Orthodontists commonly correct the position of mal-occluded and mal-aligned teeth by therapeutic tooth movement. Therapeutic tooth movement is accomplished by the application of force to teeth to reposition them. Many orthodontic appliances have been used to apply force to teeth. The most commonly used orthodontic appliance for tooth movement is commonly known as the “edgewise appliance” or more specifically the “fixed pre-adjusted edgewise appliance”—also known as the “straight-wire appliance.” The name “edgewise” refers to the general mechanism of a rectangular slot engaged by a force-generating rectangular wire. The terms “straight-wire”, “pre-adjusted”, and “pre-programmed” refer to an elective, though highly desirable, feature of an edgewise appliance system that will be described as follows.
An edgewise appliance system is a combination of many individual pieces designed to function in a coordinated fashion. The two primary components are tooth “attachments” that are attached to the teeth and “arch-wires” that engage the attachments. The attachments (brackets or bands) are semi-permanently and rigidly attached to the teeth. Typically, the attachments are fabricated of stainless steel, porcelain (ceramic), plastic, or combinations of these materials. The attachments serve as a standardized “handle” by which the tooth may be engaged by a force.
Each attachment in a system (generally referred to as a “bracket”) possesses a rectangular slot that receives the arch-wire component. Typically, all the attachments of a particular system will have the same rectangular slot dimensions of about 0.018×0.025 inches, 0.020×0.025 inches or 0.022×0.025 inches. Some operators prefer to use a combination of various size slots. The slot shape is rectangular to accommodate a wire with a rectangular or square cross section, which permits application of forces and hence control of tooth position in three dimensions.
Typically, arch-wires are made of metal alloys capable of varying degrees of elastic deflections depending on their size, cross-sectional shape, and composition. The elastic deflections in the arch-wire generate forces on the brackets, which in turn translate the forces to the teeth, thereby causing the teeth to move to a desired position.
The human teeth are arranged spatially in the upper or lower jaw (the maxillary or mandibular dental arches respectively) in the shape of an arch with their long axes generally perpendicular to the plane of the arch. The precise shape of the arch varies among individuals from more U-shaped arches to V-shaped arches to parabolic arch forms. The precise shape of any particular arch can vary substantially.
Given that the teeth are naturally arranged in this relatively flat-plane arch-form, it is commonly recognized as an objective of orthodontic therapy that this plane should be made relatively flat and that the teeth should be aligned precisely to form an arch-form shape that is similar (but improved) to the pre-existing condition of the dentition. To serve this objective, the “straight-wire”, “pre-adjusted”, or “pre-programmed” concept of appliance design was derived as a means of executing orthodontic therapy with greater ease, efficiency, and quality. The basic concept of “straight-wire” is that, if the objective of orthodontic therapy is to position teeth in a flat plane, then the force generated by elastic deformations in a flat, straight wire shaped in the form of an arch is an ideal mechanism for producing those results. In theory, the attachments are rigidly fixed to teeth at a precise “pre-adjusted” or “pre-programmed” position on the mid-facial or lingual aspect of a tooth at their respective mal-aligned state. A straight (flat) arch-shaped wire is then deflected to engage the mal-aligned attachments slots. The force generated by the elastic deformation of the wire then “pulls” the teeth along with it as it moves back towards its original shape. The attachment position on each tooth then determines the ultimate and final relative position of each tooth relative to the other teeth upon achievement of the “straight-wire” condition (the theoretical end-point).
Traditionally, the vast majority of orthodontic therapy has been performed with attachment slots placed primarily on the facial aspect of the teeth. It can be readily deduced via casual observation of an arch of teeth that the mid-facial aspects of an arch of teeth tend to align in a straight, flat arch form. However, it is also readily observed upon closer inspection that these mid-facial surfaces do not exactly line up in a straight line with their long axes residing at identical orientations. In fact, one can readily observed consistent deviations in the spatial relations of an arch of tooth crowns and roots. Each tooth type tends to deviate in a specific consistent “average” way relative to the horizontal plane. As such, early pioneers of appliance design theorized that compensations in bracket slot orientation relative to the bracket base could automatically compensate for these differences.
They also realized that the anatomy among types of teeth (upper right central incisor, versus, for instance, an upper right canine, etc.) varies substantially. But because this anatomy is consistent among different individuals for each tooth type, each tooth type, therefore, could receive its own uniquely shaped “average” bracket slot and base orientation. This pre-defined shape can theoretically be used on a particular tooth type for any particular individual. Thus, while the general shape of a bracket system might be very similar, for each particular tooth type the corresponding bracket is designed with specific compensations in base shape, base size, general shape, slot angulation, base thickness, etc. to accommodate differences in tooth type anatomy and tooth type spatial relations relative to the horizontal plane.
The intention of these design specifications was to create a universally applicable appliance that will, if brackets positions are accurately coordinated, create an ideal alignment of teeth if a straight wire is deflected into each slot and if the wire is subsequently permitted to express its original straight shape. By doing so, the operator would possess a pre-programmed mechanical system. Having realized a truly pre-programmed system, theoretically, the operator could eliminate the need for manual manipulation of the system (via the placement of compensating bends in the arch-wire component) and thus produce a highly predictable and efficient outcome.
However, as mentioned, the efficient utilization of a so-called straight-wire appliance depends largely on the orthodontist's ability to coordinate the position of the brackets on mal-aligned teeth so that the forces imposed by deflections of the resilient, straight, arch-wire will result in perfect three-dimensional alignment of the teeth. If the brackets are not properly positioned, then the degree of mal-positioning will be reflected as a proportional degree of mal-positioning of the teeth. Correcting these mal-positions would then require the operator to manually manipulate the shape of the arch-wire component via the placement of compensating arch-wire bends. This is recognized as a comparatively laborious, slow, unpredictable, and inefficient method.
Most orthodontists position the brackets on the patient's teeth using a “direct” method. “Direct” refers to the positioning of each bracket on each tooth directly, inside the patient's mouth. But when working directly inside the mouth it is very difficult to visualize precise bracket positioning and extremely cumbersome to utilize measuring instruments for determining vertical position. Because accurate positioning is so difficult, getting the bracket “close enough” is widely regarded as an acceptable compromise. Because precise positioning of an entire arch of brackets is the exception rather than the norm, the result is a huge compromise in treatment quality and efficiency.
To improve the accuracy of bracket positioning in a typical private practice setting, “indirect” positioning methods have been developed. Rather than positioning brackets directly inside the patient's mouth, the brackets are positioned on a three-dimensional model of the patient's teeth, outside the patient's mouth. In this way, improved visualization and the utilization of measuring devices are permitted, so accurate positioning becomes much more simple and attainable. Once the brackets are positioned on the model and rigidly attached, a “transfer tray” is fabricated and utilized to transfer the brackets from the model to the patient's mouth. The tray preserves the brackets position during the transfer. There are a number of known variations of indirect methods, including those described in U.S. Pat. No. 5,971,754 to Sondhi et al. and U.S. Pat. No. 4,952,142 to Nicholson, which are hereby incorporated herein by reference.
There are drawbacks to conventional bracket systems, regardless of the attachment method used. Typical brackets (both facial and lingual types) are composed of two basic structures. The first, a broad, flat base. Second, is a structure(s) protruding perpendicular to the base that forms the “open face” rectangular slot and the “tie-wings” that are used to anchor a disposable ligature that, in turn, maintains engagement of the wire component in the slot.
Generally, with a facial or lingual bracket system, all anterior and premolar brackets are designed with an open-face slot that allows the arch-wire component to be inserted into the slot along a facio-lingual vector. This bracket design requires the presence of tie-wings to engage and maintain engagement of the wire component. Because of the necessity of tie-wings, these brackets must possess a certain degree of structural profile height and shape irregularity that facilitates overall effectiveness and simple operation of the ligature/tie-wing ligation system by the operator.
Generally, with a facial or lingual bracket system, it is also common to use a tube attachment on molar teeth, rather than an open-face-slot bracket design. The tube type of attachment receives the arch-wire component via threading of the wire through the mesial or distal ends of the tube. This type of attachment has the benefit of not requiring the protruding, bulky, irregularly shaped tie-wings that are required of an open-face design. However, their applications are limited to the posterior teeth due to the necessity of threading the wire through the mesial or distal ends. It would be an impractical endeavor to attempt threading an arch-shaped wire through an entire dental arch starting from the most distal molar. Not only would the wire initial need to extend into the patients throat but the lack of a continuously consistent degree of curvature of the wire segment would preclude insertion of a wire of significant stiffness. In addition, the closed-face tube attachment precludes the placement of significant arch-wire bends, therefore, it is only practical if the attachment system is positioned with high precision and coordination.
As such, conventional bracket systems are designed to accommodate one bracket per tooth on either the facial or lingual side, but, as a practical matter, not both. They use open-face slots on anterior and most premolar teeth with tube attachments on the molar teeth. Note that many tube attachments designed for molars are also designed with a removable facial wall that allows the tube to be converted into an open-face bracket. Such designs also require the presence of tie-wings to hold the wire in place once the tube is converted to an open-face bracket.
The relatively large flat base characteristic of most conventional brackets serves several purposes. First, the relatively flat base is intended to rest against each tooth parallel to a tangent plane at the center of its mid-facial surface. This allows the operator the opportunity to use the surface of the tooth as a means of reference for establishing the properly coordinated position of each bracket—the operator simply must fully seat the bracket base against the tooth at its mid-facial surface. Doing so orients the slot at its recommended three-dimensional pre-programmed (pre-coordinated) position. Second, the base serves as the bonding interface for rigid attachment to the tooth. As such, the “tooth-side” of the base generally possesses mechanical retentive features (such as a mesh pad, particle micro-etched surface, laser-etched surface, etc.) that facilitates durable bonding to the tooth by facilitating mechanical interlocking between an adhesive and the bracket via penetration of the adhesive into the retentive features. Some brackets, depending on their material composition, may also possess a base that bonds chemically to an adhesive. The base is relatively flat and large to provide a sufficient surface area for creating a durable bond to the tooth.
But a base of any substantial length compromises the ability to custom-coordinate positioning of a bracket in particular ways. For example, if the operator desires to place the slot at an alternative facio-lingual angle, the base interferes and creates an undesirable lever arm that necessitates displacement of the slot in an unfavorable way, a greater distance from the tooth surface. As such, to achieve coordination of the remaining bracket slots would require positioning them with an equal degree of offset away from the tooth surface. Moreover, with the bracket now positioned farther from the tooth, that is, creating a higher, more protruding profile, the bracket is more prominent and protruding so as to physically annoy a patient. And even when the bracket can be positioned with the base flat against the tooth, the width of conventional brackets alone makes them comparably protrusive, when most patients would prefer them to be minimally protrusive.
In addition, because lingual side tooth anatomy is more highly variable among individual tooth types compared with facial side anatomy, using a “base-dependent” positioning system to achieve a “straight-wire” result is even less efficient than the traditional facial bracket system. That is, a “fixed bracket shape with a base” designed for the lingual tooth surface is remarkably less efficient at achieving coordination of slot positions such that a straight wire could then deflect the teeth to the desired positions. Because of this inefficiency, greater effort and greater unpredictability are realized by the operator who attempts to bend arch-wire to compensate for poorly coordinated lingual bracket slots.
If an operator desires the efficiency of a straight wire mechanical system to be used on the lingual side of teeth, this requires the ability to customize slot position for each patient. While this can theoretically be accomplished using a traditional bracket with a base and protruding tie-wings, the degree of protrusion and irregularity of shape (roughness) creates substantial discomfort for the patient. For this reason and others, lingual bracket systems have seen only very limited applications in orthodontics.
In addition, the desirability of adjustability has lead to the predominant use of open-faced slots. In fact, open-faced slots are a practical necessity because of the obvious problem that a wire possessing compensating bends of significant size cannot be threaded through tubes of small cross-section and the obvious problems with insertion of full-length arch-wires through a closed-face bracket system. But with open-faced slots, the arch-wires must be secured, which is conventionally done by using ligature tie-wings. And the tie-wings create a relatively bulky, high profile bracket system and generally result in a highly irregular surface against which lips, cheeks, and tongue will rub and create discomfort.
Because of the cost associated with the vast inventory of brackets required, most operators use a manufacturer-specified shape (not a shape customized to the unique dental anatomy of the patient) for each tooth. Existing brackets do not allow for minimizing the profile and protuberances, which would create a far more comfortable lingual bracket system. The necessity of having tie-wings to engage ligature ties for the purpose of holding the wire engaged in the slot means that uncomfortably large, irregular protuberances are unavoidable.
Accordingly, there is a need for an orthodontic bracket that has a lower profile and smoother contour, can be positioned on the lingual side of the teeth without compromising patient comfort, is less visibly noticeable, and can be positioned with great precision and flexibility. It is to the provision of such an orthodontic bracket and attachment method that the present invention is primarily directed.
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