Abstract:
An orthodontic bracket is provided that includes a cover and a base, wherein the cover can be rotated over an arch wire slot in the base portion. The present bracket invention operates to close when a frangible portion is severed upon initiating rotation of the cover, such that the cover rotates about a hinge, which may include a pin or axle. In one embodiment of the invention, the pin or axle can be moved laterally and/or vertically after the frangible portion is severed. Preferably, the bracket is manufactured to form one piece, such as using an injection molding, machining, or casting process. The bracket offers economical advantages because additional subsequent assembly is not required to attach a cover to a base.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present application claims the benefit of U.S. Provisional Application No. 60/623,715 filed on Oct. 28, 2004, the entire disclosure of which is incorporated herein by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention is generally related to one-piece orthodontic appliances that have a frangible portion, and more particularly, an orthodontic bracket that includes a frangible mechanism to permit closure of an integral cover. 
   BACKGROUND OF THE INVENTION 
   Orthodontic brackets are secured to a patient&#39;s teeth for use in selectively straightening the patient&#39;s teeth. One type of orthodontic bracket known in the art includes a base having a slot formed thereon. The slot is configured to receive an archwire that extends between different teeth. A separate cover plate is removably attached to the base for use in securing the archwire to the base. One example of the above orthodontic bracket is disclosed in U.S. Pat. No. 4,712,999. 
   SUMMARY OF THE INVENTION 
   One object of the present invention is to develop an orthodontic bracket of the kind known in the prior art that is low-cost, simple to manufacture, and compact in construction. 
   The above and other objects of the present invention are satisfied by the features of the present invention as claimed herein and in particular by an inventive orthodontic bracket having a cover and base that are integrally connected together as a single piece. The inventive orthodontic bracket is relatively low-cost and simple to manufacture. This is due in part to the fact that the orthodontic bracket comprises only one single component which does not have to be assembled. In addition, in one embodiment the inventive orthodontic bracket is made from only one single material, preferably including a metal, plastic or ceramic material. More preferably, the bracket comprises a substantially rigid metal material. Furthermore, the cover is integrally formed with the base so as to prevent unwanted separation. Advantageous embodiments are described in the description, the claims and the figures. 
   The bracket in accordance with the invention is preferably formed in a self-ligating manner, and the archwire is clamped between the cover and the base. It can be advantageous for this purpose for a plurality of locking recesses to be provided on the cover or the base in order to close the cover at different opening widths. Archwires having different cross-section sizes can be inserted into the slot in this way and be fixed there by closing the cover. 
   In one embodiment, an orthodontic bracket consists of at least two structural portions comprising a base and a ligation cover. However, the base and ligation cover are not separate, but are integrally formed as one contiguous piece by such methods as casting, injection molding, or machining. Upon being manufactured, the base and ligation over are substantially rigidly connected through one or more webs at a hinge mechanism. The web or webs are frangible, allowing the two structural portions to move relative to each other once the web or webs are sheared, yet after shearing, the base and the ligation cover remain interlocked because of the hinge. The one or more webs can be configured in a variety of geometries. For example, the web or webs may be configured horizontally, vertically, or radially from the pin or axle of the hinge. Alternatively, the web or webs by take on a helical or curved form, extending along at least a portion of the length of the pin or axle of the hinge. At some point along the structure of the web or webs, there may be an area of reduced thickness where the fracturing forces are directed. 
   In a separate aspect of the invention, the base includes a void space that preferably contains or is operatively associated with the pin or axle of the ligation cover. The shape of the void space and/or the pin or axle may be substantially round or oval, or they may be square, rectangular, triangular, hexagonal, octagonal, trapezoidal, polygonal, a parallelogram, or a free-form combination of lines and arcs. The void space may be substantially the same shape as the pin or axle, or they may be dissimilar in shape. 
   In a separate aspect of the invention, after forming the bracket, such as by casting, injection molding, or machining, the contiguous one-piece bracket consisting of the base and the ligation cover remains contiguous with an unsheared web or webs until at any time during one of the manufacturing, packaging or application processes that sufficient force is applied to fracture the integrally formed web or webs. After forming the bracket, additional manufacturing processes may include sintering, deburring, polishing, sandblasting, coating or plating, painting, and/or adhesive application. During one of these additional manufacturing processes, the web or webs may be sheared, or the shearing of the web or webs may be performed as part of a different manufacturing processes, or shearing of the web or webs may be performed at a later time. 
   In a separate aspect of the invention, the bracket preferably includes a latch or interlocking mechanism that is formed as part of the initial one-piece manufacturing process, or as part of a later manufacturing process. The latch or interlocking mechanism allows the ligation cover to be secured to the base at a location spaced apart from the hinge mechanism. In addition, the latch or interlocking mechanism allows an archwire placed within the bracket to be ligated when the ligation cover is closed. 
   Various embodiments of the present invention are set forth in the attached figures and in the detailed description of the invention as provided herein and as embodied by the claims. It should be understood, however, that this Summary of the Invention may not contain all of the aspects and embodiments of the present invention, is not meant to be limiting or restrictive in any manner, and that the invention as disclosed herein is and will be understood by those of ordinary skill in the art to encompass obvious improvements and modifications thereto. 
   Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is described below by means of example embodiments and with reference to the enclosed drawings, in which are shown: 
       FIG. 1  is a front and side perspective view of an orthodontic bracket that includes an embodiment of the present invention; 
       FIG. 2  is a side perspective view of an embodiment of the present invention; 
       FIG. 3  is a top and side perspective view of an embodiment of the present invention; 
       FIG. 4  is a front and side perspective view of the device shown in  FIG. 1  with an archwire in an archwire slot and the cover closed over the archwire; 
       FIGS. 5   a - 5   c  are a series of side perspective views of an embodiment of the present invention with its cover in a fully open, partially closed, and closed position; 
       FIGS. 6   a - 6   d  are perspective views of possible alternate configurations of the axle and frangible portions interconnected thereto; 
       FIGS. 7   a - 7   d  are side elevation views of still other alternate configurations of the axle and frangible portions interconnected thereto; and 
       FIGS. 8   a - 8   e  are side elevation views of possible configurations for the pin or axle and the void space structure associated with the present invention. 
   

   While the following disclosure describes the invention in connection with those embodiments presented, one should understand that the invention is not strictly limited to these embodiments. Furthermore, one should understand that the drawings are not necessarily to scale, and that in certain instances, the disclosure may not include details which may be necessary to manufacture particular embodiments, such as conventional details of fabrication and assembly. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , a perspective view of the side and front of an orthodontic twin bracket  10  is shown. The bracket  10  includes a gingival tie wing  12  and an occlusal tie wing  14 . The gingival tie wing  12  includes a mesial wing tip  16  and a distal wing tip  18 . Similarly, the occlusal tie wing  14  includes a mesial wing tip  20  and a distal wing tip  22 . Located between the gingival tie wing  12  and the occlusal tie wing  14  is a mesiodistal-extending archwire slot  24  holding archwire A.  FIG. 1  also illustrates the two basic structures of the bracket  10 , that is, body  26  and cover  28 . The cover  28  may comprise a ligation cover; that is, a cover that ligates the archwire A. 
   For the one-piece bracket embodiment, body  26  is preferably integrally formed together with cover  28  during manufacture of the bracket  10 . More particularly, in a preferred embodiment, body  26  and cover  28  are integrally molded such as by injection molding, casting, or machining or otherwise manufactured as a single unit, such that the body  26  and cover  28  are an integral piece. 
   Still referring to  FIG. 1 , the cover  28  of the bracket  10  is operatively associated with the body  26 . More particularly, a hinge mechanism  30  preferably interconnects the cover  28  to the body  26 , wherein the hinge mechanism  30  allows the cover  28  to be rotated in the direction of rotational arrow R toward the body  26 . The hinge mechanism  30  preferably includes a rotatable member, axle or pin  32  that interconnects the cover  28  to the mesial and distal wings of the body  26 . For the example shown in  FIG. 1 , the pin  32  interconnects the cover  28  to the mesial wing tip  20  and the distal wing tip  22  of the occlusal tie wing  14 . For the perspective view of the bracket  10  shown in  FIG. 1 , the pin  32  can be seen within the distal wing tip  22  of the occlusal tie wing  14 . 
   Still referring to  FIG. 1 , the cover  28  preferably includes a front portion  34 , a bend  36  and a lateral portion  38 . An end portion  40  of the lateral portion  38  preferably includes a cover latch member  42  that cooperates with a base latch member  44  upon rotating the cover  28  and engaging the cover latch member  42  with base latch member  44 . The cover  28  preferably ligates the archwire A upon rotating the cover  28  and engaging the cover latch member  42  with the base latch member  44 . 
   The cover interior surface  45  of the front portion  34  may include at least one projection (not shown) to provide limited surface contact between the cover  28  and archwire A. In addition, the base  26  may also include at least one projection (not shown) to provide limited surface contact between the base  26  and archwire A. 
   Referring now to  FIG. 4 , bracket  10  is shown in the closed position. Archwire A within archwire slot  24  (also referred to as “locking recesses”) is ligated between the base  26  and the cover  28 . 
   Referring now to  FIG. 4 , bracket  10  is shown in the closed position. Archwire A within archwire slot  24  is ligated between the base  26  and the cover  28 . 
   In one embodiment of the present invention, the hinge mechanism  30  preferably includes a frangible portion. More particularly, the hinge mechanism  30  includes a part that is frangible or breaks upon rotating the cover  28  to latch with the base  26 . Since the entire bracket  10  is preferably manufactured as single integral unit, the frangible portion is also produced as part of process of making the bracket  10 . Referring now to  FIGS. 5   a - 5   c , a series of side perspective views of a bracket  10  with a frangible hinge mechanism  30  are shown.  FIG. 5   a  depicts the bracket  10  having a cover  28  in a fully open position.  FIG. 5   b  depicts the bracket  10  with the frangible hinge mechanism  30  having been sheared, and the cover  28  in a partially closed position.  FIG. 5   c  depicts the cover  28  in a fully closed position over an archwire A in the archwire slot  24 . 
   Referring now to  FIG. 6   a , a first embodiment of a pin  32  having a frangible portion is shown. More particularly,  FIG. 6   a  illustrates a pin  32  that is substantially a cylinder  46 , with two frangible portions. The first frangible portion  48   a  is fin or web  50  that extends outward from the exterior lateral surface  52  of the cylinder  46 . The web  50  extends the entire length of the cylinder  46 , or from a first pin end  54  to a second pin end  56 ; however, the web  50  may occupy only a limited portion of the length of cylinder  46 . The web  50  is preferably continuous or solid. However, it may include perforations or open segments between the first pin end  54  and second pin end  56 . The web  50  is sized so that at least a portion of it can break when the cover  28  is rotated toward the base  26 . 
   Although not required, the pin  32  of  FIG. 6   a  may include more than one frangible portion. More particularly, the pin  32  may include a plurality of frangible portions, such as a second frangible portion  48   b  that also extends the entire length of the cylinder  46 . For the device shown in  FIG. 6   a , the second frangible portion  48   b  is also a fin or web  50 , and is located at a position along the exterior lateral surface  52  of the cylinder  46  that is substantially at a diametrically opposite location as the first frangible portion  48   a . However, the second frangible portion  48   b  could alternatively be located at a different position along the exterior lateral surface  52  of the cylinder  46 . For example, the second frangible portion  48   b  may be positioned at 45 degrees, 60 degrees, 90 degrees, or 120 degrees from the first frangible portion  48   a . Furthermore, as shown in  FIG. 6   a , the web  50  of the second frangible portion  48   b  may be substantially the same shape as the web  50  of the first frangible portion  48   a , or it may be a different shape. 
   The web  50  shown in  FIG. 6   a  includes a web first side  51   a , a web second side  51   b  a web third side  51   c , and a web base  51   d  that abuts the cylinder  46 . The web first side  51   a  is orientated substantially perpendicular or at about a 90 degree angle to the web second side  51   b , and the web second side  51   b  is orientated substantially perpendicular or at about a 90 degree angle to the web third side  51   c . In addition, the web first side  51   a  is substantially parallel to the web third side  51   c , and the web second side  51   b  is located opposite the web base  51   d . However, the web  50  may take on an alternate shape, such as a curved form with no sharp corners, such that shown in  FIG. 7   a . Alternatively, the web  50  may take on a pointed shape, such as that shown in  FIGS. 7   b  and  7   c . In addition, as shown in  FIG. 7   d , the web  50  may have a thinner web base  51   d  adjacent the exterior surface  52  of the cylinder  46  as compared to a width of a surface at a further radial distance, such as width of second side  51   b . Such web shapes offer advantages for providing lesser or greater resistance against shearing. Thus, a web  50  can be customized to provide a desired amount of strength, and the web  50  may be a variety of possible shapes, including geometric shapes, curved shapes and random shapes. 
   Referring now to  FIG. 6   b , an alternate embodiment of a pin  32  is shown, wherein the pin  32  includes a frangible portion  58 . The frangible portion  58  of  FIG. 6   b  is a radial web  60  that substantially circumscribes the cylinder  46 . In addition, the frangible portion  58  is preferably closer to first pin end  54  than second pin end  56 . The frangible portion  58  may include a partially wedge shaped portion  62 . In addition, the frangible portion  58  may include a radial exterior surface  64  that is longer in longitudinal length that an interior portion  66 . 
   Referring now to  FIG. 6   c , an alternate embodiment of a pin  32  is shown, wherein the pin  32  includes a frangible portion  68 . The frangible portion  68  is a spiral web or curvilinear member  70  that extends along the exterior lateral surface  52  of the cylinder  46 . The curvilinear member  70  may be continuous, or it may be perforated and segmented along its length. In addition, the curvilinear member  70  may be of uniform curvature and shape, or it may be variable in curvature and shape. As shown in  FIG. 6   c , the frangible portion  68  extends from the first pin end  54  to the second pin end  56 ; however, the frangible portion  68  may extend along only a portion of the length of the cylinder  46 . 
   Referring now to  FIG. 6   d , an alternate embodiment of a pin  32  is shown, wherein the pin  32  includes at least one frangible portion, and more preferably, a plurality of frangible portions  72   a - 72   d . As shown in  FIG. 6   d , the frangible portions  72   a - 72   d  comprise pegs  74   a - 74   d  that project from the exterior lateral surface  52  of cylinder  46 . The pegs  74   a - 74   d  are substantially cylindrical shaped members; however, they can be a variety of shapes, including rectangular blocks. In addition, the individual frangible portions  72   a - 72   d  may be different shapes, for example, frangible portion  72   b  can be a web  30 , such as that shown in  FIG. 6   a , and frangible portion  72   c  can be a curvilinear member  70 , such as that shown in  FIG. 6   c . Similar to the frangible portions  48   a ,  48   b ,  58 , and  68  shown in  FIGS. 6   a - 6   c , the frangible portions  72   a - 72   d  of pin  32  of  FIG. 6   d  are sized to shear but remain connected to the bracket  10 , including during rotation of the cover  28  toward the base  26 , thereby allowing the cover  28  to fully rotate and engage and latch with base  26 , but still remain an integral piece. 
   Referring still to  FIGS. 6   a - 6   d , it is further noted that the pin  32  can have a circular shape in cross section, such that frangible portions are operatively associated with a cylinder  46 , as described above and shown in  FIGS. 6   a - 6   d . However, the central portion of the pin  32  can also take on a variety of shapes, such as a cone shaped axle, or a faceted or multi-sided axle that includes a number of planar surfaces that form its exterior lateral surface. 
   Referring now to  FIG. 8   a , a detailed side elevation view of the hinge mechanism  30  of  FIGS. 1-5  is shown. The circular cross section of the pin  32  is shown, with the webs  50  that are operatively associated with the pin  32 . With the exception of the webs  50 , void space  76  surrounds the circumferential perimeter of the pin  32 . When the cover  28  is first rotated toward the base  26 , the webs are sheared and the pin  32  rotates. Continuing to rotate the cover  28  toward the base  26  allows the cover latch member  42  to engage the base latch member  44 , as shown in  FIG. 4 . 
   In a separate aspect of the invention, a pin is provided that can be moved vertically and/or laterally, and which preferably also rotates. More specifically, a pin  32  is provided that can be moved vertically and/or laterally within the base  26 . Several different embodiments of the present invention are discussed below that illustrate this aspect of the invention. In general, the pin  32 , can be located in a variety of orientations, and it is to be understood that the pin position in the figures is only exemplary. 
   Referring now to  FIG. 8   b , a detailed side elevation view of an alternate embodiment of a hinge mechanism is shown. Hinge mechanism  78  includes a substantially oblong, and more particularly, a substantially elliptical-shaped void space  80  with a pin  32  located in a first position  82   a , as represented by solid lines. The pin  32  is moveable within the void space  80 . For example, the pin  32  can be shifted to a second position  82   b , as represented in dashed lines. Pin  32  may be a variety of cross sectional shapes, such as circular, rectangular, square, elliptical, triangular, polygonal, etc. For the example depicted in  FIG. 8   b , the pin  32  is a hexagon in cross section. 
   The hinge mechanism  78  includes two webs  50 . However, instead of two webs  50  as depicted, the hinge mechanism  78  could alternatively be constructed of only one web, or it may be constructed of more than two webs. The hinge mechanism  78  is capable of moving inside the void space  80  because the void space  80  is larger than the pin  32 . In use, the cover that is interconnected to the pin  32  is rotated, thereby shearing the connection of the webs  50  with the pin  32 . The pin  32  can then be rotated. In addition, the pin can be shifted within the void space  80 . For example, the pin  32  can be shifted in accordance with position arrow PA from a first position  82   a  to second position  82   b , where the pin  32  in the second position  82   b  is laterally and/or vertically displaced relative to the first position  82   a . The ability of the pin  32  to move laterally and/or vertically allows for the cover  28  to be shifted during the process of latching the cover  28  to the base  26 . For example, if a substantially rigid and/or substantially inelastic material is used to form the base  26  and/or the cover  28 , the cover latch member  42  that cooperates with a base latch member  44  may not be able to deflect sufficiently to allow the cover  28  latch to the base  26 . If required, a laterally and/or vertically moveable pin  32  allows the cover  28  some motion to permit the latching process. Furthermore, even if sufficiently deformable materials are used to construct the base  26  and/or the cover  28 , the moveable pin  32  may provide reduced friction interaction between the bracket  10  and the archwire A. 
   Referring now to  FIG. 8   c , a substantially square shaped pin  32  is situated within a substantially rectangular-shaped void space  84  of hinge mechanism  86 . The pin  32  is located in a first position  82   a , as represented by solid lines, when attached to webs  50 , and the pin  32  is also shown in a second position  82   b , as represented in dashed lines. The pin  32  may rotate and may move laterally after the webs are sheared that initially hold the pin  32  in place. 
   In a separate aspect of the invention, the pin shape and the void space shape may be preferentially structured to place the pin in a restricted second position. That is, the pin shape and void space may compliment each other, whereby the pin is placed in an area of the void space that limits the lateral and/or vertical movement of the pin when the webs are sheared and the pin is in its second position. Referring now to  FIG. 8   d , a substantially elliptical-shaped pin  32  is situated within a substantially trapezoidal-shaped void space  88  of hinge mechanism  90 . The pin  32  may rotate and may move laterally after the webs are sheared that initially hold the pin  32  in place. More particularly, the pin  32  is located in a first position  82   a , as represented by solid lines, when attached to webs  50 . The first position  82   a  places the pin  32  generally in the wide portion of the trapezoid-shaped void space  88 , where the major axis Ma-Ma of the elliptical shaped pin  32  is oriented substantially parallel to the base B of the trapezoid-shaped void space  88 . Again, it is noted that the pin  32  could be located in a variety of orientations, and it is to be understood that the first position  82   a  of pin  32  in the figure is only exemplary. The pin  32  is also shown located in a second position  82   b , as represented in dashed lines. In the second position, the pin  32  is shown with it major axis Ma′-Ma′ substantially perpendicular to the base B. Furthermore, the pin  32  is confined by the unparallel edges of the trapezoid-shaped void space  88 . Thus, the pin has restricted motion in a vertical direction, where vertical is defined in  FIG. 8   d  as substantially parallel to base B of the trapezoid-shaped void space  88 . In a sense, the narrowing shape of the trapezoid-shaped void space  88  acts as a funnel, whereby the pin  32  is sheared from webs  50 , such as along shear planes  92 , and the pin  32  is then rotated by rotating the cover  28 , and the pin  32  is moved laterally to a more confined position within the void space  88 , such as second position  82   b . The shape of the void space thereby limits movement of the pin in the second position, and thus restricts movement of the pin and thus the cover during rotation, thereby helping to ensure a proper alignment of the cover  28  when latching to the base  26 . 
   Referring now to  FIG. 8   e , yet a further embodiment of the hinge mechanism is illustrated. Hinge mechanism  94  includes an oblong-shaped pin  32  situated within an unsymmetrical-shaped void space  96 . The pin  32  may rotate and may move laterally after the single web  50  is sheared which initially holds the pin  32  in place. More particularly, the pin  32  is located in a first position  82   a , as represented by solid lines, when attached to web  50 . The first position  82   a  places the pin  32  generally in a wide portion of the unsymmetrical-shaped void space  96 . Again, it is noted that the pin  32  could be located in a variety of orientations, and it is to be understood that the first position  82   a  of pin  32  in the figure is only exemplary. The pin  32  is also shown located in a second position  82   b , as represented in dashed lines. In the second position  82   b , the pin  32  is confined within a restricted area of the void space  96 . Again, the narrowing shape of the unsymmetrical-shaped void space  96  acts as a funnel, whereby the pin  32  is sheared from web  50 , such as along shear plane  92 , and the pin  32  is then rotated by rotating the cover  28 , and the pin  32  is moved laterally to a more confined position within the void space  96 , such as second position  82   b . The shape of the void space thereby limits movement of the pin in the second position, and thus restricts movement of the pin and thus the cover during rotation, thereby helping to ensure a proper alignment of the cover  28  when latching to the base  26 . Accordingly,  FIGS. 8   b - 8   e  show that the void space can take on a variety of different shapes, wherein the void space shape directs the movement of the pin  32  during rotation of the cover  28 . 
   After casting, injection molding, or machining the contiguous one-piece bracket  10  that includes the body  26  and the cover  28 , the bracket  10  remains a contiguous one-piece bracket to allow for other manufacturing processes, such as sintering, deburring, polishing, sandblasting, coating or plating, and/or paint or adhesive application. 
   To provide further written description and enablement support for the present invention, especially as to how appliances are manufactured, etc., the following U.S. patents are incorporated herein by reference in their entireties: U.S. Pat. Nos. 6,695,612, 6,659,767; 6,659,766; 6,655,958, 6,655,957; 6,616,445; 6,607,383; 6,347,939; 6,220,857; 4,712,999; and 4,419,078. 
   To assist in the understanding of the present invention the following list of components and associated numbering found in the drawings is provided herein: 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               Number 
               Component 
             
             
                 
                 
             
           
           
             
                 
               10 
               bracket 
             
             
                 
               12 
               gingival tie wing 
             
             
                 
               14 
               occlusal tie wing 
             
             
                 
               16 
               mesial wing tip (of the gingival tie wing) 
             
             
                 
               18 
               distal wing tip (of the gingival tie wing) 
             
             
                 
               20 
               mesial wing tip (of the occlusal tie wing) 
             
             
                 
               22 
               distal wing tip (of the occlusal tie wing) 
             
             
                 
               24 
               archwire slot 
             
             
                 
               26 
               body 
             
             
                 
               28 
               cover/ligation cover 
             
             
                 
               30 
               hinge mechanism 
             
             
                 
               32 
               pin or axle 
             
             
                 
               34 
               front portion 
             
             
                 
               36 
               bend 
             
             
                 
               38 
               lateral portion 
             
             
                 
               40 
               end portion 
             
             
                 
               42 
               cover latch portion 
             
             
                 
               44 
               base latch portion 
             
             
                 
               45 
               cover interior surface 
             
             
                 
               46 
               cylinder 
             
             
                 
               48a 
               first frangible portion 
             
             
                 
               48b 
               second frangible portion 
             
             
                 
               50 
               web 
             
             
                 
               51a 
               web first side 
             
             
                 
               51b 
               web second side 
             
             
                 
               51c 
               web third side 
             
             
                 
               51d 
               web base 
             
             
                 
               52 
               exterior lateral surface (of cylinder) 
             
             
                 
               54 
               first pin end 
             
             
                 
               56 
               second pin end 
             
             
                 
               58 
               frangible portion 
             
             
                 
               60 
               radial web 
             
             
                 
               62 
               partially wedge shaped portion 
             
             
                 
               64 
               radial exterior surface 
             
             
                 
               66 
               interior portion 
             
             
                 
               68 
               frangible portion 
             
             
                 
               70 
               curvilinear member 
             
             
                 
               72a-72d 
               frangible portions 
             
             
                 
               74a-74d 
               pegs 
             
             
                 
               76 
               void space 
             
             
                 
               78 
               hinge mechanism 
             
             
                 
               80 
               elliptical-shaped void space 
             
             
                 
               82a 
               pin first position 
             
             
                 
               82b 
               pin second position 
             
             
                 
               84 
               rectangular-shaped void space 
             
             
                 
               86 
               hinge mechanism 
             
             
                 
               88 
               trapezoidal-shaped void space 
             
             
                 
               90 
               hinge mechanism 
             
             
                 
               92 
               shear plane 
             
             
                 
               94 
               hinge mechanism 
             
             
                 
               96 
               unsymmetrical-shaped void space 
             
             
                 
               A 
               archwire 
             
             
                 
               B 
               base (of trapezoidal-shaped void space) 
             
             
                 
               Ma-Ma 
               major axis of elliptical-shaped pin 
             
             
                 
               PA 
               position arrow 
             
             
                 
               R 
               rotational arrow 
             
             
                 
                 
             
           
        
       
     
   
   The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.