US2698231A

US2698231A - Dental amalgam

Info

Publication number: US2698231A
Application number: US226532A
Authority: US
Inventors: Schulze Ernst; Nehse Albrecht
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1950-05-17
Filing date: 1951-05-15
Publication date: 1954-12-28
Anticipated expiration: 1971-12-28
Also published as: FR1037182A; CH299529A; GB688741A

Description

United States Patent 2,698,231 DENTAL AMALGAM Ernst Schulze, Leverkusen-Schlebusch, and Albrecht Nehse, Leverliusen-Wiesdorf, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Application May 15, 1951, Serial No. 226,532

Claims priority, application Germany May 17, 1950 1 Claim. (Cl. 5-173) The present invention relates to a process of preparing amalgam for dental purposes.

it is an object of the present invention to prepare dental amalgam by using a shaped unit of a dental metal powder containing a certain amount of silver and being composed of particles of different size.

A further object of the present invention is the shaped unit of the aforesaid metal powder, said shaped unit preferably consisting of a compact shaped, for instance, in tablet, pill or bar form.

Still further objects of the present invention will become apparent from the specification following hereafter.

It is generally recognized that the granular size of a commercial metal powder, whether composed of filings, shavings, or millings, used in the preparation of a dental amalgam, shall be as uniform as possible. For instance,

it is prescribed in the American Specification Dental Amalgam Alloy (1937) that the comminuted alloy shall be free of foreign materials and shall be uniform throughout the package. This requirement already results from the fact that separation into the component parts occurs when packing amalgam alloys of different particle size into bottles and other vessels. The fine-grained particles settle at the bottom of the vessel whilst the coarser ones accumulate in the upper section of the vessel. Hence it follows that the coarser-grained part of the powder is used first by the dentist for preparing a dental amalgam, so that, at last, an almost dust-like residue remains which, admixed with mercury, gives an amalgam with properties different from those of the amalgam prepared with the coarser-grained part of the metal powder. Since, furthermore, it is a commonly held opinion that a very uniform amalgamation of the small metal particles is desirable and that such uniform amalgamation can be accomplished only by use of a metal powder of uniform granular size, dental alloys of a uniform granular size have hitherto been put on the market.

It is further known that the amalgams prepared from these metal powders show quite different properties, especially as to their initial and final hardness and expansion, and that these properties are due to the mode of preparation of the amalgam from the metal powder. Experiments carried through in connection with the present invention have shown that these different properties are substantially caused by the way of grinding the metal powder with mercury in the mortar and, furthermore, that during such grinding the extent of comminution of the metal particles before amalgamation by the mercury plays a decisive part. This observation led to investigations on the influence of the granular size of the metal particles and resulted in finding a handy form of a metal powder that yields a uniform amalgam exhibiting inter alia a short setting time, high ultimate hardness and a controlled expansion. For this purpose, three requirements have to have fulfilled according to the invention, firstly the metal powder must be prepared from an alloy with a definite silver content, secondly the metal powder must be present during amalgamation in different particle sizes, and thirdly a fixed weight of the metal powder must be brought into a handy shape, preferably into a compact shaped, for instance, in tablet, pill or bar form, and used in this shape as a starting material for the preparation of the dental amalgam.

The metal alloy used for the preparation of dental amalgam may be obtained by milling an appropriate metal alloy. The silver content of this alloy substantially consisting of silver and tin shall amount to 60-75%,

2,698,231 Patented Dec. 28, 1954 ice preferably to 63-67%. Besides silver and tin the ,alloy may contain other customarily employed components, such as for instance, copper and zinc. Since the larger particles of this metal powder yield an expanding amalgam, whilst very fine particles yield a contractin amalgam, the mixing proportion of the finer particles and the coarser ones in the shaped unit is adjusted according to the present invention in such a manner that the expansion caused by the coarser particles overbalances or at least balances the contraction due to the finer particles. This shaped unit may, for instance, consist of a compact shaped in tablet form which tablet can be disintegrated by slight pressure into a granular mixture, two thirds of which consist of coarser particles of which the largest ones pass a sieve having 1600 meshes per square centimeter, whilst about a third of the total weight is present in form of particles whose individual weight corresponds to about of that of the coarser particles. The size of the metal powder tablets, pills etc. will preferably be such, that the amalgam prepared from it suffices for one average tooth filling.

It is evident that the desired uniform final properties of the amalgam are only accomplished by constantly and accurately proportioning the metal powder and the mercury. It is, therefore, a further object of the invention to employ the metal powder shaped, for instance, into a tablet, pill, bar etc. with an accurate quantity of mercury which may be measured off by a special dispensing device.

As a matter of fact, the mixing of the metal powder with mercury according to the invention must not result in a substantial change of the particle size. For this reason, after powdering the tablet etc., the blending in the mortar is to be accomplished by mere stirring only. lt is still more advisable to blend the metal powder and mercury in the rubber finger stall.

The advantages attained by employing the tablets, pills etc. in accordance with the present invention may be summarized as follows: By carefully measuring the ratio of the finer and coarser particles and the silver content of the tablet, pill etc., the amalgam prepared from this shaped unit shows a short setting time due to the finer particles, a high final hardness due to the coarser ones, and a controlled expansion due to the measured proportion of the finer and coarser particles. A constant mixing proportion of the metal powder and mercury is achieved by using the tablets, pills etc. together with a dispensing device for the mercury.

The invention shall be further illustrated by way of example.

Example 0.33 grain of filings of a metal alloy of 66% silver, 29% tin, 3% copper and 2% zinc, two thirds of said metal alloy consisting of coarser grains, the larger ones of which pass a sieve having 1600 meshes per square centimeter, whilst about one third of the total quantity of the metal alloy is present in form of grains whose individual weight corresponds to about of the coarser grains, are compressed into tablets under a pressure of 200 kg./cm. The tablets thus prepared are used as starting material for the preparation of amalgam with the admixture of appropriate amounts of mercury. The proportion of the filings to the mercury amounts to 121.

We claim:

A process of preparing dental amalgam, which comprises forming a compact consisting of a dental alloy powder, two-thirds of the total weight of which consists of coarser particles passing a sieve having 1600 meshes per square centimeter and one-third of the total Weight of which consists of particles whose individual Weight corresponds to about one-fiftieth of that of the coarser particles, said dental alloy containing 60-70% by Weight of silver, at least 25% of tin, not more than 6% of copper and not more than 2% of zinc, powdering said compact under a slight pressure corresponding to one which is exerted when preparing amalgam in the rubber fingerstall, whereby a dental alloy powder of different granular sizes is produced, and mixing said powder with a measured quantity of mercury.

(References on following page) 3 References Cited in the file of this patent UNITED STATES PATENTS 4 Number Country Date 473,381 Great Britain Oct. 12, 1937 482,338 Great Britain Mar. 23, 1938 OTHER REFERENCES Smith: The Chemistry and Metallurgy of Dental Materials, pub. by Blackwell Scientific Publications, Ltd., Oxford, England, pages 98 and 99.