ZINC-CONTAINING GLASS COMPOSITION

Abstract: Novel glass composition and a dental filling composition for making dental restorations. More particularly, the invention provides a radiopaque dental filling material. Specifically, the dental filling material contains a zinc-containing glass as the component imparting opacity to X-rays.

Description: Descr ption Zi nc-Coπtai ni nσ Glass Comoosition Technical Fi el d This invention relates to zinc-contain ng glass compositions and to dental filling compositions containing such glas-s composition in the form of finely divided fille *) Background Art A variety of substances has been used over the years to repair damaged teeth. The best known currently include silver amalgams, which are frequently first encountered at an early age as a filling for small cavities, even in deciduous teeth. Gold alloys are a particularly valuable filling material, used frequently when a tooth has -been considerably damaged, such as after several caviti have occurred and a lot of tooth must be restored. Fre¬ quently, for example, several smaller extending cavities, e.g. in the occlusal surface, will be combined and a restoration made with a single gold inlay or onlay. The gold alloys have gained an excellent reputation for strength, reliability and long life in service. However, both the gold alloys, and the other metals, such as the stainless steels, which have been technically successful in dental reconstructions and crowns, do not impart a natural tooth appearance. Gold and other metallic-looking restorations are used for molars and teeth which are not immediately open to view when the wearer opens his mouth or smiles. For anterior teeth, however, current practice is to use materials closer in appearance to natural teeth. These are known colloquially as porcelain or plastic fillings. They are composite materials characterized by containing usually predominantly inorganic materials, normally finely divided powders, inert to the oral environment, boύπd ' ogether with polymer c ' matari al . The inorganic materials are frequently finely-ground fused oxides, particularly glasses, or crystalline quartz, while the polymer moiety is commonly a polyacryl at . These compα- site systems are available, for example, as pastes which are polymerized n si u, after having been activated, e.g. by adding a catalyst to initiate a polymerization reaction, just before being placed f rr the prepared tooth. Fillings and restorations of this kind can be made to look, much like natural teeth. In particular, the color of the restoration carr be adjusted to a shade quite close to that of a patient's natural teeth by tinting with pigments. In- addition, the traπsluceπcy or paarlescence of the natural tooth can aTso be approximated through adjustment of the relative- refractive indices of the materials used in the restoration. When color and re¬ fractive indices are well matched, it is possible to obtain a restoration that is barely perceptible to the glance. However, the attainment of good color and overall appearance is 'tary difficult to achieve in practice. This is particularly true when one desires also to optimize other features of a good restoration, particularly radiopacity. It is highly desirable for a filling or other re¬ storation to be radiopaque, for it is by X-ray examination that a dentist determines whether or not a filling remains sound. From radiographs a dentist determines the condi¬ tion αf a filling, e.g. whether it has cracked, or whether decay is occurring at the interface between the tooth and the filling-. Fillings and restorations which are made of metal are readily observable in X-rays. Fillings of the porcelain/plastic art are not observable by X-rays unless they have radiopaque materials therein. Currently, dental filling materials are rendered radiopaque by ncorporating barium into the inorganic powder moiety of the filling material . The most effective radiopaque agents are elements of high atomic number (i.e. the "heavy elements" of the periodic table); it is unfortunate , however, that mast of these elements ar- either radioactive or toxic, such as thorium or lead. Barium is toxic also, but in certain medical uses it is ' present in a form so highly insoluble that the body is unable to metabolize enough- of it to become intoxicated. In dental applications barium glasses have ^ been used as components of dental restorations, on the hypothesis that barium ions within the structure of a glassy matrix will not be available to oral fluids (saliva, beverages, etc.) and will not, therefore, pose a problem of toxicity. Examples of the use of barium glass in dental restorations can be found in U.S. Patents 3,801 ,344; 3,808,170; 3,826,77 3,911,581; 3,959,212; 3,975,203 and 4,Q32,.504. -Unfor¬ tunately, in practice, the barium glasses are not as stable as had originally been hoped, and they have not, therefore, found favor in the art on account of the risk they pose of poisoning the patient (see, e.g. U.S. Patent 3,971,754). A further problem encountered with the barium glasses is that of matching refractive indices to that of the other components of the restoration. For example, it would be desirable to use components with refractive indices in the range of about 1.5 to 1.6 (so as to closely match the refractive index of commonly used organic binders) but most barium glasses with refractive indices in this range are unsuitable for dental use according to U.S. Patent 4,032,504. It is difficult, therefore., to-- prepare, restorations containing barium glass which present an unobtrusive appearance when used for anterior surface repair. An additional problem of the barium glasses is their alkalinity. Typically, bariuim glasses show alkalinity values of pH 9 or greater, whereas a pH of 7 is preferred. Highly alkaline fillers appear to degrade the sildxane coating resulting from etching of the prepared tooth cavity and also cause rapid decomposition of any peroxide catalyst present in the dental restorative composition during storage. Recent efforts in the field of dental restoration materials have resulted in the use of fillers other than bari m-conta ning compounds as an X-ray detectable com¬ ponent. For example, U.S. Patent 3,371,754 describes the use of certain oxides or carbonates, particularly those of lanthanum, strontium, tantalum and, less use¬ fully, hafnium. These salts are mixed with glass-making components at the time the glass is made, yielding a lanthanum, strontium, tantalum or hafnium glass which 5 possesses a measure- of radiopacity. U.S. Patents- 3,973,972 and 4,017,454 describe glass ceramics which possess both a low coefficient of thermal expansion (an advantage in dental fillings) and a useful degree of radiopacity, by virtue of a high content of rare earth I elements, particularly lanthanum. The rare earth elements absorb X-rays in the wavelength range of 0.2 - 0.3A, a range commonly available from dental X-ray machines. However, the cost and problems with availabi¬ lity of these rare earth fillers make them generally 15 unsuitable for commercial use. In another approach to preparing radiopaque composites for dental use-, organic hal .de (e.g. an a y iodide) has been incorporated into plastic materials (e.g. acryl ta polymers), from which mo. ded articles 20 are made (e.g. U.S. Patent 3,715,331). However, the articles molded from such compositions lack, the strength of restorations made from glass or ceramic materials. U.S. Patent 4,250,277 describes a glass composition used for cross! ink ng polycarboxyl i c acid cement, wherein 25 the glass contains zinc oxide and a large amount of boric oxide, in addition to other ingredients. This glass, however, is too water soluble to be useful in dental restorative compositions and prosthetic devices. U.S. Patent 4,215,033 describes a composite dental 30 material containing a glass which in one embodiment is described as single phase. However, this patent does not appear to recognize that a single phase glass containing zinc oxide can be made radiopaque. Also, the single phase glass composition described in this patent is 'mr 35 difficult to make. Furthermore, such glass does not contain any aluminum fluoride. _OMPI ~ Oisclosure of Invention In accordance with the present invention there is provided a novel glass and a dental filling composition comprising polymeri zabl resin binder and a finely divided inorganic glass filler. w ich is X-ray opaque and single phase, wherein said X-ray opaque inorganic glass filler consists essentially of, in percent by weight: Zinc oxide 20 to 35 * S l ica 45 to 65% Boric oxide 3 to 152 Al u i num oxide 0 to 102 Al umi num fl uori de At least 22 Al al i metal oxide 0 to 3% or al aline earth metal oxide wherein the combined weight of aluminum oxide and aluminum fluoride is at least about 10%, and wherein said glass exhibits an "X-ray absorption characteristic" of at least 1/16 inch (0.16 cm)-. Best Mode for Carrying Out the Invention It has been discovered that glasses containing high levels of zinc can be prepared which possess physical character stics (e.g.. refractive index, pH, coefficient of expansion) making them especially suitable for use in dental restorati ve compositions. Moreover, these glasses have been found to be radiopaque and to be capable of being made into dental composites which have greater radiopacity than those made with barium, the best Snown radiopaci fyi ng agent used heretofore. This is quite surprising, considering barium has an atomic number of 56, iodine an atomic number of 33, the -o- laπthanides having atomic numbers of 57 to 71, and zinc having an atomic number of only 30. Moreover, it has been found possible to make the new zin-c glasses with refractive indices in the desired range for deπtai restorative compositions. In addition, t a new glasses can be prepared at a pH close to 7. This is a highly desirable feature in regard to the preparation of high quality dental composites. In particular, when the glass is near neutral in pH (i.e. 5.5 to 3), the stabi- lity of the deπtai composite is s nificantly enhanced. Improved color stability, and reliable setting charac¬ teristics after the activated campαsi e is e placed in the tooth being repaired. The- new glasses are signi¬ ficantly better than the barium glasses of the prior art in this regard. It is believed tha.t the problems encountered with the barium glasses are contributed to by the relative alkalinity αf these materials. Barium is an alkaline earth element in the periodic system, and, therefore, more e ectroposit ve than zinc, which is a transition element. The higher pHs characteris ic of the barium glasses cause decomposition of the peroxide catalysts normally used in these formulations and thus greatly reduce storage stability. A significant advantage of the new glasses, which is an improvement over any known heretofore, is that they contain an element, namely, zinc, that has been in regular dental use for many years Zinc oxide-contain ng ointments have long h&^ used in medicine as safe and mild antibacter al agents and zinc oxide has long been used as a component in dental cements or adhesives. These latter agents are used for cementing prostheses, onlays, bridges, crowns, and the like, to the teeth. In this use they have proved safe and effective over many years. In other words, zinc compounds have a long history of being safe to use in the oral cavity, and are thus vastly preferable to use compared with those of unknown safety or known toxicity, such as compounds of barium. The new single phase glasses used in this invention have the following composition in percent by weight: Zinc oxide (ZnO) 20 to 35% Silica (Si0 2 ) 45 to 65% Boric oxide (B-0 3 ) 3 to 15* A 1 umi num oxide (Al 2 0 3 0 to 10% A 1 umi num fl uori de (A1F 3 ) At 1 east Z. Al al i metal oxide 0 to 3% or al al i πe earth metal oxide wherein the combined weight of aluminum oxide and aluminum fluoride is at least about 10%, and wherein the glass exhibits an "X-ray absorption characteris ic" of at least 1/16 inch (0.15 cm). The alkali metal oxide o alkaline earth metal oxide may be, for example, sodium oxide, potassium oxide, lithium oxide, calcium oxide, magnesium oxide, or the like, or combinations thereof, so long as the combined weight of such oxides does ' not exceed about 3% of the glass, thus maintaining the pH of the glass in the desired range of about 6.5 to 8. Of course, as will be recognized by those skilled in the art, various other ingredients may also be present in minor amounts so long as the resulting glass exhibits the desired X-ray opacity and the desired pH . However, it is highly preferred to avoid the inclusion -of toxic metals such as lead, cadmium, mercury, arsenic, etc. A pr-ferr&ά embodiment of the new glass for use in deπtai restoratives intended for anterior appli- cations has the following composition: Zinc oxide 25 to 28% Sil ca 46 to 48% Boric oxide 6 to S% Aluminum oxide 1 to 3% Aluminum fluoride 17 to 19% wherein the combined weight of aluminum oxide and aluminum fluoride is not greater than about 2.0%, and wherein the glass exhibits an X-ray absorption characteristic of at least 3/32 inch (0.24 cm). 5. The compositions given above are written in terms of the salts (e.g. oxides and fluorides) which are used in preparing the melt from which the glass is obtained upon cooling. This is a common practice in the glass- marking art. There is, of course, no oxide, fluoride, 0 or other simple salt in the resultant glass. Glasses used in this invention all possess a useful degree of rad o pa ci ty . The refractive index of the glass may be varied, •depending upon the particular amount of each ingredient 5 present. It is preferred that the refractive index of the glass filler be substanti lly the same as that of the binder resin when the glass is used in a deπtai filling composition, i.e. within about 0.05, whan the composition is used in anterior applications. When the binder resin comprises the well known 8-IS-GMA. the refractive index for the glass filler is pr-f^r .a ' i 1.555 + ■ 0.05. Matching of the- refractive indices of the glass filler and the binder resin is. less important when the composi¬ tion is intended for posterior dental app ications. 5 When BIS-GiMA resin is diluted with another acrylic resin (e.g. tri ethyl πeglycol dimethacryl te) to facilitate higher filler loadings to make a composition having particular use for posterior filling app ications, the resultant resin mixture may have a refractive index 0 of 1.545, for example. Consequently, far such an application it may be pn-fzrrQά. to use a glass composi¬ tion having a refractive index of 1.545 if close matching of the resin and filler is desired. When it is desired to prepare a dental filling composition which is light 5 curable it is important to obtain a close match of the refractive indices of the polymerizab e resin and the " glass filler so that complete and rapid cure of the resin will be achieved when it is exposed to the activating light. Of course, when the composition is intended for use elsewhere in the body (i.e. where esthetics are not a factor) and where the .compos i ti on is not light curable, there is no need to attempt matching the refractive index of the glass to the refractive index of the binder resi n . Radiopaci y, which reflects the materials's ability to attenuate X-rays, is conveniently measured by com¬ paring the X-ray film image density values of a disc of the cured composite of a standard thickness, e.g. 0.040 inch (0.1 cm), with corresponding values of a known standa Film image density measurements are made with a suitable deπsi tometer , such as a Macbeth Transmission Oeπsito- meter, Model TO 504, with visible light filter (manu¬ factured by Macbeth Div. of Kollmorgan Corp., Newburgh, 'N.Y.). A convenient standard is a stepped aluminum wedge, for example, a ten step wedge having a thickness of 1/32 inch (0.08 cm) at the thinnest step increasing to 5/16 inch (O.S cm) a the thickest step. One empirically determines the X-ray film image density values corresponding to steps on the wedge, which indicate degrees of X-ray beam attenuation which provide, in actua.l practice, proper differeπtia- tioπ between a composite restoration and the surrounding tooth structure. A proper level of radiopacity will permit one skilled in the art to differentiate between the restoration and primary and recurrent caries in the tooth structure, and will also visualize defects in the restoration itself. By way of il ustration, using a wedge, the glasses of this invention when tested in this manner give values of 1/16 inch (0.16 cm) at 26% ZπO; 3/32 - 1/8 inch (0.24 - 0.32 cm) at 26.5 - 28% ZnO. Typical barium glasses of the prior art, tested under identical conditions give values of 1/16 - 3/32 inch (0.16 - 0.24 cm). The typical "plastic" or "porcelain" filling materials (containing quartz or borosilicate filler) common in contemporary dental practive give values of zero. A silver amalgam gives a values of > 5/16 inch (0.3 cm). It will be understood, of course, that these values are completely empirical. Using different wedges and experimental apparatus, the actual numbers one gets may be different.. For the purposes of this invention, useful glasses exhibit an X-ray absorption characteristic of at least 1/16 inch (0.16 cm). Insofar as the preparation of the zinc glass is concerned, standard techniques well-known in the glass- making art are used. See, for example, The Handbook of Glass Manufacture, Fay and ' Tool ey» Volume I (1974). After the melt has cooled, the- glass is comminuted to a size that passes through a 325-mesh standard sieve (44 microns). For grinding the glass into smaller sizes a ball mill is used, and grinding aids such as ammonium carbonate or alcohols may be present in an amount of approximately 0.5% based on the weight of the glass. When making deπtai composite restorative, the glass powder is then prepared for incorporating into an organic binder matrix by treating the surface with a si lane com¬ pound. This is a well-known technique for rendering re¬ latively polar materials, such- as siliceous powders, more compatible with relatively non-polar materials, such as organic polymers. The z.inc glass is. then mixed into a deπtai paste. T a paste may be formed of any of the polymeri zabl e resin systems: useful in dentistry. Especially useful resin systems comprise free-radically polymerizabl e materials such as the olyfunctional acrylata systems. Particularly useful in the system is 3IS-GMA, a well- known material which is the reaction product of bispheπol- A and glycidyl ethacryl at , widely used in dentistry. Other commonly used resin binders include polyurethanes , methyl methacryl te, and isobutyl methacryl ate . Th' zinc glass may be used alone or it may be blended with other suitable materials, such as inert glass powders, when mixed into the binder - depending, I f or example, on the degree of radiOs.acity desired in the B final composite. Along with the glass, other materials may also be mixed into the paste, such as pigments for making the restoration match the patient's natural tooth color, and reagents like hydroquinoπe onomethyl ether, as an inhibitor of premature poly¬ merization of the binder. Immediately before use, and after the dentist has prepared the tooth for receiving the restoration, the paste is activated by mixing into it the appropriate amount of catalyst, such as beπzoyl peroxide. For example, the deπtai restorative composi¬ tion may be in the form of two pastes (one paste con¬ taining filler, resin binder and catalyst while the other contains filler, resin binder and accelerator) , or a liquid resin and powdered filler system, or a paste- liquid resin, or any other desired form. The mixed composition is promptly e placed in the tooth, harden¬ ing in the manner characteristic of the resin binder and catalyst system being used. For example, using the well-known BIS-GMA/benzoyl peroxide system, the composite becomes grossly rigid in about * 5 minutes and may be finely ground and polished, to give the finished restora¬ tion, in about 10 minutes. At any time after emplace¬ ment, but more particularly after significant time has elapsed, such as many months or years afterwards, the condition of the restoration and the adjacent tooth structures can be determined by diagnostic deπtai X-rays. Curable compositions which contain the novel glass and which are useful in other applications (e.g. medical and dental prostheses, pit and fissure sealants, hard tissue cements) may be prepared in similar fashion using poly erizabl e resin binders. The invention is further illustrated by means of the following representative examples wherein the term "parts" refers to parts by weight unless otherwise indicated. Example 1 Silica (47 gms), zinc oxide (25 gms), baric oxide (8 gms), aluminum oxide (1 gm) and aluminum fluoride (18 gms) are thoroughly mixed, as fine powders, in a silica-lined crucible. The mixture is heated in a muffle furnace at 1450 β F, (788 β C.) until the powder has become a trans¬ parent mel t . The molten glass is then removed from the crucible through a small hole- in the crucible wall, by. tilting the crucible and allowing a thin stream αf*g!ass to flow through, giving a filament of glass of about 1/32. inch (0.08 cn) diameter. This filament is quenched rapidly in cold water, to give a completely clear glass (as opposed tα being opalescent). Mere air cooling of the glass is not sufficiently rapid to prevent phase separation. The clear glass is then ground, e.g. in a ball mill, to a mean particle size range of 0.5 - 15 μπt. ' Example 2 Ga ma-methacry oxy-propyl tri ethoxy silaπe (2 gms) is mixed with glacial acetic acid (Q.Q33 gms) and water (44.4- gms) in a plastic beaker. Glass powder (100 gms for example, from Example 1) is added to the mixture, and the system is stirred for 1.5 hours at room tempera¬ ture. The glass slurry is dried, by warming it at 140 o F, (50 C.) for 24 hours, followed by heating it in an oven for 2.5 hours at 240 β F. (115 σ C). Example 3 Two pastes, A and 3, are prepared, having the following compositions: Ingredi ent Paste A Paste 3 3IS-GMA resin 14.48 gm 14.67 gm Triethylene glycol dimethacry tas 4.S7 4.53 Silaπe-treated filler 30.0 30.0 ( from Exarapl Z) 3eπzoyl peroxide .21 Dihydroxyethyl p-toluidine π qr edi eπt Paste A Paste B "Tiπuviπ P", a UV absorber .16 Phenyl sal icyl ate glycidyl .14 16 methacryl ate adduct, a UV absorber Butylated hydroxytαl uene - - - - ,16 Bispheπol A - - - - 14 Pigments-titani urn dioxide and .17 17 iroπ .oxide≤ - yellow raw sienna, burnt umber), ottal me TOTAL lOO.αQ gm 100.00 gm The pastes are prepared as follows: For each paste, A and B, two preliminary mixes are made. The glass (from Example 2) and the pigments are mixed thoroughly to give an evenly colored powder. This mix is the same for each paste. The resins, accelerator, UV absorbers and inhibitor are mixed to give the mix for paste A. The resins, catalyst, UV absorber, and inhibitor are mixed to give-the mix for paste B. After the two mixes, glass and resin based respectively, have been prepared, the procedure for preparing each paste, A and B , is the same . Each resin mix is added to a vessel and then the respective glass mix is added. The two mixes are first roughly blended together, such as by shaking, and are then thoroughly mixed preferably by prolonged mechanical mi xi πg . The resultant homogeneous pastes, A and 3, are the precursors to the dental restorations made from the materials of this invention. Pastes A and B are kept separate until immediately before the appropriate repair is made in a tooth which has been prepared to receive it. They are then mixed together thoroughly and promptly emplaced in the manner well-known in dental art. Examole 4 Using the procedure of Example 3, two pastas, A and 8, are prepared having the following compositions: Iπqredi ent Pasta A Paste 3 Oiacetyl 8IS-GMA resin* 19.20 gm 19.5*7 gm Si lane treated fil er 30.0 30.0 (from Exampl 2) 8eπzoyl peroxide 24 Oihydroxyethyl p-toluidine .47 "Tinuviπ P" - a UV absorber .15 Butyl ated hydroxytol uene .02 Pi ments - titanium dioxide and .17 .17 iron oxides (yellow, raw- sienna, burnt umber) , ottalu e TOTAL 100.00 gm 00.00 gm Qti. CH 7 -»C - C-Q-CH- CH. The two pastes, when mixed together, form a v r useful dental restorative, composition. Example 5 The glass filler of Example 1 was ball milled to a mean particle size of 4.5 microns and silaπe treated according to the method described in Example Z. A light- curable paste was prepared having- the following compo¬ sitions . Ingredient Parts BIS-GMA resin 5.655 Triethyleπe glycol dimethacryl ate 5.555 Trip.henyl antimony .002 N , -di ethyl ami noethyl methacryl ate .4.7 dl - ca phoroqui no-πe .043 Silane treated filler + 1.53% by 33 , 0 weight "Aerosil R-972" Ingre ient P ar* s Pigments - titanium dioxide, iron .17 oxides (yellow, raw sienna, burnt umber) and ottalu e TOTAL 100.00 The paste is prepared as follows: The milled and treated filler (from Example 2), Aerosil R-972 (colloidal silica, commercially available from DeGussa Corporation, average particle diameter of 16 millimicrons, surface area of 110 square meters/ gram) and the pigments are blended to give an evenly colored powder. The resins, inhibitor, accelerator and photoiπi tiatσr are mixed in a dark area in a vessel excluding light. The filler blend is then added to the mixing vessel containing the resin mix. The filler, resins and other components are then thoroughly mixed by prolonged mechanical mixing, with the entire opera¬ tion carried out in the absence of light. A commercially available "KULZER TRANSLUX" irra¬ diation device with a light guiding rod is * used to cure the paste. Test samples are prepared by packing the paste into an open-ended Teflon mold with a cylindrical cavity. The loaded mold is then placed between 2 pieces of clear polyester film (each 25 microns thick) . Test samples of prescribed thickness are then irradiated for a period of exposure necessary to polymerize or cure the resin in the paste. Barcol hardness measurements are made on the top and bottom of the test sample to determine the extent of polymerization. The following Barcol hardnesses are determined on cured test samples using two different sample thicknesses. Hardness 1 Min. Post Cure 1 Hr. Post Cure 2 mm sample thickness 81 - top side 91 - top side - 20 sec. exposure 64 - bottom side 82 - trottorn side 3 mm sample thickness 83 - top side 36 - to side 56 - bottom side - 20 sec. exposure 74 - bottom side 3arcol hardness values in excess of 30 are considered outstanding. Standard, commercially available deπtai restorative composites typically have Barcol hardness values of 70 - 75 after 24 hours cure. The filler loading levels of 33% attained with the zinc glass must also be considered to be extraord nary. Conventional radiopaque barium glass permits maximum filler loadings of 73 - 30% when using similar particle size distributions. Example 6 The glass filler of Example 1 was ball milled tα a mean particle size of 1.3 " microns and silaπe treated according to the method described in Example Z. A l ght-curable pasta having the following composition was prepared using the procedure of Example 5: Ingredi ent Parts SIS-GMA resin 7.09 Triethylene glycol di ethacryl te 7.09 Triphenyl antimony .003 M,M-di ethyl ami πα ethyl methacryl te .53 dl - ca phαroqui none- .059 Silane treated filler + ► 10* by weight 85. Q "QX-50" (colloidal silica com¬ mercially available from OeGussa Corporation, average particle diameter of 40 millimicrons, surface area of 50 square meters/gram) Pigments - titanium dioxide, iron .158 oxides (yellow, raw sienna, burnt umber) and ottalu e TOTAL 100.00 Barcol hardnesses were determined on 2 mm thick test samples of composition cured at two different exposure ti es : ovπ Hardness 1 in. Post Cure 1 Hr. Post Cure 20 sec. exposure 83 - top side 22 - bottom side 30 sec. exposure 53 - top side 84 - top side 54 - bottom side 75 - bottom side Example 7- The glass filler of Example 1 was ball milled to a mean particle size of 4.5 - 5.0 microns. Radiopaque impression pastes, containing the ingredients listed below, were prepared by mixing the ingredients in a con¬ ventional Ross brand mixer: Inσredi ent Paste A Paste 3 Low molecular weight v nyl 2000 grams 1800 grams siloxane polymer (2300 cps) Filler of Example 1 1700 grams 1700 grams (not silaπe treated) Chioropl ati n c acid 4.2 grams (catalyst) Hydrogen polysiloxane 70 grams The concentration of the filler may be varied, as desired, to produce compositions having various viscosities Compositions containing 30 - 40* f ller are of low viscosity, while compositions containing 80 - 90% filler have a putty consistency.

Claims: - Cl aims 1. A single phase glass composition consisting essen^ tially of, in percent by weight: Zinc oxide 20 to 35% Si 1 ica 45 to 03% Bor c oxide 3 to 15%- Aluminum oxide 0 to 10% Alum num fluoride At least 2% Alkali metal oxide or 0 to 5% alkaline earth metal oxide A deπtai filling composition comprising a pσly- erizable resin binder and a finely divided inorganic glass filler which is X-ray opaque and single phase, wherein said glass filler has the composition of claim 1. A composition in accordance with claim 2, wherein said binder comprises a free-radical y polymeri ∑abl e resin. 4*. A composition in accordance with claim 3, wherein said polymerizabl e resin binά-r comprises 3IS-GMA A composition in accordance with claim 2, wherein the index of refraction of said glass fi ler and said resin are substantially the same. A composition in accordance with claim 2, wherein said composition is in the form of two pastes, the first said paste comprising polymerizab resin binder, inorganic glass filler, and a catalyst, and the second said paste comprising poly eri zabl resin binder, inorganic glass filler, ' and an acce1 erator . 7. A composition in accordance with claim 5, wherein said filler represents at least about 70% by weight of each said paste. 3. A composition in accordance with claim 6, wherein said binder in each said paste comprises BIS-GiA. A composition in accordance with claim 4, wherein said glass filler consists essentially of, in percent by wei ght : Zinc oxide 25 to 23% Silica 46 to 43% Boric oxide 6 to 9% Aluminum oxide 1 to 3 % Aluminum fluoride 1 7 to 1 9% wherein the combined weight of aluminum oxide and aluminum fluoride is not greater than about 20%.

Inventors: RANDKLEV R
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1981
Main classification: C08K9
IPC codes: A61K6, C03C3, C03C12, C08F299, C08K9, C08L67