Abstract:
A bracket for orthodontic treatments comprises a closing spring, which is fixedly anchored at the bracket and which covers an arch wire slot formed in the bracket for receiving an arch wire in a closed position. In an end section of the closing spring covering the slot, a tongue is formed in the center and folded at an angle toward a base plate of the bracket. The spring has an end section which is held by projections formed at the bracket structure to secure the spring in its closed position. The spring may be dimensioned and pre-tensioned in a manner that an arch wire inserted into the slot is torqued by the closing spring with forces from the top and from the side.

Description:
RELATED APPLICATION 
   This application claims the benefit of DE 103 08 795.8, filed on Feb. 27, 2003, and DE 103 24 088.8, filed May 27, 2003, the contents of which are incorporated herein. 
   FIELD OF THE INVENTION 
   The present invention relates to brackets for orthodontic treatments, and, more particularly to such brackets which are mounted to teeth and moved via tension in a wire. 
   BACKGROUND OF THE INVENTION 
   A bracket of the type involving a base plate having a top and bottom side adapted to be attached to a tooth, two spaced apart wings arranged on the top side with an elongate slot extending therethrough for receiving an arch wire, and a closing spring made of a band-like material, anchored to the structure and movable between an open position in which the slot is freely accessible in an area between the wing sections and a closing position in which the free leg of the spring covers the slot is known, for instance, from U.S. Pat. No. 5,562,444. In the known bracket, an elongate leg is formed at the end of the arc of the closing spring with the free end of the leg being positioned in a broad groove formed on the bottom side of the gingival wing sections covered by the arc of the spring. This groove has a great opening angle which allows pivoting of the closing spring around the gingival wing sections between an open and a closed position, wherein the apex of the groove forms a pivot bearing together with the edge of the free end of the leg arranged in the groove. In the opening and closing positions, the spring holds on to the gingival wing sections covered by the spring by its inherent spring force by clamping effect. 
   However, it turned out in practice that when carelessly opening the spring the spring&#39;s elasticity limit can be exceeded so that the retention force by which it usually holds on to the gingival wing sections of the bracket structure is weakened. It can therefore easily get lost since the clamping force of the spring at the wing sections is the only means by which the spring holds onto its place. 
   In the above-mentioned reference, another bracket is described as including a spring which has an elongation at the end of the arc which does not cover the slot, with the elongation being bifurcated into two legs that are received by channels which extend laterally in the bracket structure below the slot and transversely thereto. In this bracket, there is also the risk of bending the spring too far, since only an arc of approximately 180° arc length is available for the bending process when opening the spring. 
   A bracket similar to the last mentioned bracket is known from U.S. Pat. No. 4,492,573, in which the bracket comprises an essentially U-shaped bent closing spring, the entirety of which, when opening the slot, can be moved transversely to the slot. 
   U.S. Pat. No. 4,144,642 also describes a bracket having a clip spring which can be shifted transversely with respect to the slot when opening and closing the slot for receiving the arch wire. 
   All the above-mentioned brackets have springs which, if they exert a force onto an arch wire inserted into the slot at all, exert a force directed towards the bottom of the slot, i.e., their springs press the arch wire towards the bottom of the slot. The spring force for each of these brackets is determined by the rigidity of the spring material and the effective spring length. The effective spring length is relatively great in all of these examples since it corresponds to the distance between the clamping location of the spring and the engagement location at the arch wire. Only when the spring rigidity is sufficiently great is sufficient closing force of the spring generated, which in turn enlarges the risk of a plastic deformation of the spring when moving it into the opening position. 
   Furthermore, a closing spring which only presses the arch wire on the bottom of the slot is less suitable for obtaining a torque which turns a treated tooth around an axis which extends through the level of the crown of the tooth. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to provide a bracket of the above-mentioned type, which is capable of generating a high closing force for securing an arch wire in the bracket slot without increasing the risk of damage of the spring during opening. The bracket may possibly also be capable of developing a high torque around an axis located on the level of a tooth crown. 
   This object may be attained according to the invention in a bracket as set forth in the opening portion of this specification by providing that the gingival wing sections of the structure covered by the arc of the closing spring have a projection on the sides facing each other. Such projections preferably have free ends which face each other at a predetermined distance. The free leg of the closing spring preferably has a central tongue-like section which is angled with respect to the free leg substantially at a right angle in the direction toward the upper side of the base plate and has a free end section with a width that is smaller than the distance between the opposing sides of the gingival wing sections but is larger than the distance between the free ends of the projections. The remainder of the tongue-like section is preferably not wider than the width of the free end section. 
   The free end section may be bent in the direction toward the arc of the closing spring so that it grips below a lower edge of the projections when in the closed position of the closing spring. 
   The lateral sections of the free ends of the closing spring adjacent to the tongue-like section, for the sake of simplicity referred to as tongue, are resilient lugs which are parallel to each other and which extend across the slot in the bracket structure to secure an arch wire positioned in the slot. Since the free end section of the tongue grips the projections, the closing and securement of the closing spring is almost exclusively determined by the tongue, the projections and the resilient lugs, so that the securement of the arch wire within the slot is substantially independent of the properties of the spring arc enclosing the gingival wing sections. 
   The free end section of the tongue may have a width which is larger than the distance between the projections, whereas an adjoining neck portion of the tongue may have a width which is smaller than such distance. The tongue of this type is adapted in a manner such that in the closed position of the spring, the end section is situated below the projections while the neck portion extends between the projections. Thus, the tongue positively secures the spring in its closed position without requiring that the end section be kept in a bent state. 
   Since the dimensions of the lugs and tongue are relatively small, their effective spring length is also relatively small. In order to enlarge the effective spring length of the tongue and lugs, a non-angled section may be provided in the root portion of the tongue on the free leg of the closing spring such that longitudinally extending slots separate the non-angled section from the free leg. 
   The closing spring comprises an extension leg preferably at an end of the arc distal of the free leg, the extension leg preferably being fixedly anchored on the structure. For this purpose, a flat continuous channel extending through the structure may be formed in the structure above the top side of the base plate but underneath the arch wire reception slot to receive the extension leg of the spring, which is formed smaller than the arc. The extension leg preferably extends through the channel and projects its free end from the channel, where it is folded to secure the extension leg, and thus the entire closing spring, onto the structure. As an alternative, an insertion slot may be provided in the structure underneath the wing covered by the arc of the spring, with the extension leg being inserted into the insertion slot and secured therein by welding, soldering or caulking. 
   It is also advantageous if an opening is formed in the closing spring adjacent to the tongue. This hole is provided for receiving a tool in the form of a needle which is used for opening the closing spring by plugging it into the hole and releasing the end of the tongue from its catch underneath the projections. 
   According to a preferred embodiment of the invention, a shoulder may be formed on the incisal wing sections of the structure, i.e., the sections which are not covered by the arc of the closing spring. Such shoulders are positioned adjacent to the slot. The lateral sections of the free leg of the closing spring, i.e., the above-mentioned resilient lugs, can rest on these shoulders in the closed position of the closing spring. 
   If the closing spring is tensioned to prefer the closed position, it can nonetheless be secured in the open position by providing the projections at the gingival wing sections with a top side which is obliquely inclined from an apex edge extending in the direction away from the arch wire slot. The free end of the angled tongue can be supported on this inclined surface in the open position of the closing spring. However, the spring can also be designed, or tensioned, to have an inherent preference for the open position. Such a spring can be held against this pre-tension in the closed position by the bent end section of the tongue which grips underneath the projections on the gingival wing sections or by the wide end section of the tongue disposed beneath the projections, depending on the embodiment of the tongue. 
   In order to enable opening and closing of the spring even when using arch wires which have cross sections that fill the entire width of the slot, the projections are spaced from the slot by a slight distance which is at least as large as the thickness of the closing spring, thereby allowing the tongue to be engaged by the projections without contacting the arch wire. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail with reference to the embodiments shown in the drawings. 
       FIG. 1  shows a plan view of an embodiment of a complete bracket; 
       FIG. 2  shows a plan view of the base plate and the structure of the bracket of  FIG. 1  elevating therefrom; 
       FIG. 3  shows a plan view of the closing spring for the bracket according to  FIGS. 1 and 2 ; 
       FIG. 4  shows a perspective view of an embodiment of the closing spring having a tongue with an enlarged effective length; 
       FIG. 5  shows a cross sectional view of the bracket of  FIG. 1  cut along line V—V with an arch wire having a round cross section inserted into the slot, the arch wire not being shown in  FIG. 1  for reasons of clarity; 
       FIG. 6  shows a cross sectional view similar to  FIG. 5  with an arch wire of a rectangular cross section inserted into the slot; 
       FIG. 7  shows a cross sectional view similar to  FIG. 5  with an arch wire of a rectangular cross section and an enlarged height inserted into the slot; 
       FIG. 8  shows a view comparable to the view of  FIG. 5  with an inserted opening tool at the beginning of the opening process, 
       FIG. 9  shows a view similar to  FIG. 8  during progress of the opening process; 
       FIG. 10  shows a view similar to  FIGS. 8 and 9  at the end of the opening process; 
       FIGS. 11 ,  12  and  13  show cross sectional views of an alternative embodiment of a bracket with an arch wire of a rectangular cross section inserted into the slot to demonstrate the torque effect that the arch wire may cause in cooperation with the closing spring; 
       FIG. 14  is a cross sectional view of another embodiment of a bracket in which its spring has a tongue with the end section disposed beneath the projections, and 
       FIG. 15  is a perspective view of the bracket of  FIG. 14 , showing the bracket with its spring in the open position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention will now be explained in detail with reference to the drawings. 
   As shown in  FIGS. 1  to  3 , the bracket consists of a base plate  1 , which comprises a bottom side  2  (see  FIG. 5 ) and a top side  3  from which a structure  4  arises. 
   The base plate  1  has an irregular contour, since this contour is adapted to the contour of the crown of a tooth at which the specially shown bracket is adapted to be attached. 
   The structure  4  has two mesial and distal wings S and  6  opposing each other at a mutual distance and divided into gingival and incisal sections  5   a ,  6   a  and  5   b ,  6   b , respectively. For example, sections  5   a  and  5   b  are easily discerned in  FIG. 15  which shows mesial wing  5 . Sections  5   a  and  5   b  are separated from one another by a slot  7  extending between them which is adapted to receive an arch wire  8 . Examples of such arch wires are shown in  FIGS. 5  to  7 . In the following, slot  7  is called arch wire slot. 
   Gap  9  separates the mesial and distal wings  5  and  6  from one another as shown in FIG.  2  and extends close to top side  3  of base plate  1 , as seen in FIG.  15 . Two nose-like projections  10  extend from gingival wing sections  5   a ,  6   a  toward each other and into gap  9 . 
   In the gingival section of structure  4  a flat channel  11  (shown in  FIGS. 14 and 15 ) is formed above base plate  1 , extends into the central portion of structure  4  and is adapted to receive an end of a closing spring belonging to the bracket. Details will be explained below. 
   Gingival wing sections  5   a  and  6   a  of structure  4  are covered by the already mentioned closing spring, which is designated by reference numeral  12 . Closing spring  12  is shown as a single member in  FIGS. 3 and 4 . Closing spring  12  has an arc portion  13  extending in several arcs connected at one end to a free, substantially straight end portion  14  and at the other, lower end to a straight extension  15 , which is formed narrower than the remainder of closing spring  12 . Extension  15  is inserted into channel  11  in structure  4  and secured therein by welding, soldering or caulking. Closing spring  12  may be made of metal or of plastics. 
   Straight end portion  14  has a tongue  17  in its central portion, the tongue being free of connection on both sides from the material of closing spring  12  and being folded toward base plate  1  of the bracket, as clearly shown in FIG.  4 . When closing spring  12  is in the closed position, tongue  17  adjoins slot  7  in gap  9 . Tongue  17  has an end section  17   a  bent backwards, which lies below the edge of projections  10  when spring  12  is closed. Lateral lugs  18  of straight end portion  14  of closing spring  12  cover arch wire slot  7  and an arch wire ( FIG. 5 ) inserted therein. The distance between the gingival wall laterally restricting arch wire slot  7  and projection  10  is at least as large as the thickness of the material of closing spring  12 . 
   Closing spring  12  has an opening  20  that is adapted to be penetrated by a needle or pin-like tool which may for instance be formed similar to a crochet hook. 
   In an advantageous embodiment, which is shown in  FIG. 4 , tongue  17  of closing spring  12  has a section  17   b  in its root portion where tongue  17  is connected to free leg  14  and is not angled with respect to free leg  14 , but is delimited on both sides by a longitudinally extending slot or recess  14   a . By these slots  14   a , the effective length of tongue  17  is enlarged without the other dimensions of closing spring  12  being changed. The enlargement of the effective tongue length helps to avoid a plastic deformation or breaking of tongue  17  when inserting or changing an arch wire. Moreover, the effective lengths of lugs  18 , which form the free end of the closing spring  12 , are also enlarged to further counteract a plastic deformation. 
   It can clearly be seen in  FIG. 5  that closing spring  12  is captively secured at the bracket structure, and as a result of the design of arcuate section  13  closing spring  12  can be bent out very far without the risk of closing spring  12  being expanded beyond its elasticity limit, i.e., without it being overstretched. 
   Nevertheless, arch wire  8  is effectively secured when inserted into the arch wire slot  7 . This securing effect is effected mainly by tongue  17  and lugs  18 , rather than by spring arc  13 . As may be seen, lower end section  17   a  of tongue  17  grips underneath projections  10  and holds spring  12  in the closed position. Two lugs  18  extend from the root of tongue  17  and over arch wire  8  disposed in arch wire slot  7 . The entire holding and securing function is consequently performed in the area around tongue  17 , i.e., by lugs  18  and projections  10 , thereby alleviating the need for the remaining spring to have an important influence thereon. Thus, it is even possible to employ closing spring  12  under pre-tension, in which closing spring  12  reaches its relieved state when in the open position, since closing spring  12  is held in its closed position by tongue  17  once it was brought into this position. 
   The basic structure of the bracket, consisting of base plate  1  and structure  4 , is preferably manufactured by casting or injection molding of metal or suitable plastic material. Closing spring  12  is positioned by inserting extension  15  into channel  11 , where it is secured in the manner already described. 
   It must also be noted that bottom side  2  of base plate  1  is adapted to be attached at the crown of a tooth by means of an adhesive or cement. This adhesive or cement is schematically shown in  FIGS. 5  to  7  by reference numeral  21 . 
   Another advantage of the invention can be seen in  FIGS. 6 and 7 , as compared to FIG.  5 . In  FIG. 5 , an arch wire  8  having a round cross section is inserted into arch wire slot  7 , with the arch wire not filling the cross section of the slot. Lugs  18  of closing spring  12  rest in a substantially tension-less manner on arch wire  8 . In  FIG. 6 , an arch wire  8  of a rectangular cross section is inserted into arch wire slot  7 , the wire filling the slot in its full height. This leads to the result that lugs  18  of closing spring  12  bend slightly upwards when closing spring  12  is secured in the closed position by locking lower tongue end  17   a  underneath projections  10 . As shown in  FIG. 7 , an arch wire  8  of a rectangular cross section inserted into slot  7  rises above the upper edge of slot  7 . This leads to the result that lugs  18  are bent even further upward if spring  12 , as shown, is secured in the closed position. As shown by the drawings, the remainder of closing spring  12  remains fully unaffected by this securing arrangement in the area of the slot. 
   With reference to  FIGS. 8  to  10  further advantages of the invention and the process of opening closing spring  12  are explained. For reasons of clarity, hatched lines typically used in sectional views are not shown. 
     FIG. 8  shows the bracket with an inserted arch wire of a round cross section (as an example) in a state comparable to that shown in FIG.  5 . The backward bent end section  17   a  of the unlatched tongue  17  of closing spring  12  lies below the lower edges of projections  10 , i.e., below the edge of projections  10  nearest base plate  1 . Lugs  18  of closing spring  12  rest next to arch wire  8 . A pin-like tool  23  is inserted into opening  20 , the tool being capable of being inserted between projections  10 . Tool  23  contacts the free edge of folded end section  17   a  of tongue  17 . 
   In  FIG. 9 , tool  23  has been pressed against the free edge of folded end section  17   a  of tongue  17  and has freed the tongue from the catch position below projections  10 . By slightly tilting tool  23  further, closing spring  12  can be tilted further away from projections  10  so that lugs  18  freely release slot  7  (FIG.  10 ). If closing spring  12  is bent sufficiently backwards, lower, folded end section  17   a  of tongue  17  can rest on the top side of each projection  10 . If each top side  22  has a suitable inclination extending from apex edge  28  in a direction away from arch wire slot  7 , projections  10  are capable of holding closing spring  12  in the open position shown in  FIG. 10  even if closing spring  12  has a pretension effective in the closing direction. 
   As an alternative, closing spring  12  may have a pre-tension effective in the opening direction. In such cases, a support for tongue  17  on projections  10  is not necessary. In any case, it can be seen from these two alternatives that any certain pre-tension of closing spring  12  is not important for securing arch wire  8  with lugs  18  and tongue  17 . The design and arrangement of lugs  18 , tongue  17  and projections  10  are the decisive factor. 
   In  FIG. 11 , an alternative embodiment, which deviates from the shown and described bracket by two independent features, is shown. In this bracket, a shoulder  19  adjoins at the upper end of arch wire slot  7  on the incisal side, with lugs  18  being able to rest on this shoulder. When an arch wire  8  does not have sufficient thickness to fill arch wire slot  7 , lugs  18  will contact shoulder  19  and will not press onto arch wire  8 . 
   The second deviating feature refers to closing spring  12  which has an extension  15  on the lower end of arc  13  which is so long that it fully penetrates a flat through channel  11 ′ formed in the bracket structure transversely to slot  7 , projects therefrom, and is secured to the bracket structure by folding spring end  16 . 
   A further advantage shown in  FIG. 11  in combination with  FIGS. 12 and 13  which can be achieved by the bracket according to the invention is that tongue  17  can be used together with a pre-tension of closing spring  12  as an instrument for exerting directional forces at an arch wire. 
     FIGS. 11  to  13  show the bracket according to the invention when being used with an arch wire  8  of a rectangular cross section. Arch wires with a rectangular cross section are typically used at the end of an orthodontic treatment with brackets if the misalignment of the teeth was corrected to such an extent that arch wires of a smaller cross section, particularly of a round cross section, are no longer able to cause those torques at the teeth that are required for bringing the teeth to the desired final position. 
   In the course of an orthodontic treatment it may be necessary to pivot the teeth not only around a horizontal axis located in the root portion but possibly around a horizontal axis located in the area of the tooth crown. An arch wire of a rectangular cross section may in combination with a bracket whose arch wire slot also has a rectangular cross section cause at the tooth provided with this bracket a torque that lies in the region of the tooth crown. This will be explained with reference to  FIGS. 11  to  13 . 
   A series of brackets are provided on a row of teeth of the upper jaw and the arch wire extends through the arch wire slots of all brackets. The arch wire&#39;s position within the slots is therefore not only determined by the individual brackets but by the cooperation of all brackets, the positions of which are determined by the position of all teeth in the respective row of teeth. Thus, the teeth align each other by the forces mutually acting at the arch wire. 
   In  FIG. 11 , arch wire  8  is canted in slot  7  due to the misalignment of the tooth (not shown) provided with the bracket shown so that wedge-shaped gaps result between the outer faces of arch wire  8  and the surfaces defining slot  7 . Closing spring  12  exerts forces by means of lateral lugs  18  and tongue  17  onto arch wire  8 , which intend to press the wire onto the bottom of arch wire slot  7  and in abutment with the slot wall opposing tongue  17 . These forces result in a torque which is exerted onto the bracket (shown in  FIG. 11  by arrows T.) 
   With the progressing effect of this torque T onto the tooth provided with the bracket, the tooth slightly yields so that the canting of arch wire  8  within arch wire slot  7  becomes smaller. This reduced state of the cant is shown in FIG.  12 . With further progress of the influence of the torque a state is finally obtained, shown in  FIG. 13 , in which the bottom surface of arch wire  8  planarly rests on the bottom of arch wire slot  7  and the side surface of arch wire  8  rests planarly on the limiting wall of arch wire slot  7  opposing tongue  17 . The consequence is that the position of the bracket in  FIG. 11  was changed into a preferred inclined position according to FIG.  13 . Thus, the position of the tooth to which the bracket is attached was changed accordingly. 
     FIGS. 14 and 15  show a particularly preferred embodiment of the invention. As may clearly be seen from  FIG. 15 , in this embodiment tongue  17  has a neck section  17   c  adjoining the tongue root, the neck section  17   c  having a width which is smaller than the distance between projections  10  at gingival wing sections  5   a ,  6   a , i.e., smaller than the width of the gap between gingival wing sections  5   a ,  6   a . An end section  17   d  adjoins to neck section  17   c  and has a width which is larger than the distance between projections  10 , but is smaller than the width of the gap between gingival wing sections  5   a ,  6   a . Tongue  17  is flat and is partially cut out from free leg  14  of closing spring  12  and bent in a direction toward the bottom of the bracket and to the front, so that a T-shaped opening  14   b  is formed by partially cutting-out free leg  14 . 
   As is shown in  FIG. 15 , wide end section  17   d  of tongue  17  is able to rest on projections  10  in the open position of closing spring  12  so that the latter is held in its open position. On the other hand, when moving closing spring  12  into its closed position, shown in  FIG. 14 , neck portion  17   c  can pass between projections  10  so that wide end section  17   d  of tongue  17  reaches a resting position below projections  10  and locks closing spring  10  in its closed position. The orthodontist may unlock the spring by inserting a pin-shaped tool through T-shaped opening  14   b  of spring  14  to push end section  17   d  of tongue  17  out of its locked position, so that end section  17   d  may slide over the surfaces of projections  10  close to arch wire slot  7 . 
   The broader end section  17   d  of tongue  17  may be bent in a manner as shown in the embodiments first explained above. Further, in the embodiment of  FIGS. 14 and 15 , tongue  17  may be formed at free leg  14  of spring  12  in a manner as is explained with respect to the first mentioned embodiments and shown in FIG.  4 . 
   Finally, it should be mentioned that all wing sections may have projections or protrusions in opposing directions, as shown in the drawings, which make it possible to attach ligatures at the bracket in the usual manner, if desired. Attachment of ligatures is often desired at the beginning of an orthodontic treatment when the pressure of closing spring  12  acting on the arch wire is not sufficiently high to effect a safe retainment of the arch wire in the arch wire slot. 
   While the principles of the invention have been shown and described in connection with specific embodiments, it is to be understood that such embodiments are by way of example and are not limiting.