Torque Overcorrection Model

Abstract

A custom orthodontic appliance comprised of brackets to be positioned on a patient's teeth, and an archwire, is customized to provide a desired torque to a tooth by selecting an angle for the slot of at least one bracket so as to provide a torque interaction between that bracket slot and the archwire. The torque interaction is computed to compensate for tooth tilt resulting from misalignment of the force vector applied by the archwire with the tooth center of resistance. The torque interaction is computed at the desired final position of the teeth, and may be computed to provide for an applied torque even where the tooth is positioned in the desired final tooth position to compensate for force diminution. Material properties of the archwire and the relative archwire slot geometry are evaluated to determine an archwire/slot angular offset in which torque is applied to the bracket.

What is claimed is: 
     
         1 . A method of forming a custom orthodontic appliance, comprising
 providing brackets to be positioned on a patient's teeth, wherein the brackets include an archwire slot that is at an angle selected to provide a desired torque to a tooth based upon the geometry of the patient's teeth and masticatory system,   providing an archwire having a noncircular cross section,   assembling the brackets to the archwire to form the custom orthodontic appliance.   
     
     
         2 . The method of  claim 1  wherein the desired torque is computed to compensate for tooth tilt resulting from misalignment of the force vector applied by the archwire with the tooth center of resistance. 
     
     
         3 . The method of  claim 1  wherein the desired torque is computed at the desired final position of the tooth. 
     
     
         4 . The method of  claim 1  wherein the slot angle is computed to provide for an applied torque when the tooth is positioned in the desired final tooth position, whereby to compensate for force diminution in the archwire. 
     
     
         5 . The method of  claim 1  wherein the slot angle is selected in response to material properties of the archwire. 
     
     
         6 . The method of  claim 1  wherein the slot angle is selected in response to relative archwire and slot geometry. 
     
     
         7 . The method of  claim 1  wherein the bracket is custom manufactured for the appliance. 
     
     
         8 . The method of  claim 1  wherein the bracket is pre-manufactured and selected from an inventory of premanufactured brackets having specific configurations.