Patent Publication Number: US-2011053109-A1

Title: Orthodontic anchoring screw

Description:
The invention relates to a fixing wire, in particular a fixing wire for applying treatment forces to a tooth. 
     The main focus in orthodontics is the specific and controlled movement and displacement of teeth in therapeutic treatment methods. In this connection, such a translatory or even rotational movement of a tooth may only be achieved by the action of external forces, which are correspondingly exerted on the tooth in order to move the tooth within the jaw. To maintain a firm fit in the jaw bone, the tooth is subjected to the external force over a long time period. This force is thus transmitted to the tooth via suitable fixing means, until said tooth adopts the desired position and/or orientation in the oral cavity. The tooth is generally subjected to an external force, therefore, via clamps, wires, rubber bands or other suitable force-exerting elements. To this end, however, the force-exerting elements always have to be correspondingly fixed in the oral cavity. 
     Such a support of the force-exerting elements is generally carried out on one or more teeth, for example two or more teeth positioned relative to one another in a suitable manner being connected to one another via a clamping element, which is subsequently tensioned, for example. Such an approach, however, has the drawback that in this case, due to the design, two or more teeth are subjected to forces in a symmetrical manner and said teeth are displaced and/or twisted in an undesirable manner with the tooth to be treated, although this is only intended and desired for the tooth to be treated. The specific displacement during the treatment of the one tooth is thus inevitably associated with an undesirable, or only partially acceptable, alteration of the position of the other tooth or the other teeth, which are used for fixing the force-exerting elements. 
     In order to counteract this, anchoring may also alternatively be carried out via one-piece or multi-piece temporary screws, so-called orthodontic anchoring screws, which may be temporarily inserted into the jaw bone and may be removed again after successful displacement of the tooth or a plurality of teeth. In contrast with dental implant materials which are designed for permanent integration into the jaw bone and stable ingrowth over the longest possible period of time, such anchoring screws have to be inserted in such a way that subsequent removal from the bone remains possible. However, with the use of such anchoring screws, it is imperative to remember that during the active treatment phase, i.e. during the actual force introduction of the desired forces into the tooth requiring treatment, a reliable and load-bearing fit of the respective anchoring screw provided as an abutment is essential. 
     Thus, care should be taken that, after being screwed in, the anchoring screw has a stability in the bone which is based on the tension of the screw with the bone. This stability is also denoted as primary stability. However, on the one hand, as the bone reacts to mechanical stresses and is displaced, this stability initially decreases with increased wearing time, as a result of the displacements. However, on the other hand, when the screw material starts to be colonised with cells, in particular bone cells, an additional stability is also created by the bonding of the cells with the screw material. This is known as oseointegration. The stability in the bone should be adequate during the entire period of insertion, in order to suffice as an abutment for the displacement of at least one tooth. 
     Where there are foreign bodies in the oral cavity, such as for example the orthodontic anchoring screw, which in addition to the teeth and soft tissue, i.e. the natural anatomical conditions in the mouth, represent an additional raised part and/or shape and thus alter the natural anatomical conditions, the surrounding soft tissue is additionally stressed. During the chewing process, the soft tissue, in particular that of the cheeks and tongue, is passed over the teeth. However, if a foreign body is located on the movement path of the soft tissue of the cheeks or the tongue, said movement sequence is interrupted. Even with deburred shapes, injuries and infections of the surrounding soft tissue frequently result. Only after a few weeks can the surrounding soft tissue become accustomed to the new situation, so that pain for the patient and infections of the soft tissue may be reduced. Thus, sharp and sharp-edged shapes should be avoided for all foreign bodies additionally introduced in the mouth and the radii kept as large as possible so that the transitions are formed as smoothly as possible. 
     For specific action on a tooth by a force and/or a torque via wires, rubber bands, clamps and other force-exerting elements, these elements have to be fixed to the orthodontic anchoring screw in the direction of the exerted force or counter to the exerted force. This fixing may be carried out in different ways. When the wires are inserted into recesses provided for them in the form of grooves, this is referred to as ligation. The ligation is intended to prevent the wires from being dislodged and/or prematurely loosened and released from the screw. If a bore exists outside the axis of the screw axis, the wire may be guided through said bore and no longer be dislodged as it would be in the case of a groove. A drawback of this embodiment is that, as a result of production, the bores have a round diameter and thus the wire is no longer secured against rotational displacement. Moreover, it is very awkward and difficult for the doctor providing treatment to pass the wire through the bore. Further possibilities for securing the wire during ligation in grooves of the heads of orthodontic anchoring screws are bonding, securing with a rubber band or winding a wire around the screw head. 
     If a round wire is bonded into a groove, it is secured against being dislodged. However, as tensile loading and rotational loading considerably stress the bond, there is a risk of the wire being released from the fastening and from the orthodontic anchoring screw during use. If, however, it is a rectangular wire, said wire is sufficiently protected against rotational loading inside the groove and there is only a risk of release from the fastening in the case of a tensile load. A further drawback of this method is that bonding the wire makes subsequent dismantling considerably more difficult and the adhesive used could cause undesirable irritation of the surrounding soft tissue. 
     If the wire is wound around the head of the orthodontic anchoring screw, and optionally additionally secured by an adhesive, then if a wire with a round cross section is used there is hardly any risk of release and it is sufficiently secured against being dislodged and against translatory and rotational displacements. Winding a wire of rectangular cross section around the head of the orthodontic anchoring screw is substantially more difficult but can be carried out by the doctor providing the treatment and subsequently also protects the wire from undesired displacement or being dislodged from the groove. However, a drawback of this fastening method is that in both embodiments of the wires there is the risk that winding around the head of the orthodontic anchoring screw could lead to pointed and sharp-edged elements of the wire irritating or even damaging the surrounding soft tissue and thus causing the patient pain. An infection of the soft tissue is even possible. Moreover, winding around the screw head unnecessarily increases the treatment time and makes dismantling more difficult. 
     The wire may also be secured against being dislodged by fastening a rubber band to the head of the orthodontic anchoring screw in a specifically provided recess in the form of a groove at least partially surrounding the head. Injuries or infections to the soft tissue may thus be avoided and/or reduced by correct positioning of the wire and of the rubber band. Wires with a rectangular cross section are additionally sufficiently secured against rotational displacement due to the geometric shape of the groove. A drawback of this method is that the wires cannot be sufficiently secured against translatory displacement. Such securing could take place by additional bonding. This would, however, make dismantling of the wire more difficult after treatment and, as already disclosed above, possibly irritate the surrounding soft tissue. Additionally, the treatment time would be increased by the use of two consecutive operating steps. 
     The object of the invention is therefore to provide a fastening means for force-exerting elements on anchoring screws, in orthodontic treatment methods, which is protected in an extremely simple manner against translatory and rotational displacements and against being dislodged, with the mounting and dismantling time kept short. 
     This object is achieved according to the invention in that the fixing wire has a widened region produced by plastic deformation, for the longitudinal fixing thereof in a corresponding fixing recess of an orthodontic anchoring screw. 
     Advantageous embodiments of the invention form the subject-matter of the sub-claims. 
    
    
     
       An embodiment of the invention is described in more detail with reference to the drawings, in which: 
         FIG. 1  shows an orthodontic anchoring screw, 
         FIG. 2  shows a screw head of an orthodontic anchoring screw, 
         FIG. 3  shows a screw head with a cross-shaped groove, 
         FIG. 4  shows a screw head with the inserted fixing wire, 
         FIG. 5-FIG .  7  show different embodiments of the fixing wire, 
         FIG. 8  shows a screw head with a fixing recess, 
         FIG. 9  shows a tool for receiving and aligning the screw head, 
         FIG. 10-FIG .  13  show different screw heads with different central bores, 
         FIG. 14  shows a fixing pin, 
         FIG. 15  shows a fixing pin on a screw head, 
         FIG. 16  shows a fixing pin with a clamping element on a screw head, 
         FIG. 17  and  FIG. 18  show a tool for receiving and aligning the screw head with a receiver pin, 
         FIG. 19  shows an orthodontic anchoring screw with a variable thread region. 
     
    
    
     In the orthodontic anchoring screw  1  according to  FIG. 1 , there is a transition region  4  adjacent to the screw head  2 , before the anchoring screw  1  passes into a threaded region  6 . The start of the screw thread  8  is adjacent to the lower end of the threaded region  6 . During the treatment, the anchoring screw is screwed into the jaw, and due to the positive connection with the surrounding bone material of the jaw, provides the possibility of anchoring during treatment for tooth displacement. A tooth to be treated is, for example, held under tension by means of wires and thus pulled and/or rotated into the desired position. For this purpose, on the anchoring screw these wires are fixed to the anchoring screw. 
     In the screw head  2  of the orthodontic anchoring screw according to  FIG. 2 , therefore, a recess is shown in the form of a groove  10 . Such a groove is inserted—as is also shown in FIG.  2 —into the screw head, preferably at right angles to the screw axis. The screw head  2  according to  FIG. 2  further comprises a base body  12  from which an upper body  14  extends. In the transition region between the base body  12  and the upper body  14  a recess in the form of a fixing groove  16  is introduced. The groove  10  used for fixing the wire divides the upper body into two halves in the screw head  2  according to  FIG. 2 , and penetrates as far as the base body  12  of the screw head  2 . 
     The screw head  2  according to  FIG. 3  contains, in addition to that according to  FIG. 2 , an additional groove  10  which is arranged both at right angles to the screw axis and to the first groove  10 . This permits the insertion of a wire from a plurality of directions. However, when using a plurality of grooves the upper body  14  of the screw head  2  is also weakened and the risk of breaking substantially increased. Thus, the number of grooves is generally restricted to two, which are arranged in a cross-shaped configuration—as shown in  FIG. 3 . 
     In the screw head  2  according to  FIG. 4 , a fixing wire  18  is already ligated into one of the grooves. Generally, these fixing wires  18  have a round or rectangular cross-sectional surface. With rectangular cross-sectional surfaces, rectangular embodiments with edge lengths of 0.22 m and 0.19 mm are preferably used. The advantage of rectangular cross-sectional surfaces of the fixing wires  18  is that, when inserted into a groove  10  which only slightly exceeds the edge length of the fixing wire  18 , the fixing wire  18  is secured against rotational displacements due to the geometrically adapted groove  10 . In a fixing wire  18  with a round cross-sectional surface, however, additional securing against rotational movements has to be carried out. 
     Security against translatory displacements, i.e. displacements along the groove  10 , may be achieved according to the invention by a plastic deformation of the fixing wire  18  with corresponding recesses in the upper body  14  of the screw body. For this purpose, the fixing wire  18  is altered in its cross-sectional geometry by plastic deformation. Such a plastically deformed wire is shown in  FIGS. 5 to 7 . A plastic deformation and or shaping may lead to different alterations to the geometry of the wire. The wire may be curved or bent back once or repeatedly, and additionally or solely thickened or thinned ( FIG. 5   a ,  5   b ,  5   c ). Preferably pliers are used for the plastic deformation. These pliers are designed so that although they deform the fixing wire  18  at the desired point, said fixing wire does not break. For this purpose, the pliers are adapted to the geometric conditions of the fixing wire  18 . The narrowing of an edge length achieved during plastic deformation by pliers results in a widening of the edges perpendicular thereto. As a result, a widened region  20  is produced which together with corresponding recesses on the screw head forms a locking mechanism. As a result, the fixing wire  18  is also protected against translatory displacements along the groove  10 . 
     As disclosed above, the fixing wire  18  is thickened, during a squeezing, pressing and/or shearing process, in a direction perpendicular to the operating direction of the squeezing, pressing or shearing process. If the surface of the thinned and thickened portion is too small, as shown in  FIG. 6 , this may result in a stress concentration which markedly reduces the stability of the wire. For this reason, the pressing length b, i.e. the length of the deformation in the wire direction, is at least half of the fixing wire width a and/or the fixing wire height. Preferably, as also shown in the fixing wire  18  according to  FIG. 7 , the pressing length b is nevertheless greater than the fixing wire width a and/or fixing wire height. 
     The screw head  2  according to  FIG. 8  has a fixing recess  22 , which is incorporated into the upper body  14  and extends on both sides of the groove  10 . A fixing wire  18  which has been plastically deformed previously—for example by a corresponding pair of pliers—is then inserted from above into the groove  10  of the screw head  2 , the widened region  20  of the fixing wire  18  being located in the fixing recess  22 . As a result, the fixing wire  18  is secured against translatory displacements along the groove  10 . 
     For additional securing against a translatory displacement along the screw axis, i.e. securing against the fixing wire  18  being dislodged, the screw head  2  has a fixing groove  16 . After the insertion of the fixing wire  18 , a securing element, for example a rubber band, is inserted into this fixing groove  16  and protects the fixing wire  18  against being dislodged from the groove  10 . The fixing wire  18  is, as a result, ligated into the screw head  2 . In this context, the fixing groove ideally has a peripheral depth of at least 0.3 mm, preferably greater than 0.4 mm, and in particular a depth of greater than 0.5 mm. The fixing wire may, however, also be fastened by bonding-in, by winding the fixing wire  18  itself or a different wire around the screw head or by different auxiliary means. 
     The shape of the fixing recess  22  in  FIG. 8  may, therefore, be designed differently and, for example, be round or rectangular depending on the intended use and/or the plastic deformation of the wire. Concave or convex shapes or other geometric shapes are also conceivable. 
     Cutting tools are suitable for producing such a fixing recess  22 . Preferably, therefore, the fixing recess  22  is drilled, turned, milled, sanded, polished, shaped and/or punched. The fixing recess  22  may, however, also be produced by other material-removing methods, such as for example laser processing, spark erosion, etching, electrolytic etching. Furthermore, methods altering the shape, such as for example forming and or bending, are also suitable. In a single groove  10 —as shown in FIG.  8 —a bore and/or countersink may result which at least partially alters the groove  10  in its width and or depth. 
     Two centrally intersecting grooves  10  are suitable for simplifying the insertion of fixing wires  18  into the screw head  2 . In this case, the fixing wires  18  are generally inserted in the direction of the dental arch. For screwing in the orthodontic anchoring screw  1 , planar side surfaces  24  are advantageously located on the base body  12  of the screw head  2 , in which surfaces the tool  26  engages for screwing in the anchoring screw  1 . However, this has the result that when screwing in the anchoring screw  1  the tool  26  covers the grooves  10  and it is not possible for the doctor providing the treatment to align the grooves  10  according to requirements. 
     The screw head  2  according to  FIG. 9  thus has twice as many side surfaces  24  as grooves  10 , but may also have a further non-circular outer contour, and the corresponding tool  26  has a correspondingly adapted internal contour of the receiver channel. These side surfaces form, as a result, a referencing zone for the tool  26 . Because two grooves, which together form a cross-shaped groove, are used in the screw head  2  according to  FIG. 9 , the tool  26  used for screwing in has four options for positioning on the screw head  2 . In a cross-shaped groove, therefore, a square tool is suitable for inserting the anchoring screw  1  into the jaw bone. Thus, the tool  26  is provided in the outer region with four marking surfaces  28 , which are positioned so as to correspond to the alignment of the cross-shaped groove. Via these marking surfaces the doctor providing the treatment may obtain information about the position of the cross-shaped groove. It is thus possible for the doctor to carry out the desired positioning of the grooves without having to remove the tool  26  from the screw head  2  during insertion. 
     The fixing recesses  22  may be inserted by the above-described method even when using a plurality of grooves  10 . The fixing recess  22  may thus refer to only one groove  10  or a part of a groove  10 . The shape of the fixing recess  22  may adopt different geometries, as disclosed in the single groove  10 . Ideally, however, the fixing recess is located on the central point of intersection of the grooves  10 . When two grooves  10  intersect—as shown in the screw head according to FIG.  10 —at the point of intersection four corners are produced, which each have an angle of approximately 90°, and have internal edges  30  extending downwards. The upper body  14  is, as a result, separated into four regions. 
     For producing the fixing recess  22 , the internal edges  30  of the four regions of the upper body  14  are abraded or shaped by one of the already disclosed methods. In this manner, the spacing of the non-adjacent regions of the upper body  14  increases. The alteration of the spacing may thus be less than 0.2 mm, but preferably greater than 0.3 mm and in particular greater than 0.4 mm. The abrasion and/or shaping of the internal edges  30  may thus take place in a plurality of operating steps and the fixing recesses  22  may have different radii and shapes. Thus, amongst others, concave shapes, convex shapes ( FIGS. 12   a ,  12   b ,  12   c ), inwardly or outwardly inclined inner edges or even meandering shapes ( FIGS. 13   a ,  13   b ,  13   c ) are conceivable. Combinations thereof or other geometric shapes are also conceivable. Said fixing recess  22  produced by abrasion or shaping should preferably be designed to extend at least as far as the base of the groove  10 , but may also be designed to be deeper than the groove  10 , in a particularly advantageous variant. 
     A variant which is very easy to produce and particularly advantageous provides a round fixing recess  22  which is preferably positioned in the centre of the groove intersection. Such a design may be produced via a standard bore or an end bore. This simplifies the production and produces a locking mechanism with many variants of the fixing wire deformation and/or shaping. The bore depth may be less than, equal to or greater than the groove depth. 
     The round, central fixing recess  22 , which preferably is positioned on the point of intersection of the two grooves, has further advantages. With this shaping, which is preferably round and in the form of a bore, components such as, for example, a fixing pin  32  according to  FIG. 14  may be inserted alone or together with a fixing wire  18  into the screw head  2 . The fixing pin  32  according to  FIG. 14  thus has a centring pin  34  adapted to the fixing recess  22 . This centring pin  34  preferably has, corresponding to the fixing recess  22 , a round cross section which simplifies the insertion of the fixing pin  32  into the screw head  2 . The fixing pin  32  has, moreover, a number of side arms  36  which when the fixing pin is inserted—as shown in FIG.  15 —engage in the groove  10 , which is transverse to the groove  10 , which is provided with the fixing wire  18 . As a result, the fixing pin  32  is secured against rotational displacements about its axis. The fixing pin  32 , together with the fixing wire  18 , is protected by the fixing groove  16  against being dislodged. In this context, a fixing element is used—in the embodiment according to  FIG. 15  this is a rubber ring  38 —which is located in the fixing groove  16 . 
     The fixing pin, moreover, has a receiver head  40  and a receiver groove  42 . By means of this receiver head additional clamping elements  44  may—as shown in FIG.  16 —be fastened to the anchoring screw  1 , and thus a plurality of teeth treated at the same time via one anchoring screw  1 . In this context wires, rubber bands, springs and other force-exerting elements are examples of possible additional clamping elements. A substantial advantage of the fixing pin  32  according to the invention is, therefore, that all clamping elements generally used by an orthodontist may be easily and securely fastened to an anchoring screw  1 . By the common fastening and/or ligating of a fixing wire  18  and a fixing pin  32 , there is even the possibility of fastening a plurality of clamping elements at the same time, as shown in  FIG. 16 . With this application, the large number of different screw types may be reduced and with the use of only one screw, a plurality of teeth may be pushed in different directions. Otherwise, a plurality of treatment steps would have to be carried out consecutively, and if it were not possible for all of the force-exerting elements conventionally used to be fastened and/or ligated onto a screw, in a further treatment step a screw might have to be removed from the jaw and replaced by a screw with a different screw head. 
     A round fixing recess  22 , for example through a bore, has a further advantage. Before the screw is screwed into the jaw, the screws are generally located in a holder, which is referred to as a trail. For simplified handling of the screw, it is advantageous if the screw is able to be fastened to the tool  26  provided for screwing into the bone, so that the orthodontic anchoring screw  1  may not be dislodged from the tool  26 . In order to achieve this, therefore, the tool according to  FIG. 17  has a receiver pin  46 . Said pin may be inserted into the fixing recess  22  of the screw head  2 , and thus produces a non-positive connection between the anchoring screw  1  and the tool  26 . If the contact points between the receiver pin  46  and the cross-shaped groove are small, the wear on the fixing recess  22  is greater than if the area between the receiver pin  46  and the cross-shaped groove were large. If the fixing recess  22  at the point of intersection of the cross-shaped groove has a round cross-sectional surface, for example formed by a bore, the contact surface is maximised ( FIG. 18 ) and the wear of the fixing recess is minimised. This leads to a long service life of the tools  26  and the anchoring screws  1 . 
     In the orthodontic anchoring screw  1  according to  FIG. 19 , in a particularly advantageous embodiment the screw head  2  is provided with a cross-shaped groove, a fixing groove  16  and an additional fixing recess  22  in the form of a central bore and formed on a shank provided with a multiple thread. This multiple thread advantageously has, in addition to the single thread, a double or multiple thread which preferably is attached in the direction of the screw head. The double or multiple thread improves the primary stability above all, but also the secondary stability of the screw in the bone. Because with a plurality of force-exerting elements greater forces and loads are exerted on the screw and thus on the bond between the screw and bone than if only one force-exerting element were attached, an improved stability of the screw in the bone proves advantageous. Advantageously, the cross-shaped groove has a width of more than 0.55 mm and a depth of more than 1 mm, but in particular more than 1.2 mm, and has a central fixing recess  22 , preferably produced by a bore, with a diameter greater than 1 mm, but preferably greater than 1.2 mm. In a head with these properties, a wire which is rectangular in profile may be ligated with a rubber band generally used by orthodontists, and locked against displacement via plastic deformation in the direction of the inserted groove  10 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Orthodontic anchoring screw 
           2  Screw head 
           4  Transition region 
           6  Threaded region 
           8  Start of threaded region 
           10  Groove 
           12  Base body 
           14  Upper body 
           16  Fixing groove 
           18  Fixing wire 
           20  Widened region 
           22  Fixing recess 
           24  Side surfaces 
           26  Tool 
           28  Marking surface 
           30  Internal edges 
           32  Fixing pin 
           34  Centring pin 
           36  Side arm 
           38  Rubber band 
           40  Receiver head 
           42  Receiver groove 
           44  Clamping element 
           46  Receiver pin 
         a Fixing wire width 
         b Pressing length