Abstract:
Described herein is a dental precision model for the odontotechnical field of the type constituted by a model ( 5 ) reproducing the denture ( 6 ) associated to a base ( 2 ) provided with means for referencing ( 13 ) and positioning ( 14  and  15 ) the model ( 5 ) and the denture ( 6 ) that the model reproduces; the model is provided with elements ( 4, 26 ) arranged in positions corresponding to the teeth to be worked on, and the base ( 2 ) carries seats ( 16, 27 ) for housing the teeth ( 6 ) and elements ( 4, 26 ) associated thereto; the elements ( 4, 26 ) and the seats ( 16, 27 ) being made of a material such as to exert a magnetic force of mutual attraction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The subject of the invention consists in improvements to dental precision models in the odontotechnical field.  
         [0002]     Known in the odontotechnical sector are various types of techniques for constructing precision models. The methods most widely used envisage that the base of the model is made of a gypsum (less advanced technology) or of Teflon/plastic (more advanced technique and actual state of the art).  
         [0003]     The method with the gypsum base first of all envisages casting of the impression; once the gypsum has hardened, the model is removed from the impression and is then squared, taking care that the bottom part of the model is as smooth as possible. Next, using a machine referred to as pin drill, drillings are made at the base of the model in the parts that will then have to be divided by the operation of sectioning.  
         [0004]     Once the holes are completed, conical or cylindrical pins are glued with an adhesive product such as cyano-acrylate. At this point, insulation of the base and of the pins with the aid of a special oil is performed.  
         [0005]     Next, the dental arch is positioned in the base-socket-mould former, after which the gypsum is poured into it until it reaches the base of the model. When the gypsum has hardened, the model is thus completed, and the parts concerned can be sectioned.  
         [0006]     This system envisages an excessively long working cycle for the construction of the model. In addition, a considerable amount of gypsum is used, and there is the risk that two different rates of expansion of the gypsum (model and base of the model) will occur. Also the use of purposely designed pin-drilling machinery entails the need for operations of maintenance of the machine and milling thereof. Finally, the system also involves the use of a large amount of glue and of insulator.  
       SUMMARY OF THE INVENTION  
       [0007]     The method that uses a Teflon/plastic base envisages positioning of the impression on a metal base with the aid of plasticine. The Teflon plate is positioned in the bottom part of the metal base and, thanks to a centring system, remains set perfectly underneath the impression previously positioned.  
         [0008]     At this point, machining is performed using machinery for drilling the Teflon plate in the parts that will then have to be divided by the sectioning operation. The plate thus drilled is extracted from the metal base, and the conical pins are positioned in the holes that have been made.  
         [0009]     Next, casting of the impression still positioned on the metal base is carried out, after which, thanks to the guides present thereon, the Teflon plate containing the inserted pins is rested to form a cap. When the gypsum has hardened, after approximately 30 minutes, the model is ready to be sectioned. This system envisages a reduced number of steps as compared to the previous system, entails a reduced use of gypsum, does not require use of glues and insulating agents, is not affected by two different rates of expansion of the gypsum, and a greater precision is noted in the completed model.  
         [0010]     Also this system presents, however, considerable disadvantages.  
         [0011]     First of all, the Teflon plate can be used just once or at the most twice. As for the system previously mentioned, there are problems of maintenance regarding the machinery used, taking into account that this is much more costly (approximately twice as much) as compared to the previous technique. Then, in order to check articulation, the system requires a further plate containing a magnet, and if the model is cleaned with a steam sterilizer there is the risk of distorting the plate slightly.  
         [0012]     Finally, an excessive attention is required when the gypsum is poured into the impression to prevent displacement thereof from its original position on the metal base with the plasticine; otherwise, the pins will then be off centre.  
         [0013]     There also exists a third system described in the U.S. Pat. No. 4,767,330, which consists in creating a model which, at the bottom, is rendered fixed to a support made of plastic material mixed with a powder of magnetic or magnetizable material. The base plate is provided with a rail indented on the external surfaces so as to form referencing means for positioning and centring of the support of the model that is applied on the base. A magnetized strip is embedded in the rail to bring about magnetic adherence of the support to the rail itself.  
         [0014]     Cutting from the model of the tooth corresponding to the one being treated is carried out together with the underlying supporting stretch.  
         [0015]     This latter system involves different processing steps, such as casting of the impression and polishing thereof, pouring of the support and polishing thereof, gluing together of the impression and of the support with possible risks of imprecision. In addition, since the models are made of two different materials, i.e., that of the impression and that of the support, there are risks of different rates of expansion of the two objects with the consequent risk of deformations that have repercussions on re-positioning of the tooth on which work has been carried out.  
         [0016]     The step of gluing of the impression and of the support is very delicate and, in the even of them coming apart during the step of selection of the teeth in question or during a step of milling thereof, it would be impossible to restore the original position of the two items with respect to one another.  
         [0017]     A further serious drawback of this system depends upon the fact that, since the support is entirely magnetized and faces a strip of the metal base which is also entirely magnetized, there can arise problems of reversal of polarity in the teeth sectioned from the model, a fact that causes repulsion of the teeth by the base instead of adhesion on said base.  
         [0018]     The dental model proposed by the present invention arises from the frequent need to find a practical, precise, fast and inexpensive solution for creating dental models, which is the starting point of any type of odontotechnical operation.  
         [0019]     In order to achieve this purpose, the invention proposes creation of a reference base, preferably but not necessarily made of metal, with characteristics for conveniently enabling mass production, which bears a complex toothed profile in relief having the shape of a dental arch, said profile constituting the precise reference for future positioning of the dental model either completely or partially. The dental model will have inside it magnets, which, by exerting a mutual action of attraction on the surface of the metal base, will keep the model in a position constrained thereto; the shape of the relief, which may vary, present on the base will prevent movements in the other two directions of the plane.  
         [0020]     The method according to the invention provides the master dental model made of gypsum or equivalent compound with parts that can be sectioned and can be slid out from a metal base.  
         [0021]     For the above and further purposes that will be understood more clearly from what follows the invention proposes dental precision models for the odontotechnical field according to claim  1 . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The dental model according to the invention will now be described in two preferred embodiments thereof with reference to the annexed plate of drawings, in which:  
         [0023]      FIGS. 1 and 2  represent respectively the dental impression with the base of the model and the equipment that is used in a first embodiment of the invention;  
         [0024]      FIG. 3  illustrates the dental model and the base according to the invention in its first embodiment;  
         [0025]      FIG. 4  is a portion of the base of  FIG. 3 ;  
         [0026]      FIG. 5  is the cross section V-V of  FIG. 4 ;  
         [0027]      FIG. 6  illustrates the base of  FIG. 3  in a second embodiment of the invention;  
         [0028]      FIG. 7  is a cross section according to the trace VII-VII of  FIG. 6 ;  
         [0029]      FIG. 8  is the view of a detail of  FIG. 6 ; and  
         [0030]      FIGS. 9 and 10  are enlarged views of the detail A of  FIG. 7  in two different operating conditions. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     With initial reference to the embodiment of  FIGS. 1-5 , the method with which the device according to the invention is obtained is described in what follows.  
         [0032]     Once the dental impression  1  has been taken, it is located in a centring device, and a base  2 , which is usually but not necessarily made of metal and is shaped like a dental arch and at the centre of which there is a structure  3  with a complex profile in relief, is aligned in a centring device aligned to the first device (see  FIGS. 1 and 2 ). The structure  3  will be defined more clearly hereinafter.  
         [0033]     Elements  4 , in the form of pins made of magnetized material, which consequently will be referred to hereinafter as magnets, are pre-installed in purposely provided seats made in the structure  3  of the metal base, in positions corresponding to the centre (see  FIGS. 4 and 5 ) of each part (tooth) which needs to be sectioned in order to carry out work thereon, with the aid of a pointing system  7  (laser or the like) moving along the axes x and y. In the plane of lie of the cast, the pointing system  7  identifies the point of correspondence between the tooth and the slot on the base  2  in which a magnet  4  is to be positioned. The system envisages two pointing beams (see  FIG. 2 ), one of which  8  indicates the part of the impression to be worked on and the other  9  the area of the toothed base where the magnets  4  are to be positioned. A reflection system  10  can be used for governing the pointing beams. This operation is repeated for all the teeth or parts concerned.  
         [0034]     At this point, the gypsum is poured into the impression  1  and over all the top surface of the metal base  2 , on which the magnets  4  have been pre-installed, in an appropriate position to enable temporary joining of the gypsum-cast impression  1  to the metal base: with the gypsum still plastic the base is turned over so as to be superimposed precisely on the impression. The gypsum cast is, thus, at the centre of the sandwich between the impression and the base and, once it has hardened, comes to form the dental model  5 . The magnets  4  attached thereto remain englobed in the gypsum still in the plastic phase of the model (see  FIGS. 4 and 5 ).  
         [0035]     When the gypsum has hardened, the device for impressions  1  and the coupled metal base  2  are removed, and the impression is removed from the hardened gypsum, after which removal from the metal base is performed, possibly with the aid of an extractor system.  
         [0036]     Once the dental model  5  is obtained (see  FIG. 6 ), sectioning  6  thereof is carried out according to the working requirements.  
         [0037]     Once work has been completed, the sectioned gypsum model  6  is re-positioned on the metal base  2 , the correct position of which is determined (see  FIG. 3 ) by the structure  3 , and in particular by its double side rack  14  and  15 , and by the presence of a numbering  13  at its side. Sealing is instead ensured by the presence of the metal magnet  4  embedded in the sectioned gypsum  6  (see  FIG. 5 ), which comes to be housed in the corresponding seat  16  ( FIG. 3 ) of a guide  17  set between the racks  14  and  15  of the structure  3 .  
         [0038]     The embodiment now described envisages that the elements  4  are magnetic and the guide  17  is simply made of (ferromagnetic) metal so that the magnets  4  adhere by magnetic force in the seats  16  of the guide  17 . It is clear, however, that the invention also envisages the reverse condition, namely, the one in which the elements  4  are made of metal, for example of ferromagnetic material, and the guide  17  is magnetized or else that both the elements and the guide are magnetized with opposite polarities. The effect of adhesion of the elements  4  on the seats  16  of the guide  17  is obviously once again the same.  
         [0039]     The invention envisages the possibility of unlimited re-use of the base and does not require further plates for checking articulation of the model. In addition, the system involves very little maintenance for the machinery in so far as there is no milling. An excellent centring device is obtained in so far as no plasticine is used, nor are glues or insulating agents used and, in the case of cleaning with a steam sterilizer, the base is not modified.  
         [0040]     The embodiment illustrated in  FIGS. 6-10  has the purpose of avoiding the step of centring of the impression, which in the previous embodiment is illustrated with reference to  FIGS. 1 and 2 .  
         [0041]     This solution envisages that the space between the racks  14  and  15  of the structure  3  (see  FIG. 3 ) of the base  2  will be left empty, i.e., that the guide  17  and the corresponding seats  16  are not provided.  
         [0042]     In its place, a plastic element  20  is inserted, of a shape such as to copy the seat, now empty, comprised between the racks  14  and  15 . The plastic element  20 , as may be noted more clearly in  FIGS. 9 and 10  has a substantially C-shaped or horse-shoe cross section provided on the outside and at the top with a protuberance  21  with lateral undercuts  22 . In the internal part, i.e., the one comprised between the side walls  25 , the element  20  is hollow, and the cavity  23  has the intermediate portion  24  of restricted width as compared to the rest.  
         [0043]     Using this solution, the procedure is the one described in what follows.  
         [0044]     The gypsum is poured into the impression  1  (see  FIG. 1 ) and over all the top surface of the base  2  on which the plastic element  20  has been pre-installed.  
         [0045]     With the gypsum still plastic, the impression  1  is turned over until it comes to be superimposed precisely on the base  2 . The gypsum thus cast is consequently located at the centre of a sandwich between the impression  1  and the base  2  and, once it has hardened, comes to form the dental impression  5  (see  FIG. 3 ).  
         [0046]     At this point, the impression  1  is detached from the ensemble, so bringing to light the dental model  5 , which will have inside it, visible from the underside, the plastic element  20  that remains fixed to the model in so far as the gypsum has filled the undercuts  22  of the appendage  21  and, since only the plastic element rests on the base  2 , nothing stops this separating from the base itself in order to remain fixed to the model  5 .  
         [0047]     Identified on the scale  13  of the base are references of the teeth of the model that are to be worked on; then the model  5  is separated also from the base.  
         [0048]     Now, it only remains to section the tooth  6  (see  FIG. 3 ) to be worked on and to insert a pin  26  of magnetic material into the empty seat of the stretch of plastic element  20  that remains embedded in the tooth  6 .  
         [0049]     The pin  26  will have a shape designed to copy the walls  23  and  24  of the seat of the element  20  to prevent it from possibly accidentally sliding out.  
         [0050]     Once this operation is completed, the tooth  6  may be positioned on the metal base  2  in the seat  27  between the racks  14  and  15  in the position previously defined on the graduated scale  13 , i.e., in the exact relative position.  
         [0051]     Also this second embodiment now described envisages that the elements  26  are magnetic and the seat  27  is simply made of (ferromagnetic) metal so that the magnets  26  adhere by magnetic force in the seat  27  between the racks  14  and  15 . It is clear, however, that the invention also envisages the reverse condition, namely, the one in which the elements  26  are made of metal, for example ferromagnetic material, and the seat  27  is magnetized or else that both the elements and the guide are magnetized with opposite polarities; the effect of adhesion of the elements  26  on the seat  27  is obviously once again the same.