Abstract:
The invention relates to a mold for producing the model of a tooth from a dental impression ( 28 ), comprising a peripheral wall ( 12 ), a model plate ( 38 ) which is tightly arranged on the top thereof and an impression spoon ( 14 ) bearing the dental impression ( 28 ). Said spoon is tightly inserted into the lower end of the peripheral wall ( 12 ). The hollow cavity ( 42 ) thus obtained is filled with molding material to give a highly precise tooth model requiring no further mechanical processing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a mould for producing a tooth model from a dental impression. 
     2. Background Art 
     Such moulds are known in the form of cup-shaped formed bodies. 
     To produce a tooth model from a dental impression, the dental impression is filled with a plastic modelling material which hardens. Immediately after filling the dental impression with the modelling material in rare cases, while the modelling material is still soft, a mostly rubber-like mould is applied to the peripheral wall of the dental impression in order, by filling the mould up to a predetermined height, to obtain a base on the tooth model. 
     To produce artificial teeth, said base is trimmed parallel to the occlusal plane mechanically by grinding; the result is a so-called toothed rim made of modelling material. 
     Then a drill and a twist drill are used to drill blind holes in the base of the toothed rim, in each case under the teeth to be restored, adjacent teeth or antagonists, and metal pins are introduced and preferably glued into the blind holes. 
     After subsequent isolation of the base mostly using an alginate-based isolating material, the toothed rim with the glued-in pins is basally aligned and introduced into a mould, which is filled to a height of around two centimeters with preferably the same plastic modelling compound, until the base of the toothed rim is just completely wetted by the plastic modelling compound. Said compound after it has hardened forms the base for the toothed rim; toothed rim and base together form the finished tooth model. 
     After hardening and mechanical trimming of the base, the toothed rim is sawn in each case at right angles to the tangent predefined by the individual tooth groups right down to the base such that the model teeth to be restored, neighbouring teeth, maxillomandibular segments or any other model teeth or model tooth groups may be individually removed from the base and precisely repositioned by means of the pins. 
     Such a saw-cut model is a prerequisite for producing any type of artificial tooth from dental impressions. 
     Another way of producing model bases is such that the parallel-trimmed, conventionally produced toothed rims are provided in a special drilling apparatus with the blind holes for the pins and at the same time mirror-image holes are drilled into a prefabricated base plate made of plastic material for receiving the pins, which are to be glued into the toothed rim, together with the toothed rim. Removal of the prepared teeth is effected by the conventional saw-cut technique. Although this dispenses with the outlay for processing a second plastic modelling compound for producing the base, expensive equipment is necessary. 
     A particular problem associated with producing tooth models, in particular toothed rims, is the filling of the mostly hydrophobic dental impression with the hydrophilic modelling material, usually dental plaster. The narrow indentations of the individually moulded teeth, undercuts occasioned by the tooth shape and fine delineation of the textured surface of the teeth in most cases promote bubble formation in the tooth model which often makes it necessary to produce a second tooth model. Such a second tooth model however is mostly of an inferior quality to the first tooth model because the removal of the latter from the dental impression simultaneously leads to the breaking-off of fine edges and surface structures as well as fine interdental lamellae or lamellae in the sulcus region. 
     In addition, defects attributable to the shaping by the dentist to obtain the dental impression are frequently only detectable on the tooth model. Because of the elaborate process of producing the latter, however, defects are mostly not spotted until several days after taking the impression from the patient. In many cases the patient has to be brought back for a new impression to be taken, which entails a high outlay and often leads to poorer impression results because a common consequence of the initial treatment is a tendency to bleed during the follow-up treatment. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a mould for producing a tooth model from a dental impression, which enables a simpler processing technique involving only a lower number of working steps and by means of which the number of error sources is reduced and tooth models of greater precision are obtained. 
     In the mould according to the invention, the bottom wall of the mould is formed by the impression tray used to produce the dental impression, wherein the dental impression for producing the tooth model remains on the impression tray. 
     The impression tray at least in portions of its outer surface has a precisely predetermined geometry and may without reworking be connected precisely and tightly to the peripheral wall of the mould. 
     As will become even clearer from the detailed description below, production of a tooth model using the mould according to the invention saves time and costs. In particular, compared to conventional production of the toothed rim, there is no need for mechanical trimming, drilling of the blind holes for the pins or manufacture of the base plate involving repeat processing of modelling material, nor is there any need for expensive equipment for producing the toothed rim. 
     The use of the mould according to the invention is to a large extent error-tolerant and may be extensively automated. 
     The invention also makes it possible for the tooth model to be produced directly at the dental surgery. All the dentist need do, after production of the dental impression, is clamp the used impression tray together with the impression itself into the peripheral wall and introduce into the mould thus obtained an adequate amount of modelling material over the dental impression. Only the tooth model thus obtained is then passed on to the dental technician. 
     Producing the tooth model at the dental surgery also has the advantage that minor defects of the dental impression are easier to spot on the tooth model and the dentist in said case may immediately take another impression from the patient before the latter leaves the premises. 
     A mould is tightly closed on all sides. 
     The mould during filling may therefore be acted upon by a pressure below or above atmospheric. The former has the advantage of keeping bubble formation very low. In both cases, the modelling material flows well even into small interstices. 
     It is moreover possible for a mould prior to introduction of the modelling material, to be thoroughly rinsed with a wetting agent or another treatment medium so that the surface of the impression is optimally prepared for subsequent contact with modelling material. 
     A mould also easily allows the production of a tooth model which, at its base side, is already flat without machining of the modelling material. 
     In said case, the development of the invention is advantageous in view of a bubble-free quality of the—during casting—top end face of the tooth model. 
     The development of the invention also serves to achieve bubble-free, complete filling of the mould with modelling material. 
     The effect achieved by the development of the invention is that the feeding of modelling material is automatically terminated when the mould is completely full of modelling material. 
     Sealing connections may be realized in a simple and reliable manner between the peripheral wall and the impression tray and/or the peripheral wall and the model plate. 
     The development of the invention is advantageous in view of precise, reproducible positioning of a model plate on the peripheral wall. 
     The development of the invention allows the realization of a tooth model which may then, by means of saw cuts effected transversally relative to the mandibular arch, be made into a saw-cut model in which individual teeth or tooth groups are removable and precisely repositionable. 
     For said purpose positioning pins may be used, which are embedded in the tooth model and in each case have a positioning portion projecting above the tooth model. 
     The blind recesses in the model plate may also be made permeable to gas so that the modelling material may penetrate into the blind recesses when the modelling material is introduced under pressure above atmospheric. When it is introduced under pressure below atmospheric, air situated in the blind recesses is extracted. The result is the formation on the tooth model of positioning pegs, which are complementary to the blind recesses. 
     The development of the invention allows reproducibly precise feeding of the modelling material to the mould cavity. 
     In said case, the development of the invention guarantees that no air bubbles are trapped between the modelling material and the dental impression. 
     The development of the invention makes it possible, while using identical basic components, to realize moulds of differing height, thereby also enabling tooth models of differing height to be produced in an identical manner. 
     The development of the invention in a simple manner allows a tight bracing of the peripheral wall with the model tray and optionally the model plate, particularly also in cases where impression tray as well as optionally model plate and peripheral wall have cooperating positive locking means which ensure, on the one hand, exact alignment of the impression tray in the peripheral wall and, on the other hand, efficient sealing of the mould cavity. 
     The development of the invention in said case guarantees that, despite the slot provided in the peripheral wall, efficient sealing of the mould cavity is achieved. 
     The developments of the invention allow external visual checking of the filling of the mould cavity with modelling material, particularly given the use of dyed modelling materials. 
     The effect achieved by the development of the invention is that the outer surface or outer lateral surface of the tooth model has a shape which is suitable for exact positioning in an articulator or similar apparatus without the outer surface of the tooth model having to be cut for said purpose. Thus, when using a mould according to the invention, there is no longer any troublesome generation of plaster dust or dust from other modelling materials in the dental laboratory. 
     Embodiments of the invention are described in detail below with reference to the accompanying drawings. Said drawings show: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 : a plan view of a mould for producing tooth models together with a diagrammatically illustrated device for filling the mould with modelling material, wherein part of a model plate forming the top of the mould is broken away; 
     FIG.  2 : a transverse section through the mould shown in FIG. 1 along the cranked cutting line II—II of FIG. 1; 
     FIG.  3 : a plan view of the model-side boundary surface of the model plate of FIGS. 1 and 2; 
     FIG.  4 : a longitudinal section through the model plate along the cutting line IV—IV of FIG. 3; 
     FIG.  5 : a plan view of the model-side boundary surface of the model plate with a sawn toothed rim of a mandibular arch carried by the model plate; 
     FIG.  6 : a plan view of the holder-side boundary surface of the model plate shown in FIG. 5; 
     FIG.  7 : a section similar to FIG. 2 through a modified mould used to produce higher tooth models; 
     FIG.  8 : a view similar to FIG. 3, which shows a modified model plate; 
     FIGS.  9  and  10 : sections through further modified model plates, which are similar to the section of FIG. 2; and 
     FIG.  11 : a view similar to FIG. 1 but showing a modified device for filling the mould with modelling material. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 show a mould for producing tooth models, which is denoted as a whole by  10 . The mould  10  has a peripheral wall  12 , the bottom portion of which is complementary to the outer surface of an impression tray  14 . 
     The illustrated impression tray  14  is a tray for producing supramaxillary impressions and comprises a bottom wall  18 , having a middle wall portion  20  modelled on the soft palate, and a boundary wall  22  extending in peripheral direction. Soldered onto the edge of the wall portion  20  and the top end of the boundary wall  22  are wire pieces  24  and  26 , which create undercuts, against which a dental impression  28  made e.g. of silicone, alginate or the like is latched. 
     Provided in the bottom third of the boundary wall  22  is a longitudinally extending groove  30 , into which a longitudinally extending rib  32  provided on the inner surface of the peripheral wall  12  positively engages. 
     A seal  34  is supported via the rib  32  by the peripheral wall  12  and cooperates with the outer surface of the peripheral wall  22 . Both by virtue of said seal and also by virtue of the keyed connection between groove  30  and rib  32  an efficient sealing and precise positioning between peripheral wall  12  and impression tray  14  are achieved. 
     As is clearly evident from FIG. 2, the contour of the inner surface of the peripheral wall  12  corresponds to the contour of the outer surface of the boundary wall  22 , which likewise assists sealing and good positioning. The outer surface of the peripheral wall  12  moreover verges smoothly into the outer surface of the impression tray  14 . 
     The outer surface of the peripheral wall  12  extends with an obliquely outward slope so that the thickness of the peripheral wall  12  increases in an upward direction. 
     A marginal recess  36  extending in longitudinal direction of the peripheral wall  12  is set back from the top end face of the peripheral wall  12 . A bottom portion of a model plate  38  engages positively into the marginal recess  36 . Inserted into the bottom of the marginal recess  36  is a seal  40 , which cooperates with the edge of the, in FIG. 2, bottom boundary surface of the model plate  38 . 
     The peripheral wall  12 , the impression tray  14 , the dental impression  28  carried by the latter and the model plate  38  therefore together delimit an outwardly sealed mould cavity  42 . 
     To enable fitting of the peripheral wall  12  on the impression tray  14 , the, in FIG. 1, bottom wall portion of the peripheral wall  12  is provided with a slot  44 . The peripheral wall  12  is made of a substantially rigid yet slightly elastically deformable plastic material so that the peripheral wall  12  by virtue of the elastic expansion enabled by the slot  44  may be clipped onto or removed from the impression tray  14 . 
     The, in FIG. 1, bottom wall portion of the peripheral wall  12  has in the vicinity of the slot  44  two dovetail parts  46 ,  48 , the dovetail faces  50  of which widen in a downward direction. When a clamping part  52  provided with complementary inner dovetail faces  54  is slipped onto the dovetail faces  50 , the peripheral wall  12  is drawn together at the slot  44  and hence applied tightly and sealingly against the outer surface of the impression tray  14 . At the same time, a seal  53  lying between the lateral faces of the slot  44  is placed under initial tension. 
     Two connection pieces  56 ,  58  are provided in the outer-lying regions of the bottom wall portion of the peripheral wall  12 . of said connection pieces the left is tightly connected to the outlet of a reservoir  60  containing a liquid modelling material (e.g. plaster). A ventilation connection of the reservoir  60  is connected by an adjustable throttle  62  to the environment. 
     The connection piece  58  contains a stopper  64 , which is permeable to gas but acts as an obstruction to modelling material. The connection piece  58  is connected by the stopper  64  to the suction opening of a suction pump  66 . The outlet of the latter is connected likewise to the ambient atmosphere. 
     As is clearly evident from FIGS. 1,  2  and  6 , the boundary surface of the model plate  38  remote from the mould cavity  42  carries radial positioning ribs  68 , which have a substantially triangular basic cross section and slope down towards the middle of the model plate  38 . The positioning ribs  68  cooperate with complementary positioning grooves of a non-illustrated holding part, as is customary with divided magnetic base systems. The holding part in turn is clamped into the articulator or a machining apparatus of the dental technician. 
     The outer-lying side of the model plate  38  moreover carries inside a flat indentation  70 , which is open towards the edge, a disk-shaped fixing part  72 , which has a shaft  73  made of magnetic or magnetizable material embedded in the model plate and cooperates with a counterpart fixing part, which is carried by the holding part and likewise made of magnetic or magnetizable material. In said manner the model plate  38  is releasably fixed on the holding part. 
     The procedure for producing a tooth model using the mould described above is as follows: 
     The impression tray  14  carrying the dental impression  28  is latched into the peripheral wall  12  and the model plate  38  is inserted into the top end of the peripheral wall  12 . Then the clamping part  52  is slipped onto the dovetail parts  46 ,  48  so that the above-mentioned parts are braced with one another. 
     The suction pump  66  is then set in operation and the mould cavity  42  is filled with liquid modelling material at a rate predetermined by the adjustment of the throttle  62 . Alternatively, the modelling material may be fed in under pressure above atmospheric, as will be described in greater detail further below with reference to FIG.  11 . 
     Preferentially, the mould cavity  42  is first evacuated and then the modelling material is fed in under pressure above atmospheric. A compressor  104  and a {fraction (2/2+L )}-way and a {fraction (3/2+L )}-way magnetic valve  106  and  108  respectively, which are operated by a suitable control unit  110 , are used for said purpose. Pressure regulators  112  and  114  are used to preselect the pressure below and above atmospheric in the mould cavity  42 . Said variant is shown by dashes in FIG.  1 . 
     The filling operation may be visually checked through the model plate  38  and/or the peripheral wall  12 . Additional shaking or vibrating of the mould  10  may even out the filling operation and cause any air bubbles trapped under modelling material in the indentations of the dental impression  28  to rise. This is preferably effected by means of a mechanical vibrator  74 , which is mechanically coupled to the mould  10  in the manner indicated by dashes in FIG.  1 . 
     At the end of the filling operation the liquid modelling material then reaches the stopper  64 . As the modelling material is unable to penetrate the stopper, the suction pump  66  then operates against a closed volume, which is acoustically easily perceptible. Where desired, it is also possible to connect to the line extending between the stopper  64  and the suction pump  66  a pressure monitor  76 , the output signal of which may be used to sound an alarm. 
     Once the modelling material has hardened, the clamping part  52  is slipped down off the dovetail parts  46 ,  48 . The model plate  38  may then be lifted in an upward direction from the impression tray  14  and the dental impression  28  carried by the latter. 
     When, prior to filling the mould cavity  42 , positioning pins  78  have been inserted in the model plate  38  at points where the finished tooth model  80  is later to have removable segments or positioning pins, it is possible in the manner shown in FIG. 5 then to produce said segments by means of saw cuts  82  so that the corresponding maxillomandibular segments are individually removable from the model plate  38  and subsequently also precisely repositionable there. 
     The positioning pins  78  each have an anchoring portion  84 , which is integrally cast in the modelling material and for the purpose of improving the frictional engagement is provided with a knurl comprising grooves or the like. The positioning pins  78  moreover have truncated cone-shaped positioning portions  86 , which are complementary to blind recesses  88  provided in a grid arrangement on the boundary surface of the model plate  38  directed towards the mould cavity. FIG. 5 shows four different removable segments  90   a ,  90   b ,  90   c  and  90   d  of the tooth model  80 , which correspond to two cavities set back from the occlusal surface, one truncated cone-like crown preparation and one lateral cavity of a tooth. 
     In the embodiments described below, mould parts which have already been described above with reference to FIGS. 1 to  6  are once more provided with the same reference characters. Said mould parts are also not described in detail again below. 
     In the modified mould  10  shown in FIG. 7, a higher mould cavity  42  is achieved by inserting between the top end of the peripheral wall  12  and the model plate  38  a distance element  92 , the inside and outside edge contour of which corresponds to the inside and outside edge contour of the top end of the peripheral wall  12 . The bottom end face of the distance element  92  is complementary to the top end face of the peripheral wall  12 , and the top end face of the distance element  92  has the same geometry as the top end face of the peripheral wall  12 . 
     A further seal  94  ensures sealing between the distance element  92  and the model plate  38 . It goes without saying that the dentist or dental technician will stock a plurality of distance elements  92  so that the height of the mould cavity  42  may be selected as close as possible to required height of the tooth model. To adjust even larger mould cavities  42 , a plurality of such distance elements may also be stacked one on top of the other. 
     FIG. 8 shows a modified model plate  38 , which is provided with a channel  96 . Said channel is connected by a stopper  98 , which has the same properties as the stopper  64 , to the suction side of the suction pump  66 . 
     In a further modification, the model plate  38  may also be provided with a plurality of such channels  96 , which are provided [sic] in each case by an associated stopper  98  to the suction pump  66 . 
     When a model plate  38  has such channels  96 , it is also possible to dispense with the connection piece  58 . 
     In the further modified model plate according to FIG. 9, the bases of the blind recesses  88  are formed by a material layer  100 , which is permeable to gas but impermeable to modelling material. 
     When a material layer  100  which is permeable to gas in one direction only but blocks in the other direction (e.g. a semi-permeable membrane) is used, it is then also possible to evacuate the mould cavity of such a modified mould. 
     Instead of this, according to claim  10  very thin ventilation bores  102  extending from the bases of the blind recesses  88  to the outer-lying side of the model plate  38  may be provided. 
     When, instead of such a model plate-gripping mould  10  being operated with pressure below atmospheric, the modelling material is fed to the mould under pressure above atmospheric, air may escape from the blind recesses  88  and modelling material may penetrate into the blind recesses  88 . The result in said case is a plurality of positioning pegs formed on the tooth model  80 . Thus, no positioning pins are required. 
     When the mould  10  is acted upon by pressure above atmospheric, removable tooth model segments may also be subsequently defined simply by sawing through the tooth model at the required points. In an embodiment according to FIGS. 1 to  6 , however, before introducing the modelling material the points at which removable model segments are to be situated have to be fixed by suitably equipping the model plate  38  with positioning pins  78 . 
     The acting upon the mould cavity  42  with pressure above atmospheric during introduction of the modelling material is achieved according to FIG. 11 by connecting the inlet of the throttle  62  to the outlet of a compressor  104 . The stopper  64  is then flow-connected directly to the ambient atmosphere. 
     Alternatively, a syringe or a mechanical feed pump may be used for feeding in the modelling material under a pressure above atmospheric. 
     To prevent the model plate  38  from lifting off the peripheral wall  12  when a pressure above atmospheric is admitted into the mould cavity  42 , a keyed connection between model plate  38  and peripheral wall  12  may be provided, e.g. a groove, which corresponds to the groove  30 , in the outer surface of the assembly plate  38  and a rib, which corresponds to the rib  32 , carried by the side wall of the marginal recess  36 . 
     In practice, work is carried out with a small number of differently dimensioned impression trays  14  in order to cover differently sized jaws of patients. It goes without saying that the dentist or dental technician will stock a corresponding number of differently sized peripheral walls  12  and model plates  38  so that with the various impression tray sizes tooth models may be produced in the manner described above. 
     It goes without saying that prior to the feeding of the modelling material the surfaces delimiting the mould cavity  42  are coated with a suitable release agent (e.g. release agent spray) so that the tooth model after hardening easily detaches from said surfaces.