Silver base casting alloy for dental use
The present invention provides an improved casting alloy for dental use such as for the manufacture of crowns, bridges and other dental prosthesis. The casting alloy is a silver base alloy. 
     German Pat. No. 27 00 853 discloses a casting alloy for dental use composed of 20% gold, 18-22% palladium, 10-14% copper, 0.1-2% indium, 0.05-0.5% iridium and/or ruthenium with the remainder being silver. Gold base alloys are expensive. 
     It is the object of the present invention to provide a silver-base casting alloy for dental use which has a yellow color and which has the good qualities of the gold base casting alloys for dental use, which does not contain gold or which only contains a small amount of gold. 
    
    
     THE INVENTION 
     The present invention provides silver base casting alloys for dental use consisting essentially of between about 40 and 60% by weight silver, between about 15 and 20% indium, between about 8 and 15% copper, between about 0.1 and 2% nickel, between about 0.1 and 2% zinc, between 0 and about 10% gold, and between 0 and about 30% palladium, a total of the gold and palladium being between 10 and 30%, and dental prosthesis comprising said alloys. 
     The following alloys are preferred embodiments of the alloys of the present invention: 47-52% silver, 16-18% indium, 10-12% copper, 0.4-0.8% nickel, 0.4-0.8% zinc, 3-6% gold, 12-19% palladium with the total of gold and palladium from 15-25%. 
     Three illustrative alloys are specifically set forth and identified in Table 1. Alloy No. 2 is particularly preferred. The physical properties of these alloys are set forth in Table 2. 
     
                       TABLE 1                                                     
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Alloy     Ag    In      Cu   Ni  Zn    Au  Pd                             
No.       %     %       %    %   %     %   %                              
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1         56    19      14   0.5 0.5   2   8                              
2         49    17      11   0.5 0.5   5   17                             
3         44    16       9   0.5 0.5   8   22                             
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                       TABLE 2                                                     
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         HARDNESS                                                         
          (VICKERS 100g)                                                  
                      DEN-    MELTING                                     
Alloy Au + Pd  Dead             SITY  RANGE                               
No.   %        Annealed Hardened                                          
                                g/cm.sup.3                                
                                      °C.                          
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1     10       165      220      9.6  770-820                             
2     22       180      225     10.0  790-840                             
3     30       190      240     10.2  810-870                             
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     The present invention also provides dental prosthesis such as crowns, bridges, inlays, etc. which are advantageously and economically manufactured utilizing one of the silver base dental alloys disclosed herein. Such prosthesis includes prosthesis such as those disclosed in U.S. Pat. Nos. 2,948,963 and 4,124,380 which are incorporated by this reference. 
     The silver base dental casting alloys of the present invention are readily processed. They are easily melted and cast. The finished castings take a very good polish. The alloys exhibit good cold working characteristics. They are of a pleasing yellow color depending upon the specific alloy content. 
     The alloys of the present invention have been subject to corrosion testing in the presence of sodium polysulfide. They exhibit good resistance to tarnishing. When utilized in the human mouth, no signs of corrosion were observed even after a period of four weeks. 
     The gold color casting alloys for dental use of the present invention have a relatively low density and therefore a cost advantage when compared with known yellow and white gold base casting alloys. They also have a cost advantage when compared with white palladium-silver base casting alloys. 
     The casting alloys of the present invention have a relatively low melting point range which provides the further advantage that in the dental casting operation, embedding (matrices) which are bonded with gypsum and therefore relatively inexpensive, may be used in place of the more expensive embedding means bonded with phosphates which are used with higher melting alloys. Gypsum bonded embedding means are also easier to work with than the phosphate bonded embedding means. 
     Various changes and modifications may be made within the scope of the inventive concept.