Abstract:
A dental prostheses modeling system includes a tray having in an upper part thereof a trough for receiving a semi-liquid modeling material or casting material such as plaster of Paris or die stone, the trough having opposed vertical walls in which are formed alternating vertically disposed ribs and grooves for forming complementary shapes in sides of a casting molded in said tray, a base portion of which has in outer walls thereof alternating vertically disposed grooves and ribs, the trough having a frangible base plate which overlies an upwardly concave cavity for receiving liquid die stone after the upper casting has solidified, hardened and been removed, the base plate being broken and removed to uncover an elongated aperture joining the upper trough to the lower cavity enabling the cast to be ejected from the tray, pins fitted into selected portions of the casting base, the casting reinserted into the trough, and the tray inverted to receive liquid die stone which hardens to form a stone base matrix for insertably receiving pins protruding downwardly from portions of the casting, the casting being then removed from the trough in the upper portion of the tray and severed into segments which are releasably re-engageable along with adjacent portions of the casting within the tray, proper registration between segments of the casting being effected by insertable receipt of pins within holes formed in the die stone base during hardening thereof, and engagement between ribs and grooves of the casting segments with complementarily-shaped grooves and ribs in the inner side walls of the upper tray trough.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    A. Field of the Invention  
           [0002]    The present invention relates to articles and methods used in the fabrication of dental prostheses such as crowns and bridges made of various combinations of metal and ceramic materials and used to overlie or replace imperfect or missing teeth. More particularly, the invention relates to a system for use in fabricating crowns and bridges, the system including an apparatus and method for making from a mold or impression of a patient&#39;s teeth, a dental model cast which is segmentable into die segments, each of which has both horizontally protruding ribs and grooves for releasably engagement with complementary-shaped grooves and ribs formed in a support tray, and a pin protruding downwardly from the die segment and adjacent segments for receipt within indexing holes formed through a base member matrix formed within the tray, the pin facilitating gripping and manipulating of the die during various fabrication operations performed by a dental technician.  
           [0003]    B. Description of Background Art  
           [0004]    A dental procedure which is routinely used to restore function and aesthetic appearance to a person&#39;s mouth after a tooth has become broken, structurally degraded by disease or removed entirely, consists of capping or replacing the tooth with a prosthetic restoration, such as a crown or bridge. One form of dental prosthesis or artificial tooth replacement which is widely used consists of a cap or crown for a tooth that is made of a resin, molded ceramic material, a precious metal such as gold or an alloy thereof, or a layered combination of metals and resins or ceramic materials. Various combinations of the foregoing materials provide tooth restorations which possess requisite durability and aesthetic appearance, as well as sufficient hardness to be suitable for chewing foods. The process of fabricating tooth restorations has been in use for a substantially long time, and includes a well-defined sequence of steps, which are briefly summarized below.  
           [0005]    According to a first step in existing methods of fabricating dental prostheses or artificial replacement teeth, a negative impression mold is made of a group of a patient&#39;s teeth, including missing, broken or decayed teeth which are to be repaired or replaced and teeth which are laterally adjacent to the defective teeth. Such impressions are typically made by positioning within the mouth of a patient, adjacent to teeth to be restored, a shallow curved tray which contains a polymer material such as alginate, elastomer, hydrocolloid or a polyether, which is capable of being indented by a tooth, and forming and retaining a stable impression of the tooth. The impression material is initially in the form of a putty, slurry or thick paste which rapidly solidifies at ambient room temperature and pressure. The tray is inserted into a patient&#39;s mouth positioned generally horizontally and in vertical alignment with a subject area of the teeth, and the patient bites down on the tray, or the tray is pressed into contact with the teeth, thus pressing the teeth into the viscous semi-liquid mold impression material held by the tray. After a few minutes, the mold impression material solidifies into a rubber-like elastomeric state which has formed therein precise negative impressions of teeth in a subject area of the patient&#39;s mouth.  
           [0006]    Dental impression trays for use as described above are available in a variety of styles. One type tray has an arcuately curved plan-view shape which is similar to the curved arrangement of teeth in the jaw. The curved arc length of the tray approximates that of about one half an upper or lower jaw and hence is referred to as a quadrant tray. A flat, paddle-like handle protruding horizontally outwards from one end of the tray is usually provided, to facilitate inserting and removing the tray from a patient&#39;s mouth. A typical quadrant tray has on one side thereof a curved trough for receiving impression mold material, may be used to make impressions of upper or lower jaw quadrants and is referred to as a standard quadrant or single-bite tray.  
           [0007]    Since an important structural feature of a dental prosthesis is proper registration and biting contact or occlusion between the prosthesis and teeth located in the opposing jaw, it is desirable to make an impression of occluding teeth in the opposing jaw in addition to the impression made of teeth that are to be restored. Therefore, it has been a trend in dentistry for the dental professional to simultaneously make impressions of teeth that are to be restored and occluding teeth in the opposing jaw. A convenient method for simultaneously making restorative and opposing impressions utilizes a tray which has a plan-view shape similar to that of a single-bite, standard quadrant impression tray, but which has upper and lower troughs for holding mold impression material in both upper and lower sides of the tray. Both the upper and lower troughs of these “double-bite” or “triple” trays are filled with viscous impression material and inserted into the patient&#39;s mouth between the upper and lower jaws in vertical alignment with teeth to be restored, whereupon the patient bites down on the tray, simultaneously forming impressions of upper and lower teeth.  
           [0008]    After impressions of teeth have been made in the manner described above, and the mold impression material solidified, the tray holding solidified mold impression material containing negative impressions of a patient&#39;s teeth is removed. The mold, typically referred to as an “impression,” is then used to make positive replicas of teeth by pouring a semi-liquid molding material such as plaster of Paris, or die stone, into the depressions formed in the impression, which are accurate negative replicas of the teeth. After the die stone has solidified into a hard stone-like casting, or cast, the cast is removed from the impression, a task which is facilitated by the fact that the impression material is elastomeric, enabling it to be readily peeled away from the die. The casting is then used to fabricate one or more tooth restorations or prostheses in the following manner.  
           [0009]    A master cast, i.e., a cast which includes replicas of teeth which are to be restored, is partitioned into one or more individual segments and/or dies, each consisting of a replica of a tooth which is to be replaced by or fitted with a dental prosthesis. Partitioning of a master cast into die segments is typically accomplished by making parallel vertical saw cuts through the master cast. The individual die segment or segments are then used as three-dimensional models or templates for fabricating crowns or bridges. In general, the exterior surfaces of the prosthesis cannot simply replicate those of the die segments. This is because the occlusal surface of the prosthetic tooth restoration, and to a lesser extent, lateral surfaces of the restoration, may require contouring which is different from that of the die segment. For example, the process of fabricating crowns for diseased or damaged teeth entails grinding decayed or broken outer portions of the tooth down until a stump of healthy dentin or enamel remains, a procedure referred to as “prepping” the tooth. Obviously, a crown which is fabricated to fit onto a stump must have a substantially different, tooth-like shape rather than a stump-like shape.  
           [0010]    From the foregoing discussion, it can be appreciated that the fabrication of dental prosthesis models from die segments is a labor-intensive task requiring the skills of a prosthodontist or skilled, experienced, dental lab technician. Fabrication of prosthetic dental models typically requires that die segments be contoured by applying a workable material to exterior portions of the die segment, and sculpting the material. The die segment is then replaced into the space in the master cast from which it has been removed, and proper occlusion of the sculpted prosthetic model confirmed by bringing model teeth replicated in the opposing cast into bite-like contacting registration with the occlusal surfaces of the prosthetic model and adjacent teeth replicas of the master cast. This registration check, generally must be repeated several times, to ensure proper sculpting of the occlusal surface of the die segment which serves as a model for fabricating a dental prosthesis. Moreover, it is essential that the biting contact or occlusion between the teeth replicated by the master cast and opposing cast precisely duplicate occlusion of the patient&#39;s teeth. Therefore, the master cast and opposing cast must be precisely and repetitively pivotably contacted against one another in a motion which simulates the opening and closing of a patient&#39;s jaws. Upon satisfactory completion of sculpting of lateral and occlusal surfaces of die segments, the die segment is used as a mold pattern for casting a metal, ceramic, or metal-ceramic composite dental prosthesis.  
           [0011]    One type of device which is used to pivotably register master and opposing dental models or arches is referred as an articulator. For example, Cho, U.S. Pat. No. 6,019,601, Tray Modeling System With Articulator Assembly And Ejection Mechanism For Producing A Dental Model, discloses a pair of trays which are removably and pivotably joined together by detachable hinge members. Each tray has formed upon an upper surface thereof a rectangularly-shaped, trough-like depression, the longest inner facing side walls of the trough having formed therein alternating vertically disposed ribs and grooves. The device is used by pouring a thick paste of liquid die stone slurry into both a dental impression and the tray, and inverting the impression to enable the liquid die stone slurries in the impression and tray to commingle. When the die stone has solidified, the impression is removed from the cast, and the cast removed from the tray by punching through a frangible base panel in the tray, forcing the cast vertically outwards from the trough. The cast is then sawed into segments, which are returnable to precisely repeatable locations within the trough because of the interlocking ribs and grooves formed in the vertical walls of the cast by die stone solidifying in the grooves and ribs, respectively, of the trough side walls, during hardening of the die stone. In the same manner, an opposing cast is made in the other tray, and the trays pivoted towards one another on the hinge pins to precisely and repeatedly bring the occlusal surfaces of the opposing cast and master cast into occlusal registration.  
           [0012]    The Cho modeling system and articulator provides a convenient means for preparing and articulating dental models. However, some dental technicians prefer working with die segments which have an elongated cylindrical pin protruding from the base of the die segment. In modeling systems using pinned die segments, the pins are insertably received in holes provided in the base of a tray, and are used to reproducibly position or relate individual die segments to adjacent portions of the master cast. Moreover, a pin protruding from a die segment provides a convenient handle which enables the dental technician to hold a die segment while working on it, including rotating the die segment a full 360 degrees by twisting the die segment pin between the thumb and forefinger of the dental technician. Thus, Sim, U.S. Pat. No. 6,402,513, Dental Model Articulator, discloses a dental model articulator which has pinned die segments. The dental model articulator disclosed in Sim utilizes a top insert which has front and rear upwardly protruding ridges that have grooved upper surfaces. The insert is detachably supported on a lower frame. To pour a master cast of a dental impression, a middle frame must be fastened to a lower frame and around the top insert by engaging slots on left and right sides of the middle frame with retentive latches which protrude upwards from the lower frame, on left and right sides of an upper opening in the lower frame which holds the top insert. According to the disclosure of Sim, the middle frame is discarded after completion, of a second pour of liquid die stone through a bottom opening of lower frame, to form a perforated matrix for receipt of pins installed in the base of the first impression casting. The grooved insert is discarded after the first pour.  
           [0013]    The present invention was conceived of to provide an improved dental prostheses modeling system which utilizes die segments which each have ribs and grooves for repeatable removal from and re-registration within a cast, as well as a downwardly protruding pin for facilitating both manipulation of the die segment and reinsertion into the cast, the die segment being quickly and easily fabricated using a sparse number of components and steps.  
         OBJECTS OF THE INVENTION  
         [0014]    An object of the present invention is to provide a dental prostheses modeling system for fabricating models of human teeth from impressions made thereof.  
           [0015]    Another object of the invention is to provide a dental prostheses modeling system which includes a tray having in an upper part thereof a trough for receiving a semi-liquid modeling material or casting material such as plaster of Paris or die stone, the trough having opposed vertical walls in which are formed alternating vertically disposed ribs and grooves for forming a casting, a base portion of which has in outer walls thereof alternating vertically disposed grooves and ribs, the trough having a frangible base plate which overlies an upwardly concave cavity for receiving liquid die stone after the upper casting has solidified, hardened and been removed, the base plate being broken and removed to uncover an elongated aperture joining the upper trough to the lower cavity, enabling the casting to be pushed upwardly out of the tray, pins fitted into selected portions of the casting base, the casting reinserted into the trough, and the tray inverted to receive liquid die stone which hardens to form a stone base matrix for insertably receiving pins protruding downwardly from portions of the casting, the casting being then removed from the trough in the upper portion of the tray and severed into segments which are releasably re-engageable along with adjacent portions of the casting within the tray, proper registration between segments of the casting being effected by insertable receipt of pins within holes formed in the die stone base during hardening thereof, and engagement between ribs and grooves of the casting segments with complementarily-shaped grooves and ribs in the inner side walls of the upper tray trough.  
           [0016]    Another object of the invention is to provide a dental prostheses modeling system which includes a pair of upper and lower trays for use in forming cast dental models of upper and lower teeth from impressions thereof, the trays being hingedly joinable to enable master and opposing dental castings formed in the trays to pivotably contact one another to ascertain proper occlusion between surfaces of teeth modeled by the master and opposing casts, each tray having in an upper part thereof a trough having formed in inner facing walls thereof alternating inwardly projecting ribs and grooves, the trough having a frangible base plate which may be pushed upwardly to cause it to break and eject a hardened dental model casting from the tray, whereupon vertically downwardly disposed pins may be installed in the bases of selected segments of the casting, the casting replaced in the trough with the pins, now coated with a release agent, protruding downwardly through the opening left by removal of the frangible base plate, and liquid die stone poured into a concave lower portion of the inverted tray to form upon hardening a base stone matrix having holes formed through its thickness dimension by the pins, whereupon the casting may be removed from the upper trough portion of the tray, and segmented by vertical cuts into a desired number of die segments each having a pin protruding downwardly from its base, and the die segments releasably replaced in the tray in precise relative relationship because of indexing provided by the die segment pins be insertably received in corresponding hoes in the base die stone matrix, and engagement between vertically disposed ribs and grooves molded in the sides of the casting with corresponding grooves and ribs in the inner facing walls of the trough.  
           [0017]    Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.  
           [0018]    It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, we do not intend that the scope of our exclusive rights and privileges in the invention be limited to details of the embodiments described. We do intend that equivalents, adaptations and modifications of the invention reasonably indexable from the description contained herein be included within the scope of the invention as defined by the appended claims.  
         SUMMARY OF THE INVENTION  
         [0019]    Briefly stated, the present invention comprehends a system which includes an apparatus and method for fabricating models of human teeth; the models are subsequently used in the fabrication of dental prostheses such as crowns and bridges made of various combinations of metal and ceramic materials and used to overlie or replace imperfect or missing teeth. According to the invention, methods and apparatus are provided for making dental impression casts which are segmentable into die segments for use as models in fabricating dental prostheses.  
           [0020]    According to one aspect of the invention, a molding tray for molding the base of a dental model cast has formed in opposed inner walls thereof horizontally outwardly protruding protrusions alternating with horizontally inwardly protruding depressions. Complementary-shaped depressions and protrusions are formed in opposed inner facing walls of the base of a cast formed from solidified liquid die stone poured into the tray. According to the invention, the tray includes a horizontally disposed, frangible base plate which is located between upper and lower surfaces of the tray. The frangible base plate serves as a support base for pouring a casting within a shallow depression or trough in the upper portion of tray. Semi-liquid die stone is poured to overflowing into a dental impression mold containing imprints of a patient&#39;s teeth and poured to overflowing into the trough in the upper portion of the tray. The filled impression is then inverted, positioned over the tray, and pressed down into semi-liquid die stone in the tray. The liquid die stone in the impression and tray co-mingle, eventually hardening to form a unitary cast comprising a base portion molded in the tray and an upper portion which replicates teeth which imprinted the impression mold. After the cast has hardened, an upwardly directed force is exerted on the underside of the frangible base plate, breaking the base plate and ejecting the hardened cast upwardly out of the tray. The hardened cast is then inverted, and blind bores are drilled into the lower surface of the inverted base of the cast, the bores being positioned in vertical alignment with cast replicas of selected teeth which are to serve as models for fabricating individual prostheses. Cylindrically-shaped pins are then inserted into the bores, and the cast is then flipped over to an upright position, with pins protruding perpendicularly downwards from the base of the cast, and reinserted into the upper opening of the tray. Ribs and grooves molded into opposite longitudinally disposed vertical sides of the cast base vertically slidably engage with complementary-shaped grooves and ribs in the inner side walls of the tray which formed the ribs and grooves of the cast. This arrangement ensures that the cast is returned to a previously predetermined lateral index position relative to the horizontal tray perimeter. Moreover, the cast is returned to a previously predetermined vertical position within the tray by abutting contact between the lower surface of the base of the cast and a flat rectangular ring-shaped upper edge wall of the tray. The tray and inserted cast are then inverted, with the casting secured from falling out of the tray by a preferred method described below. Liquid die stone is then poured into a lower opening of the tray to a level between the lower edge of the tray and the downwardly protruding ends of the indexing pins, which are coated with a liquid release agent before pouring the die stone. Liquid die stone within the lower part of the tray is then allowed to harden, forming a stone base matrix. An upwardly directed force is then exerted on the bottom surface of the stone base matrix, thereby pushing the cast upwardly out of the tray. The cast is then segmented into individual die segments for modeling individual prostheses, by making one or more saw cuts vertically through the cast, adjacent to a selected die segment. Individual die segments are once again reinserted into the upper opening of the tray, to thereby re-assemble a complete cast comprised of individual die segments and adjacent portions of the cast within the tray. Placement of the pinned die segments within the tray is facilitated by initial approximate alignment of mating ribs and grooves in the inner sides of the tray and the outer sides of the die segment effected by partial insertion of a die segment pin into the upper opening of a corresponding pin bore through the stone base matrix in the lower part of the tray. The combined aligning forces provided by insertion of a pin into a pin bore, and subsequent inserting of casting ribs into tray grooves, enables individual die segments to be quickly and easily removed from the tray, subjected to various prosthesis modeling operations, and returned to a precisely repeatable, indexed position within the cast, as many times as is required.  
           [0021]    A preferred embodiment of a pin tray modeling system according to the present invention includes an opposing tray for making a casting of a dental impression which was made of teeth opposed to those which are to be fitted with prostheses. The preferred embodiment also includes components which hingedly couple a master tray holding a master impression cast to an opposing tray holding an opposing impression cast and forming therewith an articulator mechanism which enables the occlusal surfaces of the master and opposing casts to be brought into pivotable contact with one another, thereby simulating closure of a patient&#39;s jaws and proper occlusion of the teeth modeled in the two casts. If dental prostheses are required only for one jaw, the cast made of the opposing jaw does not have to have removable die segments. Therefore, the opposing tray need not be provided with the previously described structural features which enable die segments to be removed and replaced within the tray. However, to minimize the number of different type parts required by the present system, the opposing tray may be constructed identically to the master tray, even though the frangible base and indexing grooves and ribs are not required for the opposing cast, since it may remain permanently affixed to the tray.  
           [0022]    In any event, both the master and opposing trays, which may be of identical construction, are provided with a hinge coupler bracket which extends longitudinally outwards from a short end of each tray. The bracket has the shape of a bifurcated L-bracket including a flat longitudinally disposed horizontal floor plate which extends perpendicularly outwards from a short vertical end wall of the tray. The floor plate of the bracket has a flat horizontally disposed upper surface which is recessed slightly below the upper surface of the perimeter edge wall of the tray. A pair of rectangularly-shaped connector plates protrudes upwardly from an outer longitudinal end portion of the floor plate. The outer connector plates from a pair of trays are releasably joined together by a hinge coupler member that has an upper piano-type hinge, and opposed horizontal upper support plates located on opposite sides of a horizontally disposed hinge pin. The hinge coupler has protruding perpendicularly downwardly from outer ends of each support plate a vertical connector plate which has at the lower end thereof a pair of inwardly facing C-shaped channel members which have therein opposed vertically disposed C-shaped channels adapted to insertably receive an outer upstanding end plate of a tray coupler. This construction enables the outer slotted ends of the hinge coupler to be readily slipped removably over the upstanding connector flange plates of a longitudinally aligned pair of trays, i.e., a master tray and an opposing tray, and thereby hingedly coupling the two trays together so that upper surfaces of the trays may be pivoted towards and away from one another to simulate closure and opening of a patient&#39;s jaws. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is an exploded upper perspective view of a pair of trays and a hinge coupler comprising components of pin tray dental prostheses modeling system according to the present invention.  
         [0024]    [0024]FIG. 2 is a side perspective view of the components of FIG. 1.  
         [0025]    [0025]FIG. 3 is a lower plan view of the components of FIG. 1, with the hinge coupler connected to the two trays.  
         [0026]    [0026]FIG. 3A is an upper plan view of the hinge coupler of FIG. 3.  
         [0027]    [0027]FIG. 3B is a lower plan view of the hinge coupler of FIG. 3.  
         [0028]    [0028]FIG. 4 is a perspective view showing a first step of a method for making a modeling cast or “arch” from a single quadrant impression mold made of a group of a patient&#39;s teeth located in either an upper or lower jaw and including one or more teeth to be renovated.  
         [0029]    [0029]FIG. 5 is a perspective view of the arrangement of FIG. 4 showing a second step in making a dental model cast from a single quadrant impression.  
         [0030]    [0030]FIG. 6 is a perspective view showing a completed master dental model casting residing in a first tray in which it was cast, an opposing cast positioned above the master cast with occlusal surfaces of upper and lower replica teeth in the opposing and master casts temporarily adhered together in proper occlusal registration by blobs of wax, and the first, master tray coupled to a second, opposing tray by a hinge coupler.  
         [0031]    [0031]FIG. 7 is a view similar to that of FIG. 6, but showing semi-liquid die stone applied to both the upper surface of the opposing cast, and the upper surface of the opposing tray.  
         [0032]    [0032]FIG. 8 is a view similar to that of FIG. 7, but showing the opposing tray pivoted on the axis of the hinge coupler to thereby bring the semi-liquid die stone material in the opposing tray and the upper surface of the opposing casting into contact to thereby co-mingle and cohere upon hardening, thus securing the opposing cast to the opposing tray.  
         [0033]    [0033]FIG. 9 is a perspective view showing a first step in a method of making a master dental model cast and an opposing cast from master and opposing impression molds made of teeth in opposite jaws of a patient by a double-bite or “triple” impression tray.  
         [0034]    [0034]FIG. 10 is a perspective view of a second step in fabricating master and opposing articulated casts according to the present invention.  
         [0035]    [0035]FIG. 11 is a perspective view of a third step in the method of FIG. 10.  
         [0036]    [0036]FIG. 12 is a perspective view of a fourth step of the double-tray method of FIG. 10, as well as that the single tray method of FIGS.  4 - 8 .  
         [0037]    [0037]FIG. 13 is a perspective view of a fifth step in the double tray method of FIG. 10, as well as the single tray method of FIGS.  4 - 8 .  
         [0038]    [0038]FIG. 14 is a perspective view of a sixth step in the double tray method of FIG. 10, as well as the single tray method of FIGS.  4 - 8 .  
         [0039]    [0039]FIG. 15 is a perspective view of a seventh step in the double tray method of FIG. 10, as well as the single tray method of FIGS.  4 - 8 .  
         [0040]    [0040]FIG. 16 is a perspective view of a completed articulatable model of a pair of master and opposing dental modeling system casts fabricated using the method and apparatus according to the present invention.  
         [0041]    [0041]FIG. 17 is a fragmentary view of the article of FIG. 16 on an enlarged scale, showing a die segment thereof.  
         [0042]    [0042]FIG. 18 is another fragmentary view of the article of FIG. 11 on an enlarged scale, showing part of a master cast with the die segment of FIG. 17 removed from the cast.  
         [0043]    [0043]FIG. 19 is a perspective view of a knock-out template for removing a frangible base plate of the tray shown in FIGS.  1 - 3 .  
         [0044]    [0044]FIG. 20 is a side elevation view of a knock-out tool useable with the template of FIG. 19 to remove a frangible base plate from the tray of FIGS.  1 - 3 .  
         [0045]    [0045]FIG. 21 is a perspective view of a sawing stand for use with the method of the present invention.  
         [0046]    [0046]FIG. 22 is a perspective view of a drilling alignment fixture comprising a component for use in an alternative embodiment of a pin tray dental prostheses modeling system according to the present invention.  
         [0047]    [0047]FIG. 23 is a perspective view of an alternative method for removing a frangible base plate from a tray comprising a component of the apparatus according to the present invention, without simultaneous ejection of a dental model cast from the tray, as shown in FIG. 12.  
         [0048]    [0048]FIG. 24 is a perspective view showing the tray of FIG. 23, with the frangible base plate removed and slidably supported on the drilling alignment fixture of FIG. 22.  
         [0049]    [0049]FIG. 25 is a perspective view showing how the drilling jig of FIGS. 22 and 24 is used to guide drilling of pin bores into the base of the dental model cast shown in FIGS. 23 and 24.  
         [0050]    [0050]FIG. 26 illustrates one method for installing die segment pins in pin bores formed in the dental model cast as shown in FIG. 25.  
         [0051]    [0051]FIG. 27 illustrates one method for segmenting the dental model cast of FIGS.  23 - 26  into individual die segments.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0052]    A. Drawing Description Summary  
         [0053]    FIGS.  1 - 3  and  19 - 21  illustrate components of a basic embodiment of dental prostheses modeling system according to the present invention, while FIG. 22 illustrates a drilling alignment fixture for use in an alternate embodiment of the system.  
         [0054]    FIGS.  4 - 8  illustrate steps in a method of making a dental model cast from a single quadrant impression for use in fabricating dental prostheses, according to a basic embodiment of the invention.  
         [0055]    FIGS.  9 - 11  illustrate preliminary steps in making master and opposing dental model casts from master and opposing mold impressions made by teeth in upper and lower jaws of a patient, use a “double-bite” or “triple” impression tray.  
         [0056]    FIGS.  12 - 15  illustrate further steps in the method of fabricating a dental prostheses model according to the present invention, from either a single-bite or double-bite impression.  
         [0057]    FIGS.  16 - 18  illustrate a finished pair of dental prostheses model casts mounted in an articulator according to the present invention.  
         [0058]    FIGS.  23 - 27  illustrate steps in an alternative method for making dental model casts according to the present invention.  
         [0059]    B. Detailed Description  
         [0060]    Referring now to FIGS.  1 - 3 , an apparatus  30  for making pin-tray dental prostheses models according to the present invention may be seen to include a pair of molding trays  31 A,  31 B which are releasably connectable by a hinge mechanism  32 . As shown in FIG. 16 and as will be described in detail below, hinge mechanism  32  enables trays  31 A,  31  B to be pivoted between a mutually co-planar horizontally disposition as shown in FIGS. 1 and 2, to a configuration in which one of the molding trays overlies the other in a generally parallel disposition, as shown in FIG. 16. As will be made clear in the ensuing description, only one of molding trays  31 A,  31  B need by provided with certain novel structural features according to the present invention, if a removable dental model cast is to be made of teeth in a single jaw of a patient. However, according to a preferred method of practicing to the invnetion, trays  31 A and  31 B may be identical, and for the sake of brevity in the ensuing description, the letter suffix A or B is deleted unless necessary to distinguish between two trays, e.g., a tray in which a master dental cast is molded versus a tray in which an opposing cast is molded.  
         [0061]    As shown in FIGS.  1 - 3 , each tray  31  has a longitudinally elongated rectangular plan view shape. Tray  31  preferably has flat and parallel upper and lower surfaces  33 ,  34 , respectively. Also, tray  31  has longitudinally elongated, rectangularly shaped, vertically disposed front and rear side walls  35 ,  36 , a rectangularly shaped inner (hinge side), vertical end wall  37  and an outer vertically disposed end wall  38 .  
         [0062]    As shown in FIG. 1, tray  31  has formed in an upper part thereof of a relatively shallow rectangularly-shaped depression or trough  39 . Trough  39  is concentric with the outer vertically disposed perimeter wall surface  40  of tray  31 , and is nearly as large as the outer perimeter of the tray. Thus arranged, a thin rectangularly-shaped peripheral ring  41  is formed between trough  39  and outer vertical perimeter wall surface  40  of tray  31 . Peripheral ring  41  around trough  39  has a flat, horizontally disposed base wall  42 . Peripheral ring  41  has disposed perpendicularly upwards from the base wall  42  an inner peripheral wall  43  which has inner wall surfaces, including front inner surface  45 , rear inner surface  46 , left inner surface  47 , and right inner surface  48 .  
         [0063]    As shown in FIG. 1, larger front and rear inner wall surfaces  45 ,  46  of peripheral ring  41  have formed therein a plurality of ribs  49  which protrude inwardly towards a longitudinal center line of trough  39 . Ribs  49  protrude vertically upwardly of base wall  42 , and form between each adjacent pair of ribs a vertically disposed notch or grooves  50 . As will be described in detail below, alternating ribs and grooves  49 ,  50  form complementary grooves and ribs in outer vertical surfaces of the base of a dental model cast formed in trough  39  by solidified liquid die stone poured into the trough, thus enabling the bases and individual segments cut from the base, to be removably returned to exact pre-existing locations within tray  31 , because of the indexing action of the ribs and grooves being insertably received within complementary-shaped grooves and ribs molded into the sides of the model cast by hardened liquid die stone.  
         [0064]    Referring now to FIGS. 1, 2, and  3 , it may be seen that tray  31  is provided with front and back or rear abutment flanges  55 F,  55 B, which protrude outwardly from front and rear walls  35 ,  36 , respectively, of tray  31 . As shown in the figures, each abutment flange  55 F,  55 B has the shape of a horizontally disposed, thin, longitudinally elongated rectangular rib or web which has an outer vertical wall surface  56  that is spaced outwards from an outer front or rear wall of tray  31 , and flat and parallel, horizontally disposed, upper and lower surfaces  57 ,  58 , respectively. The function of front and rear abutment flanges  55 F,  55 B are described below.  
         [0065]    Referring now to FIGS. 1 and 3, it may be seen that base wall  42  of trough  39  in molding tray  31  has a flat upper surface  59 , and includes an outer rectangular ring-shaped portion  60  which is joined to the inner wall surfaces of the front, rear, inner and outer end walls of the tray. Base wall  42  also includes a concentrically located, longitudinally elongated rectangularly-shaped center panel  61 . Base wall  42  has a thickness of less than the height of tray  31 , e.g., about {fraction (1/16)} inch for a tray height of about {fraction (7/16)} inch, and upper surface  59  of base wall  42  is located about {fraction (1/16)} inch below upper peripheral edge wall  33  of the tray. Thus arranged, base wall  42  forms within a lower portion of tray  31  a relatively deep, e.g., about ⅜ inch, lower upwardly concave opening or “matrix” trough  63  which protrudes upwardly from lower peripheral face  64  of the tray.  
         [0066]    Referring still to FIGS. 1 and 3, it may be seen that center panel  61  of base wall  42  is connected to outer rectangular ring-shaped portion  60  of the base wall by a plurality of readily breakable, or frangible members  65 . Thus, as shown in FIG. 3, outer vertical wall surface  66  of base wall center panel  61  is joined to inner vertical wall surface  67  of ring-shaped portion  60  of the base wall by a plurality of thin, breakable pins  65 , e.g., a pair of front and rear pins and a pair of left and right pins. In a preferred embodiment, a tray  31  is fabricated as a unitary molded plastic part, with outer surface  66  of center panel  61  angled downwardly and inwardly away from adjacent inner wall surface  67  of ring-shaped outer portion  60  of base wall  42 . With this construction, pins  65  may be readily molded to have a thickness substantially less than that of center panel  61 , thus enabling the pins to be readily broken and thereby permitting the center panel to be broken away and removed from tray  31 . With center panel  61  thus removed from tray  31 , base wall  42  of the tray has through its thickness dimension a concentrically located, longitudinally elongated rectangular-shaped aperture  69 .  
         [0067]    As shown in FIG. 3, center panel  61  of tray base wall  42  preferably is provided with one or more bosses  70  which protrude perpendicularly downwards from the lower surface  71  of the base wall. Although the exact shape and size of bosses  70  is not critical, the embodiment of tray  31  shown in FIG. 3 has three square cross-section bosses  70  which each have a flat lower surface  72  and a blind circular bore  73  which extends perpendicularly upwards from the lower surface. The three bosses  70  include a longitudinally centrally located center boss  70 C, and left and right bosses  70 L,  70 R spaced equal distances outwards of the center boss. The function and purpose of bosses  70  is described below.  
         [0068]    Referring still to FIGS. 1, 2 and  3 , it may be seen that each tray  31  has protruding horizontally outwards from a short end wall  37  thereof a hinge coupler bracket  74  for releasable attachment to hinge mechanism  32 . Each hinge coupler bracket  74  has a shape approximating that of an L-bracket, an upright leg of which is bifurcated into two spaced apart, parallel plates. Thus, as shown in FIGS.  1 - 3 , hinge coupler bracket  74  includes a rectangularly-shaped base plate  75  which protrudes outwardly from end wall  37  of tray  31 . Base plate  75  has horizontally disposed upper and lower surfaces  76 ,  77  which are parallel to upper surface  33  of tray  31 . Upper surface  76  of bracket base plate  75  is preferably recessed below upper surface  33  of the perimeter edge wall of tray  31 , and has protruding perpendicularly upwards therefrom a first, outer rectangularly-shaped upright leg plate  78 . Outer upright leg plate  78  has an outer vertical surface  79  which is co-planar with outer vertical edge wall  80  of a base plate  75 .  
         [0069]    Bracket  74  includes a second, inner upright leg plate  81  which is shaped similarly to outer leg plate  78 , and which protrudes perpendicularly upwards from base plate  75  at a location spaced longitudinally inwardly from the outer upright leg plate. Inner upright leg plate  81  has an outer vertical wall surface  82  which is spaced longitudinally inwards of and parallel to an inner vertical wall surface  83  of outer leg plate  78 . Preferably, a rectangularly-shaped aperture  84  is formed through base plate  75  of bracket  74 , between outer and inner upright leg plates  78 ,  81 . The purpose of aperture  84  is to facilitate elastic flexure of the outer and inner leg plates away from and towards one another, thereby facilitating elastic gripping engagement of hinge mechanism  32 , as will be described below.  
         [0070]    Referring still to FIGS.  1 - 3 , it may be seen that hinge mechanism  32  of apparatus  30  includes a pair of rectangular plan-view hinge members  85 ,  86 , each having a thin upper rectangularly-shaped plate  87 , 88 . Plate  87  has a pair of spaced apart, coaxially tubular extensions  89 , 90 , which protrude upwardly from an inner end of the plate, parallel thereto. Plate  88  has a single, centrally located tubular extension  91  which fits coaxially between tubular extensions  89 ,  90  of plate  87 , and is hingedly joined thereto by an elongated cylindrical hinge pin which is disposed rotatably through bores  89 A,  90 A, and  91 A of the tubular extensions. The other parts of hinge members  85 ,  86  are identical, and include a larger rectangularly-shaped coupler plate  92  which depends perpendicularly downwardly from outer edge  93  of each upper plate. Coupler plate  92  has at opposite sides of a lower horizontal edge wall  94  thereof a pair of vertically disposed, L-shaped guide members  95  which form therebetween a pair of vertically disposed C-shaped channels  95 A which are adapted to vertically upwardly insertably receive an inner upright leg plate  81  of a tray  31 . Each hinge member  85 ,  86  also has protruding laterally inwardly from the L-shaped guide member  95  a vertically disposed lug member  96 . Each lug member  96  has an inner vertical edge wall  97  which is located parallel to and laterally spaced apart from an inner vertical edge will  98  of coupler plate  92 . As shown in FIG. 2, inner facing edge walls  97  of lug members  96  abut to limit inward pivotable motion of the coupler plates to a parallel position. As shown in FIG. 3B, inner vertical edge wall  98  of each coupler plate  91  preferably has formed therein a plurality of parallel, horizontally disposed, triangular cross-section ribs  100  which alternate with grooves  101  to form a washboard-like surface  102 . The thickness of hinge coupler plate  92 , measured between the vertices of triangular webs  100  and outer surface  102  of the coupler plate, is slightly greater than the spacing between an inner and outer faces  103 ,  104  of outer and inner leg plate uprights  78 ,  81  of hinge coupler bracket  74  of try  31 . Thus, when coupler plate  92  is inverted downwardly into the space  104  between the tray upright leg plates, the latter flex elastically slightly apart, and ribs  100  bite into the plates slightly, thus frictionally engaging the coupler plate with the tray legs. A description of certain components of a pin tray dental prostheses modeling system according to the present invention having been given, the manner of using those components according to methods of the present invention is presented below.  
         [0071]    [0071]FIG. 4 illustrates a first step in making a dental prostheses model cast or “arch” from a single quadrant impression mold made of a group of a patient&#39;s teeth located in an upper or lower jaw of the patient. As shown in FIG. 4, the trough  39  in the upper portion of a first molding tray  31 A is fitted with a semi-liquid die stone material such as plaster of Paris, to a level slightly above upper peripheral wall  33  of the tray. As is also shown in FIG. 4, a dental impression mold A containing imprints B of a patient&#39;s teeth is also filled to overflowing with liquid die stone. The filled impression A is then inverted, positioned over tray  31 , and pressed down onto the semi-liquid die stone in the tray, as shown in FIG. 5. The semi-liquid die stone in impression A thus co-mingles with that in tray  31 . Time is then allowed for the liquid die stone in tray  31  to harden into a stone-like cast. Next, impression mold A is peeled upwardly and off from the hardened die stone in tray  31 , leaving therein a cast C which is an accurate replica of teeth which impressed or imprinted the impression mold.  
         [0072]    Next, as shown in FIG. 6, a cast D made of an impression taken of teeth opposing those which are to be restored and which imprinted impression A is positioned above first, master cast C, which replicates teeth for which prostheses are to be fabricated. Opposing cast D is positioned in proper occlusal contact with master cast C, and temporarily secured in that configuration by blobs of wax E, for example, as shown in FIG. 6. Next, as shown in FIG. 7, a second, opposed tray  31 -B, coupled by hinge mechanism  32  to tray  31 -A containing master dental model cast C, is filled to overflowing with liquid die stone, as is upper surface of opposing cast D. Then, as shown in FIG. 8, the upper surface of opposing tray  31 -B is pivoted towards contact with upper surface F of opposing cast D, causing die stone in the upper impression to co-mingie with that in the opposing tray. Time is once again allowed for the liquid die stone in opposing tray  31 -B and opposing cast D to harden. Wax blobs E are then heated slightly to melt the wax, enabling opposing tray  31 -B, now secured to opposing cast D by solidified die stone, to be pivoted away from master cast C. Further processing steps used to complete pinned dental model cast C are described below, following a description of preliminary steps for making master and opposing casts from a double-bite, or triple tray impression; the final steps of making finished casts are the same for both single quadrant and triple tray impression casts.  
         [0073]    FIGS.  9 - 11  illustrate a method of making dental model casts from double-bite or triple-tray impressions according to the present invention.  
         [0074]    [0074]FIG. 9 shows a first step in making a dental prostheses model cast from a double-bite or triple-tray impression mold G made from a patient&#39;s teeth located in lower or upper jaw and including teeth which are to be replaced by or fitted with one or more prosthetic restorations or replacements, and occluding teeth in an opposing jaw. As shown in FIG. 9, trough  39  in the upper portion of a first molding tray  31 -α is filled with a semi-liquid, hardenable modeling substance such as plaster of Paris or die stone, to a level slightly above upper peripheral wall surface  33  of the tray. As is also shown in FIG. 9, a concave depression in a first, master side H of two-sided dental impression G imprinted with teeth which are to be restored, is also filled to overflowing with liquid die stone. The filled master side impression H is then inverted, positioned over tray  31 -α, and pressed down into the semi-liquid die stone in the tray, as shown in FIG. 10. The semi-liquid die stone in the impression H thus co-mingles with semi-liquid die stone material in tray  31 -α. Time is then allowed for the liquid die stone in tray  31 -α and master impression H to harden into a stone-like master cast J. Next, liquid die stone is poured to overflowing into a second, opposing tray  31 -β, which is pivotably connected to first tray  31 -α by a hinge mechanism  32 . As is also shown in FIG. 11, a concave depression in second, opposing side K of two-sided impression mold G imprinted with teeth in a jaw opposed to the jaw containing teeth to be restored, is filled to overflowing with liquid die stone. As shown in FIG. 11, opposing tray  31 -β is then pivoted towards contact with the upper surface of semi-liquid die stone in concave impression area K of the opposing impression, causing die stone in the upper, opposing impression to co-mingle with die stone in the upper, opposing tray. Time is once again allowed for the semi-liquid die stone in opposing tray  31 -β and opposing impression K to harden into a stone-like opposing cast L. Next, a master dental model cast J formed in master tray  31 -α is temporarily and replacably removed from the tray, in the following manner.  
         [0075]    A preferred method for removing master dental model cast J from tray  31 -α consists essentially of exerting an upwardly directed force on center panel  61  of base wall  42  of the tray which is of sufficient strength to break pins  65  which join the center panel to peripheral ring panel  60  of the base wall, and then pushing upwardly on that portion of the lower surface M of a cast J that is accessible through aperture  69  through the base wall. According to a preferred method of removing cast J from tray  31 -α, a template  90  and tool  91 , shown in FIGS. 19 and 20, are employed.  
         [0076]    As shown in FIG. 19, template  90  includes a flat base  42  having a longitudinally elongated, rectangular shape. Base  92  of template  90  has protruding perpendicularly upwards from a flat upper surface  93  thereof a longitudinally elongated, rectangularly shaped lug  94  which has a vertically disposed peripheral wall surface  95  that is located concentrically with respect to the outer peripheral wall surface  96  of the base, and has a flat upper surface  97  disposed parallel to upper surface  93  of base  92 . Template  90  also includes at opposite short ends  98 ,  99  thereof a pair of opposed, vertically disposed guide structures  100 ,  101  which have formed therein a pair of opposed inner facing C-shaped guide spaces  102 ,  103  which together form an open rectangular-shaped tray receipt space  104  which is concentric with outer peripheral wall surface  95  of lug  94 . As shown in FIGS. 12 and 19, tray receipt space  104  has a rectangular plan view shape which is similar to that of tray  31 , but of larger size so that the tray may be loosely inserted downwardly into the space, the bottom surfaces  72  of bosses  70  if base wall  41  abutting upper surface  97  of lug  94 .  
         [0077]    As shown in FIG. 20, a knock-out tool  91  according to the present invention includes a rectangular block-shaped body  105  which has vertically elongated, rectangularly-shaped parallel left and right side walls  106 L,  106 R, and narrower, vertically elongated, rectangularly-shaped parallel front and back side walls  107 F,  107 B, which are perpendicular to the side walls. Body  105  has disposed perpendicularly through left and right side walls  106 L,  106 R thereof an arch-shaped tunnel  108 . Body  105  of tool  91  has a flat, horizontally disposed upper end wall  109 , and a flat lower wall surface  110 . Tunnel  108  penetrates lower wall surface  110 , thus defining between front and back side walls  107 F,  107 B a pair of front and rear legs  111  F,  111  B which have opposed lower, inner vertical wall surfaces  112 F,  112 B which border the tunnel. Legs  111  F,  111  B each has at a lower end thereof a laterally disposed rectangularly shaped foot flange  11   3 F,  11   3 B which has a flat lower surface coextensive with lower wall surface  110  of body  105 , and flat, parallel upper surfaces  114 F,  11 B. Foot flanges  113 F,  113 B protrude horizontally a short distance inwards into tunnel  108 , and have vertically disposed, inner facing parallel end walls  115 F,  115 B. Foot flange front and back end walls  115 F,  115 B are spaced apart at a distance slightly greater than the space between the outer surface of front and peripheral upper edge walls of tray  31 .  
         [0078]    [0078]FIG. 12 illustrates the use of template  90  and knock-out tool  91  to remove a dental cast J from tray  31 -α. As shown in FIG. 12, tray  31 -α containing cast J is placed in opening  104  of template  90 , with bottom surfaces  72  of bosses  70  supported on upper surface  97  of lug  94 . Knock-out tool  91  is then positioned above front and back abutment flanges  55 F,  55 B of tray  31  with lower surfaces of front and back knock-out tool flanges  113 F,  113 B contacting the upper surfaces of the abutment flanges of the tray. A sharp blow is then delivered downwardly to the upper surface of the knock-out tool which causes the knock-out tool flanges to exert a downward force on the tray abutment flanges, thus causing lug  97  to be pushed upwardly on center panel  61  of tray base wall  42 , breaking pins  65  which join the center panel to rectangular ring-shaped portion  60  of the base wall, and thereby ejecting cast J upwardly and out from the tray.  
         [0079]    As shown in FIG. 13, a fifth step in making a dental prostheses model i according to the present invention consists of drilling blind pin bores P into the base M of an inverted cast J, at locations aligned with portions of the cast which are to be severed from adjacent portions of the cast, to thereby form die segments which are to be used as models for dental prostheses. Pin bores are also drilled into locations of the base corresponding to portions of the cast adjacent to die segments.  
         [0080]    After pin bores P have been drilled into cast J as described above, cylindrical metal pins  120  are inserted into the base. As shown in FIG. 13, each pin has a short knurled end  121  and a longer smooth shank  122 . Pin bores P are drilled to a depth approximating the length of knurled end  121  of pin  120 , so that the smooth shank  122  protrudes perpendicularly downwards from lower face N of cast J. Pins  120  are preferably secured in pin bores P by coating knurled ends  121  of each pin with adhesive before inserting a pin into a bore.  
         [0081]    [0081]FIG. 14 illustrates a fifth step in making a dental prostheses model according to the present invention. As shown in FIG. 14, a release agent is applied to the outer surfaces of pins  120 , cast J is re-inserted into trough  39  of tray  31  and the tray is inverted. A release agent is applied to lower face N of cast J, and liquid die stone is then poured into open lower portion  63  of the tray, to a level between the lower end faces  123  of the pins, and the lower peripheral rim  64  of the tray. Liquid die stone within the lower portion is allowed to harden to form a rectangular block-shaped, “stone matrix”  125 . Cast J is once again withdrawn from trough  39  of tray  31 , a task which is facilitated by exerting pressure on lower faces  124  of pins  120 . Base M of pinned cast L is then placed upright in a horizontal channel  126  formed in the upper surface of a sawing stand fixture  127  of the type shown in FIG. 21. A saw S is then used to make vertical cuts-through cast J, on each side of a portion of the cast which is to be used as die segment U for use as a dental prostheses model. After one or more die segments U have been severed from dental model cast J, the die segments and adjacent portions of the cast may be repeatedly re-installed in tray  31  at precisely indexed locations, owing to the interlocking action of ribs and grooves of the cast engaging complementary grooves and ribs in the inner side walls of tray  31 . FIGS. 16, 17, and  18  show a completed articulateable model of a master cast J with replaceable die segments, and an opposing cast fabricated by the above described apparatus and method according to the present invention.  
         [0082]    FIGS.  23 - 27  illustrate a modification of the apparatus and method of the present invention described above. The modified apparatus and method employ the first three steps described above for both single quadrant and double-bite impression models. However, as shown in FIG. 23, a fourth step in the modified method comprises removing frangible center panel  61  of base wall  42  of tray  31  by grasping a center panel boss  70  between the jaws V of a pliers W, and exerting a pulling force sufficient to break center panel support pins  65 . Blind pin bores P are then drilled into the base M of a cast J, in a manner described below, using a drilling alignment fixture  130  of the type shown in FIG. 22.  
         [0083]    As shown in FIG. 22, drilling alignment fixture  130  includes an elongated, generally rectangular-shaped body  131  which has a flat lower surface  132 , and a flat upper surface  133  in which is formed an elongated, shallow rectangular-shaped channel  134  which is adapted to receive a tray  31  containing therein the base M of a cast J.  
         [0084]    Located in front and back sides of channel  134  are coplanar, horizontally disposed flat front and back ledges  135 F,  1 ′ 35 B which are of a proper spacing to support front and rear abutment flanges  55 F and  55 B of a tray  31 .  
         [0085]    Drilling alignment fixture  130  also includes a circular drill guide bushing  136  fitted through a lower wall  137  of the fixture. An index line  138  is inscribed on the outer surfaces of the fixture, in longitudinal alignment with the center line of a coaxial bushing  136 .  
         [0086]    As shown in FIGS. 24 and 25, drilling alignment fixture  130  is used by longitudinally sliding a cast J supported on ledges  135 F,  135 B of the fixture to thereby position a location of the cast where it is desired to insert a pin in longitudinal alignment with bushing bore index line  138 . Drilling alignment fixture  130  and cast J are then rotated together as a unit to expose the lower surface  139  of the fixture, whereupon a drill bit is inserted through bore  140  of bushing  136 , and rotated to drill a pin bore P at a desired location into the base M of cast J. Next, as shown in FIG. 26, pins  120  are inserted into pin bores P made as described above. Then, tray  31  containing cast J, is re-oriented to an upright position, as shown in FIG. 23, and vertical saw cuts are made into the cast to severe die segments from adjacent portions of the cast. The saw cuts are made downwards just to the upper surface levels of front and back abutment flanges  55 F,  55 B. Cutting to the common level of the upper surface of the abutment flanges ensures that the saw cuts are made completely through the thickness of base M of cast J, thus enabling a pinned die segment U to be removed from tray  31 , and re-inserted into a precisely predetermined position relative to adjacent segments of the cast, which need not be removed, and repeatedly removed and re-inserted.  
         [0087]    According to a first variation of the modified apparatus and method described above and illustrated in FIGS.  23 - 27 , after pin bores P have been drilled into the base M of a cast J as shown in FIG. 25, the cast may be ejected from a tray  31 , as for example, using a template  90  and knock-out tool as shown in FIG. 4, Then, pins  120  may be installed in the pin bores P of cast J in the manner indicated in FIG. 13, and the remaining steps of the basic embodiment of the method shown in FIGS. 13 through 15 and described above performed to produce a completed dental prostheses model. According to a second, slightly different variation of the modified apparatus and method depicted in FIGS.  23 - 27 , pins  120  may be installed in bores P of cast J prior to ejecting the cast J from a tray  31 , whereupon the steps of the basic embodiment depicted in FIGS. 14 and 18 and described above performed to produce a complete dental prostheses model.