DENTAL COMPOSITE AND PORCELAIN REPAIR

Abstract: A filled-resin composition useful for porcelain repair and as a dental composite and therefore made up of non-toxic materials and a method for repairing porcelain or teeth. The composition comprises a methacrylate functional resin us­ able in dental composites, powdered filler-colorant therein, at least one photoinitiator for the resin in an amount sufficient to initiate polymerization and complete it in depth within about half a minute when exposed to a visible-light output of at least 5,000 foot candles, the photoinitiator being an exciplex of (1) either 1,3-bornanedione or benzil and (2) either ethyl-4-dimethyl amino benzoate or ethyl-2-dimethyl amino benzoate, and at least one accelerator-free peroxide curing agent for the resin in an effective amount for completing polymerization within about one-half hour of any portion of the resin not receiving sufficient light to effectuate complete cure before then. The method comprises mixing the components together under ordinary indoor lighting conditions, emplacing the mixture within a few minutes of the mixing, and curing at least a substantial portion of the emplaced mixture in situ for one half-minute under intense visual-light illumination of at least 5000 foot-candles. Any resin then uncured by light is cured within the next half hour by the peroxide curing agent.

Description: This invention relates to two-part systems of making filled methacrylate-functional resin compositions, methods for making them and dental use of the systems as defined in the claims. Over the years many dental composites have been introduced, each composite possessing certain physical properties. However, substantially all of these dental composites can be categorized into two main groups, self-cured materials and light-cured materials. The self-cured composites have involved free radical polymerization initiated by benzoyl peroxide (or another suitable peroxide) and accelerated, typically by a tertiary amine such as N,N,dimethyl-p-toluidine. The curing agents must be stored separately from the resin they are to cure, and they are mixed together just before use. The light-cured composites have involved free radical polymerization initiated by the photoexcitation of light-sensitive compounds by ultraviolet or visible light. They are single-component systems, typically pastes, stored in opaque containers until the time of cure. Some of the photoinitiators that have been employed are the benzoin ethers, benzil ketals, dialkoxyacetophenones, benzophenones, thioxanthones, and hydroxyalkylphenones. In the practice of dentistry, some tooth repairs have been better achieved by self-cured composites and some have been better achieved by light-cured composites. While many factors have helped to determine whether a dentist would or should choose a self-cured material or a light-cured material, the prime factors have been working time, setting time, and the architecture of the cavity preparation. The light-cured composites, combined with special high-lumen lighting units employing fiber optics, have offered variable working times and fast "snap" sets. Setting can take between ten and forty seconds in many instances. However, the use of light-cured composites has been limited by the depth of the repair and the ease of light penetration. Relatively unobstructed, clean, shallow repair surfaces have been required. Visible-light-cured materials have helped in solving some of the limitations caused by repair depth, by roughly doubling the depths at which cure is effective as compared to ultra-violet light-cured material. Also, many dentists have felt more comfortable using a visible, as opposed to an ultra-violet, activating light source. The amount of cure is variable and is a function of exposure to lumens of visible light. These facts result in extremely dangerous situations in many dental restorations; because most dentists do not realize this deficiency, because light-cured systems are advertised to be able to be cured through tooth structure. In reality, the situation is, at best, a gradient level of cure obtained in relation to the amount of lumens of light energy available to the restorative resin. That is to say, layers close to the light source undergo greater percent polymerization than the underlying layers. Consequently, the incompletely polymerized restoration may wash out, leak, or fail in adhesion. Yet the surface or bulk of the restoration may appear clinically adequate, even though new secondary decay may be beginning, and, because of its concealment, result in death of the pulp or loss of the tooth. When a light-cured resin liner is used with a light-cured paste composite at a depth of around 3 mm. or greater, the resin liner may not cure because of insufficient light reaching the resin. Uncured resin liner can cause leaching, pulpal irritation, and loss of adhesion. Heretofore, the resin liner had, therefore, to be polymerized prior to placement of the composite. With this invention, such double cure is unnecessary. Self-cured systems have offered assurance of polymerization throughout the polymer mass used in any repair surface architecture. However, their use has been limited by manufacturer-determined work times and set times. The peroxide and the accelerator could be adjusted to give widely varying setting times; the quicker the set time, the quicker the placement had to be made. Thus, in order to give enough time for accurate placement, the set times had to be longer than were desirable. Generally, set times have been at least two or three minutes after mix, and placement has had to be completed within forty-five seconds after mix. This had made dentists work somewhat faster than was desirable for many placements, and even then the patient had to be immobilized longer than was desirable before the composition set. This invention overcomes the deficiencies of light-cured systems, while preserving their functional benefits. It also overcomes the deficiencies of the self-cured systems by enabling quicker set times coupled with longer placement times, if desired. The system of this invention thus offers the best properties of both types of curing systems without suffering from the limitations of either, and therefore it significantly advances the practice of dentistry and the science of dental materials. The system of the present invention can be in a powder-liquid, paste-paste, paste-powder, or gel-powder form, so that there is no loss in versatility of possible embodiments. Similar problems occur with porcelain repair systems in general, not only in dental uses, but for repairing such porcelain articles as bathtubs, and the invention solves these problems also. Summary of the Invention This invention comprises a composite system combining a small amount of peroxide curing agent, free from accelerator, with certain photoinitiator systems called exciplexes. A two-component system is required, with mixture just before use. Conveniently, the resin and its exciplex members can be stored in opaque (preferably black) containers as one component, with or without some of the filler. The peroxide is stored in a separate component, including much or all of the filler-colorant, in a container which need not be opaque. The two components are mixed just prior to application, and there is a wide latitude of mixing time, because no accelerator is used. The curing effect of the peroxide in the resin is quite slow, while the exposure of the resin and photoinitiator exciplex members in ordinary light--whether daylight or artificial light--will not result in substantial curing. The time for placement is not critical, because neither the photoinitiator exciplex nor the peroxide causes quick curing at this stage. After placement, a high-lumen light source is used with a fiber-optics bundle to effect rapid cure (typically, ten to forty seconds) down to a substantial depth. If the cavity being filled is deeper than that depth, or if some of the placed material has been shaded from the light or not adequately illuminated, the light alone does not effect sufficient cure. However, the cured deposit covering the uncured material holds the uncured material in place, and the peroxide has been found to effect cure of the uncured material in about an hour, and usually in about half that long. To explain exciplexes: as in photoinitiator systems generally, absorption of light by the ketone group of some photoinitiators results in promotion of the photoinitiator to a chemically reactive excited state; alpha-cleavage results, and free radicals are formed. "In the case of appropriate donor/acceptor systems, interaction between an electronically excited molecule and a ground-state molecule of another type may form an excited-state complex, termed an 'exciplex'." Roffey, C. G., Photopolymerization of Surface Coatings , p. 70, John Wiley and Sons, Ltd., New York, 1982. The incorporation of a suitable peroxide, preferably benzoyl peroxide, with the photoinitiated composite system has a synergistic effect on the free-radical polymerization, resulting in uniform cure without limitation after exposure to the activating light source. The peroxide content is preferably 0.05% to 0.3% of the total composition. The exciplex photoinitiators of this invention are a combination of (1) either 2,3-bornanedione or benzil and (2) either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate. The amount should be enough to initiate polymerization in the selected resin and complete it in depth within half a minute when the filled-resin composition is exposed to a visible-light output of at least 53800 lx (5,000 foot candles). The peroxide should be present in amount sufficient to complete, within about an hour, the resin's polymerization, where it is not completed by the photoinitiator-derived action, as where the light never reaches the resin in the needed amount. Thus, suitable photoinitiators for this invention are the following exciplex-forming photoinitiators: 2,3-Bornanedione with ethyl-4-dimethyl-amino-benzoate 2,3-Bornanedione with ethyl-2-dimethyl-amino-benzoate Benzil with ethyl-4-dimethyl-amino-benzoate Benzil with ethyl-2-dimethyl-amino-benzoate. There are, of course, many other compounds capable of photoinitiation. Many of these are taught in U.S. 4,222,835, to Dixon. However, Dixon's formulations were intended for industrial fabrication, whereas the present invention involves formulations which can be left in the human mouth for many years. Consequently, compounds which are known or are suspected to be toxic, carcinogenic, teratogenic or mutagenic are not considered. The present invention provides a much deeper cure than do light-cured composites and obtains a much more uniform degree of cure than do such systems. It obtains a certainty of cure under overhangs, as opposed to prior-art light-cured composites, and a more reliable cure through tooth structure than the prior-art light-cured composites. It provides more uniformity of cure, regardless of exposure time or intensity. It provides better adhesion to the teeth or to substrates such as porcelain as used in dentistry and in plumbing fixtures, apparently due to more complete polymerization. It has a longer shelf-life than self-cured composites. It has better physical properties than most prior-art light-cured composites, especially lower water absorption. It does not develop color bodies in composites using chemically active glasses, such as strontium glass, where some curing systems do develop objectionable color. Moreover, the composite, when installed and cured in a dental environment, looks like the tooth, not only in ordinary light but also in ultra-violet light. In ultra-violet light it fluoresces to substantially the same degree as the tooth itself. As stated above, the product is made up of two separate formulations, one containing all or much of the material to be cured along with the exciplex photoinitiators. This formulation is kept from light, as in an opaque container. The other formulation contains the peroxide curing agent, preferably along with any ingredient not itself cured thereby, such as the filler-colorants. Description of Some Preferred Embodiments The binders or resins to be cured comprise substantially all of those currently used in dental composites. These are all methacrylate-functional resins. Typical is ethoxylated bisphenol-A-dimethacrylate. Others include Bis-GMA and the adducts disclosed in Waller's U.S. Patent No. 3,629,187. Mixtures of resins may be used. Waller's adducts are of 2-2'-propane bis [3-(4-phenoxy)-1,2-dihydroxy propane-1-methacrylate] and a mono- or di-isocyanate. The curing agents, as said, are of two types: peroxides and photoinitiators. A suitable and preferred peroxide is benzoyl peroxide. Some other peroxides are either inoperable or have dangerous toxic side effects. The photoinitiators are in the same component as the resin, the resin- photo-initiator exciplex components mixture being kept in opaque containers until use. The peroxide is ordinarily kept separate from the resin, usually with or upon the filler-colorant or most of the filler-colorant. In paste-paste systems, some of the resin may be in the same component as the peroxide. The suitable exciplex-forming photoinitiators are the following: 2,3-Bornanedione with ethyl-4-dimethyl-amino-benzoate 2,3-Bornanedione with ethyl-2-dimethyl- amino-benzoate Benzil with ethyl-4-dimethyl-amino-benzoate Benzil with ethyl-2-dimethyl-amino-benzoate. To the best of our knowledge, no one has previously suggested that the combination of any of these light-curing exciplex photoinitiators with any peroxide could bring about better curing of these dental resins. Likewise, it is not ordinary to utilize peroxide in such small amounts as those utilized in this invention to initiate polymerization of these resins. Furthermore, peroxide curing agents are conventionally employed with accelerators, and no accelerator is used here. Consequently, the results obtained by this invention were totally unexpected. Practically all inert filler-colorants currently used or usable in dental composites are usable herein. Preferably, they are neither too coarse nor too fine. The compositions employed in this invention may contain at least 10% by weight and up to 90% by weight, and preferably 70-80% by weight, of a finely divided, inert inorganic filler-colorant. The filler-colorant, which may be in the form of spheres, platelets, fibers, whiskers, or particles of any regular or irregular shape and which preferably is transparent or translucent, may comprise for example, apatite, soda glass, barium glass, strontium glass, borosilicate glass, silica, fumed silica, flint silica, alumina, quartz or lithium aluminum silicate. Mixtures of more than one filler-colorant may be used. The particle size of the filler-colorant may range from 0.005 to 0.5 microns in the case of microfine silica, to not greater than 500µm (microns) in the case of irregularly shaped particles. Further, a range of particles sizes may be used. Where the filler-colorant is in the form of fibers, the maximum dimension of the fibers preferably is not greater than 110 µm (microns). On the other hand, where the filler-colorant is in the form of spheres or platelets or is irregularly shaped, the maximum dimension of the particles preferably is not greater than 350µm(microns). The identity of the filler-colorant is not critical, but barium-containing glass (hereinafter called "barium glass"), strontium-containing glass (hereinafter called "strontium glass"), lithium aluminum silicate, flint silica, and fumed silica are excellent fillers and mixtures of these are usually preferable to the use of just one of them. For example, lithium aluminum silicate has a negative heat coefficient of expansion, giving lower overall thermal dimensional changes to the composite. Barium and strontium glass impart opacity to X-rays. Flint silica imparts tooth-like color, and fumed silica adjusts viscosity and improves polishability. One example of barium glass is Ray-Sorb T-2000, a product of Kimble Division of Owens-Illinois Glass Company. The same company makes Ray-Sorb T-4000, an example of strontium glass. Preferably, the peroxide is dispersed on the filler-colorant powder, or by being dissolved in a suitable solvent, is sprayed on the filler-colorant powder, and the solvent evaporated. Preferably, the peroxide is deposited in combination with a silane, such as gamma-methacryloxy propyl trimethoxy silane (sold by Union Carbide as A-174 silane), which is used to improve bonding between the filler and the resin. The benzoyl peroxide and the silane may be dissolved in methylene chloride, chloroform, ether, or acetone, for example. Then a slurry is made with the powdered filler-colorant; the solvent is stripped off, leaving the silane and the peroxide deposited on the dry powder filler-colorant. Glacial acetic acid is often used, in very small amounts, because the hydrolysis reaction which attaches the silane molecule to the filler-colorant particle is carried out most effectively at a pH slightly less than neutral. Butylated hydroxytoluene is sometimes used in order to scavenge small amounts of free radicals which can form during extended shelf storage. The invention can assume the following forms: a powder-liquid form, a paste-paste form, a paste-powder form, and a gel-powder form. These forms will be considered in order. Powder-liquid systems(d) In general, the powder in this form comprises a suitable filler-colorant material, a suitable silane, such as gamma-methacryloxy propyl trimethoxy silane, and a suitable peroxide curing agent such as benzoyl peroxide. Preferably, these ingredients are in the following approximate range of proportions by weight: As stated above, the filler-colorant may be a mixture of some or several of the filler-colorants listed above, or it may be just one type of filler. The formulae may be, further generalized in a somewhat more specific manner as follows: it being understood that the various types of ingredients (e.g., filler-colorant and resin) will be used in quantities that will total to the amounts just spelled out above: Preferably, the liquid component consists essentially of a methacrylate-functional resin in an amount of 96-84% by weight and the photoinitiator incorporates as one ingredient either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of 0.7 to 10% by weight of the liquid component, the other ingredient being either 2,3-bornanedione or benzil and present in an amount of 0.01-8% by weight More specifically, the resin is a mixture of 60-84% ethoxylated bisphenol-A-dimethacrylate and 40-16% triethylene glycol dimethacrylate or a mixture comprising 55% BIS-GMA and 36% triethylene glycol dimethacrylate. The photoinitiator may comprise 2,3-bornanedione in amounts of 0.02-0.2%. Tinting agents are used to impart a more tooth-like color. Red and yellow iron oxides are usually employed. Storage life for each mixture is very long, no deterioration having been noticed so, far over a period of two and one-half years. The powder and the liquid are mixed together in a ratio of weight from 1:1 to 4:1, preferably 2:1 to 3.5:1 powder to liquid, just before they are needed. Mixing may be accomplished on a paper mixing pad, with a plastic instrument. Mixing may be done under normal room lighting conditions, as found in the dental operatory, illumination typically varying in intensity from 86 to 1076 lx (80 to 100 foot candles). Under these conditions, the paste begins to gel after 10 to 30 minutes, depending on the particular formulations and illuminations. When it is desired to initiate curing, the mixed material is exposed to the output from a dental visible light curing unit. For all examples cited herein, a Visar light curing unit, marketed by Den-Mat, Inc., Santa Maria, California, was used. This unit utilizes a type EKE or EJV quartz-halogen light bulb, operating at 21 VAC. The light is transmitted to the work site by a flexible fiber-optic bundle, 6.35mm (1/4 inch) in diameter by 1.22m (four feet) in length. Other units are available from other manufacturers. All are similar in principle and results. Results of these examples would be expected to differ only in degree if other units were used. The output of the Visar unit used is 180 x 10⁴ Candella per square meter, giving illumination of about 215,200 lx (20,000 foot candles) on the material being cured. Satisfactory operability can be achieved with 53800 lx (5,000 foot candles). Under these conditions, the material cures in from 10 seconds to 30 seconds, with a cured depth of from 0.60 to 5.60 mm. Upon further standing, that is, from 5 minutes to 35 minutes, the material exhibits a cure depth of greater than 12 mm. It shows a tensile strength, measured by the diametral method on samples 6 mm diameter by 3 mm high, of between 330.95 and 482.64.10⁵Pa (4800 psi and 7000 psi). A popular prior-art, light-cured dental composite, when tested in identical fashion, showed a cure depth of 3.05 mm immediately after exposure to the curing light, but this cure depth did not increase over a period of 16 hours after cure, and its diametral tensile strength was only 140.10⁵Pa (2030 psi). EXAMPLE 1 A-174 silane is a Union Carbide product, chemically gamma-methacryloxy propyl trimethoxy silane. The barium glass may be Ray-Sorb T-2000, a product of Kimble Division of Owens-Illinois Glass Company or may be barium aluminum silicate. The powder and the liquid were mixed together, preferably in a ratio by weight of 2:1 to 3.5:1, powder to liquid, just before they were needed. Mixing took twenty seconds. The mixtures are preferably applied within five minutes. The setting time was twenty minutes when not exposed to a dental curing light, but was less than thirty seconds on exposure to a dental curing light. The result was a hard filling. EXAMPLE 2 Hardness comparisons with some prior-art systems: A disk of a commercially available light-curable dental composite was prepared, 20 mm diameter by 1 mm thick. One-half of this disk was shaded with aluminum foil, and the disk then was placed under a photoflood lamp for 15 minutes. The sample was removed from under the lamp, the foil removed from the sample, and Barcol hardness measured on both the shaded and unshaded halves. The unshaded half showed a Barcol hardness of 82, while the shaded side had a Barcol hardness reading of less than 1. This same experiment was performed on a disk made of the mixed but uncured material of Example 1, and both sides of this disk showed a Barcol hardness of 92. EXAMPLE 3 Comparison of degree of cure: A series of tests was performed on several commercially-available light-curing composites to determine the degree of cure of the resin matrix. Testing was accomplished by preparing duplicate samples, 1 mm thick by 40 mm in diameter. These samples were cured by exposing them to a photoflood lamp for 30 minutes, and then they were placed in 37°C. water for 24 hours. The samples were then dried, and placed in a desiccator and weighted daily until constant weight ( + 0.5 mg.) was achieved. The samples were then granulated, placed in a glass thimble and extracted for 12 hours in a Soxhlett extraction apparatus with methylene chloride. After extraction, the samples were weighted and the weight loss converted to percent uncured monomer removed. When two popular commercially-available light-cured dental composites were tested in this manner, the cured product contained 3.08% and 5.26% extractables, representative of the amount of uncured monomer. The material of Example 1 of this invention, when tested in the same manner, contained only 1.87% extractables, showing a much higher degree of cure. EXAMPLE 4 Comparison of degree of water sorption: A series of three light-cured dental restoratives were tested in order to determine the degree of water sorption. Samples were in duplicate, and were configured and tested in accordance with American Dental Association Specification No. 27. Two popular commercially-available light-cured dental restoratives were found to have water sorption values of 1.05 and 0.95 mg/cm², respectively. The material of Example 1 gave a value of only 0.86 mg/cm². EXAMPLE 5 Powder-liquid system of porcelain repair: The powder-liquid system of Example 1 was tested as a porcelain repair material, as described in U.S. Patent No. 4,117,595. A commercially available material marketed to practice the above-mentioned patent had test results of 739.10⁵Pa(2015 psi)bond strength (average of 5 samples) when tested 7 days after preparation, being stored meantime in water at 37°C. The material of Example 1, when tested in the same fashion, with the same test equipment, gave results of 765.5 10⁵Pa (2400 psi) bond strength or 19.1% higher. EXAMPLE 6 Comparison with a conventional powder-liquid system (using larger amounts of benzoyl peroxide than this system): The powder and liquid were mixed in a weight ratio of 3:1 of powder to liquid and cured properly. However, a bright green color was formed on curing. The mixture was repeated after acid-washing the strontium glass, but the green color persisted. The mixture was again repeated using N,N-3,5-tetramethylaniline as a substitute for the N,N-2-hydroxyethyl-p-toluidine. Again the green color developed. The mixture was repeated once again using N,N-dimethyl-p-toluidine as activator instead of the N,N-2-hydroxyethyl-p-toluidine. This time the green color did not develop, but the curing characteristics of the composite degraded. Then the experiment was repeated, using the following powder and liquid: No color developed, the material cured satisfactorily under the output from a Visar dental light curing unit, and exhibited a depth of cure of 5.20 mm immediately after exposure to the light, and 12 mm depth of cure after 30 minutes. Diametral tensile strength was 473.67.10⁵Pa (6000 psi). EXAMPLE 7 Again, the powder and liquid were mixed together in a weight ratios varying from 2:1 to 3.5:1, powder to liquid. Curing time was 30 seconds with a depth of 5.50 mm when exposed to a visible light dental curing unit. Diametral tensile strength was 448.16 10⁵Pa(6500 psi). The paste had a workable time of 30 minutes under normal room fluorescent lighting. EXAMPLE 8 Three parts of the powder and one part of the liquid were mixed together to form a paste. This paste, when exposed to a visible light dental curing unit for 30 seconds, cured to a depth of 5.40 mm. Under normal room fluorescent lighting, the paste had a workable time of approximately 20 minutes. The diametral tensile strength was 475.74 10⁵Pa(6900 psi). EXAMPLE 9 Three parts of the powder and one part of the liquid were mixed together to form a paste. This paste, when exposed to the output from a Visar dental visible light curing unit for 30 seconds, cured to a depth of 5.30 mm. When left exposed to room fluorescent lighting, the paste had a working time of 40 minutes and a diametral tensile strength of 478.5 10⁵Pa(6940 psi). EXAMPLE 10 A comparison of curing of various powder/liquid systems utilizing different exciplex-forming photoinitiators A series of resin blends was prepared, all as indicated below as resins A-N, where all the percentages of ingredients are given by weight. Also a standard blend of powder was prepared. Benzoyl peroxide was added to the powder in different levels. The resultant powders were mixed with the resin blends and exposed to the output from a Visar dental light curing unit for 30 seconds, and the depth of cure measurement was taken. As controls resin blends were made without one or all of the exciplex members. On some of these samples, glass tubes 12 mm long were filled with the test material, and were wrapped with black vinyl tape to exclude light for 30 seconds,then the time was measured until the material at the opposite end of the tube was cured. This test will be referred to as the "Infinite Depth of Cure Test" in the following text. As a control, a popular commercially available light-cured composite was tested in the same manner. It initially cured in 30 seconds to a depth of 3.05 mm, and there was no increase in cure depth when measured after 16 hours. Resin A was mixed in a ratio of 1:2 with a powder blend containing 0.61% added benzoyl peroxide. No cure was observed. Resin B was mixed in a ratio of 1:3 with powder blends containing 0.20 and 0.22% added benzoyl peroxide. The cure depths observed were both 5.50 mm. The time in minutes after light exposure for "infinite cure" of the blend made with the 0.22% added peroxide was 30. Resin C was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 1.32 mm. There was no subsequent increase in cure depth. Resin D was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 2.55 mm. The time in minutes after light exposure for "infinite cure" of the blend was 60. Resin E was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 2.65 mm. The time in minutes after light exposure for "infinite cure" of the blend was 45. Resin F was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 2.74 mm. The time in minutes after light exposure for "infinite cure" of the blend was 60. Resin G was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 3.53 mm. The time in minutes after light exposure for "infinite cure" of the blend was 50. Resin H was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 4.06 mm. There was no subsequent increase in the depth of cure. Resin I was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 4.84 mm. The time in minutes after light exposure for "infinite cure" of the blend was 25. Resin J was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 5.02 mm. The time in minutes after light exposure for "infinite cure" of the blend was 25. Resin K was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 5.56 mm. The time in minutes after light exposure for "infinite cure" of the blend was 60. Resin L was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 1.87 mm. The time in minutes after light exposure for "infinite cure" of the blend was 45 minutes. Resin M was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 0.84 mm. The time in minutes after light exposure for "infinite cure" of the blend was 50 minutes. Resin N was mixed in a ratio of 1:3 with a powder blend containing 0.20% added benzoyl peroxide. The cure depth was 1.55 mm. The time in minutes after light exposure for "infinite cure" of the blend was 52 minutes. Paste-Paste Systems (a) Some dentists (and perhaps other users) prefer to work with pastes: most of these users also prefer to use equal amounts of the two pastes, so that paste-paste systems are usually formulated to enable use of equal amounts. In general, the paste-paste system of the present invention may be formulated as follows: Both pastes contain resin and filler material in an amount totaling over 95% thereof by weight of each paste. The two pastes are mixed in equal amounts. Mixing time, working time, and setting time are approximately the same as for the powder-liquid systems, described above, and the results in cure and hardness are approximately the same, too. Again, ordinary room lighting has little curing effect. The resin may be the same in both pastes, as may the filler. The silane is preferably deposited on the filler of both pastes prior to making the pastes. The presence of both resin and peroxide in Paste A seems not to effect a cure nor to affect substantially the storage life. More specifically considered, the paste-paste system employs the following formulations: This formulation should be read with the more general one preceding it, to supply the percentages of fillers, resins, and silane needed, along with appropriate amounts of the curing agents. All percentages are by weight. EXAMPLE 11 The fumed silica may be Aerosil 200 of Degussa Corp. of Teterboro, New Jersey. The two pastes are preferably mixed in equal quantities just before application and are cured by a dental curing light, such as Visar, or equivalent. When so mixed and exposed to a visible light curing unit for 30 seconds, the material cured to a depth of 5.43 mm. The diametral tensile strength was 487.95 10⁵ Pa (6990 psi). EXAMPLE 12 The strontium glass may be Ray-sorb T-4000 of Kimble Division of Owens-Illinois. Equal or substantially equal amounts of pastes A and B are mixed together just before use. When so mixed and exposed to a visible light curing unit for 30 seconds, the material cured to a depth of 5.50 mm. The diametral tensile strength was 330.26 10⁵Pa(4790 psi). EXAMPLE 13 The pastes from Examples 11 and 12, mixed in equal parts, were exposed to the output from a Visar dental curing unit for 30 seconds. The samples were tested to determine the time required to achieve a 12 mm (or "infinite") depth of cure. The samples were tested as described previously. Pastes A and B of Example 11 when mixed together obtained "infinite" cure in 35 minutes. Pastes A and B of examples 12 when mixed together obtained "infinite" cure in 35 minutes. Paste-Powder Systems (b) A third type of system is somewhat of a blend between the powder-liquid system and the paste-paste system. Here, the powder remains substantially the same as in the powder-liquid system, except that it has a larger percentage of peroxide. However, the paste contains the exciplex-forming members dissolved in a liquid resin, and the filler, suspended therein. This paste material should be stored in a light-free container. Typically, a black polyethylene or polypropylene syringe may be used as the container, as in the paste-paste systems. The powder is coated with a suitable silane, such as gamma methacryloxy propyl trimethoxy silane, and has benzoyl peroxide dispersed over its surface. This component may be stored in a container suited to dispersing small amounts. A small cylindrical plastic vial with a small orificed dropper tip is preferred. In practice, an amount of the paste is expressed onto a mixing pad, then a very small amount--1/10 to 1/20-- of the powder is mixed in; so the powder has more peroxide in it than in previous systems discussed. The result is that the paste is thickened--a condition desired by some dentists--and also that depth of cure and cure efficiency are improved. A general formulation may be expressed as follows: The paste comprises the mixture of resin and powdered dental filler in a total amount lying between 96 and 98% by weight of the paste. The exciplex is preferably made up of (a)2,3-bornanedione in an amount of 0.03 to 0.06% by weight of said paste and, (b) either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of 0.75 to 3.25 by weight of said paste. More specifically, the resin is a mixture of 13% ethoxylated bisphenol-A-dimethacrylate and 3.25% of triethylene glycol dimethacrylate, both by weight of said paste, or a mixture of 10% bis-GMA and 6.5% triethylene glycol dimethacrylate, both by weight of said paste. The mixture is done in a ratio varying between 20 to 1 of paste to powder to 10 to 1 of paste to powder. More specifically, this system may comprise the following, with resin, filler, etc., ingredients always lying within the above-given ranges and percentages being by weight: EXAMPLE 14 When a small amount (10% by weight) of the powder is added to the paste, the resulting heavy paste has a working time of over 20 minutes. When so mixed and exposed to the Visar curing light for 30 seconds, the depth of cure measured at least 4.50 mm. Diametral tensile strength was 344.74 10⁵Pa (5000 psi). EXAMPLE 15 The paste and powder are mixed at a weight ratio of 100:5, paste:powder. When so mixed and exposed to a Visar curing unit for 30 seconds, the depth of cure was 5.40 mm. The time to obtain a 12 mm cure was 25 minutes. The diametral tensile strength was 488.84 10⁵Pa(7090 psi). EXAMPLE 16 The paste and powder are mixed together at a weight ratio of 100:5, paste:powder. When so mixed and exposed to the output from a Visar curing unit for 30 seconds, the depth of cure was 5.15 mm. The time to a 12 mm cure was 35 minutes. The diametral tensile strength was 362.10⁵Pa (5250 psi). Gel-Powder Systems (c) Using powder like that used in the powder-liquid system but employing a gel instead of a liquid, a general formulation for these systems may be as follows: The photoinitiator is made up of (a) 2,3-bornanedione in an amount of 0.005 to 0.15% by weight of said gel and (b) either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of 2.0 to 8%, more specifically 2.0 to 7.5%, by weight of said gel. The mixture may vary from one part of powder to twenty parts of gel to three parts of powder to one part of gel. More specifically, while adhering to the general formulation above, the system may use individual ingredients as follows: More specifically, the filler for the gel component comprises, by weight of the gel, 2-5% barium glass, 5-10% lithium aluminium silicate and 7-10% fumed silica. EXAMPLE 17 Powder: The powder is the same as that of Example 16. The powder and gel are mixed together in a weight ratio of 3:1, powder to gel. When exposed to a visible light dental curing unit for 30 seconds, the material cured to a depth of 4.90 mm. Under normal room fluorescent lighting, the paste had a workable time of approximately 35 minutes. The diametral tensile strength was 399.9.10⁵Pa (5800 psi). EXAMPLE 18 Powder: The powder is the same as that used in example 16 The powder and gel are mixed in a ratio of 3:1, powder to gel. When, exposed to a visible light dental curing unit 30 seconds, the material cured to a depth of 5.40 mm. Under normal fluorescent lighting, the paste has a workable time of 25 minutes. The diametral tensile strength was 488.84.10⁵Pa(7090 psi). This restorative system may be used in the repair of fractured porcelain material, natural teeth, or in any other intra-oral situation where a resin material is desired to replace or simulate tooth structure that is capable of being polymerized by visible light and having the process continue after the light is removed. Also, this restorative system, which is essentially a light-cured system, achieves uniform polymerization within thirty minutes to one hour after insertion in the patient's mouth, even though variable amounts of light be radiated to the polymerizing resin. This system eliminates the color changes that tend to occur when certain resins mixed with curing resins are exposed to ultra-violet or visible light.

Claims: A two-part system for making a filled methacrylate-functional resin composition by mixture of the two parts, comprising: first part: dental-type methacrylate-functional resin with photoinitiator therefor; second part: dental-type filler powder with an accelerator-free peroxide curing agent for said resin; said photoinitiator being an exciplex of (1) either 2,3-bornanedione or benzil and (2) either ethyl 4-dimethylaminobenzoate or ethyl 2-dimethyl-aminobenzoate; said two-part system being any of (a) a paste-paste system, (b) a paste-powder system, (c) a gel-powder system, (d) a liquid-powder system, said photoinitiator, peroxide curing agent and first and second parts in said systems being present in an amount of: whereby the percentages are based on the components of that part of the system containing the respective compound. The composition of claim 1 wherein said photoinitiator is 2,3-bornanedione with ethyl-4-dimethyl-amino-benzoate. The composition of claim 1 wherein said photoinitiator is 2,3-bornanedione with ethyl-2-dimethyl-amino-benzoate. The composition of claim 1 wherein said photoinitiator is benzil with ethyl-4-dimethyl-amino-benzoate. The composition of claim 1 wherein said photoinitiator is benzil with ethyl-2-dimethyl-amino-benzoate. The gel-powder system of any of claims 1-5 wherein the gel contains some filler. the paste-paste system of any of claims 1-5 wherein both parts contain substantial amounts of filler. A liquid-powder system according to claim 1 the powder component consisting essentially by weight of: and the liquid component consisting essentially, by weight of: The liquid-powder system according to claim 8 wherein: said filler-colorant consists essentially by weight of ingredients totaling as in claim 8 and selected from: said powder component also. including, in addition to the silane, the peroxide curing agent, and the glacial acetic acid: said methacrylate-functional resin totaling as in claim 8 and consisting essentially by weight of ingredients: A liquid-powder system according to claim 1 wherein (a) the powder component consists essentially of a powdered dental filler-colorant, with a powdered peroxide curing agent in an amount between 0.05% and 0.7% by weight of said powder component, and (b) the liquid component, consists essentially of (1) a methacrylate-functional resin suitable for use in dental composites in an amount of 84-96% by weight of said liquid component, and (2) a photoinitiator for said resin consisting of an exciplex incorporating as one ingredient either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of 0.7 to 10% by weight of said liquid component, the other ingredient being either 2,3-bornanedione or benzil and present in an amount of 0.01 - 8%, by weight of said liquid component, for a total photoinitiator amount by weight of said liquid component of 0.7 to 18% said powder and liquid components suitable to be mixed together just before use in a weight ratio of from 2:1 to 3.5:1 powder to liquid. The system of claim 10, wherein said powder component, by weight of said powder component contains: The system of claim 10 or 11 wherein said powder component also contains glacial acetic acid and gamma-methacryloxy propyl trimethoxy silane. The system of claim 12 wherein said glacial acetic acid is present in an amount of 0.001 - 0.05%, by weight of said powder component, and said silane is present in an amount of 0.1% to 1.5% by weight of said powder component. The system according to one or more of claims 10-13 wherein said resin is ethoxylated bisphenol-A-dimethacrylate in an amount of 82 to 99.3% by weight of said liquid component. The system according to one or more of claims 10-13 wherein said resin is a mixture, by weight of said liquid component, of 60-84% ethoxylated bisphenol-A-dimethacrylate and 40-16% triethylene glycol dimethacrylate. The system according to one or more of claims 10-13 wherein said resin is a mixture, by weight of said liquid component, of 55% Bis-GMA and 36% of triethylene glycol dimethacrylate. The system according to one or more of claims 10-16 employing 2,3-bornanedione in amounts by weight of said liquid component of 0.02 - 0.2%. The system according to one or more of claims 10-17 wherein said liquid component also includes BHT (butylated hydroxy toluene) in an amount of 0.02% by weight of said liquid component. A two-paste system according to claim 1 for porcelain and dental restoration, said pastes suitable to be mixed together at the time of use in substantially equal amounts by weight, both pastes containing methacrylate-functional resin suitable for use in dental components and dental filler material in an amount totaling over 95% thereof by weight of each paste. The system of claim 19 in which each paste also contains gamma-methacryloxy propyl trimethoxy silane in an amount of 0.06 to 1.2% by weight of each paste. The system of claim 20 in which at least one of the pastes also contains glacial acetic acid in an amount of at least 0.0015% by weight of that paste. The system of one or more of claims 19-21 wherein said resin is ethoxylated bisphenol-A-dimethacrylate. The system of one or more of claims 19-22 wherein said resin is present in the peroxide-containing paste in an amount of 14 - 40% and is present in the exciplex-containing paste in an amount of 14-36%. The system of one or more of claims 19-23 where in said filler is chosen from (a) strontium glass and a mixture of barium glass with lithium aluminum silicate, and also includes fumed silica. The system of claims 24 wherein the filler comprises, by weight of each paste about 1% of fumed silica and about 80% of strontium glass. The system of claim 24 wherein the filler comprises, by weight of each paste, about 1% of fumed silica, 24% of barium glass, and 56-57% of lithium aluminum silicate. A paste-powder system according to claim 1 for use in and porcelain restoration, the paste and powder suitable to be mixed at the time of use at a ratio of paste to powder of 10:1 to 20:1, said paste comprising the mixture of methacrylate functional dental resin and powdered dental filler in a total amount lying between 96-98% by weight of the paste and having an exciplex, visual-light reactive photoinitiator, said powder consisting essentially of a dental filler and a peroxide curing agent for the resin in an amount of 0.3% -10% of the powder, said exciplex being made up of (a) 2,3-bornanedione in an amount of about 0.03% to 0.06% by weight of said paste and, (b) either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of about 0.75 to 3.25% by weight of said paste. The system of any of claims 1,10 and 27 wherein said resin is selected from ethoxylated bisphenol-A-dimethacrylate, bis-GMA a mixture thereof with an ethylene glycol dimethacrylate, and a mixture of bis-GMA with an ethylene glycol dimethacrylate. The system of claim 27 wherein the resin is from 16-63.4% ethoxylated bisphenol-A-dimethacrylate, by weight of said paste. The system of claim 27 wherein the resin is a mixture of 13% ethoxylated bisphenol-A-dimethacrylate and 3.25% of triethylene glycol dimethacrylate, both by weight of said paste The system of claim 27 where in the resin is a mixture of 10% bis-GMA and 6.5% triethylene glycol dimethacrylate, both by weight of said paste The system of claims 27 wherein at least the powder contains gamma-methacryloxy propyl trimethoxy silane, in an amount of 1.25 to 5.25% by weight of its component. The system of claim 27 or 32 wherein at least the powder contains glacial acetic acid in an amount of 0.02 to 0.17% by weight of its component. A gel-powder system according to claim 1 for use in dental and porcelain restoration, the gel and powder suitable to be mixed at the time of use for cure by visible light, in a ratio of 20:1 to 1:3 of gel to powder, the gel consisting essentially of about 3/4 methacrylate-functional dental resin and about 1/4 dental filler to a total amount of 90.7-98% by weight of said gel and an exciplex, visible-light-reactive photoinitiator having two ingredients (a) and (b), said powder consisting essentially of a dental filler and an accelerator-free peroxide curing agent for said resin in an amount of 0.05%-4.69 % by weight of said powder, said photoinitiator being made up of (a) 2,3-bornanedione in an amount of 0.005 to 0.15% by weight of said gel and, (b) either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of about 2.0 to 8% by weight of said gel. The system of claim 34 wherein said resin is ethoxylated bisphenol-A-dimethacrylate. The system of claim 10 or claims 34 wherein said filler for the powder component is selected from barium glass, strontium glass, lithium aluminum silicate, flint silica and mixtures of the members of this group with each others. The system of claim 34 wherein said filler for the powder component is a mixture of barium glass, lithium aluminum silicate and flint silica. The system of claim 37 wherein said filler for the powder component contains, by weight of the powder, 23-30% barium glass, 54-70% lithium aluminum silicate and 1-10% flint silica. The system of claim 27 or claim 34 wherein said filler for the gel component is fumed silica. The system of claim 27 or claim 34 wherein said filler for the gel component comprises a mixture of barium glass and lithium aluminum silicate. The system of claim 34 wherein said filler for the gel component comprises, by weight of the gel, 2-5% barium glass, 5-10% lithium aluminum silicate and 7-10% fumed silica. The system of claim 34 wherein at least the powder component contains gamma-methacryloxy propyl trimethoxy silane, in an amount of 0.05 to 1.5% by weight of its component. The system of claim 34 wherein at least the gel component contains glacial acetic acid, in an amount of 0.01 to 0.05% by weight of its component. A method for repairing porcelain or teeth with the aid of a two-part system, said method comprising the steps of: mixing together under ordinary indoor lighting conditions: a methacrylate functional resin usable in dental composites and photoinitiator for said resin, said photoinitiator being an exciplex of (1) either 2,3-bornanedione or benzil and (2) either ethyl 4-dimethylaminobenzoate or ethyl 2-dimethylaminobenzoate (part 1), and powdered dental filler-colorant and at least one accelerator-free peroxide curing agent for said resin (part 2), said two-part system being either (a) a paste-paste system (b) a paste-powder system, (c) a gel-powder system or (d) a liquid-powder system, said photoinitiator, peroxide curing agent and first and second parts in said systems being present in an amount of: whereby the percentages are based on the components of that part of the system containing the respective compound; emplacing the mixture within a few minutes of the mixing, and curing a substantial portion of the emplaced mixture in situ for one half-minute under intense visual-light illumination of at least 53800 lx (5,000 foot candles), any resin then uncured by light being cured within the next hour by said peroxide curing agent, with the exception of those methods falling under the scope of Art. 52(4) EPC. The method of claims 44 wherein the resin is at least one resin chosen from ethoxylated bisphenol-A-dimethacrylate, bis-GMA, and an adduct of 2,2'-propane bis [3-(4-phenoxy)-1,2-dihydroxy propane-1 methacrylate] and mono- or di- isocyanate. The method of claim 44 using a liquid-powder system and wherein said exciplex constitutes 0.7% to 18% by weight of said liquid mixture and said peroxide constitutes about 0.05 to about 0.7% of said powder mixture. The method of claim 44 using a liquid-powder system and having the step in between preparing and mixing of storing said powder in a container and of storing said liquid in an opaque container. The method of claim 44 using a paste-paste system wherein said first paste, at least, is prepared long in advance and comprising the step of storing said first paste in an opaque container until said mixing step. The method of claim 44 using a paste-paste system in which said exciplex constitutes 1.5 to 3.5% by weight of said first paste and said peroxide constitutes 0.1 to 0.75% by weight of said second paste. The method of claim 44 using a paste-powder system wherein said mixing of said paste is done well in advance of use including the step of storing said paste in an opaque container prior to said mixing of the powder with the paste. The method of claim 44 using a paste-powder system wherein said exciplex constitutes 0.7 to 3.7% of said paste and said peroxide constitutes 0.3 to 10% of said powder. A method according to claim 44 using a gel-powder system, said method comprising: mixing together under ordinary indoor lighting conditions, a gel consisting essentially of about 3/4 methacrylate-functional dental resin and about 1/4 dental filler to a total amount of 90.7 to 98% by weight of the gel and an exciplex; visible-light-reactive photoinitiator having two ingredients, one of which is (a) 2,3-bormanedione in an amount of 0.005 to 0.15% by weight and the other is (b)ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate, in an amount of 2% to 8% by weight of the gel, with a powder consisting essentially of a filler and an accelerator free peroxide curing agent for the resin in an amount of 0.05%-4.69% by weight of the powder, in a ratio of 20:1 to 1:3 of gel to powder. The method of claim 51 wherein the resin is ethoxylated bisphenol-A-dimethacrylate. The method of claim 52 wherein the filler for the gel component is fumed silica. The method of claim 52 wherein the filler for the gel component comprises, by weight of the gel, 2-5%-barium glass, 5-10% lithium aluminum silicate and 7-10% fumed silica. The method of claim 52 wherein the exciplex is made up of (a) either 2,3-bornanedione or benzil in an amount of 0.005 to 0.15% by weight of the gel and, (b) either ethyl-4-dimethyl-amino-benzoate or ethyl-2-dimethyl-amino-benzoate in an amount of 2.0 to 7.5% by weight of the gel. The method of claim 52 wherein the filler for the powder component is selected from barium glass, lithium aluminum silicate, flint silica and mixtures of the members of this group with each other. The method of claims 52 wherein the filler for the powder component contains, by weight of the powder, 23-30% barium glass, 54-70% lithium aluminum silicate and 1-10% flint silica. A method for preparing a two-part storable filled-resin composition useful for porcelain repair and as a dental composite comprising: coating, in order to prepare the second part, a powdered dental filler with at least one accelerator-free peroxide curing agent for said resin, storing said filler; mixing, in order to prepare the first part, an uncured methacrylate functional resin usable in dental composites with photoinitiator for said resin, said photoinitiator being an exciplex of (1) either 2,3-bornanedione or benzil and (2) either ethyl 4-dimethylaminobenzoate or ethyl 2-dimethylaminobenzoate, storing the resin-photoinitiator mixture in an opaque container; said two-part system being either (a) a paste-paste system, (b) a paste-powder system, (c) a gel-powder system or (d) a liquid-powder system, said photoinitiator, peroxide curing agent and first and second parts in said systems being present in an amount of: whereby the percentages are based on the components of that part of the system containing the respective compound. A system or method according to any of the preceding claims wherein the peroxide curing agent is benzoyl peroxide.

Inventors: GLACE, WILLIAM RICHARD, IBSEN, ROBERT LUIS, JENSEN, PATRICIA ANN
Applicants: DEN-MAT CORPORATION
Application year: 1984
Main classification: A61K6
IPC codes: A61K6, C08F2, C09J4