Patent Publication Number: US-2007099145-A1

Title: Colored orthodontic brackets having removable ligation cover

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of PCT Application No. PCT/EP2005/009467, filed Sep. 2, 2005, which corresponds and claims priority under the Paris Convention to U.S. patent application Ser. No. 10/932,634, filed Sep. 2, 2004. The foregoing applications are incorporated herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. The Field of the Invention  
      The present invention relates to orthodontic brackets, more particularly to self-ligating orthodontic brackets that include a base, at least one slot for receiving an arch wire, and a ligating cover.  
      2. The Relevant Technology  
      Orthodontics is a specialized field of dentistry that involves the application of mechanical forces to urge poorly positioned, or crooked, teeth into correct alignment and orientation. Orthodontic procedures can be used for cosmetic enhancement of teeth, as well as medically necessary movement of teeth to correct underbites or overbites. For example, orthodontic treatment can improve the patient&#39;s occlusion, or enhanced spatial matching of corresponding teeth.  
      The most common form of orthodontic treatment involves the use of orthodontic brackets and wires, which together are commonly referred to as “braces.” Orthodontic brackets, more particularly the orthodontic bases, are small slotted bodies configured for direct attachment to the patient&#39;s teeth or, alternatively, for attachment to bands which are, in turn, cemented or otherwise secured around the teeth. Once the brackets are affixed to the patient&#39;s teeth, such as by means of glue or cement, a curved arch wire is inserted into the slot of each bracket. The arch wire acts as a template or track to guide movement of the teeth into proper alignment. End sections of the arch wire are typically captured within tiny appliances known as “buccal tubes” affixed to the patient&#39;s molars.  
      There are two distinct classes of orthodontic brackets: those that require the use of ligatures to fasten the arch wire to the bracket, and those that are self-ligating. In brackets of the first class, small ligature wires are typically used to hold the arch wire in a securely seated position in the brackets. Ligatures or some other form of fastening means are essential to ensure that the tensioned arch wire is properly positioned around the dental arch, and to prevent the wire from being dislodged from the bracket slots during chewing of food, brushing of teeth, or application of other forces. One type of commercially available ligature is a small, elastomeric O-ring, which is installed by stretching the O-ring around small wings known as “tie wings” that are connected to the bracket body. Metal ligatures are also used to retain arch wires within the bracket slots.  
      In an effort to simplify the process of installing braces, a variety of self-ligating brackets have been developed. The term “self-ligating bracket” refers to a class of orthodontic brackets that include some sort of cover, whether separate from or hingedly or slidably attached to the base, which encloses or otherwise retains the arch wire within the slot of the base.  
      Besides the difficulties associated with the general discomfort of orthodontic brackets, many patients dislike the appearance of installed orthodontic brackets. Most existing orthodontic brackets are formed of metal, and result in a rather particular aesthetic appearance, which some patients dislike. It would be an improvement in the art to provide a self-ligating orthodontic bracket that allows the patient some flexibility in creating a desired aesthetic look, while still providing ease of use, inexpensive manufacturing, strength, and durability.  
     BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS  
      The present invention is directed to an orthodontic bracket that includes coloring means for coloring the bracket to create a desired aesthetic appearance. The orthodontic bracket includes a bracket base, an arch wire slot formed in the bracket base, a ligation cover connected to the bracket base and selectively movable relative to the bracket base between an open, non-ligating position relative to the arch wire slot and a closed, ligating position relative to the arch wire slot, and coloring means for coloring at least a portion of the bracket base and/or the ligation cover. According to one embodiment, the coloring means for coloring comprises a colored dye or pigment impregnating the thermoplastic resin from which the bracket base and/or ligation cover are formed. According to another embodiment, the coloring means for coloring comprises a curable resin containing a colored dye or pigment that has been applied and cured over at least a portion of the bracket base and/or ligation cover.  
      The orthodontic bracket may be formed by injection molding the thermoplastic resin material from which it is formed. In one embodiment, the bracket base and ligation cover may be integrally formed together as a single piece. In another embodiment, the cover may be completely separate and removable from the bracket base. Examples of suitable thermoplastic resins include, but are not limited to, polyamides (e.g., nylon), acetal polymers, polyetherimides, polycarbonates, polyarylether ketones, polysulfones, and polyphenylsulfones.  
      Any colored dye or pigment that is compatible with the bracket material may be used as coloring means for coloring, whether the colored dye or pigment is impregnated into the bracket forming resin material or included in a curable resin that is applied to the bracket base and/or cover and subsequently light or chemical cured. According to one embodiment, the colored dye or pigment may comprise food coloring.  
      In embodiments where a curable resin containing a colored dye or pigment is applied over at least a portion of the bracket base and/or ligation cover, the curable resin may be applied during manufacture of the orthodontic bracket or clinically by the orthodontist. Although other manufacturing stage application methods may be used, according to one embodiment, the curable resin is applied during manufacturing by spin coating, as known in the art. Although other clinical application methods may be used, according to another embodiment, the curable resin is applied clinically by brush coating.  
      One embodiment of the orthodontic bracket includes an elongate film hinge and a hinge guide structure. The elongate film hinge is attached at one end to the bracket base and at an opposite end to the ligation cover so as to hingedly connect the ligation cover to the bracket base. The hinge guide structure may be disposed on the ligation cover or bracket base, and provides a curved surface around which the elongate film hinge bends when the ligation cover is rotated relative to the bracket base. The curved surface causes the elongate film hinge to bend over a significant portion of its entire length.  
      Including an elongate film hinge and hinge guide structure is advantageous as it results in an especially strong and durable orthodontic bracket. The combination of the elongate film hinge and the hinge guide structure allows the forces associated with opening and closing the bracket to be distributed along a significant length of the elongate film hinge, rather than concentrating the forces at a point or line where bending occurs.  
      According to one embodiment, the curved surface of the hinge guide structure forms a part of a cam structure that is attached to an inner surface of the ligation cover and that extends toward the bracket base. The cam structure also preferably includes a camming surface, distal to the film hinge, which interacts with the bracket base so as to bias the ligation cover toward the open, non-ligating position. This makes it easier for the dental practitioner to insert the arch wire into the arch wire slot.  
      The orthodontic bracket preferably includes a latch mechanism that selectively locks and unlocks the ligation cover in the closed, ligating position. The latch mechanism may comprise an angled keyway and a locking tongue. The angled keyway may be formed within a side of the bracket base distal to the elongate film hinge. The locking tongue extends from an end of the cover distal to the elongate film hinge. The locking tongue is configured to selectively fit within the angled keyway and lock the ligation cover to the bracket base in the closed, ligating position. In the case where the ligation cover is separate and removable from the bracket base, the orthodontic bracket includes two latch mechanism on opposite sides of the bracket to keep the ligation cover securely locked to the bracket base.  
      These and other advantages and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
       FIGS. 1A-1B  illustrate an exemplary self-ligating orthodontic bracket according to the present invention;  
       FIGS. 1C-1D  illustrate an alternative self-ligating orthodontic bracket according to the invention;  
       FIGS. 2A-2B  illustrate another alternative self-ligating orthodontic bracket according to the invention;  
       FIGS. 3A-3B  illustrate another alternative self-ligating orthodontic bracket according to the invention;  
       FIGS. 4A-4B  illustrate yet another alternative self-ligating orthodontic bracket according to the invention;  
       FIG. 5A  illustrates application of a curable resin containing a colored dye or pigment over at least a portion of the ligation covers of several orthodontic brackets by brushing;  
       FIG. 5B  illustrates light curing of the curable resin applied in  FIG. 5A ; and  
       FIG. 6  illustrates bonded orthodontic brackets having a light cured colored coating.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      I. Introduction  
      A detailed description of the invention will now be provided with specific reference to Figures illustrating preferred embodiments of the invention. It will be appreciated that like structures will be provided with like reference designations.  
      II. Exemplary Orthodontic Brackets  
      The orthodontic bracket shown in  FIGS. 1A-1B  may be manufactured in one single piece as an injection molded plastic part. The orthodontic bracket  100  has a base  110  to which a cover  112  is hingedly attached. A slot  114  open to the upper side of the base  110  is provided near the center of said base  110  and serves for the insertion of an arch wire  116  therein. An additional arch wire slot  114   a  may also be provided. The arch wire  116 , shown with a square cross-section (any other cross section known in the art could be used), is arranged inside the slot  114  and serves to correct tooth alignment in a known manner.  
      The cover  112  is hingedly connected to the bracket base  110  by a single elongate film hinge  118 . The cover  112  is such that it may be selectively rotated between an open and a closed position relative to the arch wire slot  114 . The cover  112  maintains the arch wire  116  within the slot  114  when the cover is in the closed ligating position.  
      The elongate film hinge  118  of this embodiment is designed to bend along substantially its entire length rather than at a single point or line. This helps the hinge resist fatigue or fracture better than film hinges that bend along a single line.  
      The bracket embodiment illustrated in  FIGS. 1A and 1B  preferably includes an interactive cam structure  120  with a first curved surface  122  and a second curved surface  124 . The first curved surface  122  interacts with the elongate film hinge  118  to provide a curved surface that helps ensure that the elongate film hinge  118  bends gradually over its entire length rather than abruptly at any specific locale. The second curved surface  122  is curved in such a way so that it interacts with a corresponding wall  125  of the base  110  so as to bias the ligation cover  112  in an open position relative to the bracket base  110  when the ligation cover  112  is in the open position. This improves access to arch wire slot  114 , making insertion or removal of the arch wire  116  easier. The second curved surface  124  may, depending on the shape of the corresponding wall  125  of the bracket base  110 , also act to bias the ligation cover  112  to remain in a closed position when in the closed position relative to the bracket base  110 .  
      An angled keyway  126  is provided near one end of the base  110 . The cover  112  contains a corresponding locking tongue  128  that enables the ligation cover  112  to be selectively locked or unlocked relative to the bracket base  110 . The ligation cover  112  is locked to bracket base  110  (as seen in  FIG. 1B ) by closing the cover  112  so that the locking tongue  128  is inserted into angled keyway  126 .  
      In the event that the arch wire  116  pushes against the cover  112  with sufficient force to cause the cover to bulge upwardly relative to the bracket base  110 , rather than causing the tongue  128  to withdraw from the angled keyway  126 , which could result in undesired disengagement of the cover  112 , the locking tongue  128  is instead pulled more deeply into the angled keyway  126 , thereby tightening the locking mechanism. This provides added safety. To open the cover, the locking tongue  128  is pulled out of angled keyway  126  and over an outer protrusion  129  of the bracket base  110 .  
      Furthermore, a bearing protrusion  130  is provided at the inside and middle of the cover  112  to assist in fixing the arch wire  116  in the slot  114  while the cover  112  is in the closed state ( FIG. 1B ). The bearing protrusion  130  reduces the play in the system by effectively widening the ligation cover  112  in the vicinity of the arch wire slot  114 .  
       FIGS. 1C and 1D  depict an alternative embodiment of an orthodontic bracket  150  that may include coloring means for coloring at least a portion of the bracket base  152  and/or ligation cover  154 . Orthodontic bracket  150  does not include a cam structure. Instead, the orthodontic bracket  150  depicted in  FIGS. 1C and 1D  includes a bracket base  152  and a ligation cover  154  attached to the bracket base  152  by means of an elongate film hinge  156 . The bracket base  152  further includes a curved end  158  that acts as a hinge guide in order to cause the elongate film hinge  156  to bend gradually over a significant portion of its entire length. In this way, the curved end  158  of the bracket base  152  acts in similar manner to the curved hinge-guiding surface  122  of the cam structure  120  of the orthodontic bracket  100  depicted in  FIGS. 1A-1B . Thus, as the ligation cover  154  is moved from an open, non-ligating position ( FIG. 1C ) to a closed, ligating position ( FIG. 1D ), the elongate film hinge  156  at least partially abuts the curved end  158 . The abutment between the elongate film hinge  156  and the curved end  158  causes the elongate film hinge  156  to bend gradually around the curved end  158  so as to better distribute the bending forces and bending angles along substantially the entire length of the elongate film hinge  156 .  
       FIGS. 2A and 2B  illustrate another alternative bracket embodiment that may include coloring means for coloring at least a portion of the bracket base  210  and/or ligation cover  212 . Bracket  200  is similar to the bracket illustrated in  FIGS. 1A-1B  in that it includes a bracket base  210 , a ligation cover  212 , a slot  214 , an arch wire  216  (seen in  FIG. 2B ), an angled keyway  226 , a locking tongue  228 , and a bearing protrusion  230 . This example differs from the bracket illustrated in  FIGS. 1A-1B  in that although it also uses a film hinge  218  to attach the ligation cover  212  to the bracket base  210 , the hinge  218  is not as elongated as hinge  118  shown in  FIGS. 1A-1B . Bracket  200  may further include additional arch wire slots  232  and  234  for use with additional or alternative arch wires as known in the art.  
       FIGS. 3A and 3B  illustrate another alternative bracket embodiment that may include coloring means for coloring at least a portion of the bracket base  310  and/or ligation cover  312 . Bracket  300  includes a bracket base  310 , a ligation cover  312 , a slot  314 , an arch wire  316  (seen in  FIG. 3B ), a main film hinge  318 , an angled keyway  326 , a locking tongue  328 , a bearing protrusion  330 , and an additional arch wire slot  332 . This example differs from that illustrated in  FIGS. 2A-2B  in that it further has a spring element  320  attached at one end of the bracket base  310  by a film hinge  322  and at an opposite end to the ligation cover  312  by a film hinge  324 .  
       FIGS. 4A and 4B  illustrate yet another alternative bracket embodiment that may include coloring means for coloring at least a portion of the bracket base  410  and/or ligation cover  412 . Bracket  400  includes a bracket base  410 , a ligation cover  412 , a slot  414 , an arch wire  416 , a pair of angled keyways  426 , a pair of locking tongues  428 , a bearing protrusion  430 , and additional arch wire slots  432  and  434 . This example differs from those illustrated in  FIGS. 1-3  in that it includes no hinge between the base  410  and the cover  412 . The bracket base  410  could be used without the cover  412  as a traditional bracket requiring ligatures. Using the cover  412  results in a self-ligating bracket with a uniform, closed, smooth surface across the top surface of the bracket  400 , which is beneficial for patient comfort and hygiene.  
      Various other bracket designs are disclosed in U.S. application Ser. No. 09/784,525, filed Feb. 15, 2001; U.S. application Ser. No. 09/914,737, filed Aug. 29, 2001; and U.S. application Ser. No. 09/953,400, filed Sep. 12, 2001. For purposes of disclosing exemplary orthodontic bracket designs, the foregoing U.S. patent applications are incorporated by reference.  
      The orthodontic brackets may be formed by injection molding the thermoplastic resin material that it is formed from, either as separate pieces or as a single piece. Examples of suitable thermoplastic resins include, but are not limited to, polyamides, acetal polymers, polyetherimides, polycarbonates, polyarylether ketones (e.g., PEEK), polysulfones, and polyphenylsulfones  
      III. Exemplary Coloring Means  
      According to one embodiment, the coloring means for coloring may comprise a colored dye or pigment impregnating the thermoplastic resin from which the bracket base and/or ligation cover are formed. According to an alternative embodiment, the coloring means for coloring may comprise a curable resin containing a colored dye or pigment that has been applied and cured over at least a portion of the bracket base and/or ligation cover. An advantage of the latter coloring means is that it allows for changes in the color of the brackets from an initial color.  
      Any colored dye or pigment that is compatible with the bracket material may be used as coloring means for coloring, whether the colored dye or pigment is impregnated into the bracket forming resin material or included in a curable resin that is applied to the bracket base and/or cover and subsequently light or chemical cured. According to one embodiment, the colored dye or pigment may comprise any of the various food colorings known in the art.  
      In embodiments where a curable resin containing a colored dye or pigment is applied over at least a portion of the bracket base and/or ligation cover, the curable resin may be applied during manufacture of the orthodontic bracket or clinically, by the orthodontist. Although other manufacturing stage application methods may be used, according to one embodiment, the curable resin is applied during manufacturing by spin coating, as will be known to those skilled in the art.  
      Although other clinical application methods may be used, according to one embodiment, the curable resin is applied clinically by brush coating, as illustrated in  FIG. 5A . A brush  510  or other applicator is used to apply a curable resin  505  that includes a colored dye or pigment. Although any curable resin may be used, Ormocere, made by Fraunhofer in Wurzburg, Germany, is an example of a suitable curable resin that can be combined with a colored dye or pigment (e.g., food coloring) and then light cured with a light emitting device  515  as illustrated in  FIG. 5B . According to an alternative embodiment, a chemically curable resin may be used.  FIG. 6  illustrates the orthodontic brackets  100  as bonded to the teeth  520  of a patient. According to a further embodiment, small decorations (e.g., decorative jewelry, pictures, or designs) may be bonded to the orthodontic brackets, as desired.  
      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.