PERMANENT DENTAL RESTORATIVE COMPOSITIONS AND METHODS OF USING THEM

Abstract: Permanent dental restoration compositions comprise (a) from 25 to 80 parts by weight of liquid monomer system comprising methyl methacrylate and from 15 to 50%, by weight of the system, of at least one polyethylenically unsatu­ rated monomer; (b) from 20 to 75 parts by weight of (1) organic polymeric particulate substance and (2) inorganic particulate substance, (1) and (2) being insoluble in the monomer system, and (c) redox initiator. The compositions may be used to form crowns, bridges or fillings or for dental repair in general. Crowns, for example, may be prepared by mixing a composition comprising (a) and reducing agent with a composition comprising (b) and oxidising agent, filling a mould with the mixture, applying the mould to a tooth stump to set, removing the set crown for polishing and finishing, filling it with cement and applying it to the stump.

Description: PERMANENT DENTAL RESTORATIVE COMPOSITIONS AND METHODS OF USING THEM. The field of this invention is the composite dental restorative material art, and permanent dental restorations made from such materials. Compatibility of Various Materials with Oral Tissues. 1: The Components in Composite Restorations. Bowen, J. Dent. Res. 58 (5): 1493-1503, May 1979, summarizes the current state of the art with respect to composite restorative materials used for dentistry. This art is different from the art of dental prostheses, appliances, and dentures, since the restorative material must be castable in place. We have now found certain compositions which may be useful for preparing permanent dental restorations having high compressive strength and wear resistance. The invention also provides methods for making such permanent dental restorations and also the restorations themselves. The compositions of the invention may be used for preparing permanent dental restorations which can be cast in a dental office in a short period of time, or in a dental laboratory. According to the invention there is provided a composition, useful for preparing permanent dental restorations having high compressive strength and wear resistance, which comprises (a) about 25 to 80 parts by weight of a liquid monomer system comprised of methyl methacrylate and about 15 to 50E by weight, based on liquid monomer system, of at least one polyethylenically unsaturated cross linking monomer; (b) about 20 to 75 parts by weight of a solid particulate system comprised of a mixture of both organic and inorganic particulate substances, each of said substances being insoluble in said liquid monomer system; and (c) a redox initiator system. In another aspect, the invention comprises permanent dental restorations having high compressive strength and wear resistance cast from such compositions, and methods of making such permanent dental restorations comprising mixing the liquid monomer system, the solid particulate system, and the two components of the redox initiator system, filling a mould with the mixture, allowing the composition to set, and then to cure. Preferably the compositions of the invention are such that they provide, and the permanent restorations, particularly crowns, have, a minimum compressive strength of 0.2068 G Pa (30000 psi) and/or a rotary wear value of at least 20 hours/25.4 rum (20 hours/mil). In this specification and claims, these values are obtained by the methods described in example 1, and "high compressive strength and wear resistance" preferably means having the above values. In this specification and claims the term "permanent" means long lasting, as opposed to temporary dental restorations. Temporary restorations are only designed to last approximately six months or less, whereas the restorations of the invention are designed to last longer, generally for the life of the patient, although these "permanent" restorations can be removed by a dentist if necessary. The term "restorations" refers to crowns, bridges, fillings, repairs to damage caused by trauma, repairs to existing crowns, and cosmetic repair in general. "Restorative material" refers to material used for such restorations. The term "crown" refers to the whole tooth surface rather than selected portions thereof. As previously mentioned, the solid particulate system or filler is comprised of the mixture of both organic polymeric and inorganic particulate substances, each of said substances being insoluble in the liquid monomer system. The preferred organic polymeric particulate substances are those which are fluorinated, for example poly(ethyleneco-chlorotrifluoroethylene) and poly (vinylidene fluoride). Other organic polymeric particulate substances such as polyacetal, various nylons such as nylon 6, nylon 610, nylon 66, and nylon 11 are also suitable, but are less preferred. The inorganic particulate substance is preferably hydroxyapatite or stearate-coated calcium carbonate, but calcium carbonate generally, glass beads, quartz, silica, talc, clay, calcium sulfate, glass fibers, and combinations of any of the aforementioned inorganic substances can be used. About 20 to 75 parts by weight of the solid particulate system is used with about 25 to 80 parts, preferably 50 to 70 parts, of the liquid monomer system. The preferred amount of solid particulate system is about 30 to 50 parts by weight. The particle size of the inorganic particulate substance is preferably about 0.075 to about 90 microns and the particle size of the organic polymeric particulate substance is preferably about 25 to 75 microns. The weight ratio of organic polymeric particulate substance to inorganic particulate substance is preferably about 1:5 to 1:1, more preferably about 1:3 to 2:3. Although a wide range of redox initiator systems are known in the art, and are suitable, two particularly suitable systems are a combination of benzoyl peroxide and N,N-bis-(hydroxyethyl)-ptoluidine, and a second system comprised of t-butylperoxy maleic acid and calcium hydroxide. Other suitable combinations are described by J.M.Antonucci et. al., in J.Dent.Res., 58 (9), 1887-99. Preferred amounts of redox pair to be used are about 0.5 to 10 parts by weight, more preferably about 1 to 5 parts by weight, per 100 parts of the resin system. The redox pair consists of an oxidizing agent and reducing agent. In practice, it is preferred to include the oxidizing agent with the filler system as one component, and the reducing agent with the 'liquid monomer system as a second component, it being understood that the oxidizing and reducing agents are components of the redox initiator system. Further optional ingredients such as one or more of tinting agent, stabilizer to control polymerization rate, exotherm, and yellowing, fluorescing agent and x-ray opacifying agent can be included in either component. The liquid monomer system is comprised of methyl methacrylate and about 15 to 50% by weight, preferably about 20 to 50% by weight, based on liquid monomer system, of at least one polyethylenically unsaturated crosslinking monomer. The amount and type of polyethylenically unsaturated monomer may be selected so as to achieve curing in the desired length of time, to control exotherm temperature, and to synergistically contribute to the wear resistance and compressive strength of the resultant permanent dental crown. The preferred polyethylenically unsaturated monomers are polyfunctional acrylates or methacrylates or mixtures thereof, and are preferably selected from the group consisting of trimethylolpropane trimethacrylate, 2,2-bis (2-hydroxy-3-methacryloxy- propoxy)phenyl propane, (bis-GMA), divinylbenzene, diallyl maleate, ethylene and butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, butylene diacrylate, pentaerythritol tetraacrylate, and ethoxylated bis-phenol-A dimethacrylate. Besides methyl methacrylate, the composition can further include up to about 10% by weight, based on liquid monomer system, of at least one different monoethylenically unsaturated monomer such as, for example, octafluoropentyl methacrylate, hydroxyethyl methacrylate, hexafluoroisopropyl methacrylate, pentafluoropropyl acrylate, pentafluoropropyl methacrylate, heptafluorobutyl acrylate, heptafluorobutyl methacrylate, and butyl methacrylate. The composition can also include a thickener polymer dissolved, for example, in the liquid monomer system. Such thickener polymer can be any polymer soluble in the liquid monomer system, for example C1 to C4 alkyl esters of acrylic acid and methacrylic acid. Alternatively, thickeners insoluble in the liquid monomer system such as very finely divided hydrophobic silicon dioxide can be included. The permanent dental restorations of the invention may have a combination of high compressive strength and wear resistance never before achieved in the prior art, and may be competitive with amalgam, gold, or crown grade porcelain. The restorations to which this invention is most applicable are crowns and bridges, and especially crowns. The method of making the permanent dental crowns of the invention is generally to mix the liquid monomer system, the solid particulate system, and the redox initiator system, fill a tooth-shaped mould with the mixture, and apply the tilled mould to the tooth stump to which the crown is to be applied. It is important to keep the reducing agent and oxidizing agent separated until the composition is mixed at the time of use. The composition can be in the form of mixing two components, for example two pastes, a paste and a powder, or a paste and a liquid. The composition is allowed to set, and then to cure. A preferred method comprises (I) mixing (A? a first component comprising 25 to 80 parts by weight of a liquid monomer system comprised of methyl methacrylate, about 15 to 50% by weight, based on liquid monomer system, of a polyethylenically unsaturated crosslinking monomer, and a small amount of a reducing agent with (B) Åa second component comprising about 20 to 75 parts by weight of a solid particulate system comprised of a mixture of both organic polymeric and inorganic particulate substances, both of said substances being insoluble in the first component, and an oxidizing agent, (II) allowing the resultant mixture to achieve a suitable viscosity, (III) filling a toothshaped preformed mold or impression tray with thickened mixture (IV) applying the filled mold or tray to the tooth stump to which the crown is to be applied, (V) allowing the composition to set, (VI) removing the set crown from mouth and then from the mold or impression tray, (VII) finishing and polishing the cured crown, if necessary tVIII) filiing crown with dental cement and placing the dental crown on the stump. The temperature rise during the setting is desirably kept below 150C. so as to avoid discomfort to the patient, and is preferably within the range of 50C to 100C over a set time of about 5 to 15 minutes. It is preferred that the crown be prepared in a dental office by applying the composition to the tooth stump and allowing it to set, then curing the crown outside the mouth by applying heat at about 800C to 1000C for about 10 to 20 minutes, then applying dental cement to the inside of the crown, then reapplying the crown to the stump. An alternative method is to leave the crown on the stump until it sets, and then allowing it to cure in place without removing it. Another method is to send a mold of the tooth stump to a dental laboratory and making the crown from the composition of the invention at the laboratory, then having the dentist at a later time apply adhesive to the stump or the crown. The following specific examples are presented to illustrate a few embodiments of the invention, but it is to be understood that the invention is not limited thereto. EXAMPLE 1 Test specimens were prepared by mixing in a Waring Blendor the liquid monomer system, organic an4 inorganic particulate substances and redox initiator system for 20 seconds, pouring into a diskshaped mould and a tubular mould, and setting for 15 minutes at 37 0C. The initiator system consisted of 0.42% by weight 2-N,N-bis-(hydroxyethyl)-p-toluidine and 1.74% by weight benzoyl peroxide based on the weight of the monomers. Four percent by weight of high molecular weight polymethyl methacrylate thickener was dissolved in the liquid monomer system so as to aid in achieving homogeneous mixing. Tints, radio-opacifying agents, and fluorescing agents can also be included in this particular experiment. To 35 parts insoluble particulate substances comprised of a 2:1 mixture of stearate-coated calcium carbonate and poly(ethylene-co-chlorotrifluoro- ethylene) (1/1) was mixed 65 parts by weight of a liquid monomer system comprised of 60% methyl methacrylate and 40% trimethylolpropane trimethacrylate. The resultant compositions after thickening, setting reaction and cure were tested for wear life and compressive strength. The wear life test consisted of rotating a cast disc sample under an off-center ceramic scriber having a cylindrical tip 60 mils in diameter under a load of one kilogram/MM2 at 27 rpm for 64,800 revolutions. The test is conducted at 370C with continuous water washing. See Powell, J.M., and Dickson, G., J.Dent. Res.54 (Special Issue A) 134 (1975) The compressive strength test is in accordance with ASTM D-595 and consists of crushing a rod one-quarter inch in diameter by one-half inch length along its length at 0.05 in./minute after presoaking for 24 hours at 37 0C in water, and measuring the compressive strength immediately after removal from the water. EXAMPLE 2 Example 1 was repeated except using as the polyethylenically unsaturated monomer ethylene glycol dimethacrylate. EXAMPLE 3 Example 1 was repeated except using methyl meth aylate/trimethylolpropane trimethacrylate ratio of 80:20. EXAMPLE 4 Example 1 was repeated except using methyl methacrylate/trimethylolpropane trimethacrylate ratio of 90:10. EXAMPLE 5 Example 1 was repeated except using a ratio of 30 parts of particulate filler to 70 parts of liquid monomer, and using a methyl methacrylate/trimethylolpropane trimethacrylate ratio of 80:20. EXAMPLE 6 Example 5 was repeated except using polyvinylidene fluoride as the organic particulate filler. (Average particle size 50 microns). EXAMPLE 7 Example 1 was repeated except using polyvinylidene fluoride as the organic particulate filler and using calcium hydroxyap tite, reagent grade, average particle size 50 microns, at a ratio of organic to inorganic particulate of 1:1, .and using a ratio of 30 parts particulate filler system to 70 parts of liquid monomer system. EXAMPLE 8 Example 1 was repeated except using nylon 66 as the organic particulate filler, using stearate-coated calcium carbonate as the inorganic particulate filler, an organic/ inorganic filler ratio of 1:1, omitting thickener, and using a ratio of 30 parts particulate filler to 70 parts of liquid monomer. EXAMPLE 9 Example 1 was repeated except using calcium carbonate having a:.-erage particle size of 15 microns, omitting thickener, and a particulate/liquid monomer ratio of 30:70. EXAMPLE 10 Example 9 was repeated except using stearate-coated calcium carbonate which had a particle size of 0.075 microns average. EXAMPLE 11 Example 1 was repeated except using a liquid monomer system to solid filler system ratio of 70:30, using polyvinylidene fluoride as the organic particulate, and omitting thickener. EXAMPLE 12 Example 11 was repeated except using a filler to liquid monomer ratio of 40:60. EXAMPLE 13 Example 12 was repeated except using a ratio of 50:50. EXAMPLE 14 Example 7 was repeated except using calcium sulfate instead of calcium hydroxyapatite and omitting thickener. EXAMPLE 15 Example 1 was repeated except using as the inorganic particulate filler system stearate-coated calcium carbonate and uncoated calcium carbonate in a ratio of 1:1, and omitting the thickener. EXAMPLE 16 The results of wear life tests and compressive strength tests for Examples 1 to 15 are reported in the following table. TABLE Compressive Strength Wear Test Results Thousands of Pounds Example No. (hours/mil) Per Square Inch 1 41 2 39 3 44 4 16 5 63 40 6 44 36 7 72 26 8 47 31 9 46 30 10 32 30 11 72 36 12 56 30 13 43 26 14 44 29 15 61 35

Claims: CLAIMS: 1. A composition, suitable for preparing permanent dental restorations having high compressive strength and wear resistance, comprising (a) from 25 to 80 parts by weight of a liquid monomer system comprising methyl methacrylate and from 15 to 50% by weight, based on liquid monomer system, of at least one polyethylenically unsaturated cross linking monomer; (b) from 20 to 75 parts by weight of a mixture of (1) organic polymeric particulate substance insoluble in said liquid monomer system, and (2) inorganic particulate substance insoluble in said liquid monomer system; and (c) a redox initiator system. 2. A composition as claimed in Claim 1 which, when cured, has a compressive strength of at least 0.2068 G Pa (30,000 psi). 3. A composition as claimed in Claim 1 or 2 which, when cured, has a rotary wear of at least 20 hours/ 25.4m (20 hours/mil). 4. A composition as claimed in any of claims 1 to 3 in the form of two packages, one comprising component (a) and the reducing agent of component (c), the other comprising component (b) and the oxidising agent of component (c). 5. A composition as claimed in any of claims 1 to 4 containing 30 to 50 parts by weight of said mixture of (1) and (2). 6. A composition as claimed in any of claims 1 to 5 wherein the particle size of said inorganic particulate substance is from 0.075 to 90 microns. 7. A composition as claimed in any of claims 1 to 6 wherein the particle size of said organic polymeric particulate substance is from 25 to 75 microns. 8. A composition as claimed in any of claims 1 to 7 wherein the weight ratio of organic polymeric particulate substance to inorganic particulate substance is from 1:5 to 1:1. 9. A composition as claimed in any of claims 1 to 8 wherein said organic polymeric particulate substance comprises at least one of poly (ethylene-co-chlorotrifluoroethylene), poly (vinylidene fluoride), nylon, and polyacetal. A A composition as claimed in any of claims 1 to 9 wherein said inorganic particulate substance comprises at least one of hydroxyapatite, calcium carbonate, stearate-coated calcium carbonate, glass beads, quartz, silica, talc, clay, calcium sulfate and glass fiber. l1.A composition as claimed in any of claims 1 to 10 wherein the polyethylenically unsaturated monomer comprises from 20 to 50% by weight of the liquid monomer system. 12.A composition as claimed in any of claims 1 to 11 wherein said polyethylenically unsaturated monomer comprises at least one polyfunctional acrylate and/or methacrylate. 13.A composition as claimed in any of claims 1 to 11 wherein the polyethylenically unsaturated monomer comprises at least one of trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, 2,2-bis (4- 2 C2-hydroxy-3-methacryloxypropoxyg phenyl) propane, divinylbenzene, diallyl maleate, butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, butylene diacrylate, pentaerythritol tetraacrylate, and ethoxylated bis-phenol-A dimethacrylate. 14. A composition as claimed in any of claims 1 to13 which further includes up to 10 percent by weight, based on liquid monomer system, of at least one monoethylenically unsaturated monomer other than methyl methacrylate. 15. A composition as claimed in claim 14 wherein said monoethylenically unsaturated monomer comprises at least one of octafluoropentyl methacrylate, hydroxyethyl methacrylate, hexafluoroisopropyl methacrylate, pentafluoropropyl acrylate, pentafluoropropyl methacrylate, heptafluorobutyl acrylate, heptafluorobutyl methacrylate and butyl methacrylate. 16. A composition as claimed in any of claims 1 to 15 wherein said redox initiator system comprises a combination of benzoyl peroxide and an aromatic amine or t-butylperoxy maleic acid and calcium hydroxide. 17. A composition as claimed in any of claims 1 to 16 which further includes one or more of thickener tinting agent, stabilizer to control polymerization rate and exotherm, stabilizer to prevent yellowing, fluorescing agent, and x-ray opacifying agent. 18. A permanent dental restoration having high compressive strength and wear resistance prepared from a composition according to any of claims 1 to 17. 19. A method of making a permanent dental restoration having high compressive strength and wear resistance, which comprises filling a mould with a composition according to any of claims 1 to 17, allowing the composition to set or setting it and then to curing the composition or allowing it to cure. 20. A method of making permanent dental crowns having high compressive strength and wear resistance which comprises (I) mixing (A) a first component comprising from 25 to 80 parts by weight of a liquid monomer system comprising methyl methacrylate, from 15 to 50% by weight, based on liquid monomer system, of at least one polyethylenically unsaturated crosslinking monomer; and reducing agent; with (B) a second component comprising from 20 to 75 parts by weight of a mixture of (1) organic polymeric particulate substance, and (2) inorganic particulate substance, both of said substances being insoluble in said first component, and oxidizing agent; (II) allowing the resultant mixture to achieve a suitable viscosity, (III) filling a tooth-shaped preformed mould or impression tray with the thickened mixture, and (IV) applying the filled mould or tray to the tooth-stump to which the crown is to be applied, (V) allowing the composition to set, (VI) removing the resultant set crown from the mouth and then from the mould or impression tray, (VII) finishing and polishing the crown, (VIII) filling the crown with dental cement and placing the dental crown on the stump. 21. A method as claimed in Claim 20 as applied to a composition according to any of claims 2,3or 5 to 17.

Inventors: FELLMAN, ROBERT PAUL, HURWITZ, MARVIN JOSEPH, MYERS, ROBERT MARSHALL, SLACK, GERALD FREDERICK
Applicants: ROHM AND HAAS COMPANY
Application year: 1981
Main classification: A61K6
IPC codes: A61K6