Dentistry, Orthodontics, Medical Engineering, Medical Science, Orthodontic fixed appliance, and Bracket

Background Art

Orthodontics is a discipline of dentistry that specializes in treatment of malocclusion, in other words, to correct misaligned teeth and improper bite patterns of the patients. A common orthodontic treatment with fixed appliance involves the use of orthodontic brackets, arch wires and ligating devices. These interconnected elements provide the application of forces during treatment to move misaligned teeth into correct position and orientation. Small ligature wires or elastic ties (O-ring) are typically used as ligating devices to hold the arch wire into the brackets. However, it is rather difficult for clinicians to ligate the ligature wires than the elastic ties and the outcome is dependent on clinicians' experience. Therefore, the use of the ligature wires is not mentioned in this context.

An orthodontic bracket is a body, having at least one embedded slot, for receiving an arch wire, and a bracket base for bonding to the patient's tooth. The bracket slot is a labially buccally opening, extending along the body of the bracket in a mesio-distal direction. The bracket slot is defined by two parallel sidewalls and one floor. The bracket base is a pad typically connecting to the underside of the bracket body. The bracket base is contoured to match the labial/buccal surface of the tooth. The orthodontic bracket is bonded direct to the surface of the tooth through the bracket base by means of bonding material. The bonding surface of the bracket base may be specially designed or treated to increase retention of the bonding material.

Bracket wings or tie wings typically extend outwardly from the bracket body and may be perpendicular relative to the mesio-distal direction of the bracket slot when viewed

labially/buccally. An orthodontic bracket has at least one pair of opposing tie wings extending occlusally and gingivally. Once the arch wire is inserted into the bracket slot, a ligating device, such as an elastic tie, is wrapped around the bracket body, underneath the tie wings and over the arch wire to securely retain the arch wire into the bracket slot. Most brackets commonly used in orthodontic treatment are twin brackets, having two pairs of opposing tie wings spaced apart from each other. One pair of tie wings is located on the mesial end of the bracket body and the other pair of tie wings is located on the distal end of the bracket body. Arch wire is a curved metal wire, working as an ideal template to guide the teeth into proper alignment as well as a means to apply corrective forces to move the teeth during the treatment. Arch wires have different cross-sectional configurations to provide different corrective forces each stage of the treatment. For instance, round cross-sectional arch wires provide high degree of flexibility and light corrective forces, often used at the beginning stages of the treatment. On the other hand, rectangular cross-sectional arch wires are used in the retraction and finishing stages to control torque, having less degree of flexibility and greater corrective torquing forces.

Once begin the orthodontic treatment process, the orthodontic brackets are positioned and bonded directly to the surface of each individual tooth by localizing the center of the clinical crown or by distancing the incisor edge technique. When the placement of the orthodontic brackets is done, an arch wire is inserted and securely engaged to each bracket by elastic ties. The positions of the brackets on the misaligned teeth cause the engaged arch wire to change its form. The restoring force provided by the arch wire to restore its initial arch form becomes the corrective forces to move the teeth into proper alignment.

To permit the tooth movement, it is necessary to have relative motion between the brackets and the engaged arch wire in response to the corrective forces provided by the arch wire. It is recognized that frictional engagement among the brackets, the arch wire and the elastic ties influence the outcome of each treatment phase. For instance, in the leveling and aligning phase, it is desirable to reduce frictional engagement among the brackets, the arch wire and the elastic ties, allowing the engaged arch wire to slide freely within the bracket slot, to facilitate bodily tooth movement and space closure. Reduced friction increases the rate of tooth movement and decreases the amount of corrective forces required to move teeth, thus, shortening the duration of the treatment and providing more comfort to the patient. If the engaged arch wire cannot slide freely within the bracket slot, the treatment outcome and the duration of the treatment may be unpredictable. In contrast, in the finishing phase, the arch wire must be securely seated into the bracket slot to maintain positions of the teeth while maximizing accurate torque correction, thus friction becomes necessary.

For the commonly used twin brackets, an elastic tie is ligated by stretching the elastic tie and wrapping around the bracket body, locating underneath both pairs of opposing tie wings and over the arch wire to securely engage the arch wire into the bracket slot. In such configuration, the elastic tie firmly presses the arch wire downwards into the floor of the bracket slot, which increases frictional engagement among the brackets, the arch wire and the elastic tie. Such configuration prevents the engaged arch wire to slide freely within the bracket slot. Accordingly, it is difficult to achieve desirable tooth movement and may also lead to unpredictable outcome such as labial tipping or proclination of the anterior teeth during the leveling and aligning phase.

The present invention represents an improved orthodontic bracket which overcomes the problem and disadvantages associated with frictional engagement among the brackets, the arch wire and the elastic tie to above-noted orthodontic twin brackets. Summary of invention

The present invention relates to an improved orthodontic bracket that allows clinicians to selectively control the frictional engagement among the brackets, the arch wire and the elastic tie. The clinicians may choose to permit the engaged arch wire to slide freely within the bracket slot in response to the force of the arch wire, defined as passive ligation, or to securely retain the engaged arch wire into the bracket slot to maintain positions of the teeth to maximize accurate torque correction, defined as active ligation.

In order to provide such functionality, the present invention is directed to an orthodontic bracket having at least one embedded slot for receiving an arch wire, and a bracket base for bonding to the patient's tooth. The bracket further comprises three pairs of opposing tie wings. Each tie wing extends outwardly from the bracket body and its direction is perpendicular relative to the mesio-distal direction of the bracket slot when viewed labial ly/buccally. The first and the second pairs of opposing tie wings, spaced apart from each other, are located at the mesial end and distal end of the bracket body, respectively, which are defined as inner tie wings. The pair of inner tie wings, located on the mesial end of the bracket body, is defined as mesial pair of inner tie wings. The pair of inner tie wings, located on the distal end of the bracket body, is defined as distal pair of inner tie wings. The third pair of opposing tie wings is located at the central portion of the bracket body which extends further towards the labial/buccal side so this pair of opposing tie wings is raised above the mesial pair of inner tie wings and the distal pair of inner tie wings, defined as outer tie wings. In such embodiment, the portion of the labial/buccal surfaces of the inner tie wings become ligating support means to maintain the space between the elastic tie and the engaged arch wire which prevents the elastic tie to press the arch wire downwards into the floor of the bracket slot. Since the width of the outer tie wings is larger than the inter-distance between the mesial pair of inner tie wings and the distal pair of inner tie wings, when viewed labially/buccally, an auxiliary slot is formed between both pair of inner tie wings and underneath the outer tie wings.

The present invention can be employed in the following manners.

In one application, an elastic tie engages only the outer tie wings of the bracket with the engaged arch wire therein. Since the outer tie wings is located at the central portion of the bracket body and raised above the mesial pair of inner tie wings and the distal pair of inner tie wings, a portion of the elastic tie fits underneath the outer tie wings and the remaining portion is located adjacent to the mesial/distal sidewall of the outer tie wings. The portion of the elastic tie that is located adjacent to the mesial/distal sidewall of the outer tie wings lays also on the labial/buccal surfaces of the inner tie wings and across the labial/buccal opening of the bracket slot. In such

configuration, the elastic tie is supported by the labial/buccal surfaces of the inner tie wings and the space between the elastic tie and the engaged arch wire is maintained, thus, the frictional engagement among the bracket, the arch wire and the elastic tie is reduced. As a consequence, the undersized arch wire having a width less than the bracket slot width can slide freely within the bracket slot.

In another application, an elastic tie engages the mesial pair of inner tie wings and the distal pair of inner tie wings of this bracket with the engaged arch wire therein. A portion of the elastic tie fits underneath the mesial pair of inner tie wings and the distal pair of inner tie wings and the remaining portion is located adjacent to the mesial sidewall of the mesial pair of inner tie wings and the distal sidewall of the distal pair of inner tie wings. The portion of the elastic tie that is located adjacent to the mesial/distal sidewall of the inner tie wings lays over the engaged arch wire and firmly presses the engaged arch wire downwards into the floor of the bracket slot. In such configuration, there is no space between the elastic tie and the engaged arch wire, thus, the amount of the frictional engagement among the bracket, the arch wire and the elastic tie is high. As such, the engaged arch wire is subjected to maximum deformation, thus, the corrective force is maximized. For the rectangular cross-sectional arch wires, it produces maximum corrective forces to control torque and angulation of the teeth without moving teeth along the arch wire.

When the tooth is severely rotated, an elastic tie may engage the outer tie wings of the bracket together with either the mesial pair of inner tie wings or the distal pair of inner tie wings of this bracket with the engaged arch wire therein to provide de-rotational movement. In this configuration, a portion of the elastic tie fits underneath the outer tie wings and the inner tie wings that are engaged together with the outer tie wings. A part of the remaining portion of the elastic tie is located adjacent to the sidewall of the inner tie wings that are engaged together with the outer tie wings. It lays over the engaged arch wire and firmly presses the engaged arch wire downwards into the floor of the bracket slot. The other part of the remaining portion of the elastic tie is located adjacent to the opposite sidewall of the outer tie wings and lays on the labial/buccal surfaces of the inner tie wings that are not engaged together with the outer tie wings and across the labial/buccal opening of the bracket slot. The space between this portion of the elastic tie and the engaged arch wire is maintained. Therefore, the corrective force is induced only at the inner tie wings that are engaged together with the outer tie wings, which causes de- rotational movement about the long axis of the tooth.

In another aspect of this bracket embodiment, the outer tie wings that is located at the central portion of the bracket body, which extends further towards the labial/buccal side, and is raised above the inner tie wings causes the bracket to have two levels of the bracket slot depth. The first bracket slot depth is defined by the height of the side walls of the bracket slot located between the opposing tie wings of the mesial pair of inner tie wings or the distal pair of inner tie wings. It is measured from the floor of the bracket slot to the edges connecting to the labial/buccal surfaces of the mesial pair of inner tie wings or the edges connecting to the labial/buccal surfaces of the distal pair of inner tie wings. The edges connecting to the labial/buccal surfaces of the mesial pair of inner tie wings or the edges connecting to the labial/buccal surfaces of the distal pair of inner tie wings are located approximately at the same level. The second bracket slot depth is defined by the height of the central portion of the sidewall of the bracket slot located between the opposing tie wings of the outer tie wings. It is measured from the floor of the bracket slot to the edges connecting to the labial/buccal surfaces of the outer tie wings. When compared to the conventional twin bracket, this bracket embodiment is overall thicker and has a greater bracket slot depth which facilitates the placement of the second arch wire laying over the first arch wire. This overlaying technique is used to move teeth more efficient in some clinical situations. The outer tie wings that are located at the central portion of the bracket body, which extends further towards the labial/buccal side, and are raised above the inner tie wings can be employed as a post for intramaxillary elastic connection to induce additional orthodontic force to move teeth. In this configuration, the intramaxillary elastic is supported by the labial/buccal surfaces of the inner tie wings and the space between the intramaxillary elastic and the engaged arch wire is maintained. As a consequence, the connected tooth can slide freely along the engaged arch wire.

In addition, the auxiliary slot that is formed there between both pair of inner tie wings and underneath the outer tie wings is used for installation of auxiliary devices such as power arm or Kobayashi's hook to allow the application of orthodontic forces closer to the center of resistance of the tooth for more efficient tooth movement.

In another embodiment of the present invention, the mesio-distal width of the outer tie wings is equal or less than the mesio-distal inter-distance between the mesial pair of inner tie wings and the distal pair of inner tie wings, when viewed labially/buccally. The auxiliary slot, located between both pair of inner tie wings and underneath the outer tie wings, may be adjusted to have different cross-sections and dimensions or may be entirely excluded from the bracket embodiment.

Another bracket embodying the present invention has optionally an integral portion extending gingivally/occlusally from one of the tie wings, and in perpendicular relation to the mesio-distal direction of the bracket slot when viewed labially/buccally. The end of the gingival/occlusal extended portion is preferably mushroom head or hook to accommodate tracing devices (e.g. elastic band, c -chain, coil spring etc.). The integral extended portion preferably comprises a malleable material as it may be bent for soft tissue clearance or patient comfort. In the modi fled embodiment of the present invention, the outer tie wings and inner tie wings may also be optionally extended outwardly from the bracket body at an acute angle relative to the mesio-distal direction of the bracket slot when viewed labially/buccally. Such acute angle is corresponding to desirable angulation of the occluso-gingival central axis of clinical crown relative to the occlusal plan in normal occlusion. Optionally, an integral portion, preferable mushroom head or hook, extending gingivally/occlusally from one of the angled tie wings may also be disposed at an acute angle relative to the mesio-distal direction of the bracket slot and parallel to the axis of the angled tie wing.

Brief Description of Drawings

FIG. 1 is a perspective view of an orthodontic bracket embodying the present invention;

FIG. 2 is another perspective view of the orthodontic bracket of FIG.1 ;

FIG. 3 is a side plane view of the orthodontic bracket of FIG.1 when viewed mesio-distally; FIG. 4 is a top plane view of the orthodontic bracket of FIG.1 when viewed occluso-gingivally; FIG. 5 is another perspective view of the orthodontic bracket of FIG.1 , shown ligated by elastic tie at the outer tie wings with an engaged round cross-sectional arch wire therein;

FIG. 6 is a side plane view of the orthodontic bracket of FIG.5 when viewed mesio-distally; FIG. 7 is another perspective view of the orthodontic bracket of FIG.1 , shown ligated by elastic tie at the inner tie wings with an engaged round cross-sectional arch wire therein;

FIG. 8 is a side plane view of the orthodontic bracket of FIG.7 when viewed mesio-distally; FIG. 9 is another perspective view of the orthodontic bracket of FIG.1 , shown ligated by elastic tie at the outer tie wings together with a pair of the inner tie wings with an engaged round cross- sectional arch wire therein;

FIG. 10 is a top plane view of the orthodontic bracket of FIG.9 when viewed occluso-gingivally; FIG. 1 1 is a front plane view of another orthodontic bracket embodying the present invention with gingival/occlusal extended portion at one inner tie wing when viewed labio/bucco-ligually; FIG. 12 is a front plane view of another orthodontic bracket embodying the present invention with gingival/occlusal extended portion at one outer tie wing when viewed labio/bucco-ligually, FIG. 13 is a front plane view of another orthodontic bracket embodying the present invention with an acute angled occluso-gingival center axis when viewed labio/bucco-ligually; FIG. 14 is a front plane view of another orthodontic bracket embodying the present invention with mesio-distal width of the outer tie wings less than the inter-distance between the mesial pair of inner tie wings and the distal pair of inner tie wings, when viewed labio/bucco-ligually;

FIG. 15 is another perspective view of the orthodontic bracket of FIG.14 without auxiliary slot; and

FIG. 16 is another perspective view of the orthodontic bracket of FIG.14 with an auxiliary slot. Description of Embodiments

FIG.l and 2 illustrate perspective views of an orthodontic bracket (100) embodying the present invention. The bracket ( 100) comprises a bracket body (7) having at least one embedded slot (3) for receiving an arch wire. The bracket slot is a labially/buccally opening, extending along the body of the bracket in mesio-distal direction (4). The bracket slot is defined by two parallel sidewalls and one floor. The bracket base (5) is a pad typically connecting to the underside of the bracket body. The bracket base (5) is contoured to match the labial/buccal surface of the tooth. The bracket further comprises three pairs of opposing tie wings extending occlusally and gingival ly from the bracket body and its direction is perpendicular relative to the mesio-distal direction (4) of the bracket slot (3) when viewed labially/buccally. The first and the second pairs of opposing tie wings, spaced apart from each other, are located at the mesial end and distal end of the bracket body, respectively, which are defined as inner tie wings (2). The pair of inner tie wings, located on the mesial end of the bracket body, is defined as mesial pair of inner tie wings. The pair of inner tie wings, located on the distal end of the bracket body, is defined as distal pair of inner tie wings. The third pair of opposing tie wings is located at the central portion of the bracket body which extends further towards the labial/buccal side so this pair of opposing tie wings is raised above the mesial pair of inner tie wings and the distal pair of inner tie wings, defined as outer tie wings (I). In such embodiment, the portion of the labial/buccal surfaces of the inner tie wings (25) become ligating support means to maintain the space between the elastic tie and the engaged arch wire which prevents the elastic tie to press the arch wire downwards into the floor of the bracket slot (3). As the outer tie wings raised above the inner tie wings, the bracket consists of two levels of the bracket slot depth. An auxiliary slot (6) is formed between both pair of inner tie wings and underneath the outer tie wings to be used for auxiliary devices installation. FIG. 3 illustrates the side plane view of the orthodontic bracket ( 100) viewed in the mesio-distal direction, showing two different depths of the bracket slot. The first bracket slot depth is defined by the height of the sidewalls (31 ) of the bracket slot located between the opposing tie wings of the mesial pair of inner tie wings or the distal pair of inner tie wings (2). The second bracket slot depth is defined by the height of the central portion of the sidewall (32) of the bracket slot located between the opposing tie wings of the outer tie wings (1). FIG. 4 illustrates the top plane view of the orthodontic bracket when viewed occluso-gingivally, showing again the position of the outer tie wings that are raised above the inner tie wings and the position of the auxiliary slot (6) formed between both pair of inner tie wings, underneath the outer tie wings and above the bracket base (5). FIGs. 5 and 6 illustrate the perspective view and the side view of the orthodontic bracket (100) embodying the present invention with an engaged round cross-sectional arch wire (80) therein. An elastic tie (60) is engaged only the outer tie wings (1) of the bracket. In this configuration, a portion of the elastic tie fits underneath the outer tie wings and the remaining portion is located adjacent to the mesial/distal sidewall of the outer tie wings. The portion of the elastic tie that is located adjacent to the mesial/distal sidewall of the outer tie wings lays also on the labial/buccal surfaces (25) of the inner tie wings and across the labial/buccal opening of the bracket slot. The elastic tie (60) is supported by the labial/buccal surfaces (25) of the inner tie wings (2) and the space (70) between the elastic tie and the engaged arch wire (80) is maintained. The undersized arch wire having a width less than the bracket slot width can slide freely within the bracket slot.

FIGs. 7 and 8 illustrate the perspective view and the side view of the orthodontic bracket (100) embodying the present invention with an engaged round cross-sectional arch wire (80) therein. An elastic tie (60) is engaged only the inner tie wings (1) of the bracket. In this configuration, a portion of the elastic tie fits underneath the mesial pair of inner tie wings (2) and the distal pair of inner tie wings (2) and the remaining portion is located adjacent to the mesial sidewall of the mesial pair of inner tie wings and the distal sidewall of the distal pair of inner tie wings. The portion of the elastic tie that is located adjacent to the mesial/distal sidewall of the inner tie wings lays over the engaged arch wire (80) and firmly presses the engaged arch wire (80) downwards into the floor (34) of the bracket slot (3). In such configuration, there is no space between the elastic tie (60) and the engaged arch wire (80), thus, the amount of the factional engagement among the bracket, the arch wire and the elastic tie is high.

FIGs. 9 and 10 illustrate the perspective view and the side view of the orthodontic bracket (100) embodying the present invention with an engaged round cross-sectional arch wire (80) therein. The elastic tie (60) is engaged the outer tie wings (1) of the bracket together with one pair of the inner tie wings (2) of this bracket to provide de-rotational movement. In this configuration, a portion of the elastic tie fits underneath the outer tie wings (1) and the inner tie wings (2) that are engaged together with the outer tie wings (1). A part of the remaining portion of the elastic tie is located adjacent to the sidewall of the inner tie wings (2) that are engaged together with the outer tie wings ( 1). It lays over the engaged arch wire (80) and firmly presses the engaged arch wire (80) downwards into the floor of the bracket slot. The other part of the remaining portion of the elastic tie is located adjacent to the opposite sidewall of the outer tie wings (1) and lays on the labial buccal surfaces (25) of the inner tie wings (2) that are not engaged together with the outer tie wings ( I ) and across the labial/buccal opening of the bracket slot. The space between this portion of the elastic tie (60) and the engaged arch wire (80) is maintained. Therefore, the corrective force is induced only at the inner tie wings that are engaged together with the outer tie wings, which causes de-rotational movement about the long axis of the tooth.

FIG. 11 illustrates the front plane view from labio bucco-ligual direction of another orthodontic bracket embodying the present invention with an integral gingival/occlusal extended portion (70) at one of the inner tie wings (2). The extended portion is in perpendicular relation to the mesio- distal direction of the bracket slot. The end (71 ) of the gingival/occlusal extended portion is preferably mushroom head or hook to accommodate tracing devices. The integral extended portion (70) at one of the inner tie wing (2) is preferably bendable for soft tissue clearance or patient comfort. FIG. 12 illustrates the front plane view from labio/bucco-ligual direction of another orthodontic bracket embodying the present invention with an integral gingival/occlusal extended portion (70) at one of the outer tie wings ( 1 ). The extended portion is in perpendicular relation to the mesio- distal direction of the bracket slot. The end (71) of the gingival/occlusal extended portion is preferably mushroom head or hook to accommodate tracing devices. The integral extended portion (70) at one of the outer tie wing (1) is preferably bendable for soft tissue clearance or patient comfort.

FIG. 13 illustrates the front plane view from labio/bucco-ligual direction of another orthodontic bracket embodying the present invention. The outer tie wings (1) and inner tie wings (2) are extended outwardly from the bracket body at an acute angle relative to the mesio-distal direction (4) of the bracket slot when viewed labially/buccally. Such acute angle is corresponding to desirable angulation of the occluso-gingival central axis of clinical crown relative to the occlusal plan in normal occlusion.

FIG. 14 illustrates the front plane view from labio/bucco-ligual direction of alternative orthodontic bracket embodying the present invention. In this configuration, the mesio-distal width of the outer tie wings (1) is less than the mesio-distal inter-distance between the mesial pair of inner tie wings and the distal pair of inner tie wings, when viewed labially/buccally.

FIG. 15 illustrates the perspective view of alternative orthodontic bracket embodying the present invention presented in FIG. 14. In this configuration, the mesio-distal width of the outer tie wings ( 1 ) is less than the mesio-distal inter-distance between the mesial pair of inner tie wings (2) and the distal pair of inner tie wings (2), when viewed labially/buccally. The auxiliary slot is entirely excluded from the bracket embodiment (100).

FIG. 16 illustrates the perspective view of alternative orthodontic bracket embodying the present invention presented in FIG. 14. In this configuration, the mesio-distal width of the outer tie wings (1) is less than the mesio-distal inter-distance between the mesial pair of inner tie wings (2) and the distal pair of inner tie wings (2), when viewed labially/buccally. The auxiliary slot (6) with modified cross-section is located between both pair of inner tie wings (2) and underneath the outer tie wings (1) of the bracket embodiment.