BACKGROUND OF THE INVENTION

This invention relates in general to a dental composition and dental amalgam suitable for use in repairing carious tooth structure. More specifically the invention relates to a .substantially uniform admixture of two powdered alloys in the form of spheroids and irregularly-shaped or cut particles which when amalgamated with mercury exhibit improved handling characteristics.

U.S. Patent 3,985,558 teaches an improved dental alloy having a relatively low concentration of silver and a critical atomic ratio of silver plus copper to tin which exhibits enhanced mechanical properties and handling characteristics as compared to conventional high silver alloys. The alloy is also more economical to use than conventional alloys which require higher silver concentrations.

When the above dental alloy is used in the spherical form and not blended with an appreciable concentration of cut or irregularly shaped alloy particles, certain desirable working characteristics such as resistance to condensation or packing within the tooth cavity cannot be attained.

Prior art admix compositions generally combine two different alloy compositions for the respective spherical and irregularly- shaped components. This runs the risk that segregation of individual components may result and lead to inconsistent properti in the final amalgamated alloy.

OBJECTS OF THE INVENTION It is therefore an object of this invention to provide an improved dental alloy suitable for amalgamation with mercury which exhibits outstanding physical and mechanical properties and handli characteristics.

It is another object of this invention to provide a dental amalgam which exhibits outstanding physical and mechanical properties and handling characteristics.

SUMMARY OF THE INVENTION

It has now been discovered that when an alloy of the type taught by U.S. Patent 3,985,558 in the form of a substantially uniform blend of two powdered alloys comprised of spheroids and irregularly- shaped particles, is amalgamated with mercury, the final dental alloy exhibits enhanced handling characteristics. A critical ratio of spherical to irregularly-shaped particles for this alloy ranges from about 65 to 85% spherical to 15 to 35% irregular. The alloy described above is amalgamated by trituration with mercury in a concentration of about 45 to 55 weight percent mercury with the balance of the amalgam comprising the alloy.

Prior to amalgamation, the alloys are annealed by techniques well known in the art to control the work time of the final alloy. The alloys are also cleaned by chemically treating with a dilute acid.

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DETAILED DESCRIPTION OF THE INVENTION The alloy of the present invention is composed of an admixture of spherical and irregularly-shaped or "cut" particles. The alloy powder has a fine particle size (all about -325 mesh) , of both the spherical and irregular particles which allows the alloy to have the smooth carve associated with all spherical alloys, but with a firmer packing and carving consistency characteristic of conventional alloys. The particle size range for both components is from submicron to about 50 microns. Both of the particle configurations are made to the same composition: About 24 to 45 weight percent silver, 28 to 42 weight percent copper and 29 to 34 weight percent tin, and where the atomic percentage of the total amount of silver plus copper is about 3 times greater than the atomic percentage of tin. A particularly preferred composition comprises about 41% silver, 28% copper and 31 percent tin. The powder admixture must be maintained in a weight ratio of about 65 to 85 percent spherical to 15 to 35 percent irregular in order to obtain the enhanced properties described herein. The benefits of this relationship are quite clear; both of the particle configurations participate heavily in the reaction with mercury during amalgamation, therefore enhancing the consistency of the mix and the homogeneity of the amalgam. Unlike the alloy of the present invention, many other prior art admixtures because of the different composition of the two components, risk segregation of the individual components which may lead to inconsistencies. The fact that each particle in the alloy of the present invention contains copper, assures that it is distributed fully throughout the amalgam to alloy with tin to prevent formation of the unwanted gamma-2 (tin-mercury) phase. This admix alloy produces an amalgam with a smooth carve, but with the body that can be comfortably worked. The amalgam begins to "body-up" upon condensation, which allows for carving to commence almost immediately, with the resistance to carve

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increasing up until the end of working time which can be controlled typically to vary from about 6 1/2 to 11 minutes.

In the following Table the physical properties for the average of four lots of an amalgamated dental alloy of the present invention are tabulated. The alloy composition used was the preferred composition of 41% silver, 28% copper and 31% tin in a weight ratio of 70% spherical to 30 percent irregular particles. The concentration of mercury was 48% by weight and the admix alloy constituted 52 weight percent. Both alloy components were of fine particle size of less than 325 mesh. The tests were carried out according to ADA speci ication No. 1 for Dental Amalgams.

TABLE

Four Lots

DC (Microns/cm.) -1.80 Tension (psi)

15 min 857

1 hr 2620

24 hr 7870

7 day 8740

Compression (psi)

15 min 8320

1 hr 26000

24 hr 75000

7 day 81300

Creep {%) .067

In addition to providing the advantages described herein, the physical properties of the Alloy of the present invention compare favorably to those of other commercial dental alloys.

The term "spheroidal" as used to describe the shape, configuration or form of the first component in the admixture of the present invention means that the individual particles are spheres or shaped like a spheroid. The spherical component may be formed by any technique well known to the dental art.

For example it may be prepared by first forming a molten alloy in the above concentration ranges and atomizing said alloy at approximately 2,000°F. Atomization is achieved in a conventional manner as described in U.S. Pat. No. 3,305,356 at column 2, lines 9-50, which is incorporated herein by reference. The alloy is then collected and classified using a 325 mesh sieve. The fraction passing through the sieve is retained as the dental alloy product.

The term "irregularly-shaped" or "cut" as used to described the configuration or form of the second component means that the individual particles are substantially non-equiaxial and are multi-sided and generally angularly shaped or irregular, and usually with rough or otherwise relatively non-smooth surfaces. Typically they are in the form of what is variously referred to in the art as microcut material, lathe-cut material, platelets or filings. Conventional microcutting, lathe cutting or filing techniques, usually from a cast billet of the alloy, can be employed satisfactorily to obtain the irregularly-shaped particles and are well known to those skilled in the art. The irregular particles used in this invention should all be less than 325 mesh in size.

While it is essential that the dental composition of this invention be in the form of a particulate mixture of the two alloys when used, and may be supplied in such form when supplied, it should be understood that for distribution purposes the two alloys can be in the form of separate powders which can be mixed together by the ultimate user in the required proportions. Alternatively, the two admixed alloys in the required proportions can also be pressed into a tablet, used in a capsule form for convenience, or used in bulk powder dispensers. When used in tablet form the spherical to irregular weight ratio is preferably about 4 to 1; for use in capsule form the preferred ratio is about 7 to 3.

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Other modifications and ramifications of the present invention would appear to those skilled in the art upon readin this disclosure. These are also intended to be within the scope of this invention.