Dentistry – Orthodontics – Means to transmit or apply force to tooth
Reexamination Certificate
2001-12-03
2003-08-12
O'Connor, Cary E. (Department: 3732)
Dentistry
Orthodontics
Means to transmit or apply force to tooth
C433S007000
Reexamination Certificate
active
06604943
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of devices and methods for orthodontic treatment, as well as devices useful for maintaining the corrected positions of a patient's teeth after treatment, and more particularly to an improved system of springs useful for returning teeth to desired, treated positions in cases where the corrected orthodontic results have relapsed after treatment.
2. Statement of the Problem
In the field of orthodontics, particularly the area involving the commercial fabrication of orthodontic appliances by orthodontic support laboratories, it is a long-established and well-known practice to conform polymerizing materials into shapes that passively conform to a patient's teeth, gums or palate. Such “cast mass”-type appliances are typically formed from materials such as a dimethacrylate paste activated by a benzoyl peroxide-amine, a self polymerizing methyl methacrylate composition or light curable compositions such as a dimethycrylate paste activated by a camphor quinine, or other heat-softening thermoplastic urethane resins, all of which demonstrate rigid mechanical properties once cast and cured.
FIG. 1
is a top perspective view of an example of such an appliance.
It is also common practice for orthodontic laboratories to embed various types of active or passive metallic devices into such cast mass-type appliances during the casting and subsequent curing process. The metallic devices are anticipatorily pre-positioned within the cast mass by a laboratory technician to contact a patient's teeth in desirable ways once the appliance is placed in the patient's mouth. The metallic devices act to urge the teeth to move in desirable ways, including repositioning the teeth into desired or corrected positions and orientations as part of an orthodontist's overall treatment plan.
Such active appliances, when adapted to the upper teeth normally span the top of the patient's mouth in contact with the palate and extend into close proximity to the lingual gingival margins of some or all of a patient's upper teeth. When such an appliance is being fabricated for application to the lower arch, the configuration of the cast mass is significantly relieved compared to the upper configuration. This is to provide clearance for the tongue, and therefore, lower versions of this type of appliance are generally trimmed and contoured to the lateral and anterior aspects of the lingual of the lower dental arch.
The metallic devices that are typically embedded in such an orthodontic appliance are elastically loaded or stated differently, they are capable of storing energy. The metallic devices are deflected by the mal-occluded teeth or in a sense loaded as the appliance is positioned and fully seated in the mouth. The corrective force that directs the teeth into desirable positions is the dissipation, over time, of the energy stored in such deflected metallic devices.
Treatment using such cast mass-type appliances inherently involves the primary corrective forces being generated from the lingual side of the teeth, and therefore such forces are outwardly directed. Such forces are typically simple, single-vector forces that are intended to tip the crown of inwardly canted teeth outward.
Inwardly-acting forces directed to the outside (i.e. the labial and buccal surfaces of the teeth) can also be applied by this type of appliance. To accomplish this, orthodontic lab technicians will typically fabricate a cast mass-type appliance exhibiting a section of hard, stainless steel wire, with its two ends embedded in the cast mass as shown in FIG.
1
.
The mid-span of the resilient stainless steel wire is supported as the wire extends outward between teeth on either side of the patient's arch. The mid-span section of the wire spans the outer surfaces of the anterior teeth and is commonly referred to as a “labial bow”. A typical cast mass-type appliance as described, containing embedded metallic devices that act on both the inside and outside surfaces (i.e. with a labial bow on the outside of the teeth) of some or all of the teeth constitutes one common and well-known type of orthodontic appliance.
As can be appreciated, the interaction of the loaded spring devices on the inside of the teeth may push the crowns outward until such time that they contact the labial bow. Over the course of treatment, the crowns may contact the labial bow but nonetheless still exhibit an undesirable rotation. It is the continued pushing of the springs on the teeth from the inside, against the labial bow, that will slowly rotate the tooth to a desirable corrected position.
To best contrast the advantages and benefits of the present invention, it is necessary to describe the well known limitations and shortcomings of current cast-mass-type appliances. First, it must be appreciated that the physiological response elicited from current cast mass-type appliances proceeds very slowly, consuming many months of treatment time. The second and most notable shortcoming of the current-design cast mass-type appliance that the present inventive system of springs favorably improves upon is that such appliances have no control whatsoever over the important consideration of alignment of the roots of the teeth. The movement of the teeth accomplished by current cast-mass-type appliances can be likened to uprighting a “stick stuck into sand”, where the portion of the stick buried in the sand rotates around an unknown center of resistance with its lower extremities moving through the sand in one direction and its upper extremities moving in the opposite direction.
The absence of the ability to control the true location of an uprighted tooth is a major drawback and thus the use of cast mass-type appliances is limited. Nonetheless, cast mass-type appliances serve as useful adjuncts to other primary treatment methods (e.g., conventional braces) used to accomplish treatment goals during the active phase of orthodontic treatment.
To further illustrate the nature of the limitations of current cast mass-type appliances, it should be understood that the metallic devices embedded in cast mass-type appliances are capable of simple, single-vector correction of the inclination of the crowns of lingually-disposed teeth in an outward direction. The outer bow feature of such an appliance serves as a stop, limiting the correction to a roughly desired inclination. All of the limitations of such appliances described above are generally recognized by orthodontists and orthodontic laboratory technicians. In particular, such appliances are recognized, as being incapable of generating the more complex couple-type forces required to bodily move the roots of teeth through the supporting bone. The term “couple” is defined as the relationship between any two forces acting on a body where in combination, those forces tend to cause that body to rotate about a point. In contrast to a couple, the simple single-vector corrective forces generated by current cast mass-type appliances act only on the crown of a tooth and serve only to tip a tooth about its centroid.
The term “centroid” in the dental lexicon describes the theoretical center of resistance of a tooth's root as it is rotated through its alveolar bone structure in response to a single force applied, over time, to some point on its visible crown. The location of the center of resistance/center of rotation (i.e. the centroid) is hidden well below the gingival margin of a tooth at a theoretical point within the root. This biological centroid can again be thought of as being similar to the neutral rotation point as in the example above describing a stick being uprighted in sand.
Even though useful for some treatment objectives, orthodontists do not use such cast mass-type appliances as a primary corrective regimen. This is due to the inability of such appliances to bodily translate teeth through supportive bone as described. Such appliances are therefore typically relegated to serving as adjuncts to othe
Dorr, Carson , Sloan & Birney, P.C.
O'Connor Cary E.
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