Abstract:
A dental pin and bushing assembly for coupling of a removable die of a tooth to a working cast. The pin includes an axially extending head that can be secured in the die. The bushing is secured in the working cast, and includes an elongated sleeve with an interior shape for receiving the pin. A collar depends from the head of the pin for positionally locating the pin in a recess in the elongated sleeve. A body of the pin depends from the collar, and is co-axial with the head portion. An interior annular ring in the elongated sleeve mates with an annular groove of the pin when the collar portion is fully seated in the recess. The geometries of the annular ring and groove are such that the interior annular ring snaps into the annular groove, and thereby provides tactile feedback to the dental technician signaling that the pin is fully seated in the bushing.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a dental pin and bushing assembly for coupling removable dies of prepared teeth to working casts.  
         BACKGROUND OF THE INVENTION  
         [0002]    In dental restorations, the dentist prepares a candidate tooth by removing diseased portions and other portions that are required to be removed in order to mount a replacement structure on the tooth. After preparing the tooth in this manner, the dentist typically prepares a negative or impression of the tooth to be restored and of adjoining teeth, and sends this impression to a technician in a dental laboratory to be used as a mold for producing a working cast or model.  
           [0003]    Using any one of a variety of known techniques, models can be constructed in which dies of the individual teeth may be removably positioned. Typically, dowel pins are used to removably couple the dies to the working cast. A removed die, for example, may be advantageously repositioned in a specialized vise to facilitate detailed work on an associated tooth replacement structure.  
           [0004]    After the dies have been properly formed and indexed in the cast, it is important that each die may be repeatedly removed from and returned to its exact position in the cast. In addition, the dies must remain stable when positioned in the cast, even when the cast is inverted.  
           [0005]    U.S. Pat. No. 3,704,519, issued to Lystager on Dec. 5, 1972 describes the PINDEX system, a pin and bushing assembly system commercially available from Colténe/Whaledent Inc. In this system, holes are formed in a removable part of the die. Pins are then fixedly inserted into the removable part, and bushings are placed on ends of the pins extending from the removable part. The extended pin/bushing portions are then pressed downwardly into a casting material that forms a base portion of the working cast. The cast material sets with the bushings in place, after which the dies may be removed by extracting the pins from the bushings. The system employs two pins per removable part in order to ensure proper positioning of the die upon replacement.  
           [0006]    Another dental pin and bushing assembly system is disclosed in U.S. Pat. No. 4,801,264, issued to Weissman on Jan. 31, 1989, and which is hereby incorporated by reference. In the system of Weissman, the dental pin includes an offset section, which mates with a corresponding offset section of the bushing. Using this feature, a removable die may be reliably and properly repositioned in the cast by means of s single pin and bushing assembly.  
           [0007]    A number of dental pin and bushing systems, including the system of Weissman, employ a tapered pin together with a correspondingly tapered mating chamber in the bushing so that the pin may be easily inserted into the bushing, and then firmly located as the tapered pin and bushing surfaces meet. It would be advantageous if the pin and bushing system was further able to provide a recognizable tactile response when the inserted die reaches its appropriate position. It would also be advantageous if the pin and bushing system was able to indicate a secondary pin and die position, for example, to allow the temporary positioning of adjacent teeth at a slightly extended height to serve as a restoration material thickness gauge for the dental technician.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the present invention, a novel dental pin and bushing system comprises a pin having an axially extending head for secured retention in a die of a tooth, an enlarged collar depending from the head and having a radially-projecting key and a lower face, and a body portion depending from the lower face including a cylindrical rod co-axially positioned with respect to the head. The cylindrical rod further includes an annular groove near a distal end of the rod. The body of the pin is matingly received by an axially-directed sleeve in the bushing. The sleeve includes a recess and keyway for receiving the enlarged collar and key in a single positional orientation, and a cavity depending at a proximal end from a seat of the recess. At a distal end, the cavity includes an inwardly directed annular ring for mating with the annular groove of the pin.  
           [0009]    When the body of the pin is inserted into the sleeve, the annular ring of the bushing snaps into the annular groove of the pin as the lower face of the collar mates with the seat of the recess. In this manner, a tactile response is imparted to the die of the tooth and to the working cast to indicate to a technician that the die of the tooth is fully seated.  
           [0010]    In a second aspect of the invention, the enlarged collar and recess interfere when the lower surface of the enlarged collar reaches an upper surface of the bushing at an opening to the recess. As a result, a frictional force is generated that resists further engagement and allows the dental technician to temporarily rest the die of the tooth at this position. This positioning may be of benefit, for example, to provide a material gauge for an adjacent tooth. The die may subsequently be pushed downward until the snap response is felt, indicating that it has reached its fully seated position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    A more complete understanding of the invention may be obtained by reading the following description of specific illustrative embodiments of the invention in conjunction with the appended drawing in which:  
         [0012]    FIGS.  1 - 4  provide isometric views of a dental pin according to the present invention;  
         [0013]    [0013]FIG. 5 provides a perspective view of the dental pin of FIGS.  1 - 4 ;  
         [0014]    FIGS.  6 - 9  provide isometric views of a dental bushing according to the present invention;  
         [0015]    [0015]FIG. 10 provides a perspective view of the dental bushing of FIGS.  6 - 9 ;  
         [0016]    [0016]FIGS. 11A, 11B provide cross sectional views of the inventive pin and bushing of FIGS.  1 - 10  that demonstrate positioning the pin at elevated and seated positions in the bushing;  
         [0017]    [0017]FIGS. 11C, 11D illustrate features of a tooth die for receiving the inventive pin of FIGS.  1 - 4 ;  
         [0018]    [0018]FIG. 12 provides a perspective view of a working cast with removable dies using the inventive pin and bushing of FIGS.  1 - 10 ; and  
         [0019]    [0019]FIGS. 13, 14 provide perspective views of the working cast partially broken away to illustrate operation of the inventive pin and bushing of FIGS.  1 - 10 . 
     
    
       [0020]    In the various figures, like reference numerals wherever possible designate like or similar elements of the invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The following detailed description includes a description of the best mode or modes of the invention presently contemplated. Such description is not intended to be understood in a limiting sense, but to be an example of the invention presented solely for illustration thereof, and by reference to which in connection with the following description and the accompanying drawing one skilled in the art may be advised of the advantages and construction of the invention.  
         [0022]    [0022]FIG. 1 provides a top view of a pin  10  associated with the present invention. The pin  10  includes an axially-extending head  12  for insertion into a die of a tooth, an enlarged collar  14  depending from head  12 , and a body  16  depending from enlarged collar  14  and co-axially positioned with respect to head  12 . In a preferred embodiment of the present invention, enlarged collar  14  is defined to have a substantially rectangular shape. It should be noted that many other shapes are also possible for enlarged collar  14 , and are fully contemplated by the present invention.  
         [0023]    In the preferred embodiment, body  16  comprises a cylindrical rod including a tapered segment  18 , an intermediate segment  20 , and a foot segment  22 . Intermediate segment  20  and foot segment  22  are separated by annular groove  24 . Foot segment  22  may optionally be tapered toward endface  28 . At annular groove  24 , the diameter of foot segment  22  may also be smaller, for example, than the diameter of intermediate segment  20  at annular groove  24 .  
         [0024]    Annular groove  24  may be defined by a variety of shapes and geometries, which are fully contemplated by the present invention. In a preferred embodiment, groove  24  is defined by tapered groove surface  24   a  and ledge  26 . Tapered groove surface  24   a  comprises an annular cone sharing a large diameter at one end with a distal end of intermediate segment  20  and a small diameter at the other end which terminates upon ledge  26 . Ledge  26  is substantially perpendicular to a longitudinal axis  30  of pin  10 , and defines a proximal end of foot segment  22 .  
         [0025]    [0025]FIG. 2 provides a side view of pin  10 . As shown in FIG. 2, enlarged collar  14  further includes bottom surface  36 , top surface  38 , and lateral key  44 . In a preferred embodiment of the present invention illustrated in FIGS. 3 and 4, enlarged collar  14  has a substantially rectangular cross-section, and lateral key  44  has a substantially square cross-section. Key surface  44   a , at an opposing end of enlarged collar  14  with relation to lateral key  44 , is defined by a circular radius. Optionally, identifier  46  may be embossed on tapered segment  18 , collar  14 , or any other suitably large surface of pin  10 .  
         [0026]    Annular collar  40  is interposed between head  12  and top surface  38  of enlarged collar  14 , and includes collar surface  42 . As will be further described with reference to FIGS. 11C and 11D, head  12  and annular collar  40  provide surfaces which may be matably affixed to a tooth die in the working cast (not shown). Optionally, and as shown in FIG. 2, anti-rotation key  44   b  extends on a peripheral surface of annular collar  40  and on a shared axis with lateral key  44  from top surface  38  toward collar surface  42 . As will be further described with reference to FIGS. 11C and 11D, optional anti-rotation key  44   b  provides additional surfaces to be affixed to mating slot surfaces in a tooth die in a manner that prevents rotation of pin  10  within the die.  
         [0027]    As shown in FIG. 2, head  12  may include chamfer  32  at top face  34 . As illustrated in FIG. 3, head  12  may also include flat surfaces  13  on opposing top and bottom portions of its perimeter, and annular collar  40  may include flat surfaces  15  on opposing side portions of its perimeter.  
         [0028]    Head  12  and annular collar  40  are preferably glued in mating cavities in a tooth die, for example, using a conventional cyanoacrylate or other suitable glue. Cyanoacrylates and other suitable glues may tend to release gases as they cure. In an unvented cavity, these gases may expand and operate to push head  12  outwardly from the cavity before a suitable seal is made. As will be further described with reference to FIGS. 11C and 11D in order to avoid such movement of head  12 , flat surfaces  13  and  15  in conjunction with the cavities in which they are seated serve to provide passageways for venting the associated gases. In addition, flat surfaces  13  and  15  provide pockets within the respective cavities in which they are seated where glue may gather for more effective adhesion to the walls of the cavity and flat surfaces  13 ,  15 .  
         [0029]    [0029]FIG. 5 provides a front right perspective view of the pin  10 . Pin  10  may be constructed conventionally from a variety of suitable materials including, for example, a zinc alloy treated with a chromate finish. Features of enlarged collar  14  and body  16  introduced with reference to FIGS.  1 - 5  will be further described herein with reference to additional features of the present invention.  
         [0030]    [0030]FIG. 6 provides a top end view of bushing  60 . Bushing  60  includes a recess  68  for receiving enlarged collar  14  of pin  10 , and a keyway  66  for receiving key  44  of pin  10 . Bushing  60  is constructed of a suitable material (for example, Acetal copolymer resin, commercially available, for example, from DuPont Engineering Polymers, Wilmington, Del.). Recess  68  has an interior shape that is substantially identical to a peripheral shape of enlarged collar  14 . In this manner, enlarged collar  14  and key  44  may be received by recess  68  and keyway  66  in a singular positional orientation. Because bushing  60  comprises a flexible material, enlarged collar may be interferingly received by recess  68 , as will be further described herein. It should be noted that the features of enlarged collar  14 , key  44 , recess  68  and keyway  66  define one of may peripheral shapes that may be used to locate pin  10  within bushing  60  in a singular positional orientation, all of which are fully contemplated within the scope of this invention.  
         [0031]    As illustrated in FIG. 6, bushing  60  optionally includes lateral ribs  62 , which extend from keyway enclosure  67  and recess enclosure lower edge  63 . Ribs  62  provide additional lateral surface area for immovably retaining bushing  60  within the working cast.  
         [0032]    [0032]FIG. 7 presents a top view of bushing  60  illustrating lateral rib  62  extending from keyway enclosure  67 , and optional annular rib  64  extending from barrel  65 . Annular rib  64  is also seen in FIG. 8, which provides a cross-section of bushing  60  through section A-A of FIG. 6. Annular rib  64  provides additional external surface area for immovably retaining bushing  60  within the working cast.  
         [0033]    As shown in FIG. 8, top recess  68  is adjacent to entry cavity  70  at seat surface  69 , and entry cavity  70  is adjacent to a proximal end of intermediate cavity  72 . As shown in FIGS. 8 and 9, exit cavity  76  is defined by inner diameter  75  of inwardly directed annular ring  74  at a distal end of intermediate cavity  72 . Cavities  70 ,  72  and aperture  76  are coaxially located along longitudinal axis  31 . Entry cavity  70  may be optionally tapered, for example, to facilitate insertion of pin  10  into the bushing  60  and to reduce the amount of material required to fashion bushing  60 . Entry cavity  70  and intermediate cavity  72  are fashioned to permit free passage of pin body  16 . Annular ring  74  is formed to be retained in the annular groove of pin  10 .  
         [0034]    [0034]FIG. 10 provides a right front perspective view of bushing  60 . As shown in FIG. 10, a surface defined by recess enclosure side edge  61  may be extended along rib  64  and barrel  65  in order to provide a flat surface  77  on each side of bushing  60  for immovably retaining bushing  60  within the working cast.  
         [0035]    [0035]FIGS. 11A, B provide a cross sectional views of bushing  60  as in FIG. 8 with pin  10  of FIG. 2 respectively placed in each of two seated positions in bushing  60 . As shown in FIG. 11A, pin  10  is partially inserted into bushing  60 , at a position where bottom surface  36  of enlarged collar  14  meets upper bushing surface  71 , and in which key  44  is properly aligned with keyway  66 . Before reaching this position, pin  10  passes freely through bushing  60 . At this position, however, enlarged collar  14  begins to interfere with recess  68 , and generates a frictional force resisting further insertion of pin  10 . Accordingly, pin  10  may rest in this position at a height  79  above its fully seated position until additional force is applied to pin  10  to overcome the frictional force. This elevated positioning of pin  10  at height  79  above its fully seated position may be useful, for example, to the dental technician for use of the associated elevated tooth die as a gauge for establishing a desired replacement structure material thickness in an adjacent tooth die.  
         [0036]    [0036]FIG. 11B illustrates the pin  10  and bushing  60  of FIG. 11A after the pin has been forced into a fully seated position. In FIG. 11B, additional downward force has been applied to pin  10  to cause bottom surface  36  to rest against seat surface  69 . In this position, the annular groove  24  in pin  10  has moved to a position laterally adjacent to internal annular ring  74 . As ledge  26  moves past endface  80  of bushing  60 , internal annular ring  74  snaps into annular groove  24 . The action of annular ring  74  snapping into the annular groove  24  causes a tactile impulse to be transmitted back through pin  10  and through the associated tooth die. Accordingly, the dental technician is actively signaled that the die has been fully seated.  
         [0037]    [0037]FIGS. 11C, 11D illustrate how pin  10  may be matably affixed to a tooth die  110 . As illustrated in FIG. 11C, head  12  of pin  10  is inserted into an aperture  117  in tooth die  110 . Aperture  117  has an inner diameter approximately equivalent to an outer diameter of head  12 , thereby holding inserted head  12  in an approximately fixed position. As shown in FIG. 11C, the diameter of head  12  may be reduced at flat surfaces  13  of head  12 , thereby creating passageways  119  between pin  12  and aperture  117 . As earlier described with reference to FIG. 2, passageways  119  provide a means for venting gases that may be released by glue positioned in an upper cavity  120  defined by top face  34  of head  12  and distal end of aperture  117 . As also described with reference to FIG. 2, passageways  119  provide additional cavities for accumulating glue in order to affix head  12  within aperture  117 .  
         [0038]    As shown in FIG. 11D, aperture  118  is coaxial to aperture  117 , has a larger diameter than aperture  117 , and terminates at a seat  118   a  coplanarly positioned with respect to a proximal end of aperture  117 . Aperture  118  also terminates in opposition to seat  118   a  at lower die surface  115 , and has an inner diameter approximately equivalent to an outer diameter of annular collar  40 , thereby holding inserted annular collar  40  in an approximately fixed position. The circumference of aperture  118  is at least partially confined inside a a periphery defined by top surface  38  of enlarged collar  14 , so that when pin  10  is inserted into tooth die  110 , top surface  38  is retainably positioned against lower die surface  115 . As shown in FIG. 3, annular collar  40  may also include flat surfaces  15  to define passageways within aperture  118  for venting glue gases and for accumulating glue.  
         [0039]    Tooth die  110  may also include slot  116  (as illustrated in FIGS. 11C, 11D) laterally relieving aperture  118  across and beyond a diameter of aperture  118 . Slot  116  may typically be produced, for example, by means of a conventional tooth die separating disk, and provides a cavity for fixably locating anti-rotation key  44   b  of FIG. 11C. Slot  116  limits the orientation of pin  10  to tooth die  110  to two radial positions, and upon receiving anti-rotation key  44   b , prevents rotation of pin  10  with respect to tooth die  110 . One skilled in the art may easily devise a variety of geometries for one or more antirotation keys  44   b  associated with head  12  and/or annular collar  40  and one of more slots  116  associated with tooth die  110 , all of which are contemplated within the scope of the present invention.  
         [0040]    FIGS.  12 - 14  illustrate operation of the present invention in a working cast  100 . In FIGS.  12 - 14 , working cast  100  includes a base portion  102  and an upper die portion  104 . Upper die portion  104  is sectioned by conventional means to produce removable dies  106 ,  108  and  110 . In FIG. 12, die  110  is shown in a removed state, with enlarged collar  14  and body  16  of pin  10  extending from die  110 .  
         [0041]    In FIG. 13, consistent with the illustration of FIG. 11A, body portion  16  of pin  10  has been inserted into bushing  60  so that bottom surface  36  rests on upper surface  71  of bushing  60 . End segment  22  of pin  10  protrudes a short distance through bushing  60 , such that a screwdriver or other similar implement may be inserted into recess  114  of base  102  in order to press upwards on pin  10  to release die  110  and pin  10  from bushing  60 . Alternatively, die  110  can be pulled directly out of bushing  60 .  
         [0042]    [0042]FIG. 14 shows die  110  fully inserted into base  102 . Here, consistent with the illustration of FIG. 11B, bottom face  36  of rectangular collar  14  sits directly on seat surface  69 , and interior annular ring  74  of bushing  60  is snapped into the annular groove  24  of pin  10 . Die  110  may be removed by pulling die  110  out of base  102 , or by inserting a screwdriver or other similar instrument in recess  114  and pressing upwards on foot segment  22 .  
         [0043]    While the present invention has been described at some length and with some particularity with respect to the several described embodiments, it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment, but it is to be construed with references to the appended claims so as to provide the broadest possible interpretation of such claims in view of the prior art and, therefore, to effectively encompass the intended scope of the invention.