Patent Publication Number: US-6712607-B2

Title: Orthodontic bracket for visual positioning

Description:
This application is a continuation of U.S. patent application Ser. No. 09/422,495, filed Oct. 21, 1999 now U.S. Pat. No. 6,358,044 which is a continuation of U.S. patent application Ser. No. 08/933,269, filed Sep. 18, 1997, now U.S. Pat. No. 5,993,206, which is a continuation application of abandoned U.S. patent application Ser. No. 08/641,903, filed May 2, 1996 abandoned, both entitled “Visual Positioning Orthodontic Appliance and Method”, all hereby expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the positioning of orthodontic appliances on the teeth of a patient, and more particularly, to the configuration of orthodontic appliances, particularly orthodontic brackets, for the visual positioning thereof on the teeth of patients. 
     BACKGROUND OF THE INVENTION 
     When bonding orthodontic appliances, a major tenet to be considered by the orthodontist is the location of the appliance in the mouth of the patient. In the case of bonded orthodontic brackets, this location is the position and orientation of each of the brackets on one of the teeth of the patient. 
     Most of the preadjusted appliances that are currently employed for maxillary application are designed to be located at the facial axes of the maxillary teeth of the patient. The facial axis, or FA point of a tooth illustrated as Point FA in FIG. 1A, is defined as dead center vertically on the clinical facial surface of a fully erupted crown and at the height of contour mesiodistally of the mid-developmental lobe of the tooth, for example, right maxillary central  20 . This definition is based on the criteria that the plane of the archwire will pass through the point FA. Furthermore, appliances should be aligned angularly in the FA plane, which is the plane tangent to surface of the tooth at the FA point, at a line angle represented by line LA in FIG.  1 A. This angle LA generally coincides with the line along the height of the contour of the tooth&#39;s mid-developmental lobe  21 . So angularly aligned, the appliance will better deliver the appropriate final angular position or tip of the tooth. These criteria are referred to as the concept of morphological centering and angular alignment. This concept is quite often implemented visually by the orthodontist or other clinician who places the appliance on the tooth by making a visual determination of the location of the point FA and the orientation of the line LA. The visual implementation of this concept can be rendered difficult for the orthodontist by varying degrees of eruption that leaves an unerupted portion  22  of a tooth  20   a , as illustrated in FIG. 1B, by virtue of chipped or worn incisal tooth edges  23  of a tooth  20   b , as illustrated in FIG. 1C, or by virtue of the existence of other aberrations of the typical tooth profile. Teeth for mandibular application are also often visually placed in accordance with mandibular placement criteria. 
     While the concept of morphological centering and angular alignment is familiar to orthodontists, the clinical difficulty of achieving its placement goals is well known. Several approaches have been developed to alleviate this problem but all have drawbacks. The most common approach has been to use measuring instruments to position the appliances at fixed vertical heights. These heights typically represent something akin to the average distance from the incisal edge of a tooth to the FA point of the tooth, and are usually expressed in millimeters. The awkwardness of this approach is that teeth come in various sizes, which precludes placement of the appliance at the proportional center of the tooth in all but the truly average patient. Additionally, due to the highly probably presence of a malocclusion and to the lack of access because of the tooth&#39;s position in the mouth (e.g. as with posterior segments or crowding) there is often insufficient space to use these instruments effectively. 
     When the appliances are not placed at the design location, adverse effects occur with respect to the final positioning of the teeth. First, if the appliance such as an upper right central bracket  24  is placed incorrectly in the vertical plane, the faciolingual inclination of the tooth is effected, producing an inclination error  25  as illustrated in FIG.  1 D. Secondly, at the same time, the apparent thickness of the appliance is effected, resulting in a labial-lingual offset error  26  from the desired placement of a tooth on the dental arch. 
     Another approach to this problem is that known as “indirect bonding.” This approach involves positioning of the appliances on a model or cast of the patient and then using a transfer mechanism or tray to transfer the positioned appliances to corresponding positions on the teeth of the patient. The indirect bonding approach has its detracting features. For instance, often the tray does not seat fully, causing simultaneous incorrect placement of a multitude of individual appliances. Other problems include appliance adhesive failure and excessive “flash.” Further, brackets are typically, although not always, placed by eye on the model, which offers little improvement over direct placement on most patients. These difficulties have been sufficient to severely limit the use of the indirect bonding technique. 
     An understanding of why the centering and aligning of appliances has been so clinically troublesome can be obtained by examining the morphology of the appliances and the dentition. Teeth, as most anatomical entities, have a generally flowing shape which does not lend itself to description or visualization using geometric determinants, as can be seen from the profile of a typical upper right cuspid  40  in FIG.  1 E. Appliances such as brackets and their bonding pads, on the other hand, are typically generated from orthogonal geometric designs that lend themselves to ease of appliance manufacture, as can be seen from a typical upper right cuspid bracket  42 . Further complicating this situation with respect to vertical placement is the varying torque or inclination angle of the archwire slot relative to the base of the appliance. This occurs whether an angle of a slot is cut in a bracket support, i.e. “torque in the face”, or an angle is formed in the mounting surface of a bracket, e.g., “torque in the base”. Because of this angle, the true plane of the archwire, which should intersect the FA point, is difficult for the orthodontist to visualize. Thus, positioning of the appliance, such as with the illustrated high torque upper right central bracket  24   a , using either the bracket body or the facial view of the slot, will yield the positioning of the bracket on a tooth, such as tooth  20 , with the archwire plane AWP intersecting the tooth  20  at a point displaced from the point FA, by an amount  28 , as illustrated in FIG.  1 F. Such a view afforded the clinician when placing the appliances often incorrectly influences the positioning. For the clinician to attempt to minimize this problem by viewing directly into the slot of the appliance during placement is at least awkward and not always possible clinically. 
     Additionally, when placing the appliance mesiodistally, the geometric appearance of the bracket and bonding pad can also be misleading, as seen when the rhomboid geometry of some individual appliances is compared to the dental anatomy. For example, FIG. 1G illustrates the difference between the shapes of orthogonal upper right cuspid bracket  42  and the anatomical shape of the upper right cuspid  40  with the bracket  42  correctly placed on mid-developmental lobe  41  that is not coincident with the mesiodistal center of the tooth. Further, when a clinician uses the bracket body portion of an appliance as the primary landmark, parallax is also a complicating circumstance that gives the clinician an incorrect apparent view of appliance position, as illustrated in FIG.  1 H. 
     Notwithstanding the problems and disadvantages stated above, the concept of visual positioning of orthodontic appliances on the teeth of patients remains a technique that clinicians must use. Therefore, there remains a need for a solution to the problems of the prior art and for greater accuracy and reliability in visual appliance positioning. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to alleviate the deficiencies of the prior art appliances that render inefficient and imprecise the visual positioning of orthodontic appliances on the teeth of patients. It is a particular objective of the present invention to provide an orthodontic appliance that provides a visual signal to the clinician that enhances the ability and the likelihood of achieving precise and accurate placement of the appliance on the teeth of a patient. 
     In accordance with the principles of the present invention, the orthodontic appliance, and particularly the portion thereof that lies against the tooth of a patient, is contoured in a way that corresponds to the profile of the tooth on which the appliance is to be positioned, so as to provide a signal that guides the clinician in the easy and precise positioning of the appliance on the tooth. It is a particular objective of the present invention to provide orthodontic appliances with tooth mounting surface thereon that are shaped to provide to the clinician who is placing the appliance on the tooth of a patient a placement signal that will facilitate the centering of the appliance on the tooth of the patient and will override erroneous signals that are caused by irregularities in the actual profile or shape of the patient&#39;s teeth. 
     In accordance with the preferred embodiment of the invention, orthodontic appliances such as orthodontic brackets are provided with bases of pads that have shapes related to the frontal anatomies of the specific respective teeth to which the appliance is to be attached. The archwire support portion of the appliance is, in one embodiment, fixed relative to the pad so that the plane of the archwire passes through the FA point of the tooth when the pad is properly positioned on the tooth. In alternative embodiments, the wire support portion of the bracket is fixed to the pad, extending rigidly from the pad, so that the archwire plane intersects the tooth at a position other than through the FA point that meets some intended placement criteria offset from the FA point. 
     In one preferred embodiment of the invention, the archwire support portion of a bracket is fixed to a pad so that the pad can be positioned upon the mesiodistal center of the tooth by a visual centering of the tooth in a facial view with the bracket at the height of the contour of the mid-developmental lobe. Such support portions are fixed to the pad, either by being formed separate from the pad and being attached to the pad by welding, fusing or other bonding technique or by being formed integral with the pad in a molding, forging, casting, machining or other such manufacturing operation. The brackets being so formed, the support portion extends rigidly from the pad and is located on the opposite side of the pad from the mounting surface at which the pad is to be attached to a tooth. The position of the archwire support on the pad may be defined in relation to a point on the mounting surface, thereby making it possible to locate the support by properly positioning the pad on a tooth. 
     In accordance with the principles of the present invention, the bases or mounting pads of the appliances are shaped to conform to the outlines or profiles of the teeth to which the bases are to attach. The profiles are preferably the silhouettes of the specific teeth when viewed from the facial side of the tooth in a lingual direction in the archwire plane. The sizes of the pads, so shaped, are preferably geometrically reduced or scaled down from the sizes of the profiles of specific teeth. The profile shapes are preferably statistically average shapes for each tooth type among the members of a population segment. The appliances having bases so shaped send to the clinician, who is mounting the appliances on the teeth of a patient, a strong visual signal, which, when received by the eye of the clinician, guides the clinician in the placement of the appliances at the visual centers of the teeth. With the bases or pads to be so located, the archwire support portions of the appliances can be either centered on the bases or offset from the centers of the bases so that they assume their intended positions on the teeth. 
     With the preferred embodiment of the invention, the shapes of the pads or bases of the appliances are determined by producing an outline or profile of the tooth as would be seen by the installing clinician from the facial side of the teeth. This outline is then scaled downward in size to a size that is appropriate for the appliance base or pad. The size reduction of the shapes from that of the tooth outline to that of the finished appliance base or pad may be carried out according to a scale that differs in the horizontal and vertical directions. For example, a bracket pad may be scaled in the horizontal direction to 50% of the horizontal dimension of the tooth while being scaled in the vertical direction to 25% of the dimension of the tooth. 
     The appliances of the present invention and the methods of making and placing such appliances provide the advantages of more efficient and precise visual placement of the appliances on the teeth. In addition, such appliances and methods provide for a reduction in bracket adhesive failure, since the shaped pads may easily have at least a twenty percent increase in bonding area, and in some cases, much more. This increase may be provided without noticeable deterioration in esthetics by carefully enlarging the pad only in areas where the increase would be unnoticed when a ligature and archwire are present. This is accomplished while still maintaining the anatomical placement registration. 
     In addition, the difficulty of excess adhesive cleanup is reduced because the pads have no sharp corners, so that cleanup can be achieved with fewer discreet moves than with an orthogonal pad. Additionally, the tie wings of the brackets can be more easily made so as not to extend beyond the pad and therefore be less likely to snag on the cleanup instrument and thereby dislodge or alter the position of the appliance. Also, the likelihood of appliance drift prior to adhesive polymerization is further reduced because the ratio of the area of the pad to the mass of the assembly is greater in relation to that of the standard orthogonal pad, thereby lessening the propensity for the appliance to move due to gravity before the adhesive polymerizes. 
     A further advantage of the tooth-shaped pad is that the pad itself serves as a bracket identifier that is different for each tooth type and also for each quadrant, because the tooth-shaped pads carry tooth specific anatomic information that visually describes which tooth the appliance is designed for, simplifying identification of the particular appliance. 
     Patient hygiene and iatrogenic decalcification are improved with the tooth-shaped pads because the bracket tie wings need not exceed the perimeter of the pads, and therefore the patient is able to access this area with a toothbrush to minimize the decalcification commonly seen at the gingival edge of the pad. Additionally, the pads may be designed to cover the gingival areas where decalcification is common. 
     The quality of pad fit with respect to tooth curvatures is further increased with the pads shaped according to the present invention, because, while the pad of a standardized bracket is unlikely to fit any tooth perfectly, the tooth-shaped pads have less in the way of corners than do orthogonal pads, so teetering across the diagonal corners of the orthogonal pads is lessened. 
     The present invention is particularly advantageous in the application of appliances to the maxillary teeth, although certain features of the invention provide advantages in the application of appliances to mandibular teeth. 
     These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description of the drawings of the preferred embodiment of the invention, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A through 1H are a series of diagrams illustrating problems in the visual placement of orthodontic appliances on teeth with appliances of the prior art. 
     FIG. 2 is a series of diagrams illustrating the prior art placement of a conventional appliance on a tooth. 
     FIG. 3 is a series of diagrams illustrating the placement on a tooth of an appliance embodying principles of the present invention. 
     FIG. 4A is a facial diagram illustrating the prior ad placement of a set of conventional brackets on right maxillary teeth, while FIG. 4B is a similar diagram illustrating the placement on right maxillary teeth of tooth-shaped brackets according to principles of the present invention. 
     FIGS. 5A-5B and FIGS. 5C-5D are facial diagrams comparing the placement of the appliances of FIG.  3  and FIG. 2, respectively, in situations where the outline of the tooth on which it is placed is unclear. 
     FIGS. 6A and 6B are mesial diagrams illustrating effective placement of the appliance of FIG. 3 for both standard and high torque prescriptions. 
     FIG. 7 is a facial diagram illustrating how off center placement of a bracket support can be achieved with the present invention. 
     FIG. 8 is a mesial diagram illustrating an appliance positioned with a vertically offset archwire plane in accordance with an embodiment of the present invention. 
     FIG. 9 is a series of diagrams illustrating one preferred manner of proportionally scaling the shape of the tooth profile to arrive at tooth-shaped brackets of the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The present invention recognizes that many errors occurring in the orthodontic positioning of appliances on teeth are caused by erroneous visual signals that result from a lack of similarity between different shapes. With the present invention, the appliance is rendered easy to position by providing the bonding pad to which the appliance is precisely fixed with a shape related to the outline of the tooth to which it is to attach. With the present invention, the bracket is located with sufficient precision on the pad, which results in variations in placement being lessened by the more dominant visual signal sent to the clinician due to the congruity of the pad and the dental anatomy. With the preferred embodiment of the invention, brackets are provided with pads that, for each tooth type, are shaped to conform to the dental anatomical outlines of the specific tooth of the type to which the bracket is to attach, with geometric reductions then performed on the pad shapes for each tooth type to create reduced size shapes that send more “signal” to the eye of the clinician. 
     FIG. 2 illustrates the outline of a pad  29  of a conventional maxillary right central bracket, the outline of the maxillary right central tooth  20 , the pad outline  29  properly positioned on the tooth  20 , and the assembled conventional bracket  24  with its pad  29  positioned on the tooth  20 . The pad  29  of the bracket  24  has a standard orthogonal shape. As can be seen from FIG. 2, when centered on the tooth  20 , the upper left corner  30  of the pad  29  is the closest to the perimeter of the profile of the tooth  20 , making the pad  29  and bracket  24  appear to be off center to the left. Such a visual signal has a tendency of causing the clinician to place the bracket  24  on the tooth slightly to the clinician&#39;s right of its proper position. 
     Referring to FIG. 3 is illustrated the outline of a pad  31  of a maxillary right central appliance according to principles of the present invention. The pad  31  has the same general peripheral shape as the outline of the maxillary right central tooth  20 . When the pad  31  is properly centered on the tooth  20 , the outline of the pad  31  is proportionately spaced from the outline of the profile of the tooth  20  and appears visually centered on the tooth  20 . Thus, a maxillary right central bracket  33  that is similar to the standard bracket  24  but has the tooth-shaped pad  31  has the visual appearance of being centered on the tooth  20 . Such a tooth-shaped pad  31  gives a visual signal to the clinician who is placing the bracket  33  on the tooth  20  that the bracket  33  is properly centered on the tooth  20 . With the pad  31  of the bracket  33  so shaped to conform to the outline of a maxillary right central  20 , the practitioner receives this visual signal that causes the pad  31  to appear to “snap” into place visually, whereas no such visual signal is produced by the orthogonal design of the pad  29 . Preferably, the pad  31  is shaped to conform to the profile or outline of a statistically average maxillary right central of a population segment that is representative of the patient being treated with the appliance  33 . 
     The pads of brackets of the present invention are preferably each designed for the different specific teeth of a patient. For each of the specific teeth of a patient (for example, for the maxillary right central  20 , lateral  35 , cuspid  40 , first bicuspid  44  and second bicuspid  47 ), standard orthogonal brackets  24 ,  36 ,  42 ,  45  and  48  differ usually primarily in that the sides of their respective pads  29 ,  37 ,  43 ,  46  and  49  are parallel to the wings  50  of the brackets and correspond to the tip of the axis  19  of the respective tooth, as illustrated in FIG.  4 A. Such a bracket configuration is described in U.S. Pat. No. 4,415,330 of Daisley et al., hereby expressly incorporated by reference herein. The brackets  24 ,  36 ,  42 ,  45  and  48  of FIG.  4  and of the Daisley et al. patent each have distal and mesial tie wings  11  and  12 , respectively. The distal tie wings  11  are fixed to the respective bracket base pads  29 ,  37 ,  43 ,  46  and  49  and each includes a gingival tip  13  and an occlusal tip  14 . The mesial tie wings  12  are also fixed to the respective base pads and each includes a gingival tip  15  and an occlusal tip  16 . The respective gingival and occlusal tips define between them an archwire slot  10 . The distal and mesial tie wings  11  and  12  have parallel distal and mesial sides. The archwire slot  10  provides a reference line  17  in the archwire plane AWP for orientation parallel to the occlusal plane of a patient. The sides of the tie wings  11  and  12  are inclined at an oblique angle to the reference line  17 , so that the tie wings  11  and  12  can be generally vertically disposed parallel to the tooth long axis  19  and still be inclined at an oblique angle to the reference line  17 . The gingival tips  13  and  15  and the occlusal tips  14  and  16  of respective tie wings  11  and  12  have top and bottom surfaces that are substantially equidistant from, and in mutual alignment parallel to, the reference line  17 . The tie wings  11  and  12  together form a rhomboidal configuration and the axis of the archwire slot bisects the tie wings  11  and  12   50  that the gingival tips  13  and  15  and the occlusal tips  14  and  16  are of equal size. 
     With the appliances of the present invention, brackets  33 , and  51 - 54  are provided with pads  31 , and  55 - 58  that are shaped to conform respectively to the outlines of the profiles of average teeth,  20 ,  35 ,  40 ,  44  and  47 , as illustrated in FIG.  4 B. Such pads, shaped so as to conform to the outlines of these teeth, are similarly illustrated. Such shapes additionally identify the brackets  33 ,  51 - 54  as being intended for the specific respective teeth  20 ,  35 ,  40 ,  44  and  47 . These tooth-shaped pads are illustrated in FIG. 46 in combination with the bracket archwire supports of the Daisley et al. patent described above. 
     With the tooth-shaped pads  31  and  55 - 58 , calculated and precise location of the support portion of the brackets  33  and  51 - 55  upon the pads assures that the archwire plane AWP passes through the anatomical center of the pad irrespective of the particular appliance prescription chosen by the clinician. For example, as illustrated in FIGS. 6A and 66 respectively, for a bracket  33  having a standard prescription and for a bracket  33   a  having a high torque prescription, the true archwire plane AWP will tend to pass through the FA point with visual placement of the bracket  33  or  33   a  on the tooth  20 . In addition, as illustrated in FIG. 7, when brackets having tooth-shaped pads are employed on teeth having a mid-developmental lobe  41  that is not in the middle of the facial view of the tooth, such as for the illustrated maxillary cuspid  40 , the bracket  52  can accommodate the off-center lobe  41  by an adjusted placement of the bracket  52  on the pad  56 , so that when the pad  56  is placed on the facial center of the tooth  40 , the bracket will be mesiodistally displaced an appropriate amount. Compared with the bracket  42  having the standard orthogonal bracket pad  43  (FIG.  4 A), the visual placement of the bracket  52  places the bracket  52  at the height of contour of the mid-developmental lobe  41  of the tooth  40 , while the pad  56  will be placed by the clinician at the center in the facial view of the tooth  40 . 
     Also, the tooth-shaped bracket, such as the bracket  33   a , can easily be designed so as to offset the archwire plane AWP vertically from the classic FA point on the tooth, for example, tooth  20 , by a predetermined amount where the appliance is intended for such placement, as illustrated in FIG.  8 . Such an offset position is likely to be accepted as a preferred modification to classic placement as the clinical bracket positioning art matures and more clinical evidence with respect to ideal placement is obtained. Such a bracket  33   a  is fixed so its support is at a vertical offset position on pad  31 , which is still centered on the tooth  20  by visual placement, to give placement of archwire plane AWP by a predetermined distance  60  that is above or below FA point if desired. 
     The preferred method of the invention for determining the shapes of the bases of the appliances described above includes first producing outlines or profiles of each of the teeth of a patient, or of the teeth of a class of patients using statistical tooth shape data so that a standard outline for each tooth type, i.e., cuspid, central, etc., is produced. Preferably, each standard outline corresponds to a statistically average shape for all patients or statistical group of patients. From such outlines, a scaled down representation of each tooth shape is generated by reducing the tooth profiles in size to the desired sizes of the appliance bases. The size reduction may be uniform in all directions, but, preferably, different scales are used for different coordinates, such as by employing different vertical and horizontal dimension reductions. Most preferred is the use of a greater reduction of the vertical dimensions than of the horizontal dimensions, for example, by making the pads to a size of from 20 to 40% of the corresponding vertical dimensions of the tooth shape outlines and to from 40 to 60% of the corresponding horizontal dimensions of the tooth shape outlines. 
     In FIG. 9 are illustrated a scaling of the outlines of a representative square profile  81 , a circular profile  82  and an arbitrary shape  83  that can be regarded, for illustration purposes, as representative of the shape of a tooth. In each of the profiles  81 - 83  is respectively illustrated a correspondingly shaped form  84 - 86  which may be considered representative of the shape of an orthodontic appliance base or pad. The preferred method of proportionate size reduction used in each illustrated case scales the profiles by different amounts vertically and horizontally. The reduction illustrated uses a 25% scale factor in the vertical direction and a 50% scale factor in the horizontal direction. The centers of the profiles of each of the original shapes  81 - 83  are indicated at  87 - 89 , respectively, on which the shapes of the pads  84 - 86  are respectively centered. Corresponding points on the corresponding shapes of the tooth outline and the pad outline, for example, points  91   a  and  91   b , points  92   a  and  92   b  and points  93   a  and  93   b , are respectively moved in the scaling step, vertically to one fourth of the original vertical distances V 1 , V 2 , V 3  from the horizontal centerlines, and horizontally one half of the horizontal distances H 1 ,H 2 ,H 3  from the vertical centerlines. 
     The appliances for which the present invention is most useful are the maxillary incisors, cuspids and bicuspids, on which the appliances are most often and most easily positioned visually. 
     Accordingly, those skilled in the art will appreciate that the application of the present invention herein are varied, that the invention is described in preferred embodiments, and that additions and modifications can be made without departing from the principles of the invention. Therefore, the following is claimed: