US3527861A

US3527861A - Cast dental prosthesis and method of making same

Info

Publication number: US3527861A
Application number: US614334A
Authority: US
Inventors: Abraham B Weinstein; Jacob Biscow
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-02-06
Filing date: 1967-02-06
Publication date: 1970-09-08
Anticipated expiration: 1987-09-08

Description

Sept. 8, 1970 A'. B.WEINSTEIN ETAL 3,527,861

CAST DENTAL PROSTHESIS AND METHOD OF MAKING SAME Filed Feb. 6, 1967 FIG. 2

INVENTORQ ABRAHAM B. WEINSTEIN BY JACOB B|sco w ATTORNEY United States Patent 01 fice 3,527,861 Patented Sept. 8, 1970 3,527,861 CAST DENTAL PROSTHESIS AND METHOD OF MAKING SAME Abraham B. Weinstein, 23 Ralsey Road S., Stamford,

Conn. 06902, and Jacob Biscow, 70 E. 8th St., Brooklyn, N.Y. 11215 Filed Feb. 6, 1967, Ser. No. 614,334

Int. Cl. A61c 13/04, 13/08 US. Cl. 264221 13 Claims ABSTRACT OF THE DISCLOSURE The method of casting flowable materials in a vacuum by first connecting an air tight mold to a container filled above the connection with the casting material, exhausting air therefrom, and thereafter slowly lowering the vacuum and thereby forcing the flowable material into the air tight exhausted mold until filled with the casting material.

This invention relates to cast parts and to a method of casting such parts.

In dentistry, cast parts may consist of inlays, bridges, crowns, and other prosthetic appliances. Hitherto they were made by the lost wax process, sometimes employing centrifugal casting or other techniques for eliminating voids in the castings.

An object of the present invention is to provide a cast part which is more precisely molded, free-r of voids, and more dense than parts made by previously used processes in the dental arts.

We accomplish these and other objects and obtain our new results as will be apparent from the casting and the method of making the same described in the following specification, particularly pointed out in the claims, and illustrated in the accompanying drawing, in which FIG. 1 is a wax replica of a part it is desired to cast, and

FIG. 2 is a cross-sectional view partly in side elevation of a vacuum forming and containing apparatus for casting the part.

FIG. 3 is an enlarged cross-section of the mold.

Broadly the invention comprises the formation of the cast part in a vacuum. In a specific application of our process, We may first make of wax or its equivalent, a replica or pattern of the part to be cast, as is commonly done in the dental art, and in some industrial applications. Such a replica is shown in FIG. 1. This is preliminary to manufacturing a mold of the replica.

If the pattern can be destroyed in the process of making the mold, the replica may then be covered with a thin surface adhering material 12 which can be electroplated. One such material is a fine silver powder containing liquid known as Barnett Silverizer, made by Precious Metals Research Works of Brooklyn, NY. Any other suitable thin adherent, conducting coating for electroplating nonconductors, as is known in the prior art, will do.

The pattern is then provided with a transparent tube 16 open at one end only, and attached at the open end to the wax pattern, a sprue section 18 built up at the other end of the pattern, and the pattern and sprue copper plated as at 14, to the desired thickness, say .010 inch. At this point the wax replica 10 is heated and the wax withdrawn from the copper plated mold through the sprue opening. The mold is then attached to the neck 24 of a receptacle 26. The entire mold and all joints are finally sealed with a compound 22, allowing the transparent tube 16 to re main visible. The sealing compound used may be made of wax.

The receptacle 26 has an opening to allow the material 28 supplied for casting to enter the neck 24 into the mold. If the receptacle is also used as a mixing vessel, a paddle 30 for mixing the material to be cast, and conforming to the vessels inner surface 29 may be employed.

The mixing material may be a porcelain based mix and its hardener, such as is disclosed in copending application entitled Cast Porcelain Dental Prosthesis and Method of Making the Same, Ser. No. 335,305, filed Jan. 2, 1964, now US. Pat. No. 3,400,097.

This material is capable of flowing into the mold and is hardenable when cast.

The casting operation is performed within an evacuated apparatus or shell 32. It is preferably made of glass or transparent plastic to permit the molded material in the transparent tube 16 to be observed. In order to simplify the construction, only a single outlet to the vacuum chamber is provided through the base 34 upon which the glass shell is seated and sealed. A conduit 36 connects the base to the vacuum pump 38. A release valve 40 is positioned on the conduit 36, connecting to the atmosphere for terminating the vacuum in the chamber. Within the shell a stand 42 is supported on the base 34. Upon the stand, the vessel 26 is placed, to which the mold is affixed. The paddle 30 is operated by a motor 44, also secured to the stand by means of bracket 46.

To reduce the number of connections to the vacuum chamber, a self-contained unit for driving the motor is provided. It comprises a source of energy, namely the battery 48, secured to the stand by arm 50, a flexible diaphragm pressure-controlled switch 52, mounted to the battery by support '61, and a fixed contact 54, all connected and supported in a manner hereinafter described.

The flexible diaphragm 56 of switch 52 carrying a movable contact 58 is mounted to a sealed air containing chamber 60. When a vacuum is formed inside the glass shell, the flexible diaphragm is outwardly expanded until movable contact 58 engages fixed contact 54 mounted to the stand. The current from the battery is then allowed to pass through

connections

62 and 64 respectively by reason of the closed circuit through contacts 58 and 54, into the motor 44, which then proceeds to rotate the paddle 30 mixing the materials in the mixing receptacle.

When the vacuum pressure is slowly reduced at valve 40, the flexible diaphragm 56 is thereby allowed to retract towards the sealed chamber 60, pulling the movable contact 58, away from stationary contact 54, opening the circuit and stopping the motor.

The method of casting is as follows: the mixing receptacle and attached mold are placed in position on the stand, and the vessel filled with a small excess of material to be cast into the desired form. The valve 40 is then closed, the transparent shell suitably sealed to the base, and the vacuum pump started.

At the moment the shell is satisfactorily exhausted, the movable contact 58 is designed to engage contact 54, closing the electrical circuit inside the shell thus starting the motor. The thorough mixing of the casting material is thus initiated and continues until the vacuum is broken. This is accomplished by slowly opening valve 40 and stopping the vacuum pump. The flexible diaphragm of -the switch becomes less distended until the contacts separate and the circuit opened, stopping the motor and the mixing operation. The casting material is slowly forced into the mold by the incoming air in the chamber, until the material is visible in the transparent tube 16 signalling the completion of the filling operation. When further movement of the material in the transparent tube ceases, the valve is fully opened, the shell removed, and the mold removed from the receptacle.

When the porcelain based casting has become hardened by elapsed time or cured by heating, or whichever process is employed for hardening the casting material, the mold is broken or separated from the casting, the sprue and tube 16 removed, the casting 66 trimmed, providing an extremely accurate replica of the desired part.

We have found that air should be allowed to enter the exhausted chamber slowly to properly fill the mold, and that the time is dependent on the viscosity of the casting material. Using the compound described in the copending application, the filling operation for the average inlay should take about 30 seconds. A large restoration may take as long as minutes.

It may be noted that the mold may be made of metal, or other materials that may be readily separated from the cast part, and in two or more sections which are separated to release the casting. It is of course important that the mold be sealed at all joints to permit the casting material only to enter the mold through the sprue opening when the vacuum is broken.

The result is an extremely dense cast part, free of voids in the surface of the part and in the cast material itself.

We have thus described our invention, but we desire it understood that it is not confined to the particular form or uses shown and described, the same being illustrative, and that the invention may be carried out in other ways without departing from the spirit of our invention, and therefore we claim broadly the right to employ all equivalent instrumentalities coming within the scope of the appended claims, and by means of which, objects of our invention are obtained, and new results accomplished, since the particular embodiment herein shown and described is only one of the many that can be employed to obtain these objects and accomplish these results.

We claim:

1. The method of casting material in a mold from a vessel containing the casting material, which method comprises the steps of connecting the mold through a sprue to the vessel, evacuating the air from the vessel, casting material, and the mold cavity through the casting material without substantially filling the mold cavity; and thereafter opening the vacuum to pressure fill the mold cavity completely with the casting material.

2. The method of claim 1 in which the vessel, the casting material and the mold are positioned in one chamber during evacuation.

3. The method of claim 1 in which the casting material in the vessel is mixed while the vessel is evacuated.

4. The method of claim 3 in which the mixing in the vessel is begun when the vacuum reaches a predetermined degree in the chamber.

5. The method of claim 1 in which the casting material is sueked into the mold from the vessel through a passageway extending outside the mold.

6. The method of claim 4 in which the mixing operation is automatically stopped when the vacuum is opened to the atmosphere.

7. The method of claim 5 in which the mold is provided with a tubular extension having a closed end positioned oppositely of the passageway, having a size sufiicient to permit the casting material to enter.

8. The method of claim 7 in which the tubular extension is made transparent to permit the contents to be visible.

9. The casting formed by the process of claim 1.

10. In the method of claim 1 of preparing a cast part from a mold, the step of preparing a wax pattern in the exact shape it is desired to reproduce, applying a sprue to the wax pattern, coating the pattern with a layer of conducting material, electrolytically depositing a layer of metal over the coating to form a rigid shell, and thereafter heating the mold and pouring the wax from the mold.

11. The method of claim 10, in which a reinforcing and sealing material covers and seals the mold.

12. The method of claim 10 in which a transparent tube is attached to the wax pattern.

13. The method of claim 10 in which the mold is connected to a casting material dispensing receptacle, and sealed thereto, about the mold opening.

References Cited UNITED STATES PATENTS 1,644,543 10/ 1927 Richmond 264- 1,991,009 2/1935 Browne et al. 264-101 2,317,008 4/1943 Werner 264-16 2,477,273 7/1949 Tognola 264-102 2,566,596 9/ 1 Cantor 264--102 2,803,054 8/1957 Kohring 264-101 3,059,278 10/1962 Daniel 264102 3,271,491 9/1966 Mikkelborg 264-102 2,490,193 12/ 1949 Barr. 2,696,022 12/ 1954 Steinbock et al. 2,877,494 3/ 1959 Wright et al. 3,005,232 10/ 1961 Steinbock et al. 3,064,309 11/ 1962 Steinbock et al. 3,081,492 3/ 1963 Grzegorczyk.

" DONALD J. ARNOLD, Primary Examiner A. H. KOECKERT, Assistant Examiner US. Cl. X.R.