Abstract:
The invention relates to a method for establishing a releasable connection between a tool connection or coupling piece, which is formed on a dental handpiece, and the tool shank of a dental hand instrument. In order to connect a journal-like fastening section, which tapers toward a free end, on one of the elements to be connected, is inserted into an opening while matching the same, which is adapted to this section, on the other of the elements to be connected.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method of releasably connecting a tool to a dental handpiece and the connection between the tool and the dental handpiece. 
         [0002]    Especially for dental ultrasonic instruments or handpieces, the fastening of the respective tool (instrument tip) to the instrument or handpiece is problematic, since the transfer of the ultrasonic energy to the tool is maintained to the required degree only by means of an absolutely rigid connection of the tool to the connecting or coupling element of the instrument or handpiece. For this reason it has been standard practice in the past to implement the connection between the ultrasonic instrument or handpiece and the tool as a screw connection, which makes the process of connecting and releasing the tool unnecessarily complicated and time-consuming. 
         [0003]    It is an object of the invention is to provide a method that enables an absolutely rigid connection of a tool to a instrument or handpiece. 
       SUMMARY OF THE INVENTION 
       [0004]    The adhesion between the dental instrument or handpiece and the tool and therefore in particular also the connection between the instrument or handpiece and the tool or tool shaft required for transfer of the ultrasonic energy is achieved by at least one journal-shaped mounting section that is tapered toward the free end, for example by a cone. The tool can be secured on the instrument or handpiece in a wide variety of manners, for example purely mechanically, e.g. through the connection of overlapping securing elements, by a bayonet-type connection and/or threaded interlocking, through a conical thread, by which locking takes place by turning by a maximum angle of 200°, preferably only by an angle of 120° or 180°, etc. 
         [0005]    The tool can also be secured by form-changing elements, in particular also such elements that change their form under the influence of a magnetic field, through temperature influences, etc., for example elements that change their form by a bi-metal effect as a result of temperature influences. Further, such elements can also be used to increase the pressing forces in the connecting area and/or to change the angle of the taper. 
         [0006]    To secure and/or increase the anchoring and pressing forces between the surfaces adjoining each other in the area of the connection and/or to improve the transfer of the ultrasonic energy, chemical means can also be used, for example chemical surface treatment, adhesive means, including films or glues, the use of fluids, in particular also such fluids with controllable viscosity and/or adhesive force and/or otherwise changeable chemical and/or physical properties. 
         [0007]    Further, measures are preferably taken to achieve a torsionally rigid connection and/or a connection between the tool and the hand instrument that ensures a defined positioning of the tool on the instrument or handpiece. This can be achieved, for example, by making the connection by means of several projections or fastening or coupling sections that are tapered toward the end and/or by the at least one journal-shaped tapered fastening section having a profile that deviates from the circular form at least on a partial length, namely with an accordingly adapted seat or opening. This can be achieved, for example, by providing the at least one journal-shaped fastening section with at least one groove extending in the longitudinal direction of said section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention is described in more detail below based on exemplary embodiments, in which: 
           [0009]      FIGS. 1 &amp; 2  each show a schematic representation as a partial section of a instrument or handpiece coupling element, together with a dental tool fastened to said coupling element; 
           [0010]      FIG. 3  shows a similar depiction as in  FIG. 1 , however in a further embodiment; 
           [0011]      FIG. 4-9  show very schematic depictions of further embodiments of the invention; 
           [0012]      FIG. 10  shows a front view of the coupling section of the connection of  FIG. 9 ; and 
           [0013]      FIG. 11  shows a cross section through the coupling section of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  shows a coupling element  1  provided or formed on a dental instrument or handpiece for connecting a dental tool, of which  FIG. 1  shows only the shaft  2  and which comprises an electro-mechanical vibration generator, for example for generating vibrations between 5 and 10 kHz or also preferably in the ultrasonic range. 
         [0015]    The coupling element  1  is accordingly the resonant body of an ultrasonic instrument or handpiece, which is driven by an electro-mechanical converter, for example by a magnetostrictive converter for an oscillating motion in the ultrasonic range, accommodated in the instrument or handpiece. 
         [0016]    The coupling element comprises an opening  3  that is open toward a front side of said coupling element and arranged on the same axis or not on the same axis with the coupling element which is for example cylindrical on its outer surface, which (opening) starting from the open side toward the closed end is tapered slightly conically, and the cone angle α/2 depicted exaggeratedly in  FIG. 1  is between 0.01 and 8 degrees, preferably between about 0.5 and 2 degrees. On the end to be connected to the coupling element  1  the tool shaft  2  is provided with a likewise tapered section  2 . 1 , which is adapted to fit the opening  3  with regard to diameter, taper angle, etc., so that the tool shaft  2  is held so that it fits in the opening  3 , in particular also if the coupling element  1  made of metal and the tool shaft  2 , likewise made for example of metal or ceramic, both have the same temperature. The size of the cone angle is adapted for example to the frequency of the vibration generator and is also dependent on the materials used. 
         [0017]    With the small taper angle α and cone angle α/2, the connection between the coupling element  1  and the tool or tool shaft  2  is possible by inserting the coupling section  2 . 1  into the opening  3 , without danger of the section  2 . 1  slipping axially out of the opening  3  during operation. 
         [0018]    The axial length of the cone surfaces used for the connection, i.e. the axial length of the coupling section  2 . 1  and also the axial length of the opening  3  accommodating said coupling section is at least 0.5 mm and not greater than 15 mm, for example. This makes it possible for these cone surfaces to be interrupted by shoulders, so that the axial total length of the individual cone surfaces corresponds to the total of the aforementioned values. 
         [0019]    The cone surfaces to be connected with each other are surface-treated in a suitable manner, namely polished for example, e.g. high-gloss polished, so that the cone surfaces to be connected with each other, i.e. the cone surface of the coupling section  2 . 1  and the cone surface or inner surface of the opening  3  are designed so that they match very exactly. The cone surfaces in this regard are for example high-gloss polished and/or rolled, in which case not only a high-precision fit is achieved, but also a compression of the material on the cone surfaces at least in the surface area. 
         [0020]    In principle, it is also possible to profile the opening  3  and/or the section  2 . 1  on their taper surfaces in a suitable manner, which for example can be achieved by roughening of the surface, by coating the surfaces with suitable materials that produce surface roughness, for example also with nano-technology and/or by producing grooves, recesses, etc. in the surfaces. 
         [0021]    The roughness likewise depends on the frequency of the electromagnetic vibration generator and/or the materials used and/or the special design of the tool between 0.01 μm and 100 μm, while a wide variety of ranges of roughness are possible in combination, e.g. between 0.01 and 0.1 μm, between 0.1 and 1.0 μm, between 1.0 and 5 μm, between 5.0 and 20 μm and between 20 and 100 μm. 
         [0022]    For the use of the tool shaft  2  with a coupling element  1 , said coupling element or its opening  3  can be expanded according to a special embodiment of the invention by heating, so that after inserting the section  2 . 1  into the opening  3  and after the return of the coupling element  1  by cooling to the normal condition of the tool shaft  2 , the entire tool is connected especially rigidly with the coupling element  1 . 
         [0023]    The expansion of the coupling element  3  and of the opening there is achieved by heating the coupling element  1 , for example with ultrasound, through an electromagnetic coil  4  enclosing the coupling element  1  and generating an induction current in the coupling element  1  or through a heating coil enclosing the coupling element. 
         [0024]    A material is then preferably used for the coupling element  1  that differs from the material of the coupling element  2 . 1  and has the maximum possible temperature expansion coefficient. To prevent the tool from being inserted too deep, a depth stop controls the final position. 
         [0025]    The absolutely rigid seat of the tool shaft  2  in the coupling element  1  ensures optimum transfer of the ultrasonic energy from the instrument or handpiece to the tool connected with said instrument or handpiece, especially when the instrument or handpiece is designed as an ultrasonic instrument or handpiece. 
         [0026]    To release the tool  2  or the coupling section  2 . 1  from the opening  3 , the coupling element  1  is again heated. To ensure reliable release during this heating the coupling element  1  is made of a material having a higher heat expansion coefficient than the material of the shaft  2  or of the coupling section  2 . 1 . 
         [0027]      FIG. 2  shows as a possible embodiment a coupling element  1   a , which differs from the coupling element  1  essentially in that the opening  3  is provided on its open side with a catch  5 , namely in the depicted embodiment in the form of a ring-shaped projection concentrically enclosing the axis of the opening  3 . The coupling section  2 . 1   a  of the tool shaft  2   a  in this embodiment is provided with a ring-shaped collar  6 , which is engaged by the catch  5  when the tool or tool shaft  2   a  is fastened in the coupling element  1   a . In this embodiment also the coupling element of the opening  3  is expanded by heating for connecting the shaft  2   a , so that the coupling section  2 . 1   a  with the collar  6  can be pushed over the catch  5 . After cooling of the coupling element  1   a  the coupling section  2 . 1   a  is not only anchored positively and rigidly in the opening  3 , but is also additionally secured by the catch  5  engaging the collar  6 . 
         [0028]      FIG. 3  shows as a further possible embodiment a instrument or handpiece coupling element  1   b  on which a tapered projection  7  is provided on which the respective tool can be placed with its tool shaft  2   b  or with an opening  8  there that is adapted to the shape and size of the projection  7 . In this embodiment the tool or the tool shaft  2   b  is heated prior to fastening, therefore enlarging the opening  8 , so that after cooling, an absolutely rigid connection between the tool and the coupling element  1   b  is achieved by shrinking. To remove the tool, the tool shaft  2   b  is again heated to expand the opening  8 , so that the tool can then be removed from the coupling element or the projection  7 . 
         [0029]    In the embodiment of  FIG. 3  the previously described means for additional axial securing, for example roughening of the contacting surfaces between the coupling element and the tool shaft  2   b , additional catches, etc. can likewise be provided. 
         [0030]      FIG. 4  shows in a very simplified schematic depiction and in side view the instrument or handpiece coupling element  1   c  together with the tool shaft  2   c  releasably fastened to said coupling element. To secure the tool shaft  2   c  and therefore the tool on the instrument or handpiece a securing hook  9  is provided which bridges the connecting area between the coupling element  1   c  and the tool shaft  2   c , i.e. on the one hand is held on the tool shaft  2   c , for example so that it can pivot, and on the other hand positively engages with its other end, in secured state, the coupling element  1   c , for example in the area of a ring-shaped bulge  10 . 
         [0031]      FIG. 5  again shows, in a depiction similar to  FIG. 4 , the coupling element  1   c  and the tool shaft  2   c , together with a partial view of a pressing tool  11 . The pressing tool is designed for example similarly to the securing hook  9 , so that this pressing tool  11  applied to the tool shaft  2   c  engages with the bulge  10  with a partial surface or with a section  11 . 1  to press the tool shaft or the coupling section of said tool shaft into the opening of the coupling element  1   c , so that when the pressing tool  11  is moved in the direction of the axis of the coupling element in the tool shaft  2   c  is pressed corresponding to arrow B into the opening of the coupling element. Further, a tool  12  for releasing the tool shaft  2   c  from the coupling element  1   c  is depicted. This tool  12  likewise engages with the section  12 . 1  with the bulge  10 , in this case with the side of the bulge  10  facing the tool shaft  2   c , so that when the section  12 . 1  is moved corresponding to arrow D in the direction of the arrow C, i.e. in the direction of the axis of the coupling element  1   c  along the bulge  10 , a force is exerted for releasing the tool shaft  2   c.    
         [0032]      FIG. 6  shows an embodiment in which the transition between the coupling element  1   d  and the tool shaft  2   d  is covered by a sleeve  13  made of a rubber elastic material, for example by a silicon sleeve  13 . To release the tool shaft  2   d  from the coupling element  1   d , an axially moveable ram  14  is provided in said coupling element, which (ram) can be moved via a manually controllable slide  15  provided on the outer surface of the coupling element  1   d , so that said ram  14  is moved into the opening  3  of the coupling element  1   d , therefore releasing the tool shaft  2   d  from the coupling element. 
         [0033]      FIG. 7  shows an embodiment in which the releasable connection between the coupling element  1   e  and the tool shaft  2   e  is achieved by a coupling section  2   e . 1 , which likewise is formed by a tapered projection  16 , and by several further coupling sections  2   e . 2 , which likewise are formed by tapered projections  17 . The projections  17  are radially offset from the projection  16  and provided in a distributed array around the projection  16 . The projection  16  corresponds to a tapered opening  8  adapted to the shape of said projection on the coupling element  1   e  and each projection  17  corresponds to an opening  8 . 1  adapted to the shape of said projection. The projection  17  and the corresponding openings  8 . 1  enable a torsionally rigid connection between the tool shaft  2   e  and the coupling element  1   e , said connection being exactly oriented with respect to the angular position on the axis of the journal  16 . 
         [0034]      FIG. 8  shows an embodiment in which a front-side extension  21  is provided on the coupling section  2   f . 1 , likewise formed by a tapered projection or journal  20 , which (extension) exhibits a cross section deviating from circular and to which a recess  23  corresponds on the bottom of the opening  22  adapted to the form of the journal  20 . The cross section of the recess  23  is adapted to the cross section of the extension  21 , so that a connection between the tool shaft  2   f  and the coupling element  1   f  is possible only in one or more pre-defined angular positions. 
         [0035]      FIGS. 9 and 10  show an embodiment in which the coupling section  2   g . 1  is likewise formed by a tapered journal  25 , which comprises on its circumferential or peripheral surface several grooves  26 , each extending in a surface line. A recess or opening  27  is provided in the coupling element  1   g , the shape of which (opening) is adapted to the shape of the journal  25 , i.e. likewise tapered and comprising projections  28  that fit into the grooves  26 . 
         [0036]    In principle it is possible with this embodiment to provide grooves instead of projections  28  in the recess  27 , into which (grooves) projections engage that are provided instead of the grooves  26  on the coupling section  2 . 1   g . The grooves and the projections adapted to said grooves produce a torsionally rigid connection between the instrument or handpiece or coupling element  1   g  and the tool shaft  2   g . The distribution of the grooves  26  and the projections  28  also enables coding, e.g. in the form that the tool can be fastened in the instrument or handpiece only in a pre-defined position, and this position can differ from tool to tool or from tool type to tool type, and/or that only certain tools can be used on a instrument or handpiece. 
         [0037]      FIG. 11  shows a very schematic depiction of a cross section through a journal  24  forming a coupling element, which (journal) although likewise tapered toward its free end, is not rotationally symmetrical to a journal axis, so that this journal form alone and the corresponding form of the corresponding opening receiving the journal  24  when connected can achieve a torsionally rigid releasable connection between the coupling element on the instrument or handpiece and the tool shaft, in addition to a unique angular position. 
         [0038]    The invention was described above based on exemplary embodiments. It goes without saying that numerous modifications and variations are possible without abandoning the underlying inventive idea on which the invention is based. Especially for such tools which can be operated under pressure, even with a larger taper angle α, additional means for axially securing the connection between the tool and the coupling element are not necessary. 
         [0039]    Further, it is also possible, instead of the described means for additional axial securing of the connection or in addition to these means, to provide mechanical locking means, which in secured state engage with a surface on the respective tool shaft and therefore prevent the release of the tool shaft from the coupling element. 
       REFERENCE LIST 
       [0000]    
       
           1 ,  1   a ,  1   b ,  1   c ,  1   d ,  1   e ,  1   f ,  1   g  coupling element 
           2 ,  2   a ,  2   b ,  2   c ,  2   d ,  2   e ,  2   f ,  2   g  tool shaft 
           2 . 1 ,  2 . 1   a ,  2 . 1   e ,  2 . 1   f ,  2 . 1   g  coupling section 
           3  opening 
           4  electric coil 
           5  catch 
           6  collar 
           7  projection 
           8  opening 
           9  securing tool 
           10  bulge 
           11  pressing tool 
           11 . 1  tool section 
           12  releasing tool 
           12 . 1  tool section 
           13  covering sleeve 
           14  ram 
           15  slide 
           16 ,  17  projection or journal 
           18 ,  19  opening 
           20  projection or journal 
           21  journal extension 
           22  opening 
           23  recess 
           24 ,  25  projection or journal 
           26  groove 
           27  opening 
           28  projection 
         A, C movement of the tool 
         B, D direction of force