Abstract:
A method for manufacturing one or several dental prostheses, comprising the steps of: performing a rapid prototyping method for manufacturing one or several dental prostheses and subsequent working, such as reworking, of the one or several dental prostheses with a machining method, such as a milling method. In addition, a method for creating a data record which can be used for a rapid prototyping method for manufacturing a dental prosthesis wherein an end data record is obtained from a starting data record, so that in at least one area of a dental prosthesis manufactured with the end data record excess material is provided, compared to a dental prosthesis manufactured with the starting data record.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for manufacturing dental prostheses, a method for creating a data record as well as a computer-readable medium. 
     BACKGROUND 
     It is known from the prior art to manufacture dental prostheses for example by laser sintering. In the process, for example a metal powder is locally melted so that it solidifies upon cooling in the molten area. In this manner, a three-dimensional dental prosthesis can be manufactured by applying powder in layers and subsequently selectively sintering the same. A disadvantage of this method is that normally step-like or very rough surfaces result from the application of material in layers and subsequent local sintering. The precision desired for dental prostheses can often not be achieved. 
     It is furthermore known from the prior art to mill dental prostheses out of solid material. By this method, dental prostheses of sufficiently high precision can be made. In this process, however, material consumption can be considerable, so that the manufacture is cost-intensive. 
     It is the object of the present invention to provide a method for manufacturing dental prostheses, a method for creating a data record and a computer-readable medium by which dental prostheses can be manufactured. Preferably this is accomplished according to the invention less expensively and at the same time with sufficiently high precision. 
     SUMMARY OF THE INVENTION 
     According to one embodiment, a dental prosthesis is manufactured by a rapid prototyping method. This can be done relatively quickly and inexpensively as material for the dental prosthesis is only used to the extent to which it is concretely required for a dental prosthesis. The thus manufactured dental prostheses are subsequently processed by a machining method, such as a milling method. Thereby, the desired precision of the dental prostheses can be achieved. The processing can be e.g. finishing where only slight modifications of the dental prosthesis are made, such as smoothing surfaces etc., but the dental prosthesis is essentially already finished. 
     It is, for example, in particular avoided in the process that a tool of a machining method (e.g. a cutter head for milling) is occupied for a relatively long time with removing material which is far away from the surface of the dental prosthesis, so that removal can be essentially restricted to fine machining, which, however, can be performed relatively quickly. 
     The rapid prototyping method can be a laser sintering method (as already described above), or else any other rapid prototyping method, such as for example stereolithography, laser generation, fused deposition modeling, laminated object modeling, 3D-printing, contour crafting or multi-jet modeling as well as a polyjet method. 
     Each of these methods is suited for manufacturing a dental prosthesis, so that it can be subsequently (re)worked by a machining method, such as a milling method. 
     In case of dental prostheses which are to be covered, a certain surface roughness in certain areas is absolutely desirable. For example porcelain covers or other covers can be attached to rough surfaces enduringly. Insofar, the rough surface produced with rapid prototyping can be advantageous. 
     In a milling method, a steel or, even better, a diamond milling cutter can be used. With diamond milling cutters, particularly precise and smooth surfaces can be made. 
     A method where in particular the area of a preparation line or the internal area of a dental prosthesis is (re)worked with the milling method is particularly advantageous. In particular in the area of the preparation line, a shape of the dental prosthesis as exact as possible is desired to thus achieve a good enclosure. On the exterior, reworking is as a rule rather not desired as here a rough surface can be advantageous, in particular for covering. If the dental prosthesis is not to be covered, reworking with a machining method (e.g. milling method) can be also performed externally. 
     Furthermore, a method where a referencing is generated with the rapid prototyping method is advantageous. This referencing can be used to position the dental prosthesis or a milling cutter for the milling procedure. That means, by means of the referencing, the position of the manufactured dental prosthesis can be identified and/or defined for the milling procedure. 
     It is furthermore advantageous to create a shell or frame with the rapid prototyping method where the dental prostheses are held, so that the dental prostheses can be transported and/or positioned together with the shell or frame, for example, for the machining method, such as the milling procedure. 
     With the machining method, in particular the worked areas are to be advantageously smoothed. 
     It is furthermore advantageous to form excess material at least in one predetermined area with the rapid prototyping method, and to subsequently rework this area, where the excess material is removed (at least partially). 
     It is furthermore advantageous if in those areas where no rework is to be performed, the produced shape that has been manufactured in the rapid prototyping method remains within predetermined surfaces or is e.g. partially spaced from the same. In particular, by a surface roughness typical of the rapid prototyping method, areas result which are spaced from a predetermined surface if the surface otherwise altogether remains within the predetermined surface. The predetermined surface can be, for example, the surface that is to be manufactured according to a predetermined data record. 
     In the method, dental prostheses can be made of very diverse materials. Thus, a dental prosthesis of plastics, glass-fiber reinforced plastics, or a glass-fiber reinforced copolyamide are suitable. A metal or metal alloy, such as for example cobalt, cobalt alloy, chromium cobalt alloy, titanium or titanium alloy, gold or a gold alloy are also suitable. Ceramics, such as zirconium ceramics (in particular yttrium-stabilized zirconium ceramics), or aluminum oxide are also suitable as material for the dental prosthesis. 
     Furthermore, an embodiment where a manufactured dental prosthesis is sintered after manufacture and before working is advantageous. Thereby, the shaping manufacturing process of the dental prosthesis can be completed and the exact desired shape can be manufactured. Distortion of the dental prosthesis by subsequent sintering is thus excluded. It is, however, also possible to first rework a dental prosthesis with a milling method and to subsequently subject it to dense sintering. This is in particular advantageous with respect to the wear of milling cutters which is comparably low in the working of not yet completely sintered materials. 
     Another embodiment of the invention is a method for creating a data record, wherein a starting data record is used to obtain an end data record, so that in at least one area of a dental prosthesis manufactured with the end data record, excess material is provided compared to a dental prosthesis manufactured with the starting data record. The excess material results from the comparison of the two data records or from two dental prostheses manufactured according to the respective data record. The manufacture of the two dental prostheses according to the two data records need not be part of the method but only serve for defining the excess material. 
     The area or areas where excess material is to be present can be automatically determined; for this, the shape data themselves, and also other information can be used in the starting data record. Alternatively, the information can also be entered by an operator. 
     In the starting data record, e.g. the area of a preparation line and/or the internal area can be stored, besides the actual shape data. The information saying which part of the shape or the shape data represents the preparation line and/or the internal area is thus already provided. However, the information can also be automatically identified by computer analysis or entered by an operator. 
     Several end data records can also be further processed to form a production data record. Here, a data record is created with which a work piece can be produced where several dental prostheses are connected with connecting means, such as webs, one or several frames, one or several shells, etc. 
     One or several end data records as well as one production data record can serve for the manufacture of the dental prostheses with a corresponding rapid prototyping method. The thus prepared dental prostheses and/or the thus prepared work piece can be subsequently worked with a machining method, in particular with a milling method. 
     Another embodiment of the invention is a computer-readable medium comprising instructions performing one of the methods described above or below when they are read into a computer. 
     The manufacture of dental prostheses can be performed with two different computer-based manufacturing processes which are performed one after another. The manufacture can be furthermore performed batch-wise (lot-wise). That means, first a higher number of dental prostheses is manufactured with the first computer-based method, and subsequently (after completion of the first method for all dental prostheses manufactured thereby) they are worked with the second computer-based method. More than 50, 100, 150, 200 or 250 dental prostheses can be made in one batch. 
     The dental prostheses can be inlays, overlays, onlays, small caps, crowns, primary crowns, secondary crowns, bridges, shells, dentures (false teeth), abutments, implants, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the method are to be illustrated with reference to the enclosed figures, wherein: 
         FIG. 1 : shows a conventional manufacture of dental prostheses; 
         FIG. 2 : shows certain typical areas of dental prostheses; 
         FIG. 3 : shows the shape of dental prostheses according to one embodiment of the invention; 
         FIG. 4 : shows a schematic representation of the manufacturing process according to one embodiment of the invention; and 
         FIG. 5 : shows a schematic representation of a computer system for implementing the prototyping and/or manufacturing according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1   a , a blank  2  from which a dental prosthesis  1  can be milled out is shown. For this, the complete shaded area of material has to be removed, which is relatively time consuming. With this milling method, it furthermore has to be taken into consideration that the portion of blank  2  which is not used for the dental prosthesis  1  is machined, that means it cannot be directly reused. 
     In  FIG. 1   b , an example of a rapid prototyping method is shown, in this case laser sintering. A powdery or liquid material is provided in area  8  which has been applied in layers, for example with a slider and locally melted (or otherwise modified) with a focused (see reference numeral  6 ) laser beam  5 , so that it is subsequently solidified after cooling (or the like). The surface of the powder is marked with reference numeral  7 . 
     In the section in  FIG. 1   b , the dental prosthesis  3  has a relatively high surface roughness  4 . This is the result of the application of the material  8  to be solidified in layers and of the local solidification. This always results in step-like surfaces. 
     In  FIG. 2 , an enlarged section of a dental prosthesis  1  is shown, here a portion of a bridge which is to be placed onto a polished tooth or implant support. The area which comes into contact with the polished tooth or the implant support is the internal area  9 . A portion of this internal area  9  is the area of the preparation line  10 , that means the area which has to be worked particularly precisely in order to seal well the internal area  9  of the dental prosthesis  1  from the outside. This is important to avoid penetration of bacteria or other tooth-destroying substances. 
     The external area is marked with reference numeral  11 . On the external area, covers or facings can be applied, for example of porcelain or the like. The external sides  11  can, however, also remain without facing. 
     In  FIG. 3   a , an internal side of a dental prosthesis, manufactured according to an embodiment of the invention with a rapid prototyping method, is shown in section. In the upper portion of the internal side, the manufactured shape remains within the dashed line  15 . Line  15  shows the shape which would optimally match with the polished tooth or implant support. This shape can be, for example, be specified by a corresponding data record. In the areas  17  of the step-like surface of the dental prosthesis, the surface of the prosthesis is situated on this line  15 . In the corners  16 , the surface is spaced apart from line  15 . Here, for example a distance d 3  is provided. 
     In the areas of the preparation line  10  (see  FIG. 2 ), the surface of the manufactured dental prosthesis may also be spaced apart from the line  15 , here projecting over the line  15  to the outside. The concave corners (see distance d 1 ) as well as the convex corners (distance d 2 ) are situated outside the limiting surface  15 , and comprise excess material  18 . 
     On the right side of the preparation line of  FIG. 3   a , the corners  19  are situated on line  15  coming from the outside, however, excess material is provided in the areas between the corners  19 . 
     The excess material  18  can be removed with a milling cutter  20 . In  FIG. 3   a , an example of a milling cutter is schematically shown (see arrow of rotation  21 ) which is a triaxial milling machine (see 3D arrows marked as reference numeral  23 ). However, 3+1, 4 or 5-axial milling machines can also be provided. 
     The result of a (re)working of the area of the preparation line  10  is shown in  FIG. 3   b . Here, excess material  18  is removed creating smooth surfaces  24  which are situated preferably as exactly as possible on the desired line  15  (dashed line). 
     While  FIG. 3  shows a case where excess material exists only in the area of the preparation line  10  (see  FIG. 2 ), there also is the possibility of providing the complete internal side  9  (see  FIG. 2 ) with excess material and to subsequently rework it with the machining method. Thus, this area, which provides good support of the dental prosthesis and should have the desired shape preferably as exactly as possible, can be exactly made. 
     The outer side of the dental prosthesis  1  not represented in  FIGS. 3   a  and  3   b  (or only indicated at the bottom) is step-like, as it is shown for example in  FIG. 1   b . This rough surface is well-suited for being subsequently covered. 
     According to one embodiment of the invention, it is also possible to rework the external side  11  or a portion thereof with the milling method. Excess material may be provided on the complete external side or a portion of the external side of the prototype prosthesis, some or all of which is then removed, e.g., by milling. 
     Even if the complete surface of the dental prosthesis which has been manufactured with the rapid prototyping method is reworked with the milling procedure, the milling procedure is relatively quick as it is normally sufficient to once pass over the surface with the milling cutter. A removal of volume material as it is, for example, necessary for forming the cavity of the cavity in the area of the internal side  9 , can be omitted here. Thus, the milling working can be relatively quickly performed. This in general applies to any machining method. Furthermore, here relatively little material is machined, so that the manufacturing costs remain low. 
     In  FIG. 3   a , a starting data record  15  is shown (represented by the dashed line  15 ). The starting record has been modified such that in the area of the preparation line  10 , excess material  18  is formed. The dental prosthesis that would have been manufactured with the starting data record  15  would not comprise such excess material. 
     The area of the preparation line, the internal area or any other area where excess material is to be arranged can be automatically identified and/or determined. Thus, e.g. the shape data  15  shown in  FIG. 3   a  can be evaluated to identify the corresponding areas. Moreover, apart from the actual shape data, other data can also be provided in a data record by which the areas which are to be provided with excess material are marked. Thus, e.g. the area of a preparation line or the internal area can be marked and this information can be utilized for providing excess material in this area. 
     In  FIG. 4 , reference numeral  25  schematically represents one embodiment of a rapid prototyping device. It is shown in a condition where the manufactured work piece can be seen in a section and subsequently has to be finished at the top. Liquid or powdery material which is locally modified to thus produce a solidified structure is provided in a reservoir. In  FIG. 4 , a frame  27  from which webs  28  extend to dental prostheses  29  can be seen. The webs  28  can also be connected to each other without a frame  27  being provided. Furthermore, the dental prostheses  29  can also be arranged such that they are directly held by a frame  27  without webs. However, the variant shown in  FIG. 4  is preferred, where there is a frame  27  from which webs extend and hold the dental prostheses  29 . By way of example, two dental prostheses are shown, on the left hand a dental prosthesis  29  with two elements and on the right hand one with three elements. Several webs  28  extend to each dental prosthesis  29  to stably hold the dental prostheses  29 . This is advantageous for working with a machining method. 
     For performing the rapid prototyping method according to one embodiment, a data record is used in which, apart from the data for the dental prostheses, also data for connecting means (webs, frames, etc.) are included. Such a data record can be created before the beginning of the rapid prototyping method from one or several end data records. 
     After the performance of the rapid prototyping method, the dental prostheses  29  can be completely removed at the frame  27 . While in  FIG. 4  two dental prostheses  29  are shown, the method is in particular advantageous for 50, 100, 150, 200, 250 or even more dental prostheses can be produced together. By the connection of the dental prostheses  29  with a frame  27 , thus even more than 50, more than 100, 150, 200, 250 or more dental prostheses can be together produced and then removed from the rapid prototyping device. Furthermore, all dental prostheses can be together transferred to a milling device as one work piece (see right of  FIG. 4 ). 
     In the right of  FIG. 4 , the work piece finished with the rapid prototyping method is shown. It comprises the frame  27  with the webs  28  which extend to the now completely shaped dental prostheses  29 . The dental prostheses  29  held by the webs  28  can be correspondingly reworked with a milling cutter  20  (in the bottom of  FIG. 4  schematically indicated), as explained above. Other machining methods than milling are also possible. 
     It is advantageous to form a referencing  32  with which the position of the dental prostheses  29  can be determined for the milling procedure. The geometrical relation between the dental prostheses  29  and the referencing  32  are known from the manufacturing data with which the rapid prototyping method is performed. This known relation can be utilized for determining, from the defined positioning of the referencing  32 , the position of the dental prostheses  29 . For referencing, any of various shapes, such as pyramids, cuboids, rectangles, triangles, hemispheres or combinations thereof can be employed. Any characteristic shape suited for defining or identifying the position of the work piece is suited for this. Referencing can be given by a projecting part and/or an indentation (see  FIG. 4 ). In  FIG. 4 , for example, an element  31  of the machine for performing a machining method is shown which can be included in the referencing  32  or on which the referencing  32  can be guided, so that the position of the frame  27  or of the dental prostheses  29  is clearly defined. 
     As it is now possible to position the dental prostheses in a well-defined manner by referencing, the dental prostheses can also be first positioned in an undefined manner, then, however, the position can be determined by means of the referencing. Then, a milling cutter or a corresponding device of a machine for a machining method can correspondingly adjust the position of a correspondingly machining device, e.g. a cutter head. 
     For example, optically detectable shapes or marks can be provided, such as for example hemispheres in a certain geometry or the like, which can be optically easily detected, to then draw a conclusion on the position of the dental prostheses  29  after the detection of the referencing. 
     In  FIG. 4 , clamping jaws  33  with which the frame  27  for the milling procedure can be held are also schematically shown. The frame  27  can also be inserted into a correspondingly prepared supporting frame and subsequently fixed in this position. This is advantageous for the desired stability during the milling process. More than two, three, four or five means for supporting and/or fixing/defining the position of a work piece can also be provided. 
     After the treatment with the milling procedure, the individual dental prostheses are separated from the webs by breaking them out or detaching them. For this purpose, in the rapid prototyping method or milling (or any other machining method), corresponding break-off areas can be provided at the transitions between web or frame and the dental prosthesis. 
     For performing the methods, according to various embodiments of the invention, correspondingly adapted devices can be provided, such as a combined rapid prototyping device with a means for a machining method, such as a milling device or correspondingly equipped computers, e.g. with the mentioned computer-readable media.  FIG. 5  is a schematic of a computer  35  (e.g., processor and memory) for implementing the instructions on the computer-readable medium to perform the various methods of the invention as described herein, including the prototyping method  36  and/or the machining method  37 .