Process for the Manufacture of Tooth Parts from Dental Grade Metal Powder

Abstract

When producing tooth replacements from metal, the conventional method of casting is almost exclusively employed, even though said method is a relatively complicated one. The object of the invention is therefore to make available a method that is considerably simpler. In this method, an aqueous suspension, still containing microcrystalline wax and ethoxylated alcohols, is generated with the dental-grade metal powder. The metal powder is deposited on a model by electrophoresis, resulting, for example, in the formation of a cap (4). This cap (4) is filled with investment compound (5) and placed on a firing support (6), where it is sintered in this position. A cap is obtained which, in terms of its strength characteristics, is the equal of a cap that has been produced by casting. Alternatively, the cap (4) can be stabilized, during sintering, on a plated stump or in a muffle filled with a temperature-resistant powder.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a submission to enter the national stage under 35 U.S.C. 371 for international application number PCT/DE/2006/000134 having international filing date 31 Jan. 2006, for which priority was based upon patent application 10 2005 025 589.2 having a filing date of 3 Jun. 2005 filed in Germany and patent application 10 2005 052 113.4 having a filing date of 2 Nov. 2005 filed in Germany.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

(Not Applicable)

REFERENCE TO AN APPENDIX

(Not Applicable)

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a process for the manufacture of tooth parts from dental grade metal powder.

2. Description of the Related Art

The lost wax casting technique is still predominantly used for the manufacture of caps for individual teeth, frameworks for bridges, and full metal crowns, whereby a wax mold, whose shape corresponds to the object that is to be cast, is modeled on a working model. The hollow zone is formed in a casting mold with the help of this wax model, whereby the casting mold then has metal poured into it. Since this process is very expensive, several attempts have already been made to arrive at the desired shape via the sintering of metal powder.

In accordance with FR 2 660 224 A1, the model of a tooth stump is coated with platinum foil while preserving the shape of the stump, and then an adhesive is applied to this foil, whereupon a layer of small nickel chromium globules with diameters of 50-300 μm is applied to the adhesive. A form of sintering then takes place as a result of heating. The sintered cap can then be removed from the platinum foil.

U.S. Pat. No. 5,362,438 A describes a process for mixing metal powder into, e.g., propylene glycol in order to manufacture a paste that is applied to a fire resistant model on which it is sintered. Titanium, among others, is indicated to be a material for the metal powder, whereby the titanium is coated with a metal protective layer (palladium) in order to prevent oxidation during sintering.

A further process for the manufacture of tooth parts from metal powder is freeform laser sintering, which is described in EP 1 358 855 A1 and EP 1 021 997 A1.

However, none of the previous processes has been able to gain acceptance relative to the lost wax process. One reason for this resides in their similar operating expense and increased costs.

Over the last several years, electrophoresis has gained markedly in importance for the manufacture of full ceramic crowns and bridges. The following publications are designated as being representatives of this technology: WO 99/50 480 A1, DE 100 21 437 A1, DE 101 27 144 A1, DE 103 39 603 A1, and WO 2004/04 1113 A1. Since the objective of these inventions is the manufacture of full ceramic dental prostheses, the inclusion of dental grade metal powder as a material for dental prostheses was initially ruled out in the case of these known processes. Moreover, it could not be expected that metal powder could be applied by means of electrophoresis since short circuits in the electrophoresis cell would probably arise because of the conductivity of the metal.

The problem for the invention, which is indicated in Claim 1, is to make available a simple process for the manufacture of tooth parts from dental grade metal.

Advantageous embodiments of the invention are described in the dependent Claims 2-13.

The invention will be elucidated in more detail by means of an example and FIGS. 1 and 2.

BRIEF SUMMARY OF THE INVENTION

The invention is a process for the manufacture of tooth parts from dental grade metal powder. It is characterized by the fact that a metal powder layer is deposited from a suspension liquid onto a model (1) by means of electrophoresis, whereby this metal powder layer has the shape of the desired tooth part (4). The tooth part (4) is stabilized for the sintering process by way of the following steps: it is affixed to a firing support (6); or it remains on a duplicated model; or it is placed in a muffle that has been filled with embedding material or temperature-resistant powder.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following aspects are shown:

FIG. 1 shows the electrophoretic coating of a tooth stump model;

FIG. 2 shows a cap that is located on a firing support.

DETAILED DESCRIPTION OF THE INVENTION

A device that is known as such for the electrophoretic coating of tooth models is shown schematically in FIG. 1. A stump 1 of a working model or, alternatively, a duplicated model is immersed in a suspension 3 that comprises a liquid and a dental grade metal powder, whereby this suspension is located in a conductive vessel 2. A deposit, which corresponds to the shape of a cap, is formed as a result of the application of a voltage. In this connection, the steps which are described below are taken in a particular case.

First of all, the model 1 is manufactured from gypsum plaster or another suitable material and then thinly coated with a release agent in order to ensure the easier withdrawal of the as yet non sintered cap. A suitable release agent is described in DE 198 12 664 A1. The release agent is then coated with a conductive layer, e.g., a conventional silver lacquer, in order to ensure conductivity for electrophoresis.

In the search for a suitable suspension aid, it has been found that pure or almost pure water is unsuitable, whereby this is in contrast to the electrophoresis of ceramic powder. Petrolite D 900 (a registered trademark of the Baker Hughes firm) has proven to be especially suitable for the electrophoresis of metal powder. Petrolite D 900 comprises 30 60 wt % of microcrystalline wax, 5 10 wt % of ethoxylated alcohols with more than 14 C atoms in the chain, and 30 60 wt % of water.

A metal powder with the name Nicrobaz 135 (a registered trademark of the Wall Colmonoy firm) was used as the metal powder. It is a nickel compound with 1.9% B, 3.5% Si, and max. 0.06% C. The particle size is around 2 3 μm.

Electrophoresis at 30-40 V and 20-90 mA took place following the manufacture of a suspension comprising Petrolite and approximately 20 wt % of Nicrobaz, whereby this led within seconds to the formation of a cap on the model stump. Owing to the release agent, the as yet extremely fragile cap can be lifted off the stump. The interior of the cap is then filled with the embedding composition 5 as shown in FIG. 2, and the workpiece is placed on a firing support 6. A fully ready to use cap is formed after sintering at 1125° C. using a sintering time of 8-10 min. The sintering temperature is naturally governed by the material, and it is not permitted to exceed the fusion temperature.

It has been found that stabilization of the tooth part 4 does not necessarily have to take place on a firing support. If the model 1 is a duplicated model, then the tooth part can naturally remain on the duplicated model during the sintering process, whereby this does however lead as a consequence to the destruction of the duplicated model. The duplicating of the working model is, however, associated with other disadvantages such as mold defects and extra work.

Since the majority of metals are prone to oxidation during sintering, it is recommended that sintering be carried out either under vacuum or in a protective gas, such as argon, or that the ceramic powder or the pre shaped framework be coated with a conventional oxidation-stopping lacquer.

A third possibility for sintering is to put the tooth part into a muffle that has been filled with embedding material. Because of its higher specific gravity, the tooth part sinks in the embedding material. The muffle is then sintered in an oven. The removal of the sintered tooth part from the muffle and the cleaning of the tooth part in terms of removing the embedding material do not present any difficulty.

Instead of the embedding material that is known to the dental technician, use can also be made of a temperature-resistant powder. A mixture comprising alumina powder and graphite powder with a 5-50% proportion of graphite has proven to be especially suitable. The graphite hereby prevents oxidation of the metal. Compaction of the powder via the application of pressure, e.g., by means of a pressure-operated plunger device, is also recommended prior to the sintering process.

The process in accordance with the invention is usable for all conventional dental grade metals, especially those based on gold. The special advantage of the process in accordance with the invention is that with appropriate adaptation, it is usable for all the electrophoresis processes that have actually been developed for the manufacture of full ceramic tooth parts. Mention is made merely of the above-cited WO 2004/041113 as being representative of these processes.

Claims

1. Process for the manufacture of tooth parts from dental grade metal powder, characterized by

the fact that a metal powder layer is deposited from a suspension liquid onto a model (1) by means of electrophoresis, whereby this metal powder layer has the shape of the desired tooth part (4), and the tooth part (4) is stabilized for the sintering process by way of the following steps: a) it is affixed to a firing support (6) or b) it remains on a duplicated model or c) it is placed in a muffle that has been filled with embedding material or temperature-resistant powder.

2. Process in accordance with claim 1, characterized by the fact that the suspension liquid comprises 30-60 wt % of microcrystalline wax, 5-10 wt % of ethoxylated alcohols with more than 14 C atoms, and 30-60 wt % of water.

3. Process in accordance with claim 2, characterized by the fact that the model is coated with a release layer.

4. Process in accordance with claim 3, characterized by the fact that a conductive layer is applied to the release layer.

5. Process in accordance with claim 4, characterized by a particle size of the metal powder of 1-10 μm.

6. Process in accordance with claim 5, characterized by the fact that electrophoresis is carried out at 30-40 V.

7. Process in accordance with claim 6, characterized by the fact that electrophoresis is carried out at 20-90 mA.

8. Process in accordance with claim 7, characterized by gold as the basic metal for the dental grade metal powder.

9. Process in accordance with claim 8, characterized by the fact that the tooth part is a cap (4) or a bridge.

10. Process in accordance with claim 9, characterized by the fact that sintering is carried out under vacuum and/or the metal powder is coated with an oxidation stopping lacquer.

11. Process in accordance with claim 10, characterized by the fact that sintering takes place in a protective gas.

12. Process in accordance with claim 11, characterized by the fact that the temperature-resistant powder comprises a mixture that comprises a metal oxide and an oxygen consuming powder.

13. Process in accordance with claim 12, characterized by the fact that use is made of a mixture that comprises alumina powder and graphite powder.