US3667937A

US3667937A - Dental filling

Info

Publication number: US3667937A
Application number: US78990A
Authority: US
Inventors: Clyde E Ingersoll; Reginald V Williams Sr
Original assignee: ELIZABETH P WILLIAMS; JOHN A WILLIAMS; WILLIAMS GOLD REFINING Inc
Current assignee: ELIZABETH P WILLIAMS; JOHN A WILLIAMS; WILLIAMS GOLD REFINING Inc
Priority date: 1970-10-07
Filing date: 1970-10-07
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

A METAL ALLOY DENTAL FILLING CONSISTING OF ABOUT 99.7 TO 99.95 PARTS PURE GOLD ALLOYED WITH ABOUT .05 TO .30 PART CALCIUM IS CONDENSED IN A PREPARED TTOTH CAVITY. THE ADDITION OF CALCIUM TO PURE GOLD RESULTS IN A SIGNIFICANTLY HARDER FILLING.

Description

United States Patent O 3,667,937 DENTAL FILLING Clyde E. Ingersoll, Tonawanda, and Reginald V. Williams,

Sr., deceased, late of Buffalo, N.Y., by John A. Williams and Elizabeth P. Williams, executors; said Ingersoll assignor to Williams Gold Refining Incorporated, Buffalo, N.Y. No Drawing. Filed Oct. 7, 1970, Ser. No. 78,990

Int. Cl. C22c 5/00; A61k 5/02 U.S. Cl. 75-165 2 Claims ABSTRACT OF THE DISCLOSURE A metal alloy dental filling consisting of about 99.7 to 99.95 parts pure gold alloyed with about .05 to .30 part calcium is condensed in a prepared tooth cavity. The addition of calcium to pure gold results in a sig nificantly harder filling.

BACKGROUND OF THE INVENTION This invention relates to dental filling alloys and, more particularly, to gold alloys used as dental fillings.

It has been known for many years that pure gold in various forms can be condensed into a prepared tooth cavity to form a filling of exceptionally long life. Gold has many qualities admirably suited for tooth fillings, but a pure gold filling does not exhibit the desired degree of hardness and furthermore tends to lose some of its limited hardness over a periodof time. A pure gold filling also is deficient in abrasion resistance. It has been proposed to alloy small quantities of other metals to pure gold, in an effort to produce a dental filling which retains the desirable properties of gold while providing better abrasion resistance and increased hardness. However, such prior art efforts have not been particularly successful. By way of example, platinum and tin have been proposed as additives. However, gold alloyed with platinum alone is not sufficiently hardened. Tin renders the gold alloy non-cohesive, with the result that cold welding of successive layers could no longer be effectively accomplished. Also, some additives render the gold alloy too hard, so that condensation cannot produce a dense, porosity free, finished filling.

In addition, it has been recognized in recent years that pure gold, if stressed sufficiently during deformation, will anneal or soften at room temperatures. Accordingly, it is desirable to find an additive which, when combined with pure gold, will preclude this undesirable self-annealing of gold and will form a gold alloy of the desired level of hardness and abrasion resistance while not so hard initially as to prevent proper condensing into the tooth cavity.

SUMMARY OF THE INVENTION detailed description 3,667,937 Patented June 6, 1972 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A dental filling gold alloy should be sufiiciently malleable and cohesive initially to permit ready condensation by compression into a prepared tooth cavity with the usual dental office equipment to produce a dense, impermeable finished filling. The alloy should possess the ability to form a strong bond between successive layers of the alloy and produce a filling exhibiting the requisite degree of hardness and capable of withstanding abrasion forces normally encountered in the human mouth due to biting, chewing, brushing and other frictional engagement against or between the teeth. It is particularly important that the alloy retain the desired degree of hardness over a long period of time thereby avoiding frequent replacement. All of this is accomplished by the dental filling alloy of the present invention which consists primarily of pure gold to which is added a minor amount of calcium. We have found that gold alloy having the above properties can be obtained by alloying these components within the following ranges, expressed in percentages by weight:

Gold: 99.7% to 99.95% Calcium: .05%.to 30% The proportion of the above alloying elements may be varied within the limits specified, the preferred alloy for most dental fillings comprising about 99.85% pure gold and 0.15% calcium. However, it should be appreciated that in some dental filling applications, greater strength is required than in other applications. Accordingly, where greater strength is required, the calcium content will be increased within the limits specified above. However, a calcium content above .3% will excessively harden the gold alloy, causing it to become brittle and thereby susceptible to fracture. A calcium content below .05% on the other hand, will not appreciably affect the properties of the pure gold in the alloy.

An important feature of the present invention is that the calcium present in the gold alloy is effective to preclude self-annealing of the gold component and thereby of the condensed filling. It has recently become known that if pure gold is stressed sufficiently during its deformation in the cavity, it has a tendency to anneal or soften at room temperature. Calcium has a crystal structuresufficiently different from that of gold so as to block selfannealing of the gold constituent. While calcium, like gold, is face centered cubic in structure, it has a substantially different lattice constant (5.57 as compared to 4.0783 for gold) so as to effectively block self-annealing of the latter.

This large difference in lattice constant also facilitates the compression or cold working of the alloy in place in the tooth cavity. During condensation, the gold alloy is hardened to a significantly greater extent than pure gold would be. For example, fillings made of pure gold foil by six dentists averaged 70.8 Brinell hardness while gold alloy fillings made in accordance with the present invention placed by the same six dentists averaged 90.9 Brinell hardness. The low solid solubility of calcium in gold adds considerably to the cold working effect of the alloy.

The gold-calcium alloy of the present invention preferably is electrolytically precipitated into a powder form. The powder is collected, washed, dried, formed into strips or sheets and sintered to form a cohesive, spongy mass. This spongy mass can be utilized in such form or, during the sinte'ring operation, a veneering coat of pure gold or gold-calcium foil can be applied. Although the goldcalcium alloy is preferably formed into a powder by the above mentioned electrolytic precipitating technique and then converted into a spongy mass, it should be understood that the gold-calcium alloy can be produced in various forms within the purview of this invention. For

example, it can be beaten into a =foil or leaf, if desired.

In use, pieces of the alloy of this invention are placed in a prepared cavity and condensed with an appropriate condenser. Further pieces of the alloy are added which, on condensing, cold weld with previously added pieces to produce a filling. The addition of calcium to pure gold in accordance with this invention results in as much as a 30% higher hardness in the condensed filling.

A preferred embodiment of this invention having been disclosed in detail, it is to be understood that this has been done by Way of illustration only.

What is claimed is:

1. A dental filling produced by condensing in place within a prepared ca-vity successive layers of an alloy consisting of gold in an amount ranging from 99.7% to 4 99.95% by weight and calcium in an amount ranging from 0.05% to 0.30% by weight.

-2. A dental filling as set forth in claim 1 whereinthe alloy consists of about 99.85% gold, the remainder being calcium.

References Cited UNITED STATES PATENTS 2,947,623 8/1960 Lincoln 75165 U.S. Cl. X.R. 32.-l5