Orthodontic brackets which are applied to teeth, either by attachment to a band or by direct bonding to a tooth, for the purpose of applying a moving force to the tooth to which the bracket is attached are known in the art. The moving force is generated by a wire attached to the orthodontic bracket which wire is also attached to similar brackets attached to adjoining teeth. The moving force applied to teeth over a period of time permits the movement of the teeth to accomplish desired alignment of the teeth.
There are two basic techniques for applying this moving force currently in practice in the orthodontic field. The conventional edgewise technique of applying this moving force is characterized by the use of a bracket having a rectangularly sectioned archwire receiving slot (edgewise slot). The moving force in this type of bracket (edgewise bracket) is applied to the tooth by the application of an angular or round sectioned archwire. The archwire is captured in the edgewise slot by a relatively small gauge stainless steel tie wire or by a small donut-shaped retaining member made from a resilient rubber-like material. The edgewise bracket is typically used for bodily movement of teeth. As a result of its design, that is, the archwire slot opening to the facial side of the bracket, only slight mesio-distal tipping of the brackets can occur when an archwire is engaged in the archwire slot.
A built-in design feature of other prior art edgewise brackets is "in/out" compensation. In/out compensation relates to the distance between the archwire slot and the base of the bracket (base thickness). Base thickness is determined for each bracket according to the crown facial prominence of the tooth to which that particular bracket is to be attached. Crown facial prominence is determined by measuring the distance from an imaginary line at the level of the crown's midtransverse plane that would connect the most facial portions of the contact areas of a single crown, or of all crowns, in an arch when they are optimally positioned, to each crown's most prominent facial point. This imaginary line is known as the embrasure line. The prior art brackets are designed to be attached to the teeth so that the occlusal/gingival midpoint of the edgewise slot is aligned with the most prominent facial point of each crown. If the teeth in the mandibular and/or maxillary arch are properly aligned a line drawn along the midtransverse plane of the teeth will pass through each crown's most prominent facial point. This line is know as the Andrews plane. A vertical line drawn perpendicular to Andrews plane that intersects the embrasure line at the most facial point of the distal contact area of each tooth, will be referred to hereafter as the Cannon plane. If the distance from the archwire slot to the Cannon plane is equal for all teeth in a given arch, proper in/out compensation is established for all the brackets in that arch. See L. Andrews, "Straight Wire- The Concept and Appliance," L.A. Wells Co., 1989.
Average maxillary crown facial prominence ranges from approximately 2.9 mm for upper first molars to 1.65 mm for upper lateral incisors. In the mandible arch, crown facial prominence ranges from 2.5 mm for lower first molars to 1.2 mm for lower anteriors. In the maxillary arch the first molar is the tooth with the greatest crown facial prominence, and, therefore, would have the bracket with the smallest base thickness. Likewise, the maxillary lateral incisors have the smallest crown facial prominence, and therefore, would have the bracket with the largest base thickness. The sum of the base thickness of the bracket and the crown facial prominence of the tooth is equal to the distance from the base of the edgewise slot to the Cannon plane. This same principal would also be true in the mandibular arch.
When an archwire is applied to a series of edgewise brackets with proper "in/out" compensation, a smooth curve of the archwire will meet all of the edgewise brackets. Therefore, a series of complicated bends do not have to be made in the archwire in order to properly engage each edgewise slot. The bending of an archwire to fit the "in/out" of a particular patient's teeth requires a significant amount of time and effort. Therefore, edgewise brackets with built in "in/out" compensation are desirable. An example of an edgewise orthodontic bracket with built-in "in/out" compensation is shown in U.S. Pat. No. 3,660,900.
The other orthodontic technique which is presently used is known as the Begg lightwire technique. This technique involves the use of a relatively light, round sectioned archwire. A lightwire bracket typically includes a gingival opening mesio-distally extending slot for receiving the archwire. The archwire slot, with its sloping mesial and distal shoulders, is designed to allow free tipping of the brackets on the archwire. The archwire is captured and secured in the archwire slot by a pin having an elongate body portion and an enlarged head portion. The pin is inserted into a slot in the body of the lightwire bracket which thereby captures the archwire between the head of the pin and the body of the bracket. The pin is then secured to the lightwire bracket by bending the elongate portion of the pin over the body of the bracket. An example of a lightwire bracket is shown in U.S. Pat. No. 3,178,821.
The aforementioned design of the archwire slot of the lightwire bracket in conjunction with the pin method of attaching an archwire thereto permits free tipping of the brackets (either labio-lingually or mesio-distally) on the archwire. Since heretofore, lightwire brackets of the prior art have not been known to include proper "in/out" compensation, a series of complicated bends must be made in the archwire in order to engage the archwire into the lightwire slot and have the moving force generated by the archwire result in optimum alignment of the teeth.
Both the edgewise technique and the lightwire technique have advantages under different circumstances. Furthermore, both techniques may be used at different times on the same patient. Therefore, in addition to edgewise brackets and lightwire brackets, there have been developed combination brackets. Such combination brackets permit the use of either the edgewise technique or the lightwire technique using the same bracket. Examples of such combination brackets are shown in U.S. Pat. Nos. 3,178,822 and 3,163,933. Although in/out compensation is provided in prior art combination brackets for an edgewise slot, in/out compensation has not heretofore been provided for both the edgewise slot and the lightwire slot.
Furthermore, because of the configuration of prior art orthodontic brackets, both an archwire in the edgewise slot and an archwire in the lightwire slot could not be attached to the bracket using a simple singular fastening pin. The use of a compound and/or complex fastening member to attach both an archwire in the edgewise slot and an archwire in the lightwire slot is undesirable because of the additional cost. Also, prior art combination brackets have heretofore been undesirably large causing difficulties in application and patient discomfort. Therefore, a combination orthodontic bracket has long been sought which can be used for both edgewise and lightwire corrective techniques, which provides proper "in/out" compensation in both the edgewise slot and the lightwire slot, which requires only a simple singular fastening member to attach both an archwire in the edgewise slot and an archwire in the lightwire slot to the bracket and which is relatively small and comfortable to wear.