This invention relates to orthodontic appliances or instrumentalities and, more particularly, to extra-oral traction apparatus for applying traction to a patient's teeth via an orthodontic instrumentality.
Extra-oral devices are normally of the type in which the teeth are placed in traction by tensioning means connected to a neckband or headband, the traction being applied to the teeth via an orthodontic instrumentality on the teeth (e.g., a maxillary arch band or a mandibular arch band). The tensioning means may include two J-shaped rods, one one each side of the mouth extending back on the sides of the face and secured to the neckband or headband by a tensioning device. One such type of tensioning device is an elastic band arrangement such as is shown in U.S. Pat. Nos. 2,968,097 and 3,203,099. Use of an elastic band, i.e., a rubber band, has several disadvantages, however, one being that it is difficult precisely to establish the desired amount of traction with such an assembly. Moreover, such an assembly can be pulled beyond the point of no return, in which case it no longer exerts traction, and it might even snap or break.
These problems are alleviated by a second type of tensioning device in which traction is developed by compressing a member (e.g., a spring) rather than by applying tension to it. Reference may be made to U.S. Pat. Nos. 3,765,093 and 3,772,709 showing orthodontic traction devices of this general type. Generally, these latter prior art traction devices are adjustable by the orthodontist to apply a desired amount of traction force to the teeth. These devices have not, however, been readily adjustable for varying the angle at which such force is applied to the teeth. Moreover, these tensioning devices have not been readily adjustable from a high pull position especially suitable for applying traction to the upper teeth via a maxillary arch band or the like, to a low pull position especially suitable for applying traction to the lower teeth via a mandibular arch band.