Method of making dental porcelain

Patented May 7, 1935

2,000,285

UNITED STATES PATENT OFFICE

2,000,285

METHOD OF MAKING DENTAL PORCELAIN

Fred P. Hoffmann, Evanston, DI., assignor, by mesne assignments, to American Porcelain Company, Chicago, HI.

No Drawing. Application March 19, 1932, Serial No. 600,069

Claims. (Cl. 106—6)

This invention relates in general to porcelain and has more particular reference to dental porcelain and the manufacture thereof.

Among the objects of the invention are to pro5 vide a novel and improved porcelain powder for use; for example, by dentists in the preparation or construction of full or partial dentures, crowns, inlays, and other dental structures, characterized by the features of substantially the consistency 10 of a heavy paste or putty when wet, whereby to facilitate formmg the porcelain in or about a mold in a continuous homogeneous block prior to fusion or vitrification; of substantial freedom from shrinkage or cracking with the consequent 15 loss of time and. materials in the final fusion of the dental structure due to cracking, the filling of the cracks with powdered porcelain and refusing of the dental structure as was heretofore frequently the case; of a porcelain powder when 20 formed and fused, which will not be susceptible to substantial internal stresses and strains, rendering dental structures made therefrom weak and friable as a result of undue shrinkage at the final fusion of the structure; of a porcelain 25 powder which may readily be formed into dental structures that are fully as hard, tougher, and stronger than known porcelain dental structures; of a preliminary mixture wherein a portion of the material imparting translucency to the final 30 product in the proper proportion with the material, imparting strength whereby to obviate some of the numerous fusing steps heretofore employed in making porcelain, and to make this preliminary mixture of such characteristics that 35 the coloring agent employed will have the most beneficial results so that the final powder will have the translucency, hardness, and color required for the dental structure desired; and a novel method of so combining feldspar, silex, and 40 kaolin with a coloring agent to produce porcelain powder having the above mentioned advantages and improved properties.

Other objects of the invention will be apparent from the following description.

in order to accomplish the foregoing objects, I make a preliminary mixture of substantially 224 parts by weight of feldspar, with substantially 346 parts by weight of a flux containing in uncombined form about 11 parts by weight 50 of soda or sodium carbonate, 191 parts by weight of borax, and substantially 144 parts by weight of silex or crystalized silica. This mixture is then melted or fused and drawn or run while hot into cold water to break it up into small 55 pieces which are subsequently ground to a fine powder. By combining or binding a portion of the feldspar with the flux in this preliminary mixture, I succeed in fixing the silex, as well as the volatile constituents of the feldspar, in such proportions that scarcely any shrinkage occurs 5 when the final powder is formed, as for example, a dental structure, and fused.

To the foregoing preliminary fusion mixture I add a suitable coloring agent, such as uranium oxide, titanium oxide, or any other metallic oxide 10 having the desired color characteristics to obtain, for example, the uranium yellow color or tint instead of the dark or green color which usually results if the uranium oxide is. added at a subsequent stage. 15

To accomplish this coloring, I prefer to grind the small pieces obtained from the preliminary fusion step in a ball mill, to an impalpably fine powder which may be divided into two portions. To one portion thereof I add about 6% by weight 20 of, say, uranium ’ oxide, and bake the mixture until it is fused. This portion with the uranium oxide, is next ground to a powder which is mixed in equal proportions with the portion which was not admixed with the coloring compound, so that 25 the coloring compound now makes up about 3% by weight of the mixture.

A final mixture may now be made of this colored material by mixing it in a ball mill with feldspar and with kaolin (to impart plasticity to 30 the material), fusing the mixture and grinding it to prepare it for use in the manufacture of dentures or other dental structures. I have found that an excellent formula for the final mixture comprises substantially the following proportions 35 by weight:

Percent Preliminary mixture31.7

Feldspar________________________________ 66.3.

Kaolin 2

If desired, dehydrated kaolin may be employed rn the final mixture, but the porcelain powder described above fuses only at relatively high temperatures, for example 1700° F. or above, and 45 therefore the kaolin may be dehydrated in the final fusion step just described:

, It will, of course, be apparent that the foregoing formula is merely illustrative of the present preferred embodiment of my invention, and 50 the steps in the process as outlined, as well as the formula, may be modified without departing from the spirit or scope of the invention. For example, equal portions by weight of the powder resulting from the final fusion and grinding, as ⁵⁵

2,000,285 described above, may be mixed with the powder after the addition of the kaolin and feldspar, but before the final fusion, and this mixture is fused to produce an excellent porcelain powder for 5 dental purposes.

The final powder after grinding, may be prepared for molding by mixing it with water to a paste. This paste is readily adapted for forming in or about a mold of any desired size and shape 10 and may thereafter be fused to produce the desired dental structure. In molding the wet powder, I have observed a marked advantage over known powders. My powder has when wet the consistency of a thick paste or of putty, as dis15 tinguished from the sandlike or granular appearance of known porcelain powders. This feature facilitates the molding operation and renders the wet porcelain readily conformable to, for example, denture molds.

When porcelain powder is made as described above, it may readily be formed into strong and tough dentures without cracking or checking, and without requiring the filling of shrinkage cracks with additional powder and re-fusing or 25 re-baking as was done with prior art porcelains.

Such a porcelain powder by virtue of its, relative freedom from shrinkage, substantially avoids internal stresses and strains which have prior to this invention materially weakened or rendered 30 friable the known porcelain dentures.

While I have described a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention and I do not wish to be limited to the precise 35 details of construction set forth but desire to avail myself of all changes within the scope of the appended claims.