Abstract:
An orthodontic bracket is provided for correcting teeth alignment. The orthodontic bracket allows for not relying on how an operator is skilled in ligation and also for minimizing the friction. The orthodontic bracket includes a slot having an opening into which an orthodontic wire can be inserted, and a shutter that can slide to block or unblock the opening. The orthodontic wire is placed in the slot by causing the shutter to slide and unblock the opening, inserting the wire through the opening, and causing the shutter to slide and block the opening. The orthodontic wire will not disengage from the slot, whereby rotation control, tipping control, and torque control may be reliably performed. Further, it is not necessary to perform ligation that causes the wire to be securely pressed against the bottom of the slot. Since the ligation is not tight, the tooth in question can be smoothly shifted.

Description:
[0001]    This application claims priority under 35 U.S.C. 119 from Japanese patent application serial no. 2009-149185, filed Jun. 23, 2009 entitled “Orthodontic Bracket”, which is incorporated herein by reference in its entirety 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an orthodontic bracket attached to a tooth to correct teeth alignment. 
       BACKGROUND OF THE INVENTION 
       [0003]    In recent orthodontics, orthodontic brackets attached to teeth and a wire attached to the brackets have been disposed on the inner side of the teeth, that is, on the lingual side, from an aesthetic point of view. For example,  FIG. 1  illustrates a prior art orthodontic bracket  10  which is described in Japanese Examined Patent Publication (Kokoku) No. 57-44967. The orthodontic bracket  10  includes a plate-shaped pad  13  glued to a surface  12  of a tooth  11  that is on the lingual side (inner side) and a bracket body  14  integrated with the pad  13  by brazing or any other suitable method in such a way that the bracket body  14  stands erect from the pad  13  (see  FIG. 1 ). 
         [0004]    The bracket body  14  has a portion that looks like three fingers, which forms a main slot opening  15  and a sub-slot opening  16 . The main slot opening  15  is positioned vertically downward (when the orthodontic bracket  10  is used in the maxilla) or upward (when the orthodontic bracket  10  is used in the mandible) in a state in which the orthodontic bracket  10  is attached to the lingual surface of the tooth  11 . The sub-slot opening  16  horizontally toward the lingua when the orthodontic bracket  10  is attached as described above. A metal wire  17  made of, for example, an alloy and having a rectangular or any other suitable cross-sectional shape is then inserted into the slot  15  or  16 . 
         [0005]    The intrinsic elasticity of the wire  17  produces a bending force, a tension, or any other force as a restoring force that serves as a corrective force or moment acting on the tooth  11 , which deviates from a normal dental arc or is skewed incorrectly, and the force or moment shifts or rotates the tooth  11  over time to a position on the normal dental arc. Further, undercut portions  18  and  19  formed as upper and lower gaps between the bracket body  14  and the pad  13  are used to catch a thin wire, a rubber band, or any other suitable fastener for ligating and securing the wire  17  inserted into the main slot  15  (or the sub-slot  16 ) to the orthodontic bracket  10 . 
         [0006]      FIG. 2  shows another prior art orthodontic bracket  20 , which is described in U.S. Pat. No. 4,337,037. The orthodontic bracket  20  includes a pad  13 , similar to the one used in the orthodontic bracket  10  of  FIG. 1 , and a bracket body  24  integrated with the pad  13 . The bracket body  24  may include a main slot opening  25  positioned horizontally toward the lingua in a state in which the orthodontic bracket  20  is attached to the tooth  11 , as shown in  FIG. 2 . Further, similar to the orthodontic bracket  10  of  FIG. 1 , upper and lower undercut portions  18  and  19  are formed between the bracket body  24  and the pad  13 , and at least one of the undercut portions can be used to ligate and secure a wire  17 , which is inserted in a predetermined position in the main slot opening  25 . 
         [0007]    When any of the orthodontic brackets of the prior art described above is used to perform lingual orthodontics, it has been pointed out that the ligation is a cumbersome task. In particular, an orthodontic bracket used in the maxilla and having a large anterior tooth torque does not provide a force large enough to press the wire to the bottom of the slot, and a single tie results in a poor ligation. In this case, ligation using double over tie, which is more cumbersome, has been used. When a small-sized orthodontic bracket is used, since the width of the slot is narrow and the depth thereof is shallow, it is important to perform ligation very carefully in order to reliably press the wire into the slot. If the ligation is loose, the play between the slot and the wire is large, which adversely affects rotation and torque control. 
         [0008]    An orthodontic bracket having a horizontally oriented slot is problematic, for example, in that loose ligation may not allow improvement in rotation or may cause the wire to disengage from the slot during anterior retraction, resulting in torque control failure. On the other hand, when an orthodontic bracket having a vertically oriented slot is used, loose ligation may not allow tipping, height control, or sufficient torque control as well. As a result, in both the horizontally and vertically oriented slots, loose ligation prevents reliable three-dimensional tooth control. On the other hand, tight ligation that allows the wire to be securely pressed against the bottom of the slot may increase the friction between the wire and the ligation wire, preventing smooth tooth motion. 
       SUMMARY OF THE INVENTION 
       [0009]    To solve the problems described above, an object of the present invention is to provide an orthodontic bracket that does not rely on how an operator is skilled in ligation and can minimize the above mentioned friction. 
         [0010]    A first aspect of the present invention is an orthodontic bracket attached to a tooth to correct the row of teeth, the orthodontic bracket comprising a slot having an opening into which a wire can be inserted in the vertical direction, and a shutter that can slide to block or unblock the opening. The wire is placed in the slot by causing the shutter to slide and unblock the opening, inserting the wire through the opening, and causing the shutter to slide and block the opening. 
         [0011]    According to a second aspect of the present invention, the slot has a square cross-sectional shape. 
         [0012]    According to a third aspect of the present invention, the length of the slot ranges from 1.0 to 2.0 mm or from 2.0 to 3.5 mm. 
         [0013]    According to a fourth aspect of the present invention, the position of the center of the slot is determined in such a way that the ratio of the distance from the crown lower end to the crown height ranges from 0.2 to 0.5 or from 0.3 to 0.7. 
         [0014]    According to the first aspect of the present invention, the wire will not disengage from the slot, whereby the torque control can be reliably performed. Further, it is not necessary to perform ligation that causes the wire to be securely pressed against the bottom of the slot. Since the ligation is not tight, the tooth in question can be smoothly shifted. 
         [0015]    According to the second aspect of the present invention, the play between the wire and the slot in the horizontal direction can be the same as that in the vertical direction. 
         [0016]    According to the third aspect of the present invention, an optimum corrective force and moment can be obtained. 
         [0017]    According to the fourth aspect of the present invention, it is possible to use a wire having a straight configuration including a simple smooth curve, such as an arc, and straight lines connected to both ends of the curve. 
         [0018]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments, are intended for purposes of illustration only and are not intended to necessarily limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a side view of a prior art orthodontic bracket. 
           [0020]      FIG. 2  is a side view of another prior art orthodontic bracket. 
           [0021]      FIGS. 3A ,  3 B, and  3 C are a plan view, a side view, and a bottom view of an orthodontic bracket according to an embodiment of the invention. 
           [0022]      FIG. 4  is a plan view of a wire useable with the orthodontic bracket shown in  FIGS. 3A-3C . 
       
    
    
       [0023]    In the appended figures, the portion having the same or similar functions may have the same reference label and no redundant description thereof will be made in the present specification. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The ensuing description provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiment(s) of the disclosure. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the appended claims. 
         [0025]      FIGS. 3A ,  3 B, and  3 C represent, respectively, a plan view, a side view, and a bottom view of an orthodontic bracket according to the embodiment of the present invention. The orthodontic bracket may  30  include a bracket body  31 , a shutter  32 , a shutter holder  33 , and a pad  34 . 
         [0026]    The bracket body  31  features a slot  35  formed therein, to which a wire  40 , which will be described later, is attached. The slot  35  has a square cross-sectional shape and has a short length. In addition, the slot  35  includes an opening  35   a  into which the wire can be inserted in the vertical direction. Conversely, the slot of the orthodontic bracket of the prior art has a rectangular cross-sectional shape. When a thin, round wire is used to perform leveling, in particular, the play between the horizontally oriented slot and the wire is large, and hence sufficient improvement in rotation often cannot be made. To mitigate this problem, the slot  35  of the orthodontic bracket  30  of the present embodiment has a square cross-sectional shape and has a short length so that three-dimensional control including rotation control, tipping control, and torque control may be performed with low friction. 
         [0027]    The play between the slot  35  and the wire  40  in the horizontal direction is the same as that in the vertical direction, which is significantly advantageous in improving the rotation control, tipping control, and torque control, as compared to a rectangular slot of the prior art. 
         [0028]    The length of one side of the square cross-sectional shape of the slot preferably ranges from about 0.015 to 0.019 inches. When the length of one side is within this range, an optimum corrective force and moment can be obtained by adjusting the length of the slot, the distance between the brackets, the size of the wire, and other parameters. 
         [0029]    The length of the slot  35  can be about, for example, 1.5 mm when the orthodontic bracket  30  is used in the maxilla, whereas it can be about 1.3 mm when used in the mandible. 
         [0030]    It is however noted that the length of the slot is not limited to the values described above. The length of the slot  35  preferably ranges from about 1.0 to 2.0 mm. When the length of the slot is within this range, an optimum corrective force and moment can be obtained by adjusting the length of one side of the square cross-sectional shape of the slot, the distance between the brackets, the size of the wire, and other parameters. 
         [0031]    As described above, the length of the slot of the orthodontic bracket of the present embodiment can be shorter than the length of the slot of an orthodontic bracket of the prior art. 
         [0032]    Since the length of the slot of the orthodontic bracket of the present embodiment is shorter than the length of the slot of an orthodontic bracket of the prior art, the following advantages are provided. First, reducing the length of the slot allows the distance between adjacent brackets to be increased. Thus, a large distance between adjacent brackets prevents the wire from being plastically deformed due to a large magnitude of stress acting thereon. Second, no plastic deformation results in any increase in friction. 
         [0033]    The torque θ of the slot  35 , shown in  FIG. 3B , preferably ranges from about 40 to 70 degrees. When the torque θ of the slot is within this range, the orthodontic bracket  30  may be attached to a tooth in accordance with the form thereof. 
         [0034]    The slot  35  is formed in the bracket body  31  in such a way that the opening  35   a  of the slot  35  is oriented in a substantially vertical direction, whereby the wire  40  is readily placed in the slot  35  and at the same time the wire  40  is readily bent in this process. 
         [0035]    As shown  FIG. 3B , the slot  35  is positioned in a lower portion of the orthodontic bracket  30 . The orthodontic bracket  30  is attached to the tooth in such a way that the slot  35  is positioned on the labial side. 
         [0036]    The vertical position of the centroid of the square cross-sectional shape of the slot  35  is now defined as the “position of the center of the slot.” The ratio of the distance from the lower end of the crown of the tooth to the height of the crown is further defined as the “ratio of the distance from the crown lower end to the crown height.” The position of the center of the slot is preferably determined in such a way that the ratio of the distance from the crown lower end to the crown height ranges from about 0.2 to 0.5. When the position of the center of the slot is determined in this way, a wire having a “straight configuration” formed of a simple smooth curve, such as an arc, and straight lines connected to both ends of the curve may be advantageously used. 
         [0037]    The shutter  32  is attached to the bracket body  31  via the shutter holder  33  so that the shutter  32  slides to block or unblock the opening  35   a  of the slot  35 . The shutter  32  includes a rectangular plate-shaped shutter body  36 , a rectangular plate-shaped stopper  37 , and a rectangular plate-shaped spacer  38 . A lid  36   a  that blocks or unblocks the opening  35   a  of the slot  35  is formed at the lower end of the shutter body  36 . A tab  37   a  is formed at the lower end of the stopper  37  so that the shutter  32  does not disengage from the shutter holder  33 . 
         [0038]    The shutter body  36  and the stopper  37  are overlaid with the spacer  38  interposed therebetween at the upper end thereof and joined with each other. The shutter holder  33  has a U-like cross-sectional shape; the upper end of the shutter  32  is inserted into the U-shaped portion, and both ends of the U-shaped portion are joined with the pad  34 . When the lid  36   a  of the shutter body  36  blocks the opening  35   a  of the slot  35 , the tab  37   a  of the stopper  37  abuts the shutter holder  33  and hence the shutter  32  does not disengage from the shutter holder  33 . In this way, the lid  36   a  is reliably secured to cover the opening  35   a  of the slot  35 , and serves as a sturdy inner wall of the slot  35 . Pressing the lower end of the stopper  37  toward the shutter body  36  so that the stopper  37  is bent and lifting the lower end of the stopper  37  cause the tab  37   a  of the stopper  37  to enter the U-shaped portion of the shutter holder  33 . Since the shutter  32  can thus be lifted, the lid  36   a  of the shutter body  36  unblocks the opening  35   a  of the slot  35 . 
         [0039]    When torque control is performed, the configured slot  35  does not allow the wire  40  to disengage from the slot  35  during anterior retraction. Therefore, even when the wire  40  has a square cross-sectional shape, the play in the torque is small and the torque control can be sufficiently performed. Among others, since the low friction provides a smaller continuous corrective force, smooth tooth motion is likely achieved. Furthermore, since the smaller force provides a sufficient corrective force, the pain that the patient may feel at the tooth under orthodontic treatment is likely reduced. 
         [0040]    The pad  34  has a rectangular plate shape and is integrated with the bottom of the bracket body  31  by brazing or any other suitable method. The pad  34  is glued or otherwise attached to the lingual-side surface of the tooth. Since the pad  34  is thin and attached to a portion close to the gingiva, even when the orthodontic bracket  30  is attached to an anterior tooth in the maxilla and faces the tip of an anterior tooth in the mandible, the tip of the anterior tooth in the mandible does not tend to hit the orthodontic bracket  30 . Therefore, since the orthodontic bracket  30  will not come into contact with the tip of any anterior tooth in the mandible, no gap will be formed between upper and lower molar teeth, whereby there is no risk of root resorption at the anterior tooth. It should be noted that when the pad  34  is glued onto the lingual-side surface of a tooth, any indentation in the surface of the tooth can be filled with an adhesive or the angle of the surface of the pad  34  to the surface of the tooth can be delicately adjusted by using an adhesive. 
         [0041]    The wire  40  is a straight arch-shaped wire, smoothly curved at a large radius of curvature with no sharply bent portion, which requires almost no additional bending force to produce plastic deformation. The wire  40  has a straight configuration formed of a simple smooth curve, such as an arc, and straight lines connected to both ends of the curve without any step between the curve and the straight lines. Additionally, the wire  40  has no bent portion through plastic deformation, and rests entirely in a horizontal plane when it is not biased, as shown in  FIG. 4 . When the wire  40  is attached to a tooth for correction, the wire  40  is deformed within its elasticity limit (when a wire made of a shape memory alloy is used, the wire is deformed within its super-elasticity limit) and inserted into the slot  35  of the orthodontic bracket  30 . The elastic force of the wire  40  then produces a corrective force or moment acting on the tooth via the orthodontic bracket  30 . 
         [0042]    Since this configured wire  40  does not need in advance any plastically deformed bent portion, the wire  40  may be readily produced and industrially manufactured in volume, providing a significant advantage of cost reduction. Further, when the position of the wire  40  is shifted and adjusted relative to the orthodontic bracket  30  in the course of orthodontic treatment, no cumbersome operations, such as re-bending any bent portion and re-ligation, are necessary, unlike the mushroom-shaped archwire of the prior art, whereby the sliding adjustment of the wire  40  is very readily carried out. Therefore, the burdens on both the operator and patient are reduced, and additionally the effect of individual skills among the operators is relatively reduced. Further, the fact that it is not basically necessary to bend the wire  40  so that the shape thereof conforms to the dental arch of each individual patient is significantly advantageous. This advantage lies in a fact that it is possible to use a material which more flexibly undergoes super-elastic deformation compared to a wire of the prior art which is extremely difficult to be bent through plastic deformation, such as a shape memory alloy made of nickel, titanium, copper, or other elements. 
         [0043]    It should be noted that when the orthodontic bracket of the present embodiment is used in treatments, the chair time and treatment time are shortened. Additionally, shifting a tooth, such as tipping control and rotation control, is also reliably performed in a short period of time. More specifically, this period of time is reduced by an amount of about 10 to 40% compared to a case where an orthodontic bracket of the prior art is used. 
         [0044]    While, in this embodiment, the orthodontic bracket  30 , pertaining to the present invention, is attached to the lingual side of the tooth, in other embodiments the orthodontic bracket  30  may be attached to the labial side of the tooth. 
         [0045]    In this embodiment, the length of one side of the square cross-sectional shape of the slot  35  preferably ranges from about 0.018 to 0.022 inches. When the length of one side is within this range, an optimum corrective force and moment may be obtained by adjusting the length of the slot  35 , the distance between the brackets, the size of the wire, and other parameters. 
         [0046]    The length of the slot  35  preferably ranges from about 2.0 to 3.5 mm. When the length of the slot is within this range, an optimum corrective force and moment may be obtained by adjusting the length of one side of the square cross-sectional shape of the slot, the distance between the brackets, the size of the wire, and other parameters. 
         [0047]    The torque θ of the slot  35  preferably ranges from about −5 to 30 degrees. When the torque θ of the slot  35  is within this range, the orthodontic bracket  30  can be attached to a tooth in accordance with the form thereof. Depending on the value of the torque θ, it is possible to provide, as appropriate, an opening  35   a  into which a wire may be horizontally inserted and a shutter  32  that can slide to block or unblock the opening  35   a.    
         [0048]    The position of the center of the slot  35  is preferably determined in such a way that the ratio of the distance from the crown lower end to the crown height ranges from about 0.3 to 0.7.