EP0604487A1

EP0604487A1 - Amalgam-glass ionomer bonding system

Info

Publication number: EP0604487A1
Application number: EP92919048A
Authority: EP
Inventors: Thomas J. Arnold
Original assignee: Mion International Corp
Current assignee: Mion International Corp
Priority date: 1991-08-22
Filing date: 1992-07-30
Publication date: 1994-07-06
Also published as: AU2515492A; EP0604487A4; CA2116099A1; WO1993003682A1

Abstract

L'invention se rapporte à l'application d'un ciment humide à l'ionomère de verre sur une lésion dentaire. Avant que le ciment ne durcisse, on applique l'amalgame humide sur le ciment à l'ionomère de verre. L'ionomère de verre se fixe à la dent, et l'interface du ciment humide et de l'amalgame humide permet de créer de fortes liaisons entre le ciment à l'ionomère de verre et l'amalgame, pour assurer une liaison extrêmement forte entre l'amalgame et la dent. Des bases métalliques, des sels métalliques et/ou des oxydes métalliques sont ajoutés à une formule d'amalgame de reconstitution s'utilisant en conjonction avec un ciment à l'ionomère de verre pour réparer une lésion dentaire. L'additif se compose d'une quantité suffisante de bases métalliques, de sels métalliques et/ou d'oxydes métalliques, tels que de la poudre d'un ciment dentaire au polycarboxylate, pour améliorer la force de liaison entre le ciment humide à l'ionomère de verre appliqué à la dent et l'amalgame humide amélioré appliqué au ciment humide. En conséquence, la durabilité d'une telle reconstitution est améliorée et peut ainsi permettre d'obturer une lésion avec un amalgame plutôt que de nécessiter l'extraction de la dent ou l'application d'une prothèse.The invention relates to the application of a wet cement to the glass ionomer on a dental lesion. Before the cement hardens, wet amalgam is applied to the glass ionomer cement. The glass ionomer attaches to the tooth, and the interface of the wet cement and the wet amalgam creates strong bonds between the cement to the glass ionomer and the amalgam, to ensure an extremely strong bond between the amalgam and the tooth. Metal bases, metal salts and / or metal oxides are added to a reconstitution amalgam formula for use in conjunction with a glass ionomer cement to repair a dental lesion. The additive is made up of a sufficient amount of metal bases, metal salts and / or metal oxides, such as powder of polycarboxylate dental cement, to improve the bonding strength between the wet cement glass ionomer applied to the tooth and improved wet amalgam applied to wet cement. Consequently, the durability of such a reconstruction is improved and can thus make it possible to fill a lesion with an amalgam rather than requiring the extraction of the tooth or the application of a prosthesis.

Description

AMALGAM - GLASS IONOMER BONDING SYSTEM Field of the Invention

This invention relates to a system for the restoration of lesions in living teeth, and in particular, to a system for chemically bonding amalgam to dentin. Background of the Invention

Because conventional fillings rely purely on mechanical retention to the tooth, they are not suitable in instances when a tooth is severely decayed and has little structure left to which the filling may be attached. A conventional filling in a tooth with even only a moderate amount of decay may fail over time due to recurrent decay, lack of retention, or continued stress breakdown of the remaining tooth structure. Therefore, the patient is often faced with the choice of removing the tooth or the application of a prothesis such as a crown.

In some instances, retentive pins are used to affix restorations to a tooth. However, pins tend to weaken the restoration, create stresses within the tooth, and may also result in pulpal exposure. Thus, it is desirable to provide a dental restoration system which does not utilize pins or other similar mechanical mechanism so as to limit the stress placed on the tooth.

Many types of materials have been used to affix a restoration to a tooth, including glass ionomer cement and dentin bonding systems. Glass ionomer cement bonds to tooth structure dentin and has been used for restorative materials, cavity liners, bases, and crown cements. As a crown cement, the glass ionomer cement which is known to adhere to cast metals is mixed, placed into the crown and, before the cement hardens, the crown is placed over the prepared tooth. As the glass ionomer cement hardens, the crown is retained on the tooth, and, after complete hardening of the cement, an excellent bond between the tooth and crown is formed. In other situations, glass ionomer cement may be applied to a tooth and allowed to harden to form a liner or base on which the amalgam may then be applied to restore the tooth using conventional techniques which require that the surface onto which the amalgam is applied be completely dry.

Studies have been conducted to determine the capability of glass ionomer cements to adhere to various materials, including the tests disclosed in Hotz, et al., The Bonding of Glass lonomer Cements to Metal and Tooth Substrates. British Dental Journal, 1977; 142: 41-47. This study demonstrated that glass ionomer cement bonds well with dentin and enamel, and also adheres to some cast solid metals. Adherence to a cast solid metal is most successful when the surface of the metal is first etched with an acid, such as citric acid, before applying the glass ionomer cement.

Results of studies such as Hotz et al., have provided a basis for the use of glass ionomer cements in various dental procedures. For example, in U.S. patent no. 4,654,007, a layer of glass ionomer cement is applied to a tooth before attaching a porcelain restoration. After proper hardening of the cement, the cement is etched with an acid to create microscopic surface irregularities or tubules, which facilitate mechanical retention of the porcelain restoration to the tooth. The method disclosed in U.S. patent no. 4,738,722 is similar in that the glass ionomer cement disclosed is hardened and etched with an acid before the restoration material is placed into the cavity preparation. This method protects the pulp of the tooth by providing a layer of glass ionomer cement above the pulp.

The current restoration methods using glass ionomer cements have proven to be successful in restoring significant lesions. For example, Matis, et al., How Finishing Affects Glass lonomers. 1991; 122: 43-46, preformed a five year study to determine the effectiveness of restorations involving the use of glass ionomer cements finding that the glass ionomer cements are outstanding in their retentive capability. Also, researchers continue to improve the retention capability of the cements. For example, the polymerizable cement mixtures disclosed in U.S. patent no. 4,872,936 demonstrate increased mechanical strength, lower solubility, and have no outstanding separation phenomena.

However, one shortcoming of using glass ionomer cements in present restorative techniques is the glass ionomer cement must be allowed to harden before it is etched with acid. This results in an undesirable time delay, and the risk that tooth damage to the nerve might occur while etching the hardened glass ionomer. Therefore, it is desirable to develop a dental restoration system which is efficient and requires relatively little time to perform.

In instances when hardened glass ionomer is used as a base for amalgam, studies show that the glass ionomer shrinks, leaving a slight 60-80 urn gap between the hardened glass ionomer and the hardened amalgam. Scherer, Reinforced Glass lonomer Cement vs. Zinc Phosphate Cement. 18th Annual Session of the American Association for Dental Research, San Francisco, California. Thus, the hardened glass ionomer does not bond the amalgam to the tooth. Dentin bonding systems which utilize cements other than glass ionomers, such as those discussed in Johnson, et al., Dentin Bonding Svstems: A Review of Current Products and Techniques. The Journal of the American Dental Association, 1991 ; 122: 34-41, have recently become available. The cements used in these dentin bonding systems are applied to the tooth prior to filling the tooth or to the application of a restoration. However, before being applied to the tooth, the tooth is etched with an acid to create tubules to which the dentin bonding systems are micromechanically bonded. These systems have not been well-received due to the risk of pain and damage if the acid contact sensitive dental nerves. In fact, Johnson et al. identifies several cautions in the use of dentin bond systems, and in fact, suggests the use of a protective liner for deep lesions. Therefore, it is desirable to develop a dental restoration system which does not require etching of the tooth or of the cement.

It is also known to fill a tooth lesion with composite materials, which may include a glass ionomer mixed with amalgam powder used as a base. However, these restorations do not bond as well to dentin as glass ionomer alone. Moreover, these materials have a tendency over time to discolor the dentin and provide an unsightly aesthetic appearance.

It is also desirable to develop a dental restoration system that works well with conventional materials, such as amalgam, to allow the tooth to be filled instead of using a crown or bridge, as amalgam is less expensive and is easy to handle. Objects of the Invention

Accordingly, it is one object of the present invention to provide a dental restoration method which is reliable, inexpensive and expedient. It is another object of the present invention to provide a dental restoration system that does not require pins or acid etching.

It is another object of the present invention to provide a dental restoration system which bonds to dentin, fills dentin tubules and eliminates the need for unnecessary extraction. It is another object of the invention to provide a dental restoration system that internally bonds the remaining crown of a tooth together so as to avoid continued cracking of the tooth enamel.

It is another object of the present invention to provide a dental restoration system which is able to strongly hold large amalgam fillings.

It is another object of the invention to provide an amalgam filling with an increased life expectancy.

It is another object of the invention that provide a restoration system that may be used with amalgam having a reduced mercury content. It is another object of the invention to provide an amalgam filling strongly bonded to dentin. Summary of the Invention

Wet glass ionomer cement is applied to a tooth lesion. Before the cement hardens, wet amalgam is applied on top of the glass ionomer cement. The glass ionomer bonds to the tooth, and the interface of the wet cement and wet amalgam allows strong bonds to form between the glass ionomer cement and the amalgam, to provide an exceptionally strong bond between the amalgam and the tooth. Metal bases, metal salts and/or metal oxides are added to an amalgam restoration formula for use in conjunction with a glass ionomer cement to restore a tooth lesion. The additive is comprised of an amount of metal bases, metal salts and/or metal oxides, such as the powder of a polycarboxylate dental cement, sufficient to improve the bond strength between wet glass ionomer cement applied to the tooth lesion and the wet improved amalgam applied to the wet cement. As a result, the retentive quality of such a restoration is improved and therefore may permit a lesion to be filled with amalgam rather than requiring extraction or the application of a prosthesis. Detailed Description

A tooth lesion is first prepared to receive an amalgam filling using conventional techniques. If sufficient tooth structure is present, the tooth may be undercut to provide improved mechanical retention for the completed filling. Liquid glass ionomer cement is then applied to the prepared tooth lesion. The glass ionomer cement preferably has a set time of 5 - 10 minutes and contains fluoride ions to assist in preventing tooth decay by releasing fluoride ions into the dentin over time. Glass ionomer cement is available from a variety of sources including the Giaslonomer Cement, Type I distributed by Shofu Dental Corporations of Menlo Park, California. While the glass ionomer cement layer is still wet, a layer of wet amalgam, such as Valiant Phd, is placed disposed on the glass ionomer layer using conventional amalgam application techniques. The wet glass ionomer and wet amalgam layers are allowed to harden to form a solid laminate structure that sufficiently restores the preferred form of the tooth.

As noted above, the adhesion of glass ionomer cement to dentin is well documented. However, the present invention results in a remarkably strong bond between the glass ionomer cement and the amalgam, after both the glass ionomer cement and the amalgam has hardened. The precise explanation for the bond is not fully appreciated, but it is believed that an ionic bond is created between the wet glass ionomer cement and the wet amalgam. Specifically, it is believed that because both constituents are interfaced while in a liquid state, the glass ionomer ions (having strong negative charges) and the metal particles (including tin) in the amalgam (having strong positive charges) are able to physically move and align themselves before the constituents harden. When aligned, a strong ionic bond is created between the constituents. This level of ionic bonding does not occur when wet amalgam is applied to a hardened glass ionomer layer as in the prior art. The nature of the ionic bond also suggests that bond strength may be increased by employing amalgam with an increased tin content, as the tin particles provide a particularly strong ionic bond. Likewise, increasing the fluoride content of the glass ionomer cement may increase the bond strength.

In another embodiment of the invention, the amalgam powder component of an amalgam is mixed with the glass ionomer cement before the cement is applied to the tooth. Amalgam powder is one component of what is known as amalgam. Specifically, amalgam powder comprising various alloyed metals is mixed with mercury to create amalgam. For the present invention, the amalgam powder preferably has substantially the same metals in the same percentage as the amalgam to be used as filling material, as this will reduce the risk of galvanic activity. The amount of amalgam powder may vary from about 2% to 50% by volume of the glass ionomer cement. Adding the amalgam powder to the glass ionomer cement provides several benefits. First, when first introduced, the amalgam powder initiates ionic activity in the glass ionomer by causing disassociation of the ions, thus preparing them to bond to the wet amalgam. Therefore, ionic bonds to the wet amalgam will occur at a higher rate. Because there is an overabundance of ions in the glass ionomer cement, there is no diminution in ions available to bond to the wet amalgam. Second, the subsequent bond to the amalgam will have an increased shear strength due to internal bonding in the cement with the amalgam particles. Preliminary tests have shown the amalgam - glass ionomer bond strength to be about 40 psi, which is much stronger than conventional amalgam fillings without mechanical retention and the bond between glass ionomers and porcelain, or acrylic restorations. Thus, this method may be used to repair a tooth which might otherwise require extraction or a crown. Moreover, because the entire amalgam surface contacting the glass ionomer cement is ionically bonded, the amalgam holds the tooth crown together to thereby prevent cracking. Also, the risk of exposing dental pulp to acid as used in other techniques is eliminated.

The present invention also allows use of an amalgam having a reduced mercury content. Specifically, the viscous glass ionomer cement layer fills small crevices which ordinarily are required to be filled by amalgam in a conventional filling. Since, in the present invention, amalgam does not fill the small crevices, the content of the amalgam need not be as fluid as is required for conventional fillings. The reduction of mercury content of fillings is very important in reducing the potential risk to the patient and to the dentist for undesirable exposure to mercury.

It will be appreciated by those of skill in the art that the restoration of major tooth lesions according to the present invention can be accomplished in instances where more expensive crowns or bridges would ordinarily be required. In addition, the procedure of the present invention can be accomplished in much less time. Moreover, due the strong ionic bond with the amalgam, the restoration will last longer than conventional amalgam fillings, even for large lesions. The use of glass ionomer cement seals dentin tubule, which helps eliminates post restorative sensitivity. Finally, since the glass ionomer cement may contain fluoride, it provides a fluoride release which assists in inhibiting recurrent decay. Conventional amalgam of the type commonly used in dentistry is comprised of two components: amalgam powder comprised of various alloyed metals, and mercury. Generally, the amalgam powder, commonly referred to as "amalgam alloy," is comprised of a silver-tin alloy, with trace amounts of copper with or without zinc. When amalgam powder is mixed (also referred to as trituration or amalgamation) with mercury, the substance known as amalgam results. The present invention includes a composition for amalgam which strengthens the bond of a restoration to a tooth where that restoration has been created through the application of wet amalgam onto wet glass ionomer cement. Specifically, in one embodiment, a source of alloy-forming compounds, such as metal salts, metal bases and metal oxides, is added to the amalgam powder prior to amalgamation and application of the amalgam in the above-identified dental procedure. Metal bases, metal salts and metal oxides include, for example, phosphates, nitrates, sulfates, carbonates, oxides, hydroxides and halogens of the particular alloy- forming metal utilized. Materials of this type which have been used in dentistry for other purposes with some prevalence and considered most likely candidates as additives include zinc phosphate, zinc oxide, magnesium sulfate, stannous fluoride and silver nitrate. Other additives are contemplated for use herein, but must be scrutinized according to the effect such additives may have in the patient. For example, iodine has adverse affects in many patients whereas tin oxide does not affect the patient.

One readily available source of metal bases, metal salts, and metal oxides is the powder component of a polycarboxylate cement. Polycarboxylate cements are created by mixing a powder component, usually containing zinc oxide and magnesium sulfate and, often, stannous fluoride, with a liquid comprising an aqueous solution of polyacrylic acid. The constituents of the polycarboxylate cement powder are not alloyed as are the constituents of an amalgam powder. In the present invention, only the powder component of the polycarboxylate cement is used as an additive. Favorable results have been obtained using the powder component of Dureloπ^® polycarboxylate cement manufactured in West Germany and distributed by Premier Dental Products Company of Norristown, Pennsylvania, and Veratex, a zinc polycarboxylate cement distributed by Veratex Corporation of Troy, Michigan.

In one embodiment of the present invention, small quantities of the powder component of the polycarboxylate cement are added to the amalgam powder prior to the addition of mercury to the amalgam powder and to the trituration of the mixture to thereby result in an improved amalgam. As used herein and in the claims, "improved amalgam powder" means a dental amalgam powder or silver-tin alloy to which a constituent comprising metal bases, metal salts and/or metal oxides has been added. Also, as used herein and in the claims, "improved amalgam" means an improved amalgam powder mixed with mercury.

Pull strength tests using the improved amalgam of the present invention were performed using KETAC^®-CEM Radiopaque glass ionomer cement distributed by ESPE Premier Sales Corp. of Norristown, Pennsylvania and an improved amalgam comprising Sybraloy amalgam, available from Kerr

Manufacturing Company of Romulus, Michigan, and Durelon^® polycarboxylate cement powder. In these tests, the improved amalgam powder was created by mixing 11 milligrams of the powder component of the Durelon^® polycarboxylate cement with 400 milligrams of amalgam powder. The improved amalgam powder was then triturated with 400 milligrams of mercury in the usual manner, thereby forming the improved amalgam. In the samples tested, the additive comprised about 2.7% by weight of the powder mixture, or 1.4% by weight of the improved amalgam. Several plugs of equal size, shape and proportion were formed using the improved amalgam and the glass ionomer cement. Specifically, a sandwich of wet improved amalgam, wet glass ionomer cement, and wet improved amalgam was formed in plastic molds, the plastic of which does not adhere to amalgam or to glass ionomer cement. These plugs were then allowed to harden for 24 hours. One end of the plug, comprising hardened improved amalgam, was clamped to a fixed table surface, and the other end, also comprising hardened improved amalgam was attached to a scale. Weights were then added to the scale until the plug broke apart at the interface between the hardened glass ionomer cement and the hardened amalgam. Comparative plugs were also formed using conventional amalgam, i.e., amalgam to which no additives were made, and glass ionomer cement. These comparative plugs were tested for pull strength as described above to provide as baseline upon which to compare the bond strength of the improved amalgam to conventional amalgam.

The comparative plugs exhibited a bond strength of 147 psi, whereas the plugs formed from the improved amalgam exhibited a bond strength of 187 psi. It will be appreciated by those of skill in the art that bond strengths of 187 psi are quite significant and help to ensure that the restoration remains securely in place so as to minimize future restorations of the same lesion.

Durelon^® and Veratex are suitable for use as additives with a variety of commercially available amalgams, such as Ionosphere distributed by Goldsmith & Revere of Englewood, New Jersey, and Luxalloy^® manufactured by Dequssa AG of Frankfort, West Germany, and similar improvements in bond strengths may be obtained.

Various amalgam additives may be used to enhance the bond between the glass ionomer cement and the improved amalgam. These include metal bases, metal salts and metal oxides. It is believed that the additives improve the bonding reactions as they produce carboxylate ion groups upon contact with the polyacrylic acid of the wet glass ionomer cement. It is further believed that the carboxylate ions of the glass ionomer cement then ionically bond to the available cations of the amalgam. The glass ionomer cement's polyacrylic acid groups form metal carboxylate salts with the metal cations of the improved amalgam. This "neutralization" of the carboxylic acid improves wetting of the surface of the improved amalgam through its interaction with the polyacrylic acid component of the glass ionomer cement, and further ionic bonding is created by the metal carboxylate salts forming at the reacted surfaces. These results, which are strong bonds forming at the surface of the amalgam, increase the strength of the resulted union between the cement and amalgam.

It is interesting to note that the improved amalgam powder containing the conventional amalgam powder and the additive of polycarboxylate cement powder, when mixed with the prescribed amount of mercury for the amalgam powder results in a "wetter" mixture than when no additive is present. Therefore, as will be appreciated by those of skill in the art, it is possible that the amount of mercury required for use with the improved amalgam powder to create improved amalgam could be reduced to obtain handling characteristics like those of conventional amalgam. By reducing the content of mercury in the improved amalgam, the potential risk to the patient is thereby reduced. It is believed that the amount of additive required to result in an improved amalgam according to the present invention ranges from a trace, 0.001%, to 25% of the total weight of the improved amalgam. Actual percentages by weight of additives in the improved amalgam may vary according to the weight of the compounds containing metal bases, metal salts or metal oxides added, and is limited only by the distortion of the amalgam in the presence of excessive additive. Preferably, the additive comprises about 1-5% by weight of the improved amalgam powder.

It will be appreciated by those of skill in the art that the restoration of major tooth lesions according to the present invention can be accomplished in instances where more expensive crowns or bridges would ordinarily be required. In addition, the procedure of the present invention can be accomplished in much less time. Moreover, due to the strong bond of the amalgam to the glass ionomer cement, the restoration will last longer than conventional amalgam fillings, even for large lesions. Also, the use of glass ionomer cement seals dentin tubules, which helps eliminates post restorative sensitivity. Finally, since the glass ionomer cement may contain fluoride, it provides a fluoride release which assists in inhibiting recurrent decay.

The amalgam restorative formula which is improved as described herein should be considered as a restorative material termed an improved amalgam. It will be appreciated by those of skill in the art that other amalgam bonding systems or methods utilizing materials other than those disclosed herein will find the improved amalgam to be compatible with the particular system or material (such as acrylic bonding agents) used. Also, as noted herein, an improved amalgam is "wetter" than a conventional amalgam which implies that the amount of mercury required for use of the improved amalgam in accordance with the restoration method disclosed herein, or the use of any amalgam, conventional or improved, utilized for any other purpose, may be reduced. Hence, the use of the improved amalgam for any dental procedure is anticipated and is expected by this invention.

Claims

ClaimsWhat is claimed is:

1. A method of restoring lesions in a living tooth, comprising the steps of: applying a wet glass ionomer cement to the lesion; placing a wet dental amalgam directly on the wet glass ionomer cement enabling the glass ionomer cement to bond the amalgam to the tooth; and allowing the wet glass ionomer cement and wet dental amalgam to harden, such that the glass ionomer cement is bonded to the amalgam.

2. The method of restoring lesions in a living tooth of claim 1 wherein the bond between the glass ionomer cement and the amalgam is ionic.

3. The method of claim 1 wherein the wet dental amalgam comprises tin.

4. The method of claim 1 wherein the glass ionomer cement further comprises amalgam particles.

5. The method of claim 4 wherein the amalgam particles in the glass ionomer cement have substantially the same metallic composition as the metal particles of the wet dental amalgam.

6. The method of claim 1 wherein the ionic bond between the layer of glass ionomer and the layer of amalgam has a bond strength greater than

10 psi.

7. The method of claim 6 wherein the ionic bond between the layer of glass ionomer and the layer of amalgam has a bond strength of at least 40 psi.

8. A composition for restoring lesions in a living tooth, comprising; a layer of glass ionomer cement bonded to the tooth; and a layer of amalgam disposed on the layer of glass ionomer cement, the composition having been formed according to the method of claim 1.

9. The composition for restoring lesions in a living tooth of claim 8 wherein the bond between the glass ionomer cement and the amalgam is ionic.

10. The composition of claim 8 wherein the glass ionomer cement comprises fluoride.

11. The composition of claim 8 wherein the amalgam comprises tin.

12. The composition of claim 8 wherein the glass ionomer cement further comprises amalgam particles.

13. The composition of claim 12 wherein the amalgam particles in the glass ionomer cement have substantially the same metallic composition as the metal particles of layer of amalgam.

14. The composition of claim 8 wherein the ionic bond between the layer of glass ionomer and the layer of amalgam has a bond strength greater than

10 psi.

15. The composition of claim 14 wherein the ionic bond between the layer of glass ionomer and the layer of amalgam has a bond strength of at least 40 psi.

16. A tooth having a restored lesion, the restored lesion being formed by the process of claim 1.

17. The tooth having a restored lesion of claim 16 wherein the bond between the glass ionomer cement and the amalgam is ionic.

18. A method of restoring lesions in a living tooth, comprising the steps of: applying a wet glass ionomer cement to a lesion; placing a wet improved amalgam restorative material directly on the wet glass ionomer cement; and allowing the wet glass ionomer cement and the wet improved amalgam to harden, thereby bonding the improved amalgam restorative material to the tooth.

19. The method of claim 18, wherein the amalgam restorative material is prepared by the steps of: providing an amalgam alloy; introducing an additive selected from the group consisting of metal salts, metal bases and metal oxides to the amalgam alloy to form an improved amalgam alloy; and, triturating the improved amalgam alloy with mercury to form the amalgam restorative material.

20. The method of claim 18, wherein the improved amalgam restorative material comprises the combination of amalgam and an additive, said additive being present in the amalgam in an amount sufficient to improve the bonding strength between the glass ionomer cement and the improved amalgam restorative material, said additive comprising at least one of a metal base, metal salt and metal oxide.

21. The method of claim 19, wherein the additive comprises the powder component of polycarboxylate cement.

22. The method of claim 20, wherein the additive comprises at least one of zinc phosphate, zinc oxide, magnesium sulfate, stannous fluoride, silver nitrate and tin oxide.

23. The method of claim 19, wherein the additive is present in the amalgam restorative material in an amount of from about 0.001% to about 25% by weight of the restorative material.

24. The method of claim 19, wherein the additive is present in an amount of from about 1% to about 5% by weight of the amalgam alloy.

25. The method of claim 20, wherein the additive is added in an amount sufficient to form a bond between the glass ionomer cement and the amalgam restorative material having a bond strength of at least 40 psi.

26. The method of claim 20, wherein the additive is added in an amount sufficient to form a bond between the glass ionomer cement and the amalgam restorative material having a bond strength of at least 180 psi.

27. In a method of restoring lesions in a living tooth, of the type wherein a layer of glass ionomer cement is applied to the lesion, and a layer of amalgam is thereafter applied to the layer of glass ionomer cement, the improvement comprising: adding an alloyable metal compound to the amalgam in an amount sufficient to improve the bond strength between the glass ionomer and the amalgam; and applying the layer of amalgam to the layer of glass ionomer cement when the glass ionomer cement and the amalgam are wet.

28. The method of claim 27, wherein the alloyable metal compound is selected from the group consisting of metal bases, metal salts and metal oxides.

29. The method of claim 28, wherein the alloyable metal compound is at least one of zinc phosphate, zinc oxide, magnesium sulfate, stannous fluoride, silver nitrate and tin oxide.

30. The method of claim 27, wherein the alloyable metal compound is added to the amalgam in an amount sufficient to form a bond between the glass ionomer cement and the amalgam restorative material having a bond strength of at least 40 psi.

31. The method of claim 27, wherein the alloyable metal compound is present in the amalgam in an amount of from about 0.001% to about 25% by weight of the amalgam.

32. The method of claim 27, in which the alloyable metal compound is added to amalgam alloy prior to trituration of the amalgam alloy to form an amalgam, said alloyable metal compound comprising polycarboxylate cement powder, said polycarboxylate powder comprising about 2.7% by weight of the amalgam alloy.

33. A dental amalgam composition for use with glass ionomer cement in restoring lesions in a living tooth, comprising: a dental amalgam, said dental amalgam comprising an amalgamation of amalgam alloy and mercury; and an additive to said amalgam, said additive comprising a sufficient amount of an alloyable metal compound to enhance bonding between the glass ionomer cement and the dental amalgam composition.

34. The composition of claim 33, wherein the additive comprises at least one of a metal base, metal salt and metal oxide.

35. The composition of claim 33, wherein the additive is added in an amount sufficient to form a bond between the glass ionomer and the dental amalgam composition having a bond strength of at least 40 psi.

36. The composition of claim 33, wherein the additive comprises at least one of zinc phosphate, zinc oxide, magnesium sulfate, stannous fluoride, silver nitrate and tin oxide, and wherein said additive comprises between about 0.001% and 25% by weight of the dental amalgam composition.

37. The composition of claim 33, wherein the additive is added in an amount sufficient to form a bond having a bond strength of at least 180 psi between the glass ionomer cement and the dental amalgam composition when a layer of wet dental amalgam composition is applied to a layer of wet glass ionomer cement, and the layers are allowed to harden.