Stainless dental alloy for application of low-fusing opaqueing porcelain

The present invention provides a stainless dental alloy which may be used in producing crowns, bridges, inlays, and the like. It also provides an alloy which is especially adapted for the application of low-fusing opaqueing porcelain for adhesion to such dental appliances. The alloy of the present invention has a melting point approximating 2650.degree. F. In its broadest aspect the alloy consists of cobalt 40 to 60%, chromium 18 to 35%, tungsten 5 to 20%, molybdenum 1 to 4%, copper 0.5 to 2%, iron 1 to 3%, manganese 0.5 to 2%, niobium 0.5 to 2%, and silicon 0.25 to 1%.

The present invention relates to a stainless dental alloy especially 
adapted for use in the dental field for the preparation of crowns, 
bridges, inlays, and other dental prostheses to which it is desired to 
apply a porcelain surface. The principal advantage of the alloy of the 
present invention is that it provides an alloy to which a low-fusing 
porcelain can be adhered by fusion, with none of the disadvantages of 
heretofore known alloys. 
It is also an economy alloy in that it does not contain any of the higher 
priced precious metals such as gold and platinum. 
BACKGROUND OF THE INVENTION 
In the dental field it is now well recognized that the alloy to which 
low-fusing porcelain can be successfully applied so as to have complete 
adhesion must be compatible from the standpoint of coefficient of linear 
expansion and contraction at the fusing temperature of the porcelain; and 
that such alloy must provide on its surface oxides which facilitate the 
adhesion of the porcelain. Furthermore, the oxides have to be an integral 
part of the alloy, so that such oxides cannot be lifted from the alloy by 
the fluxing effect during the application of opaque porcelain to the 
alloy. 
It is also well understood that after application of the porcelain to the 
alloy, the porcelain surface should not check, crack or separate from the 
base alloy. 
There are on the market today various opaque porcelains which are 
especially prepared and sold for application to dental alloys. The 
opaqueing materials of such opaque porcelains vary from one to the other 
and the basic ingredients of such opaque porcelains are not fully 
disclosed in any literature with which I am familiar. 
Among the various opaqueing porcelains with which I am familiar is one 
offered for sale and sold by Dentsply International Inc. of York, 
Pennsylvania under the trademark BIOBOND. Another is offered and sold by 
Vita Zahnfabrik H. Rauter K.G., of Sackingen, Germany, under the trademark 
VITA. 
I also know that there are other opaque porcelains sold under the trademark 
CERAMCO by Ceramco, Inc. of Long Island City, New York and under the 
trademark HOWMEDICA by Howmedica, Inc. of New York, New York. 
Essentially all of these opaque porcelains for dental application are said 
to be low fusing in that they will fuse at a temperature of about 
1800.degree. F. to dental alloys and will adhere to the same provided all 
other conditions are met for fusing such porcelains to the metal alloy. 
SUMMARY OF THE INVENTION 
According to the present invention, and after considerable experimental 
work, I have found that a stainless alloy consisting of the following 
elements in its preferred form can be fused to BIOBOND, VITA, CERAMCO and 
HOWMEDICA opaque porcelains with excellent results. The preferred 
formulation for such an alloy is: 
Cobalt 56% 
Chromium 28% 
Tungsten 10% 
Molybdenum 2% 
Copper 1% 
Iron 1% 
Manganese 0.80% 
Niobium 0.70% 
Silicon 0.50% 
According to tests which I have conducted, I can state that an alloy of 
this preferred formulation has the following mechanical characteristics: 
Melting Point 2650.degree. F. 
Thermal coefficient of expansion 1.4.times.10.sup.-5 per .degree.C.

DESCRIPTION OF THE INVENTION 
Supplementing what is set forth under the foregoing heading of "Summary of 
The Invention", I have found that an alloy prepared according to the 
preferred formulation set forth, is ideally suited for fusing at 
approximately 1800.degree. F. with opaque porcelains such as BIOBOND, 
VITA, CERAMCO and HOWMEDICA. The first coating of opaque porcelain is 
fused to the alloy at 10.degree. F. above the recommended temperature of 
approximately 1800.degree. F., in order to achieve the tenacious union 
between the oxides of the alloy and the opaque porcelain. The second 
coating of the opaque porcelain may be applied at the recommended 
temperature of approximately 1800.degree. F. After fusing and cooling, 
such porcelains are so adherent to the alloy that it is impossible to 
separate the same under repeated hammer blows. 
It is my firm belief from considerable experimental work in this area that 
the elements molybdenum, niobium, copper, manganese and iron, which are 
only added in small quantities to the basic alloy of cobalt, chromium and 
tungsten, contribute totally to the porcelain adhesive characteristics 
imparted to the alloy, and that without such additives insufficient oxides 
would be formed on the surface of such alloy. The small amounts of these 
elements form oxides which resist lifting of the porcelain from the alloy 
during fluxing of the porcelain. Molybdenum, copper and niobium in the 
small quantities recommended contribute most in providing the tenacious 
oxides for adherence of the opaque porcelain. 
In my copending application Ser. No. 51,003, filed June 22, 1979, I have 
disclosed a non-precious stainless dental alloy having a melting 
temperature of 2550.degree. F. which is especially adapted for bonding to 
opaqueing porcelains such as BIOBOND and VITA mentioned above. According 
to the present invention, I have found that the present alloy which melts 
at 2650.degree. F. is especially adapted for bonding to all opaque 
porcelains, such as BIOBOND, VITA, CERAMCO and HOWMEDICA, as identified 
above. 
From my experimentation I have found that the alloy of my copending 
application which contains niobium and gallium in small quantities and 
which melts at approximately 2250.degree. F., is ideally suited for fusion 
to BIOBOND and VITA opaque porcelains; whereas the alloy of the present 
invention which contains no gallium but instead contains molybdenum, 
copper and niobium in small quantities, is ideally suited for fusion to 
all opaque porcelains. 
In the broader aspect of the invention, I have found that the various 
elements constituting the alloy of the present invention may vary within 
the following ranges: 
Cobalt 40 to 60% 
Chromium 18 to 35% 
Tungsten 5 to 20% 
Molybdenum 1 to 4% 
Copper 0.5 to 2% 
Iron 1 to 3% 
Manganese 0.5 to 2% 
Niobium 0.5 to 2% 
Silicon 0.25 to 1% 
Within these ranges the three principal elements of cobalt, chromium and 
tungsten must be so proportioned as to assure that the coefficient of 
expansion and contraction of the alloy is suitable for porcelain 
application. Such coefficient of expansion must be approximately 
1.4.times.10.sup.-5 per .degree.C. It can be slightly higher or slightly 
lower. The desired coefficient of expansion is accomplished by increasing 
the amount of chromium and tungsten and reducing the amount of cobalt. 
It should also be noted that the amounts of molybdenum, copper, niobium, 
manganese and iron, which chiefly provide the oxides for porcelain 
application, are limited to very minor ranges. Of these elements, 
molybdenum, copper and niobium perform the same functions as niobium and 
gallium in my earlier application Ser. No. 51,003.