Title:
ALLOY FOR DENTAL AMALGAM
United States Patent 3762917
Abstract:
The alloy 26 percent Sn, 8-10 percent Au and Ag qs to 100 percent, on mixing with mercury, forms an amalgam particularly suitable for dental use.
US Patent References:
Process for the conversion of metals and metal alloys in finely divided form for themanufacture of dental amalgams
Kaufmann et al. - January 1942 - 2271264
Dental amalgam alloy
Poetschke - May 1942 - 2281991
Pulverized silver alloys for use in producing dental amalgams
Rohm - July 1964 - 3141761
Dental amalgam
Youdelis - February 1967 - 3305356
Process for the conversion of metals and metal alloys in finely divided form for themanufacture of dental amalgams
Kaufmann et al. - January 1942 - 2271264
Dental amalgam alloy
Poetschke - May 1942 - 2281991
Pulverized silver alloys for use in producing dental amalgams
Rohm - July 1964 - 3141761
Dental amalgam
Youdelis - February 1967 - 3305356
Application Number:
05/160208
Publication Date:
10/02/1973
Filing Date:
07/06/1971
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Export Citation:
Primary Class:
International Classes:
A61K6/05; C22C5/06; A61K6/02; C22C7/00
Field of Search:
75/173R,173C,169
Primary Examiner:
Rutledge, Dewayne L.
Assistant Examiner:
Weise E. L.
Claims:
I claim
1. An alloy consisting essentially of 26 percent Sn, 8-10% Au and Ag qs to 100 percent quick-cooled from the melt.
2. A method for preparing an alloy adapted for use in dental amalgams which comprises spray drying a molten mixture consisting essentially of 26 percent Sn, 8-10 percent Au and Ag qs to 100 percent.
3. A dental amalgam prepared by triturating an alloy consisting essentially of 26 percent Sn, 8-10 percent Au and Ag gs to 100% with about 50 percent of mercury by weight of the alloy, said alloy having been quick-cooled from its melt.
1. An alloy consisting essentially of 26 percent Sn, 8-10% Au and Ag qs to 100 percent quick-cooled from the melt.
2. A method for preparing an alloy adapted for use in dental amalgams which comprises spray drying a molten mixture consisting essentially of 26 percent Sn, 8-10 percent Au and Ag qs to 100 percent.
3. A dental amalgam prepared by triturating an alloy consisting essentially of 26 percent Sn, 8-10 percent Au and Ag gs to 100% with about 50 percent of mercury by weight of the alloy, said alloy having been quick-cooled from its melt.
Description:
This invention relates to a novel alloy particularly intended for use in dental amalgams.
Dental amalgams are unique materials prepared according to rather detailed and strict specifications. Conventional alloys for dental amalgam use contain 68-70 percent silver and about 25 percent tin with the balance mainly cooper. When the alloy (essentially Ag 3 Sn) is triturated with about 50 percent by weight of mercury, the setting reaction results in the formation of two phases, Ag 2 Hg 3 and Sn 7 Hg; excess Ag 3 Sn remains embedded as particles in a matrix of these two phases.
It has now been found that the second or Sn 7 Hg phase is relatively weak and is the phase most subject to destructive corrosion. Based on these considerations, it would appear desirable to eliminate the Sn 7 Hg phase from dental amalgams. However, the presence of tin, which accelerates the rate of amalgamation and reduces expansion on setting, also appears desirable.
I have discovered that the second or Sn 7 Hg phase can be eliminated, tin retained and an improved single-phase matrix, non-expanding dental amalgam prepared from the novel alloy 26 percent Sn, 8-10 percent Au and Ag qs to 100 percent. Alloys containing lesser amounts of gold are ineffective to bring about the diffusion of tin and mercury necessary to form a single-phase matrix. Alloys containing greater amounts of gold yield amalgams exceeding American Dental Association specifications for maximum permissible expansion and lessened ultimate tensile strength.
In addition to containing the optimum amount of gold indicated above, the alloy must be prepared by a quick-cooling or quenching procedure. Alloys prepared in the conventional way by slow cooling from the melt do not form a single-phase matrix. It appears that quick cooling is required to produce an alloy structure capable of effecting the subsequent diffusion of tin and mercury necessary for single-phase formation.
Dental amalgams prepared from alloys according to the present invention, in addition to forming a strong single-phase, non-expanding matrix, are highly corrosion resistant and exhibit little creep or flow. My invention is further illustrated by means of the following non-limiting examples:
An alloy mixture containing 10 percent Au, 64 percent Ag and 26 percent Sn, all by weight was spray cooled from the melt. Amalgams were prepared from this alloy by conventional techniques, i.e., trituration with about 50 percent by weight of mercury. X-ray diffraction patterns of the amalgam taken after 1 hour showed a peak corresponding to the second or Sn 7 Hg phase but much smaller than that obtained with conventional amalgam. X-ray patterns taken after storage at body temperature for 14 days showed peaks attributable only to the first phase; the second or Sn 7 Hg phase was no longer present.
An alloy having the same gross composition was prepared as an ingot from the melt. Powder was milled from the ingot, balled milled and made into an amalgam with 50 percent by weight of mercury. The amalgam did not form a single-phase matrix.
Corrosion tests were run on amalgams made from the spray cooled alloy powder of the invention at -0.25 volt, plotting time against the current required for corrosion. Comparable tests were run on conventional amalgams. The amalgam of the present invention was much more noble after 1 hour and the dissolution of specimens aged at body temperature for 14 days was virtually negligible.
Tensile strength tests were run on amalgams made from the spray dried alloy powder of the invention and on conventional amalgams. The present alloys, after setting several days, had tensile strengths of 8,000-10,000 p.s.i., roughly 10-30 percent greater than the conventional amalgam controls. The average value of creep for 5 samples was about 0.94 percent compared to values of about 1.0-1.7 percent for conventional amalgam controls.
Dental amalgams are unique materials prepared according to rather detailed and strict specifications. Conventional alloys for dental amalgam use contain 68-70 percent silver and about 25 percent tin with the balance mainly cooper. When the alloy (essentially Ag 3 Sn) is triturated with about 50 percent by weight of mercury, the setting reaction results in the formation of two phases, Ag 2 Hg 3 and Sn 7 Hg; excess Ag 3 Sn remains embedded as particles in a matrix of these two phases.
It has now been found that the second or Sn 7 Hg phase is relatively weak and is the phase most subject to destructive corrosion. Based on these considerations, it would appear desirable to eliminate the Sn 7 Hg phase from dental amalgams. However, the presence of tin, which accelerates the rate of amalgamation and reduces expansion on setting, also appears desirable.
I have discovered that the second or Sn 7 Hg phase can be eliminated, tin retained and an improved single-phase matrix, non-expanding dental amalgam prepared from the novel alloy 26 percent Sn, 8-10 percent Au and Ag qs to 100 percent. Alloys containing lesser amounts of gold are ineffective to bring about the diffusion of tin and mercury necessary to form a single-phase matrix. Alloys containing greater amounts of gold yield amalgams exceeding American Dental Association specifications for maximum permissible expansion and lessened ultimate tensile strength.
In addition to containing the optimum amount of gold indicated above, the alloy must be prepared by a quick-cooling or quenching procedure. Alloys prepared in the conventional way by slow cooling from the melt do not form a single-phase matrix. It appears that quick cooling is required to produce an alloy structure capable of effecting the subsequent diffusion of tin and mercury necessary for single-phase formation.
Dental amalgams prepared from alloys according to the present invention, in addition to forming a strong single-phase, non-expanding matrix, are highly corrosion resistant and exhibit little creep or flow. My invention is further illustrated by means of the following non-limiting examples:
An alloy mixture containing 10 percent Au, 64 percent Ag and 26 percent Sn, all by weight was spray cooled from the melt. Amalgams were prepared from this alloy by conventional techniques, i.e., trituration with about 50 percent by weight of mercury. X-ray diffraction patterns of the amalgam taken after 1 hour showed a peak corresponding to the second or Sn 7 Hg phase but much smaller than that obtained with conventional amalgam. X-ray patterns taken after storage at body temperature for 14 days showed peaks attributable only to the first phase; the second or Sn 7 Hg phase was no longer present.
An alloy having the same gross composition was prepared as an ingot from the melt. Powder was milled from the ingot, balled milled and made into an amalgam with 50 percent by weight of mercury. The amalgam did not form a single-phase matrix.
Corrosion tests were run on amalgams made from the spray cooled alloy powder of the invention at -0.25 volt, plotting time against the current required for corrosion. Comparable tests were run on conventional amalgams. The amalgam of the present invention was much more noble after 1 hour and the dissolution of specimens aged at body temperature for 14 days was virtually negligible.
Tensile strength tests were run on amalgams made from the spray dried alloy powder of the invention and on conventional amalgams. The present alloys, after setting several days, had tensile strengths of 8,000-10,000 p.s.i., roughly 10-30 percent greater than the conventional amalgam controls. The average value of creep for 5 samples was about 0.94 percent compared to values of about 1.0-1.7 percent for conventional amalgam controls.