There are two principal types of orthodontic appliances for straightening teeth or holding them in position after correction. Non-removable appliances are based on the use of wires coupled to elements cemented to the teeth and removable only by mechanical means. While this is an accepted and proven approach, the non-removable appliances require cumbersome and unsightly devices which are very inconvenient to the user and which must often be left in place for a long period of time. The other principal class is the removable appliance, one of which typically employs a pair of resilient arch wires, one for the labial side of the teeth, and the other for the lingual side. These wires are welded or soldered to a clasp or anchoring structure typically coupled to midregion teeth on each side and secured together across the roof of the mouth by an expansion plate or wire. By adjusting the length or curvatures of the labial and lingual arch wires, teeth can be urged toward the more ideal position. Although there are a substantial number of variations of this general class of orthodontic appliance, they all present particular difficulties in one or a number of specific respects. After repositioning displaced teeth a retaining appliance must be used for a substantial period of time because the teeth in 80% of the cases tend to relapse within various periods of time. If relapse has occurred the ordinary or usual retainer will not fit; therefore, retreatment with fixed appliances is necessary depending on the degree of relapse. Again the problem of unsightliness must be confronted.
For most treatments using resilient arch wires a succession of adjustments are needed as the teeth gradually are moved to the desired positions and orientations. This means that the wearer must repeatedly be examined, the adjustments made and tested, and then the appliance must be worn for a time, until a final adjustment is made for the last increment of repositioning. In one widely used prior art system lingual springs are used until a degree of repositioning is achieved, following which a high labial wire is used with descending pins at each tooth to control position. Using conventional arch wires of high spring force, problems typically arise from the amplitude or time-varying characteristic of the forces that are exerted. If the forces applied are too great, the root of a tooth can be pathologically loosened. If the force drops off substantially as positions change, a long time may be required to reach the final position for an adjustment. In comparison, removable orthodontic appliances typically have had to be used, with successive adjustments, over long periods of time, i.e. typically more than several years. The orthodontic corrections required can involve much more than movement of teeth in the posterior or anterior direction. Individual teeth may require rotation in a distal or mesial manner relative to a vertical or horizontal axis and this, of course, should be done concurrently with other repositioning. In other words, teeth may be moved in three planes of spaces to positions selected to occlude properly with teeth in opposing arches.
Appliances, whether removable or not, often interfere with both speaking and eating. Moreover, improperly placed or large bodies beneath the tongue tip are disruptive of the proprioceptive sense and represent a particular problem. The expansion plate used to bridge the palate is not only a large bulky appliance, but can introduce painful pressures if asymmetric forces are generated in the occlusal (biting) direction.
In very early work on correctional appliances a different approach was proposed by Drissler in U.S. Pat. No. 1,139,170. Drissler suggested primarily that anchoring structures on each side in the region of the back teeth could be interconnected by a pivotable arch wire, a proposal of questionable merit. He also suggested, however, that correction of front tooth position, both in the radial direction and to some extent rotationally, could be made by using spring wires not attached to the teeth. His proposed device used a labial spring wire and a pair of free-ended lingual spring wires, each anchored in a rearward position and extending forwardly to a separating gap. This device was not satisfactorily employed, as far as is known, and a number of obvious reasons present themselves. For example, the outward forces exerted along the length of the free-ended lingual wires vary with position. Also, the wires inevitably are displaced along the slanted tooth surfaces toward the tooth ends, thus diminishing or even eliminating completely the forces exerted. They probably also are displaced merely because of gravity. In addition, the Drissler structure interposes a mass of wires interfering with tongue action and produces blocking of normal contact with the rugae.
There is therefore a general need for a removable orthodontic appliance that is less obvious cosmetically, provides more uniform forces, requires less adjustment and introduces a minimum of interference into the functions of the tongue and teeth. In addition, there are needs for appliances which can be utilized not only in repositioning teeth and retaining tooth position after corrections have been made. The device should be readily adjustable to match the specific needs and conditions of the individual patient. Thereafter, however, it should be able to perform its function indefinitely without need for change, but should be adjustable if the need arises. Further, it is preferable to be able to prefabricate as much of the device as is feasible, to reduce costs and improve uniformity.