Method and material for dental structures

Abstract: The invention relates to a method and material for reinforcing a dental metal structure in forming, repairing or reinforcing a dental restoration. The reinforcing material comprises a metal composition including a substantial proportion of particles of high fusing temperature metal having a melting temperature preferably above about 1300°C with such high fusing temperature metal particles being below 100 microns in size and with said composition having a minor proportion of a low fusing temperature metal which is adapted to melt upon heat treatment at a temperature below said high fusing melting temperature and preferably below 1200°C. The method and material of the present invention forms a mass which retains its shape but does not suffer any shrinkage from heat treatment and is accordingly ideal for use in dental procedures where shrinkage cannot be tolerated.

Description: This application related to a method and a dental material for forming reinforcing or repairing a dental metal structure. In crown and bridge prosthodontics, a wide diversification of retainers and pontics can be used in various combinations for constructing a bridge. A ceramic to metal restoration uses a framework of metal as reinforcement for the crown and bridge upon which is applied a fired-on coating of a ceramic material such as porcelain. The framework of metal may either be cast or formed from prefabricated units of preformed copings and pontics. In accordance with present practice, a framework may be altered by soldering, but otherwise cannot be modified or reinforced without involving investment and casting operations. Present practice is limited because of the unavailability of commercial materials with which to build up or extend the framework. To reinforce a framework without investment and casting requires adding material to the framework which upon heat treatment will become an integral part of the frame-work. The material must be capable of being molded into a desired shape and must be self-supporting in the molded configuration as well as capable of retaining the shape in which it was molded under heat treatment. To be able to shape the material into a desired configuration, the material should be relatively soft and workable. Under heat treatment, the material should solidify into a rigid mass of metal without losing the shape in which it was molded prior to heat treatment. The material should fuse to the metal framework and should have a hardness characteristic of at least equal but preferably greater than the hardness of the material before heat treatment. Such a material could be used, for example, to build up a cervical shoulder around a retaining member at the gingival margin without the need for investment or casting. For example, a finishing shoulder can be formed around a prefabricated metal coping which was preformed without a shoulder margin. The finishing shoulder can be molded into any shape by the dental technician. Likewise, the material can be used to build metal cusps upon a metal coping before ceramic porcelain is added to provide buccal and/or lingual cusp reinforcement. The material may also be used to strengthen joints at predetermined locations in the framework or for general bridgework repair. The latter is, at present, relatively impossible. Heretofore, the dentist and dental technical were essentially limited to use of cast dental structures and to materials useful as solders or fluxes. Neither the conventional solder nor flux is capable of being molded into a self-supporting configuration nor is either material capable of retaining a shape under heat treatment. Soldering alloys are, in fact, designed to melt and flow freely under the heat of a soldering flame and function to join metals by fusion. A flux is a non-oxidizing agent. Although no dental material is presently commercially available for reinforcing a dental restoration, there have been attempts in the past to form such a material. All such attempts are based on using a composition which solidifies into a solid mass upon being heat treated and suffers from substantial shrinkage. EP-A-214 341 discloses a process for the production of a dental prosthesis having a metallic matrix consisting of a mixture of metal powders with a multi-modal particle size distribution of coarse and fine fractions, whereby the particle size of the the coarsest fraction does not exceed 100 µm. The powder mixture is conditioned with water to a brushable mass, molded to the desired shape and sintered at a temperature which is higher than the solidus temperature of at least one component of the powder mixture. FR-A-2 036 946 discloses a process for forming a sintered metal structure which consists of fine metal particles having a diameter of about 2 to 25 µm with a binder for forming a mastic, the binder being volatile at a temperature below the sinter temperature. Then the mastic is molded to the desired shape, the mold is heated for removing the binder and finally heated for sintering the metal particles to form an essentially non-porous mass. The metal particles comprise low and high-fusing particles, with the low fusing particles constituting the major fraction. The present invention relates to a dental material for forming upon heat treatment a porous sponge-like metal structure for use in the fabrication or repair of a dental restoration comprising a composition of particles of different metals and a binder, which gives the dental material a paste or putty-like constituency and will volatize during heat treatment, wherein said composition has a proportion of particles of a high fusing temperature metal component with a melting temperature above at least about 1300°C and a particle size no greater than 100 µm and said composition has a proportion of a low fusing temperature metal component with a melting temperature below said high fusing temperature, with said proportion of high fusing temperature particles being 50 to 98 % of the combination of both said components, said high fusing temperature particles being irregular in shape and at a size of up to no more than ten times larger in size than said low fusing temperature particles, for forming upon said heat treatment a porous sponge-like mass of interconnected particles of said high fusing temperature metal component. Further, the present invention relates to a method for forming, reinforcing or repairing a dental structure comprising forming a material composition of particles of different metals and a binder, which gives the dental material a paste or putty-like constituency and will volatise during heat treatment, wherein said material composition is such that it comprises a metal composition component of a high fusing temperature metal component and a low fusing temperature metal component, with a proportion of said high fusion temperature component of 50 to 98 % of the combination of both said components, particles of said high fusing temperature metal being irregular in shape and of a size of up to no more than ten times larger in size than those of said low fusing temperature metal, and adding the material to the dental structure molding the material composition into a predetermined shape; heat treating the material composition, performing said heat treatment at a temperature below the melting temperature of said high fusing temperature metal component and at a temperature level sufficient to cause melting of said low fusing temperature component for forming a porous sponge-like structure of interconnected particles of said high fusing temperature metal component; and, after heat treatment, adding particles of a low melting temperature filler to said porous sponge-like structure of metal and heat treating said filler particles to cause said filler particles to melt into the sponge-like structure whereby a solid reinforced structure is formed. The method and material of the present invention forms a mass which retains its shape but does not suffer any shrinkage from heat treatment and is accordingly ideal for use in dental procedures where shrinkage cannot be tolerated. In addition, the present method results in very little waste of precious metal and is thus highly cost effective. The method of the present invention is particularly useful for reinforcing a metal structure in a dental restoration. In following the method of the present invention, the porous sponge-like mass forms an intermediate product following the first heat treatment step which is filled in with a filler of low temperature metal or ceramic and again heat treated to form a solid mass. This two-step process in which the low fusing temperature component is melted and then the filler is melted is an important feature of the invention. In the second melting, the added filler combines to form an integral solid mass. A ceramic material may be applied over the solid, reinforced structure in a conventional fashion and fired in a furnace to form a ceramic to metal dental restoration. The low fusing metal particles preferably melt below 1200 °C. Broadly the dental material of the present invention is a composition of metal particles which can be molded upon heat treatment into a desired self-supporting shape for forming a dental reinforcement in forming or repairing a dental restoration. The dental material of the present invention permits the dental material to be formed into a solid mass without suffering any shrinkage. The dental material preferably includes a minor proportion of a low fusing temperature, precious metal component of a single metal or metal alloy in the form of particles or clad to the particles of the high fusing temperature, precious metal. Under heat treatment, the low fusing temperature component melts to fuse the high temperature particles together at its point of contact to form a porous sponge-like structure which retains the shape it is given prior to heat treatment. A binder is added to the composition of metal particles in forming the dental material of the present invention to give the material a paste or putty-like constituency. This should make the material easier with which to work. A binder should be selected which will volatize during heat treatment without leaving a residue. Any suitable organic resinous or synthetic resinous material is acceptable such as, for example, ethylene or polyethylene glycol. In addition to a binder, a flux such as borax may be added to form the dental material of the present invention. The flux eliminates the formation of oxides. The composition of metals forming the dental material should be bio-compatible for use in the mouth. Accordingly, precious metals and precious metal alloys are preferred although not essential. The precious metals may also be used in combination with non-precious metals. In the foregoing embodiment of the invention, the high fusing temperature metal composition is primarily composed of a combination of from 0 to 100% platinum and from 100 to 0% palladium, with or without other minor constituents such as gold. Gold may be added to the high fusing temperature metal composition to increase the affinity of the particles of the high fusing temperature component to the low fusing temperature component. The particles of the low fusing temperature metal is preferably composed of a gold alloy with gold as the major constituent or entirely of gold. The preference for gold as the major constituent of the low fusing component is based on its known characteristics of workability, non-oxidizing property and its color. The size of the particle of the high fusing temperature metal component is an important characteristic of the present invention. Best results are achieved when the largest particle size of the high fusing temperature component is below about 100 µm and preferably below 74 µm. The high fusing temperature component particles should also be larger in size than the particle size of the low fusing component. The high fusing temperature component should preferably be about 5-10 times larger than the particle size of the low fusing component. When the low fusing component is cladded to the particles of high fusing particles, the latter should also be much larger in size based upon relative thicknesses between the clad components. The shape of the particles of the high fusing component is considered important to the present invention, but is not a critical characteristic. Irregularly shaped particles in the form of flakes appear to function best. An irregular shape allows the particles to form a mesh or open interlocking network of particles. The low fusing metal component fuses the particles of the high fusing temperature at the contact points in the open network to form a porous sponge-like mass under heat treatment. Any shape is acceptable including a spherical shape, although strips and irregularly contoured shapes (particularly a crescent shape) is preferred. Although the material of the present invention is a composition of metal particles, the method of forming the particles is not critical to the present invention and as stated earlier, the low fusing component particles may be cladded to the high fusing component particles to form a composite of a high fusing temperature component and a low fusing temperature component. The cladded particles may have one component totally encapsulating the other or only partially covering one another. Cladded particles may be formed, for example, from multiple layered sheets which may have been laminated. Various other known deposition processes may also be used to form layered sheets or to encapsulate the particles one within the other including, for example, electrodeposition and cathode sputtering. Where the metal particles are cladded to one another, the proportion of the high fusing component to the low fusing component in the total composition would be based on the difference in the thickness between the cladded metals. Preferably the thickness of the low fusing component should be in a range of 8 to 15 µm for reasons which will be discussed hereafter. The low fusing temperature component is intended to function solely as a soldering agent for fusing the particles of the high fusing temperature metal together at their points of contact upon heat treatment. Accordingly, the high fusing temperature component is present, relative to the combination of particles of the high and low fusing temperature components, in an amount of 50 to 98 % and preferably 50 to 75 %. The dental material is added to a dental structure, such as a metal coping or bridge, to add reinforcement to the structure at desired specific locations or to extend the structure, etc. The dental material may be applied to the structure by a brush or spatula and burnished or molded by hand into a desired shape. The dental structure including the dental material is then heat treated by subjecting it to the flame of a Bunsen burner or by sintering in a furnace at a temperature below the melting temperature of the high fusing temperature component. The melting temperature of the high fusing temperature component should be above about 1300°C whereas the heat treatment should be carried out at a temperature below about 1200°C and preferably between about 1075°C to 1175°C. Heat treatment causes the dental material to form a porous mass of metal in the form of an open network of interconnected metal particles of generally sponge-like appearance which fuses to the dental structure. The porous sponge-like mass of metal retains the shape it was given prior to heat treatment and does not suffer any shrinkage during heat treatment. After heat treatment particles of filler having a low melting temperature are added to the porous mass of metal and heat treated to cause the filler particles to melt into the sponge-like porous mass whereby a solid reinforced structure is formed. The particles of filler are preferably metal particles of gold. Heat treatment of the filler particles can be carried out at the same heat treatment temperature as originally carried out to form the porous mass. The low fusing temperature material in the porous mass was melted during heat treatment to form an alloy with the high fusing metal at the points of contact where the low fusing component solidifies. The metal alloy has a higher melting temperature than the melting temperature of the original low fusing component and accordingly it will not remelt upon renewed heat treatment at the same temperature. Alternatively, filler particles can be selected with a different melting temperature than the original melting temperature of the low fusing metal component. For example, the filler particles can be gold and the low fusing metal a gold alloy, or they can both be pure gold or gold alloys. Other metals may also be used. Moreover, the porous sponge may be filled with filler particles of a ceramic composition such as porcelain, where strength is not required and particularly for repair of a chipped porcelain restoration. The low fusing metal component may consist of a single metal such as pure gold or an alloy thereof or of more than one metal alloy in combination. When the low fusing component is plated onto the particles of the high fusing component to form cladded particles, it is important that the thickness of the low fusing component be small relative to the thickness of the high fusing component. The preferred thickness is between 8-15 µm. The high fusing metal component may be a composition of gold, platinum and palladium with minor additions of other constituent elements, with the combination of palladium and/or platinum being the major constituent. It should be understood that the invention is not to be construed as limited to any given dental application for the material. The material may, for example, be added to a dental framework after the porcelain has been fired. If, for example, a crown is too short at the margin, this material may be used to extend the crown. Accordingly, the word "reinforce" is not to be given a narrow interpretation, but is instead to be given a much broader definition so that it specifically encompasses the idea of increasing the size and physical dimensions of the framework by simply adding to or extending the framework. In the same manner, the material of the present invention may be used to fill a space between adjacent teeth upon which a fired-on ceramic veneer may be applied, if desired, or to form a coping for a dental restoration.

Claims: A dental material for forming upon heat treatment a porous sponge-like metal structure for use in the fabrication or repair of a dental restoration comprising a composition of particles of different metals and a binder, which gives the dental material a paste or putty-like constituency and will volatize during heat treatment, wherein said composition has a proportion of particles of a high fusing temperature metal component with a melting temperature above at least about 1300 °C and a particle size no greater than 100 µm and said composition has a proportion of a low fusing temperature metal component with a melting temperature below said high fusing temperature, with said proportion of high fusing temperature particles being 50 to 98 % of the combination of both said components, said high fusing temperature particles being irregular in shape and of a size of up to no more than ten times larger in size than said low fusing temperature particles, for forming upon said heat treatment a porous sponge-like mass of interconnected particles of said high fusing temperature metal component. A dental material as defined in claim 1 wherein said high fusing temperature metal comprises particles of precious metal selected from the group comprising platinum and palladium. A dental material as defined in claim 2 wherein said low fusing temperature component comprises gold. A dental material as defined in claim 3 wherein at least some of the said low fusing temperature metal component particles and up to 100% thereof is in a form cladded to the particles of said high fusing temperature metal component. A dental material as defined in claim 4 wherein the thickness of said cladded low fusing metal particles is between 8-15 µm. A method for forming, reinforcing or repairing a dental structure comprising forming a material composition of particles of different metals and a binder, which gives the dental material a paste or putty-like constituency and will volatize during heat treatment, wherein said material composition is such that it comprises a metal composition component of a high fusing temperature metal component and a low fusing temperature metal component, with a proportion of said high fusion temperature component of 50 to 98 % of the combination of both said components, particles of said high fusing temperature metal being irregular in shape and of a size of up to no more than ten times larger in size than those or said low fusing temperature metal, and adding the material to the dental structure, molding the material composition into a predetermined shape; heat treating the material composition, performing said heat treatment at a temperature below the melting temperature of said high fusing temperature metal component and at a temperature level sufficient to cause melting of said low fusing temperature component for forming a porous sponge-like structure of interconnected particles of said high fusing temperature metal component; and, after heat treatment, adding particles of a low melting temperature filler to said porous sponge-like structure of metal and heat treating said filler particles to cause said filler particles to melt into the sponge-like structure whereby a solid reinforced structure is formed. A method as defined in claim 6 wherein said material composition of metal particles comprises precious metals. A method as defined in claim 7 wherein said high fusing temperature metal component is composed of particles selected from the class consisting of platinum and palladium. A method as defined in claim 8 wherein said low fusing temperature component comprises gold. A method as defined in claim 9 wherein said high fusing temperature metal particles are of a size no greater than 100 µm. A method as defined in claim 10 wherein said filler comprises particles of a metal or metal alloy. A method as defined in claim 11 wherein said filler particles comprise gold. A method as defined in claim 6 wherein said filler comprises a ceramic composition. A method as defined in claim 13 whereas said ceramic is porcelain.

Inventors: SHOHER ITZHAK DR, WHITEMAN AHARON, SHOHER, ITZHAK, DR., WHITEMAN, AHARON
Applicants: SHOHER ITZHAK, WHITEMAN AHARON, SHOHER, ITZHAK, DR., WHITEMAN, AHARON
Application year: 1987
Main classification: A61K6
IPC codes: C22C1, B22F1, A61C13, A61K6