Positioning stud for master models
BACKGROUND OF THE INVENTION 
     The present invention relates to positioning studs for master models for dental prostheses and the like. 
     Conventionally, positioning studs which are used are simple smooth shanks. The shanks are adapted and placed in holes, which correspond to the model, by using an adhesive or glue. This requires that the adhesive be very fast-drying to ensure that the adhesive secures completely and quickly and that great care be taken when placing the positioning studs in the holes so that they do not slant. This implies a combination of special care, speed and accuracy, which are difficult to combine. Therefore, there will always be disadvantages in using smooth shanks, which are normally utilized. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an easy-to-place positioning stud which is accurate and overcomes the difficulties in using conventional positioning studs. The stud has a threaded area, limited from the rest of the stud by a small boss. The stud is intended to be inserted mechanically into a hole previously made in the model and does not need any type of glue. The stud is perfectly secured and leaves the rest of the stud, which is a smooth shank, to remain in its proper place. The end of the shank is shaped like a tongue or groove to assist with the screwing of the shank by a respectively auxiliary tool, which is applied to the tongue or groove. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The positioning stud for master models of the present invention will be described in detail, with reference to the attached drawing which shows a preferred form of embodiment of the invention. The preferred form is simply by way of example and is not limiting, but is subject to any variations in detail which do not involve a fundamental alteration of its essential features. 
     FIG. 1 is an elevational plan view of a stud with a groove at the free end of the stud. 
     FIG. 2 is an elevational plan view of between projected areas taken from the left or right of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show a positioning stud for master models that comprises a cylindrical body with a suitable diameter. About one third of the length of the body 1 is provided with a threaded area 2, which is specifically designed for each particular application. A boss 3 separates the threaded area 2 from the smooth area 1. The boss has a slightly larger diameter than the stud so that it forms a stop when inserted. The end of the smooth area 1 forms a diametrical groove 4 (FIG. 1) 5 (FIG. 2) or any other shape, such as a star, for example, where the suitable auxiliary screwing tool fits. 
     The stud made in this way is placed in the base of a plaster positive, in which holes have previously been made. The holes have a suitable diameter for enabling the threaded area 2 to be inserted in them by means of the screw pitch of the threaded area. In this manner, the plaster positive is perfectly secured to the stud by a screw threaded system without the presence of any type of glue whatsoever. 
     After the studs 1 have been placed in the plaster positive, the respective parts corresponding to the model concerned in each case are fitted on the smooth area 1. Advantages of the invention include eliminating the need for glues, ensuring a perfectly secure fit by screwing, and enabling the possibility of removing the studs by unscrewing when required for use elsewhere. Conventional studs at present cannot be re-used, because they are secured by glues and their point of application cannot be corrected once in place. 
     The shape, materials and dimensions may be varied and accessories added provided this does not alter, change or modify the essential nature of the present invention.