Abstract:
A casting abutment for a dental implant comprising: an apical socket portion, a transition portion bordering coronally on the socket portion, an occlusal portion bordering coronally on the transition portion and having an apical lower rim, wherein the occlusal portion, starting from its lower rim, is provided on its peripheral surface with an area having indentations, whose crests face the transition portion.

Description:
[0001]    The present invention generally provides a casting abutment for a dental implant, preferably made of gold, with an improved connection to a modeling aid. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the art of dental implantology, abutments have become widely known. They are attached to the dental implant which was previously implanted in a patient&#39;s jaw bone. This is normally done by means of a screw joint, wherein torques within the range of 35 Ncm are used to connect the abutment to the dental implant. 
         [0003]    In the manufacturing of a prosthesis, supports are frequently used which facilitate three-dimensional modeling of a precisely fitting dental prosthesis. There is the possibility of direct gating at a pre-formed casting abutment which most of the time consists of a gold alloy. This casting abutment is fixed to the implant or the implant analogue, respectively, by means of a screw. For achieving a clean screw channel during subsequent gating, a support, called in the following modeling aid and made of a plastic which can be burnt out, is plugged onto the casting abutment. This modeling aid can be modified as required. 
         [0004]    For the manufacturing of the dental model, the desired shape of the individual secondary part is formed with a wax in the area of the collar of the casting abutment and the modeling aid, and subsequently a mold for casting is formed around the wax model according to methods well-known in the art. Then the modeling aid and the wax are burnt out for exposing the structure to be produced or the dental model as a die. A well-known method for producing these dies is lost-wax casting, wherein a die is manufactured, the wax is molten out during the casting process and the modeling aid is burnt without any residue. As a further step, a precious metal alloy is cast into this die through a cast channel, whereupon the highly liquid metal is flowing into the die and is attached to the surface of the casting abutment. At the same time, the die produced by the molten wax model is filled with the wax model copy. 
         [0005]    Practice has shown that tightening of the occlusal screw for fixing the casting abutment to the dental model can cause tensions which may lead e.g. to a shift of the modeling aid in the vertical direction. This can cause formation of a gap between the casting abutment and the modeling aid, which gap is filled, during manufacturing of the casting pattern, with the encapsulant surrounding the modeling aid and the casting abutment. During gating, this area is not filled with metal, but remains occupied by the encapsulant so that the finished casting will have a gap, i.e. a casting error. 
         [0006]    From SA-2003/9354, an abutment for dental implants is known wherein a (precious) metal cylinder is arranged on a dental implant, on whose occlusal end a plastic sleeve for manufacturing a socket is fastened. On its side facing the metal cylinder, the sleeve has an inner thread engaging a corresponding outer thread on the abutment for enabling casting of a metal post in the metal cylinder of the abutment and around the metal cylinder and for fixing it to the abutment. For a flawless casting process, the threaded joint must have very close tolerances in order to guarantee a very tight closure. In practice, these close tolerances can be achieved by means of fine threads which are, however, costly and very sensitive to handling. 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, it is an object of the present invention to provide a casting abutment for a dental implant which avoids the above problems. 
         [0008]    Within the framework of this object, a special task of the present invention is to implement a casting abutment for a dental implant which provides an enhanced connection to a modeling aid. 
         [0009]    Furthermore, it is a special object of the present invention to provide a casting abutment for a dental implant which can be produced at a lower cost and with much less expenditure. 
         [0010]    In addition, it is an object of the present invention to simplify assembly of the casting abutment for producing a dental model by means of a modeling carrier. 
         [0011]    Also, it is an object of the present invention to expose the structure of the casting abutment during model production to forces which are as low as possible, or to transmit the forces during processing or modeling as well as possible, so that an employed modeling aid is not displaced from the casting abutment. 
         [0012]    The above and other objects to be found in the following specification are achieved by a casting abutment according to the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Other features and advantages of the present invention as well as the mode of operation of the exemplary embodiment of the present invention are described below with reference to the accompanying drawings which illustrate the present invention and are intended to explain, together with the specification, the principles of the invention and to enable the person skilled in the art to manufacture and use the invention, wherein: 
           [0014]      FIG. 1A  shows a side or approximal view of a casting abutment according to an embodiment of the invention; 
           [0015]      FIG. 1B  shows an approximal view of a casting abutment according to  FIG. 1A ; 
           [0016]      FIG. 1C  shows a top view of the casting abutment according to  FIG. 1A ; 
           [0017]      FIG. 2A  shows an approximal view of a modeling aid according to  FIG. 1A ; 
           [0018]      FIG. 2B  shows a view of the modeling aid according to  FIG. 2A  from below at an angle; 
           [0019]      FIG. 2C  shows a top view of the modeling aid according to  FIG. 2A ; 
           [0020]      FIG. 3  shows a side or approximal view of the casting abutment according to the invention with the modeling aid forced onto the abutment. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    With reference to  FIGS. 1A through 1C , a currently preferred embodiment of the casting abutment for a dental implant according to the present invention will be described. The casting abutment generally designated by reference number  1  has a socket portion  2  adapted to be received in a dental implant (not shown). The person skilled in the art will appreciate that the socket portion  2  has profiled areas in order to guarantee a precise fit or rotational securing of the casting abutment  1  with the implant. Moreover, the casting abutment  1 , as known in the art, is provided with a through bore  3  adapted for receiving an occlusal screw (also not shown) to secure the casting abutment  1  to the dental implant fixed inside the jaw bone. During modeling of the dental model, the screw can further be used to fix the model on a modeling carrier (not shown) for machining. In the latter case, the screw is passed through the cylindrical bore  16  in the modeling aid  11  and screwed to the modeling carrier. 
         [0022]    The socket portion  2  of the casting abutment  1  borders on a circular symmetric transition portion  4  which is preferably provided as a truncated cone. The transition portion  4  borders on an area  5  which, in the view shown in  FIG. 1A , is provided with a planar rim  6 . 
         [0023]    The area designated by reference number  5  borders on a circular symmetric occlusal portion  7  of the casting abutment  1 , a planar collar area  12  of even width being present between the planar rim  6  of the area  5  and the lower rim  8  of the circular symmetric occlusal portion  7 , as can be clearly seen in  FIG. 1B . The area of the occlusal portion  7  which borders on the lower rim  8  has, on its cylindrical outer surface, a plurality of stripe shaped or ring shaped indentations or tine like formations  10 , which extend over an area of preferably approximately 75% of the cylinder area of the occlusal portion  7 . Directly bordering on this, up to the upper rim  9 , the surface of the occlusal portion  7  is smooth, permitting an easy placement of the modeling aid  11 . The indentations  10 , which are inclined downwards at an angle of preferably approximately 80° to the horizontal axis and whose ends form crests  15  facing the planar collar area  12 , make it possible to force on a modeling aid  11  non-positively and tightly. During manufacturing of the dental model, the downwardly inclined crests  15  of the indentations  10  prevent a displacement or detachment of the modeling aid  11 . 
         [0024]      FIG. 2A  shows the cylindrical modeling aid  11  which consists of combustible plastics and can be employed advantageously in combination with the casting abutment according to the invention. The modeling aid  11  has a smooth through bore  16  (see  FIG. 2C ) forming a channel for passing through the screw (not shown) which, after the dental model has been completed, is fastened to the patient&#39;s dental implant fixed inside the jaw bone. Inside the bore  16  which is designed to be plugged onto the casting abutment, a stop  17  is provided which, as shown in  FIG. 2B , limits the distance a modeling aid  11  can be forced onto the cylindrical occlusal portion  7  when the stop  17  contacts the upper rim  9  of the casting abutment. Thus, advantageously, only a limited area  13  of the bore  16  of the modeling aid  11  is available for non-positive connection with the indentations  10 , as is subsequently explained with reference to  FIG. 3 . 
         [0025]    As explained above, the occlusal portion  7  of the casting abutment is cylindrical and has indentations  10 , and therefore, according to the invention, a modeling aid  11  can be pressed on without any other aid. This enables manufacturing of casting abutments and modeling aids and prefabrication on a large scale. 
         [0026]    According to the invention the tensions during modeling and manufacturing of the tooth, which are applied to the casting abutment and the modeling aid, do not lead to a shifting or sliding of the modeling aid. 
         [0027]    Moreover, the invention produces an even and positive engagement between the collar area  12  of the casting abutment and the modeling aid  11 , therefore preventing, after the casting process, a tedious and time-consuming finishing of the model which could even lead to destruction of the model. 
         [0028]      FIG. 3  is a representation of a casting abutment with a forced-on modeling aid such as is used for manufacturing a dental model on a modeling carrier (not shown). When the modeling aid is pressed on, the distance surrounding the occlusal portion  7  of the casting abutment is limited by the stop  17  shown in  FIG. 2B , creating a gap A between the lower edge  14  of the modeling aid and the collar area  12  of the casting abutment. This gap ensures good adhesion of the molding wax. 
         [0029]    In particular, it has been noted in trials in connection with the gap A that an omission of the area between the collar area  12  of the casting abutment and the lower edge  14  of the plugged-on modeling aid  11 , as shown in  FIG. 3 , can lead to an improvement of the quality and attachment of a precious metal applied in a gating process, preferably gold or highly precious alloys. This is due to the fact that during the gating process, the wax directly in contact with the casting abutment within the area of gap A is burnt out faster than the plastics of the modeling aid  11  so that gap A provides a space within which the heated plastics, which tends to swell up, can spread out. This minimizes tensions and cracks in the encapsulant or the mold and, consequently, flaws in the finished precious metal casting. In addition, even at the beginning of the gating process, the precious metal can penetrate at the casting abutment or casting abutment collar and establish contact with the same. Thus, the previously mentioned design of the modeling aid offers special advantages during the gating process for a precious metal. 
         [0030]    Another advantage consists in that the total thickness of the molded wax can be lower within the area of gap A because of the missing modeling aid  11  since only the wax is present in this area. Therefore, the precious metal casting may be slimmer in the area of gap A, which leaves more room for subsequent formation of the dental prosthesis. 
         [0031]    Although the invention has been described in connection with a one-piece casting abutment, the person skilled in the art will readily understand that it also applies to two-piece casting abutments, with naturally the same advantages being achieved as in connection with a one-piece casting abutment. 
         [0032]    The disclosures in EPA No. 06123857.2 from which this application claims priority are incorporated herein by reference.