Abstract:
Method of producing a dental ceramic structure by digitizing a model or partial model of the prosthesis to be produced and generating a CAD data set, cutting each section of the muffle based on the CAD data set to form the cavity, pressing the ceramic into the cavity by way of at least one sprue, removing the hardened ceramic from the cavity with the sprue or flash and removing the sprue or flash based on the CAD data set.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method of producing a dental ceramic structure, in particular, for pressing against, over or around a supporting structure made of metal or ceramic using a muffle having two sections which define a cavity corresponding to the negative form of the structure, flowable material being supplied into the cavity via at least one sprue. 
     A corresponding method is known, for example, from DE-A 196 30 412 for producing a ceramic dental structure. With this method, the steps are as follows: an impression of the mouth situation is taken with inserted ceramic root pin, a mold is made from the impression whereby the pin protrudes from the mold, a reconstruction is made from an annealable material, a sprue attached, a pin and waxed parts are embedded in a muffle with a hardenable embedding substance, the wax is removed by heating and finally the ceramic pressed in. 
     The quality of the dental ceramic structure thereby depends, on the one hand, on the skill of the dental technician who undertakes the molding of the reconstruction and, on the other hand, on the formation of the cavity with the embedded substance which surrounds the molding. 
     A corresponding method can also be found in DE-A 101 36 584 A1. 
     A method of producing dental prostheses is known from U.S. Pat. No. 5,092,022. In this case, according to the embodiment of FIG. 27, a molded part is formed by cutting, from a block consisting, for example, of metal, on the basis of stored data which corresponds to the outer geometry of a dental ceramic structure to be produced. The cavity thus formed is defined by a mold part accommodating a metal structure A sprue into which the liquid material, e.g. synthetic resin, is introduced extends between the mold parts. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to further develop a method of the aforementioned type in such a manner that highly precise dental ceramic structures are provided in which defects can be largely avoided due to manual intervention. 
     To solve the object, the invention provides the following method steps:
     a) digitizing a model or partial model of the dental prosthesis to be produced and generating a CAD data set of the dental prosthesis to be produced,   b) cutting each section of the muffle based on the CAD data set to form the cavity,   c) pressing the ceramic, as the material to be supplied, into the cavity byway of the at least one sprue,   d) after hardening the ceramic, removing the structure from the cavity with the sprue or flash thereof extending from the structure, and   e) removing the sprue or flash on the basis of the CAD data set of the structure to be produced.   

     In particular, the method in which the dental ceramic structure comprises a supporting structure is distinguished in that the structure is placed in the cavity after it has been formed (procedural step b), after which the ceramic is pressed into the cavity over the structure and procedural steps d) and e) are ultimately carried out. 
     In particular, the mold cavity is formed from a hardened embedding substance. 
     According to the invention, the supporting structures are molded or pressed over for e.g. crowns or bridges in an automated production based on CAD data. For this purpose, the negative mold of the structure to be produced is, for example, worked out by milling in a suitable blank such as an embedding substance. The volume of the ceramic material to be pressed in is then produced from the geometry obtained on the basis of the CAD data and thus its volume less the volume of a prefabricated and used structure. The molding ceramic is then pressed onto or around the structure. The dental structure, such as a crown or bridge, can then be removed from the mold in order to then be basically used immediately. If necessary, a minimal refinishing is required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, advantages and features of the invention can be found not only in the claims, the features found therein—alone and/or in combination—but also in the following description of a preferred embodiment found in the drawings, in which: 
         FIG. 1  shows a basic representation of a muffle with a dental ceramic structure formed in it, and 
         FIGS. 2-5  show basic representations to illustrate the method of producing the dental ceramic structure. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a muffle  10  is shown which consists of sections  12 ,  14  that have been fitted together. The sections  12 ,  14  define a cavity  22  in which a dental ceramic structure is to be produced by pressing around a supporting structure  18 . 
     The internal geometry of the cavity  22  is produced on the basis of CAD data of the dental ceramic structure to be produced from blanks by machining, e.g. by cutting such as milling, which forms the sections  12 ,  14 . 
     The volume of the cavity  22  not filled by the structure  18  is calculated on the basis of the available CAD data in order to then inject molding ceramic (hatched area  22 ) via a sprue  20 . After hardening, the sections  12 ,  14  are separated from one another, the dental ceramic structure removed and then the flash of the sprue  20  is removed. This takes place automatically since the data available for this are used. 
     To generate the CAD data, an impression can be made of the tooth stump or stumps from a dental preparation, the impression forming a negative mold of the situation in the patient&#39;s mouth. The surface of the tooth stump or stumps, approximate surfaces of the adjacent teeth and counter bite are thereby determined. A positive mold, preferably consisting of plaster or plastic, is obtained from this mold. The dental ceramic structure can then be calculated taking into consideration the data obtained from the positive mold by scanning in order to machine, e.g. cut, the sections  12 ,  14  of the muffle  10  on the basis of the CAD data then available, in order to form the cavity  22  as a whole. 
     The corresponding procedural steps follow from a synopsis of  FIGS. 2 ,  4  and  5 , Thus, a positive mold of one or more tooth stumps is shown in principle in  FIG. 2  which are to be provided with a dental ceramic structure. The positive mold  24 , i.e. the area which is to be e.g. crowned, is scanned, for example, by means of a mechanical scanner  26  in contact with it or by means of a laser in a non-contact manner, in order to then supply the corresponding data to a computer  28 . The corresponding data are then processed by means of a CAD program  30  to obtain data  32 , on the basis of which the section  14  of the muffle is produced mechanically, e.g. by cutting. Furthermore, data  34  are produced which correspond to the entire dental ceramic structure with the result that the section  12 , with respect to the area which defines the cavity  18 , can be produced from the data  32 ,  34 . Furthermore, data  36  can be generated which correspond to a structure to be produced. If the corresponding data are available, they must first be input into the computer  28  to obtain adapted data  34  for the dental ceramic structure without a supporting structure. 
     Alternatively, a molding for the dental ceramic structure can be prepared on the positive mold, a corresponding supporting structure for a crown or a bridge being situated on the tooth stump or stumps. The finished mold is then scanned in order to be able to work out the cavity  22  in the muffle  10  on the basis of this data. Of course, it is thereby necessary that the data of the supporting structure used be taken into consideration. 
     As in the previous explanations, e.g. a cap  38  can be formed on the positive mold  24 , the cap corresponding to the dental ceramic structure. The cap  38  is then scanned by non-contact or contact in order to supply the corresponding data to a computer  40  by means of which and by means of a suitable CAD program data  42  for forming the section  12  in its area defining the cavity and, in the event data of the structure is not already available, data for the structure  44  are then generated. 
     Based on the data  32  or  34 ,  42 , the lower section  14  or the upper section  12  is then formed in a CNC-controlled manner, for example, by means of a milling tool  46 . The surfaces  48 ,  50  thus produced define the cavity  18 . Furthermore, it can be seen that the sprue  20  should not be formed in section  12  (hatched illustration), namely also based on the existing digitalized data. 
     The muffle is then inserted into a known muffle system in order to press flowable ceramic into the cavity  22  or the cavity not filled by the supporting structure  18  via the sprues  20 . Press dies are used in the conventional manner for the molding. However, in this respect, reference is made to sufficiently known techniques and constructions. For example, reference is made to DE-U 90 01 740 or DE-A 101 36 584. 
     Since, as mentioned, the data of the cavity and thus the outer geometry of the finished dental ceramic structure are available, it is easy to automatically remove the flash of the sprue  20 .