

The major portion of the filler component of the composite material can be substantially any siliceous filler particulate material such as, for example, amorphous silica, fused silica, quartz, crystalline silica, soda glass beads, ceramic oxides, particulate silicate glass or synthetic crystalline materials such as beta-eucryptite (LiAISiO4).

The thorium oxide or tantalum oxide alone, or mixtures of both of these oxide compounds is added as such to the inorganic siliceous filler and simply uniformly blended together by any suitable blending technique, including manual and mechanical mixers.

The finely-divided particulate filler composition is preferably capable of passing, for example, through a 325 mesh screen and may have particles of an average particle diameter of about 30 microns or less such as about 2-5 microns or less.

Unlike conventional radio-opaque filler compositions utilizing barium glass, which contain about 35% or more of barium glass, it is only necessary to include as little as about 10% by weight, or less of the oxides of thorium and/or tantalum in the present filler compositions. This represents a substantial economic advantage and is due, at least in part, to the higher radio-opacity of thorium and tantalum as compared to barium making the oxides of the former elements more effective on a weight basis than barium oxide. Thus, 0.497 parts of Ta205 and 0.236 parts of ThO2 are equivalent to one part of BaO in terms of opacity to x-rays. For example, it has been found that 1 gram of thorium is equivalent to about 4.3 grams of barium in terms of capability of absorbing x-rays.This converts to about 13.1 grams of barium glass (32% by weight of barium) for each gram of thorium oxide (ThO2) and 7.9 gram barium glass per gram of Tea205.

Accordingly the x-ray opaque filler compositions used in the present invention need only contain as little as about 3% by weight, of thorium oxide, a preferred range being about 3% to about 5% of thorium oxide when it is used as the sole x-ray absorbing constituent. When tantalum oxide alone is utilized in the filler composition is is preferred to use about 4 to 10% based on the total filler composition.

The filler composition containing the x-ray absorbing oxide or oxides may be blended with the organic polymer binder in any suitable proportion, for example, about 20-80 parts, by weight, of filler to about 20-80 parts, by weight of organic polymer binder. However, more highly filled composites are especially useful in dental restorative composites. The weight ratio of filler to polymerizable and other reactive monomers in the binder system is preferably about 1:1 to about 6:1, especially 3:1 to about 5:1. Optimally, the filler constitutes about 6585% weight, of the combined filler and binder.

The organic polymerizable monomer can be broadly selected, but particularly for dental restorative purposes, it is preferably a dimethacrylate such as 2,2-propane bis[3(4-phenoxy)-1 ,2-hydroxy propane1 -methacrylate], commonly referred to as BIS--OO-MA, blended with other dimethacrylates. Suitable resin materials are described, for example, in the aforementioned patents to Jerucic, Muller, Rockett, Rogers, Dietz and also U.S. Patent No: 3066122 and 3179623 to Bowen and U.S. Patent No: 4032504 to H. Lee Jr., et al. Other suitable systems in which the tantalum oxide and/or thorium oxide x-ray absorbing filler particles can be used are described, for example in U.S. Patent Nos: 3539533 to Johnson and Johnson, 3709866 to Dentsply Int., 3730947, 3751399, 3766132, 3774305 to Lee Pharmaceuticals, 3835090, 3845009, 3853962 to Johnson and Johnson, 3860556 to 3M Co. and 3991008 to Temin.

The composite resin composition of the present invention is comprised of a liquid resin binder system, including the polymerizable monomer(s) and other reactive monomers (often referred to as "reactive diluents" for lowering the viscosity of the binder to a workable paste), a catalyst or initiator, and an accelerator or activator (the catalyst and acclerator react to form free radicals which catalyze the polymerization reaction) and the finely-divided inorganic filler. The binder system can also include stabilizers for increasing the shelf life of the unpolymerized composite resin compositions and UV absorbers. The composite can be prepared, for example, by mixing each of the above ingredients in any conventional manner, preferably after treating the filler with a suitable silane coupling agent in a manner which is also well known in the prior art.Examples of suitable coupling agents include, for example, vinyltrichlorsilane, tris (2-methoxyethoxy) silane, tris (acetoxy) vinylsilane, 1-N (vinylbenzylaminoethyl)aminopropyl trimethoxysilane-3, 3-methacryloxypropyl trimethoxysilane etc.

The silane coupling agent can also be added to the polymerizable resin binder prior to addition of the inorganic particulate filler. Further, any of the ingredients can be premixed prior to addition of the remaining ingredients. It is preferred to keep the catalyst and polymerizable resin binder separated until just prior to use of the composite. These techniques are all well known in the art and do not, per se, form any part of the present invention. A particular packaging system is disclosed, for example in U.S. Patent No: 3926906 to Lee, Jr., et al., the disclosure of which is incorporated herein by reference.

The dental restorative composite compositions of this invention may include about 20 to about 80 parts, by weight, preferably about 20 to about 50 parts, by weight, of the polymerizable monomer(s) and other optional reactive monomers, about 0.1 to about 3.0%, by weight, of catalyst, about 0.1 to about 2.0%, by weight of accelerator, the weights of catalyst and accelerator being based on the weight of the polymerizable and reactive monomers, about 0 to about 5%, preferably about 1 to about 4% based on the weight of the polymerizable and reactive monomers of silane coupling agent, and about 20 to about 80 parts, by weight, preferably about 50 to about 80 parts, by weight, of finely-divided filler composition, wherein the filler composition includes from about 3% to about 10% by weight, of thorium oxide (ThO2) or both thorium oxide (the2) and tantalum oxide (Ta205), preferably about 3 to 7% by weight, of thorium oxide (ThO2), or about 3 to 5% thorium oxide (ThO2) and about 1% to about 7% tantalum oxide (tea205).

The composite composition cen also include other ingredients, such as, for example, polymerization inhibitors, stabilizers, UV absorbers, the nature and amounts of which will naturally depend on the nature and amounts of the polymerizable resin binder; and pigments or dyestuffs, for example. iron oxides, cadmium yellows and oranges, fluorescent zinc oxides, titanium dioxide etc., in amounts required to more closely approximate in the cured composite material the nature colour of the tooth enamel with which the composite material is being used.

Some embodiments of the invention will now be described in the following Examples.

COMPARATIVE 1 To compare the rates and amounts of elution of the radio opaque dental composite materials of this invention with conventional radio-opaque dental composites utilizing barium-containing glass fillers, samples of barium glasses were stirred in water buffered at pH 7 with ammonium acetate and in distilled water. After one hour, the aqueous phase was removed and replaced with fresh aqueous phase.

The resulting aqueous solutions, after removal of the cured composite material, were subjected to atomic absorption analysis, utilizing a Perkin-Elmer Model 306 AA apparatus.

The following results were obtained: TABLE 1 Barium Elution from Corning 7724 Glass in Distilled Watera Ba in Ba extracted water per gram of glass Leaching pH (ppm) (ug) 1 8.9 125 250 2 9.0 140 280 3 9.0 115 230 4 9.0 90 1 80 TABLE II Barium Elution from Corning 7724 Glass in Buffered Waterb Bairn Bapergram H20 of glass Leaching pH (ppm) (ug) 1 8.8-9.1 400 800 2 8.7-9.0 450 900 3 8.6-8.9 250 500 4 8.2-8.5 250 500 a. 25 g of glass stirred one hour with 50 ml distilled water.

b. 50 g of glass stirred one hour with 100 ml of water containing 0;1 g ammonium acetate COMPARATIVE 2 A similar leaching of Kimble's Ray-Sorb T-2000 in buffered water (1 g ammonium acetate per 1000 g water), originally at pH 7, caused a rise in pH to 9.5 and over 500 ppm barium was eluted in one hour.

In contrast the thorium and tantalum oxides have substantially zero leachability.

EXAMPLE 1 A filler for a radio-opaque composite resin was prepared by blending 2.4 g ThO2 (obtained from J. T. Baker Chemical Co., Phillipsburg N.J., 325 mesh size) and 76.4 g of IMSIL A-1 0 (an amorphous silica of less than 10 micron particle size obtained from Illinois Minerals Co.). The mixture contained minor amounts (less than 0.001 g) of pigments to achieve a tooth matching coloration. This filler was thoroughly mixed, using an electric mortar and pestle, with 26.2 g of a mixture consisting of 12.5 g of BIS--GMA (purchased from Freeman Chemical Co.), 12.5 g of hexamethylene dimethacrylate (purchased from Sartomer Resins Co.) and 1.2 g of y-methacroyloxypropyl trimethoxysilane.To one half of the resulting paste was added 4%, based on weight of monomers, of cumene hydroperoxide while to the other half was added 2%, based on weight of monomers, of acetyl thiourea (purchased from Eastman Chemicals Co.). Several equal small portions of the two pastes were thoroughly mixed by spatulation and the mixture placed in a Teflon mold to prepare cylinder for compression strength measurement. Testing (Instron machine) showed the cured composite samples had an average compression strength of about 45,000 psi.

X-ray examination, using commercial dental x-ray equipment, showed that the ThO2-containing composite had an opacity to x-rays equivalent to a composite containing a filler comprised of 50% amorphous silica and 50% Corning 7724 barium glass by weight.

EXAMPLE 2 A restorative composite was prepared as described in Example 1 except that the filler was comprised of 4 g of tantalum pentoxide (approximately 400 mesh, purchased from Kawecki Berylco Industries Inc.) and 74.8 g of IMSIL A-10. The cured composite had physical properties similar to the composite described in Example 1 and an x-ray opacity equal to that of a composite containing filler consisting of 50% by weight of Corning 7724 barium glass.

Claims (8)

1. A radio-opaque dental restorative composite composition formed from a liquid polymerizable organic resin binder and finely-divided, inert, inorganic radio-opaque filler particles, using as substantially the only x-ray absorbing constituent of the radio-opaque filler particles, from about 3 to about 10% by weight of the total filler of thorium oxide (ThO2) or tantalum oxide (Ta2O5) or a blend of thorium oxide (ThO2) and tantalum oxide (Ta2O5).

2. A composite composition as claimed in Claim 1 wherein the radio-opaque filler particles comprise 95-97 weight percent of siliceous or ceramic filler particles and 3 to 5 weight percent of thorium oxide.

3. A composite composition as claimed in Claim 2 wherein the radio opaque filler particles comprise 90-96 weight percent of siliceous or ceramic filler particles, 3 to 5 weight percent of thorium oxide and 1 to 7 weight percent of tantalum oxide.

4. A composite composition as claimed in Claim 1 wherein the radio-opaque filler particles comprise about 90-96 weight percent of siliceous or ceramic filler particles and about 4-10 weight percent of tantalum oxide.

5. A radio-opaque dental restorative composite composition substantially as described in the Examples.

6. A finely-divided, particulate filler composition, which is substantially insoluble and nonleachable in an aqueous environment, which is essentially colourless or translucent and which will impart x-ray opacity to a dental restorative composite composition filled with said filler composition, consists essentially of a uniform blend of from about 90 to about 97% by weight, of siliceous, glass or ceramic filler particles and about 3 to about 10%, by weight of thorium oxide (ThO2) or tantalum oxide (Ta2O5) or a mixture of thorium oxide (ThO2) and tantalum oxide (Ta2O5), said oxide or oxides being substantially the only x-ray absorbing materials present in said composition.

7. A finely-divided particulate filler composition substantially as described in the Examples.

8. A radio opaque composite material useful as a dental restorative which contains a polymerisable resin binder, a catalyst for the binder and a finely divided inorganic filler containing a minor amount of a thorium oxide, tantalum oxide or a mixture thereof, the filler material being substantially free from radio-opaque soluble or leachable constituents.