Dentistry – Orthodontics – Bracket
Reexamination Certificate
2002-07-19
2004-04-27
O'Connor, Cary E. (Department: 3732)
Dentistry
Orthodontics
Bracket
C433S010000
Reexamination Certificate
active
06726474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of orthodontic brackets. More specifically, the present invention discloses a removable module that can be attached to a conventional orthodontic bracket to provide a selectively removable self-ligation capability.
2. Statement of the Problem
The orthodontic tooth brace (more correctly known as the orthodontic bracket) is a central component of current, conventional orthodontic treatment practice. For an orthodontic patient's treatment, an orthodontist will typically attach brackets to each of a patient's teeth to serve as the primary receptors of corrective tooth-positioning forces. Such corrective forces are transmitted through brackets to the crowns of the teeth and then translated to the roots of teeth where they elicit certain osteogenic responses from the adjacent supportive bone, allowing the slow corrective repositioning of teeth according to the vector sum of the combined corrective forces applied to the bracket and tooth.
FIG. 1
is front perspective view of a typical orthodontic bracket assembly. The bracket
30
has a bonding pad for secure attachment to a tooth
10
. The rectangular shaft extending through the bracket
30
represents a section of an archwire
20
. An elastomeric ligature
31
is retained under the four tie wings
32
of the bracket
30
. The ligature
31
serves to retain the archwire
20
in the archwire slot of the bracket
30
.
The orthodontic bracket was first developed by Dr. Edward Hartley Angle in the late 1800's and in spite of significant improvement in design, materials and manufacturing processes that have occurred since Dr. Angle's time, the bio-mechanical functioning of orthodontic brackets remains essentially unchanged. Central to the functioning of an orthodontic bracket is the archwire slot. The archwire slot is a generally horizontal, outwardly opening, rectangular-shaped trough formed in the structure of a bracket that accepts a separate, correspondingly rectangular-shaped archwire. The orthodontic bracket taught by Dr. Angle is known as the “Edgewise” bracket, Edgewise being a descriptive term referring to the rectangular interfit of the archwire slot and the archwire typically employed for Edgewise orthodontic therapy. The archwire is rectangular in cross-section and is retained in the rectangular-shaped archwire slot by ligation means that positively hold an archwire fully constrained and seated within the bracket's archwire slot. During orthodontic treatment, an archwire normally extends around a patient's arch and is ligated into the archwire slots of all of the brackets of a patient's upper or lower dental arch. A patient will normally be treated with one set of brackets and an archwire for the upper dental arch and another set for the lower.
As can be appreciated, the Edgewise interfit of the wire and the slot allows for a semi-rigid connection between the archwire slot and the archwire. Being engaged in this way, an archwire can transmit corrective forces to the structure of a tooth that serve to cause that tooth to be uprighted to a desirable inclination, which is known as correction in terms of “torque.” A tooth can also be uprighted laterally, known as correction in terms of “angulation.” An archwire can impart corrective forces known as “rotation” which cause a tooth to desirably rotate around its central axis. Other corrective forces can be transmitted from an archwire to a tooth through its corresponding bracket that tend to intrude or extrude a tooth into or out of it's bony support. Such corrective forces are known as “intrusive” or “extrusive.” An archwire can influence a tooth to move bodily outward or inward, and such forces are said to position a tooth in terms of “prominence.” Since the Edgewise relationship between an archwire and a bracket's archwire slot does not preclude a relative sliding movement between an archwire and a bracket, other tractive or compressive forces may be applied to a tooth that urge a tooth to desirably slide along the mesio-distal extent of an archwire into a new position. Over the course of orthodontic treatment, patient's teeth are moved to corrected positions through a combination of most, if not all of these forces acting simultaneously on the teeth.
At the beginning of orthodontic treatment, a patient's teeth are of course out of alignment. Since the exact location and orientation of a bracket on a patient's teeth ultimately determines the final treated position of a tooth relative to an archwire, the skill with which an orthodontist can attach brackets at ideal positions and orientations on the teeth is paramount. To fully appreciate this, the brackets are first visualized on teeth that are ideally positioned at the conclusion of treatment. All bracket slot walls are aligned and coincident so that a full-size, naturally-curving archwire lies passively in all of the slots. Next, imagine the archwire removed and the teeth gradually moved out of position, carrying their brackets with them until the teeth are as malaligned as they were prior to treatment. The slots have of course become as malaligned as the teeth. This is in fact the condition that actually exists when brackets are properly sited on the crowns of a patient's teeth.
After brackets have been placed on the teeth at the start of orthodontic treatment, an orthodontist ligates the first of a series of sequential archwires into the archwire slots of the brackets. Commercially-available archwires are manufactured to a form that mirrors the natural gentle curve of the human dentition. As described above however, the archwire slots at the beginning of treatment are as malaligned as the teeth they are attached to. Because of this, the archwire may be required to undergo sometimes severe bending and zigzagging as the orthodontist ligates the archwire into one archwire slot after another. In this manner, the act of deflecting an otherwise flat, elegantly curving archwire away from its passive form causes energy to be stored in the archwire just as energy can be stored in a spring. It is the slow dissipation of this stored energy the drives the slow biological responses allowing the teeth to desirably reposition.
As can be appreciated, at the onset of treatment, one tooth may be intruded, distal-ligually rotated and lingually inclined for example, and an adjacent tooth may be super-erupted, mesio-lingually rotated and flared labially. In such a case, an archwire passing through the archwire slots of the two brackets attached to the teeth of this example must undergo a severe deflection. Later during the course of treatment, after the two teeth in the example above have responded and moved into a somewhat closer alignment, the severity of the required deflection will be lessened. To exploit this, and to custom-tailor the forces applied to teeth as treatment progresses, orthodontists will typically begin a patient's treatment with an archwire that has mechanical properties that include a relatively low tensile strength of about 140 KSI UTS, combined with a modulus of elasticity in the range of 5,000,000 to 12,000,000. Such wires are compliant and can tolerate such severe deflections encountered at the beginning of treatment without taking a permanent set, while still being capable of delivering physiologically-effective tooth-moving forces. Such initial archwires are typically round in cross-section and are not intended to mechanically take advantage of the rectangular Edgewise configuration of the archwire slot. Archwires fitting the above descriptions may for example be 0.012 inch in diameter and formed from a relatively soft temper stainless steel alloy, or 0.016 inch diameter super-elastic nickel titanium alloy. Other wires falling into this beginning category may be formed from a braided, multi-strand cable.
As treatment progresses, the severe deflections encountered at the beginning of treatment become less severe and an orthodontist can progress to
Dorr, Carson, Sloan, Birney & Kramer, P.C.
O'Connor Cary E.
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