Abstract:
A holding device that can be braced in a surveying machining together with an individual preparation model produced by dental laboratory techniques. The holding device has a mechanically stable frame with bores disposed at a distance (a) to one another, in which at least two holding pins are locked that can be displaced at least in the axial direction (A).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation application of co-pending application Ser. No. 10/433,876 which was filed on Jun. 3, 2003 entitled HOLDING DEVICE FOR A DENTURE OR BASE STRUCTURE MODEL. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a holding device comprising an individual tooth replacement or basic framework model produced by dental technology and means for clamping the device in a measuring machine. The invention also relates to a method for positioning a model of this type in a holding device.  
         [0003]     Tooth replacement or basic framework models, hereinafter called preparation models, have different shapes and sizes. They consist primarily of modelling wax or modelling plastics material. It is necessary to measure them to work the tooth replacement or the basic framework for tooth restorations from an industrially preproduced blank with the aid of manual, semi-automatic or automatic production apparatus. Tooth restorations are, for example, tooth crowns and bridges comprising a load-bearing basic framework on which further layers made of porcelain, ceramic or plastics material are applied. Basic frameworks are individual productions and are usually produced once individually for a patient in the normal procedure. It is similar for a tooth replacement which, apart from the basic framework, already contains layers made of porcelain, ceramic or plastics material.  
         [0004]     Preparation models which are produced individually for a patient vary with respect to length, width and positioning of the individual parts. They can be differently bent both in the cranio-caudal and bucco-palatinal direction according to the anatomical conditions. Basic frameworks consist of a small cap for tooth crowns. These have an inside and an outside, which may be completely or partially coated, forming the cavity. The inside of the cavity fits precisely on the natural tooth prepared by the dentist, the tooth stump or else on an artificial tooth stump, for example an implant. Tooth bridges consist of a plurality of connected members of which at least one is designed as a small cap, while the others can be designed as bridge and/or exstress members. Cavities per se have to be free of undercuts in alignment to the other cavities, so the tooth restoration can be placed as a whole onto the prepared teeth.  
         [0005]     Measuring a preparation model offers an important advantage compared to measuring a plaster model, in that the dental technician can design and assess the physical model as previously with his familiar aids. With objects shaped as complexly as this, visual and touch impressions are very important. Supplementing the measuring data on the computer does not offer the dental technician the same familiar impressions and is therefore much more challenging to his powers of abstraction and imagination. Producing preparation models from wax, plastics material or other easily processible materials is known in dental technology as general expert knowledge and guide to handling and therefore prior art. This technology is also used, in particular for moulding methods, for example in the widespread casting and hot press technology. Measuring such preparation models requires them to be fixed in a measuring machine, preferably on its rotary shaft.  
         [0006]     Preparation models, in other words in particular models for basic frameworks for tooth crowns and bridges, are already frequently used in dental technology. They are formed by the casting method and hot press method, for example a negative mould of the basic frame being developed in a fireproof mould. The negative mould represents a cavity which is then filled with dental material. These methods are not considered here.  
         [0007]     Other methods measure the preparation model digitally, or they transfer the mould of the preparation model during measurements, by means of mechanical coupling, to the machining tools. All methods of this type need a suitable holding device for the preparation model.  
         [0008]     DE,C1 19916148 describes a universal holder for holding operating means, inter alia models in tooth technology. Owing to the combination of rigid and formable parts in the holder any adjustment angles can be achieved. The formable part is designed like a cushion and has a reversibly formable outer skin, which is filled with granules. This allows a spatial, single-handed orientation of workpieces during machining, in particular during casting of dental impressions and dental technology models.  
         [0009]     An automatic machine tool for measuring preparation models and producing basic frameworks, in particular for tooth crowns and/or tooth bridges of precise three-dimensional design, is described in PCT/CH00/00623. This machine tool comprises a machine frame or a machine housing, with a rotary shaft for a support for the blank on one side and a support for the preparation model on the other side, at least one machining unit, at least one measuring or digitalising unit and an electronic computing and control unit for all the drive members. A movement unit with three axes of translation in the x, y and z directions is formed for machining unit(s) and measuring unit(s). The digitalisation of the preparation model and machining of the blank are carried out on the same machine tool, at different times. Prior to machining the blank the machining paths for the blank are calculated from the determined and stored digitalisation data, a preset, material-specific scale factor and the tool geometry.  
         [0010]     With a view to the prior art it can be established that no convincing specific holding device for dental preparation models is known; there are merely rudimentary aid solutions.  
         [0011]     The object of the present invention is [therefore] to provide a holding device of the type mentioned at the outset, in which the individuality of the preparation model and its complex form is particularly taken into account. The preparation model must be fixable free of undercuts. Moreover, a method for positioning a preparation model in its holding device is to be provided.  
       SUMMARY OF THE INVENTION  
       [0012]     The object is achieved according to the invention in that a holding device comprises a mechanically stable frame with holes arranged at a spacing, in which at least two holding pins which can be displaced in the axial direction are locked, the holding pins being connected on the end face by means of a bonding agent to the preparation model which is aligned free of undercuts in relation to a defined position, and fixing it rigidly and without stress to the frame, and the equipped frame can be clamped into the measuring machine in a manner secured against slipping and rotation by a clamping adapter on the machine side.  
         [0013]     The position and number of the holding pins are established owing to the experiences of the person skilled in the art and/or calculations for optimisation. These depend in particular on the form and size of the preparation model. The above-mentioned position with respect to the preparation model is defined by the clamping adapter and, for example, a flattening.  
         [0014]     Experiences and/or calculations also advantageously take into consideration that the position and dimensioning of the holding webs of the workpiece which is worked from the blank later or simultaneously, is established by also measuring the holding pins. This blank must be held securely during machining.  
         [0015]     The frame used according to the invention can be designed in different shapes, widths, lengths and cross-sectional shapes. This frame may also be closed or U-shaped in design, the two sides preferably extending over the entire length of the preparation model.  
         [0016]     The frame suitably consists of a metal, for example aluminium or an aluminium alloy, or a mechanically rigid plastics material, for example a Macrolon. The holding pins for the preparation model may consist of the same material, or else of a mechanically rigid plastics material.  
         [0017]     In the case of a rigid frame designed to be square or rectangular, the holes are preferably arranged distributed over the entire frame, generally with regular spacing. At points which are important for holding the preparation model, a plurality of holes may also be recessed.  
         [0018]     The longitudinal axes of the holes extend basically on the centre plane of the frame, in each case suitably perpendicularly to the inner plane of the relevant frame part. Obviously, the longitudinal axes of the holes could also be located individually or in groups outside the mentioned plane and/or otherwise be arranged obliquely.  
         [0019]     It is of essential importance that the holding pins can be freely displaced along their longitudinal axis, so the distance between the frame and the preparation model is optimally bridged.  
         [0020]     A pivotable cylinder, preferably with a longitudinal axis extending parallel or perpendicular to the frame, or a ball-and-socket head, can be installed in the frame at one or more positions, with at least one positionable holding pin, in each case.  
         [0021]     For more complicated preparation models, it is advantageous if the frame is designed at least partially in two parts, with at least one fixed guide rail designed for example so as to be cross-sectionally dovetail-shaped, I-shaped or T-shaped and at least one lockable slide sliding thereon, having at least one hole for a holding pin. In this way the positioning of the holes along the frame need not only be at specific positions, but may be continuously adjustable.  
         [0022]     According to a further development a pivotable cylinder can be formed in a slide formed as above, preferably with a longitudinal axis extending parallel or perpendicular to the frame.  
         [0023]     At least one rotatable and longitudinally displaceable hollow cylindrical slide with at least one hole can also be arranged on a cylindrical fixed guide rail. A further degree of freedom is therefore obtained; the holding pins cannot only be displaced in one direction of the frame, but can also be pivoted perpendicular thereto.  
         [0024]     Finally, according to a third variation, at least one ball-and-socket joint head can be mounted in one or more slides, so the holding pins cannot only be displaced longitudinally but are also pivotable in any direction.  
         [0025]     Both the slides and also the pivoting cylinder and ball-and-socket joint head can be locked in any position by means which are known per se, in particular with a fixing screw.  
         [0026]     With respect to the method for positioning a preparation model in a holding device, the object is achieved according to the invention in that the frame and the preparation model are fixed outside the measuring machine, the number and position of the holding pins is established, the pins are guided into the relevant hole and with the bonding agent applied to the end face, placed on the surface of the preparation model and all the holding pins and their holders are fixed in the frame. The equipped holding device is uncovered once the bonding agent has cured. The holding device can then be clamped in a predefined position in the measuring machine.  
         [0027]     It is of essential significance to the invention that the holding pins are not pressed on the surface of the preparation model, but are placed without the exertion of pressure so no stresses develop.  
         [0028]     Particularly simple and therefore advantageous fixing of the holding pins takes place by stippling some wax or adhesive onto the relevant part of the frame. Moreover, all fixing screws and similar fastening means are tightened.  
         [0029]     As already mentioned, the preparation model together with the holding pins is measured. Firstly, one side of the preparation model is measured, then the holding device clamped to the rotary shaft of a measuring machine is turned and the second side of the preparation model is measured or digitalised.  
         [0030]     The holding device according to the invention has a plurality of advantages:  
         [0031]     The individuality of preparation models is completely taken into account by the possibility of variation in the holding positions.  
         [0032]     The alignment of the preparation model, free of undercuts, may take place outside the measuring machine and is therefore not impeded by limited possibilities for viewing and moving.  
         [0033]     The holding device can be reused after the development of the preparation model. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]     The invention will be described in more detail with the aid of embodiments shown in the drawing, which are also the subject of dependent claims. The drawings show schematically:  
         [0035]      FIG. 1 a  perspective view of a closed frame,  
         [0036]      FIG. 2 a  view of an open frame,  
         [0037]      FIG. 3 a  view of a closed frame with a preparation model,  
         [0038]      FIG. 4 a  lateral view of  FIG. 3  in cross-section,  
         [0039]      FIG. 5 a  cut-open view of a holding pin inserted in a frame,  
         [0040]      FIG. 6 a  variation of  FIG. 5 ,  
         [0041]      FIG. 7 a  further variation according to  FIG. 5 , in a sectional plan view,  
         [0042]      FIG. 8 a  section through a frame with a ball-and-socket joint,  
         [0043]      FIG. 9 a  section through a two-part frame,  
         [0044]      FIG. 10 a  view according to  FIG. 9 ,  
         [0045]      FIG. 11 a  section through a variation of a two-part frame,  
         [0046]      FIG. 12 a  part section along the longitudinal centre plane of a frame,  
         [0047]      FIG. 13 a  section according to XIII-XIII in  FIG. 12 ,  
         [0048]      FIG. 14 a  variation according to  FIG. 12 , and  
         [0049]      FIG. 15 a  section according to XV-XV in  FIG. 14 .  
     
    
     DETAILED DESCRIPTION  
       [0050]      FIG. 1  shows a closed frame  10  of a holding device according to the invention. The frame  10  consists of an aluminium alloy and is mechanically stable. Holes  12  for holding pins, which are not shown in  FIG. 1 , are provided over the entire periphery of the frame  10  having a rectangular basic form, at a regular spacing a. The holes  12  extend perpendicular to the inner face  14  of the frame  10 , the longitudinal axes A of the holes are provided on the centre plane of the frame. A clamping adapter  16  is flanged on the machine side in the centre of a longitudinal side of the frame. This clamping adapter  16  is fastened in a specific position so as to be secure against slipping and rotation on the rotary shaft of a measuring machine, not shown. According to one variation, the clamping adapter  16  is flanged on the centre of the narrow side of the frame  10 .  
         [0051]      FIG. 2  shows an open, substantially U-shaped frame  10 . The two sides of the frame  10  are approximately of the same length as the narrow sides of a closed frame. In the holes  12  of the frame shown by dashed lines two holding pins are inserted to different depths and each is fastened with a fixing screw  20 . Because of the low effective forces, the frame does not have to be very rigid in design. The open frame  10  according to  FIG. 2  provides improved accessibility and also the possibility of receiving very bent preparation models. At most, the positioning of the holding pins  18  is slightly limited relative to a closed frame  10 . A rotation prevention device  17  is provided on the clamping adapter  16  and is designed in the form of a flattening or a bolt and thus represents a predetermined indicator for the position of the holding device free of undercuts.  
         [0052]      FIG. 3  shows an individually produced three-membered preparation model  22  made of wax, in the present case a basic framework model, which is fastened with three cylindrical holding pins  18  in a rectangular frame  10  of the holding device  56 . The frame consists in the present case of plastics material, is 50 mm in length and 30 mm in width and has a rectangular recess of 42 mm in length and 22 mm in width. The cross-section of the frame is rectangular having a height of 6 mm and a width of 4 mm. Five through-holes  12  are formed on the narrow side of the frame  10 , six holes  12  on the longitudinal side of the clamping adapter  16 , and seven holes  12  on the opposing longitudinal side. The holes each have a diameter of 1.25 mm. Three straight cylindrical holding pins made of plastics material with a diameter of 1.2 mm are pushed through three predetermined holes  12 . The preparation model  22  is initially aligned free of undercuts, so a milling tool could potentially machine the surface from one direction, its machining direction. The preparation model  22  is preferably aligned with the cavities  24 , as this part of the surface represents the most difficult and quality-determining part. The preparation model  22  is held precisely in this aligned position and the frame  10  is placed with the holding pins  18  with the recess over the preparation model  22 . The holding pins  18  are carefully pushed along their axial direction A until they contact the preparation model  22  with the bonding agent  34  (wax) applied to the end face, and therefore waxed on.  
         [0053]     The holding pins  18  are mesially and distally connected to the outside of the two small caps  25  and lingually to the bridge member  26 . The holding pins  18  are fixed to the frame  10  by fixing screws  20 , not shown.  
         [0054]     This equipped frame with the holding pins  18  and the inserted preparation model  22  is inserted in a measuring machine in a manner secured against slipping and rotation by means of the clamping adapter  16  on the machine side. The clamping adapter  16  preferably has a marking, for example a flattening or a transverse pin, so that it adopts a predetermined position in the measuring machine.  
         [0055]     After clamping, the preparation model  22  can initially be measured on one side then on the other side. The holding pins  18  are measured together with the preparation model  22  and serve to reliably receive the machining forces during the later material removal from a blank. The holding forces are small during measuring, predominantly acceleration forces, gravitational forces and at most the pressure force of tactile measuring occur. After measuring, the frame  10  with the preparation model  22  is taken from the measuring machine, the fixing screws  20  are released and the holding pins  18  detached by turning from the preparation model  22 . The frame  10  and the holding pins  18  are reusable, regardless of whether they consist of metal and/or plastics material.  
         [0056]     During insertion, as mentioned, a bonding agent  34  is applied to the end faces of the holding pins  18 , generally a wax or a thermoplastic adhesive, which fixes the holding pin  18  when applied to the preparation model  22 . Even if the pins  18  are already inserted in the through-holes  12 , the bonding agent  34  can subsequently be applied to the holding pins  18  shortly before contact with the preparation model  22 .  
         [0057]     The holding pins  18  protruding outwardly from the frame  10  are preferably severed flush with the surface.  
         [0058]     According to the embodiment of  FIG. 5 a  hole  12  is formed with an internal screw thread. A holding pin  18  provided with an external thread  28  is screwed therein. A diagonal slot  30  allows the turning of the holding pin  18  with a screwdriver, indicated by a double arrow  32 . A second double arrow  33  indicates the axial movement directions of the holding pin  18 .  
         [0059]     According to the variation of  FIG. 6 , a holding pin  18  is inserted with play (loose fit) into a hole  12  in the frame  10 . It can be freely displaced in the axial direction A and this is indicated by the double arrow  33 . Fixing takes place by means of a bonding agent  34 , a wax or an adhesive, which partially penetrates into the gap between the frame and holding pin and thus ensures good fixing.  
         [0060]     In  FIG. 7  the direction of viewing is in the longitudinal direction of the holding pins  18 , also inserted loosely into holes  12  in the frame  10 . The holding pins  18  are here fixed by fixing screws  20 .  
         [0061]     All the fixing possibilities can be freely combined. The property that the holding pins  18  can be pushed onto the preparation model  22  ( FIG. 3 ) by displacement in their axial direction A, can be placed there and then fixed in the frame, is important.  
         [0062]     According to a further variation according to  FIG. 8 , a holding pin  18  can be mounted by means of a ball-and-socket joint head  36  in a corresponding joint socket  38  of the frame  10 . The holding pin  18  can be inserted in the axial direction A during fastening of the preparation model  22  ( FIG. 3 ) and because of the capacity of the ball-and-socket joint  36  to rotate can be pivoted in two directions which are linearly independent of one another, which is indicated by two crossed double arrows  40 . Once the bonding agent  34  has cured on the surface of the preparation model  22  ( FIG. 3 ) the holding pin  18  with the bonding agent  34  is fixed in the central hole  42  of the ball-and-socket joint head  36  and the ball-and-socket joint head  36  is then locked with a fixing screw  44 . A recess  60  limits the pivoting region of the holding pin  18  in the direction of the double arrows  40 .  
         [0063]      FIG. 9  shows a cross-section through a two-part frame  10 . A slide  48  which is held by way of a dovetail guide  49  slides on a fixed guide rail  46 . The slide  48  can be freely displaced along the dovetail guide  49  and can be locked in any position by a fixing screw  50 . A ball-and-socket joint head  36  or a pivotable cylinder  52  is mounted in a corresponding recess of the slide  48 . The holding pin  18  which can be axially displaced in the direction A of the double arrow  33  can thus be brought with its end face covered by a bonding agent  34  to any position in the frame. Displacement in the direction of the double arrow  33  is limited by the design. Once the bonding agent  34  has cured on the preparation model  22  ( FIG. 3 ) locking takes place with a bonding agent  34  for the holding pin  18 , a fixing screw  44  for the ball-and-socket joint head  36  or the pivotable cylinder  52  and the fixing screw  50  for the slide  48  which is displaceable in the direction of the double arrow  54 .  
         [0064]      FIG. 10  shows the variation with the ball-and-socket joint  36  of  FIG. 9  from another viewing direction.  
         [0065]      FIG. 11  shows a further embodiment with a fixed guide rail  46  with a cylindrical cross-section and a hollow cylindrical slide  48  which can be freely displaced and rotated thereon. Displacement of the slide  48  takes place in the direction of the double arrow  54 , the rotation in the direction of the double arrow  58 . The holding pins which are displaceable in the axial direction A in the direction of the double arrow  33  can thus with their end face find any point on the surface of the preparation model  22  ( FIG. 3 ). Once the bonding agent  34  has cured on the surface of the preparation model  22 , the fixing screws  44  and  50  are tightened and the holding pins  18  and the slide  48  are thus fixed.  
         [0066]      FIG. 12, 13  show a cylinder  52  mounted in the frame  10  with a pivoting axis S extending on the frame plane, the pivoting axis S also extending parallel to the relevant inner face  14 . A holding pin  18  is longitudinally displaceably guided in the cylinder  52 , which can be pivoted in the direction of the double arrow  58 , and is fixed with a bonding agent  34 . The pivoting movement in the direction of the double arrow  58  is limited by the dimensions of a recess  60  with a cylindrical roller bearing  62 . The pivoting position of the cylinder  52  is limited by a fixing screw  44 .  
         [0067]      FIG. 14, 15  substantially correspond to the previous two figures. However, the axis S of the cylinder  52  extends perpendicularly to the frame plane and parallel to the relevant inner face  14 .  
         [0068]     It is obvious that more than one holding pin  18  per cylinder can also be arranged in all the embodiments according to  FIG. 12  to  15 .