GB2094326A - Resin-calcium hydroxide composite restorative dental material - Google Patents

Abstract

A restorative dental material for both lining deep cavities and providing temporary fillings includes calcium hydroxide, an organic resin binder, which can be polymerized by a redox reaction and which includes a bisphenol-A glycidyl methacrylate prepolymer, and a polymerization catalyst such as an organic peroxide and an amine. Also provided are compositions according to the invention in kit form which are ready for mixing by the dentist.

Description

SPECIFICATION Resin composite calcium hydroxide restorative material This invention relates generally to restorative dental materials and more particularly to a calcium hydroxide organic resin composite cavity liner.

In dealing with deep cavities, dentists usually line the bottom of a cavity with a layer of calcium hydroxide before filling the cavity with a permanent restorative material. Calcium hydroxide liners are known for their ability to stimulate the growth of secondary dentin and to neutralize the effects of acids and other chemicals.

Currently, liners of calcium hydroxide and the reaction products of 1,3-butylene glycol and methylsalicylate are widely used. By acid-base reaction, the reaction products of 1,3-butylene glycol-methylsalicylate react with the calcium hydroxide to form a set material. Two drawbacks of this system are its lack of strength when subjected to high condensing pressures, which can result in cracking of the liner when a filling is inserted, and its high solubility which limits its useful life.

A number of patents describe compositions which are useful as dental cements or cavity liners.

U.S. Patent 2,656,277 relates to an underfilling material which includes Ca(OH)2, CaO, and casein which is mixed in water prior to application. U.S. Patent 3,047,408 relates to a composition which contains Ca(OH)2 and a ester of salicylic acid and a polyhydric alcohol. U.S.

Patent 3,367,788 relates to a cavity liner composition containing a calcium compound, preferably Ca(OH)2, a radiopaque compound such as silver and an alkyl cellulose, preferably methyl cellulose, as a thickener. U.S. Patent 3,929,493 relates to a cavity liner which is prepared by mixing a calcium silicate and an organic acid such as tartaric acid, to form a calcium organic acid salt suspended in a network of silica. A dental base material which consists primarily of calcium hydroxide and which is reinforced by various materials such as polymethyl methacrylate to increase the compression strength to as high as 12,000 psi (82.7 MPa) is described as having a high pH which may damage the odontoblasts, thus impeding healing (col. 1 lines 61-68). U.S.

Patent 4,064,619 relates to a cavity liner composition which includes a metal or alloy and an adhesive cement such as bis GMA which may be synthesized from the reaction of bisphenol A and glycidyl methacrylate (col. 4 lines 12-1 9).

Although filled organic resin binder materials are mechanically strong, they are biologically unkind to the dental pulp in that they can cause irritation and inflammation of the pulp.

The present invention is based on the discovery that dental cavity lining compositions and temporary fillings made from a calcium hydroxide and polymerizable organic resin binder which contains a bisphenol-A glycidyl methacrylate prepolymer and optionally an acrylic comonomer provide a strong, therapeutic cavity lining and temporary filling material. In particular, and surprisingly it has been found that when this organic resin binder is in combination with the calcium hydroxide, the irritation and inflammation which results from the use of the resin alone is greatly reduced or avoided.

In accordance with this invention, there is provided a dental restoration kit comprising calcium hydroxide, an organic binder material which can be polymerized by a redox reaction which includes a bisphenol-A glycidyl methacrylate prepolymer and a polymerization catalyst for the binder. Also provided is a cavity lining and temporary filling composition comprising a mixture of calcium hydroxide and the polymerized organic resin binder. The composition can also include other materials, such as glass and/or quartz fillers, pigments to match the tooth color, and inhibitors to enhance the shelf life.

The compositions of the invention include calcium hydroxide powder with the finely powdered U.S.P or F.C.C. grade preferred. The calcium hydroxide is preferably used in amounts of from about 0.3 to 1 part by weight per part by weight of binder.

The organic binders in the compositions of the invention include resin systems which can be polymerized by a redox reaction. The binder systems which are preferred are based on materials which have been widely used in dentistry because of their easy handling and good mechanical properties. The system includes a bisphenol-A glycidyl methacrylate (BAGM) prepolymer with diluting acrylate monomers.

Preferred monomers are difunctional methacrylates such as, for example, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and mixtures thereof.

The diluting monomers copolymerize and/or crosslink with the polymer to provide a set material having good adhesion to the tooth structure. The proportion of monomers to polymer can vary, depending upon the binder system over a range as is known to those skilled in the art. The amount should be sufficient to provide a workable mix but less than the amount which would impair the strength of the set system. Generally amounts of from about .05 to 3 parts by weight of monomer per part by weight of polymer can be used. The inclusion of small amounts (about .5 percent of weight of binder) of methacrylic acid in the bisphenol-A glycidyl methacrylate prepolymer system enhances the setting of the mixture to provide a quick hard set after the components of the kit are mixed and placed in the cavity.

The polymerization and crosslinking of the binder systems is initiated using an organic peroxide. Benzoyl peroxide (BPO) is used for this purpose in amounts which depend upon the binder system and which generally range from about 0.1 to 3 percent by weight of the binder. An amine co-catalyst or accelerator is used, with the prepolymer system, to provide a redox catalyst system. Suitable amines for this purpose are known in the art and include aromatic amines such as, for example, N,N-dihydroxyethyl-ptoluidine (DHET) and dimethyl-p-toluidine (DMT) and mixtures thereof. Suitable amounts range from about 0.1 to 1 percent by weight of the binder.

Inhibitors or stabilizers are added to the monomer portion of the kits to provide longer shelf life particularly when the monomer portion includes an accelerator. Suitable inhibitors include, for example, p-methoxyphenol (MEHQ) and 2,6-di-tert-butyl-4-methylphenol (BHT).

Amounts of from about .02 to 0.2 percent by weight of binder are used.

The compositions of the invention can also include filler materials of, for example, glass, quartz and amorphous fine silica. The filler materials can be silane treated to improve the resin to filler binding. The filler is used in amounts up to about 1.4 parts by weight per part by weight of binder with a preferred range of about 1 to 1.4. Suitable glasses are described, for example, in U.S. Patents 4,224,023 and 3,971,754 whose teachings are incorporated herein by reference. The glass compositions of U.S. Patent 4,224,023 are silane treated and have the following composition range by weight: 130-45 parts of quartz 2. 20-30 parts of aluminum oxide 3. 10-20 parts of cryolite 4. 4-10 parts of aluminum phosphate 5. 10-20 parts of fluorspar.

The glass compositions of U.S. Patent 3,971,754 include x-ray absorbing compounds such as strontium oxide and carbonate so that the boundaries of the filling are delineated on diagnostic x-rays.

Other ingredients which can be added to the compositions of the invention include pigments, inert liquids and plasticizers. The pigments are added in trace amounts to match the natural tooth color. Suitable pigments are oxides and sulfides of non-toxic metals such as yellow and red iron oxide (Fe2O3) and cadmium sulfide. Inert liquids such as N-ethyl-toluene sulfonamide are added in sufficient amounts to form pastes from dry ingredients. Suitable plasticizers for the compositions include, for example, metal stearates in amounts of about 0.1 to 0.3 percent by weight of the binder.

The above listed weight ranges of the relative proportions of the materials in the final compositions are approximate because the various ingredients of the compositions are divided into separate powder, liquid and/or paste components to form a kit. The components of the kit are then mixed just prior to use in volume rather than weight portions for the convenience of the user.

Examples of three kits of the invention are generally described below wherein parts are parts by weight unless otherwise indicated.

Kit A (two powders and one liquid) Powder A I Parts Ca(OH)2 100 Fe2O3 trace (to make paste yellow) PowderA II Parts Filler (4 to 10 micron particle size) 100 Benzoyl Peroxide 0.2 to 2 Catalyst (BPO) where the filler can be one or any combination of (1) quartz (2) Glass as described in U.S. 4,224,023 (3) Glass as described in U.S. 3,971,754 (4) Amorphous fine silica (Cab-o-sil, G. L.

Cabot Inc.) LiquidA Parts Bisphenol-A glycidyl 95 to 50 methacrylate prepolymer (BAGM) Monomers 5 to 50 Methacrylic Acid (MAA) 0.5 Amine accelerator 0.1 to 1 inhibitor 0.02 to 0.2 wherein the monomers include any one or a combination of: (1) Ethylene glycol dimethacrylate (EGDMA) (2) Triethylene glycol dimethacrylate (3) Tetraethylene glycol dimethacrylate (4) Hydroxyethyl methacrylate (HEMA) (5) Hydroxypropyl methacrylate where the amine accelerator is: N,N-dihydroxyethyl-p-toluidene (DHET) or dimethyl-p-toluidine (DMT) and mixtures thereof where the inhibitor is:p-methoxyphenol (MEHQ) or 2,6-di-tert-butyl-4methylphenol (BHT) The composition is formed by mixing equal volumes of powders A I, A II and liquid A on a mixing pad. Optionally the pigment can be included in either or both of A I or A II.

Kit B (3 pastes) Paste A Parts Filler (as in Kit A, Powder A li) 70 to 50 Prepolymer (BAGM) 23 to 36 Monomer (EGDMA) 7 to 14 Catalyst (BPO) 0.1 to 0.75 Inhibitor (MEHQ) 0.05 to 0.1 Paste B Parts Filler (as in Kit A, Powder A II) 70 to 50 Prepolymer (BAGM) 23 to 36 Monomers 7 to 14 Amine accelerator (DHET) 0.1 to 1 Inhibitor (MEHO) c 0.05 to 0.1 Fe203 (red) trace (to make paste slightly red) where the monomers include HEMA or EGDMA or a mixture of both.

Paste C Parts Ca(OH)2 powder 40 to 60 Zinc Stearate plasticizer 0.1 to 0.3 N-ethyl-toluene sulfonamide 60 to 40 inert liquid FeiO3 (yellow) trace (to make paste yellow) The composition is formed by mixing equal volumes of each paste.

Kit C 2 liquids and 1 paste Liquid A Parts Prepolymer (BAGM) 23 to 36 Monomer (EGDMA) 7 to 14 Catalyst (BPO) 0.1 to 0.75 Inhibitor (MEHO) 0.05 to 0.1 Liquid B Parts Prepolymer (BAGM) 23 to 36 Monomers 7 to 14 Amine accelerator (DHET) 0.1 to 1 Inhibitor (MEHQ) 0.05 to 0.1 Fe203.(red) trace (to make paste slightly red) where the monomers include HEMA or EGDMA or a mixture of both.

Paste C Parts Ca(OH)2 powder 40 to 60 Zinc Stearate plasticizer 0.1 to 0.3 N-ethyl-toluene sulfonamide inert liquid; 60 to 40 Fe203 (yellow) trace (to make paste slightly yellow) The composition is found by mixing equal volumes of the two liquids and paste.

Example 1 A clinical evaluation was performed using a kit according to Kit A having the following component compositions: Powder A I Parts Ca(OH)2 powder F.C.C. grade by Baker Chemicals Co. 100 Powder A II Parts Silane treated glass of U.S.

Patent 4,224,023 100 BPO containing 20% water 1.3 Fine silica 0.1 Fe203 yellow pigment 0.02 Liquid B Parts BAGM 56 HEMA 15 EGDMA- 28 MAA ' 0.5 MEHQ 0.06 DHET 0.5 The composite mixture is formed by mixing equal volumes of Powder A I and A II with 5 drops Df Liquid A using an eyedropper.

Properties: Working time - about 2 minutes Compressive strength *1 5,000 to 20,000 psi Ph of water immersing a specimen 11 - after 5 minutes The test method used is siriiilar to ADA specification #8,4.3.4 except that the mixture has to be placed into the mold within 1 T minutes after commencing the mixing.

A clinical evaluation was made on monkeys with good pulp response at 3,21 and 60 days after placement in deep cavities. Reparative dentin was observed 60 days after placement.

Example 2 As a comparison, the typical composition and properties of a conventional calcium hydroxide cavity liner are as follows:- Calcium hydroxide paste Parts Ca(OH)2 U.S.P 2 N-ethyl-toluene sulfonamide 1 Zinc oxide 0.5 Salicylate paste Parts Titanium dioxide 1 1 ,3-Butanediol-methyl salicylate reaction product 1 (U.S. 3,047,408) Equal volumes of the two pastes are mixed.

Properties: Working time 3 to 4 minutes Compressive strength 1 ;oat to 2,000 psi pH in water 12 in 5 minutes Clinical: similar to Example 1.

The evaluations of the composite material of Example 1 demonstrate that the compositions of the invention possess the therapeutic properties of calcium hydroxide liners and the strength of resins without the inflammation usually associated with filled resins. The strength properties also provide the ability to use the compositions as temporary filling materials. The compressive strength, in comparison to the conventional calcium hydroxide liner of Example 2, enhances the ability of the liner to protect the tooth structure because it it less subject to cracking and leakage of harmful materials into the tooth beneath the filling.

Claims (14)

Claims

1. A dental restorative kit or composition for lining or temporarily filling dental cavities which comprises calcium hydroxide and a polymerizable organic binder, wherein the binder comprises a bisphenol-A glycidyl methacrylate prepolymer.

2. A kit or composition according to claim 1, containing from 0.3 to 1 part by weight of calcium hydroxide per part by weight of the organic binder.

3. A kit or composition according to claim 1 or 2, wherein the binder comprises a mixture of a bispheno!-A glycidyl methacrylate prepolymer and an acrylic comonomer.

4. A kit or composition according to claim 3, wherein the binder contains from 0.05 to 3 parts by weight of acrylic comonomer per part by weight of prepolymer.

5. A kit or composition according to claim 3 or 4, wherein the comonomer is a difunctional methacrylate.

6. A kit or composition according to claim 5, in which the binder additionally contains up to 0.5% by weight of methacrylic acid.

7. A kit or composition according to any one of claims 1-6, which additionally contains a filler.

8. A kit or composition according to claim 7, wherein the filler comprises glass, quartz or amorphous silica.

9. A kit or composition according to claim 7 or 8, wherein the filler is present in an amount of from 1 to 1.4 parts by weight per part by weight of the binder.

10. A kit according to any one of claim 1-8, wherein additionally contains a catalyst for the polymerization of said binder.

11. A kit according to claim 10, wherein the catalyst in an organic peroxide.

12. A kit according to claim 11, wherein the peroxide is benzoyl peroxide.

13. A kit according to any one of claims 712, in which at least one of the components of the kit comprises an amine polymerization accelerator.

14. A kit according to any one of claims 1013, in which the binder component comprises a polymerization inhibitor.

1 5. A kit according to any one of claims 10-14, which contains three separate components ready for admixture to form the lining or temporary filling material, the three separate components comprising, respectively A. calcium hydroxide B. the binder C. the catalyst 1 6. A kit according to claim 15, as dependent upon claim 7, 8 or 9, wherein the filler is contained in component B and/or C.

1 7. A kit according to claim 1 5 or 16, as dependent upon claim 14, wherein component C contains a proportion of the bisphenol-A glycidyl methacrylate prepolymer and/or the acrylic comonomer, if present, plus at least a proportion of the catalyst and at least a proportion of the polymerization inhibitor.

1 8. A dental cavity lining or temporary filling material comprising a composition as claimed in any one of claims 1-9 in which the calcium hydroxide, the binder and the filler, if present, are in an admixture, and in which the binder has been cured by in situ polymerization of the bisphenol-A glycidyl methacrylate and acrylic comonomer, if present, initiated by a redox polymerization catalyst.

1 9. A material according to claim 18, wherein the binder is cured by polymerization initiated by a redox polymerization catalyst comprising an organic peroxide and an amine polymerization accelerator.