Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-07-20
2001-12-04
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C419S036000, C419S038000
Reexamination Certificate
active
06325839
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the manufacture of dental restorations and more specifically to the manufacture of dental restorations using microwave sintering processes.
BACKGROUND OF THE INVENTION
Currently, dental restorations may be made by sintering metal powders. Metal powders are usually mixed with a binder to assist in the shaping or injection molding of the restorations. These restorations are made in larger dimensions to accommodate shrinkage that occurs during the sintering process. The binder may be present in an amount of up to about twenty percent with the remainder of the mixture being the powder. Restorations made from the binder/powder mixture undergo a binder removal step that occurs in the preheating stage, followed by sintering at a suitable temperature and in a suitable atmosphere in conventional heating ovens. These steps require long processing times and impose poor control on dimensional tolerance.
It has been found that microwave sintering has been effective in the manufacture of machine parts such as drill bit inserts, as set forth in U.S. Pat. No. 6,066,290. The patent discloses drill bit inserts manufactured from tungsten carbide and cobalt. Sintering by microwave is accomplished in a short period of time leaving the integrity of the alloy unchanged. U.S. Pat. No. 6,004,505 is directed to a process and apparatus for the preparation of particulate or solid parts. Hard wear parts are made from tungsten carbide or silicon nitride particles that are packed into a mold or cavity and sintered in a microwave sintering apparatus. U.S. Pat. No. 5,808,282 discloses a microwave sintering process for ceramics, ceramic composites, and metal materials. The process involves surrounding the material with a granular susceptor bed, flowing a protective gas around the material, and irradiating the material and bed with microwave energy. The patent is directed to the sintering of cutting tools. None of the prior art address the sintering of certain powder metals used in the manufacture of dental restorations.
It is beneficial to reduce the processing and sintering time required in the manufacture dental restorations. It is desirable to be able to better control the properties of dental restorations during manufacture thereof.
SUMMARY OF THE INVENTION
These and other objects and advantages are accomplished by the process of the present invention wherein metal materials are sintered using microwave energy to provide high strength dental restorations. The metal materials used to manufacture the dental restorations herein are sintered to high density to provide high strength products that have a density close to the density achieved when the same materials are cast. A dense solid having a fine microstructure is achieved using microwave heating. Through the process described herein, higher heating rates may be achieved, reducing the time necessary for sintering the materials. The process is faster than conventional processes used in the manufacture of dental restorations, eliminates time-consuming steps typically involved in the lost wax process and provides materials with better grain-size control and properties. It is possible to produce high strength dental restorations at lower temperatures having high hardness and density and small grain size.
DESCRIPTION OF THE INVENTION
As will be appreciated, metal materials are sintered using microwave energy to provide high strength dental restorations. The process is broadly applicable to the manufacture of all types of dental restorations including but not limited to orthodontic appliances, bridges, space maintainers, tooth replacement appliances, splints, crowns, partial crowns, dentures, posts, teeth, jackets, inlays, onlays, facing, veneers, facets, implants, abutments, cylinders, and connectors.
In one embodiment herein, metal powder in combination with a vehicle is used to manufacture a dental restoration. The vehicle is preferably a binder material used to hold the metal particles together. The combination metal powder/binder is preferably in a paste or sheet form. Accordingly, the paste may be pressed onto and around the die or the sheet may be cut to a desired shape to fit onto the die. The die is typically a model of a tooth or teeth to be restored. Alternately, the metal powder may be packed into a mold without a binder or with the addition of a binder to assist in holding the metal particles together.
Materials and methods useful herein for the fabrication and preparation of materials for the manufacture of a dental restoration prior to sintering are disclosed in commonly owned, copending provisional application Ser. Nos. 60/175,361 filed Jan. 10, 2000, 60/182,388 filed Feb. 14, 2000, 60/182,155 filed Feb. 14, 2000, 60/193,591 filed Mar. 30, 2000, and 60/201,067 filed May 1, 2000 which are all hereby incorporated by reference. U.S. Pat. Nos. 4,997,699, 4,814,008, 4,742,861, and 4,828,495 further discuss materials and fabrication techniques for the preparation of dental restorations and hereby are incorporated by reference.
Any metal or alloy used in the manufacture of dental restorations may be used in the process herein. The metal powder is preferably a high fusing metal and may comprise one or more precious metals, non-precious metals and alloys thereof. Preferably, the metal powder comprises a non-oxidizing metal. More preferably, the metal powder is selected from one or more of gold, platinum, silver and alloys thereof whereby the alloys may comprise one or more of the metals in combination with one another and/or with a different metal, such as copper, rhodium, palladium, indium, tin, gallium, germanium, cobalt, chromium, iron and mixtures thereof. One preferred alloy comprises about 85 to about 99% Au, 0 to about 15% Pt, and 0 to about 15% of one or more of Ga, Zn, Ge, Cu, Sn Ag, Pd, Rh, In, Ru, and Ta. The particle size of the powder is in the range of about 0.1 to about 150 microns and preferably from about 0.1 to about 40 microns.
Typical binder materials include, but are not limited to filler-free wax, ammonium caseinate, ammonium stearate, pectin, hexamine, ethyl cellulose, anthracene, triacetyl starch, dulcin, carbazole and tetraphenyl ethylene. The binder may be mixed with a solvent prior to mixing with the metal powder. Solvents include, without limitation, propylene glycol, water, eugenol, light paraffin oil, butyl acetate, butyl benzoate, diacetone alcohol, and dibutyl phthalate. The binder and solvent are driven off during the sintering process.
The powder/ binder mixture comprises about 75 to about 100 percent powder and about 0 to about 25 percent binder and preferably about 90 to about 99 percent powder and about 1 to about 10 percent binder. Preferably, the powder is present in about 96 percent by weight and the binder is present in about 4 percent by weight. Examples of commercially available metal materials useful herein include SinterKor™ 90
+
Pt sheets and SinterKor™ 24 kt sheets, each available from Jeneric/Pentron Inc., Wallingford, Conn.
In an alternate embodiment, the metal may be in the form of a thin metal foil containing one or more of gold, platinum, silver and alloys thereof whereby the alloys may comprise one or more of the metals in combination with one another or with a different metal, such as copper, rhodium, palladium, indium, tin, gallium, ruthenium, germanium, cobat, chromium, iron and mixtures thereof. U.S. Pat. Nos. 4,492,579, 4,797,100,4,273,580, 4,861,267 and 4,459,112 are directed to dental restorations fabricated from metal foils and are hereby incorporated by reference.
After the material has been modeled onto the die, molded to the desired form or inserted into a mold, the model created is ready for firing. The model is sintered in a microwave atmosphere to provide a high strength metal restoration. The sintering process takes place in a microwave apparatus which is similar to a conventional porcelain oven, but which supplies microwave energy to sinter the materials placed therein. Examples of microwave devices useful herein inc
Cohen Gordon S.
Prasad Arun
Jeneric/Pentron Inc.
Knab, Esq. Ann M.
Mai Ngoclan
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