WO1995007067A1

WO1995007067A1 - Liquid mordant suitable for binding filling materials to dental tissues (enamel and dentin)

Info

Publication number: WO1995007067A1
Application number: PCT/BY1993/000004
Authority: WO
Inventors: Aleksei D. Sidorik; Nikolai N. Grinchik
Original assignee: Byelocorp Scientific, Inc.
Priority date: 1993-09-10
Filing date: 1993-09-10
Publication date: 1995-03-16

Abstract

A liquid mordant comprising a solution of glycerophosphoric acid in a solvent, and a method of treating dental tissue using this advantageous liquid mordant, are disclosed. The mordant preferably comprises a solution of about 20 to 55 % by weight of glycerophosphoric acid in distilled water. The glycerophosphoric acid both changes the relief of the etching surface of dental tissue and chemically bonds filling resin to dental tissue, resulting in greater bond strength than with previously known methods, while having less toxicity.

Description

LIQUID MORDANT SUITABLE FOR BINDING FILLING MATERIALS TO DENTAL TISSUES (ENAMEL AND DENTIN) FIELD OF THE INVENTION

This invention relates to liquid mordants, more particularly to compounds useful for binding filling materials to dental tissues (enamel and dentin) .

BACKGROUND OF THE INVENTION

An important parameter of dental filling materials is the strength of their bond to dental tissues. Bond strength is composed of three types of bonds; mechanical retention, adhesion (i.e. electrical and intermolecular interactions) and chemical bonds between the filing material and tooth.

Depending on the type of filling material and dental surface relief, one, two or all of these bonds can occur.

In 1955, M.G. Buonocore disclosed a use of a surface treatment of 85 percent phosphoric acid to determine the effect on adhesion. Buonocore, "A Simple Method of Increasing the Adhesion of Acrylic Filling Materials to Enamel Surfaces," Journal of Dental Research, 34, 849-53 (1955) . Buonocore describes an increased adhesion of acrylic filling materials to enamel using a phosphoric acid solution. One disadvantage associated with the use of phosphoric acid in adhesion of dental fillings to tissue is that the acid typically is used in conjunction with other compositions, requiring a multi-step preparatory process. Furthermore, some of these compositions can be very toxic to the pulpa of a tooth. For example, U.S. Patent Nos. 4,521,550, 4,588,756, 4,659,751 and 4,964,911 disclose the pretreatment of dental tissues with an acid or a salt solution with a low pH. For instance, U.S. Patent 4,588,756 discloses that the preferred acid is nitric acid, but also describes that phosphoric acid or other acids might also be effective. However, subsequent stages of treatment in these references involve the application of such toxic substances as acetone, N- phenylglycine ("NPG"), the adduct of N-(p-tolyl)glycine and glycidyl methacrylate ("NTG-GMA") , the addition reaction product of pyromellitic acid dianhydride and 2-hydroxyethyl methacrylate ("PMDM") , and the addition reaction product of 3,3' ,4,4'-benzophenonetetracarboxylic dianhydride and 2- hydroxyethyl methacrylate ("BTDA-HEMA") .

Phosphoric acid also is corrosive and difficult to use, especially when it is necessary to etch both the enamel and dentin of a tooth. Generally, phosphoric acid is thought to be capable of penetrating into the dentin canaliculi to a substantial depth and injuring the dental pulpa. As a result, phosphoric acid is usually not used on the dentin. Despite its strength, phosphoric acid is usually left on the dental enamel for sixty seconds.

Attempts have been made in the art to develop other materials capable of increasing the bond strength of dental filling materials. However, to date filling materials have not been developed which form strong and stable chemical bonds. SUMMARY OF THE INVENTION

In light of the foregoing, it is an object of the present invention to provide a mordant capable of bonding dental filling materials and dental tissues. It is another object of this invention to provide a mordant which forms a chemical bond with dental tissue and filling materials and is resistant to water and mouth liquid. It is a further object of this invention to provide for improving the adhesion of dental filling materials to tissue which has a relatively low toxicity. It is another object of this invention to provide a mordant capable of etching enamel and dentin, without substantial damage to the dental pulpa. It is a further object of this invention to provide a process for adhering dental filling materials to tissue. These and other objects of the invention are achieved with a liquid mordant comprised of a solution comprising about 20 to 55% by weight of glycerophosphoric acid in a suitable solvent, such as distilled water.

The invention also includes a method for treating dental tissue comprising forming a cavity for receiving a filling material; applying a liquid mordant comprising a solution of about 20% to 55% by weight glycerophosphoric acid in a solvent to an application area in the cavity consisting of (i) dental enamel or (ii) dental enamel and dentin; washing the application area; drying the application area; and adding a filling material to the cavity.

Both the alpha and beta isomers of glycerophosphoric acid can be active as a mordant, and a solution containing both isomers can be used with the invention. While not wishing to be bound by theory, it is believed that glycerophosphoric acid improves the bond strength of filling materials in two ways: 1) by changing the relief of the etching surface and 2) by causing tooth surfaces to become chemically bound with polymerizable filling materials (acrylic resins, polyacrylic cements, composite materials, etc.).

The glycerophosphoric acid of this invention allows bonding of filling materials to dental tissue with increased bond strength, lower toxicity, greater resistance to water and mouth liquids, and better affinity with dental tissues ("biochemical affinity") when compared with presently known methods of increasing bond strength.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a cross-sectional view of a decayed tooth which has been bored in preparation for filling with a mordant of the invention.

Figure 2 is a cross-sectional view of a decayed tooth which is drilled at a 45° angle α in preparation for filling with a mordant of the invention.

Figure 3 is a cross-section of a tooth portion having a hook inserted in a filling material adhered with a mordant of the invention, useful for testing the bond strength of the filling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In typical dental filling operations, a cavity is prepared for filling using conventional means in which a tooth is drilled, and then the area to be filled is cleaned and sterilized. Next,, the tooth often is treated with one or more mordant solutions intended to increase the bond strength between a filling material to be added to the cavity and the surrounding dental tissue, though this step may not be necessary where mineral cements are employed as the filling material. Finally, the filling material is added to the cavity.

The liquid mordant of the present invention comprises solution of about 20 to 55% by weight of glycerophosphoric acid in a suitable solvent. Distilled water is the most preferred solvent. In addition to glycerophosphoric acid and solvent, other suitable components can also be employed in the mordant, such as gelatinizing additives or other additives which do not interfere substantially with the adhesive qualities of the mordant. The most preferred embodiment of the invention comprises a 30% by weight solution of glycerophosphoric acid in distilled water.

While not wishing to be bound by theory, it is believed that the solution is capable of increasing the strength of the bond between filling materials and dental tissues by providing a chemical link between the filling material and dental tissues. Glycerophosphoric acid has a relatively low toxicity to healthy dental tissue, and therefore is desirable for this purpose. As compared with phosphoric acid, glycerophosphoric acid is less toxic for several reasons. First, glycerophosphoric acid is not as strong as phosphoric acid. Also, due to its high ability to absorb moisture, glycerophosphoric acid does not penetrate deeply into the dentin canaliculi and therefore is not as injurious to the dental pulpa. In addition, glycerophosphoric acid need only be applied to the cavity area for shorter periods of time to be effective, as compared to phosphoric acid.

Moreover, since glycerophosphoric acid has a relatively good ability to absorb moisture, it can be used for etching not only enamel, but also dentin without danger of significantly damaging the dental pulpa. In a decayed tooth, the dentin canaliculi can contain microorganisms which decay the dentin and pulpa. When a glycerophosphoric acid solution is applied to the dentin surface, the solution absorbs fluid from the canaliculi, and the fluid flows onto the dentin surface. The fluid washes the microorganisms out of the canaliculi and decreases the levels of harmful bacteria in the dentin. Since the fluid flow is directed from the dentin to the surface, glycerophosphoric acid should not penetrate significantly into the canaliculi or cause significant injury to the pulpa.

An advantage of using a glycerophosphoric acid solution as a dental mordant is its ability to act as a relatively strong chemical link between the filling material and dental tissues. This action is believed to be the result of chemical binding at several active sites, as shown below: Dental Tissue

Dental Tissue

Where "R" and "R¹" each are molecules of a filling material.

One active bonding site is at the acidic groups which bind with the calcium atoms of dental tissue. This reaction is believed to occur relatively quickly and substantially completely due to its biochemical affinity with dental tissues. The reaction can take place in about thirty seconds in preferred embodiments, and its speed and completeness can contribute to lower toxicity of the mordant. The calcium salt which results from the reaction is substantially insoluble, and resists both water and mouth liquids.

Another active site of the glycerophosphoric acid molecule capable of chemically bonding is at the alcohol radical. The alcohol radical is believed to be highly reactive and capable of bonding with many suitable filling resins. Such resins may be, for example, polyacrylic cements, acrylic resins (including cyanaerylic polymers) , epoxy resins, and polyurethane resins. Some suitable filling materials believed to be capable of bonding with the alcohol radical are polycarboxylic cements, acryloxide, and filling resins sold under the trade names Evicrol (in Czechoslovakia) , Vivadent (in Germany) , Carbodent (in the Ukraine) , and Microrest (in Japan) . The bonds produced at the alcohol radical can be ether bonds or ester bonds, depending on the composition of the filling material, as shown below:

Dental Tissue

Shown above are ester bonds with a polyacrylic acid molecule in the case of an alpha-isomer of glycerophosphoric acid.

I—Ca —COOCHo

Dental

Tissue CH, / h*Ca CH₂ —— O — C — COOCH₃ CH,

Shown above are ether bonds with two methylmethacrylate molecules in the case of beta-isomer of glycerophosphoric acid.

The glycerophosphoric acid of the present invention can be produced by methods known to one skilled in the art. One method of producing glycerophosphoric acid comprises heating a mixture of concentrated (76%) solution of orthophosphoric acid in water with glycerin at a 1:1 molar ratio. At the boiling temperature of the mixture, which typically is approximately 178°C, the combination will yield a golden-colored syrupy liquid, which is subsequently diluted to a 30% solution by weight by the addition of distilled water. The color is believed to be caused by small amounts of impurities present in glycerin. When very pure (distilled) glycerin is used, the final product is practically colorless. If gelatinized additives are included, they preferably are added after dilution of the glycerophosphoric acid to the desired concentration.

Glycerophosphoric acid also can be produced by heating a mixture of crystalline phosphoric acid and glycerin to a temperature of 110°C. Each of these processes yields a mixture of alpha and beta isomers of glycerophosphoric acid, each of which is equally active in increasing the bond strength of dental fillings. In a preferred embodiment of the invention, the mordant comprises both isomers. In an alternate embodiment, the isomers can be separated, and only one isomer can be employed in the composition. Where the mordant contains only one isomer, a mixture of a and β isomers can be produced using the processes described above, and can then be separated. A suitable compound used for separation of the isomers is barium nitrate, which reacts with β glycerophosphoric acid to produce the hard soluble salt 2C₃H₇0₆PBa.Ba(N0₃)₂.

A decayed tooth can be treated according to the invention as follows. First, a caries cavity can be drilled, as shown in Figure 1, with the area drilled 4 extending through the enamel 1 and into the dentin 2, but not to the pulpa 3. Where only the enamel portion of the tooth is to be treated with glycerophosphoric acid, it may be desirable to increase the contact area of the acid to the tissue by drilling the dental cavity at 45 degrees a as shown in Figure 2.

With the present invention, it is preferred not to pretreat the drilled dental tissue with ethyl alcohol, which sometimes is used for treatment of decay cavities as an antiseptic and drying agent. However, the alcohol can dehydrogenate the dental canaliculi. Ethyl alcohol has a relatively high ability to absorb moisture and induces the same processes in the dentin canaliculi as glycerophosphoric acid. If an ethyl alcohol pretreatment is followed by glycerophosphoric acid application to the dentin, there is a possibility that glycerophosphoric acid may flow into dry canaliculi and injure the pulpa.

After the caries cavity is drilled to the desired specifications, a mordant comprising a solution of glycerophosphoric acid is applied to the dental tissue. In a preferred embodiment of the liquid mordant of the present invention, a solution containing a concentration of approximately 30% by weight glycerophosphoric acid is applied to dental tissue. The solution preferably is a mixture of the alpha and beta isomers of glycerophosphoric acid. The amount of solution should be sufficient to apply a thin layer covering the whole surface being etched, and typically is ■ about 1 to 3 drops. The solution can be applied by a brush, cotton ball, or a dentist's ordinary tools, such as a spatula or probe.

After application of the mordant, a suitable bonding time is then permitted to elapse, preferably about 30 seconds. The cavity can then be washed out, preferably by water, such as through use of a water jet. The dental cavity can then be dried, such as by an air jet.

The above-described etching process typically will produce a visibly detectable mat surface on the dental tissue. However, in some instances dental tissues are more highly resistant, such that visible changes may not be observed. In such instances, glycerophosphoric acid can be reapplied, preferably for a shorter period than the initial application, and more preferably for about 10 seconds. The cavity can then be washed out and dried, as with the first application.

The etching of dental tissues with glycerophosphoric acid solution in this manner can result in a greater bond strength of acrylic resin, polyacrylic, and other filling composites to dental tissues. After the cavity is dried out, a suitable filling material can be added to the cavity and permitted to bond with the dental tissue using the mordant.

The following examples are illustrative of the invention.

Example 1 An amount of 30% glycerophosphoric acid solution sufficient to apply a thin layer covering the whole surface being etched was applied to a tooth surface that had been prepared for filling using conventional drilling means. After application of the solution, a total of thirty seconds passed, and the surface was washed out using a water flow and dried by an air jet. Next, the tooth was filled with acryloxide, a filling composite produced by Kharkov Factory of Medical Plastics and Dentistry Materials, the Ukraine. The acryloxide was made by combining (a) a powder composition comprised of methylmethacrylate, buthylmethacrylate, powdered quartz, benzoyl peroxide, sodium benzolsulfonate, titanium dioxide, and pigments, and (b) a liquid comprised of methylmethacrylate, methacrylic acid and ED-16 epoxy resin adduct, dimethylparatolundin, ethyl alcohol and hydroxinone. A hook 1 was embedded into the filling material 2, after which the tooth 3 was chemically hardened, or cured, for a period of 8 to 10 minutes. The specimen was then kept in water for three days.

The bond strength of the filling to the tooth then was measured by extracting the filling material from the tooth surface using the hook. The force used to disrupt the filling material was considered a measure of the bond strength. As determined by this procedure after a series of trials, the bond strength was 21.5 ± 1.4 kg/cm².

Example 2 An amount of 30% glycerophosphoric acid solution sufficient to apply a thin layer covering the whole surface being etched was applied to a tooth surface that had been prepared for filling using conventional drilling means. After application of the solution, a total of about thirty seconds passed, and the surface was washed out using a water flow and dried by air jet. Next, the tooth was filled with a polycarboxylate cement, a commercial product of the Kharkov Factory of Medical Plastics and Dentistry Materials, the Ukraine. The polycarboxylate cement was made from a powder comprised of (a) zinc oxide thermally treated by heating to about 1000 °C, with a relatively small amount of magnesium oxide, and (b) a liquid consisting of concentrated water solution of polyacrylic acid. A hook, such as is depicted in Figure 3, was embedded into the filling material after which the tooth was cured for a period of 8 to 10 minutes. The specimen was then kept in water for three days.

The bond strength was measured by detaching the filling material from the tooth surface, in the same manner as Example 1, for a series of trials. The bond strength was determined to be 22 ± 1.3 kg/cm².

Comparative Example 1 A tooth surface was filled with acryloxide, using no mordant. After curing, the specimen was kept in water for three days. The bond strength then was measured by detaching the filling material from the tooth surface in the same manner as Example 1 for a series of trials. The bond strength was determined to be 1.4 ± 0.9 kg/cm²,

Comparative Example 2 A tooth surface was filled with polycarboxylate cement, using no mordant. After curing, the specimen was kept in water for three days. The bond strength then was measured by detaching the filling material from the tooth surface in the same manner as Example 1 for a series of trials. The bond strength was determined to be 2.1 ± 0.8 kg/cm².

Claims

WHAT IS CLAIMED IS:

1. A liquid mordant suitable as an adhesive for binding dental tissue to a filling material, comprising a solution of about 20 to 55% by weight of glycerophosphoric acid in a solvent.

2. The liquid mordant according to claim 1, wherein the solvent is distilled water.

3. The liquid mordant according to claim 1, wherein the glycerophosphoric acid is comprised of a mixture of alpha and beta isomers.

4. The liquid mordant according to claim 1, wherein the solution comprises about 30% by weight of glycerophosphoric acid in distilled water.

5. The liquid mordant, according to claim 1, further comprising a gelatinizing additive.

6. A method for treating dental tissue comprising:

(a) forming a cavity for receiving a filling material;

(b) applying a liquid mordant comprising a solution of about 20% to 55% by weight glycerophosphoric acid in a solvent to an application area in the cavity consisting of (i) dental enamel or (ii) dental enamel and dentin;

(c) washing the application area;

(d) drying the application area; and

(e) adding a filling material to the cavity.

7. The method according to claim 6, wherein the solvent is distilled water.

8. The method according to claim 6, wherein the glycerophosphoric acid is comprised of a mixture of alpha and beta isomers.

9. The method according to claim 6, wherein the filling material is selected from the group consisting of polyacrylic cements, acrylic resins, cyanacylic resins, epoxy resins, and polyurethane resins. acrylic resins and polyacrylic cements.

10. The method according to claim 6, wherein the step of washing the application area comprises applying water to the tissue and wherein the drying step comprises air drying.

11. The method according to claim 6, further comprising re-applying a mordant comprising a solution of about 20% to 55% by weight of glycerophosphoric acid in a solvent to the tissue after drying the cavity and prior to adding the filling material.

12. The method according to claim 6, wherein the liquid mordant further comprises a gelatinizing additive.