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 closing position. In an end section of the closing spring covering the slot, a tongue is formed in the center and folded at a right angle towards a base plate of said bracket. The spring has an end section which is held by projections formed at the bracket structure to secure the spring in its closing position. The spring may be dimensioned and pre-loaded in a manner that an arch wire inserted into the slot is loaded by the closing spring with forces from the top and from the side.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention refers to a bracket for orthodontic treatments, comprising a base plate, which has a bottom side and a top side adapted to be attached at a tooth, with a structure being arranged on the top side of said base plate, having two wings arranged at a mutual distance, said wings being each interrupted by an elongate slot flushly extending through both wings, said slot dividing each wing into a gingival section and an incisal section and being suitable for receiving an arch wire, and of a closing spring made of a band-like material, anchored to the structure, said spring comprising an arc extending over the gingival wing sections and a free leg connected to the arc, and being 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.  
         PRIOR ART  
         [0002]    A bracket of this type is known e.g. 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 distal of the slot, the free end of said leg being arranged in a broad groove formed on the bottom side of the gingival wing sections covered by the arc of the spring. This groove as a great opening angle, which allows to pivot the closing spring around the gingival wing sections between an opening and a closing position, wherein the apex of the groove forms a pivot bearing together with the edge at the free end of the section of the spring leg arranged in the groove. In the opening and in the closing positions, the spring holds on to the gingival wing sections covered by the spring by its inherent spring force by clamping effect.  
           [0003]    However, it turned out in practice that when carelessly opening the spring, said spring is sometimes bent open by exceeding its elasticity limit so that the retention force suffers by means of which it usually holds on to the gingival wing sections of the bracket structure. It can therefore easily get lost since the clamping force of the spring at the wing sections adjoining same is the only means by which the spring holds on to its place.  
           [0004]    In the above-mentioned reference, another bracket is described including a spring which has an elongation at the end of the arc distal of the slot, said 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 a too heavy bending of the spring, since an arc of approx. 180° arc length only is available for the bending process when opening the spring.  
           [0005]    A bracket similar to the last mentioned bracket is known from U.S. Pat. No. 4,492,573, said bracket comprising an essentially U-shaped bent closing spring, which for opening the slot can totally be moved transversely to the slot.  
           [0006]    U.S. Pat. No. 4,144,642 also describes a bracket having a clip spring, which for opening and closing the slot for receiving the arch wire can be shifted transversely with respect to the slot.  
           [0007]    All above-mentioned brackets have in common that their springs exert a force onto an arch wire inserted into the slot, if at all, which is directed towards the bottom of the slot, i.e. it presses the arch wire towards the bottom of the slot. The spring force is determined by the rigidity of the spring material and the effective spring length which is relatively great in all examples, since it corresponds to the distance between the clamping location of the spring and the engagement location at the arch wire. Only if the spring rigidity is sufficiently great is the required closing force of the spring generated, which in turn enlarges the risk of a plastic deformation of the spring when moving same into the opening position.  
           [0008]    Furthermore, a closing spring, which presses the arch wire on the bottom of the slot only, is less suitable for obtaining a torque which turns a tooth provided with the bracket around an axis which extends on the level of the crown of the tooth treated.  
         SUMMARY OF THE INVENTION  
         [0009]    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 shall possibly also be capable of developing a high torque around an axis located on the level of a tooth crown.  
           [0010]    This object is attained according to the invention in a bracket as set forth in the opening portion of this specification in 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, the projections have free ends, which face each other at a predetermined distance, the free leg of the closing spring has a central tongue-like section, which is angled with respect to same substantially at a right angle in the direction towards the upper side of the base plate and has a width at least at a free end section that is smaller than the distance of the opposing sides of the gingival wing sections but is larger than the distance between the free ends of the projections, the remainder of said tongue-like section being not wider than the width at said free end section.  
           [0011]    Said send section may be bent in the direction towards the arc of the closing spring, so that it grips below a lower edge of said projections in the closed position of the closing spring.  
           [0012]    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 therefore resilient lugs parallel to each other, which extend across the slot in the bracket structure and which are capable of securing an arch wire in the slot inserted therein. Since the free end section of the tongue grips under said projections, the closing and safety effect of the closing spring is almost exclusively determined by said tongue, the projections and the resilient lugs, so that said effect is substantially independent of the properties of the spring arc enclosing the gingival wing sections.  
           [0013]    The free end section of the tongue may have a width which is larger than the distance between the projections at said wings, whereas an adjoining neck portion of said tongue has a width which is smaller than said distance. The tongue of this type is adapted in a manner that in the closing position of the spring, said end section is situated below said projections, whereas the neck portion extends between said projection. Thus, the tongue positively secures the spring in its closing position, without said end section having any bent therein.  
           [0014]    Since the dimensions of the lugs and of the tongue are relatively small, their effective spring length is also relatively small. In order to enlarge the effective spring length of the tongue and of the lugs, a non-angled section may be provided in the root portion of the tongue, said non-angled section being located on the level of the free leg of the closing spring opposite thereto but which is limited on both sides by a longitudinally extending slot.  
           [0015]    The closing spring comprises an extension leg preferably at and end of the arc distal of the free leg, said extension leg 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, and the extension leg of the spring, which is formed smaller than the arc, extends in said channel and projects on its free end from the channel, where it is folded to secure the extension leg and thus the entire closing spring on 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, said extension leg being secured therein by welding, soldering or caulking.  
           [0016]    It is also advantageous if an opening is formed in the closing spring adjacent to the tongue. This hole is determined for receiving a tool in the form of a needle, which is used for opening and closing the closing spring by plugging it into the hole and by means of which the end of the tongue is released from its catch underneath the projections.  
           [0017]    According to a preferred embodiment of the invention, a shoulder is formed on the incisal wing sections of the structure not covered by the arc of the closing spring adjacent to the slot. On this shoulder the lateral sections of the free leg of the closing spring, i.e. the above-mentioned resilient lugs can rest on this shoulders in the closing position of the closing spring.  
           [0018]    If the closing spring is loaded in the closing position, it can be secured in the opening position in that the projections at the gingival wing sections each have a top side which is obliquely inclined starting out from an apex edge and extending 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 such that it is loaded with inherent tension in an open position. It is held against this pre-tension in the closing position by the bent end section of the tongue which grips underneath the projections on the gingival wing sections or the wide end section of the tongue disposed beneath said projections, according to the embodiment of said tongue.  
           [0019]    In order to enable opening and closing of the spring even if arch wires are used whose cross section fills the entire width of the slot, a light distance exists between the projections and the slot, said distance being at least as large as the thickness of the closing spring. 
       
    
    
     SHORT DESCRIPTION OF THE DRAWINGS  
       [0020]    The invention will now be described in detail with reference to the embodiments shown in the drawings.  
         [0021]    [0021]FIG. 1 shows a plan view onto a first embodiment of a complete bracket;  
         [0022]    [0022]FIG. 2 shows a plan view onto the base plate and the structure of the bracket of FIG. 1 elevated thereon;  
         [0023]    [0023]FIG. 3 shows a plan view onto the closing spring for the bracket according to FIGS. 1 and 2;  
         [0024]    [0024]FIG. 4 shows a perspective view of an especially advantageous embodiment of the closing spring with an enlarged effective length of the tongue;  
         [0025]    [0025]FIG. 5 shows a sectional view of the bracket of FIG. 1 cut along line V-V of FIG. 1 with an arch wire of a round cross section wire being inserted into the slot, said arch wire not being shown in FIG. 1 for reasons of clarity;  
         [0026]    [0026]FIG. 6 shows a sectional view similar to FIG. 5 with an arch wire of a rectangular cross section being inserted into the slot;  
         [0027]    [0027]FIG. 7 shows a sectional view similar to FIG. 5 with an arch wire of a rectangular cross section of an enlarged height being inserted into the slot;  
         [0028]    [0028]FIG. 8 shows a view comparable to the view of FIG. 5 with an inserted opening tool at the beginning of the opening process,  
         [0029]    [0029]FIG. 9 shows a view similar to FIG. 8 during progress of the opening process;  
         [0030]    [0030]FIG. 10 shows a view similar to FIGS. 8 and 9 at the end of the opening process;  
         [0031]    [0031]FIG. 11 to FIG. 13 show sectional views of an alternative embodiment of a bracket with an arch wire of a rectangular cross section inserted into the slot to explain the torque effect that the arch wire causes in cooperation with the closing spring;  
         [0032]    [0032]FIG. 14 is a sectional view of another embodiment of a bracket, its spring having a tongue, the end section of which is disposed beneath the projections, and  
         [0033]    [0033]FIG. 15 is a perspective view of the bracket of FIG. 14, showing the bracket in the opening position of its spring. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    The invention will now be explained in detail with reference to the drawings. According to 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 arises, which is designated by  4 . 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 shall be attached.  
         [0035]    The structure  4  has two mesial and distal wings opposing each other at a mutual distance, said wings being designated by  5  and  6  and being divided into gingival and incisal sections  5   a ,  6   a  and  5   b ,  6   b , respectively. The sections  5   a  and  5   b  are easily distinguishable in FIG. 5 by the example of the mesial wing  5 , and they are separated from one another by a slot  7  extending between them, which is adapted to receive an arch wire  8 , examples of which being shown in FIGS.  5  to  7 . In the following, said slot  7  is called arch wire slot.  
         [0036]    The gap separating the mesial and distal wings  5  and  6  from one another is designated by  9  in FIG. 2 and reaches close to the top side  3  of the base plate, see in this respect FIG. 5. Two nose-like projections  10  extend from the gingival wing sections  5   a ,  6   a  towards each other into this gap  9 .  
         [0037]    In the gingival section of the structure  4  a flat channel  11  is formed above the base plate  1 , which extends in the central portion of the structure  4  into same and is adapted to receive an end of a closing spring belonging to the bracket. Details will be explained below.  
         [0038]    The gingival wing sections  5   a  and  6   a  of the structure  4  are covered by an already mentioned closing spring, which is designated by  12 . The closing spring  12  is shown as a single member in FIGS. 3 and 4. It has an arc portion  13  extending in several arcs at whose one top end a free, substantially straight end portion  14  adjoins and at whose other, lower end an also straight extension  15  adjoins, which is formed narrower than the remainder of the closing spring  12 . The extension  15  is inserted into the channel  11  in the structure and secured therein by welding, soldering or caulking. The closing spring may be made of metal or of plastics.  
         [0039]    The straight end portion  14  has a tongue  17  in its central portion, said tongue being unlatched on both sides from the material of the closing spring and being folded towards the base plate  1  of the bracket, as clearly shown in FIG. 4. The tongue  17  is arranged in the closing position of the spring  12  shown in FIG. 5 in a manner that it adjoins the slot  7 . It has en end section  17   a  bent backwards, which lies in a level below the edge of the projections  10  adjoining the top side  3  of the base plate  1 . The lateral lugs  18  of the straight end portion  14  of the closing spring  12  that are not folded cover the arch wire slot  7  and an arch wire (FIG. 5) inserted therein, not shown in FIG. 1. The distance between a wall laterally restricting the arch wire slot  7  and the projecting  10  extending close to said wall is at least as large as the thickness of the material of the closing spring  12 .  
         [0040]    In the center the closing spring  12  has a 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.  
         [0041]    In an advantageous embodiment, which is shown in FIG. 3 b , the tongue  17  of the closing spring  12  has a section  17   b  in its root portion where the tongue  17  is connected to the free leg  14 , which in a manner not angled with respect to the free leg  14 , is delimited on both sides by a longitudinally extending slot or recess  14   a . By these slots  14   a , the length of the tongue effective for suspending the tongue  17  is enlarged without the other dimensions of the closing spring  12  being changed. The enlargement of the effective tongue length helps to avoid a plastic deformation or breaking of the tongue  17  when inserting or changing an arch wire. Moreover, the effective lengths of the lugs  18 , which form the free end of the closing spring  12 , are also enlarged, which also counteracts a plastic deformation.  
         [0042]    It can clearly be seen in FIG. 5 that the closing spring  12  is captively secured at the bracket structure, and as a result of the relatively far stretched arcuate section  13  with several arcs it can be bent out very far without the risk of the spring being expanded beyond its elasticity limit, i.e. without it being overstretched.  
         [0043]    Nevertheless is a great securing effect achieved at the arch wire  8  inserted into the arch wire slot  7 . This securing effect is decisively determined by the tongue  17  and the lugs  18 , but less or not at all by the spring arc  13 . As may be seen, the lower end section  17   a  of the tongue  17  grips underneath the projections  10  and holds the spring  12  in the closing position. At the root of the tongue  17  the two lugs  18  start, which extend over the arch wire  8  disposed in the arch wire slot  7 . The entire holding and securing function is consequently developed in the area around the tongue  17 , the lugs  18  and the projections  10 , without the remaining spring having an important influence thereon. Thus, it is even possible to hold the closing spring  12  under pre-tension, which presses it in the relieved state into an open position, since the closing spring is held in its closing position by the tongue once it was brought into this position.  
         [0044]    The basic structure of the bracket consists of the base plate  1  and the structure  4 , it is preferably manufactured in a casting or injection molding method of metal or a suitable plastic material. The closing spring  12  is positioned by inserting the extension  15  into the channel, where it is secured in a manner already described.  
         [0045]    It must also be noted that the bottom side  2  of the 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 .  
         [0046]    The advantage of the invention can be seen in FIGS. 6 and 7, compared to FIG. 5. In FIG. 5, an arch wire  8  having a round cross section is inserted into the arch wire slot  7 , said arch wire not filling the cross section of said slot. The lugs  18  of the spring rest in a substantially tension-less manner on the arch wire  8 . In FIG. 6 an arch wire  8  of a rectangular cross section is inserted into the arch wire slot  7 , said wire filling the slot in its full height. This leads to the result that the lugs  18  of the spring slightly bend upwards when the closing spring is secured in the closing position by locking the lower tongue end  17   a  underneath the projections  10 . According to FIG. 7, an arch wire  8  of a rectangular cross section is inserted into the slot  7 , said arch wire rising above the upper edge of the slot  7 . This leads to the result that the lugs  18  are bent even further in the upward direction if the spring  12 , as shown, is secured in the closing position. As shown by the drawings, the remainder of the closing spring remains fully unaffected by the type of safety state in the area of the slot.  
         [0047]    With reference to FIGS.  8  to  10  further advantages of the invention and the process of opening the closing spring  12  are explained. For reasons of clarity, the hatched lines as usual used in sectional views are not shown.  
         [0048]    [0048]FIG. 8 shows the bracket with an inserted arch wire of a round cross section (as an example) in a state comparable to that of FIG. 5. The backward bent end section  17   a  of the unlatched tongue  17  of the closing spring lies below the lower one of the edges of the projections  10 , i.e. below the edge of the projections  10  close to the base plate. The lugs  18  of the closing spring  12  rest next to the arch wire  8 . A pin-like tool  23  is inserted into the opening  20 , said tool being capable of being inserted between the projections  10 . It contacts the free edge of the folded end section  17   a  of the tongue  17 .  
         [0049]    In FIG. 9 the tool  23  is pressed against the free edge of the folded end section  17   a  of the tongue  17  and has freed the tongue from the catch position below the projections  10 . By means of the tool  23 , i.e. by a slight further tilting of same, the closing spring  12  can further be tilted backwards so that the lugs  18  freely release the slot  7  (FIG. 10). If the closing spring  12  is bent sufficiently backwards, the lower, folded end section  17   a  of the tongue  17  can rest on the top side of the projections  10 . If this top side  22  has a suitable inclination, which extends from the apex edge in a direction extending away from the arch wire slot  7 , the projections  10  are capable of holding the closing spring  12  in the open position shown in FIG. 10, even if the closing spring  12  has a pre-tension effective in the closing direction.  
         [0050]    As an alternative, the closing spring may have a pre-tension effective in the opening direction. A support of the tongue  17  on the projections  10  is then not necessary. In any case, it can be seen from these two alternatives that a certain pre-tension of the closing spring  12  is not important for a securing effect of the lugs  18  and of the tongue  17  at the arch wire. The material constant and the dimensioning in the area of the lugs  18 , the tongue  17  and the projections  10  are the decisive factor.  
         [0051]    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 the arch wire slot  7  on the incisal side, with the lugs  18  being able to rest on this shoulder. Except for an arch wire cross section, which does not fully fill the arch wire slot  7 , the lugs  18  do therefore not press onto the arch wire  8 .  
         [0052]    The second deviating feature refers to the closing spring  12  which has an extension  15  on the lower end of the arc  13 , said extension being so long that it fully penetrates a flat through channel  11 ′ formed in the bracket structure transversely to the slot  7  and projects therefrom and is secured there by folding the spring end  16 .  
         [0053]    A further advantage can be seen in FIG. 11 in combination with FIGS. 12 and 13 that can be achieved by the bracket according to the invention in that the tongue is used together with a pre-tension of the closing spring as an instrument for exerting directional forces at an arch wire.  
         [0054]    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 used at the end of an orthodontic treatment with brackets if the misalignment of the teeth was corrected due to the progress of the orthodontic treatment 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.  
         [0055]    In the course of an orthodontic treatment it may be necessary to pivot the teeth not only around an axis located in the root portion but possibly around an 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 .  
         [0056]    In a row of teeth of e.g. an upper jaw provided with a series of brackets the arch wire extends through the arch wire slots of all brackets. Its position within said slots is therefore not only determined by the individual brackets but by the cooperation of all brackets, which in turn is 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.  
         [0057]    In FIG. 11, the arch wire  8  is canted in the slot  17  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 the arch wire  8  and the surfaces delimiting the slot  7 . The closing spring  12  exerts forces by means of the lateral lugs  18  and the tongue  17  onto the arch wire, which intend to press the wire onto the bottom of the arch wire slot  7  and in abutment with the slot wall opposing the tongue  17 . These forces result in that a torque is exerted onto the bracket, which is shown in FIG. 11 by arrows T.  
         [0058]    With a progressing effect of this torque T onto the respective tooth provided with the bracket, the tooth slightly yields so that the canting of the arch wire  8  within the 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, which is shown in FIG. 13, in which the arch wire  8  planarly rests on the bottom of the arch wire slot  7  and also rests planarly on the limiting wall of the arch wire slot  7  opposing the tongue  17 . The consequence is that the still relatively steep position of the bracket in FIG. 11 was changed into a further inclined position according to FIG. 13. Thus, the position of the tooth to which the bracket is attached was changed accordingly.  
         [0059]    [0059]FIGS. 13 and 14 show a particularly preferred embodiment of the invention. As may clearly be seen from FIG. 14, in this embodiment the tongue  17  has a neck section  17   c  adjoining the tongue root, said neck section  17   c  having a width which is smaller than the distance between the projections  10  at the gingival wing sections  5   a ,  6   a , i.e. the width of the gap between the gingival wing sections  5   a ,  6   a . An end section  17   d  adjoins to the neck section  17   c , said end section  17   d  having a width which is larger than the mutual distance of the projections  10 , but is smaller than the width of the gap between the gingival wing sections  5   a ,  6   a . In total, the tongue  17  is flat and is partially cut out from the free leg  14  of the closing spring  12  and bent in a direction towards the bottom of the bracket and to the front, so that a T-shaped opening  14   a  is formed by that partially cutting-out within the free leg  14 .  
         [0060]    As is shown in FIG. 14, the wide end section  17   d  of tongue  17  is able to rest on the projections  10  in the opening position of the closing spring  12   so  that the latter is held in its opening position. On the other hand, when moving the string into its closing position, which is shown in FIG. 13, the neck portion  17   c  can pass between the projections  10 , so that the wide end section  17   d  of the tongue  17  obtains a rest position below said projections  10  which locks the closing spring  10  in its closing position. The orthodontist may unlock the spring by inserting a pin-shaped tool through the T-shaped opening  14   a  of spring  14  to push the end section  17   d  of tongue  17  out of its locking position, so that the end section  17   d  may slide over the surfaces of the projections  10  close to the arch wire slot  7 .  
         [0061]    It is to be mentioned that the broader end section  17   d  of tongue  17  may be bent in a manner as shown in the embodiments first explained above. Further, it may be noted that in the embodiment of FIGS. 13 and 14, tongue  17  may be formed at the free leg  14  of spring  12  in a manner as is explained with respect to the first mentioned embodiments and shown in FIG. 4.  
         [0062]    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 this shall be desired particularly at the beginning of an orthodontic treatment, when the pressure of the 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.