US2083052A - Dental alloy and method of making same - Google Patents

Description

Patented June 8, 1937 mm f STATES I I 2,083,052 I I DENTAL ALLOY AND METHOD OFMA'KING, I I SAMEI Edward L. Chott, Riverside, Ill." I

No Drawing. Application April 2,4;1935; I I Serial No. 17,931 I I 3 Claimsp (Cl. 75-173) I his invention relates to an alloy adaptable I zinc which have been combined in carefully I worked out and definite range of proportions This. alloy of my invention when finely comminutedand triturated with the properproportionof mercury, results in a plastic mixture which will readily harden into a rigid metallic body in a relatively short time, and to a hardness r equal to that which will sustain apress ureconsiderably in excess of dental alloys preparedwith presentlyrknown proportions and methods;

Most alloys used at present contain a large proportion oi silver anc l have combined therewith a substantial amount ofcopper, it being understood and assumed by makers of dental alloys that copper isan essential ingredient and used for I the pre s ently assumed essential functionof limiting and stabilizingthe hardening of amalgam made with such a11oys..,It is also known that the coppercontent of dental alloys materially increases the discoloration and tarnishing of presently known alloys due to reactions thereofwith the sulphur and other com- 0 pounds contained'in foods,

the use of copper and likewise eliminates its aforesaid lundesirable characteristics, at the same time; possessing'the same properties of relatively quick'hardening and lir'nitedbut desirable degree of "expansion anda hard tough resultant body which is free from cracks or pores. Various objects of my invention are set forth as -fol- I lows,

An' important object' of my invention is the r sure of approximately 3,500 pounds per square I inch. 7

A further object of my invention is the provision of an alloy composed of proper proportions of silver, tin and zinc, and no copper whatever, which at the same time will not only have the desirable amount of expansion when setting, but which also has the important characteristic of I t I The alloy of my invention and its method of preparation eliminates at the same maintaining the natural'zcolorbf the alloy and not susceptible to discoloration or tarnish when it has come in contact with sulphur and other numerous agents presentin various foods.

A furt her important object of my invention is the provision of a dental alloy for use in dental amalgams-which is composed of only silver, tin

and zinc in predetermined range of proportions and which has. astrong characteristic of maintaining its natural color as possessed by itbefore actual use, namely, avoidingfltarnishland dis colorationTwhich. are caused upon presently known dentalalloys containing silver by sulphur, and other agentsfound in .food andin the atmosphere in;the form of gaseous "compounds.

Aiurther object of my invention is'the provision of' a n' alloy which avoids "the conventional use of copper, copperbeing considered 'a s a necessary'j-ingredient of; presently known alloys, I copperfhaving undesirable characteristics of discolorationand tarnish and heretofore considered asia stabilizer tovprevjentpver-expansion during setting andi hardening, my said alloy being mixable with mercury to make a plastic mixture which will harden in a relatively short time to a degree measurable to withstand a pressure of approximately 3,500 pounds per square inch, and which has a desirablefdegree ofex pansion on setting suflicient to preventjleakage from within the tooth cavity intowhich the amalgam is inserted.

A further object of myinvention is the provi- I use in a novel dental'am alg'am which comprises melting the component metals in a sealed -furnace, thence pouring thejs'ame'into moulds; then dividing the sameinto fine particles by chipping, shaving and crushing and" then sealing and annealingthe same toprevent contraction or'over-' expansion when the amalgam made from such alloy is fully set and to control the hardening time thereof, such annealing being accomplished by placing the alloy in small containers under vacuum and boiling for desired periods of time.

Another object of my invention is toovercome the undesirable characteristic brought about by the conventional use of copper, providing an alloy of finely divided particles which have been sieved or crushed to a small size so that one troy ounce will measure from 8 to '10 cubic centimeters and which will yield an amalgam providing a complete filling and sealing of the cavity without voids, cracks or channels, either in the amalgam body or between it and the tooth.

It is well known by those familiar with ordinary sion of anovel process .of preparing an alloy for and presently known dental alloys that such ordinary alloys contain copper as a base ingredient, it being the assumption that the copper has the property of preventing over-expansion of the alloy upon setting and thereby acting as a stabilizer. Because of the general use of copper as a basic ingredient in presently known alloys for making dental amalgam, all such alloys have the v undesirable characteristic of quickly becoming tarnished and discolored due to the action of agents contained in foods, particularly sulphur, which in a very short time tarnishes the tooth filling to a dark and unnatural appearance, usually a bluish gray color. lengthy and repeated investigation that the use of copper can be entirely eliminated providing the proper proportions of the remaining ingredients specified hereinafter are combined in a manner and method which is novel in the art and which varies materially from presently known methods of preparing the dental alloy.

I first separate silver of a high degree of fineness (in a preferred proportion ranging from 71% to 78% of the total mass sought to be prepared) and melt the same in an electric or other suitable furnace, preferably of the induction type, so that during the melting process the alloy will be protected from contamination or oxidation. Tin of a proportion of from 21% to 28%, preferably 21.5% to 27.5%, and zinc of a proportion of less than one per cent and not less than 1., of one per cent or any zinc proportion between of one per cent and 1%, is also melted in a suitable furnace in like manner and combined with the melted silver, whereafter I then pour the molten alloy into moulds, preferably round bars or tubes, and allow the same to cool and harden. I have found that while any preparation of the three ingredients herein stated within the ranges aforesaid ishighly satisfactory, the most preferable proportions of tin is from 21.5% to 27% and of zinc from 1%- of one per cent to and including 1%. Thereafter I cut the moulded bars or tubes into fine chips or shavings, either in a lathe, milling or filing machine. The resultant filings or shavings are then further reduced in size by sieving and crushing to a size so that from 8 to 10 cubic centimeters thereof will weigh one troy ounce.

The next step in my method of preparing my dental alloy is the annealing thereof which imparts properties thereof to control the setting and hardening time to prevent contraction and excessive expansion after the alloy is set in the tooth cavity. The first step in my annealing process is to pour the sieved and crushed alloy of the desired fineness into either glass or preferably metal tubes, the bottom of which tubes have been sealed with an air-tight cap and the upper end of said tube preferablyvhaving a screw capped I have found after fitting with a valve therein. I then withdraw most of the air from each said tube by pumping the same out through aforesaid valve which will be closed against the entrance of air thereafter. I then place the tubes containing the alloy and in which partial vaccum is created into a tank of cold water, which water is slowly heated to the boiling point and left to boil for an interval of time. If the size of the alloy particles contained in the tube is slightly larger than those which I I have specified in my preferred example, the duration of the boiling of such water during said annealing process should be proportionately longer. Further, the duration of the boiling time may also be gauged by the setting time required in order to obtain a fully annealed alloy which will retain its size after slight expansion (ranging from 3 to 13 microns) when setting in a tooth cavity.

I am aware that numerous details of proportion may be varied through a wide range without departing from the principles of this invention, and I therefore do not desire to limit the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. A comminuted ternary alloy for dental amalgams composed of from 71% to 78% silver and from 21% to 28% tin and 1% zinc and which has and will maintain its natural color and appearance, which will not have an excessive amount of expansion on setting; and which is uncontaminated due to maintenance thereof out of contact with the atmosphere during its melting, chipping, crushing and annealing steps.

2. An alloy for dental amalgams composed of from 72% to 78% silver and from 21.5% to 27.5%

' tin and fi% of one per cent to one per cent zinc,

in finely divided form and annealed and which has the desirable characteristics of maintaining its natural color and avoiding discoloration when placed in contact with food agents and gaseous atmospheric compounds, and which when triturated will form a hard body equal to a hardness capable of sustaining a pressure of 3,500 pounds per square inch and which will not expand excessively or to great degree on setting.

3. The method of preparing an alloy for dental amalgams which comprises melting from 72 to 78 parts of silver; 21 to 27 parts of tin and zinc of from to one percent; thence casting the same into relatively small moulds; thence comminuting the same into relatively fine particles; thence placing the comminuted alloy into airtight containers; thence exhausting most of the air from such containers and thence boiling said containers and contained alloy in boiling water for a short interval of time to anneal said contained alloy to the desired degree.

I EDWARD L. CHOTT.